Cellulose Recovery from Waste Denim Fabrics through Indigo Vat Dye Reduction and Spandex Dissolution

Abstract

This study addresses environmental conservation by tackling end-of life management for post-consumer denim garments through the recycling of cotton fibres from waste denim. The purification process involved dithionite reduction of vat dyes in the presence of an alkali followed by selective dissolution of spandex using N,N dimethylformamide (DMF). Optimal conditions for dye removal were determined at 90°C for 120 minutes with sodium hydroxide at 25 g/L, sodium dithionite at 6 g/L and PVP at 4.5 g/L, while spandex extraction was achieved using a 5% DMF solution at 70°C for 4 hours. Ultraviolet (UV)-vis spectrophotometric analysis indicated a significant increase in whiteness (DL*). ATR-FTIR and TGA confirmed the purity and structural integrity of the recovered cellulose, comparable to pure cotton. This research demonstrates effective removal of vat dyes and spandex, supporting potential applications for the recycled cotton.