In low-temperature carbonization stage, stabilized polyacrylonitrile (PAN) fibers are pyrolyzed and recombined to transform into low-temperature carbonized fiber with rudiment of turbostratic graphite structure. The temperature regulation of low-temperature carbonization has an important influence on the structure and performance of the final carbon fibers. The reaction process of stabilized fiber during low-temperature carbonization stage, the effect of the regulation of low-temperature carbonization temperature gradient on the structural evolution of stabilized fiber and the structure and performance of carbon fiber were studied through 13C-NMR, Raman, XRD and mechanical property analysis. The results indicate that: in the process of low-temperature carbonization heat treatment of stabilized fiber, the carbon structure shows the degree of branched chain reaches a maximum of 0.99, after heat treatment at 450 ℃. When the heat treatment temperature reaches 550 ℃, the main reaction is the recombination crosslinking reaction of stabilized fiber's aromatic chain segments. The low-temperature carbonization temperature gradients affect the structural evolution of stabilized fibers. When the temperature gradient is 350-450-650 ℃, the 13C-NMR shift of the —C C group in the low carbon fiber treated at 450 ℃ is the largest, the branching crosslinking reactions in fiber are the most, causing the d002 of the low carbon fiber treated at 650 ℃ and the IA/IG of the corresponding high-temperature carbon fiber are the largest, the relative content of amorphous carbon is the largest and the mechanical properties of the final carbon fiber are the worst. However, when the temperature gradient is 350-550-650 ℃, the cracking and recombination crosslinking reaction in fiber are carried out in an orderly manner, resulting in the structure of low-temperature carbonized fiber and carbon fiber more perfect, and the density and mechanical properties of carbon fiber are improved.
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