Viscosity reduction of cellulose + 1-butyl-3-methylimidazolium acetate in the presence of CO2

Viscosities of microcrystalline cellulose + 1-butyl-3-methylimidazolium acetate ([bmIm][Ac]) solutions (0.6–1.2 wt%) in contact with CO2 were measured at 312 K with a resonant vibrational viscometer. At 4 MPa and 312 K, the CO2 could reduce the viscosity of 1.2 wt% cellulose + [bmIm][Ac] solution by about 80 %, whereas N2 at the same conditions gave less than a 10 % reduction in viscosity. The viscosity-averaged degree of polymerization and IR spectrum showed that cellulose did not decompose during experiments and that [bmIm][Ac] acted as a non-derivatizing solvent during the dissolution and viscosity reduction process. Further, although CO2 does react with [bmIm][Ac] to form 1-butyl-3-methylimidazolium-2-carboxylate, the reaction seems to be reversible and it does not affect the cellulose. Thus, [bmIm][Ac] with CO2 provides an effective solvent for cellulose and the solvent system can probably be recycled or reused.