Exfoliation and dispersion of graphene nanoplatelets for epoxy nanocomposites

This article presents a systematic review over recent preparation techniques and their mechanisms for epoxy/graphene nanocomposites. Special honeycomb lattice nanostructure of graphene provides epoxy resins with mechanical stiffening, toughening, thermal and electrical conductivities, and anti-corrosion performance. To form epoxy/graphene nanocomposites with optimized structure and mechanical and functional performance, many efforts have been undertaken to exfoliate and disperse graphene nanoplatelets (GNPs) in epoxy, by utilizing single or combined mechanical, thermal, electromagnetic, and chemical strategies. Below is a list of design criteria summarized from recent studies: (i) the lowest thickness (below 10 nm) with appropriate lateral dimension is always preferred for GNPs prior to compounding with epoxy, (ii) physical techniques such as heat and sonic waves, mechanical methods like shearing, and chemical surface modification should be combined to achieve a high degree of exfoliation and dispersion of GNPs in epoxy, (iii) the destruction of graphene lattice must be carefully controlled during preparation because otherwise it deteriorates the intrinsic properties of graphene and hence the resulting nanocomposites, and (iv) the fraction of GNPs in epoxy should also be carefully determined due to a trade-off between the mechanical performance and the functional properties of the nanocomposites. Noteworthy are those recent less toxic or surfactant-free yet effective methods for the modification of graphene surface and the preparation of epoxy nanocomposites. All in all, cost-effective and environmentally friendly approaches are always preferred, forming a major research theme in the years to come.