Hierarchical structure and unique impact behavior of polypropylene/ethylene-octene copolymer blends as obtained via dynamic packing injection molding

Controlling the hierarchical structure of melt-processed polymers is vital to “structuring” processing and tailoring properties of the product. In this work, polypropylene (PP)/octene-ethylene copolymer (POE) blends were injection-molded using so-called dynamic packing injection technique, which imposed oscillatory shear on the gradually cooled melt during the packing solidification stage. In this way, samples with highly oriented PP matrix and elongated POE particles were obtained. Most interestingly, it was found for the first time that the elongated POE particles could not improve any impact toughness of oriented PP, which is completely different from that for the isotropic ones. Polarized optical microscope, scanning electron microscope, micro-Fourier transform infrared spectroscopy and differential scanning calorimetry were used to characterize the microstructures along sample thickness. The crack-initiation term, impact fractured surface and cross-section of the impact surface were inspected to understand the difference in impact behavior between the oriented PP/POE blends and their isotropic counterparts. The results show that massive crazing or plastic flow of the matrix could not be effectively initiated in the oriented blends. Our work provides a good example for better understanding structure–property relationship of polymers via well controlling their internal hierarchical structure.