Tailor-Made Calcium Carbonate

Omyafiber® Calcium Carbonate for Polyester and PLA Fiber and Nonwovens

By Barbara Bonavoglia, Martin Brunner and Christophe Roux

Calcium carbonate is widely used for decades in rigid and flexible polymer applications and is, for example, a functional mineral modifier in sensitive products like hygiene breathable films. The use of calcium carbonate with a tailored particle size and particle size distribution is already known in polypropylene (PP) nonwoven applications1 and this article will highlight the advantages of using calcium carbonate in polylactic acid (PLA) and polyester (PES) fiber and nonwoven applications.

Given the sensitivity of the fiber spinning processes, partly linked to the denier of the fibers themselves, it is clear that a finely ground and highly pure calcium carbonate needs to be selected, in order to secure stable production. A strict control on larger residues and contamination is also required to meet the high-quality standards and durable performance requirements of the final articles.

Since calcium carbonate for polymer applications is typically commercially available in powder form and direct addition of powders during the fiber spinning extrusion process is not possible on commercial scale, first the development of suitable masterbatches is needed. The masterbatch can then be fed to the spinning extrusion line to achieve the desired target concentration of calcium carbonate in the fiber.

During the production of the masterbatch particular attention is needed in securing the right dispersion of the mineral modifier in the polymer matrix. From a calcium carbonate perspective, the particle size distribution and surface treatment play critical roles for achieving excellent dispersion as they influence powder flowability and compatibility to the polymer matrix. Another important factor to consider is the temperature stability of the surface treated calcium carbonate to avoid the formation of die build-up and deposits which directly lead to spinning disruptions and quality issues.

Polymers of the polyester family, like polyethylene terephthalate and polylactic acid, are also often sensitive to degradation by hydrolysis. The choice of surface treatment for calcium carbonate is therefore very important to minimize the natural hygroscopicity of the mineral. Various chemistries are available for coating calcium carbonate, a wise choice of functionality, as developed by Omya, can reduce humidity pick up and protect the polymer from degradation.

To validate the performance of the above mentioned surface treated calcium carbonate, extensive technical evaluations in PES and PLA nonwoven systems were done at well-known research institutes, e.g. the European Centre of Innovative Textiles (CETI, Tourcoing) in France and the Saechsisches Textilforschungsinstitut (STFI, Chemnitz) in Germany. For all the trials the surface treated calcium carbonate Omyafiber® 800 from Omya International AG, Switzerland, was used.

During the first trial, bobbins of 2 denier PES filaments were produced on the Hills melt spinning line at CETI adding calcium carbonate via a 50% concentrated masterbatch (Figure 1). As base resin for the fibers, the Invista grade RT 5140 was used and addition levels of 5% and 10% of calcium carbonate in the fi- nal fiber were achieved. The fibers were stretched on 110˚C heated godets at a stretch ratio of 1:3 and the line was running at a final speed of 1490 m/min. No processing issues were highlighted during the trial which lasted for several hours.

Similar to what is seen in PP nonwovens1, the addition of calcium carbonate to PES fibers and nonwovens is significantly improving the whiteness, increasing the opacity and reducing the gloss, giving a more natural appearance and cotton like haptics to the fibers.

On top of reduced gloss, the effect of adding the treated calcium carbonate in a PES nonwoven is that of improved visual homogeneity and better coverage, as can be seen in Figure 2, where 50 GSM spunbond thermal bonded nonwovens with (right) and without (left) calcium carbonate can be compared.

Other solutions currently exist in the market to increase whiteness and opacity of fibers and nonwovens, the main one being titanium dioxide (TiO2). The carbon footprint of TiO2 is however quite high2 with a Greenhouse Gas (GHG) emission value of 4900 kg CO2eq/1000kg, compared to only 300 kg CO2eq/1000kg for surface treated calcium carbonate3. Considering a typical dull fiber formulation based on polyester an increase of +1.3% in GHG emissions over the value of the pure polymer4 would be expected by add- bonate via 50% concentrated polyester masterbatch. ing 2% TiO2. If, instead, the same lustre is achieved by adding calcium carbonate, a reduction in GHG emissions is obtained, as shown in Figure 3.

The data presented in Figure 4 show a typical bonding curve measured on a 50 GSM nonwoven. The darker colors represent the machine direction (MD) values and the lighter colours the cross direction (CD) values. The bonding temperature is reported on the x-axis.

Another advantage of adding calcium carbonate is expected when fibers and nonwoven are consolidated by means of heat, e.g. via thermal calendering or airthrough bonding process. Given the difference in thermal conductivity between polymers and calcium carbonate (Table 1), heat is indeed expected to transfer faster upon addition of calcium carbonate, enabling bonding at lower calender or oven temperatures.

To confirm these assumptions, trials were performed at CETI on their Hills spunbond and thermal calender system using Invista RT 5140 as base polyester resin and adding the treated calcium car-

In grey the tenacity of the nonwoven system without calcium carbonate at different calender temperature is reported, with its optimum achieved at 222.5˚C. On the right hand side of the graph, the bonding curve upon addition of 5% calcium carbonate can be seen (blue bars). Already at 205˚C excellent MD and CD values can be achieved, that can only be slightly improved by increasing the calender temperature up to 218˚C. The positive effect of calcium carbonate on reducing energy costs by reducing the bonding temperature without compromising on performance was confirmed in this pilot scale trial.

The second polymer system tested in combination with the surface treated calcium carbonate was polylactic acid (PLA). Before starting with nonwoven production, it was however important to validate that the masterbatch containing calcium carbonate received the certification of industrial compostability, since PLA is often the polymer of choice when

Amount extracted in water (mg/sqinch) < LoQ < LoQ

Amount extracted in heptane (mg/sqinch) < LoQ < LoQ

Organoleptic defect deriving from packaging –Olfactory test (odor assessment)

Organoleptic defect deriving from packaging in contact with food – Gustatory test (taste assessment) it comes to industrially compostable applications. For this purpose, a sample of the masterbatch MB 165-CBN based on PLA and 65% surface treated calcium carbonate was sent to TÜV in Austria for validation and it indeed received the certificate approving the use of the “OK Compost Industrial” conformity mark.

We therefore proceeded with tests on PLA nonwovens systems, which were performed at STFI on their Reicofil 4 spunbond and thermal calender line. The PLA used were the 6100D and 6202D grades from NatureWorks Ingeo Biopolymer and the surface treated calcium carbonate was added via the TÜV approved, 65% concentrated masterbatch based on PLA. During the trial, 30 and 50 GSM nonwovens were produced with the addition of 5% and 10% calcium carbonate and results for the 50 GSM nonwoven based on PLA 6100D are reported in Figure 5. Like in previous graphs, the light colour represent the values in cross direction and the darker colors the values in machine direction. The nonwoven was bonded with a calender temperature of 150˚C.

As can be seen, a further advantage was confirmed when adding calcium carbonate with the appropriate surface treatment to PLA. Given the sensitivity of PLA to degradation and hydrolysis, the addition of an untreated calcium carbonate or of a calcium carbonate with an unsuitable surface treatment would have led to loss of mechanical performance, e.g. of tensile strength. Adding, instead, calcium carbonate with the appropriate surface treatment leads, as seen in Figure 5, to an improvement of tensile proper-

Odor intensity of sample significantly equal to the reference

Organoleptic defect intensity of sample significantly equal to the reference ties that is proportional to the mineral modifier concentration.

Similar results were seen on 30 GSM nonwovens as well as when using the Luminy L130 from TotalEnergies Corbion.

Last but not least, another interesting aspect of using the suitable surface

Odor intensity of sample significantly equal to the reference

Organoleptic defect intensity of sample significantly equal to the reference treated calcium carbonate in polyester and PLA nonwovens is the significant improvement in process stability and the reduction of static charges leading to a safer material handling and production process.

From a regulatory perspective, the suitable surface treated calcium carbonate used in above studies is food contact approved according to U.S. Food and Drug Administration (FDA) and European Union regulations. When fibers and nonwovens are used as packaging components in contact with food, it is however also important that no undesired substances migrate into the food and that the organoleptics of the aliments are not negatively impacted. For this reason tests at Merieux Nutrisciences laboratory were performed with PLA nonwovens. For the taste and odor evaluation and the migration tests in water and heptane respectively the ISO 13302:2003 method and the FDA 21 CFR 176.170 were followed. The exposure of the PLA nonwoven to water and heptane was of 30 min at respectively 100˚C and 49˚C and the limit of quantification (LoQ) was 0.4 mg/sqinch for both. Results are summarized in Table 2.

The nonwovens had been produced on the Hills spunbond line at CETI and the surface treated calcium carbonate had been added to PLA (NatureWorks Ingeo Biopolymer 6100D) via a 65% concentrated masterbatch.

As can be seen, the addition of this specific calcium carbonate in PLA does not change the taste and odor performance of the packaged aliments, nor does it increase the level of migrated substances in food simulants like water and heptane. It can therefore be recommended for use in food packaging applications like for example tea bags (Figure 6).

Next to food packaging applications, hygiene, personal care and textile applications also have stringent requirements when it comes to product safety. Samples of the surface treated calcium carbonate as well as breathable film samples containing up to 50% calcium carbonate were therefore shared with the Merieux Nutrisciences and the Senzagen Laboratory respectively for skin irritation patch testing according to the MP 1299 rev 4 2019 procedure and skin sensitization testing according to GARDskin assay methodology. Both tests gave the response of “no skin irritation” and “no skin sensitization”.

Considering that the final concentration of the treated calcium carbonate in PES and PLA fibers and nonwovens is lower than 50%, it can be concluded that the addition of the treated calcium carbonate is safe in use.

To conclude, the results of several fiber trials confirmed that the addition of calcium carbonate can have beneficial effects on the process and performance of polyester and PLA fiber and nonwovens.

References

1. M. Brunner, M. Knerr, L. Clapp, “Calcium carbonate enables sustainability in polymer fiber applications,” International Fiber Journal, Issue 1, 2021

2. TDMA (Titanium Dioxide Manufacturers Association) August 2021

3. Industrial Minerals Association North America, Fact Sheet, Life Cycle Analysis Calcium Carbonate

4. Eionet Report – ETC/WMGE 2021/3 “Greenhouse gas emissions and natural capital implications of plastics (including biobased plastics)”

5. https://matweb.com

The selection of the right surface treatment and the tailored particle size and particle size distribution enabled running several trials without issues like rise in pressure or formation of die build-up. A reduction of static charges as well as the opportunity to reduce calender temperature, without compromising on nonwoven performance, were demonstrated.

Especially in the case of PLA the mechanical performance of the nonwoven was even improved, thanks to the protective effect of the surface treated calcium carbonate on the polymer.

In polyester nonwovens, the improvements in natural appearance, brightness and haptics can pave the way to a more sustainable nonwoven solution for example in personal care or textile applications.

Last but not least, calcium carbonate has a very low carbon footprint and can be considered as a renewable raw material8 hence enabling production of more sustainable solutions. The specific surface treated calcium carbonate tested in this study is also food contact compliant and was proven to be non skin irritant and non skin sensitizing, making it a perfect solution for sensitive applications like for example hygiene, food and personal care.

NOTE: This development was done by Omya. Omya is a global producer of calcium carbonate for industrial applications. It is a privately owned Swiss company with more than 175 plants and own mineral deposits around the world. Omya implements sustainable business principles throughout the entire organization. More detailed technical results are available from Omya for further discussion.

6. O. Zmeskal, L. Marackova, T. Lapcikova, P. Mencik, R. Prikryl, “Thermal properties of samples prepared from polylactic acid by 3D printing”, AIP Conference Proceedings, 2305 020022 (2020)

7. M.D. Roussel, A.R. Guy, L.G. Shaw, J.E. Cara, “The use of calcium carbonate in polyolefins offers significant improvement in productivity”, 2005 PLACE conference proceedings

8. Calcium Carbonate Association – Europe, ”Calcium Carbonate is a Renewable Raw Material,” 2016, https://www.ima-europe.eu/sites/ima-europe.eu/files/ publications/Renewability%20Statement.pdf

Barbara Bonavoglia, Ph.D., earned a master degree in Chemical Engineering from Politecnico di Milano, Italy, and a doctorate in Polymer Chemistry from the ETH Zurich, Switzerland. Prior to joining Omya she worked for 16 years in Application Development for the Polyethylene Business of Dow Chemical, where she was responsible for the development of solutions for the hygiene, packaging and fiber markets. After 1 year as Marketing Director for the Hygiene Business at Berry Global, she joined Omya in May 2022 in the Innovation Department of the Polymer Business. She holds numerous patents and scientific publications in a variety of polymer applications. She can be reached at +41 62 789 2929 or barbara.bonavoglia@omya.com.

Martin Brunner is a Technical Service manager for polymer applications with Omya AG. He has a degree in Chemical Engineering. Prior to joining Omya, Brunner was employed by Ciba-Geigy and Ciba Specialty Chemicals in Switzerland where he focused on R&D for the company Plastic Additives Segment. He developed several successful commercial products for Ciba and Omya, and he has authored and co-authored several scientific publications and holds 30 patents and patent applications. He can be reached at +41 62 789 2411 or martin.brunner@omya.com.

Christophe Roux earned a Master in Physics and Chemistry of Materials with a specialty in Polymers completed by a MBA in Business Management from Grenoble University (France). In Omya since 20 years, he acted in various Sales positions before joining the group Sales and Marketing as Head of Market Development and Innovation Europe for Polymers applications in 2016. Prior to joining Omya he worked for 11 years for Multibase Company, a French compounder, in various positions as Pilot plant manager, Technical Service for Packaging applications, Sales and Purchasing. He can be reached at +33 6 80 41 44 75 or christophe. roux@omya.com.