Relationship between the gas and liquid water permeabilities and membrane structure in homogeneous and pseudo-bilayer membranes based on partially hydrolyzed poly(ethylene-co-vinyl acetate)

The permeation of CO2, O2 and liquid water through homogeneous and pseudo-bilayer membranes based on partially hydrolyzed poly(ethylene-co-vinyl acetate) (EVA) was studied as a function of the hydroxyl group content. It was found that the transport properties for gas and water are related to the membrane structure. Increasing the rigidity of the polymer chains and the crystallinity of the films, through longer hydrolysis, leads to enhance water and gas barrier properties, even though the films become more hydrophilic. When the hydroxyl group content increases, the ideal separation factors of water to gas permeation are significantly improved in the pseudo-bilayer membranes in comparison with the homogeneous membranes. In the pseudo-bilayer membranes, the water flux from the partially hydrolyzed layer towards the EVA layer is higher than the flux in the opposite direction. This reverse flow effect becomes more pronounced with a longer hydrolysis reaction time. The anisotropy of the water flux is governed by the partially hydrolyzed layer, which is less permeable than the EVA layer. The water permeation through the membranes used in this study is more affected by the water diffusivity than by the affinity between the material and the water molecules.