Preparation Of Carbon Fiber Hierarchical Reinforcement Using Click Chemistry Approach And The Mechanical Properties Of Its Composites

Carbon fiber composite materials have an irreplaceable position in aerospace,automotive,building materials and other fields.For carbon fiber composite materials,good interface is the guarantee of the mechanical properties of the material.However,due to the smooth surface and few active groups on the surface of the carbon fiber,the interfacial interaction between the carbon fiber and resin matrix is weak,making the mechanical properties of the carbon fiber composite material far from expectations.Therefore,it is necessary to modify the surface of carbon fiber to improve the wettability between carbon fiber and resin,and improve the interfacial properties of the composites.In this paper,the graphene oxide,hyperbranched poly(thioether-ester)and hyperbranched polyester were quickly and efficiently grafted onto the carbon fiber surface via click chemistry.Then,the resulted hierarchical reinforcement composites were prepared by using the epoxy resin as matrix.The addition of graphene oxide improves the surface roughness of the carbon fiber and greatly increases the mechanical meshing effect of the fiber and the resin matrix.In addition,the incorporation of hyperbranched polymers can effectively improve the chemical bonding and wettability between fiber and epoxy resin.Therefore,the introduction of graphene oxide and hyperbranched polymers can significantly improve the compatibility between the carbon fiber and the resin matrix,and increase the interfacial strength.Based on this,two different grafting methods("grafting from" and "grafting to")are used to achieve the grafting of hyperbranched polymer and graphene oxide on the surface of carbon fiber.The specific research content is as follows:(1)After the carbon fiber was degummed,the surface treatment of the carbon fiber was carried out by nitric acid oxidation and plasma oxidation,respectively,to obtain oxidized carbon fiber(CF-Oxi).The resulted CF-Oxi was characterized by Fourier infrared spectrometer(FT-IR).The results show that both methods can introduce active groups on the surface of the carbon fiber.After comparing the experimental conditions and the final grafting effect of the two methods,the plasma method is found to be safer,simpler and more efficient.(2)The surface of carbon fiber and graphene oxide was modified by ?-mercaptopropyltrimethoxysilane(KH590),and the mercapto-functionalized carbon fiber(CF-KH590)and mercapto-functionalized graphene oxide(GO-KH590)were characterized by FT-IR and thermal gravimetric analyzer(TGA).The results show that KH590 was successfully grafted on the surface of carbon fiber and graphene oxide,and the grafting rate is about 5.13% and 6.70 %,respectively.(3)Based on the idea of hierarchical structural design,the graphene oxidehyperbranched poly(thioether-ester)-carbon fiber(GO-HPTEE-CF)hierarchical reinforcement and the graphene oxide-hyperbranched polyester-carbon fiber(GO-H20-CF)hierarchical reinforcement were prepared by two different grafting methods("grafting from" and "grafting to"),and the products were characterized by FT-IR,TGA,X-ray photoelectron spectroscopy(XPS).The results show that the hierarchical reinforcements are successfully prepared.The introduction of hyperbranched polymers can effectively prevent the agglomeration of graphene oxide on the surface of carbon fiber,and can effectively improve the mechanical properties of carbon fiber.(4)The composites were prepared by using epoxy resin E-51 as the matrix,triethylenetetramine as the curing agent,and the carbon fibers after each stage of modification as reinforcement.The experimental results show that the surface modification can effectively improve the interfacial properties of composites,which can help the composites to transfer more loads and avoid stress concentration.Compared with the original carbon fiber,the monofilament tensile strength and multifilament tensile strength of GO-H20-CF hierarchical reinforcement increase by 35.66% and 44.34%,respectively.The bending strength,interlaminar shear strength and interfacial shear strength of GO-H20-CF reinforced composites increase by 34.58%,59.94% and 147.99%,respectively.Compared with the original carbon fiber,the monofilament tensile strength and multifilament tensile strength of GO-HPTEE-CF hierarchical reinforcement increase by 21.45% and 34.19%,respectively.The bending strength,interlaminar shear strength and interfacial shear strength of the GO-HPTEE-CF reinforced composites increase by23.99%,50.19% and 136.96%,respectively.Field emission scanning electron microscopy results showed that few fibers were pulled out at the fracture of the two hierarchical reinforcement composites,and the fiber fracture was uneven,and a large amount of resin were attached to the carbon fiber surface,indicating good interfacial adhesion between the hierarchical reinforcement and the resin matrix,which could improve the interfacial properties of composites.