Study On The Controlled Preparation Of Spinnable Mesophase Pitch And The Pre-oxidation Performance Of Carbon Fiber

Mesophase pitch carbon fiber is widely used in high-tech fields due to its high-strength and high-modulus properties,and its performance depends on the properties of the precursor pitch.In this thesis,the use of cycloalkyl-rich aromatic hydrocarbon oil,through the control of thermal polycondensation-solvent extraction coupled molecular distillation polycondensation process to prepare spinnable mesophase pitch,and melt spinning,pre-oxidation,carbonization to obtain carbon fiber.This project evaluated the spinnability of pitch,and investigated the pre-oxidation performance of the fiber and the mechanical properties of carbon fiber.First,using UPC pilot test 2020 and HCTO-2-2 two feedstock oils,using the same thermal polycondensation-molecular distillation polycondensation conditions,the properties of the feedstock oil and the influence of the low pressure period of thermal polycondensation on the preparation of mesophase pitch were found.When the feedstock oil is reacted at low pressure for 3 h,the product obtained has a lower softening point,a higher content of mesophase and good spinning performance,and the product made by HCTO-2-2 is better.Then,using UPC pilot test 2020 and UPC pilot test 2020（processed）two feedstock oils,using the same thermal polycondensation-molecular distillation polycondensation conditions,the properties of the feedstock oil and the influence of molecular distillation vacuum on the preparation of mesophase pitch were found.When the raw material oils are distilled at 5mm Hg,the product obtained has a lower softening point and a higher content of mesophase,and the product produced by UPC pilot test 2020（processed）is better.The raw oil contains a suitable amount of alkyl and cycloalkyl structures,which can release small molecular free radicals during the thermal reaction process,participate in the regulation of free radical reactions,and inhibit the out-of-plane disordered cross-linking between large molecular free radicals,which is beneficial Prepare high-quality spinnable mesophase pitch.Finally,using HCTO-2-2,using thermal polycondensation-solvent extraction coupled molecular distillation polycondensation method,the product is better when the ratio of agent to oil is 4:1.Next,the prepared fiber precursor was pre-oxidized in two modes of constant temperature and heating,and the effects of constant temperature,heating rate and oxidizing atmosphere on the fiber structure and performance were studied,and the pre-oxidation performance of different fibers was compared.For the mesophase pitch fiber prepared in this laboratory,the optimal oxidation weight gain is 5%～8%.The fiber made from the precursor pitch with lower condensation degree,aromatic degree and softening point has good oxidation activity.The fiber crystallite structure after oxidation at 280℃and oxidation in slow mode in air is the best.After oxidation,the hydrogen-containing functional groups in the fiber gradually disappear,and oxygen-containing groups such as C=O and O-C-O are produced.When oxidized at 280℃,the asphaltene molecules in the fiber are connected by oxygen-containing functional groups to form a relatively dense radial structure.Finally,the pre-oxidized fiber is carbonized.The microcrystalline structure of the carbonized fiber obtained after oxidation at 280℃is the best,and the microcrystalline structure of the carbonized fiber after oxidation in the air slow mode is the best.After carbonization treatment,the miscellaneous peaks in the infrared spectrum of the fiber are reduced and become smoother and more regular,leaving basically only the C=C absorption peak at 1600 cm^-1.The three kinds of fibers have the best tensile properties when the pre-oxidation temperature is 280℃;lower heating rate and the use of pure oxygen oxidation are conducive to obtaining carbon fibers with better tensile properties.The cross-section of the carbonized fiber obtained after oxidation at 280℃is radial,and the carbon lamellar structure is dense.Finally,carbon fiber which has a tensile strength of about 650 MPa and a Young’s modulus of about 150 GPa was obtained.