Study on Strengthening and Surface Modification of F-3A Aramid Fibers by γ-Ray Irradiation

Author:Xie Fei

Supervisor:liu li


Degree Year:2018





Aramid fiber has many advantages such as low density,high strength,high modulus,high specific hardness,corrosion resistance,wear resistance,good thermal stability,low conductivity,etc.It is widely used as a high-performance reinforcement material in aviation,aerospace,military and civilian areas.However,the aramid fiber has noticeable"skin-core"structure,and the surface of the aramid fiber is smooth and inert,resulting in poor interface binding properties of the composite material.These two factors constrain the application of aramid fibers to the aerospace and other military fields.Therefore,the development of high-tech weapon in China urge researchers to carry out basic research work from the perspective of structural adjustment and interface optimization of aramid fiber.The high-energy irradiation technology was used to modify the aramid fiber,improve the structure of the fiber skin core,activate the fiber surface,and improve the interface of the fiber-reinforced resin.On this basis,the aramid fiber was treated by irradiation grafting technique,through grafting different reactive groups.The surface activity of the fiber was increased,the wettability and adhesion of the aramid fiber in the resin were improved.The mechanism of the interface strengthening between aramid fiber surface microdomains and its composites was analyzed.After treated withγ-ray irradiation,the intrinsic viscosity of the F-3A fiber is the greatest,the tensile strength is increased by 9.61%.The surface roughness and surface energy also increased,fiber reinforced resin composites have significantly improved ILSS and IFSS.When the irradiation intensity was 600 kGy,the better properties of the fiber were obtained,with significantly improved the interfacial properties.It was confirmed that 6 kGy.h-1,600 kGy was the best irradiation treatment process for domestic aramid fiber F-3A.By comparing the changes of mechanical tensile strength and deformation displacement of irradiated F-3A fibers which wasfurther treated with1,4-dichlorobutane,it is believed that the F-3A fiber breaks in the tensile fracture mode.The destruction of the"core"after the"skin"layer was followed by a sharp cross-linking reaction within the fiber,resulting in an increase in intermolecular forces and the strength of the cortex structure and the core.The skin-core structure has been improved.Under the co-irradiation of high-energyγ-rays,1,4-dichlorobutane was grafted onto the F-3A fiber surface,and a chemical etching reaction was initiated on the surface of the fiber.The ILSS of fibers after grafting can reach to 54.51 MPa and IFSS can reach to 46.56 MPa.The aminated F-3A fiber was prepared by direct amination of Cl-Af fiber irradiated with 1,4-dichlorobutane in ammonia/ethanol solution.The experimental results show that the amination reaction successfully converts-Cl to-NH2.The surface energy of A-Afs fiber is greatly improved,and the interfacial shear strength of the fiber-reinforced resin composite can be increased to51.09 MPa.The failure mode of the composite material changes from the interface to the resin matrix and fiber surface.However,during the amination process,the cellulose hydrolysis reaction is initiated and the mechanical strength of the fiber is reduced.Hydroxylation of Cl-Afs fibers with NaOH solution introduces-OH onto the fiber surface.APS and OH-Afs were reacted to prepare APS-grafted F-3A fibers,which introduced amino groups on the fiber surface.The experimental results show that APS is evenly coated on the fiber surface,and the groove on the fiber is nearly almost disappeared,due to the protective grafting of APS.APS-Afs can be chemically crosslinked with the resin at the interface of the composite to improve the interfacial properties of the composite.The IFSS of APS-Afs reinforced composites can reach 54.87 MPa.The aramid fiber and acrylonitrile monomer are co-irradiated prepare the acrylonitrile-grafted aramid fiber by taking advantage of the high penetration and non-selective characteristics ofγ-ray to activate the fiber and acrylonitrile monomer simultaneously.Acrylonitrile monomer initiates free radical polymerization on the fiber surface,and the resulting polyacrylonitrile adheres to the fiber surface in the form of particles with a size of 200 nm.PAN particles on the F-3A surface improves the mechanical riveting of the interface between the fiber and the resin matrix,leading to improved interface binding performance of the fiber-reinforced resin composite.The interfacial shear strength of PAN2-Afs fiber reinforced resin composites reached 62.31MPa,which is an 71.50%increase,showing that the interfacial properties of fiber reinforced resins were greatly improved.