Effect of Annealing the Polypropylene Spherulites

The effect of annealing the polypropylene (PP) spherulites was examined by density measurements, dilatometry, small angle X-ray scattering, microbeam X-ray diffraction, polarizing microscope and electron microscope observations. Samples were isothermally crystallized and annealed at appropriately elevated temperatures, TA (between melting temperature and crystallization temperature Tx). On annealing partial melting of crystals followed by recrystallization with thicker lamellae was observed. On the other hand, changes in spherulitic extinction patterns during annealingcould be observed: for example a spherulite, isothermally crystallized at 136°C, haying an irregular extinction pattern showed a well defined Maltese cross after the annealing for 40hr at 160°C. According to the electron micrographs and microbeam X-ray patterns of PP spherulites, pronounced changes in spherulitic microtexture (i. e. appearance of regular lamella distribution, narrowing of line profiles and disappearance of haloes) were also observed with the elapse of annealing time. These results enable us to conclude that spherulitic microtextures are changed into regularly oriented textures along the radial direction of spherulites during the annealing.