Synergistic Effect of SiO₂ on Intumescent Flame-retardant Polypropylene

Abstract

The flammability of polypropylene and its intumescent flame retardant composites consisting of ammonium polyphosphate (APP), pentaerythritol (PER) and SiO 2 were studied and the synergistic effect of SiO 2 , as well as the synergistic mechanism was discussed in detail. For the composites, the content of SiO 2 varied from 0 to 12 wt.% where the total addition of APP/PER/SiO 2 was constant at 30 wt.%. The flammability properties were characterized by Limiting Oxygen Index (LOI) and UL-94 tests, while the synergistic mechanism of SiO 2 was investigated by a combination of thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectrometry and scanning electron microscopy (SEM). The results showed that SiO 2 had a synergistic effect on the PP/APP/PER system, with an optimum addition at 3.5 wt.%. The introduction of SiO 2 improved the flame retardant properties of the PP/APP/PER system and the strength of the char layer.