Fibres, Textiles
Fibres, Textiles Targeted control of biodegradability New test methods and development of multi filament and nonwoven production processes In a project of the Institute of Textile Technology at RWTH Aachen University (ITA) and the Fraunhofer Institute for Environmental, Safety and Energy Technology UMSICHT possibilities for targeted control of the biodegradability of multi filament yarns and nonwovens were investigated. To achieve sustainability goals such as a circular economy, it can be reasonable to use biodegradable plastics in applications, where products enter and remain in the environment e.g., geotextiles for the reinforcement of embankments [1]. During their product life, the materials must fully meet the required technical properties and should subsequently biodegrade completely. Aim It is known that there are many factors involved in the biodegradability process of polymers [2]. The surface area and crystallinity can be regulating parameters to make targeted control of biodegradability possible. A high crystallinity slows down the biodegradation process of the polymer [2]. The aim of the project “DegraFib” was to investigate how fibre crystallinity and fibre surface area influence the degradation of fibres and textiles. In the project, different cross-section geometries of filaments and therefore different surface areas were produced to test the influence on the biodegradation process of filaments and nonwovens. Melt spinning and ageing trials At first, suitable biobased and biodegradable polymers such as polylactic acid (PLA) grades from NatureWorks, Minnetonka, USA and polybutylene succinate (PBS) grades from Mitsubishi Chemical Performance Polymers, Düsseldorf, Germany were selected and a melt spinning process for multi filament yarns was developed [3, 4]. Filaments were extruded successfully in the melt spinning process, varying the cross-section geometry to adjust the available filament surface area. Round, flat, crossshaped and star-shaped filaments were produced with yarn counts between 200–700 dtex (see Figure 1). The influence of the filament surface at constant yarn count on the biodegradability of multifilament yarns and nonwovens was investigated. To determinate the correlation between filament parameters and the degradation rate of filaments in substrate, a new test method was developed inspired by testing standards [5, 6, 7]. Additionally, a transfer of the findings to the textile level was carried out by producing nonwovens from selected multifilament yarns (weight: approx. 300 g/m 2 ) and developing a new test method to determine the degradation rate of the nonwovens. An example of the nonwoven degradation test method is shown in Figure 2. Analytics and results During the degradation trials, the temperature was varied between 20 and 58 °C in different trials to simulate industrial as well as home composting conditions. The optical and mechanical properties of the multi filament yarns and nonwovens produced were analysed before and after ageing in substrate. Additionally, a thermal analysis via differential scanning calorimetry (DSC) was carried out for the filaments. Degradation or ageing of the filaments and nonwovens could be detected. The results of the degradation tests indicate that filament relaxation and polymer crystallinity have a complex influence on the degradation rate of fibres. Some results of the nonwovens made from PBS fibres are shown in figure 3. For each tested sample group means of the tensile strength as well as standard deviations were calculated and statistical analyses were performed. Figure 1: Cross-sectional geometries of the extruded multi filament yarns [a) star-shaped, b) cross-shaped] 22 bioplastics MAGAZINE [05/21] Vol. 16
By: Figure 2: Insertion of the nonwoven samples into the substrate for the ageing test Sophie Boas1, Amrei Becker1, Mona Duhme2, Pia Borelbach2, Thomas Gries1 1 Institute of Textile Technology at RWTH Aachen University, Germany 2 Fraunhofer UMSICHT Oberhausen, Germany The nonwovens made of filaments with a round crosssection geometry with samples taken in machine direction showed a significant difference. The mean was 76 % lower on day 14 compared to day 0 before aging. The samples taken from nonwovens made from filaments with a crossshaped cross-section geometry showed no significant differences in the mean of tensile strength. The mean was 26 % lower on day 14 compared to day 0 before aging. These results indicate that a larger surface area of the filaments does not lead to a faster degradation. Slight mass losses could be detected after two weeks in substrate for both filament types (0.4–3.6 %). Similar results were generated in publications with biodegradable polyester (Estar Bio) an aliphatic aromatic polyester with structural units similar to PET) and cellulose acetate fibres from other research groups [8, 9]. It was assumed that besides a slight mass loss the loss in tensile strength in the first weeks is sufficient as an indicator for the starting hydrolysis [8, 9]. Long-term tests will be carried out in future projects at ITA and Fraunhofer UMSICHT to clarify the results. Conclusion Several multi filament yarns and nonwovens made from biodegradable polymers were produced at the ITA at RWTH Aachen University. New test methods to investigate biodegradation of filaments and nonwovens were developed and ageing trials with multi filament yarns and nonwovens were carried out at the ITA and Fraunhofer UMSICHT. The results of the degradation tests indicate that a complex filament cross-section geometry delays the onset of polymer degradation. The manufacturing processes and disintegration tests for filaments and nonwovens developed in the project provide a basis for further analyses and test methods. If nonwovens, or fibres and textiles in general, are used and left in nature, fibres made of biodegradable polymers are an alternative to non-biodegradable fibres. Though, biodegradability should be verified before the products are left in nature. The project “Biodegradability on demand of filament yarns by changing the filament cross-section geometry and polymer crystallinity (DegraFib)” was funded from 2019 to 2020 by the German Federal Ministry of Food and Agriculture (BMEL). The final report is available at www.fnr. de under the funding codes 22023618 and 2219NR213. References: [1] Thielen, M.: Bioplastics: Basics. Applications. Markets; Polymedia Publisher GmbH, 2020, S. 70 [2] Burgstaller, M.; Potrykus, A.; Weißenbacher, J.; et al., Umweltbundesamt (Hrsg.): Gutachten zur Behandlung biologisch abbaubarer Kunststoffe. Dessau-Roßlau 07.2018 [3] https://www.natureworksllc.com/Products/6-series-for-fibers-andnonwovens, 27.04.2021 [4] https://www.mcpp-global.com/fileadmin/mcpp_data/documents/ Products/4-Bio/PTTMCC_2019_Brochure.pdf, 27.04.2021 [5] DIN EN 12225, Berlin: Beuth Verlag GmbH, 2000 [6] DIN EN 14995, Berlin: Beuth Verlag GmbH, 2007 [7] DIN EN ISO 11721-1, Berlin: Beuth Verlag GmbH, 2001 [8] Suh, H.; Duckett, K.; Bhat, G.: Biodegradable and Tensile Properties of Cotton/ Cellulose Acetate Nonwovens. Textile Research Journal (April 1996), H. 66 (4), S. 230–237 [9] Twarowska-Schmidt, K.; Ratajska, M.: Biodegradability of Non-Wovens Made of Aliphatic-Aromatic Polyester. Fibers & Textiles in Eastern Europe (2005), Vol. 13, H. 1 (49), S. 71–74 www.ita.rwth-aachen.de | www.umsicht.fraunhofer.de From Sicience & Research Figure 3: Results of the ageing test of nonwovens made from PBS fibres with round and cross-shaped filament cross-section geometry (* p
