Graphite Nanoplatelets and Their Application to Polymer Composites

O. Choi¹ and H.T. Hahn^1,2

¹Materials Science and Engineering Department

²Mechanical and Aerospace Engineering Department

University of California, Los Angeles

CA 90095

Nanocomposites hold promise for bringing forth revolutionary advances in the creation of lightweight, energy-efficient, multifunctional systems. Since nanocomposite development is still in its infancy, optimizing their design and manufacture requires thorough, basic scientific investigations. The present paper discusses the development of nanoplatelet reinforced composites (NRCs), which are comprised of graphite nanoplatelets (GNPs) dispersed within a polymer matrix.

Unlike nanofibers, nanoplatelets with high aspect ratio provide reinforcement in two directions and hence offer an excellent opportunity to improve mechanical properties of polymers, as has already been shown by organoclay nanoplatelets.  In addition, GNPs yields a low percolation threshold in giving desirable functionalities such as high thermal and electrical conduction.  However, the expected benefits will not be realized unless we can achieve a high aspect ratio through exfoliation and good bonding through proper surface treatment. 

In the present work, commercially available GNPs were intercalated first with potassium to make KC₄₈ compounds and then further with benzene.   These intercalation compounds (GICs) were treated in three different ways to prepare their surfaces for improved bonding.  They included washing in alcohol to improve wetting, cryogenic treatment to roughen the surface, and nitric acid immersion to oxidize the surface.   The GICs were mixed in Epon 862 resin using a shear mixer followed by sonication.  The GNP weight fraction was maintained at 2%.

The best improvements were observed with KC₄₈-benzene compound treated with nitric acid although all composites performed better than the neat epoxy.  Compared with the neat epoxy, the young’s modulus increased 100%, the strength 65%, and the electrical conductivity from   10^-12 to 10^-4 S/cm.   It is noted that the observed increase in Young’s modulus is close to a predicted value of 150%. 

The results so far indicate that GNPs with proper exfoliation and surface treatments offer a great potential to improve mechanical and electrical properties of polymers.  It goes without saying that their low cost makes their commercial applications much more viable.