Elimination of orientation in perfluorinated ionomer membranes

Abstract

An investigation was performed into the effect of processing on microstructural orientation in the perfluorinated ionomer membrane, Nafion® (registered trademark of E. I. du Pont de Nemours and Company). The aim of the study was to explore methods by which such orientation, determined from the azimuthal width of the small-angle X-ray "cluster" peak, could be reduced or eliminated. The processing consisted of biaxial deformation, both of the commercial membrane and the precursor resin, as well as high-temperature treatment of the Nation membrane. It was found that membranes produced by film blowing were less oriented than commercial membranes produced by flat-film extrusion of the precursor. Biaxial drawing of commercial membranes at temperatures above the glass-transition temperature of the fluorocarbon matrix (Tg,m) resulted in a reduction in orientation. However, even the most isotropic of these samples were significantly more oriented than membranes made by film blowing. Orientation was eliminated from commercial membranes by annealing at temperatures above Tg,m for periods in excess of 24 h. © 2005 Society of Plastics Engineers.