Choline hydroxide-based deep eutectic solvents as a medium for cellulose dissolution, regeneration, and modification

Choline hydroxide-based deep eutectic solvents (DESs) were studied as media for cellulose dissolution, regeneration, and modification. DESs composed of choline hydroxide (ChOH) with oxalic (OA), lactic (LA), and citric (CA) acids were prepared using both aqueous (55% of water) and partially dried ChOH (20% of water; dryChOH) to evaluate the influence of water content on solvent performance. Rheological analysis revealed that all cellulose/DES systems exhibited non-Newtonian shear-thinning behavior with dominant elastic characteristics. Drying of ChOH significantly enhanced cellulose-solvent interactions, leading to improved solvation and increased relative viscosity, particularly in LA-based systems. Structural analysis (NMR, XRD) revealed that the cellulose I allomorph was largely preserved, with partial amorphization depending on solvent composition. Among the studied systems, the dryChOH/LA system demonstrated the highest apparent dissolution/dispersion efficiency under the tested conditions, as evidenced by improved relative viscosity, decreased crystallinity index, and the proportion of internal crystalline chains. In contrast, CA-based DESs showed minimal impact on cellulose structure, indicating poor dissolution capability. Attempts at cellulose modification via transesterification with vinyl ester in DES were unsuccessful, likely due to incomplete dissolution and water interference.