Reactive and water-soluble lignin-base dye for efficient coloration of silk fabric

Lignin is the second most abundant biopolymer in nature next to cellulose. Utilizing this non-fossil low-cost resource to develop textile dyestuffs will help to promote a green and sustainable textile industry. In this study, we proposed a novel modification strategy in which the chlorotriazine and sulfonate groups were sequentially grafted on lignin molecules through two successive nucleophilic substitution reactions to obtain a reactive and water-soluble lignin-derived dye. The successful fabrication of the dye (LN-Tr-SO₃Na) was confirmed by FTIR, NMR, and UV-Vis spectra analysis. Investigation of the dyeing mechanism and dyeing properties revealed that LN-Tr-SO₃Na had characteristics of reactive dyes. As compared with the silk fabric dyed with unmodified lignin, the fabric dyed with LN-Tr-SO₃Na under optimum dyeing conditions (i.e. pH 8, 90 °C, 20 g/L NaCl, and 4 % owf dye) had 2.5 times higher shade depth and 2-3 grade-improved color fastnesses to washing, rubbing and sunlight exposure. Besides, the LN-Tr-SO₃Na was also found suitable for dyeing wool fabrics. More importantly, it did not show any cytotoxicity to the human skin cells which indicates safety for textile use. The proposed strategy could also be used to develop sustainable, low-cost biomass-based dyes.