Abstract
The generated sp2 hybrid conjugate structure of a C atom, which resulted from the chemical reaction affected by temperature and time, is an effective six-membered ring planar structure of the final carbon fiber. This kind of hybrid conjugate structure determined the formation of the final structure and mechanical properties of carbon fiber. In this paper, the formation and evolution of sp2 hybrid conjugated structures of PAN precursor during thermal stabilization were investigated by Raman, UV-vis and 13C-NMR methods. The results indicated that with the increase of stabilization temperature, the degree of the sp2 hybrid conjugated structure of stabilized PAN fiber increases “linearly”, while the content of the sp2 hybrid carbon atoms increases with “S-type”. The final sp2 hybrid conjugated ring structure is mainly composed of single-ring, double-ring, triple-ring, and double-bond structures. Compared with the time factor, the temperature effect plays a decisive role in the formation of the sp2 hybrid conjugate structure.
Highlights
PAN-based carbon fiber has applied in various fields due to its unique properties such as high ratio strength and modulus
Chemical and structural transformations occur already at the stage of fiber production [1,2,3,4]. Thermal stabilization is another key process of the preparation for polyacrylonitrile (PAN)-based carbon fibers, in which PAN linear molecular chains are transformed into a heat-resistant ladder structure through chemical reactions
Since it is an initial stage of the organic–inorganic structural transition, thermal stabilization has had an important influence on the properties of final carbon fibers [5,6,7,8]
Summary
PAN-based carbon fiber has applied in various fields due to its unique properties such as high ratio strength and modulus. Thermal stabilization is another key process of the preparation for polyacrylonitrile (PAN)-based carbon fibers, in which PAN linear molecular chains are transformed into a heat-resistant ladder structure through chemical reactions. It is of great significance to study the formation of the sp hybrid conjugated structure in the process of thermal stabilization for obtaining high-performance carbon fibers. The effects of temperature and time on the formation and evolution of sp hybrid conjugated structures of PAN thermal-stabilized fibers were studied by Raman spectroscopy. The crosslinking of this conjugated ring structure, that is, the formation of the skeleton of the ladder structure, was traced by UV-visible absorption spectroscopy (UV-vis) and nuclear magnetic spectroscopy (13 C-NMR)
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