Core–shell structure flame retardant Salen-PZN-Cu@Ni-Mof microspheres enhancing fire safety of epoxy resin through the synergistic effect

Phosphorus-containing organic–inorganic hybrid flame retardant with core–shell structure (Salen-PZN-Cu@Ni-Mof) was prepared. Thermogravimetric analysis (TGA) showed that when the additive amount was only 3wt%, the introduction of Salen-PZN-Cu@Ni-Mof significantly improved the thermal stability of epoxy resin (EP) composites. The results of the cone calorimeter test showed that adding 3wt% Salen-PZN-Cu@Ni-Mof made the peak of heat release rate (PHRR), total heat release (THR), smoke production rate (SPR) and total smoke production (TSP) of epoxy resin composites reduced by 30.4%, 10.8%, 29.5% and 6.8%, respectively. It was proved that Salen-PZN-Cu@Ni-Mof could significantly enhance the fire safety of epoxy resin composites, which was attributed to the synergetic combination of the flame retardant effect of the phosphazene structure itself, the catalyzed carbon formation of various metal ions and the porous mof materials with strong adsorption properties. Besides, it was found that the Ni-Mof could strengthen the compatibility between the flame retardant and the EP matrix effectively through the tensile test. The novel core–shell structure flame retardant Salen-PZN-Cu@Ni-Mof promised to be a functional filler that integrated features of flame retardancy and high ductility.