NOVEL ROLLTRUDED MEMBRANES .3. THE EFFECT OF PROCESSING TEMPERATURE ON THE GAS-TRANSPORT PROPERTIES OF ISOTACTIC POLYPROPYLENE

The solubility and diffusivity of CO2, N-2, and CH4 in isotactic polypropylene [iPP] thin films produced via rolltrusion solid-state processing have been studied. Processing temperatures between 50 and 125 degrees C and draw ratios between 1 and ca. 10 are reported. Variations in the transport coefficients and the activation energies, in conjunction with the molecular theory of diffusion of Pace and Datyner,(22,23) were used to assess changes in the micromorphology of the polymer due to this unique processing mode. Specifically, it has been found that the formation and destruction of microvoid volume were necessary to account for the large increases in solubility and decreases in the heats of solution. Additionally, changes in the tortuosity of the diffusive pathways-due in part to crystallite orientation and to the formation of impermeable amorphous regions in the microfibrillar morphology-were found to influence the diffusivity significantly. The tortuosity actually decreased in contrast to the behavior obtained for uniaxially drawn films. Based upon these observations, it is suggested that triaxial stresses induced in rolltruded polymer films are responsible for this morphology and its function in polymer membranes. (C) 1995 John Wiley & Sons, Inc.