GAS PERMEATION THROUGH PSF-PI MISCIBLE BLEND MEMBRANES

The permeation rates of He, H-2, CO2, N-2 and O-2, are reported for a series of miscible polysulfone-polyimide (PSF-PI) blend membranes synt hesized in our laboratory. For gases which do not interact with the po lymer matrix (such as He, H-2, N-2 and O-2), gas permeabilities in the miscible blends vary monotonically between those of the pure polymers and can be described by simple mixture equations. In the case of CO2, which interacts with PI, blend permeabilities decrease somewhat, comp ared to pure PSF and PI. This, however, is accompanied by a two-fold i mprovement in the critical pressures of plasticization vs. polyimide. Permselectivities of CO2/N-2 and H-2/CO2 in the blends deviate from mi xing theory predictions, in contrast to selectivities of gas pairs whi ch do not interact with PI. Differential scanning calorimetry measurem ents of pure and PSF/PI blend membranes show one unique glass transiti on temperature, supporting the miscible character of the PSF/PI mixtur e. Optical micrographs of the blend membranes clearly indicate perfect homogenization and no phase separation. Frequency shifts and absorpti on intensity changes in the FTIR spectra of the blends, as compared wi th those of the pure polymers, indicate mixing at the molecular level. This compatibility in mixing PSF and PI, results essentially in a new blend polymer material, suitable for the preparation of gas separatio n membranes. Such membranes combine satisfactory gas permeation proper ties, reduced cost, advanced resistance to harsh chemical and temperat ure environments, and improved tolerance to plasticizing gases.