Effect of vinyl acetate/dibutyl maleate copolymers on gas transport properties of poly(ethylene oxide-b-amide 6) membranes: a comprehensive study on permeability, diffusivity, solubility, and permselectivity of carbon dioxide

Poly(ethylene oxide-b-amide 6) (PEBAX (R) 1657) blend membranes containing 10, 30, and 50% (by weights) of dense and rubbery vinyl acetate/dibutyl maleate (VAc/DBM) copolymers with different chemical compositions as CO2-philic additives were made by solution casting method and were studied for the separation of CO2/CH4 and CO2/N2 gas systems. Chemical interaction, thermal properties, and morphology of the membranes were investigated using FTIR, DSC, and FE-SEM analyses, respectively. The solubility coefficient of carbon dioxide as well as the solubility selectivity showed an upward trend with the addition of vinyl acetate-based copolymers, especially at 50% (by weight). In the membranes containing 10 and 30% (by weights) of vinyl acetate-based copolymers, both key factors of solubility and diffusion coefficient had an almost appropriate trend, which improved the performance of the blend membranes compared to pure Pebax 1657. In the membranes containing 50% (by weight) additive, the diffusion and diffusion selectivity decreased due to the change of the dominant phase from polyethylene oxide to vinyl acetate-based copolymers, resulting in the reduction of the permeability. By increasing of the pressure, the permeability of carbon dioxide was increased which can be attributed to the increase in the solubility of carbon dioxide and then to the rubbery and resistance properties of the added copolymers against pressure. Compared to a pure Pebax 1657, gas separation performance of the blend membranes containing 10 and 30% (by weights) of vinyl acetate-based copolymers were closer to Robeson's curve, confirming the improvement of permeability properties in these membranes.