The Structure Evolution And Surface Properties And Mechanical Properties Of Carbon Fiber Along Different Radial Domains Under X-ray Irradiation

Carbon fiber is widely used in composites because of its excellent mechanical properties such as high strength and high modulus.However,its mechanical properties still have a huge room for improvement.Meanwhile,the inert fiber surface and poor interfacial adhesion with the composite matrix seriously affect the interfacial properties of the composites and limit the wide application of carbon fibers.As an efficient,environmentally friendly and low-cost modification technology,γ irradiation can not only enhance the mechanical properties of carbon fibers but also improve the surface bonding properties of fibers.However,the evolution mechanism of carbon fiber surface characteristics and mechanical properties under y irradiation is still unclear.In this paper,the evolution rule of different microstructures along the radial direction in y-irradiated high strength T1000 and generic T700 carbon fibers is analyzed by partition structure model composed of outer-surface,sub-surface and core part.The relationship among outer-surface,sub-surface,core,surface and mechanical properties of y-irradiated T700 carbon fibers is analyzed by the stress analysis and the mechanical model.The tensile strength and Young’s modulus of T1000 carbon fiber are improved after irradiation in argon,air and epoxy chloropropane(ECP).The tensile strength increased by 14.7%,14.4%and 12.4%,respectively and Young’s modulus increases by 16.4%,15.6%and 13.4%,respectively.The surface property of T1000 carbon fiber is studied by X-ray photoelectron spectroscopy(XPS)and surface energy test.The results show that the O/C value of fiber surface is increased from 0.1056 to 0.2728,an improvement of 158.3%and the amount of carboxyl and carbonyl groups is increased obviously after irradiation in ECP.The surface energy increases by 48.3%.X-ray diffraction(XRD)test show that the graphite layer spacing d002 of T1000 carbon fiber irradiated in different media is decreased and the average graphitization degree of carbon fibers increased.Raman spectra from fiber section show that the change of ID/IG values of T1000 carbon fiber after irradiation is more obvious than that of core.The structure evolution of outer-surface,sub-surface,core and the change in mechanical properties of T700 carbon fiber irradiated in argon and ECP are similar to that of T1000 carbon fiber.Meanwhile,interfacial shear strength(IFSS)of T700 carbon fiber composite material irradiated in ECP is increased by 75.03%.Scanning electron microscope(SEM)show that the outer-surface groove of the fiber is more clearly after carbon fiber irradiation in ECP.X-ray photoelectron spectroscopy combined with in situ argon sputtering,Raman spectra from fiber section,stress analysis and mechanical model are used to study the relationship between the microstructures and mechanical properties of T700 carbon fibers under γ irradiation.The results show that the irradiation medium only plays an important role in the outer-surface of T700 carbon fiber(～12nm).The oxygen-containing functional groups are intercalated into the graphite layer on outer-surface of fiber,destroying the outer-surface structure and improving the outer-surface activity of the fiber.The formation of the covalent cross-linking structure between graphene layers of surface-layer(1.5μm)may be the main reason for the improvement of mechanical properties in y-irradiated T700 carbon fiber.