Synthesis of hexakis (γ-aminopropylsilanetriol) cyclotriphosphazene and application in intumescent flame retardant polypropylene

A novel charring agent named as hexakis (γ-aminopropylsilanetriol) cyclotriphosphazene (HKHPCP) was synthesized by using hexachlorocyclotriphosphazene (HCCP), p-hydroxy benzaldehyde and γ-aminopropylsilanetriol (KH553). The intumescent flame retardant polypropylene (PP) matrix composites (APP-HKHPCP-NOR116/PP) was prepared using HKHPCP and ammonium polyphosphate (APP) as the anti-dripping agent and N-alkoxy hindered amine (NOR116) as the synergistic agent by the melt compounding method. The chemical structures of intermediate and HKHPCP were characterized by FTIR, ¹H nuclear magnetic resonance (¹H NMR) and ³¹P NMR. The effects of the flame retardant APP-HKHPCP-NOR116/PP on the thermal degradation, flame retardancy and char layer structure were investigated by thermogravimetric analysis (TGA), limiting oxygen index (LOI), vertical burning test (UL-94), cone calorimetric test, SEM and laser Raman spectroscopy, respectively. The TGA results show that the temperature of 5% mass loss of HKHPCP in oxygen is 300.2℃, and the residues at 1 000℃ of HKHPCP in oxygen is 34.8%. The results show that the LOI value of APP-HKHPCP-NOR116/PP is 43%, while the intumescent flame retardant loading is 30wt%. The APP-HKHPCP-NOR116/PP could reach a V-0 rating in the UL-94 tests. The cone calorimetry results indicate that heat release rate (HRR), total heat release (THR), smoke produce rate (SPR) and total smoke production (TSP) are reduced by 75.0%, 50.5%, 88.0% and 80.8%, respectively. In addition, the APP-HKHPCP-NOR116/PP can form a compact and more graphitic carbon char layer during combustion.