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

The combustion performance of polyphenylene oxide (PPO), high impact polyst yrene (HIPS), or PPO/HIPS blend fire retarded by resorcinol bis(diphenyl ph osphate) (RDP) was studied by OI and UL94 tests. RDP is an efficient fire r etardant 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 yi eld from the plastics. Chemical analysis and infrared indicate that very li ttle phosphorus volatilizes from the PPO/HIPS blend either during thermal d ecomposition or in combustion. The fire retardant action of RDP is discusse d in terms of chemical interaction between PPO and RDP and the catalytic ef fect of RDP.