Characterization of polyethersulfone/polyimide blend membranes prepared by a dry/wet phase inversion: Precipitation kinetics, morphology and gas separation

Flat sheet gas separation membranes of polyethersulfone (PES), polyimide (Matrimid, MI) and their blends were fabricated by a spin casting method followed by a dry/wet induced phase inversion process. The mixing compatibility and thermal stability of the blend membrane were studied by Fourier transform infrared spectroscopy (FTIR) and thermal gravimetric analysis (TGA) respectively. The forming behavior was investigated by the ternary phase diagram and an optical microscope with PES, MI and PES/MI blend (5:5). In this ternary system, the average of diffusion coefficient, D_e, of PES, MI and EM5050 were respectively 8.35 × 10^-5, 10.22 × 10^-5 and 3.09 × 10^-5 cm²/s. The morphology of membranes was studied by a scanning electron microscope (SEM). All prepared membranes had an ultrathin dense skin layer (<1 μm) on the top of the membrane. The blend membrane with MI composition from 40 to 80 wt.% showed sponge-like sub-layer whereas pristine membrane as well as the rest of the composition showed the finger-like sub-layer (macrovoids). Gas permeance of N₂, increased with increase in feed pressure irrespective of blend composition. The permselectivity of PES/MI (30/70 wt.%) decreased from 5.4 to 4.9 with increase in the feed pressure.