Non-isothermal crystallization kinetics and its effect on the mechanical properties of homopolymer isotactic polypropylene

Abstract

The non-isothermal crystallization of the isotactic Polypropylene (iPP) was studied using differential scanning calorimetry and polarizing optical microscopy. Jeziorny’s model and Ozawa’s theoretical approaches were applied to study the non-isothermal kinetics of the iPP. Jeziorny’s approach proved to be the most relevant model to the present material. Simultaneously, the activation energy was calculated with Kissinger’s method and Vyazovkin’s iso-conversional approach. Indeed, the latter provides an activation energy varying between 100 and 176 kJ/mol. Furthermore, the WAXD scans indicated the presence of a single crystalline form in the used material. To study the effect of the microstructure on the mechanical properties of the iPP, multiscale tensile tests were carried out for different film microstructures. At macroscopic scale, the increase in the diameter of spherulites, inevitably accompanied by a rise in the crystallinity rate, induces the growth of rigidity, brittleness, and elastic limit. Moreover, the results of the in-situ micro-tensile tests present the evolution of spherulites during loading.