The Effect Of Oxygen On The Progress Of Thermal Stabiliztion Of Pan-Based Fiber

Pre-oxidation is a pivotal step in the preparation of PAN-based carbon fiber. It functions as a connection from precursor to carbonized fiber, and has a very incompatible influence on the fiber. The process of pre-oxidation is very complicated and is affected by lots of factors, such as temperature field, time hierarchy, atmosphere and tension. Not too much research has been taken on the relationship between oxygen and the process of thermal stabilization of PAN precursor.This dissertation starts with evolvement and influence of oxygen both in the process of pre-oxidation and high temperature treatment, and gradually investigates the stabilization reactions (including dehydrogenization, cyclization, and oxidization) happened during the entrance of oxygen to the inside of fiber, and the influence of the oxygen deprivation on the composition and structure of fiber during pyrolysis. Different pre-oxidized fibers were prepared from a free-oil precursor by a continuous pre-oxidation with different conditions. Different measuring instruments and methods were applied to learn the influence of oxygen on the stabilization process of PAN precursor., such as FTIR, XRD, XPS, DSC, TGA-FTIR, PGC-MS, EA, ultramicrotomy, density gradient apparatus, and tensile strength. The results showed that:1. As pre-oxidation time extended in low temperature treatment, oxygen content increased linearly, while thermal stability of fiber increased with a decreasing rate.2. Oxygen content stayed high while the pre-oxidation temperature was high; thermal stability of fiber increased linearly as oxygen content increased. As the temperature gradient became dense, the increasing rate of oxygen content became high, whereas thermal stability of fiber increased not very distinctly as oxygen content increased.3. Oxygen content of fiber was as lower as the starting carbonization temperature became higher. The stabilization structure would probably be decomposed if the starting carbonization temperature exceeded450℃.4. Pyrolysis was divided into two sections, including dehydrogenization&cyclization in low temperature zone and cross linkage&rearrangement in high temperature zone. The deprivation form of oxygen was same in fibers with different oxygen content during heat treatment. The more denser the temperature gradient was, the less mass loss the fiber would have, and the less amount of pyrolysis gas would release in high temperature zone.