POSS-functionalized graphene oxide hybrids with improved dispersive and smoke-suppressive properties for epoxy flame-retardant application

Functionalized graphene oxide sheets (FGO) with improved dispersive and smoke-suppressive properties were synthesized by covalently grafting octa (propyl glycidyl ether) polyhedral oligomeric silsesquioxane on graphene oxide sheets (GO) with γ-aminopropyl triethoxysilane as a chemical bridge. The good dispersion of FGO sheets in the epoxy resin (EP) matrix endowed EP composites with stable thermal resistance, enhanced tensile and smoke-suppressive properties. Cone calorimeter tests indicated that the addition of 0.7 wt% FGO sheets to EP composites reduced the peak of heat release rate, total heat release, and total smoke release by 49.7%, 34.3%, and 41.5%, respectively. Two important effects that originated from FGO promoted this improvement; that is, well-dispersed FGO sheets exhibited a tortuous effect by lengthening the heat path and inhibiting heat diffusion in the EP matrix, and the increase in char residue and the reduction in gas volatiles confirmed the barrier effect of FGO sheets by forming protective char structures on the surface of the matrix, which restrained smoke release. This method provided a feasible concept for effectively enhancing the flame retardancy of EP composites by combining the characteristics of graphene and polyhedral oligosilsesquioxane through the construction of effective interfacial interactions.