Flammability of polystyrene layered silicate (clay) nanocomposites: Carbonaceous char formation

Polymer layered‐silicate (clay) nanocomposites have not only the unique advantage of reduced flammability, but also improved mechanical properties. This is a key advantage over many flame retardants, which reduce flammability but also reduce the mechanical properties of the polymer. In our efforts to further understand the mechanism of flame retardancy with polymer‐clay nanocomposites, we investigated the effect of the clay, the loading level and polymer melt viscosity on the flammability of polystyrene‐clay nanocomposites. The nanoscale dispersion of the clay in the polymer was analysed by wide‐angle X‐ray diffraction (XRD) and transmission electron microscopy (TEM). Cone calorimetry and gasification studies were used to evaluate the flammability of these nanocomposites. There were major reductions in peak heat release rates (HRRs), and increased carbonaceous char formation, for these nanocomposites. It was determined that while the viscosity of the PS nanocomposite played a role in lowering the peak HRR, the clay loading level had the largest effect on peak HRR. Finally, it was found that clay catalysed carbonaceous char formation, and the reinforcement of the char by the clay was responsible for the lowered flammability of these nanocomposites. Published in 2002 by John Wiley & Sons, Ltd.