Maintenance-Free Cellulose Solvents Based on Onium Hydroxides

Here, we report maintenance-free cellulose solvents that dissolve much cellulose within a few minutes under mild conditions even in the presence of water. We have examined a series of aqueous solutions of tetraalky-phosphonium and tetraalkyl-ammonium hydroxides to clarify the effect of cation species on cellulose dissolving. Aqueous solutions of the many hydroxides examined here were found to dissolve cellulose at room temperature, and electrostatic interaction and/or steric hindrance of component ions are suggested to affect the cellulose-dissolving ability. In spite of increasing water content after dissolution of wet cellulose, the water content automatically reduced to less than 60% just by keeping the filtrated solution in the air. The solvation state of cellulose in aqueous onium hydroxide solutions is discussed with 13C NMR chemical shift of cellobiose signals in these solutions. They dissolve cellulose only when the 13C NMR signal of the carbon atom at the 12 position of cellobiose is 64.8 ppm or larger in the hydroxide aqueous solution.