Effects of hydrostatic extrusion on the mechanical and thermal properties of polypropylene

The structure change in spherulites for hydrostatically extruded polypropylene (PP) was studied by the use of internal friction measurements and thermophotometry tests. The onset temperature of the beta-loss peak of the PP sample decreases with increasing reduction in area, R. For the extrudates below R = 50%, the peak temperature of a-loss shifts to lower temperature. The alpha and beta absorptions for the extrudates up to R = 50% become broad and overlap with each other. The intensity of the beta-loss peak, Delta(max), is maximum for the extrudate with R = 50%. The results of tan delta, damping, and the intensity of the beta-loss peak indicate that the mechanism of molecular chain deformation is divided into two stages, below and above R = 50%. The results are due to spherulitic changes, i.e. the shape of spherulites changed from spherical to elliptical in the extrudates above R = 50% and the spherulite with R = 50% changed from coarse structure to a finer one by the imposition of hydrostatic pressure.