Effect Of Raw Material Components On The Structure And Performance Of Mesophase Pitch

Mesophase pitch has the characteristics of high carbon content,high aromaticity,rich raw material sources,good optical anisotropy and rheological properties,so it is an excellent precursor for many new carbon materials.Mesophase pitch is a liquid crystal material prepared by thermal condensation polymerization of heavy aromatics in raw materials,so its structure and performance are closely related to the raw material composition.Therefore,the influence of raw material components on the structure and performance of mesophase pitch was explored,so as to establish the relationship between the raw material components and the structure and performance of mesophase pitch.It has important guiding significance for the research and preparation of high-quality mesophase pitch.In this thesis,the method of fractional distillation is used to classify different raw materials,and the differences in the structure and properties of raw materials and their fractions are explored.Then select different raw materials to prepare mesophase pitch using the two-stage heat-condensation method of pressure-vacuum,and explore the influence of different raw materials on the structure and performance of mesophase pitch.Then use different mesophase pitch as raw materials to prepare mesophase pitch-based carbon fiber,and explore the effect of different mesophase pitch on the structure and performance of carbon fiber.In addition,the comparatively high-quality mesophase pitch was taken as the research object to explore the co-carbonization behavior of mesophase pitch and graphene oxide.The results obtained are as follows:(1)Taking 5 different raw materials as research objects,and it was found that:?The H/C molar ratio of raw materials is expressed as raw material-1>raw material-2>raw material-3>raw material-4>raw material-5.Both the aromatic index Iar and the aromatic carbon rate fA are expressed as raw material-1<raw material-2<raw material-3<raw material-4<raw material-5.?Raw material-1 and raw material-2 have a microcrystalline structure in which aliphatic hydrocarbon chains are arranged and stacked.Raw material-3,raw material-4 and raw material-5 have a microcrystalline structure formed by the arrangement and arrangement of aromatic flakes.And the graphite microcrystalline layer spacing d002 is expressed as raw material-3>raw material-4>raw material-5,the microcrystalline stacking thickness Lc,the crystallite size La and the graphite sheet layer number M are expressed as raw material-3<raw material-4<raw material-5.For raw material-5,d002=0.365nm,Lc=1.083nm,La=1.170nm,M=4.0.?In the heat treatment process,raw material-1 and raw material-2 have not formed mesophase,while raw material-3,raw material-4 and raw material-5 can see the formation and growth process of mesophase spheres.In particular,the temperature at which raw material-5 induces mesophase formation is the lowest,and the growth speed of the spheres is moderate and relatively uniform.(2)The mesophase pitch(MP)was prepared from three different raw materials,and it was found that:?The H/C molar ratio of MP showed MP-3>MP-4>MP-5.The aromatic index is expressed as MP-3<MP-4<MP-5,indicating that MP-5 has the most aromatic hydrocarbon structure content and the smallest aliphatic hydrocarbon structure content.?The spacing d002 of MP's graphite crystallites is MP-3>MP-4>MP-5,and the thickness of the crystallites is Lc.The crystallite size La and the graphite sheet number M both showed MP-3<MP-4<MP-5.For MP-5#2,d002=0.348nm,Lc=2.945nm,La=2.208nm,M=9.5.?MP-3 eventually developed into a mosaic-type mesophase structure with a mesophase content of over 80%.MP-4 eventually developed into a streamlined and partially wide-area mesophase structure with a mesophase content of over 90%.MP-5 eventually developed into a wide-area streamlined mesophase structure with a mesophase content of 100%.?The softening point of MP is MP-3<MP-4<MP-5.Although MP-5 has the highest softening point,its spinnability is better.?The n-heptane soluble(HS)component of MP-5 provides it with more aliphatic hydrocarbon structure.The quinoline insoluble(QI)component provides a large number of condensed ring aromatic hydrocarbon structures and a better graphite crystal structure.(3)Carbon fiber(MPCF)and graphitized fiber(MPGF)were prepared from 3 kind of MP.It was found that:?The cross-sectional structure of MPGF-3 has irregular inner layer arrangement,while the cross-sectional structures of MPGF-4 and MPGF-5 present a radial arrangement within a certain range in the radial direction.?The graphite layer spacing d002 of MPGF show MPGF-3>MPGF-4>MPGF-5,while the microcrystalline stacking thickness Lc,the crystallite size La and the number of graphite sheet layers M all show MPGF-3<MPGF-4<MPGF-5.Among them,d002=0.337nm of MPGF-5,Lc=22.352nm,La=23.402nm,M=67.3.?The tensile strength and modulus of MPGF are both MPGF-3<MPGF-4<MPGF-5,of which the tensile strength of MPGF-5 is 2.12GPa and the tensile modulus is 630GPa.In addition,the resistivity shows MPGF-3>MPGF-4>MPGF-5,and the thermal conductivity shows MPGF-3<MPGF-4<MPGF-5.Among them,the electrical resistivity of MPGF-5 is 2.08??·m,and the thermal conductivity is 569w/(m·K).(4)Taking MP-5 as the research object,it was found that with the increase of the addition amount of graphene oxide(GO),the diffraction peak of the 002 crystal plane of the co-carbonized product prepared by MP-5 and GO shifted to the right,and the graphite crystallite layer spacing d002 showed an increasing trend.For the microcrystalline stacking thickness Lc,the crystallite size La and the graphite sheet number M both showed a decreasing trend.The reason may be that the content of heteroatoms in the system increases,and crosslinking,cracking,aromatization and other reactions increase.At the same time,small molecules escape from the carbonized product,which hinders the arrangement and growth of graphite crystallites of the co-carbonized product of MP-5 and GO.