| For domestic PAN fiber, There are two mainstream production methods which are dry-jet wet spinning and wet spinning. Whether it is the production process or laboratory research the later has reached a perfect point.While the former started later, there are many blanks to fill out. At the same time as the dry-jet wet spinning method can implement fast speed and stability spinning and effectively reduce industrial costs,our country has gradually focus on this aspect. therefore, this paper is focus on dry-jet wet spinning and wet spinning me silk for comparison.Based on the different spinning characteristics of the two kinds of fibers,research the structural changes of the two kinds of fibers by the change of Pre - oxidation process temperature zone. And then on the basis of the best process to product two kinds of spinning fiber carbon fiber production. The purpose of this study is to study the chemical structure,crystal structure and morphological changes of carbon fibers in the process of pre-oxidation and carbonization .First of all, through SEM, DSC, XRD and other test work by the two kinds of fiber precursor It is concluded that the diameter of the two fibers is similar in magnitude, and the diameter of the dry-jet wet spinning fibers is slightly smaller and the surface is smooth and without defects.While the wet spinnig fiber diameter is slightly larger with roughness Surface and pleated dent. The activation energy of Peak1 characteristic peak of dry and wet fiber is higher while the activation energy of Peak2 characteristic peak of wet fiber is higher. Indicating that the pre-oxidation reaction stage of the wet and dry fiber cyclization reaction activation energy is high, the oxidation reaction activation energy is low. The results show that the diffraction peaks of the two different crystal faces of the dry and wet spinning fibers are larger than those of the wet spinning fibers.the grain size and the grain orientation degree of two kinds of fibers,indicating that the dry and wet spinning fiber quasicrystal content, the segment regularity is good, the crystal area along the fiber axial arrangement closely.In order to compare the trend of structural evolution in the two kinds of fiber production processes, it is necessary to optimize the process of the two kinds of fibers. Therefore, the experiment is carried out by pre-oxidation process of two kinds of fibers. It is found that the process changes of the different stages in the pre-oxidation process will have effect on the mechanical properties of the carbon fiber, and the influence of the early stage and the later stage is relatively large. The carbon fiber producted by the dry and wet spinning process can reach 5.02Gpa tensile strength and with a bulk density of 1.3766g / cm-3 while the carbon fiber producted by wet spinning of 4.45Gpa tensile strength and density is 1.3690g / cm-3. The degree of cyclization during the preoxidation process changes significantly by the change of Pre-period temperature in preoxidation,while the change of the oxygen content is smaller. In the comparison of the two kinds of fibers, the cyclization degree of the dry and wet spinning fiber is not obvious only about 35%, but the wetting fiber can reach about 50%. In pre-oxidation process, the latter part of the process temperature change has a great impact of oxygen content, the degree of cyclization also have a certain impact. There were no significant differences in the degree of cyclization and oxygen content between the two different spinning fibers. The final degree of pre-oxygen fiber cyclization between 70% -80%, and finally the pre-oxygen fiber oxygen content increased between 6% -7.5%.Then we use the best craft to product carbon fiber. and the samples were collected for FTIR, elemental analysis, SEM, EDS, XRD and other test methods in order to analyze the structural change. Dry-jet wet spinning fibers are subject to a high degree of crystallinity in the pre-period of pre-oxidation,cyclization growth is slow, in the medium and late cyclization reaction began to accelerate.while the wet spinning fiber in the early start began a much cyclization reaction. the two kinds of fibers of the final pre-oxygen fiber cyclization is basically similar. Under the optimum process, the oxidation reaction of the two fibers in the pre-oxidation period is less and the incease of oxygen content is not large.The final pre-oxidation fiber oxygen content of the wet fiber because of its special surface morphology is a little more than dry and wet spinning fiber. The bulk density of the two kinds of fibers is affected by the dehydrogenation reaction and the oxidation reaction. Dry and wet spinning fiber due to the reaction in pre-period of pre-oxidation is less,the density change is also gentle, in the latter period of pre-oxidation density began to accelerate the increase. and the wet spinning fiber because of its cyclization activation energy is small, the crystal area is less,the fiber density growth with the temperature change is more general along with period of pre-oxidation. The final pre-oxygen fiber radial oxygen elements are presented with a special U-shaped on behalf of the two spinning fibers prepared by the pre-oxygen fibers have a certain core structure. Wet spinning fiber outer layer of oxygen content is more, the core layer is smaller, and dry and wet spinning fiber is the outer layer of oxygen content compared to the wet fiber less core layer is more. As the outer structure of the outer structure is relatively easy to combine oxygen,when at a lower temperature has been combined with enough oxygen to form a dense ring structure and prevent the oxygen element to the internal diffusion process. and because of the internal structure of the dry and wet spinning fiber precursor is more perfect, leading to the distribution of the radial elements of the dry and wet spinning fibers, and the distribution of the radial oxygen elements in the wet fibers is "less inside and more outside". The final dry and wet spinning carbon fiber crystal structure is more perfect, The grain size is larger while the interplanar spacing is small, and the porosity is small too. The advantages structure of these carbon fibers are largely inherited from the superior performance of dry and wet spinning in the fiber precursor stage. The morphology of the two kinds of carbon fiber also has the difference. Dry and wet spinning fiber whether the surface or cross section morphology are relatively intact and has no holes structure or defect structure, while the wet fiber is very rough, from the cross section of the wet fiber inside and outside the gap Large internal structure loose, many defects. while dry and wet spinning fiber is very flat with the opposite. |
PDF Full Text Request