Crystallization after orientation relaxation in polypropylene

Abstract

We investigated the isothermal crystallization of polypropylene after the relaxation of shear orientation by using a digital polarized microscope and Hv light scattering. Small spherulites with diffuse Maltese cross extinction patterns are obtained by crystallization after orientation relaxation while large mixed spherulites with no Maltese cross patterns are obtained by crystallization under quiescent conditions, suggesting the suppression of subsidiary lamellae by crystallization after the orientation relaxation. The Hv light scattering intensity increased gradually during the radial growth and then steeply in spite of the cessation of the radial growth of the spherulites. A theoretical analysis of the scattering profile, based on random orientation approximation, revealed that the size of the domain consisting of lamellae arranged in parallel increases in the spherulite in spite of the cessation of the radial growth of the spherulite. Such characteristic crystallization behavior might be attributed to the locally oriented chains that remain after orientation relaxation. © 2008 The Society of Polymer Science.