Crystalline structure, morphology and mechanical properties of β-nucleated controlled-rheology polypropylene random copolymers

Abstract

β-nucleated controlled-rheology polypropylene random copolymers (CRPPRs) were prepared by peroxide-initiated degradation via adding dicumyl peroxide (DCP) to β-nucleated PPR. Melt flow index (MFI) and mechanical properties of β-nucleated PPR and CRPPRs were analyzed and compared with PPR. Wide-angle X-ray diffractometer (WAXD), differential scanning calorimeter (DSC) and polarized light microscope (PLM) were used to study the crystalline structure and morphology. The results indicate that the MFI of β-nucleated CRPPR increases linearly with increasing DCP content. The strain hardening rate and impact strength of β-nucleated CRPPRs well reflect the degree of degradation and β-phase content. No significant change of yield strength and strain at break is seen with increasing DCP content, except for an increase of the latter when DCP content reaches 0.15 wt%. The maximum crystallinity is observed at 0.05 wt% DCP. β-nucleated CRPPRs show increased crystallization temperature and decreased β-crystal content and crystal size as DCP content increases.