Selective Oxidative Fractionation of Poplar Biomass via a Mild Ethyl Acetate–Hydrogen Peroxide System: Achieving High Delignification and Carbohydrate Retention

Selective delignification remains a central challenge in lignocellulosic biomass processing. In this study, a mild ethyl acetate–hydrogen peroxide (EA-HP) treatment was developed for the efficient fractionation of poplar biomass into carbohydrate-rich substrates and lignin-derived oxidation products, where peracetic acid was formed in situ. By optimizing solvent concentrations, the EA-HP system achieved 98.0% selective delignification while preserving up to 99.3% cellulose and 79.2% hemicellulose. The treated substrates exhibited improved enzymatic digestibility, with glucose yields reaching 86.3%. Spectroscopic and structural analyses confirmed the preferential degradation of lignin with minimal loss of polysaccharide. Based on the composition of the oxidation products generated, plausible oxidative depolymerization pathways of lignin were inferred. This work demonstrated a mild and effective strategy for selectively degrading lignin, enabling concurrent preservation of carbohydrate-rich fractions that are suitable for subsequent valorization into functional products and advanced materials.