Method for preparing polyacrylonitrile-based carbon fiber

The invention provides a method for preparing a polyacrylonitrile-based carbon fiber which is obtained through the preoxidation, low temperature charring, and high temperature charring of a polyacrylonitrile precursor. The peroxidation and the high temperature charring in the invention have fixed technology conditions. Under the conditions of a fixed low temperature charring temperature and a fixed operating speed, through changing the extending rate of the low temperature charring, different extending rates in each low temperature charring technology are realized. In the low temperature charring stage, about 43.3% of the fiber weight is pyrolyzed. Through controlling the extending rate, increasing the compactness and orientation degree of the carbon fiber, decreasing fiber surface defects, namely the fiber defect number, and decreasing the defect size, excessive tension which causes filament breakage, broken filament, and the like can be avoided, fiber defects further increased by an incomplete reaction caused by excessive tension can also be avoided, thereby improving the mechanical properties of the carbon fiber product, and the tension strength of the carbon fiber can reach 4621 Mpa.