Novel [BMIM]PF6 modified flake-ANP flame retardant: Synthesis and application in epoxy resin

Abstract

A novel ionic liquid-modified flake-NiNH4PO4·H2O (IL-ANP) hybrid material was prepared using a mechanochemical method with weak interactions. Characterization methods, including scanning electron microscope, Fourier transform infrared, X-ray diffraction and thermogravimetric analysis indicated the successful synthesis of IL-ANP. The prepared IL-ANP was incorporated into epoxy resin (EP) to improve the flame retardancy and mechanical properties. The limiting oxygen index (LOI) and cone calorimeter tests showed that IL-ANP enhanced the flame retardancy of EP composites. The 6 part per hundred resin (phr) IL-ANP/EP achieved excellent flame retardancy with the LOI value of 30.3% (that of pure EP was 24.4) and a significant decrease in the peak heat release rate, total heat release rate and the maximum release rates of CO production. This is attributed to the synergistic effect of the condensed phase and gas phase. During combustion, IL-ANP generated an incombustible gas (ammonia gas), nickel phosphate and nickel phosphide. On one hand, the incombustible gas diluted the concentrations of the combustible gas and oxygen in the gas phase. On the other hand, the phosphorus compounds catalyzed the carbonisation of EP to form a stable char layer and accumulated on the char layer surface as a physical barrier to delay the heat release. Additionally, the IL-ANP/EP composites exhibited excellent tensile strength, elongation at break, and impact strength, owing to their good compatibility and dispersion.