Experimental Study And Numerical Simulation On The Varying Cooling Rates Crystallization Kinetics Of Polymer

In actual processing of semi-crystalline polymers, the crystallization actually happens in polymer melt under temperature condition with varying cooling rates. The microstructures of the crystals are the key factors which determine the final aggregated structures and the properties of products. Therefore, to explore the crystallization behavior or the growth of crystallinity and study the crystallization kinetics of polymers have great guiding significance for characterizing crystallization properties of polymers and confirming the optimal processing conditions.The following works focused on the experimental study and numerical simulation of the crystallization kinetics of polymers with varying cooling rates have been finished:(1) Three widely used polymers, isotactic polypropylene (iPP), high density polyethylene (HDPE) and nylon 6 (PA6), are characterized by means of the Differential Scanning Calorimetry (DSC) and Polarization Microscope (PLM) to study the isothermal crystallization kinetics, constant cooling rates as well as varying cooling rates crystallization kinetics of them.(2) Based on the assumption that the process of varying cooling rates can be regarded as the addition of a range of constant cooling rates intervals, the thermodynamics model of RAO and the isokinetics approach of Nakamura have been both deduced to find integral methods to simulate the crystallization kinetics with varying cooling rates.(3) Calculate the kinetic parameters of the RAO model and the Nakamura equation for the three polymers (isotactic polypropylene, high density polyethylene and nylon 6) and simulate the crystallization kinetics under conditions with constant cooling rates and varying cooling rates of them. The comparisons suggest that both models show good agreement between the predicted and experimental results for three polymers under crystallization conditions with the constant cooling rates as well as varying cooling rates. But the RAO model exhibits better simulating results than that of the Nakamura equation. (4) Based on the effect of shearing action on the equilibrium melting point, some primary works have been attempted to build crystallization kinetics model under steady shear condition by introducing the equilibrium melting point under shear field into the RAO model.