Thermophysical Characterization and Crystallization Kinetics of Semi-Crystalline Polymers

Abstract

Final properties and behavior of polymer parts are known to be directly linked to the thermomechanical history experi- enced during their processing. Their quality depends on their structure, which is the result of the interactions between the process and the polymers in terms of thermomechanical kinetics. To study the actual behavior of a polymer during its transformation, it is necessary to take into account all the thermal dependencies of their thermophysical properties. In this paper, a complete experimental thermal characterization of a semi-crystalline polymer is performed. Thermal con- ductivity is measured using the hot wire method. The PVT diagram is obtained by means of an isobaric piston type di- latometer. Heat capacity is characterized versus temperature by differential scanning calorimetry (DSC). A modification of the Schneider rate crystallization equations is proposed, allowing to identify in a simple way all the crystallization kinetics parameters, using only DSC measurements. Finally, a multiphysical coupled model is built in order to numeri- cally simulate the cooling of a polypropylene plate, as in the cooling stage of the injection molding process. Calculated evolutions of temperature, crystallinity, pressure and specific volume across the plate thickness are presented and com- mented.