Deep eutectic solvent (TMAH·5H₂O/Urea) with low viscosity for cellulose dissolution at room temperature

A deep eutectic solvent (DES) formulated with tetramethylammonium hydroxide pentahydrate /urea (TMAH·5H₂O/Urea) was designed for the first time to dissolve cellulose at room temperature. The optimized system, characterized by a 1:3 M ratio, demonstrates the capability to dissolve approximately 7.5 wt% cellulose, boasting a high degree of polymerization (DP = 526). Notably, both the pure DES and 4.0 wt% cellulose/TMAH·5H₂O/Urea mixtures manifests low viscosity, establishing its potential as an effective spinning aid in fiber manufacturing. The structural analyses shows that the cellulose crystal type shifts from type I to type II form, accompanied by a reduction in both crystallinity and DP. A pivotal aspect of this research involves determining Kamlet-Taft parameters for TMAH·5H₂O/Urea-DES with different molar ratios. The results reveal these solvate DESs exhibit the high hydrogen bond basicity, which enables them to easily form hydrogen bonds with hydroxyl groups of cellulose and demonstrate good cellulose solubility. In conclusion, this solvent system presents notable advantages, including straightforward synthesis procedures, low viscosity, and well cellulose solubility, paving the way for new approaches and techniques in cellulose utilization.