Eco-friendly ternary synergistic P/N/B intumescent flame-retardant uv-curable coating with enhanced thermal stability and smoke suppression

Intumescent flame-retardant (IFR) systems are attractive alternatives to conventional halogenated flame retardants due to their halogen-free composition, efficiently reduced heat release, and low toxicity generation. Herein, a nitrogen–boron (N B) dual-element flame retardant, melamine borate (MB), was synthesized and subsequently incorporated into a UV-curable resin based on bis(2-methacryloxyethyl) phosphate to construct a ternary synergistic N/P/B IFR coating system. The structure, thermal stability, and flame-retardant properties of the resulting coatings were systematically investigated by various techniques and combustion tests. Increasing MB content raised the glass transition temperature (T g ), indicating enhanced network compactness and stability. The coating containing only 4 wt% MB achieved a UL-94  V -0 rating and exhibited a 56.35 % reduction in total smoke production (TSP), along with significantly improved thermal stability in terms of decomposition temperature and char residue. The synergistic contributions of phosphorus, nitrogen, and boron promote catalytic charring, gas release, and glass-phase reinforcement, leading to the formation of a dense, stable char barrier. This eco-friendly ternary IFR system overcomes the high loading requirements and toxicity concerns of conventional flame retardants, providing a promising strategy for the efficient and sustainable flame-retardant modification of polymeric coatings.