Study On The Interface Properties Of Ti₃C₂T_x MXene Surface Modified High Modulus Carbon Fiber And Its Epoxy Resin Matrix Composite

High modulus carbon fiber(HMCF)has a more extreme modulus than standard carbon fiber,so it is widely used in aerospace,wind turbine blades and other fields that require higher material performance.However,due to the extremely inert surface of HMCF,the resin matrix cannot be fully wetted on its surface,resulting in the failure of the excellent performance of the composite material to be fully utilized,so the surface needs to be modified.At present,most HMCF surface modification technologies are complex and difficult to achieve large-scale industrial application transformation.Therefore,it is of great significance to study high-performance HMCF surface modification technologies suitable for current industrial equipment.In this paper,using the good hydrophilic properties of Ti3C2Tx MXene twodimensional nanomaterials,the MX/EP composite sizing agent obtained by mechanically blending MXene aqueous dispersion and epoxy emulsion sizing agent was used to modify the surface of HMCF,and the MXene sheet was studied.The regulation law of diameter and load on the surface properties of HMCF and the interface properties of composite materials.In addition,in order to further promote the development of MXene-modified HMCF,the first attempt was made to modify HMCF by electrodeposition MXene,and the surface properties of the resulting product and the interface and flame-retardant properties of the composite material were analyzed.(1)The multi-layer Ti3C2Tx MXene material with "accordion" morphology was prepared by the etching method of a mixed solution of hydrochloric acid(HCl)and lithium fluoride(LiF),and used X-ray photoelectron spectroscopy(XPS)and thermogravimetric analysis(TG).)The surface chemical state and thermal stability were analyzed and characterized.The results show that the surface of Ti3C2Tx MXene contains-OH,=O and-F groups,and the thermal decomposition temperature in nitrogen reaches 678.4?,the initial oxidation temperature in air is 314.3?,and the final oxidation decomposition temperature is 742.5?.Afterwards,the multi-layer Ti3C2Tx MXene was explored for exfoliation and size adjustment using ultrasonic and high-energy ball milling techniques,and characterized by scanning electron microscope(SEM),transmission electron microscope(TEM)and laser particle size analysis techniques.The result proves that the purpose of peeling off the sheet layer and adjusting the size of the sheet diameter can be achieved at the same time by changing the time.When the ultrasonic time is 2 h and 4 h,the proportion of MXene lam(?)a with a particle size of less than 0.5 ?m is 57.2%and 80.0%,respectively;when the ball milling time is 12 h and 16 h,the peeling effect of the lamella is obvious,respectively.A few layers of Ti3C2Tx MXene with an average chip diameter of 15 ?m and 0.5 ?m were obtained.Finally,MX/EP composite sizing agent and MXene electrophoresis solution with higher stability were obtained by mechanical blending.(2)The sizing technology was used to modify HMCF with MX/EP sizing agents of different sheet diameters and concentrations.The SEM results showed that the 0.5 ?m Ti3C2Tx MXene nanosheets formed a large number of small convex microstructures on the fiber surface,which could be used as bonding sites for mechanical engagement with the resin matrix.TG results show that the coating of MX/EP sizing agent on the surface of HMCF can significantly improve its heat resistance.When the sizing agent concentration is 2.0 mg/mL,the corresponding temperature of modified CF at 5%weight loss is 641.1?.Compared with before treatment,it has increased by nearly 140?,and the thermal weight loss rate has also been greatly reduced.The dynamic contact angle and surface energy results show that the wetting performance of the modified carbon fiber surface is significantly improved,especially when the concentration of MX/EP sizing agent is 1.0 mg/mL,the surface energy value of the fiber reaches 48.16 mN.m-1.Compared with unsizing carbon fiber,it is 241.8%higher.At this time,the interlaminar shear strength(ILSS)of the corresponding CF/EP composite material also reached the maximum value of 85.9 MPa,which was 47.1%higher than that of the unsizing fiber.The main reason is that the substantial increase in surface energy of HMCF improves the wettability of the resin matrix on its surface.In addition,the numerous small protrusions on the fiber surface also play a role in mechanical engagement and enhancing the bonding strength of the interface layer.(3)Ti3C2Tx MXene was introduced onto the surface of HMCF by electrophoretic deposition technology.SEM and XPS results prove that the deposition density and O/C ratio of MXene on the fiber surface can be adjusted by controlling the deposition voltage.Especially when the deposition voltage is 15 V,MXene achieves a uniform and high-density deposition on the surface of HMCF.The ratio of O/C is increased by 215%compared with unsizing CF.The dynamic contact angle test results prove that under the deposition voltage of 15 V,the surface energy of the fiber is increased by 102.0%compared with the unsizing fiber.Mainly because the introduction of MXene improves the wettability of the resin matrix on the surface of HMCF and enhances the mechanical bonding between the two phases,so that the ILSS value of the modified CF/EP composite material is increased by 40.9%compared with the unsizing fiber.In addition,the introduction of Ti3C2Tx MXene on the surface of HMCF has also significantly improved the fire and flame retardant properties of CF/EP composites,and the limiting oxygen index(LOI)has increased by 32.9%compared to before treatment.