| In this paper polyacrylonitrile (PAN)-based carbon nanotubes (CNTs) composite were produced by insitu polymerization and solution blending. Effects of CNTs content on the structure and the performance of composite were studied. The structure and proformance of CNTs before and after treated with structures and properties of composite were observed, which were characterized by Fourier transform infrared spectroscopy (FTIR), Raman spectra (LRS), X-ray diffraction (XRD), thermal gravimetric analysis (TG), differential scanning calorimetry (DSC), R/SCC coaxial cylinder rheometer, scanning electron microscopy (SEM) and transmission electron microscopy(TEM). The surface resistivity of composite film was tested by using Fluke 1508 type insulation resistance tester.It has been found that we can remove the impurities of CNTs by using nitric acid (65%) in room temperature very well, and can graft-COOH,-OH group onto the CNTs whitout disrupting the excellent length-diameter ratio stucture of CNTs. The dispersion for CNTs in different solvent was tested as follows:dimethylacetamide (DMAc)>dimethylsulphoxide (DMSO)>dimethyl formamide (DMF) in room temperature.Composites which produced by insitu polymerization were studied and found some phenomenon as follows:with the increase of the content of CNTs, the reactions conversion increased gradually, but when the content reached to 0.3%, the conversion began to decline; at the same time, the preoxidation temperature of polymer was in advance because of CNTs, and alleviated the exothermic reaction, all of which would improve the peoperty of PAN; in some extent, it hindered polymer crystallization, but the structure and crystal of polymer could change.The investigation on the composites solution rheology showed that the viscosity reduces fristly and then increases with the CNTs content increases, which was produced by solution blending. Solution viscosity became lower when the CNTs content achieved 0.5%, but in high shear rate this phenomenon disappeared, this indicated that thickening role can be reflected with low content of CNTs. The viscosity and the structure viscous index became higher, the Non-Newtonian index was smaller and the physical stability was worse while the content of CNTs was higher. The solution was temperature-sensitive with the low content of CNTs but was tended to be shearing-sensitive with the higher one.The analysis of DSC,XRD showed that the carbon nanotubes could improve the thermal properties of composite materials, and alleviated the exothermic reaction. During the preoxidation process the position of crystallization of composite was varied from 20≈16°to 29≈25°, which suggested the structure of aromatization appear; in addition, they produced a shoulder peak at about 20≈10°～40°in carbonization stage, the cyclization was completed, it had different distribution of the order and the disorder region.The analysis of FTIR showed that during the preoxidation process the stretching vibrations of nitrile (C≡N) and the methane group (CH2) decreased and nearly disappeared such as C=C and C=N during the preoxidation process(255℃), which represented the ladder structure appeared and became stronger gradually. At the same time the dope of C=N group in composite film decreased quickly than that the formed pure PAN, and the cycilzation rate of film increased from 20.24% to 70.41%, when the content of CNTs was 2%, however, the effect of CNTs was not basically discovered in carbonization stage (400℃). On one hand, the part of carbon nanotubes in the composites was in a single dispersion state, on the other hand, the aggregate structure of the carbon nanotubes was found.When the content of CNTs reached to 5%. the surface resistivity of composite film reduced to 5.74 MΩfrom> 104 MΩquickly, and it has a little change with the content of CNTs increase. |
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