Synergistic effects of silicotungistic acid on intumescent flame-retardantpolypropylene

The synergistic effects of silicotungistic acid (SiW12) as a catalyst in po lypropylene (PP) flame-retarded by the intumescent flame-retarder (IFR) bas ed 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), an d 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 th at SiW12 increases the thermal stability of the PP/IFR systems at high temp erature (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 micro structures. The morphological structures observed by SEM have demonstrated that SiW12 can promote formation of compact intumescent charred layers. Thu s, a suitable amount of SiW12 plays a synergistic effects with the IFR in i ncreasing the LOI value and the thermal stability at high temperature and p romoting the formation of charred structures in the PP blends. (C) 2001 Els evier Science Ltd. All rights reserved.