Bio-based crosslinkers: Oxidized polysaccharides for improving the colorfastness of natural polyphenol dyes-colored silk fabrics

Natural polyphenol dyes are traditionally and widely used for the coloration of natural fibers, e.g. silk. However, the poor affinity between polyphenol dyes and natural fibers often leads to low colorfastness. To address this issue, we developed a green fixation strategy using periodate-oxidized polysaccharides (OPS) as bio-based crosslinkers. Four structurally diverse polysaccharides—pullulan, pectin, starch, and hyaluronic acid—were selectively oxidized to generate reactive aldehyde groups capable of covalently binding with silk fibers and tannins. The successful oxidation and subsequent network formation between tannins, polysaccharides, and silk proteins were verified by FTIR NMR, and XPS analyses. Compared with untreated silk, OPS pretreatment significantly improved dye uptake and colorfastness of dyed silk. Among them, oxidized pullulan (OPullu) exhibited the best performance: achieving a shade depth of K/S = 10.2 and colorfastness grades of 3–4/4 under optimized conditions (pretreatment: pH 6, 80 °C, 6 % OPullu; dyeing: pH 2, 80 °C). Most significantly, OPullu exhibited no cytotoxicity to skin cells, supporting its safe use in textiles. Moreover, the approach was effective for other polyphenolic dyes, including anthocyanins, quercetin, and tea pigment. OPS pretreatment offers a simple, eco-friendly, and versatile approach for improving the colorfastness of silk fabrics dyed with natural polyphenolic colorants.