How does DOPO flame retard polybutylene succinate? An in-depth mechanism investigation

• 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) has a strong flame inhibition effect preventing polybutylene succinate (PBS) ignition • DOPO at 10 wt% in PBS delays the time to ignition by almost 35 minutes under a heat flux of 25 kW/m² • Combustible gases (tetrahydrofuran and succinic anhydride) are released in huge amounts prior to ignition 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) is an efficient phosphorus-based flame retardant which may act in the gas phase to flame retard polyesters. When it was incorporated at 10wt% loading in polybutylene succinate (PBS), it was observed, in mass loss cone test (MLC) that the time to ignition (TTI) was dramatically increased from 119 s to 467s and 2206 s under a heat flux of 35 kW/m 2 and 25 kW/m 2 respectively. Various techniques have been used to investigate its mode of action. Mass spectra (MS) results indicate that the sublimation and thermal decomposition products of DOPO are formed in the gas phase. A large quantity of combustible gases (mainly tetrahydrofuran and succinic anhydride) was observed before ignition by an in-situ infrared spectra combining with MLC (IR-MLC). Therefore, decomposition/sublimation products of DOPO have a strong flame poisoning effect that prevents the material's ignition until the combustible gases reach a critical concentration and ignite.