Modeling Specific Volume of Semi-Crystalline Thermoplastics During Fast Cooling Under Pressure

This work presents a time-dependent pressure–specific volume–temperature (pvT) model for semi-crystalline thermoplastics under rapid cooling, crucial for understanding material behavior during manufacturing. The individual model components were evaluated against experimental pvT and calorimetric data, while the coupled model was used to predict the specific-volume evolution under rapid cooling conditions. The focus was on establishing an accessible procedure for determining material parameters, independent of geometry or process, through an inductive approach. A time-dependent description of the plastic’s pvT behavior was achieved by considering equilibrium states affected by pressure and temperature changes. The modeling incorporated temperature, pressure, and time dependence, alongside crystallization kinetics. The Dual Nakamura model was calibrated using isothermal DSC- and FSC measurements at ambient pressure, while pressure dependence was introduced through the pressure-dependent equilibrium melting temperature derived from pvT measurements. The pressure-dependent pvT behavior was experimentally characterized between 100 and 500 bar, whereas the crystallization kinetics were determined at ambient pressure. In contrast to the classical Tait model, the proposed approach explicitly accounts for time-dependent crystallization and cooling history. The calibration workflow represents a basis for cooling-rate-dependent material descriptions in injection-molding simulations.