Flammability performance of poly(vinyl alcohol) nanocomposites with zirconium phosphate and layered silicates

Nanocomposites of poly(vinyl alcohol) with α-type zirconium phosphate (PVA/ZrP) and with layered silicates (montmorillonite and hectorite) were prepared by solution blending. Thermal properties and flame retardancy of the materials were characterized by thermogravimetric analysis and microscale combustion calorimetry. PVA/ZrP nanocomposite showed a faster charring process in temperature range between 200 and 350 °C but higher thermal stability and greater char yields above 350 °C and a different heat release rate feature, compared to clay-based samples. Observation of the micrographs of the chars from the nanocomposites present two distinct structures; one constituted by the stacked clay layers on the surface combined with clay-reinforced foams in the interior residue, and the other formed by carbon covered on the tightly curled ZrP nanoplatelets. The results indicated different flame retardant mechanisms of the two nanocomposites, which depend on the chemical/physical effects from the inherent properties of the nanofillers.