Solubility of Cellulose in tetrabutylammonium acetate/dimethylsulfoxide（TBAA/DMSO）Mixed Solvents

Tetrabutylammonium acetate（TBAA）/dimethyl sulfoxide（DMSO）mixed solvent dissolves cellulose in a short time under mild temperature conditions and can be reused. Cellulose regeneration process using this solvent（Ogaki method）is expected to be an alternative method to the viscose method. In this study, we aimed to clarify the effect of water content in the solvent on the solubility of cellulose in TBAA/DMSO mixtures. Sample solvents were prepared by adding approximately 1, 5, and 9% water to TBAA/DMSO mixed solvents with various TBAA ratios （20‒50%）. The β value of the Kamlet‒Taft parameter, which is considered to be closely related to cellulose dissolution, was larger for higher TBAA ratios and lower water content. The cellulose sample was tested for dissolution in these solvents, and the best solubility was observed in mixtures with a TBAA ratio of 20‒30% with 1% water added, while solubility was low at TBAA ratios of 40 and 50% despite the high β value. When 5% water was added to a solvent with a TBAA ratio of 20%, the solubility of cellulose was significantly reduced and not even 1% of cellulose could be dissolved, whereas 3% of cellulose could be completely dissolved with a TBAA ratio of 30%, indicating that the latter composition of the solvent has a high tolerance for water contamination. This is advantageous in terms of easier control of the moisture content of the raw pulp and solvent. Dissolution of cellulose in TBAA/DMSO mixed solvents in this study was more favorable in solvents with β values greater than 1 and lower viscosity. In solvents with a TBAA ratio of 20‒30%, the addition of water did not affect the viscosity, but it decreased the β value and thereby the solubility of the cellulose. On the other hand, the solubility of cellulose in solvents with high TBAA ratio was not large due to their high viscosity, but it was assumed that the addition of water has the effect of decreasing viscosity, contributing to the increase in solubility.