The taxonomy of graphite nanoplatelets and the influence of nanocomposite processing

The reinforcement efficiency of graphene in a nanocomposite relies on the size, morphology, defects and agglomeration of flakes. However, the characterisation is usually undertaken only for the raw materials and any changes that take place during processing are not taken into consideration. In this work, epoxy nanocomposites reinforced by graphite nanoplatelet (GNP) were prepared and nano-scale X-ray computed tomography was used to visualize the geometry, morphology and defects of the flakes, as well as the three dimensional agglomerates that are normally difficult to characterise by other techniques. In combination with micromechanical analysis, the taxonomy of the nanoplatelets is shown to be of great importance in controlling the mechanical properties of nanocomposites, and this has been shown to explain the deviations of the predictions of micromechanical models from the measured values. Particularly, it is shown that taking single average values of flake size may not be appropriate and the entire distribution of flake size need to be taken into consideration. Furthermore, it is shown that the Young's modulus of a nanocomposite is controlled principally by a small number of large flakes and that volume average distributions of flake size are more appropriate to use rather than number average ones.