The ubiquity of polymers in everyday life speaks to the versatility and ease with which many polymers, particularly thermoplastics, can be formed to complex functional shapes over a range of sizes spanning four to five orders of magnitude. High performance applications in aerospace and transportation require superior mechanical properties to those obtained from neat polymers. Carbon fiber polymer composites have greatly expanded the performance envelope and are found in the newest commercial airliners, although fibers must often be aligned, are expensive and are not compatible with high speed molding processes typical of those needed to broadly penetrate the automotive market.
We have developed a molten polymer processing method that employs high levels of elongational stretching of thin films of polymer/graphite mixtures such that the graphite is exfoliated into single and multilayer graphene sheets. Processing devices have been developed that expose the polymer/graphite mixtures to greater than 107 alternating pulses of shear with rates as high as 105 s-1. This process results in at least 50 percent exfoliation of the graphite, although some of the multilayer graphene sheets can be 60- 70 atomic layers thick. In addition to generating graphene by exfoliation, the process also fractures the brittle graphene sheets to generate dangling bonds on the graphene edges. Such free radicals combine with unsaturated polymer linkages, or other polymer free radicals to form covalent connections between the graphene and the polymer, thus greatly enhancing load transfer capability. The polymer composites generated initially by this approach have elastic moduli similar to carbon fiber composites and calculations suggest that further developments will produce materials with mechanical properties similar to aluminum metal. A thermoplastic material of such properties that is injection moldable at polymer temperatures to form a wide variety of structural parts for aerospace and automotive applications has the potential to transform the manufacturing paradigm for these industries.
This talk will address these polymer composites from two perspectives:
- The first will examine processing dynamics of high shear exfoliation of graphite in a polymer melt, with a particular focus on the qualitative mechanics of peeling graphene layers from bulk graphite. The additional step of fracturing the graphene sheets to form bonds with the polymer matrix will be discussed from a chemo-mechanical perspective focusing on critical platelet size.
The second perspective will be directed towards properties and applications, and the potential role of this technology in generating a new manufacturing platform for several critical industries.
Richard Lehman is professor and chair in the Rutgers University Department of Materials Science and Engineering. He received his BS, MS, and PhD degrees from Rutgers and then worked in the fiber glass and industrial chemical industries for eight years prior to joining the Rutgers faculty. Dr. Lehman's research interests center on the glass transition and the processing and properties of inorganic and organic glasses, particularly the mechanical, optical and chemical behavior of commercially important systems. His current research is focused on the mechanical and chemical properties of polymer blends, with principal attention towards immiscible blends, the behavior of multiphase composite interfaces, and applicability of these systems in structural and biomedical applications. He is also active in developing manufacturing technologies for commercial soda lime silicate glasses, particularly in the area of recycled raw materials. He is a fellow of the American Ceramic Society and was recently awarded the John Cope Leadership Award from the International Crystal Federation.
For more information please contact Vanessa Irizarry at [email protected]