Hydrogen peroxide pre-oxidation breaks down the recalcitrance of poplar biomass during acid/pentanol biphasic fractionation

Abstract

The dense and recalcitrant structure of poplar biomass presented a major obstacle to efficient lignin–carbohydrate separation in biphasic pretreatment systems. In this study, environmentally friendly physical and chemical preprocessing strategies for poplar—freeze–thaw and hydrogen peroxide (H₂O₂) pre-oxidation—were employed to enhance the fractionation performance of an acid/pentanol biphasic system. Freeze–thaw physically disrupted the compact cell wall matrix of poplar, increasing porosity and acid accessibility, resulting in hemicellulose and lignin removal rates increasing from 88.1% and 78.5% (only acid/pentanol pretreatment) to 89.2–89.4% and 85.2–84.8%, respectively. H₂O₂ pre-oxidation showed superior performance by initiating oxidative cleavage of lignin–carbohydrate linkages (benzyl ether and ester) and depolymerizing native lignin via disruption of β–β and β-5 interunit bonds. These structural modifications reduced lignin condensation, enhanced hydrophilicity, and facilitated subsequent solvent penetration. As a result, hemicellulose removal and delignification reached 92.6% and 90.2%, respectively, while cellulose saccharification efficiency increased to 89.1%. Moreover, the lignin recovered from the organic phase was enriched in phenolic and carboxylic groups, exhibiting enhanced antioxidant capacity. These findings deepened the mechanistic understanding of how oxidative and physical preprocessing facilitated subsequent biomass fractionation and presented a green, modular strategy with strong industrial potential for scalable lignocellulosic biorefinery applications.