STUDIES OF THE EFFECTS OF PHOSPHORUS NITROGEN BROMINE SYSTEMS ON THE COMBUSTION OF SOME THERMOPLASTIC POLYMERS

A study has been made of red phosphorus (P) (or phosphates) and nitrogen compounds as flame retardants/smoke suppressants for thermoplastic polymers [plasticized poly(vinyl chloride), polystyrene, high density polyethylene and poly(methyl methacrylate)], both on their own and in combination with a brominated flame retardant (decabromobiphenyl). The techniques used were limiting oxygen index, the Michigan smoke chamber, thermoanalysis and i.r. spectrometric analysis. The nitrogen compounds used serve as mild flame retardants but perhaps their most important effect is to decrease smoke formation from the polymers and in particular to nullify the large increase in smoke levels caused by the incorporation of P. In many systems, there is flame retardance and smoke suppression synergism, since the combination of P and nitrogen compounds decreases flammability and specific smoke formation to a greater extent than the additive effects of the individual materials. The nitrogen compounds appear to act by extending considerably the temperature range over which the system decomposes, and thus decreasing the average rate of production of volatiles. They also catalyse oxidation of P, which is the flame retardant mechanism for this material. The nitrogen compounds also break down to yield inert gases, which cause dilution of the gas mixture to outside the flammable range. All nitrogen compounds used, except benzotriazole, give large quantities of ammonia on decomposition; benzotriazole is the only nitrogen compound used which does not reduce flammability. In conclusion, it is considered that the disadvantages of P as a flame retardant outweight its advantages for the systems studied.