The Investigation Of Aggregation Structure Regulation Of Polyacrylonitrile Fiber And Its’ Influence On Pre-Oxidation Process

PAN based carbon fiber has been widely used in many fields. For application materials, internal structure determines the apparent performance. Therefore, the improvement of material performance is depending on the internal microstructure. The preparation of PAN precursor is a key step in the preparation of carbon fiber. The structure of PAN precursor can be directly transmitted to the pre-oxidized fiber, carbon fiber, thereby affecting its performance and application. External environment determines the accumulation structures of PAN precursor. The controllable preparation purposes can be achieved by understanding the relations between the establishment of aggregation structures and the spinning factors, and then it can guide the preparation of PAN precursor and carbon fiber. The study on the aggregation structure of precursor have been involved many times, mainly, some macro structure parameters, such as crystallinity, orientation degree. The research on the relationship between aggregation structure and the pre-oxidation extent mainly focused on the macro parameters.According to the research, PAN crystals have different crystal forms (Orthorhombic, hexagonal). Then, the fundamental effect of crystallinity, crystal orientation degree on pre-oxidation is which kind of crystal which has not yet been involved; Exploring the effect of crystal type and crystal plane on pre-oxidation can be very clear to the pre-oxidation reaction. The precursor can be prepared to cater to the pre-oxidation reaction. The study of the effect of PAN precursor aggregate structures on the pre-oxidation process has important guiding significance, which needs further investigation.In this paper, the relationships between the crystal properties (crystal type) and spinning factors are established. In addition, by exploring the evolution law, controlling the preparation of different crystal properties (crystal type) of raw silk, the influence of the structure on the pre-oxidation process is discussed. The fundamentally influence mechanism on pre-oxidation process is mentioned.In this thesis, the XRD method are used for characterizing the evolution of crystal features (crystal form), building the association of external factors and crystal properties. The IR method are established to illustrate the evolution of one-level structure (conformation). Relationships are built between external factors and structured. By studying the effect of crystal properties on the pre-oxidation process, we can explain the fundamental role of pre-oxidation reaction; crystal originates from one-level structure (conformation) and forms different crystal planes. Then we can achieve the analysis of the effect on pre-oxidation process fundamentally. The experiments also study the forming and changes of accumulation structures by Tensiometer, Rheometer, DSC, TMA and other instruments.The results indicate that:1, During the spinning process, the fiber is hexagonal/orthorhombic coexistence, irregular composite system. The change of the field environment can change the relative content of these two kind of crystals.2, Molecular chain conformation is inherent, depending on the properties of polymeric fluid. The change of external field will only affect the relative content of helical conformation; Helical conformation is more easily arranged into hexagonal.3, The pre-oxidation reaction initiates in helical conformation. Under the same spinning solution, Finally, pre-oxidation degree of fiber which possesses the high relative content of hexagonal and helical conformation is higher than the fiber with with low content of hexagonal and helical conformation.4, Molecular chain level structure determines crystal characteristics, finally affect the macroscopic parameters, such as the degree of crystallization, crystal orientation. Thus, the performance of the impact of macro parameters on subsequent oxidation reaction is emerged.Through this study, to explore the evolution of PAN aggregation structure during the spinning process, relationships are established between external factors and aggregation structures, from the level of Molecular chain level structure (conformation), the crystal properties, to the macro structure (different crystalline orientation, crystallinity), and impact on the pre oxidation process which depends on the effect of PAN precursor microstructure. The PAN precursor can be controlling prepared which provides certain guiding significance.