(340g) The Formation of Cellulose Acetate Membranes Using Ionic Liquid, [BMIM]SCN, as the Solvent Via Phase Inversion

In the last decade, ionic liquids have gained worldwide attention as a group of environmentally-friendly solvents with unique properties, which make ionic liquids appear to be striking alternatives to replace the traditional volatile organic solvents in many chemical processes including organic synthesis, catalysis, separations and material preparation. In addition, the good capability of ionic liquids in dissolving macromolecules and the miscibility of imidazolium-based ionic liquids with water inspire us to employ ionic liquids as a new generation of solvents to replace the organic solvents for membrane preparation.

This study explored, for the first time, the fundamental science and engineering of using ionic liquids as a new generation of solvents for the fabrication of flat sheet membranes and hollow fiber membranes. The fundamentals and characteristics of membrane formation of cellulose acetate (CA) membranes have been investigated using 1-butyl-3-methylimidazolium thiocyanate ([BMIM]SCN) as the solvent via phase inversion in water. For elucidation, other solvents, i.e. N-Methyl-2-pyrrolidinone (NMP) and acetone, were also studied. It is found that [BMIM]SCN has distinctive effects on phase inversion process and membrane morphology compared to NMP and acetone because of its unique nature of high viscosity and high diffusivity into water. Membranes cast or spun from CA/[BMIM]SCN have a macrovoid-free dense structure full of nodules, implying the paths of phase inversion are mainly nucleation growth and gelation, followed possibly by spinodal demixing and then solidification. The recovery and reuse of [BMIM]SCN have also been demonstrated and achieved. The derived flat sheet membranes made from the recovered [BMIM]SCN show similar morphological and performance characteristics with those from the fresh [BMIM]SCN. It is believed that this study could enrich the understanding of membrane formation using environmental-benign ionic liquids.