Quantifying effects of graphene nanoplatelets on slowing down combustion of epoxy composites

This paper investigates the effects of graphene nanoplatelets (GNP) on combustion behaviour of epoxy resin (ER). In particular it presents, for the first time, a numerical modelling methodology that quantifies the effects of GNP in reducing the peak rate of heat release of epoxy resin with different amounts and types of GNP. Five different GNP/ER composites were prepared via the solution mixing method. Geometric characteristics and dispersion state of GNP in epoxy resin were characterized by three-dimensional (3D) X-ray CT scan. Thermogravimetric analysis (TGA) tests were carried out on pure epoxy and GNP/ER composites in N2. Bench-scale cone calorimeter tests were used to obtain combustion properties of the prepared nanocomposites. These test results provide input data for validating the modelling methodology. The cone calorimeter tests found significantly lower peak heat release rate (PHRR) for GNP/ER composites than pure epoxy. For example, at 3 wt% GNP loading, the PHRR was reduced by 47%. This drastic reduction in PHRR due to GNP is attributed to two principal contributions of GNP: reduced permeability to slow down movement of volatiles to the surface to cause combustion, and reduced radiant conductivity of GNP/ER at high temperatures owing to GNP being able to promote the formation of a continuous and compact char layer, which decreases temperatures and hence slows down chemical reactions. This paper provides a new method, through numerical pyrolysis modelling, to quantify these two contributions and their effects in reducing PHRR of GNP/ER. A comparison between numerical simulation results and test results confirms assumptions of this quantitative method. This simulation model has the potential to improve material design process of graphene based composites and predict the fire behaviour of such composites in realistic fire conditions.