Synergistic Effect of Phosphorus-Containing Montmorillonite with Intumescent Flame Retardant in Polypropylene

Phosphorus-containing montmorillonite (P-MMT) was successfully prepared via intercalating resorcinol bis(diphenyl phosphate) (RDP) into montmorillonite (MMT) layers, and was utilized as a synergistic agent in the polypropylene/melamine pyrophosphate/pentaerythritol (PP/MPP/PER) intumescent flame retardant (IFR) system. The synergistic effect of P-MMT and IFR was investigated by dynamic mechanical analysis (DMA), thermogravimetry (TG), limiting oxygen index (LOI), UL-94 test, cone calorimeter test (CCT), and scanning electron microscopy (SEM). It was found that P-MMT could significantly improve the thermostability and flame retardancy of the PP/IFR composite. When 2.0 wt% P-MMT replaced the same amount of IFR in the composite, both the onset decomposition temperature (T onset) and the maximum-rate decomposition temperature (T max) of the PP/IFR composite were increased by more than 14°C. Meanwhile, the LOI value was increased from 29.5% to 32.5%, the UL-94 rating was enhanced from V-1 to V-0, and the heat release rate (HRR), total heat release (THR), and mass lose rate (MLR) were decreased dramatically, which proved that P-MMT had a good synergistic effect with IFR in flame retardant PP.