Chemo-Enzymatic Route for Covalent Cellulose Fiber Dyeing

The conventional textile dyeing process, based on reactive dyes, allows covalent dye fixation but requires toxic or hazardous chemicals that raise significant environmental pollution and health concerns. In this study, we present a proof-of-concept, two-step chemo-enzymatic process for grafting aminated dyes onto cotton surfaces. Our aim is to demonstrate the feasibility of covalent dye attachment, while noting that full sustainability has yet to be achieved. First, cotton fibers are oxidized using the laccase/TEMPO system to introduce carbonyl groups, which then react with the amino group of dyes to form C-N bond through reductive amination. Reductive amination of laccase-oxidized cotton threads was achieved with rhodamine 123 and acid red 33. Covalent dyeing was evidenced by LC-MS analyses of hydrolysates obtained after cellulase action. The process was successfully transferred to cotton fabrics, and acid red 33 showed excellent color uniformity and fastness. By comparing results with different dyes (acid red 266, acid violet 19, acid black 41, and acid blue 25), useful criteria to guide dye design were identified. Our study presents a chemo-enzymatic approach to covalent cotton dyeing and offers insights into the future development of dyes.