Thermal degradation of fire retardant formulations and dispersion of clay in polymer/clay nanocomposites

In general, fire retardancy is evaluated in terms of either self-extinguishing properties or the reduction in heat release rate. Since there is a close relationship between thermal degradation behavior of polymer and its fire retardancy, this dissertation mainly deals with the degradation behavior of fire retardant formulations. In the case of self-extinguishing fire retardant formulations, many studies have focused on systems that exhibit synergistic fire retardant properties. However, no feasible fire retardant formulations showing synergistic fire retardancy have been developed since the introduction of the halogen/antimony fire retardant system. In this study, polycarbonate shows two main degradation pathways, which are chain scission of isopropylidene linkage and alcoholysis/hydrolysis of carbonate linkage. By incorporating aryl phosphate with polycarbonate, the carbonate linkages are stabilized, because the phosphates undergo the alcoholysis reaction more readily with the alcohol products decomposed from PC than does the carbonate linkage of PC. The synergistic fire retardant effect comes from the alcoholysis reaction between the degraded products and phosphate. Through the degradation study of the clay composites of polystyrene (PS), polyamide 6 (PA6), poly(styrene-co-acrylonitrile) (SAN) and acrylonitrile-butadienestyrene (ABS), it appears that the common degradation pathway in polymer nanocomposites showing a large reduction in peak heat release rate (PHRR) is to have significant inter-chain reactions; PS/clay nanocomposites exhibit radical recombination and PA6/clay nanocomposites show increased inter-chain aminolysis/acidolysis. SAN/clay nanocomposites exhibit decreased radical recombination compared to that of PS/clay nanocomposites. The effect of the butadiene rubber component in ABS is to stabilize the SAN phase in terms of mass loss. Summarizing the above results, the well dispersed clay confines the degrading polymer during thermal degradation and this confinement permits further reactions, such as extensive random scission or inter-chain reactions. Therefore, it is possible that the degradation behavior can be correlated with the reduction in PHRR as a function of the extent of inter-chain reaction for many different polymers. The relationship between the solubility parameter of the polymer and dispersion of clay was suggested through the study of model polymers having different solubility parameter and by including previously reported results. It was shown that the polymers having high solubility parameter readily form the nano-dispersed clay morphology and the type of surfactant is less important as long as the introduction of surfactant to the gallery enlarges the d-spacing of the clay