The formation of β-pp crystals in a compatibilized blend of isotactic polypropylene and polyamide-6

A blend of β-nucleated isotactic polypropylene (PP) and polyamide-6 (PA6) compatibilized with maleic anhydride grafted polypropylene (MA-g-PP) was prepared by twin-screw compounding and followed by injection molding. The blend is referred to as Blend-0.3 in this paper. The injection molded sample was studied by differential scanning calorimetry (DSC) and wide angle x-ray diffraction (WAXD). It was observed that high β-PP content had developed in Blend-0.3 at slow cooling rate. The β-crystallinity measured by DSC was in agreement with the WAXD results. From analyzing the crystallization kinetics, it was revealed that the rate of crystallization for the β-PP crystals in Blend-0.3 was very slow. This is the major reason for the observed difficulties in obtaining high β-PP content in Blend-0.3. The higher crystallization temperature of β-PP than that for α-PP explains why the high β-PP content can develop in Blend-0.3 when it was cooled down at slow cooling rates.