Fabrication and Gas Permeation Studies on Polyimide/Layered-Aluminum Phosphate Nanocomposite Membranes

Polymer – clay nanocomposites have improved thermal, mechanical, and barrier properties when compared with the pure polymer. The objective of this study was to examine if gas separation performance could be improved by introducing a layered nanopourous aluminum phosphate with a large aspect ratio into a polymeric matrix. The aluminum phosphate has eight membered rings, which could potentially serve as a size selective medium. A hexafluorinated polyimide, 6FDA-6FpDA-8%-DABA, was used as the polymeric matrix. The polyimide and the aluminum phosphate were synthesized separately according to well documented procedures. The two materials were blended and fabricated into nanocomposite membranes. The effect of mixing temperature and percentage of layered aluminum phosphate added to the polymer on the permeation properties were examined. These factors had a direct effect on the degree of intercalation and exfoliation of the nanocomposite structure. Transmission FTIR, TEM, DMTA, and X-ray diffraction were used to characterize the morphology, structure, and composition of these nanocomposite films. The permeation properties of the nanocomposite membranes were evaluated using pure gases (He, O₂, N₂, CH₄, CO₂) at 35°C and a feed pressure of 4 atm. In general, the permeability decreased and the selectivity coefficients increased when adding 10 wt% aluminum phosphate to the polyimide. Furthermore, the membranes showed size selectivity, consistent with the pore size in the layered aluminum phosphate.