Deformation mechanism of polyethylene spherulites estimated by crystal orientation distribution function and small angle light scattering under Hv polarization condition

Abstract

The deformation mechanism of polyethylene spherulites was studied by using melt films of high density polyethylene with a 78% crystallinity in terms of crystallite orientation distribution estimated by X-ray diffraction technique and small angle light scattering under Hv polarization condition. In doing so, a model relating crystal orientation to the deformation of polyethylene spherulite was proposed. The distribution function of crystallites within a spherulite was assumed to be a function of crystal lamella. The distribution functions of reciprocal lattice vectors of given crystal planes were derived from two functions of the crystallites and lamellae with several parameters. The best values of each parameter were determined by the simplex method associated with direct research method to obtain the object function on the basis of trial and error. As a result, it was found that at an initial elongation ratio of 1.5, the most important factor in fitting the model to experimental results, was the preferred orientation of lamellar axis but most of the crystallites within the lamella were maintained without taking characteristic orientation. The Hv scattering from a deformed three-dimensional spherulite was formulated on the basis of the proposed model. The scattered intensity distribution in an undeformed state showed the typical four-leaf clover pattern and the lobes extending in the horizontal direction indicated the deformation of spherical to ellipsoid structure with a draw ratio of 1.5. The calculated patterns were in good agreement with those observed.