Abstract
The flammability of polypropylene and its intumescent flame retardant composites consisting of ammonium polyphosphate (APP), pentaerythritol (PER) and SiO2 were studied and the synergistic effect of SiO2, as well as the synergistic mechanism was discussed in detail. For the composites, the content of SiO2 varied from 0 to 12 wt.% where the total addition of APP/PER/SiO2 was constant at 30 wt.%. The flammability properties were characterized by Limiting Oxygen Index (LOI) and UL-94 tests, while the synergistic mechanism of SiO2 was investigated by a combination of thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectrometry and scanning electron microscopy (SEM). The results showed that SiO2 had a synergistic effect on the PP/APP/PER system, with an optimum addition at 3.5 wt.%. The introduction of SiO2 improved the flame retardant properties of the PP/APP/PER system and the strength of the char layer.