| Carbon nanotubes (CNTs), due to their unique physical properties and many potential applications, have been extensively studied in the past two decades for their high thermal conductivity, especially, making them ideal fillers to prepare nanocomposites with good thermal conduction. However, carbon nanotubes in the matrix are easy to aggregate with each other, difficult to disperse and have poor wettability with the matrix. Therefore, the surface of CNTs must be modified to improve their dispersion in the polymer matrix and the interface interaction. Nano-alumina (nano-Al2O3) have not only small size effect, surface effect and other outstanding features, but also a wide range of sources, low prices, are widely used in the preparation of thermally conductive materials. But their major disadvantage is that their polarity is so strong that they are easy to get together in the matrix, affecting the play of thermal conductivity. In this paper, we used liquid phase chemical deposition method, successfully prepared CNTs-Al2O3nanocomposites, carbon nanotubes and alumina synergies, not only to improve the dispersion and specific surface area of aluminum oxide in the polymer matrix, but also to improve the dispersibility of CNTs in polymer matrix and binding to the polymer, thereby improving the thermal conductivity of the composites.Since there is little active site on the surface of nanotubes, it is difficult to introduce aluminum compound under normal temperature and pressure, so this paper aimed to modify CNTs by poly(dopamine) functional method. Dopamine which is a biological macromolecule, could occur polymerization on the surface of a variety of materials in alkaline environment (pH=8.5), to form the poly-dopamine (PDA) coating. PDA contain catechol structure and-NH-,-N=that can further react with metal ion (e.g., Ag+, Cu2+, Al3+, etc.) or other functional groups (such as epoxy groups, the Si-OH, carboxyl group, etc.) to form non-covalent bond covalent binding to provide favorable conditions for the second functional materials.In this thesis, CNTs-Al2O3nanocomposites are successfully prepared with PDA as a bridge, and prepare NR/CNTs@α-Al2O3composites with good thermal conductivity. The details are discussed as follows:1. CNTs are modified by dopamine self-polymerization in weak alkaline solution. The results of XPS, XRD and HR-TEM indicate that PDA form homogeneous coating on the surface of CNTs, and the thickness is about2-3nm. The finger print region of CNTs become not clear, but their crystal structure has been not affecter during the process of dopamine self-polymerization.2. CNTs-PDA-Al(OH)3namocomposites were prepared by liquid phase chemical precipitation method.-N=in PDA coordinate with Al3+, so that Al3+ is immobilized on CNTs surface, then react with NH3·H2O to form Al(OH)3Al(OH)3is successfully loaded on the surface of CNTs by XPS, TGA and HR-TEM test, and Al(OH)3loading can be adjusted by adjusting Al3+concentration.3. CNTs-PDA-Al(OH)3nanocomposites are heat-treated at different temperatures to prepare amorphous alumina, y or α-type crystal alumina and CNTs composites. TGA and SEM tests show that carbon nanotubes will occur decomposition if exposed in oxygen and the temperature is above600℃. XPS, XRD results show that when preparing a crystalline alumina loaded carbon nanotubes, a thermal decomposition of poly(dopamine) occurs, and the tube lattice defects reduce.4. NR/CNTs, NR/CNTs-PDA and NR/CNTs@a-Al2O3composites are prepared by machine blending method. The test results show that the thermal conductivity of natural rubbers added in CNTs@a-Al2O3is0.178W/(m·K),17percent higher than NR without CNTs, and5percent higher than NR/CNTs. |
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