Synergistic effects of sepiolite on intumescent flame retardant polypropylene

In this paper, the effects of sepiolite as a synergistic agent on the flame retardancy of intumescent flame retardant polypropylene (PP/IFR) were studied using the limiting oxygen index (LOI), the UL-94 test, thermogravimetric analysis (TGA), laser Raman spectroscopy (LRS), cone calorimeter test (CCT) and scanning electron microscopy (SEM), and the IFR system mainly consisted of the ammonium polyphosphate modified with gamma-aminopropyltriethoxysilane coupling agent, melamine and dipentaerythritol. The results from the LOI and UL 94 tests show that sepiolite added to the PP/IFR system has a synergistic flame retardant effects with the IFR system. The TGA results reveal that sepiolite enhances the thermal stability of the PP/IFR composite and increases the char residue formation. The cone calorimeter results indicate that the heat release rate, mass loss rate, total heat release and average specific extinction area of the PP/IFR/sepiolite composite decrease in comparison with the PP/IFR composite. The LRS measurements provide useful information on the carbonaceous microstructures. The morphological structures observed by SEM have demonstrated that sepiolite promote the formation of the reinforced and homogeneous char barrier on the surface of the composites. Simultaneously, the Young's modulus and flexural modulus of the PP/IFR composites are also much better improved with the increase of sepiolite added.