Surface Treatment Of Polyacrylonitrile Based High Modulus Carbon Fibers

First, anodic oxidation of polyacrylonitrile(PAN) high modulus carbon fibers through was investigated in comparison with that of ordinary modulus carbon fibers. The mechanical and interfacial properties of the treated fibers along with their surface structures were studied with X-ray photoelectron spectroscopy, atomic force microscope, contact angle analyzer, tensile strength instrument and Raman spectrometer. The results show that the high modulus carbon fibers were inactive during anodic oxidation for the higher graphitic carbon, while the ordinary modulus carbon fibers were active and the surface oxygen content got saturated soon. The dynamics of anodic oxidation for the fibers can be described by a homogenous thickness reduction model, which indicated that the kinetic constant of anodic oxidation for the high modulus carbon fibers was only one sixth of that for the ordinary modulus carbon fibers. Surface roughness contributed to the improvement on fiber/matrix adhesion as well as the surface oxygen content. The achievement of the surface treatment was proved by Raman spectroscopy mapping the stress of the fiber inside an epoxy resin droplet. The increase of interfacial shear strength from the untreated high modulus carbon fibers to the anodized ones was 160%(from 65 to 170 MPa), much higher than 70% that from untreated ordinary modulus carbon fibers to the anodized ones (from 135 to 230 MPa).In order to give a greater improvement of the interfacial shear strength between high modulus carbon fibers and matrix, poly(maleic acid-co-itaconic acid) were electrografted on fibers in anode with the presence of dilute sulfuric acid medium. Anodic oxidation and electropolymerzation conducted simultaneously. Fourier transform infrared spectrometer indicates that electropolymerization brought more carboxylic groups onto the surface of high modulus carbon fibers, which could form free radical sites, then the mode of reaction was inferred. The SEM images indicate that polymeric nuclei formed first and then grew to be a continuous coating. The thickness of the coating grew with the increased of charge density. The achievement of the polymer layer was proved by Raman spectroscopy mapping the stress of the fiber inside an epoxy resin droplet. The results show that interface shear strength has a greatly increase from 65 to 174 MPa with the charge density of 0.9C/cm2, which consider that the effect of electropolymerzation is better than electrochemical oxidation.