Synergetic effects of a matrix crystalline structure and chain mobility on the low temperature toughness of polypropylene/ethylene–octene copolymer blends

Abstract

It is believed that the good toughness of β-modified polypropylene (PP) is due to its easier lamellar slippage compared with that of α-modified PP, while the improvement in toughness of PP caused by annealing is due to increased chain mobility in the amorphous part of PP. The aim of this work is to reveal the combined effects of the matrix crystalline structure and amorphous chain mobility on the low temperature toughness of PP/ethylene–octene copolymer (POE) blends by β-modification and annealing. An impact test was performed over a wide range of temperatures (room temperature, 0 °C, −20 °C and −40 °C) to verify the enhancement in toughness, and various characterizations were carried out to inspect the structural evolution and toughening mechanism. The results show that β-modification and annealing will work synergistically to toughen the blend and reduce the POE content necessary for effective toughening over the temperature range tested, due to the synergetic enhancement in the matrix cavitation ability. Besides, the tensile properties will not be lowered by β-modification and annealing. This work not only provides a more efficient way to improve the impact resistance of polymers with stiffness–toughness balance, but also demonstrates the vital role of matrix microstructures on the toughness of the material.