Polymer Nanocomposites from Exfoliated Graphite (Graphene) Nanoplatelets: Mechanical, Thermal and Electrical Properties
L.T. Drzal, H. Fukushima, I. Do, M.R. Knox
XG Sciences, Inc., US
Keywords: graphene, nanoplatelets, nanocomposite, conductivity, barrier
Abstract:Nanocomposites composed of polymers reinforced with exfoliated clays and carbon nanotubes are being considered for applications such as interior and exterior accessories for automobiles, structural components for portable electronic devices, and films for food packaging. Another type of carbon nanomaterial, exfoliated graphite (graphene) nanoplatelets (“xGnP®”), exhibits thermal and electrical properties similar to carbon nanotubes with a morphology similar to the exfoliated clays. When used as reinforcement in nanocomposites, xGnP is capable of producing properties that combine excellent thermal and electrical conductivity with superior mechanical and barrier properties. Graphite is the stiffest material found in nature (Young’s Modulus = 1060 MPa), having a modulus several times that of clay, and also exhibits the highest electrical conductivity of the non-metals. With the appropriate surface treatment and dispersion in a thermoset or thermoplastic polymer matrix, the resulting composite displays a combination of mechanical, electrical and thermal properties that can be tuned for a variety of structural or non-structural applications. Furthermore, the economics of producing nanographite platelets support a sales price in the range of $10-$20 per pound at commercial volumes. This paper presents examples of the properties attainable in nanocomposites made from both thermoset and thermoplastic matrices combined with xGnP. For example, nylon 66 matrix composites have been successfully fabricated using xGnP of various diameters and at various concentrations up to 20 vol%. These composites showed a flexural modulus of 12GPa, which was significantly greater than composites reinforced with carbon fibers (CF), vapor grown carbon fibers (vgCF) and particulate carbon black (CB) at the same concentrations. The electrical and thermal properties of these composites showed significant differences based on reinforcement size, concentration, and morphology. AC Impedance measurements detected a reduction of ~10 orders of magnitude in the composites made from xGnP at a concentration of 2 vol%, compared to similar composites made with CB. Thermal conductivity measurements show xGnP platelets can attain higher thermal conductivities than any of the other nanoreinforcements measured in this study. Results to be presented indicate that nanoplatelet surface chemistry, dispersion, morphology and concentration are all important factors in achieving a balance between mechanical, thermal and electrical properties of nanocomposites.