Thermal degradation mechanism of highly filled nano-SiO2 and polybenzoxazine

Abstract

Effects of high nano-SiO2 loading (up to 30 mass%) on polybenzoxazine (PBA-a) thermal degradation kinetics have been investigated using nonisothermal thermogravimetric analysis (TG). The DTG curves revealed three stages of thermal decomposition process in the neat PBA-a, while the first peak at low temperature was absent in its nanocomposites. As a consequence, the maximum degradation temperature of the nanocomposites shifted significantly to higher temperature as a function of the nano-SiO2 contents. Moreover, the degradation rate for every degradation stage was found to decrease with the increasing amount of the nano-SiO2. From the kinetics analysis, dependence of activation energy (E a) of the nanocomposites on conversion (α) suggests a complex reaction with the participation of at least two different mechanisms. From Coats-Redfern and integral master plot methods, the average E a and pre-exponential factor (A) of the nanocomposites showed systematically higher value than that of the PBA-a, likely from the shielding effect of the nanoparticles. The main degradation mechanism of the PBA-a was determined to be a random nucleation type with one nucleus on the individual particle (F1 model), while that of the PBA-a nanocomposite was the best described by diffusion-controlled reaction (D3 model). © 2013 Akadémiai Kiadó, Budapest, Hungary.