Depolymerization and demethylation of lignin for sustainable coloration and functionalization of silk fabric

Conversion of agricultural biomass waste into textile dyes enhances both the environmental sustainability and the textile industry's green and sustainable development. This study introduced a novel strategy to transform the lignin (LN) from corn cob to a polyphenol-rich dye through depolymerization followed by demethylation. The successful modifications were confirmed via FT-IR, UV-vis, and NMR analysis. Depolymerization and demethylation significantly reduced the molecular weight and particle size of LN, from 2797 to 865 g/mol and 3.9 to 0.9 μm, respectively. Consequently, the dye had a 36.1 % higher dye exhaustion rate on silk fabric compared to the unmodified LN. After mordanting with Al³⁺ ions, the dyed silk fabrics achieved color fastnesses of grade 3-5, meeting the requirement (≥grade 3) for commercial use. Furthermore, demethylation resulted in a 3.7-times increase in the content of phenolic-OH groups of the dye, significantly improving the UV protection and antibacterial properties of the dyed fabrics. The dyed fabrics did not show cytotoxicity to the human skin cells, indicating the high safety for textile use. This work provides a novel way to add value to LN biowaste while simultaneously preparing a functional LN-based dye.