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 ≤ 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 (<i>E</i>) 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 (<i>k</i>), while its<i> E</i> is 20 kJ/mol higher than that of the PVA host. <br />