NOVEL ROLLTRUDED FILMS .4. GAS SEPARATION CHARACTERISTICS OF ROLLTRUDED ISOTACTIC POLYPROPYLENE

The gas separation characteristics of isotactic polypropylene (iPP) thin films produced via the rolltrusion solid-state processing technique have been studied in order to establish some principles underlying permeation/separation behaviour in relation to membrane texture. Ideal and actual separation factors have been determined for various processing temperatures and draw ratios to assess the impact of the unique triaxial morphology produced during rolltrusion. Previously, we have shown that this unique morphological texture can improve the gas permeability of iPP by reducing the diffusive pathway tortuosity and by increasing the microvoid content in the polymer. In this study we show that the separation factors generally improve in iPP as a result of rolltrusion processing. However, the actual separation factors for a mixture of CO2 and N2 are less than the ideal values for all processing conditions studied, although this difference decreases with increasing draw ratio and decreasing processing temperature. This discrepancy between the actual and ideal separation factors is attributed to a depression in the permeability of CO2 in the mixture compared to the pure gas because of the presence of N2.