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

摘要

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(I'm)of PP/insol-EPR blends than the neat PP.For the blends cooled in air from the melt,both alpha and beta crystals were observed.At low weight fraction(0-10),EPR enhances the relative content of beta crystals.When the weight fraction of EPR exceeds 10,sol-EPR and insol-EPR decrease the relative content of beta 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.