Synergistic toughening of polypropylene random copolymer at low temperature: β-Modification and annealing

The synergistic effect of β-modification and annealing on the impact toughness of a commercially available polypropylene random copolymer (PPR) was investigated. Interestingly, the impact toughness of β-nucleated PPR after annealing at low temperature (0 °C) was almost five times as high as that of the virgin PPR without annealing. The crystalline structure, supermolecular structure, phase morphology, the relaxation of chain segments and fracture behavior of matrix were investigated to explore the toughening mechanism related to the β-modification and annealing. It was found that annealing improved the mobility of chain segments in amorphous phase as well as the strength of ligament of PPR matrix with profuse β crystals having the intrinsic low plastic deformation resistance, responsible for the superior toughness achieved. This work provides a possible method to toughen semi-crystalline polymers at low temperature by combination of β-modification and suitable annealing.