EFFECT OF COMPOSITION ON ORIENTATION, OPTICAL AND MECHANICAL-PROPERTIES OF BI-AXIALLY DRAWN PEN AND PEN PEI BLEND FILMS/

The influence of biaxial deformation on the development of thermal, op tical and mechanical properties of PEN and PEN/PEI blends were investi gated. The refractive indices in the normal direction of biaxially str etched films decreased with the areal expansion ratio, lambda(MD) x la mbda(TD) The Wide angle X-ray results showed that this is caused by th e orientation of naphthalene planes that become parallel to the film s urface as the expansion ratio increases. Blending PEI with PEN at conc entration up to 20% was also found to reduce the naphthalene plane ori entation, thereby improving the deformation behavior of PEN by elimina ting highly localized neck formation attributed to this orientation be havior. The WAXS pole figure studies further indicate that biaxially o riented PEN films show bimodal ('cross-hatched') orientation of the ch ain axes one population in the MD I direction and another distinct pop ulation in MD2 direction. This is also reflected in the mechanical pro perties where moduli exhibit equal values in MD1 and MD2 directions bu t lower values in other directions in the film plane. When blended wit h PEI at 10%-20% concentrations, the bimodal orientation is eliminated and the equal biaxially stretched films was found to exhibit in-plane isotropy. (C) 1998 Elsevier Science Ltd.