Two-dimensional small-angle X-ray scattering studies on oriented poly(ethylene terephthalate) films

Abstract

The supermolecular structure of uniaxially drawn (5.4≤ λ≤7.3) poly(ethylene terephthalate) (PET) films exhibiting a very high orientation of the chain molecules was investigated by two-dimensional small-angle X-ray scattering studies. Depending on the drawing history, the intensity distribution along the meridional layer line as well as at the equator was analysed. With the incident beam perpendicular to the film plane, the drawn PET samples revealed so-called two-point or four-point meridional scattering patterns. From the intensity distribution along the meridional layer line, a lamellar structure with stacks of comparatively short crystalline lamellae, both perpendicular and inclined with respect to the drawing direction, was concluded. Parameters like the inclination angle, the lamellar periodicity along the drawing direction as well as the normal to the lamellae and the half-widths of the meridional layer line reflexes were determined. As a result, large orientation changes in the normal to the lamallae with regard to the drawing direction during stretching were found. Even for already highly oriented and semicrystalline PET structures, further drawing changes the orientation of the lamellae dramatically.