Wide angle X-ray diffraction study of the microstructure of chain-folded polyethylene crystals

Abstract

The profile of the 002 diffraction peak of polyethylene is related to microstructural parameters for the [001] direction. The parameters considered are the mean crystal thickness, distribution of thicknesses, shape function and the degree of paracrystalline disorder in the lattice.

An analytical relation describing the peak profile is derived for trapezium models of the shape function. Calculations are made of peak profiles and their correlation functions for various trapezium models, levels of paracrystalline disorder and Gaussian widths for the distribution of crystal thicknesses. Particular attention is paid to the effect of these parameters on the subsidiary maxima to the 002 peak.

The 002 peak of linear polyethylene (RIGIDEX 50) crystallized from solution in xylene at 70°C is analysed in terms of the above parameters. The results are interpreted in terms of the buried fold model and indicate the presence of well defined zones of highly disordered material (probably nematic) within the crystal entities.The frequency of the zones increases as the fold surfaces are approached.