The Effect Of New Comonomers On The Aggregation State Of PAN Fibers

High quality PAN fiber is the foundation for fabricating high performance carbon fiber (CF). Copolymerization is a commonly used way to modify the thermal properties of PAN fiber, to obtain a good basis of CF fabrication. The previous research was focused on carboxylic acids, carboxylic acid esters and amides comonomers, which hardly satisfied the requirement of high performance CF fabrication. β-ethylitaconate and 1-viny-3-ethyl-imidazolium bromide was selected as comonomers for producing PAN fibers. The effects of comonomers on radical solution polymeration and formation of fiber is invesgated.In this thesis, three copolymerize systems were built, which are β-EIA-AN (Acrylonitrile copolymerized with β-ethylitaconat), [VEIm]Br-AN (Acrylonitrile copolymerized with 1-viny-3-ethylimidazolium)and β-EIA-[VEIm]Br-AN(Acrylonitrile copolymerized with both β-ethylitaconat and 1-viny-3-ethylimidazolium). Those systems were characterized in viscosity-average molecular weight, monomer conversion rate, molecular structure, solution viscosity and rheological property. Among these 4 copolymerized system, [VEIm]Br-AN copolymerized system exhibits higher polymeration rate and final monomer conversion rate, a higher viscosity-average molecular weight was also observed in [VEIm]Br-AN copolymer. β-EIA-AN and IA-AN copolymerized system have lower monomer convention rate and viscosity-average molecular weight. The results were compared with Itaconic acid copolymerized Acrylonitrile system. In different copolymerization system, the PAN macromolecule was always a random copolymer, but there are slight differences, among which the [VEIm]Br-AN copolymer has more isotactic structure and less syndiotactic structure. The elasticity and viscosity of [VEIm]Br-AN copolymer solution were higher than those of the other three kinds of copolymer solution, but lower viscoelastic transition frequency; β-EIA-AN and IA-AN copolymer solution viscosity and viscoelasticity is relatively low, with higher viscoelastic transition frequency; the viscosity change rate of IA-AN copolymer solution has temperature sensitivity.[VEIm]Br-AN copolymer/DMSO solution was applied for preparing PAN fiber using wet spinning technique. The effect of co-monomer on fiber morphology, crystal structure, orientation structure and thermal properties were investigated. The result indicated the crystallinity, grain size and degree of orientation were increased with higher draw ratio. The maximum draw ratio was 5.0 for boiling water drawing and 2.4 for steam drawing respectively.The [VEIm]Br-AN and co-polymerized fiber start the exothermic process at 262.88℃, peaked at 276.62℃. The co-polymerized fiber obtained more concentrated exothermic in cyclization and oxidation process, under both nitrogen and air atmosphere.The β-EIA was used as the third co-monomer to modify the thermal properties of [VEIm]Br-AN PAN fiber. The addition of β-EIA obtain higher orientation and crystallinity with finer grains. It was also effective to lower the initiate cyclization temperature and widen the exothermic peak for PAN fiber.