| Nanoparticles have the potential to impart multiple desirable properties to polymers and composites due to their theoretical high properties and easier processing. Compared with other nanoparticles, graphite or graphene nanoplatelets are drawing more and more attention because of their combination of exceptional mechanical, electrical, thermal properties that are equal to carbon nanotubes but with the same two-dimensional platelet morphology as nanoclay, which also makes them capable of providing improved barrier properties in polymers. However, the 2D structure of graphite nanoplatelets also requires additional attention to be directed at the processing of these nanoparticles in polymers. Unlike symmetric nanofillers such as carbon black, the dispersion of 2D platelet fillers in a polymer matrix is more difficult due to the strong action between their surfaces. Besides getting good dispersion, the orientation of 2D particles also needs to be taken into account due to their anisotropic properties. However, if done properly, both dispersion and orientation can be controlled through nano-structuring to create novel materials with unique morphologies and properties.;In this research, graphite nanoplatelets were fabricated through exfoliation route to preserve the exceptional electrical and thermal properties. A novel polishing and plasma etching process for scanning electron microscopic observation of these nanocomposite samples has been developed to study the relationships among processing, morphology and performance. As a result, the dispersion and orientation of GNP could be used to explain the mechanical and electrical properties of the composites. It was discovered that orientation of GNP particles is the main factor in achieving high mechanical properties. Orientation that causes high mechanical properties and low electrical conductivity can be controlled by annealing the composite under high temperature.;Based on these principles, methods for nanostructuring of the exfoliated graphite nanoplatelets were identified and investigated to optimize desired properties. First, composites with uniformly aligned filler particles can be produced by cast film extrusion. Improvement of both tensile modulus and strength along with barrier properties was observed compared with injection and compression molded samples. Second, pre-coating of polymer powder and solid state ball milling (SSBM) were used to create percolated networks at low GNP concentrations to enhance electrical conductivity. A combination of melt-extrusion and SSBM resulted in the composites with both high mechanical properties and high electrical conductivity. Third, GNP particles were assembled into a thin paper-like film to create a flexible, durable and light-weighted material with extremely high electrical conductivity (∼2200 S/cm) and thermal conductivity (∼313W/m/K), low permeability to small molecules and the engineering possibility to be incorporated into fiber reinforced composites. |
