Mechanical and electrical properties of aligned carbon nanofiber/epoxy nanocomposites
Carbon Nanofibers (CNFs) are high aspect ratio nanofillers that possess excellent mechanical and electrical properties. Hence, CNFs have been incorporated into polymer to fabricate nanocomposites with superior mechanical and electrical properties. Studies have shown that nanocomposites with superior mechanical and electrical properties can be fabricated with relatively low concentration of nanofillers by properly aligning them in polymer resins through AC electric field. In this work, functionalized CNFs have been incorporated into a high-strength epoxy-based resin and aligned into a preferential direction using AC electric field to tailor aligned carboxylic-functionalized CNFs (O-CNFs) and amine-functionalized CNFs (A-CNFs) reinforced polymeric nanocomposites. Both mechanical and electrical properties were quantified in order to examine the effect of addition and alignment of functionalized CNFs on the properties of final nanocomposites. Optical images revealed negligible agglomeration before and after curing of nanocomposites, at the same time, they showed alignment arrays of functionalized CNFs in the nanocomposites that were subjected to AC electric field. Additionally, the configuration of alignment for low concentration of aligned O-CNFs and A-CNFs filled nancomposites was slightly different compare to aligned nanocomposites with high concentration possibly due to elevated localized interaction of adjacent functionalized CNFs. An increase of 11.34% in compressive modulus and 8.36% in compressive strength were achieved when adding 3wt% and 4.5wt% of O-CNFs to the base resin system, respectively. By comparing different concentration of aligned and non-aligned A-CNFs reinforced nanocomposites correspondingly, it was found that the percentage change of compressive modulus for aligned A-CNFs filled samples was two to three times higher than nonaligned samples. Meanwhile, a four order magnitude of reduction in electrical resistivity to 10⁶ Ω.cm was obtained by aligning the functionalized CNFs in the epoxy resin. Furthermore, the electrical percolation threshold of aligned O-CNFs filled nanocomposites was estimated to be 0.75wt%. A possible trend of electrical resistivity of aligned A-CNFs filled nanocomposites was extrapolated up to 4.5wt% and suggested that the percolation threshold of electrical resistivity would occur at 0.75wt%, which is similar to aligned O-CNFs nanocomposites. Moreover, it is also suggested that the electrical resistivity of 4.5wt% aligned A-CNFs filled nanocomposites would reduce to 10⁴ Ohm.cm range.
Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Mechanical Engineering.