Preparation Of C-Type Pitch-Based Carbon Fiber And The Mechanism Of Its Anode Oxidation

The anodic oxidation mechanisms of pitch-based carbon fiber and the adhesion between carbon fiber and matrix were studied in this paper.The isotropic pitch was reformed by Naptha cracking bottom (NCB) oil. The C-type carbon fiber was spun by it. Different type carbon fiber such as round, hollow, bended and C shaped can be spun with C-shaped nozzles in variation spinning temperature. The tensile strength of carbon fibers was chiefly related to the oxidation time and carbonization temperature if oxidation temperature was fixed. Under optimal oxidation time the tensile strength of carbon fibers was increased.Surface anodic oxidation treatment of isotropic C-type pitch-based carbon fiber was carried out with our previous self-designed apparatus. The oxygen functional groups increased and the interfacial adhesion between carbon fiber and matrix improved. However, the increase was limited because the facts of anodic oxidation have not been considered completely.So the anodic oxidation apparatus was mended and C-type carbon fibers were treated again. By the XPS, the Ols/Cls ratio of fibers was improved to 22.91%; the functional groups were changed regularly. With the observe of SEM and AFM, the anodic oxidation mechanism of isotropic pitch-based carbon fiber was brought forward based on the theories of the electrochemical.The surface anodic oxidation treatment of carbon fiber was a process of functional group's reaction balances on the fiber's surface, that is the process of the carbon atom and its functional groups become to -COOH and CO2 finally. Many reaction were occurred in this process simultaneous, one reaction would be occurred first if its enthalpy small than others. Functional groups' reaction was the main reaction under low current and reaction of occurring to CO2 that is etched on fiber's surface became to main reaction if the current or time was improved. The surface of the carbon fiber would become smoother when the etching occurred. While the -COOH on the surface improved to a high level, the anodic oxidation would become slow or stopped. The amounts of every kinds functional group would be fixed.The distinguishability of SEM is too poor to distinguish the small change on the surface of CF after treatment. AFM illustrated the surface form on a microscopic scale effectively compared to SEM. Combining XPS with AFM can characterize the process of electrochemically oxidizedpitch-based carbon fiber.The adhesion between CF and matrix was improved while the CF was treated. The improvement of adhesion mainly depends on the functional groups and has a little relationship to the roughness of the CF's surface.