Selective Deconstruction of Natural Lignocellulose/ Eucommia ulmoides Gum Composite by Recyclable Acidic Deep Eutectic Solvents

INTRODUCTION: Eucommia ulmoides biomass is a natural composite comprising E. ulmoides lignocellulose (LC) and E. ulmoides gum (EUG). However, the full utilization of this composite system is hindered by its structural complexity. OBJECTIVES: The aim of this study was to identify an optimal acidic deep eutectic solvent (DES) system for the selective deconstruction of the lignocellulose/E. ulmoides gum (LC/EUG) composite and to unlock the application potential of this natural composite. METHODS: E. ulmoides Oliver pericarp (EUP) was used as a feedstock in this study, and the composition and structure alterations induced in the LC/EUG system by pretreatment with six acidic choline chloride-based DES formulations were systematically evaluated. RESULTS: Under optimized conditions (ChCl/oxalic acid, solid-to-liquid ratio 1:35, molar ratio 1:2, 110°C, 3 h), delignification and hemicellulose removal reached 88.72% and 85.46%, respectively, with more than 90% cellulose retention. Moreover, the relative content of EUG in the solid substrate increased from 11.81% to 21.26%. The DES still maintained an efficiency of over 70% in removing hemicellulose and lignin even after five recycling cycles, which highlights its good sustainability. In addition, DES pretreatment led to an increase in the crystallinity index (CrI) of cellulose from 56.68% to 63.35%, disruption of the lignin-hemicellulose matrix, and the formation of a highly porous, cellulose-rich surface. The extracted lignin featured low condensation and a high specific surface area, rendering it suitable for synthesizing high-value-added materials and chemicals. CONCLUSION: This work provides insights into targeted modulation of natural polymer composites in biomass and offers references for green solvents in E. ulmoides valorization.