PROCESSING, WEAR, AND MECHANICAL PROPERTIES OF POLYETHYLENE COMPOSITES PREPARED WITH PRISTINE AND ORGANOSILANE-TREATED CARBON NANOFIBERS

Thesis (Ph.D.), School of Mechanical and Materials Engineering, Washington State UniversityPolymers and nanocomposites have been increasingly used for tribological applications over the last few decades. In particular, ultrahigh molecular weight polyethylene (UHMWPE) is a high performance polymer with excellent strength, toughness, and wear resistance. Because of these properties, UHMWPE is an ideal material for a variety of applications including body armor, components of sporting goods such as skies and snowboards, and liners in total joint replacement. Though the toughness and wear resistance far exceed that of most other polymeric materials, there is a high demand for improving the tribological and mechanical properties of UHMWPE for many applications. The approach used in this work for improving such properties is through nanocomposite technology, specifically via the incorporation of carbon nanofibers. In order to obtain the full potential of nanocomposite technology, two critical issues need to be addressed: appropriate interactions between the filler and matrix and proper dispersion of the nano-reinforcement. These critical issues are particularly important for UHMWPE nanocomposites in that UHMWPE is an extremely viscous polymer and thus cannot be processed conventionally, typically resulting in dispersion issues far worse than that of other composite systems. Furthermore, UHMWPE is non-polar, so interactions between filler and matrix will be limited to Van der Waals forces for untreated nanofillers. Therefore, the research presented aims at solving these issues by using a paraffin-assisted processing method and applying appropriate surface treatment to the carbon nanofibers. Under optimized processing conditions, wear and mechanical properties of UHMWPE composites can be substantially improved.School of Mechanical and Materials Engineering, Washington State Universit