Investigation On The Chemical Modification Of Carbon Nanotubes And Carbon Nanotubes-polymer Composites

Due to its excellent mechanical, optical and electrical properties, study of carbon nanotubes (NTs) has becoming a hotspot in the material research field. Carbon nanotubes consist of one or several graphene sheets rolled up into a seamless tube, forming single-walled (SWNTs) or multi-walled (MWNTs) nanotubes, respectively.The following works were carried out in this thesis:1. The optimization of the oxidation conditions of MWNTIt is well known that the properties of MWNT vary with the parameters such as the diameter and length of the tubes, the arrangement of the atoms, and the synthesis method, etc. Oxidation of MWNT, as the first step of chemical modification, has great influences on the properties of the modified MWNT. In this paper, the oxidation conditions of MWNT, especially the acidification time was optimized. During the process, the structure of the oxidized MWNT was observed by TEM, the electrical properties were measured and the 1H NMR spectra were also performed. The oxidation conditions of MWNT are determined as follows: oxidation with a mixture of nitric and sulfuric acid (1:3 by volume), and sonicated for 12hours.2. Synthesis and Characterization of Octadecylamine Grafted Multi-walled Carbon NanotubesA series of octadecylamine (ODA) grafted MWNT samples were prepared and characterized by NMR, FTIR, DSC and XRD. It was revealed that the ODA chains grafted on MWNT are partially crystalline, though the packing structure is not as perfect as the pure ODA. It is believed that ODA are preferably grafted to certain active sites, such as the tube-ends and the defects on thesidewall of MWNT. A quantitative NMR technique was developed to determine the weight percent of ODA in modified MWNT. The relationship between the content of ODA and the solubility of soluble MWNTs was also discussed.3. Synthesis and Characterization of PEO Grafted Multi-walled Carbon Nanotubes and the Copolymerization with MMAA novel MWNT that is soluble in both organic solvent and water, was synthesized by reaction with double bond functionalized poly (ethylene oxide) (PEO). The 13C NMR spectra shows that the PEO chains grafted on the MWNT are amorphous. This demonstrated that there exist n-TT interactions between the n-orbitals of the PEO ether oxygen and the Tr-system of MWNT.The soluble MWNT were then copolymerized with MMA monomer. A transparent and homogeneous material was obtained. Extraction experiment proved that MWNT-PEO was chemically copolymerized with MMA, not physically blended. The mechanical properties were enhanced compared with pure PMMA.4. Synthesis and Characterization of MWNT-containing Polyurethane-urea Based on the typical two-step polyurethane-urea synthesis,self-crosslinkable polyurethane-urea compounded of PTMO (Poly (tetramethylene oxide)), MDI (4,4'-diphenylmethane diisocyanate) and extended by AEAPS (aminoethyl aminopropyl trimethoxysilane) were prepared.On the other hand, a multi-walled carbon nanotubes (MWNT)-amine adduct was synthesized by reacting MWNT with excessive APES (aminopropyl triethoxysilane) and introduced into the polyurethane-urea to form the homogenous and transparent MWNT-containing polyurethane-urea films. A series of MWNT-containing polyurethane-urea samples of different MWNT contents are prepared and the mechanical properties of samples were recorded. The results show that only 0.5wt% MWNT can improve the Young'smodulus to about 400%, while the elongation decreases only limitedly.It is interesting that with the increasing of added MWNT/APES amount, the swelling ratio of polymers in water is increased while it is decreased in DMF. The almost linear increasing of swelling ratio in water is quite understandable, since, with the introducing of more MWNT/APES, more silsesquioxane formation was formed, which enables more water to be combined. On the other hand, the increase of MWNT/APES brings about more crosslinks, so the sample becomes more difficult to be swollen in DMF.