Activated carbon spheres (ACS)@SnO2@NiO with a 3D nanospherical structure and its synergistic effect with AHP on improving the flame retardancy of epoxy resin

A novel activated carbon spheres (ACS)@SnO2@NiO hierarchical hybrid architecture was first synthesized and applied for enhancing the flame retardancy of epoxy (EP) resin via a cooperative effect. Herein, using activated carbon microspheres as the template, SnO2 and NiO nanospheres were successively anchored to it by a sedimentation-calcination strategy. The well-designed ACS@SnO2@NiO significantly enhanced the flame retardancy for consistency of EP composites, as demonstrated by thermogravimetric and cone calorimeter experiments. For instance, the incorporation of 2 wt% ACS@SnO2@NiO decreased by 15.5% maximum in the total smoke production, accompanying the higher graphitized char layer. In addition, the synergetic mechanism of flame retardancy between ACS@SnO2@NiO and aluminum hypophosphite (AHP) was investigated. The obtained sample satisfied the UL-94 V-0 rating with a 5.0 wt% addition of AHP and ACS@SnO2@NiO (the ratio of the mass fraction of AHP to ACS@SnO2@NiO is 4.5:0.5). Notably, the incorporation of AHP and ACS@SnO2@NiO resulted in a significant decrease in the fire hazard properties of EP resin; for instance, 4.5AHP-0.5ACS@SnO2@NiO/EP resulted in a maximum decrease of 32.4% in the total smoke production as compared with that of pure EP resin. It should be noted that the improved flame-retardant performance for the EP composites is primarily attributed to the synergistic effect of ACS@SnO2@NiO and AHP in promoting the formation of residual char in the condensed phase.