Research Of Surface Microstructure Evolution Of High Modulus Carbon Fiber And Its Interface Modification Mechanism For Resin Matrix Composites

Polyacrylonitrile(PAN)based high modulus carbon fiber(HMCF)reinforced resin matrix composites have excellent characteristics such as high specific strength,high specific modulus and low linear thermal expansion coefficient,and play an irreplaceable role in structural materials with special application requirements such as light weight,high stiffness and high dimensional stability.Because the high modulus of carbon fiber comes from the high orientation and structural rearrangement of graphite microcrystal structure along the fiber axis during graphitization,high modulus carbon fiber has a high degree of graphitization and a large surface inertia,and its interface performance with matrix resin is poor,which is not conducive to the mechanical properties of its reinforced resin matrix composites.Therefore,how to obtain high-performance interface phase is also one of the key research contents in the field of high modulus carbon fiber reinforced resin matrix composites.Interfacial properties are closely related to the surface structure of carbon fiber,the stiffness of sizing agent transition layer and the modulus of resin matrix.In this paper,high performance interface was designed,the evolution of surface structure of high modulus carbon fiber,the construction of high modulus transition layer and the control of matrix stiffness of cyanate ester resin were investigated,the optimization method of interface multi-level structure performance was established,which provided a scientific basis for the preparation of high modulus carbon fiber and its high performance composites.The main research results were as follows:The relationship mechanism between microcrystalline structure,surface physical and chemical structure characteristics,interface properties and fiber modulus of high modulus carbon fiber was expounded.Through Raman and its imaging technology,the growth of radial graphite microcrystal structure of carbon fiber and the evolution of plane orientation of carbon network with temperature were revealed.It was also found that with the increase of graphitization temperature,the growth and stacking of carbon mesh plane mainly occured on the surface of carbon fiber.In addition,the graphitization degree and the orientation of graphite microcrystals gradually increased from the center to the surface along the radial direction of fiber.Based on the above theoretical basis,three typical high modulus carbon fibers with modulus of380 GPa,500GPa and 560 GPa were successfully prepared.The surface physical and chemical structure of high modulus carbon fiber and the variation of interfacial properties of its composites with fiber modulus were studied.The results show that with the increase of modulus,the graphitization degree and the stacking thickness of graphite microcrystals increase,while the surface roughness and active functional group content decrease,which leads to the decrease of its surface activity.The interfacial adhesion between high modulus carbon fiber and resin matrix is poor,and this trend is gradually aggravated with the increase of modulus,which leads to the interfacial failure of its composites more easily occurring on the fiber surface.A method to improve the interfacial properties of high modulus carbon fiber/epoxy resin composites from the perspective of interfacial phase was established.Epoxy resin modified multi-walled carbon nanotubes(MWCNTs-EP)were used to stiffen the interfacial layer of sizing agent.The relationship between the concentration of MWCNTs-EP and the interfacial properties of the above three typical high-modulus carbon fiber/epoxy resin composites was studied,and the mechanism of interfacial phase stiffness in improving the interfacial properties of the composites was clarified.The results show that under the optimum MWCNTs-EP concentration,the modulus transition and carbon element distribution at the interface of high-modulus carbon fiber composites are more uniform,which can make the interface between high-modulus carbon fiber and resin matrix have better modulus matching,and the interfacial shear strength and interlaminar shear strength of the composites are increased by 25.2%,24.0%,18.1% and 54.4%,58.1% and35.0% respectively.From the perspective of resin matrix,by using aliphatic epoxy resin(7810M)and POSS(7810S)to regulate the stiffness of bisphenol A dicyanate resin,a method for optimizing the interfacial properties of high modulus carbon fiber / cyanate resin composites was proposed.The curing reaction and mechanical properties of modified cyanate ester resin and pure cyanate ester resin were studied.The relationship between matrix modulus of cyanate ester resin and interfacial properties of composites was established,and its mechanism was discussed.The results show that compared with pure cyanate ester resin,the curing reaction of 7180 M and 7180 S is more complete,and it also has higher crosslinking density and rigidity.Compared with CCM55J/CE composites,CCM55J/7180 M and CCM55J/7180 S composites have higher interfacial phase modulus,and the attenuation transition of elements and modulus in the interfacial phase is relatively smooth,so the stress concentration can be effectively reduced under stress,and the interfacial shear strength of monofilament,transverse tensile strength of bundle and interlaminar shear strength are increased by 42.5% and 30.6% and 152.2%respectively.In addition,due to the increase of resin crosslinking density in CCM55J/7180 M and CCM55J/7180 S composites,it can effectively prevent the growth of microcracks,thus preventing the penetration of water molecules,and improving the humidity and heat resistance and space performance of the composites.