Epoxy-based flame retardant nanocomposite coatings: Comparison between functions of expandable graphene and halloysite nanotubes

This work presents a study on the flammability of epoxy coatings containing two types of nano-scale fillers as potential flame retardants: expandable graphite EG and halloysite nanotubes HNTs. Both nanocomposites are prepared by incorporation of the same amount of nanofiller into the epoxy resin for the sake of comparison. Fire retardant nanocomposite coatings are cured through a two-stage procedure in a mold and oven, respectively. The cone calorimeter test is performed to investigate the effect of using these flame retardants on the peak of Heat Release Rate pHRR, Total Heat Release THR, Total Smoke Production TSP and Time-To-Ignition TTI. It was found that the thermal behavior of blank epoxy and epoxy/EG was quite different and loading EG leaded to a significant fall in pHRR. In the presence of EG, the thin layer of residue was formed at first stages of ignition, grown rapidly and became denser acting as a strong barrier against fire. This barrier could retard the burning and doubled the total time of burning. By contrast, HNTs could not affect as an efficient flame retardant in the epoxy-based coating. Even by high loading level of 9 wt., HNT could not influence pHRR, TTI and THR parameters.