Synergistic effects of silicotungistic acid on intumescent flame-retardant polypropylene

The synergistic effects of silicotungistic acid (SiW12) as a catalyst in polypropylene (PP) flame-retarded by the intumescent flame-retarder (IFR) based on the NP28 phosphorus-nitrogen compound were studied using the limiting oxygen index (LOI), the UL-94 test, thermogravimetric analysis (TGA), real time Fourier transform infrared (FTIR), laser Raman spectroscopy (LRS), and scanning electron microscopy (SEM). The LOI data show that SiW12 added to PP/IFR systems has a synergistic FR effect with NP28. The TGA data show that SiW12 increases the thermal stability of the PP/IFR systems at high temperature (T > 500 degreesC). The FTIR results provide positive evidence that IFR can improve the thermal stability of PP and SiW12 and can efficiently promote the formation of charred layers with phosphocarbonaceous structures. The LRS measurements provide useful information on the carbonaceous microstructures. The morphological structures observed by SEM have demonstrated that SiW12 can promote formation of compact intumescent charred layers. Thus, a suitable amount of SiW12 plays a synergistic effects with the IFR in increasing the LOI value and the thermal stability at high temperature and promoting the formation of charred structures in the PP blends. (C) 2001 Elsevier Science Ltd. All rights reserved.