Modification Of Carbon Fiber By Grafting Pyrocarbon/PAMAM Dendrimers And Performance Of Epoxy Composites

Due to the superior mechanical properties including high-specific strength and modulus,low density and thermal expansion,heat resistance,and chemical stability,carbon fibers as reinforcement materials have provided the impetus for developing high-performance composite materials.Nowadays,carbon fiber reinforced plastics(CFRP)are widely applied in the industries of aeronautic,aerospace,sporting goods,as well as new energy.However,carbon fiber surface is smooth and chemically inert,which leads to the poor bonding performance between carbon fiber and polymer matrix.This weak interfacial property limits full exploitation of its excellent comprehensive performance in composite material.In order to increase the surface activity of carbon fiber,it is necessary to modify the carbon fiber surface via chemical or physical method,aiming to promote the interface bonding strength.At present,many surface treatment methods will more or less cause some damage to the tensile strength of the carbon fiber body,making it impossible to improve both the interfacial bond strength of the composite material and fiber intrinsic strength.Here,carbon fiber/epoxy composites,which are commonly used in advanced polymer matrix composites,were chosen as the research system.Based on the surface structure characteristics of carbon fiber,different generations of PAMAM dendrimers are selected,combined with a variety of modification methods,to treat the surface of the carbon fiber including atmospheric pressure plasma,pyrolysis deposition and chemical grafting methods.The intrinsic strength of the carbon fiber was enhanced and the interfacial properties of the carbon fiber/epoxy composite was also improved simultaneously.In order to improve the intrinsic strength of carbon fiber,its surface was modified by pyrolysis deposition combined with plasma treatment.By characterizating the surface morphology of carbon fiber,testing the strength of the body,and analyzing its effect on the interfacial properties of the composite,the optimal treatment time of ethanol pyrolysis deposition was determined to be 5 min deposition and 1 min plasma treatment.After treatment,the carbon fiber surface is covered with a uniform pyrolytic carbon layer.Elemental analysis results show higher surface carbon content.The interfacial shear strength(IFSS)of the carbon fiber/epoxy composite increased by 27.7 % from 65 MPa for pristine fiber to 83 MPa for the treated fibers.In order to improve the interfacial properties of carbon fiber/epoxy composites,G0,G0.5,G1.0,G1.5,G2.0,G2.5,and G3 PAMAM dendrimers were used to graft on carbon fiber surfaces.Graft modification was performed to modify the surface morphology,surface chemical composition,fiber surface infiltration,and bulk strength of the carbon fiber before and after nitric acid treatment and different generations of PAMAM graft modification.After grafting treatment,the surface of the carbon fiber produced a large number of PAMAM molecules.Some molecules around the gully or in the gullet covered or partially filled the longitudinal grooves of the carbon fiber surface.The PAMAM molecular volume showed a dramatic increase with the increase of the grafting number,making significant increase of carbon fiber surface roughness.The surface energy is also increased,leading to improved wettability between the carbon fiber and the resin,thereby improving the interface properties of the carbon fiber/epoxy resin composite.Molecular dynamics simulations show that the introduction of PAMAM molecules will increase the interfacial binding energy between carbon fiber and epoxy resin,which is consistent with the experimental results.Plasma pretreatment,combined with the method of ethanol pyrolysis deposition and grafting of PAMAM macromolecules,renders the carbon fiber surface to be modified for both fiber reinforcement and interface strength improvement.After modification,the carbon fiber intrinsic strength increased by 16.7%.At the same time,IFSS value of carbon fiber/epoxy composites increased by 26.56%.Through characterization of carbon fiber surface micro-morphology,surface chemical elements,wettability,the modulus of the interfacial phases of the composite material was investigated.The results showed that the method of pyrolysis deposition combined with chemical grafting presents good reinforcement and toughness effect on the interface of composites.Three main factors contribute to this improvement: rougher the surface roughness of the fiber,the enhanced wettability of the fiber and the substrate,and the formation of the transitional carbon layer in the interface micro zone.