Grafting of epoxy chains onto graphene oxide for epoxy composites with improved mechanical and thermal properties

Epoxy composites filled with both graphene oxide (GO) and diglycidyl ether of bisphenol-A functionalized GO (DGEBA-f-GO) sheets were prepared at different filler loading levels. The correlations between surface modification, morphology, dispersion/exfoliation and interfacial interaction of sheets and the corresponding mechanical and thermal properties of the composites were systematically investigated. The surface functionalization of DGEBA layer was found to effectively improve the compatibility and dispersion of GO sheets in epoxy matrix. The tensile test indicated that the DGEBA-f-GO/epoxy composites showed higher tensile modulus and strength than either the neat epoxy or the GO/epoxy composites. For epoxy composite with 0.25 wt% DGEBA-f-GO, the tensile modulus and strength increased from 3.15 ± 0.11 to 3.56 ± 0.08 GPa (∼13%) and 52.98 ± 5.82 to 92.94 ± 5.03 MPa (∼75%), respectively, compared to the neat epoxy resin. Furthermore, enhanced quasi-static fracture toughness (KIC) was measured in case of the surface functionalization. The GO and DGEBA-f-GO at 0.25 wt% loading produced ∼26% and ∼41% improvements in KIC values of epoxy composites, respectively. Fracture surface analysis revealed improved interfacial interaction between DGEBA-f-GO and matrix. Moreover, increased glass transition temperature and thermal stability of the DGEBA-f-GO/epoxy composites were also observed in the dynamic mechanical properties and thermo-gravimetric analysis compared to those of the GO/epoxy composites.