Abstract
In this research,multi-walled carbon nanotube(MWCNT) was modified with different conditions. The modified MWCNT was analyzed by FT-IR, Raman spectrum and X-ray photoelectron spectroscopy (XPS). The unmodified and modified MWCNT were added to polyimide, epoxy and PMMA to prepare MWCNT/polyimide, MWCNT/epoxy and MWCNT/PMMA nanocomposites. This dissertation contains four parts. The first part was the preparation and characterization of MWCNT/polyimide composites. Unmodified, acid-modified, amine-modified and soluble polyimide grafted multiwalled carbon nanotube (MWCNT) were added separately to the polyamic acid and heated to 300℃ to form polyimide/carbon nanotube composite. SEM and TEM microphotographs show that acid-modified MWCNT, amine-modified and soluble polyimide grafted MWCNT dispersed uniformly in the polyimide matrix. Silane modified MWCNTs formed interpenetrate network in polyimide network. Effect of the MWCNTs on the surface and volume electrical resistivities of the MWCNT/PI composites has been investigated. Mechanical properties of the nanocomposites were enhanced significantly by modified MWCNTs. Acid modified multiwalled carbon nanotubes (MWCNTs) were grafted with 3-isocyanato-propyltriethoxysilane(IPTES) and (3-aminopropyl) triethoxysilane (APTES); Unmodified multiwalled carbon nanotubes (MWCNTs) were grafted with vinyltriethoxysilane(VTES). Silane grafted MWCNTs were then mixed with the polyamic acid(BDTA/ODA) and heated to 300℃ to form a carbon nanotube/polyimide composite. During the imidization processes, the silanes on the MWCNT surface reacted with each other. TEM microphotographs showed that the silane grafted MWCNTs were connected. The composite material possesses an interpenetrating network in which polyimide molecules were interpenetrated into the MWCNT network. The electrical resistivity of silane grafted MWCNT/polyimide decreased very significantly compared to those only containing acid treated MWCNTs for the same loading with MWCNTs. The second part was the preparation of MWCNT/epoxy composites, multiwalled Carbon nanotubes (MWCNT)/Epoxy Composites have been prepared. The characteristics and morphological properties were studied. SEM microphotographs showed that MWCNTs were aggregated in the epoxy resin. Epoxy resin and acid modified multiwalled carbon nanotube(MWCNT) were treated with 3-isocyanato- propyltriethoxy-silane (IPTES). SEM and TEM microphotographs of the MWCNT/epoxy composites have been investigated. The molecular motion of silane modified MWCNT/Epoxy composites were studied using high-resolution solid-state 13C NMR. Results show that 1.0wt% silane modified MWCNT/Epoxy exhibits less molecular motion than that of the lower silane modified MWCNT content. Dynamic mechanical analysis (DMA) data of the MWCNT/Epoxy composites showed the storage modulus (at 50℃) and Tgs of the IPTES modified Epoxy increased with IPTES-MWCNT content. Tensile strength and Young’s Modulus of cured silane modified MWCNT(1.0wt%)/Epoxy composites increased significantly comparing to the neat epoxy. In the third part, a unique titanium oxide (TiO2) coated multiwalled carbon nanotube(MWCNT)/Epoxy has been prepared. Multiwalled carbon nanotubes were coated with a layer of TiO2 and then modified with 3-(aminopropyl)triethoxysilane (APTES). The TiO2 coated MWCNT and APTES modified TiO2 coated MWCNT(AT-MWCNT) were analyzed by X-ray photoelectron spectroscopy(XPS). The AT-MWCNT was added to the Diglycidyl ether of bisphenol A type epoxy to prepare silane grafted TiO2 coated MWCNT/epoxy composites. The amine functional groups on AT-MWCNT surface reacted with epoxy. Consequently, the adhesion between MWCNT and epoxy was improved. Mechanical properties of the AT-MWCNT/epoxy composites increased dramatically. The TiO2 coated MWCNTs/epoxy system was cured with silane. Silane may react with TiO2 surface and improves the adhesion between the MWCNT and epoxy matrix. X-ray photoelectron spectroscopy and X-ray diffraction (XRD) were utilized to analyze the TiO2 coated MWCNTs. TEM microphotographs showed the effect of titanium (IV) n-butoxide on the morphology of the TiO2 coated MWCNT. The dispersion of TiO2 coated MWCNT in the epoxy matrix is better than that of unmodified MWCNT. Mechanical properties of the MWCNT/epoxy composites were improved significantly by the TiO2 coated MWCNTs. The fourth part was the preparation of MWCNT/PMMA composites. Mutiwalled carbon nanotubes (MWCNT) were modified using 3-isocyanato- propyltriethoxysilane (IPTES). Crosslinkable PMMA was prepared from MMA monomer and Vinyltriethoxysilane (VTES) (PMMA-VTES).The IPTES-modified MWCNT (Si-MWCNT) was mixed with the PMMA-VTES copolymer and crosslinked with catalyst to form Si-MWCNT/PMMA-VTES composites. The degree of condensation of tri-distribution structure of the Si-MWCNT/PMMA-VTES composites decreases as the Si-MWCNT content increases. The morphology of the Si-MWCNT/PMMA-VTES composites was analyzed by SEM and TEM. The MWCNTs were well dispersed in the PMMA-VTES matrix. Surface and volume electrical resistivity decreased as the MWCNT content increased. The thermal conductivity of the PMMA-VTES composites increased by 87.5% when 0.99wt% Si-MWCNT content was added to neat PMMA-VTES. The thermal stability of the PMMA-VTES in nitrogen and air increased significantly even when a small quantity (0.5wt%) of Si-MWCNT was added.