Laccase and Xylanase Incubation Enhanced the Sulfomethylation Reactivity of Alkali Lignin

Alkali lignin (AL), from poplar alkali pulping process, was activated by laccase and laccase/xylanase system (LXS). When incubated with 10 U/g laccase for 24 h, the sulfomethylation reactivity of AL could increase by 33%. The functional group content and H-1 NMR analysis showed that the cleavage of various ether linkages and demethylation, resulting in the increase of phenolic groups and decrease of steric hindrance, contributed to the improvement of sulfomethylation reactivity. Xylanase addition could increase the laccase incubation rate. Bonds between lignin-carbohydrate complexes (LCCs) were disrupted with the addition of xylanase. Hence, AL was more accessible to laccase, leading to a higher incubation rate. Due to the increased reactivity, the dispersion performance of sulfomethylated lignin on TiO2 slurry was obviously improved.