A comparative study on recovery and recycle of acid dye and silk fibroin from colored waste silk textiles through dye stripping and silk dissolution

Abstract

Effective recovery of dyes from discarded textiles is essential for energy conservation and environmental protection. This study explores recovery of acid dye from waste silk textiles through dye stripping and silk dissolution. Silk, wool and nylon fabrics were dyed with the recovered dye to explore optimal dyeing condition and the re-dyeing performance. A comparative analysis of the two recovery methods highlights their respective dyeing efficiencies and practical viability. Results show that dye stripping rate from fabric decolorization reaches 86 % when 50 % ethanol is used. An optimal dye uptake of over 95 % can be achieved when re-dyeing silk, wool and nylon with stripping dye. While fabric dye uptake from dissolved dye is relatively low (around 70 %), protein in the dissolved solution can play a certain role in modifying surface of the dyed fabric and in acting as leveling agent to ensure uniform coloration. A comparison of ternary solution of CaCl₂/ethanol/water and LiBr as silk dissolving agent reveals similar dyeing effects, with the ternary solution emerging as the more cost-effective alternative due to its significantly lower price. The printed patterns on cotton with regenerated colored protein from dissolved silk are vivid, sharp, and well-defined, exhibiting satisfactory colorfastness at protein content of 15 %. The successful application of recovered acid dye on cotton expands its potential use beyond traditional protein-based textiles. Both dye recovering methods employed in this study are simple, green and economical. The recovered dyes are able to retain the original dye structure. These findings provide valuable insights into a sustainable recovery and reuse of dyes from discarded textiles, offering practical implications for eco-friendly dyeing/printing practices and colored waste textile recycling.