Balanced toughening and strengthening of ethylene–propylene rubber toughened isotactic polypropylene using a poly(styrene-b-ethylene–propylene) diblock copolymer

Abstract

For ordinary rubber toughened plastics, the introduction of rubber will inevitably bring about the severe decline in mechanical strength due to the low modulus and rigidity of elastomers. To fabricate toughened polypropylene (PP) materials without significant strength degradation, the poly(styrene-b-ethylene–propylene) diblock copolymer (SEP) was used as the third component in an isotactic polypropylene/ethylene–propylene random copolymer (iPP/EPR) to prepare a series of PP/EPR/SEP blends. The phase morphology, dynamic mechanical behavior, crystallization behavior and mechanical properties of PP/EPR/SEP blends were systematically investigated, and compared with PP/EPR blends. The dynamic mechanical analysis results revealed that SEP has good compatibility with both EPR phase and amorphous PP phase, which led to an improvement of interfacial adhesion between them. The mechanical properties testing results indicated that the introduction of SEP could effectively promote the brittle–ductile transition for PP/EPR blends and that PP/EPR/SEP blends presented a good toughness without strength loss. Considering the fact that the individual EPR or SEP could not achieve good toughening, it was proposed that SEP and EPR have a synergistic effect on toughening PP and a modified PP with balanced toughness and tensile strength can be achieved by simultaneously adding EPR and SEP into iPP.