Polymerization reactivity of sulfomethylated alkali lignin modified with horseradish peroxidase

•A new technology to prepare high molecular weight soluble alkali lignin is proposed.•The molecular weight of lignin increases over 20 times after HRP modification.•The structure changes of lignin during HRP modification are investigated.•Sulfonation and HRP modification were mutually promoted.•HRP modification can improve the adsorption quantity of lignin.

Alkali lignin (AL) was employed as raw materials in the present study. Sulfomethylation was conducted to improve the solubility of AL, while sulfomethylated alkali lignin (SAL) was further polymerized by horseradish peroxidase (HRP). HRP modification caused a significant increase in molecular weight of SAL which was over 20 times. It was also found to increase the amount of sulfonic and carboxyl groups while decrease the amount of phenolic and methoxyl groups in SAL. The adsorption quantity of self-assembled SAL film was improved after HRP modification. Sulfonation and HRP modification were mutually promoted. The polymerization reactivity of SAL in HRP modification was increased with its sulfonation degree. Meanwhile, HRP modification facilitated SAL’s radical-sulfonation reaction.