Deep Eutectic Solvents for Polyester–Cotton–Elastane Textile Waste: Component-Selective Separation and a Proposed Sequential Recycling Framework

The increasing use of blended textiles has created waste streams that are difficult to recycle because chemically dissimilar fiber components must be separated without unnecessarily destroying their material value. Polyester–cotton blends containing elastane are particularly challenging, yet they are increasingly relevant to post-consumer textile recycling. Deep eutectic solvents (DESs) offer a tunable platform for selectively interacting with polyester, cellulose, and polyurethane-based elastane through dissolution, swelling, hydrolysis, glycolysis, or other depolymerization pathways. This review critically examines DES-assisted recycling from a component-selective perspective, focusing on how DES chemistry and process conditions determine which fiber is targeted, the form in which it is recovered, and the extent to which accompanying components are preserved. Reported approaches for PET removal, cotton dissolution or deconstruction, and elastane separation are compared with emphasis on the experimental evidence distinguishing polymer-preserving dissolution from chemical degradation. Recent advances demonstrate selective recovery routes for individual components and binary blends; however, a fully integrated DES-based process capable of sequentially recovering PET, cotton, and elastane from a realistic ternary textile has not yet been demonstrated. On this basis, the review identifies component-specific design principles and proposes sequential separation as a conceptual research framework for complex blended waste, derived from independently demonstrated component-selective processes rather than an established experimentally validated recycling process. Solvent selectivity, preservation of non-target polymers, solvent recovery, process severity, and downstream product quality are identified as key requirements for translating DES chemistry into scalable textile recycling.