Andic oxidation of high-modulus carbon fibers in sulfuric acid under different electric fields

Abstract

The inert surface of high-modulus carbon fiber leads to the weak interface between it and the resin matrix， which limits the performance of high-modulus carbon fiber composite in many application scenarios. Anodic oxidation is the only surface treatment technology that can be combined with carbon fiber production lines until now，but the commonly used alkaline electrolytes represented by ammonium bicarbonate exhibit limited effect on the oxidation of high-modulus carbon fiber. The acidic electrolyte system has stronger oxidation ability， lacks systematic researches on anodizing mechanism . In this paper， dilute sulfuric acid was used for the anodic oxidation for carbon fiber with a modulus of 371 GPa. The effects of key factors such as current density， electrolyte concentration on the polar structure of the surface of high-modulus carbon fiber were systematically studied， and then the effects of surface treatment on the interfacial shear strength of carbon fiber/epoxy resin composites were investigated. The correlation between surface treatment factors and interfacial properties of composites was established. The results show that after the treatment， the surface morphology and graphitized structure of the carbon fiber are maintained， and oxidation reactions occur in the amorphous carbon and aromatic ring structure regions of the carbon fiber. After the reaction， the graphitization degree of the fiber decreases apparently， the surface energy increases， and the content of surface oxygen-containing functional groups increases. When sulfuric acid concentration is 1.0%（mass fraction） and current density is 0.26 mA/cm2， the surface energy of carbon fiber is the highest （57.7 mN/m）， which is 62.08% higher than that of untreated carbon fiber. The interfacial shear strength between carbon fiber and epoxy resin reaches 80.9 MPa， which is 2.7 times higher than that of untreated one corresponding to 21.8 MPa.Furthermore， the single fiber tensile strength of the treated carbon fiber exhibits undamaged.

Keywords

• high-modulus carbon fiber
• anodic oxidation
• sulfuric acid
• interfacial performance
• tensile strength