Activation of Enzymatic Hydrolysis Lignin by NaOH/Urea Aqueous Solution for Enhancing Its Sulfomethylation Reactivity

Enzymatic hydrolysis lignin (EHL), from straw bioethanol process, was activated using NaOH/urea aqueous solution under low temperature condition to enhance its sulfonation degree and dispersion property. The sulfonation degree of EHL increased by 62.60% after the activation of NaOH/urea aqueous solution at −10 °C for 12 h, which is resulted from the breakage of the hydrogen bonds and ether bonds in lignin–carbohydrate complexes (LCCs) and the removal of residual carbohydrate. The functional group content, 2D-HSQC, and AFM analysis indicated that the increase of phenolic groups and the weakened aggregation degree of EHL after the activation are in favor of the increase of activity sites and decrease of steric hindrance, which is beneficial to the enhancement of sulfomethylation reactivity. Owing to the enhancement of reactivity, the dispersion properties of sulfomethylated EHL on graphite suspension were significantly enhanced.