# Opportunities and Limitations in Recycling Fossil Polymers from Textiles
### Fibres Used in Textile Products  
Textile fibres currently present in commercial products are categorized as either natural or man-made (Figure 2). On the molecular level, these are built up by polymer chains where the monomers and the polymer linkage are specific for each fibre type. The natural fibres fall into three different chemical classes:  
* Cellulos, which originate from various parts of plants
* Protein fibres, which are obtained from wool, hair and silk
* Mineral fibres, where asbestos is the only one naturally occurring  
A natural fibre consists of thousands of polymer chains which aggregate to form complex patterns and build up very specific layered structures accounting for much of the properties of the fibre. Natural fibres range in length from a few centimeters for cotton, to around one decimeter for wool, and up to several hundred meters for silk. Shorter fibres, such as cotton and wool, are spun together to form a continuous yarn. The man-made fibres can also be divided into three sub-groups:  
* Regenerated fibres, consisting of natural polymers, mainly cellulose, that were chemically modified
* Synthetic fibres, which are produced from monomers by polymerization
* Inorganic fibres, such as glass or ceramic fibres  
Man-made fibres are formed by extruding the melted or dissolved polymer through the small openings of a spinneret. With this process, both filament yarns, in which the yarn is comprised of one infinitely long fibre, or spun yarns, in which the fibres are cut to shorter pieces and spun together, can be produced [9]. Synthetic polymers mainly used in textile products are polyester, polyacrylic, polyamide, elastane and polypropylene [14; 15]. Polyesters correspond to poly(ethylene terephthalate) (PET), also used for producing containers for packaging (bottles). The polyester used in textile has a lower molecular weight and a higher crystallinity than the PET used for bottles. In the past, PET for textiles was produced by polycondensation of dimethyl terephthalate and ethylene glycol, whereas the PET for bottles was produced from terephthalatic acid and ethylene glycol. In fact, the latter method results in less regular polymer chains, which is more suitable for an amorphous material. More recently, the synthesis from terephthalatic acid has become the most diffused [16] because of its economical and industrial advantages. Post-consumer PET from beverage bottles is currently recycled in packaging or in textile  
Figure 2: Scheme of fibres used in textiles. products. PET fibres are used alone or mixed with natural fibres like cotton, for improving breathability, or with elastane, to produce stretch fabric. Polyacrylic fibres consist of poly(acrylonitrile) (PAN) macromolecules, often copolymerized with another monomer to improve dyeability and textile processability. Typical comonomers are vinyl acetate or methyl acrylate [17]. Acrylic fibres are produced by both wet and dry spinning and are mainly used to be knitted for producing wool-like fabrics. They can be used alone or mixed with other natural or synthetic fibres. The most diffused polyamides, used in technical fabrics or in synthetic wool, are polyamide 6,6 and polyamide 6. The former is obtained by polycondensation from adipic acid and hexamethyle diamine, the latter by anionic polymerization of \(\varepsilon\)-caprolactone [18]. Polyamide is used alone or mixed with cotton or other synthetic fibres. Polypropylene, produced with an isotactic structure by updated methodologies based on Ziegler-Natta catalysts, is a polyolefin commonly used in the production of non-wovens for hygienic applications and personal protection, because of its low cost and high water repellency, which discourages the growth of bacteria [19]. Elastane is a polyurethane-based copolymer, based on flexible poly(ethyleneglycol) blocks and rigid polyurea blocks (Figure 3). It is fundamental for producing stretched fabrics based on polyester, polyamide and natural fibres and thus is often mixed with these fibres [20].