Abstract
The stabilization of PAN-fibers without additional co-monomers was investigated with thermo-gravimetry and evolved gas analysis (FTIR-spectroscopy and MS-spectrometry). One fiber type had been drawn after spinning, while the other was used as-spun. During the thermal treatment, fiber shrinkage was either restricted or unrestricted. Investigations of influencing chemical and physical reactions regarding this restriction were conducted. Differences in the mass loss and gas emissions were observed, depending on the strained or unstrained state of the fibers. The change of crystallinity and molecular orientation of the fiber as reason of the measured variations was discussed. The emission of ammonia and other nitrogen containing gases (supposedly nitriles/ isocyanates) could be attributed to different aspects of the stabilization process. The length restriction resulted in a change in ammonia emission, associated with the cyclization reaction of poly acrylonitrile. The onset and amount of side reactions were influenced as well.
Highlights
Carbon fibers established themselves as a new material class of lightweight high performance fibers for composites [1]-[3]
Certain aspects of the reaction processes will be further analyzed by the results from evolved gas analysis
The reactions of PAN fibers under stabilization conditions were studied by thermogravimetry and coupled evolved gas analysis
Summary
Carbon fibers established themselves as a new material class of lightweight high performance fibers for composites [1]-[3]. (2016) Influence of PAN-Fiber Stretching during Thermal Treatment on the Stabilization Reactions. PAN fibers undergo a series of reactions resulting in a material structure suitable for further carbonization treatment. Three main reactions have been established: 1) Cyclization of neighboring nitrile groups leads to the formation of ring structures in the molecule. 2) Dehydrogenation results in the formation of double bonds and (in combination with cyclization) partially aromatic structures mostly conjugate. 3) Oxidation is leading to oxygen functional groups in the arising ladder molecule. The result is a cyclized, partially aromatic structure with oxygen functional groups that does not fuse or degrade in the high-temperature carbonization treatment. Side reactions like chain scission as well as degradation have to be taken into consideration regarding the mechanism of structural changes during stabilization, dehydrogenation and oxidation
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