Mechanical properties and adhesive behavior of epoxy-graphene nanocomposites

The influence of the type and content of graphene nanoplatelets (GNP) on the thermo-mechanical and adhesive properties of epoxy-graphene nanocomposites was investigated. Two types of graphene have been used: un-functionalized and functionalized graphene. The functionalized graphene (GNPNH2) contains amine groups that react with the epoxy prepolymer. Two types of un-functionalized graphene with different nanoplatelet dimensions were used. A universal testing machine was used to determine the Young's modulus, deformation at break, mechanical strength and toughness at 22 ºC. Dynamic Mechanical Thermal Analysis experiments were performed to compare the glass transition temperature and the storage modulus in the glassy and rubber states. Epoxy-graphene nanocomposites were used as adhesives on aluminum substrates in single lap geometry, and the shear strengths were determined. All nanocomposites presented higher modulus than the neat epoxy thermoset. The increase in the storage modulus was higher in the in the rubbery state than in the glassy state. Nanocomposites showed lower tensile strength and were more fragile than the neat epoxy thermoset, which was attributed to the aggregation of graphene nanoplatelets. Epoxy/GNPNH2 nanocomposites presented a lower decrease of tensile strength and less fragile behavior. Epoxy/graphene adhesives presented lower lap shear strength than neat epoxy adhesive. Increasing GNP content caused the lap shear strength to decrease.