Self-assembly of Ni–Fe layered double hydroxide/graphene hybrids for reducing fire hazard in epoxy composites

Ni–Fe layered double hydroxide/graphene hybrids were synthesized by a one-pot in situ solvothermal route. X-ray diffraction and X-ray photoelectron spectroscopy analyses showed that the formation of Ni–Fe layered double hydroxide (Ni–Fe LDH) and the reduction of graphene oxide occurred simultaneously during the one-pot solvothermal process. TGA results showed that the incorporation of Ni–Fe LDH significantly improved the thermal stability of the graphene. Subsequently, Ni–Fe LDH/graphene hybrids were introduced into epoxy resins for reducing their fire hazard. With the incorporation of 2.0 wt% of Ni–Fe LDH/graphene, the onset thermal degradation temperature of the epoxy composite was significantly increased by 25 °C compared to that of pure epoxy. Also, the addition of Ni–Fe LDH/graphene hybrids imparted excellent flame retardant properties to the epoxy matrix, evidenced by the dramatically reduced peak heat release rate and total heat release values obtained from a micro combustion calorimeter and cone calorimeter. This dramatically reduced fire hazard was mainly attributed to the synergistic effects of Ni–Fe LDH/graphene hybrids: the adsorption and barrier effect of graphene slowed down the thermal degradation of the polymer matrix, inhibited the heat and flammable gas release and promoted the formation of graphitized carbons, while Ni–Fe LDH improved the thermal oxidative resistance of the char layer.