Surface Modification of Exfoliated Graphite Nano-Reinforcements

Nano forms of graphite and carbon, such as flakes, worms, and tubes, can significantly modify the properties of polymers when used as reinforcements. Challenges remain in processing composites with these nano-reinforcements in the form of attaining uniform dispersions. Many of these difficulties are due to a lack of wetting of the nano-reinforcements by the polymer. Poor wetting is caused by the very low surface energy of the as-produced graphite nano-reinforcements. Opportunities exist for modifying the surface chemistry and energy of nano-reinforcements that will allow improved wetting and provide a means for chemical bonding at the interface with high temperature polymers such as PMR-II-50 polyimide. Two approaches for surface modification are proposed: (1) oxidative plasma treatments to populate the graphite surface with carboxyl and hydroxyl groups, and (2) bonding of polyimide oligomers to the nano-reinforcements using reactive coupling agents. Both of these approaches have proven successful with micron size carbon and graphite fibers and with nanofibers. As such, these treatments should result in nano-reinforced composites with superior mechanical properties and environmental durability.