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Fibres & Textiles Rayon

Fibres & Textiles Rayon and more – Biobased chemical fibres By: André Lehmann, Johannes Ganster, Hans-Peter Fink Fraunhofer Institute for Applied Polymer Research IAP Potsdam, Germany The first chemical fibres manufactured on an industrial scale were in fact biobased and date back to 1905 when Courtaulds Fibres in the UK started the production of viscose fibres. They were wet-spun from chemically modified high purity wood pulp with subsequent regeneration of the pure cellulose in fibre form. Even today, they are the most important family of biobased chemical or man-made fibres. With the introduction of nylon (polyamide) fabric at the 1939 New York World’s Fair, oil-based fibres set out to conquer the world markets being produced by the much more effective melt spinning technology. Today, with the increasing number and availability of biobased or at least partially biobased thermoplastics, new opportunities for melt-spun biobased fibres arise, notably with poly(lactic acid) and, again, with polyamides. Even more on the high-tech side, the possibilities to produce less expensive carbon fibres from biobased feedstock, namely lignin-containing precursor systems, are being explored in the US and Europe. Both melt and solvent processes are followed for precursor spinning. Cellulose man-made fibres Viscose fibres have an ever increasing market share with over 5 million tonnes p.a. today and are used mainly for textile applications. An alternative method to manufacture cellulose man-made fibres is the Lyocell technology introduced in the 1990s. Today the main producer of Lyocell fibres is Lenzing AG (Austria) with an annual output of 222 kt for textile applications. Cellulose acetate fibres, dry spun from acetone solution are mainly used for cigarette filters. Technical viscose fibres, often called rayon, amount to some 100 kt mainly used for rubber good reinforcement, in particular fast running and run-flat tyres. For these so called Super 3 tyre cord yarns typical (single filament) tensile strengths are around 850 MPa with moduli in the range of 20 GPa. With a density of 1.5 g/cm³, light weight construction potential in composite manufacture is offered by this kind of biobased fibres. The suitability of these fibres for reinforcing both petro- and biobased thermoplastics has been demonstrated in [1]. Benefits versus glass fibre reinforcement are found mainly in improved impact behaviour, reduced weight, less abrasion and better recycling. Using various alternative methods it has been demonstrated that cellulose technical fibres can be manufactured with drastically improved tensile properties. None of these methods, however, is currently in production but there shall be named a few. On a pilot plant scale, fibres with 1.3 GPa strength and 45 GPa modulus were developed by Acordis (NL) at the beginning of this century spun from an anisotropic super phosphoric acid solution [2]. Less critical solvents can be used in the combination of the Lyocellmethod with the cellulose carbamate derivative leading to liquid crystalline solutions to be dry-jet wet spun into fibres with strengths up to almost 1 GPa and moduli in the range of 50 GPa [3]. Most recently, in the group of Prof. Sixta (Aalto University, Espoo Finland) ionic liquids have been employed to spin the so-called IonCell fibre with properties in between Lyocell and Bocell [4]. Melt-spun fibres Melt spun fibres are by far the most dominating in the world market. The annual output of polyester (polyethylene terephthalate – PET) fibres alone amounts to more than 41 million tonnes, while the figures for nylon (polyamide - PA) and polypropylene (PP) fibres are 3.9 and 2.8 million tonnes, respectively [5]. One of the main reasons for that is doubtlessly 24 bioplastics MAGAZINE [04/14] Vol. 9

Fibres & Textiles the high efficiency of the manufacturing process. Today, spinning speeds of over 8000 m/min are reached which is at least 40 times faster than what is attainable with solution spinning. Moreover, no solvent must be recycled and from the spinning dope (in this case molten thermoplastic) 100 % fibre product is obtained. However, solution spun cellulose fibres (viscose) have unique properties, e.g. in terms of moisture regulation and wear comfort which warranties their (increasing) share in the world fibre market. Traditionally, all melt spun fibres are based on fossil feedstock. However, with the progress made in synthesizing biobased and partially biobased thermoplastics, as well as their increasing availability on the market, corresponding fibres can be melt-spun in principle. Of course, many requirements have to be met, e.g. in terms of molecular weight distribution, processing additives, stabilisers etc. in order to produce a so-called spin-type polymer. Efforts have been and are being made to provide such types depending on the market demand. Fig. 1 View on the 3k wet-spinning line at Fraunhofer IAP Pioneers in this direction are, in the PLA-sector, NatureWorks who offer spin-types which can be used for textiles, for carpets (BCF-yarn) or even for meltblownnonwovens. Advantages to be mentioned are, depending on the specific application, low moisture absorption and high resistance to ultra violet light and biodegradability. Mechanical properties are typically in the range of 400 MPa strength and 6 GPa modulus. Moreover, PLA and PLA-copolymer fibres are used in surgical applications as suture materials taking advantage of their bio-compatibility and metabolisability in the body. Polyamide fibres, mainly from PA6 and PA6.6, play an important role in the textile sector for apparel, carpets, and other mostly woven fabrics. In the technical field, monofilaments for brushes, fishing lines etc. are produced. The polyamide family provides a good example for the introduction of biobased raw material. For decades, PA11 has been produced on the basis of castor oil. More recently, partially biobased PA6.10, PA10.10, and PA4.10 have been on the market. Their application in fibre form is still somewhat limited. PA11 is used for eyelash brushes while PA6.10 is found in carpet applications. Properties of the fibres depend of course on spinning conditions and polymer recipes, molecular mass etc., but also on the position of the specific polyamide in the polyamide family. For example, due to its more aliphatic character, PA11 has a significantly lower moisture absorption and a better chemical resistance than PA6 or PA6.6. The possibility of spinning micro-fibres from PA11 with diameters less than 10 µm has been demonstrated at Fraunhofer IAP (Fig. 2). Fig. 2 SEM-photograph of melt-spun PA11 micro-fibre prepared at Fraunhofer IAP Fig. 3 Carbonization oven at Fraunhofer IAP In the class of aromatic polyesters, poly(trimethylene terephthalate) (PTT) should be mentioned with 37 % biobased content from the 1,3-propanediol unit. The commercial product Sorona ® by DuPont gives fibres with good softness, comfort stretch and recovery as well as moisture management which find applications in carpets, apparel and automotive flooring. While PLA is a sort of new polymer type, and PA6.10 etc. resemble their petro-based relatives, the third category in this series are so-called drop-ins. They are chemically identical to completely petro-based polymers but their feedstock is completely or partially biobased. To this category belong biobased PE (Braskem) produced with bio-ethanol bioplastics MAGAZINE [04/14] Vol. 9 25

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