Recovery and Reuse of Reactive Dyes Extracted from Cotton Using a DMSO/Water-NaOH System

This study investigates the recovery of reactive dyes from dyed cotton fabrics using a DMSO/water solvent system under alkaline conditions. Five commercial reactive dyes, including two hot-dyeing types (Red 120, Blue 171) and three warm-dyeing types (Black 5, Blue 19, Red 23), were evaluated to determine the effects of the DMSO/water ratio and NaOH concentration on dye extraction efficiency. A 70/30 DMSO/water ratio provided optimal fiber swelling and dye solubilization, while NaOH promoted cleavage of the dye-fiber covalent bonds. Spectral analysis indicated that Red 120, Blue 171, and Black 5 retained their chromophoric integrity, whereas Blue 19 and Red 23 underwent partial degradation at higher NaOH concentrations. The recovered dyes were successfully used in subsequent dyeing processes. The hot-dyeing reactive dyes and Black 5 demonstrated clear dyeability on silk under acidic dyeing conditions, while Red 120 and Blue 171 produced reproducible shades on cotton under a direct dyeing process. DMSO/water extraction caused a measurable but manageable strength loss in cotton fabrics. This work demonstrates a practical approach for recovering and reusing reactive dyes while maintaining fiber and dye performance, supporting more circular and resource-efficient pathways for cotton textile recycling.