LAUSR

Abstract Heat transfer during cooling process influences the formation of crystal modification of polypropylene (PP) with nucleating agent (β-nucleated polypropylene). In this study, finite element method (FEM) was applied to simulate the cooling process in PP. Additionally, the skin-core crystalline structure of β-nucleated polypropylene cooled at different temperatures was studied by a wide angle of X-ray diffraction (WAXD). The non-thermal crystallization behaviour of β-nucleated polypropylene was further studied based on the results of FEM. The results indicated that, based on temperature field, FEM was capable of calculating the cooling rate in the skin and core layers of samples. When the cooling temperature increased from 20 °C to 100 °C, the cooling rate decreased from 702.64 °C/min to 79.04 °C/min, and from 119.49 °C/min to 40.00 °C/min in the skin layer and core layer, respectively. The difference of cooling rates from the skin layer to the core layer decreases with the increasing of cooling temperature. Correspondingly, the skin-core crystalline structure is proved to react to the gradient of cooling rate. The non-thermal crystallization also implies that the relative content of β-phase increases with the increasing of temperature, which may attribute to the longer residence time in the temperature range from 105 °C to 140 °C.