Mechanism on flame retardancy of polystyrene/clay composites-The effect of surfactants and aggregate state of organoclay

Effects of organically modified montmorillonites (OMMTs) with different type and amount of modifiers on flame retardancy of polystyrene (PS) have been studied. The results from morphology analysis, gas chromatography-mass spectrometry and cone calorimeter have showed different mechanisms for the flame retardancy of PS/OMMTs composites, depending on surface property of OMMTs. One is the catalysis of acid sites formed on the surface of octadecylammonium modified MMT (c-MMT) via Hoffman decomposition on the carbonization of degradation products, which promotes the formation of clay-enriched char barrier. The other is related to chemical effect of inherent properties of MMT sheets on reactive intermediates during combustion, which work in PS/Na-MMT and PS/sodium dodecylsulfonate modified MMT (a-MMT) composites. Furthermore, the effect of the aggregate states of a-MMT on the flame retardancy of PS/a-MMT composites was studied. In the case of a-MMTs from spraying drying, a good protective layer with foam-like aggregate state of MMT sheet was formed in the residue, which results in low peak value of heat release rate of PS/a-MMT composites.