Preparation and curing kinetics of intrinsic flame retardant epoxy resin system based on polyoxometalates

In this work, phosphomolybdic acid (PMoA) was used as a kind of eco-friendly flame retardant precursor. Then, a green intrinsic flame retardant was successfully prepared by chemically modifying PMoA with imidazolium (IM), which can be well dispersed in epoxy matrix without using any solvent. DSC results demonstrated that IM-PMoA can chemically react with epoxy monomer under heating with a moderate heat release, which greatly reduced the migration resistance of PMoA in water (1.2871% vs. 0.0439%). Meanwhile, curing kinetics indicates EP/IM-PMoA composites have higher activation energy (98.06 kJ mol −1 ) than pure EP (75.48 kJ mol −1 ). Besides, epoxy composite can pass V-0 rating with 8 mass% IM-PMoA addition. Compared to pure epoxy, the obvious decrease in the values of peak heat release rate and total smoke release were 37.78% and 31.03%, respectively. In addition, Raman spectrum indicated that the residual carbon is highly graphitized, which may be attributed to the superb catalytic carbonation ability of PMoA. The high-quality char layer can be used as physical barrier for inhibiting the heat diffusion and degradant transfer. As a result, excellent flame retardant and smoke suppression properties were achieved. This work provides a new idea to prepare a green intrinsic flame retardant for epoxy based on imidazolium.