Polyurethane-Based Blend Membrane Containing Polycarbonate for Gas Separation: Compatibility Analysis, Microstructure Evaluation, and CO₂ Separation Performance

In this research, gas separation blend membranes composed of polyurethane (PU) and polycarbonate (PC) were developed, and the influence of incorporating PC into the PU matrix on the microstructure and separation performance was investigated. The PU polymer was synthesized using a two-step polymerization approach. The blend membranes were thoroughly characterized using SEM, DSC, XRD, AFM, and FTIR analyses. The compatibility of the PU/PC blend was theoretically analyzed using surface energy and Gibbs free energy methods. The results showed that the PU/PC blends are partially compatible. Accordingly, the maximum achievable PC loading in the PU matrix was 25 wt %. Analysis of the SEM results revealed that the blend membrane containing 25 wt % PC demonstrated decreased levels of PU/PC interaction compared to the membranes with PC contents below 25 wt %. Incorporating PC into the PU matrix led to a decreased chain mobility, increased membrane crystallinity, and the development of a rough microstructure. The CO2/N-2 selectivity of the neat PU and PC membranes was measured to be 32.5 and 120, respectively. However, the blending of 10 wt % PC increased the CO2/N-2 selectivity to 41.2. Notably, the PU95/PC5 blend membrane demonstrated the highest selectivity (11.85) for the CO2/CH4 separation. Moreover, increasing the upstream pressure enhanced the permeabilities of the CO2, CH4, and N-2 through all membranes.