Synthesis of organo-modified Multiwall carbon nanotubes (MWCNTs) and application for polymer/MWCNT nanocomposites

• Main Authors: Chia-Ming Chang, 張家銘
• Other Authors: Ying-Ling Liu
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/87279242507680751983

博士 === 中原大學 === 化學工程研究所 === 101 === Functionilization of multiwalled carbon nanotubes (MWCNTs) is critical to increase the interphase compatibility between MWCNTs and the polymer matrix.In this work, two approaches have been explored and investigated to exctend the scopes of organo-modfied MWCNTs and their application in advanced nanocomposites of MACNTs and polymers. The first approach involves Diels-Alder (DA) reaction for the functional- ization of MWCNTs. MWCNTs could serve as dienes or dienophiles in the DA reaction. A molecule or a polymer possessing diene or dienophile groups could be easily incorporated onto MWCNTs to result in the organo- functionalized MWCNTs. The performance of the DA reaction and the chemical structures of the functionalized MWCNTs have been demonstratyed with Fourier transform infrared spectroscopy (FTIR), thermogravimetric analyzer (TGA) and Raman spectroscopy. Moreover, the adducts (the 6-member ring formation with the DA reaction) of DA reactions could undergo a reverse DA reaction (the retro-DA reaction) up heating to generate the component molecules.. As a result, the functionalization of MWCNTs is thermally reversible. The thermally-reversible feature has shown an attraction in preparation of electrically-conductive polymer/MWCNMT nanocomposites. Incorporation of the DA-adduct- functionalized MWCNTs into poly(vinylidene fluoride) (PVDF) increases the electrical conductivity of PVDF.After a thermal treatment, the sample possessing 0.5 wt % of functionalized MWCNT shows an increase in the electrical conductivity from 2×10-12 S cm-1to 4×10-8 S cm-1, as the performance of the thermally-induced retroDA reaction to recoverthe electrical conductivity of MWCMTs from defunctionalization. It is noteqorthy that the mechanical properties of the nanocomposites do not change with the thermal process. The results demonstrate an approach to employ small amount of MWCNTs for the preparation of electrically-conductive MWCNT nanoocmposites. The second approach demonstrates the approach to chemically incorporate non-reactive polymer chains to MWCMTs through an ozone-mediated process. Ozonization of polymers generates peroxide and hydroperoxide groups in the polymer chains.These groups thermally decompose into oxygen radicals, which are reactive toward the bundles of MWCMNTs. In this work, four different polymers including poly(vinylidene fluoride) (PVDF), polysulfone(PSF), poly(2,6-dimethylphenylene oxide) (PPO), and poly(phthalazinone ether ketone) (PPEK) have been used to prepare polymer-functionalied MWCNTs through the ozone-mediated process. The chemical structures of the polymer-functionalized MWCNTs have been demonstratyed with FTIR, TGA, Raman spectroscopy and high-resolution transmission electron microscopy (HRTEM). Matrix-polymer-functionalized MWCNTs are especially useful to increase the reinforcement efficiency for polymer-MWCNT nanocomposites because the chain entanglements between the bonded to MWCNTs and the matrix polymer, so as to increase the perfection of dispersion of MWCNTs in the matrix polymer and the load transfer efficiency from polymer matrix to MWCNTs. As a result, MWCNT-PVDF/PVDF nanocomposite shows better mechanical and electrical properties compared to the nanocomposites possessing the unmodified and PSF-modiofied MWCNTs. On the other hand, a small loading amount of MWCNT-PVDF (0.07 wt %) has shown a great efficiency on toughening PVDF with a 180-fold increase in the toughness of the polymer. The ozone-mediated process has been utilized in preparation of Nafion- and polybenzimidazole (PBI)-functionalized MWCNTs (MWCNT-Nafion and MWCNT-PBI). The funtionalized MWCNTs have been utilized in the preparation of PBI/MWCNT nanocomposites for using as proton exchange membranes for fuel cells. The polyelectrolyte-fuctionalized MWCNTs not only enhance the mechanical property but also increase the proton conductivity of the membranes. In single fuel cell test at150℃, significant enhancement of cell performance has been obversed with the membranes modified with the polyelectrolyte-fuctionalized MWCNTs. Furthermore, MWCNTs which are anchored with Fe3O4 magnetic nanoparticles (MNP) and functionalized with Nafion has been prepared. Under a magnetic field, alignment of the MWCNTs has been observed to result in a further increase in the proton conductivity of the membrane. Moreover, the Fe3O4anchored MWCNTs block the methanol crossover of the membranes. With the results from small-angle X-ray scattering and positron annihilation lifetime spectroscopy, the hydrophilic clusters(contribute in to the methanol permeation) of the membrane have been altered with MWCNT-MNP-Nafion addition, so as to result in the decrease in the methanol permeability of the mmebranes. The increase in proton conductivity and decrease in methanol permeability result in the high cell performance of the membrane in single fuel cell test at 70℃ with a maximum power density of 109.3 mW cm-2.