Destruction mechanism of core–shell particles in impact polypropylene copolymer during short molten-state annealing

Abstract

Morphology evolution of the dispersed phase with a multilayered core–shell structure in impact polypropylene copolymer (IPC) during molten-state annealing was systematically studied through scanning electron microscopy (SEM), phase contrast microscopy (PCM) and dynamic rheological test. To demonstrate the evolution path of the dispersed phase comprised of ethylene-propylene random copolymer (EPR) and ethylene–propylene block copolymer (EbP) during annealing, different binary blends comprised of different fractions were prepared and their diffusion behavior during liquid–liquid phase separation was investigated. Compared with EPR, EbP presented a higher diffusion rate in propylene homopolymer (hPP) matrix, owing to its lower molecular weight and lower entanglement density. The statistical results of EbP and EPR domain sizes reveal that the coalescence of EbP is faster than that of EPR. In addition, the interaction parameters of EbP/hPP and EbP/EPR estimated using the Nishi–Wang equation show that EbP has a stronger affinity for hPP than EPR. Based on the diffusion rates, entanglement densities of components and great disparity in viscosity between EPR and hPP, a potential mechanism was proposed for the morphology evolution of core–shell dispersed particles in IPC during molten-state annealing.