Dependence of cellulose dissolution in quaternary ammonium-based ionic liquids/DMSO on the molecular structure of the electrolyte.

We synthesized a series of quaternary ammonium acetates (QAAcOs) and assessed their solutions in DMSO as cellulose solvents. NBz111 AcO/DMSO did not dissolve cellulose; substitution of its methyl groups resulted in efficient cellulose solvents; NBz31 AcO/DMSO dissolved cellulose with difficulty. We attribute the inefficiency of both QAAcOs to: strong anion-cation interactions, NBz111 AcO; steric effects and cation-cation hydrophobic interactions, NBz31 AcO. Using isothermal titration calorimetry, we determined the enthalpies (HE ) of QAAcO (endothermic) dissolution, and QAAcO/cellobiose (exothermic) interactions; both in dimethyl sulfoxide/acetonitrile. The ratios of HE are 5.34:1:1.45, for NBz111 AcO, NAl2Bz1 AcO, and NBz31 AcO, respectively, i.e., dissolution of the first and third QAAcO in the solvent requires more energy. The corresponding ratios for QAAcO interaction with cellobiose are: 0.74:1:0.79, i.e., the second QAAcO interacts more strongly with cellobiose. This order of solvent efficiency is corroborated by SEM images of regenerated cotton linters. Light scattering showed that dissolved cellulose can be regenerated as nanoparticles by dialysis.