Surface Modification And Application Of Carbon Fiber Based On Electropolymerization Technology

With the rapid development of high-performance composite materials in the world,carbon fiber?CF?as an important new reinforcement material have been widely used in aerospace,chemical and many other fields.However,CF has a low surface energy and poor interface with a resin,which makes it difficult to exhibit the excellent performance of the CF reinforced composites.Therefore,the surface properties of CF and resin groups were improved by modifying the surface of CF.Electrochemical polymerization was a method of polymerizing on the surface of electrode to form a polymer.The method has the advantages of simple operation,easy adjustment and control of process parameters,thus became a hot spot in the surface modification treatment of CF.In this paper,LiClO₄ was used as electrolyte and acetonitrile was used as solvent.In order to improve the surface properties of CF,CF was modified by cyclic voltammetry electrochemical polymerization using a biocompatible methoxy polyethylene glycol acrylate?MPGA?and a highly conductive polythiophene?PTh?as monomers.The effects of monomer concentration,cycle number,scan rate and electrolyte concentration on the peak potential and current of electropolymerization were studied.In addition,the effect of different concentration ratios of MPGA and PTh on electrochemical copolymerization was studied.Electrochemical properties and mechanism of the modified CF were analyzed by AC impedance spectroscopy.The polymer structure on the surface of CF was characterized by infrared spectroscopy?FTIR?,energy spectrum analysis?EDS?,thermogravimetric analysis?TGA?,contact angle test and scanning electron microscopy?SEM?.The results showed that the increase of number of cycles lead to an increase in the surface polymer of CF.When MPGA was circulated 60 times and PTh cycle was 50 times,the electrochemical polymerization reaction was completed.When MPGA and PTh were electrochemically copolymerized on the surface of CF with a concentration ratio of 3:1,the double-layer interface capacitance C_dll value reached the maximum,and the electrochemical copolymerization effect of CF was the best.The reaction mechanism of electrochemical polymerization obtained by analog circuit analysis is a free radical polymerization mechanism,and the polymerization mechanism conformed to the cationic radical polymerization.Infrared analysis showed that the surface of CF?MPGA-CF?of electropolymerized MPGA was grafted with C=O,C-O-C functional groups.The surface of CF?PTh-CF?of electropolymerized thiophene was grafted with C=C,C-S-C functional group.The electrochemically copolymerized MPGA and thiophene CF?CMP-CF?were grafted with C=O,C-O-C,C=C and C-S functional groups.The infiltration property of CF was improved after electropolymerization modification,from hydrophobic to hydrophilic,and the contact angle of MPGA-CF was decreased most obviously 47.4o.The thermal performance analysis found that the grafting rate of MPGA-CF was about 10%.The SEM photograph showed that there were a large amount of polymer on the surface of the modified CF,which effectively improved the surface structure of CF.The effect of CF modified by electropolymerization on the interfacial properties of epoxy resin matrix composites were investigated by using MPGA-CF and PTh-CF as reinforcing phases.The tensile strength of MPGA-CF and PTh-CF/epoxy composites increased by 156.4%and86.37%,respectively.The interlaminar shear strength?ILSS?increased by 134.81%and 76.75%respectively,and the yield strength increased by 4.1 times and 1.76 times,respectively.SEM photographs show that there were large gaps and grooves between the unmodified CF and resin matrix,and the interfacial adhesion is poor.The bond between MPGA-CF,PTh-CF and epoxy resin was good and no obvious grooves on the cross sectiont,and the interface performance is obviously improved.