Anisotropic crystallization in polypropylene induced by deformation of a nucleating agent network

Abstract

Memory effects in propylene/ethylene copolymer (cPP) systems containing different amounts of dibenzylidene sorbitol (DBS) have been studied using wide-angle X-ray scattering techniques. It has been observed that shear flow deformation applied to the melt state containing small amounts of DBS is templated into the crystalline state. After crystallizing a sheared cPP/DBS melt, an anisotropic texture is observed by X-ray scattering, whereas the crystals produced from sheared pure cPP melts are randomly distributed. We attribute this directly to the DBS structure within the polypropylene copolymer melt. Different DBS concentrations and varying flow conditions have been explored and show that, below a certain temperature, the DBS self-organizes into a three-dimensional network within the cPP melt. When deformation is applied to this gel state, it is templated into the polymer lamellae that subsequently form, whereas when the melt is sheared at a temperature where the DBS is dissolved in the polymer, no memory of the deformation process is retained on crystallization.