Chemical structure evolution and mechanism during pre-carbonization of PAN-based stabilized fiber in the temperature range of 350-600 °C

A series of PAN-based pre-carbonized fibers were prepared in pilot carbonization line at gradient temperature of 350-600 °C. DSC, FTIR, X-ray diffraction, EPR and elemental analysis were used to study the evolution of chemical structures in these pre-carbonized fibers. At the same time, the reaction mechanism during the pre-carbonization was also explored. According to the chemical structural changes, the process of pre-carbonization below 600 °C can be divided into three stages. Below 450 °C, cross-linking and aromatization are the main reactions accompanied by heat liberation and rearrangement of oxygen-containing groups. But around 500 °C the pyrolysis reactions acquire the priority and the aromatization structure is dominant in the fibers. Until 600 °C the ladder polymers cross-link to form the carbon basal planes, resulting in the growth of aromatization structures. Based on the dependence of fiber structure on temperature, the pre-carbonization technology was optimized.