The Research Of The Chemical Structure And The Temperature Dependence During The PAN Fiber Stabilization Process

The stabilization of polyacrylonitrile precursor fibers (pre-oxidation) process is one of the key steps of carbon fiber technology. Investigating the chemical reaction of PAN fiber functional groups, mastering the relationship between the chemical structures, chemical reactions and temperature, which have significant importance for controlling the structure that the PAN fiber stabilization turns forming and the final structure of carbon fiber.In this paper, we take PAN fibre from homopolymers as research target, taking heat treatment under N2 in temperature sequence from low to high in order to study the new generative structures at different temperature,then figure out how the dominant reactions of PAN fiber functional groups dependence on temperature and speculate the reaction mechanism.In virtue of DSC,FT-IR and NMR techniques, we work over the heat effect, chemical structures, the relationship between chemical reactions and temperature. And found that:1. Under N2 atmosphere, the heat reaction of PAN fibre has high activation energy, which means it need high temperature to reach to the energy barrier. Whereas, owing to the presence of oxygen under air, the activation energy is low so the heat reaction could be carry through at low temperature. And at the same temperature, the reaction constant under N2 is much bigger than that of under air.2. PAN fiber's functional groups CN, CH2, CH have different chemical reactivity, C=N bond in PAN molecules has a low activity energy prior to form free radicals, its initiate cyclization reaction and then transforms into a C=N bond at 150℃. CH2\CH group need a higher activation energy to initiate dehydrogenation. At 170℃, the C=N bond reacts with a C=C group that resulted from CH2/CH-functional-group dehydrogenation. This reaction contribute to the conjugate structure,-C=N-C=C-3. At the range of 170℃-260℃, Cyclization and dehydrogenation reactions occur during the heat treatment,then the conjugated skeleton structure of-C=C-C=N-is gradually increased. Before 230℃, nitrile group leads a dominant reaction, it evidently disappear at 230℃. Over 230℃, dehydrogenation reaction still happens. 4. Over 260℃, Polyacrylonitrile intramolecular occurs isomerization reaction, and crosslinking reaction occurs between molecules,finally PAN fibers form the stable ladder structure in a plane.