Crystallization kinetics behavior, molecular interaction, and impact-induced morphological evolution of polypropylene/poly(ethylene-co-octene) blends: insight into toughening mechanism

In this paper, SEM, POM, DSC, FTIR, polarized FTIR, and part-impact test were performed to investigate the effect of dispersed POE phase on crystallization kinetics behavior, molecular interaction, and impact-induced morphological evolution in polypropylene/poly(ethylene-co-octene) (PP/POE) blends. The main focus was to establish a systematic and deep toughening mechanism from microscopic molecular interaction to macroscopic deformation. The results showed that the existence of POE particles played the role of an obstacle during the crystallization process of a PP matrix, which could increase the growth path of PP lamellae or ordered PP molecules and reduce the growth space of spherulites, resulting in a slower spherulite growth rate and smaller spherulite size. This behavior was explained by a crystallization model. Most interestingly, a coated structure was formed in the interface, which was a transition state structure of molecules with different morphologies. The as-formed coated structure can be considered the origin of the cavitation effect and impact-induced morphology evolution of POE particles during the impact process. Moreover, micro-plastic deformation in PP/POE blends during the fracture process was a multi-stage mechanism, in which the POE content played a decisive role.