Effect of water on the dissolution of flax fiber bundles in the ionic liquid 1-ethyl-3-methylimidazolium acetate

Abstract

This work investigated the dissolution rate of flax fibers in the ionic liquid 1-ethyl-3-methylimidazolium acetate [C2mim] [OAc] with the addition of a cellulose anti-solvent, water. The dissolution process was studied as a function of time, temperature and water concentration. Optical microscopy is used to analyse the resultant partially dissolved fibers. Distilled water was added to the solvent bath at the concentrations of 1%, 2% and 4% by weight in order to understand its influence on the dissolution process. The effect of the addition of even small amounts of water was found to significantly decrease the speed of dissolution, decreasing exponentially as a function of water concentration. The resulting data of both pure (as received from the manufacturers) ionic liquid and ionic liquid/anti-solvent mixtures showed the growth of the coagulated fraction as a function of both dissolution time and temperature followed time temperature superposition. An Arrhenius behavior was found, enabling the measurement of the activation energy for the dissolution of flax fiber. The activation energy of the IL as received (0.2% water) was found to be 64 ± 5 kJ/mol. For 1%, 2% and 4% water systems, the activation energies were found to be 74 ± 7 kJ/mol, 97 ± 3 kJ/mol and 116 ± 0.6 kJ/mol respectively. Extrapolating these results to zero water concentration gave a value for the hypothetical dry IL (0% water) of 58 ± 4 kJ/mol. The hypothetical dry ionic liquid is predicted to dissolve cellulose 23% faster than the IL as received (0.2% water).