Wide-angle X-ray scattering studies using an area detector: crystallite orientation in semicrystalline PET structures

Abstract

By means of a Nicolet area detector, the crystallite orientation of uniaxially multi-step drawn poly(ethylene terephthalate) (PET) film strips with large draw ratios from 5.4 to 7.3 has been studied. As orientation parameters, 〈 cos n φ〉, 〈 P 2(cos φ)〉 and 〈 P 4(cos φ)〉 were determined from the equatorial wide-angle X-ray scattering reflexes (0 1 0), (1 1 0) and (1 0 0), where φ corresponds to the angle between the drawing direction and the normal of the chosen ( h k l) lattice planes. Using both the experimental 〈cos 2 φ hk0 〉 and Wilchinsky's method, the crystallite orientation was calculated in terms of the mean-square cosine of the angle σ between the c-axis of the unit cell and the drawing direction. For the highly drawn and semicrystalline structures, the results reveal a nearly perfect alignment of the crystallite c-axis along the drawing direction with a narrow orientation distribution. Despite large variations of the drawing conditions leading to significant differences in the superstructure as well as the Young's modulus, only slight changes of the crystallite orientation are observed.