PAPERmaking! Vol.8 No.2 2022 by pita.co.uk

PAPERmaking! The e-magazine for the Fibrous Forest Products Sector

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Paper Technology International®

Volume 8 / Number 2 / 2022

PAPERmaking! FROM THE PUBLISHERS OF PAPER TECHNOLOGY TE INTERNATIONAL®

Volume 8, Number 2, 2022

CONTENTS: FEATURE ARTICLES: 1. Recycling: Effect of fibre wettability on tensile strength. 2. Hot Pressing: An efficient way to improve mechanical performance of boards. 3. Decarbonisation: A case study for the Austrian Industry. 4. Testing: Determination of bending stiffness of 5-layer corrugated. 5. Seaweed: Using brown algae waste in papermaking. 6. Biorefinery: Co-production allocation methods – an Austrian case study. 7. Wood Panel: Alternative materials from agro-industry. 8. Energy Recovery: Energy recovery from waste paper and deinking sludge. 9. Filing: How to organise your paperwork in 7 steps. 10. Burnout: How to recognise the signs and what to do about it. 11. Active Listening: 10 top tips for a soft skill we can all learn and use. 12. Soft Skills: 8 soft skills to learn and use in 2022. SUPPLIERS NEWS SECTION: News / Products / Services: Section 1 – PITA Corporate Members: ABB / VALMET Section 2 – PITA Non-Corporate Members VOITH Section 3 – Non-PITA Members TOSCOTEC DATA COMPILATION: Events: PITA Courses & International Conferences / Exhibitions Installations: Overview of equipment orders and installations since late March 2022 Research Articles: Recent peer-reviewed articles from the technical paper press Technical Abstracts: Recent peer-reviewed articles from the general scientific press

The Paper Industry Technical Association (PITA) is an independent organisation which operates for the general benefit of its members – both individual and corporate – dedicated to promoting and improving the technical and scientific knowledge of those working in the UK pulp and paper industry. Formed in 1960, it serves the Industry, both manufacturers and suppliers, by providing a forum for members to meet and network; it organises visits, conferences and training seminars that cover all aspects of papermaking science. It also publishes the prestigious journal Paper ® Technology International and the PITA Annual Review, both sent free to members, and a range of other technical publications which include conference proceedings and the acclaimed Essential Guide to Aqueous Coating.

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Contents

PAPERmaking! FROM THE PUBLISHERS OF PAPER TECHNOLOGY TE INTERNATIONAL®

Volume 8, Number 2, 2022

Relationship between wettability of pulp fibers and tensile strength of paper during recycling HAILAN JIN

1,4,

RYOTA KOSE , NOBUSHIGE AKADA & TAKAYUKI OKAYAMA .

The wettability of the paper surface is greatly affected by the wettability of the pulp fibers. We conducted this study in order to understand the relationship between the wettability of a single fiber of recycled pulp and the strength of recycled paper, as well as the inter-fiber bonding strength. The contact angle was determined from a series of photographs of the pulp fiber and the water silhouettes at the point of contact. The contact line and profile history were continuously photographed in every 1 s after the initial contact. The recycled softwood kraft pulp fibers were clearly much less hydrophilic than the original fibers, regardless of whether the fibers had been bleached or not. The contact angle of the original chemi-thermomechanical pulp fiber was much higher than that of the original softwood bleached kraft pulp fiber. Furthermore, increased number of recycling decreased the contact angle of the chemi-thermomechanical pulp fiber. The Page equation was used to evaluate the strength contributions of single fiber and fiber–fiber bonding to tensile strength of paper. As a result, an increase in weakness factor of fiber–fiber bonding strength was obtained for the recycled softwood kraft pulp handsheet. On the other hand, the weakness factor of the original chemi-thermomechanical pulp handsheet decreased with recycling. In addition, the weakness factor of fiber–fiber bonding strength and the contact angles of the provided softwood bleached kraft pulp fibers bore a proportional relationship to each other. Contact information: 1. Key Laboratory of Bio-based Material Science & Technology (Northeast Forestry University) Ministry of Education, No. 26 Hexing Road, Harbin 150040, China. 2. Division of Natural Resources and EcoǦMaterials, Institute of Agriculture, Tokyo University of Agriculture and Technology, 3Ǧ5Ǧ8 SaiwaiǦcho, Fuchu, Tokyo 183Ǧ8509, Japan. 3. Faculty of Agriculture, Tokyo University of Agriculture and Technology, 3Ǧ5Ǧ8 SaiwaiǦcho, Fuchu, Tokyo 183Ǧ8509, Japan. 4. State Key Laboratory of Biobased Material and Green Papermaking, Qilu University of Technology, Shandong Academy of Sciences, Jinan 250353, China. Nature Scientific Reports 2022, 12, 1560. https://doi.org/10.1038/s41598-022-05514-2 Creative Commons Attribution 4.0 License

The Paper Industry Technical Association (PITA) is an independent organisation which operates for the general benefit of its members – both individual and corporate – dedicated to promoting and improving the technical and scientific knowledge of those working in the UK pulp and paper industry. Formed in 1960, it serves the Industry, both manufacturers and suppliers, by providing a forum for members to meet and network; it organises visits, conferences and training seminars that cover all aspects of papermaking science. It also publishes the prestigious journal Paper Technology International® and the PITA Annual Review, both sent free to members, and a range of other technical publications which include conference proceedings and the acclaimed Essential Guide to Aqueous Coating.

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Article 1 – Recycling and Wettability

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Ƥ ͷǡͺ*ǡ ͸ǡ ͹ Ƭ ͸* ơ Ƥ Ǥ Ƥ ǡ ǦƤ Ǥ Ƥ Ǥ Ƥ ͷ Ǥ Ƥ Ƥ ǡ Ƥ Ǥ Ǧ Ƥ Ƥ Ǥ ǡ Ǧ Ƥ Ǥ Ƥ Ƥ ȂƤ Ǥ ǡ Ƥ ȂƤ Ǥ ǡ Ǧ Ǥ ǡ Ƥ ȂƤ Ƥ Ǥ Paper is said to be environmentally friendly as a natural recycling material and a sustainable recycling resource. The paper recycling system has been constructed as an advanced field of recycling. In particular in Japan, recycling of used paper has been promoted from the viewpoint of effective use of resources and solution of waste problems. The wastepaper recovery rate began a rapid and long-term rise as recovery efforts in recent years. The recovery rate in Japan had reached 79.5% in 20191. The wastepaper utilization rate at 64.3% within Japan was trailing by 15.2% compared with the recovery rate. However, the ratio of wastepaper to the raw material of paper and paperboard in Japan is one of the world’s leading. Although Japan’s waste paper recovery is at a fairly high level, there is a concern that the paper and paperboard recyclability will decline as the recovery rate rises. The utilization of recovered paper for high-grade paper such as printing and communication papers has been limited because using recovered paper tends to reduce the quality of these papers. Mckee2 performed recycling of papermaking, drying, wetting and disintegration up to 6 times using softwood unbleached kraft pulp (SUKP). It was reported for the first time that physical properties of paper such as paper density, tensile strength, bursting strength, elongation, bending resistance and zero span tensile strength, decreased by recycle treatment but tearing strength and Taber stiffness increased when compared at the same freeness. Numerous studies have been conducted on the papermaking potential of recycled pulp fibers during the past decades3–6. The cell wall of wood pulp fiber can be distinguished into a primary wall (P layer) and a secondary wall (S layer), and the S layer is further divided into an outer layer (S1), a middle layer (S2), and an inner layer (S3). Among them, the S2 layer occupies approximately 70–80% of the cell wall thickness and is the main cell wall. In the case of chemical pulp, since lignin and the like are removed in the process of pulping, voids are formed in the cell wall portion and the pulp becomes porous7. When the chemical pulp is repeatedly defibrated in water, ͷ

Ǧ Ƭ ȋ Ȍ ǡ Ǥ ͸ͼ ǡ ͷͻͶͶͺͶǡ Ǥ ͸ Ǧ ǡ ǡ ǡ ͹ǦͻǦ; Ǧ ǡ ǡ ͷ;͹Ǧ;ͻͶͿǡ Ǥ ͹ ǡ ǡ ͹ǦͻǦ; Ǧ ǡ ǡ ͷ;͹Ǧ;ͻͶͿǡ Ǥ ͺ ǡ ǡ ǡ ͸ͻͶ͹ͻ͹ǡ Ǥ * ǣ ̻ͷͼ͹Ǥ Ǣ ̻ Ǥ Ǥ Ǥ Ƥ |

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dewatered on wet presses and dried on a paper dryer up to several times, not only are strength properties of the paper, such as tensile and bursting strengths significantly reduced, but also the micro-structure of the pulp fibers is damaged8. The recycling process causes morphological changes such as delamination and crack formation in cell wall of the pulp fibers8,9. The solute exclusion method has been devised by Stone and Scallan to elucidate the structure of pulp fiber cell walls in the presence of water10,11. The solute exclusion method utilizes the phenomenon that solute molecules invade pores in the cell wall according to the molecular diameter when the wet pulp is immersed in monosaccharides and dextran aqueous solutions having various molecular diameters. It was found by using the solute exclusion method that the pore volume in cell wall of the pulp fibers decreased with the number of recycling increased10,12. Stone and Scallan13 also noted significant decreases in the specific surface areas of once-dried bleached sulfite pulp by using nitrogen adsorption technique. It was confirmed that the decrease in the specific surface areas of the dried bleached sulfite pulp increased with an increase in drying temperature. The decrease in the potential of recycled pulp fibers with respect to the strength of paper is largely due to changes in the cell wall structure of the fibers themselves. This change affects the swelling potential and conformability of the fibers in the papermaking process, and controls the refining characteristics14,15. In the pulp fiber wall, the S2 layer repeatedly swells and shrinks due to recycling treatment, and microscopically forms a matrix structure with few fine pores. However, on the other hand, densification causes a twitching phenomenon in the matrix, and macroscopically, layered cracks are generated in the fiber wall, and cracks are also generated in the radial direction. Therefore, the inter-fiber bond formed by recycling is broken, and the strength of the paper sheet is also reduced8,9. The so-called “hornification” of pulp fibers caused by recycling is the irreversible loss of fiber swelling, which is determined as water retention value. The irreversible hornification leads to remarkable reductions in fiber–fiber bonding. It occurs strongly in the fiber cell wall matrix of chemical pulp, but not so much in mechanical pulp6. Cidir et al.16 also confirmed that as a result of papermaking using refined bleached sulfite pulp (BSP) and then recycling, the tensile strength, tearing strength and elongation of the paper decreased, but the opacity improved. Furthermore, by measuring and substituting the zero-span tensile strength, which is an index of single fiber strength, into the Page’s equation17, it was evaluated that the decrease in paper tensile strength due to recycling depended on the decrease in fiber–fiber bonding strength. Howard et al.18 showed that there is few changed in both wet and dry zero-span tensile strength during recycling of various pulps. Regarding the strength of paper such as tensile and bursting strengths, hydrogen bonds are considered to be the most important for the bonding strength of cellulose fibers in paper. The ability of cellulose fibers to form fiber–fiber bonds depends on the hydrophilicity of the fiber surface, that is, the ability to form hydrogen bonds based on it19. Since fiber–fiber bonds are formed between fibers interacting in water, wet adhesion influenced by the wetting of a fiber–fiber bonding and the strength of fiber network. It is important to gain a better understanding of the effect of the surface behavior of a single pulp fiber, because the fiber–fiber bonding strength is influenced by both the physicochemical properties of the pulp fiber surface and the contact area. The evaluation of the paper surface wettability contributes to the control of various industrial processes. Young20 prototyped a contact angle measuring device using Wilhelmy’s principle and determined the wettability of single pulp fibers. That is, after measuring the weight increase and the peripheral length of the fibers generated when the pulp fibers are suspended from a balance and immersed in a liquid, the contact angle is calculated using the following equation, and the wettability W is calculated by F/P.

F = PγLV cos θ

(1)

where F is the tensile force acting on the solid rod immersed in the liquid, P is the peripheral length of the rod along the boundary line of the three phases, γLV is the surface tension of the liquid, θ is the contact angle. The contact angle of pulp fibers with water was reported to be 52° for Douglas fir unbleached kraft pulp (UKP) fibers and 43° for Aspen thermomechanical pulp (TMP) fibers. From the dynamic wetting test of wood pulp fiber by Wilhelmy method, unbleached neutral sulfite semi-chemical pulp (NSSCP) fibers have higher wettability than UKP and TMP fibers. The reasons for this were the degree of removal of lignin on the fiber surface, the presence of hemicellulose, other carbohydrates and extract components, and suggested the effect of the sulfone group introduced into lignin20. Klungness21 modified Young’s equipment to improve measurement accuracy and determined the contact angle of water to loblolly pine kraft pulp fibers with different lignin contents. As a result, it was confirmed that the contact angle with water increases due to the hydrophobic effect of lignin as the lignin content in the pulp fiber increases. Jacob et al.22 measured the contact angle of pulp fibers using liquids with different surface tensions and attempted to calculate the critical surface tension from the Zisman technique. Although the results showed significant variations in surface characteristics within a single fiber type, chemi-thermomechanical pulp (CTMP) fibers were more wettable compared with softwood and hardwood UKP fibers. When the critical surface tension was measured by the Zisman technique using a film sheet prepared from each of the three main constituents of wood, it was estimated that a relatively large amount of lignin was distributed on the fiber surface in UKP23,24. On the other hand, in the case of TMP fibers, it depends on the temperature condition during the process because of the relationship with the softening temperature of lignin. Therefore, it was concluded that the wettability of pulp fibers depends on the chemical composition and structure of the fiber surface20. In general, chemical pulp fibers such as bleached kraft pulp (BKP) and UKP with low lignin content have been found to be more hydrophilic than high yield pulp fibers such as groundwood pulp (GP), refiner mechanical pulp (RMP) and TMP fibers with high lignin content25. Berg26 evaluated the surface free energy, including the contribution of acid–base interactions, from the wetting measurements of pulp fibers. As a result, it was shown that the BKP fiber has a slightly larger dispersion force component γsd and a considerably smaller electron donor (base) parameter γs—of the surface free energy

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SKP

Sample

Softwood pulp samples

Delignification treatment

SBKP

Bleached kraft pulp

ECF-bleached

0.0

SUKP

Unbleached kraft pulp

–

5.7

DSUKP

Unbleached kraft pulp

Delignified

CTMP

Chemi-thermomechanical pulp

–

Klason lignin (%)

3.5 37.9

Table 1. Klason lignin content of softwood pulp samples.

than the CTMP fiber. In addition, Yoshinaga et al.27,28 devised a method of directly measuring the contact angle by continuously photographing the contact interface between the wood pulp fiber and the wet liquid using a stroboscope every 0.2 s. The dry and wet recycling treatment for pulp significantly increased the contact angle of water with respect to the pulp fibers, but tended to decrease the contact angle of water on the paper surface. In addition, Okayama et al.29 evaluated the change in surface free energy generated in pulp fibers by recycling, including the contribution of acid–base interaction, and found that γs hardly changed but γs-decreased. Although many studies on paper recycling have been conducted over the years, it is well known that recycled pulp fibers reduce the strength of paper, mainly tensile strength, compared to virgin fibers. The effect of repeated wetting and drying treatments on the reduction of bond-forming ability between pulp fibers has been mainly due to the loss of the bond region caused by the hornification of fibers. Therefore, it has been considered important to improve the fiber flexibility in order to regain the bond-forming ability of fibers. However, it is not easy for the recovery of the tensile strength of paper prepared from recycled fibers by refining to reach the level of undried fibers15. This indicates that the recovery of the bond-forming ability of dried fibers does not reach that of undried fibers. Eastwood et al.30 examined the effects of additional refining of pulp, stock preparation by adding sizing agents, and papermaking with hand-made or machine-made paper on the physical properties of paper for each recycling of semi-bleached kraft pulp. It was clarified that the recycling process by preparing the hand-made paper has a significant decrease in the tensile strength of the paper and greatly reduces the hemicellulose content in the paper as compared with the machine-made paper using a white water circulation system. As a result, it was concluded that the decrease in paper strength due to recycling is caused not only by the decrease in swelling capacity of secondary fibers but also by the deterioration of the fiber surface condition. Seth and Page31 and Gurnagul et al.32 argued that the decrease in the tensile strength of paper during drying is affected not only by the relative bond area but also by the decrease in shear bond strength from the examination by the Page’s equation. Therefore, in order to improve the strength characteristics of recycled paper, it is necessary to focus on increasing the bonding strength between fibers32,33. The wettability of the pulp fiber surface is an important factor for the fiber–fiber bonding force, and it is considered that the improvement thereof increases the swelling property, flexibility and specific surface area of the fiber and leads to the strengthening of the fiber–fiber bonding force34,35. The wettability of the pulp fiber surface has a great influence on the swelling of the fiber and the liquid permeability of the paper, and the surface free energy of the pulp fiber can be calculated from the measurement of the contact angle of the liquid on the fiber surface. However, few studies have clarified the effect of the wettability of pulp fibers on the paper strength and fiber–fiber bonding of recycled fibers. In this study, in order to investigate the effect of the physicochemical properties of recycled pulp fibers on the paper strength, recycled pulps with different lignin contents prepared from softwood UKP and CTMP was examined from the change in the fiber–fiber bonding force based on the Page equation.

Ǥ Commercially available softwood bleached kraft pulp (SBKP), softwood unbleached kraft pulp (SUKP) and chemi-thermomechanical pulp (CTMP) were used (Table 1). SUKP and SBKP were manufactured from mixed chips of Japanese larch, Douglas fir and slash pine, and CTMP was manufactured from Todo fir.

Ǥ Chlorine dioxide bleaching treatment was performed on SUKP to prepare chlorine dioxide bleached softwood kraft pulp (DSUKP). For chlorine dioxide bleaching, 20 g of pulp was placed in a Lamizip. After 8 g of sodium chlorite powder was added, 4 ml of acetic acid were poured into the Lamizip together with 1200 ml of water. The zipper of the Lamizip was closed to prevent chlorine dioxide gas from escaping to the outside, and the Lamizip was placed in a hot water bath at 70–80 °C. After reacting for 1 h, 8 g of sodium chlorite and 4 ml of acetic acid were added. SUKP repeated this process twice. After completion of the reaction, the contents of the Lamizip were suction-filtered on a Büchner funnel, washed until acetic acid was exhausted, and finally washed with hot water. Lignin content was measured for all pulp samples according to TAPPI TEST METHOD T222. The results are shown in Table 1. Ǥ Pulp samples were beaten using a Valley beater according to ISO 5264- at a pulp concentration of 2% until a freshness of 400– 450 mL CSF. In order to prepare recycled pulps, handsheets were prepared from each beaten pulp sample based on ISO 5269-1. The handsheets were used as a sample (hereinafter abbreviated as R0) that was recycled 0 times. On the other hand, a part of the handsheets were dried at 80 °C for 24 h in a forced air circulation oven after Ƥ |

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Figure 1. Schematic diagram of measuring water contact angle between single pulp fiber and water.

the pressing. Further, after immersing the dried handsheets into water for 1 h, the handsheet was sufficiently defibrated by a disintegrator to prepare the handsheet again. This was used as a sample for one recycle (hereinafter abbreviated as R1). In this procedure, wetting and drying were repeated up to 3 times to prepare recycled pulp handsheet samples (hereinafter abbreviated as R3). The prepared test handsheet was adjusted for humidity all day and night under environmental conditions of 23 °C and 50% RH, and then the sheet density and tensile strength were measured according to ISO 5270, and the zero-span tensile strength was measured according to ISO 15361.

Ƥ Ǥ The optical technique to measure directly the contact angle of a water drop against a single pulp fiber was used for characterizing fiber-liquid interactions. A system consisting of a single-lens reflex camera (Nikon D3), a 24 mm wide-angle lens (Nikon), a bellows attachment (Nikon MD-4), an extension bellows attachment (Nikon BP-6E) was used for the measurement (Fig. 1). A xyz stage (Chuo Precision Industrial) was also used to hold a pulp fiber. The 24 mm wide-angle lens mounted to the bellows attachment was attached to the camera. The extension bellows attachment connected in series to increase the shooting magnification. The handsheet was carefully torn so as not to break the inter-fiber bonds in the paper sheet, and the surrounding fibers were excised, leaving one pulp fiber in the torn handsheet cross-section36. Pulp fibers were selected from relatively straight samples and measured 20 times per sample. After fixing the tip of the pulp fiber downward, the height of the tip of the pulp fiber was made constant. Pure water was put onto a slide glass in which a liquid reservoir was placed on the z-direction lift, and the z-direction lift was raised to make the tip of the pulp fiber pure water. The altitude at which the z-direction lift was raised was also constant, and the distance at which the pulp fibers were inserted into the water was the same27,29. After the tip of the pulp fiber came into contact with water, the area around the pulp fiber was continuously magnified and photographed every second for 10 s or more (Fig. 2). The P values between all of the data were all 0.05 or less, thus indicating a significant difference. The starting point of measurement (0 s) was defined as the point where fiber insertion could be confirmed from the continuously captured images. When the pulp fiber is in contact with water, the contact surface is quickly wetted and absorbed water. At this time, the contact angle changes to a certain extent, until the contact angle becomes stable when it is saturated (Figs. 3, 4, 5, 6).

ơ Ƥ Ǥ Figures 3, 4, 5 and 6 show the changes over time in the contact angle of water in various recycled pulp fibers. In the case of SBKP, the contact angle increased with the number of recycling increased (Fig. 3). The contact angle at 1 s after water comes into contact with the pulp fiber was 32° for the pulp fiber (R0) before recycling, while it was 44° after the first recycling (R1). However, the contact angle was 44° even after 3 times of recycling (R3). There was little difference in the contact angle at 1–3 s after the contact, even if the number of recycling treatments increased. Therefore, it was suggested that the first recycling treatment out of the three recycling treatments had a particularly large effect on the wettability of pulp fibers. The increase in contact angle due to the recycling process of pulp fiber can be caused by both the hornification of the pulp fiber surface shown in the decrease in pore volume in the fiber cell wall12,15, and the decrease in surface bonding potential30,32,33. On the other hand, Wistara et al.37 measured the contact angle of water using the Wilhelmy method to evaluate the surface properties of recycled pulp fibers, and found that the recycling treatment reduced the contact angle of bleached kraft pulp fibers. Regarding the change in wettability on the pulp fiber surface due to recycling, our results tended to differ from their results because of the difference in the treatments of the recycling process. That is, in the test of Wistara et al., the pulp was beaten after being repeatedly defibrated in water, dewatered and dried in the recycling process, but in our experiment, the fact that the pulp was not beaten after the recycling process Ƥ | Vol:.(1234567890)

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Water contact angle (degree)

Figure 2. Water contact angle of a single pulp fiber. R0

40 30 20 10 0 0

Time (sec)

Water contact angle (degree)

Figure 3. Effect of recycling on water contact angle of SBKP fibers with time variations.

40 30 20 10 0 0

Time (sec)

Figure 4. Effect of recycling on water contact angle of SUKP fibers with time variations.

had an effect. It is presumed that the surface of the pulp fiber after the recycling treatment was roughened by the subsequent beating treatment, the chemical composition of the fiber surface was changed, the hydrophilic surface was exposed, and as a result, the wettability was improved. The contact angle of water on the fiber surface before and after recycling (R0 and R1) has been stabilized at 4 s after the contact of water with the SBKP fiber. However, the water contact angle for the fibers after the three recycling treatments (R3) was lower after 4 s of contact compared to the fibers after the first recycling treatment

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Water contact angle (degree)

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40 30 20 10 0 0

Time (sec)

Wate rcontact angle (degree)

Figure 5. Effect of recycling on water contact angle of DSUKP fibers with time variations.

50 40 30 20 R0

0 0

Time (sec)

Figure 6. Effect of recycling on water contact angle of CTMP fibers with time variations.

(R1). The contact angle of water showed a tendency to gradually decrease as the number of recycling increased after 4 s of contact. This can be related to the appearance of radial cracks in the S2 layer of the fiber cell wall confirmed by TEM observation, when the SBKP fiber is recycled 3 times or more8,9,15. That is, the reason why the contact angle of water on the surface of SBKP fiber recycled 3 times or more gradually decreases is that as the contact time between the fiber surface and water becomes longer, water is penetrated into the cracks generated in the fiber cell wall of the recycled pulp. As a result, it is estimated that the water contact angle has decreased. As with the SBKP, the contact angle of water with respect to the SUKP fibers increases as the number of recycling increases (Fig. 4). The contact angle of the SUKP fiber after 1 s contact with water was 35°, which was slightly higher than that of the SBKP fiber. The SUKP fiber contains 5.7% of lignin (Table 1), and the change in the contact angle of water is influenced by the residual hydrophobic lignin. It would be caused that the surface of cellulosic fibers becomes hydrophobic again due to the redistribution of olefinic substances derived from wood materials, in addition to hornification of pulp fibers and cleavage due to hydrolysis of covalent bonds of cellulose chains during recycling38. In unbleached chemical pulp and mechanical pulp, lignin remains in the pulp, and the presence of triglyceride fat, fatty acid, resin acid and unsaponifiable matter has been confirmed, and it is possible to defibrate pulp fibers and heat-dry paper in the papermaking process. It is said that storage causes a self-sizing phenomenon in which these low-surface free-energy substances migrate and spread to the surface of pulp fibers34,39,40. Hodgson et al.25 determined the water contact angle of pulp fibers using the Wilhelmy method after heattreating Douglas fir kraft pulp at 105 °C for 16 h, and found that this heat treatment increased the contact angle. Therefore, it is shown that the wettability of the pulp fiber is suppressed by the self-sizing effect. Therefore, the contact angle of the SUKP pulp fibers after the first recycling increased to 41°, and after third recycling, the contact angle increased to 45°, showing a tendency for the contact angle to increase with the number of recycling. It is considered that this is due to the effect of self-sizing. In addition, the contact angle of water with respect to the SUKP fiber after three recycling treatments was larger than that of the SBKP regardless of the passage of time. When the SUKP was delignified (DSUKP), the recycling treatment increased the contact angle of the pulp fibers (Fig. 5). The contact angle of the DSUKP pulp fiber before recycling is 30°, which is lower than that of the SUKP. The lignin content of the DSUKP pulp fiber was 3.5%, when the SUKP was delignified. It is considered that as the hydrophobicity of the pulp fiber was reduced, the contact angle was lowered. In addition, it was confirmed that the contact angle of the pulp fiber increased to 41° after the first recycling treatment and 43° after three recycling treatments, but it was somewhat lower than the SUKP. Ƥ | Vol:.(1234567890)

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Tensile index (Nm/g)

Figure 7. Effect of recycling on contact angle of pulp fibers immersed in water after contact 1 s.

SBKP

SUKP

DSUKP

CTMP

80 60 40 20 -1

Number of cycles

Figure 8. Effect of recycling on tensile strength of handsheets prepared from various pulps.

In the case of the CTMP, the contact angle of pulp fibers tended to decrease after the recycling treatment (Fig. 6), showing a tendency different from that of softwood pulp fibers (SKP) whose water contact angle increased due to recycling. The contact angle before the recycling treatment was 48°, and the contact angle decreased to 43° after the first recycling treatment and 38° after three recycling treatments. It is presumed that the decrease in contact angle with the increase in the number of recycling is due to the decrease in the content of lignin and wood-derived resin during the recycling process. A slight increase in the tensile strength of the CTMP sheet due to the recycling process (Fig. 8) also supports this possibility. The contact angle of CTMP is higher than that of softwood pulp fiber, and it can be judged that the effect of hydrophobicity of lignin and resin increases the contact angle with water21. Figure 7 shows the effect of recycling treatment on the contact angle of pulp fibers at 1 s after contact with water. It was clarified that the contact angle of SBKP and SUKP fibers tends to increase as the number of recycling treatments increases, but the contact angle of CTMP fibers decreases as the number of recycling increases.

ơ Ǥ Figure 8 shows the changes in the tensile strength of handsheets prepared from each pulp sample by recycling. As the number of recycling treatments increased, the tensile strength of the handsheets prepared from the SKP pulps tended to decrease. In the case of the SBKP, the tensile index of handsheets gradually decreased from 65.9 N m/g in R0 to 55.7 N m/g in R1 and 53.8 N m/g in R3 due to the recycling process. There was a tendency that the tensile index of the SUKP handsheets is lower than that of the SBKP, which decreases from 63.4 N m/g in R0 to 54.5 N m/g in R1 and 48.0 N m/g in R3 due to recycling. It was revealed that delignification (DSUKP) treatment using sodium chlorite and acetic acid improves the tensile strength of handsheets before recycling. In addition, the tensile strength of DSUKP handsheets was higher than that of the SUKP regardless of the presence or absence of recycling treatment. Since the presence of lignin interferes with the formation of interfiber bonds in the handsheets, the delignification treatment could improve the tensile strength of the handsheets. The tensile index of DSUKP handsheets decreased from 71.2 N m/g before recycling (R0) to 65.4 N m/g for R1 and 61.1 N m/g for R3 as the number of recycling increased. On the other hand, in the case of the CTMP in which components other than cellulose such as lignin remain, the tensile index of handsheets increases from 28.6 N m/g in R0 to 32.2 N m/g in R1 and 36.8 N m/g in R3 as the number of recycling increases. R3 showed a tendency to increase slightly to 36.8 N m/g. This is partly due to the fact that in experiments conducted by Howard et al.18 using groundwood pulp (GP) and CTMP, Ƥ |

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SBKP

SUKP

DSUKP

CTMP

0.025 0.020 0.015 0.010 0.005 0.000 -1

Number of cycles

Figure 9. Changes in factor of weakness inter-fiber bond strength during recycling.

recycling treatment tends to increase strengths such as tensile strength and burst strength of papers produced from mechanical pulp. It is considered that lignin was removed by washing in the recycling process and the inter-fiber bonding between pulp fibers was strengthened in the papermaking process of defibration in water, dewatering and drying, which contributed to the improvement of tensile strength. Nazhad25 showed in experiments on the recycling process of CTMP that the fiber coarseness of CTMP was reduced and the fiber flexibility was added regardless of the degree of delignification treatment with sodium chlorite. Furthermore, it has been reported that in CTMP that has been subjected to the delignification treatment, the strength of the handsheets decreases due to the increase in the number of recycling, regardless of the amount of lignin content. On the other hand, in the CTMP experiment of this study, it was confirmed that the tensile strength of the handsheets tends to increase or relatively little change as the number of recycling increases. On the other hand, in the CTMP experiment of this study, it was confirmed that the tensile strength of handsheets tends to increase or relatively little change as the number of recycling increases. The effect of the recycling treatment on the tensile strength of the CTMP handsheets obtained in this study is different from that of SUKP and DSUKP because the wettability on the surface of the CTMP fiber improved and the fiber–fiber bond strength increased as the number of recycling increased.

ơ Ƥ ȂƤ Ǥ To clarify the factors that influence the tensile strength of paper sheets, the Page equation17,31 has been proposed. Furthermore, Cildir et al.16 applied the Page equation below to calculate the fiber–fiber bond strength from the viewpoint that the resistance to fracture consists of two comparable resistances. It was presumed that the decrease in tensile strength was mainly the decrease in the fiber–fiber bond strength.

1/T = 1/F + 1/B

(2)

F = 8Z/9

(3)

where T: tensile index of sheet, F: fiber strength index of sheet, Z: zero-span tensile index of sheet, B: bond strength index of sheet. Using Eqs. (2) and (3), it should be possible to calculate the fiber–fiber bond strength index of sheet, B, if the tensile strength of sheet, T and the zero-span tensile index, Z are measured. Figure 9 shows the effect of the number of recycling treatments on the fiber–fiber bond strength index. As the number of recycling treatments increased, the factor of fiber–fiber bond weakness (1/B) of all SKP paper sheets tended to increase, and it became clear that the fiber–fiber bond strength became weaker. In addition, 1/B of DSUKP was lower than that of SUKP. By applying the delignification treatment, the lignin content in the paper sheet is reduced and the formation of fiber–fiber bonds is promoted. Comparing 1/B of SBKP and DSUKP, despite the fact that the DSUKP had a smaller of 1/B and a higher lignin content in pulp (Table 1), the result was obtained that the fiber–fiber bond strength of DSUKP was higher. On the other hand, in the CTMP paper sheet, 1/B decreased with the number of recycling, which means that the fiber–fiber bond strength in the paper sheet was improved.

ơ Ƥ Ƥ ȂƤ Ǥ The tensile strength of the paper sheet, the wettability of the pulp fiber, and the change in the bond strength between the pulp fibers in the paper sheet were evaluated by the recycling experiment of the SKP pulp fiber, and the correlation was examined. When all the values were evaluated for each sample used in this study, the correlation between the tensile strength of the sheet and the fiber–fiber bond weakness index was R2 = 0.98 (Fig. 10). The p value of the correlation coefficient was 0.000, which was judged to be significant at the 5% significance level. Therefore, it was found that the correlation between the tensile strength of the sheet and the fiber–fiber bond strength is considerably high. When the relationship between 1/B and the contact angle of water with respect to the pulp fiber in the SKP sample was examined, R2 = 0.71 was obtained (Fig. 11). In this case, the p value was 0.004, which was significant Ƥ | Vol:.(1234567890)

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Tensile index (Nm/g)

80 70 R² = 0.9804

60 50 40 0.0

0.5

1.0

1.5

Factor of weakness, 1/Bx10-2

Water contact angle (degree)

Figure 10. Factor of bonding weakness, 1/B versus tensile index of SKP handsheets.

R² = 0.7145

0 0.0

0.5

1.0

1.5

Factor of weakness, 1/Bx10-2

Figure 11. Factor of bonding weakness, 1/B versus water contact angle after contact 1 s (SKP).

when the t test was performed (p < 0.05). It was found that it was not uncorrelated, and it was confirmed that the correlation between the two factors was relatively high. Therefore, it was clarified that the better the wettability of the pulp fibers, the easier it is to form fiber–fiber bonds and the greater the tensile strength of the paper sheet. In addition, it was speculated that the main cause of the decrease in the tensile strength of the paper sheet due to recycling was the decrease in the fiber–fiber bond strength of the paper sheet, and that the decrease in the fiber–fiber bond strength was related to the decrease in the wettability of the pulp fibers.

Pulp samples prepared from softwood bleached kraft pulp (SBKP), softwood unbleached kraft pulp (SUKP) with different lignin contents and chemi-thermomechanical pulp (CTMP) are subjected to one or three repeated wet and dry treatments. The contact angle of water with respect to each pulp fiber over time was measured. Furthermore, the effect of the wettability of pulp fibers on the tensile strength of the paper sheet was evaluated from the change in the fiber–fiber bond strength based on the Page equation. 1. In the case of the SBKP, repeated dry and wet recycling treatment increased the contact angle of water with fibers and reduced wettability. The pulp fiber (R3) that had been recycled three times maintained a contact angle similar to that of R1 within 1–3 s after contact. After 4 s of contact, it was smaller than the contact angle of the pulp fibers (R1) that had been recycled once. On the other hand, the CTMP fiber showed a different behavior from the softwood kraft pulp fiber (SKP) because the contact angle with water decreased as the number of recycling increased. 2. The tensile strength of softwood kraft pulp (SKP) paper sheets, including paper sheets prepared from bleached, unbleached and delignified pulp, tended to decrease as the number of recycles increased. On the other hand, in the paper sheet prepared from CTMP, the tensile strength tends to increase slightly as the number of recycling increases, suggesting that the fiber–fiber bond may be strengthened. 3. By measuring the tensile strength and zero-span tensile strength of a paper sheet prepared from recycled softwood kraft pulp (SKP) fibers and applying it to the Page equation, the change in the contact angle of water with respect to the pulp fiber over time can be determined. The effect of the wettability of pulp fibers on the tensile strength of paper, especially the fiber–fiber bond strength, was evaluated. As a result, the tensile strength of the paper sheet from the recycled SKP pulp fibers

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decreased with the increase of the factor of fiber–fiber bond weakness index (1/B). Furthermore, it was clarified that the wettability of pulp fibers is improved and 1/B is decreased. Therefore, the decrease in the tensile strength and fiber–fiber bond strength of the paper sheet due to the pulp recycling process could be associated with the decrease in the wettability of the pulp fiber. Received: 7 October 2021; Accepted: 11 January 2022

1. Paper Recycling Promotion Center, 2019 Statistics of recovered paper in Japan. http://www.prpc.or.jp/wp-content/uploads/2007082019-statistics-of-recovered-paper-in-Japan.pdf. Accessed 8 July 2020. 2. MaKee, R. C. Effect of repulping on sheet properties and fiber characteristics. Paper Trade J. 155(21), 34–40 (1971). 3. Ellis RL, Sedlachek KM, Chapter 2 Recycled- versus virgin-fiber characteristics: a comparison. In: Spangenberg RJ (ed) Secondary fiber recycling. TAPPI PRESS, 7–19 (Atlanta, 1993). 4. Aspler JS, Chapter 3 Print quality of recycled-fiber papers: a review. In: Spangenberg RJ (ed) Secondary Fiber Recycling. TAPPI PRESS, 21–27 (Atlanta, 1993). 5. Howard RC, The effects of recycling on pulp quality. In: McKinney RWJ (ed) Technology of Paper Recycling. Blackie Academic and Professional, 180–203 (Glasgow, 1995). 6. Ackermann C, Göttsching L & Pakarinen H, Chapter 10 Papermaking potential of recycled fiber. In: Göttsching L, Pakarinen H (ed) Recycled Fiber and Deinking. Fapet Oy, 358–438 (Helsinki, 2000). 7. Isogai, A. The effects of chemical and mechanical modifications of pulp fibers. Kami-pa-gi-kyō-shi 62(7), 830–838 (2008). 8. Okayama, T. The effects of recycling on pulp and paper properties. Japan Tappi J. 56(7), 62–68 (2002). 9. Okayama, T., Yamagishi, Y. & Oye, R. Influence of recycling on wood pulp fibres III. Morphological changes in cell walls of pulp fibres with recycling. Japan Tappi J. 36(2), 311–320 (1982). 10. Stone, J. E., Scallan, A. M. & Abrahamson, B. Influence of beating on cell wall swelling and internal fibrillation. Svensk Papperstidn 9(10), 687–694 (1968). 11. Stone, J. E. & Scallan, A. M. A structural model for the cell wall of water-swollen wood pulp fibers based on their accessibility to macromolecules. Cellul. Chem. Technol. 2(3), 343–358 (1968). 12. Okayama, T., Kitayama, T. & Oye, R. Influence of recycling on wood pulp fibres II. Changes in pore volume of pulp fibres by recycling. Japan Tappi J. 35(12), 27–32 (1981). 13. Stone JE & Scallan AM, Influence of drying on the pore structures of the cell wall. In: Bolam F (ed.) Consolidation of the Paper Web. Tech. Sec. British Paper and Board Makers’ Assoc, 145–174 (London, 1966). 14. Wang, X., Maloney, T. C. & Paulapuro, H. Internal fibrillation in never-dried and once dried chemical pulps. Appita J. 56(6), 455–459 (2003). 15. Kitayama, T., Okayama, T. & Oye, R. Changes of chemical pulp fibres during recycling. Sen’i Gakkaishi. 43(9), 486–494 (1987). 16. Cildir, H. & Howarth, P. The effect of re-use on paper strength. Pap. Technol. 13(5), 333–335 (1972). 17. Page, D. H. A theory for the tensile strength of paper. Tappi 52(4), 674–681 (1969). 18. Howard, R. C. & Bichard, W. The basic effects of recycling on pulp properties. J. Pulp Paper Sci. 18(49), 151–159 (1992). 19. Robinson JV, Chapter 7 Fiber bonding. In: Casey (ed) Pulp and Paper Chemistry and Chemical Technology. Third Edition Vol. II. Wiley, 915–963 (N.Y., 1980). 20. Young, R. A. Wettability of wood pulp fibers: Applicability of Methodology. Wood Fiber Sci. 8(2), 120–128 (1977). 21. Klungness, J. H. Measuring the wetting angle and perimeter of single wood pulp fibers: A modified method. Tappi J. 64(12), 65–66 (1981). 22. Jacob, P. N. & Berg, J. C. Zisman analysis of three pulp fiber furnishes. Tappi J. 76(2), 105–107 (1993). 23. Luner, P. & Sandell, M. The wetting of cellulose and wood hemicellulose. J. Polym. Sci. Part C 28, 115–142 (1969). 24. Lee, S. B. & Luner, P. The wetting and interfacial properties of lignin. Tappi 55(1), 116–121 (1972). 25. Hodgson, K. T. & Berg, J. C. Dynamic wettability properties of single wood pulp fibers and their relationship to absorbency. Wood Fiber Sci. 20(1), 3–17 (1988). 26. Berg, J. C. The importance of acid-base interaction in wetting, coating, adhesion and related phenomena. Nordic Pulp Paper Res. J. 8(1), 75–85 (1993). 27. Yoshinaga, N., Okayama, T. & Oye, R. Dynamic wettability on pulp fiber and paper surface (Part 1). Measurement on wettability of pulp fiber at short time intervals. Sen’i Gakkaishi 49(6), 287–293 (1993). 28. Yoshinaga, N., Okayama, T., Oye, R. & Sawatari, A. Effect of various treatments on wettability of pulp fiber. Sen’i Gakkaishi 49(9), 493–499 (1993). 29. Okayama, T., Yoshinaga, N. & Hashizume, K. Liquid transfer characteristics of recycled pulp handsheets. Japan Tappi J. 58(4), 92–100 (2004). 30. Eastwood FG & Clarke B, Handsheet and pilot machine recycling degradation mechnisms. In: The Fundamental Research Committee (ed) Fibre-water interactions in paper-making, Tech. Div. British Paper and Board Ind. Fed., 2, 835–855 (London, 1978). 31. Seth, R. S. & Page, D. H. The problem of using Page’s equation to determine loss in shear strength of fiber–fiber bonds upon pulp drying. Tappi J. 79(9), 206–210 (1996). 32. Gurnagul, N., Ju, S. & Page, D. H. Fibre–fibre bond strength of once-dried pulps. J. Pulp Pap. Sci. 27(3), 88–91 (2001). 33. Nazhad, M. M. Recycled fiber quality—A review. J Ind. Eng. Chem. 11(3), 314–329 (2005). 34. Tze, W. T. & Gardner, D. J. Swelling of recycled wood pulp fibers: Effect on hydroxyl availability and surface chemistry. Wood Fiber Sci. 33(3), 364–376 (2001). 35. Xie, J. et al. Role of a “surface wettability switch” in inter-fiber bonding properties. RSC Adv. R. Soc. Chem. Eng. 8(6), 3018–3089 (2018). 36. Katsura, T., Murakami, K. & Imamura, R. Single fiber extraction test using long fiber sheets. Mokuzai Gakkaishi 24(8), 552–557 (1978). 37. Wistara, N., Zhang, X. & Young, R. A. Properties and treatments of pulps from recycled paper. Part II Surface properties and crystallinity of fibers and fines. Cellulose 6, 325–348 (1999). 38. Back EL, “Discussion”. In: Fiber-Water Interactions in Paper-Making, Trans. Symp. Oxford, Sept. 1977, Tech. Div. British Paper and Board Ind. Fed., 2, 873 (London, 1978). 39. Hubbe, M. A., Venditti, R. A. & Rojas, O. J. What happens to cellulosic fibers during papermaking and recycling? A review. BioResources 2(4), 739–768 (2007). 40. Lyne, M. B. & Aspler, J. S. Wetting and the sorption of water by paper under dynamic conditions. Tappi J. 65(12), 98–101 (1982).

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This research was supported by the Foundation (KF 201812) of State Key Laboratory of Biobased Material and Green Papermaking, Qilu University of Technology, Shandong Academy of Sciences.

Data curation: N.A. Formal analysis: H.J., R.K., T.O. Investigation: H.J., R.K., T.O. Writing—original draft: H.J.. Writing—review and editing: R.K., T.O.

The authors declare no competing interests.

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Volume 8, Number 2, 2022

Lignin Inter-Diffusion Underlying Improved Mechanical Performance of Hot-Pressed Paper Webs 1

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AMANDA MATTSSON , TOVE JOELSSON , ARTTU MIETTINEN , JUKKA A. KETOJA , GUNILLA 1 1 PETTERSSON & PER ENGSTRAND . Broader use of bio-based fibres in packaging becomes possible when the mechanical properties of fibre materials exceed those of conventional paperboard. Hot-pressing provides an efficient method to improve both the wet and dry strength of lignin-containing paper webs. Here we study varied pressing conditions for webs formed with thermomechanical pulp (TMP). The results are compared against similar data for a wide range of other fibre types. In addition to standard strength and structural measurements, we characterise the induced structural changes with X-ray microtomography and scanning electron microscopy. The wet strength generally increases monotonously up to a very high pressing temperature of 270°C. The stronger bonding of wet fibres can be explained by the inter-diffusion of lignin macromolecules with an activation energy around -1 26 kJ mol after lignin softening. The associated exponential acceleration of diffusion with temperature dominates over other factors such as process dynamics or final material density in setting wet strength. The optimum pressing temperature for dry strength is generally lower, around 200°C, beyond which hemicellulose degradation begins. By varying the solids content prior to hot-pressing for the TMP sheets, the highest wet strength is achieved for the completely dry web, while no strong correlation was observed for the dry strength. Contact information: 1. Department of Chemical Engineering, Mid Sweden University, SE-85170 Sundsvall, Sweden. 2. MoRe Research Örnsköldsvik AB, Box 70, SE-89122 Örnsköldsvik, Sweden. 3. Department of Physics, University of Jyvaskyla, P.O. Box 35, FI-40014 Jyvaskyla, Finland. 4. VTT Technical Research Centre of Finland Ltd., P.O. Box 1000, FI-02044 Espoo, Finland. Polymers 2021, 13, 2485. https://doi.org/10.3390/polym13152485 Creative Commons Attribution International License 4.0

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Article 2 – Hot Pressing

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Lignin Inter-Diffusion Underlying Improved Mechanical Performance of Hot-Pressed Paper Webs Amanda Mattsson 1, * , Tove Joelsson 1,2 , Arttu Miettinen 3,4 , Jukka A. Ketoja 1,4 , Gunilla Pettersson 1 and Per Engstrand 1 1

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Citation: Mattsson, A.; Joelsson, T.; Miettinen, A.; Ketoja, J.A.; Pettersson, G.; Engstrand, P. Lignin Inter-Diffusion Underlying Improved Mechanical Performance of Hot-Pressed Paper Webs. Polymers 2021, 13, 2485. https://doi.org/ 10.3390/polym13152485

Department of Chemical Engineering, Mid Sweden University, SE-85170 Sundsvall, Sweden; tove.joelsson@more.se (T.J.); jukka.ketoja@vtt.ﬁ (J.A.K.); gunilla.pettersson@miun.se (G.P.); per.engstrand@miun.se (P.E.) MoRe Research Örnsköldsvik AB, Box 70, SE-89122 Örnsköldsvik, Sweden Department of Physics, University of Jyvaskyla, P.O. Box 35, FI-40014 Jyvaskyla, Finland; arttu.i.miettinen@jyu.ﬁ VTT Technical Research Centre of Finland Ltd., P.O. Box 1000, FI-02044 Espoo, Finland Correspondence: amanda.mattsson@miun.se

Abstract: Broader use of bio-based fibres in packaging becomes possible when the mechanical properties of fibre materials exceed those of conventional paperboard. Hot-pressing provides an efficient method to improve both the wet and dry strength of lignin-containing paper webs. Here we study varied pressing conditions for webs formed with thermomechanical pulp (TMP). The results are compared against similar data for a wide range of other fibre types. In addition to standard strength and structural measurements, we characterise the induced structural changes with X-ray microtomography and scanning electron microscopy. The wet strength generally increases monotonously up to a very high pressing temperature of 270 ◦ C. The stronger bonding of wet fibres can be explained by the inter-diffusion of lignin macromolecules with an activation energy around 26 kJ mol−1 after lignin softening. The associated exponential acceleration of diffusion with temperature dominates over other factors such as process dynamics or final material density in setting wet strength. The optimum pressing temperature for dry strength is generally lower, around 200 ◦ C, beyond which hemicellulose degradation begins. By varying the solids content prior to hot-pressing for the TMP sheets, the highest wet strength is achieved for the completely dry web, while no strong correlation was observed for the dry strength.

Academic Editors: Domenico Acierno and Antonella Patti

Keywords: hot-pressing; paper web; ﬁbre; lignin; diffusion; activation energy

Received: 3 July 2021 Accepted: 23 July 2021 Published: 28 July 2021

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Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

1. Introduction Microplastic emissions are one of the world’s greatest environmental threats. The amount of these emissions has been steadily increasing for many years and is expected to continue to do so [1]. Thus, material options that are both renewable and biodegradable have been extensively searched for. A particular challenge is to develop materials that have similar or better properties in humid or wet conditions as their oil-based counterparts. This should be the case not only for strength but also for dimensional stability and barrier properties, which are important, e.g., in packaging and construction applications [2]. Recent studies have shown that hot-pressing of lignin-rich paper webs could provide at least a partial solution to the above challenge. Clear improvements are observed for both wet and dry tensile strength (later also referred to as only wet and dry strength) compared to non-treated webs [3,4], enabling applications in several packaging areas. Joelsson et al. [5] showed that the tensile strength of paper based on chemithermomechanical pulp (CTMP) could be improved even by 100% when passing the paper through a hot nip (200 ◦ C, 6 MPa) with a pressing time of 1.5 s and 70 s after hold. Moreover, by hot-pressing, the wet strength increased dramatically to a value of about 16 kNm/kg from the level of 2 kNm/kg

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found for non-heat treated paper. It could be seen that the amount of lignin was of great importance [5,6]. Thus, such a hot-pressing technology could provide innovative product solutions once both suitable raw materials and optimal process conditions are defined by a deeper understanding of underlying strengthening mechanisms. Also, other properties that are important for the final applications of packaging papers, such as water resistance, have shown promising results. Contact angle measurements showed increased values for the hot-pressed paper samples [5], which suggests a more hydrophobic surface [7]. Similar results and conclusions, that heat treatment of this material increases the hydrophobicity, have been observed in the area of thermal modification and welding of wood [8,9]. Joelsson et al. [5] postulate that softened lignin from fibres redistributes within the consolidated structure, enabling strong inter-fibre bonding even in a wet fibre network. In other words, lignin acts as a natural wet-strength additive. Similar heat-induced bonding was already found by Gupta et al. in 1962 [10]. They applied isolated lignin to paper samples and pressed them together at high temperature. The appearing inter-layer bonding increased the strength properties. The optimal bonding temperature depended on lignin type and differed for wet or dry paper. This was explained by the thermal transition of lignin and by the plasticizing effect of water, which reduces the glass transition temperature (Tg) by 70–165 ◦ C depending on the type of lignin [11]. The importance of water for the viscoelastic properties of wood was reviewed in 1982 by Back and Salmén [12], who concluded that water-saturated native lignin has a softening temperature of about 115 ◦ C. This could be further lowered by sulphonation. Joelsson et al. [13] have recently shown that the softening effect of sulfonation also occurs when a sulfite-enriched paper is hot-pressed. In this case, a lower temperature is required to maintain strength. Lignin is often referred to as a by-product in industries such as the production of paper, ethanol, biomass, etc. [14]. However, the polymer is seen to have a huge technological potential, and related research has expanded in recent years. Nevertheless, there are currently only a few commercial products based on lignin. For example, there are pulping processes where the lignin is not totally removed, leading to so-called high yield pulps (HYP). Their yield can be as high as 95%, which can be compared to the yield of about 50% for chemical pulp with removed lignin [15]. Thus, high yield pulping is a preferred option from the viewpoint of efficient utilisation of wood raw material. The main reason for removing the lignin in chemical pulping is to achieve high brightness and strength, which are important properties, e.g., white packaging, copy paper and some heavily-coated brochure papers. On the other hand, HYP and particularly thermomechanical pulp (TMP) are mainly used for magazine paper, newspaper and book paper, for which high opacity and light scattering are more important than brightness or strength. However, the share of paper usage has declined rapidly during recent years, which leaves a considerable amount of space for new markets. At the same time, the process targets should be reconsidered based on the changed product requirements. The aim of this work is to investigate mechanisms underlying the above improved mechanical properties obtained by hot-pressing. In particular, we would like to know how to control lignin redistribution in fibre networks without deteriorating other fibre polymers such as hemicelluloses. Moreover, the high temperature and moisture content of fibres may introduce also other structural changes that affect the mechanical properties of the hotpressed web. These changes are characterized by X-ray tomography and scanning electron microscopy (SEM). The experimental results are interpreted with the help of theoretical ideas on polymer inter-diffusion. In addition to analysing the results carefully for webs containing TMP, we show that the same diffusion mechanisms explain the wet-strength improvement for a wide variety of other pulps despite their different lignin content.

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2. Materials and Methods 2.1. Materials The paper materials used in this study were based on different mechanical and chemical kraft pulps obtained from Swedish mills, together with some pulps produced in a laboratory. Mechanical pulps with a lignin content of 26–28% included the following types: TMP (Holmen AB Braviken mill, Norrköping, Sweden), CTMP (Rottneros AB Rottneros mill, Sunne, Sweden, and SCA AB Östrand mill, Timrå, Sweden), and high-temperature chemithermomechanical pulp (HTCTMP) produced at the test pilot refinery at Valmet AB, Sundsvall, Sweden. Chemical kraft pulps with a lignin content of 0–12% were unbleached kraft liner (SCA AB Obbola mill, Umeå, Sweden), bleached kraft liner (Metsäboard Husum mill, Örnsköldsvik, Sweden), bleached kraft (Södra Cell Värö mill, Varberg, Sweden), and unbleached kraft with different rest-lignin contents produced at the laboratory pilot of MoRe Research (Örnsköldsvik AB, Örnsköldsvik, Sweden). The mechanical pulps and the pilot-produced chemical kraft pulps were based on Norway spruce, and the rest of the chemical pulps were based on softwood (a mixture of spruce and pine). The lignin content was measured by the Klason method (T222). All paper material except that containing TMP were prepared using a Rapid Köthen sheet former (Paper Testing Instruments, Pettenbach, Austria) according to ISO 5269-2:2004, resulting in uniform fibre orientation. The TMP paper was produced in an XPM Fourdrinier paper machine at the laboratory of MoRe Research (Örnsköldsvik AB, Örnsköldsvik, Sweden). The web width was 0.225 m, the machine speed was 1.4 m/min, and the fibre orientation ratio was 1.7 between machine direction (MD) and cross-machine direction (CD). The grammage of the paper materials was in the range of 100–150 g/m2 . In both of the above production methods, the structure forming step is followed by water removal with wet-pressing at relatively low temperatures, which significantly affects the density of the formed paper material. However, the largest changes in density take place during the final hot-pressing process. 2.2. Pressing Methods Two different pressing methods were applied in the experiments (Figure 1). Firstly, test points pressed at temperatures equal to or lower than 200 ◦ C were performed using an oil-heated cylinder press (Figure 1a). Moist sheets were fed into the press on a felted fabric with a rate of 1 m/min and a nip pressure of 6 MPa. The pressing time in the nip was 1500 ms (at a nip length of about 25 mm) and after-hold was 70 s. Secondly, test points hot-pressed at temperatures higher than 200 ◦ C were performed using a test pilot press with an infrared-heated steel belt carrying the paper samples through a nip shown in Figure 1b. The speed was 3 m/min, corresponding to a pressing time of 40 ms (nip length was about 2 mm) and the after-hold was 23.5 s. The nip load was estimated to be 8 MPa, and the press load of the steel belt was 0.15 MPa. In both cases, nip lengths were measured with sensor films from Fujifilm Holdings Corporation (Tokyo, Japan), Prescale LW 2.5–10 MPa. Thin blotter papers on both sides of an actual paper sample were used in all tests to prevent sticking. The solids content of paper sheets was 50–60% before pressing at the cylinder press, and at the infrared-heated steel belt press test pilot solids content of TMP sheets was 50–100%. 2.3. Sheet Testing Sheet testing was carried out after conditioning according to ISO 187. Grammage and density were determined according to ISO 536 and ISO 534 respectively. The standard sheet thickness was measured according to ISO 5270. Dry tensile strength was determined according to ISO 1924-3. Wet tensile strength was measured according to ISO 3781 after immersion in water for one hour.

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Figure 1. (a) Felted, oil-heated cylinder press [16] operated at MoRe Research Örnsköldsvik AB, Örnsköldsvik, Sweden. Illustration: Mats Rundlöf, Capisco, Norrköping, Sweden. (b) Infrared-heated press based on a steel belt [17] produced by Ipco AB, Sandviken, Sweden. Both pictures are reproduced under the terms of the CC BY license.

2.4. Characterisation 2.4.1. Scanning Electron Microscope (SEM) Image analyses using a high-resolution SEM (Tescan Maya3-2016, TESCAN Brno, s.r.o., Brno, Czechia) were performed on TMP sheets with different pressing conditions. The applied electron beam voltage was 3.00 kV and the beam intensity was 1.00. To obtain images of the structures at different scales, magnifications 500×, 2000× and 10,000× were used. These magnifications correspond to pixel sizes of 270 nm, 67 nm and 13 nm, respectively. The corresponding beam spot sizes were 26 nm, 26 nm and 4 nm, respectively. A secondary electron detector was used to capture the images. The working distance to the sample, which ranges from 5 to 7 mm, was adjusted for each image to achieve the best possible image quality. The cross-sections were polished either using an argon ion milling system (Hitachi IM4000Plus, Hitachi High-Tech Co., Tokyo, Japan) or by freeze-drying the specimens at −110 ◦ C and vacuum for 12 h followed by crushing to produce the transverse sections. Lastly, the samples were prepared by sputtering them with a 5–10 nm thin layer of iridium prior to imaging. 2.4.2. X-ray Microtomography X-ray tomography images of the sheets pressed at different temperature levels were acquired using an X-ray microtomograph (CT) (Xradia MicroXCT-400, Xradia Inc., Concord, CA, USA). A sample approximately 1 mm wide was cut from the sheet with a surgical knife and glued to the top of a carbon fibre rod, which served as a sample holder. Images were acquired with 0.6 μm pixel size, corresponding to 1.5 μm spatial resolution (MTF10%), at 40 kV X-ray tube accelerating voltage and 4 W power. 1750 projection images per sample were acquired with an exposure time of 10 s per projection. The projections were reconstructed into a 3D volume image using the filtered backprojection algorithm. The volume images show an area of approximately 1.1 mm × 1.1 mm of the sheet. The reconstructed images were denoised using bilateral filter (spatial sigma = 1.5 μm, radiometric sigma ≈ 7% of dynamic range) [18]. The filtered images showed a high contrast-to-noise ratio (typically ≈ 40) and could therefore be segmented using the simple Otsu thresholding method [19]. After the thresholding procedure, the remaining small image artefacts were removed by deleting all contiguous regions whose size was less than 100 voxels. This procedure results in a visually correct segmentation, as shown in Figure 2.

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Figure 2. Visualisation of the X-ray microtomograph (CT) image of a sample pressed at 190 ◦ C temperature (grayscale), edges of segmented regions (red) and surfaces of the sheet (blue).

The surfaces of the paper sheets were defined using the Carpet method [20] which works by lowering a surface following quenched noise Edwards-Wilkinson dynamics towards the segmented paper sheet. The bright pixels corresponding to the paper eventually slow down and stop the evolution of the surface. The paper surface is then defined by the position where the motion of the dynamic surface stops. An example of the surfaces is shown in Figure 2. The total volumes of the sheet, pores, and fibres were determined by counting the number of pixels classified to each material phase. The pore size distribution was determined using the local thickness algorithm [21]. Image analysis was performed using the freely available software pi2 (https://www.github.com/arttumiettinen/pi2, accessed on 28 July 2021), and 3D visualisations were created using MeVisLab (MeVis Medical Solutions AG, Bremen, Germany). 3. Results 3.1. Porosity of the Fibre Networks from X-ray Microtomography Hot-pressing narrows the pore-size distribution of a sheet significantly as can be seen in Figure 3. This effect is strongest at very high temperatures. Still, the mean pore size in all cases is several micrometres and thus clearly higher than the resolution of X-ray imaging. Therefore, it is reasonable to assume that the measurement of total pore volume gives reliable results.

Figure 3. Pore-size distributions for the unpressed reference sheet and hot-pressed sheets with temperature of 190 ◦ C (cylinder press) and 270 ◦ C (steel belt press).

The average porosity, 0.74, is quite high for the unpressed reference sheet. In this case, lumens are still partly open, and the above value for porosity is similar as in earlier

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similar measurements [22]. During hot-pressing, density increases and porosity decreases significantly as lumina collapse and fibres soften (Figure 4). Moreover, a slight decrease in sheet porosity is also observed when temperature and pressure are increased, from 0.34 at 190 ◦ C and 6 MPa (cylinder press) to 0.32 at 270 ◦ C and 8 MPa (steel belt press), despite the much shorter pressing time in the latter case. Thus, plastic fibre deformations take place very rapidly at high temperatures when the polymer components of fibres soften.

(a)

(b)

(c)

Figure 4. 3D visualisations of the CT images of samples. (a) Unpressed reference, (b) pressed at 190 ◦ C, and (c) pressed at 270 ◦ C.

Table 1 shows the resulting sheet densities. The values obtained from 3D structural images are higher than those obtained with standard sheet density measurements mainly because of the surface roughness volume excluded when calculating the effective value from the CT data. Table 1. Effective density of the TMP sheets obtained from the X-ray microtomography (CT) compared with the standard measurement. Sample Unpressed Pressed 190 ◦ C Pressed 270 ◦ C

Effective Sheet Density (CT) kg/m3

367 955 kg/m3 1000 kg/m3

Sheet Density (ISO 534) 313 kg/m3 694 kg/m3 734 kg/m3

The effective ﬁbre density ρ f can be measured from sheet grammage G, area of sample A, and total volume of ﬁbres Vf determined from the 3D images, ρf =

GA Vf

(1)

Equation (1) gives the values 1440 kg/m3 (unpressed reference), 1450 kg/m3 (190 ◦ C, cylinder press) and 1460 kg/m3 (270 ◦ C, steel belt press) for the density of the fibres. The wall density without lumen is about 1500 kg/m3 for natural wood fibres [23]. The slightly lower values can be explained by a small total volume of pores whose size is below the imaging resolution. However, the main conclusion is that the hot-pressing does not induce any noticeable density change in the fibre walls, despite a large reduction in the network porosity and mean pore size. 3.2. Visual Observations on Pressing-Induced Changes in Fibres Figure 5 shows SEM images of the TMP paper sheets pressed at different temperatures. The unpressed sample (Figure 5a) has a porous structure, with fibres having their characteristic oval shape. For the sheets pressed at higher temperatures, 190 ◦ C (Figure 5b), and 270 ◦ C (Figure 5c), fibres consolidate into ribbon-like structures with an almost perfectly closed lumen. The sample pressed at 190 ◦ C (cylinder press) is treated for a much longer time, 1.5 s in the nip and 70 s after hold, compared to the sample at 270 ◦ C (steel belt press),

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treated 40 ms in the nip and 23 sec in after hold. This difference appears as a more closed surface for the 190 ◦ C sample, despite its slightly higher overall porosity (see Section 3.1).

Figure 5. SEM images of the structures for three different pressing temperatures for the material, (a) unpressed reference, (b) pressed at 190 ◦ C, and (c) pressed at 270 ◦ C. SEM images of the cross-sections polished with an argon ion miller for three different pressing temperatures for the material, (d) unpressed reference, (e) pressed at 190 ◦ C, and (f) pressed at 270 ◦ C. SEM images of the freeze-dried cross-sections of the ﬁbre wall for three different pressing temperatures for the material, (g) unpressed reference, (h) pressed at 190 ◦ C, and (i) pressed at 270 ◦ C. The working distance for the samples was in the range from 5 to 7 mm.

The porosity differences in different samples are best visible in SEM cross-sections of these structures, obtained after polishing the samples with an argon ion milling machine. In addition to inter-fibre pores, also fibre lumens stay partly open for the unpressed sheets (Figure 5d). On the other hand, the highest 270 ◦ C temperature causes an almost complete disappearance of lumen space due to thermal softening (Figure 5f), whereas most of the collapsed lumens are still visible at the lower 190 ◦ C temperature (Figure 5e). In order to look closer at the nano-/microstructure inside the fibre wall, cross-sections were prepared also by freeze-drying the material prior to breaking the sheets. However, in these cross-sections (Figure 5g–i), it is not possible to observe any substantial differences in the porous structure when comparing the unpressed sample and the ones pressed at high temperatures. This suggests that lignin and other matrix polymers are not extracted from the fibre wall to the same extent as for some chemical treatments of wood fibres [24],

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where the extra microporosity is clearly visible. This observation is in alignment with the fibre wall densities obtained from the CT analyses (see Section 3.1). 3.3. Lignin Inter-Diffusion Affecting Wet Tensile Strength The dependence of wet tensile strength index (wet tensile strength divided by the grammage) on pressing temperature seems to be defined by the activation energy for the inter-diffusion of lignin between fibre surfaces. The inter-diffusion is expected to be Ea proportional to exp (− RT ) [10], where Ea is the activation energy, T is temperature, and R is gas constant. We obtained Ea /R by plotting ln(Wet tensile strength index) vs. 1/Temperature (1/T) and taking the slope of the linear fitting line. In Figure 6, this is done first for TMP only (Figure 6a) and then for the whole data (Figure 6b) with different furnishes at temperatures exceeding 150 ◦ C. The relationship between ln(Wet tensile strength index) and 1/T seems quite linear in the range of 150–270 ◦ C for all pulps. This is striking taking into account that the press type and associated nip dwelling time are different below (cylinder press) and above (steel belt press) 200 ◦ C for the data. The above exponential temperature-dependence of lignin diffusion rate thus dominates over other factors when the level of wet tensile strength of pressed material is set by these processes.

(a)

(b)

Figure 6. The logarithm of wet tensile strength index plotted against 1/Temperature when pressed with either cylinder press (T = 150 ◦ C, 190 ◦ C; 6 MPa) or steel belt press (T = 230 ◦ C, 270 ◦ C; 8 MPa): (a) TMP sheets with preferred MD fibre orientation pressed at an initial solids content of 61%. The points represent an average of 10 data points and their confidence intervals. (b) Varied pulps and pressing conditions for standard laboratory sheets with uniform fibre orientation. Solids content varies in the range of 50–65%. The overall trend is described by a similar activation energy of 26 kJ mol−1 as in (a).

The temperature behaviour of TMP (Figure 6a) is quantitatively similar to that of the whole data (Figure 6b) with Ea /R ≈ 3080 K, i.e., Ea ≈ 26 kJ mol−1 . This value is close to the value of 29 kJ mol−1 obtained earlier for the diffusion of dissolved lignin from the interior of the chip to the bulk liquor, during the kraft pulping of Eucalyptus globulus wood [25]. Thus, the diffusion rate does not seem to be very sensitive to the type of lignin. We studied the effect of lignin content of ﬁbres by making similar plots for different pulps separately. A systematic increase in lignin content in the range of 0–12% was obtained for chemical kraft pulps by varying the cooking time. The results for these pulps were compared with similar data for CTMP (lignin content 27%) and TMP (lignin content 28%). Figure 7 shows both estimated Ea and extrapolated wet strength at 1/T = 0 for the different cases. Here the 1/T = 0 limit, plotted on a logarithmic axis, describes the order of magnitude of wet strength achievable in hot-pressing. On the other hand, a low Ea value seen for the smallest lignin contents indicates a relatively weak temperature dependence, which is generally coupled with a low 1/T = 0 limit as well. It seems that at least c.a. 7% of

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lignin in kraft fibres is required to raise wet strength to a similar level as for the other pulps. On the other hand, lignin content of fibres higher than 12% does not seem to improve wet strength further, as both the activation energy and the 1/T = 0 limit saturate in Figure 7. In other words, the main improvement on wet strength is achieved already for moderate lignin content of fibres. This suggests that a fairly thin surface layer of diffused lignin is sufficient to provide the maximal bonding between wet fibres.

Figure 7. The apparent activation energy (left vertical axis) and extrapolated ln(Wet tensile strength index) at 1/T = 0 (right logarithmic axis) for different pulps with varied lignin content. The extrapolation omits the degradation of ﬁbre-wall polymers and therefore does not describe the true high-temperature limit of wet tensile index. The points up to 12% lignin content describe kraft pulps with varied cooking times in pulping. These results are compared with similar data for CTMP and TMP with lignin content of 26–28%.

In addition to the primary effects of pressing temperature and lignin content (i.e., pulp type) mentioned above, it is interesting to consider other parameters. Wet strength appears to have a similar level and temperature behaviour for sheets with uniform (Figure 6b) and non-uniform (Figure 6a) fibre orientation. This further suggests that the effective bonding of the contacting inter-fibre surfaces is more important for wet strength than the geometry of the fibre network. This idea is also supported by the observation that wet strength is surprisingly insensitive to nip pressure. When studying heat-treated sheets with and without applied nip pressure, we found no correlation between measured wet strength and average sheet density. On contrary, wet strength and solids content before pressing are correlated as shown in Figure 8. However, the total variation here is much smaller than that for varied temperatures. One possible reason for the correlation between the wet strength index and solids content could be the higher sheet temperature achieved when pressing a drier sheet, which accelerates the lignin inter-diffusion and thus enhances bonding.

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Figure 8. Wet tensile strength index of TMP sheets improves when the pressing is done on a dried web. Here the initial solids content is varied for the constant pressing temperature of 230 ◦ C, keeping other process conditions fixed for all trial points. The points represent an average of 10 data points and their 95% confidence intervals. The applied pressure is 8 MPa for the blue markers, and 0 MPa for the red markers. Wet tensile strength seems not to be very dependent on pressure or density. The applied pressure (0.15 MPa over 23 s) exerted by the steel-belt after the pressing nip seems sufficient to improve wet tensile strength to the same level as when using the 8 MPa nip pressure.

3.4. Network Stiffness and Dry Tensile Strength The same varying solids contents prior to pressing as in Figure 8 were used for the data in Figure 9, where elastic modulus and dry tensile strength index (dry tensile strength divided by the grammage) are compared against sheet density. The elastic modulus for oriented TMP sheets in MD increases with density (Figure 9a). This is expected as density generally determines the relative bond area for random fibre networks [26]. Nevertheless, the correlation between dry strength and density is rather poor for this particular fibre type (Figure 9b), suggesting that the inelastic behaviour after yielding of the fibre network is important for dry strength. All in all, it seems that the mechanisms underlying dry strength are much more complex than the inter-diffusion mechanism previously discussed in the case of wet strength. For example, in Figure 9b, there is a much higher dry strength value for a particular pressing condition corresponding to 62% solids content. In this case, the parallel measurements have very good reproducibility. Curiously, the elastic modulus, calculated from the same measurement curves, does not differ from the general trend observed for other conditions, as shown in Figure 9a. It is possible that the dry strength (and associated inelastic straining) is more sensitive to overheating of the fibre polymers than the wet strength. Thus, maximising dry strength may require a delicate balance of temperature and process dynamics for optimal moisture removal during hot-pressing. Generally, inelastic deformations are controlled by amorphous fibre components such as hemicelluloses, whose mechanical behaviour changes dramatically with varying moisture content and temperature [27–29].

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(a)

(b)

Figure 9. (a) Elastic modulus (MD) of hot-pressed sheets with and without nip pressure follows the density as expected. (b) Correlation between tensile strength index (MD) and density is still rather weak. The solids contents prior to pressing are indicated in the ﬁgures. Note the highest value, which appears like an outlier here, comes from the same measurement as the corresponding point in (a). The points represent an average of 10 data points and their 95% conﬁdence intervals.

The deterioration temperatures of cellulose and hemicellulose differ slightly, and some differences for the high-temperature behaviour of elastic modulus and dry tensile strength could be expected. The hemicelluloses degrade at 230–315 ◦ C, whereas lignin decomposes over a broader temperature range of 200–500 ◦ C [30,31]. However, as seen in Figure 10 for varied pulp types, both elastic modulus and dry strength peak around 150–200 ◦ C, followed up by a decrease for most cases when further increasing the temperature. In other words, the above slight differences in polymer degradation do not seem to change the big picture concerning the mechanical behaviour of materials with different pulp types. The only exceptions are a few kraft pulp samples, which contain some lignin that might shield hemicelluloses, and for which a similar decrease of mechanical properties beyond 200 ◦ C is not observed.

Figure 10. Elastic modulus and dry tensile strength index for a wide data set of sheets with uniform ﬁbre orientation and different furnishes. One should notice that samples above 200 ◦ C have been pressed using the steel-belt press, and those in the range of 20−200 ◦ C have been pressed with cylinder press. The dashed trend lines describe the average behaviour for varied pressing temperatures.

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Standard carbohydrate analysis (performed with SCAN-CM 71:09) of some of the samples pressed at 20 ◦ C and 270 ◦ C showed a small reduction in hemicellulose content (calculated according to KA 10.314) caused by hot-pressing. The samples containing nearly 100% carbohydrate showed the largest decrease in hemicelluloses (less than 10% decrease), perhaps due to the lack of “protecting” lignin. However, in general, the changes are rather small in all cases, which is in agreement with earlier findings in wood welding studies [32]. This means that it is not possible to explain the decrease in mechanical properties caused by hot-pressing, as seen in Figure 10, solely by observing the changes in hemicellulose content. 4. Discussion Hot-pressing often produces a significant increase in the wet tensile strength of paper webs. This effect is strongest when the lignin content of the fibres exceeds 7–12% and the pressing temperature is as high as possible. It is possible that there is an optimum range of lignin contents for wet strength. The relative change in wet strength with temperature is similar for very different pulps, which is explained by a similar lignin inter-diffusion mechanism that strengthens inter-fibre bonding under wet conditions. The strong exponential temperature dependence of the diffusion rate appears to overrule other factors such as pressing time or changes in network density (affected by nip pressure) in determining wet strength levels. This suggests that the wet-strengthening mechanism described above is not sensitive to the amount of lignin diffusing into the bond region between fibres. Even a very thin layer of lignin is sufficient to glue fibre surfaces together so that the bond formed is water resistant. However, it appears that a lignin content of at least 7% is required to cover the surfaces well enough for the wet strength improvement to reach its full potential. When investigating wet strength for TMP papers with varying initial solids content, the best results were obtained when pressing an initially dry web, which is also expected to have the highest web temperature. It should be noted that the theoretical intra-fibre vapour pressure can become very high, several tens of bars, when the temperature is 200 ◦ C or higher and the solids content is below 80% (see Appendix A). This high internal pressure in the fibre walls does not appear to accelerate lignin transfer, at least when considering the observed changes in wet strength at different solids contents. In other words, lignin and water transport mechanisms seem to decouple from one another. This is very interesting since it is known that the presence of water critically affects the softening (i.e., Tg) of lignin. The dry tensile strength of hot-pressed TMP paper shows a very complex behaviour under varying process conditions. Rather than having clear trends with varying solids content or temperature, certain conditions appear to be more optimal than others in unexpected ways. This behaviour differs depending on the pulp being pressed, e.g., mechanical pulp or chemical pulp, so it is difficult to draw general conclusions. However, it seems that softening, e.g., by water or sulfonation [13], is important for dry strength. It should be noted that dry strength is quite high even without pressing, so the relative changes are smaller than for wet strength. In addition, polymer degradation can degrade strength at high temperatures. Therefore, evaporation of water in the fibre walls can appropriately control the temperature rise and prevent polymer degradation. Perhaps the best conditions consist of pressing times and temperatures that are just sufficient to evaporate most of the water from the fibres but do not cause over-drying or heating of the fibres that degrades their strength properties. 5. Conclusions The main findings in this study are highlighted below:

• •

Hot-pressing does not cause a noticeable change in density in the ﬁbre walls, despite a large reduction in network porosity and mean pore size. The wet strength increases with increasing pressing temperature. The stronger bonding of the wet ﬁbres can be explained by inter-diffusion of lignin macromolecules (with an activation energy around 26 kJ mol−1 ) after lignin softening. The associated

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•

exponential acceleration of diffusion with temperature dominates the setting of wet strength over other factors such as process dynamics or ﬁnal material density. The highest solids content before hot-pressing for the TMP sheets was found to give the highest values for wet strength. A possible explanation for this is that when a drier sheet is pressed, a higher temperature is reached, which accelerates the inter-diffusion of the lignin and thus enhance bonding. No signiﬁcant correlation was observed between the varied solids content before pressing and dry strength. The elastic modulus increases with the increasing density of the sheets after hotpressing, as expected. On the other hand, the dry strength does not show the same trend, indicating that the inelastic behaviour after yielding is responsible for the observed differences among the trial points. For dry strength and elastic modulus, the optimum pressing temperature is lower than for wet strength due to the degradation of hemicelluloses.

Author Contributions: Conceptualisation, A.M. (Amanda Mattsson) and J.A.K.; methodology, A.M. (Amanda Mattsson), T.J., A.M. (Arttu Miettinen) and J.A.K.; formal analysis, A.M. (Amanda Mattsson), T.J., A.M. (Arttu Miettinen) and J.A.K.; investigation, A.M. (Amanda Mattsson) and J.A.K.; writing—original draft preparation, A.M. (Amanda Mattsson), T.J., A.M. (Arttu Miettinen) and J.A.K.; writing—review and editing, A.M. (Amanda Mattsson), T.J., A.M. (Arttu Miettinen), J.A.K. and P.E.; visualisation, A.M. (Amanda Mattsson), A.M. (Arttu Miettinen) and J.A.K.; funding acquisition, G.P. and P.E. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by The Kamprad Family Foundation for Entrepreneurship, Research & Charity (grant number 20180234), The KK foundation, and Kempestiftelserna. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: The data in this study are available on request from the corresponding author. Acknowledgments: The authors thank Licentiate of Engineering Javier Brugés for the help with editing the figures. Conflicts of Interest: The authors declare no conflict of interest.

Appendix A The vapour pressure Pv inside a ﬁbre wall at elevated temperatures can be estimated based on the theory developed by Flory and Huggins [33]. We assume that all water is bound to the (hemi)cellulose gel. In a binary polymeric solution (w water, c cellulose) [33], the vapour pressure Pv is given by Pv vw ln = ln(φw ) + 1 − (A1) φc + χφc2 P0 vc where P0 is the vapour pressure of pure solvent, approximated by the Antoine equation log10 P0 = A −

B ; A = 8.071, B = 1731 ◦ C, C = 233.4 ◦ C ( P0 in Torr ) C+T

(A2)

In Equation (A1), φi is volume fraction, vi is molar volume (molar mass divided by mass density), and χ is Flory–Huggins interaction parameter (for cellulose at moderate water contents). According to reference [34], the speciﬁc volume (or density) of cellulose does not vary much with temperature up to 190 ◦ C if the pressure remains below 20 MPa. Assuming that the lignin content of ﬁbre is cl , the cellulose content is 1 − cl . The volumes

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of the different components are (assuming bulk phase dominates the volume for both components when the moisture content is high). Mi ρi

(A3)

(1 − c l ) M f ρc

(A4)

Vi = For cellulose, we obtain the volume Vc =

where M f is dry ﬁbre mass and ρc is cellulose density. The water mass in terms of moisture content mc and dry ﬁbre mass M f becomes mc M f 100 − mc

(A5)

mc M f (100 − mc)ρW

(A6)

Mw = leading to the water volume Vw =

where ρw is water density. The total volume of the water-cellulose gel can be approximated as mc 1 − cl (1 − cl )(100 − mc)ρw + mcρc VT ≈ Vc + Vw = + M f (A7) Mf = ρc ρc (100 − mc)ρw (100 − mc)ρw Thus, we can write volume fractions as φw =

Vw mc ρc ≈ VT (1 − cl )(100 − mc)ρw + mcρc

(A8)

φc =

Vc (1 − cl )(100 − mc) ρw ≈ VT (1 − cl )(100 − mc)ρw + mcρc

(A9)

In Figure A1 we show the behaviour of vapour pressure for varied temperatures and solids contents. The used values of the parameters are presented in Table A1.

(a)

(b)

Figure A1. (a) Vapour pressure as a function of temperature for three different levels of solids content, 90%, 70%, and 50%. (b) Vapour pressure as a function of solids content for three different temperature levels, 20 ◦ C, 190 ◦ C, and 270 ◦ C.

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Table A1. The values of the parameters used for plotting the vapour pressure as a function of temperature and solids content in Figure A1. Parameter

Value

Molar volume of water (vw ) Molar volume of cellulose (vc ) Flory–Huggins interaction parameter (χ) Density of water (ρw ) Density of (crystal) cellulose (ρc ) Lignin content of ﬁbre (cl )

18.02 cm3 /mol 101.3 cm3 /mol 0.67 [35] 1000 kg/m3 1600 kg/m3 25%

References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28.

Ourworldindata. Available online: https://ourworldindata.org/plastic-pollution (accessed on 3 March 2021). Östlund, S.; Niskanen, K. Mechanics of Paper Products; De Gruyter: Berlin, Germany, 2021; ISBN 9783110617412. Karlsson, M.; Paltakari, J. Papermaking Science and Technology; Karlsson, M., Ed.; Papermakin; Fapet Oy: Atlanta, GA, USA, 2008. Norgren, S.; Pettersson, G.; Höglund, H. Strong paper from spruce CTMP—Part II: Effect of pressing at nip press temperatures above the lignin softening temperature. Nord. Pulp Pap. Res. J. 2018, 33, 142–149. [CrossRef] Joelsson, T.; Pettersson, G.; Norgren, S.; Svedberg, A.; Höglund, H.; Engstrand, P. High strength paper from high yield pulps by means of hot-pressing. Nord. Pulp Pap. Res. J. 2020, 35, 195–204. [CrossRef] Joelsson, T.; Pettersson, G.; Norgren, S.; Svedberg, A.; Höglund, H.; Engstrand, P. Improving paper wet-strength by increasing lignin content and hot-pressing temperature. Tappi J. 2020, 19, 487–499. [CrossRef] Good, R.J. Contact Angles and the Surface Free Energy of Solids BT—Surface and Colloid Science: Volume 11: Experimental Methods; Good, R.J., Stromberg, R.R., Eds.; Springer: Boston, MA, USA, 1979; pp. 1–29, ISBN 978-1-4615-7969-4. Vaziri, M.; Karlsson, O.; Abrahamsson, L.; Lin, C.F.; Sandberg, D. Wettability of welded wood-joints investigated by the Wilhelmy method: Part 1. Determination of apparent contact angles, swelling, and water sorption. Holzforschung 2021, 75, 65–74. [CrossRef] Karlsson, O.; Torniainen, P.; Dagbro, O.; Granlund, K.; Morén, T. Presence of water-soluble compounds in thermally modified wood: Carbohydrates and furfurals. BioResources 2012, 7, 3679–3689. [CrossRef] Gupta, P.R.; Rezanowich, A.; Goring, D.A.I. The adhesive properties of lignin. Pulp Pap. Mag. Can 1962, 63, 21–30. Goring, D.A.I. Thermal softening of lignin, hemicelluolose and cellulose. Pulp Pap 1963, 64, T517–T527. Back, E.L.; Salmen, N.L. Glass Transitions of Wood Components Hold Implications for Molding and Pulping Processes. Tappi 1982, 65, 107–110. Joelsson, T.; Persson, E.; Pettersson, G.; Norgren, S.; Svedberg, A.; Engstrand, P. The impact of sulfonation and hot-pressing of low-energy high temperature chemi-thermomechanical pulp. Holzforsch 2021, submitted. Thakur, V.K.; Thakur, M.K.; Raghavan, P.; Kessler, M.R. Progress in green polymer composites from lignin for multifunctional applications: A review. ACS Sustain. Chem. Eng. 2014, 2, 1072–1092. [CrossRef] Bajpai, P. Pulp and Paper Production Processes and Energy Overview; Elsevier: Amsterdam, The Netherlands, 2016; ISBN 9780128034118. Pettersson, G.; Norgren, S.; Engstrand, P.; Rundlöf, M.; Höglund, H. Aspects on bond strength in sheet structures from TMP and CTMP—A review. Nord. Pulp Pap. Res. J. 2021, 36, 177–213. [CrossRef] Joelsson, T.; Svedberg, A.; Norgren, S.; Pettersson, G.; Berg, J.-E.; Garcia-Lindgren, C.; Engstrand, P. Unique steel belt press technology for high strength papers from high yield pulp. SN Appl. Sci. 2021, 3, 561. [CrossRef] Tomasi, C.; Manduchi, R. Bilateral filtering for gray and color images. In Proceedings of the Sixth International Conference on Computer Vision (IEEE Cat. No. 98CH36271), Bombay, India, 7 January 1998; pp. 839–846. Otsu, N. A Threshold Selection Method from Gray-Level Histograms. IEEE Trans. Syst. Man Cybern. 1979, 9, 62–66. [CrossRef] Turpeinen, T.; Myllys, M.; Kekalainen, P.; Timonen, J. Interface Detection Using a Quenched-Noise Version of the EdwardsWilkinson Equation. IEEE Trans. Image Process. 2015, 24, 5696–5705. [CrossRef] [PubMed] Hildebrand, T.; Rüegsegger, P. A new method for the model-independent assessment of thickness in three-dimensional images. J. Microsc. 1997, 185, 67–75. [CrossRef] Ali, C.M.; Jean-Francis, B.; Elodie, B.; Patrice, M. 3D synchrotron X-ray microtomography for paper structure characterization of z-structured paper by introducing micro nanofibrillated cellulose. Nord. Pulp Pap. Res. J. 2016, 31, 219–224. [CrossRef] Kellogg, R.M.; Wangaard, F.F. Variation in the cell-wall density of wood. Wood Fiber Sci. 1969, 1, 180–204. Li, K.; Wang, S.; Chen, H.; Yang, X.; Berglund, L.A.; Zhou, Q. Self-Densification of Highly Mesoporous Wood Structure into a Strong and Transparent Film. Adv. Mater. 2020, 32, 2003653. [CrossRef] Simão, J.P.F.; Carvalho, M.G.V.S.; Baptista, C.M.S.G. Heterogeneous studies in pulping of wood: Modelling mass transfer of dissolved lignin. Chem. Eng. J. 2011, 170, 264–269. [CrossRef] Kaarlo, N. Paper Physics; Paperi ja Puu Oy: Atlanta, GA, USA, 2008; ISBN 9525216292. Niskanen, K. Mechanics of Paper Products; De Gruyter: Berlin, Germany, 2011; ISBN 9783110254617. Lucenius, J.; Valle-Delgado, J.J.; Parikka, K.; Österberg, M. Understanding hemicellulose-cellulose interactions in cellulose nanofibril-based composites. J. Colloid Interface Sci. 2019, 555, 104–114. [CrossRef]

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Sorieul, M.; Dickson, A.; Hill, S.J.; Pearson, H. Plant fibre: Molecular structure and biomechanical properties, of a complex living material, influencing its deconstruction towards a biobased composite. Materials 2016, 9, 618. [CrossRef] Börcsök, Z.; Pásztory, Z. The role of lignin in wood working processes using elevated temperatures: An abbreviated literature survey. Eur. J. Wood Wood Prod. 2021, 79, 511–526. [CrossRef] Hubbe, M.A.; Pizzi, A.; Zhang, H.; Halis, R. Critical Links Governing Performance of Self-binding and Natural Binders for Hot-pressed Reconstituted Lignocellulosic Board without Added Formaldehyde: A Review. BioResources 2017, 13, 2049–2115. [CrossRef] Delmotte, L.; Ganne-Chédeville, C.; Leban, J.-M.; Pizzi, A.; Pichelin, F. CP-MAS 13C NMR and FT-IR investigation of the degradation reactions of polymer constituents in wood welding. Polym. Degrad. Stab. 2008, 93, 406–412. [CrossRef] Khansary, M.A. Vapor pressure and Flory-Huggins interaction parameters in binary polymeric solutions. Korean J. Chem. Eng. 2016, 33, 1402–1407. [CrossRef] Jallabert, B.; Vaca-Medina, G.; Cazalbou, S.; Rouilly, A. The pressure–volume–temperature relationship of cellulose. Cellulose 2013, 20, 2279–2289. [CrossRef] Hakalahti, M.; Faustini, M.; Boissière, C.; Kontturi, E.; Tammelin, T. Interfacial mechanisms of water vapor sorption into cellulose nanofibril films as revealed by quantitative models. Biomacromolecules 2017, 18, 2951–2958. [CrossRef]

PAPERmaking! FROM THE PUBLISHERS OF PAPER TECHNOLOGY TE INTERNATIONAL®

Volume 8, Number 2, 2022

Pulp and Paper Industry: Decarbonisation Technology Assessment to Reach CO2 Neutral Emissions—An Austrian Case Study 1 2 1 MAEDEH RAHNAMA MOBARAKEH , MIGUEL SANTOS SILVA & THOMAS KIENBERGER .

The pulp and paper (P&P) sector is a dynamic manufacturing industry and plays an essential role in the Austrian economy. However, the sector, which consumes about 20 TWh of final energy, is responsible for 7% of Austria’s industrial CO2 emissions. This study, intending to assess the potential for improving energy efficiency and reducing emissions in the Austrian context in the P&P sector, uses a bottom-up approach model. The model is applied to analyse the energy consumption (heat and electricity) and CO2 emissions in the main processes, related to the P&P production from virgin or recycled fibers. Afterward, technological options to reduce energy consumption and fossil CO2 emissions for P&P production are investigated, and various low-carbon technologies are applied to the model. For each of the selected technologies, the potential of emission reduction and energy savings up to 2050 is estimated. Finally, a series of low-carbon technology-based scenarios are developed and evaluated. These scenarios’ content is based on the improvement potential associated with the various processes of different paper grades. The results reveal that the investigated technologies applied in the production process (chemical pulping and paper drying) have a minor impact on CO2 emission reduction (maximum 10% due to applying an impulse dryer). In contrast, steam supply electrification, by replacing fossil fuel boilers with direct heat supply (such as commercial electric boilers or heat pumps), enables reducing emissions by up to 75%. This means that the goal of 100% CO2 emission reduction by 2050 cannot be reached with one method alone. Consequently, a combination of technologies, particularly with the electrification of the steam supply, along with the use of carbon-free electricity generated by renewable energy, appears to be essential. Contact information: 1. Chair of Energy Network Technology, Montanuniversitaet Leoben, Franz-Josef Straße 18, A-8700 Leoben, Austria. 2. Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal. Energies 2021, 14, 1161. https://doi.org/10.3390/en14041161 Creative Commons Attribution 4.0 International License

The Paper Industry Technical Association (PITA) is an independent organisation which operates for the general benefit of its members – both individual and corporate – dedicated to promoting and improving the technical and scientific knowledge of those working in the UK pulp and paper industry. Formed in 1960, it serves the Industry, both manufacturers and suppliers, by providing a forum for members to meet and network; it organises visits, conferences and training seminars that cover all aspects of papermaking science. It also publishes the prestigious journal Paper Technology International® and the PITA Annual Review, both sent free to members, and a range of other technical publications which include conference proceedings and the acclaimed Essential Guide to Aqueous Coating.

Page 1 of 31

Article 3 – Decarbonisation

energies Article

Pulp and Paper Industry: Decarbonisation Technology Assessment to Reach CO2 Neutral Emissions—An Austrian Case Study Maedeh Rahnama Mobarakeh 1, * , Miguel Santos Silva 2 and Thomas Kienberger 1 1

Citation: Rahnama Mobarakeh, M.; Santos Silva, M.; Kienberger, T. Pulp and Paper Industry: Decarbonisation Technology Assessment to Reach CO2 Neutral Emissions—An Austrian Case Study. Energies 2021, 14, 1161. https://doi.org/10.3390/en14041161 Academic Editor: Daniel Sánchez García-Vacas

Chair of Energy Network Technology, Montanuniversitaet Leoben, Franz-Josef Straße 18, A-8700 Leoben, Austria; Thomas.kienberger@unileoben.ac.at Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal; miguel.santos.silva@tecnico.ulisboa.pt Correspondence: maedeh.rahnama-mobarakeh@unileoben.ac.at; Tel.: +43-384-2402-5411

Abstract: The pulp and paper (P&P) sector is a dynamic manufacturing industry and plays an essential role in the Austrian economy. However, the sector, which consumes about 20 TWh of final energy, is responsible for 7% of Austria’s industrial CO2 emissions. This study, intending to assess the potential for improving energy efficiency and reducing emissions in the Austrian context in the P&P sector, uses a bottom-up approach model. The model is applied to analyze the energy consumption (heat and electricity) and CO2 emissions in the main processes, related to the P&P production from virgin or recycled fibers. Afterward, technological options to reduce energy consumption and fossil CO2 emissions for P&P production are investigated, and various low-carbon technologies are applied to the model. For each of the selected technologies, the potential of emission reduction and energy savings up to 2050 is estimated. Finally, a series of low-carbon technology-based scenarios are developed and evaluated. These scenarios’ content is based on the improvement potential associated with the various processes of different paper grades. The results reveal that the investigated technologies applied in the production process (chemical pulping and paper drying) have a minor impact on CO2 emission reduction (maximum 10% due to applying an impulse dryer). In contrast, steam supply electrification, by replacing fossil fuel boilers with direct heat supply (such as commercial electric boilers or heat pumps), enables reducing emissions by up to 75%. This means that the goal of 100% CO2 emission reduction by 2050 cannot be reached with one method alone. Consequently, a combination of technologies, particularly with the electrification of the steam supply, along with the use of carbon-free electricity generated by renewable energy, appears to be essential.

Received: 21 January 2021 Accepted: 16 February 2021 Published: 22 February 2021

Keywords: pulp and paper sector; greenhouse gas emissions; CO2 emissions reduction; abatement technology

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional afﬁliations.

1. Introduction Disturbing climate changes have marked today’s world. They make global warming and its catastrophic consequences more evident day by day. To tackle this problem efﬁciently, the European Union (EU) has deﬁned a set of ambitious targets to limit the increase in average global temperature. These include reducing greenhouse gas (GHG) emissions by 40% by 2030 and by 80–95% before 2050, compared to the 1990 levels [1]. To achieve this target, the EU must effectively localize the source of emissions and look for alternatives to the current processes in a short period. The main sources of GHG emissions in Europe are energy-producing industries, followed by fuel combustion by users (Fuel combustion by users (excl. transport): emissions from fuel combustion by manufacturing industries and construction, and small scale fuel combustion for space heating and hot water production for households [2]), the

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transport sector, industrial process and product use (Industrial Process emissions occurring from chemical reactions during the production [2]), and agriculture [2]. In 2017, the CO2 emission reduction of industrial processes was one of the top priorities in Europe’s emission reduction strategy. The contribution of this sector for the EU-28 was reported as 9% of total emissions in 2017 [3]. However, for Austria the industrial sector accounted for 21% of GHG emissions caused by production processing [4] and 28% of the total final energy consumption, respectively [5] in 2017. This was one of the motivations for the creation of NEFI (www.nefi.at, accessed on 21 January 2021) (New Energy for Industry), a consortium of Austrian companies, research institutes, and public institutions. One of the objectives of NEFI is to provide an integrated approach to profound decarbonization pathways for the energy system in Austria, driven by a transformation of the industrial sector towards being sustainable, efficient, and a low-carbon economy. The present work seeks fulfillment of this objective for the pulp and paper industrial sub-sector. The pulp and paper sector (P&P) is one of the oldest and most significant industrial sectors in Austria, and accounted for 0.89% of the Austrian gross domestic product (GDP) in 2017 [6,7]. The process of paper production consists of three stages, each of which has several sub-processes and can take different routes. This makes the sector very complex and energy-intensive, ranking it the highest final energy consumer in industry, by approximately 20 TWh in 2017 (corresponding to 23% of total final industrial energy use). [5] The P&P sector is also responsible for 7% of industrial emissions, and can play an essential role in the decarbonization of the Austrian industrial energy system. Although the sector has started to reduce CO2 emissions, by 20% in the last decades [8], due to improvements in energy efficiency (e.g., waste heat recovery) and the reduction of fossil fuel consumption (from 58% in 2000 to 40% in 2017 [9]) by replacement with biofuels (mostly black liquid), a significant emission reduction potential still exists. 1.1. State of Research In recent years, many studies have started to consider the potential for reducing energy consumption and the options for cutting CO2 emissions in the pulp and paper industry. The Joint Research Centre (JRC) prepared a report by Moya and Pavel in 2018 [10]. They predicted a 1.1% increase in the European P&P sector’s energy consumption and CO2 emissions of 4.8% in 2050 compared to 2015 without technological updates. Their analysis, using a bottom-up model, showed that the application of the best available technologies in papermaking could lead to a 14.4% reduction in energy consumption in Europe, resulting in a 62.2% reduction in CO2 emissions due to the contribution of technological improvement. Most of the energy improvement came from the integration of state-of-the-art technologies into new equipment, such as heat recovery, black liquor gasification, and highly efficient appliances. However, most CO2 savings were due to the conversion from fossil fuels to biofuels and the use of new technologies. In 2012, Fleiter et al. [11] investigated the diffusion of 17 process technologies for improving energy efficiency and resulting CO2 reduction for the German pulp and paper sector up to 2035 using a techno-economic approach. Based on their results, electricity and fuel consumption in 2035 would be reduced by 16% and 21%, respectively, in the technodiffusion scenario compared to the frozen efficiency scenario. This energy-saving could reduce CO2 emissions by 19%. They stated that the most impressive technologies are waste heat recovery in paper mills and new paper drying technologies. Several other energysaving technologies were not included in the study. They concluded that a significant potential for saving still exists, especially if the system boundaries extend across the enterprise level. P. Griffen et al. [12] conducted a study on the decarbonization of the P&P sector in the UK in 2018. They believe that the P&P sector is a heterogeneous sector with a wide range of product outputs, and lies roughly on the borderline between energy-intensive and nonenergy-intensive industrial sectors. They developed a series of low carbon technology

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roadmaps based on various alternative scenarios for the UK paper sector. The results of their study indicate that achieving a significant reduction in GHG emissions in the long term will depend on the adoption of some key technologies such as heat recovery techniques, energy efficiency improvements, use of bioenergy, and electrification (besides the decarbonization of grid electricity). Based on their assumptions, under a reasonable action scenario, the sector’s total greenhouse gas emissions would decrease by about 80% over the period 1990–2050 through the installation of all efficiency technologies by 2025 and the replacement of retired equipment with the best practice by 2030. The Confederation of European Paper Industries (CEPI) [13] has been working to develop a roadmap for the transition to a competitive low-carbon economy in 2050. CEPI aims to reduce CO2 emissions by 80% compared to 1990, and cut CO2 emissions to 12 million tons (10 million tons direct), compared to 49 million tons (32 million tons direct) in 2015. CEPI also has a goal to reduce energy demand in the wood fiber industry by 20% and to increase product value by 50% by 2050, compared to the 2010 benchmark, using improved energy efficiency, fuel switching, and demand-side flexibility. They introduced a group of breakthrough technologies that can reduce CO2 emissions in various areas from 20% (e.g., deep eutectic solvents technology) to 100% (100% electricity technology). These were presented in the report “Two Team Project”. 1.2. Open Research Questions and Structure of This Paper The previous section provided the current state of research that considered energy consumption and carbon emission reduction potential in the P&P sector. However, there are still some less addressed topics in the literature, which are discussed in this paper:

• • • •

An energy flow Sankey diagram and allocation of the total, final and useful energy consumption A bottom-up model for energy efficiency and CO2 reduction potential for various P&P products and the sector as a whole A comprehensive technology overview by considering the best available technology (BAT) and innovative technology (IT) A bottom-up technology model and analysis of high-impact technologies toward the climate goal.

To tackle the mentioned issues, this work considers the Austrian pulp and paper sector as a case study, and the possibility of decarbonization by 2050 is evaluated based on the following steps. In Section 2, an extensive literature review was made on the main processes and the state of the art in the industry, emphasizing the energy consumption of each step. In this section, the current situation of the Austrian P&P sector is also examined in terms of CO2 emissions and energy consumption. Section 3 describes the methodology for model development to calculate CO2 emissions and energy consumption at the process level for the different types of pulp and paper production. The model is based on a technology-based linear bottom-up approach, and will also be used in the next section to analyze decarbonization paths. Section 4 evaluates the opportunities and challenges of reducing carbon dioxide (CO2 ) and industrial energy demand in the Austrian P&P sector. In this section, based on the literature review, a technology database is presented in two groups: BAT and IT. Six promising technologies are selected from the database and explained with further details for the Austrian case. Subsequently, in Section 5, the technology-specific information is integrated into the bottom-up model to evaluate the decarbonization pathways and scenarios. The impact of energy efficiency and the emission reduction potential of each technology on the sector is investigated through six individual scenarios. Finally, Section 6 presents the conclusions of the most important results. These findings help to identify the steps that need to be taken by experts and policymakers to ensure the decarbonization of the Austrian paper sector.

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2. The Pulp and Paper Industry 2.1. Structure of Pulp and Paper Sector The paper industry is one of the most expressive industries globally, producing over 400 million tons of paper per year [14]. Pulp and paper mills are highly complex, and involve various process steps, including wood preparation, pulp production, chemical recovery, bleaching, and papermaking, to transform the wood into the ﬁnal product [15]. Paper mills can be fully integrated or non-integrated mills. Integrated mills include a pulp mill and a paper mill on the same site. These types of mills receive logs or chips and produce paper. In contrast, non-integrated mills produce pulp and paper in separate mills. The non-integrated paper mill uses dried pulp as the feedstock for paper production. The dried pulp is produced in integrated mills or non-integrated pulp mills and sold on the open market. Integrated mills are usually larger, more cost and energy effective, and have cheaper production than separate mills. Nevertheless, smaller non-integrated mills can strategically beneﬁt from being closer to the consumer. Figure 1 shows the main process steps in the integrated paper mill for the two most common steps of pulping (thermomechanical pulping (TMP) and sulphate (kraft) pulping and paper making [16,17].

Figure 1. Overview of wood preparation, mechanical/chemical pulping, and papermaking processes design based on Joint Research Centre (JRC) [17] and ICF [16] reports.

2.1.1. Raw Material Preparation Wood is the primary raw material for the production of pulp. Wood comes to the mill in the form of long raw logs (with bark) in the wood yard. The main processes in the raw material preparation are debarking the wood logs to remove the bark, wood chipping (which reduces the wood logs to small chips), and screening to ensure that the wood chips are the right size for further processing. In general, the wood yard operations are independent of the type of pulping process [15].

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The two major products resulting from the raw material preparation process are chips and bark. The chips are the main product. Their quality is of high importance, as the consumption of raw material increases if the chips produced are not homogeneous. Furthermore, a homogenized chip distribution improves the energy efﬁciency of the system. Another main product is the bark, which is the by-product and is typically used as fuel in the burner for energy production, or can be sold for other purposes off-site [15]. Raw material processing consumes roughly 10% of electricity use [15]. The main energy consumers are conveyor motors, debarking operational motors, and wood chipping motors (see Table 1). Thermal energy is only needed in some mills in cold climates, where the logs have to be de-iced with hot water before debarking [16]. Table 1. Speciﬁc electricity and heat consumption of the wood processes in pulp and paper production. Process

Speciﬁc Electricity Consumption (kWh/twood )

Speciﬁc Heat Consumption (GJ/twood )

Reference

Debarking Chipping and conveying

8.5 (7–10 KWh/m3 wood) 30.3

0.0 0.0

[15,17,18] [15,18]

2.1.2. Pulp Production The second step in paper processing is the production of pulp from raw materials (virgin wood or recycled fibers). Wood is usually composed of about 60–65% cellulose and hemicelluloses, the paper’s main fibrous components [15,19]. The remaining material mass consists mostly of lignin, with small amounts of extractives and ash. The fundamental aim of the pulping process is to release the fibers from the lignin that holds the fibers together in the wood. Typically, wood is composed of about 50% fiber, 20 to 30% non-fibrous sugars, and 20 to 30% lignin [15,17]. In the pulping process, wood chips are separated into individual cellulose fibers by removing the wood lignin [15,17]. The pulp is produced by three main methods: mechanical, chemical, and recycled fiber (RCF) pulping (There are another types of pulp production, semi-chemical, dissolving, and non-wood pulp, which are not considered in this paper).

•

Mechanical pulp: the primary form of pulping is mechanical pulping, which has been extensively replaced by chemical pulping. Mechanical pulping processes separate the ﬁbers from each other by mechanical means, retaining part of the lignin in the paper and increasing the yield (mass of pulp/mass of original ﬁber source) to around 85–90%.

The main kinds of mechanical pulping are the production of groundwood pulping (GW), refiner mechanical pulping (RMP), thermomechanical pulping (TMP), and chemithermomechanical pulping (CTMP). Two main techniques are used to produce mechanical pulping: pressing logs against a rotating grindstone for GW pulping, and feeding the wood chips between metal finishing discs and defibrating them for RMP, TMP, and CTMP. Typically, mechanical pulp is used for low-grade paper such as newsprint and magazines, the fibers with this pulp type are short and weak, and sometimes need to be combined with strong chemical fibers (especially for GW). The main energy source for mechanical pulp is electricity, which is usually converted into heat that can be partially recovered and used in other processes. However, some types of pulp (TMP, CTMP) use steam on the wood chips before they are used in the equipment (see Table 2) [15,17].

•

Chemical pulp: The most common pulping process is chemical pulping, divided into two types: kraft (sulphate) pulp and sulphite pulp. In both types, the digester processes the raw material with watery chemical solutions at high temperatures and high pressure to extract pulp ﬁbers.

Kraft pulp is the most common kind of chemical pulp, accounting for about 80% of the world’s pulp production. As illustrated in Figure 1, for kraft pulp, the wood chips are mixed with a strongly alkaline solution known as white liquor, which includes sodium

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hydroxide and sodium sulfide, in the batch or continuous digester for several hours under high pressure and high-temperature (155–175 ◦ C) conditions [17]. After the cooking step in the digester, the hot pulp is transferred under pressure to the blow tank, where softened wood chips decompose into fibers or pulp. Then, in the next stage, in the filtering and washing step, the pulp and the cooking liquor, which is called black liquor, are separated. During the cooking process in the digester, almost half of the wood is not solved, and as a result, black liquor includes organic and inorganic substances. In the next step, black liquor is sent into the chemical recovery system to recover the cooking chemicals and energy. Chemical recovery is an essential part of the chemical pulping process. The chemical recovery system by evaporating the water content of the black liquor in the recovery boiler, on the one hand, recovers the white liquor (by causticizing the green liquor with lime (Figure 1)) and, on the other hand, generates high-pressure steam. The white liquor is returned to the digester, and the steam is used in the heat and power plant (CHP) to generate the process steam (medium-low pressure steam) and electricity. In most cases, the recoverable black liquor’s fuel value is sufficient to make the kraft pulp mills largely selfsufficient in heat and electrical energy. Chemical recovery also offers the mill regeneration of chemical digestion at a rate up to 98%, which leads to a significant reduction in the costs of purchasing process chemicals and energy [15,17]. The production of sulphite pulp is not so common compared to the production of kraft pulp. Pulp produced by sulphite pulp usually has weaker strength properties compared to kraft pulp, although sulphite pulp offers other advantageous properties for some specialty pulp applications (such as textile production). In the sulphite pulping process, the wood chips are digested with the cooking liquor, an acidic mixture of sulphurous acid and bisulphite ion. The acidic solution in the cooking liquor leads to a decomposition of the lignin bonds between the wood fibers. Like the kraft pulp, energy can be recovered in the sulphite process, and the solvent can be regenerate. Due to sulfite pulp’s lower color content, it can be bleached more easily than kraft pulp, but it is not as strong [15,17]. In total, chemical pulping has a low fiber yield, in the range of 40–55%, compared to mechanical pulping, but the pulp produced is of very high quality and is mainly used to produce higher-grade paper, such as office paper. Nowadays, chemical pulp consumption has grown because the demand for printing and writing paper is increasing. In contrast, due to the rising use of social media, newsprint consumption has decreased, causing a reduction of mechanical pulp demand [15].

•

Recycled fibers pulp (RCF): this type of pulp production requires a more straightforward process than the pulping of virgin wood, and consumes less energy than the other types. The main step in RCF pulping is to dissolve the shredded paper in hot water by mechanical means to separate the fibers without damaging and destroying them. For paper grades requiring white pulp, an additional step of de-inking takes place. Recycled fiber pulp is also subjected to mechanical removal of impurities. In some pulp mills, recycled fiber and virgin fibers are used together, and recycle fiber is added to the virgin (wood) pulp [15].

After the pulp has been produced by mechanical, chemical, or RCF processes, the pulp is washed and screened to remove impurities such as remaining pieces of wood and uncooked chips that have not been properly pulped. In the ﬁnal step, depending on the product’s end-use, bleaching is applied to give the pulp a white color by adding chemical components. This is not an essential process and is only applied to paper types that require good optical properties: graphic paper, whiteboard, etc. An additional drying step is required when the pulp and paper mills are not in the same location (non-integrated mills). The pulp drying process is energy-intensive and not signiﬁcant for the paper manufacturing process. Therefore, cost and energy savings can be achieved by integrating the pulp and paper mills.

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Table 2. Speciﬁc electricity and heat consumption of the pulp processes in pulp and paper production. Speciﬁc Electricity Consumption (kWh/tAD pulp 1 )

Speciﬁc Heat Consumption (GJ/tAD pulp )

Reference

Groundwood Pulp Reﬁner-Mechanical Pulp Thermomechanical Pulp Washing and Screening Bleaching

Mechanical Pulp 1650.0 (1100–2200) 1972.0 (1600–3000) 2041.0 (1800–3600) 50.0 100.0

0.0 0.0 0.9 (0.03–0.93) 0.0 0.0

[15,17] [15,17] [15–17] [11] [11]

Kraft Digester sulphite Digester Washing and Screening Oxygen Deligniﬁcation 3 Bleaching 4 Pulp Drying 5

Chemical Pulp 406.0 572.0 (226.5–1358) 30.0 75.0 159 (60–185) 155.0 (90–160)

4.4 (2.43–5.64) 2 4.2 (4.11–6.48) 0.0 0.5 4.3 (0.4–4.3) 4.5 6

[15,16] [15,16] [20] [20] [15,18,21] [15,18]

Process

Liquor Evaporators Recovery Boiler Kiln and Recausticizing

Chemical Recovery Process 25.0 58 50.0

4.4 (2.2–5.4) 1.1 1.19 (0.77–2.69)

[15,18] [15] [20,22]

Recycled Fibers Pulp Screening De-inking Concentration and Dispersion Bleaching

Recycled Fibers Pulp 392.0 (256.1–428.6) 50.0 80.0 40.0 30.0

0.0 0.0 0.0 0.54 0.0

[15,16] [11] [11] [11] [11]

tAD Pulp : Air Dry ton of Pulp [17] 2 . Depends on the continuous or batch digester. 3 . Oxygen deligniﬁcation is applied only to kraft pulp, not sulﬁte pulp. 4 . The energy demand varies depending on the number and type of bleaching grades [21]. 5 . The values of energy consumption for drying of pulp are assumed to be the same for all pulp types due to missing information in the literature. 6 . The energy requirement for pulp drying is about 25% of the total thermal energy and 15–20% of the total electrical energy consumption for pulp production. It might be at a lower rate (2.5–3.5 GJ/t pulp ) [17].

2.1.3. Paper Production After pulping, the bleached or unbleached pulp is transferred to the papermaking process. In most paper mills, more than one type of pulp is used to obtain paper with the desired properties. The pulp is delivered in the form of a fiber suspension to integrated mills or in dry form (10% moisture content) to non-integrated mills. First, the pulp undergoes preparation steps to ensure that it is delivered to the paper machine in the best condition, such as fiber slurry (dissolving in a suspension), blending of different pulps, or refining (to change the morphology of the fibers). Other processes such as cleaning or screening can be used to achieve a better paper quality, depending on the pulp’s conditions. Paper fillers may also be added to the pulp. Mineral fillers are used to reduce pulp consumption and change the properties of the paper produced, or chemical additives are added to improve quality and optical properties, such as texture and brightness. After the stock preparation steps, the pulp is fed into the paper machine through the headbox. In the paper machine, the paper is formed, and most of the paper’s properties are established. The paper machine is a large dewatering device consisting of a headbox, a wire section, a press section, and a dryer section [17]. The headbox aims to produce a homogeneous distribution of the fibers over the papermaking process’s entire width to achieve uniform paper formation. In the wire section (forming section), pulp with a fiber content of about 0.5% to 1% [17,23] is introduced and supported by a single/twin-wire, then the water is removed from the bottom side by gravity or other elements, and the pulp leaves the section with a fiber content of 15–20% [17]. After that, the formed paper, which is still very week, enters the press section. In this section, the paper web is passed through a set of rollers to remove water and increase the fiber content to 45–50% [17,23].

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The remaining water is then removed from the paper in the drying part, and the fiber content is increased to 90–95% [17]. Drying is normally carried out with steam-heated cylinders enclosed in a hood. The dryer section consumes a large amount of energy in the form of steam (see Table 3 for the dryer section’s energy consumption for each paper type). However, all paper mills have installed heat recovery systems in the drying section to utilize the exhaust air (generally with the temperature 80 to 85 ◦ C and humidity 140 to 160 gH2 O /KgDA ) and recover it in a heat exchanger [17]. Afterward, the paper can be subjected to finishing processes, namely coating and calendering. Coating is the application of chemicals to the paper to give it superior surface properties. It is only applied to some types of paper. The drying process can be divided into pre-coating drying and post-coating drying when the coating is needed. The calendering process consists of running the paper through a set of rolls, increasing surface smoothness, and improving its appearance. Finally, the paper is rolled and stored for delivery to market. Table 3. Specific electricity and heat consumption of the paper processes in pulp and paper production. Process

Speciﬁc Electricity Consumption (kWh/t paper )

Forming and Pressing Drying

422.0 29.31

Forming and Pressing Drying

527.5 29.3

Forming and Pressing Drying

527.5 29.31

Forming and Pressing Drying

533.4 131.88

Forming and Pressing Drying

269.6 14.7

Speciﬁc Heat Consumption (GJ/t paper )

Reference

0.0 4.29

[15,21] [15,21]

0.0 5.48

[15,21] [21]

0.0 5.27

[15,21] [21]

0.0 4.22

[15,21] [21]

0,0 4.22

[15,21] [21]

Newsprint

Printing (Coated) Paper

Writing (Uncoated) Paper

Tissue

Packing paper

While pulping (i.e., chemical peeling) is more energy self-sufﬁcient, the energy needed for papermaking must be supplied from the grid. 2.2. Austrian Pulp and Paper 2.2.1. Overview of the Pulp and Paper Sector Today, more than 90 million tons of paper are produced in about 900 pulp and paper mills in the EU [24]. With around 5 million tons of paper in 2017, Austria accounted for 5.3% of EU paper production [24]. The Austrian P&P sector consists of 21 companies with 24 mills [9]. According to the Association of the Austrian paper industry (Austropapier (https://austropapier.at/unternehmen, accessed on 30 November 2020)), the paper manufacturers’ production capacity and structure are not particularly equal. The three largest companies account for more than one-third (39% or 2280 kilo tons) of the annual production (pulp, market pulp, and paper). Eleven medium-sized mills account for 54% of total production, and the remaining smaller mills have a low production capacity of less than 7% (426 kilo tons) [25]. About 25% of pulp and 88% of paper production is exported, mainly to European countries such as Germany, Italy, and Slovenia [9]. The production processes of pulp and paper are quite heterogeneous: approximately 51% of the total pulp is produced from raw wood using mechanical (16%), chemical (62%, (approx. 75% kraft pulp and 25% sulphite pulp [14])), and textile (22%) pulp, and the rest of the pulp is RCF pulp from (de-inked and non-deinked) recovered paper (The paper recycling rate was 74% in 2017 in Austria [9]). Paper production is also divided into graphic

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paper (53%), paper and board for packaging (41%), and special types of paper such as sanitary and beverage labels (6%) [9]. Based on the Austropapier data from 2017, Figure 2 prepares a general description of the pulp and paper sector’s material ﬂow and sectoral production activities.

Figure 2. Material ﬂow in the Austrian pulp and paper sector in the year 2017 [9], illustration inspired by CEPI (Confederation of European Paper Industries) [24].

2.2.2. Energy Use and Emission Impacts of Paper Production As mentioned in the previous sections (Sections 2.1.1–2.1.3), paper production is an energy-intensive process and requires energy input in the form of heat and electricity. Heat is typically consumed as high-pressure steam in turbo generators to produce electricity. The heat is then extracted to medium and low-pressure steam for utilization in production processing, such as wood chipping, pulp production, heating of cooking liquor in chemical pulping, evaporating water from the pulp, and paper sheet in the dryer section, etc. [15]. In Austria, the paper sector is the largest industrial final energy consumer, with a consumption of 23%, which corresponded to 20 TWh of the total industrial final energy consumption in 2017. This amount of final energy is consumed for steam generation in the drying and separation processes (73.5%), industrial furnaces (3.1%), electric motors (20.1%), and space heating (2.5%) [26]. In total, the sector utilized 4.532 TWh electricity and 11.3 TWh steam as useful energy [9] for the production of pulp and paper. About 75% of this energy is used in papermaking processes (67% in the drying section [15]), 10% in chemical pulping, and 4% in mechanical pulping processes [27]. However, the Austrian P&P sector is equipped with local heat and power generators, especially in integrated paper mills and chemical pulping mills. The biofuel obtained from chemical pulping, mainly black liquor, and bark and wood wastes are used in the cogeneration plants (CHP) and generate the main part of the electricity demand, approximately 2.856 TWh, corresponding to 63% of the total

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electricity demand in 2017, through the use of high-pressure steam in turbines (about 5% of this electricity is produced by on-site hydropower plants) [9]. Subsequently, the steam output at medium/low-pressure is applied to production processing, making the sector completely self-sufficient in terms of steam generation. The excess heat and electricity are also fed into the grid [9]. Based on Austropapier [9] and Statistics Austria data [5,28,29], Table 4 presents a clear distribution of energy consumption (total, final, and useful), energy self-production, and system self-sufficiency in the year 2017. Table 4. Energy consumption and production in the Austrian Pulp and Paper sector in the year 2017 [5,9,28,29]

Total energy consumption Final energy consumption Useful energy consumption Self-energy production Self-sufﬁciency

(TWh) (TWh) (TWh) (TWh) (%)

∑ Sum

Fuel Consumption

Thermal Energy

Electrical Energy

22.5 20.8 15.84 15.45 68

18 16.22 -

11.312 12.595 111.34

4.532 4.532 4.532 2.856 63

As shown in Table 4, a large amount of fuel is required to generate energy (heat and electricity). In 2017, the total fuel consumption was 18 TWh, of which about 40% was fossil fuels (e.g., coal, oil, natural gas) and 60% was biofuels (e.g., bark, sludge, and black liquor) [28,29]. The use of more renewable energy and biofuel instead of fossil fuel energy to reduce the fossil fuel CO2 emission is a priority of Austrian climate and energy policy. The Austrian P&P industry has also followed this policy [9,30]. The pulp and paper industry, on one hand, is a signiﬁcant energy consumer, but on the other hand, it is a source of energy production, by producing black liquor and waste wood as biofuel during the production processing. Hence the industry has decided to use more inside-produced biofuels instead of fossil fuels. This can be seen in the historical development of fuel consumption in the sector from 2000 to 2017 in Figure 3; it is evident that the energy source has changed signiﬁcantly. While fossil fuel consumption decreased dramatically from 60% in the year 2000 to 40% in 2017, the share of and biofuel increased from 40% to 60% during this time.

Figure 3. Historical trend of fuel consumption in the P&P industry in Austria [9,30–34].

To give a general overview of the energy ﬂow in the pulp and paper sector, Figure 4 shows a Sankey diagram in which all fuel types and the Austrian P&P sector’s own energy production are considered as a case study.

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Figure 4. Energy Flow Sankey diagram of the Austrian Pulp and Paper Industry in the year 2017 [26,28,29].

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While pulp and paper is an energy-intensive sector and consumes a lot of energy in Austria, it is one of the least CO2 -intensive industrial sectors. Greenhouse gas emissions in P&P can be attributed to direct and indirect emissions. Direct emissions are emissions from the burning of fuels on-site (fossil fuels and biofuels) and non-energy related sources such as carbon dioxide emissions as a by-product of the chemical reaction in the lime kiln. The in-direct emission comes from the external power supply that has been purchased for the plant [15,17]. For calculating the total CO2 emissions from the P&P sector, only fossil fuel emissions are taken into account. The biofuel emissions are classiﬁed as carbon-neutral, according to the GHG Protocol of the Intergovernmental Panel on Climate Change (IPCC) [35]. The carbon neutrality of bioenergy does not mean that emissions from bioenergy are not considered. Instead, they are assigned to the forest and land-use sector [36]. Hence, the main reason for the difference in carbon dioxide intensity between paper manufacturing and other industrial sectors is the extensive use of biofuel as an energy source [15]. In 2017 the total emission of the Austrian P&P sector was 1811 kilotons (kt) [8], which was 90% direct and 10% indirect emissions, corresponding to 7% of total industrial emissions. As illustrated in Figure 5, P&P showed a general decreasing trend in direct fossil CO2 emissions from 2157 kt (0.54 kt CO2 per kt paper) in 2000, to 1639 kt (0.37 kt CO2 per kt paper) in 2017 [8,9]. This was mainly due to the increased use of biofuel instead of fossil fuels as an energy source. (Figure 4).

Figure 5. Historical trend of CO2 emission in the P&P industry in Austria 2000–2017 [9,30,32–34].

3. Modeling Approach To assess the potential of technology-based energy efficiency improvement and CO2 mitigation measures on the P&P processes, we developed an analytical model based on a linear bottom-up approach. By calculating the energy consumption of each step of the production process, the fuel consumption and CO2 emissions can be estimated. This approach makes it possible to calculate the impact that selected measures in a specific process would have on the energy consumption and CO2 emissions of the entire production process. The first application of the model is the calculation of annual emissions and energy consumption of each paper product individually (printing and writing paper, tissue, newsprint, and packing paper), considering different production conditions such as integrated (int) or non-integrated (n.int) production, type of pulp used, and RCF content, to obtain the specific

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energy consumption and CO2 emission of each of those products and to understand the sources of CO2 throughout the process. In the second application, the model is used to calculate the energy consumption and CO2 emissions of the entire sector in Austria, using as input the pulp and paper’s annual production. Since the pulp is sold separately as market pulp, the total production of pulp is not directly related to paper production, so the calculation methodology for the entire industry considered the production of pulp and paper separately (instead of pulp produced to sustain the production of paper). The two variants of the model diverge on the method used to calculate fuel consumption. Table 5 compares the two variants of the applied model. Table 5. Comparison of the two variants of the model used.

Pulp and paper produced

Individual Paper Grades

Austrian P&P Production

Considers the production of 1 ton of the speciﬁc paper grade, and the production of pulp necessary, according to pulp yield

Considers the total annual production of pulp and paper in Austria, unrelated to one another.

Similar

Energy consumption calculation method Fuel consumption calculation method

Assumes the typical energy production technology used in P&P mills

Calculated from the industry reported values of heat and fuel consumption (according to Section 2.2)

Similar

CO2 emission calculation method

Speciﬁc (Per ton of paper produced)

Results

Absolute

With both approaches, the impact of selected new technology on energy and emission savings, by considering the time required for the diffusion of the technology, can be analyzed. 3.1. Mathematical Formulation: Energy and Fuel Consumption for Speciﬁc Paper Grades The energy consumption to produce each paper grade depends on the characteristics of the paper produced, which are deﬁned in the model by the following variables:

• • • • •

Paper grade produced (printing and writing paper, tissue, newsprint, or packing paper); Mineral ﬁller mass content in the paper (mf ); Integrated or non-integrated production; Type of virgin pulp used: chemical (kraft, sulphite), mechanical (GW, TMP); Recycled ﬁbers (RCF) content in pulp (r);

Seven different cases were studied (ﬁller content is always considered 10%), shown in Table 6. Table 6. Production speciﬁcations of the cases studied. Grade

Writing (int.)

Writing (n. int.)

Printing (int.)

News (int.)

Packing (int.)

Tissue (kraft) (int.)

Tissue (RCF) (int.)

Virgin Pulp mf r

Kraft 10% 0%

GW 10% 0%

TMP 10% 50%

Kraft 10% 50%

Kraft 10% 0%

10% 100%

For each case, the impacts of producing one ton of paper are calculated (M paper = 1 ton). The dry mass of ﬁllers and pulp necessary for the production are calculated according to Equations (1) and (2), respectively. m f represents the mass percentage of paper ﬁllers in the paper. (1) M f iller = M paper ·m f

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M pul p = M paper − M f iller

(2)

The pulp used is considered to be a mixture between one type of virgin pulp and RCF pulp, and the mass of each type of pulp was calculated based on r, which represents the mass percentage of RCF in the pulp. MRCF = M pul p ·r Mvirgin

pul p

(3)

= M pul p − MRCF

(4)

The wood used to produce the virgin pulp (chemical and mechanical) is calculated by using the pulp yield (dry mass of pulp over the dry mass of wood: Equation (5)) of each pulping process (Table 7). Mvirgin pul p Pul p yield = (5) Mwood Table 7. Pulp yield of the different types of pulp considered. Pulping Process

Pulp Yield [37]

Kraft Sulﬁte Groundwood Reﬁner Mechanical Thermomechanical

50% 45% 94% 94% 85%

The absolute heat consumption for each sub-process (p) used to produce x is then the product of the speciﬁc heat consumption of the process (h p,x , kWh/t) by the mass output of the process (M p , t). The speciﬁc heat consumption per ton of pulp or paper (h x , kWh/t) corresponds to the sum of all processes used for production (found in Tables 1–3) divided by the pulp or paper produced (Mx , t): Equation (6). The same calculation is made for electricity (ex , kWh/t): Equation (7). hx =

∑ M p · h p,x Mx

(6)

ex =

∑ M p ·e p,x Mx

(7)

This study assumes that the paper mill is equipped with a CHP plant (biofuel and natural gas CHP unit) to generate the required heat and electricity. The power to heat ratio is also considered to be 30% in the CHP unit. 3.2. Mathematical Formulation: Energy and Fuel Consumption of the Entire Industry in Austria The total consumption of heat needed for the total annual production of P&P in Austria of each product (x, t: pulp or paper) is calculated by the multiplication of the speciﬁc heat need (h x , kWh/t: Equation (6)) for the production of product (x) with the annual production of the product (P) (Px,y , t). The total heat consumption by the industry (Hy , kWh, Equation (8)) corresponds then to the sum of the heat needed for the production of all products. The same methods are used for electricity consumption (Ey , kWh, Equation (9)), using the speciﬁc electricity needs (ex : Equation (7)) to produce each product Hy =

∑ hx · Px,y

(8)

∑ ex · Px,y

(9)

Ey =

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Following, the values of fuel consumption are estimated. Fuel is used to cover the industry’s heat demands and produce electricity (excess electricity is sold). The heat demand is the main driver of fuel consumption. For each year analyzed, the ratio between the total heat consumption by the industry in Austria and total fuel consumption was calculated (αy , Equation (10)) from the values reported each year by Austropapier (Hy,data , kWh and Fy,data , kWh, respectively) [9,30–34], and used to calculate the amount of fuel needed to cover the heat demands calculated previously, according to the equation (Equation (12)). Similarly, the ratio between the values of electricity consumption (Ey,data , kWh) and fuel consumption was calculated (β y , Equation (11)). The time evolution of α and β from 2009 to 2018 is presented in Figure 6. αy =

Hy,data Fy,data

(10)

βy =

Ey,data Fy,data

(11)

Figure 6. Evolution of α and β from 2009 to 2018 [9,30–34].

The prediction of the total fuels used (Fy ), and the total electricity consumption (Ey ) in the future is then estimated based on αy and β y ; Equations (12) and (13), respectively. Fy = Hy /αy

(12)

Ey = Fy · β y

(13)

The fractions of fossil fuels (coal, oil, and natural gas) and biofuels used every year in the P&P sector ( f i,y ) were also obtained from the same source. Equation (14) represents the consumption of each fuel in year y. Fi,y = Hy /αy · f i,y

(14)

The estimation of the purchased electricity was made by calculating the ratio between the electricity consumed from the grid and the total electricity consumption gy (Equation (15)), Ey,grid,data and Ey,data , respectively, were also reported by Austropapier [9,30–34]. gy =

E purchased,data,y Ey,data

(15)

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For future prospection, the total electricity purchased from the grid each year (Egrid,y ) was then estimated based on gy (Equation (16)). E purchased,y = gy · Ey

(16)

3.3. Mathematical Formulation: CO2 Emission The CO2 emissions due to the consumption of fossil fuels (CO2 direct , t) is calculated as the summation of the amount of fossil fuels consumed (Fi , t) multiplied by the emission factor of each fossil fuel (e f i , tCO2 /tfuel ), reported to Austria’s National Inventory Report [38] (Equation (17)). (17) CO2 direct = ∑ Fi ·e f i i

The CO2 emitted due to the consumption of grid electricity (CO2 indirect , t) is calculated as the product of the grid electricity consumed (E purchased , kWh) multiplied by the respective emission factor for the paper industry (e f grid , tCO2 /kWh). To calculate e f grid (Equation (19)), the total emissions from energy production of the electricity grid (CO2 grid,y , t) is estimated as the summation of the product of the consumption of each fuel used to power the grid (Fgrid,i,y , t) [39] and the respective emission factors (Equation (18)). The grid emission factor is then calculated as the division between CO2 grid,y and the total grid electricity in year y (Egrid,y ). The value used in this section corresponds to the most recent data available. (18) CO2 grid,y = ∑ Fgrid,i ·e f grid i

e f grid =

CO2 grid Egrid

(19)

The CO2 emission due to the purchase of grid electricity is then calculated (Equation (20)). CO2 indirect = E purchased ·e f grid

(20)

The mentioned equations in Sections 3.1–3.3 are also used for each selected technology, and will analyze the decarbonization scenario. 4. Decarbonization Technology Selection Based on the literature, there are already a number of opportunities for reducing energy consumption and greenhouse gas emissions in the pulp and paper industry, and others will be available in the future. In general, upgrading existing mills with energyefficient technologies, such as switching fuel from fossil fuels to on-site produced biofuels (bark and black liquor) in combination with CHP, improving the energy management system, increasing the use of waste paper and paper recycling, and implementation of innovative technologies are the key options identified to reduce CO2 emissions and energy consumption in the P&P sector [10,16,40]. In this work, a list of best available technologies (BAT) and emerging innovative technologies (IT) has been compiled based on a comprehensive literature review in Tables 8 and 9. These technologies are applicable at different stages of the pulping and papermaking process. For each technology, the energy-savings (heat or electricity) and the CO2 reduction potential in the associated process are considered, and to find out how mature the technology is, the technology readiness level (TRL) is monitored.

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Table 8. An overview of the best available technologies (BAT) for the pulp and paper sector based on the literature review. Process

Energy Production

Mechanical pulping

Kraft pulping

Type of Technology

Estimated Energy Saving

TRL

Biomass gasiﬁcation

8–9

Biomass CHP

Biogas production from sludge

Waste heat recovery

Energy management

15%

Focus on maintenance

10%

3.5 GJ/ton pulp or 1.07 GJ/ton paper

Biological pre-treatment

1.8 GJ/ton pulp

8–9

Heat recovery

3.5 GJ/ton pulp

8–9

Steam cycle washing

30–40%

7–8

Ligno Boost

Black liquor gasiﬁcation

RCF Pulping

Estimated Emission Reduction

10%

Recycled paper fractionation Efﬁcient screening High consistency pulping Sludge dryer

2 GJ/ton pulp

8–9

11–13% EL 40% Heat

Description Wood waste is used for gasification instead of combustion. The syngas is utilizing in a combined cycle gas turbine (CCGT). Energy recovery of waste biomass through a combined-heat-and-power (CHP) cycle. Use of the sludge from the water cycle to produce biogas in an anaerobic wastewater treatment plant, burning in the CHP to produce electricity. During production processing, such as pulp drying, and paper drying, a large amount of heat is lost. By recovering and reusing the waste heat, the energy efficiency will be improved, and emissions will be reduced. A recovery system such as recovery boiler closed hoods, and heat pumps can be used. An energy management system, such as steam, electricity, and gas consumption line monitoring, can improve energy flow control throughout the system and the measurement of energy efficiency. Frequent maintenance, especially on electrical equipment such as pumps, motors, fans, dryer systems, etc., can improve energy efficiency and reduce emissions. This technology, by using in mechanical pulping, reduces energy consumption. The technology makes modifications to the cell wall of the fiber and improves the strength of the fiber. Fungal and enzymatic are two common biological pre-treatment technologies for wood chips during mechanical pulping. The electricity use in mechanical pulping is converted into heat (2 tone steam production per ton of pulp), and heat can be recovered with a recovery boiler (up to 80% recovered as steam in TMP). Chemical pulp output from the digester can be washed by steam more than water, which has energy-saving potential. Part of the lignin (25–50%) is extracted from the black liquor by solving CO2 and lowering the pH, which causes lignin to precipitate. Lignin is then purified. It can after be used as a quality fuel or a useful product for other industries. BLG is an emerging commercial technology capable of efficiently recovering energy from the black liquor’s organic content using a recovery boiler and gasification process. Ink particles can be removed in an earlier step before de-inking by separating long and short fibers (tested in the Andritz mill). Improving the screening and filtering in the recycling pulping process can save energy from 5 to 30%.

Ref.

[10,41–43] [44]

[10,15,41,43]

[15,44]

[44]

[10,42,43]

[10]

[15,42,43]

[43]

[10,15,42,43]

[42] [11,44]

15%

Pulping with lower water content, reducing energy consumption to circulation, and pumping of pulp.

[11,44]

8–9

Drying the sludge (using waste heat) can decrease water contact and increase the sludge caloriﬁc value. Replacing fossil fuels with this sludge reduces the emissions due to fossil fuel consumption.

[44]

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Table 8. Cont. Process

Paper Machine

Forming

Press section

Drying

Type of Technology

Estimated Emission Reduction

Estimated Energy Saving

TRL

Closed hood

13%

45% EL

Transport membrane Condenser Laser Ultrasonic Stiffness Sensor Steam box

High consistency forming

8% EL

Dry sheet forming

42%

50%

Hot pressing

0.61 GJ/ton paper

7–8

Impulse drying of paper

30%

20%

Condebelt dryers

The use of a closed hood (instead of an open or semi-open one) over the paper machine reduces energy consumption and CO2 emission. Energy recovery system for the low-temperature exhaust heat from the paper drying section using a ceramic membrane tube. Sensor to measure stiffness, allowing real-time control of production. This technology reduces energy and raw material consumption.

Displacement Pressing

Description

0.44 GJ/ton paper

1.6 GJ steam & 20 KWh EL/ton paper

7–8

Steam box preheats the water used to form the paper, improve dewatering efﬁciency, and allowing higher dry contents to be attained in the press section. Pulp enters the forming section with smaller water content (3% ﬁbers). Suitable for low weight grades such as tissue. Use of turbulent air in place of water as the paper carrier, meaning that there is no water added to the dry pulp, reducing energy for drying Hot pressing increases water removal in the press section, reducing the heat needs in the drying section. Combination of mechanical and air pressure, increasing solids content by up to 60%. Impulse drying uses the heat and pressure in mechanical dewatering before the drying section. It can reduce the water content and increase the solid content by up to 65%. In this technology, the paper is dried between two steel belts in high pressure (max. 10 bar) conditions. The temperature for drying is max. 180 ◦ C, and the steam and electricity consumption can be reduced.

Ref.

[10,44]

[18]

[11,42,44]

[18,43,44]

[15,42,44]

[15,44] [15,18,43]

[43,44]

[15,18,43]

Table 9. An overview of the innovative technologies (IT) for the pulp and paper sector based on the literature review. Process

Type of Technology

Estimated Emission Reduction

Estimated Energy Saving

TRL

Microwave pre-treatment Pre-treatment technology

Chemical pre-treatment with oxalic acid Hemicellulose extraction before chemical pulping

25%

6–8

Description By changing the cellular microstructure of wood, this technology increases the chemical component’s permeability to the chips. It applies to chemical pulping and can reduce energy consumption and the amount of chemical needed. The technology is used in mechanical pulping and can improve fibers’ separation rate (defibration), and refines efficiency by using chemical components such as oxalic acid. Extraction of hemicellulose before pulping decreases alkali consumption, improves the energy efficiency, and increases the production capacity of kraft pulping

Ref.

[18,43]

[18,42,43]

[18,42]

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Table 9. Cont. Process

Type of Technology

Estimated Emission Reduction

Estimated Energy Saving

TRL

Use of Hydrogen as a fuel

7–8

Direct electric heating

7–8

Heat pump recovering waste heat

6–7

Carbon capture and storage

Steam production

Deep eutectic solvents (DES)

20%

40%

Utilization of green liquor

25%

7–8

Membrane concentration of black liquor

36%

6–7

Pulp Production

Paper Production

Functional surface

8–9

New ﬁbrous ﬁllers

25%

5–6

Flash Condensing

50%

20%

3–5

Dry pulp for cure-formed paper

55%

25%

Forming

Press Section

Displacement pressing

30%

5–6

Description Using hydrogen (purchase (especially green H2 ) or on-site production by electrolysis) instead of natural gas can significantly reduce CO2 emissions. By replace fossil fuels with electricity and using an electric boiler instead of a fossil fuel boiler (natural gas boiler) to generate heat (steam) demand, fossil fuel emissions could be eliminated. If the electricity is supplied with renewable sources, net-zero emissions could be reachable. By recovering the waste heat (at low temperature <100 ◦ C) from the process using a heat pump and converting it into medium-temperature heat (max. 160 ◦ C) (Direct information from heat pump manufacturer), energy efficiency would improve, and fossil fuel emissions could be drastically reduced. It may be applied through pre-combustion (associated with black liquor gasification), post-combustion (which is the more straightforward technology), or oxy-combustion technologies DES are produced naturally by plants and can break down wood and selectively extract cellulose fibers required in the papermaking process. This technology could replace the traditional chemical and mechanical pulping techniques by enabling dissolving the wood and extracting lignin, hemicellulose, and cellulose at low temperatures and atmospheric pressure. Deep eutectic solvent could be applied to pulp production from both wood and recovered paper with minimal energy consumption and CO2 emissions. Pre-cooking of wood in green liquor (20–30% of the green liquor) without the lime reaction, reducing energy consumption, lime kiln load, increasing pulp yield, and bleachability. Partial replacement of the evaporation of black liquor by membrane concentration, reducing the thermal energy needed. This technology aims to reduce the weight of paper without impacting its quality or structure (reducing the amount of material by 30% per square meter). Lighter weight paper needs less energy (steam and electricity) for drying, pumping, and transporting. Wood fibers are partially replaced by fibrous filters (based on calcium and silica), which increase the solid contact of the paper web and then reduces the energy required for the drying section. The concept of this technology is to produce waterless paper using high turbulent steam combined with dry fibers. The technology can be applied to any kind of pulp (chemical, TMP, RCF) and reduces energy consumption and fossil fuel CO2 emissions. This technology produces paper without water by using two techniques: a dry pulp technique, which consists of a highly viscous solution and contains higher concentrated fibers, and a cure formed technique, which allows the formation of thin sheets. In the press section before the paper drying, water can be removed from the web using a combination of mechanical and air pressure. This technology increases the solids content to 55%, which leads to a reduction in energy consumption in the drying area.

Ref.

[41,45]

[10]

[13,42]

[42,43]

[13,42]

[42,44]

[13,44]

[13]

[18,43]

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Table 9. Cont. Process

Type of Technology

Estimated Emission Reduction

Estimated Energy Saving

TRL

Supercritical CO2

45%

20%

Superheated steam drying

50%

25%

3–5

Gas-ﬁred dryers

10–20%

6–7

Boost dryer

12%

6–7

Microwave Drying

12%

3–4

Drying

Description Supercritical CO2 is a new process design that can be applied to pulp and paper drying sections. In this technology, the pulp or paper is dried by changing pressure and temperature, which consumes lower energy than the traditional method. Replacing the air needed to remove water from the paper in the drying section with superheated steam can improve heat recovery (full recovery) and increase energy efficiency. The recovered steam can be used in the next steps of paper production. Dryers are heated with hot gases from gas combustion (which may occur in the drum) instead of steam. This dryer technology improves energy efficiency by 75–80% compared to the 65% of the usual system. This technology is mainly used in the packaging and board paper drying sector. Boost drying by utilizing two combined drying technologies (condensation and press) improves drying efficiency by 12%, and reduces energy consumption and drying time. Paper is dried by exposure to microwave radiation. This technology increases the drying rate and reduces the total energy consumption.

Ref.

[13]

[15,18,43]

In Austria, in line with other European paper production sites, the P&P sector has started to improve its energy efﬁciency in recent decades. The implementation of best available technologies as the use of waste heat recovery systems, the switch from fossil fuels to on-site biofuel production in integrated mills (Figures 3 and 4), and the use of recycled paper in paper processing in the Austrian P&P sector have led to a reduction of CO2 emissions by around 30% in the last twenty years (Figure 5) [9,25]. However, to reach the target of decarbonization of the entire industry by 2050, direct emissions remain a challenge for the sector, and further efforts in the P&P sector are needed. Regarding the state-of-the-art situation of the Austrian P&P sector, mentioned in the previous paragraph, six technologies were selected from those listed in Tables 8 and 9 in this study, and their individual impacts on the Austrian P & P sector were evaluated. The technology selection was based on three criteria: 1.

2. 3.

The selected technologies are applied in one of the energy-intensive steps: Chemical pulping and drying, which use approximately 67% of the total energy required for paper making [10,15] of paper production. In this case study, they have a high energy saving potential (electricity/steam) and inﬂuence directly or indirectly CO2 emissions. The technologies have a high TRL (min 6) and have been proven on an industrial scale or are almost commercial in the short and medium-term. Finally, not yet employed in the Austrian P&P sector. The chosen technologies are as following:

•

Steam cycle washing (SCW): This is a new washing technology that uses steam to wash the pulp after chemical pulping instead of water. As a result, it is possible to produce higher consistency and stronger (10%) pulp, and reduce energy for pumping and heating in the thickening, screening, and evaporation operations. The global effect is a reduction of 30–40% of the energy needed (fuel or steam consumption) for kraft pulping (overall, not just digesting). This process is in demonstration and is close to the commercialization phase with a TRL 7–8 [15,43,46]. Impulse drying (ID): This technology is not a replacement for the current drying section. It is a modiﬁcation in the press section, which consists of pressing the paper against a high-temperature element. This way, the dry content in the paper may become as high as 65%, resulting in an energy saving of 0.44–0.9 GJ per ton of paper,

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•

corresponding to 10–25% energy (steam) consumption reduction in papermaking. This technology is in the demonstration phase with TRL 7 [15,43,47]. Condebelt drying (CD): This is a replacement of the current drying section, in which the paper web is dried in a drying chamber between two steel belts instead of on traditional steam-heated cylinders, achieving higher dryer rates and efficiency. This dryer improves fiber properties such as strength (20–60% increasing), smooth surface, dimensional stability, and moisture resistance. With Condebelt drying, the same strength values can be achieved with recycled fibers as with fresh fibers in conventional drying. The CD reduces energy consumption by 15% (1.6 GJ steam per ton of paper and 20 kWh electricity per ton of paper). This technology is in the demonstration phase with TRL 7–8 [15,43,47]. Gas-fired dryers (GFD): Gas-fired dryers are an alternative to the current drying drums heating by steam, in which the same method is applied but the drums are heated by combustion inside the drum. This process has a much higher efficiency (energy efficiency increase from 60–65% in steam-operated, compared to 75–80% in gas-operated), and higher temperatures are achieved, resulting in higher drying rates and a faster process. This method reduces the drying energy consumption by 10–20% and increases the production rate by up to 20%. The technology is still in the pilot stage with TRL 6–7, and has low CAPEX since it is an adaptation of the technology used today [15,43,48]. Dry sheet forming (DSF): A new method of forming which results in large reductions of drying energy. In this method, the paper is formed without the addition of water to the pulp. The sheet is supported by an air jet and a solution of resigns is sprayed on the surface to help to form the paper sheet. This forming method is only suitable for tissue or hygienic paper since the surface smoothness decreases and the thickness has higher variations, but the resulting paper is soft. It is estimated that by using this technology, 50% of the drying energy requirement (fuel used for heat production) can be saved, but the electricity consumption may increase 150 to 250 kWh per ton of paper in an air-layered system to maintain the airflow and motor drive for the equipment. This technology is semi-commercial for the production of special products and will be further developed in the near future for the production of standard paper grades. The TRL of this technology is near 7 [15,43,47]. Direct electric heating (DEH): DEH can contribute to the electrification of the steam supply of the P&P industry by replacing fossil fuels (especially natural gas) with electric boilers with an efficiency of 90%. Since electric boilers exist and are commercially available, this technology can be easily installed in P&P mills. Since the energy demand for paper production by applying this technology is the same with current production processing (and only fossil fuels are replaced by electricity), the feasibility of this option strongly depends on the power grid capacity to achieve such a high load increase without increasing the use of fossil fuels. The generation of a CO2 -free electricity grid would lead to complete decarbonization of the P&P sector by electrification options [41,45,49].

The abovementioned technologies are applied as single technologies (no technology combination) in the relevant paper grades shown in Table 6. Steam cycle washing, impulse drying, Condebelt drying, and direct electric heating are used in integrated writing paper mills and gas-fired dryer, and dry sheet forming in the non-integrated writing paper and integrated tissue paper mills. The effects of every single technology on the individual paper grade were analyzed using the developed model. The specific energy (heat and electricity) consumption and specific CO2 emissions of paper grade utilizing the technology were compared with the current situation of the selected paper grade, shown in Figure 7.

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Figure 7. The effect of technology application on the CO2 emission, heat, and electricity consumption compared to the current status of paper grade production.

The comparison between writing paper production by the integrated and non-integrated mills shows that the first one consumes less energy (especially heat), which directly affects the emission reduction. As depicted in Figure 7, the modeling results reveal that the use of drying technologies reduces the specific CO2 emissions in each paper grade due to energy (heat) demand reduction. 5. Scenario Definition and Results In this section, energy efficiency improvement and CO2 emission reduction in the P&P sector are predicted using several scenarios for Austria until 2050. The business-asusual (BAU) scenario analyzes the situation of the sector without significant technological improvement, and six alternative scenarios will be used to analyze the impact of implementing each of the six selected technology individually. In this work, a combination of technologies is not considered. All scenarios have a starting point based on the development of consumption of paper products in Europe, as predicted by Lamberg et al. [50] in Table 10. The P&P production growth rate could be affected by unexpected future events and trends, such as the increasing digitalization of media and communication, energy and raw material prices, etc. However, considering this effect is not this study’s argument, it is assumed that paper production will follow the same trend as paper consumption in Europe. Table 10. Predictions for paper consumption used in the model (AAGR: annual average growth rate) [50].

AAGR (%)

Newsprint

Printing and Writing

Packing Materials

Household and Sanitary

Other Paper and Board

Total Demand

0.2

0.3

0.0

0.2

For each investigated technology, the deployment year was assigned based on its commercial status: demonstrated and semi-commercial technologies with TRL 7–8 are applied in the year 2025 and pilot or scaling technologies with TRL 6–7 in the year 2030. The maximum relative deployment (share of production using the technology) in the sector for the ﬁrst year of technology usage was estimated, taking into account two factors: CAPEX (capital expenditure) and the need to adapt the production process to the new technology.

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From this starting point, the deployment rate increases linearly until 2050 to 100%. A 100% deployment of technology to the production of one grade of paper means that it is assumed that all production lines of this grade of paper utilize this technology, but not lines producing other grades. To calculate the scenarios, the variables were divided into two groups: dynamic variables, which evolve according to the speciﬁc assumptions of each trend, and constant variables. The constant variables are: -

The ratio between heat consumption and fuel consumption (αy ), with a value of 0.63 corresponding to the base year 2017; The average emission factor associated with grid electricity consumption is the same (efgrid ); The emission factors of each fuel used (ei ) corresponding to the base year.

To analyze the scenarios, the impact of the selected technologies across the P&P sector was assessed in annual time steps up to 2050, and CO2 emissions and energy consumption was calculated using the developed model. The results of such an analysis do not provide an accurate prediction for the pulp and paper sector due to the impact of other options, e.g., the uncertainty regarding the decarbonization of the energy system, power generation resources, ﬂexibility options, and the use of renewable energy policies, etc., which are not addressed in this work. However, these results provide valuable conclusions on the inﬂuencing factors that need to be considered by experts and policymakers. Figure 8 presents the modeling results for the projection trend of paper production and CO2 emissions for the BAU scenario, without technological improvements and changes to the type of energy source consumed for heat generation.

Figure 8. Projection of CO2 emissions in the BAU (business as usual) scenario and paper production trend of the Austrian P&P sector.

The projection trend of CO2 emission and energy consumption in the six alternative scenarios are presented in Figures 9–12.

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Figure 9. Projection of energy consumption in alternative scenarios compared to the BAU scenario.

Figure 10. Projection of CO2 emission by alternative scenarios without DEH (direct electric heating) technology.

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Figure 11. Projection of CO2 emission by alternative scenarios with DEH technology.

(a)

(b) Figure 12. Cont.

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(c)

(d)

(e)

(f)

Figure 12. Projection of emission reduction and energy consumption according to three selected scenarios: (a) estimation of CO2 emissions due to the application of dry sheet forming (DSF) up to the year 2050; (b) estimation of energy consumption due to application of dry sheet forming (DSF) up to the year 2050; (c) estimation of CO2 emissions due to the application of condebelt drying (CD) up to the year 2050; (d) estimation of energy consumption due to application of condebelt drying (CD) up to the year 2050; (e) estimation of CO2 emissions due to the application of direct electric heating (DEH) up to the year 2050; (f) estimation of energy consumption due to the application of direct electric heating (DEH) up to the year 2050.

6. Discussion The result of the BAU scenario indicates that without technological development and improvement of energy efﬁciency, CO2 emissions of the Austrian P&P sector in 2050 will be 8.7%, and the energy consumption 10%, higher compared to the base year 2017. This is mainly due to the increase in paper production. According to the potential for reduction of CO2 emissions in 2050, the result of other suggested scenarios can be divided into the following groups:

•

Low emission reduction (<5%): this group includes two technologies, SCW (steam cycle washing) technology for chemical pulp production with a maximum carbon reduction of 1.8%, and DSF (dry sheet forming) technology for small production segments of tissue paper with a reduction of emissions in the P&P sector of less than 3% and a decrease in total energy consumption of 2% compared to the BAU scenario. Although these technologies have a significant impact on the specific grade applied (DSF is able to reduce the emission of tissue paper production by 80% due to reduction of fuel consumption), their impact on the overall sector is minor. Medium emission reduction (5–10%): this is the category of scenarios in which drying technologies are applied with a maximum carbon reduction of 10% compared to the BAU scenario. The promising technologies in this group are CD (Condebelt drying) with 10% emission reduction potential, ID (impulse drying) with 9.8% emission reduction potential, and GFD (gas-fired dryers) with 7.5% emission reduction potential. The first two options, CD and ID, represent greater heat savings (11%), but GFD would require a less radical change in the production line and a lower investment,

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•

which could mean higher deployment in the future. The gas-fired dryer increases the efficiency of heat supply to the drying process but depends on methane combustion, so CO2 emissions are unavoidable. Nevertheless, methane can be obtained from biogas or biomass gasification, and emissions can be prevented, at least partially. High emission reduction (>75%): this category includes the electrification of the P&P sector using DEH (direct electric heating) technology. DEH replaces the fossil fuel boiler for steam supply with the electric boiler, providing no sustainable improvement in energy efficiency, but eliminating up to 75% of CO2 emissions. The total energy consumption in this scenario is the same as in the BAU scenario by 2050; however, fossil fuels are completely replaced by grid electricity, which has a significant impact on reducing CO2 emissions. By applying this technology, direct CO2 emissions from fossil fuel combustion are removed, and only indirect emissions are calculated, which can be realized depending on the CO2 intensity of the electricity generation. Electrification of the P&P sector with DEH has the potential to fully decarbonize the sector if CO2 -free electricity is available in sufficient quantities. In 2016, about 63% of Austria’s electricity was generated from renewable sources (hydropower, wind, photovoltaic, etc.), 30% from fossil fuels, and 7% from other sources [51]. However, an electricity supply from entirely renewable sources is doubtful because, on the one hand, renewable resources in Austria are limited. On the other hand, the demand for renewable energy by other sectors such as industry (use as raw materials), heat-generating industry, transport sector, etc., is increasing and makes this an uncertainty [52].

This work addresses only a few of the promising technologies from the literature. Although some of the investigated technologies had only a small impact on emission reduction, such measures should be taken to improve energy efficiency and avoid carbon dioxide emissions at each stage of the production process (i.e., pulp production and paper drying). It must be noted that the efficiency measures calculated in this work are based on an additional paper demand, and a lower paper demand or the use of more recycled paper would be helpful in this case. In addition changing the technology in the production process, and decarbonization of the steam supply system also play an important role. Decarbonization of the steam supply system is achieved by electrifying the heat using equipment, such as the electric boiler or replacing fossil fuels with biofuels (e.g., using clean methane or hydrogen instead of natural gas). However, ensuring carbon-free electricity and sufficient biofuel resources is crucial for limiting GHG emissions in the supply chain. Other technologies besides those considered are expected to play an essential role in the future of the P&P sector. Specifically, the increase of heat recovery and process control, the implementation of black liquor gasification along with carbon capture and storage, and utilizing other electrification options, such as electric heat pumps and electrolysis, alongside the decarbonization of the electricity supply. 7. Conclusions and Outlook The P&P sector is a dynamic manufacturing industry that will keep its role in Austria’s industrial production, and as an important economic sector. However, the sector, which consumes about 20 TWh of final energy, is responsible for 7% of Austria’s industrial CO2 emissions. For the purpose of reducing CO2 emissions and energy consumption during the production process, this study analyzed the role of mitigation technologies individually for energy consumption and CO2 emissions of the Austrian P&P sector until 2050. This was achieved by using a bottom-up model. The model was applied to analyze the energy consumption (heat and electricity) and CO2 emissions in the main process, related to the P&P production from virgin or recycled fibers. Afterward, technological options to reduce energy consumption and fossil CO2 emissions for P&P production were investigated, and various low-carbon technologies were applied to the model. The modeling results revealed that the technologies applied in the production process (chemical pulping and paper drying) would have a minor impact on emission reduction (maximum 10% due to the use of an impulse dryer), whereas the electrification of the steam supply by replacing

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fossil fuel boilers with a direct heat supply (such as commercial electric boiler) would enable reducing emissions by up to 75%. This means that the goal of 100% CO2 emission reduction by 2050 cannot be reached with a single method alone. Therefore, the following points appear to be essential, and should be taken into account in the future:

• • •

Selecting a combination of technologies, particularly with the electriﬁcation of the steam supply, along with the use of carbon-free electricity generated by renewable energy. Close cooperation with stakeholders to select the most promising decarbonization options. Consideration of industry sectors coupling to explore the possibility of using waste heat and biofuel generated in nearby industries.

Author Contributions: Conceptualization, designed the research, and developed the method M.R.M. and M.S.S.; methodology, M.R.M.; software, M.S.S. and M.R.M.; writing—original draft preparation, M.R.M.; review and editing, T.K. All authors have read and agreed to the published version of the manuscript. Funding: This work was carried out as part of the NEFI_Lab project. The NEFI_Lab project is supported with the funds from the Climate and Energy Fund and implemented in the framework of the RTI-initiative “Flagship region Energy”. Acknowledgments: We are grateful to Tânia Alexandra Dos Santos Costa e Sousa for her helpful comments and suggestions. Conﬂicts of Interest: The authors declare no conﬂict of interest.

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Van Berkel, A. Raising Steam for Industry without Emitting CO2 : Taking the C out of Steam; Lux Research Inc.: Boston, MA, USA, 2018. Muehlethaler, E.; Starkey, Y.; Salminen, R.; Harding, D. Steam Cycle Washer for Unbleached Pulp: (Final Report DE-FC36-04GO14304); DOE: Washington, DC, USA, 2008. Martin, N.G.; Worrell, E.; Ruth, M.; E Price, L.; Elliott, R.; Shipley, A.; Thorne, J.H. Emerging Energy-Efﬁcient Industrial Technologies; Lawrence Berkeley National Laboratory: Berkeley, CA, USA, 2000. EPA. Available and Emerging Technologies for Reducing Greenhouse Gas Emissions from the Pulp and Paper Manufacturing Industry; U.S. Environmental Protection Agency: Washington, DC, USA, 2010. Möllersten, K.; Gao, L.; Yan, J. CO2 Capture in Pulp and Paper Mills: CO2 Balances and Preliminary Cost Assessment. Mitig. Adapt. Strat. Glob. Chang. 2006, 11, 1129–1150. [CrossRef] Lamberg, J.-A.; Ojala, J.; Peltoniemi, M.; Särkkä, T. The Evolution of Global Paper Industry 1800–2050. A Comparative Analysis; Springer: Dordrecht, The Netherlands, 2012; ISBN 978-94-007-5430-0. Treibhausgasemissionen Von Strom. Empfehlungen zur Öko-Bilanzierung; Umweltbundesamt GmbH: Vienna, Austria, 2018; ISBN 978-3-99004-472-8. Sejkora, C.; Kianberger, T.; Moser, S.; Hofmann, R.; Haider, M.; Brunner, C. Renewables4Industry Abstimmung des Energiebedarfs von Industriellen Anlagen und der Energieversorgung aus Fluktuierenden Erneuerbaren; Diskussionspapier (Endberichtsteil 2 von 3); Energieinstitut an der JKU Linz: Linz, Austria, 2018.

PAPERmaking! FROM THE PUBLISHERS OF PAPER TECHNOLOGY TE INTERNATIONAL®

Volume 8, Number 2, 2022

Analytical Determination of the Bending Stiffness of a Five-Layer Corrugated Cardboard with Imperfections

1 2 TOMASZ GARBOWSKI & ANNA KNITTER-PIA˛TKOWSKA .

Bending stiffness (BS) is one of the two most important mechanical parameters of corrugated board. The second is edge crush resistance (ECT). Both are used in many analytical formulas to assess the load capacity of corrugated cardboard packaging. Therefore, the correct determination of bending stiffness is crucial in the design of corrugated board structures. This paper focuses on the analytical determination of BS based on the known parameters of the constituent papers and the geometry of the corrugated layers. The work analyzes in detail the dependence of the bending stiffness of an asymmetric, five-layer corrugated cardboard on the sample arrangement. A specimen bent so that the layers on the lower wave side are compressed has approximately 10% higher stiffness value. This is due to imperfections, which are particularly important in the case of compression of very thin liners. The study showed that imperfection at the level of a few microns causes noticeable drops in bending stiffness. The method has also been validated by means of experimental data from the literature and simple numerical finite element model (FEM). The obtained compliance of the computational model with the experimental model is very satisfactory. The work also included a critical discussion of the already published data and observations of other scientists in the field. Contact information: 1. Department of Biosystems Engineering, Poznan University of Life Sciences, Wojska Polskiego 50, 60-627 Poznań, Poland. 2. Institute of Structural Analysis, Poznan University of Technology, Piotrowo 5, 60-965 Poznań, Poland. Materials 2022, 15, 663. https://doi.org/10.3390/ma15020663 Creative Commons Attribution 4.0 International License

The Paper Industry Technical Association (PITA) is an independent organisation which operates for the general benefit of its members – both individual and corporate – dedicated to promoting and improving the technical and scientific knowledge of those working in the UK pulp and paper industry. Formed in 1960, it serves the Industry, both manufacturers and suppliers, by providing a forum for members to meet and network; it organises visits, conferences and training seminars that cover all aspects of papermaking science. It also publishes the prestigious journal Paper Technology International® and the PITA Annual Review, both sent free to members, and a range of other technical publications which include conference proceedings and the acclaimed Essential Guide to Aqueous Coating.

Page 1 of 18

Article 4 – Testing

materials Article

Analytical Determination of the Bending Stiffness of a Five-Layer Corrugated Cardboard with Imperfections Tomasz Garbowski 1, *

2 and Anna Knitter-Piatkowska ˛

Department of Biosystems Engineering, Poznan University of Life Sciences, Wojska Polskiego 50, 60-627 Poznań, Poland Institute of Structural Analysis, Poznan University of Technology, Piotrowo 5, 60-965 Poznań, Poland; anna.knitter-piatkowska@put.poznan.pl Correspondence: tomasz.garbowski@up.poznan.pl

Abstract: Bending stiffness (BS) is one of the two most important mechanical parameters of corrugated board. The second is edge crush resistance (ECT). Both are used in many analytical formulas to assess the load capacity of corrugated cardboard packaging. Therefore, the correct determination of bending stiffness is crucial in the design of corrugated board structures. This paper focuses on the analytical determination of BS based on the known parameters of the constituent papers and the geometry of the corrugated layers. The work analyzes in detail the dependence of the bending stiffness of an asymmetric, five-layer corrugated cardboard on the sample arrangement. A specimen bent so that the layers on the lower wave side are compressed has approximately 10% higher stiffness value. This is due to imperfections, which are particularly important in the case of compression of very thin liners. The study showed that imperfection at the level of a few microns causes noticeable drops in bending stiffness. The method has also been validated by means of experimental data from the literature and simple numerical finite element model (FEM). The obtained compliance of the computational model with the experimental model is very satisfactory. The work also included a critical discussion of the already published data and observations of other scientists in the field.

Citation: Garbowski, T.; Knitter-Piatkowska, ˛ A. Analytical

Keywords: bending stiffness; analytical solution; imperfections; corrugated board; thin-walled structures

Determination of the Bending Stiffness of a Five-Layer Corrugated Cardboard with Imperfections. Materials 2022, 15, 663. https:// doi.org/10.3390/ma15020663 Academic Editor: Alexey Smolin Received: 29 December 2021 Accepted: 14 January 2022 Published: 16 January 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional afﬁliations.

Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

1. Introduction A sign of the present times is the constant pursuit of the purchase of various merchandise, and thus the need for their packaging and safe transport, both in traditional forms of sale and e-commerce. The foremost desirable characteristics of the packaging are naturally adequate strength in relation to light weight and, in the interest of the natural environment, reusable, recyclable and biodegradable. Corrugated cardboard packaging perfectly meets all the above-mentioned requirements. Going further, the popularity of this type of packages is associated with the intensive development of a separate branch of industry and research. In view of the laws governing the free market, manufacturers strive for the most cost-effective solutions while maintaining the appropriate load-bearing capacity of cardboard packaging. The scientists, who have been developing for many years new methods to determine the material properties of the corrugated cardboard [1,2] and are constantly trying to understand the nature of the packaging performance, through numerous studies, involving a variety of techniques, are here to help. The task is challenging mainly due to the layered structure of the corrugated cardboard with two characteristic in-plane directions of orthotropy associated with the mechanical strength of the paperboard—the machine direction (MD) perpendicular to the main axis of the fluting and parallel to the paperboard fiber alignment, and cross direction (CD) which is parallel to the fluting. Moreover, there are a number of factors that reduce the strength of a cardboard itself or corrugated cardboard packaging, the impact of which has been analyzed and is still is the subject of investigation, e.g., [3] in particular time and storing conditions [4,5], stacking load [6–8],

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openings, ventilation holes and perforations or indentations [9–14], shifted creases on the flaps [15] or imprinting on packaging cardboard [16], e.g., product or seller logos. Much of the research presented in the literature is devoted to the assessment of the load-bearing capacity of the cardboard. Analytical methods were described 70 years ago [17], where simple and fast solutions for the assessment of the strength of simple standard boxes was presented. The proposed formulae have evolved over the decades and have been enriched, expanded and improved, i.e., by introducing the Poisson’s ratio, dimensions of the box, the buckling influence or modification of constants and exponents [18–23]. A conventional numerical approach engaged for the assessment of load-bearing capacity of a cardboard is the finite element method (FEM). The numerical strength estimation of the paperboard tubes was discussed in [24] while consideration on the corrugated board packages load-bearing capacity was presented in [25–28] and bending stiffness (BS) estimation in [29,30]. Buckling and post-buckling phenomena while applying FEM have been taken into account in [31], and torsional and transversal stiffness of orthotropic paper materials influence on the strength of cardboard in [32–36]. The acquisition of mechanical properties of the paperboard during the simulation of its creasing involving FEM is discussed in [37–42]. FEM can also be utilized to perform a numerical homogenization [43]. Homogenization is a method that enables to simplify a multi-layer model to a single-layered one and ascertain the equivalent stiffnesses and effective thicknesses of the model. This procedure requires the determination of material parameters of individual cardboard layers; however, it allows for a significant saving of computation time while maintaining accurate results. This approach is being intensively developed [44–52], as are analytical [53], asymptotic [54] and multiple scales homogenization methods [55]. Experimental methods are very common and frequently used to assess the load capacity of corrugated boards. The box compression test (BCT) and the edge crush test (ECT) are the most prevalent. The bending test (BNT), which allows to define the bending stiffness, the shear stiffness test (SST), the torsional stiffness test (TST) and humidity testing are also pertinent to the assessment of the mechanical properties of the cardboard box. Non-contact measurement methods are increasingly used to measure displacements or strains, even in routine laboratory tests. A technique that allows to gather the data from the outer surface of the specimen, in accordance with the measurement of the relative distances between pairs of points tracked across images acquired at various load values, is a video extensometry [56,57] which is similar to the digital image correlation (DIC) that is a full-field non-contact optical measurement routine [36,58–64]. The two most significant mechanical parameters of corrugated board are the bending stiffness (BS) and the edge crush resistance (ECT). They are exploited in analytical formulae to estimate the load-bearing capacity of corrugated cardboard boxes. The paper presents the analytical determination of BS of five-layer corrugated cardboard in four-point bending test basing on the known parameters of the constituent papers and the geometry of the corrugated layers. It was assumed that only flat layers, without the participation of corrugated layers are taken into account in the calculations. In the analytical model the presence of initial imperfections in compressed segments of the corrugated board was assumed. In addition, FEM numerical models have been built to validate the aforementioned assumptions. Two cases have been discussed—in the first one, both liners and fluting were taken into account to determine BS and in the second one, the stiffness of the corrugated layers was reduced to imitate a situation in which they are excluded from the computation. The method has also been validated by means of experimental data taken from the literature [29]. The obtained compliance of the computational model with the experimental model was very satisfactory. The optimal selection of the arrangement of corrugated cardboard layers is fundamental for the load-bearing capacity of packages. For that reason, sensitivity analysis with respect to mechanical properties of liners and the flute geometric parameters was conducted to answer the question of which of the parameters have the greatest impact on BS. The main contribution of this study was the derivation of analytical relationships that

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explain the differences in the bending stiffness of asymmetrical corrugated boards when the layers on the B or E ﬂute side are compressed. 2. Materials and Methods 2.1. The Four-Point Bending Test of a Sample with an Asymmetric Cross-Section In the case of four-point bending of a sample with an asymmetric cross-section, especially when its cross-section consists of thin-walled faces (an example of such board is the corrugated cardboard), the dependence of the bending stiffness on the direction of the moment can be noticed. Using theoretical models as well as linear numerical models, this effect cannot be capture. This phenomenon belongs to the imperfection class of problems. Since in the four-point bending test, the mid-segment is bent with a constant moment M (see Figure 1) and all other section forces are not present, therefore, the problem is greatly simpliﬁed. In the case of asymmetrical sections in such test, the sample can be placed and, consequently, examined in two positions, which results in different values of the determined bending stiffness.

Figure 1. 4-point bending test.

Thin-walled structures, when they undergo bending (i.e., one part of the cross-section is compressed and other part is in tension), have higher bending stiffness if the “stronger” part of the cross-section is compressed (see Figure 2a). On the other hand, when the “weaker” part of the cross-section is compressed (see Figure 2b), the BS is lower—this is due to the preliminary buckling of the compressed fragments of the thin-walled cross-section. More information and a short discussion on this phenomenon can be found in the following subsections.

(a)

(b)

Figure 2. Two possibilities of placing the corrugated board in the 4-point bending test: (a) B-ﬂute upwards (BE); (b) E-ﬂute upwards (EB).

In our case, where a ﬁve-layer corrugated cardboard sample is tested, the stronger part of the cross-section is on the E-wave side. Therefore, from now on, the following description is used to distinguish two cases: (a) EB—compression of a part of the cross-section on the B wave side (see Figure 2b) and (b) BE—compression of a part of the cross-section on the E wave side (see Figure 2a). In the BE conﬁguration, higher BS values are obtained. 2.2. Corrugated Cardboard-Samples This study uses the results of the research presented in the work by Czechowski et al. [29]. The authors presented the mechanical parameters of the component papers (cor-

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rugated and flat layers; see Table 1), the geometric parameters of the five-layer corrugated cardboard (5EB; see Table 2) and the results of four-point bending tests for six boards made of various combinations of component papers. In this paper, the above experimental data were the starting point for in-depth studies on the cause of the difference in the bending stiffness of samples bent with a positive and negative moment. The geometric characteristics of the corrugated layers are also shown in Figure 3. It was assumed that the shape of wavy layers is described by a trigonometric function with the amplitude hi and the period 2π/pi . Table 1. Stiffness moduli for individual flat layers of corrugated board. Mode ID Board 1 Board 2 Board 3 Board 4 Board 5 Board 6

Stiffness Modulus E1 in MD (Nmm−2 ) Liner 1 Liner 2 Liner 3 5700 6690 5700 5700 6690 5700

6460 5200 6460 5720 5200 5730

5650 5520 5650 5650 5520 5520

Table 2. Geometrical parameters of corrugated layers.

Layer

Period (mm)

Height (mm)

Take-Up Factor

Flute E Flute B

3.40 6.10

1.20 2.58

1.262 1 1.362 1

Length of medium to liner ratio.

Figure 3. Five-layer corrugated board–waves geometry.

Since in the adopted calculation model (details will be discussed in the next subsection), only ﬂat layers affect the machine direction (MD) bending stiffness, therefore only the MD stiffness moduli for liners only for all six boards are listed in Table 1. The corrugated layers play the role of keeping the liners at the right distance to ensure adequate bending stiffness. The geometry of the separated, undulating layers is presented in Table 2. In the geometrical description of the corrugated board, however, the thickness of the individual layers should also be taken into account, see Figure 4. Therefore, the total height of the corrugated cardboard 5EB is: H=

∑ (hi∗ ) +

i =1

t1 t + 3, 2 2

(1)

where hi∗ are the distances between the central axes of the liners. So the corrected E-ﬂute height is: h1∗ = h1 + 0.5t1 + 0.5t2 + t4 , (2)

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while the corrected B-ﬂute height is: h2∗ = h2 + 0.5t2 + 0.5t3 + t5 .

(3)

Figure 4. Thickness of all corrugated board layers and axial distance between liners in the computational model.

Table 3 summarizes the thicknesses of all corrugated cardboard layers for six boards and the calculated distances between liners (i.e., corrected heights of the corrugated layers), according to Equations (2) and (3). Table 3. Thickness of individual layers of corrugated board and height of corrugated layers. Mode ID Board 1 Board 2 Board 3 Board 4 Board 5 Board 6

Liner 1

Flute E

Thickness (μm) Liner 2

Flute B

Liner 3

h*1

Height (mm) h*2

142 185 142 142 185 142

164 227 199 177 199 177

126 177 126 139 177 164

164 199 139 177 199 177

146 186 146 146 186 186

1.498 1.608 1.523 1.518 1.580 1.530

2.880 2.961 2.855 2.899 2.961 2.930

As already mentioned, the measured thicknesses of the constituent papers (see Table 3) and the geometry of the corrugated layers (see Table 2) were taken from [29]. 2.3. Bending Stiffness of Assymetric Corrugated Board with Imperfections It is assumed in this study that only liners are involved in bending in the MD, which means that fluting has only the role of supporting the liners in the correct position. Therefore, their tensile/compression and bending stiffnesses are negligible. In order to derive the model, first, all liners were segmented between the supporting wave crests in the corrugated layer (see Figure 5). Preliminary geometric imperfections were included in the compressed segments, which reduced the stiffness of these elements. These assumptions allow to capture the difference in BS depending on the sign of a bending moment in the asymmetric boards. Since the five-layer corrugated board consists of three liners, three different segment lengths can be distinguished: L1 and L3 correspond to the E and B wave periods, respectively. On the other hand, the length L2 can reach the maximum value of p1 (where p1 is a lower wave period, see Figure 3). However, usually every second segment is divided into two sections by the crest of wave B, indicated by L2 on Figure 5. Therefore, the average length equal to 2/3 p1 was adopted in the middle liner for further analyses.

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Figure 5. Compressed and stretched segments of a corrugated board cross-section during bending.

For a compressed i-th segment (see Figure 6) with a geometric imperfection, the longitudinal shortening of i-th segment, δi can be computed by the classical equation: δi =

L Ni N i 0

Ei Ai

dx +

L Mi M i 0

Ei Ii

dx,

(4)

where: Ni = Pi is the normal force; N i = 1 is a virtual normal force; Ai = bti is the crosssection area (with b—segment width and t—segment thickness); Ii = bt3i /12 is the crosssection moment of inertia; Mi = Pi wi ( x ) is the bending moment; and Mi = 1 wi ( x ) is a virtual bending moment. By inserting all the relationships described above into Equation (4) and taking all the constant values out of the integral, the longitudinal deﬂection takes the form: L i Pi 12Pi Li dx + (5) δi = (wi ( x ))2 dx, Ei ti b 0 Ei t3i b 0 where the deﬂection function wi can be described by e.g., the sine function: x , wi ( x ) = f i sin 2π Li

(6)

with the maximum deﬂection f i in the middle of the element span Li (see Figure 6), which was assumed here as a small fraction of the element length: f i = Li · 10−k while the value of k is a quantity assumed between 2 and 4.

Figure 6. Compression of a single segment with a geometric imperfection.

When measuring the bending stiffness of ﬁve-layer corrugated board one can place a corrugated board sample with the E wave facing upwards or vice versa. As the result, in one case, two liners are compressed on the E wave side (see Figure 7) while in the other case, a single liner on the B wave side (see Figure 8) is compressed. In a case where two liners on the E-ﬂute side are compressed, a higher value of bending stiffness is usually obtained. This is because larger number and shorter (therefore, less slender) segments are compressed and even when imperfections are present, the effect is less pronounced.

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Figure 7. Corrugated board bending–compressing the layers of lower ﬂuting.

Figure 8. Corrugated board bending–compressing the layer of higher ﬂuting.

In a four-point bending test, only the bending moment occurs in the center of the specimen, so the model simplifies to pure bending. In this model, the moment is balanced by the normal forces Pi acting in the liners on the arms zi (see Figure 7) with respect to the neutral axis z0 : ∑ N zi ti b z0 = i N . (7) ∑i ti b The starting point for determining the bending stiffness is the kinematic excitation in the form of rotation φ (see Figure 7), which causes elongation or contraction δi of liners (see Figure 8). By taking a small value δ1 (e.g., 10−2 mm) and using the known values of zi , the remaining values δi can be determined (see Figure 8) and finally the rotation angle φ can be obtained: δ φ = atan 1 . (8) z1 By solving the integrals in Equation (5), it is possible to determine the longitudinal deflection in liners under compression or tension: δi =

6Pi Li f i2 Pi Li . + Ei ti b Ei t3i b

(9)

For the known deﬂection δi , the compressive force Pi in the i-th liner can be determined: Pi =

Ei ti δi b

Li 1 + 6 f i2 ti−2

(10)

while the tensile force Pi (for f i = 0) is: Pi =

Ei ti δi b . Li

Mi =

∑ Pi zi ,

The i-th bending moment is:

(11)

(12)

i =1

and the bending stiffness can be calculated as the sum of the integrals from the formula: EI =

N Li

∑ i

N Mi ML dx = ∑ i i . φ φ i =1

(13)

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If, instead of bending, the corrugated board cross-section is compressed or stretched in MD, the equation for compression/tensile stiffness can also be derived: EA =

N Li

∑ i

N Pi PL dx = ∑ i i . δi δi i =1

(14)

The theoretical bending stiffness (valid for a perfect model without imperfections) as the product of the stiffness modulus in MD and the moment of inertia of liners only is: EI =

∑

N i =1

Ei b

t3i + ti z2i . 12

(15)

In order to normalize the theoretical values and the results of four-point bending tests, both values are divided by the width of the sample b. Hence, ultimately, the bending stiffness is: EI BS = . (16) b The presented derivation allows to explain the differences between the bending stiffness obtained from testing of the corrugated board sample placed with the E wave upwards or vice versa—B wave. 3. Results In the ﬁrst step, the theoretical assumption, in which only liners affect the stiffness of the entire section, was validated. For this purpose, two simple numerical models of a ﬁve-layer corrugated cardboard in a plane state (i.e., a beam model) were built (see Figure 9). Both models consist of classic Bernoulli 2-node beam elements and were implemented in Matlab software (Mathworks Inc., Natick, MA, USA) [65]. Small rotation φ was applied in both ends and the corresponding reaction moments M were determined in order to calculate BS from Equations (13) and (16). In all cases, displacements resulting from φ rotation wrt neutral axis were applied on both ends of the model (in external nodes on the left and right sides of the model).

(a)

(b) Figure 9. Numerical model of corrugated board: (a) 2-period FE model (b) 4-period FE model.

In the first model all layers were modeled according to their geometry and mechanical parameters, while in the second model, the stiffness of the corrugated layers was significantly reduced (by 100 times) to mimic a situation where only liners are active. The results are shown in Figure 10. Naturally, this assumption is not valid if one would like to derive the BS in CD, where all liners as well as both corrugated layers are equally important. In order to eliminate a possible error related to the discretization of numerical models, the influence of the number of finite elements and the number of waves in the model was also checked. The results are summarized in Table 4. All FE models consist of 2-node linear beam elements with a seed equal to 0.1 mm, which generated the following number of nodes and elements in four models: 1. 2. 3. 4.

FEM-1 (1-wave), number of nodes: 375, number of elements: 377; FEM-2 (2-waves), number of nodes: 746, number of elements: 754; FEM-3 (3-waves); number of nodes: 1118, number of elements: 1131; FEM-4 (4-waves); number of nodes: 1489, number of elements: 1508.

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Figure 10. BS calculated by a theoretical model for all 6 boards in which only ﬂat layers are active (blue bars) and by two numerical models where corrugated layers are included in the calculation (red bars) or are excluded from the calculation (yellow bars). Table 4. The bending stiffness computed by the numerical model with included ﬂuting with different number of periods. FEM-2–a model with two periods (see Figure 9a), FEM-4–a model with four periods (see Figure 9b). Name Board 1 Board 2 Board 3 Board 4 Board 5 Board 6

BS (Nm) FEM-1

FEM-2

FEM-3

FEM-4

8.187 12.129 8.213 8.322 11.983 9.652

8.198 12.135 8.231 8.332 11.991 9.669

8.160 12.069 8.182 8.292 11.926 9.625

8.160 12.069 8.182 8.293 11.926 9.626

In the next step, the influence of imperfection amount on the bending stiffness in the analytical model was analyzed. The results for the parameter k ranging from 2 to 4 are shown in Figure 11. The selected value of k = 2.3 is marked on all graphs along with corresponding BS values for both case EB and BE. The selected value of k gives the best agreement between the results obtained with the proposed model and the available experimental data. Because the presented analytical model takes into account the initial imperfections of compressed segments in the corrugated board, thus allows to distinguish between the bending stiffness of the corrugated board whether the E wave or the B wave is compressed. The bending stiffness not only decreases with the increase of the initial imperfection, but also the BS difference between the EB and BE increases as the imperfections increase (see Figure 12). In other words, as the initial imperfections increase, the bending stiffness of the sample in the EB configuration (compression on the B wave side) decreases faster than the bending stiffness of the sample in the BE configuration.

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(a)

(b)

(c)

(d)

(e)

(f) Figure 11. The dependence of BS on the imperfection parameter calculated using the EB model (with the E wave upwards) and by the BE model (with the B wave upwards): (a) Board 1; (b) Board 2; (c) Board 3; (d) Board 4; (e) Board 5; (f) Board 6.

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(a)

(b)

(c)

(d)

(e)

(f)

Figure 12. The difference in BS between the EB and BE conﬁguration: (a) Board 1; (b) Board 2; (c) Board 3; (d) Board 4; (e) Board 5; (f) Board 6.

The difference in bending stiffness between the EB and BE configurations can be as high as 25%. However, this applies to cross-sections in which the imperfection amounts to 1% of the initial length of the compressed segment, Li . In our case, the initial imperfection, for the selected value of the k-factor, is 0.5% of Li . The practically zero difference between EB and BE case can be observed for the coefficient k equals to 3, i.e., initial imperfection equals to 0.1% of Li . Table 5 gathers all bending stiffness values for all 6 boards determined from experimental data [29], theoretical model (no imperfections), simplified FEM model (2D beam model—no imperfections), full 3D shell FE model [29]—no imperfections, and proposed here analytical model with imperfections.

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Table 5. BS for all considered models. The values in parentheses represent BS calculated using the FEM-Beam model without taking into account both corrugated layers. Title 1

Face-up

EXP (Mean) (Nm)

Theoretical EI/b (Nm)

FEM-Beam (Nm)

FEM [29] (Nm)

Analytical (Nm)

Board 1

EB BE

8.32 8.47

8.11

8.20 (8.14)

7.62 7.58

7.13 7.84

Board 2

EB BE

10.97 11.58

11.92

12.14 (12.02)

9.88 9.81

11.15 11.65

Board 3

EB BE

7.25 9.50

8.12

8.23 (8.15)

7.61 7.53

7.15 7.85

Board 4

EB BE

9.10 11.10

8.24

8.32 (8.27)

7.53 7.45

7.24 7.98

Board 5

EB BE

11.46 12.97

11.78

11.99 (11.89)

10.42 10.37

10.89 11.52

Board 6

EB BE

8.20 9.12

9.60

9.67 (9.60)

8.45 8.40

8.86 9.27

As the differences in the results summarized in Table 5, especially the differences between the experimental measurements and all computational models, suggest some errors in the experimental data, the sensitivity analysis was performed in the last step. This analysis was to show which of the parameters have the greatest impact on BS and therefore to point out which measurements require careful re-checking in order to find possible inaccuracies in experimental data presented in [29]. Figure 13 presents all sensitivities of BS in two configurations: EB and BE with respect to mechanical properties of corrugated board and the flute geometric parameters. All graphs in Figure 13 show the BS sensitivity to 10% perturbations of (a) thickness of all corrugated cardboard layers, (b) liners stiffness moduli as well as (c) E and B wave heights. All other parameters do not affect the bending stiffness in both wave orientation (E wave up or B wave up). Certainly, the shape of the corrugated layer (apart from the amplitude) has no effect on BS because, as already proved in this paper, the flute itself contributes less than 1% to overall bending stiffness of corrugated cardboard.

(a)

(b) Figure 13. Cont.

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(c)

(d)

(e)

(f) Figure 13. The sensitivity analysis of BS in EB and BE conﬁguration with respect to all layers’ thicknesses, ti , elastic properties of liners, Ei and ﬂute geometric parameters, hi : (a) Board 1; (b) Board 2; (c) Board 3; (d) Board 4; (e) Board 5; (f) Board 6.

4. Discussion The results presented in the study were obtained while using derived analytical or numerical models, in which the experimental data presented in [29] were utilized. All experimental data used in the work are summarized in Tables 1 and 2. The heights of the corrugated layers (E-flute and B-flute) have been corrected and are compiled in Table 3. To the best of our knowledge, there are no other studies in the literature on this subject, although several observations made by various scientific groups have already indicated this phenomenon, e.g., Östlund and Niskanen [66]. The proposed analytical model does not take into account the corrugated layers in the calculation of the bending stiffness of the five-layer corrugated cardboard. Two numerical models were therefore built to validate this assumption. In the first of them, both flat and corrugated layers were used to determine BS. In the second one, the stiffness of the wavy layers was reduced to emulate a situation in which corrugated layers are excluded from the computation. For the comparison, the theoretical model was additionally employed, in which also just flat layers are considered in BS computation. All three models gave almost the same results presented in Figure 10. The differences were between 0.72% and 1.75%. Since the presented model takes into account the influence of initial imperfections in the compressed segment of the corrugated board, the first attention was focused on determining the initial imperfection values. Figures 11 and 12 present BS in two configurations: (a) EB—E wave upwards and (b) BE—B wave upwards, as a function of imperfection value.

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In Figure 11 it can be clearly noticed that for the imperfection value at the level of 0.1% of the initial length of the compressed segments (which corresponds to k equal to 3), not only the difference between the EB and BE configurations is not noticeable, but also the difference between the BS values for both EB and EB do not differ from the reference value (dashed lines) computed while using the theoretical model (see Equation (15)). The difference between the bending stiffness in the case of EB and BE increases with the augmentation of the imperfection coefficient and for the value k = 2 (i.e., imperfection equals to Li · 10−2 ) it is between 12% and about 22% (see Figure 12). In this work the assumed imperfection coefficient is 2.3, which corresponds to the initial imperfections in the compressed elements at the level of 0.5% of the initial length of these segments. Table 5 summarizes all calculated and literature values of bending stiffness for six examples of five-layer corrugated board. It is clearly seen than in just two cases the theoretical BS is higher than the experimentally measured BS. It can be evidently noticed that only in two cases (Board 2 and Board 6) the theoretical BS is higher than experimentally measured BS. This is an alarming observation, because in the case of real structures made of corrugated board, the cross-section is rarely ideal (usually the corrugated board is slightly crushed [67,68]), which means that the measured bending stiffness values should rather be lower than theoretical. Not only the theoretical values of BS are lower than those measured experimentally. Virtually all the results presented in Table 5 follow a similar trend, both the results obtained with the use of analytical and numerical models, including the results from the literature (column 6) [29]. Due to this observation, the results of experimental research presented in [29] may contain some errors or are incorrectly ordered. Despite these doubts the results obtained while using the analytical model are very good for Examples 2 and 6 (marked in Table 6), for other Examples the results are not as good but still better than results presented in [29] (see Table 6). The mean absolute error generated by the analytical model is 11.7% for all cases while the mean absolute error of the results presented in [29] is 16.4%. Table 6. Percentage error between BS measured experimentally and computed BS. Title 1 Board 1 Board 2 Board 3 Board 4 Board 5 Board 6

Face-up EB BE EB BE EB BE EB BE EB BE EB BE

FEM [29] (%) 9.18 11.74 11.03 18.04 4.73 26.16 20.85 48.99 9.98 25.07 2.95 8.57

Analytical (%) 16.69 8.04 1.61 0.60 1.40 21.02 25.69 39.10 5.23 12.59 7.45 1.62

Due to the relatively large discrepancies between the calculated and measured values of bending stiffness, and due to the suspected measurement error or incorrect compilation of results in [29], the sensitivity analysis of the analytical model was also carried out in this study. The graphs shown in Figure 13 clearly indicate that both the EB and BE models have the greatest sensitivity to the change in the stiffness modulus and thickness of the ﬂat inner and outer layers (i.e., Liner-1 and Liner-3). The sensitivity of BS to changes in the height of the corrugated layer B, h2 , is similarly high. Thus, even a small change of these parameters (just a few percent), can dramatically change the computational value of bending stiffness of the corrugated board.

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5. Conclusions In this study, a detailed analysis of the effect of imperfections in thin-walled asymmetrical sections bent with a constant moment was carried out. The main contribution of this work was the derivation of analytical relationships that accurately describe the phenomenon of the difference in bending stiffness depending on the sign of the moment loading the asymmetric corrugated cardboard sample in machine direction. The paper showed that the applied analytical model satisfactorily reflects the real behavior of bent fivelayer corrugated cardboard. The adopted simplifications did not affect the quality of the proposed solution, which was proved by a simple numerical model. Finally, the developed model was compared with the results of experimental research available in the literature. The obtained results are much closer to the experimental results than the results generated by other models available in the literature. Additionally, proposed model is very easy to implement, which makes it possible to use it in practice by cardboard manufacturers. This study also includes the sensitivity analysis, which indicates the most important parameters directly affecting the BS and, therefore, can be very helpful in more conscious design of optimal corrugated board. Author Contributions: Conceptualization, T.G.; methodology, T.G.; software, T.G.; validation, A.K.-P. and T.G.; formal analysis, T.G.; investigation, A.K.-P. and T.G.; resources, A.K.-P.; data curation, A.K.-P.; writing—original draft preparation, T.G. and A.K.-P.; writing—review and editing, A.K.-P. and T.G.; visualization, T.G.; supervision, T.G.; project administration, T.G.; funding acquisition, T.G. and A.K.-P. All authors have read and agreed to the published version of the manuscript. Funding: The APC was funded by the Ministry of Science and Higher Education, Poland, the statutory funding at Poznan University of Life Sciences, grant number 506.569.05.00. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: The data presented in this study are available on request from the corresponding author. Conflicts of Interest: The authors declare no conflict of interest.

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PAPERmaking! FROM THE PUBLISHERS OF PAPER TECHNOLOGY TE INTERNATIONAL®

Volume 8, Number 2, 2022

Valorization of Seaweed: Using Brown Algae Waste in Papermaking 1 2 1 3 1 ANA MORAL , ROBERTO AGUADO , JOSE AMAYA , ANTONIO TIJERO & MENTA BALLESTEROS .

In this work, the brown alga Dictyota dichotoma was explored as a new reinforcing material for papermaking. Performing the typical chemical tests for cellulosic substrates on D. dichotoma evidenced large amounts of ethanol:benzene extractable substances (7.2%) and ashes, algae-specific results. Also, even if lipophilic compounds are removed, brown seaweed are not a primary source of fibers because it contains low proportion of cellulose. However, its elevated content of insoluble carbohydrates (51.4%) suggest there is some potential in association with conventional cellulosic pulps, as fibrous elements contribute to sheet forming and other components fill the spaces in the paper web without noteworthy loss of strength. Extraction was carried out with clean processes: hydrogen peroxide and mixtures (hydrogen peroxidehydrochloric acid and hydrogen peroxide-sodium perborate), sodium hydroxide and sodium hypochlorite, always aiming for low reagent concentrations, in the range of 1-12%. The results show that sodium hydroxide and sodium hypochlorite were the treatments that lead to paper sheets with better structural and mechanical properties without further bleaching or refining, thus highlighting the suitability of these algae for papermaking applications. Contact information: 1. Pablo de Olavide University: Universidad Pablo de Olavide. 2. University of Girona: Universitat de Girona. 3. Complutense University of Madrid: Universidad Complutense de Madrid. Research Square. https://doi.org/10.21203/rs.3.rs-1034462/v1 Creative Commons Attribution 4.0 International License

The Paper Industry Technical Association (PITA) is an independent organisation which operates for the general benefit of its members – both individual and corporate – dedicated to promoting and improving the technical and scientific knowledge of those working in the UK pulp and paper industry. Formed in 1960, it serves the Industry, both manufacturers and suppliers, by providing a forum for members to meet and network; it organises visits, conferences and training seminars that cover all aspects of papermaking science. It also publishes the prestigious journal Paper Technology International® and the PITA Annual Review, both sent free to members, and a range of other technical publications which include conference proceedings and the acclaimed Essential Guide to Aqueous Coating.

Page 1 of 15

Article 5 – Seaweed as Pulp

Valo orization of Seaweed: Using Brown Alg gae Waste in Papermaking Ana Moral Pablo de Olavide University: Universidad Pablo de Olavide Roberto Aguado (  roberto.aguado@udg.edu ) University of Girona: Universitat de Girona https://orcid.org/0000-0001-9864-1794 Jose Amaya Pablo de Olavide University: Universidad Pablo de Olavide Antonio Tijero Complutense University of Madrid: Universidad Complutense de Madrid Menta Balle esteros Pablo de Olavide University: Universidad Pablo de Olavide

Research Article e Keywords: algae, Dictyota, hydrogen peroxide, sodium hydroxide, sodium hypochlorite, valorization of waste Posted D ate: December 13th, 2021 D OI OI:: https://doi.org/10.21203/rs.3.rs-1034462/v1 License:   This work is licensed under a Creative Commons Attribution 4.0 International License. Á Read Full License

Page 1/14

Ab bstract In this work, the brown alga Dictyota dichotoma was explored as a new reinforcing material for papermaking. Performing the typical chemical tests for cellulosic substrates on D. dichotoma evidenced large amounts of ethanol:benzene extractable substances (7.2%) and ashes, algae-speci¦c results. Also, even if lipophilic compounds are removed, brown seaweed are not a primary source of ¦bers because it contains low proportion of cellulose. However, its elevated content of insoluble carbohydrates (51.4%) suggest there is some potential in association with conventional cellulosic pulps, as ¦brous elements contribute to sheet forming and other components ¦ll the spaces in the paper web without noteworthy loss of strength. Extraction was carried out with clean processes: hydrogen peroxide and mixtures (hydrogen peroxide-hydrochloric acid and hydrogen peroxide-sodium perborate), sodium hydroxide and sodium hypochlorite, always aiming for low reagent concentrations, in the range of 1-12%. The results show that sodium hydroxide and sodium hypochlorite were the treatments that lead to paper sheets with better structural and mechanical properties without further bleaching or re¦ning, thus highlighting the suitability of these algae for papermaking applications.

ntroduction Depending on the meteorological conditions, tides and geography, large amounts of algae can be deposited in coastal areas. These accumulations are managed as municipal waste and often end up in land¦lls. Its collection is necessary because they cause environmental and health problems affecting the local tourism (Moral et al., 2019; Rajkumar et al., 2014). Regardless of the dead biomass in beaches, since the beginning of the century there has been a notorious increase in seaweed harvest globally, from 11.4 million wet tons in 2000 to 19 million in 2010, to 28.4 million in 2014 and to 35.8 million in 2019 (FAO, 2018, 2021; Thompson et al., 2019). Cultivation for human food and cosmetics is especially common in China, Indonesia and Rep. Korea but, unless severe extractive processes are carried out, these are not safe applications for beach waste. A frequent suggestion for the non-food valorization of seaweed is biofuel production, aiming to obtain biodiesel from the lipids and bioethanol from the saccharides (El-Sheekh et al., 2019; Patil et al., 2017). Another option, which should not be seen as competing but as complementary, is papermaking. This is a common approach to reuse agricultural waste (Aguado et al., 2018; Jiménez et al., 2008; Nagpal et al., 2020). The lack of lignin in most seaweed can make them even more appealing than ¦eld residues, as cellulose extraction becomes easier (Moral et al., 2019). However, while green algae have been successfully used as source of cellulosic ¦bers (Wahlström et al., 2020), the different composition of brown algae present certain challenges and, at the same time, new opportunities. Among all the best-known types of marine algae (red, green and brown), Phaeophyceae (brown algae) are the most commonly found in the debris along the Mediterranean coasts (Deniaud-Bouët et al., 2014) and encompass approximately 2000 species (Thompson et al., 2019). Some studies have shown that the Page 2/14

area-based cultivation productivity of brown algae is higher than that of red and green algae (Lee and Lee, 2016), likely due by a higher photon absorption rate during photosynthesis (Thompson et al., 2019). The main components in the cell walls from brown algae (up to 45% of algal dry weight) are anionic polysaccharides such as alginates and fucoidans (Kloareg and Quatrano, 1988). In some brown algae, alginate constitutes up to 60% of the total sugars (Lee and Lee, 2016). Intertidal and supratidal brown algae, including Dictyota dichotoma (Terauchi et al., 2012), roughly present an average weight ratio of 3:1:1 in alginates, fucoidans and cellulose, respectively (Kloareg and Quatrano, 1988). Siddhanta et al. (2011) found little variation in cellulose content among six brown algae investigated, including three different orders (Dictyotales, Fucales and Scytosiphonales), accounting for values around 10%. This little amount of cellulose changes the strategy of the papermaking approach for valorization. In order to use the ¦brillar cell walls with an acceptable yield and without severely damaging their structure, extraction requires particularly mild processes that, while removing most materials which hinder ¦ber dispersion and sheet formation, do not seek to isolate cellulose. In fact, the paper industry uses plenty of polysaccharides other than cellulose, including starch and, precisely, alginates (Bai et al., 2017). Carrageenan from red algae, which shares similarities with fucoidans, has been proven to strengthen both paper (Liu et al., 2017) and plastic ¦lms (Sudhakar et al., 2021). Hence, there are reasons to hypothesize that biomass from Phaeophyceae, when combined with conventional cellulosic ¦bers, can lead to the production of paper of good quality. The purpose of this study is to valorize dead biomass from brown algae as a new supporting material to be added to a conventional pulp, once enriched in carbohydrates by sulfur-free and preferably mild chemical extraction methods. With this objective in mind, D. dichotoma was subjected to the key composition tests in papermaking. Moreover, mild extraction processes with hydrogen peroxide (alone and combined with hydrochloric acid or sodium perborate), sodium hydroxide, sodium hypochlorite and hot water were carried out. The characterization of the paper sheets fabricated with the resulting pulps was done. As far as we know, this is the ¦rst study on the production of pulp and paper including brown marine algae, and not a particular extract from them.

Exxperimental

Harvesting and cooking Tidal wastes were harvested from “Playa de Costacabana” in the south of Spain (Almería). Samples were exhaustively washed with freshwater and screened in order to remove sand and other macroscopical impurities. Brown algae were selected from a mixture of marine plants and other algae, identi¦ed and dried at 40 ºC during 3 days such shown in Figure 1 that schematizes the sequence of experiments. Clean, dried brown algae were homogenized, crushed (size < 5mm), and cooked to do the extraction. Cooking was performed in a stainless steel batch reactor. Liquor to solid ratio was held at 8. Cooking liquor consisted of hydrogen peroxide, hydrogen peroxide–sodium perborate (SPB; 0.5% w/w), hydrogen Page 3/14

peroxide–hydrochloric acid (1% w/w), sodium hydroxide and sodium hypochlorite, all diluted with distilled water. All chemicals were supplied by Panreac AppliChem and used without further puri¦cation. Temperature and inner pressure were held constant thorough the process. The different conditions tested are summarized in Table 1. The resulting product was washed, screened, crumbled, dried (temperature: 40ºC, time: 72 h) and stored at room temperature. Table 1 Dictyota dichotoma cooking conditions. Extraction agent

D osage (w/w %)

T (ºC)

Time (min)

H2O2 (alone or with HCl or SPB)

105

NaOH

NaClO

Chemical characterization The pulp obtained was characterized chemically in accordance with the common TAPPI test methods for raw materials and/or pulps (TAPPI 2019). The samples for analysis were prepared according to T 264 cm-07. Solid-liquid extractions followed T 204 cm-17 for ethanol-benzene extractives and T 207 cm-08 for hot water solubility, while the ash content was determined by means of a mu©e furnace in accordance with T 211 sp-11. The test for the determination of acid-insoluble (Klason) lignin was carried out with H2SO4 24N (T 222 om-15). Between 3 and 6 repetitions were carried out for each experiment and all solutions were provided by Panreac. In the case of seaweed, as shown in previous works (Moral et al., 2019), this test targets acid-insoluble compounds that do not correspond to lignin, and thus they will be referred as Klason-positive compounds. Likewise, the results from T 203 cm-09, generally followed to estimate the content of alphacellulose, has to be understood here as the carbohydrate fraction which is resistant to consecutive Page 4/14

treatments with 17.5% and 9.45% NaOH solutions. A chlorite oxidation was carried out on a sample which had undergone water and ethanol-benzene extractions to measure the total water-insoluble carbohydrate content, since the ClO2 formed in the process does not target polysaccharides (Ahlgren and Goring, 1971).

Sheet forming and testing The conventional sheet-former method (ISO 5269-1) was used. Sheets from D. dichotoma pulps have low values of mechanical properties. For quality paper, pulp from brown algae was mixed in different proportions with an unbleached pine kraft pulp (PKP) obtained from the wood of Pinus pinaster Ait., from industrial origin. Agitation was done by hand, with a standard stirrer. Couch weights and standard plates were used to collect the handsheets. Sheets were left at 23ºC and 50% RH, while pressed by drying rings, for 24 h. The grammage of the handsheets was 60 g/m2. The tensile test for the breaking length and stretch, the burst test and the tear test were performed by means of appropriate testing machines from Houns¦eld, Metrotec and Messmer, respectively, and in accordance to the ISO standards 1924, 1974 and 2470 (ISO TC/6, 2011). Brightness was determined by means of a spectrophotometer from Lorentzen & Wettre, following ISO 2470 (ISO TC/6, 2011). Between 5 and 10 repetitions were carried out for mechanical properties and between 10 and 20 repetitions were performed for brightness.

Resultts And Discussion

Chemical characterization The results of the characterization of Dictyota dichotoma dead biomass, not being a lignocellulosic material, have to be taken with caution. In this case, the TAPPI standards commonly used to estimate the chemical composition of plant biomass do not give out percentages of lignin, α-cellulose and hemicellulose, but insights into the technological feasibility of using this material for papermaking. During the process, the biomass is involved in treatments with hot water, alkaline media, etc., and the end product is expected to be free from proteins and lipids. Table 2 displays the results of the tests. The amplitude of con¦dence intervals is four times the standard deviation. The ethanol:benzene extractables, hot water solubles and ashes, however, are qualitatively similar to what can be expected from vascular plants, allowing for a more comprehensive comparison. Wood is known to have very low contents of lipophilic compounds, not exceeding 2.6 % in Pinus pinaster and 1.2 % in Eucalyptus globulus (Jiménez et al., 2008). The high value detected in Dictyota dichotoma (7.2 ± 1.1%) can be explained by the abundance of lipids, mainly diacylglycerol derivatives, and the presence of pigments of the algae highlighting different types of chlorophyll, fucoxanthin and beta-carotene (Ryabushko et al., 2019). In any case, similar or even larger amounts of lipophilic compounds, as found in date palm rachis (6.3% in ethanol–toluene) (Khiari et al., 2010), Arundo donax (7.3%), sorghum stalks (8%) (Jiménez et al., 2008) or Tunisian vine stems (11.3%) (Mansouri et al., 2012), have not made researchers refrain from proposing those alternative materials for papermaking. Page 5/14

Table 2 Chemical characterization of Dictyota dichotoma and comparison with other raw materials. HWS: hot water solubility. EBE: ethanol-benzene extractives. WICH: water-insoluble carbohydrate content. ARCH: alkali-resistant carbohydrate content. KLAS: acid-insoluble compounds Genus

Dictyota

Ulva

Rhizoclonium

Cladophora

HWS (%)

20.2 ± 0.6

33.4

34.6

EBE (%)

7.2 ± 1.1

3.8

9.43

ASH (%)

15.8 ± 3.1

19.8

15.9

2.48

WICH (%)

51.4 ± 4.5

47.8

44.1

21.4

ARCH (%)

30.6 ± 1.1

40.7

17.1

KLAS (%)

16.1 ± 0.5

7.9

3.8

4.64

Source

This work

Moral et al.2019

Chao et al. 1999

Mukherjee and Keshri 2019

A ¦fth of the seaweed mass, including inorganic salts and some carbohydrates, was found to be soluble in hot water (20.2 ± 0.6 %). Seemingly, inorganic salts accounted for most of that, as the ash content in D. dichotoma was as high as 15.8 ± 3.1 %. Sand, deposits or encrusted carbonates greatly contribute to the mineral fraction. In spite of silt being commonly removed during ash determination, in practice it represents part of the chemical composition of the harvest (Sculpthorpe, 1967). Rupérez and SauraCalixto (2011) found ashes in some Spanish seaweeds to be very abundant and variable (21-39.8%) in all the species studied. The percentage of water-insoluble carbohydrates (51.4 ± 4.5%) is well below any cellulosic or lignocellulosic raw material, in which this fraction encompasses α-cellulose and hemicelluloses accounting for 60-80% (Jiménez et al., 2008). However, it was unexpected that 30.6 ± 1.1% resisted alkaline extractions, which makes way for an easy solubilization of proteins and lipids while keeping enough material to be used as papermaking additive. Finally, the acid-insoluble content (16.1 ± 0.5%), while lower than the aromatic-rich lignocellulosic sources (26.2%) (Jiménez et al., 2008), looks surprisingly high when compared to other algae (Chao et al., 1999; Moral et al., 2019; Mukherjee and Keshri, 2019). Taking into account the absence of structural lignin, this value can be due to certain ligninlike compounds, aromatics, alkyl derivatives and some salts.

Carbohydrate extractions and effects on paper properties As can be seen in Table 3, the yield obtained after oxidation with hydrogen peroxide was lower when algae were exposed to more severe conditions. It should be remembered that, although not repeated here, a higher concentration was accompanied by a higher temperature and a longer time (Table 1). Interestingly enough, severe conditions increased breaking length, stretch, burst and tear indexes and brightness. The sheet having better characteristics was the one formed with a lower proportion of alga (25 % seaweed and 75% pine) and subjected to treatment with hydrogen peroxide and hydrochloric acid at the highest concentration (6%). Hydrogen peroxide is a powerful oxidizer that, at least without Page 6/14

inorganic ions, hardly targets carbohydrates but can react with aromatics, nucleic acids, lipids, or proteins (Liu et al., 2021). Hence, results indicate that the best effect is achieved by removing, by extraction, as many non-carbohydrate compounds as possible. When H2O2 concentration was 3% (w/w), the presence of HCl removed more extracts and, thus, less yield, since both alkali and acid solutions help extracting proteins, and some oxidizing power should be expected from the small amounts of chlorine that are generated. This chlorine was rapidly reduced to chloride by H2O2 under more severe conditions (6%), in which HCl was actually a deactivator. As for sodium perborate, it has been demonstrated to be a more powerful bleaching agent than peroxide as long as high temperatures (70-80ºC) are used (Pesman et al., 2014). However, possibly due to its low concentration, additions of SPB did not give out a consistent increase of brightness. In addition, Table 3 shows that samples obtained after extracting with soda or sodium hypochlorite treatments results in paper sheets with higher quality than those obtained with hydrogen peroxide (alone or combined). In all cases, the relative standard deviation lied below 5%. As the best results were obtained at the highest concentrations of reagent, experiments with 9 and 12% of soda or sodium hypochlorite where carried out and presented in Figures 2 and 3, in order to compare both process with paper sheets formed with the greater proportion of algae (75%).

Page 7/14

Table 3 Properties of paper sheets from Phaeophyceae obtained by different treatments (P: hydrogen peroxide; P-HCl: hydrogen peroxide and hydrochloric acid; P-PBS: hydrogen peroxide and sodium perborate; HW: hot water, blank). Paper sheets are formed mixing pulps of Phaeophyceae and Pine pinaster at different proportions (75:25 and 25:75). Y: Yield, TI: Tear index, ST: Stretch, BR: Burst index, BL: Breaking length and Brightness (%)

(%)

Prop.

Y (%)

TI (Nm2/g)

S T (%)

BI (kN/g)

BL (km)

BR (%)

75:25

78.7

4.6

0.24

0.84

7.8

45.2

70.0

5.8

0.37

0.92

7.9

48.4

31.8

7.5

0.63

2.24

16.5

50.8

78.7

7.6

0.39

1.16

7.9

58.0

70.0

7.9

0.58

1.29

8.1

58.7

31.8

10.4

0.72

2.48

23.3

59.2

77.5

6.2

0.36

0.95

8.2

46.2

50.3

6.6

0.49

1.08

7.9

51.5

39.4

8.2

0.68

2.65

19.6

51.1

77.5

9.4

0.52

1.09

7.9

58.0

50.3

10.2

0.66

1.36

8.2

58.7

39.4

11.7

0.86

2.99

30.0

59.3

80.9

4.8

0.20

0.88

7.6

50.4

76.8

4.8

0.34

0.96

7.5

48.8

63.1

8.6

0.55

2.15

15.9

50.9

80.9

8.0

0.33

0.96

7.5

58.1

76.8

8.2

0.47

1.00

7.9

57.3

63.1

11.5

0.68

2.65

20.7

47.8

81.6

6.3

0.37

1.07

8.3

48.4

92.4

7.3

0.45

1.25

8.6

42.9

68.6

11.4

0.67

2.09

21.5

45.8

81.6

8.4

0.54

1.14

8.8

57.3

92.4

9.7

0.78

1.47

9.0

54.6

68.6

14.2

0.82

3.05

37.7

56.3

P+HCl

P+SPB

NaOH

25:75

75:25

25:75

75:25

25:75

75:25

25:75

Page 8/14

NaClO

(%)

Prop.

Y (%)

TI (Nm2/g)

S T (%)

BI (kN/g)

BL (km)

BR (%)

75:25

83.4

6.6

0.22

1.09

9.1

46.3

76.5

7.5

0.36

1.22

9.5

45.6

57.5

8.2

0.77

2.62

29.6

66.4

83.4

8.2

0.35

1.03

9.7

58.2

76.5

9.0

0.50

1.47

10.2

57.2

57.5

13.5

0.80

2.91

37.5

62.4

25:75

75:25

82.5

4.1

0.25

0.78

8.2

47.9

25:75

82.5

4.7

0.28

0.80

8.2

55.7

Both treatments lead to lower yields at higher reagent concentrations. However, from 9% the decrease on yield percentage is less abrupt (Figure 2a). Tear index, burst index and stretch increase at higher concentrations of caustic soda or sodium hypochlorite during pulping and no signi¦cant differences were found with both reagent (Figure 2b-e). Brightness is independent from the concentration of NaOH and increases with the concentration of NaClO, owing to the latter’s capability to oxidize pigments (Figure 2f).

Conclu usions Phaeophyceae seaweed from coastal residues could not be used alone for papermaking, due to its low cellulose content and the abundance of lipophilic compounds. However, after easily extracting most proteins, lipids and pigments, the carbohydrate-rich product from brown algae constitutes a good addition to long cellulosic ¦bers, allowing for acceptable paper strength even when the percentage of conventional pulp was as low as 25%. Sheets formed after extractions with NaOH or NaClO presented higher quality than those obtained with hydrogen peroxide or hot water. While brightness of paper sheets was higher after NaClO treatments, hydroxide and hypochlorite extractions differed little in mechanical properties, as both produced a four-fold increase in tensile strength. These results indicate that dead biomass from these brown algae, naturally occurring along coastlines and currently needing to be treated, can be successfully reused to partially replace wood pulp in the manufacturing of non-graphical papers.

Declarations Ethics approval and consent to participate Not applicable. No studies involving humans and/or animals. Consent for publication Not applicable. Page 9/14

Funding This work was funded by Universidad Pablo de Olavide, via its IV Internal Research Plan, B8: Own Research Lines – High Purity Cellulose from Microalgae.Á Con§icts of interest/Competing interestsÁ The authors declare that there is no con§ict of interest and that they do not have competing interests. Availability of data and materialÁ All data are displayed in the article itself, as the mechanical testers readily presented average values. Code availabilityÁ Not applicable. Authors' contributionsÁ Conceptualization: A.M. and M.B. Methodology: A.M. and J.A. Validation: M.B., R.A. and A.T. Experimentation: J.A., A.M. and M.B. Resources: A.M. Data curation: J.A., A.M., M.B and R.A. Writing— original draft preparation: R.A., M.B. and A.T. Writing—review and editing: A.M. Visualization: A.T. Supervision: A.M. and M.B. All authors have read and approve the ¦nal manuscript.

References Aguado R, Moral A, Tijero A (2018) Cationic ¦bers from crop residues: Making waste more appealing for papermaking. J Clean Prod 174:1503–1512. https://doi.org/10.1016/j.jclepro.2017.11.053 Ahlgren PA, Goring DAI (1971) Removal of wood components during chlorite delignification of black spruce. Can J Chem 49:1272–1275 Bai YY, Lei YH, Shen XJ, Luo J, Yao CL, Sun RC (2017) A facile sodium alginate-based approach to improve the mechanical properties of recycled ¦bers. Carbohydr Polym 174:610–616. https://doi.org/ 10.1016/j.carbpol.2017.06.091 Chao KP, Su YC, Chen CS (1999) Chemical composition and potential for utilization of the marine algaÁRhizoclonium sp.ÁJ Appl Phycol 11:525-533 Deniaud-Bouët E, Kervarec N, Michel G, Tonon T, Kloareg B, Hervé C (2014) Chemical and enzymatic fractionation of cell walls from Fucales: insights into the structure of the extracellular matrix of brown algae. Ann Bot 114:1203–1216 El-Sheekh MM, Gheda SF, El-Sayed AB, Abo Shady AM, El-Sheikh ME, Schagerl M (2019). Outdoor cultivation of the green microalga Chlorella vulgaris under stress conditions as a feedstock for biofuel. Page 10/14

Environ Sci Poll Res 26:18520–18532. https://doi.org/10.1007/s11356-019-05108-y FAO (2018) The global status of seaweed production, trade and utilization. Globe¦sh Research Programme Vol. 124. Rome, pp. 1–6. FAO (2021) Global seaweeds and microalgae production, 1950–2019. https://www.fao.org/3/cb4579en/cb4579en.pdf. Accessed 30 October 2021. ISO TC/6 (2011) ISO Standards Collection on CD-ROM. Paper, board and pulps. International Organization for Standardization, Geneva (Switzerland). Jiménez L, Rodríguez A, Pérez A, Moral A, Serrano L (2018) Alternative raw materials and pulping process using clean technologies. Ind Crops Prod 28:11–16. https://doi.org/10.1016/j.indcrop.2007.12.005 Khiari R, Mhenni MF, Belgacem MN, Mauret E (2010) Chemical composition and pulping of date palm rachis and Posidonia oceanica – a comparison with other wood and non-wood ¦bre sources. Bioresour Technol 101:775–780 Kloareg B, Quatrano RS (1988) Structure of the cell walls of marine algae and cophysiological functions of the matrix polysaccharides. Oceanogr Mar Biol Ann Rev 26:259–315 Lee O, Lee F (2016) Sustainable production of bioethanol from renewable brown algae biomass. Biomass Bioener 92:70-75. https://doi.org/ 10.1016/j.biombioe.2016.03.038 Liu Z, Li X, Xie W (2017) Carrageenan as a dry strength additive for papermaking. PLOS ONE 12(3): e0173938 Liu J, Jiang W, Sun L, Lv C (2021) Bleaching §ax roving with poly(acrylic acid) magnesium salt as oxygen bleaching stabilizer for hydrogen peroxide. Cellulose 28. https://doi.org/10.1007/s10570-021-04262-2 Mansouri S, Khiari R, Bendouissa N, Saadallah S, Mauret E, Mhenni F (2012) Chemical composition and pulp characterization of Tunisian vine stems. Ind Crops Prod 36:22–27 Moral A, Aguado R, Castelló R, Tijero A, Ballesteros M (2019) Potential use of green algae Ulva sp. for papermaking. BioResources 14:6821–6862 Mukherjee P, Keshri JP (2019) A comparative biomass compositional analysis of ¦ve algal species from the Paddy Fields of Burdwan District, West Bengal, India, to determine their suitability for handmade paper pulp formulation. Waste Biomass Valoriz 10:327-340 Nagpal R, Bhardwaj NK, Mahajan R (2020) Synergistic approach using ultra¦ltered xylano-pectinolytic enzymes for reducing bleaching chemical dose in manufacturing rice straw paper. Environ Sci Poll Res 27:44637–44646. https://doi.org/10.1007/s11356-020-11104-4

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Patil PD, Reddy H, Deng SM (2017) Biodiesel fuel production from algal lipids using supercritical methyl acetate (glycerin-free) technology. Fuel 195:201–207. https://doi.org/10.1016/j.fuel.2016.12.060 Pesman E, Imamoglu S, Kalyoncu EE, Hüseyin K (2014) The effects of sodium percarbonate and perborate usage on pulping and §otation deinking instead of hydrogen peroxide. BioResources 9:523– 536 Rajkumar R, Yaakob Z, Takriff MS (2014) Potential of the micro and macro algae for biofuel production: A brief review. BioResources 9:1606–1633 Rupérez P,ÁSaura-Calixto F (2001)ÁDietary ¦bre and physicochemical properties of edible Spanish seaweeds. Eur Food Res Technol 212:349–354. https://doi.org/10.1007/s002170000264 Ryabushko VI, Kamnev AN, Gureeva EV, Prazukin AV, Nechoroshev, MV (2019) Content of lipids, fatty acids, and fucoxanthin in branches of different ages of Cystoseira barbata (Stackhouse) C. agardh (Phaeophyceae). Int J. Algae 21:349–358 Sculthorpe DC (1967) The biology of aquatic vascular plants. Edward Arnold Publisers, London Siddhanta AK, Chhatbar MU, Mehta GK, Sanandiya ND, Kumar S, Oza MD, Prasad K, Meena R (2011) The cellulose contents of Indian seaweeds. J Appl Phycol 23:919–923 Sudhakar MP, Peter DS, Dharani G (2021) Studies on the development and characterization of bioplastic ¦lm from the red seaweed (Kappaphycus alvarezii). Environ Sci Poll Res 28:33899–33913. https://doi.org/10.1007/s11356-020-10010-z TAPPI (2019) TAPPI Standards, Technical Information Papers, and Useful Methods CD. TAPPI Press, Atlanta, GA. Terauchi M,ÁNagasato C,ÁKajimura N,ÁMineyuki Y,ÁOkuda K,ÁKatsaros C,ÁMotomura T (2012)ÁUltrastructural study of plasmodesmata in the brown alga Dictyota dichotoma (Dictyotales, Phaeophyceae).ÁPlanta 236:1013-1026 Thompson TM, Young BR, Baroutian S (2019) Advances in the pretreatment of brown macroalgae for biogas production. Fuel Process Technol 195:106151. https://doi.org/10.1016/j.fuproc.2019.106151 Wahlström N, Edlund U, Pavia H, Toth G, Jaworski A, Pell AJ, Choong FX, Shirani H, Nilsson KPR, RichterDahlfors A (2020) Cellulose from the green macroalgae Ulva lactuca: isolation, characterization, optotracing, and production of cellulose nano¦brils. Cellulose 27:3707–3725. https://doi.org/10.1007/s10570-020-03029-5

Figures Page 12/14

Figure 1 Diagram of the experimental procedure: collection, isolation of algal biomass, analysis and preparation of handsheets. Pictures show beakers of seaweed ready to be treated (left) and handsheets from pine wood pulp and algae (right)

Page 13/14

Figure 2 In§uence of reagent concentration on processing yield (a) and or the ISO brightness (b) of paper sheets

Figure 3 In§uence of reagent concentration on paper strength: tensile properties (a, b), tear resistance (c) and burst index (d)

Page 14/14

PAPERmaking! FROM THE PUBLISHERS OF PAPER TECHNOLOGY TE INTERNATIONAL®

Volume 8, Number 2, 2022

Practitioners’ Perceptions of CoProduct Allocation Methods in Biorefinery Development—A Case Study of the Austrian Pulp and Paper Industry

1 1 2,3 1 JULIAWENGER , STEFAN PICHLER , ANNUKKA NÄYHÄ & TOBIAS STERN .

The utilization of coproducts is a strategy that can be applied to increase the economic and environmental performance of industrial processes and thus reach an objective targeted in several environmental policies. In multi-output production processes, allocation needs to be performed to assess the products’ environmental and economic performance. It is crucial to choose an adequate allocation method, because this choice has been shown to strongly influence overall outcomes. Consequently, rash choices can lead to poor decision-making. Various ways to apply and combine allocation methods can be found in the academic literature, but it is often difficult to find sufficient guidance on how to choose an allocation method for a specific context. This study explores practitioners’ perceptions of the cost and environmental impact allocation methods used in biorefinery development (lignin, fiber fines) by applying the analytic hierarchy process (AHP). Results indicate that professional background represents a major factor influencing individual preferences and, thus, the selection of specific allocation methods. Policy makers should be aware that practitioners with different professional backgrounds have varying preferences for different allocation methods and that this influences the overall assessments. These factors, in turn, affect the interpretation of results, further decision-making and, ultimately, the realization of environmentally sound and economically viable biorefinery projects. This issue deserves more attention in biorefineries, but also in other multi-output production processes. The findings indicate a need to consider multidisciplinary, diverse views and knowledge when conducting such assessments and to display the underlying approaches transparently. Contact information: 1. Institute of Systems Sciences, Innovation and Sustainability Research, University of Graz, Merangasse 18/I, 8010 Graz, Austria. 2. School of Business and Economics, University of Jyväskylä, 40014 Jyväskylä, Finland. 3. School of Resource Wisdom, University of Jyväskylä, 40014 Jyväskylä, Finland. Sustainability 2022, 14, 2619. https://doi.org/10.3390/su14052619 Creative Commons Attribution 4.0 International License

The Paper Industry Technical Association (PITA) is an independent organisation which operates for the general benefit of its members – both individual and corporate – dedicated to promoting and improving the technical and scientific knowledge of those working in the UK pulp and paper industry. Formed in 1960, it serves the Industry, both manufacturers and suppliers, by providing a forum for members to meet and network; it organises visits, conferences and training seminars that cover all aspects of papermaking science. It also publishes the prestigious journal Paper Technology International® and the PITA Annual Review, both sent free to members, and a range of other technical publications which include conference proceedings and the acclaimed Essential Guide to Aqueous Coating.

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Article 6 – Biorefinery

sustainability Article

Practitioners’ Perceptions of Co-Product Allocation Methods in Bioreﬁnery Development—A Case Study of the Austrian Pulp and Paper Industry Julia Wenger 1 , Stefan Pichler 1 , Annukka Näyhä 2,3 and Tobias Stern 1, * 1

2 3

Citation: Wenger, J.; Pichler, S.; Näyhä, A.; Stern, T. Practitioners’ Perceptions of Co-Product Allocation Methods in Bioreﬁnery Development—A Case Study of the Austrian Pulp and Paper Industry. Sustainability 2022, 14, 2619. https:// doi.org/10.3390/su14052619

Institute of Systems Sciences, Innovation and Sustainability Research, University of Graz, Merangasse 18/I, 8010 Graz, Austria; julia.wenger@uni-graz.at (J.W.); stefan.pichler@denkstatt.at (S.P.) School of Business and Economics, University of Jyväskylä, 40014 Jyväskylä, Finland; annukka.nayha@jyu.ﬁ School of Resource Wisdom, University of Jyväskylä, 40014 Jyväskylä, Finland Correspondence: tobias.stern@uni-graz.at

Abstract: The utilization of coproducts is a strategy that can be applied to increase the economic and environmental performance of industrial processes and thus reach an objective targeted in several environmental policies. In multi-output production processes, allocation needs to be performed to assess the products’ environmental and economic performance. It is crucial to choose an adequate allocation method, because this choice has been shown to strongly influence overall outcomes. Consequently, rash choices can lead to poor decision-making. Various ways to apply and combine allocation methods can be found in the academic literature, but it is often difficult to find sufficient guidance on how to choose an allocation method for a specific context. This study explores practitioners’ perceptions of the cost and environmental impact allocation methods used in biorefinery development (lignin, fiber fines) by applying the analytic hierarchy process (AHP). Results indicate that professional background represents a major factor influencing individual preferences and, thus, the selection of specific allocation methods. Policy makers should be aware that practitioners with different professional backgrounds have varying preferences for different allocation methods and that this influences the overall assessments. These factors, in turn, affect the interpretation of results, further decision-making and, ultimately, the realization of environmentally sound and economically viable biorefinery projects. This issue deserves more attention in biorefineries, but also in other multi-output production processes. The findings indicate a need to consider multidisciplinary, diverse views and knowledge when conducting such assessments and to display the underlying approaches transparently.

Academic Editor: Marzena Smol Received: 15 January 2022 Accepted: 21 February 2022 Published: 24 February 2022

Keywords: allocation of costs and environmental impacts; corporate environmental management; wood bioreﬁneries; stakeholder perception; analytic hierarchy process (AHP); multicriteria decision-making

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional afﬁliations.

1. Introduction Biorefineries are viewed as being an important part of circular bioeconomy development, having the potential to contribute to the more sustainable use of environmental resources and, overall, to sustainability transition [1–3]. Several biorefinery definitions, approaches and developments exist [4], whereby the key aims are to be competitive in the market and replace fossil based products at the same time. In biorefineries, several products similar to the portfolios of crude oil refineries can be manufactured, but instead of fossil based oil, biorefineries utilize renewable resources [5]. The biorefinery concept includes various technologies that can separate such biomass resources (e.g., wood) into their building blocks (e.g., carbohydrates, lignin) [5]. These components can be further converted into various biofuels, chemicals, materials, feed and food, all of which have

4.0/).

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specific features, production costs, markets and prices [6,7]. Ahlgren et al. (2015) highlighted the need for various products to be coproduced in a symbiotic manner, allowing biorefineries to operate in a way that is economically, energetically and resource efficient. Nearly all types of biomasses can be utilized through various, jointly applied conversion technologies [5]. Lignocellulosic biomass (e.g., wood or residuals such as straw) accounts for most of the biorefinery concepts presented in scientific papers [4]. The consideration of feedstocks, such as industrial residues, lignocellulose and algae, has increased significantly in recent years. One of the key reasons is believed to be the food versus fuel debate and the broader search for more sustainable raw material sources [4]. Forest based biomass and the related new businesses are often central to a vision of the transition to the sustainable and circular bioeconomy, particularly in many forest rich countries [8,9]. Numerous studies have recently been carried out to analyze conceptual and methodological developments that are taking place during the transition to more sustainable biorefineries [5,7,10,11]. However, the results differ depending on, for example, site specific conditions, chosen technology, sustainability assessment methodology and the allocation basis in multifunctional processes [6,12–14]. In joint (“multi-output”) production, allocation (i.e., the “partitioning the input or output flows of a process or a product system between the product system under study and one or more other product systems”; ISO 14044:2006 definition) is a necessity for companies, as it enables them to assess their products’ performance (economic and environmental) [15]. It is crucial that they choose an adequate allocation method, because rash choices can lead to poor decisionmaking, such as when a more sustainable alternative to a product is sought, and the impacts of potential biorefinery products are considered and compared to those of the fossil based counterpart or other alternatives [16,17]. Various ways to apply and combine allocation methods can be found in the academic literature, and allocation is a heavily discussed topic in the literature on life-cycle assessments [14,18,19]. However, it is often difficult to find sufficient guidance on how to choose an allocation method in a specific context [20,21]. If more than one allocation method seems suitable for a production system, it may be useful to apply different approaches and to compare the outcomes [6,22]. However, the current and rather vague recommendations to apply the most “suitable” allocation method or to compare the outcomes of employing different options seem insufficient for practical application. Thus, a better understanding of the underlying decision-making process is needed. Accordingly, Frischknecht (2000) explained the important roles that subjectivity and value judgments played in the allocation procedure, because the allocation key can only be determined objectively in a few situations. The kinds of factors that actually influence the allocation method choice in practice (i.e., which methods are preferred) and the reasoning behind these choices are still unclear. The sustainability impacts of biorefinery operations need to be assessed, and allocation(s) needs to be performed on a case to case basis, as the underlying conditions and assumptions are case specific and may influence the outcome [14,19]. Therefore, in the context of biorefineries and the sustainability of such operations, firms need to understand what allocation methods exist, how and why individuals choose particular allocation methods, and what kind of impacts these choices can have on the firms’ calculated environmental performance and, accordingly, on strategic management decisions. More knowledge is needed about the issues affecting the choice of allocation methods in practice, for example, when developing more sustainable production processes, new business strategies, environmental management practices, or planning future operations in companies. In addition, increasing the knowledge and transparency regarding the choice of allocation methods in biorefineries helps relevant stakeholders, such as investors, policy makers, or customers, in their decision-making processes [13,23,24]. This study was carried out to determine the perceptions of practitioners (from Austrian pulp and paper companies) regarding how they would choose allocation methods in biorefinery development. The study outcomes, thus, bring practical perspectives into the prevailing academic discussion. Distinct characteristics of allocation methods that

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may guide the practitioners’ choices were described in detail and structured. By using a multicriteria decision method called the analytic hierarchy process (AHP), the practitioners’ preferences and context related perceptions were explored. More specifically, the following research questions were addressed in the study: RQ 1: What are the distinct characteristics of allocation methods that may guide the practitioner’s choice of allocation methods in biorefinery process development? RQ 2: What preferences do practitioners in wood biorefinery process development have regarding the distinct characteristics of allocation methods? RQ 3: How are these preferences based on context related perceptions induced by:

• • •

product characteristics? type of impact (economic or environmental)? professional background?

Overall, this study was carried out to reveal another facet of the allocation issue, in particular, with regard to its application in the practical context of firms that deal with multifunctional processes. By connecting life cycle assessment (LCA) literature about allocation methods with empirical research on practitioners’ viewpoints, we aim to contribute to more transparent and inclusive assessment approaches and, consequently, to cleaner processes and products from biorefineries and other multi-output production systems. 2. Materials and Methods 2.1. Wood Biorefineries with Multiple Product Outputs On a larger scale, the separation of wood components takes place in wood pulping processes. These processes have, so far, mostly been developed and optimized for the extraction of cellulose [25]. The resulting lignin is available at an estimated quantity of about 40–50 million tons per annum globally (so called technical lignin), illustrating the global significance of this byproduct [26]. It is currently used mainly on site (about 95–98%) to obtain energy and recover the process chemicals [27], but is also expected to play major roles in biorefinery concepts in the future (e.g., in various kinds of material applications) [28]. Fiber fines are the smallest fraction of fibers (i.e., they can pass through a 200-mesh screen). These fines, which are generated during the pulping, bleaching and pulp-refining processes [29], account for only 3–8% of the kraft pulp [30] and were chosen as a complementary product to lignin in this study. The fines influence the properties of paper products; however, their separation is a topic of discussion (e.g., to save bleaching costs and for material applications) [29]. Currently, fiber fines are part of the pulp and are not (yet) separated from it. If this fiber fraction were separated, this would lead to a quantitatively small amount of obtained fines as compared to the biorefinery output of lignin (as lignin accounts for approximately 18–35% of wood) [31]. 2.2. Allocation in Multifunctional Process Assessments Frischknecht (2000) defined multifunctional processes as processes that contribute to multiple product systems. Coproducts are products of a joint production process that have a relatively high total sales value, while products that only have a low sales value as compared to others are referred to as byproducts [32]. A definition by Suh et al. (2010) suggests that the product should be considered as a byproduct if an increased demand for a product in joint production does not lead to an increase in the production volume due to its limited contribution to the total revenue [33]. However, the issue of allocating, for example, costs or environmental impacts of shared production to specific products prevails in such multiple product systems. While the question of cost allocation in production processes was raised early on, the allocation of environmental impacts emerged within the context of the LCA during the first half of the 1990s (see [34]). LCA practitioners commonly need to address allocation issues, and particularly when multifunctional processes such as multi-output systems exist [19,35]. Choosing which allocation procedure to apply is one of the most extensively debated and controversial topics discussed among LCA practitioners, especially because

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it can have a significant impact on the outcome of an LCA study [19,36]. Even though the allocation methods are applied from both environmental and economic perspectives, their application has not often been discussed from both perspectives in the scientific literature. The economic and environmental burdens of joint production processes can be categorized by allocation method [13,19]. Two major procedures are mentioned in the scientific literature, namely, system expansion and partitioning methods [13]. System expansion refers to the extension of the initial production system boundaries to include a possible alternative production of the co- and byproducts in question (e.g., [19]). Regarding biorefinery co- and byproducts, the production of fossil alternatives can be used as reference products (e.g., biofuel versus conventional fuel). Figure 1 illustrates the idea behind system expansion, contrasting the defined main product of the production system and the coproducts with the avoided production of their reference product.

Figure 1. Schematic illustration of system expansion with respect to a joint production process, including one main product and various coproducts, as well as the potentially avoided production of substitutes for the coproducts (adapted from [19]).

When allocation is based on certain characteristics of the resulting co- and byproducts, this allocation is called partitioning [13]. Criteria frequently used for the partitioning method are the mass, volume, energy, exergy, or economic measures of the co- and byproducts (and combinations thereof) [19]. Figure 2 illustrates how partitioning can be applied to deﬁne the share of the impacts of each co-/byproduct in the production process, based on the energy content.

Figure 2. Schematic illustration showing how impacts are partitioned, based on the product energy content in a joint production process that includes three products (adapted from [19]).

Ekvall and Finnveden (2001) cited examples in which partitioning offers a better solution than system expansion and vice versa [37]. Heijungs and Guinee (2007) stated that system expansion is based on too many assumptions and, therefore, its usefulness as a scientiﬁc tool is debatable [38]. Weidema (2000), on the other hand, preferred system expansion over partitioning as an allocation method [17]. Guidelines for allocation procedures in multi-output processes exist [39,40], but in many contexts, such as those

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prevalent in biorefineries, several specific challenges, advantages, and disadvantages of respective allocation methods can be identified. These often lead to a lack of consensus in practice [14]. Allocation method choices can significantly influence the outcome of LCAs; this was demonstrated by Hermansson et al. (2020), who applied twelve different allocation methods to a study case on lignin (climate impact). 2.3. Strategic Decision-Making Process and Managerial Impact Currently, the issue of managerial impact on decision-making is being studied in many disciplines. Recent research in the field of investment decision-making suggests that “human” aspects of decision-making [41], including the decision-makers’ emotional acumen (e.g., [42]), are playing a significant role. The importance of the nature of human action has also been noted in studies on corporate environmental and sustainability related decisionmaking [24,43]. Schaltenbrand et al. (2018, pp. 129–130) stated “in an ideal world, managers would make decisions based on what is purely relevant to the situation at hand. They would initiate the decision making process by filtering out all irrelevant matter to prevent any form of partiality. Indeed, rooted in the view of homo economicus, the underlying assumption in corporate decision-making is that of managerial impartiality; decisions are made without the influence of any irrelevant matter. However, corporate decision making is more of an interpretive endeavor rather than an analytic computation.” Overall, this statement also indicates that the managers’ decision-making is affected by numerous issues. Despite the fact that the roles of individual managers and their interactions with the surrounding environments have increased in importance in many fields, the underlying determinants that affect managerial decisions in many contexts are still poorly understood [44]. 2.4. Assessment of Allocation Preferences To assess the allocation preferences of practitioners, a multicriteria decision-making approach was chosen. The AHP was developed by Thomas L. Saaty in the 1970s [45]. Saaty emphasized the importance of structuring decisions and accomplished this by arranging complex problems into a hierarchical structure: He placed an overall goal at the top, ranking the criteria and subcriteria below this, and placed the alternatives representing possible choices near the bottom [45,46]. The pairwise comparisons of (sub-)criteria and alternatives represent core elements of the AHP, whereby a rating scale from 1 to 9 was proposed by Saaty [45,46]; this scheme is illustrated in Table 1. Table 1. Applied judgment scale (adapted from [45,46]). Intensity of Importance

Deﬁnition

Explanation

Equal importance

Two activities contribute equally to the objective

Weak/Moderate importance of one over another

Experience and judgment slightly favor one activity over another

Essential or strong importance

Experience and judgment strongly favor one activity over another

Very strong/Demonstrated importance

An activity is strongly favored, and its dominance demonstrated in practice

Absolute/Extreme importance

The evidence favoring one activity over another provides the highest possible order of afﬁrmation

Reciprocals

If activity i has one of the above numbers assigned to it when compared with activity j, then j has the reciprocal value when compared with i

Applications of AHP are manifold and have been reviewed by Sipahi and Timor [47] and Ho and Ma [48]. The former noted that the use of AHP has increased signiﬁcantly in various application areas, such as manufacturing, environmental management and

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agriculture [47]. Ishizaka and Labib [49] reviewed the methodological developments of AHP and discussed some of the method’s advantages and disadvantages. 2.4.1. Development of the Hierarchy: Identification of Alternatives, Criteria and Sub-Criteria AHP was performed to choose the most appropriate approach from a practitioner’s individual viewpoint that could be taken to allocate the environmental impacts and costs of a biorefinery production process to two selected byproducts (goal). The most commonly applied allocation methods (alternatives) and their most prominent features were identified in a review of scientific papers on allocation issues. These features were summarized to form a smaller set of criteria and subcriteria for the sake of clarity and to reduce the risk of inconsistent answers. Thereafter, the hierarchy was derived, and this process is further described and illustrated in the Results section (Figure 3).

Figure 3. Structure and explanation of the AHP hierarchy, including the goal, criteria, subcriteria and alternatives.

2.4.2. Execution of the AHP In this study, the rating scale shown in Table 1 was used, and the relative weights, consistency ratios (a measure for the consistency of the given pairwise ratings within a matrix) and final priorities were calculated as described by Saaty [50]. As a rule of thumb, Saaty (1987) stated that if the “consistency ratio exceeds 0.10 appreciably, the judgments often need reexamination” (Saaty 1987, p. 165). However, in practical fields such as managerial research, a consistency ratio (C.R.) lower than 0.2 can be considered as tolerable [51]; therefore, when a single judgment had a C.R. lower than 0.2, it was tolerated. Matrices with a higher consistency ratio were either excluded (criteria and subcriteria rankings by the interviewees) or the weighting was repeated (rankings of alternatives). The pairwise comparisons of the alternatives regarding the (sub-)criteria were drawn with reference to the scientific literature on allocation, as described in detail in the Results section. For the weighting of (sub-)criteria, experts were selected (s.f. Section 2.4.3). As the focus of this study was placed primarily on comparing the different practitioners’ preferences regarding the (sub-)criteria rankings and the potentially different outcomes resulting from

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these, the respective individual judgments were used as the main basis for the analysis. In addition, aggregations of the judgments were also performed (with regard to the allocation type, byproduct and practitioners’ professional backgrounds) using the geometric mean, as described and recommended by Saaty and Shang [52] and as performed by several authors regarding different topics [53]. This approach enabled us to attain quite low consistency ratios for the aggregated criteria rankings (the highest C.R. was 0.0308, described in detail in the Results section). Microsoft Excel (Excel version 2108, Microsoft Office LTSC Professional Plus 2021, Microsoft Corporation, Redmond, WA, USA) was used to perform all AHP calculations, and R (R version 4.1.2, R Foundation for Statistical Computing, Vienna, Austria; RStudio version 2021.09.2, RStudio Inc., Boston, MA, USA; packages: base 4.1.2 and tidyverse 1.3.1) as well as Microsoft PowerPoint (PowerPoint version 2108, Microsoft Office LTSC Professional Plus 2021, Microsoft Corporation, Redmond, WA, USA) were used for the illustrations. 2.4.3. The Specific Cases of Lignin and Fiber Fines, and Involvement of Experts The AHP was carried out on two different potential biorefinery (by-)products from the wood pulping process that are expected to have practical relevance: lignin and fiber fines. In addition to these two wood biorefinery byproducts, two subjects for allocations were investigated: the allocation of costs and the allocation of the environmental impacts to the byproducts. Experts were identified and asked to perform pairwise comparisons of the criteria with respect to the goal (four pairwise comparisons per interviewed person: cost and environmental allocation for lignin and fines) and pairwise comparisons of the two subcriteria with respect to the economic criterium (also resulting in four pairwise comparisons per interviewee). Representatives were contacted from three different Austrian pulp and paper companies that were familiar with both lignin and fines due to their participation in related research project activities [54]. Within each company, people with three different professional backgrounds were taken into consideration (research and development, production, finance and controlling). Additional requirements for the selection of experts were: a profound knowledge level in their respective professional field (ideally, employees in management positions), familiarity with both lignin and fiber fines, and their availability and willingness to invest time to complete the whole survey consistently, which might be considered by some as burdensome [55]. Seven interviewees (three from R&D, two from production, two from finance and controlling) participated in the survey, which resulted in the collection of 26 responses, 21 of which were valid (the response composition appears in Table 2). The approach and survey were explained to the participants beforehand and conducted using the online survey web application tool LimeSurvey; if needed, additional calls were made by telephone to clarify the subject and procedure. The survey can be found in the Appendix: therewith, the criteria and corresponding subcriteria were compared pairwise to identify the respective preferences of the stakeholders. These ratings were then used to derive the matrices, and the AHP procedure was carried out [50]. Table 2. Composition of the sample (altogether, 21 valid matrices were derived from the answers of seven (7) participants who conducted pairwise comparisons of the criteria and subcriteria). By-Product

Impact Category

Professional Background

Lignin (n = 10) Fiber ﬁnes (n = 11)

Costs (n = 10) Environmental impact (n = 11)

R&D (n = 7) Production (n = 8) Finance and controlling (n = 6)

3. Results 3.1. Development of the Hierarchy: Identiﬁcation of Alternatives, Criteria, and Sub-Criteria The structure of the hierarchy, including the overall goal, criteria, subcriteria and alternatives, is explained and illustrated in Figure 3. The allocation approaches (alternatives)

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to be compared were system expansion, physical partitioning and economic partitioning. Nine potential features of allocation methods were identified in a review of scientific papers on allocation issues. These features referred to the consideration of market mechanisms (e.g., reference products, geographical context, changes in prices) [6,13,16,19,33]; considerations of the physical properties of coproducts [6,13,15,16,32]; method resistance towards changes, such as price fluctuations and changing reference products [6,13,19,22,56]; ease of applying the method [13,22]; ease of understanding and interpreting the allocation results (transparency) [13,57]; amount of data required [38,57]; ability to take small quantities of byproducts into consideration [22]; ability to handle diverse physical properties of the coproducts [6,16,58]; and ability to reflect on socioeconomic factors and/or driving forces for the production process [19,22]. Accordingly, the following criteria were defined to establish a hierarchy that could be applied to choose an appropriate allocation method: physical system [6,13,15,16,32], economic system [6,13,16,22,32,33,58], stability [6,13,19,22,56], calculability and interpretation [13,22,38,57] and flexibility [6,16,22,58]. The subcriteria ability to bear and market environment were then added to the economic criterion (hierarchy illustrated in Figure 3). 3.2. Pairwise Comparison of the Alternatives with Respect to (Sub-)Criteria Referring to the selected scientific literature and the judgment scale given in Table 1, the three alternatives (economic partitioning, system expansion and physical partitioning) were compared pairwise with regard to the (sub-)criteria physical system, ability to bear, market environment, system stability, calculability and interpretation and flexibility. The resulting relative weights of the alternatives (allocation methods) with respect to the (sub-)criteria are illustrated in Figure 4 (consistency ratios: physical system, 0.0000; ability to bear, 0.0692; market environment, 0.1797; system stability, 0.0000; calculability and interpretation, 0.0000; flexibility, 0.0000).

Figure 4. Relative weights of the alternatives (allocation methods) with respect to the (sub-)criteria.

3.3. Pairwise Comparison of the Criteria with Respect to the Goal The execution of the pairwise comparisons by the biorefineries’ representatives resulted in 26 responses, five of which were excluded due to inconsistencies (i.e., C.R. ≥ 0.2). The different criteria weightings assigned by the practitioners were compared to investigate their preferences, and the results were grouped to identify potential influencing factors (impact type, type of byproduct and the respective professional background). Regarding the overall results (n = 21), the respective relative weights of the five criteria are fairly balanced, with the criterion flexibility lagging slightly behind (using geometric means: system stability, 25.82%; economic, 21.07%; calculability and interpretation, 20.85%; physical system, 19.27%; flexibility, 12.98%; C.R.: 0.0046). Only minor differences were observed in the weightings regarding the allocation type (cost allocation and environmental impact allocation) and the byproducts (lignin and fines); aggregated results (using geometric means) are given in Table 3 (Figure S1 on the respective

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weightings is provided in the supplementary material). Regarding the cost allocation (aggregated results), the criterion calculability and interpretation was assigned a lower relative weight, and the criteria economic and flexibility were given higher relative weights, as compared to the environmental impact allocation. The physical system criterion was rated as less important for fines than for lignin. Table 3. Aggregated results (geometric means) of criteria weights with respect to the allocation subject (cost allocation: n = 10, environmental impact allocation: n = 11) and byproduct (fines: n = 11, lignin: n = 10).

Cost A. (n = 10) Env. I. A. (n = 11) Lignin (n = 10) Fines (n = 11)

Calculability and Interpretation

Economic

Flexibility

Physical System

System Stability

C.R.

16.81% 26.10% 19.76% 21.79%

23.18% 18.48% 21.09% 20.87%

15.20% 10.72% 12.36% 13.45%

18.49% 19.94% 22.58% 16.60%

26.31% 24.75% 24.20% 27.30%

0.0064 0.0143 0.0042 0.0088

On the contrary, major differences were noted regarding the different professional backgrounds of the participants (ﬁnance and controlling, production, research and development). This is illustrated in Figure 5, and the respective geometric means are given in Table 4. Most prominently, people with a background in ﬁnance or controlling ranked the economic criterion higher and the physical system lower than people from the production area and vice versa.

Figure 5. Weighting of criteria and subcriteria with respect to the professional background (ﬁnance/controlling: n = 6, production: n = 8, research/development: n = 7).

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Table 4. Aggregated results (geometric means) of criteria and subcriteria weights with respect to the professional background (ﬁnance/controlling: n = 6, production: n = 8, research/development: n = 7). Calculability and Interpr.

Economic

Flexibility

Physical System

System Stability

C.R.

Ability to Bear

Market Env.

Finance and C. (n = 6)

18.66%

33.55%

8.29%

9.80%

29.69%

0.0308

53.52%

46.48%

Production (n = 8)

22.21%

11.92%

16.75%

28.80%

20.32%

0.0067

60.16%

39.84%

R&D (n = 7)

18.43%

24.09%

12.17%

19.10%

26.21%

0.0307

81.72%

18.28%

Concerning the weightings of the subcriteria with respect to the criterion economic (ability to bear and market environment), 21 consistent pairwise comparisons were obtained. The subcriterion ability to bear (ability of a method to use market prices, thus reflecting the ability of products to bear certain costs or environmental impacts, i.e., products with higher market prices also bear higher costs/environmental impacts) was rated higher than market environment (methods that are able to include changes in the market outside the production system) (overall n = 21), and using geometric means (ability to bear, 66.74%; market environment, 33.26%). As seen for the criteria, differences in the subcriteria weightings are also minor with regard to the different kinds of allocation (cost or environmental impact allocation; lignin or fines), but, again, are larger when comparing the different professional backgrounds. The latter aspect is illustrated in Figure 5, and the geometric means are given in Table 4. People with backgrounds in the fields of finance or controlling tended to rate both subcriteria as almost equally important, but production employees tended to weigh the importance of ability to bear more highly (60.16% vs. 39.84%), and research and development employees much more highly than market environment (81.72% vs. 18.28%). 3.4. Choice of Allocation Method Regarding the final results for the 21 full AHPs, the final weightings of the respective alternatives are fairly balanced (illustrated in Figure S2), with a slightly higher weight assigned to the alternative physical partitioning (using geometric means: 38.31%), followed by economic partitioning (33.33%) and, finally, system expansion (28.37%). As the results for the (sub-)criteria weightings show, only minor differences could be observed when comparing either the byproducts lignin and fines or the cost and environmental impact allocation (aggregated, all four would result in the choice of physical partitioning). However, differences become more evident regarding the professional backgrounds (illustrated in Figure 6).

Figure 6. Final weights of the allocation alternatives with respect to different professional backgrounds of the interviewees (finance/controlling: n = 6, production: n = 8, research/development: n = 7).

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Regarding allocation choices made on the basis of individual judgments (highest respective weights), people with a finance or controlling background preferred economic partitioning (3 out of 6 AHPs) over system expansion (2 out of 6) and physical partitioning (1 out of 6). People with a professional background in production, however, executed the (sub-)criteria weightings such that physical partitioning would have been chosen most of the times (6 out of 8 cases; 2 led to economic partitioning). Meanwhile, the judgments made by research and development employees resulted either in the choice of economic partitioning or physical partitioning (3 out of 7, respectively; 1 rating resulted in system expansion). The final choices derived from the aggregated results (using geometric means) led the aggregated professional groups production (43.98%) and R&D (37.41%) to choose physical partitioning for both, and led the aggregated group of practitioners from finance and controlling (34.35%) to choose economic partitioning. 4. Discussion Unlike previous studies that applied different allocation approaches to compare the outcomes [6,14,22] or suggested new case specific approaches [59,60], this study applied user preferences regarding the identified (sub-) criteria to determine how allocation methods would be selected by practitioners. The potential environmental or economic impacts of biorefinery implementations have been assessed several times [5,7,61]. However, major variations are observed in the results of these assessments, with allocation choices in multifunctional processes representing one of the key issues that affects the final outcome [6,13,14]. Both the companies themselves and their stakeholders assign importance to allocating costs and environmental impacts to the products. Thus, determining the respective impacts of and attaining information about each product in the production process is also important [19,23,62]. As a reasonable number of scientific papers are available that address the issue of allocation from various theoretical and applied viewpoints, it was possible to identify several distinct characteristics of allocation methods that may guide practitioners’ choices (RQ1). Nine potential features were derived from these papers. Although some of these features are reported frequently (e.g., market mechanisms), others are cited as single cases (e.g., referring to small quantities of byproducts). Hence, this type of comprehensive overview was performed for the first time, allowing five criteria (and two subcriteria) to be defined that can be applied to choose allocation methods. The resulting decision hierarchy provides guidance on how an allocation method could be chosen easily and transparently for a specific context in practice. The overall results of the assessment indicate that no clear preference for a specific allocation method could be identified among the participants (physical partitioning was favored slightly over economic partitioning and system expansion). Furthermore, the different criteria (based on methodological characteristics), which were relevant for the selection of allocation methods (as shown in Figure 3), were rated rather indifferently, with most average weights (geometric means) hovering around 0.2 (RQ2). Only the criterion flexibility was perceived as relatively less important, and system stability as slightly more important. The respondents weighted the criteria for allocation method selection in different ways: the economic criterion showed higher levels of variation than calculability and interpretation, which indicates that the less constant factors might be more decisive under variable conditions. To a certain degree, these results may reflect (or are reflected by) the ongoing academic discussion on allocation methods [14,19,63]. High ratings assigned to the criterion market environment (subcriterion of economic) and—to some extent—flexibility, favor system expansion, while ability to bear (subcriterion of economic) favors economic partitioning (Figure 4). This finding reflects those of Ekvall and Finnveden [37], who showed the better fit of certain allocation procedures in specific situations. According to Heijungs and Guinee [38], the strength of system expansion in terms of flexibility and consideration of the (dynamic) market environment [17] is also its disadvantage, depending

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on the suitability for specific tasks. Hence, the results in this study also confirm the context dependency of the selection of allocation methods. How exactly did context factors influence the allocation method preferences of the responding practitioners? The study results are quite mixed. Neither the product characteristics nor the type of considered impact (environmental or cost) seem to provide consistent evidence for an influence on practitioners’ preferences. The results in this respect are surprisingly homogeneous (see Table 3 and Figure S1). Considering the rather distinct discussion and development of cost and environmental impact allocation (see [34]), this result is somewhat unexpected. It could also have been expected that the product characteristics (e.g., large vs. small volume products) would influence the preferences for the criteria physical system or economic. Indeed, the average preference for physical system was higher for lignin (large volume) than for fines (small volume), but the difference was rather small. The criterion calculability and interpretation was also rated as slightly higher with regard to environmental impact allocation as compared to cost allocation (possibly due to the comparably broader interpretability of the term “environmental impact”). All in all, this study did not reveal empirical evidence that practitioners’ preferences for certain allocation methods are substantially governed by variations in considered products or impacts. Although influencing factors regarding product or impacts were not distinctly identified, the clear influence of the respondents’ professional backgrounds can be considered a key finding of this study. In other words, the professional background can be considered as a major factor in contextualizing allocation preferences. Respondents working in the field of production favored the physical system and, hence, preferred taking physical partitioning approaches, while their counterparts from finance and controlling favored the economic criterion (considering both its subcriteria nearly equally), making economic partitioning and system expansion the more preferred approaches. Respondents working in research and development (R&D), meanwhile, assigned ratings in a rather balanced way (but focused much more strongly on the subcriterion ability to bear): their judgments mostly fall between those of the other two professional groups, with the most preferred allocation methods identified as physical partitioning and economic partitioning. Subjectivity in allocation choices, as detected in this study, strengthens the view of LCA as an interpretative process [64] in which the reasoning, views and choices behind these need to be understood more fully than is currently often the case. These findings from our study are supported by the strategic management field and its core theoretical premises of decision-making: the role of individual managers is essential in strategic decision-making in firms, and managerial decisions are affected by numerous, human related factors, such as the managers’ skills and capacities or maybe even their daily routines. These results also reflect other results published in the corporate decision-making literature, including in the paper by Schaltenbrand et al. [43], who stated that corporate decision-making is more of an interpretive endeavor than an analytic computation. In the other words, we need a fuller understanding of selective perceptions [65] and various determinants in managerial decision-making [44,66]—all of which have an impact on the choice of allocation methods—for strategic management in biorefinery companies. To our knowledge, these issues have neither been addressed by researchers conducting biorefinery LCAs nor by those looking at allocation choices made in the other fields. Although these findings revealed the relevant effect of the professional background on preferences for allocation methods, the underlying drivers and more specific attributes for this observation have not yet been identified. This would require more research approaches to be taken in the future, including qualitative social research approaches such as the laddering technique [67]. Despite making several requests, we did not manage to involve more participants in the study. This could have been due to their time constraints and unfamiliarity with the topic of impact allocation and/or the type of questioning (i.e., the pairwise comparisons). In addition, the tasks of answering the questions and assigning consistent ratings might have been perceived as burdensome. Therefore, the results cannot be considered as repre-

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sentative; however, this was also not intended considering the quasi-experimental nature of the study. As the participants from the companies were not familiar with the impact allocation literature and with the process of comparing allocation alternatives with respect to certain criteria, the pairwise comparisons of the alternatives regarding the (sub-)criteria were performed with reference to the scientific literature on allocation issues. This was found to be an appropriate information base for this task, and also made the process more objective and transparent. 5. Conclusions This study provides valuable information about this relevant but rarely studied issue by exploring the practitioners’ perceptions of allocation methods in biorefinery development. Specifically, we gathered information on the perceptions of Austrian pulp and paper company representatives regarding their choices of appropriate allocation methods. The practical implication of the study findings is that different allocation procedures can be preferred or applied within one company, one biorefinery, one product and even one impact category. Furthermore, the relevance of professional background to allocation related decision-making suggests that environmental managers and other decision-makers (e.g., in firms) should be properly trained on allocation issues and their implications. The versatile combination of capacities, skills and other human factors would enable allocation options to be viewed from multiple perspectives. In this way, more conscious decisions, which are not bound to single manager’s or department’s perceptions, could be formulated. Subramanian et al. [68], for example, emphasized that implementing meaningful decision models that can have positive environmental and economic impact should involve all departments in a business, as well as industrial ecologists and business managers. Policy makers—for example participating in decision-making processes on European Union research projects and demonstration plants—should be aware that practitioners with different professional backgrounds can have various perspectives on and preferences for allocation methods, and that this may influence the results of environmental and cost assessments significantly. This, in turn, affects the interpretations and decisions made by these practitioners and by the policy makers themselves. It is therefore recommended that, in biorefinery research and implementation, multidisciplinary and diverse views and knowledge are included in the assessment of both the environmental impacts and the costs—and, thus, also the reasonableness and feasibility—of such projects. Through interdisciplinary work and communication, urgently needed common allocation principles for practitioners could be developed, thus allowing them to respond better to the current challenges. Supplementary Materials: The following supporting information can be downloaded at: https: //www.mdpi.com/article/10.3390/su14052619/s1; Figure S1: Weighting of criteria with respect to the allocation subject (cost allocation: n = 10, environmental impact allocation: n = 11) and byproduct (fines: n = 11, lignin: n = 10); Figure S2: Overall results (n = 21) of the AHPs (final weights of the alternatives); survey on the topic of cost and environmental allocation in biorefinery processes. Author Contributions: J.W.: conceptualization, data curation, formal analysis, methodology, project administration, visualization, writing—original draft; S.P.: investigation, data curation; A.N.: conceptualization, supervision, writing—original draft; T.S.: conceptualization, funding acquisition, methodology, supervision, writing—original draft. All authors have read and agreed to the published version of the manuscript. Funding: Open access funding was provided by University of Graz. Julia Wenger, Stefan Pichler and Tobias Stern received funding through the project FLIPPR2 (Future Lignin and Pulp Processing Research—PROCESS INTEGRATION; FFG project number: 861476), which is financially supported by the industrial partners Sappi Austria Produktions-GmbH & Co KG, Zellstoff Pöls AG and Mondi Frantschach GmbH, as well as the Competence Centers for Excellent Technologies (COMET), which are promoted by BMVIT, BMDW, Styria and Carinthia and managed by the Austrian Research Promotion Agency (FFG).

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Institutional Review Board Statement: Not applicable. Informed Consent Statement: Informed consent was obtained from all subjects involved in the study. Data Availability Statement: The Excel sheet with the matrices and detailed calculations can be made available if desired. Acknowledgments: We sincerely express our gratitude for the support received from the University of Graz and from Jyväskylä University School of Business. We gratefully acknowledge the industrial partners Sappi Austria Produktions-GmbH & Co., KG, Zellstoff Pöls AG, and Mondi Frantschach GmbH, as well as the Competence Centers for Excellent Technologies (COMET), which are promoted by BMVIT, BMDW, Styria and Carinthia and managed by FFG, for their financial support of the K-project FLIPPR2 (Future Lignin and Pulp Processing Research—PROCESS INTEGRATION; FFG project number: 861476). Conflicts of Interest: The authors declare no conflict of interest.

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PAPERmaking! FROM THE PUBLISHERS OF PAPER TECHNOLOGY TE INTERNATIONAL®

Volume 8, Number 2, 2022

Alternative Materials from AgroIndustry for Wood Panel Manufacturing—A Review 1

NICOLAS NEITZEL , REZA HOSSEINPOURPIA , THOMAS WALTHER & STERGIOS ADAMOPOULOS . The growing demand for wood-based panels for buildings and furniture and the increasing worldwide concern for reducing the pressure on forest resources require alternatives to wood raw materials. The agricultural industry not only can provide raw materials from non-wood plants but also numerous residues and side streams. This review supplies an overview of the availability, chemical composition, and fiber characteristics of non-wood lignocellulosic materials and agricultural residues, i.e., grow care residues, harvest residues, and process residues, and their relevance for use in wood panel manufacturing. During the crop harvest, there are millions of tons of residues in the form of stalks, among other things. Usually, these are only available seasonally without using storage capacity. Process residues, on the other hand, can be taken from ongoing production and processed further. Fiber characteristics and chemical composition affect the panel properties. Alternatives to wood with long fibers and high cellulose content offer sufficient mechanical strength in different panel types. In general, the addition of wood substitutes up to approximately 30% provides panels with the required strength properties. However, other parameters must be considered, such as pressing temperature, adhesive type, press levels, and pretreatments of the raw material. The search for new raw materials for wood panels should focus on availability throughout the year, the corresponding chemical requirements and market competition. Panel type and production process can be adapted to different raw materials to fit niche products. Contact information: 1. Department of Forestry and Wood Technology, Linnaeus University, Georg Lückligs Plats 1, 35195 Växjö, Sweden. 2. IKEA Industry AB, Skrivaregatan 5, 21532 Malmö, Sweden. 3. Department of Forest Biomaterials and Technology, Swedish University of Agricultural Sciences, Vallvägen 9C, 75007 Uppsala, Sweden. Materials 2022, 15, 4542. https://doi.org/10.3390/ma15134542 Creative Commons Attribution 4.0 International License

The Paper Industry Technical Association (PITA) is an independent organisation which operates for the general benefit of its members – both individual and corporate – dedicated to promoting and improving the technical and scientific knowledge of those working in the UK pulp and paper industry. Formed in 1960, it serves the Industry, both manufacturers and suppliers, by providing a forum for members to meet and network; it organises visits, conferences and training seminars that cover all aspects of papermaking science. It also publishes the prestigious journal Paper Technology International® and the PITA Annual Review, both sent free to members, and a range of other technical publications which include conference proceedings and the acclaimed Essential Guide to Aqueous Coating.

Page 1 of 28

Article 7 – Agrowaste & Wood Panel

materials Review

Alternative Materials from Agro-Industry for Wood Panel Manufacturing—A Review Nicolas Neitzel 1 , Reza Hosseinpourpia 1 , Thomas Walther 2 and Stergios Adamopoulos 3, * 1

2 3

Citation: Neitzel, N.; Hosseinpourpia, R.; Walther, T.; Adamopoulos, S. Alternative Materials from Agro-Industry for Wood Panel Manufacturing—A

Department of Forestry and Wood Technology, Linnaeus University, Georg Lückligs Plats 1, 35195 Växjö, Sweden; nicolas.neitzel@lnu.se (N.N.); reza.hosseinpourpia@lnu.se (R.H.) IKEA Industry AB, Skrivaregatan 5, 21532 Malmö, Sweden; thomas.walther@inter.ikea.com Department of Forest Biomaterials and Technology, Swedish University of Agricultural Sciences, Vallvägen 9C, 75007 Uppsala, Sweden Correspondence: stergios.adamopoulos@slu.se

Abstract: The growing demand for wood-based panels for buildings and furniture and the increasing worldwide concern for reducing the pressure on forest resources require alternatives to wood raw materials. The agricultural industry not only can provide raw materials from non-wood plants but also numerous residues and side streams. This review supplies an overview of the availability, chemical composition, and fiber characteristics of non-wood lignocellulosic materials and agricultural residues, i.e., grow care residues, harvest residues, and process residues, and their relevance for use in wood panel manufacturing. During the crop harvest, there are millions of tons of residues in the form of stalks, among other things. Usually, these are only available seasonally without using storage capacity. Process residues, on the other hand, can be taken from ongoing production and processed further. Fiber characteristics and chemical composition affect the panel properties. Alternatives to wood with long fibers and high cellulose content offer sufficient mechanical strength in different panel types. In general, the addition of wood substitutes up to approximately 30% provides panels with the required strength properties. However, other parameters must be considered, such as pressing temperature, adhesive type, press levels, and pretreatments of the raw material. The search for new raw materials for wood panels should focus on availability throughout the year, the corresponding chemical requirements and market competition. Panel type and production process can be adapted to different raw materials to fit niche products.

Review. Materials 2022, 15, 4542. https://doi.org/10.3390/

Keywords: agricultural residues; wood panels; particleboard; straw; stalks; sustainability

ma15134542 Academic Editor: Marco Corradi Received: 17 May 2022 Accepted: 24 June 2022 Published: 28 June 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional afﬁliations.

1. Introduction Sustainable management and the use of raw materials have become increasingly important during the last decades. The global interest and online search for sustainable products have grown by over 71% since 2016 [1]. The world population is projected to reach 8.5 billion in 2030 and increase further. This goes hand in hand with an increasing demand for living space and thus for building and furniture materials [2]. Given the growing global demand for sustainable products, the pressure on the forestry sector as a main source of renewable raw materials is more signiﬁcant than ever [3]. Likewise, biodiversity, the quantity and quality of forests, and their protection are integral parts of current global and regional policies, for example, in the European Union Biodiversity Strategy for 2030 or the United Nations Sustainable Development Goals (SDGs) [4]. This, together with the increasing timber prices, as well as delivery difficulties due to affected logistics, urge the wood panel industry to look for alternative raw material sources. Non-wood lignocellulosic materials (NWLM) and agriculture residues (AR) can be promising alternative raw materials for the wood industry since they originate from renewable sources and are widely available [5]. ARs are often burned for energy production [6] or used as animal feed [7] and as a natural fertilizer left in the ﬁelds. Some ARs are also

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partially burned in the fields since removal or mechanical incorporation into the soil is economically inviable [8]. However, since combustion releases greenhouse gases and causes high levels of air pollution, the field burning of agricultural waste or residues is not permitted in most of the European Union’s member states, among other places [9]. Valorizing the ARs into value-added products, such as in wood panel manufacturing (mainly particleboards and fiberboards), increases their value and brings ecological benefits. Simultaneously, it relieves the pressure on virgin forest raw materials. Although there are various studies on the utilization of NWLMs and ARs for wood-based panels [10–13] and reviews that collected and summarized the findings [5,14–16], there is still a lack of information about the critical requirements of these materials to serve as a partial or entire replacement of wood. Some material properties, such as the anisotropic and hygroscopic characteristics of NWLM and ARs are similar to that of wood, while their density is generally lower [14]. This brings an advantage for producing low-density composites. The wood particles or fibers cannot be replaced with alternative materials in a one-to-one ratio due to their low mechanical strength and high proportion of fines [17]. Therefore, the application of alternative materials in panel manufacturing is only feasible up to a certain amount in the presence of wood. Otherwise, higher amounts of adhesives are required to meet the required mechanical strength level of the panels. Although massive amounts of NWLMs and ARs exist worldwide, the majority of those are only seasonal and not evenly available throughout the year [18]. In the past 20 years, the production volume of wood-based panels has almost doubled from approximately 180 million m3 in 2000 to over 361 million m3 in 2020 [19]. The share of oriented strand boards (OSB) and plywood production increased only slightly in the period. On the other hand, the production volume of particleboard and especially fiberboard panels has increased significantly by 32% (Figure 1). Considering an average density of 750 kgm−3 for each fiberboard panel, about 184 million tons of raw lignocellulosic materials are required to meet this production volume without considering the required adhesives and production losses. OSB

Particleboard

Plywood

Fiberboard

WoodȬbasedȱpanelȱproductionȱ (millionȱm³)

400 350 300 250 200 150 100 50 0 2000

2002

2004

2006

2008

2010

2012

2014

2016

2018

Figure 1. Production volume of wood-based panels from 2000–2019 worldwide [19].

According to the Food and Agricultural Organization (FAO), about 850 million tons of residues (wheat stalks and husks) were incurred in European agricultural operations in 2018 [19]. The large number of available NWLMs and ARs may cover some part of the demands for raw materials for the wood panel industry. Nevertheless, the potential expected volume of materials depends on the geographical region. For instance, Europe

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has a forest area of over 10.17 million km2 and a cropland area of about 2.89 million km2 , while these areas in Asia are 6.24 and 5.90 million km2 , respectively (Table 1). Table 1. Forest land vs. cropland area in the world in 2019 (million km2 , [19]). Area

Forest Land

Cropland

Africa Asia Europe North America Oceania South America

6.41 6.2 10.17 6.57 1.85 8.46

2.76 5.90 2.89 1.99 0.33 1.32

This article presents a review of the research performed on using alternative NWLMs and ARs from the agricultural industry for wood panel manufacturing. It encompasses information on raw material categories and availability, their ﬁber and chemical characteristics, and utilization in panel manufacturing with the partial or entire replacement of wood. The performance of manufactured panels at various production parameters is included as a common requirement in the initial development stages when using new materials. The pretreatment and processing of these raw materials are also discussed. The opportunities and challenges of using such alternative materials are described, and promising materials for further investigation are proposed. 2. Categories of Different Alternative Materials A variety of lignocellulosic materials from various sources and agricultural production processes have received attention as alternative raw materials for wood-based panel manufacturing and mainly include by-products, side streams, and residues. These materials can be further categorized as non-wood lignocellulosic materials and three types of agricultural residues, i.e., grow care residues, harvest residues, and process residues (Figure 2).

Figure 2. Different agriculture production processes and their related available side-streams.

Non-wood lignocellulosic materials (NWLM) are derived from crops primarily cultivated for use in the food and textile industry. They can be found around the world but to a varying degree. About 1.1 million tons of ﬁbers are produced annually from growing ﬂax, of which 97.1% are from Europe [19]. Due to the legislative approval and increasing interest in cannabidiol, hemp cultivation in the United States has also increased enormously since

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2018 [20]. Only in 2019, about 3.4 million tons of jute and 0.2 million tons of sisal were produced worldwide [19]. Flax and hemp are mainly cultivated because of their seeds to produce oil in the food industry [21,22], while their fiber, together with kenaf and sisal, are used in textiles (clothes, mattresses, ropes, etc.) due to their high length, strength, and durability [23,24]. Kenaf fibers are commercially used as an insulating material in constructions. The NWLM category also includes ornamental plants that are grown for decorative purposes, such as rhododendrons or alternatives like bamboo. The fast-growing grass bamboo is used for various applications, such as construction, food, biofuel, pulp, and panel making. This diversity is mainly due to its considerable growing number annually, which is over 0.32 million km2 worldwide [25]. Grow care residues are the first group of agricultural residues from plant materials and arise during crop maintenance. When fruits grow, the plants are pruned to allow the fruit bodies to reach the ideal growth [26]. There is no economic use proposed for this biomass type rather than burning, i.e., thermal use of apple and olive tree pruning [27,28], or an attempt to produce ethanol from it, i.e., ethanol production from olive tree pruning [29]. There are no accurate numbers for available existing materials from grow care residues as they are not measured in most cases. Harvest residues or primary residues are mainly stalks, straws, leaves, sticks, and roots. These materials are collected during the harvest of cereals or other crops, and they are mainly used for animal feed, bedding animals, or in pallet form as an energy source [30]. However, most of this material type is left in the field without further application, which can sometimes lead to disposal problems for farmers [31]. The terms stalks, straw, and sticks are named stalks hereafter. A ton of rice, wheat, oat, and rye harvest produces about 1.3–1.6 tons of stalks. These numbers for cotton and sorghum harvesting are about 3.4 and 2.4 tons, respectively [19]. The quantity of harvest residues can be assessed by considering the residue-to-crop ratio through a ton of the produced main product, i.e., wheat grain, of a specific cultivated plant. The average residue-to-crop ratio of available harvest residues in Europe and worldwide is presented in Table 2. Table 2. Residue-to-crop ratio and amount of crop production in 2018 (million tons, [19]). Crop Sugarcane Corn Rice Wheat Potato Soybean Sugar beet Oil palm Coconut Sorghum Groundnut Cotton Millet Oat Barley Rye Coffee Cacao Total

Residue-to-Crop Ratio

Production

Stalks

Husks

Leaves

Stalks

Husks

Leaves

World

Europe

World

Europe

World

Europe

World

0.26 1.96 1.33 1.28 0.25 1.53 0.25 0.31 2.44 3.4 2.54 1.42 1.35 1.61 -

0.22 0.25 1.09 0.49 0.47 0.26 1.32 1.5

0.2 2.6 0.47 -

1907.0 1147.6 782.0 734.0 368.2 348.7 274.9 272.1 61.9 59.3 46.0 41.2 31.0 23.1 14.1 11.3 10.3 5.3 6137.9

2.3 128.6 4.0 242.1 105.2 12.1 185.1 0.1 1.1 0.5 0.4 13.5 83.1 9.1 787.3

495.8 2249.3 1040.1 939.6 92.0 533.5 68.7 84.3 144.8 140.0 78.8 32.7 19.1 18.2 5936.9

0.6 252.0 5.4 309.9 26.3 18.4 46.3 2.6 1.9 1.0 19.2 112.2 14.7 810.6

252.5 195.5 380.1 30.3 21.6 10.7 13.6 7.9 912.2

28.3 1.0 13.1 0.1 42.6

381.4 707.3 29.1 1117.8

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Process residues, including agro-industrial residues or secondary residues, are created when the plants are processed from the primary resource. Husks, hulls, peels, coir, bagasse, and skins are produced during the processing of the main product. The terms husk, shell, and hull can be used interchangeably [32] or with different meanings [33]. Since there is no standard terminology, all main crop’s protective surrounding materials are named husks in this work. Husk material is first produced in the field during the harvest and can also be collected during mechanical cleaning in industrial processing. Different products are obtained during the processing of cereal grain, for instance, husks, flour, and bran. The bran is a combination of ground husks and flour. Most of these residues are used as animal feed. However, due to their high fiber content, they can also be consumed by humans and are considered to be healthy [34]. As a food source, it is estimated that the consumption alone is about 90 million tons per year [35]. Bagasse is a side-stream of sugarcane stalks, and it is mainly used as an energy source in factories [36]. In addition to being used as fodder, it is also a raw material in the pulp and paper industry [37]. However, since the annual quantities are enormous and not everything is used, there is a huge potential for creating added value from bagasse and other ARs than solely used for thermal incineration. Harvesting one ton of soybeans produces around 1.09 tons of husks (Table 2). The quantities for producing a ton of coffee and rice are respectively 1.32 and 0.25 tons [19]. The exact conversion factors can vary widely due to different influencing elements, such as soil conditions, weather, and the harvesting process [38]. In addition, growth phases in northern regions are shorter than in regions near the equator. 2.1. Characteristics of Alternative Materials The performance of composite panels depends greatly on the characteristics of their constituents. The chemical composition and fiber morphology of lignocellulosic materials from the agricultural industry vary considerably with the plant species, age, climate, and soil conditions. The individual species in a plant family can also show different chemical composition and fiber morphology. There are, for example, many different types of bamboo or rice and sunflower varieties. In order not to list each species individually, plant families were grouped and a range of their chemical constituents and fiber morphology is given (Tables 3 and 4). 2.1.1. Chemical Composition of Alternative Materials As an organic material, wood is mainly composed of cellulose, hemicelluloses, lignin, extractives, and some minerals [39]. Hardwoods consist of 42–49% cellulose, 24–30% hemicelluloses, 25–30% lignin, 2–9% extractives, and 0.2–0.8% minerals/ ash. In contrast, softwoods contain 42–51% cellulose, 27–40% hemicelluloses, 18–24% lignin, 1–10% extractives, and 0.2–0.8% ash [40]. The chemical composition of different alternative furnish materials is summarized in Table 3. For classic wood-based panels, it has been well described previously how the chemical composition of the raw material influences the properties of the manufactured panels. Cellulose and hemicelluloses are the skeleton and backbone of the wood. Accordingly, a high level of strength is achieved with a high cellulose content [41]. At the same time, hemicelluloses lead to water absorption because of their hydrophilic properties. Lignin and extractives tend to be more hydrophobic in nature. It reduces water absorption of the panels and thickness swelling [42]. Extractives can also have various other impacts on the panel properties. Depending on the extractive type and share, they can influence the bonding behavior of common synthetic adhesives, lead to low or higher formaldehyde emissions or even improve the bonding behavior (i.e., tannins) in the panel [43]. The amount of ash also influences the bond quality. Ash components have no wettability, which can cause poor adhesive distribution [44].

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Table 3. Chemical composition (%) of alternative NWLMs and agricultural residues (black bars) as compared with wood (softwoods and hardwoods combined, and green background bars), adopted from references. Material

Chemical Composition, (%)

References Cellulose

NWLM Bamboo Flax Hemp Kenaf Miscanthus Sisal

[45–48] [45,47,48] [45,47,48] [45,47,48] [49] [45,48,50]

Grow care residues Kiwi pruning Orange pruning Pinecone Vine pruning

[51] [52] [53] [54,55]

Harvest residues Banana wood Barley stalks Canola stalks Corn stalks Cotton stalks Date palm Oil palm Pineapple leaves Rice stalks Sorghum stalks Sunﬂower stalks Tomato stalks Wheat stalks

[45–48] [56] [57] [58] [55] [59] [60] [50,56] [45,56] [55,56] [55] [58] [45,56]

Process residues Almond husks Coconut coir Coffee husks Corn husks Durian peel Hazelnut husks Oat husk Oil palm fruit husks Peanut husks Pineapple peel Rice husks Sugarcane bagasse

[61] [45,47,48,56] [33] [58] [62] [63] [64] [59,60] [63] [65] [45,48] [45,66]

Hemicelluloses

Lignin

Extractives

Ash

Although the NWLMs contain similar components as wood, their proportion varies. For instance, flax and hemp have a considerably higher cellulose content than wood, i.e., the respective cellulose contents in flax and hemp are 65–85% and 60–68%, while their lignin content is obviously lower, i.e., flax has 1–4% lignin, and hemp has 3–10% [45,67]. Miscanthus, however, has a similar chemical composition to wood by having 40–60% cellulose, 20–40% hemicelluloses, 10–30% lignin, and 2.2–4.9% ash content [49]. This is also valid for different types of bamboo grasses [45–48].

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The grow care residues from pruning and trimmings mostly have similar properties compared to their fruit plants [54,68]. As an example, kiwi pruning composes of 38.3% cellulose, 35.2% hemicelluloses, and 25.5% lignin while vine pruning contain 41.4% cellulose, 26% hemicelluloses, and 20.3% to 21.0% lignin [51,54,55]. The cellulose and lignin contents of harvest residues, such as canola, corn, or wheat stalks, are lower than that of wood, i.e., the cellulose content of cereal stalks is approximately between 27% to 38%, and their lignin amount is generally between 12% to 31%. However, their hemicelluloses content is approximately 19% to 38%, which is in the range of wood [45,55–58]. Stalk materials commonly contain high levels of extractives such as waxes, fats, terpenes, and phenols [39,69]. Their ash content is up to ten times higher than wood [58]. For example, the ash content of wheat stalks is 6–8% [45]. The harvest residues generally have a significant amount of inorganic elements. In some cases, like tomato stalks, the ash content can reach up to 20% of their composition [48,58,64]. Canola stalks with 4.7–6.7% and barley stalks with 2–9% also have a significantly higher ash content than wood [56,57]. Among different types of process residues, sugarcane bagasse has a closer amount of hemicellulose, lignin, and ash content to that of wood, while its cellulose content is considerably higher. Pandey et al. [66] and Faruk et al. [45] reported that sugarcane bagasse has 50–55% cellulose, 16.8–25% hemicellulose, 24–26.3% lignin, and 1.4–3.4% ash. The chemical composition of process residues is mainly influenced by annual growth conditions and regions [70]. The husks of cereals usually have low cellulose content, i.e., the respective cellulose content in corn, oat, and rice husks are 18%, 38.7%, and 25–45%, and vary with the growth conditions. Nevertheless, the ash content is generally higher than wood, which may cause some limitations for their processing by reducing the service life of machinery, i.e., tool wear, cutting or grinding machines [14,71,72]. A high ash content might be advantageous for specific applications. Beh et al. [73] showed recently that the use of wood ash in a coating of steel beams increases fire resistance. 2.1.2. Fiber Characteristics of Alternative Materials The morphology of the fibers is essentially relevant for their application in fiber form in relevant wood-based panels (i.e., fiberboards). However, if NWLM or ARs are used in particle form, the particle properties are also influenced by the fiber structure. For the production of fiberboards, long fibers with a higher aspect ratio are preferred [42]. Long fibers provide a larger surface area, allowing the adhesive to spread more evenly. At the same time, it allows for more contact surfaces and overlaps between the fibers [74]. Also, long fibers, compared to short ones, tend to arrange themselves horizontally in the mat during panel production rather than vertically. This has a positive effect on the bending behavior of the panels. Fiber diameter and density are closely related to the cell-wall thickness. A thin cell wall allows the fiber to deform more flexible without breaking. This, in turn, leads to more contact areas with other fibers within the panel. Thick cell walls, therefore, tend to reduce the bending properties [75]. The fibers from NWLMs are generally longer than wood fibers and therefore have a higher surface area (Table 4). For instance, the respective length of flax and hemp fibers are 10–65 mm [67] and 5–55 mm [76], while the fiber lengths in softwoods and hardwoods are approximately 2.8–7.2 mm [77] and 0.3–2.5 mm [76], respectively. The densities of flax and hemp fibers are approximately 1.4–1.5 gcm−3 [48], which is similar to that of wood fibers [78]. With a similar density of 1.45 gcm−3 to wood, sisal also has comparable fiber lengths of 0.8–8 mm [67]. In contrast, bamboo fibers with a length of 1.5–4.4 mm and diameter of 7–27 μm have a density of 0.6–1.1 gcm−3 . The length of bamboo fibers is comparable to miscanthus fibers, with a length of 0.81–1.05 mm [79].

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Table 4. Fiber characteristics of alternative materials as compared with wood ﬁbers. Material

Wood NWLM Bamboo Flax Hemp Kenaf Miscanthus Sisal Grow care residues Harvest residues Banana wood Canola stalks Corn stalks Cotton stalks Oil palm wood Pineapple leaves Rice stalks Sorghum stalks Sunﬂower stalks Tomato stalks Wheat stalks Barley stalks Process residues Coconut coir Coffee husks Corn husks Durian peel Oil palm fruit husks Rice husks Sugarcane bagasse

Fiber Characteristics Length (mm)

Diameter (μm)

Density (gcm−3 )

References

0.3–7.2

10–45

1.4–1.5

[48,76–78,80]

1.5–4.4 10–65 5–55 3.55–5.5 0.81–1.05 0.8–8

7–27 5–38 1–5 12–37 11.8–16.7 7–47

0.6–1.1 1.4 1.4–1.5 1.4 1.45

[48,76] [67] [48,76,81] [48,67,82] [79] [50,67]

n.a.

0.17 1.22 1.22 0.84 0.66 0.4–3.4 1.8 1.18 0.83–1.13 1.1–1.13 0.7–3.1

13.6 28 24.3 23.9 29.6–35.3 20–80 4–16 13.8 21.5 13.24–17.26 11.9–15.3 7–24

1.35 1.45–1.85 0.7–1.55 1.526 0.38 0.154 0.58 -

[50,67] [83] [84] [83,85] [50,67,86] [87,88] [89,90] [91] [84,92] [93,94] [95] [56]

20–150 0.05–0.8 0.5–1.5 0.84–2.38 0.89–0.99 1.59

10–460 15 10–20 170–447 19.1–25 170 20.96

1.15 1.15–1.31 0.7–1.55 1.16 0.99

[81] [33] [56] [96] [67] [97,98] [97,99]

There is limited data available on fiber dimensions from grow care residues. Ntalos and Grigoriou [54] reported that the anatomical and chemical components of the grow care residues correspond to those of the main plant. In comparison with wood and NWLMs, the harvest residues have noticeably shorter fibers, as their fiber lengths are mainly ranged from 1.1 mm for wheat stalks [95] to 1.8 mm for sorghum stalks [91], which is about half of wood fibers. The fiber diameter is, on average, approximately 30% smaller than wood [83,84,92]. The fiber morphology of harvest residues could, therefore, have a negative impact on the bending properties. As with the chemical composition, the fiber dimensions of process residues are also varied due to growth and processing conditions and some individual settings. However, since these materials are collected after the processing of the crops, their fibers are generally shorter than wood fibers [100]. The length of fibers from different husks, such as coffee husks or oil palm fruit husks, ranges from 0.05 to 0.99 mm [33,56,67]. With 15 μm, 10–20 μm, and 19.1–25 μm, the fiber diameters of coffee, corn, and oil palm fruit husks is roughly half that of wood fibers [33,56,67]. Due to the clearly shorter dimensions, the lengthwidth ratio of process residues differs from wood fibers, as they have a cubic form. For example, coconut coir and rice husks have with their large fiber diameters of 10–460 μm and approximately 170 μm in length relatively short fiber geometries [81,98]. The integration of process residues in wood-based panels could therefore be a challenge.

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3. Utilization of Alternative Furnish Materials for Panel Manufacturing The application of NWLM and other alternative furnish materials solely or mixed with wood fibers or chips in panel production has been extensively studied during the last decades. Various studies are summarized in Tables 5–8, where these materials were used as raw materials in fiberboard or particleboard, in combination with another material, as well as the type and quantity of adhesives. Tests in which NWLM or ARs were only used as a filler or as an adhesive component were not considered. The produced panels were evaluated for their mechanical and physical properties, i.e., internal bond (IB), modulus of elasticity (MOE), modulus of rupture (MOR), thickness swelling (TS), and water absorption (WA). Table 5. NWLM used for panel production with information on whether MOR and IB meet ( ) or not ( ) the standard requirements (ﬁberboard EN 622-3:2004; particleboard EN 312:2003). Panel Type

Materials

Resin Type SL; CL (%)

MOR (Nmm−2 )

IB (Nmm−2 )

References

Fiberboard

Bamboo Kenaf Kenaf Rhododendron Rhododendron

Bagasse ﬁber ind. wood ﬁbers

UF UF UF UF

4 10 11 11

12 18 * 29.14 40 * 32 *

1.4 0.2 * 0.33 0.63 * 0.60 *

[74] [82] [101] [102] [102]

Particleboard

Bamboo Bamboo Bamboo Bamboo Bamboo Bamboo Bamboo Bamboo Flax Flax Hemp Hemp Jose wheat grass Kenaf Miscanthus Miscanthus Miscanthus Seaweed

Eucalyptus Rice stalks Pinus taeda Eucalyptus ind. wood chips ind. wood chips -

UF UF UF UF PF PF UF UF UF UF UF UF pMDI UF pMDI UF pMDI UF

8 8 8 8 8 8 8 8 13 13 10; 8 10; 8 4 8 6 12 6 25

22.57 25.25 14.36 13.44 13.6 17.68 11.25 12.79 11.72 13.22 16 * 16 * 19.6 12.88 24.2 11 5.7 2.6 *

1.61 1.62 0.1 0.32 0.26 0.4 0.22 0.22 0.09 0.43 0.78 * 0.78 * 0.86 0.11 0.67 0.23 5.8 *

[103] [103] [103] [104] [104] [104] [105] [105] [106] [106] [107] [107] [108] [101] [80] [80] [109] [110]

* derived from ﬁgure, CL (core layer), ind. (industrial), PF (phenol-formaldehyde), pMDI (polymeric diphenylmethane diisocyanate), SL (surface layer), and UF (urea-formaldehyde).

Table 6. Grow care residues used for panel production with information on whether MOR and IB meet ( ) or not ( ) the standard requirements (ﬁberboard EN 622-3:2004; particleboard EN 312:2003). Panel Type

Materials

Resin Type SL; CL (%)

MOR (Nmm−2 )

Fiberboard

Pinecone

ind. Wood ﬁber

13.3

Particleboard

Grass clipping Grass clipping Kiwi pruning Kiwi pruning Needle litter Needle litter Vine pruning Vine pruning Vine pruning Vine pruning Vine pruning Yerba mata pruning Yerba mata pruning

Eucalyptus chips ind. wood chips ind. wood chips ind. wood chips ind. wood chips

UF UF UF UF UF UF UF UF UF UF UF UF UF

12 12 10; 8 10; 8 12 12 8 8 9 10 8 8 8

4.19 8.39 8.42 10.47 6.83 9.15 8.5 3.75 13.6 4.17 14 9.6 14.5

IB (Nmm−2 )

References

0.4

[111]

0.08 0.189 0.527 0.555 0.152 0.208 0.69 0.3 1.32 0.33 0.84 1.05 1.28

[112] [112] [113] [113] [114] [114] [54] [115] [116] [115] [54] [117] [117]

CL (core layer), ind. (industrial), SL (surface layer), and UF (urea-formaldehyde).

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Table 7. Harvest residues used for panel production with information on whether MOR and IB meet ( ) or not ( ) the standard requirements (ﬁberboard EN 622-3:2004; particleboard EN 312:2003). Panel Type

Resin Type SL; CL (%)

Materials

MOR (Nmm−2 )

IB (Nmm−2 )

References

Fiberboard

Canola stalks Corn stalks Rice stalks Wheat stalks

UF UF pMDI UMF

9 10 3 14

18.95 22.26 26 * 31 *

0.414 0.415 1.3 0.7 *

[83] [118] [119] [120]

Particleboard

Canola stalks Canola stalks Canola stalks (CL) Canola stalks Canola stalks (CL) Canola stalks Coconut wood Cotton stalks Cotton stalks Cotton stalks Date palm Eggplant stalks Eggplant stalks Mustard stalks Mustard stalks Oil palm wood Pepper stalks Pepper stalks Pepper stalks Primrose stalks Primrose stalks Primrose stalks Reed stalks Rice stalks Rice stalks Rye stalks Sorghum stalks Sunflower stalks Sunflower stalks Sunflower stalks Sunflower stalks Sunflower stalks Tomato stalks Tomato stalks Tomato stalks Triticale stalks Wheat stalks Wheat stalks Wheat stalks

MUPF pMDI

8 8

11.1 14.7

0.31 0.82

[121] [121]

10; 8

13 *

0.12 *

[107]

0.28

[121]

ind. wood chips

10; 8

14.5 *

0.21 *

[107]

ind. wood chips ind. wood chips trop. hardwood pine chips (SL) pine chips (SL) pine chips (SL) ind. wood chips ind. wood chips ind. wood chips ind. wood chips pine chips Popolus alba L. ind. wood chips -

UF EMDI PF UF UF UF MUF UF UF UF UF UF UF MUPF pMDI UF pMDI pMDI UF pMDI UF PF UF PF UF UF MUF UF UF pMDI MDI PF UF

12 4 12; 10 10 10 11; 9 12; 10 12; 10 12 12 12; 10 8 8 12; 10 8; 6 12; 10 6; 4 4 12 6; 4 8 12 11; 9 12 11; 9 11; 9 12; 10 12; 10 12 6; 4 4 10 8

9.1 14.21 17.95 14.6 8.1 18.14 13.2 13.14 14.5 14.7 4.9 * 12.32 12.2 14.2 14.3 19 15.7 14.1 * 14 * 7* 29 * 10 * 10.28 15.65 6.98 18.74 22.03 12.75 10.89 12.5 * 25 * 11.45 16.9 3.96

0.25 0.54 0.591 0.6 0.34 0.67 0.966 0.5 0.29 0.59 0.37 * 0.83 0.61 0.71 0.57 0.9 0.41 0.31 * 0.46 * 0.15 * 0.32 * 0.61 * 0.16 0.46 0.11 0.58 0.51 0.69 0.53 0.38 * 0.32 * 0.64 0.68 0.11

[122] [121,123] [107,124] [122,125] [123,126] [127] [128] [128] [129] [129] [130] [131] [132] [132] [133] [133] [133] [134] [44] [44] [134] [91] [135] [136] [135] [137] [136] [138] [138] [94] [134] [139] [140] [139]

* derived from ﬁgure, CL (core layer), EMDI (emulsiﬁed diphenylmethane diisocyanate), ind. (industrial), MUF (melamine urea-formaldehyde), MUPF (melamine urea phenol-formaldehyde), PF (phenol-formaldehyde), pMDI (polymeric diphenylmethane diisocyanate), SL (surface layer), and UMF (urea melamine-formaldehyde).

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Table 8. Process residues used for panel with information on whether MOR and IB meet ( ) or not ( ) the standard requirements (ﬁberboard EN 622-3:2004; particleboard EN 312:2003). Panel Type Fiberboard

Particleboard

Resin Type SL; CL (%)

Materials Hazelnut husks (30%) Oil palm fruit husks Oil palm fruit husks Almond husks Almond husks Almond husks Coconut Coir Coconut Coir Coconut Coir Coffee husks Coffee husks Coffee husks Corn stover Hazelnut husks Hazelnut husks Hazelnut husks Macadamia husks Olive stone Peanut husks Peanut husks Rice husks Rice husks Soybean husks Soybean husks Sugar beet pulp (CL) Sugar beet pulp (CL) Sugarcane bagasse Sugarcane bagasse Sugarcane bagasse Sugarcane bagasse (CL) Sugarcane bagasse (CL) Walnut husks Walnut husks Waste tea leaves Waste tea leaves

MOR (Nmm−2 )

IB (Nmm−2 )

References

ind. wood ﬁbers

13.9

0.22

[141]

32.8

0.114

[142]

27.2

0.24

[142]

ind. wood chips pine chips Durian husks ind. wood chips ind. wood chips ind. wood chips -

UF UF UF UF UF MUPF pMDI UF soy MUF PF UF

11; 9 11; 9 11; 7 11; 7 12 15 8 15 10 10; 8 10; 8 10; 8

14.01 7.41 10.2 15.1 17.5 36.8 11.9 14.1 13.1 16.5 * 10.1 12 11.9

0.90 0.27 0.36 0.40 * 0.32 0.3 0.34 0.6 0.41 0.8 * 0.39 0.482 0.505

[143] [61] [61] [144] [144] [62] [33] [33] [33] [145] [146] [146] [146]

4.3

1.33

[147]

pine chips Bamboo ind. wood chips

PU UF UF UF UF UF UF

20 10; 8 10; 8 8 8 10 10

15.56 9.9 11.32 4.69 6.74 11.02 20.84

0.316 0.35 0.04 0.07 0.23 0.40

[148] [63] [63] [105] [105] [149] [149]

10; 7

6.29

0.51

[150]

ind. wood chips

10; 8

9.97

0.51

[150]

0.01 *

[151]

pMDI

0.86

[152]

pMDI

40 *

1.8 *

[151]

10; 8

17 *

0.42 *

[107]

ind. wood chips

10; 8

17.5 *

0.45 *

[107]

ind. wood chips ind. wood chips

UF UF UF UF

11; 9 11; 9 8 8

5.86 8.62 37 * 35 *

0.24 0.34 0.16 * 0.22 *

[153] [153] [154] [154]

* derived from ﬁgure, CL (core layer), ind. (industrial), MUF (melamine urea-formaldehyde), MUPF (melamine urea phenol-formaldehyde), PF (phenol-formaldehyde), pMDI (polymeric diphenylmethane diisocyanate), PU (polyurethane), and SL (surface layer).

In most cases, however, only some of the properties were examined in the various studies. Since IB and MOR were predominantly tested and are included in the standard and industry requirements for the application of panels in the dry interior, IB and MOR values are presented in the tables. In addition, it is highlighted whether they meet the minimum requirements of the European Norm (EN) 622–3: 2004 for ﬁberboard and EN

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312: 2003 for particleboard. The panel thickness and density were considered in each case. Unless otherwise noted, material mixes are at a 1:1 weight ratio. In general, it can be stated that the combinations of NWLM (Table 5) or AR (Tables 6–8) with a wooden material usually show better properties than panels without wood content. Up to a proportion of approximately 30% of wood substitutes, the required strength properties are usually achieved. Beyond that level, the properties decrease significantly. Compared to AR, panels containing NWLM achieve higher MOR values, which could be due to the longer fibers. Tröger et al. [80] reported that the addition of long flax fibers by 20% in the surface layer (SL) increased the bending properties and decreased the IB values in three-layer particleboards. Papadopoulos and Hague [106] mixed industrial wood chips and flax fibers (0%, 10%, and 30%) in single-layer particleboards by using a 13% urea-formaldehyde (UF) resin binder. Panels with a 30% flax share met the European Standard of P3 particleboard requirements in terms of MOR, IB, and TS. However, the mechanical strength of panels made from 100% wood was always higher. Particleboards made with 100% flax fibers had an insufficient IB strength but an acceptable MOR for P2 boards. The authors attribute the low IB to the relatively thin cell walls of flax. Bamboo particles as raw material for particleboards bond with 8% UF resin were examined by Hiziroglu et al. [103]. The single-layer panels of 100% bamboo, or combined with rice stalks or Eucalyptus, showed acceptable strength to meet the standard requirements of EN 312:2003. Nikvash et al. [107] investigated three-layer particleboards with different combinations of industrial wood chips and bagasse, canola, or hemp in the core layer (CL). A UF adhesive dosing of 10% in the surface layer and 8% in the core layer was used as a binder in all panels. The results were compared with the control boards made from 100% industrial wood chips. It was shown that particleboards with 50% bagasse or hemp in the core layer fulfilled the standard requirements for IB, MOR, and TS. The IB strength of the panels with 50% canola share was considerably low. However, the panels with a 30% canola share also met the IB requirements (EN 312:2003). Three-layer particleboards with bagasse in the core and coconut fiber in the surface layer bonded with 15% (SL) and 12% (CL) polyurethane (PUR) resin were examined by Fiorelli et al. [155]. The boards met all the ANSI A20.1-1999 requirements for interior particleboards (Figure 3a). Akgül and Çamlibel [102] and Yushada et al. [110] considered the use of the rather unusual non-wood lignocellulosic materials rhododendron and seaweed for the production of MDF (medium density fiberboard) and particleboards. MDF panels produced with 100% rhododendron fibers and 11% UF met the minimum requirements of IB, MOR, and MOE for indoor application according to the EN 622-3:2004 standard. Single-layer particleboards produced with seaweed and different level of adhesive loads (25%, 28%, and 30% UF) showed acceptable IB strength by reaching the standard level (Japanese Industrial Standard JIS A 5908). In comparison, the measured MOR and MOE values were significantly below the minimum requirements of the standard, even at the highest adhesive load of 30% UF. The low values could be explained by incomplete curing of the UF adhesive with the seaweed particles [110]. Balducci et al. [109] studied the performance of one-layer particleboards made with miscanthus and 6% polymeric diphenylmethane diisocyanate (pMDI) or an unknown amount of UF resin. The pMDI-bonded boards met the standard for all properties (IB, MOE, MOE), while the UF-bonded ones did not meet the minimum requirements for IB (EN 312:2003). Compared to single-layer boards, three-layer particleboards bonded with an undefined amount of UF adhesive had a lower IB but higher MOR, MOE, and TS values. An example of one-layer particleboards from miscanthus compared to a spruce particleboard is given in Figure 3b.

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Figure 3. (a) three-layer particleboard with green coconut ﬁbers in the outer layer and sugarcane bagasse in the inner layer [155], (b) spruce vs. miscanthus single-layer particleboards [156], (c) threelayer particleboard with rice husk core and a jute surface layer bonded by soybean protein [157], the (d) olive stone particleboard [148].

The research on using grow care residues for panel manufacturing is rather scarce (Table 6). Three-layer particleboards prepared by replacement of wood chips with 50% vine pruning particles in the core layer showed comparable mechanical properties to panels made with 100% wood chips. Those panels used 12% and 8% UF resin in the surface and core layers, respectively. A negative effect on the mechanical properties of the panels was observed with the increased content of vine pruning particles. Similar performance reduction was also observed when vine pruning particles were used in onelayer particleboards [54]. According to the authors, the reduction is due to the lower length to thickness ratio compared to wood particles, as well as the certain amount of pith particles in the material. With single-layer particleboards from vine pruning waste and 9% UF, Ferrandez-Villena et al. [116] showed that it is even possible to reach the minimum requirements for furniture manufacturing. However, with a high panel density of approximately 865 kgm−3 . Nemli et al. [113] investigated different versions of three-layer particleboards with kiwi pruning particles in the core layer. An industrial UF resin was used with 11% and 8% in surface and core layers, respectively. An increase of kiwi pruning particles in the core layer negatively affected the panel properties. The reduction is also justiﬁed by the proportion of pith and bark in the kiwi pruning material. Panels containing up to 50% kiwi pruning particles exceeded the minimum requirements of MOR according to EN 312:2003 for general purposes. The mechanical strength of the panels was improved slightly by increasing the adhesive content by 1% for each panel version.

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Ayrilmis et al. [111] used ground pinecones from 0 to 50% to replace wood fibers in MDF panels bonded with 10% of UF adhesive. The authors reported that the water resistance of MDF panels was improved by increasing the pinecone content up to 10%. The mechanical properties of the MDF panels, however, decreased with increasing the amount of pinecone. It was assumed that the pinecone material acted more as a formaldehyde scavenger than as a strength provider since the formaldehyde emissions decreased with increasing the pinecone content. In the case of harvest residues, particleboard panels were studied more than any other panel type (Table 7). Harvest residues from castor [158], cotton [124], eggplant [128], pepper [132], canola [83], rice [44], sorghum [159], sunflower [135], tomato [138], wheat [120], and mustard stalks [129] processing were used in a series of combinations with industrial wood chips and UF adhesive for the production of single and three-layer particleboards. A maximum of 30% replacement of wood chips with canola stalks in the core layer of three-layer particleboards, with 10% UF resin in the surface layer and 8% in the core layer, showed comparable IB strength to the standard requirements [107]. Grigoriou and Ntalos [158] quoted that a 50% share of castor stalks was the optimum amount to reach an acceptable MOR and IB strength in single-layer particleboard panels using 8% UF adhesive. Application of corn, triticale, or rye stalks in the surface layer of three-layer particleboard panels together with 4% pMDI resulted in higher MOR and MOE than the control panels prepared with sole pine chips. Panels with reed stalks in the surface layer, on the other hand, had lower MOR and IB than the controls. All prepared panels fulfilled the standard requirements for MOR and MOE; however, only the ones made with corn stalks met the minimum requirements for IB strength [134]. Compared to the control panels, TS was lower in all experimental panels. Panels made from rye had 15% less TS than controls. The authors reported that the reduction in TS of the particleboards could be attributed to the hydrophobic nature of the rye stalks. Single-layer particleboard panels made with different mixing ratios of hardwood and pepper stalk particles and 8% of UF resin, showed decreasing mechanical properties with an increased amount of pepper stalk particles [132]. According to Khristova et al. [135], and Grigoriou and Ntalos [158], the utilization of pith from sunflower stalks is not recommended as it negatively affects the mechanical strength and water-related properties of particleboards. Palm tree wood was used with UF adhesive for the production of particleboard and plywood panels [127,160], and the results showed that three-layer particleboards made from 100% palm particles, and a respective adhesive load of 11% and 9% in the surface and core layers, met the minimum requirements for interior fitments in IB, MOR, and TS (EN 312:2003). Hashim et al. [130] studied the performance of binderless singlelayer particleboards made with oil palm wood and reported that the panels achieved the minimum requirements for IB but not for MOR according to the Japanese Industrial Standard (JIS A-5908 Type-8). The low MOR is explained by the lack of an adhesive. Among the side streams from the agricultural industry, process residues and industrial food residues have received the most attention for panel production recently (Table 8). Pirayesh and Khazaeian [61] reported that three-layer particleboards manufactured with almond husks, 9% UF resin in the core layer, and 11% in the surface layer, met the minimum requirements for MOR and IB (EN 312:2003) at a maximum level of 30% replacement of wood chips. With a higher proportion of husks, the generally poorer bonding of the resin and the almond husks lead to significantly reduced mechanical properties. 30% was also given as the highest proportion in fiberboard panels with hazelnut husk [141] and particleboard panels with sugar beet pulp [150]. Binderless single-layer particleboards from almond husk pressed at low temperature (120 ◦ C) for 30 min met the minimum requirements for panels for interior use. The achieved strength has been attributed to the high sugar content. After such long pressing time, the sugar acted as a binder between the particles [143]. Guler et al. [63] studied the performance of three-layer particleboards using peanut husks and UF resin (10% surface layer and 8% core layer).

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They suggested 25% peanut husks as the optimum level to achieve the standard requirements for boards in interior applications. The MOR and MOE values, in particular, decreased with a higher proportion of peanut husks. The panels with 100% peanut husks, on the other hand, showed lower TS than the ones with 25% husks. High density (>940 kgm−3 ) one-layer particleboards made with 15%, 30%, and 100% oat husks and 10% polyurethane resin reached the acceptable level of the EN 312:2003 standard for general purpose in MOR and IB [161]. Recently, Farag et al. [148] used olive stones together with an unsaturated polyester liquid resin for preparing single-layer particleboard panels, and they found that the panels fulfilled the MOR requirements for general purpose (EN 312:2003) at 20% adhesive load (Figure 3d). However, the maximum permitted values mentioned in the EN 312:2003 standard for the wet condition in TS were slightly exceeded. Single-layer particleboard panels from rice husks and 8% UF were tested by Melo et al. [105]. The rice husk panels showed significantly lower MOR, MOE, IB, and higher TS than the reference panels from industrial wood particles. The authors report that one reason may be the cylindrical and hollow structure of the hole rice husk particles, which could act as a barrier during gluing. Likewise, a lower permeability of the husks for the resin could have a negative effect on an even distribution of the adhesive. Faria et al. [149] investigated three-layer particleboards from Eucalyptus wood, different proportion of soybean husks in the CL and 10% UF. Panels with 100% soybean husks in the core layer did not meet any standard requirements. However, a high MOR was observed with a 1:1 ratio of Eucalyptus wood and soybean husks. The MOR increase was attributed to various factors, such as a higher interaction of the particles due to the increase of the compression ratio and better adhesive distribution on the particles. A combination of raw materials from non-wood lignocellulosic and agricultural sources was also used for panel preparation [160]. Khedari et al. [62] reported particleboards with low thermal conductivity using coconut coir and durian peel and combinations thereof, bonded with 12% UF resin. They found that a 90:10 mix ratio of coconut coir and durian peel was the optimum to fulfill the minimum requirements for IB values according to the Japanese Industrial Standard (JIS A-5908 Type-8). Nicolao et al. [157] developed particleboard from a combination of rice husks and jute fibers. The three-layer panel consisted of a rice husk core and different numbers of jute fiber surface layers bonded with 10% soybean protein adhesive (Figure 3c). With MOR from 12.6 to 27.9 Nmm−2 , the bending properties improved with an increased number of jute surface layers. In addition to the classic panel types, fiberboard, and particleboard, investigations were also conducted with plywood or special panels but to a lesser extent. Abdul Khalil et al. [160] tested five-layer plywood with UF or PF from oil palm wood (500 gm−2 ), as well as five-layer hybrid plywood with two layers consisting of oil palm empty fruit bunch fibers. The hybrid plywood achieved higher MOR and MOE than the oil palm wood plywood. It was attributed to the higher density of the hybrid panel. The studies described in Tables 5–8 show that NWLM and ARs, especially in fiberboards and particleboards, were extensively tested and the requirements were met in many cases. In particular, NWLM benefit from their long fibers in the panels. Grow care residues have been little studied thus far, and their integration into panels also negatively influences the bending behavior. The much-noticed harvest residues are generally well suited for both fiberboard and particleboard. They perform particularly well in combination with wooden material. Various husk types of process residues could not achieve sufficient bending strength values. Other process residues, such as coconut coir or sugarcane bagasse, appear suitable as raw materials for panels.

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4. Panel Manufacturing Parameters The performance of the panels prepared from alternative furnish raw materials are highly influenced by production parameters, including adhesive type and ratio, panel density, and pressing factors (speed and press temperature). Previous studies have shown a direct relation between the panel’s adhesive type and ratio and mechanical properties [91,162]. Papadopoulos et al. [163] revealed that the mechanical properties of bamboo particleboards increased with increasing the UF adhesive loads from 10% to 14%. Similar results were reported for UF-bonded particleboards made with cotton stalks [125]. UF, phenol-formaldehyde (PF), and melamine urea-formaldehyde (MUF) adhesives at 10% and 8% load were used for the manufacturing of three-layer particleboards with hazelnut husks, and the results illustrated identical mechanical properties for panels bonded within UF and PF, and lower MOR and IB values for those with MUF [146]. Barbu et al. [164] compared single-layer particleboards from walnut and hazelnut husks bonded with 10% MUF or PUR adhesive. Both panels with PUR adhesive illustrated higher bending properties (MOR and MOE) and lowered TS values than the MUF-bonded panels. The compatibility of various alternative furnish materials with conventional adhesive systems is rather challenging. For instance, the curing behavior of a standard UF adhesive in the hot press depends not only on the hardener type and the pressing temperature but also on the pH value of the raw material [165]. The presence of a high amount of wax and silica in stalks and husks cause poor interactions at the interfaces between the adhesive and the substrates. It also hampers the proper poly-condensation of the MUF adhesive, which results in weak bond lines [33]. Apart from the common UF and MUF adhesives, other adhesive types were also investigated for manufacturing panels from NWLM and ARs, such as pMDI [33], PF [166], bio-based systems [167], natural rubber [168] and soybean flour [139]. When using pMDI, the panel requirements are met in almost all studies (Tables 5, 7 and 8). Pan et al. [169] evaluated the performance of the single-layer particleboards made with rice stalks and a 4% adhesive mixture of pMDI and rice bran. The authors suggested that 20% of the adhesive can be replaced by rice bran while achieving a comparable mechanical strength to the control panel. Single-layer rice stalk particleboards with UF and corn starch as adhesive were compared by Hussein et al. [170]. With 10% adhesive load in each case, MOR and IB were significantly lower with corn starch bonded panels than with UF. Methylene diphenyl diisocyanate (MDI), UF, soybean protein isolate (SPI), and defatted soybean flour (SF) based adhesive systems were compared in single-layer wheat stalk particleboards [139]. The mechanical properties (MOR, MOE, and IB) of the panels prepared by 8% UF, 10% SPI, and 15% SF were identical or inferior to the ones manufactured with 4% MDI. Single-layer particleboards prepared with corn stover and 10% soy-based adhesive reached the minimum requirements for the bending properties (MOR, MOE) according to American National Standards Institute (ANSI) but not for IB [145]. Battegazzore et al. [167] evaluated the bending properties of fiberboards made with hemp fibers and particleboards with rice husks. Both panel types were bonded with corn starch (37.5% for hemp and 50% for rice husks) and were formed through a wet process. The results showed that both panel types achieved the minimum requirements for the MOR (EN 312:2003). It is well known that the mechanical properties of wood-based panels are directly related to their density [171,172]. The density of a wood-based panel usually correlates linearly with its mechanical and physical properties. One reason is the increased contact area of the particles or fibers covered by the adhesive. A higher density also allows the adhesive to spread more widely but compromises heat transfer during the pressing process [173]. The property can also be transferred to panels from NWLM and ARs [120]. Since the materials generally have a lower density than wood (Table 4), the density of the final panels can also be lower. Previous studies on panels with alternative materials reported density values ranging from 400 [124] to 780 kgm−3 [128,138], depending on the material type used. Many studies have though focused on panel densities of about 700 kgm-3 [110,125,136,174].

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Although the density of raw materials plays a significant role in defining the final density of the panels, the panel density can also be adjusted by other manufacturing parameters, i.e., compression ratio, water content, press temperature, pressing schedule, or adhesive load [175], which may increase the cost of the final product. The pressing temperature is an essential factor that influences the performance of the panels by providing the thermal energy for curing the adhesive and mechanical compression force to consolidate the mat [176]. The effect of pressing temperature varies with the density of raw material and panel type, as the higher density panels have higher maximum core temperatures due to their capability to build higher internal gas pressure [177]. Binderless particleboards prepared with oil palm trees showed higher mechanical properties by increasing the press temperature [130]. The MOE, IB, and TS of MDF panels made from corn stalks and 10% UF adhesive were improved by increasing the press temperatures from 170 to 180 ◦ C, while a negative effect was observed with further increasing the pressing temperature to 190 ◦ C. MDF panels produced with cotton stalks and 10% UF adhesive demonstrated higher bending properties and lower TS values with increasing pressing temperatures from 170 to 190 ◦ C, while opposite results were obtained for IB strength [118]. Nogueira et al. [178] tested three-layer particleboards from sugarcane bagasse and waste plastic bags. A reduction in TS and WA could be observed as the press temperature increased from 160 to 220 ◦ C. 5. Material Processing and Pretreatment In addition to the type of raw materials and manufacturing parameters, the processing and pretreatment affect the properties of the final panel. The raw materials from non-wood lignocellulosic and agricultural sources have been mainly processed mechanically and some were chemically pretreated to create evenly sized particles or to improve their performance in final panels [72,126,139]. The mechanical processing of NWLMs and ARs, such as canola stalks, with a hammermill, has often been used to prepare the raw material [122]. Ndazi et al. [179] produced single-layer particleboards with ground (8 mm sieve) and untreated rice husks and 15% of PF. The results showed that the mechanical properties of the panels decreased by grinding. Many factors can be varied in fiber production for fiberboard raw material. Zawawi et al. [180] investigated the influence of refining conditions, pressure and temperature on oil palm fruit husk’s fiber and fiberboard properties. It was found that higher pressure and a higher temperature in the refiner ultimately led to increasing MOE, MOR, IB and reduced water absorption. Overly aggressive refining conditions, however, produced shorter fiber lengths and consequently reduced the fiberboards’ physical and mechanical properties. Chemical pretreatments of raw materials are performed to optimize the bonding capability of the particles and the adhesive. Due to the increase in reactive hydroxide (OH) groups during an alkali treatment, the binding of the raw material and the adhesive improves [181,182]. The hydrophilic nature of raw materials can also reduce mechanical properties due to water absorption and a reduction of the water resistance. Acetylation can increase the hydrophobicity of a raw material, which leads to less thickness swelling and improved mechanical strength. [183]. Cotton stalks pretreated with 1–5% sodium hydroxide (NaOH) were used to prepare single-layer particleboards in combination with 10% UF adhesive [126]. The NaOH decomposes the lignin and reduces the content of hemicelluloses and extractives. In relative terms, since cellulose is more resistant to NaOH, the proportion increases. In addition, the surface roughened by the NaOH treatment offers better bonding between raw material and adhesive [184]. The results showed that the static bending properties of the panels (MOE and MOR) improved by 1% NaOH treatment, while pretreatment of the cotton stalks at 3% and 5% of NaOH resulted in the strength reduction of the panels. Treatment at a higher concentration degrades the cell wall components stronger and deforms the particle structure, resulting in a reduction in mechanical strength. Figure 4 shows NaOH treated canola stalks with rougher surface than untreated ones. Mo et al. [139] bleached wheat stalks with 3% sodium

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hypochlorite in a ratio of 1:10 for 30 min at 50 ◦ C. When bleaching lignocellulosic materials, the hydrophobic wax and inorganic components on the surface, such as silica, are removed.

Figure 4. Increase of surface roughness of canola stalks (a) for particleboard panels after treatment with sodium hydroxide (b) [184].

This increases the wettability of the stalks and the bonding ability of the entire panel with water-based adhesives [185]. The pretreatment led to a significant improvement in mechanical properties (MOE, MOR, and IB) of single-layer particleboards bonded with 8% UF adhesive. Despite the intensification of the hydrophilic nature of the stalks, TS and WA only increased slightly. Among other things, TS is closely related to the bonding quality. As this could be significantly enhanced, less water could penetrate into the panels, and the increased hydrophilicity had little effect [139]. To optimize the curing behavior of UF resin in fiberboards made with wheat stalks, Halvarsson et al. [120] pretreated the stalks with a 10% sulfuric acid solution to decrease the pH value below 6 before fiber refining. However, no significant changes in the mechanical properties of the panels were determined. Ciannamea et al. [72] compared the effects of alkaline and alkaline-oxidation pretreatments on the performance of single-layer particleboards made with rice husks using 10% of a modified soybean protein adhesive. The authors reported that the two-phase pretreatment, NaOH followed by a hydrogen peroxide treatment, resulted in higher mechanical strength and lower water resistance in comparison with panels prepared by only alkaline pre-treated rice husks and also with those with untreated husks. This is due to the reduction of lipids and waxes after the peroxide treatment, thus, allowing a better bonding of the raw material and the adhesive.

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Single-layer particleboard panels made from corn stalks and 10% soy-based resin were tested by Ren et al. [145]. The corn stalks were fermented in a process similar to the common procedure used in agriculture. Crops were stored under anaerobic conditions to inhibit undesirable microbial growth and prevent deterioration. The boards from corn stalks, fermented for 21 days, showed improved MOR and MOE as well as significantly increased IB values. TS and WA were also noticeably reduced. However, with a longer fermentation than 21 days, all mechanical and physical properties deteriorated again. The reason was assumed to be the interaction of several biological factors. The surface structure may have increased due to the hydrolysis of carbohydrates, and a micro biofilm may act as an adhesive. 6. Conclusions and Future Scopes Lignocellulosic materials from non-wood and agricultural sources represent a potential alternative choice to wood materials for wood-based panel manufacturing. These materials are derived from renewable sources and can be used as a partial or entire replacement for wood chips and fibers. One advantage of most of these materials for easier integration in industrial manufacturing processes of wood panels is their similar nature to wood materials in terms of chemical composition and fiber morphology. However, these alternative raw materials suffer from several different issues that prevent their application in industry. Some NWLMs have to be cultivated separately, and they are in direct economic competition with food agriculture and its land use. Economically practical use of grow care residues currently appears rather unlikely for wood-based panels as they result in low-performing panels. The different stalk types of harvest residues usually show shorter fiber lengths and a high extractive content, which can primarily affect the bonding quality and affinity to the adhesive in the panel. It should be noted that laboratory panels from alternative panels were tested for their use in interior furniture, and their strength performance is sufficient for load-bearing purposes. A great challenge is that the agricultural harvest is only performed seasonally, and therefore no continuous flow of raw materials can be guaranteed. Storage capacities would be required to ensure constant production with seasonal harvest residues. This would result in high costs, and the influence of long-term storage on the raw material should be examined beforehand. The bulk density of most alternative materials is low, thereby, making their handling more expensive than wood [131] and contributing to high logistic costs for their transportation [30]. In addition, it appears that there is an upper limit on the wood replacement ratio. If the proportion of an alternative raw material to wood is higher than 30% in combination with traditional UF resin, the mechanical properties deteriorate significantly. The thickness swelling and water absorption of experimental panels are also relatively high. However, the use of alternative synthetic adhesives, especially pMDI, shows that panels from 100% agricultural residues can also fulfill the requirements. A life cycle assessment (LCA) for sugarcane bagasse added in particleboard demonstrated that the agricultural residue can replace the traditional wood as a raw material due to its better environmental performance. The required mechanical properties of panels can be achieved, comparatively less land is occupied, and further material use reduces abiotic depletion and ecotoxicity [186]. The selection of new raw materials should focus on plants grown for various purposes and have an appropriate structural composition. There should be no competition for the use of the residues, their price should be low, and sufficient quantities should be available. The industrial production of wood-based panels is a process that has been optimized over decades, and a modification of the handling and processing of raw materials requires long-term optimization processes. Therefore, initially, small volume niche products should be considered as more feasible panel types for those materials. The increased production volume of fiberboards in the last few decades provides good future opportunities. Since the production of fiberboards has increased considerably (Figure 1), the high availability of hemp and flax fibers provides an advantage for using

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these materials. Compared to wood, the fibers are longer and have a higher cellulose content. The use of 100% flax fibers in panels was proven to be sufficient to produce mechanically robust panels at a laboratory scale, though further optimization is needed to improve their internal bond strength. Trunks of wood species from which the fruit is used commercially can serve as a substitute raw material. For example, large amounts of harvest residues from oil palm production can be used more effectively. Panels made from oil palm wood, which is less tied to seasonal harvest, have mostly shown adequate mechanical properties. Harvest residues are suitable as raw materials because they have an enormously high production potential. When harvesting wheat and rice, more than the same amounts of stalk residues accumulate. In addition, the tested panels achieved acceptable properties with a suitable adhesive. An advantage of the process residues is that, typically, they are already integrated into an industrial material flow system, e.g., flour production, which can reduce the logistical effort for panel manufacturing. For example, oat and hazelnut husks have similar chemical compositions. Furthermore, the panels produced can meet the minimum requirements for mechanical strength. In addition, the materials have already been removed from the ecosystem, and using them as raw material for panels adds value and enhances sustainability compared to thermal incineration only. An integration of husks for special panel types with adapted requirements should be considered. Consequently, selected raw materials from the various categories can be used in wood-based panels. The first thing to consider is their local availability and the intended use. Focus should be given to an appropriate type of adhesive and dosing. In particular, alternatives to UF, such as pMDI or PF, have proven that panels made entirely of agricultural residues can meet the requirements. It should be kept in mind that additional costs might occur for the pretreatment of some raw materials as a necessary or optional approach to improve the panel performance. The information gathered in this review provides the set of current knowledge in this research field. It identifies promising alternative raw materials and their challenges in replacing partially or entirely standard wood materials for more sustainable wood-based panel production. Finally, it should be noted that this review has its limitations. No definite conclusions can be made on ideal alternative materials from agro-industry to substitute wood in woodbased panels as there are many factors to consider. Further investigations should focus on regional availability of such materials and demand for specific product types. Then, suitable alternative materials could be identified more clearly. The search for new raw materials could also be expanded, such as to include raw materials from short-rotation plantations or plantations in general. The focus of this work has been on fiberboard and particleboard panels. The wide range of applications of non-wood lignocellulosic materials and agricultural residues in other panel types, such as wood–plastic composites, should also be considered in the future. Author Contributions: Conceptualization, N.N. and S.A.; methodology, N.N., R.H., T.W. and S.A.; investigation, N.N. and T.W.; data curation, N.N.; writing—original draft preparation, N.N.; writing— review and editing, N.N., R.H., T.W. and S.A.; supervision, S.A.; project administration, S.A.; funding acquisition, S.A. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by FORMAS, grant number 2018-01371, project title: “Agroindustry feedstocks and side streams for increasing the sustainability of wood panel production”. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Conflicts of Interest: The authors declare no conflict of interest.

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Shaikh, A.J.; Gurjar, R.M.; Patil, P.G.; Paralikar, K.M.; Varadarajan, P.V.; Balasubramanya, R.H. Particle Boards from Cotton Stalk; Central Institute for Research on Cotton Technology: Mumbai, India, 2010. 126. Yasar, S.; Icel, B. Alkali Modification of Cotton (Gossypium hirsutum L.) Stalks and its Effect on Properties of Produced Particleboards. BioResources 2016, 11, 3. [CrossRef] 127. Nemli, G.; Kalaycioglu, H.; Alp, T. Suitability of date palm (Phoenix dactyliferia) branches for particleboard production. Holz Roh Werkst. 2001, 59, 411–412. [CrossRef] 128. Guntekin, E.; Karakus, B. Feasibility of using eggplant (Solanum melongena) stalks in the production of experimental particleboard. Ind. Crops Prod. 2008, 27, 354–358. [CrossRef] 129. Dukarska, D.; Ł˛ecka, J.; Szafoni, K. Straw of white mustard (Sinapis alba) as an alternative raw material in the production of particle boards resinated with UF resin. Acta Sci. Pol. Silvarum Colendarum Ratio Ind. Lignaria 2011, 10, 1. 130. 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149. Faria, D.L.; Guimarães, I.L.; Sousa, T.B.; Protásio, T.D.P.; Mendes, L.M.; Guimarães, J.B., Jr. Technological properties of medium density particleboard produced with soybean pod husk and Eucalyptus wood. Sci. For. 2020, 48, 126. [CrossRef] 150. Borysiuk, P.; Jenczyk-Tolloczko, I.; Auriga, R.; Kordzikowski, M. Sugar beet pulp as raw material for particleboard production. Ind. Crops Prod. 2019, 141, 111829. [CrossRef] 151. Nonaka, S.; Umemura, K.; Kawai, S. Characterization of bagasse binderless particleboard manufactured in high-temperature range. J. Wood Sci. 2013, 59, 50–56. [CrossRef] 152. Xu, X.; Yao, F.; Wu, Q.; Zhou, D. The influence of wax-sizing on dimension stability and mechanical properties of bagasse particleboard. Ind. Crops Prod. 2009, 29, 80–85. [CrossRef] 153. Pirayesh, H.; Khazaeian, A.; Tabarsa, T. The potential for using walnut (Juglans regia L.) shell as a raw material for wood-based particleboard manufacturing. Compos. Part B Eng. 2012, 43, 3276–3280. [CrossRef] 154. Batiancela, M.A.; Acda, M.N.; Cabangon, R.J. Particleboard from waste tea leaves and wood particles. J. Compos. Mater. 2014, 48, 911–916. [CrossRef] 155. Fiorelli, J.; Bueno, S.B.; Cabral, M.R. Assessment of multilayer particleboards produced with green coconut and sugarcane bagasse fibers. Constr. Build. Mater. 2019, 205, 1–9. [CrossRef] 156. Klímek, P.; Wimmer, R.; Meinlschmidt, P.; Kúdela, J. Utilizing Miscanthus stalks as raw material for particleboards. Ind. Crops Prod. 2018, 111, 270–276. [CrossRef] 157. Nicolao, E.S.; Leiva, P.; Chalapud, M.C.; Ruseckaite, R.A.; Ciannamea, E.M.; Stefani, P.M. Flexural and tensile properties of biobased rice husk-jute-soybean protein particleboards. J. Build. Eng. 2020, 30, 101261. [CrossRef] 158. Grigoriou, A.H.; Ntalos, G.A. The potential use of Ricinus communis L. (Castor) stalks as a lignocellulosic resource for particleboards. Ind. Crop. Prod. 2001, 13, 209–218. [CrossRef] 159. Iswanto, A.H.; Azhar, I.; Susilowati, A.; Supriyanto; Ginting, A. Effect of Wood Shaving to Improve the Properties of Particleboard Made from Sorghum Bagasse. Int. J. Mater. Sci. Appl. 2016, 5, 113. [CrossRef] 160. Khalil, H.P.S.A.; Fazita, M.R.N.; Bhat, A.H.; Jawaid, M.; Fuad, N.A.N. Development and material properties of new hybrid plywood from oil palm biomass. Mater. Des. 2010, 31, 417–424. [CrossRef] 161. Varanda, L.D.; Nascimento, M.F.D.; Christoforo, A.L.; Silva, D.A.L.; Lahr, F.A.R. Oat hulls as addition to high density panels production. Mater. Res. 2013, 16, 1355–1361. [CrossRef] 162. Guler, C.; Buyuksari, U. Effect of production parameters on physical and mechanical properties of particleboards made from peanut (Arachis hypogaea L.) hull. Bioresources 2011, 6, 5027–5036. 163. Papadopoulos, A.N.; Hill, C.A.S.; Gkaraveli, A.; Ntalos, G.A.; Karastergiou, S.P. Bamboo chips (Bambusa vulgaris) as an alternative lignocellulosic raw material for particleboard manufacture. 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Thermal insulation and physical properties of particleboards from pineapple leaves. Int. J. Phys. Sci. 2011, 6, 4528–4532. 169. Pan, Z.; Cathcart, A.; Wang, D. Properties of particleboard bond with rice bran and polymeric methylene diphenyl diisocyanate adhesives. Ind. Crops Prod. 2006, 23, 40–45. [CrossRef] 170. Hussein, Z.; Ashour, T.; Khalil, M.; Bahnasawy, A.; Ali, S.; Hollands, J.; Korjenic, A. Rice Straw and Flax Fiber Particleboards as a Product of Agricultural Waste: An Evaluation of Technical Properties. Appl. Sci. 2019, 9, 3878. [CrossRef] 171. Canadido, L.S.; Saito, F.; Suzuki, S. Influence of Strand Thickness and Board Density on the Orthotropic Properties of Oriented Strandboard. Mokuzai Gakkaishi 1990, 36, 632–636. 172. Sumardi, I.; Ono, K.; Suzuki, S. Effect of board density and layer structure on the mechanical properties of bamboo oriented strandboard. J. Wood Sci. 2007, 53, 510–515. [CrossRef] 173. Cai, Z.Y.; Wu, Q.L.; Lee, J.N.; Hiziroglu, S. 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PAPERmaking! FROM THE PUBLISHERS OF PAPER TECHNOLOGY TE INTERNATIONAL®

Volume 8, Number 2, 2022

Energy Recovery from Waste Paper and Deinking Sludge to Support the Demand of the Paper Industry: A Numerical Analysis SIMONA DI FRAIA & M. RAKIB UDDIN. The recovery of fibres from waste paper (WP) and deinking sludge (DIS) reduces the stress on nature compared to the collection of virgin pulp for paper production. Moreover, if not recycled, WP and DIS are mainly landfilled and incinerated, being thus responsible for the release of greenhouse gases (GHGs) into the atmosphere. In this context, energy recovery from WP and DIS would contribute to increasing energy independence and improving waste management in the pulp industry. From a broader perspective, it would increase renewable energy generation, supporting the paper industry in reducing fossil fuel consumption and GHGs emissions, in line with the goals of the European Union (EU) Green Deal 2021. For these reasons, in the present study, the combined heat and power generation potentiality of WP–DIS blends through gasification in combination with an internal combustion engine is numerically assessed for the first time. The air gasification process is simulated by applying a restricted chemical equilibrium approach to identify the optimum operating temperature (850°C) and equivalence ratio (0.2). Electrical and thermal energy generation potentiality, considering WP and DIS production in the EU in 2019, is estimated to be in the ranges of 32,950–35,700 GWh and 52,190–56,100 GWh, respectively. Thus, it can support between 25 and 28% of the electrical and 44–48% of the thermal energy demand of the paper manufacturing sector, reducing the CO2 emission in the range of 24.8–28.9 Gt. Contact information: Department of Engineering, University of Naples “Parthenope”, 80143 Napoli, Italy. Sustainability 2022, 14, 4669. https://doi.org/10.3390/su14084669 Creative Commons Attribution 4.0 International License

The Paper Industry Technical Association (PITA) is an independent organisation which operates for the general benefit of its members – both individual and corporate – dedicated to promoting and improving the technical and scientific knowledge of those working in the UK pulp and paper industry. Formed in 1960, it serves the Industry, both manufacturers and suppliers, by providing a forum for members to meet and network; it organises visits, conferences and training seminars that cover all aspects of papermaking science. It also publishes the prestigious journal Paper Technology International® and the PITA Annual Review, both sent free to members, and a range of other technical publications which include conference proceedings and the acclaimed Essential Guide to Aqueous Coating.

Page 1 of 19

Article 8 – Energy Recovery

sustainability Article

Energy Recovery from Waste Paper and Deinking Sludge to Support the Demand of the Paper Industry: A Numerical Analysis Simona Di Fraia

and M. Rakib Uddin * Department of Engineering, University of Naples “Parthenope”, 80143 Napoli, Italy; simona.difraia@uniparthenope.it * Correspondence: mohammadrakib.uddin001@studenti.uniparthenope.it

Citation: Di Fraia, S.; Uddin, M.R.

Abstract: The recovery of fibres from waste paper (WP) and deinking sludge (DIS) reduces the stress on nature compared to the collection of virgin pulp for paper production. Moreover, if not recycled, WP and DIS are mainly landfilled and incinerated, being thus responsible for the release of greenhouse gases (GHGs) into the atmosphere. In this context, energy recovery from WP and DIS would contribute to increasing energy independence and improving waste management in the pulp industry. From a broader perspective, it would increase renewable energy generation, supporting the paper industry in reducing fossil fuel consumption and GHGs emissions, in line with the goals of the European Union (EU) Green Deal 2021. For these reasons, in the present study, the combined heat and power generation potentiality of WP–DIS blends through gasification in combination with an internal combustion engine is numerically assessed for the first time. The air gasification process is simulated by applying a restricted chemical equilibrium approach to identify the optimum operating temperature (850 ◦ C) and equivalence ratio (0.2). Electrical and thermal energy generation potentiality, considering WP and DIS production in the EU in 2019, is estimated to be in the ranges of 32,950–35,700 GWh and 52,190–56,100 GWh, respectively. Thus, it can support between 25 and 28% of the electrical and 44–48% of the thermal energy demand of the paper manufacturing sector, reducing the CO2 emission in the range of 24.8–28.9 Gt.

Energy Recovery from Waste Paper and Deinking Sludge to Support the Demand of the Paper Industry:

Keywords: waste paper; deinking sludge; pellet; gasiﬁcation; restricted chemical equilibrium model; syngas; sensitivity analysis; optimization; combined heat and power

A Numerical Analysis. Sustainability 2022, 14, 4669. https://doi.org/ 10.3390/su14084669 Academic Editor: Agostina Chiavola Received: 18 March 2022 Accepted: 12 April 2022 Published: 13 April 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional afﬁliations.

1. Introduction The pulp and paper industry presents a significant energy demand, mainly satisfied by fossil fuels [1,2], which cause high greenhouse gases (GHGs) and pollutant emissions [3]. Moreover, the pulp and paper industry generates a considerable quantity of waste as a small fraction of starting biomass is transformed into the final products of paper [1]. Thus, this sector could increase renewable energy production by recovering its waste, contributing to the sustainable energy transition. Another way to increase the eco-efficiency of this sector is recycling used paper to extract the pulp. Indeed, such a practice is globally increasing to reduce the stress on nature to collect virgin pulp from trees and the environmental pollution caused by landfilling or incinerating the used paper [4–6]. It is estimated that pulp collection from recycled used paper could save on average 8.2 million trees annually [7]. Cellulosic fibre length, as well as strength, decreases during the collection of pulp, requiring its blending with virgin fibres for paper production. However, used paper can be recycled three to eight times to collect cellulosic fibres, then the used paper has to be discarded as solid waste [8,9]. Based on the data presented in the CEPI-2020 (Confederation of European Paper Industries) report, in 2019, world average used paper recycling was 58.6% with the highest rate in the European Union (EU) (72.5%), followed by North America (65.7%), Asia (53.9%), Latin America (47.2%), and Africa (35.2%) [4]. During the recycling of used paper to collect the pulp, waste paper (WP) and deinking sludge (DIS) are generated as waste products. WP consists of fibre lumps, staples, sand,

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glass, and plastics. A wide variety of constituents is present in DIS, which are short fibres, chemicals used as coatings, and fillers employed during paper manufacturing from virgin or recycled pulp to improve the paper quality, such as kaolin (Al2 O3 , SiO2 ), talc (Mg3 Si4 O10 (OH)2 ), calcium carbonate (CaCO3 ), clays, ink particles, extractive substances, and deinking additives applied for used paper recycling (e.g., Na2 SiO3 , NaOH, H2 O2 , CaCl2 , fatty acid, and fatty acid soap) [10,11]. The lower heating value (LHV) of WP and DIS fluctuates from 15.0 to 26.61 MJ/kg as dry solid (DS) and 4.0 to 7.57 MJ/kg as DS, respectively [6,11]. In 2019, new paper and board production in the EU was 75.8 Mt of which 57.5 Mt were recycled generating 24.3 Mt of WP [12]. The quantity of DIS generated during the recycling of used paper is between 20% (for newsprint) and 40% (for tissue paper) of WP and is expected to reach between 48 and 86%, respectively, in the next 50 years [13,14]. In 2019, DIS production in the EU was in the range of 4.86 to 9.72 Mt as DS. The most common practices for disposal of the WP and DIS generated during used paper recycling are landfilling and incineration, which are responsible for the release of GHGs of CH4 , NO, N2 O, CO2 , CO, SO2 , HCl, mercury, dioxins, furan, polychlorinated biphenyls, and polycyclic aromatic hydrocarbons to the environment [6,15–19]. However, many studies have considered energy recovery from municipal solid waste (MSW), whereas the potential benefits of WP and DIS appear to be underestimated [20] even though their valorisation could contribute to decreasing the energy consumption from fossil sources in the paper manufacturing sector. This, together with the avoided waste disposal, would reduce the GHGs emissions of such a sector. Thermal treatment appears to be very promising compared to the biological method for energy recovery from WP and DIS due to:

• •

the higher conversion rate of carbonaceous content to energy product (more than 80% for thermal treatments whereas in the range of 30–60% for biological methods); the lower processing time (thermal treatments require 30 to 70 min, whereas biological treatment needs between seven and 105 days) [21–23].

Considering the more common thermal treatments used for energy recovery from biomass, gasiﬁcation is characterized by:

• • •

a high carbon conversion efficiency (CCE) (from 60 to 80%) and cold gas efficiency (CGE) (between 60 and 90%); that migration of heavy or toxic metals from fed materials to the product phase is negligible; the possibility to use the gaseous product as a fuel in internal combustion engines (ICE) or gas turbines or microgas turbines without any modification [17,24–30].

Gasification is a thermal treatment that converts the energy content of a biomass to a gaseous phase at a temperature higher than 700 ◦ C and atmospheric pressure in oxygendeficient conditions. The gaseous product formed during biomass gasification consists of H2 , CH4 , CO, CO2 , and other lighter hydrocarbons with tar content and is commonly designated as syngas. Due to the easier availability and low cost, the air is frequently used as a gasifying agent to supply oxygen in the gasification process. However, based on the specification of syngas properties, other gasifying agents like pure O2 , steam, CO2 , a mixture of air–steam, O2 –steam, and CO2 –steam, may be also used. LHV of syngas varies between 3.0 and 9.73 MJ/Nm3 depending on the properties of biomass used for the gasification and operating conditions [22,24,25,31,32]. Syngas composition and LHV as well as the performance of the conversion process (CCE and CGE) during air-gasification of biomass depends on the quality of fed materials and operating parameters, such as temperature and equivalence ratio (ER) [24,25]. For the sake of completeness, ER is the ratio between the actual air to biomass weight fed to the gasifier to the stoichiometric air to biomass weight required for complete combustion [33]. The available studies on the gasification of WP and DIS are limited [11,34]. Air gasification of WP and DIS blends (95% WP and 5% DIS by weight) in a pilot-scale circulating

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fluidized bed reactor (FBR) are analysed by Rivera et al. (2016) [11]. They obtain a syngas with a tar concentration of 11.44 g/Nm3 and an LHV of 5 MJ/Nm3 , considering a process temperature of 850 ◦ C and an ER of 0.3. An experimental campaign on co-gasification of WP–DIS pellets (consisting of 80% reject fibres and 20% mixed plastic by weight) with wood chips was carried out by Ouadi et al. (2013) [34]. Through 12 experimental tests, the authors identify optimum conditions: a blending ratio of WP–DIS pellets and wood chips of 80:20 by weight, a temperature of 1000 ◦ C, and an ER of 0.22. The generated syngas presents a tar concentration of 5.8 g/Nm3 and an LHV of 7.3 MJ/Nm3 . Identifying optimum operating parameters for biomass gasification through experimental campaigns is time-consuming and costly as several tests, in the range of 10 to 23, have to be performed [33–38]. Using computer-aided simulations of the biomass gasification process based on experimental outcomes can significantly reduce the time and cost of predicting the optimum operating parameters and process performances. As an example, Aspen Plus software allows identifying the conditions to improve the plant design, process limitations, or even failure conditions, which can improve the profit of an existing or proposed production plant [39]. The analysis of the literature highlights that no works are available on numerical modelling of gasification of WP and DIS except for an article where a mixture of used paper discarded as MSW is analysed [40]. In such a paper, Safarian et al. (2019) [40] develop a model to simulate the gasification of mixed-used paper and validate it by considering experimental outcomes related to the gasification of wood presented in the literature, founding an acceptable agreement. The authors identify the optimum operating temperature (1000 ◦ C) and ER (0.3) to maximize the concentration of H2 and CO of syngas, which is characterized by an LHV of 4.62 MJ/Nm3 . Regarding the process performance, they observe a CGE of 70.6%. Extending the literature review on biomass gasification highlights the significant interest of the scientific community in this topic. However, focusing on numerical simulation to assess the CHP generation potentiality of biomass through gasification integrated with an ICE, the available literature is limited [41–43]. Energy recovery from sewage sludge (SS) through gasification integrated with an ICE was assessed by Di Fraia et al. (2021) [41]. The authors develop a numerical model through the software Aspen Plus estimating the electrical (29.2%), thermal (45.92%), and cogeneration efficiencies (53.1%). The same biomass was analysed by Brachi et al. (2022) [42], which estimate electrical (19.3%) and thermal (48.7%) efficiencies for a similar energy recovery configuration. An integrated system composed of a gasifier and an ICE was investigated also by Villarini et al. (2019) [43], taking into account the energy valorisation of hazelnut shell and olive pruning, estimating an electrical efficiency of 30% and 26%, respectively, and a cogeneration efficiency of 64% and 41%. Based on average global pulp and paper industries’ energy demand data, the electrical and thermal energy required to produce paper from wood is estimated as 1.68 MWh/ton and 1.55 MWh/ton, respectively [1,44]. Energy recovery from WP and DIS through a gasifier integrated with an ICE could supply a fraction of the electrical and thermal energy demand for the paper production process. Therefore, in the present study, a numerical model is developed to assess the CHP generation potentiality of WP–DIS blends through gasification in combination with an ICE using Aspen Plus V8.8 software (Bedford, MA, USA), for the first time. The gasification model is developed by applying a restricted chemical equilibrium approach [24,41,42,45]. The model is calibrated against experimental data available in the literature related to the gasification of WP–DIS blends [11] and validated by considering the outcomes of an experimental campaign on bamboo chips gasification [46]. The developed model is used to predict the optimum operating parameters for gasification of WP–DIS pellets (made by mixing 85 wt% WP and 15 wt% DIS) by analysing the effect of process temperature and ER on syngas composition, process performances, and net power obtained from gasification products. Finally, electrical and thermal energy that could be generated by considering the proposed system to treat WP and DIS produced in the EU in

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2019 is assessed, together with the achievable reduction of CO2 emissions compared to the use of conventional fuels. Therefore, the present article presents a sustainable and energy-efﬁcient solution for the paper and pulp industry. Indeed, CHP from WP and DIS may contribute to: -

reduce the waste landﬁlling; increase the energy dependence of the paper and pulp industry; at the global level, increase renewable energy generation and reduce GHGs.

The paper is organized as follows. The numerical model developed together with modelling assumptions is described in Section 2. The input parameters of the analysed case study and the main results of the study, including those of the sensitivity analyses, are illustrated in Section 3. Finally, the main findings and future developments of the work are presented in Section 4. 2. Materials and Methods Energy recovery as CHP from WP and DIS generated during recycling of pulp from used paper through gasification integrated with an ICE is numerically analysed. The numerical model proposed in this work is calibrated against experimental data on syngas generation from WP–DIS pellets consisting of 95 wt% WP and 5 wt% DIS in a pilot-scale FBR, characterized by 300 mm reactor diameter, 8764 mm height, and recirculation pipe diameter 127 mm where gasifying agent air completes the fluidization of the bed [11]. After calibration, the model is validated against the experimental outcomes of bamboo chips gasification in a laboratory scale fixed bed gasifier with 100 mm diameter and 1400 mm height [47]. Two distinct WP–DIS pellets are considered in the analysis, from now on M1 (95% WP and 5% DIS by weight) and M2 (85% WP and 15% DIS by weight). The detailed experimental procedure for WP and DIS collection, sample pellets preparation, and characterization as well as details on the experimental campaign, are available in the literature [11]. The numerical model to simulate the conversion of WP–DIS blends to CHP is developed in Aspen Plus V8.8. The software library does not have a unique block for either the gasification process or the ICE. Thus, gasification is modelled considering the processes from which it is composed: drying, pyrolysis, gasification, and partial combustion to transform the energy content present in the WP–DIS pellet to syngas [22,48]. As commonly proposed in the available literature, the ICE is simulated by considering four consecutive blocks, a compressor followed by a chemical reactor to complete the combustion at constant volume, a turbine, and finally, a heat exchanger for cooling at constant volume [41,43,49,50]. The process flowsheet to simulate the CHP generation from WP–DIS pellets is presented in Figure 1.

Figure 1. Flowsheet related to the simulation on CHP generation from WP–DIS pellets.

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The first two processes, drying, and pyrolysis of the fed stream (WP–DIS), are completed in an RYield reactor (DECOMP). Such a block decomposes the non-conventional stream of WP–DIS pellet to conventional (C, H2 , N2 , Cl2 , F2 , S, and H2 O) and nonconventional (ash) components, based on ultimate elemental analysis implemented through a FORTRAN subroutine in a calculator. The temperature of the DECOMP block is set at 400 ◦ C, which is indicated in the pertinent literature as the optimum temperature for pyrolysis of biomass [31]. The product exiting from DECOMP block (DECMPSS) is separated in a separator (SEP) into two sub-streams: a fraction of carbon that participates in gasification reactions (GASFED) and the remaining that forms char and ash (C-CHAR). The gasification fed stream (GASFED) is mixed in a mixer (MIXERG) with air (HOTAIR) preheated in a heat exchanger (AIRHTR) to reach the gasification temperature. RGibbs reactor (GASIFIER) is chosen to simulate the remaining two processes (gasification and combustion) involved in the gasification of WP–DIS pellets by minimizing Gibbs free energy. Each gasification reaction is restricted by assigning a specific temperature. This allows for reducing the deviation between predicted results and experimental values in terms of syngas composition and LHV [41,51]. The product stream (RAWSYNG) generated from WP–DIS pellets gasification is mixed with char and ash in a mixer (MIXER) to generate a unique flow (MIXFLOW). The char and ash temperature are increased in a heat exchanger (ASCHTR) to equalize that of syngas. Syngas is then cleaned to separate ash and char in an SSplit block (CYCLONE) and cooled down to the ambient temperature of 30 ◦ C in a heat exchanger (COOLER) to meet the engine specifications [43]. The simulation of the ICE is completed by connecting three consecutive blocks of the Aspen Plus library [41,43,49,50]:

• • • •

a compressor (COMPR) that models the pressure increase of the incoming air through an isentropic compression; an RGibbs reactor (BURN) that simulates the conversion of syngas internal energy to thermal energy through combustion at constant volume by minimizing Gibbs free energy; a turbine (TURB) that converts the thermal energy of combustion exhausts (CMBSTGAS) to kinetic energy through an isentropic expansion; a heat exchanger (UTIL) where thermal energy present in the stream exiting the turbine (EXITGAS) is extracted by cooling the exhausts to usable temperature (80 ◦ C) [41]. Such thermal energy may be employed in the paper production process or for the district or ofﬁce heating purposes based on the productivity of the plant.

2.1. Modelling Assumptions The gasification model is developed by applying a non-stoichiometric equilibrium approach based on the minimization of Gibbs free energy as it gives a better agreement with the experimental outcomes than a stoichiometric and kinetic approach, in terms of syngas composition and process performance. Indeed, applying this approach reduces the deviation between numerical and experimental results, significantly increasing the accuracy of the model [52]. The thermodynamic properties of all the conventional components are estimated through the Peng–Robinson equation of state with Boston–Mathias alpha function (PR-BM) [48,53]. Enthalpy and density of non-conventional components (WP– DIS pellets and Ash) are evaluated by Aspen Plus built-in coal models HCOALGEN and DCOALIGT, respectively. Several simplifying assumptions are considered to avoid the complexity in the gasification and cogeneration model. Assumptions for gasification [46,52–54]:

• • •

model is zero-dimensional; gasiﬁcation reactions are completed with a steady-state condition; pyrolysis is completed instantaneously;

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• • • • • • • • •

•

for a specific zone, the temperature inside the reactor is uniform in all directions (radially and axially) ensuring the isothermal condition; hydrodynamic characteristics of the reactor are neglected; all the reactions reach an equilibrium condition; reaction pathways to form intermediate products are not considered; ash, sulphur, nitrogen, and halogen present in WP–DIS pellet are considered nonreactive; char is composed of 100% carbon; gaseous components show ideal behaviour; gasification is completed at ambient pressure; tar formation is neglected as commonly considered in numerical modelling of biomass gasification [24,25,41,45]. Indeed, the present analysis aims at evaluating the CHP generation potentiality of WP–DIS pellets, and this simplifying assumption does not significantly affect the goal; among the several reactions that occur during biomass gasification, only the six reactions presented in Table 1 with their heat of the reaction [55,56] are considered.

Table 1. List of chemical reactions considered for the development of air-gasiﬁcation of WP–DIS pellets model with their heat of reaction [55,56]. Reaction ID

Reaction Formula

Reaction Name

Δ (Heat of Reaction), KJ/mol

R1 R2 R3 R4 R5 R6

C + H2 O → H2 + CO C + O2 → CO2 C + 2H2 → CH4 CO + H2 O → H2 + CO2 C2 H4 + 3O2 → 2H2 O + 2CO2 2H2 + O2 → 2H2 O

Water gas Carbon combustion Methanation Water gas shift Ethene combustion Hydrogen combustion

+131.0 −393.0 −74.0 −41.0 −964.0 −242.0

Assumptions for the cogeneration model simulation [57]:

• • •

cogeneration process is steady-state; potential and kinetic energy changes throughout the system are neglected; pressure drops and heat loss from the combustion chamber of the ICE with surroundings are neglected.

2.2. Gasification Model Calibration During gasification modelling, a unique temperature is set for all the reactions mentioned in Table 1. Each reaction has a different equilibrium constant that highly depends on the temperature [58]. Therefore, all the gasification reactions do not reach an equilibrium condition for a specific temperature. Consequently, by using this approach, results predicted in terms of syngas composition and process performances (CCE and CGE) would significantly deviate from the experimental outcomes, reducing the reliability of the model [24]. According to the available literature, the deviation should be lower than ±20% to claim the developed model represents the experimental process [24,41,56]. This condition can be achieved by restricting the equilibrium position of the individual gasification reactions to a specific temperature. Such a temperature can be identified by calibrating the model through experimental results. Consequently, the equilibrium temperature for each reaction differs from the gasification temperature and is calculated using Equation (1): TEqlm = TGas f + ΔTAppr ,

(1)

where, TEqlm is the equilibrium temperature, TGas f is the gasification temperature, and ΔTAppr is a specific value of temperature to which the gasification is restricted.

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The difference between the results in terms of individual syngas composition, LHV of syngas, CCE, and CGE predicted through the developed model and experimental outcomes generate a deviation, which is calculated through Equation (2): Deviation (%) =

Simulation result − Experimental result ·100, Experimental result

(2)

The average deviation of the overall syngas composition is calculated considering the deviations of the individual components according to Equation (3): Average Deviation (%) =

1 n

∑i=1 | Deviation|,

(3)

where, n represents the number of syngas components considered during gasiﬁcation model calibration and validation. 2.3. Assessment of Process Performance Process performances of WP–DIS pellets conversion to syngas through gasiﬁcation . are evaluated by assessing syngas LHV, CGE, and CCE as well as net power ( Pnet ) available from the conversion process. The LHV of syngas depends on its composition and is calculated using Equation (4) [59]: LHVsyng (MJ/Nm3 ) = 0.108yH2 + 0.126yCO + 0.358yCH4 ,

(4)

where, yH2 , yCO , and yCH4 denote the volume fraction of H2 , CO, and CH4 , respectively, present in syngas. The ratio between the energy flow rate of the syngas and that of the material fed to the gasifier is defined as CGE and is evaluated according to Equation (5) [23]: .

CGE (%) =

LHVsyng ·vsyng .

LHVf ed ·m f ed

·100,

(5)

where, LHVsyng and LHVf ed represent the LHV of syngas in MJ/Nm3 and WP–DIS pellet . . in MJ/kg, respectively, whereas vsyng and m f ed stand for the volumetric flow rate of syngas (Nm3 /h) and mass flow rate of WP–DIS pellet (kg/h). The ratio of carbon flow rate by weight between the product streams (syngas) and reactant (WP–DIS pellet) is the CCE that is assessed by Equation (6) [23]: .

vsyng 12 CCE(%) = · . ·100, 22.4 m f ed ·C%· ∑5i=1 ni ·yi

(6)

where, i represents the carbon-containing constituent present in the syngas, C% is the weight fraction of carbon present in the WP–DIS pellet, ni is the carbon number, and yi is the fraction of i compound by volume in syngas (i.e.: C1 –C5 ). The difference between primary power available from the generated syngas and that . required to complete air preheating is deﬁned Pnet and is stated in Equation (7): .

Pnet = Psyng − P prht , .

(7) .

where, Psyng is the primary power obtained from syngas and P prht denotes the power required to complete air preheating.

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The performance of the ICE is assessed by electrical (ηel ), thermal (ηth ), and system (ηsys ) efﬁciencies, that are calculated according to Equations (8) to (10), respectively. .

N TURB ηel (%) = ·100, . LHVSyng ·vsyng

(8)

Q EX ηth (%) = ·100, . LHVSyng ·vsyng .

ηsys (%) =

N TURB + Q EXCH + Q EX .

(9)

LHVf ed ·m f ed + Q I NPUT

·100,

(10) .

where, N TURB denotes the effective power obtained from the ICE, Q EXCH represents the thermal power accessible during the cooling of syngas before entering the ICE system, . Q EX is the thermal power that can be recovered by cooling the turbine exhausts to usable . temperature (80 ◦ C) [41], and Q I NPUT is the rate of power associated with RGibbs reactor including air preheating to complete the gasification process. 3. Results and Discussion 3.1. Input Parameters Data related to the operation of the gasifier and the ICE are collected from the literature. The characteristics of the two different WP–DIS pellets (M1 and M2) used in the present research with LHV are illustrated in Table 2, whereas the operating conditions of airgasification of M1 with corresponding syngas properties are shown in Tables 3 and 4. The gasification model is calibrated by applying the operating conditions and syngas composition mentioned in Tables 3 and 4 for the gasification of M1. Since data on the gasification of M2 is not available in the literature, the model is validated against the experimental results related to the gasification of bamboo chips [47]. Indeed, such biomass presents a composition, in terms of ultimate elemental analysis, similar to M1 as highlighted in Table 2. The operating conditions and syngas composition of bamboo chips gasification, used for model validation, are presented in Tables 3 and 4. Table 2. Composition of WP–DIS pellets (M1 and M2) and bamboo chips with LHV [11,47]. Properties

M1d.b.

M2d.b.

Bamboo Chipd.b.

Proximate analysis (wt.%)

Moisture content Volatile matter Fixed carbon Ash content

3.2 75.2 11.7 13.1

2.9 71.4 10.2 18.4

7.14 80.06 18.33 1.61

Ultimate element alanalysis (wt.%)

C H2 N2 S Cl2 O2

55.6 7.6 0.35 0.07 1.56 21.72

50.9 6.9 0.39 0.08 1.55 21.78

44.83 5.96 0.35 0.15 47.1

LHV (MJ/kg)

24.84

22.42

18.32

d.b. = Dry Basis.

CHP generation through the ICE is simulated based on available literature data, presented in Table 5 [41,43,53].

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Table 3. Operating parameters applied for the gasiﬁcation of M1 and bamboo chips [11,47]. Operating Parameters, Units

Test conditions Temperature, ◦ C Pressure, bar ER, (-) Fed ﬂow rate, kg/h Air ﬂow rate, kg/h

850 1.0 0.30 1.0 2.45

Bamboo Chips I

III

0.40

0.50

2.21

2.77

800 1.0 0.20

0.30 1.0

1.11

1.66

Table 4. Syngas properties for gasiﬁcation of M1 and bamboo chips [11,47]. Syngas Composition

M1 *

Test conditions CO H2 CO2 CH4 C 2 H4 Syngas LHV, (MJ/Nm3 )

6.9 3.8 11.8 4.7 2.9 5.0

Bamboo Chips ** I 24.13 16.96 56.30 3.26 5.98

II 18.70 11.74 68.70 1.74 4.21

III 11.30 7.17 81.30 1.30 2.65

IV 6.96 3.48 88.70 0.85 1.48

* % vol. (Dry basis), ** % mol (Dry and N2 free basis).

Table 5. Operating conditions and performance parameters employed for ICE system simulation [41,43,53]. Operating Parameters, Units

Value ◦C

Temperature of the syngas entering the ICE, Temperature of the air entering the compressor, ◦ C Stoichiometric air ratio used for syngas combustion, (-) Pressure of the air exiting the compressor and entering the combustion chamber, bar Isentropic compression and expansion coefﬁcient, (%) Pressure of the fume exiting the turbine, bar Temperature of the turbine exhausts, ◦ C

30.0 20.0 3.0 20.0 90.0 1.0 80.0

3.2. Gasification Model Development The limit of temperatures estimated to restrict the equilibrium of each gasification reaction together with the fraction of carbon that participates in the reactions to form syngas is illustrated in Table 6. Table 6. Predicted limit of temperature to restrict the equilibrium of gasification reactions and fraction of carbon participating in the reactions. Reaction ID.

ΔTAppr (◦ C)

R1 R2 R3 R4 R5 R6 Fraction of carbon that participates in gasiﬁcation reactions (%)

−311.83 −62.62 −520.73 238.51 43.94 108.24 77.98

The comparison between syngas composition and LHV predicted through the developed model and the experimental outcomes available in the literature [11,47] is depicted in Figure 2 for the calibration step and in Figure 3 for the validation.

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Syngas composition (vol.%), Dry basis

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16 12 8 4 0 -4 CO (vol.%)

ƀȱǻ ǯƖǼ ƀȱǻ ǯƖǼ Ƃȱǻ ǯƖǼ ƀ Ƃȱǻ ǯƖǼ

LHV (MJ/Nm3)

Syngas properties

Experimental Result

Simulation Result

Deviation (%)

Average Deviation (%)

Figure 2. Comparison between simulation results predicted during gasiﬁcation model calibration and experimental outcomes with the corresponding deviation. 6

80 4

60 40

Syngas LHV (MJ/Nm3)

Syngas composition (mol%), ¢ȱ ȱ ƀȱ ȱ

100

20 0

0.2

0.3

ER (-)

0.4

0.5

ƀǱȱ ¡

ƀǱȱ

CO: Experiment

CO: Simulation

ƀǱȱ ¡

ƀǱȱ

ƂǱȱ ¡

ƂǱȱ

LHV: Experiment

LHV: Simulation

Figure 3. Difference between the predicted syngas composition and LHV and the experimental data during model validation.

It can be observed that the developed model has a good agreement with the experimental analysis as the average deviation of the syngas composition is 3.46% during model calibration and 11.31% during validation, which satisﬁes the limit (lower than ±20%) suggested in the literature [24,41,56]. The maximum deviation is obtained for the constituents with the lowest concentration in syngas (C2 H4 during calibration and CH4 for validation). However, the average deviation obtained in the present simulation is substantially lower compared to that of other similar studies that are in the range of 13.70–28.37% [24,41,49,60]. The estimated energy content of the syngas is 1.91%, lower than the experimental one during calibration, due to the over-prediction of CO2 , which does not directly affect the LHV but creates a dilution effect [54,61,62]. Syngas LHV is over- or underpredicted due to CO2 under- or overprediction during model validation. After validation, the developed model is used to predict the optimum operating conditions of temperature and ER for the conversion of the M2 pellet to syngas through a sensitivity analysis.

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3.3. Sensitivity Analysis To optimize the process, the effect of gasification temperature and ER on composition, . LHV, and density of syngas, CGE, CCE, and Pnet obtained from thermal treatment of the M2 pellet is analysed by setting a fed flow rate of 1.0 kg/h. 3.3.1. Effect of Temperature Gasification temperature is varied in the range of 700 to 1000 ◦ C at a fixed ER of 0.3 to estimate its optimum value. The fluctuation of syngas composition with gasification temperature is presented in . Figure 4. The variation of LHV and density of syngas, CGE, CCE and Pnet is presented in Figure 5.

Syngas composition (vol.%), ǻ ¢ȱ ȱ ƀȱ ȱ Ǽ

0 700

800

900

1000

Temperature (°C)

ƀ Ƃ

65 0.3 55

0.2 700 CGE

800 900 Temperature (°C) CCE

1000

Syngas density

(a)

5.5

4.8

4.5

4.6

Net Power (kW)

0.4

Syngas LHV (MJ/Nm3)

CGE and CCE (%)

Syngas density (kg/Nm3)

Figure 4. Effect of gasiﬁcation temperature on syngas composition.

4.4 700

800 900 1000 Temperature (°C) LHV

Net Power

(b)

Figure 5. Effect of gasiﬁcation temperature on CGE, CCE, and syngas density (a) and syngas LHV and net power from gasiﬁcation products (b).

The concentration of CO and H2 increases continuously with temperature, whereas that of CO2 , CH4 , and C2 H4 shows an opposite trend due to the alteration of exothermic and endothermic reaction rates with temperature [49,51,63]. Endothermic reactions (water–gas and water–gas shift reactions in this case) move in the forward direction with temperature,

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being responsible for the increment of CO and H2 concentration in syngas. Conversely, exothermic reactions (methanation, ethene formation, and all the combustion reactions) move in the opposite direction with temperature and are responsible for the reduction of CO2 , CH4 , and C2 H4 concentration in syngas [37,64]. CGE and CCE increase continuously with temperature whereas syngas density decreases. The energy flow rate exiting from the gasifier associated with the syngas increases with temperature due to the raise of CO and H2 concentration in syngas, as shown in Figure 4. As a consequence, the CGE increases as well [23,59]. The raising of carbon fraction in the syngas through CO concentration with temperature is higher compared to the cumulative decrement of the other three carbon-containing species (CO2 , CH4 , and C2 H4 ). Additionally, the syngas flow rate increases with temperature, and consequently CCE raises [23]. The kinetic energy of molecules present in syngas increases with temperature decreasing its density [65]. . The gasification temperature similarly affects syngas LHV and Pnet . Syngas LHV increases continuously with temperature due to the raise of CO and H2 concentration [22,59,66]. Compared to M1 pellets, considering the same operating conditions, the syngas LHV is slightly lower due to the higher ash content. The primary power of the product stream increases with temperature as syngas LHV raises. However, the thermal power required for air preheating increases simultaneously with temperature. For this reason, the net power available from the gasification products increases continuously with temperature up to 850 ◦ C and afterward, it decreases as the energy required for air preheating (to raise the gasification temperature from 850 to 900 ◦ C and afterward) is higher than the energy gain. Based on the current analysis, 850 ◦ C appears to be the optimum temperature for gasification of WP–DIS pellets (M2). Indeed, increasing the gasification temperature above this value does not appear to be convenient in terms of the net energy that can be recovered from the gasification products. 3.3.2. Effect of ER .

The variation in composition, LHV, and density of syngas, CGE, CCE and Pnet is assessed by varying the ER from 0.1 to 0.4 at the predicted optimum temperature of 850 ◦ C. The results are presented in Figures 6 and 7. Regarding syngas composition, the concentration of CO2 , H2 , and CO increases with ER whereas that of CH4 and C2 H4 decreases due to the movement of oxidation reaction to the forward direction with the raise of O2 concentration inside the gasifier, as explained by Le Chatelier’s principle [54]. CGE continuously decreases with ER, whereas CCE and syngas density experience an opposite trend. The concentration of C2 H4 and CH4 decreases by 76.8% and 46.9%, respectively, with the increase of ER within the tested range. Conversely, the concentration of CO increases by 24.2% and that of H2 by 53.8%, as clearly presented in Figure 6. The contribution of CH4 fraction to the energy content of syngas is almost three times compared to that of CO and H2 [22,59,66]. Consequently, the CGE decreases continuously with ER. Carbon transformation from input biomass to the gasification product increases due to the raise of oxidation reactions with ER. Additionally, the syngas flow rate increases with ER, and consequently CCE raises continuously [23]. The concentration of N2 inside the gasifier raises with ER being responsible for the reduction of molecular movement in the reacting medium due to its inert nature. This causes an increase in the syngas density [67]. Syngas LHV decreases with ER due to the increase of N2 volume inside the reactor, . which causes a dilution effect [54,61,62]. Pnet obtained from syngas decreases with ER due to the reduction of LHV. At the same time, the incoming air flow rate increases with ER . requiring more thermal energy for air preheating, further decreasing the available Pnet .

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Syngas composition (vol.%), ǻ ¢ȱ ȱ ƀȱ ȱ Ǽ

0 0.1

0.2

0.3

0.4

ER (-)

ƀ Ƃ

60 0.25 45

0.2

30 0.1

0.2

0.3

0.4

5.2

4.8

4.6 0.1

0.2

ER (-) CGE

CCE

Syngas density

(a)

Net Power (kW)

0.3

Syngas LHV (MJ/Nm3)

CGE and CCE (%)

Syngas density (kg/Nm3)

Figure 6. Fluctuation of syngas composition with ER.

0.3 ER (-)

LHV

0.4

Net Power

(b)

Figure 7. Effect of ER on CGE, CCE, and syngas density (a) and syngas LHV and net power from products (b).

The estimated optimum ER appears to be at least 0.2. Indeed, although syngas LHV, . CGE, and Pnet are higher at ER 0.15, thermal treatment of biomass by applying an ER lower than 0.2 leads to pyrolysis rather than gasification, which generates more tar, char, ash, and other impurities [49,68]. The removal of all the impurities from syngas, including tar content, is required before its use in an ICE, to ensure a high conversion efficiency and engine lifetime. The cleaning process for syngas generated at ER 0.15 would be more costly compared to the reduction of energy content obtained at 0.2 [69]. The fluctuation of composition and LHV of syngas, CCE, and CGE predicted in the current analysis with temperature and ER is in accordance with the studies on syngas generation through thermal treatment of biomass available in the literature [24,25,33,41,42,49,51,54,60–62,68,70,71]. 3.3.3. Cogeneration Process Performances The exhaust gas of the ICE fuelled with syngas from gasification of WP–DIS pellets contains CO2 , NOX, and HCl. The variation of emission profiles with the analysed operating parameters is presented in Figure 8.

0.9

0.6

0.3

0 700

800 900 1000 Temperature (°C) ƀ

NOx

120

1.4

1.05

0.7

0.35

0 0.1

HCl

0.2 0.3 ER (-) ƀ

(a)

Nox

0.4

NOX and HCl concentration (gm/Nm3)

1.2

ƀȱ ȱǻ Ȧ 3)

100

NOX and HCl concentration (gm/Nm3)

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CO2 oncentration (gm/Nm3)

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HCl

(b)

Figure 8. Variation of ICE emission proﬁle with gasiﬁcation operating parameters of temperature (a) and ER (b).

As shown in Figure 8, the concentration of NOX increases with the temperature as the NOX formation reaction is endothermic and moves in the forward direction when the temperature increases [67]. The concentration of the remaining two constituents (CO2 and HCl) in the exhaust does not significantly change with gasification temperature. Analysing the effect of ER, the concentration of NOX decreases with ER whereas that of CO2 and HCl increases. With the raise of ER, combustion reactions move into forward direction, and consequently the concentration of CO2 and HCl increases. At the same time, the raising of N2 concentration inside the gasifier with ER creates a dilution effect, reducing the temperature, and, thus, NOX formation decreases continuously [54,61,62]. The estimated potentiality of CHP generation from the WP–DIS is 1.14 kWh/kg as DS of electrical energy and 1.80 kWh/kg as DS of thermal energy. A summary of the predicted CGE, ηel , ηth , and ηsys obtained in the present study, together with their comparison with relevant analysis available in the literature, is illustrated in Table 7. Table 7. Comparison of CGE, ηel , ηth , and ηsys predicted in the present analysis with similar studies available in the literature. Biomass

CGE

ηel

ηth

ηsys

Ref.

WP–DIS pellet (M2)

61.90 n.r. 58.1 60.0 35.0 59.0 70.0 n.r. 84.0

18.32 29.20 19.3 30.0 26.0 19.1 n.r. 27.0 27.0

46.86 45.92 48.7 n.r. n.r. 20.0 33.5 40.0 39.0

73.87 53.10 n.r. 64.0 41.0 40.1 n.r. 67.0 66.0

Present study [41] [42]

SS Hazelnut shell Olive pruning MSW Olive kernel Wood

[43] [52] [53] [70] [71]

n.r. = Not reported.

Based on the data related to WP and DIS generated in the EU in 2019, it is estimated that 32,950–35,700 GWh of electrical and 52,190–56,100 GWh of thermal energy could be produced based on the DIS generation in the range of 20–40 wt% of WP [4,12]. By considering the emission factors for electricity consumption and natural gas combustion, the avoided CO2 emissions resulting from using the producible electrical and thermal energy would be in the ranges of 12998–15164 and 11781–13744 Mt of CO2 per year, respectively. Finally, by considering the estimated CHP generation potentiality from WP–DIS in 2019, it is estimated that between 25 and 28% and from 44 to 48% of the electrical and

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thermal energy demand, respectively, of the pulp and paper manufacturing sector, could be fulfilled in the EU. 4. Conclusions An energy-efficient solution for the paper industry, based on energy recovery from waste paper and deinking sludge, is presented in this work. The proposed solution consists of CHP generation from waste paper and deinking sludge blends through gasification in combination with an internal combustion engine. A gasification model is developed considering the experimental results on gasification of waste paper and deinking sludge blends and bamboo chips available in the literature. Sensitivity analyses were performed to predict the optimum operating conditions of temperature and equivalence ratio by assessing their effect on syngas composition, lower heating value, cold gas efficiency, carbon conversion efficiency, and net power obtained from the conversion process. Temperature raising has a positive impact on the process as it increases the syngas lower heating value, cold gas efficiency, carbon conversion efficiency, and net available power whereas the equivalence ratio has a reverse effect. Estimating CHP generation potentiality from waste paper and deinking sludge in the EU in 2019 through the proposed system allows us to highlight that:

• •

between 25 and 28% of the electrical and between 44 and 48% of thermal energy demand in the pulp and paper manufacturing sector could be supplied; this would allow saving between 24.8 and 28.9 Gt of CO2 per year.

Therefore, the proposed system can significantly contribute to reducing greenhouse gas emissions caused by the current management practices used for waste disposal in the paper recycling industry as well as by its consumption of electrical and thermal energy, which comes from fossil fuels. This, in accordance with the goals of the EU Green Deal 2021, would also reduce greenhouse gas emissions and increase the renewable energy generation in this sector [72]. In order to better analyse the environmental benefits of the proposed system, a life cycle assessment should be carried out as future development of this study. Author Contributions: Conceptualization, S.D.F. and M.R.U.; methodology, S.D.F. and M.R.U.; software, S.D.F. and M.R.U.; validation, S.D.F. and M.R.U.; formal analysis, M.R.U.; investigation, S.D.F. and M.R.U.; resources, M.R.U.; data curation, S.D.F. and M.R.U.; writing—original draft preparation, M.R.U.; writing—review and editing, S.D.F.; visualization, M.R.U.; supervision, S.D.F. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Conflicts of Interest: The authors declare no conflict of interest.

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How To Organize Your Paperwork in 7 Steps Some jobs require the ability to deal with a large volume and variety of documents. When handling digital or physical paperwork, it is essential to organize your files and workspace in a way that supports your productivity and increases your efficiency. This article explores methods of creating an efficient filing system for your workplace. Written by Indeed Editorial Team, updated September 21, 2021 https://www.indeed.com/career-advice/career-development/organize-your-paperwork

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How to organize documents The following steps can guide you in sorting, categorizing and storing your physical paperwork and help you design an effective filing system: 1. Separate documents by type. 2. Use chronological and alphabetical order. 3. Organize the filing space. 4. Color-code your filing system. 5. Label your filing system. 6. Dispose of unnecessary documents. 7. Digitize files. Let’s explore each of these steps in more detail so you can apply this simple organization system in your own workplace. 1. Separate documents by type Sort your physical documents into categories such as reports, client documents or billing invoices. You can further separate each category into levels of subtypes. For example, you can sort client documents based on each client before organizing a single client’s documents into reports, correspondence and more. This layered sorting strategy can help you identify what documents to keep and organize for easy access. If you find documents that do not fit into a major category, make a miscellaneous stack along with a pile of documents you intend to shred or recycle. It is also wise to make a stack of documents that you want to convert into digital files. Starting with a simple survey and categorization of your documents can help initiate the filing process. 2. Use chronological and alphabetical order Some documents are time-stamped and dated to keep track of activities and decisions within the organization. Once separated by type and subtype, consider sorting each document in chronological order, if applicable. For example, if you sort your documents by client, consider placing dated documents in order from newest to oldest so the most recent documents are in front. You can also order the documents from oldest to newest if you would rather see the client's full history to date. You can organize undated documents by importance or by how frequently you use them. Finally, consider alphabetizing your documents before placing them into your filing space. You can alphabetize by client name or by major categories like invoices or reports. Whichever method you choose, make sure that you select a system that feels natural and fits within your current workflow. 3. Organize your filing space Filing cabinets and drawers can offer customizable storage space. Use file folders to store groups of documents based on their type and subtype. You can continue using chronological or alphabetical order when placing folders into cabinets or drawers. For example, you can sort alphabetically by client name or chronologically by the most recent client you acquired. Storing paperwork away from your workspace helps keep your desk clear for you to complete tasks more efficiently. Consider investing in a file shelf to place on your desk to organize documents you review or access regularly, such as forms you fill out every day. Each shelf can be assigned a specific type or subtype to maintain categorization. You can also use the shelf to streamline your filing process as you receive new documents. Separate new files into a few major categories, and place them on the appropriate shelf. This method can make it easier when you file them away later. 4. Color-code your filing system Visual markers, such as colored tabs, can save you time when browsing for documents. You can use different colored folders for your various types and subtypes of documents. Some folders include label tabs Page 2 of 3

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in various colors. With either of these options, you can create a color-coded key to keep track of the color assigned to the document category. 5. Label your filing system Labeling your document categories can help you quickly identify your intended folder. Some folders come with paper to make your own labels. You can either hand-write the labels or print out a sheet of typed labels all at once. You can further optimize your labeling system by using different colored pens or ink that match your colorcoded key. Highlighters can also be used on black text to color code the label. Label makers can also allow you to quickly print out single-label stickers. This tool is especially helpful when labeling a filing shelf or cabinet, or if you need to replace current labels with new ones. 6. Dispose of unnecessary documents Creating an organized filing system can help you find ways to reduce the amount of paperwork you store. Recycle documents that are no longer relevant in order to reduce clutter, or shred them for extra security. Consider placing a small recycling can or a dedicated basket for documents you want to shred near your desk. Regularly disposing of unnecessary files and documents can help keep your workspace clean and organized. 7. Digitize files In some cases, it might be more efficient to convert physical documents into digital files stored on your computer. Doing so can make them easily accessible, sendable and reduces clutter. If this is the case, scan paperwork into digital documents for storage in organized folders on your computer. Consider following the same steps you took when creating a physical filing system: 1. Sort by type and subtype. 2. Use chronological and alphabetical order to organize files. 3. Color-code by type and subtype using the file color or flag feature on your operating system. 4. Label documents clearly with type or subtype and document date, if applicable. An efficient document titling system might look like this: “Client ABC_Invoice_Mar2021.” Digitizing files can allow you to quick-search documents on your computer. It also reduces clutter and the need for physical storage space. While creating a system for navigating paperwork can feel overwhelming, you can make steady progress if you follow this process and focus on each step. With an established procedure in place, you can streamline your workflow, reduce stress and increase productivity. Even if you already have an organization system, it is wise to set aside time on a regular basis for upkeep and maintenance, as it is easy for files to build up during busy times.

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It’s Time to Break Up with Burnout. Here’s How. What’s your current relationship status with burnout? Do you wish you could break up for good? You’re not alone. Across the globe, individuals, organizations, and communities are experiencing increased stress and uncertainty – and as a result, employees are dealing with burnout at unprecedented levels. The impact is staggering. A recent study from Mental Health America reports that 75% of workers are struggling with overcoming burnout, and about 40% say it was a direct result of the coronavirus pandemic. Burnout is pervasive across all industries right now, and the human services, public, and nonprofit sectors are particularly hard-hit. Saving the world is exhausting, and many nonprofit workers and the communities they serve are feeling an even greater strain today, with resignations compounding the already high levels of stress and burnout. During the post-pandemic period we find ourselves in, leaders at all types of organizations are being pulled in multiple directions in the face of physical, mental, social, and economic upheaval. With long hours and less funding, many nonprofit leaders, especially, are dealing with burnout themselves, and so may not feel equipped to offer their teams strategies to become more resilient and effective. Leaders approaching or experiencing burnout may feel physical symptoms, cynicism about work, emotional exhaustion, and reduced performance. Sound familiar? Remember, it’s not you. It’s burnout. Written by Andi Williams, 23 June 2022

https://www.ccl.org/articles/leading-effectively-articles/its-time-to-break-up-with-burnout-heres-how/

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Article 10 – Burnout

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FROM THE PUBLISHERS OF PA APER TECHNOLOGY®

Volume 8, Number 2, 2022

HOW ORGANIZATIONS CAN SUPPORT THEIR PEOPLE IN OVERCOMING BURNOUT What can organizational leaders do to support their workers in dealing with burnout, and in tandem, address turnover rates? Senior leaders can bring intention and attention to creating the conditions for everyone to bring their best selves to work and foster an environment that supports their people and the communities they serve. For the nonprofit sector in particular, philanthropic organizations and foundations can play several essential roles. First, grantmakers, executive directors, and senior leaders can consider their own personal and professional practices and how those are contributing to how they show up for their constituents. Second, they can stop doing anything that doesn’t support creating and cultivating the conditions for nonprofit teams and organizations to flourish. Whatever your industry, if you’re a leader, you can build your own resilience by stopping and starting these 6 things to help create the conditions for colleagues to overcome burnout and “burn bright” instead. ADVICE FOR DEALING WITH BURNOUT 6 Tips for Leaders: What to Stop & Start Doing 1. Stop repeating the same things. Start trying something new. Do the conditions of the pandemic have you feeling like you’re living the same day over and over, like your own personal Groundhog Day movie? In addition to fostering boredom, unexamined routines can also diminish energy and focus. Consider how much you might be mindlessly defaulting to behaviors reinforced by the pandemic conditions, and what you might do differently today to shake things up. Our brains actually thrive, and we feel happier, when we have novel experiences. Brain research has found that a rush of dopamine comes with any new experience. And it doesn’t have to be big to be effective – even small changes can help to create an immediate shift in energy and focus. Make a commitment to trying new things as a way of helping you and your colleagues with overcoming burnout. It could be as simple as trying a new route on a morning walk. How might you encourage others to try something novel? Perhaps add “sharing new things tried” to your one-on-one check-ins or an upcoming team meeting and start creating space for colleagues dealing with burnout to share ideas with one another. 2. Stop holding your breath. Start an intentional breathing practice. You might not even notice that you hold your breath or take very shallow breaths during the day, especially when you feel pressure. The moment we get anxious or stressed, we can assume some control and agency by breathing properly. Even less than a minute of intentional breathing can make a big difference. The research is clear: if we breathe shallow and fast, it causes our nervous system to up-regulate, and we feel even more tense and anxious. But if we breathe slowly, taking a deep breath with a focus on our exhale, it turns on our body’s anti-stress response. Breathing is convenient, free, and a fast way to ground into a state of calm. One simple practice for dealing with burnout is to anchor intentional deep breathing to something you do every day — maybe just before joining another online meeting, or as you transition from work to home tasks. You might experiment with expanding this practice to include everyone participating in a meeting you’re leading. Simply invite team members to breathe fully for one minute at the start, or take a pause for a “breathing break” in the middle. 3. Stop sending generic messages of thanks. Start personalizing gratitude. Have you ever received a generic, “reply-all” thank you message that fell a little flat? You’re not alone. While the intent is positive and it’s better than no gratitude, it can lack sincerity and reduce the overall impact. Giving thanks will actually make you a better leader and personal notes that include specific details about the value of an individual’s contribution are far more effective than mass communications, research finds. Just 512 formal, individualized, sincere gestures of thanks per year can significantly cut an employee’s propensity to leave and help with overcoming burnout. Take a couple of minutes and write a brief note (even just 2-3 sentences) to a person that you’ve been meaning to thank at work. By doing so, you’ll not only share gratitude with the individual you’re sending the note to, but you’ll also be modeling this behavior for other leaders in your organization. Make it your practice to send your team members a brief but personalized thank-you note on a consistent basis.

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Article 10 – Burnout

g PAPERmaking!

FROM THE PUBLISHERS OF PA APER TECHNOLOGY®

Volume 8, Number 2, 2022

4. Stop holding meetings by default. Start building an intentional meeting culture. Meetings are a constant presence in our lives, and with the rise of the remote and hybrid workforce, they’re more prevalent than ever. Yet, meetings can be draining, feel like a waste of time, and force after-hours work. They can even feel isolating when there’s not an opportunity to connect. Meetings are critical to getting our work done, however, so take some time to really examine and update your organization’s meeting culture. The next time you’re about to schedule a meeting, ask yourself the question, Is this meeting really necessary, or are we simply defaulting to a meeting because that’s how we’ve always done it? Consider whether you can handle the agenda via email or in a real-time messaging app, or explore shortening the allotted time. This allows people to avoid attending back-to-back meetings all day. Lighten “Zoom fatigue” by making some virtual meetings audio-only when being on camera isn’t really necessary. Or, if it’s an option, suggest team members take the call while walking outdoors to incorporate some movement and fresh air. Bonus points if a walk-and-talk meeting can be done together in person. Meetings are a prime opportunity for connection, so make them count and use them to improve your organization’s virtual collaboration and communication practices. 5. Stop perpetuating a 24/7 work week. Start encouraging boundaries. How have your boundaries around work and home shifted over the course of the pandemic? For many of us operating in a hybrid workplace context, we no longer “work from home” as much as we “live at work.” A boundaryless experience like this can take a serious toll on our health and contribute to burnout. Because of this shift, you may want to consider how you might be unintentionally creating expectations of working longer hours, including evenings and late nights, when your employees typically have been untethered from work. If you or your colleagues are dealing with burnout, notice the communication patterns that have emerged for yourself and your team recently. If you find yourself often catching up on emails after hours or on weekends, reflect on this habit. How might you create or influence new expectations that support recharging and disconnecting from work? How can you actively support both a work ethic and a “rest ethic”? And what rituals can you start that signal to yourself that you’re “clocking out”? Consider closing the laptop and leaving it in a designated workspace, collecting virtual or physical files and putting them away, or sending your team a friendly “I’m out and you should be, too” email at the end of the day or week, or when leaving on vacation. This will help your employees manage their work-life conflicts and increase their ability to unplug from work when the day is over or when they’re taking some much-needed time to rest and recharge. 6. Stop the early morning phone scroll and caffeine hit. Start your morning with intentional, mindful movement. Do you check your phone before your feet hit the floor in the morning? Is making coffee or tea your next step after that? These behaviors, while very common, may be eroding your energy before your day even begins. Checking your email, social media, and texts as soon as your eyelids open quickly hijacks your attention and emotions, often triggering anxiety before you’ve even gotten out of bed. You’ve probably already heard the advice not to keep your smartphone in your bedroom – but turning off notifications, curbing social media use, and removing as many apps off your phone as possible are all helpful, too. As for your unexamined caffeine routine, simply delay it a bit. When you wake up, the energizing hormone cortisol is at its peak – adding caffeine on top of that is like throwing a match on a fire that’s already crackling. You’ll experience a greater caffeine boost by waiting an hour or 2 if you can. Replace that immediate screen time and caffeine jolt with a little movement — a quick walk, some yoga, or even just stretching – and then something mindful like journaling, reading, or listening to music for a few minutes. Then, hydrate with water before you caffeinate. Give it a try for a few days and see if your energy improves and if these practices help with overcoming burnout. When you assess personal habits and default organizational practices that may be aggravating stress and burnout, you can start building a culture that values resilience and gives employees permission to take care of themselves. Be mindful about recharging, and modeling those behaviors for your team, and say goodbye to dealing with burnout for good.

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Article 10 – Burnout

PAPERmaking! FROM THE PUBLISHERS OF PAPER TECHNOLOGY TE INTERNATIONAL®

Volume 8, Number 2, 2022

10 tips for active listening Listening is an important skill in all areas of life, whether you’re supporting a loved one through health problems, dealing with colleagues or in family relationships. But most of us aren’t as good at listening as we’d like to think. When we show we’re really listening, it’s much more rewarding for the person talking to you, and you’ll get more out of it too. This is called active listening, and it can help avoid misunderstanding and reduce the potential for conflict. Here are 10 easy ways to make your communication more effective and make the other person feel more valued. https://www.bhf.org.uk/informationsupport/heart-matters-magazine/wellbeing/how-to-talk-about-healthproblems/active-listening

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Article 11 – Active Listening

g PAPERmaking!

FROM THE PUBLISHERS OF PA APER TECHNOLOGY®

Volume 8, Number 2, 2022

1. Face the speaker and have eye contact Eye contact is an important part of face to face conversation. Too much eye contact can be intimidating, though, so adapt this to the situation you’re in. Try breaking eye contact every five seconds or so, or to show you’re listening attentively, look at one eye for five seconds, then another eye for five seconds, then switch to looking at their mouth. When you look away, looking to the side or up is better than looking down, which can seem like you want to close the conversation. Check your posture and make sure it’s open – avoid crossed arms or crossed legs, which can make you look ‘closed’ or defensive. Leaning slightly forward or sideways whilst sitting can show that you’re listening – as can a slight tilt of your head or resting your head on your hand. 2. “Listen” to non-verbal cues too Facial expressions, tone of voice and gestures can tell you just as much as what is being said in words. Pay attention to what the other person is saying with their body language - are they smiling, for example, or are their arms crossed defensively, or are they rubbing their eyes as if they're tired or upset. Even on the phone, you can learn a lot from the other person’s voice, which might sound subdued or upbeat. 3. Don’t interrupt Being interrupted is frustrating for the other person – it gives the impression that you think you’re more important, or that you don’t have time for what they have to say. If you are naturally a quicker thinker or speaker, force yourself to slow down so that the other person can express themselves. Remember, a pause or a few seconds of silence doesn’t mean that you have to jump in. Letting the other person speak will make it easier for you to understand their message, too. Even interruptions that respond to something that they’ve said can be distracting if it means the conversation gets sidetracked from what they were trying to tell you about. If this does happen, steer the conversation back to “So, you were telling me about…”. 4. Listen without judging, or jumping to conclusions If you start reacting emotionally to what’s being said, then it can get in the way of listening to what is said next. Try to focus on listening. Equally, don’t assume that you know what’s going to be said next. 5. Don’t start planning what to say next You can’t listen and prepare at the same time. 6. Show that you’re listening Nod your head, smile and make small noises like “yes” and “uh huh”, to show that you’re listening and encourage the speaker to continue. Don’t look at your watch, fidget or play with your hair or fingernails. 7. Don’t impose your opinions or solutions It’s not always easy, but lending a listening, supportive ear can be much more rewarding than telling someone what they should do. When a loved one has health problems is a time when they probably want to tell you how they’re feeling, and get things off their chest, rather than have lots of advice about what they should be doing. In other areas of life too, most people prefer to come to their own solutions. If you really must share your brilliant solution, ask first if they want to hear it – say something like “Would you like to hear my suggestions?” 8. Stay focused If you're finding it difficult to focus on what someone is saying, try repeating their words in your head as they say them – this will reinforce what they’re saying and help you to concentrate. Try to shut out distractions like other conversations going on in the room. And definitely don’t look at your phone. 9. Ask questions Asking relevant questions can show that you’ve been listening and help clarify what has been said. If you’re not sure if you’ve understood correctly, wait until the speaker pauses and then say something like “Did you mean that x…” Or “I’m not sure if I understood what you were saying about…”

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Article 11 – Active Listening

g PAPERmaking!

FROM THE PUBLISHERS OF PA APER TECHNOLOGY®

Volume 8, Number 2, 2022

You should also use open questions where you can, like “How did that make you feel?” “What did you do next?” 10. Paraphrase and summarise Sometimes called reflecting, this is repeating what has been said to show that you understand it. This may seem awkward at first, but really shows you’ve been paying attention, and allows the speaker to correct you if you haven’t understood correctly. If you’re not sure how to do this, try starting a sentence with: "Sounds like you are saying…” And remember….practice makes perfect Old habits are hard to break, so you’ll need to make a conscious effort to become an active listener. Try spending a week in which you summarise the main points or outcomes at the end of each conversation or meeting. This will help you get into the habit.

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Article 11 – Active Listening

PAPERmaking! FROM THE PUBLISHERS OF PAPER TECHNOLOGY TE INTERNATIONAL®

Volume 8, Number 2, 2022

The Top 8 Soft Skills You Need to Succeed in 2022 Today’s business landscape is changing more rapidly than ever. The Covid-19 pandemic has highlighted the need for businesses to be agile, adaptable and forward-thinking and, as a result, soft or interpersonal skills are now just as important in the workplace as hard job-specific skills. Perhaps surprisingly, at a time when most businesses are increasingly reliant on technology, the human element is still the key to success. As the technical aspects of many jobs become automated, soft skills such as communication, teamwork and empathy are the ones that will set you apart and give you a competitive advantage in a crowded job market. When recruiting staff, companies across all sectors are increasingly looking for employees with a willingness to learn, listen to others and embrace change with a flexible mindset. If you are looking for a career change or promotion in 2022, here are eight of the top skills that employers are looking for: By Ase Anderson|17 Jan 2022|Business Etiquette, Life Skills https://thebritishschoolofexcellence.com/business-etiquette/do-you-have-the-skills-you-need-to-succeed/

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Article 12 – Soft Skills

g PAPERmaking!

FROM THE PUBLISHERS OF PA APER TECHNOLOGY®

Volume 8, Number 2, 2022

1. Creative thinking Creative thinking is not just relevant for those in ‘creative’ industries such as art, design or music. The ability to generate new ideas and think outside the box to come up with imaginative solutions to problems, are sought-after skills for employees in any field. In the workplace, creative thinking also means taking risks and not being held back by the fear of making a mistake. Fear of failure is one of the main obstacles to innovation and those who accept that the road to success is paved with setbacks are more likely to reach their desired destination. 2. Communication skills This is a huge area, encompassing not only your face-to-face interactions but also your digital communication with clients, colleagues, team members and senior managers. An estimated 246 billion emails are sent and received globally every day and each email you write needs be properly worded to stand out for the right reasons. Improving your verbal and non-verbal communications skills is one of the best investments you can make. Being able to clearly and calmly convey your ideas and opinions will help you advance your career and improve your relationships, no matter what industry you work in. 3. Time management Knowing how to organise both your daily and long-term schedule to get your projects done efficiently and on time is particularly important when so many people are working remotely. Are you disciplined enough to set goals for yourself and focus on your work without a manager looking over your shoulder? Good time management skills will help you increase productivity by eliminating distractions and prioritising your tasks. It also has the added benefit of reducing stress and boosting your reputation for being a trusted and reliable member of the team. 4. A growth mindset People with a growth mindset are motivated to learn new skills to adapt to changes and reach higher levels of achievement. They recognise that learning is a life-long process and that investing in yourself is essential if you want to get ahead. If you have a fixed mindset, you are more likely to respond defensively to feedback and feel intimidated by other people’s success. Developing a growth mindset will help you view feedback as an opportunity to learn and grow. You will also be more inclined to celebrate your colleagues’ accomplishments and draw inspiration from them. 5. Adaptability This past year has highlighted the need for employees to cope well with change in the workplace. Adaptability is important when it comes to taking on additional responsibilities, tackling new projects and adjusting to new strategies or team members. Having the ability to respond effectively even when things don’t go as planned and embracing new ways of working are also key for anyone in a leadership position. 6. Emotional intelligence (EQ) Professional networking site LinkedIn identified emotional intelligence as one of the top five soft skills employers were looking for in 2020 and its importance has only become more prominent in the wake of the Covid-19 pandemic. Emotional intelligence refers to your ability to recognise and manage both your own and other people’s emotions. Highly developed EQ skills enable you look at situations from other perspectives, treat your coworkers with empathy and better navigate the interpersonal relationships that develop in the workplace. 7. Collaboration ‘Team work makes the dream work’ but sometimes collaborating with your co-workers is easier said than done. Conflicts and disagreements are an inevitable part of working with others but open communication and a collaborative approach to problem solving will help you move past them in a calm, measured way.

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Article 12 – Soft Skills

g PAPERmaking!

FROM THE PUBLISHERS OF PA APER TECHNOLOGY®

Volume 8, Number 2, 2022

Effective collaboration requires everyone in the team to be open-minded, inclusive and transparent. Learning to trust others, exchanging ideas and working as a group will pave the way for a more productive, efficient and harmonious workplace. 8. Active listening Being an active listener is not just about concentrating on what the other person is saying. You have to engage in the conversation by asking questions, making eye contact and nodding. Perhaps most importantly, active listening means withholding judgement about what is being said and not interrupting to make your own point. In short: listen to understand, not to respond.

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Article 12 – Soft Skills

PAPERmaking! FROM THE PUBLISHERS OF PAPER TECHNOLOGY TE INTERNATIONAL®

Volume 8, Number 2, 2022

Products & Services & News PITA CORPORATE SUPPLIER MEMBERS Page 2 ABB KPM KB2 Break Detector Page 3 ABB KPM KC7 Microwave Consistency Page 4 Valmet Press Roll Cover PL Page 5 Valmet Mobile Maintenance Application

PITA NON-CORPORATE SUPPLIER MEMBERS Page 6 Voith OnQuality 4.0 Scanners & Sensors NON-PITA SUPPLIER MEMBERS Page 7 Toscotec TT Induction SYD Page 9 Toscotec INGENIA tissue concept machine

The Paper Industry Technical Association (PITA) is an independent organisation which operates for the general benefit of its members – both individual and corporate – dedicated to promoting and improving the technical and scientific knowledge of those working in the UK pulp and paper industry. Formed in 1960, it serves the Industry, both manufacturers and suppliers, by providing a forum for members to meet and network; it organises visits, conferences and training seminars that cover all aspects of papermaking science. It also publishes the prestigious journal Paper Technology International® and the PITA Annual Review, both sent free to members, and a range of other technical publications which include conference proceedings and the acclaimed Essential Guide to Aqueous Coating.

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Products & Services

g PAPERmaking! FROM THE PUBLISHERS OF PAP PER TECHNOLOGY INTERNATIONAL®

Volume 8, Number 2, 2022

ABB EXPANDS KPM PORTFOLIO TO INCLUDE LONG-DISTANCE, CALIBRATION BREAK DETECTION FOR ALL GRADES AND COLORS

SINGLE

ABB is launching their new KPM KB2 Ranger Model, a sheet break detection device that is invulnerable to paper jams, color and grade changes for the highest uptime with the lowest required maintenance. As the latest addition to ABB’s industry-leading KPM Sheet Break Detector portfolio, this non-contact optical sensor will prove particularly important for paper or board producers making frequent grade changes or colored papers. The single, one-button calibration removes the need for complicated, grade-specific settings, while the RGB break profiling method reduces false positives and automatically updates for more robust detection over time. The KPM KB2 Ranger model offers a longer measurement distance – up to 1.5 meters – and side installation to keep the sensor head outside the machine. It can provide reliable break detection in all configurations, such as against felt, wire or cylinders, and its freely adjustable sensor head is able to detect breaks from any angle. This removes the possibility of paper getting stuck on the sensor head, enabling higher reliability and accuracy across all paper and board grades, regardless of color. While the sensor head can withstand high temperatures, the electronics unit is mounted outside the machine hood using fiber optic cables, preventing the electronics from being affected by dirt, steam or temperature and maintaining high reliability even in a high humidity environment. Unlike comparable solutions that require in-machine installation, ABB’s KPM KB2 Ranger model augments the current offering to deliver higher uptime and reduced unplanned downtime. It requires minimal, if any, maintenance and cleaning due to its air-purged sensor that keeps the unit clean for continuous and trouble-free operation. “Our KPM Sheet Break Detector is recognized as the best on the market and the proven choice for installations in harsh environments or where space is limited,” said Karin Hermansson, Product Line Manager, ABB. “We are pleased to unveil the new KB2 Ranger Model to offer additional options for mills facing frequent grade changes or color-related issues, while proving our commitment to continual innovation surrounding mill optimization solutions.” KB2 is applicable globally across paper, tissue, board and pulp machines, and can be used on press or drying sections.

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Products & Services

g PAPERmaking! FROM THE PUBLISHERS OF PAP PER TECHNOLOGY INTERNATIONAL®

Volume 8, Number 2, 2022

ABB EXTENDS TO OFFER NEW INSERTION DESIGN AND LARGER FLOW-THROUGH OPTIONS ABB has updated its KPM KC7 Microwave Consistency Transmitter portfolio with a larger flowthrough sensor to fit process pipes with a diameter of up to 16”, giving more customers the choice to measure the total consistency of mixed pulps with a flow-through sensor. The technology leader has also launched a redesigned insertion type with a new dualplate sensor. Both of the device options will be used in the stock preparation area of mills, which feeds the wet end of the paper machine. The enlarged flowthrough model, extending from a previous maximum of 12”, expands ABB’s market reach to those with wider diameter pipes that previously could only use insertion types, but that can now consider both. The larger size, capturing the whole pipe diameter, means the most representative measurement on the market and provides precise, reliable measurements of total consistency regardless of flow rate for superior process control. For mills opting for the insertion style, the dual-plate design is the only one on the market with an optional temperature sensor that can be retracted for abrasive and unscreened processes, a feature also available with the flow-through model. The parallel antennas avoid microwave reflections in the pipe and generate a self-cleaning effect, removing the risk of obstructions and therefore increasing uptime and reducing maintenance costs compared to other devices. Microwave measurement is becoming more popular due to its low calibration requirements, high accuracy, and ability to measure total consistency independent of process variables and fiber properties. Unlike optical and sheer force technologies, KPM KC7 is unaffected by both process changes, such as flow speed, pressure and turbulence, and variations in pulp species, fiber length and freeness. “ABB individually verifies each sensor before implementation to ensure high accuracy, said Karin Hermansson, Product Line Manager at ABB. “With this update to fit larger pipes, reduce obstructions and ensure smooth temperature readings for even the most difficult processes, we can now meet the most diverse requirements in the complex world of papermaking.” The expansion means that ABB’s KPM KC7 sensor portfolio is now equipped with an added pressure sensor – available as a spare part – to further improve diagnostics. With no moving parts or preventive maintenance requirements, the updated sensors - compatible with thirdparty couplings for simple upgrades and replacements - make for easy operation and maintenance to ensure a low total cost of ownership. The application usage extends across paper, tissue, board and pulp producers, from recycled pulping to end of machine stock preparation, and can even be used for municipal and industrial wastewater. KPM KC7 is particularly good for users of recycled raw material and pulp and paper mill teams that prefer to measure and control total consistency with microwave technology. Page 3 of 10

Products & Services

g PAPERmaking! FROM THE PUBLISHERS OF PAP PER TECHNOLOGY INTERNATIONAL®

Volume 8, Number 2, 2022

THE NEW VALMET PRESS ROLL COVER PL LEADS TO ENERGY SAVINGS IN TISSUE PRODUCTION To broaden its offering for tissue machines, Valmet launches a new polyurethane roll cover, Valmet Press Roll Cover PL. The roll cover’s wear-resistant material and adaptive structure are developed to cope with the harsh operating conditions in tissue production, thus leading to longer lifetime of roll cover and energy savings. Tissue machines represent the most challenging environment for press rolls due to high machine speeds and extreme Yankee cylinder temperatures – placing high demands on the roll covers as well. “The new Valmet Press Roll Cover PL is a long-lasting polyurethane roll cover especially designed for tissue pressing applications. It complements the existing applications on the market with unique properties that further improve the tissue production line’s efficiency, capacity, and product quality,” says Ulla Kanerva, Global Technology Manager, Roll Covers and Maintenance, Valmet. Compared to other cover products, Valmet Press Roll Cover PL is available with wider hardness range together with improved mechanical properties, from 5P&J to 50P&J. Significant cost-saving potential The adaptive roll cover structure of Valmet Press Roll Cover PL helps to achieve more uniform nip profiles and bulk savings. “To limit the energy needed for drying the tissue sheet, we usually concentrate on improving the post-press dryness. It reduces the energy demand on the Yankee dryer, which in turn removes bottlenecks in the dryer’s performance and operating costs,” Ulla Kanerva explains. Valmet Press Roll Cover PL offers the possibility for high open grooved areas and large void volumes, assuring maximal nip dewatering and consistent tissue quality. By selecting optimal roll covers and surface topography with a matching press felt, tissue makers can further improve dewatering. “To summarize, choosing Valmet Press Roll Cover PL leads to energy savings, better runnability and improved time efficiency in tissue production. On the other hand, the wearresistant polyurethane material also extends the roll cover change intervals, leading to further cost savings,” Kanerva continues. For further information, please contact: Ulla Kanerva, Global Product Manager, Roll Covers and Maintenance, Services business line, Valmet, tel. +358 40 728 6653 Tiina Olkkonen, Director, Roll Covers and Maintenance, Services business line, Valmet, tel. +358 40 192 7088 Read more about Valmet Press Roll Cover PL

Page 4 of 10

Products & Services

g PAPERmaking! FROM THE PUBLISHERS OF PAP PER TECHNOLOGY INTERNATIONAL®

Volume 8, Number 2, 2022

VALMET LAUNCHES VALMET MOBILE MAINTENANCE APPLICATION TO STREAMLINE MAINTENANCE PERSONNEL’S AND PRODUCTION OPERATORS’ WORK Valmet launches Valmet Mobile Maintenance (VMM) application to make maintenance data available at any time and to create smoother workflows in mill maintenance operations. VMM is a mobile application for both iOS and Android devices. The application is designed to streamline the maintenance personnel’s and production operators’ work. They can save time and improve work efficiency by creating fault notifications and reviewing work orders on the go. “We noticed that maintenance personnel and production operators spent a lot of time in front of the computer with complicated systems, making fault notifications from their own notes on paper. Their time was not efficiently spent,” says Timo Harjunpää, Director, Maintenance Development and Outsourcing Services, Valmet. “The application allows the personnel to work through their mobile phones in real time anywhere at the mill. It makes all information available to the whole team at once, saves unnecessary work, and gives the management a better overview and control,” says Hemmo Lahtinen, Reliability Manager, Services, Valmet. Quick, easy, and safe to implement Equipment identification is easily done via Near Field Communication (NFC) or QR codes. The VMM application uses the same Valmet Cloud platform as all Valmet Industrial Internet applications and has an integration package for SAP, which makes it easy to implement. The application implementation can be done 100% remotely. The VMM application can be used on both Wi-Fi and mobile data networks. Only relevant data is transferred. The technical solution meets industrial cybersecurity standards, follows all best practices and guidelines and is audited by an external accredited cybersecurity service provider. The application is part of Valmet’s maintenance development and outsourcing services allowing customers to focus on their core business. For further information, please contact: Timo Harjunpää, Director, Maintenance Development and Outsourcing Services, Valmet, tel. +358 40 824 4253

Page 5 of 10

Products & Services

g PAPERmaking! FROM THE PUBLISHERS OF PAP PER TECHNOLOGY INTERNATIONAL®

Volume 8, Number 2, 2022

WITH ONQUALITY 4.0, VOITH SETS NEW STANDARDS IN THE FIELD OF QUALITY CONTROL SYSTEMS OnQuality.Scanners and OnQuality.Sensors are successfully used in over 750 installations worldwide to continuously improve production and quality processes. Thanks to their compact design, the scanners can be installed extremely flexibly in existing and new plants. Based on the leading solutions, Voith now presents OnQuality 4.0, the next level for digitalization of the paper mill. The new system consists of all the important elements required for perfect quality measurement and control: a secure cloud solution with many analysis tools and functions, virtual sensors for online and real-time measurement, as well as location- and time-independent technology consulting. The OnQuality 4.0 system can be upgraded modularly for all Voith OnQuality systems already installed and is ready for use within a very short time. “With OnQuality 4.0, we are introducing the most advanced quality measurement and quality control system currently available for manufacturers of all paper grades. Time-consuming collection, search and conclusion of quality data and control strategies are a thing of the past. With our intuitive cloud solution, virtual sensors as well as remote technology consulting, the foundation for the digitalization of your paper mill is laid.” Marc Stampfer, Global Product Manager QCS Scanners & Sensors at Voith Paper Perfect interaction between cloud solution, sensors and technology consulting OnQuality 4.0 uses virtual sensors to overcome the limitations of classic physical online sensor technology. Using artificial intelligence, the virtual sensors continuously, reliably and in real time predict quality parameters such as tensile strength, stiffness and softness that can otherwise only be measured in the laboratory. The cloud platform collects and stores all relevant production and quality data and enables users to perform in-depth analyses through personalized dashboards. With just a few clicks, profile charts, color maps, maintenance cockpits, trends and reports can be intuitively created and viewed on mobile devices. OnQuality 4.0 thus quickly and directly shows deviations from the critical target quality and enables significant savings in resources, scrap and costs. The OnPerformance.Lab (OPL) remote service center completes OnQuality 4.0, with OPL experts providing round-the-clock support for realtime emergencies. With the help of the indepth know-how in the field of paper and control technology, tailor-made optimization measures are carried out together with the customer, such as for MD and CD controls and grade change processes. Consequently, the efficiency of the machine increases while costs decrease. Further optimizations are planned for the future. Voith is currently working on visionary OnQuality.Scanner concepts, which are being developed as part of the Papermaking Vision design study. “With intuitive and state-of-the-art operating and visualization interfaces directly on the scanners; an intelligent light and alarm system; and an attractive, maintenance-friendly design, we will once again make everyday work much easier for operating and maintenance personnel.” Marc Stampfer, Global Product Manager QCS Scanners & Sensors at Voith Paper

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Products & Services

g PAPERmaking! FROM THE PUBLISHERS OF PAP PER TECHNOLOGY INTERNATIONAL®

Volume 8, Number 2, 2022

TOSCOTEC LAUNCHES BREAKTHROUGH IN STEEL SUSTAINABLE PAPERMAKING

YANKEE

DRYERS FOR

Toscotec, the global market leader of Steel Yankee Dryers, introduces TT Induction SYD, a carbon-reduction breakthrough that redefines Yankee dryer technology entirely. TT Induction SYD uses electrical induction instead of steam energy to dry the paper web, thereby cutting direct greenhouse gas emissions to zero. In 2000, Toscotec pioneered a major technological innovation, TT SYD, the first Yankee dryer entirely made of steel. Steel Yankees have since surpassed their cast-iron equivalent to become the benchmark for drying efficiency and safety in the paper industry. TT Induction SYD is now set to be the new game changer in tissue for its capability to use clean energy and slash direct carbon emissions associated with the drying process. A disruptive innovation for dry crepe and TAD tissue machines With TT Induction SYD, the internal steam distribution and steam/condensate removal systems are entirely replaced by an induction system composed of static coils installed inside the shell and electrical controls and instrumentation located outside for easy maintenance and monitoring. As a result of precise coil geometry, the induction system delivers a very fast and accurate heating effect exactly on the areas of the shell where it is required, while preventing residual circulating currents in other areas. Steam-heated Yankees use steam energy typically generated by burning fossil fuels. TT Induction SYD uses electrical energy that can be derived from renewable energy sources while delivering the same result, i.e. uniformly heating up the Yankee’s shell in contact with the paper web to achieve dryness. TT Induction SYD is suitable for installation on dry crepe as well as Through-Air-Drying (TAD) tissue lines. Luca Ghelli, Toscotec R&D Director, says, “Sustainability is the guiding idea of TT Induction SYD’s design. As a proven industrial technology, an induction system offers multiple advantages when applied to the most energy-intensive section of the tissue machine. The efficiency of this cutting-edge technology will dramatically reduce the carbon footprint of papermaking. Based on our expertise in steam-heated TT SYD and induction systems, we succeeded in developing a more efficient and sustainable steel Yankee dryer.” Substantial carbon reduction with unchanged productivity and paper quality Normally, approximately half of the carbon dioxide emissions produced by a tissue machine originate from the operation of the Yankee dryer. By using clean energy, TT Induction SYD achieves zero direct emissions, while maintaining productivity unchanged and reducing energy consumptions because of the higher efficiency of the induction system. Due to the precise heating of the shell, it also eliminates possible moisture profile issues related to uneven condensate removal, thereby ensuring an improvement in moisture uniformity in both cross direction (CD) and machine direction (MD). Page 7 of 10

Products & Services

g PAPERmaking! FROM THE PUBLISHERS OF PAP PER TECHNOLOGY INTERNATIONAL®

Volume 8, Number 2, 2022

Maximum safety, easier operation, and maintenance TT Induction SYD was designed without any electrical, mechanical, and radiation risk to ensure maximum safety. Besides offering safe operations, it also clears all issues related to the maintenance of steam-heated Yankees, including pressure vessel’s mandatory and planned controls, maintenance of condensate straw pipes against potential plugging and of special heads for steam and condensate inlet and outlet. The entire Yankee system is simplified in the absence of steam: the heads, the internal surface which is groove-less, and the steam and condensate auxiliary system disappears entirely, including the steam generator with related maintenance and controls and delicate controls for steam quality. TT Induction SYD simply requires relatively easy maintenance on the electromagnetic induction system.

Page 8 of 10

Products & Services

g PAPERmaking! FROM THE PUBLISHERS OF PAP PER TECHNOLOGY INTERNATIONAL®

Volume 8, Number 2, 2022

TOSCOTEC LAUNCHES NEW CONCEPT MACHINE FOR A MORE SUSTAINABLE STRUCTURED TISSUE Toscotec launches INGENIA, a new concept tissue machine to produce premium quality structured tissue paper. The quality generated by INGENIA line is substantially higher than textured tissue and close to Through Air Drying (TAD) produced paper, but using 35% less energy. With INGENIA Toscotec responds to the challenge of today’s paper market calling for premium quality tissue obtained with lower energy use and lower capital investment than TAD lines. INGENIA’s concept is based on consolidated technologies for premium tissue, building on vast internal know-how of Toscotec’s and Voith’s R&D, and field data validation on TAD and structured paper systems. Paolo Raffaelli, Toscotec Chief Technology Officer, says: “The key factor for energy reduction compared to TAD, is that INGENIA achieves significantly higher dryness through non-thermal dewatering on a structured moulding fabric. With TAD, the thermal drying starts from 24-26%, whereas INGENIA achieves a much higher dryness level without using hot air or steam. This maintains the premium quality obtained through rush transfer and structured moulding fabric, but uses much less energy.” Ultra-premium tissue quality Through non-compressive water removal technologies and efficient fiber moulding, INGENIA produces much higher tissue quality properties than other technologies for textured or conventional DCT tissue. These properties include bulk, softness, stretch, and absorbency, which improve the tactile “hand” feel and the final paper characteristics that compete with premium segments for toilet, facial and towel tissue grades. The specific pattern of the structured fabric and the use of a calender can further enhance the quality of end products. Energy Efficiency through Process Innovation The process of this new concept machine begins with a dilution profiling layered TT Headbox-ML operating on a twin-wire forming section. Like TAD machines, INGENIA operates wire rush transfer at low consistency, but its key capability is an enhanced vacuum de-watering system without pressing the paper web, which ensures that dryness is greatly increased while fibers are being supported in the same shape as they originally formed when fully water saturated. At the end of the wet section, TT NextPress shoe press uses low loading pressure to gently stabilize the web dryness content and transfer the paper to the drying section without bulk compression. The combined action of a third-generation design TT SYD Steel Yankee Dryer and high-efficiency TT Hood achieves the final desired dryness. The process is completed by dry creping, sheet stabilization integrated with dust removal, and precision winding using an electro-mechanical TT BulkyReel fitted with a Center Wind Assist on the primary and the secondary arms. The Center Wind Assist fully preserves bulk by reducing the nip pressure against the reel drum during the winding process.

Page 9 of 10

Products & Services

g PAPERmaking! FROM THE PUBLISHERS OF PAP PER TECHNOLOGY INTERNATIONAL®

Volume 8, Number 2, 2022

Flexible Configuration The new INGENIA offers top flexibility, as it can easily swing from the production of premium quality structured tissue to conventional DCT. When in conventional mode, INGENIA delivers top machine speed and production capacity. INGENIA features widths up to 6 m, a production capacity from 100 to 250 tpd, and operating speeds up to 1,500 m/min in structured tissue mode or 2,000 m/min in conventional mode, depending on machine size and customer requirements.

Page 10 of 10

Products & Services

PAPERmaking! FROM THE PUBLISHERS OF PAPER TECHNOLOGY TEC INTERNATIONAL®

Volume 8, Number 2, 2022

CALENDAR OF EVENTS - 2022 PITA TRAINING COURSES PITA / MCP

Maintenance Planning & Scheduling

26-27 Sep.

PITA

Fundamentals of Wastewater Treatment

4-5 Oct.

PITA

Modern Papermaking

18-19 Oct.

PITA

Introduction to Wet End Chemistry

9-10 Nov.

PITA / Gernsbach

Fundamentals of Papermaking

6-8 Dec.

INTERNATIONAL CONFERENCES & EXHIBITIONS PRIMA 2022, Amsterdam, The Netherlands (10% off with code PRIMA22PT)

6-7 Sep.

Specialty Papers Europe 2022, Amsterdam, The Netherlands (10% off with code SPEU22PITA)

6-7 Sep.

Paper One Show Symposium, Turkey

7-10 Sep.

Tissue & Paper, Bangkok, Thailand

14-16 Sep.

London Packaging Week, UK

21-22 Sep.

MIAC, Lucca, Italy

12-14 Oct.

Technologie Kring, The Netherlands

23-24 Nov.

Page 1 of 1 Events

PAPERmaking! FROM THE PUBLISHERS OF PAPER TECHNOLOGY TE INTERNATIONAL®

Volume 8, Number 2, 2022

Installations The following pages contain a summary of the various installations and orders from around the world of papermaking, wood panel and saw mills, and bio-power generation, received between March 2022 end early July 2022.

Page 1 of 9

Installations

g PAPERmaking! FROM THE PUBLISHERS OF PAP PER TECHNOLOGY INTERNATIONAL ®

Volume 8, Number 2, 2022

COMPANY, SITE ADFORS Czech Republic Águas do Tejo Atlântico Alcantara Lisbon Portugal Ankutsan A.S. Adana Turkey Anon Italy Anon two manufacturers North America Anon South America

SUPPLIER Projet BV

ORDER DESCRIPTION cleaning system on a saturator wire (glass fibre mat) solids measurements and Valmet Sludge Dewatering Optimizer (water treatment plant)

URL link

Runtech

vacuum system (PM2)

link

Pasaban

two sheeters for premium FBB cardboard several steel drying cylinders

link

vacuum system for tissue machine (supplied to Replus Tissue) Fiber Furnish Analyzer (Valmet MAP Q) with services

link

Arctic Paper Kostrzyn Poland Asia Symbol Group China

Valmet

software and service contract to provide the ABB Ability™ Manufacturing Execution System (MES) for a new production line fine paper line (PM14)

link

Asia Symbol Rizhao Shandong province China B&B Triplewall Containers Krishnagiri Mill Tamil Nadu India Berneck SA Curitibanos Brazil BillerudKorsnäs Frövi/Rockhammar pulp mill Örebro Sweden BMC Moerdijk Moerdijk Netherlands Burgo Mosaico Lugo plant Italy Cartiere di Guarcino Guarcino paper mill near Frosinone Italy Cartonificio Sandreschi Villa Basilica Paper Mill Italy

Valmet

Voith

new OCC stock preparation system and approach flow (PM1)

link

Dieffenbacher

world’s largest drum dryer

link

Andritz

a LimeDry lime mud filter for the recausticizing plant

link

Andritz

SMART service contract to power boiler using remote web platform entire renovation of the Jagenberg sheeter drive and automation rebuild of forming and press sections (PM2)

link

rebuild of forming and press sections (PM1)

link

Valmet

Toscotec

Runtech

ABB

SAEL

Toscotec (& Voith)

Toscotec

Page 2 of 9

Installations

link

g PAPERmaking! FROM THE PUBLISHERS OF PAPER TECHNOLOGY INTERNATIONAL ®

Volume 8, Number 2, 2022

COMPANY, SITE Celulosa Arauco y Constitución (ARAUCO) various Pulp Mill sites Chile

SUPPLIER AFRY

CENIBRA Belo Oriente Pulp Mill Brazil

Valmet

Cheng Loong Corporation Vietnam City Group Hoshendi Economic Zone near Dhaka Bangladesh Crane Currency Tumba Sweden Dexco Brazil

ABB

Domtar Kingsport Tennessee USA Dongfang Smart Energy Co. Ltd. (Shaanxi Power Generation Group) Wugong County Xianyang City Shaanxi Province China DS Smith Dueñas Paper Mill Spain DS Smith Kemsley Mill Kent UK DS Smith Paper Ltd Kemsley Mill Kent UK Dunapack Packaging Plovdiv Plant Bulgaria

Projet BV

ORDER DESCRIPTION frame agreement to provide engineering and consulting services for several phases of current investment projects as well as adjustments to existing systems modernisation of fiberline No.1 plant comprising an oxygen delignification stage and four sets of washing equipment L&W Autoline automated paper testing solution turnkey tissue line

URL link

Pasaban

upgrade the foil stamping line for FS1

link

AFRY

develop an Industrial Digital Plan (IDP) based on an Industry 4.0 approach (wood panel) ProCleaners for fabric cleaning

link

Andritz

two paper machine approach flow systems and LC (low consistency) refiners

link

Runtech

modify PM2 vacuum system

link

ABB

upgrade of DCS and paper machine drives across PM3, PM4 and PM6

link

Runtech

rebuild of PM4 vacuum system

link

Valmet

Valmet IQ Warp Control System (corrugator)

link

Toscotec

Page 3 of 9

Installations

link

link link

link

g PAPERmaking! FROM THE PUBLISHERS OF PAP PER TECHNOLOGY INTERNATIONAL ®

Volume 8, Number 2, 2022

COMPANY, SITE Ecowipes Poland

SUPPLIER Voith

ORDER DESCRIPTION second carded pulp line for flushable wipes (in collaboration with Trützschler Nonwovens) drying, air and energy technology for two tissue machines (PM3 & PM4)

URL link

Essity Menasha Wisconsin USA ETAP Borg Elarab Paper Mill near Alexandria Egypt Favini Group Rossano Veneto plant Italy Fedrigoni Verona Mill Italy Forestal y Papelera Concepción Chile

Andritz

Toscotec

press section rebuild of testliner machine (PM2)

link

De Iuliis (DJM)

update drying section with new dryer cans

link

SAEL

new sectional drive for PM3

link

Valmet

remote monitoring technology, a new RF-3 refiner for stock preparation, web stabilizers and suction stabilizer boxes for the first two sets of dryers (board machine) replacement rolls for NTT Tissue machine

link

Forestal y Papelera Concepción Chile Greenpac Mill Niagara Falls New York USA Guapi Papéis Brazil Hitachi Zosen Inova AG Slough Berkshire UK Jiangxi Five Star Paper Co. Ltd. China

Valmet

additional three years of Performance Agreement

link

Hergen

new Fourdrinier machine (PM1)

link

Valmet

automation of energy-from-waste plant

link

Andritz

high-capacity chemithermomechanical pulping system (Pre-Conditioning Refiner Chemical Alkaline Peroxide Mechanical Pulp) new drying (No.5) as part of the new Siempelkamp MDF plant pressurized refining system for MDF line

link

Kastamonu Entegre AS Turkey Kim Tin MDF Chon Thanh Corporation Binh Phuoc province Vietnam Kim Tin Group Chon Thanh, Binh Phuoc province & Dau Giay, Dong Nai province both Vietnam

Büttner

two MDF plants

link

Andritz

Dieffenbacher

Page 4 of 9

Installations

link

link link

g PAPERmaking! FROM THE PUBLISHERS OF PAPER TECHNOLOGY INTERNATIONAL ®

Volume 8, Number 2, 2022

COMPANY, SITE Koskisen OY Kärkölä Finland Kotkamills Group Oyj Finland

SUPPLIER Hekotek AS

ORDER DESCRIPTION log-feeding equipment (saw mill)

URL link

Bellmer

link

Kuhmon Lämpö Oy Kuhmo sawmill Finland Laboratoire Naturel ZetTechnology Group Russia Lemit Papers LLP Chokadi Gujarat India Liaoning Yusen Sanitary Products Liaoning Yusen mill Tai’an Liaoning province China Liansheng Pulp & Paper (Zhangzhou) Co. Ltd. Zhangzhou Pulp Mill Fujian province China Manifattura Fontana Sioen Group Romano d’Ezzelino site Italy Maruti Papers Limited Uttar Pradesh India Mekong Wood MDF Vietnam Mercer Rosenthal Lignin Center Thuringia Germany Metsä Board Husum Mill Sweden

KPA Unicon

rebuild of press and pre-dryer section, and installation of new pulpers (PM1) bio boiler to produce heat for the residents of the city of Kuhmo and the sawmill complete spunlace line (nonwovens)

Valmet

DNA automation system in secondary fibre pulp mill and board making line

link

Valmet

two tissue machines

link

Andritz

all main process islands in the fibre production and the chemical recovery plant

link

Andritz

complete needlepunch (nonwovens)

link

Cellwood Machinery

dispersing unit

link

Siempelkamp

complete MDF plant

link

Valmet

LignoBoost plant for extraction of kraft lignin from pulp mill black liquor

link

AFRY

link

Metsä Fibre Kemi Bioproduct Mill Finland

Caverion

Industry 4.0 digital solution will act as the data information hub, directing the assigned logistics devices from the board machine to the planned destination process electrification of new mill

Andritz

Page 5 of 9

Installations

link

g PAPERmaking! FROM THE PUBLISHERS OF PAP PER TECHNOLOGY INTERNATIONAL ®

Volume 8, Number 2, 2022

COMPANY, SITE Metsä Group Kemi Mill site Finland Metsä Group all mills in Finland

SUPPLIER Timi Tec OY

Mufindi Paper Mills Ltd. Mgololo Tanzania Nanning Sun Paper Nanning Pulp & Paper Mill Guangxi Province China

Valmet

Natron-Hayat Pulp and Paper Mill Maglaj Bosnia-Herzegovina

Valmet

ND Paper USA

Projet BV

Nippon Paper Industries Co. Ltd. Akita Mill Japan Nippon Paper Asahikawa Mill Hokkaido Japan Norske Skog Bruck Austria Papelera Guipuzcoana de Zicuñaga Hernani Spain Papierfabriek Doetinchem Netherlands

Padmavati Paper & Pulp Maharashtra India

Cellwood Machinery

ORDER DESCRIPTION maintenance contract for both the new bioproduct mill and board mill eight Turbo Blowers in seven different tissue and board machines to upgrade vacuum systems recovery boiler rebuild

URL link

link

Valmet

pulp production technologies for the fiberline and lime kiln plant as well as energy-saving OCC lines and a complete reject treatment system for RDF (refuse-derived fuel) production press technology upgrade including two refurbished Twin Roll Presses and additional equipment and services to secure the trouble-free operation of the presses two dry end high pressure tail cutters (order to YueLi of Taiwan) wash press and screw conveyor

Enerquin

heat recovery system

link

Valmet

automation and quality control system (PM3)

link

Andritz

new lime kiln

link

Andritz

upgrade the wet sections of PM1 and PM3 speciality machines, including new headboxes, headbox screens and pumps dispersing unit

link

Runtech

Andritz

Page 6 of 9

Installations

link

g PAPERmaking! FROM THE PUBLISHERS OF PAPER TECHNOLOGY INTERNATIONAL ®

Volume 8, Number 2, 2022

COMPANY, SITE PFNonwovens Hazleton Pennsylvania USA Port Townsend Paper Pt. Townsend Washington state USA Productora Nacional de Papel San Luis Potosi Mexico Reno de Medici (RDM Group) mills across Italy, France, the Netherlands and in the Iberian Peninsula Romatex (Pty) Ltd. Cape Town South Africa Saigon Paper Vietnam Siam Cement Group (SCG) Thailand Saudi Paper Group (SPG) Dammam second industrial city Saudi Arabia SCGP Navanakorn Plant Thailand Shandong Canfield Wood Industry Chiping County Liaocheng City Shandong Province China Shanying Paper (Jilin) Co. Ltd. Fuyu City Songyua Jilin Province China Shawano Specialty Papers Shawano Wisconsin USA Shotton Mill Limited Eren Paper Shotton Mill UK Shotton Mill Limited Eren Paper Shotton Mill UK

SUPPLIER A.Celli

ORDER DESCRIPTION master winders and slitter rewinders, along with automated handling and packaging equipment (nonwovens) Three dryer fabric cleaners for PM1

URL link

sizing section rebuild including new film press and afterdryer section (BM1) to modernise their core business processes and enable digitalisation in across nine mill

link

Andritz

batt forming line for stitchbonding (nonwovens)

link

ABB

spare parts and maintenance program high pressure showers for Press Felts for PM1 new tissue line (capacity 60ktpy)

link

Valmet

QCS for corrugated box board plant

link

Andritz

pressurised refining system

link

Andritz

a complete OCC line, including fibre recovery and reject handling system

link

Toscotec

steel yankee (PM3)

link

Arup

transformation of Shotton Mill site (also involving architects AHR)

link

Valmet

containerboard line (PM3)

link

Projet BV

Valmet

Tietoevry

Projet BV Toscotec

Page 7 of 9

Installations

link

link link

g PAPERmaking! FROM THE PUBLISHERS OF PAP PER TECHNOLOGY INTERNATIONAL ®

Volume 8, Number 2, 2022

COMPANY, SITE Siempelkamp Maschinen- und Anlagenbau GmbH (for two anonymous panelboard plant end customers, one in Europe and one in Asia) Smurfit Kappa Wrexen Paper & Board GmbH Germany Södra Cell Mönsterås Sweden Sofidel Kisa Tissue Mill Sweden SOPREMA Group Chavelot France Steico Sp. z o.o. Gromadka Poland Steinbeis Papier GmbH Glückstadt Germany

SUPPLIER Valmet

ORDER DESCRIPTION two chip washing and defibrator systems

URL link

Runtech

dryer section modification (including contactless web stabilizers) of PM3 the world’s first electrical folding machine for pulp bales

link

Andritz

upgrade of hood technology to use syn-gas in drying hood

link

Siempelkamp

wood fibre insulation board plant

link

Valmet

link

Stora Enso Ingerois Mill Finland Stora Enso Skutskär Mill Sweden

BTG

Sumapel Toledo Spain Suzano Aracruz Espírito Santo Brazil Suzano Cerrado Brazil TTCL Vietnam Corporation Ltd Bac Ninh province Vietnam Vattenfall Juktan Sweden Veolia Services Suomi (integrated into Metsä Fibre’s bioproduct mill) Äänekoski Finland

Pasaban

two second-generation defibrator systems (insulation materials plant) a complete stock preparation line for conventional wastepaper and special grades (capacity from 78-200tpd) implementation of dataPARC software platform on board machine rebuild bleach plant No.4 (which will include both new equipment, and reuse of plant moved from Oulu Mill) sheeter for coated cardboard

Andritz

modernization of lime kiln B

link

Projet BV

two new wet end Tail Cutters for the new Pulp Lines (to Andritz, Austria) waste-to-fuel plant to separate municipal solid waste into refuse derived fuel feasibility study for restoring pumped storage power plant

link

a biomethanol purification plant

link

Valmet

Andrex

Andritz

BMH Technology Oy AFRY

Andritz

Page 8 of 9

Installations

link

g PAPERmaking! FROM THE PUBLISHERS OF PAPER TECHNOLOGY INTERNATIONAL ®

Volume 8, Number 2, 2022

COMPANY, SITE Versowood Otava sawmill Finland Vilnius Combined Heat and Power Plant Lithuania Visy Paper Gibson Island Brisbane Australia Yanpai Filtration Technology Co. Ltd. Tiantai China Zweckverband Müllverwertung Schwandorf Schwandorf Germany

SUPPLIER KPA Unicon

Valmet

BMH Technology

Andritz

Page 9 of 9

ORDER DESCRIPTION major modernisationof mill, particularly installation of bioboiler biomass boiler, flue gas cleaning and flue gas condensing system works new fuel preparation plant to ensure efficient and sustainable operation of the upgraded MultiFuel Boiler (MFB) four needlepunch lines (nonwovens)

URL link

retrofit of the flue gas cleaning system in a furnace line at the municipal waste incineration facility

link

Installations

link

PAPERmaking! FROM THE PUBLISHERS OF PAPER TECHNOLOGY TE INTERNATIONAL®

Volume 8, Number 2, 2022

Research Articles Most journals and magazines devoted to the paper industry contain a mixture of news, features and some technical articles. Very few contain research items, and even fewer of these are peer-reviewed. This listing contains the most recent articles from three of the remaining specialist English language journals alongside one Korean journal and one Japanese journal, both of which publish original peer-reviewed research: x x x x x

IPPITA JOURNAL (Peer-reviewed and other) JAPAN TAPPI JOURNAL (English abstract only) JOURNAL OF KOREA TAPPI (English abstract only) NORDIC PULP & PAPER RESEARCH JOURNAL TAPPI JOURNAL

Notes: 1. IPPTA JOURNAL seems to have replaced IPPTA PAPYRUS 360° after only 2 editions of the latter, as of late 2021. 2. JAPAN TAPPI JOURNAL is a members-only journal that contains excellent research articles – abstracts are in English but articles are in Japanese. 3. JOURNAL OF KOREA TAPPI is an excellent open-access research journal – abstracts are in English but articles are in Korean.

The Paper Industry Technical Association (PITA) is an independent organisation which operates for the general benefit of its members – both individual and corporate – dedicated to promoting and improving the technical and scientific knowledge of those working in the UK pulp and paper industry. Formed in 1960, it serves the Industry, both manufacturers and suppliers, by providing a forum for members to meet and network; it organises visits, conferences and training seminars that cover all aspects of papermaking science. It also publishes the prestigious journal Paper Technology International® and the PITA Annual Review, both sent free to members, and a range of other technical publications which include conference proceedings and the acclaimed Essential Guide to Aqueous Coating.

Page 1 of 6

Research Articles

g PAPERmaking! FROM THE PUBLISHERS OF PAP PER TECHNOLOGY INTERNATIONAL®

Volume 8, Number 2, 2022

IPPTA JOURNAL, Vol.33(3), 2021 1. A Natural, Ecofriendly & Sustainable Approach towards Odor Control in the Recycled Kraft Pulp & Paper Industry 2. A New Horizon of Utilization of Bamboo for Production of food packaging Pulp, Paper and Board 3. Addressing safety concerns for producing high quality food packaging papers 4. Artificial Intelligence in Pulp and Paper Industry 5. Best Manufacturing Practices for Barrier Coatings with Eco-Friendly Materials 6. Best practices in the field of HR 7. Best practices in the field of Manufacturing – SPB, Erode unit 8. Energy Analysis of Multiple Effect Evaporator in an Indian Pulp & Paper Industry 9. Environmental Conservation in Paper Industry 10. Magnetic Bearing Technology a clean and green practice with in turbocompressor 11. MEPA - an Innovative way for ESP upgrade for Cleaner Environment in Pulp & Paper Plants 12. New Opportunities with Paper Mill Pulpers 13. Odour Control in Rcf Mills with Closed-Loop Anaerobic Technology 14. Resilient Indian Paper Industry – Gearing up for the New Normal: Driven by clear macro trends, further accelerated by Covid-19 impact 15. Resource Management in Indian Pulp & Paper Industry: Challenges & Prospective 16. Rethink Sales Channel as a Strategic tool for Business Performance 17. Review & Adoption of Best Practices For Recovery Plant & Environment Control For Efficient operation & Cost reduction 18. Skills Gaps in Pulp and Paper Industry 19. Stepping Stones: ITC PSPD’s Transforming Practices in 2 Decades of Excellence Journey 20. Stickies & Odour Control In Papermaking 21. Turning Around Sick / Under Performing Units JAPAN TAPPI JOURNAL, VOL.76(1), January 2022 1. BTG High Performance Creping Blade with Yankee Coating Visualization System 2. Energy Savings by Newly Developed Conical Refiner for Stock Preparation 3. Analysis of Phase Transfer of Thermal Chemicals in Linerless Thermal Labels 4. Thickness Reduction Control System on RB, Using Immersion UT Inspection Technology 5. Introduction of Toscotec S.p.A 6. Key Points for Creating and Operating a Pest Management Strategy 7. Safety Monitoring Solution for Factory Workers “Anzen Mimamori kun” and Introduction to Smart Factories JAPAN TAPPI JOURNAL, VOL.76(2), February 2022 1. Manufacturing and Application Development of Phosphorylated Cellulose Nanofibers 2. Characteristics and Applications of Xanthated Cellulose Nanofiber 3. All-Cellulose Structural Material 4. Characteristics of Bamboo- and Wood-derived Cellulose Nanofibrils Produced by Aqueous Counter Collision

Page 2 of 6

Research Articles

g PAPERmaking! FROM THE PUBLISHERS OF PAP PER TECHNOLOGY INTERNATIONAL®

Volume 8, Number 2, 2022

5. 6. 7. 8. 9.

TEMPO-oxidized Pulp Related Products in Nippon paper Industries: Expanding the Utilization Technology of Chemically Modified Cellulose Not Only for CNF Paragon Winding: Our Revolutionary Patent-pending Winding Technology Introduction on How KAWANOE Realizes “Together with Our Customers” Utilizing Our Pilot Plants and the Tissue Machine for Hygienic Paper Andritz Tissue Pilot Machine Trends in Nanocellulose Related Standards

JAPAN TAPPI JOURNAL, VOL.76(3), March 2022 1. General Review of 45th Pulp and Paper Process Control Symposium - process Control and Automation Committee 2. IoT Measures for Production Facilities with General-purpose AC Drives 3. European Commission Energy-Related Products Ecodesign Directive and Fujitsu’s Environmentally Conscious Design Regarding Electrical and Electric Equipment 4. Approach to Smart Maintenance with Digital Technology 5. Contribution to Carbon Neutrality through Optimization Technology 6. The Time to Start Archiving the Operation Data and Its Full Leverage in Pulp & Paper Industry at the “Big Data” Era 7. Implementation of “Smart Factory 4.0” for the Paper Mills: Cost Benefits Achieved with Prediction Models and APC 8. Efforts to Make Maintenance Work Smarter 9. Sharing and Early Resolution of Issues Through Digitalization of Operational Information Toward DX 10. Process Optimization by OnEfficiency.Strength 11. dataPARC for Digital Transformation: First Step for Digitalization in Pulp & Paper Mill 12. Making Conductive Materials from Paper as an Insulator: Chemically Morphology-Retaining Carbonization from Various Cellulosic Materials without Thermal Decomposition JAPAN TAPPI JOURNAL, VOL.76(4), April 2022 1. HSE Improvement and Machine Condition Monitoring by Wireless Noise Surveillance System 2. Improving Operations by Optimizing Chemicals ! - A Practical Chemical Approach to Solving Problems in Wastewater Treatment Process 3. Know Your Pulp, Control Your Process 4. ACA Permi Online Air Premeability Analyzer and RoQ Roll Hardness Profiler 5. Numerical Simulation in Compressive Strength Analysis of Corrugated Box 6. Analysis of the Bleeded Compounds on Paper Surface by XPS and TOF-SIMS 7. Report on the Results of the Fiscal 2021 Follow-up Survey on “JPA’s Carbon Neutrality Action Plan” and Related Information on Measures against Global Warming in the Japanese Paper Industry 8. Yokogawa Bio Fronitier Inc. 9. Properties of Mitsumata Paper Produced by Pressurized Cooking Process JAPAN TAPPI JOURNAL, VOL.76(5), May 2022 1. Development of Coated Paper Products for Packaging, “barricote®” and “barrisherpa®” 2. Cellophane or Paper Packaging as Alternative for Plastic Packaging 3. New Concept Paper Container “SPOPS” to Replace Plastic Refill Pouch

Page 3 of 6

Research Articles

g PAPERmaking! FROM THE PUBLISHERS OF PAP PER TECHNOLOGY INTERNATIONAL®

Volume 8, Number 2, 2022

4. 5. 6. 7.

Effort for Deplasticization and Plastic Reduction by Utilizing wood Pulp Material Development of Moisture Resistant Coating agents Derived from Biodegradable Biomass Material Water Based Coating Agent to Impart Barrier Layer, for Paper and Paperboard Revision of JIS P 8116 Paper - Determination of tearing resistance - Elmendorf tearing tester method

JAPAN TAPPI JOURNAL, VOL.76(6), June 2022 1. Report of the 26th Saving Energy Seminar 2. Decarbonization Solution by Using Renewable Electricity 3. Initiatives for low-carbonization in Kanto Mill (Katsuta) 4. Fuel Conversion of Lime Kiln 5. Activities for Energy Saving in Ishinomaki Mill 6. Control System to Optimize Cooling Tower Type Condenser Cooling Water System 7. New way of Applying Stabilized Halogen Application in Paper Mill 8. The Latest Trends in Technologies of Heat Transfer Improvement: Kurita Dropwise Technology 9. Contributes to Power Saving (CO2 Emissions Reduction) and Maintenance Cost Cut with HFD System (Hyper Flat Drive System) JOURNAL OF KOREA TAPPI, Vol.54(2), April 2022 1. Different Chemical Compositions of Korean Red Pine Wood from Different Growth Sites 2. Utilization of TEM with Automated Tile Scan Technique for Length Determination of CNF 3. Organosolv Pulping of Hemp Stem for a Potential Papermaking Pulp 4. Dissolution of HwBKP with [Bmim]Cl-DMF Solvent and Production of Cellulose Beads: Effect of Mixing Ratio of Solvents 5. Paper Defects Recognition Based on Deformable Convolution 6. Evaluation of Hydrophobicization of Cationic Cellulose Nanofibers Depending on the Type of Rosin Sizing Agents NORDIC PULP & PAPER RESEARCH JOURNAL, Vol.37(2), June 2022 1. Chemical pulping: The effects of high alkali impregnation and oxygen delignification of softwood kraft pulps on the yield and mechanical properties 2. Bleaching: Evaluation of pulp and paper properties produced from two new bleaching sequences 3. Mechanical pulping: The effects of wood chip compression on cellulose hydrolysis 4. Mechanical pulping: Physical meaning of cutting edge length and limited applications of Specific Edge Load in low consistency pulp refining 5. Paper technology: Enhancement in tissue paper production by optimizing creeping parameters such as application of various blade material (MOC) and creep pocket geometry 6. Paper physics: The effect of some office papers quality characteristics on offset printing process 7. Paper chemistry: Application of hydrophobically modified hydroxyethyl cellulose-methyl methacrylate copolymer emulsion in paper protection 8. Paper chemistry: Application of cyclohexene oxide modified chitosan for paper preservation

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Volume 8, Number 2, 2022

9. 10. 11. 12. 13. 14. 15. 16. 17. 18.

Paper chemistry: Application of carboxymethyl cellulose-acrylate-OVPSS graft copolymer emulsion in paper reinforcement and protection Coating: Application of BBR-DCMC/KH-791-SiO2/HPDSP multifunctional protective fluid in paper reinforcement and protection Nanotechnology: Research on ink blot evaluation of aged paper before and after restoration Chemical technology/modifications: Physical properties of kraft pulp oxidized by hydrogen peroxide under mildly acidic conditions Miscellaneous: High calcium content of Eucalyptus dunnii wood affects delignification and polysaccharide degradation in kraft pulping Miscellaneous: Refining gentleness – a key to bulky CTMP Miscellaneous: Electrospinning hydrophobically modified polyvinyl alcohol composite air filter paper with water resistance and high filterability properties Miscellaneous: Hydroxypropyl methylcellulose films reinforced with cellulose micro/nanofibrils: study of physical, optical, surface, barrier and mechanical properties: Valorization cellulosic materials for films production Miscellaneous: Effects of localized environment on the eucalypt clones quality aiming kraft pulp production Miscellaneous: Oxidation process concept to produce lignin dispersants at a kraft pulp mill

TAPPI JOURNAL, March 2022 1. Editorial: Unlock the gates! TAPPI Journal moves to fully Open Access research for all 2. Numerical investigation of the effect of ultrasound on paper drying 3. Predicting strength characteristics of paper in real time using process parameters 4. The Shendye-Fleming OBA Index for paper and paperboard 5. Considerations in managing wastewater odor at pulp and paper operations TAPPI JOURNAL, April 2022 1. Editorial: ”Didn’t know we knew that” • Rediscovering the fundamentals 2. Effects of agitator blade scaling on mixing in dissolving tanks 3. Comparative study of guar gum and its cationic derivatives as pre-flocculating polymers for PCC fillers in papermaking applications 4. Ultrastructural Behavior of Cell Wall Polysaxxharides 5. The chemistry of aluminu salts in papermaking TAPPI JOURNAL, May 2022 1. Editorial: Reflections on the Page equation, laboratory work, and new concepts 2. Development of paper quality parameter measurement in China 3. Improving refining efficiency with deflocculation 4. Web instability in the open draw and the impact on paper machine efficiency 5. The Effect of Component Removal Upon the Porous Structure of the Cell Wall of Wood. II. Swelling in Water and the Fiber Saturation Point TAPPI JOURNAL, June 2022 1. Editorial: TAPPI’s 2022 Nanotechnology Conference convenes in Finland 2. Effects of rings on flow and temperature in lime kilns 3. Water chemistry challenges in pulping and papermaking – fundamentals and practical insights: Part 1: Water chemistry fundamentals and pH

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4. 5.

Rewet suppression through press felt engineering The Influence of the Fine Structure of Cellulose on the Action of Cellulases

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PAPERmaking! FROM THE PUBLISHERS OF PAPER TECHNOLOGY T INTERNATIONAL®

Volume 8, Number 2 2022

Technical Abstracts The general peer-reviewed scientific and engineering press consists of several thousand journals, conference proceedings and books published annually. In among the multitude of articles, presentations and chapters is a small but select number of items that relate to papermaking, environmental and waste processing, packaging, moulded pulp and wood panel manufacture. The abstracts contained in this report show the most recently published items likely to prove of interest to our readership, arranged as follows:

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Coating Energy Moulded Pulp

Page 3

Nano-Science Packaging Technology

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Papermaking

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Testing

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Tissue

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Waste Treatment

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Wood Panel

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Volume 8, Number 2, 2022

COATING “Sustainable paper coating with enhanced barrier properties based on esterified lignin and PBAT blend”, Rohan Shorey & Tizazu H. Mekonnen, International Journal of Biological Macromolecules, Vol.209, Part A, pp.472-484 (1 June 2022). Sustainable and biodegradable packaging materials are appealing alternatives to the petrochemicalderived and non-biodegradable plastics that currently dominate the market. However, their inferior barrier properties and high cost inhibit their widespread applications. In this work, pristine and esterified lignin were investigated as a functional filler of poly (butylene adipate-co-terephthalate) (PBAT) based bioplastic paper coating formulations. For this, the pristine and esterified lignin (10–50wt%) were separately dispersed in a solvent and incorporated in PBAT solutions and applied on paper substrates. The effects of varying concentrations of pristine and esterified lignin on the rheology, mechanical, morphology, and barrier properties of the coated paper substrate were investigated. Comprehensive characterization of esterified lignin/PBAT coatings exhibited enhanced dispersion of the lignin fraction in the PBAT, resulting in excellent wet tensile properties and enhanced water, oil, and oxygen barrier performance. Overall, the studied coating formulations have appealing properties for food contact materials, such as paper wraps and paperboard applications, as a sustainable and eco-friendly alternative to the incumbent coating materials, such as petroleum sourced waxes and polyolefin-based coatings. ENERGY “Pulp and paper industry in energy transition: Towards energy-efficient and low carbon operation in Finland and Sweden”, Satu Lipiäinen, Katja Kuparinen, Ekaterina Sermyagina & Esa Vakkilainen, Sustainable Production and Consumption, Vol.29, pp.421-431 (Jan. 2022). Mitigation of global warming, energy security and industrial competitiveness urge the energy-intensive pulp and paper industry (PPI) to transform energy use practices. This study investigates how the PPI has responded to the need for the energy transition in the 2000s. Finland and Sweden as forerunners of energyefficient operation and decarbonization of the PPI are used as target countries. Understanding of changes in energy consumption is complemented using decomposition analysis (Logarithmic Mean Divisia Index Method) and the energy efficiency index approach. Analysis of companies’ investments in energy technologies is used for explaining changes in energy production. Evidence of significant development towards the more sustainable operation of the PPI was found. Energy consumption per produced unit has decreased, i.e., energy efficiency has improved. Fossil fuels have been partially replaced with bio-based alternatives. Thus, the CO 2 intensity has decreased substantially. The generation of renewable electricity has increased in both countries. Examples of Finland and Sweden indicate that the PPI has great potential to contribute to CO 2 emission reduction worldwide in the future as energy efficiency can be further improved, and the share of fossil fuels can be decreased increasing the use of biofuels and self-generated green electricity at least in kraft pulp mills. MOULDED PULP “Improving Mechanical Strength and Water Barrier Properties of Pulp Molded Product by Wet-End Added Polyamide Epichlorohydrin/Cationic Starch”, Chengrong Qin, Jing Li, Wei Wang, & Wei Li, ACS Omega, 7, 26, pp.22173-22180 (2022). As desirable food packaging materials, pulp molded products have attracted great attention from both academia and industry. To endow the products with high mechanical strength and water barrier properties by low-cost wet-end additives to broaden their application fields, polyamide epichlorohydrin (PAE) or/and cationic starch (CS) were added to the pulp slurry after the addition of oil- and water-proof agents. Results showed that the Page 2 of 9

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Volume 8, Number 2, 2022

optimal pulp molded product was obtained at a PAE and CS content of 1.0 and 0.6%, respectively. The resulting product had a dry strength of 24.4kN/m, a wet strength of 4.22kN/m, and a water absorption of 51.5%. The addition of CS was beneficial to the properties of the PAE wet-end added product due to the formation of hydrogen bonding with cellulose fibers and PAE, which also led to a decreased PAE dosage for health concern as food packaging materials. Finally, the PAE/CS wet-end added pulp molded product was applied for orange fresh-keeping in the fridge. The product displayed much more shape stability and lower weight increase in comparison with that of the product without the addition of PAE and CS. This indicated the great application prospects of our designed pulp molded product as a fruit freprospectssh-keeping packaging material. “Dynamic performance analysis and optimization of pulp-molding machine frames”, Junbin Lou & Yaping Gong, The International Journal of Advanced Manufacturing Technology, online (2022). The pulp-molding product is a new degradable and pollutionfree packaging material replacing traditional packaging materials. Countries are strongly recommending that pulp-molding machines are mainly used to produce pulp-molding products. The stability, efficiency, and rapidity of its products’ molding and processing quality are largely controlled by the structural dynamic mechanics of the molding machine frame. Its equipment’s dynamic performance is measured by the 1st-order natural frequency. The pulp-molding machine frame was taken as an example for optimizing the design and investigating the dynamic performance in the work. Based on finite elements, the beam structure was divided into finite elements, and the global independent generalized displacement coordinates of equipment were extracted using multi-point constraint elements. The global independent generalized displacement coordinates and the Lagrange equation were used to establish the device’s elastic dynamic model. Besides, the correctness of the theoretical model was verified by the finite element method. Finally, the first natural frequency was taken as the optimization design goal, and the particle swarm optimization algorithm was utilized to optimize the section size of the beam in equipment. The results could optimize the molding machine’s design and analyze the dynamic performance at the pre-design stage. NANO-SCIENCE “Role of cellulose nanofibrils in improving the strength properties of paper: a review”, Thabisile Brightwell Jele, Prabashni Lekha & Bruce Sithole, Cellulose, Vol.29, pp.55-81 (2022). The pursuit for sustainability in the papermaking industry calls for the elimination or reduction of synthetic additives and the exploration of renewable and biodegradable alternatives. Cellulose nanofibrils (CNFs), due to their inherent morphological and biochemical properties, are an excellent alternative to synthetic additives. These properties enable CNFs to improve the mechanical, functional, and barrier properties of different types of paper. The nanosize diameter, micrometre length, semicrystalline structure, high strength, and modulus of CNFs have a direct influence on the mechanical properties of paper, such as tensile index, burst index, Scott index, breaking length, tear index, Z-strength, E-modulus, strain at break, and tensile stiffness. This review details the role played by CNFs as an additive to improve strength properties of paper and the factors affecting the improvement in paper quality when CNFs are added as additives. The paper also includes techno-economic aspects of the process and identifies areas that need further research. PACKAGING TECHNOLOGY “The effect of ply properties in paperboard converting operations: a way to increase formability”, Gustav Lindberg & Artem Kulachenko, Cellulose, online (2022). This Page 3 of 9

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study addresses the question of how the difference in mechanical properties of the individual layers in a multi-ply commercial paperboard affects the outcome of the trayforming operation. Two commercially produced paperboards with nearly identical mechanical properties when conventionally tensile tested were considered. These boards are produced on different machines with the same target grammage and density. Despite the similar mechanical properties, their performance in a given tray-forming operation was drastically different, with one of the boards showing an unacceptable failure rate. To investigate the difference seen during converting operations, a detailed multi-ply finite element model was built to simulate the converting operation. The present model considers a critical area of the paperboard known to exhibit failures. To derive the constitutive relations for each ply in the sub-model, both boards were split to single out individual plies which were then tensile tested. Including the properties of individual plies revealed large differences between the boards when it comes to the distribution of the properties in the thickness direction. In particular, the top plies differed to a large extent. This is attributed to the difference in refining energies for the plies. The results from the three-ply sub-model demonstrated the importance of including the multi-ply structure in the analysis. Weakening of the top ply facing the punch by using lower refining energy considerably increased the risk of failure of the entire board. These results suggest that there is room for optimizing the board performance by adjusting the refining energy at the ply level. “Improving water vapor barrier of cellulose based food packaging using double layer coatings and cellulose nanofibers”, Mohammed Z. Al-Gharrawi, Jinwu Wang & Douglas W. Bousfield, Food Packaging and Shelf Life, Vol.33, 100895 (Sept. 2022). Paper based packaging has the potential to replace many plastic-based systems if the required barrier properties can be obtained. Water borne barrier coatings have the potential to generate good barrier layers, but their performance is often less than expected. Recent work has shown improved performance of these coatings when applied on paper that has a cellulose nanofiber layer. Here, papers with a cellulose nanofiber layer were coated with barrier coatings at different coat weights applied as single-layers, as double-layers, and single-layers pressed together in a hot press in order to generate a packaging system that has good barrier properties. The performance of double-layer samples resulted in moisture transmission rates that were 40–70% of the value of the single-layer systems. Surprisingly, the hot-pressing of two dry layers showed no advantage compared to the single-layer system. A barrier pigment added to one formulation improved the performance further and followed the same trends. Three dimensional models of diffusion through layers that have defects help explain the results. The work shows a potential path to produce paper-based packaging that has both good oxygen and water vapor barrier properties. PAPERMAKING “Janus particles stabilized alkenyl succinic anhydride emulsion as internal sizing agent”, Hongzhen Wang, Jujie Sun, Yongxian Zhao, Zhongqin Zhang & Shijie Cheng, Cellulose, Vol.29, pp.6361-6372 (2022). Alkenyl succinic anhydride (ASA) is widely used in papermaking industry as an internal sizing agent. In situ emulsification of ASA using cationic starch is conventionally practiced because of the low shelf life of ASA emulsion. We synthesized Janus particles by surfactant-free seeded polymerization to stabilize ASA emulsion. The morphology evolution and anisotropic compositions of Janus particles were confirmed by transmission electron microscopy. The Janus particles showed a strong tendency to adsorb at the ASA–water interface and enhanced the stability of ASA emulsion. The droplet size of ASA emulsion decreased and emulsion Page 4 of 9

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Volume 8, Number 2, 2022

phase volume increased with the concentration of Janus particles increased. In comparison with cationic starch, Janus particles exhibited superior emulsification performance in ASA emulsion. The ASA emulsion stabilized by Janus particles was used as an internal sizing agent for cellulose paper. The results of sizing degree and Cobb 30 showed that the sizing performance of ASA emulsion stabilized by Janus particles was significantly improved. Our study provides a better choice of preparing ASA emulsion for paper sizing and promotes the application of Janus materials in paper industry. “Preparation of cross-linking PVA copolymer modified by DAAM/ADH and application in paper surface sizing”, Kaibin Li, Xiaorui Li, Dan Wang, Baoping Yang, Yihe Liu, Haihua Wang & Yiding Shen, Cellulose (2022). Herein, a novel modified polyvinyl alcohol(DA-IPVA) used as sizing agent was prepared by using diacetone acrylamide(DAAM)/adipic dihydrazide(ADH) as graft monomer and N(isobutoxymethyl)acrylamide(IBMA) as self-cross-linking monomer. The effect of the amount of DAAM on the properties of emulsion, film and sizing paper was discussed. The surface micro-structure of the sizing paper was characterized by SEM and AFM. The addition of DAAM/ADH and IBMA endowed DA-IPVA with cross-linked active group and increased cross-linking density and hydrophobicity after ADH was added into the emulsion and the cross-linking structure was formed. The enhancing mechanism of surface sizing agent for paper was revealed. The DA-IPVA can be cross-linked on the surface and inside of the paper to form a dense network structure, which improves the bonding force between the fibers. When the mole fraction of DAAM of the cross-linking monomer is 8%, the surface sizing performance of the paper is obviously improved compared with the base paper. The dry and wet strength is increased by 266.5% and 334.3% respectively, and the folding resistance is increased 2946.67%. This study can have a profound impact on the development of the technology of cross-linking surface sizing agent for paper. TESTING “Determination of the surface charge of lignocellulosic fiber by a derived spectroscopic technique”, Ning Yan, Yu-Ting Zhang, Xin-Sheng Chai & Zhao-Qing Lu, Cellulose, Vol.29, pp.5547-5556 (2022). This paper proposed a derived spectroscopic technique for determining the surface charge of lignocellulosic fiber. In this method, chitosan quaternary ammonium iodide with higher molecule weight was selected to minimize its interaction with the negative charge inside of fiber pores. It was based on spectroscopically measuring the UV absorbance of I− (the counter ion) in the filtrates from a set of solutions that containing the fixed amount of fibers and the different amount of cationic polymer (from under- to over-saturation). By plotting the derived absorbance at 245nm versus the volume of chitosan addition, a transition point is determined, from which the fiber surface charge can be calculated. The results showed that the present method has a good measurement precision (RSD < 3.24%) and accuracy (relative differences < 3.11%, when compared with the conductivity titration method). It is suitable to be used for determining the surface charge of lignocellulosic fibers. “Bending behavior and geometrical optimization of five-layered corrugated sandwich panels with equal in-plane principal stiffness”, A Vakilifard, H Mazaheri & M Shaban, Journal of Composite Materials, online (May 2022). In this work, bending properties of five-layer sandwich panels with corrugated three-layer core are investigated both numerically and experimentally. Sheet metal forming is employed to construct the corrugated core and three-point bending tests are performed to experimentally evaluate the bending behavior of the panels. Besides, reliable finite element model is developed and validated by the experimental results. The results show that the phase difference of Page 5 of 9

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Volume 8, Number 2, 2022

the external core has no considerable effect on the panel behavior. Next, the effect of orientation for the corrugated cores is studied for two 0/90/0 and 90/0/90 layups. The results show that bending rigidity of 90/0/90 is greater than other case due to more bending rigidity of the external cores. To design an optimum sandwich panel, genetic algorithm is utilized by constraining the mass and height of the panel. For optimization purpose, an analytical formulations that is validated by presented experimental and numerical results are used. Based on optimization results, optimized sandwich panel is constructed and exposed to TPB test. Good agreement is observed between all the numerical, analytical and experimental methods. The results indicate that the optimized configuration can achieve notable higher bending resistance in the same weight especially for the 90/0/90 case. Finally, an isotropic multilayered sandwich panel is introduced and optimized to overcome the drastic anisotropic properties of corrugated cores. The optimized isotropic panel have equal bending rigidity in two principal axes of the panel. TISSUE “Enhanced water absorption of tissue paper by cross-linking cellulose with poly(vinyl alcohol)”, A. Cláudia S. Ferreira, Roberto Aguado, Raquel Bértolo, Ana M. M. S. Carta, Dina Murtinho & Artur J. M. Valente, Chemical Papers, Vol.76, pp.44974507 (2022). Tissue paper was the only paper grade whose consumption increased during 2020 in Europe. In a highly competitive context, this work explores a strategy based on bisacrylamide cross-linkers and poly(vinyl alcohol) (PVA), seeking to enhance the water uptake of pulps for tissue paper and the key properties of the resulting tissue sheets: water absorption capacity, capillarity, softness, porosity, and strength. For that, α-cellulose from cotton and a kraft hardwood pulp, in parallel, were reacted with N,N’methylenebisacrylamide, both in the absence and in the presence of PVA. The water desorption rate of the modified polymers was monitored. Pulp blends were then mixed with a conventional softwood pulp (30%) to prepare laboratory tissue paper sheets (20g m–2). For cotton cellulose, cross-linking with PVA more than doubled the water uptake, up to 7.3g/g. A significant enhancement was also obtained in the case of pulps, up to 9.6g/g, and in the case of paper, to 11.9g/g. This improvement was consistent with a drastic increase in porosity, and it was not detrimental to paper strength. “Insights into Gum Arabic interactions with cellulose: Strengthening effects on tissue paper”, A. Cláudia S.Ferreira, Roberto Aguado, Ana M.M.S. Carta, Raquel Bértolo, Dina Murtinho & Artur J.M. Valente, Materials Today Communications, Vol.31, 103706 (June 2022). Competitiveness in the market for tissue paper, the only paper grade whose consumption increased during 2020 in Europe, requires seeking viable options to continuously improve its properties. This work explores the combination of gum Arabic, which is a naturally found, biodegradable, cheap and versatile heteropolymer, with bleached cellulosic pulps. Blends of pulps and alkaline gum Arabic (GAb) were analyzed in terms of their thermal degradation behavior, morphology, water absorptivity and drying rate. It was found that water uptake increased by 23% for the maximum proportion of GAb tested (30%, w/w) and that water desorption followed quasi-zero-order kinetics. Furthermore, these blends were used to prepare light-weight paper handsheets by bulk addition, in which small proportions of GAb (3%) were enough to significantly improve tensile strength. Remarkably, the most unexpected result came from the surface addition of alkaline GAb by spray coating, as the tensile index was increased from 7 to 18N m g–1. Overall, even though it was not possible to improve and enhance simultaneously all properties, the use of pre-blended GAb in papermaking revealed significant potential when it comes to increasing strength, a key property in different tissue products, such as multipurpose and kitchen rolls, or even in handtowels. Page 6 of 9

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Volume 8, Number 2, 2022

WASTE TREATMENT “Recycling Waste Paper for Further Implementation: XRD, FTIR, SEM, and EDS Studies”, Sarita Manandhar, Bindra Shrestha, Flavien Sciortino, Katsuhiko Ariga & Lok Kumar Shrestha, Journal of Oleo Science, 71 (2022). Recycling technology contributes to sustainability and has received considerable interest in fulfilling consumable products’ social demands, including papers. Recycled fibers are the primary source of the papermaking industry. Papers, valuable daily used materials, can be further recycled for further implementation. Here, we report a simple method for recycling waste papers for further use. Our method includes re-pulping, deinking, bleaching, and papermaking. The sample and the recycled papers were characterized by X-ray diffraction (XRD), Fouriertransform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energydispersive X-ray spectroscopy (EDS). XRD data shows the presence of cellulose and filler minerals in the sample and the recycled papers. FTIR analysis confirmed the presence of hydroxyl, carbonyl, and methyl functional groups in the recycled papers suggesting that the deinking and bleaching did not cause any structural changes. The fibrous structures were also sustained after recycling, as confirmed by SEM studies demonstrating that the recycling was successful and the papers can be further used and recycled. EDS analysis further confirmed the filler minerals in the sample paper with a trace amount of lead, which decreased upon bleaching the paper. The structure and properties of the sample and the recycled papers were quite similar, inferring that waste papers can be recycled again and different products from low to higher grade papers can be fabricated. “Impact of effluent of Pulp & Paper industry on the flora of river basin at Jaykaypur, Odisha, India and its ecological implications”, A.P.Tripathy, P.K. Dixit & A.K.Panigrahi, Environmental Research, Vol.204, Part A, 111769, (March 2022). The JK Paper industry located at Rayagada discharges biologically untreated effluent more than the permissible limit prescribed by Pollution Control Board, Odisha in to the environment. The industry is seriously polluting the surrounding aquatic and terrestrial environment. No detailed intensive study was carried out by previous workers on this industry earlier. The present study aims at finding out the impact of effluent on the flora at the contaminated site. The chemically treated effluent (TE) contained significant amount of mercury and cadmium. The TE has high BOD, COD, dissolved solids and suspended solids when compared to normal river water at the site of discharge. The TE deteriorated the natural water bodies changing the physico-chemical properties of natural river water. After meeting the river water the TE was diluted after 1 km distance from the meeting point of the river. Crop plants collected from the contaminated site showed higher level of residual Hg and Cd and significant depletion in pigment was observed. Plants collected from both the sides of the treated effluent canal showed significant amount residue mercury and cadmium in the plant leaves. The plants exposed to the TE, showed variation in chlorophyll and Phaeophytin pigment content when compared to their respective control values in all terrestrial plants collected from the contaminated site. In some plant leaves little increment in the pigment level was noted but the values were not significant. The changes observed in the plant pigment might be due to heavy metal accumulation. The presence of residual Hg and Cd in crop plants and plant leaves grazed by grazing animals after absorption, accumulation and enrichment may lead to a possible biological magnification, warrants attention. Proper biological treatment, treatment of effluent by modern methods and removal of heavy metals from the effluent before discharge by the industry is suggested. “Kinetics of Pulp and Paper Wastewater Treatment by High Sludge Retention Time Activated Sludge Process”, Ahmad Hussaini Jagaba, Shamsul Rahman Mohamed Page 7 of 9

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Kutty, Azmatullah Noor, Abubakar Sadiq Isah, Ibrahim Mohammed Lawal, Abdullahi Haruna Birniwa, Abdullahi Kilaco Usman, Sule Abubakar, Journal of Hunan University Natural Sciences, Vol.49(2), 2022). Paper and pulp industrial processes lead to the discharge of wastewater that contains high pollutants concentrations into the environment, which subsequently contaminate freshwater. Thus, it necessitates a sustainable treatment approach. This study focused on the start-up of the bench-scale activated sludge system fed with pulp and paper wastewater to verify the influence of HRT, wastewater concentration, and sugarcane bagasse on COD and ammonia removal efficiencies during the treatment process. An activated sludge process was operated at a flow rate of 5 L/day, while the reactor kept running at 72h, 48h, and 24h HRT, respectively. Wastewater concentrations were set at 1039, 3158, 5248mgCOD//L and 13.74, 40.37, 67.04mgNH4+-N/L corresponding to 10, 50 and 100% respectively. Findings revealed high removal efficiencies up to 98.11% and 92.67% for COD and ammonia, respectively. After treatment, effluent concentrations for both parameters have satisfactorily met the Standard "A" standard limits for industrial discharge at 48 hours HRT. Therefore, further testing is not required. The First order and Modified Stover-Kincannon models evaluated substrate removal rates. In the Modified Stover–Kincannon model, high correlation coefficients R2 of 0.9999 and 0.9998 were obtained for COD and ammonia, respectively. Unfortunately, the activated sludge process in the bioreactor could not be described by the first-order kinetic model. The modified Stover-Kincannon model proved to best suit the experimental data. WOOD PANEL “Making Ultra-thin High Density Fiberboard Using Old Corrugated Container with Kraft Lignin”, Peng Luo, Chuanmin Yang & Tao Wang, BioResources, Vol.17(2), pp.2696-2704 (2022). Ultra-thin high-density fiberboards (HDFs), a newly developed variety of fiberboards, broaden and extend the applications of medium thick medium- and high-density fiberboards and are capable of replacing cardboards for most applications. Old corrugated container (OCC) is an important packaging solid waste. The mechanical strength of OCC deteriorates after repeated recycling processes. Application of OCC fibers for value-added ultra-thin HDFs can be of much interest. Because the OCC fibers have more surface area than the wood particles, the resin coverage per surface area of the OCC is much lower than wood particles during panel board formation. Therefore, the performance of the OCC fiber-based board is poor and the resin adhesive consumption is high. To overcome these problems, a novel method of using OCC to make ultrathin HDFs was developed and investigated. In this work, the OCC was shredded and pulped before making the ultra-thin HDFs. To protect consumers from exposure to harmful formaldehyde, kraft lignin was used as a binder. The target density and thickness of the ultra-thin HDFs were 1.0kg/m³ and 2mm respectively. The resulting ultra-thin HDFs were evaluated for their physical and mechanical properties. Comparisons with the Chinese Standards for Wet-Process Fiberboards are presented. The results indicate that OCC could be a potential sustainable resource for ultra-thin HDFs production. “Utilisation possibilities of waste medium-density fiberboard: A material recycling process”, S.Thirugnanam, R. Srinivasan, Kshitij Anand, Abhishek Bhardwaj, G. Puthilibai, P. Madhu & A. Karthick, Materials Today Proceedings, Vol.59 Part 2, pp.1362-1366 (2022). Currently, most of the waste medium-density fiberboards (MDF) are incinerated or landfilled due to lacking of appropriate recycling methods. In this study MDF waste particles were undergoes via a thermal treatment through pyrolysis process. Pyrolysis experiments were carried out in a lab-scale fixed bed reactor at various reaction temperatures of 350, 400, 450, 500 and 550°C at the heating rate of 20°C/min. The yields of the products were impacted by the pyrolysis temperature in this study. The maximum Page 8 of 9

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g PAPERmaking! FROM THE PUBLISHERS OF PAPER TECHNOLOGY INTERNATIONAL ®

Volume 8, Number 2, 2022

yield of bio-oil of 41.9wt% was obtained at the temperature of 450°C. Gas chromatography (GC) was used to determine the chemical composition of the liquid oil product. The results shows that pyrolyzing MDF might produce renewable fuels by prevent the environmental issues associated with waste management. “Influences of hardening agent on some physical and mechanical properties of medium-density fibreboard”, Osman Çamlibel & Murat Aydin, Turkish Journal of Forestry, Vol.23 (2), pp.128-134 (2022). Effects of Ammonium chloride (NH4CI) as a hardening agent on thickness swelling (TS), water absorption (WA), screw holding resistance (SHR), Janka hardness, modulus of rupture (MOR), modulus of elasticity (MOE), and internal bonding (IB) properties of medium-density fiberboard (MDF) were evaluated. Target densities were 712 and 715kg/m³ for hardener applied (0.75kg/m³ solid as 10% solution (fiber dry wt.)) and unmodified factory made 18mm thick MDF, respectively. A total of 400 samples were tested. Boards produced without hardener presented better mechanical properties except for SHR. Indeed, SHR was around 9.2% improved by hardener utilization. However, hardener utilization caused around 8.4%, 7.3%, 3.6%, and 1.3% decreases for MOE, MOR, IB, and Janka hardness, respectively. Surprisingly, soaking time caused opposite results for TS and WA. The TS and WA of the hardener utilized MDF decreased around 40.3% and 29.6% for short-term soaking (2h) but remarkable increases (around 62.4% and 20%, respectively) were observed for long-term (24h) soaking. Statistical analysis proved that there were statistically significant (P<0.05) differences between all the evaluated properties. “Effects of application conditions on the bending strength of oriented strand board (OSB)”, Chen Chaoyi, Li Wanzhao & Mei Changtong, Journal of Beijing Forrestry University, 44(6), pp.138-134 (2022). Objective Oriented strand board (OSB) is composed of cross-oriented layers consisting of thin and rectangular wooden flakes or strands, which are compressed and bonded together with synthetic resins. OSB is an important engineered wood product. The influence of application environment on the bending properties of OSB can provide necessary theoretical support for optimizing the processing technology and application method of OSB. Method Samples prepared from 13mm thick OSB panel were conditioned under different relative humidity (RH) conditions. Three-point bending tests were performed to measure the fatigue deflection of OSB under cyclic loading, strain distribution was recorded using digital image correlation (DIC) simultaneously. This contributes to reveal the causes of deflection results. Result: The increase of RH increased the moisture content and thickness of OSB, and enlarged the voids among wood strands and cracks in wood strands. The deflection of OSB increased significantly after conditioning at (95 ± 3)% RH, and after conditioning the samples at (65 ± 3)% RH, the deflection was still larger than the initial deflection. The samples’ deflection was close to their initial deflection if conditioning them at (95 ± 3)% RH and (65 ± 3)% RH without adding loading. The effect of loading cycles on the deflection was slight when the samples were conditioned at unchanged (65 ± 3)% RH. The deflection of the first cycle loading obviously increased, which was not found as increasing loading cycles. Strain distribution was homogeneous if the samples were conditioned only at (65 ± 3)% RH. The increase of moisture content could hamper the strain transfer and induce strain accumulation. Specifically, bending strain was prone to accumulate on the top and bottom surfaces, and shear strain would occur in the two opposite directions in high moisture content samples. Conclusion: The findings of this work explore the effect of application conditions and loading cycles on the bending strength of OSB. The outputs of this work are helpful for optimizing the manufacturing strategies and enlarging application field of OSB. Page 9 of 9

Technical Abstracts

PAPERmaking! Vol.8 No.2 2022

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DSUKP Unbleached kraft pulp Delignified 3