The Preparation And The Structure-Property Relation Of MWNT/PAN Carbon Fibers

Carbon fibers are new-style materials, which have high tenacity, high modulus, heat-resistance, corrosion resistance, and a series of excellent performances. As a kind of reinforcing fiber of advanced materials, it is widely used in all kinds of fields. PoIyacrylonitrile(PAN) fiber is one of commercially important polymeric fibers. Among the precursors available for producing carbon fibers, PAN fibers are the most commonly used and promising precursors. Now, it is well accepted that the quality of high-performance carbon fibers mainly depends on the composition and quality of the precursor fibers.In this thesis, PAN precursor was modified by Carbon nanotubes(MWNT) to improve its mechanical property. The effects of MWNT on the DMSO solution and fiber performance were discussed. The MWNT/PAN composite fibers were obtained by means of dry-jet wet-spinning technology. The thesis mainly deals with the oxidization and carbonization process of carbon fibers from the MWNT/PAN composite fibers.1. Purification of MWNTMWNT were modified by using concentrated acid to improve their dispersion in a solvent and the matrix polymer. Optical microscope was used to characterize the dispersion of the MWNT. The results showed the dispersion of the modification of MWNT in the solution were improved.2. Preparation and properties of PAN/MWNT mixture solutionThe mixture solution was prepared through blending the modified MWNT and PAN in DMSO. The dynamic rheological behavior of the solution was investigated, indicating that the system showed shear thinning. The addition of MWNT reduced the complex viscosity, but had little effect to the spinnability of the solution.3. Preparation and properties of MWNT/PAN composite fibersDry-jet-wet spinning technology was used to produce the composite fibers with different MWNT loadings. The morphology, structures and properties of the composite fibers were studied. TEM images confirmed the dispersion of MWNT in PAN matrix. The addition of MWNT improved the mechanical properties. XRD spectra showed that the addition of MWNT did not affect the crystal lattice of PAN, whereas they had a slight influence on the crystal dimension and crystallinity of PAN. The effect of the orientation of the composite fibers was discussed. In general, the composite fibers with the amount of the 1 % MWNT had the best overall performance.4. Pre-oxidization and carbonization of MWNT/PAN fibersA typical producing technology of carbon fibers was used to pro- oxidization and carbonization of MWNT/PAN composite fibers. TEM was used to observe the morphology of pre-oxidization and carbonization of MWNT/PAN fibers. The effect of MWNT on the mechanical properties composite fibers was improved.