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

Abstract 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 ( E α ( 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 E α ( 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 R n 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 D n (diffusion-controlled reactions) and F n (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.