Assessment of role of morphology in gas permselectivity of membranes based on polypropylene/ethylene vinyl acetate/clay nanocomposite

This paper reports on the influence of morphology on gas permeability and selectivity of membranes made from polypropylene (PP)/ethylene vinyl acetate copolymer (EVA)/clay (OMMT) nanocomposites. The morphology was adjusted by variation in the EVA (25, 50wt%), OMMT (0 and 5wt%) and compatibilizer (PP-g-MAH) (0 and 5wt%) contents. Gas permeation properties of membranes with different morphologies, were studied for pure CO₂, O₂ and N₂ gases. X-ray diffraction (XRD) patterns showed no changes in crystalline structure of samples. TEM analysis confirmed high tendency of OMMT flacks for locating in the EVA phase. SEM results revealed that an increase in OMMT loading decreases the EVA droplet size (D_n) in samples with droplet type morphology and increases continuity index of EVA (CCI) in the samples with co-continuous morphology. Changes in compatibilizer/OMMT ratio imposed a dual effect on the morphology of the system with respect to D_n and CCI. A good correlation could be established between these morphological parameters with gas solubility parameters, gas permeability and CO₂/N₂ as well as CO₂/O₂ gas selectivity. Annealing was shown to change the morphology which in turn had a very strong influence on the membranes gas permeability behavior.