Efficient pretreatment of tea stems using biocompatible ionic liquid and monoethanolamine: Toward improved enzymatic hydrolysis and UV-blocking PVA-LNPs composite films

In this study, an efficient and environmentally friendly pretreatment system was developed by combining the biocompatible ionic liquid choline levulinate (ChLA) with monoethanolamine (MEA) to enhance the fractionation and valorization of tea stems (TS). Under optimized conditions (140 °C, 2 h, 20 % water content, ChLA:MEA molar ratio of 1:2), the system achieved high retention of cellulose (89.2 ± 1.4 %) and hemicellulose (76.6 ± 1.4 %), alongside substantial lignin removal (76.9 ± 0.7 %). Spectroscopic and morphological analyses (FTIR, XRD, SEM) confirmed effective disruption of the lignin-carbohydrate complex, a reduction in cellulose crystallinity, and enhanced substrate accessibility. Consequently, enzymatic hydrolysis of the pretreated biomass yielded glucose and xylose at 93.7 ± 0.6 % and 85.7 ± 0.7 %, respectively, representing a more than 212 % improvement in saccharification efficiency compared to untreated TS. Furthermore, the pretreatment selectively cleaved lignin-carbohydrate ester linkages, enabling the recovery of lignin nanoparticles (LNPs) characterized by a high β-O-4 linkage content, low condensation degree, and low molecular weight. These LNPs were incorporated into polyvinyl alcohol (PVA)-based nanocomposite films, which exhibited improved mechanical properties, hydrophobicity, and UV-shielding performance. Overall, this work presented a sustainable and integrated strategy for the comprehensive utilization of lignocellulosic biomass into high-value multifunctional materials.