Study On The Interface Structure And Properties Of CNT/CF Multi-scale Composites

Carbon fiber has a series of excellent properties such as high specific strength,high specific modulus,high temperature resistance,corrosion resistance,etc.It is widely used in aerospace,transportation and other fields.But,due to the inertness of the carbon fiber,the interface bonding strength between the carbon fiber and the polymer matrix is low,and the carbon fiber is easily debonded with the matrix,which severely limit the application of the carbon fiber.Therefore,it is necessary to properly modify the carbon fiber or matrix material,optimize and design the interface structure of the composite material so as to improve the interface bonding performance and whole mechanics properties of the composite material.In recent years,the method of introducing carbon nanotubes into the surface of carbon fiber to fabricate a multi-scale reinforcement structure to improve the interfacial bonding between carbon fiber and resin matrix has become a research hotspot.In order to study the interface enhancement effect of this multi-scale reinforcement structure and its interface enhancement mechanism.carbon fiber was processed by electrochemical oxidation and electrophoresis deposition,through the self-made continuous processing equipment,to prepare carbon nanotubes/carbon fiber multiscale structures in this paper.The surface morphology,infiltration properties and tensile strength were characterized,.The interfacial crystallization behavior and interfacial shear properties of multi-scale reinforced composites were studied emphatically.From the microscopic point of view,the interfacial reinforcement mechanism of carbon nanotubes/carbon fiber multi-scale fibers was analyzed.The main research content of this paper is as follows:Carbon nanotube/carbon fiber multi-scale reinforcements were prepared by electrochemical oxidation and electrophoretic deposition,and their properties were characterized.The results show that after electrochemical oxidation and electrophoretic deposition,a layer of carbon nanotubes is uniformly attached to the carbon fiber,which not only changes the surface morphology of the carbon fiber,but also significantly improves the fiber roughness and infiltration properties.After electrochemical oxidation,the average diameter of carbon fibers decreased by 4.88%,and the tensile strength of single carbon fibers decreased by 6.8%.After electrophoretic deposition,the average diameter of carbon fibers decreased by 2.61%,and the tensile strength of single fibers increased by 3.0%.Since the oxidation treatment causes the surface of the carbon fiber to be etched,and the surface of the fiber is covered with a layer of carbon nanotubes after the electrophoretic deposition treatment,which plays a certain healing effect on the defect of the fiber surface,the tensile properties are improved.The interfacial crystalline morphology and interfacial crystallization behavior between carbon fiber and polypropylene matrix before and after surface treatment were studied by polarized light microscopy.The experiment results show that the interface crystallization behavior of the composites changed greatly after electrophoretic deposition.Polypropylene matrix generated a transverse crystal structure at the interface and formed an obvious interface layer,induced by the multi-scale reinforcement fiber.Under isothermal crystallization conditions,the crystallization temperature has a great influence on the crystallization behavior of multi-scale reinforced composites.The higher crystallization temperature caused the smaller nucleation density on the surface of the fiber,the slower crystal growth,and the later onset of crystallization;Under the non-isothermal crystallization conditions,the cooling rate has a great influence on the crystallization behavior of multi-scale composites.The slower cooling rate led to the higher temperature at which the nucleus starts production and the wider size of the transverse crystals.The interfacial shear behavior of the composites was characterized by the single fiber break test,and the interface enhancement mechanism of multi-scale reinforcements was analyzed.The experimental results show that compared with untreated carbon fiber,the interfacial strength of multi-scale fiber and matrix is obviously improved.There is a strong interface between multi-scale fibers and epoxy resin or polypropylene matrix.Compared with the untreated carbon fiber,the interfacial shear strength of carbon nanotube/carbon fiber multi-scale fiber and epoxy resin increased by 51.1%,and the interfacial bonding between multi-scale fiber and polypropylene was also significantly improved.The good interfacial bonding between multi-scale reinforcements and the matrix has given rise to a certain degree of increase in the tensile properties of the composites.