Effect of reduction time of functionalized graphene oxide on the morphology and properties of epoxy composite foams

Abstract

In this study, N-aminoethylpiperazine (AEP)-functionalized and reduced graphene oxide (RGO) with different structures and properties was prepared by simply tuning the reduction time and then its effect on the rheological, curing and foaming behavior of epoxy resin was carefully investigated using the environment-friendly carbamate as a chemical foaming agent. As the reduction time of RGO increased, the reduction degree of RGO first increased and then levelled off but the grafted AEP was little affected by the reduction time. The addition of RGO undergoing long reduction time improved the viscoelasticity of epoxy/reduced graphene oxide (EP/RGO) composites but weakened the interfacial compatibility of RGO and EP. With increasing the reduction time of RGO, the cell size of EP/RGO composite foams decreased and the cell density increased. However, as compared with pure EP foam, the composite foams containing RGO with lower reduction degree had a larger cell size and a lower density. These results were attributed to the complicated effect of RGO, which not only acted as the heterogeneous nucleating and foaming agent but also affected the viscoelasticity of composites. In addition, as the reduction time of RGO increased, the initial thermal decomposition temperature, storage modulus at room temperature, electrical conductivity, thermal conductivity, and compressive properties of EP/RGO composite foams increased while the glass transition temperature remained unchanged. These results were related not only to the intrinsic properties and dispersion of RGO, but also to the density and cell morphology of the composite foams.