Study on the dissolution behavior of different celluloses in quaternary ammonium base/imidazole compound solvent system

In this study, tetraethylammonium hydroxide solution and imidazole compounds (1-methylimidazole, 1-ethylimidazole, 1-propylimidazole) were used to develop a new green solvent system with high solubility, wide solubility range and fast dissolution rate. This system dissolved up to 18 wt% microcrystalline cellulose (DP = 171), and the solubility reached 15 wt% even at room temperature. At the same time, this solvent system exhibited strong solubility for cellulose with different degrees of polymerization, and dissolved 16 wt% cotton pulp cellulose (DP = 527) and 14 wt% hemp cellulose (DP = 2146), with significantly improved solubility. The dissolution behavior of cellulose in a quaternary ammonium/imidazole solvent system was studied using XRD, FT-IR, TG, NMR and other characterization techniques. The results showed that imidazole compounds reduced the crystallinity of cellulose, weakened the inter-sheet bonding and van der Waals force of cellulose without destroying hydrogen bonds, and promoted the encapsulation of water molecules and quaternary ammonium cations, making the OH^- dispersion more uniform, thereby improving the ability of quaternary ammonium solution to dissolve cellulose. In the non-derivative quaternary ammonium base/imidazole compounded solvent system, there was no chemical reaction between the solvents, and the cellulose structure did not change before and after dissolution. This system did not significantly degrade cellulose with a low degree of polymerization. However, since high temperature conditions were required for dissolution, the DP of cellulose with a higher DP decreases significantly.