Effect of Microstructure of EPR on Crystallization and Morphology of PP/EPR Blends

Abstract

Two ethylene-propylene random copolymer (EPR) fractions (sol-EPR: soluble part and insol-EPR: insoluble part in n-octane) were blended with polypropylene (PP). It was found hat sol-EPR has a random sequence distribution and is nearly amorphous, whereas insol-EPR contains long ethylene and propylene sequences and is partially crystalline. The crystallization and melting behaviors, linear spherulitic growth rate, crystal structure, and morphology were investigated with differential scanning calorimetry, polarized optical microscopy, wide angle X-ray diffraction, and scanning electron microscopy. It was observed that the PP/insol-EPR blends have a smaller domain size of EPR and a rougher fracture surface. The better compatibility between insol-EPR and PP leads to lower melting temperature (T m) of PP/insol-EPR blends than the neat PP. For the blends cooled in air from the melt, both α and β crystals were observed. At low weight fraction (0–10%), EPR enhances the relative content of β crystals. When the weight fraction of EPR exceeds 10%, sol-EPR and insol-EPR decrease the relative content of β crystals in the blends to different extents. This difference can be correlated to the fact that sol-EPR and insol-EPR reduce the linear spherulitic growth rate (G) of PP to different extents.