【作者】 陈涛；

【导师】 吕永根；

【作者基本信息】 东华大学 ， 材料与化工， 2022， 硕士

【摘要】 中间相沥青基炭纤维具有高模量和高导热的优点,广泛应用于航天、航空、军工等领域,是一种不可代替的新型轻质高力学性能材料。其制备过程主要分为中间相沥青原料的调制、熔融纺丝、预氧化、炭化以及石墨化等步骤,最终形成了沿纤维轴向高度取向的类石墨层片结构。中间相沥青的性质决定了可纺性,从而决定了纤维可承受牵伸的能力。由于中间相沥青纤维承受牵伸能力差,容易发生脆断,限制了纤维的细旦化,并且在炭化后易产生典型劈裂现象,严重影响其性能,因此如何提高可纺性,进而在保证稳定纺丝的同时降低纤维直径以及改善劈裂现象是提高炭纤维力学性能的关键。本文采用共混的方式将聚苯硫醚(PPS)引入到萘系中间相沥青中,以PPS柔性高分子自身特性改善由刚性沥青分子层片组成的中间相沥青的可纺性。通过粘温流变分析、傅立叶红外光谱分析、偏光显微镜分析等手段研究添加少量PPS对中间相沥青可纺性的影响,并细化纺丝温度研究区间及选择合适共混量。通过实验室自制单孔纺丝机研究中间相沥青原料和PPS原料各自的纺丝性能并对不同PPS共混量下的沥青原料熔融纺丝,探讨共混PPS对中间相沥青最大牵伸比的影响及纤维的细旦化。采用单丝强力仪、扫描电镜(SEM)、热重分析(TG)、X射线分析(XRD)等仪器手段对炭纤维进行测试,重点考察了共混对炭纤维力学性能、截面结构、类石墨微晶尺寸的影响,并分析了PPS与沥青的共炭化效应以及对纤维结构的影响机理。研究内容及结论如下:(1)研究了PPS共混对中间相沥青原料可纺性的影响,并细化研究区间和选择合适共混量。研究发现所用中间相沥青在340-350℃研究温度区间整体粘度处于6 Pa·s以下,PPS用量为5%以内时原料在335-350℃研究温度区间整体粘度处于10 Pa·s以下,具备较好可纺性;红外分析、偏光显微镜分析表明少量的PPS共混并没有对分子结构以及中间相沥青形态及含量产生较大影响。(2)研究了中间相沥青原料和PPS原料各自的纺丝性能,探讨共混PPS对原料最大牵伸比的影响及纤维的细旦化。研究发现347℃,0.5 MPa是该沥青原料的稳定纺丝条件,获得的沥青纤维平均直径为29.25μm;PPS共混量为5%以内时可显著提高中间相沥青的可纺性,进而提高原料可承受的最大牵伸比,最终实现稳定纺丝(连续可纺22min以上)前提下直径的下降。共混5%PPS后,原料可承受最大牵伸比从42.19提升至82.72,稳定纺丝沥青纤维直径也从29.25μm下降至20.89μm。(3)研究了PPS共混对炭纤维的截面结构以及力学性能的影响,并探讨PPS与中间相沥青的共炭化效应以及对纤维结构的影响机理。研究发现PPS共混能有效抑制中间相沥青基炭纤维辐射型结构和劈裂形貌的生成。由可纺性的改善所引起的纤维的细旦化、炭纤维截面劈裂的抑制最终有利于力学性能的提升。添加量为5%时,炭纤维拉伸强度从432 MPa提升至611 MPa,提升幅度为41%;研究发现PPS与中间相沥青发生共炭化反应,加速了炭化450-550℃阶段含氧官能团的脱除,促进炭化中芳构化反应,最终提升了碳收率。更多还原

【Abstract】 Mesophase pitch based carbon fiber has the advantages of high modulus and high thermal conductivity,which is widely used in aerospace,aviation,military and other fields,is a kind of lightweight and high mechanical performance materials.The preparation process is mainly divided into mesophase pitch material modulation,melt spinning,pre-oxidation,carbonization and graphitization steps,and finally formed along the fiber axial highly oriented graphite-like layer structure.The properties of mesophase pitch decided the spinnability,thus determines the drawing ability.The mesophase pitch fibers under drafting ability is poor,prone to brittle fracture,limits the fine diameter of fiber,and typical splitting easy generation after carbonization phenomenon,so how to improve the spinnability,and the guarantee of stable spinning at the same time reduce the fiber diameter and improving fracturing phenomenon is the key to improve mechanics performance of carbon fiber.In this paper,polyphenylene sulfide(PPS)was introduced into naphthalene mesophase raw material by blending,and the spinnability of mesophase pitch composed of rigid pitch molecular layers was improved by PPS flexible polymer.The influence of adding a small amount of PPS on mesophase pitch spinnability was studied by softening point analysis,viscosity temperature rheological analysis,Fourier infrared spectroscopy analysis,polarizing microscope analysis and other means,and the research interval of spinning temperature was refined and the appropriate blending amount was selected.The spinning properties of mesophase pitch and PPS were studied by using a single-hole spinning machine made in the laboratory,and the influence of PPS blending on the maximum draft ratio of mesophase pitch and the fineness of fibers was discussed.We adopt monofilament power meter,scanning electron microscopy(SEM),thermogravimetric analysis(TG),X ray analysis(XRD)instrument means to test carbon fibers,focuses on the blend’s influence on the mechanical properties,the structure of the cross section,the influence of graphite crystallite size of the carbon fiber,and analyzes the cocarbonization and the influence mechanism of the PPS blending fiber structure.The research contents and conclusions are as follows:(1)The influence of PPS blending on the spinnability of mesophase pitch raw materials was studied,and the study interval was refined and the appropriate blending amount was selected.The results show that mesophase pitch has a good spinnability when the overall viscosity is less than 6Pa·s at 340-350℃,and the overall viscosity is less than 10 Pa·s at 335-350℃ when PPS blending is less than 5%.Infrared analysis and polarizing microscope analysis showed that a small amount of PPS blending did not affect the molecular structure,morphology and content of mesophase pitch.(2)The spinning properties of mesophase pitch material and PPS material were studied,and the influence of PPS blend on the maximum draft ratio of the material and the fineness of the fiber were discussed.It was found that 347 ℃ and 0.5 MPa were the stable spinning conditions of the pitch material,and the average diameter of the pitch fiber was 29.25 μm.When PPS blending amount is less than 5%,the spinnability of mesophase pitch can be significantly improved,thus increasing the maximum draft ratio that the raw material can bear,and finally realizing the diameter reduction under the premise of stable spinning(the continuous spinning time can reach more than22min).When 5% PPS was mixed,the maximum draft ratio increased from 42.19 to 82.72,and the diameter of stably spun pitch fiber decreased from 29.25 to 20.89 μm.(3)The effect of PPS blending on the cross section structure and mechanical properties of carbon fibers was studied,and the cocarbonization effect of PPS and mesophase pitch and its influence mechanism on fiber structure were discussed.It is found that PPS blending can effectively inhibit the formation of mesophase pitch-based carbon fibers radiating structure and splitting morphology.The reduction of fiber diameter and the reduction of cross section splitting caused by the improvement of spinnability are beneficial to the improvement of mechanical properties.When adding amount was 5%,the tensile strength of the carbon fiber increase from 432 to 611 MPa,with an increase of 41%.It was found that the cocarbonization reaction between PPS and mesophase pitch accelerated the removal of oxygen-containing functional groups during carbonization at 450 to 550℃,promoted the aromatization reaction during carbonization,and finally improved the carbon yield.更多还原