Preparation Of Acrylonitrile-Acrylamide Copolymer Nanofiber And Its Pre-oxidation Behaviour

Polyacrylonitrile (PAN)-based carbon fibers have been appreciated in various areas because of their excellent characteristics since its advent. The effect of carbon nanofiber reinforcing polymer-based composites is better than the common carbon fiber. Electrospinning is the only way to manufacture nanofibers directly and continuousely. From todays progress of fiber reinforced polymer-based composites, we can know there is great prospect of application in fabrication of carbon nanofiber based on PAN by electrospinning.In this work, acrylonitrile (AN) homopolymer, AN-acrylamide (AM) copolymers and AN-AM-methyl acrylate (MA) ter-polymers were synthesised with azodiisobutyronitrile (AIBN) as initiators and dimethysulfoxide (DMSO)/ water solution as solvents, as well as comparison with redox polymerization of AN-AM. The structure and properties of the copolymers was studied by Fourier transform infrared (FT-IR), X-ray diffraction (XRD) and thermogravimetry (TG). An attempt was made to associate the PAN structure with the preparation of PAN nanofiber precursor. The electrostatic spinning technique of producing nano-PAN fiber mat was introduced, pre-oxidation of the as-spun PAN nanofibers in air atmosphere was investigated, and the influence of amide-group (CONH2) on the pre-oxidation of PAN nanofibers was discussed, in order to offer some technical reliance and guidance to the preparation of carbon nanofiber. The main research content and the conclusions are as follows:(1) Copolymerization of AN-AM. The effect of reaction temperature, time and mixing ratio of mixed solvents on the polymerization were investigated. As the monomer could be dissolved in both DMSO and H2O while the polymer could be dissolved in DMSO only, it would facilitate to the distribution of monomers and the growth of molecular chains, and the chain transfer constant of DMSO and H2O is small. By optimizing polymerization conditions, higher molecular weight , higher crystalline degree and lower molecular defects of PAN polymers could be obtained. (2) Cyclization of the copolymers. The thermal properties and cyclization of PAN polymers were studied by TG, the result shows that the cyclization of copolymer was easier to take place under the lower temperatures because the introduction of AM. It was found that amide-group (CONH2) drastically promoted the activity of the cyclization of the molecular chains. It was helpful to use MA as comonomer in order to adjust the speed of cyclization because MA could retard the cyclization of cynic-group in the copolymers.(3) Preparation of nanofibers. The certain conception of PAN/DMAc solution was prepared by mixing and stirring, and the electrostatic spinning technique was used to produce PAN nanofiber mat with diameters below 1000 nanometers. Except the fixed wire meshes was used as the collector, as a comparison, a homemade rotating wire meshes was used as the collector. Within the spinablity of PAN solutions, the average diameter of PAN nanofibers presented the trend of first increase then decrease with the increase of the solid content. Utilization of the rotating collector enhanced the alignment of the as-spun fibers. Under the same concentration of spinning solution and the same spinning process, compared with the nanofibre collected by the fixed collector, it was discovered that the former was uniform, slim and better for alignment. The change of PAN nanofibers is similar to the original precursor in diameter during the process of pre-oxidation.(4) Pre-oxidation of PAN nanofibers. The as-spun PAN nanofibers were heat-treated in air atmosphere by using an oven under the relaxed state. Compare to the increasing of the temperature of the heat-treatment, the color of the surface of the fiber mat turn yellow from white in a short time. That because the introduction of AM made the pre-oxidation of fibers easily. The image of heat-treated nanofibers were investigated by SEM, it found that the average diameter of the fibers presented the trend of first decreased then increased with the increase of the temperature during the heat-treatment. The PAN nanofibers collected by fixed collector were easier to form network structure while the fibers collected by rotating collector arranged in bundle after the heat-treatment.