INFLUENCE OF UNIAXIAL DRAW ON NEAR-SURFACE STRUCTURE IN POLY(ETHYLENETEREPHTHALATE)

Relative amounts of surface crystallinity and amorphous structure and their respective surface orientations were examined as a function of depth from the surface for a series of uniaxially drawn poly (ethyleneterephthalate) (PET) films using polarized attenuated total-reflectance infrared spectroscopy (ATR-IR). Qualitative depth resolution on a scale from ca. 0.5 to 5-mu-m is obtained. The results indicate a higher degree of extended trans segments and a higher degree of extended trans orientation near the surface in the machine direction, relative to the bulk film. These quantities also increase with increasing uniaxial draw ratio. No evidence for orientation of the gauche conformer at the surface as a function of uniaxial draw ratio is observed. All conclusions are consistent with the presence of increased crystallinity at the surface of the films. Increases in trans structure and orientation measured by ATR-IR measurements are consistent with bulk crystallinity measurements from density and x-ray scattering measurements.