Graphene oxide (GO) was functionalized using three different diamines, namely ethylenediamine (EDA),
4,40-diaminodiphenyl sulfone (DDS) and p-phenylenediamine (PPD) to reinforce an epoxy adhesive, with
the aim of improving the bonding strength of carbon fiber/epoxy composite. The chemical structure of
the functionalized GO (FGO) nanosheets was characterized by elemental analysis, FT-IR and XRD. Hand
lay-up, as a simple method, was applied for 3-ply composite fabrication. In the sample preparation, the
fiber-to-resin ratio of 40:60 (w:w) and fiber orientations of 0, 90, and 0 were used. The GO and FGO
nanoparticles were first dispersed in the epoxy resin, and then the GO and FGO reinforced epoxy (GO- or
FGO-epoxy) were directly introduced into the carbon fiber layers to improve the mechanical properties.
The GO and FGO contents varied in the range of 0.1e0.5 wt%. Results showed that the mechanical
properties, in terms of tensile and flexural properties, were mainly dependent on the type of GO functionalization
followed by the percentage of modified GO. As a result, both the tensile and flexural
strengths are effectively enhanced by the FGOs addition. The tensile and flexural moduli are also
increased by the FGO filling in the epoxy resin due to the excellent elastic modulus of FGO. The optimal
FGO content for effectively improving the overall composite mechanical performance was found to be
0.3 wt%. Scanning electron microscopy (SEM) revealed that the failure mechanism of carbon fibers pulled
out from the epoxy matrix contributed to the enhancement of the mechanical performance of the epoxy.
These results show that diamine FGOs can strengthen the interfacial bonding between the carbon fibers
and the epoxy adhesive.