Preoxidized Structure Regulation Of PAN Fiber And The Influence On High Temperature Thermal Cracking And Restructuring Behavior

Complex Preoxidized structures was formed during the Polyacrylonitrile fiber pre-oxidation treatment, and the structures have a significant impact on the subsequent heat cracking and restructuring behavior. Different pre-oxidized structure leads to the high temperature cracking and restructuring behavior differences.In this paper, using means of IR, XPS, NMR to have a research on PAN fiber cyclized and oxidized structure evolution, using TG to study the pre-oxidized fiber cracking behavior, using Raman to characterized the structures of PAN fiber after thermal cracking and restructuring. Establishing the relationship between the pre-oxidized structure and cracking and restructuring behavior. The results indicated that:1、The weight loss process under inert atmosphere heat is divided into 1 zone (280℃-320℃),2 zone (320℃-400℃),3 zone (400℃-500℃),1 zone weight loss dues to the cracking of uncyclic linear chain,2 zone weight loss dues to the cracking of intermolecular cross areas,3 zone weight loss is mainly the cracking of not perfect cylized molecules. Oxygen enters to improve the crosslinking degree of molecules, weight loss peak move to high temperature region, finally only exist one weight loss peak, so as to improve the thermal stability of the fiber.2、Heat treatment at higher temperature to pre-oxidized fibers leads to different cracking behaviors, in a certain temperature (under 340℃), with the heat treatment temperature increased, PAN fiber has higher thermal stability. Higher temperature heat treatment of samples, damage the internal structure and promote the cracking behavior.3、During the heat treatment process, the cracking behavior does not affect the reorganization before 600℃, conducive to the better growth of graphite structure; with the increase of heat treatment temperature (after 600℃), thermal cracking of the fiber defects, expressed as Raman F WHM of peak G increased.4、Cyclic content increase will restrain the cracking, and the oxygen content increase will accelerate the cracking. Higher heat treatment to PAN pre-oxidized fiber can increase the cyclic content can restrain fiber cracking behavior. Higher cyclic content before pre-oxididation can enhance the binding ability of the oxygen, the oxygen content increase accelerates the cracking behavior. Cracking behavior leads to negative effect on density.In this paper, Study on the cracking regularity and effect of cyclic structure and oxygen structure on the cracking and restructuring behavior of high temperature heat treatment. Establish the relationship between pre-oxidized structure and cracking behavior.