Study on the formation of β-crystal during the crystallization process of polypropylene reactor granule

A notable amount of PP β-crystal (30%, by X-ray diffraction pattern) has been found in the PP samples as polymerized at normal static isothermal crystallization conditions without using any extra nucleating agents. Existence of catalyst residues in the sample is decisive, which slows down the crystallization rate facilitating the formation of β-form spherulites. Comparatively, high molecular weight PP favors the formation of β-form spherulites, deducting from no β-crystal detected in the degraded samples. Finally, high isotacticity is also required for obtaining qualitative β-form spherulites, demonstrated by increased β-crystal content after removal of weak crystalline fraction of the sample.