Zeolitic imidazolate framework-8 was coated with silica and investigated as a flame retardant to improve the flame retardancy and smoke suppression of epoxy resin

A material (ZIF-8@SiO2) with a nuclear shell structure was synthesized to improve the flame retardancy and smoke suppression of epoxy resin (EP) through a synergetic catalytic effect. Zeolitic imidazolate framework-8 (ZIF-8) was synthesized and its surface was coated with SiO2 by hydrolyzing tetraethyl orthosilicate. Core-shell structured ZIF-8@SiO2 was obtained. Then ZIF-8@SiO2 was added to EP to explore its effect of flame retardancy and smoke suppression on the EP composite. The results of a cone calorimeter test showed that the peak heat release rate, total heat release, smoke production rate and total smoke production of the material were decreased by 75.9%, 38.9%, 51.1% and 39.8%, respectively, after 2 wt% ZIF-8@SiO2 was added to EP. Besides, through the analysis of char residue, the mechanism of ZIF-8@SiO2/EP's flame retardancy and smoke suppression was determined to be due to the physical barrier effect of SiO2 and the co-effect of SiO2 and ZnO decomposition by ZIF-8.