Formation of β-iPP in isotactic polypropylene/ethylene–propylene rubber blends: Effects of preparation method, composition, and thermal condition

Abstract

The effects of preparation method, composition, and thermal condition on formation of β-iPP in isotactic polypropylene/ethylene–propylene rubber (iPP/EPR) blends were studied using modulated differential scanning calorimeter (MDSC), wide angle X-ray diffraction (WAXD), and phase contrast microscopy (PCM). It was found that the α-iPP and β-iPP can simultaneity form in the melt-blended samples, whereas only α-iPP exists in the solution-blended samples. The results show that the formation of β-iPP in the melt-blended samples is related to the crystallization temperature and the β-iPP generally diminishes and finally vanishes when the crystallization temperature moves far from 125 °C. The phenomena that the lower critical temperature of β-iPP in iPP/EPR obviously increases to 114 °C and the upper critical temperature decreases to 134 °C indicate the narrowing of temperature interval, facilitating the formation of β-iPP in iPP/EPR. Furthermore, it was found that the amount of β-iPP in melt-blended iPP/EPR samples is dependent on the composition and the maximum amount of β-iPP formed when the composition of iPP/EPR blends is 85:15 in weight. The results through examining the effect of annealing for iPP/EPR samples at melt state indicate that this annealing may eliminate the susceptibility to β-crystallization of iPP. However, only α-iPP can be observed in solution-blended samples subjected to annealing for different time. The PCM images demonstrate that an obvious phase-separation happens in both melt-blended and solution-blended iPP/EPR samples, implying that compared with the disperse degree of EPR in iPP, the preparation method plays a dominant role in formation of β-iPP. It is suggested that the origin of formation of β-iPP results from the thermomechanical history of the EPR component in iPP/EPR. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1704–1712, 2007