A ground breaking polymer blend for CO2/N2 separation

The commercial polyetherimide sulfone polymer Extem was blended with polyethersulfone (PES) to achieve a new, highly selective membrane for CO2/N2 separation in order to allow for a breakthrough in carbon capture applications. The miscibility and molecular interaction between PES and Extem for blend compositions 80/20, 50/50 and 20/80 w/w were evaluated. Differential Scanning Calorimetry showed that of all the blend compositions, only the 20/80 blend is miscible as a single glass transition temperature was observed, lying between the glass transition temperatures of PES and Extem. FTIR spectra revealed shifts in functional group frequencies of the polymer blends, suggesting inter-molecular interactions between the polymer chains of Extem and PES. XRD patterns of the 20/80 blend showed a much lower characteristic peak intensity compared to other blend compositions, which indicates strong inter-molecular interactions. The density of the polymer blends was lower than that of the pure polymers, which is related to a decrease in fractional free volume. The separation performance of membranes synthesized with these blends was investigated for a gas mixture containing 15% vol. CO2. Blend membranes were limited by the tradeoff between permeability and selectivity, except for the 20/80 blend, which interstingly had a permeability and selectivity more than threefold that of other membranes, as the values hovered around the Robeson's upper bound. The miscibility of Extem/PES therefore resulted in a new polymer material, which is a potential candidate for carbon capture applications.