The Radial Structure Of PAN Fibers And The Correlation Between It And Pre-Oxidation Reaction

PAN fibers prepared by wet-spinning had significant difference in theradial structure; the macroscopic difference was mainly the difference of densedegree. This was caused by solidification formation mechanism. Meanwhile,oxidized fibers had gotten the skin-core structure caused by the radial structureof PAN precursors during pre-oxidation period. Now, by changing thepre-oxidation process conditions to control the formation of skin-corestructure is common, but the oxidation reaction is very complicated, so thatthe oxidized fiber structure was affected by many factors easily, such astemperature or time. Therefore, it’s very difficult to regulate the formation ofskin-core structure.In this thesis, the mechanism of the dissolution of PAN fibers inDMSO/H2O solution was investigated. Based on the dissolution mechanism,combined with scanning electron microscopy (SEM), the radial structure ofPAN fibers prepared in different conditions of the coagulation process and thedesiccation process during spinning process was analyzed. The effect of different radial structure of PAN fibers on the pre-oxidation reaction wasstudied by Fourier Transform Infrared spectroscopy (FT-IR), DifferentialScanning Calorimetry (DSC), X-ray powder diffraction (XRD) and densitytest. The skin-core structure of pre-oxidized fibers was also characterized. Theresults were showed as following.1. The dissolution of PAN fibers in DMSO/H2O solution develops fromthe inside out. On the basis of this dissolution mechanism, the characterizationof PAN fibers radial structure is established mainly contained the specificconditions, the experiment methods and the definition of evaluations.2. By studying the variation of the radial structure of PAN fibers duringspinning process, the coagulation and desiccation process are the key linksthat affected the formation of the radial structure.3. There are different influences on pre-oxidation reaction when theradial structures of PAN fibers are different from each other. When the densedegree of radial structure of PAN fibers is low and dense degree of theboundary region is close to core, but different from skin, it is moreadvantageous to pre-oxidation reaction; however, it is more likely to form thesignificant skin-core structure.Through the research, the characterization of the radial structure of PANfibers was established, the variation and the influencing factors of the radialstructure during spinning process was revealed, and the correlation between the radial structure and pre-oxidization reaction was analyzed. Above all, thepre-oxidized fibers skin-core structure can be controlled.