Fire retardant action of resorcinol bis(diphenyl phosphate) in a PPO/HIPS blend

The combustion performance of polyphenylene oxide (PPO), high impact polystyrene (HIPS), or PPO/HIPS blend fire retarded by resorcinol bis(di phenyl phosphate) (RDP) was studied by OI and UL94 tests. RDP is an efficient fire retardant additive in PPO/HIPS because of its very high efficacy in PPO. In HIPS, RDP shows moderate fire retardant activity. Thermogravimetry carried out either in inert atmosphere or in air reveals that RDP increases char yield from the plastics. Chemical analysis and infrared indicate that very little phosphorus volatilizes from the PPO/HIPS blend either during thermal decomposition or in combustion. The fire retardant action of RDP is discussed in terms of chemical in teraction between PPO and RDP and the catalytic effect of RDP.