Covalent functionalization of graphene oxide with flame retardant and its effect on thermal stability and flame retardancy of epoxy composites

In order to improve the dispersion and fire retardant property in epoxy resin (EP), graphene oxide (GO) was functionalized via surface modification by a flame retardant which was synthesized by the reaction of methyl dichlorophosphate and 10-(2,5-dihydroxyl-phenyl)-9,10-dihydro-9-oxa-10-phosphaphenan-threne-10-oxide (DOPO-BQ). The property of functionalized GO (FGO) was characterized by fourier transform infrared spectroscopy, H- and P- nuclear magnetic resonance, X-Ray photoelectron spectroscopy and thermogravimetric analysis (TGA). Series different ratios of GO- and FGO- epoxy nanocomposites were obtained by in situ polymerization. The incorporation of FGO enhanced the thermal stability and flame retardancy of epoxy nanocomposites effectively. The thermal properties of the nanocomposites were investigated by TGA test in nitrogen atmosphere, indicating that FGO can improve the char residues. The flame retardancy of the nanocomposites was characterized by cone calorimeter test. The results showed that the incorporation of 2 wt.% FGO into EP decreased the value of peak heat release rate, total heat release, average effective heat of combustion, peak values of the CO release rate and CO2 release rate by 25%, 28%, 29.5%, 27% and 29%, respectively. This work confirms that the FGO is an effective solution for improving the thermal stability and flame retardancy of epoxy resins.