The Formation Mechanism For The Radial Structure Of Pan Fiber During Pre-Oxidative Stabilization

PAN fiber will form the skin-core structure in pre-oxidation process. And the difference of radial structure will lead to structural defects of the final carbon fiber and affect the mechanical properties. The cyclization leads that the structure of surface become compact. And the compact structure hinder the diffusion of oxygen molecules in air to the inside of the fiber, thereby oxidation degree of core is much low. According to the view many scholars put forward a series of improvement scheme which can eliminate skin-core structure formed during pre-oxidation process.According to the pre-oxidation behavior and characteristic, this thesis questioned the generally accepted view of physical barrier, and through the research of the cyclic structure and oxidation behavior. The oxidation reaction is the main reason resulting in the inhomogeneity of radial structure is revealed. The results show that:1. In the pre-oxidation process, the reason of uneven radial structure is that oxygen structure is not evenly distributed in the radial direction; and the oxidation reaction occurs immediately after formation of cyclic structure, which leads the oxygen containing of surface is more than the core part.2. With the increase of temperature, the content of the imine gradually increased and then decreased. The content of conjugation and enamine increased with the increase of temperature, and the growth rate of enamine was faster.3. At the same temperature, there are no chemical reactions with the extension of time in the fiber. The time characteristics are the change of the extent of chemical reaction under a certain temperature.4. The enamine of PAN fiber was oxidated more easily than other characteristics structure. Then the color oxygen structural is formed. It leads to color differences in the radial direction of fiber.5. The formation mechanism for the radial structure of PAN fiber during pre-oxidative stabilization:In this process, the oxidation reaction accurs immediately after the formation of enamine in PAN fibers, at the same time, the new enamine is generated and further oxidated. The enamine on the surface continuously reacts with oxygen so that oxygen is hard to diffuse into the core of fiber. So the uneven radial structure forms.