Effect of morphology development on the low-temperature tensile properties of PP/POE blends

The application of polypropylene (PP) is greatly restricted by its poor low-temperature tensile properties. In this work, a polypropylene random copolymer (rPP) and polypropylene/ethylene-propylene-diene monomer graft copolymer (gPP) were used to improve the toughening effect of polyolefin elastomer (POE) on PP. The influences of this addition on the phase morphology, crystallization, and rheological and mechanical properties were investigated. The results revealed that rPP both reduced the size of PP spherulites and improved the interfacial cohesion of the PP/POE blend, which endowed the material with greater tensile properties and melt flow rate. The elongation at break of PP/POE/rPP at 23, 0, -20, and -40 degrees C was 400%, 221%, 205%, and 106%, respectively. These represented increases of more than 200% compared with those of PP/POE. The tensile strengths of PP/POE/rPP were 15.0, 19.1, 21.5, and 27.4 MPa at 23, 0, -20, and -40 degrees C, respectively, which were comparable to those of PP/POE. Finally, the effects of the injection molding process parameters on the mechanical properties and phase morphology of rPP-modified PP/POE blends were studied.