Engineered CuAl-LDH/black phosphorus nanohybrids for flame retardancy, smoke suppression, and mechanical reinforcement of polyurea

Polyurea (PUA) is widely used in protective coatings and structural applications owing to its excellent mechanical robustness and environmental resistance. However, intrinsic flammability and severe smoke release significantly limit its use in fire-critical environments. Herein, we report a highly synergistic combination of CuAl-layered double hydroxides (LDH) coated onto the surface of black phosphorus (BP) via high-energy ball milling, with chloro-4,4′-diaminodiphenylmethane (ML) serving as a molecular “bridge” to enhance dispersion and interfacial adhesion within PUA matrix. Beyond the barrier effect of the layered structure, BP contributes to gas-phase radical scavenging while CuAl-LDH acts as an effective catalytic charring agent in the condensed phase. Owing to this multi-synergy effect, PUA/BP@LDH@ML nanocomposite exhibits suppressed melt dripping and reduced combustion intensity achieving a limiting oxygen index (LOI) of 26.5% with a potential to pass the UL-94 rating. Furthermore, the peak heat release rate (PHRR) and total smoke production (TSP) decreased by 39.2% and 52.9%, respectively. Notably, the incorporation of BP@LDH@ML simultaneously enhances mechanical performance of PUA, increasing tensile strength and elongation at break by 64.6% and 39.8%, respectively. This work demonstrates a rational interfacial engineering strategy for developing PUA composites with high fire-safety and mechanical performance for diverse advanced applications.