Synergistic effect of boron containing substances on flame retardancy and thermal stability of clay containing intumescent polypropylene nanoclay composites

The functions of nanoclay and three different boron containing substances, zinc borate (ZnB), borophosphate (BPO4), and boron silicon containing preceramic oligomer (BSi), were studied to improve the flame retardancy of polypropylene (PP)-nanoclay-intumescent system composed of ammonium polyphosphate (APP) and pentaerythritol (PER). The flame retardancy of PP composites was investigated using limiting oxygen index (LOI), UL-94 standard, thermogravimetric analysis (TGA), and cone calorimeter. According to the results obtained, the addition of 20 wt% intumescent flame retardant (IFR) improved the flame retardancy by increasing the char formation. Addition of clay slightly increases the LOI value and reduces the maximum heat release rate (HRR). Addition of clay also increases the barrier effect due to intumescent char, especially in thin samples. Boron compounds show their highest synergistic effect at about 3 wt% loading. According to UL-94 test and LOI test, 3 wt% ZnB containing composite shows the highest rating (V0) and BPO4 containing sample shows the highest LOI value (26.5). Copyright (C) 2010 John Wiley & Sons, Ltd.