Tackling Challenges of Textile Recycling: Color Removal from Cotton Textile Waste via Sequential Reductive–Oxidative Bleaching

Abstract

An effective pathway for textile recycling could be the successful integration of the textile waste into a closed-loop system; however, one of the key challenges is the removal of color from textile waste. In this study, we developed a two-step reductive-oxidative treatment to convert reactive-dyed textile waste into a white feedstock suitable for textile recycling. The process includes a reductive stage using Na2S2O4, followed by oxidative bleaching with H2O2. Colorimetric, mechanical, morphological, polymeric, elemental, and thermal analyses were performed using standard methods to evaluate the characteristics of the color-stripped fabrics. Under optimized conditions, up to 99.3% color stripping was achieved, along with high lightness (L* = 89.1) and whiteness index (WI = 87.6). The average tensile strength retention of 87.2%, maximum weight loss of 3.5%, limited surface fibrillation observed under scanning electron microscopy, and a minimum degree of polymerization of 1404 suggested that only limited cellulose degradation occurred, allowing the treated materials to retain the properties required for subsequent chemical recycling. Bulk and surface elemental analyses further confirmed a significant reduction in nitrogen content and the complete removal of sulfur, demonstrating effective dye removal and the restoration of the fabric to a composition closely resembling that of the undyed material, while the data from X-ray diffraction revealed only minor changes in the crystallinity index, indicating that the polymer structure remained stable. Thermogravimetric analysis likewise indicated that the thermal profile of the fabrics after dye removal was restored to that of the undyed fabric. The excellent redyeability and uniform color uptake of the color-stripped fabrics indicated their promising potential to be reintroduced into circular textile systems through either chemical recycling into new textile products or mechanical recycling via shredding and blending with virgin fibers.