Valorization of enzymatic hydrolysis lignin via PEG grafting to enhance hydrothermal pretreatment performance and saccharification efficiency of poplar sawdust.

Lignocellulosic biomass is inherently recalcitrant due to lignin's spatial obstruction and non-productive enzyme binding, which are the major barriers to economic biorefining. This work developed a valorization and reintegration process for lignin to convert enzymatic hydrolysis lignin (EHL) into PEG-grafted lignin material (PLM), then reused it in both hydrothermal pretreatment (HP) and enzymatic hydrolysis of poplar sawdust (PS). Characterization confirmed successful PEG grafting onto EHL, yielding a morphologically transformed product with improved surface physicochemical properties. Adding PLM (30 g/L) during HP boosted lignin removal (42.6 %) and hemicellulose solubilization (99.0 %), suppressed lignin repolymerization, and increased the relative content of β-O-4 bonds. As a result, cellulose accessibility increased 3.4-fold and surface hydrophobicity dropped by 66.1 %. In enzymatic hydrolysis, adding 0.8 g/L PLM protected the residual lignin from non-productive adsorption and preserved the enzyme activity, thereby attaining a hydrolysis efficiency of 80.1 %. Surface plasmon resonance analysis verified that PEGylation modulated lignin-cellulase interaction kinetics and reversibility, explaining the suppressed non-productive adsorption of the enzyme. This study validated a lignin valorization and reintegration strategy, which upgraded waste lignin into an effective process additive to simultaneously enhance sugar production efficiency and lignin resource utilization.