Orientation of copolymer polyacrylonitrile （PAN） chains during their deformation prior to stabilization and the further effect on the stabilization were investigated in detail. Results reveal that the orientation of...Orientation of copolymer polyacrylonitrile （PAN） chains during their deformation prior to stabilization and the further effect on the stabilization were investigated in detail. Results reveal that the orientation of PAN chains presents a saturation point of 69.51% when the deformation ratio reaches approximately 1.07, meanwhile the cyclization rather than the oxidation has a stronger dependence on the orientation of PAN chains during stabilization. The cyclization is facilitated that the cyclization degree is increasing while the activation energy is decreasing obviously as a consequence of the developing orientation of PAN fibers before the saturation point; however, it is restrained during the further deformation of PAN fibers after the point. The resulting carbon fibers obtained from the PAN fibers prepared at the saturation point possess the highest mechanical properties of 4.07 GPa in tensile strength and 249.0 GPa in tensile modulus.展开更多
The stabilization of PAN-fibers without additional co-monomers was investigated with thermo-gravimetry and evolved gas analysis (FTIR-spectroscopy and MS-spectrometry). One fiber type had been drawn after spinning, wh...The stabilization of PAN-fibers without additional co-monomers was investigated with thermo-gravimetry and evolved gas analysis (FTIR-spectroscopy and MS-spectrometry). One fiber type had been drawn after spinning, while the other was used as-spun. During the thermal treatment, fiber shrinkage was either restricted or unrestricted. Investigations of influencing chemical and physical reactions regarding this restriction were conducted. Differences in the mass loss and gas emissions were observed, depending on the strained or unstrained state of the fibers. The change of crystallinity and molecular orientation of the fiber as reason of the measured variations was discussed. The emission of ammonia and other nitrogen containing gases (supposedly nitriles/ isocyanates) could be attributed to different aspects of the stabilization process. The length restriction resulted in a change in ammonia emission, associated with the cyclization reaction of poly acrylonitrile. The onset and amount of side reactions were influenced as well.展开更多
The effect of structural evolution polyacrylonitrile (PAN) on mechanical properties was investigated in stabilization and carbonization. PAN spun fibers were stabilized in a convection oven with a constant tension for...The effect of structural evolution polyacrylonitrile (PAN) on mechanical properties was investigated in stabilization and carbonization. PAN spun fibers were stabilized in a convection oven with a constant tension for various times at 250℃. Fourier Transform Infrared spectroscopy (FTIR) and gel fraction results suggested that intra and intermolecular stabilization reactions occurred simultaneously. X-ray diffractograms revealed a disruption of crystalline structure and an appearance of pre-graphitic structure of PAN fibers due to stabilization. These structural changes by stabilization resulted in the significant decrease of tensile properties of fibers. In Raman spectra with heat treated fibers from 400℃ up to 1200℃, the intensity ratio of the D to G bands (ID/IG) decreased as heat treatment temperature increased, indicating an increase of basal plane of graphitic layer of heat treated fibers. Tensile strength of heat treated fibers at 1200℃ was found to be as high as 2.2 GPa.展开更多
基金supported by the National Natural Science Foundation of China(Nos.51073011 and 50673011) the,National High Technology Research and Development Program of China("863 Program",No.2006AA06Z382)the National Basic Research Program of China("973 Program",No.2006CB605304)
文摘Orientation of copolymer polyacrylonitrile （PAN） chains during their deformation prior to stabilization and the further effect on the stabilization were investigated in detail. Results reveal that the orientation of PAN chains presents a saturation point of 69.51% when the deformation ratio reaches approximately 1.07, meanwhile the cyclization rather than the oxidation has a stronger dependence on the orientation of PAN chains during stabilization. The cyclization is facilitated that the cyclization degree is increasing while the activation energy is decreasing obviously as a consequence of the developing orientation of PAN fibers before the saturation point; however, it is restrained during the further deformation of PAN fibers after the point. The resulting carbon fibers obtained from the PAN fibers prepared at the saturation point possess the highest mechanical properties of 4.07 GPa in tensile strength and 249.0 GPa in tensile modulus.
文摘The stabilization of PAN-fibers without additional co-monomers was investigated with thermo-gravimetry and evolved gas analysis (FTIR-spectroscopy and MS-spectrometry). One fiber type had been drawn after spinning, while the other was used as-spun. During the thermal treatment, fiber shrinkage was either restricted or unrestricted. Investigations of influencing chemical and physical reactions regarding this restriction were conducted. Differences in the mass loss and gas emissions were observed, depending on the strained or unstrained state of the fibers. The change of crystallinity and molecular orientation of the fiber as reason of the measured variations was discussed. The emission of ammonia and other nitrogen containing gases (supposedly nitriles/ isocyanates) could be attributed to different aspects of the stabilization process. The length restriction resulted in a change in ammonia emission, associated with the cyclization reaction of poly acrylonitrile. The onset and amount of side reactions were influenced as well.
文摘The effect of structural evolution polyacrylonitrile (PAN) on mechanical properties was investigated in stabilization and carbonization. PAN spun fibers were stabilized in a convection oven with a constant tension for various times at 250℃. Fourier Transform Infrared spectroscopy (FTIR) and gel fraction results suggested that intra and intermolecular stabilization reactions occurred simultaneously. X-ray diffractograms revealed a disruption of crystalline structure and an appearance of pre-graphitic structure of PAN fibers due to stabilization. These structural changes by stabilization resulted in the significant decrease of tensile properties of fibers. In Raman spectra with heat treated fibers from 400℃ up to 1200℃, the intensity ratio of the D to G bands (ID/IG) decreased as heat treatment temperature increased, indicating an increase of basal plane of graphitic layer of heat treated fibers. Tensile strength of heat treated fibers at 1200℃ was found to be as high as 2.2 GPa.
