Development of a closed-loop solvent-based recycling process for dyed denim waste

The sustainable recycling of indigo-dyed denim waste remains a major challenge due to the chemical stability and strong fiber affinity. In this study, a closed-loop process for the recycling of indigo-dyed denim waste is developed using dimethyl sulfoxide (DMSO) as a recyclable solvent for color stripping and dye recovery. The influence of solvent composition revealed that 100% DMSO, achieved superior indigo extraction compared to aqueous DMSO systems, achieving colour removal efficiencies of up to 98%. Key process parameters, including treatment time, temperature, and material-to-liquor ratio, were optimized to maximize stripping efficiency. Mechanical characterisation revealed excellent preservation of the cellulose substrate, with tensile strength retention of approximately 98%. The stripped denim exhibited high lightness values (L* > 81), making it potentially a good white feedstock for further recycling or re-dyeing. The recovered DMSO was successfully reused for at least five consecutive stripping cycles without a noticeable loss of performance, demonstrating excellent solvent recyclability. This work provides a potential approach for the closed-loop recycling of indigo-dyed denim waste, supporting circular economy principles and contributing to the development of more sustainable textile recycling processes.