Properties Of Polypropylene Random Copolymer/Isotactic Polypropylene Blend Modified By β Nucleating Agent

Isotactic polypropylene (iPP) is rigid and brittle. Polypropylene random copolymer (PPR)is less stereoregular than iPP, but its impact resistance and pressure resistance is better thanthose of iPP. Nucleating agent has significant effect on the toughness of iPP or PPR. PPR andiPP are compatible because their molecular structure is similar. We adopt two kinds of rareearth complexes (nucleating agent) to study the mechanical properties and thermal propertiesof modified PPR/iPP blend. The crystallization process and surface morphology areinvestigated by differential scanning calorimeter (DSC) and wide angle X-ray diffraction(WAXD) etc.Nucleating agent has an obvious effect on the crystallization ability of PPR/iPP blends.The Izod impact strength of PPR, PPR/iPP（70/30,50/50,30/70）blends and iPP was elevatedfrom42.7,33.7,14.5,8.3and5.1kJ/m2to87.8,63.4,29.3,13.9and8.2kJ/m2, respectively,while the reduction magnitude in the tensile strength was less than10%with0.05wt%ofβ-nucleator. DSC and WAXD results showed that0.05wt%of β-nucleator significantlypromoted the formation of β-form crystal in PPR and the PPR/iPP(70/30) blend and the Izodimpact-fractured sections were characteristic of a typical ductile fracture according to theirSEM morphologies. The nucleation of α-form crystallization of the blends was strengthenedby0.2wt%of β-nucleator to induce a decrease in the impact toughness.Nucleating agentⅡhas also obvious effects on the toughness of PPR/iPP blends by theaddition of0.25wt%. DSC and WAXD results showed that0.25wt%of β-nucleator promotedthe formation of β-form crystal of PP/PPR. With increasing the crystallization rate duringnon-isothermal crystallization process, β-nucleating agent enhances the crystallizationtemperatures and broadens the crystallization temperatures of30PPR and70PPR. At the samerate, the time for the blends with the nucleating agent is relatively longer than those withoutthe agent to achieve the same degree of crystallinity. The non-isothermal crystallizationprocesses can be fitted well by the methods proposed by Jeziorny or Mo,but not by Ozawa’s.