Crystallite Orientation Distribution in Biaxially Oriented Polyethylene

Abstract

The procedure of Roe for describing the crystallite orientation in polycrystalline samples having general texture is tested using two samples of biaxially drawn polyethylene. An automated four‐circle diffractometer was used to obtain 12 pole figures (4332 fixed points) for the film having stretching ratios 3.0 × 2.0, and 13 pole figures (4693 fixed points) for the film having stretching ratios 1.7 × 1.6. The selection of measurement geometry, procedures for data reduction and correction, and methods for computer calculation of the crystallite orientation distribution are described. While the best representation of the crystallite orientation distribution was obtained from the series of generalized associated Legendre polynomials by retaining terms through l = 12 , the characteristic features of the distribution are already evident when the series is truncated at l = 6 . Thus, for materials belonging to the orthorhombic crystal class, as few as four or five pole figures suffice to determine the principal features of the crystallite distribution in biaxially oriented samples. The crystallographic b axis is found to be normal to the film plane in both samples examined. The a and c axes are nearly randomly arranged in the film plane for the sample having stretching ratios 1.7 × 1.6, while the 3.0 × 2.0 sample exhibits a combination of this texture and that previously observed for uniaxially drawn polyethylene.