Studies On The Correlation Between Polyacrylonitrile Precursor Orientation And Tensile Modulus Of Carbon Fiber

Tensile modulus is an important property of carbon fiber. Generally, methods of regulating the tensile modulus of carbon fiber are changing carbonization temperature, draft ratio, and controlling the content of specific structure generated during pre-oxidation process. However, the regulating results are not obvious. Besides, there is mechanical properties difference between domestic carbon fiber and foreign product. Tensile modulus of CCF-1 and CCF-3 of some manufacturers is higher than that of Toray’s carbon fiber, and tensile modulus of CCF-4 of some manufacturers is lower than it. Therefore, studying the correlation between polyacrylonitrile precursor orientation and tensile modulus of carbon fiber and achieving the regulation of tensile modulus during spinning stage are significant.By changing draft ratio in the precursor preparation and spinneret aperture, polyacrylonitrile precursor with different orientation was prepared, and pre-oxidized fiber and carbon fiber were gained. Using XRD, Raman, DSC, FTIR, and sound speed measuring instrument, this thesis studied the relationship between polyacrylonitrile precursor orientation and tensile modulus of carbon fiber.The results showed that:1. Under the same pre-oxidation and carbonization conditions, tensile modulus of carbon fiber rises with the increasing crystalline orientation and amorphous orientation of polyacrylonitrile precursor, and crystalline orientation has a more obvious effect on tensile modulus of carbon fiber than that of amorphous orientation.2. Tensile modulus of carbon fiber rises with the increasing orientation of polyacrylonitrile precursor. Orientation of carbon fiber, lining thickness of crystallite and area of graphite net rise with the increasing orientation of polyacrylonitrile precursor, and these lead to the increasing tensile modulus of carbon fiber.3. Orientation of pre-oxidized fiber and aromatic structure size rise with the increasing orientation of polyacrylonitrile precursor. As turbostratic graphite structure is developed from aromatic structure of pre-oxidized fiber, PAN precursor orientation has an effect on crystalline structure size and orientation of carbon fiber.4. Polyacrylonitrile precursor orientation has an effect on pre-oxidation process. With the increasing orientation of polyacrylonitrile precursor, pre-oxidation degree of PAN fiber reduces. Tensile modulus of carbon fiber rise with the decreasing of pre-oxidation degree.