Study On Preparation And Conductivity Of PA66/MWCNTs Composites

Since the industrialization, with its excellent performance in the field of engineering plastics and fibers nylon 66 are widely used, and the production and demand are growing steadily. With the world's economic development, the new and higher requirements are proposed in every materials field, and the development of modified nylon 66 also showing a trend in full swing. Since the discovery of carbon nanotubes (CNTs) by Iijima in 1991, CNTs have attracted tremendous attention due to their unique properties such as high aspect ratio, high mechanical strength, and high electrical and thermal conductivity. Nylon/CNTs composites have been reported a lot in the past decade, however there are few reports about PA66/CNTs composites. PA66 was selected as the matrix, a variety of methods were used for multi-wall carbon nanotubes(MWCNTs) oxidation and modification, to improve the carbon nanotubes in the composite dispersion. PA66/MWCNTs composites were prepared by solution blending after the MWCNTs treated by the amino. The electrical properties, thermal stability, crystallization behavior of PA66/MWCNTs composites were investigated. The main results are as follows:1. MWCNTs have been oxidated and modified via multiplicate methods. Structure and properties of modified MWCNTs were characterized by FTIR, Raman spectroscopy and TGA, and the morphology was observed by SEM. The results showed that carboxyl group was grafted to MWCNTs by a reflux process in HNO3 and H2SO4 mixed acids (volume ratio is 1:3) at 110℃for 2 hours. Ethylene diamine reacted with carboxyl group under the participation of condensating agent N, N-Dicyclohexyl carbodiimine (DCC), and amido group was grafted to MWCNTs surface after 12 hours. It was found that acidification MWCNTs can adsorb hexadecyl trimethyl ammonium bromide (HTAB) after circumfluent in ammonia at 100℃for 2 hours. The CNTs treated with HTAB can suspend in the water without stratification for 1 week.2. Four series of nylon 66 composites, PA66/MWCNTs, PA66/r-MWCNTs, PA66/f-MWCNTs and PA66/H-MWCNTs were prepared by solution blending.3. Conductivity of the composite performance test showed that there was a greater increase in conductivity. Volume resistivity and Surface resistivity of PA66/MWCNTs composites were reduced at most 10 orders of magnitude. Volume transfusion threshold value of the composites is 3.55wt%, Surfacee transfusion threshold value of the composites is 3.62wt%. Volume resistivity of PA66/r-MWCNTs,PA66/f-MWCNTs and PA66/H-MWCNTs composites were reduced at most 9 orders of magnitude. Surface resistivity of PA66/r-MWCNTs,PA66/f-MWCNTs and PA66/H-MWCNTs composites were reduced at most 10 orders of magnitude. Volume transfusion threshold value of PA66/r-MWCNTs composites was 3.40wt%, Surfacee transfusion threshold value of the composites was 3.49wt%. Volume transfusion threshold value of PA66/f-MWCNTs composites was 3.75wt%, Surfacee transfusion threshold value of the composites was 3.40wt%. Volume transfusion threshold value of PA66/H-MWCNTs composites was 3.51wt%, Surfacee transfusion threshold value of the composites was 3.54wt%.4. The modified carbon nanotubes and ultrasound treatment increased the dispersion of the carbon nanotubes in the matrix and carbon nanotubes in the matrix formed the conductive network.the MWCNTs had increased heat decomposition temperature and strengthened the heat stability of nylon 66。There was only one melting peaks in the second melting curves of composites, modified carbon nanotube composites improved the initial crystallization temperature and crystallization temperature of PA66. MWCNTs had served as nucleating agents in PA66 matrix and decreased the initial melting temperature and peak melting temperature of the composites than that of pure nylon 66, crystalline width of half height larger and melting range had slowed the overall rate of crystallization.