Exfoliated graphite nanoplatelets

Introduction

Exfoliated Graphite Nano-Platelets (xGnP) are new types of nanoparticles made from graphite. These nanoparticles consist of small stacks of graphene that are 1 to 15 nanometers thick, with diameters ranging from sub-micron to 100 microns. Since xGnP is composed of the same material as carbon nanotubes, it shares many of their electrochemical characteristics, although not their tensile strength. The platelet shape, however, offers xGnP edges that are easier to modify chemically for enhanced dispersion in polymers.

Composite materials made with polymers, like plastics, nylon, or rubber, can be made electrically or thermally conductive with the addition of small amounts of xGnP. These nanoparticles can change the fundamental properties of plastics, enabling them to perform more like metals with metallic properties. These new nanoparticles also improve barrier properties, modulus, and surface toughness when used in composites.

XGnP

xGnP is a platelet consisting of several sheets of graphene with an overall thickness of approximately 5 nanometers (ranging from 1 nm to 15nm) and particle diameters that can range from sub-micron to 100+ microns.

   Density: ~2.0g/cm 3
   Chemical Composition: Graphene
   Electrical Resistivity: ~ 50 x 10-6 Ω cm
   Thermal Conductivity: 3000 W/m K
   Tensile Modulus: ~1.0 TPa
   Tensile Strength: ~10-20 GPa

Electrical Conductivity

In various laboratories around the world, graphene has been found to be extremely conductive of electricity. xGnP has been found to have a percolation threshold of 1.9 wt% or better in a control thermoplastic matrix. At densities of 2 % to 5 wt%, conductivity reaches sufficient levels to provide ESD, RFI or EMI shielding. When combined with carbon fibers, cross-fiber conductivities can be achieved to promote large-surface ESD or RFI/EMI shielding. xGnP can also be combined with glass fibers or other matrix materials to provide sufficient conductivity for electrostatic painting or other applications requiring electrical conductivity..

Thermal Conductivity

xGnP has been found to significantly outperform most other forms of carbon when used at densities of 20 wt% in control resins. At these densities, of course, xGnP also confers significant electrical conductivity as well as improved mechanical properties to most thermoplastic, thermoset, or elastomeric systems. At lesser densities, xGnP adds thermal stability to a variety of matrix materials.

Mechanical Properties

As opposed to materials like carbon black, xGnP improves mechanical properties of most composites, particularly stiffness and tensile strength. Elastomeric compounds have been shown to experience increased life and reduced surface wear when reinforced with xGnP.

Barrier Properties

Because of the platelet shape, xGnP significantly improves the impermeability of composites when used at densities of ~3 wt% or greater. xGnP particles can be aligned using an e-field, although no special alignment has been found necessary when used in most extrusion systems. Because xGnP also imparts electrical conductivity for ESD at these densities, the resulting composites offer attractive cost savings for applications like fuel lines or fuel tank linings.

References

Transmaterial

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