Carbon Fiber Modified By Electrochemical Polymerization And Its Influence On Properties Of Composites

Carbon fiber reinforced epoxy resin composite possessed excellent physical and chemical properties,but the surface activity of carbon fiber and interaction between carbon fiber and epoxy resin were poor,so the mechanical properties of carbon fiber reinforced epoxy resin composites depended on interface properties between carbon fiber and resin matrix.To solve this problem,electrochemical polymerization of acrylic acid and acrylamide on carbon fiber was carried out by using cyclic voltammetry in the presence of H2SO4 as electrolyte.Cycles,monomer mass ratio,scan rate,electrolyte type and H2SO4 concentration had a significant effect on the electrochemical polymerization and electrochemical impedance spectroscopic behavior of modified carbon fiber.With increasing cycle numbers,carbon fiber surfaces had more polymers and the electrochemical properties of polymer film were more stable.When the mass ratio of acrylic acid and acrylamide was 3:1,the effect of carbon fiber modification was best.It was also favorable for the electrochemical polymerization with 0.2mol/L H+ and 0.05V/s.Compared to H2SO4 and NaOH,using LiClO4 as electrolyte was more favorable for the electrochemical polymerization.The Nyquist diagrams showed that the impedance spectra in the whole frequency range was a large capacitive arc and capacitive behaviors of coated carbon fiber were defined.FTIR,EDS and TGA were applied for the characterization of chemical composition,thermal stability of the copolymer on the carbon fiber,respectively.When the mass ratio of acrylic acid and acrylamide was 1:1,it was more possible to generate alternating copolymer of acrylic acid and acrylamide and the orderliness and length of chain segment would be better.A possible reaction mechanism of electrochemical polymerization was proposed,acrylic acid and acrylamide were grafted onto the carbon fiber surface by the reduction of carbon-carbon double bond.It was also suggested that the electrochemical polymerization reaction proceeds through an anion radical addition mechanism.The monomers were grafted onto the anion radical formed on carbon fiber surface during the electrochemical reduction.By testing the contact angle of ultrapure water and carbon fiber,compared with unmodified carbon fiber,the contact angle between the modified carbon fiber and ultrapure water was obviously decreased and always less than 90°,the carbon fiber surface activity was increased,and the wettability was also improved obviously.Systematic experiments were conducted to determine the mechanical property of carbon fiber/epoxy resin composites before and after modification.As a result,Compared with unmodified carbon fiber/epoxy resin composites,the tensile strength of modified carbon fiber/epoxy resin composites was improved greatly and it has been improved about 73% with 0.45% carbon fiber especially.The yield strength of the composites reinforced by the carbon fiber coated with the copolymers has been enhanced about 68.3%.After electrochemical modification,the elongation of untreated carbon fiber reinforced epoxy resin composites was nearly 1.88 times higher than the carbon fiber coated with the copolymer reinforced epoxy resin composites.Surface morphology of the polymer films on carbon fiber was investigated by using scanning electron microscopy.With increasing scan rate,polymer film grew along the axial direction of carbon fiber and many deeper trenches were found.The coarse part of carbon fiber formed more polymeric active points.The SEM of carbon fiber composite fracture showed that the surface of untreated carbon fiber was smooth and residual epoxy resin was not viewed,at the same time,clear void between carbon fiber and epoxy resin was observed,but the surface of modified carbon fiber became rough and epoxy resin adhered to the surface of carbon fiber,it showed that the interface performance between modified carbon fiber and epoxy resin was remarkable excellence.