Formation and Evolution of sp² Hybrid Conjugate Structure of Polyacrylonitrile Precursor during Stabilization

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.