Enhanced thermal and flame retardant properties of flame-retardant-wrapped graphene/epoxy resin nanocomposites
Functionalized reduced graphene oxide (FRGO) wrapped with a phosphorus and nitrogen-containing flame retardant (FR) was successfully prepared via a simple one-pot method and well characterized. Subsequently, FRGO was covalently incorporated into epoxy resin (EP) to prepare flame retardant nanocomposites. The FRGO was well dispersed in the matrix and formed strong interfacial adhesion. Thermogravimetric analysis results revealed that the presence of RGO, FR or FRGO in an EP matrix led to a slight thermal destabilization effect under air and nitrogen, which increased the char yield at 700 °C and reduced the maximum mass loss rate. Furthermore, the glass transition temperature of the FRGO/EP nanocomposite with an FRGO loading of 4 wt% (FRGO/EP4) was remarkably increased by 29.6 °C, probably due to the improved crosslinking density and confinement effect of graphene sheets on the mobility of polymer networks. The evaluation of combustion behavior demonstrated that a 43.0% reduction in the peak heat release rate (PHRR) for the FRGO/EP nanocomposite containing 2 wt% FRGO and a 30.2% reduction in the total heat release (THR) for FRGO/EP4 over pure EP were achieved by the addition of FRGO. These notable reductions in fire hazards were mainly due to the synergistic effect of FRGO and the flame retardant: the wrapped flame retardant accelerated the degradation of the EP matrix, promoting the formation of additional char residues; the flame retardant improved the thermal oxidative resistance of the graphene; a high-thermal-stability char layer, consisting of graphene sheets, retarded the permeation of heat and the escape of volatile degradation products.