Study On Structure Control And Performance Of Mesophase Pitch-based Carbon Fiber

Mesophase pitch-based carbon fiber(MPCF)has excellent properties such as high modulus,high thermal conductivity and low expansion coefficient.So,it has many important applications in aerospace,aviation and nuclear industries,and so on.The preparation process of MPCF includes melt spinning,fiber pre-oxidation,carbonization and graphitization.The melt-spinning parameters,structure and properties of mesophase pitch are the key factors affecting the structure and property of the prepared carbon fibers.Therefore,it is of great significance to control the structure and property of MPCF by adjusting the used mesophase pitch and spinning parameters.In this thesis,the MPCFs were prepared using the self-made mesophase pitch as raw material.The influence of spinneret structure,spinning temperature and mesophase pitch on the structure and property of carbon fiber was studied.The main research results are as follows:1.The basic properties of the used mesophase pitchare that:mesophase content of 100%,H/C atomic ratio of 0.56,ash content of about 42.31 ppm,n-heptane soluble component of 5.31%,and quinoline insoluble component of 40.52%.The softening point is about 260?;the preferred spinning temperature zone is 315?-355?.2.Three kinds of spinnerets were used to get carbon fibers with different structures.The cross-sectional structure of the final fiber obtained from the small Y-shaped spinning hole is radial radial,and the crystal size is slightly lower with the largest orientation degress(93.44%);the thermal conductivity of the CF is about 650 W/(m K),and the tensile strength is 2.26 GPa.The cross-sectional structure of the final fiber obtained by the spinning hole is hollow,and the graphite sheet is arranged substantially concentrically.The crystal size is the largest among the three fibers,the tensile strength is only 1.75 GPa,and the thermal conductivity is 550 W/(m K).The cross-sectional structure of the final fiber obtained by the circular spinning hole is mostly disordered and irregularly arranged,the fiber crystal size is small,the thermal conductivity is only 460 W/(m K),and the tensile strength is 2.31 GPa.The small Y-shaped spinning hole facilitates the radial arrangement of the graphite crystallites of the prepared fiber in the radial direction,and is easy to obtain high thermal conductivity.3.The pitch fibers were spinned at different temperatures using the small Y-shaped spinneret.When the spinning temperature are from 315,320,325,330,335 and 348?,the section shapes of the resulted MPCFs are triangular,nearly triangular,circular and hollow-type,respectively.For the MPCFs originating from fibers spinned at low temperature,the profile degrees are more great.The profile degree of the MPCF decreases with increasing the spinning temperature in the range of 320 to 345?.The hollow-structure MPCFs could be obtained at 345? of the spinning temperature.The crystal size of the fiber obtained by spinning in the range of 320?-335? generally increases first and then decreases.At 320?,the fiber cross-section is elliptical,the fiber layer is radially arranged,the crystal size is larger,the degree of graphitization is the highest,reaching 76.5%,the thermal conductivity is up to 650 W/(m K),and the tensile strength is 2.26 GPa.4.Four kinds of mesophase pitches MP-1,MP-2,MP-3 and MP-4 with different structures were used for MPCFs,whose structures are mosaic type,mosaic type and fine streamlinetype,respectively.And the crystal size increased in turn;the middle of the streamlined stream.The final MPCF shave a crystallite thickness Lc of 31.96 nm,a graphite sheet size of 43.88 nm,a graphite sheet layer of 73.8,and a thermal conductivity of 1070 W/(m k).The tensile strength is 2.92 GPa.