Microwave-Assisted Sulfonation of Lignin for the Fabrication of a High-Performance Dye Dispersant

Designing a valorization approach of lignin is essential to achieve “lignin-first” biorefining, which enables the economic feasibility of the lignocellulosic biorefinery industry. Herein, microwave-assisted sulfonation of lignin was investigated with multiple chemicals for the production of a lignin-based dye dispersant, and the effect of the aliphatic chain of sulfonation reagents on the dispersive performance of the sulfonated lignin was revealed. Structural characterization recommended that 1,4-butanesultone exhibited the best reaction activity, and its sulfonation product (SL4) exhibited the highest molecular weight (7190 Da) and sulfonic group content (1.59 mmol·g –1 ) among all samples, because of its long aliphatic chain. The high content of sulfonic group and the high molecular weight of SL4 improved the dispersive performance with excellent high temperature stability in which the dyeing rate was 87.9%. The fiber staining effect evaluation of sulfonated lignin dispersants demonstrated that the etherification by 1,4-butanesultone could reduce the phenolic hydroxyl content of lignin to prevent the adsorption of the dispersant on fiber, limiting the fiber staining by sulfonated lignin during the dyeing process. This highly efficient lignin sulfonation can facilitate the valorization of lignin by fabricating the lignin-based dye dispersant for widespread industrial applications.