Modeling Evolution of Phase Interface of Poly (Lactic Acid) During a Solidification Process: Case Analysis and Application in Cooling Time Prediction

ABSTRACT Polylactic acid (PLA) has been widely utilized in modern industries; however, during practical processing operations such as extrusion and injection molding, it consistently exhibits a sufficiently slow crystallization rate and low crystallinity. This study intends to investigate the influence of processing conditions on the solidification behavior of PLA during the injection molding process. The enthalpy transformation method (ETM) was employed to analyze the temperature decays throughout the entire injection process, with a focus on the effects of different cooling parameters on solidification kinetics. Four cooling conditions (denoted as Cases A–D) were compared, and the analysis results of these cases revealed that the melt cooling rate was heavily influenced by the mold temperature. The movement of the phase interface during melt solidification under various scenarios was also examined. Based on the experimental results, position‐dependent characteristics of the phase transition plateau were identified. It was found that its width gradually increased from the wall to the sample centerline. This finding can be utilized in designing the cooling parameters for crystalline polymers during the injection operation. A comparative analysis was conducted between experimental cooling time and predicted cooling curves of PLA. Under varying cooling conditions, a generalized equation derived from fitting parameters using TPM (Three‐Parameter Model) II was found to provide reasonably accurate estimates for injection‐molded crystalline polymers, as supported by both experimental and calculated results. The present work offers valuable insights for designing cooling parameters for crystalline polymers in injection molding processes and provides a theoretical foundation for the future development of PLA composites.