Effect of the acetate group content on gas permeation through membranes based on poly(ethylene-co-vinyl acetate) and its blends

• EVA copolymers and their blends were used to prepare membranes for gas separation.
• EVA blends show superior gas transport performance.
• The physical properties of EVA materials were measured and correlated with transport characteristics.
• Specific interactions between CO2 and acetate groups have an impact on membrane separation performance.

The transport of gases through poly(ethylene-co-vinyl acetate) (EVA) of vinyl acetate (VAc) content ranging from 25 to 70 wt%, and through the respective EVA blends was studied. The both types of materials exhibited the same order of decreasing permeability CO2>He>O2>N2. However, the membranes prepared from EVA copolymers were found to be more permeable than those obtained from the blends, showing a maximum of P value at 46 wt% of VAc, while the composition dependence of P for the blends was observed to comply with a rule for miscible blends. The observed differences in permeation behavior were correlated with physical properties of the membrane materials such as density, Tg, crystallinity, and FFV. All the membranes studied exhibited high selectivities (α) for CO2/N2, and the low separation ability for O2/N2. The values of α for the blend materials were found to be larger than those for the copolymers with the same VAc content, and to increase more sharply with the increasing amount of VAc. These results indicate that polymer blends may offer advantages over single component polymer system in the approach of increasing membrane separation performance by using favorable interactions of polar groups with CO2.