An effective color stripping process for reactive dyed cotton waste

Dyes are one of the main obstacles for sustainable recycling and developing an effective dye removal technique is essential to promote textile circularity. In this study, a two-step color stripping treatment is proposed to address the challenge of removing covalently bonded reactive dyes from the cellulose structure. Four different colored cotton fabrics (i.e., green, gray, black and navy) were subjected to a two-step stripping process, involving initial treatment in a hot alkaline sodium hydroxide (NaOH), followed by sodium chlorite (NaClO2) treatment under acidic conditions. Key process parameters influencing the color stripping process such as chemical concentration, temperature and treatment duration were systematically studied and optimized. The color stripping was achieved of 99%, with Lightness (L*) and Whiteness Index (WI) values above 85 and 80, respectively, for all dyed fabrics at optimized conditions. The physicomechanical properties of the color stripped fabrics such as tensile strength and weight loss were found to be 12% and 4%, respectively. Moreover, color stripped fabrics showed 4–6% increase in crystallinity index. In addition, elemental analysis confirmed the complete removal of reactive dyes from treated fabrics, as no sulfur was detected after the treatment. Color stripped fabrics also showed sharper, more stable thermal degradation with less residue, indicating effective dye removal. Furthermore, the reusability of stripping filtrate was investigated up to 3 cycles to assess color stripping performance.