Multilevel engineering of Ti3C2TX/Ni-Fe-based hydrotalcite nanolaminates via Co-doped polydopamine bridging for ultra-efficient flame retardancy and smoke suppression in epoxy coatings

In this study, using Ti 3 C 2 T X (MXene) as a substrate, Co-doped polydopamine (PDA@Co), phytic acid (PA), and flake-like Ni-Fe/LDH were loaded onto the MXene surface via hierarchical assembly to prepare a novel multifunctional flame retardant (MPPA@Ni-Fe/LDH). Among these, MXene and LDH formed a multi-level physical barrier that suppressed flame spread and delayed the escape of oxygen and combustible gases. The introduction of PDA and PA improved the interfacial dispersion of the material, promoted the dehydration and carbonization of the matrix, and interrupted the combustion chain reaction, thereby synergistically constructing a dense C-N-P flame-retardant network. Furthermore, the presence of multiple transition metals further enhanced catalytic carbonization at high temperatures, and the generated metal oxides also improved the thermal insulation and strength of the char layer. The results of a series of fire tests demonstrated that the backside temperature of steel plates coated with MPPA@Ni-Fe/LDH/EP was as low as 168.9 °C, with expansion heights and expansion rates of 26.4 mm and 20.31, respectively, and the smoke density rating reached a minimum value (35.4%). This indicates that the composite coating exhibited excellent thermal insulation, expansion, and smoke suppression properties. In TGA analysis, the high char yield of the MPPA@Ni-Fe/LDH/EP sample confirmed its high thermal stability and the effective catalytic carbonization ability of the multi-metal system. Furthermore, microscopic analysis of the carbon residues revealed that the MPPA@Ni-Fe/LDH-filled coating exhibited the most intact and dense carbon layer, providing favorable conditions for its excellent thermal insulation performance. This novel flame retardant, incorporating a multi-layer barrier effect, high phosphorus and nitrogen content, and strong catalytic carbonization capability, offers a new approach for developing multifunctional intumescent flame-retardant coatings.