# Opportunities and Limitations in Recycling Fossil Polymers from Textiles
## Recycling Fossil Polymers
### Enzymatic Recycling: To Monomers or New Products  
Polymer biodegradation consists in reduction of molecular weight under the transformative action of microbial enzymes. Enzymes consist of mainly peptide natural polymers with a 3D structure of folded long chains, and they can behave as catalysts of various reactions. Synthetic polymers have a high molecular weight and diffuse with difficulty across a cell wall or microbial cytoplasmic membrane. Thus, the reduction of the polymer molecular weight is necessary for the bacteria. Enzymes engaged in polymer degradation (defined as exoenzymes) show oxidative or hydrolytic functionality [157]. The enzymatic action can be described as depolymerization, and the obtained monomers and/or oligomers could be used in a subsequent polymerisation process. Chemical structural features of polymers as well as their crystallinity content can play a pivotal role in polymer biodegradation. A high crystallinity can limit biodegradation, suppressing molecular diffusion in the material. During the enzyme-catalysed reaction, the synthetic polymer's substrate binds to \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Project Acronym and** & **Input Stream** & **Product** & **Key Information** \\ \hline \hline \multirow{8}{*}{RESYNTEX [152]} & \multirow{8}{*}{Cotton, nylon, PET, wool} & \multirow{8}{*}{Monomers (glucose, TPA, EG) protein hydrolysates, polyamide oligomers} & UE HORIZON 2020, from June 2015 to May 2019. It developed a new demonstration process based on a synergistic chemical and biotechnological cascading separation/transformation approach of textile basic components (proteins, cellulose, polyamide and polyester) from textile blends as basic feedstock materials for chemical and textile industries. Liquid and solid waste treatment and valorisation closed the loop \\ \hline \hline \multirow{8}{*}{Trash2 Cash [153]} & \multirow{8}{*}{Blended textile and paper waste} & \multirow{8}{*}{Regenerated cellulose} & From June 2015 to November 2018. A newly developed eco-efficient cotton fibre regeneration process (Cellulosic Regeneration), a new polyester regeneration technology (PET De-Re-polymerisation) and a polyester recycling technique (Chain Extension Upgrading) were developed \\ \hline \hline \multirow{8}{*}{RETEX [154]} & \multirow{8}{*}{Cotton, Polyester} & \multirow{8}{*}{Fibre} & Interreg (V programme) EU Project, from October 2016 to October 2020. Three value chains were identified to be developed to obtain fibre and plastic by mechanical recycling: (1) Cotton/polyester blends; (2) 100\% cotton; (3) 100\% polyester \\ \hline \hline \multirow{8}{*}{CISUTAC [155]} & \multirow{8}{*}{Horizon Europe project} & \multirow{8}{*}{Fibre} & Horizon Europe project, co-funded by the European Union, from September 2022 to August 2026 (ongoing). Tests for fibre-to-fibre textile recycling technologies for post-consumer polyester and cotton were carried out. Pilot scale processes demonstrated the industrial application of new technologies for textile circularity \\ \hline \hline \multirow{8}{*}{T-REX [156]} & \multirow{8}{*}{Cotton Polyester Polyamide} & \multirow{8}{*}{Fibre} & Horizon Europe project, from October 2022 to August 2025. It collected and sorted household textile waste and demonstrated the full recycling process of polyester, polyamide 6, and cellulosic materials from textile waste into new garments. \\ \cline{1-1} \cline{2-4}  & & & Horizon Europe project, from October 2022 to August 2025. It collected and sorted household textile waste and demonstrated the full recycling process of polyester, polyamide 6, and cellulosic materials from textile waste into new garments. \\ \hline \hline \end{tabular}
\end{table} 
Table 2: European projects dealing with chemical recycling of textiles. the highly specific enzymes' active site. Compared to the chemical recycling processes, biocatalytic recycling processes are generally eco-friendlier [158]. Moreover, the efficiency of the enzyme-catalysed biotechnological processes can be improved through enzyme engineering [159].