Kinetics of thermo-oxidative degradation of PS-POSS hybrid nanocomposite

The thermo-oxidative degradation kinetics of a hybrid nanocomposite comprised of polystyrene and polyhedral oligomeric silsesquioxane (PS-POSS) was studied by dynamic thermogravimetry. The dependence of the activation energy on the conversion (Eα(T)) was determined by means of a model-free isoconversional method and the kinetic mechanisms involved throughout the degradation process were determined by comparison of convolution functions with master curves of kinetic models. The Eα(T) values remained practically constant in the range of 80 to 120 kJ mol−1 throughout the process, indicating that the degradation is essentially limited by a single step process. The degradation proceeded via Rn mechanisms (phase boundary-controlled reactions) in the range of α = 0 to α ≈ 0.8, whereas for α > 0.80 there was a gradual change to Dn (diffusion-controlled reactions) and Fn (chemically-controlled reactions) mechanisms. This demonstrates that volatilization occurs from the surface toward the center of the sample up to α ≈ 0.8 and then becomes governed by the concentration, reactivity and diffusion of the gases.