Local mechanical properties of graphene/polyethylene-based nanocomposites by depth-sensing indentation

• Different routes to functionalize graphene in PE nanocomposites have been tested.
• Nanoindentation offers a comprehensive understanding of macroscopic performance.
• Mapping of the mechanical properties can also reveal specific details at the surface.
• A thiol-ene click route seems the best strategy in terms of achieved properties.

Local mechanical properties of modified-graphene high-density polyethylene nanocomposites are investigated using depth-sensing indentation. Three different chemical routes are employed to boost filler dispersion by functionalizing graphene with polyethylene brushes and incorporating a small amount of free short-chain polyethylene. At large penetration depths the results reveal distinct mechanical properties for the different chemical approaches. Hardness, modulus and creep resistance are discussed in terms of filler dispersion, polymer nanostructure and plasticization of the amorphous regions by the short-chain polyethylene. By reducing the indentation size, maps of the surface mechanical properties are generated, and graphene agglomerates that appear in some nanocomposites can be clearly identified. However, these agglomerates present significantly inferior mechanical properties than those usually reported for graphene, and results at the nanoscale suggest that modification of graphene together with the viscous “liquid-like” character of the polymer host represent strong impediments for effective reinforcement. Notwithstanding, one of the nanocomposites (from the thiol-ene click reaction) overcomes these issues, achieving a macroscopic mechanical performance similar to that of the neat polymer, combined with outstanding electrical conductivity.

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