Phase morphology evolution upon melt annealing treatment and corresponding mechanical performance of impact-resistant polypropylene copolymer

The evolution of phase morphology upon melt annealing and the corresponding changes in mechanical properties of impact-resistant polypropylene copolymers (IPCs) have been systematically investigated. A distinct coarsening process is observed during melt annealing and the statistical analysis of stereology reveals that the increase of dispersed domain size well follows the Ostwald ripening mechanism. Mechanical tests suggest that the notched impact strength and elongation at break decrease gradually with increasing annealing time, while the tensile strength remains relatively constant. The decrease of toughness is consistent with the size increase of dispersed domains, which may result from the development of late-stage phase separation of IPC. However, the tensile strength, which is mainly dominated by the crystalline phase structure, remains relatively constant during the annealing treatment. On the basis of these results, the probable relationship between the change of mechanical properties and phase morphology evolution has been proposed.