Solvent-Free Thermomechanical Exfoliation of Graphite into Graphene Nanoplatelet Flakes: Implications for Conductive Composites

We present an industrially relevant, single-step, chemical- and solvent-free, thermomechanical exfoliation (TME) process to produce graphene nanoplatelet (GNP) flakes, comprising mixtures of few- and multilayered graphene (FLG and MLG, respectively), starting from flake graphite. The specific energy required to produce GNP flakes with specific surface area (SSA) as high as 430 m2/g and aspect ratio as high as 250 is between 36 and 61 kJ/g. The evolution of the material is tracked throughout the process to elucidate the mechanism of graphite delamination. Bulk characterization methods, including thermogravimetric analysis, Raman spectroscopy, X-ray diffraction, and Brunauer–Emmett–Teller (BET) physisorption analysis, are used to monitor the changes in SSA, combustion temperature, relative composition, and to assess the extent of exfoliation. The process can be used to delaminate a range of graphitic materials, including fine (−325 mesh) and coarse (+50 mesh) graphite flakes, and expanded graphite to produce flake-shaped GNPs, suitable for various functional applications, including conductive polymer composites and coatings, supercapacitors, batteries, lubricants, and sensors.