Diffusion of ethanol and water through PU membranes

Abstract

A series of hydroxyl-terminated polybutadiene (HTPB) and 4,4'-dicyclohexylmethane diisocyanate (H 12 MDI)-based polyurethanes (PUs) were synthesized by solution polymerization. PU membranes were prepared by a dry/wet phase inversion method. The effects of membrane formation method and preparation condition on gas permeability and permeability ratio (ethanol permeability/water permeability) were investigated. We found that the variation in morphology of these membranes was contributed to by the difference in surface energy between the nonpolar HTPB soft segment and the polar hard segment. The permeation of the ethanol/water mixture and permeability ratio were tested by pervaporation and the side-by-side method. The permeability of water or ethanol using the side-by-side test through dry/wet membranes, which are prepared using different phase inversion conditions, can be controlled from 50 to 1100 g/m 2 .hr. A strange phenomenon was discovered, in that the permeation increased with the increase of hard segment content of PU membranes, while the permeability ratio decreased.