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

Different sample thicknesses were adopted to investigate the effect of temperature gradient on the development of beta 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 beta 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 beta 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