[SY-H5] Monte Carlo simulation predicting generation and growth of spherulites in thermoplastic polymer
Crystalline thermoplastic polymers have a complicated hierarchical structure consisting of lamellae of amorphous phases with a random coil structure and crystalline phases in which molecular chains are regularly arranged. The lamellae grow radially repetition of secondary nucleation on a surface of growing lamellae and spherulite structures are generated. Peculiar mechanical characteristics of the crystalline thermoplastic polymers, such as nonlinear elasticity, strain softening after yielding, propagation of necking, and orientation rehardening cannot be seen in the case of metals. Mechanical properties of crystalline thermoplastic polymers depend on the complicated microstructures, and the microstructures varies depending on molding conditions. A theoretical model predicting the microstructure and reproducing the mechanical properties are expected in the field of industrial CAE to enhance formability and reliability of the crystalline thermoplastic polymers. Phenomenological models on macroscopic crystallinity or crystallization rate are popular in terms of industrial availability. Such models cannot investigate effects of sizes, shapes, and distribution of spherulites. In this study, we construct a model expressing generation of spherulite structures for prediction of microstructures of crystalline thermoplastic polymers depending on thermal conditions. A spherulite growth are represented by initial nucleation in an amorphous phase and secondary nucleation on surfaces of spherulites. Rates of the both nucleation are identified by experimental observations of spherulites growth under different thermal conditions. Monte Carlo simulations are performed using the constructed method to reproduce the generation and growth of spherulites in an amorphous phase. In addition, we evaluate effects of crystallization temperature on the nucleation rate and the growth rate by comparison of experiment and analysis results.