Effects of talc particle size on the non-isothermal crystallization kinetics and activation energy of isotactic polypropylene-based composites

This study investigates the non-isothermal crystallization behavior of isotactic polypropylene (iPP) reinforced with two types of talc fillers: micrometric talc (μ-talc) and standard talc (S-talc). Composites containing 20 wt% filler were analyzed using differential scanning calorimetry (DSC), wide-angle X-ray scattering (WAXS), and scanning electron microscopy (SEM). Non-isothermal crystallization at cooling rates β = 5–20°C/min was evaluated using the Ozawa, Kissinger, Coats-Redfern, and Criado methods. Both μ-talc and S-talc act as efficient nucleating agents compared with neat iPP, but they operate through distinct mechanisms. μ-talc, owing to its finer particle size and higher surface area, increases the number of nucleation sites, thereby reducing the half-crystallization time (t1/2) and accelerating the crystallization kinetics. By contrast, S-talc, despite its lower surface area, enhances crystallization by virtue of its lamellar morphology, which promotes selective chain orientation, raises the crystallization temperature (Tc), and stabilizes secondary crystallization. Kinetic analysis confirmed this distinction: the activation energy (Ea) increased from neat iPP (≈185 kJ/mol) to μ-talc/iPP (≈215 kJ/mol) and further to S-talc/iPP (≈274 kJ/mol). The Coats-Redfern and Criado analyses consistently identified a second-order (F2) mechanism for the S-talc composites across all cooling rates, underscoring their stabilizing role in crystallization.