Mechanical properties of beta-crystalline polypropylene/ethylene-propylene rubber blends

Abstract

In this research, PP/EPR blend was nucleated and its morphology, thermal and mechanical property were studied with the aim to improve its impact strength. Several nucleating agents, i.e., sodium benzoate (NaBz), dimethyl dibenzylsorbital (DMDBS), talc and bicomponent mixture of calcium stearate and pimelic acid (Ca-Pim) were added individually into PP/EPR blend and their mechanical property was measured. The results indicated that Ca-Pim filled PP/EPR blend had the highest Izod impact strength which was slightly higher than the unfilled one. However, talcfilled PP/EPR blend exhibited the highest flexural strength which was much higher than the unfilled one. Therefore, both Ca-Pim and talc were simultaneously added into PP/EPR blend in order to optimize its Izod impact strength and flexural modulus and comparing to PP filled with Ca-Pim and talc at the same added amount. It was found that an increase in talc loading caused the reduction in the Izod impact strength regardless of the inclusion of 0.1%wt Ca-Pim for both pp and PP/EPR blend. Consequently, nucleating the P-form of pp in PP/EPR blend had been focused on the utilization of lone Ca-Pim. By varying the amount of Ca-Pim, it was found that 0.00 l%wt. of Ca-Pim filled PP/EPR blend showed the maximum K-value as revealed by WAXD measurement. From the corresponding SEM micrograph, the β-crystalline PP has been observed as a bundle of lamellae. The β -crystalline formation had also been confirmed by DSC which presented endothermic melting peak at 148 ℃ The influence of α- β transformation of PP/EPR blend on the impact strength was also investigated. The results showed that the β-PP/EPR blend at 0.00l%wt of Ca-Pim had much higher impact strength, lower tensile strength and flexural modulus than the unfilled PP/EPR blend which mostly was α-PP. However, the impact strength of filled PP/EPR blend decreased when Ca-Pim loading content increased with a sudden drop at 0.05%wt Ca-Pim and higher.