Regulation Of Surface Chemical Structure Of Carbon Fiber By Anodic Oxidation Based On Sulfuric Acid

The interfacial bonding between carbon fiber and resin matrix is the key point in the preparation of carbon fiber reinforced resin matrix composites,and the weak interfacial properties mask the mechanical properties of carbon fiber.The elevated modulus of carbon fiber brings challenges to the interfacial properties of the composites.The traditional anodic oxidation technique with ammonium bicarbonate as the electrolyte has limited effect on the surface treatment of high modulus carbon fiber.Exploring new anodic oxidation methods is of great value to solve the interfacial problems of high modulus carbon fiber.Based on the systematic summary of the electrochemical behavior of different electrolytes under the electric field and the mechanism of anodic oxidation on high modulus carbon fiber surface,this thesis selected dilute sulfuric acid as the electrolyte and systematically investigated the influence of key factors such as current density and electrolyte concentration on the polar structure of high modulus carbon fiber surface.Then,the effect of surface treatment on the interfacial shear strength(IFSS)of carbon fiber/epoxy resin composite was investigated.The correlation between the surface treatment factors and the interfacial properties of the composites was established.On this basis,the effect of surface treatment on carbon fibers with different moduli was further investigated,and the effect of graphitized structure of carbon fiber surface on the oxidation reaction process was explored.The results showed that:(1)Taking carbon fiber with tensile modulus of 371 GPa as the research object,and 0.5 wt%sulfuric acid aqueous solution as the electrolyte,the current density can significantly affect the surface energy of carbon fiber.As the current density of surface treatment increases,the contact angle of carbon fiber with water and diiodomethane decreases,the surface energy of carbon fiber increases,and the interfacial adhesion between carbon fiber and epoxy resin increases.When the current density was 0.26 m A/cm~2,the IFSS of the carbon fiber/epoxy composite was the largest,reaching 77 MPa,which is 2.5 times higher than that without treatment.The results of Raman spectroscopy and scanning electron microscope tests proved that the anodizing sites were concentrated at the amorphous carbon and the edge of aromatic ring structure,and the graphite structure of carbon fiber was not destroyed,and no significant etching occurred on the surface of carbon fiber.The results of single fiber tensile tests showed that the mechanical properties of carbon fiber did not decrease before and after surface treatment.(2)Under the current density of 0.26 m A/cm~2,increasing sulfuric acid concentration can enhance the surface activity of carbon fiber and improve the IFSS of the fiber and epoxy resin without significantly reducing the tensile strength of carbon fiber.When the concentration of sulfuric acid was 1.0 wt%,the surface energy of carbon fiber was the highest(57.7 m N/m),which was62.08%higher than that of untreated carbon fiber,and the IFSS was the highest(80.9 MPa),which was 2.7 times higher than that of untreated carbon fiber.If the electrolyte concentration continued to increase,the contact angle of carbon fiber increased,the surface energy decreased,and the IFSS decreased,indicating that the high electrolyte concentration would lead to the removal of functional groups on the carbon fiber surface.(3)As the tensile modulus of carbon fiber increased from 304 GPa to 455GPa,the surface energy decreased from 38.51 m N/m to 32.32 m N/m,and the chemical inertness of the fiber increased significantly.Surface treatment with sulfuric acid as electrolyte can significantly improve the surface energy of carbon fiber and the IFSS of composites.Under the conditions of sulfuric acid concentration of 1.0 wt%and current density of 0.26 m A/cm~2,surface treatment can effectively improve the surface energy of carbon fiber with different moduli.When the carbon fiber modulus was 455 GPa,the surface energy of carbon fiber increased from 32.32 m N/m to 43.73 m N/m,and the IFSS correspondingly increased from 11.8 MPa to 41.7 MPa by 253.4%.Compared with the previous treatment with ammonium bicarbonate,the maximum increase of interlaminar shear strength(ILSS)of carbon fiber/epoxy resin composite was 86%,so the acid electrolyte system showed significant comprehensive advantages.