Multifunctional Graphene Nanocomposite Foams for Space Applications

This research focused on the development of light-weight materials for applications in aerospace technologies. Light-weight materials are especially attractive for aerospace industry to help reduce payloads. In addition to decreasing the actual weight of the material another way to gain weight savings is by making the material multifunctional thereby reducing the number of materials needed. Recent research has demonstrated the potential of nanoparticles to increase the functionality of common materials. Graphene is an especially promising nanomaterial because of its inherent multifunctionality. The material has been shown to have excellent mechanical, thermal and electrical properties and has improved the corresponding properties to the materials to which it has been added. In this research graphene nanoplatelets, which consists of a stack of a few layers of graphene, was added to polymeric matrices with cellular structures to decrease the density, and add multifunctionality while maintaining overall performance. The first matrix material was polyurethane, a very common polymer having tunable properties and an inexpensive price. This material can also be utilized as a foam formed by a variety of processes. This project focused on the use of a chemical blowing agent that allows the liquid to expand as it polymerizes. In this way the GnP was added to the liquid precursor polymer and dispersed in the ribbed structure of the foam. GnP is a commercial material that comes in many different sizes all of which contain functional edge groups. These edge groups were attached with either molecules or polymer chains to improve the bonding between the GnP nanoparticles in the matrix. In any composite, having good bonding in the interface region is key to having good mechanical performance. Utilizing different sizes and edge-groups attached to the GnP prior to being added to the polymer improved the compressive strength, elastic modulus, electrical properties and dielectric performance while in general also improving the thermal stability of the overall nanocomposite foam. The amount of improvement, however, was dependent on the type and especially size of GnP used and affected the different properties unevenly. Large nanoplatelets with the largest aspect ratio demonstrated the most improvement to the electrical and dielectric properties and increased the reflectance of the nanocomposite when exposed to electromagnetic (EM) waves. These same large particles did not improve the mechanical performance the way the smaller platelets did and were much more effective at increasing the ability of the nanocomposite foam to absorb EM waves resulting in improvement of the EM interference shielding effectiveness of the material. These results did demonstrate the ability of only a small amount of nanoparticles of 8 wt% or less to change the overall performance of the foam improving the multifunctionality of the material while not sacrificing its light-weight. The variable properties of the nanocomposite suggests that these materials would be able to be tailored to specific applications.