Synergy between piperazine pyrophosphate and aluminum diethylphosphinate in flame retarded acrylonitrile-butadiene-styrene copolymer

Acrylonitrile-butadiene-styrene (ABS) copolymer was combined with piperazine pyrophosphate (PAPP) and aluminum diethylphosphinate (AlPi) to prepare the flame retarded ABS (FRABS) composites by melt blending method. The PAPP/AlPi mixture with a mass ratio of 4:1 achieved an optimum synergy at a 25 wt.% flame retardant loading. The relevant composite (FRABS-3) reached the UL-94 V-0 rating (3.2 mm) and got a limiting oxygen index (LOI) of 30.8%. The synergistic flame retardancy mechanism of PAPP and AlPi was investigated using thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analyzer coupled with an FTIR spectrometer (TG-FTIR), cone calorimeter test (CCT), scanning electron microscope (SEM), and X-ray photoelectron spectroscopy (XPS). The synergism is based primarily on the Lewis acid-base interactions between PAPP and AlPi. The interactions lead to the formation of a cohesive, uniform, and thermally stable char layer before ABS starts to decompose. The barrier effect of the high-quality char layer plays a dominant role in reducing the flammability of FRABS-3. Furthermore, fuel dilution and flame inhibition effects of the evolved gases also contribute to the superior flame retardancy of FRABS-3 to some extent.