Multi-core-shell MHS@PZS@Ni, Al-LDH: Synergistic flame retardancy and weather resistance enhancement for high-performance epoxy composites

With the widespread use of epoxy resin (EP) in construction, higher demands are placed on its flame retardancy and weather resistance. This study develops a synergistic flame retardant strategy based on a multi-core-shell structure, consisting of a spherical mesoporous hollow silica (MHS) core, a cyclic polyphosphazene (PZS) inner shell, and a Ni, Al layered double hydroxide (LDH) outer shell. At 2 wt% addition, the EP composite achieves a limiting oxygen index (LOI) of 33.7% and passed the UL-94 V-0 rating. Meanwhile, the peak heat release rate (HRR) and total heat release (THR) decreased by 37.61% and 42.85%. Smoke release (TSR) and peak CO production rate (COP) decreased by 45.10% and 40.70% respectively, demonstrating remarkable flame retardancy and smoke suppression. MHS retains heat and inhibits diffusion, the PZS layer captures free radicals and enhances the char formation. And the Ni, Al-LDH shell releases non-flammable gases and catalyzes graphitization, realizing synergistic flame retardancy. Additionally, it improves interfacial compatibility and stress dispersion, enhancing mechanical and weather performance. Chemical resistance tests showed a 13.7% reduction in tensile strength after 30 days of HCl immersion, while ultraviolet (UV) aging caused minimal degradation. This research provides a promising approach for high-performance, multifunctional epoxy composites.