| In this thesis, the electrochemical oxidation method was mainly employed to produce electrochemically modified nano-graphite which was then compounded with polymer matrix to synthesize polymer based nanocomposites. This electrochemical oxidation method is facile, environmentally friendly, together with simple post-treatment of crude products and low energy cost. The electrochemical oxidation reaction will induce the formation of diverse functionalized nanoparticles, e.g., with variable extents of oxidation, under different electrolysis conditions. In addition, all of the electrochemically modified nano-graphite was well-dispersed in water medium. On one hand, the electrochemically modified nanoparticles (EM-GNPs) with high extent of oxidation were treated by a chemical reducer such as hydrazine and then reduced back to a certain amount of the starting graphitic crystalline structure, resulting in the partial restoration of the electrical conductivity, from (1.38±0.05)×10-6 (before reduction) to (1.02±0.05)×10-3 S/cm (after reduction). Moreover, the characteristic X-ray diffraction peak of the 002 plane in graphitic crystal reoccurred after the reduction treatment of EM-GNPs. On the other hand, the hydrophilicity of EM-GNPs with polar surfaces was changed to lipophilicity by organic modification with a cationic surfactant such as dodecylamine.The electrochemically modified graphite nanosheet (EM-GN) with low oxidation extent was another type of nano-structure which possessed high aspect ratio and could be well-dispersed in water medium. EM-GNs were homogeneously and stably dispersed in a water-soluble macromolecule matrix such as poly(vinyl alcohol) (PVA) and formed an exfoliation type nanocomposite film. The properties of EM-GNs filled PVA nanocomposite films such as electrical, thermal, and mechanical properties were improved. The electrical conductivity was changed from an insulator to a semiconductor with a percolation threshold only about 6 wt.%; After compounding 5 wt.% loading of EM-GNs with PVA, the high temperature degradation resistance was improved by 45℃and glass transition temperature enhanced by 14℃, along with the improvement of the mechanical tensile properties including tensile strength and elongation toughness.Properly treating EM-GNPs by using electrochemical oxidation method retained graphitic crystal structure. Meanwhile, a certain amount of oxygen containing functional groups and a graphite oxide-like structure were generated in the EM-GNPs, leading to the excellent graphitic in-plane properties combined with the peculiar graphite oxide-like surface properties. This special structure of EM-GNPs was favorable to be used as a filler to produce high-performance epoxy nanocomposites. The EM-GNPs with low oxidation extent were well-dispersed into epoxy matrix under intense ultrasonic irradiation. The average diameter of the particles dispersed in the matrix doubled compared with the starting EM-GNPs, which was possibly due to the sliding effects between the ultra-thin sheets consisting of EM-GNPs, but without complete separation from each other. Due to the special structure of EM-GNPs dispersed in epoxy matrix, the synergistic reinforcing and toughening effects of GNPs on the epoxy were obtained. The tensile strength and toughness of the 5 wt.% EM-GNPs filled epoxy nanocomposites were improved by about 17 MPa and 6 %, respectively, along with ca. 19℃improvement of the high temperature degradation resistance. |
PDF Full Text Request