Compatible cyclophosphazene-functionalized graphene hybrids to improve flame retardancy for epoxy nanocomposites

To construct effective interfacial interactions between graphene-based flame retardants and epoxy resin (EP) matrixes, reactive cyclophosphazene was chemically synthesized with amino groups and grafted on graphene oxide (GO) to prepare a flame-retardant fGO nanosheets for EP nanocomposites. The obtained fGO presented good compatibility and endowed the composites with improved thermal stability and dynamic mechanical properties. With a low content of 1.0 wt.% fGO added, the EP nanocomposites exhibited distinctly lowered the peak of heat release rate, total heat release, and total smoke production by 49.0%, 21.1%, and 51.9%. Compact char residue layers and suppressed volatile products indicated the formation of protective char structures derived from fGO nanofillers. The flame-retardant mechanisms were investigated and ascribed to the effects in condensed and gas phases from phosphazene modified graphene components.