Dynamic X-ray Diffraction Studies for Assigning the Alpha and Beta Mechanical Dispersions of Spherulitic Poly-alpha-olefines

Abstract

The dynamic tensile deformation mechanism of spherulitic poly-alpha-olefins, high-density polyethylene, isotactic polypropylene, and isotactic polybutene-1, was investigated by an advanced dynamic X-ray diffraction technique at various temperatures and frequencies in order to assign the a and (3 mechanical dispersions of the materials, explicitly. The uniaxial orientation distribution function qj(ζj, 0) of the j-th crystal plane and its dynamic response Δj'(ζj, 0) in-phase with dynamic strain are observed for several crystal planes, and then the orientation distribution function w(ξ,0,η) of crystal grains and its dynamic response Δw'(ξ,0,η), also in-phase with the dynamic strain, were determined by a well-known mathematical transformation procedure proposed by Roe and Krigbaum on the basis of the Legendre addition theorem. The temperature and frequency dependences of Δw'(ζ,0,η) are analyzed in terms of a spherulite deformation model combining affine orientation of crystal lamellae with several types of preferential reorientation of the crystal grains within the orienting lamellae. The following assignments are made: i) The a mechanical dispersion must be assigned to the dynamic orientation dispersions of the crystal grains within the lamellae, involving two types of preferential rotations of the grains to result in lamellar detwisting mostly in the equatorial zone of uniaxially deformed spherulites and lamellar tilting mostly in the polar zone of the spherulites. Both processes are ‘intralamellar grain-boundary phenomena’, and the former process of lamellar detwisting is hardly activated for polypropylene and polybutene-1 spherulites in contrast to polyethylene spherulites, ii) The β mechanical dispersion must be assigned to the dynamic orientation dispersion of the crystal lamellae behaving as rigid bodies, not accompanied by any of the reorientation mechanisms of the crystal grains within the orienting lamellae. This process is an ‘interlamellar grain-boundary phenomenon’ associated with orientational and/or distortional dispersions of noncrystalline materials between the lamellae. The more pronounced the lamellar orientation dispersion (β mechanical dispersion) and the less pronounced the reorientation dispersion of the crystal grains (α mechanical dispersion), as the specimen changes from polyethylene to polypropylene and to polybutene-1. © 1983, The Society of Rheology, Japan. All rights reserved.