Rapid Hydroxylation Modification of Lignin Under H3BO3/H2O2 System

Lignin is the primary waste in pulp and paper industries. Its complex, large-molecule structure results in low reactivity, limiting its potential for high-value utilization. This paper introduces a novel method for rapid hydroxylation modification of lignin (M-EHL) that offers advantages in terms of processing temperature and time compared to conventional demethylation, hydroxy-methylation, and phenolation methods. Using single-factor and orthogonal experiments, the optimal reaction conditions were determined. The modified lignin was characterized using 1H-NMR, FTIR, GPC and potentiometric titration. The result shows that the reaction, with the molar ratio (boron acid and hydrogen peroxide) to lignin at 1:0.4, reacting for 1.5 h at 80 ℃ reaches the highest yields. The phenolic hydroxyl content increased from 3.2167 mmol/g to 17.95 mmol/g. FTIR analysis revealed little structural changes in lignin, except for an increase in hydroxyl absorption peaks, suggesting little side reactions. Compared to unmodified lignin, GPC result reveals that M-EHL exhibited increased molecular weight and narrower distribution.