Poly(vinyl alcohol)/silica nanocomposites: morphology and thermal degradation kinetics.

The morphology of self-assembled poly(vinyl alcohol)/silica (PVA/SiO2) nanocomposites is investigated with atomic force microscopy (AFM) and transmission electron microscopy (TEM). It is found that the SiO2 nanoparticles are homogenously distributed throughout the PVA matrix in a form of spherical nano-cluster. The average size of the SiO2 clusters is below 50 nm at the low contents (SiO2 < or =5 5 wt%), while particle aggregations are clearly observed and their average size markedly increases to 110 nm when 10 wt% SiO2 is loaded. The thermogravimetric analysis (TGA) shows that the nanocomposite significantly outperforms the pure PVA in the thermal resistance. By using a multi-heating-rate method, the thermal degradation kinetics of the nanocomposite with a SiO2 content of 5 wt% is compared to the PVA host. The reaction activation energy (E) of the nanocomposite, similar to the pure PVA, is divided into two main stages corresponding to two degradation steps. However, at a given degradation temperature, the nanocomposite presents much lower reaction velocity constants (k), while its E is 20 kJ/mol higher than that of the PVA host.