Recent Advances in Polymer Blend Membranes for Gas Separation and Pervaporation

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

A ground breaking polymer blend for CO2/N2 separation

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The intermolecular interactions and miscibility behavior of two polyimide blend systems, Extem/Matrimid and Extem/U-Varnish, in compositions of 100/0, 80/20, 50/50, 20/80, 0/100 have been evaluated. The polymer blend systems have been characterized by different analytical techniques such as optical microscopy, Differential Scanning Calorimetry (DSC), Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD) and rheological measurements. DSC results for the Extem/U-Varnish system showed the existence of a single glass transition temperature (Tg) in each composition, suggesting the miscibility of the blends, whereas DSC analysis of Extem/Matrimid system indicated immiscibility but compatibility between two polymers. In order to study the specific interactions between Extem and U-Varnish polymers, the Tgs of the polymer blends were estimated by theoretical equations and compared with experimental data. The empirical Tg values formed a concave curve as a function of composition and exhibited a positive deviation from the linearity, indicating the presence of specific interactions between Extem and U-Varnish polymer chains; this was confirmed by FTIR spectra. Interactions between studied polymer systems and four aprotic solvents including N -methyl-2-pyrrolidone (NMP), Dimethylacetamide (DMAc), Dimethylformamide (DMF) and Dimethyl sulfoxide (DMSO) were assessed on the basis of the difference between their solubility parameters. Among the selected solvents, DMAc showed the highest affinity with both blend systems. XRD patterns and rheological behavior of Extem/U-Varnish system revealed that the crystalline nature and viscosity of the blend polymers decreases as the ratio of Extem/U-Varnish increases. As an overall conclusion, Extem and U-Varnish were found to constitute a miscible pair at a molecular level over the entire composition range whereas Extem and Matrimid could not form a miscible blend.

Rouzbeh Ramazani

Papers

Miscibility of polyimide blends: Physicochemical characterization of two high performance polyimide polymers