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Issue 05/2016

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  • Bioplastics
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Fibres & Textiles

Fibres & Textiles Biobased polyester fibres – PLA for textile applications With 96 million tonnes oil-based synthetic fibres generated a world fibre market share of 62 % in 2015, followed by cotton (25 %), and (wood-based) cellulose regenerated fibres (6 %) [1]. Already in 2013 the world production of PET polyester fibres alone amounted to 41 million tonnes [2]. The demand for fibre materials, in particular textile fibres, is steadily increasing, not least owing to the growing world population and rising standard of living, causing companies to extend and optimize their production. In this connection, the use of biobased or at least partially biobased feedstock is seriously considered being aware of the global challenges such as climate change and sustainability [3, 4]. The biobased polymer polylactic acid (PLA) [5] synthesized from lactic acid or dilactide is a semicrystalline polyester. Probably PLA is the most prominent biobased plastic material with a market availability of more than 200 kt/a and a price of 2 to 2.5 €/kg. Its thermoplasticity allows for highly productive processing such as melt spinning using large and well engineered industrial facilities [6]. Melt spinning featuring high processing speeds up to 8000 m/min and optimal material efficiency is economically more advantageous than solution spinning (for, e.g., PAN, Viscose or Kevlar fibres). However, melt spinning has high requirements for the polymer melt ensuring high regularity and process stability at enormous strain and cooling rates. The filaments have to withstand up to 1000 fold stretching between nozzle and winding unit [3]. The most important PLA manufacturer is NatureWorks LLC with its Ingeo product line [7]. They offer grades for injection moulding and film production as well as for spinning to be applied in textiles, carpets (BCF yarns) and nonwovens [8]. The properties of PLA fibres are well suited for a number of textile applications. Stress-strain curves are similar to those of wool fibres [9]. PLA fibres offer a soft feel as well as a good recovery of 93 % (after elastic strain of 5 %) [10]. The good UV resistance with a relatively high Limiting Oxygen Index (LOI) of 26 % (for PET: 22 %) and less smoke emission than PET during combustion [9] are further advantages compared to many other fibres. It is beneficial in terms of moisture control to have a low moisture uptake of 0.4-0.6 % (PET: 0.2-0.4 %, wool: 14-18 %) and short times for moisture distribution and drying which is relevant for textiles, and not only for sports clothing. By now, PLA monofilaments are used as a standard material for 3D printing, due to their low shrinkage and favorable solidification properties. The biodegradability of PLA offers promising applications in biomedical technology such as suture materials, fixations, drug delivery and tissue engineering [11]. The Fraunhofer-Institute for Applied Polymer Research IAP based in Potsdam/Germany investigated the processing behavior of PLA during melt spinning within a large collaborative project funded by the German Agricultural Ministry through its agency FNR (Fachagentur Nachwachsende Rohstoffe e.V.) [12,13,14] Utilizing an industrial relevant pilot system for bicomponent melt spinning (see Fig. 1) Fraunhofer IAP produced high-strength PLA multifilaments for possible technical use. Controlling the process parameters (feed rate, temperature- and stretching profile, etc.) the filament fineness was varied over a wide range down to 1 dtex. The resulting textile-physical properties (tensile strength 45 cN/tex; elastic modulus 600 cN/tex; elongation at break 30 %) were based on a wide range of super-molecular structures with crystallinities of up to 50 %. Subsequent stretching lead to properties relevant for technical use (tensile strength 63 cN/tex; elastic modulus 740 cN/tex; elongation at break 25 %; crystallinity 61 %). The high modulus corresponds to the highly oriented crystalline structure as illustrated in Fig. 2 by an X-ray diffraction pattern. In this way, PLA multifilaments were produced with mechanical performance (tensile test) approaching the properties of technical synthetic fibres. On the other hand, the low thermal stability of PLA fibres still hampers their use for technical applications. Fig. 2: X-Ray diffraction pattern of highly oriented PLA filaments. Fig. 3: PLA filaments leaving a 70-hole nozzle with trilobal cross-section. Fig. 4: PLA multifilament yarn. 16 bioplastics MAGAZINE [05/16] Vol. 11

Fibres & Textiles By: Evgueni Tarkhanov, André Lehmann, Johannes Ganster Abb. 1: Fourné bicomponent melt spinning line at Fraunhofer IAP. Fraunhofer-Institute for Applied Polymer Research IAP Potsdam, Germany The low melting and glass transition temperatures of about 165 °C and 60 °C, respectively, exclude PLA fibres from use at elevated temperatures. In the future, a mixture of both PLA enantiomers, i.e. PLLA and PDLA, could be utilized to yield high melting point materials (230 °C) due to the formation of stereo complex crystallites from the molten state. Simultaneously, this process has a positive impact on the softening behavior at low temperatures [15]. Due to their biodegradability and the resulting environmental benefits, an optimistic forecast for PLA fibres may be made for textile applications. For technical applications the relevant mechanical properties could be reached. However, further improvements in terms of thermal stability are necessary. References: [1] [2] Man-made Fibre Year Book 2013, Deutscher Fachverlag, Oktober 2013, 4 [3] E. Tarkhanov, A. Lehmann, „Biobasierte Synthesefasern für textile und technische Anwendungen“, Plasteverarbeiter (voraussichtlich September 2016) [4] A. Lehmann, E. Tarkhanov, J. Ganster, „Biobasierte Chemiefasern – Viskosefasern und mehr“, Technical Textiles, Trendbook 2016/2017, (S.18-21) [5] R.Auras, L.-T. Lim, S.Selke, H.Tsuji,” Poly(Lactic Acid) – Synthesis, Strucures, Properties, Processing, and Applications”, Wiley Verlag, 2010 (S.343) [6] V.B.Gupta, V.K.Kothari, “Manufactures Fibre Technology”, Springer, 1997 (S.67) [7] [8] [9] R.S.Blackburn, “Biodegradable and Sustainable Fibres” , Crc Press Inc, 2005 (S.199-200) [10] A.Mohanty, M.Misra, L.Drzal, “Natural Fibres, Biopolymers, and Biocomposites”, CRC Press Inc, 2005 (S.567) [11] K.M. Nampoothiri, N.R. Nair, R.P.John, “An overview of recent developments in polylactide (PLA) research”, Bioresource Technology 101, 2010 (S 8493-8501) [12] [13] E.Tarkhanov, A.Lehmann, Fraunhofer IAP, Annual Report 2014 (S.40-41) [14] E.Tarkhanov, A.Lehmann, Fraunhofer IAP, Annual Report 2015 (S.36-37) [15] H. Tsuji, „Poly(lactide) Streocomplexes: Formation, Strucure, Properties, Degradation, and Applications“, Mocrom. Biosci. 5, 2005 (S. 569-597) bioplastics MAGAZINE [05/16] Vol. 11 17

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