Effects of graphene network formation on microstructure and mechanical properties of flax/epoxy nanocomposites

Abstract Various contents of graphene nanoplatelets (GNPs), ranging from 0 to 0.7 wt%, with an efficient solvent method were used to reinforce flax/epoxy composites and thereby correlate GNPs network formation with the degree of reinforcement in resultant nanocomposites. The microstructural features characterised by wide X-ray diffraction (WAX), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) determined a correlation between GNPs reinforcing efficiency, nanolayers network formation and the number of layers. TEM analysis clarified that with a change in GNPs content, the distribution of nanolayers transformed from a zonal distribution to efficiently bridged networks contributing to maximum improvement in tensile and flexural properties at 0.5 wt% of GNPs. This was supported by morphological observations developed by SEM confirming various reinforcing mechanisms thanks to GNPs networks leading to enhanced interfacial adhesion between fibre and matrix. Likewise, with formation of networks, crack length at the interface of fibre and matrix and crack density in nanocomposites, determined from optical microscopy images of tensile-tested samples, received a significant decrease. TEM observations also proved that plane-to-plane and edge-to-edge contact areas of GNPs had paramount influences on reinforcement efficiency in nanocomposites. Exceeding the optimum content (0.5 wt%), the load transfer capability induced by GNPs network formation was adversely affected by plane-to-plane contacts of GNPs eventually leading to substantial reductions in mechanical properties. In drop weight impact analysis, GNPs networks also enhanced crack initiation energy and consequently reduced crack propagation energy and damage area in nanocomposites.