Effect of temperature gradient on the development of β phase polypropylene in dynamically vulcanized PP/EPDM blends

Different sample thicknesses were adopted to investigate the effect of temperature gradient on the development of β phase polypropylene (PP) in the compression-molded dynamically vulcanized thermoplastic elastomers (TPVs) based on PP/ethylene-propylene-diene rubber blend. Differential scanning calorimetry and wide-angle X-ray diffraction were employed to study the melting behavior and crystalline structures. The results indicated that the content of β phase increased with the sample thickness of TPV increasing, while the total crystallinity of PP almost kept constant. The simulation of the temperature field showed that there was a temperature gradient along the direction of sample thickness, and the strength of the temperature gradient increased with the thickness of TPV increasing. The reason for the change of β phase content was found to lie in the reduction of the entropy in the temperature gradient field, which was a result from the decrease of the molecular chain conformation.