EFFECTS OF HYDROSTATIC EXTRUSION ON THE MECHANICAL AND THERMAL-PROPERTIES OF POLYPROPYLENE

The structure change in spherulites for hydrostatically extruded polyp ropylene (PP) was studied by the use of internal friction measurements and thermophotometry tests. The onset temperature of the beta-loss pe ak of the PP sample decreases with increasing reduction in area, R. Fo r the extrudates below R = 50%, the peak temperature of a-loss shifts to lower temperature. The alpha and beta absorptions for the extrudate s up to R = 50% become broad and overlap with each other. The intensit y 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 deformat ion is divided into two stages, below and above R = 50%. The results a re due to spherulitic changes, i.e. the shape of spherulites changed f rom spherical to elliptical in the extrudates above R = 50% and the sp herulite with R = 50% changed from coarse structure to a finer one by the imposition of hydrostatic pressure.