Building a “Multi-Level Synergistic” Flame Retardant Barrier for Epoxy Resins: An Innovative Strategy Combining Inorganic Catalyzed Carbonization with Hydrogen-Bonded Organic Frameworks

Epoxy resin (EP) is widely used due to its excellent processability and stability, but its inherent flammability limits its application in flame-retardant scenarios. This study aims to develop an EP composite material that integrates highly effective flame retardancy, smoke suppression, thermal conductivity (TC), and mechanical properties. An innovative “multi-level synergistic” flame retardant strategy was proposed. Hexagonal boron nitride (h-BN) nanosheets were exfoliated via green mechanical ball milling. Subsequently, a molybdenum phosphide (MoP) catalytic layer and a P–N-containing hydrogen-bonded organic framework (PA-HOF) were sequentially constructed in situ on its surface. This successfully yielded a core-shell structured h-BN@MoP@PA-HOF composite flame retardant. This flame retardant exhibits outstanding synergistic effects in the EP matrix. Compared to neat EP, composites containing only 4 phr of this flame retardant exhibited a significant 54.27% reduction in peak heat release rate (PHRR), along with decreases of 48.98% and 31.59% in smoke production rate (SPR) and total smoke release (TSP), respectively. The production rates of CO and CO2 were also greatly reduced. Concurrently, the mechanical properties of the composite material remained largely unaffected, thereby resolving the trade-off between flame retardancy and mechanical performance inherent in traditional flame retardant systems. Furthermore, with 12 phr of the flame retardant added, the composite achieved UL-94 V-1 rating, while its TC improved by 36.68%.