Hybrid fillers composed of attapulgite (ATP) nanorods attached on graphene oxide (GO) nanoplatelets were produced at various combinations and employed in epoxy composites. Both thermal and mechanical properties of the matrix material were increased through the introduction of ATP–GO hybrid fillers. Although the dispersion of ATP–GO became worse because of decreased functionality, a better interfacial interaction can be obtained with proper ATP content by increasing the roughness of GO surfaces. Therefore remarkable enhancement on tensile properties and fracture toughness were achieved by addition of A1G02 (1 wt% ATP and 0.2 wt% GO), which is the optimum composition in the hybrids for composite mechanical properties. The yielded improvements were 36%, 16%, 27% and 19% in Young’s modulus, tensile strength, critical stress intensity factor (KIC) and critical energy release rate (GIC), respectively. It is obvious that the behavior of ATP and the composition of ATP–GO hybrids played an important role in composite performance.

Amino- and epoxy-functionalized graphene oxide (GO) were synthesized separately through a wash-and-rebuild process utilizing two differently terminated silane coupling agents. The modified GO sheets were then incorporated into an epoxy resin to prepare nanocomposites. The addition of 0.2 wt% amino-functionalized GO (APTS-GO) yielded a 32% increase in Young's modulus (3.3 GPa) and 16% increase in tensile strength (81.2 MPa). Less reinforcement was observed with the epoxy-functionalized GO (GPTS-GO) but there was a more significant increase in ductility for GPTS-GO/epoxy, with the fracture toughness (critical intensity factor, KIC) and fracture energy (critical strain energy release rate, GIC) nearly doubling at 0.2 wt% loading (1.46 MPam1/2 and 0.62 kJ/m2 for KIC and GIC, respectively). Raman spectroscopy measurements revealed that the GPTS-GO was dispersed more uniformly than the APTS-GO in the epoxy matrix, and better interfacial stress transfer was found for the APTS-GO. Thus the wash-and-rebuild process affords a novel strategy for controlling the functionality of graphene in the quest to develop high-performance graphene-based nanocomposites.