Is expanded graphite acting as flame retardant in epoxy resin?

In this study, expanded graphite (EG) was investigated as flame retardant for epoxy resin based on DGEBA. Various amounts of EG (up to 50 wt%) were incorporated into the epoxy and the composites were studied using X-ray diffractometer, scanning electronic microscopy, cone calorimeter, pyrolysis-combustion flow calorimeter, thermogravimetric analysis, instrumented epiradiator and laser-flash method. Quite unexpectedly, EG leads to a significant increase in pHRR in cone calorimeter tests. Nevertheless, EG also allows delaying strongly the time-to-ignition. Such behavior was assigned mainly to the increase in thermal diffusivity which allows transferring heat faster from the surface to the bulk.