| Nowadays, the major spinning methods domestic enterprises used for preparing high performance PAN fibers are wet spinning and dry-jet wet spinning. Most researchers focused on wet spinning PAN fiber struc-ture and properties, structure evolution during the thermal oxidation sta-bilization, carbon fiber structure and properties, while dry-jet wet spin-ning PAN fiber lack of relevant researchs. So. In this paper, some analyt-ical techniques, including X-ray diffraction (XRD), Scanning electron microscope(SEM), Differential scanning calorimetry (DSC), FT-IR, Ra-man spectroscopy, Elemental analysis (EA), carbon fiber tensile strength and density test, are used to study on the dry-jet and wet spinning PAN fiber structure and properties, their structure evolution during the thermal oxidation stabilization, carbon fiber structure and properties via a labora-tory scale continuous stabilization and carbonization facility. Eventually, the conclusion of this paper will be served for dry-jet wet spinning carbon fiber industrialization.The SEM, DSC and XRD characterization methods were used to study the two PAN fibers apparent morphology, crystalline structure and thermal properties. The results showed that wet spinning PAN fiber sur-face has obvious grooves which aligned along the fiber axis direction and its fracture morphology exhibits an oval cross section which shows jag-ged fracture. Besides, the cross section has a distinct skin-core structure. While the surface of dry-jet wet spinning PAN fiber is smooth and almost has no glooves, the cross section is smooth and regular, radial structure has no significant difference. The crystalline size of dry-jet wet spinning PAN fiber (100) face is 8.7nm, degree of crystallinity is 65.1%, and crystal orientation is 91.7%. While the crystalline size of wet spinning PAN fiber (100) face is 7.7nm, degree of crystallinity is 55.9%, and crystal orientation is 82.2%. As for the activation energy in N2 atmos-phere and air atmosphere, dry-jet wet spinning PAN fibers are 184.4kJ/mol,161.4kJ/mol respectively, wet spinning PAN fibers are 166.6 kJ/mol,156.0 kJ/mol respectively. The dry-jet wet spinning PAN fiber needs higher temperature to initiate reaction during the thermal oxi-dative stabilization.The XRD, FT-IR and OM characterization methods, density and oxygen content of stabilized fibers are used to study the two PAN fibers chemical structure, crystalline structure, skin-core structure and their properties evolution during the thermal oxidative stabilization. The results showed that:The initial temperature of thermal oxidative stabilization is 210℃ to 235℃. When the temperature under 225℃, the amorphous region of dry-jet wet spinning PAN fiber starts to cyclization, while the cyclization rate is low, and then gets higher when the temperature ups to 225℃. Wet spinning PAN fiber gets cyclization smoothly during the 210℃ to 235℃, and its cyclization rate is higher than dry-jet wet spinning PAN fiber at the same temperature. Besides, the dry-jet wet spinning PAN fiber only has cyclization during this low temperature and the cyclization degree is 9.9% to 37.0%, while the wet spinning PAN fiber cyclization degree is 24.1% to 50.2% and has oxidative dehydrogenation at the same time along with the cyclization reaction. The crystalline structure evolution of two PAN fibers are similar, the crystalline size and degree of crystallinity get lager firstly and then get down with the temperation getting higher. When the temperature gets to 215℃, the dry-jet wet spinning fiber gets the biggest crystalline size of 12.6nm and crystallinity degree of 67.9%, while the wet spinning fiber gets the biggest crystalline size of 11.2nm and crystallinity degree of 60.9% at the temparature of 210℃. The den-sity of two fibers change slightly during the low temperation, the final density of dry-jet wet spinning fiber is about 1.360 g/cm3 and wet spin-ning fiber is about 1.381 g/cm3.When the thermal oxidative stabilization temperature is of 260℃ to 285℃, the cyclization rate of two fibers get down. The cyclization degree of dry-jet wet spinning is 64.2% to 80.3%, wet spinning is 68.1% to 83.1%. When the temperature ups to 280℃, the cyclization degree gap of two fibers narrowed. As for the crystalline structure evolution, the origi-nal crystalline structure disappeared and new crystalline structure ap-peared at the 2θ≈25.5°. Besides, the new diffraction peak intensity of wet spinning fiber is stronger than dry-jet wet spinning fiber. The termi-nating temperature has a big influence on the fiber oxygen content and density, the oxygen content and density of dry-jet wet spinning fiber are 6.2% to 8.2%,1.333 g/cm3 to 1.397 g/cm3 respectively, while the wet spinning fiber are 7.4% to 8.7%,1.369 g/cm3 to 1.410 g/cm3 respective-ly.To observe the skin-core structure evolution during the thermal oxi-dative stabilization temperature of 225℃ to 270℃. When the tempera-ture was under 245℃, the fiber skin-core structure is not obvious, and then gets aggressive with the temperature up to 245℃. Dry-jet wet spin-ning fiber has a thin skin area, the skin and core don’t have obvious boundary. Besides, the black and yellow area distribute alternately. Com-pared with the Dry-jet wet spinning fiber, wet spinning fiber skin area appears black, core area appears yellow. The skin-core structure is very obvious.The Raman and XRD characterization methods are used to study the structure and properties of two PAN carbon fibers. The results showed that the max density and tensile strength of wet spinning carbon fiber are 1.796 g/cm3,4.38GPa respectively, while the dry-jet wet spinning carbon fiber are 1.818 g/cm3,5.17GPa respectively. The crystalline srtucture of two PAN carbon fibers are similar. With the crystalline size getting larger and lattice plane distance smaller, the tensile strength of PAN carbon fiber increases, but the dry-jet wet spinning PAN carbon fiber has larger crys-talline size and smaller lattice plane distance. The radial structure of dry-jet wet spinning carbon fiber is compact and nearly has no skin-core structure, while the wet spinning carbon fiber skin-core is obvious. The radial distribution of carbon fiber graphitization degree values R is calcu-lated by Raman spectroscopy. The results showed that R is low in the fiber skin area, and then get larger across to the core area. Besides, the value R of dry-jet wet spinning carbon fiber is much lower than wet spin-ning carbon fiber and in skin area and core area have small difference.In this paper, Rsc is defined as carbon fiber skin-core structure index that is skin area value R divided by core area value R. With the tensile strength increasing, the Rsc increases and closes to 1. The value Rsc of dry-jet wet spinning carbon fiber is larger than wet spinning carbon fiber. |
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