Flame retardance and thermal degradation mechanism of polystyrene modified with aluminum hypophosphite

A phosphorus-containing inorganic compound, aluminum hypophosphite (AP), was used to prepare flame-retardant polystyrene (PS). The flammability of the PS/AP composites was investigated by the limiting oxygen index (LOI), vertical burning test (UL-94) and cone calorimeter test. When the content of AP reaches 25 wt%, the LOI of PS/AP is 25.6% and it passes UL-94 V-0 rating. The results of cone calorimeter test show that the heat release rate (HRR), the total heat release (THR) and the mass loss rate (MLR) of PS/AP composites are significantly reduced. The thermal degradation mechanism of PS/AP was investigated by thermogravimetric analysis (TGA), Fourier transform infrared spectrometry (FTIR), thermal gravimetric-Fourier transform infrared spectrometry (TG-FTIR), pyrolysis gas chromatography-mass spectrometry (Py-GC/MS), and X-ray photoelectron analysis (XPS) tests. The results indicate that PS/AP has a combined gas-phase and condensed-phase activity in the combustion and degradation of the composites. Consequently, a possible flame-retardant mechanism of PS/AP composites is proposed.