Study On Controllable Grafting Polymerization Of Carbon Fiber And Simulation Of Composite Interface

Carbon fiber reinforced polymer composites(CFRP)have many advantages,such as high specific strength,high specific modulus and good designability.Therefore,they have been widely used in aerospace,weapon,automobiles,sports equipment and building materials fields.However,carbon fibers are graphited at high temperatures in inert gas,so make few active groups on the carbon fiber surface,and the surface is chemical inert.As a result,there are poor wettability and interfacial interaction between carbon fibers and matrix resin,and the interface is prone to damage.It will seriously affect the overall performance and the service life of CFRP.In this paper,the comb-like polymer was introduced onto the carbon fiber surface via living radical polymerization to prepare comb-like polymer/carbon fiber multiscale reninforcement.The resulted multiscale reninforcement was used to reinforce the epoxy resin to prepare composites.The mechanical properties and interfacial properties of composites were characterized to study the influence of the introduction of comb-like polymer on the properties of the composites.In addition,molecular simulation was used to build the model of CFRP to investigate the influence of carbon fiber multiscale reninforcement on the interface from the perspective of interface energy.The specific steps to complete are as follows:(1)The surface pretreatment of raw carbon fiber(CF-Raw)with acetone-nitric acid and silane coupling agent(KH550)was carried out to obtain CF-KH550,and then the reversible addition-fracture chain transfer polymerization(RAFT)agent was grafted onto CF-KH550 surface via esterification.Finally,comb-like polymer(poly(4-vinylbenzyl chloride-g-glycidyl methacrylate),P(VBC-g-GMA))was grafted onto carbon fiber surface via RAFT and atom transfer radical polymerization(ATRP)to prepared carbon fiber multiscale reinforcement(CF-P(VBC-g-GMA)).Fourier transform infrared spectrophotometer(FT-IR),thermo-gravimetric(TG),X-ray photoelectron spectroscopy(XPS)results show that comb-like polymer was successfully grafted on carbon fiber surface,and the grafting rate is 26.37%.Field emission scanning electron microscope(FE-SEM)indicates that CF-P(VBC-g-GMA)surface was coated with comb-like polymer,and the grooves caused during the oxidation were healed.(2)The carbon fibers after each stage of modification were used as rinforcement,bisphenol A type epoxy resin(E-51)as matix,tri-vinyltetramine(TETA)as curing agent to prepare CFRP by using hot-pressing molding process.Compressive tests show that the monofilament tensile strength and multifilament tensile strength of CF-P(VBC-g-GMA)increase by 22.00% and 14.25%,respectively,compared to the raw carbon fiber.The bending strength of composite increases by 23.70%,and the interlaminar shear strength(ILSS)increases by 31.29%,compared to the raw carbon fiber reinforced composites.The interfacial shear strength(IFSS)of CF-P(VBC-g-GMA)monofilament increase by 101.88%,compared to the raw carbon fiber.The results of FE-SEM show that many carbon fibers are pulled out from the CF-Raw reinforced composites,and the pulled-out carbon fiber shows smooth surface.In contrast,few carbon fibers are pulled out from CF-P(VBC-g-GMA)reinforced composites,and the pulled-out carbon fibers are coated by resin.FE-SEM resultes demonstrate that the interfacial adhension between CF-P(VBC-g-GMA)and resin is improved,which leads to the enhancement of the interfacial shear strength.(3)The CFRP model constructed by Materials Studio(MS)was used to study the influence of interface layer on the mechanical properties of the composites from atomic scale.Geometrical optimization of the model was carried out by using Forcite as the computing environment via molecular mechanics calculation.The molecular dynamics was calculated in the NVT ensemble and Universal force field,and the calculation results show that the cross energy between carbon fiber surface and resin is the main factor to change the interface energy.The distance between carbon fiber and resin at interface of CF-P(VBC-g-GMA)reinforced composite was 16.84 ?,which was discreased by 23.42% compared to that of CF-Raw reinforced composite.The decrease in interface distance and the increase in interaction strength between carbon fiber and resin rsult in the increament in the interface strength of composite and the mechanical strength.