# Opportunities and Limitations in Recycling Fossil Polymers from Textiles
### Fibres Used in Textile Products
All the described polymers are thermoplastic, so fibres can be produced by melt spinning. The orientation of polymeric macromolecules induced by the applied draw ratio favours the extensive formation of crystals that determine an increase in fibre strength. The recycling of the polymers by melt processing and re-spinning (mechanical recycling) could be advantageous. Nevertheless, the melting of mixed thermoplastics would result in a blend of immiscible polymers. Polymer blends are generally studied to achieve toughened materials, but not for the material strengthening. On the other hand, the crystallization process is often hindered by the presence of different polymeric phases. Thus, mechanical recycling is difficult because of the impossibility of separating the different fibres that are of a micrometric thickness [21; 22]. Currently, the textile sector is starting to make more and more use of biobased polymers (Figure 4) [23]. Figure 3: General structure of the main synthetic fibres widely used in the textile market. In 2022, 333 ktons of bioplastics were used to produce fibres, and forecasts are predicting that in 2027 they will grow to 690 ktons [23]. Thus, in the group of man-made fibres, some bioplastics [24, 25], like poly(lactic acid) (PLA), poly(butylene succinate) (PBS), bio-PET, poly(ethylene furanoate) (PEF), could also be included in the future. Replacing fossil-based products with biobased polymers is undoubtedly advantageous [26] because each fossil-based product at its end of life can generate a positive contribution to greenhouse gas (GHG) emissions. On the contrary, biobased materials of vegetal origin are carbon-neutral, because the CO\({}_{2}\) that they can emit at their end of life (because of incineration or degradation due to microorganisms) is balanced by the CO\({}_{2}\) consumed during the development of the plant. Hence, the use of man-made materials based on biobased monomers is currently promoted by institutions and adopted by companies, especially for short lifecycle applications. In this scenario, PLA, being both renewable and biodegradable in industrial composting plants, can represent an interesting perspective for replacing fossil-based polymers such as PET and PP [27, 28], whereas biobased polyamides were developed to replace fossil-based polyamides in the near future [29]. Polyhydroxycalcanoates (PHA), synthesized by microorganisms, can be considered for producing natural bioplastic fibres [30], but their high cost and difficult processability is currently directing them mainly towards biomedical applications. Natural fibres based on biopolymers such as proteins [31] and polysaccharides [32, 33], obtained by waste from the agro-food chains, are also explored for applications in the textile sector, to promote the application of circular economy principles. For instance, casein from waste milk possesses high barrier properties to non-polar molecules and has been considered a candidate for fabricating paper coatings, adhesives, food packaging, textiles, and fibres [34]. Cellulose recovered from biomass [35, 36] can be converted into regenerated cellulose fibres for textiles.