Study On Surface Treatment And Properties Of Carbon Fiber With High Inertness

The content of non-carbon elements on the surface of the high-modulus carbon fiber(high inert surface,HISCF)is extremely low due to the high temperature graphitization treatment.Moreover,the highly graphitized structure makes its surface chemically stable and difficult to be oxidized.The aim of this paper is to establish an efficient and practical surface treatment method.Firstly,the influence of electric field environment on the surface structure of HISCF was discussed,and the optimum anodizing conditions were determined.Next,the effects of electrolyte systems on the properties of HISCF and its composites were studied,and the suitable electrolytes for HISCF were selected.Then,the effects of two-stage anodic electrolytic oxidation on the mechanical properties of HISCF and its composites were discussed.Finally,a method was proposed to improve both oxygen and nitrogen groups by combining electrochemical oxidation and electrochemical grafting.The results show that:(1)When NH4HCO3 is used as the electrolyte,the oxygen content on the surface of HISCF can be increased by increasing the current density or increasing the electrolyte temperature within a certain range,while the oxygen content on the fiber surface tends to be stable or even slightly decreased after exceeding this range.However,due to the high inertia of the fiber surface,the current density and electrolyte temperature have little influence on the chemical composition and graphitization structure of the fiber surface.Changing the electric field environment can not effectively improve the oxidation effect of carbon fiber on high inert surface.(2)The oxidative property of acid electrolyte to carbon fiber with high inert surface is stronger than that of basic electrolyte.NH4HSO4 has the strongest ability to oxidize and etch the fiber surface.After surface treatment,the fiber surface grooves are significantly deepened and widened,the surface roughness is significantly increased,and the surface oxygen content is significantly increased.The oxidation capacity of NH4H2PO4 is similar to that of(NH4)2SO4,but the etching capacity of(NH4)2iSO4 is slightly less than that of NH4H2PO4.The oxidation and etching abilities of NH4HCO3 are relatively weak.After surface treatment,the roughness does not change much and the oxygen content does not increase significantly.NH4HSO4 and NH4H2PO4 have great damage to the tensile strength,which seriously affects the performance of carbon fiber composites after surface treatment.(3)When NH4HCO3 and(NH4)2SO4 are used to modify the HISCF by two-stage anodizing treatment,less active groups are generated on the fiber surface due to low oxidation strength of the method for NH4HCO3?NH4HCO3.The oxidation strength for(NH4)2SO4?(NH4)2SO4 is strong,but it will cause excessive oxidation of the fiber surface.More active groups will generate on the surface of HISCF when using the method of cross-combination between NH4HCO3 and(NH4)2SO4,which will effectively improve the interface bonding between HISCF and resin matrix.(4)When the combination of electrochemical oxidation and electrochemical grafting was used to treate the surface of HISCF,the addition of NH4HCO3 electrolyte in DETA solution will promote the grafting reaction of DETA and increase the grafted amount of DETA on its surface.The addition of(NH4)2SO4 electrolyte can not only promote the grafting reaction,but also further oxidize the surface of the fibers to produce more oxygen-containing groups.This method can greatly improve the ILSS of the composites while maintaining the tensile properties of the fibers.