# Opportunities and Limitations in Recycling Fossil Polymers from Textiles
## Recycling Fossil Polymers
### Chemical Recycling to Obtain Separated Materials, Monomers or New Products  
Various chemical recycling technologies have been developed for textile waste, and for each one drawbacks, advantages, and disadvantages can be found. These processes are described below. Pyrolysis/gasification could be utilized with unsorted and multi-material textile products even if most of the current studies used a single-type textile waste as the substrate [136]; however, it requires high temperatures and therefore is a process with a high energy consumption. Pyrolysis of textile waste typically results in pyrolytic gas (H\({}_{2}\)O, CO\({}_{2}\), CO, H\({}_{2}\), CH\({}_{4}\) and other light hydrocarbons) and solid residues (>20% by weight). During pyrolysis, a large amount of heat must be transferred across the reactor, hence the type of reactor used for pyrolysis is crucial for obtaining a high process efficiency. Generally speaking, a continuous flow pyrolyser led to a higher yield of gas pyrolysate, while a semi-batch pyrolyser led to higher yields of liquid pyrolysate and solid residue [137]. However, almost all studies used a single set of parameters and limited types of pyrolyser (e.g., batch or fixed-bed reactor). Many pyrolysis processes have focused on the production of carbon materials for different applications, for example as adsorbents for pollutant removal. For this application, pre- and post-treatment procedures are necessary to enhance the surface area and porosity of the textile waste-derived carbon residue. Several studies have reported that polyester textile waste-derived adsorbents show better performance than other biomass-derived activated carbons [138]. Only rough economic and environmental assessments and estimations are available, and comprehensive studies on the energy and economic analysis of the pyrolysis process for textile waste recycling are necessary [139]. In general, in chemical recycling, plastics are broken down into chemical intermediates (oligomers) or their basic building blocks (monomers) by adding chemicals. Regarding chemical recycling of PET in particular, degradation, alkaline and acid hydrolysis, methanolysis, glycolysis, microwave, ionic liquid, phase-transfer catalysis, combination glycolysis-methanolysis, glycolysis-hydrolysis, methanolysis-hydrolysis and the kinetic study are reviewed by [PERSON] et al. [89]. Various processes are described in the literature for chemically recycling PET textiles [140]:  
-Hydrolysis; -Alcoholysis (glycolysis/methanolysis); -Aminolysis  
At the end of these processes, the oligomers or monomers must be purified by filtration and/or separation processes, and dyes may be difficult to remove. After purification, the purified oligomers or monomers can be processed into new plastics or other chemical products. The economic efficiency of chemical recycling is only given with larger mass flows. In addition, it must be considered that today's processes are usually very energy-intensive, and the economic viability depends strongly on the quality of the purification. Generally, only individual fibre types can be dissolved and processed from chemically recycled textile blends. New technologies for chemically recycling textile fibres are emerging around the world. They have the potential to substantially reduce the textile industry's huge environmental footprint. Consumers could soon be wearing brand-new clothes made from garments that otherwise would have ended up in a landfill or incinerator. However, the technologies are far from mature [141]. Chemical recycling has been especially pursued in the case of the separation of polyester and cotton. According to [PERSON] from Chalmers University of Technology, four approaches can be followed to deal with polycotton waste streams [142]: (1) Dissolve cellulose, maintain PET; (2) Degrade cellulose, maintain PET; (3) Maintain cellulose, dissolve PET; (4) Maintain cellulose, degrade PET.