Upcycling polyester from post-consumer blended textile waste into hydrogel for dye removal

• Polyester (PET)/cotton blended textile waste was successfully recycled. • PET was chemically degraded into oligomers, while cotton was recovered as fibers. • PET oligomers were upcycled into hydrogel. • The hydrogel exhibited an adsorption capacity of up to 379 mg/g for the anionic dye. • The hydrogel is reusable, but its efficiency is affected by co-existing ions. Upcycling textile waste presents a significant opportunity to enhance circularity within the textile industry. This study focuses on upcycling the polyethylene terephthalate (PET) component from polyester/cotton blended textile waste into hydrogels for dye adsorption, while simultaneously recovering intact cotton fibers. Blended fabrics were treated via glycolysis and aminolysis, achieving dye removal efficiencies of up to 97.4 ± 0.7 % within 15 min under aminolysis and 81.2 ± 0.4 % within 3 h via glycolysis. The recovered cotton retained crystallinity indices of 75–84 % depending on treatment and exhibited thermal degradation temperatures between 230–290 °C, confirming its suitability for closed-loop cellulose recycling. PET depolymerization through aminolysis generated water-soluble aminated oligomers, which were subsequently crosslinked with ethylene glycol diglycidyl ether to form hydrogels. The resulting hydrogels displayed pH-responsive swelling, with maximum expansion under acidic conditions, and achieved adsorption capacities of 379, 363, and 369 mg/g for Congo red in PPD12, CPD13, and DPA13 hydrogels, respectively. Adsorption followed Langmuir isotherm behaviour and pseudo-second-order kinetics, indicating monolayer chemisorption processes. The hydrogels maintained >80 % dye removal efficiency across six regeneration cycles, while activated carbon incorporation further enhanced adsorption stability for dyed textile-derived hydrogels. These findings highlight a dual-benefit approach, where PET hydrogel production and cotton fiber recovery contribute to sustainable textile waste valorization, advancing circularity in the industry.