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Sulfur-Free Pulping Of Crateva Adansonii From Sudan Osman T. Elsaki 1, Selim Otuk, 2 and Tarig O. Khider 3 (1)

Institute of Technological Research, NCR, Khartoum, Sudan E-mail: (2) University of Upper Nile, Malakal, South Sudan (3) University of Bahri-College of Applied and industrial sciences, Khartoum Sudan E-mail: (Received: August 04, 2012; Accepted: September 02, 2012) 

Abstract— The wood of Crateva adansonii DC. (Dabker) as an important indigenous Sudanese hardwood species was examined to determine its suitability for pulp and papermaking. Physical and morphological studies, basic density, bark-to-wood ratio, and fiber dimensions were studied. The chemical composition of the wood was studied. Soda and soda-anthraquinone pulping as sulfur-free processes were applied. The produced pulp batches were evaluated and papermaking characteristics were tested. C. adansonii wood showed lower basic density (0.39 g/cm3). The average bark-to-wood ratio by mass (3.52%) and by volume (11.67%) was in the normal average for pulpwood. The fibers of C. adansonii were short. The average fiber length was 0.660 mm with an average cell wall thickness of 0.001mm and lower felting ratio (24.95). The wood showed lower ash content (0.63%) which may lead to less consumption of pulping chemicals and reduction of chipper knives wear in paper mills. The wood when pulped with 12-16% alkali charge as Na2O for 120 minutes at 170 °C gave bleachable Kappa values. The addition of 0.13% anthraquinone (AQ) to pulping liquor reduced the active alkali consumption by 2-2.3% and increased the pulp yield.

Index Terms— Crateva adansonii; Fiber Dimensions; Pulping Conditions; Papermaking.

I. INTRODUCTION he demand for paper and paper products in Sudan has grown rapidly with continuous development. There are many important Sudanese wood species which could be studied for their suitability as raw material for pulp and paper production. Different pulp yields are expected depending on the suitability of the raw material and pulping processes and conditions. Although kraft pulping process has several significant advantages, it has a number of disadvantages. It generates odoriferous environmental polluting compounds [1],[2]. Many alternative sulfur-free processes were introduced among which are soda and soda-anthraquinone pulping processes [3],[4]. Sudan is rich in different hardwood species many of which could be a good source of pulp production [5]. Among the important indigenous Sudanese hardwood species is C. adansonii (Dabker). C. adansonii


* corresponding author Osman T. Elsaki

belongs to the family Capparaceae [6],[7]. It is small to medium sized deciduous tree between 6-15 meters high [8],[9],[10]. The fruits of the tree are edible [11].The species is naturally distributed in Kassala, Blue Nile, Southern Darfur and Kordofan and South Sudan [12] Low cost and environmentally-friendly sulfur-free processes are needed for wood pulping in order to reduce sulfur pollution in pulp and paper industry. II. MATERIALS AND METHODS Five C. adansonii trees from Jelhag natural forest were randomly selected. The trees were felled and the branches were removed. Five logs about 100 cm long were prepared according to TAPPI standards [13]. The average basic density was determined using wood specimens according to the British Standards [14]. Wood fibers were macerated using 60% nitric acid. Fiber dimensions were determined microscopically at X100 and X300 magnifications. Standard deviation and arithmetical mean were used for determination of fiber properties. Chemical analysis of wood samples was carried out using 40 to 60 mesh wood meals in accordance with the standard methods of TAPPI [13]. Soda and sodaanthraquinone pulping was carried out in a 10-litre capacity rotating autoclave. Active alkali charges of 12-16% as Na2O were used. Anthraquinone (0.13% on oven dry wood base) was added to the pulping liquor in the autoclave. The cooking conditions were kept constant that time to reach maximum temperature was 90 minutes and time at maximum temperature was 120 minutes. Unbleached pulp was evaluated at 25 and 40 degrees Schopper Reegler (oSR) freeness. Handsheets were prepared using a Rapid- Kothen sheet forming machine and tested using TAPPI standards. III. RESULTS AND DISCUSSION The results of physical properties of crateva adansonii wood as shown in Table (1) indicated that the average basic density (on the bases of oven dry wood and green volume) of the wood was (390 kg/m3). This was in the lower range for commercial pulpwoods according to Casey [15]. This will lead to the ease of chopping and will not cause wear on chipper knives in pulp mills. It is well known that the


J OURNAL OF FOREST PRODUCTS & INDUSTRIES, 2012, 1(1), : 23-26 presence of bark and specks of dirt affects the quality of pulp. Due to this fact the lower bark-to-wood ratio by mass (3.52%) for C. adansonii makes it a suitable wood for pulping. The bark-to-wood ratio by volume (11.67 %) was in the medium range for tropical hardwoods according to Rydholm [16] and within the range for commercial temperate pulp woods according to Casey [15]. The most important fiber characteristics affecting the strength of paper are the fiber length and cell wall thickness [17 and 18]. The average fiber length (Table 2) for C. adansonii was

0.660 mm. hence it is considered as a short fibred species. This means that it needs to be mixed with other long fibered wood pulp to obtain good paper properties. Due to the low felting ratio, dabker tissues were expected to collapse and produce good surface contact between adjacent fibers and hence, strong fiber-to-fiber bonding. The felting ratio values indicate also that C. adansonii wood could give paper with medium tear strength.

Table 1 Physical Properties of Crateva adansonii from Sudan.

properties Basic Density (g/cm3) Bark-to-wood ratio by mass % Bark-to-wood ratio by volume%

Values 0.39 3.52 11.67

Table 2 Fiber Dimensions and Morphological Indices for C. adansonii From Sudan

Fiber Dimensions Av fiber length (mm) Av. Fiber Diameter (mm) Cell wall thickness (mm) Morphological Indices Felting power Flexibility coefficient Coefficient of cell rigidity Runkle ratio The chemical characterization of crateva wood meal (Table 3) showed that the average values for the inorganic constituents as indicated by the ash, and silica contents (0.63% and 1.44% respectively) were lower. This lower ash and silica content is expected to decrease alkali consumption during pulping, reduce coloration and minimize wear and blunting of chopper knives in paper mills.

0.660 0.030 0.002 24.95 0.784 0.17 0.55 The average cellulose content (44%) for C. adansonii was in the normal range for tropical hardwoods according to Hale classification [17]. For this reason, good pulp yields could be expected. The lignin content was rather low which indicates easier delignification of wood chips and good bleachable pulp. The higher Pentosans content (23.8%) will give the pulp resistance against carbohydrates degradation.

Table 3 Chemical Composition of Carteva adansonii.

Chemical Composition (%) Ash Sulfate ash Total silica Alkali soluble silica Cellulose Hemi cellulose Lignin Cold water extractives Hot water extractives Pentosans

C. adansonii 0.63 0.36 1.44 8.00 44.00 23.80 24.40 2.90 19.00 23.80



Table (4) shows pulping conditions and yield for C. adansonii. At the same pulping conditions the wood chips have shown lower yield (41.5 and 44.0 %) when cooked with soda process while the yield was increased with the use of 0.13% AQ up to 48.5%. The use of active alkali charge of 12% as Na2O with the soda process at fixed maximum temperature (170 o C) has increased the yield at first but a decrease in the yield was show

when the alkali charge was raised to 16% as Na2O. This means that more alkali charges lead to overcooking and cellulose degradation. The use of 0.13% AQ with the same active alkali charges gave higher yields and a little increase in the yield with the increase of the alkali charge from 12 to 16% as Na2 O.

Table 4 Soda and Soda AQ pulping conditions and yield for Crateva adansonii.

Pulping process Cook code

Soda P1




Active alkali as Na2O on oven dry wood % AQ on oven dry wood .% Liquor to wood ration on oven dry wood % Pulping Maximum temperature (°C ) Time at max. temp.( min ) Yield on oven dry wood %

12 0 5:2 170 120 44.0

16 0 5:2 170 120 41.5

12 0.13 5:2 170 120 48.0

16 0.13 5:2 170 120 48.5


Table 5 Unbleached pulp evaluation at 25 o SR and 40 o SR freeness for Crateva Adansonii.

Beating degree

Kappa number

Tensile index Nm /g

Tear index,mNm2/g

Burst index, kpam2 / g

Folding endurance Log n*

2 5 o SR






40 o SR






REFERENCES Table (5) shows that at the beating degree to 25 °SR gave lower tensile index than beating to 40 degree SR which gave higher tensile index, Tear index, burst index, and folding endurance. The mechanical strength properties of pulps made from C. adansonii wood are acceptable and unbleached pulps could be used for warping paper and paperboard.

IV. CONCLUSIONS From the above results and based on the physical and morphological properties, the Crateva adansonii wood could be considered as a medium range and short fibered pulp wood. The wood could be mixed with long fibered species to produce paper with good properties. The anatomical features of C. adansonii wood do not indicate serious problems with liquor penetration and impregnation. The use of Soda-AQ pulping process as sulfur-free pulping process for C. adansonii wood has accelerated delignification and beating rate, decreased the alkali consumption and increased pulp yield. ACKNOWLEDGMENT The authors would like to express their thanks to the NCR for facilities and support.

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