QUANTITATIVE POLE FIGURE ANALYSIS OF ORIENTED POLYETHYLENE FILMS, J.H. Butler, S.M. Wapp and F.H. Chambon, pp. 141-150

Depending on their molecular compositions and thermomechanical histories, extruded polyethylene (PE) films can exhibit large variations in their (usually row-nucleated) semicrystalline morphologies. In order to measure their textures quantitatively, we have optimized a procedure for the acquisition and analysis of x-ray pole figure data. Film orientation studies are often concerned with the alignment of PE molecules relative to the process machine direction (MD), thus it is of great interest to obtain a quantitative distribution of the (002) pole figure, which is parallel to the crystalline chain axes but cannot be directly measured. Using the popLA software suite this is achieved through successive mathematical operations. The first manipulation entails tilting the (llO), (200) and (020) pole figures in order to project their distributions onto a plane perpendicular to MD. Next a quantitative orientation distribution function (ODF) is calculated to produce a set of fourth order generalized spherical harmonics. From these coefficients the original pole figures are recalculated and the (002) pole figure is generated. We then plot the distribution of crystalline chain axes relative to MD. We conclude that the c-axis distributions are generally not radially symmetric about MD, an assumption that is inherent in second order analyses, such as Her-mans’ function or directional cosine approaches. Orientation variations have been observed in films made by different processes, as well as in films made by a given process but under different conditions. Distinctly different orientation distributions are also seen in films made under identical conditions, but with different molecular compositions.