Thermal decomposition kinetics of polypropylene composites filled with graphene nanoplatelets

Three polypropylene (PP) composites filled separately with different sizes of graphene nano-platelets (GNPs) were prepared using a melt blending method. Thermal gravimetric analysis of the samples was conducted to investigate the effects of the GNP size on the thermal decomposition behavior. Some probable thermal decomposition mechanism parameters were determined through the Malek method, and then the most probable thermal decomposition mechanism functions of these composite systems were obtained using the Achar and Coats-Redfern methods. The thermal decomposition kinetics equation with integral form of the thermal degradation mechanism function for these composites was g(α)=1-(1-α)1/3. The thermal degradation mechanism was a phase boundary controlled reaction (contracting volume). The calculated activation energies of the three composites were, respectively, 277.4, 283.1 and 300.5 kJ/mol. This indicated that the GNPs could improve the activation energy of PP composites, and the activation energy increased with increasing the GNP lateral dimension. Moreover, the thermal decomposition was simulated by applying the thermal decomposition kinetics equation and the determined function parameters; good agreement was found between the simulations and the experimental values.