Probing solidification kinetics of high-density polyethylene during injection molding using an in-situ measurement technique

The largest part of an injection molding cycle is occupied by melt cooling, which significantly influences the properties of the final parts, especially for crystalline polymers which undergo both solidification and crystallization processes simultaneously. Based on non-isothermal crystallization characterization, solidification kinetics of high density polyethylene was investigated via an in-situ measurement of in-cavity temperature profiles throughout the injection molding process. Existence of the turning point in the cooling curve of ln θ vs. ln t, which can be employed for estimation of the minimum cooling time, was for the first time validated experimentally. Good agreement was achieved through the comparison between experimental observations and theoretical predictions using the enthalpy transformation method (ETM). The present study will be instructive for the optimization of processing variables, and gives insight into the formation of various crystalline structures in injection molded articles, as well as forecast of cooling time of injection moldings of crystalline polymers.