Structural Evolution And Kinetic Analysis During Oxidative Stabilization Of Polyacrylonitrile-based Fibers

Pre-oxidation of polyacrylonitrile(PAN) precursor fibers is an essential process that affects the quality of carbon fibers. It is important to study intensively on the thermal behavior and reaction mechanism of PAN fibers, and on the structrul evolution during the oxidative stabilization process.Time and temperature are two important technological conditions in oxidative stabilization processes. In this paper, the effects of pre-oxidation time and pre-oxidation temperature upon thermal behavior, structure evolution, cyclization kinetics of fibers were studied by means of differential scanning calorimetry (DSC), fourier transform infrared spectroscopy (FTIR), element analysis (EA), nuclear magnetic resonance (NMR),density, and so on. The results showed that:1.Thermal behavior of PAN precursor can be affected by atmospheres obviously. In nitrogen, the centralized exothermic phenomenon of PAN fibers is apparent. While in air, the exothermic phenomenon is relieved, and in the initial stage of pre-oxidative reaction, it can be promoted by oxygen and the initial reaction temperature is lowered, in the later stage, the reaction is restrained by oxygen and the end temperature is increased.2.Oxygen-containing structure of pretreatment fibers can affect consequent reaction obviously, generating double peak of DSC exotherm. 3.The effect of pre-oxidation time is related to temperature, at 180℃, the cyclization index, density, relative cyclization index remain virtually unchanged over time. At higher temperature, they increase gradually over time and the trend slow down.4.Pre-oxidation extent and density of PAN fibers are affected greatly by pre-oxidation temperature. With the temperature rising, the pre-oxidation extent increase obviously and the trend become pretty obvious, which showed that the effect of temperature on them are more obvious than the effect of time.5.Cyclization kinetics parameter can be obtained by cyclization index and the result is consistent with Kissinger method and Ozawa method.