Thermal History—Dependent Thermomechanical Response of Talc-Filled and Unfilled Polypropylene

The thermomechanical response of semicrystalline polypropylene (PP) depends not only on temperature and loading conditions, but also on its prior thermal state. While the effects of post-crystallization and annealing are well documented, the combined influence of these processes on thermal expansion, thermome-chanical viscoelastic response, and crystalline fraction under service-relevant conditions in an automotive context remains inadequately quantified. In this study, unconditioned and thermally preconditioned unfilled and talc-filled PP were investigated by dilatometry, dynamic mechanical analysis, and differential scanning calorimetry over temperature and frequency ranges that are representative of service-relevant conditions. Thermal preconditioning resulted in a modification of the temperature-dependent coefficient of thermal expansion, as well as alterations in stiffness and damping levels. However, the characteristic relaxation temperatures remained predominantly unaltered. These alterations occurred in conjunction with an increase in the crystalline fraction, indicating a modified structural condition subsequent to thermal treatment. The incorporation of talc led to a decrease in the overall level of thermal expansion, an increase 1 in stiffness and crystallinity, and an effect on the high-temperature relaxation associated with the crystalline phase, without influencing the glass transition temperature. The findings demonstrate that the thermal history of polypropylene (PP) modifies its structural state, thereby affecting its thermal expansion and dynamic viscoelastic response in both filled and unfilled systems. This is essential for constrained automotive exterior assemblies, which require dimensional stability and tolerance retention.