Molecular Dynamics Simulation Of Helical Laminated Carbon Fiber Precursor And Their Preparation Process

Carbon fiber is a kind of inorganic fiber material with more than 90%carbon content,which is widely used in the military industry and civilian fields.The defect of carbon fiber is considered the "natural enemy" of carbon fiber.The quality of carbon fiber has a great influence on the post-treatment process and the mechanical properties of carbon fiber.Eliminating the defect of carbon fiber is expected to make the mechanical properties of carbon fiber approach its theoretical value.In this paper,based on the "hemp rope theory",a new idea of preparing helical laminated carbon fiber primordium by using micro-nano laminated basic technology is proposed.However,the theoretical understanding of the preparation of helical laminated carbon fiber is seriously insufficient.In this paper,the molecular dynamics method was used to simulate the tensile behavior and preparation process of the helical laminated primordium.The main research process and important conclusions are as follows:(1)Starting from spiral PE nanofibers with simple linear molecules,this paper simulated the stretching process of spiral PE nanofibers with different helix angles,and explored the influence of helix action on polymer nanofibers.The tensile stress-strain curves of polymer nanofibers with different helical angles were calculated,and the microstructure of helical PE nanofibers and the effect of helical action on the tensile strength of nanofibers were analyzed.The results show that the tensile strength of the nanofibers decreases first and then increases with the increase of twisting Angle.The tensile strength of nanofibers at a twist Angle of 50? is improved compared with that of conventional nanofibers.At the same time,it is found that the density of the nanofibers is denser than that of the conventional nanofibers in the radial direction after being twisted,and the degree of compactness is greater with the increase of the helix Angle.These results fully demonstrate that the helical structure has two kinds of effects on the mechanical properties of nanofibers.First,the helical structure weakens the contribution of bond stretching to tensile stress,thus reducing the tensile strength of nanofibers.Secondly,the helical structure can reduce the slip of molecular chains by enhancing the friction between molecular chains,thus improving the tensile strength of nanofibers.In general,the helical structure can improve the tensile properties of nanofibers.(2)The above simulation results verified the feasibility of preparing spiral laminated carbon fiber primordium,so this paper continued to explore the tensile behavior of spiral laminated PAN carbon fiber primordium at different temperatures by combining atomic and molecular dynamics simulation.The results show that the temperature has little effect on the tensile behavior of PAN nanofibers,and the helix angle affects the tensile properties of the nanofibers from two aspects.On the one hand,with the increase of helical Angle,PAN nanofibers a rapid increase in the average radial internal accumulation stress spiral PAN fiber internal radial stress can improve the density of nanofibers,avoid PAN fiber strand structure defects,at the same time,the fibers radial stress increases the friction between the molecular chain of PAN,reduce the slip between the molecular chain during the process of stretching,eventually played a role to improve the performance of PAN fiber strand tension.On the other hand,the average axial stress of PAN nanofibers decreases first and then increases with the increase of twisted Angle.This result is consistent with the results of tensile strength.When the helix angle is small,the axial stress of the PAN nanofibers decreases,and even if the radial stress increases,the radial stress has little effect on the lost axial stress,so the tensile strength of the PAN nanofibers with small helix angle is lower than that of the conventional nanofibers.In conclusion,the helical shape of carbon fiber fibers can not only maintain the density of the fibers,avoid the formation of micropore defects and core-skin structure,but also improve the mechanical properties of PAN fibers.(3)Finally,based on the mechanism of gel spinning,a method of co-extrusion lamination of PAN/DMSO with water was proposed to achieve the gelation of laminated PAN films.To explore the laminated structure of PAN gelation mechanism of molecular dynamics simulation is based on the joint atomic multilayer structure of PAN/DMSO and water model,explores the different temperature,all kinds of compression and tensile condition inquiry of PAN/DMSO and water co-extrusion laminated the effects of DMSO diffusion rate in the process,based on the diffusion after PAN multi-layer fiber structure interface morphology and porosity of the analysis and evaluation of the quality of the differential nano laminated film.The research results show that DMSO diffusion behavior is highly affected by the temperature,diffusion rate under different temperature by DMSO contrast,DMSO after diffusion rate increases with the rise of temperature to reduce,this is because the temperature increase the ability of molecular movement,at the same time as the temperature rises,the fiber swelling,easier to spread,so DMSO however as temperatures rise further,DMSO diffusion rate gradually reduced,because the temperature is too high lead to fiber coagulation,forming dense surface,preventing the proliferation of DMSO.Secondly,when the PAN/DMSO solution was co-extruded with water,the diffusion rate of DMSO can be increased and the equilibrium time can be shortened by increasing the extrusion rate or axial tensile rate.So by micro-nano laminated principle,preparation of PAN when the laminated membrane along by applying compression conditions along the fiber direction of film thickness or along the fiber membrane extending direction of the applied tensile deformation promotes the dissolution of DMSO,finally through unceasingly in the diffusion process of fiber membrane porosity decreases,and further illustrates the co-extrusion laminated with water PAN/DMSO solution preparation of PAN strand uniform structure,fewer defects and high quality.