Synergistic modification of ZIF and silica on carbon spheres to enhance the flame retardancy of composites coatings

Herein, carbon spheres (CS) were obtained by a simple hydrothermal reaction using glucose as the raw material, which can be used as a green, cost-effective inorganic flame retardant. Then, the zeolitic imidazolate framework-8 (ZIF) nanoparticles were uniformly anchored on the surface of the CS, which could promote the formation of carbon residues, while the release of inert gas could reduce the substrate surface temperature, thereby delaying the combustion reaction. In addition, the SiO2 film was coated on the surface of ZIF-loaded CS (CS/ZIF) to fill the micropores left by thermal decomposition of ZIF nanoparticles. More importantly, the residual SiO2 shell after combustion can effectively improve the barrier effect of char layer on flame and heat. The effect of the obtained CS/ZIF@SiO2 hybrids on the fire performance of epoxy resins was characterized by fire performance tests. The experimental results showed that the backside temperature of the CS/ZIF@SiO2 based composite coating was stabilized at the lowest value (173.6 ℃) due to the combined effect of ZIF nanoparticles and silica film. In addition, the CS/ZIF@SiO2/EP showed the maximum expansion height and expansion rate after burning in a muffle furnace for 60 min. Meanwhile, the composite coating exhibited the maximum residual carbon (29.1%) and thermal decomposition temperature (Tmax, 378.1 ℃). The results of smoke density test proved that the composite coating had higher smoke suppression effect compared with other samples. [Display omitted] •ZIF nanoparticles were uniformly loaded on the CS surface by a simple hydrothermal method.•SiO2 film was further loaded on CS/ZIF surface to fill the defects left by ZIF decomposition.•Residual SiO2 and ZnO enhanced the strength and fire resistance of the char layer.•The synergistic effect of ZIF and SiO2 further enhanced the heat shielding effect of char.