WO2023155282A1 - 大晶区化高结晶度碳质纤维的制备方法 - Google Patents

大晶区化高结晶度碳质纤维的制备方法 Download PDF

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WO2023155282A1
WO2023155282A1 PCT/CN2022/085936 CN2022085936W WO2023155282A1 WO 2023155282 A1 WO2023155282 A1 WO 2023155282A1 CN 2022085936 W CN2022085936 W CN 2022085936W WO 2023155282 A1 WO2023155282 A1 WO 2023155282A1
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graphene
dimensional
crystallinity
preparation
polymer
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高超
明鑫
许震
刘英军
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浙江大学
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    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
    • D01F9/00—Artificial filaments or the like of other substances; Manufacture thereof; Apparatus specially adapted for the manufacture of carbon filaments
    • D01F9/08—Artificial filaments or the like of other substances; Manufacture thereof; Apparatus specially adapted for the manufacture of carbon filaments of inorganic material
    • D01F9/12—Carbon filaments; Apparatus specially adapted for the manufacture thereof
    • D01F9/14—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments
    • D01F9/20—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments from polyaddition, polycondensation or polymerisation products
    • D01F9/21—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments from polyaddition, polycondensation or polymerisation products from macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
    • D01F9/22—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments from polyaddition, polycondensation or polymerisation products from macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds from polyacrylonitriles
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/15—Nano-sized carbon materials
    • C01B32/182—Graphene
    • C01B32/184—Preparation
    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
    • D01F1/00—General methods for the manufacture of artificial filaments or the like
    • D01F1/02—Addition of substances to the spinning solution or to the melt
    • D01F1/09—Addition of substances to the spinning solution or to the melt for making electroconductive or anti-static filaments
    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
    • D01F1/00—General methods for the manufacture of artificial filaments or the like
    • D01F1/02—Addition of substances to the spinning solution or to the melt
    • D01F1/10—Other agents for modifying properties
    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
    • D01F9/00—Artificial filaments or the like of other substances; Manufacture thereof; Apparatus specially adapted for the manufacture of carbon filaments
    • D01F9/08—Artificial filaments or the like of other substances; Manufacture thereof; Apparatus specially adapted for the manufacture of carbon filaments of inorganic material
    • D01F9/12—Carbon filaments; Apparatus specially adapted for the manufacture thereof
    • D01F9/14—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments
    • D01F9/145—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments from pitch or distillation residues
    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
    • D01F9/00—Artificial filaments or the like of other substances; Manufacture thereof; Apparatus specially adapted for the manufacture of carbon filaments
    • D01F9/08—Artificial filaments or the like of other substances; Manufacture thereof; Apparatus specially adapted for the manufacture of carbon filaments of inorganic material
    • D01F9/12—Carbon filaments; Apparatus specially adapted for the manufacture thereof
    • D01F9/14—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments
    • D01F9/16—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments from products of vegetable origin or derivatives thereof, e.g. from cellulose acetate
    • D01F9/17—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments from products of vegetable origin or derivatives thereof, e.g. from cellulose acetate from lignin
    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
    • D01F9/00—Artificial filaments or the like of other substances; Manufacture thereof; Apparatus specially adapted for the manufacture of carbon filaments
    • D01F9/08—Artificial filaments or the like of other substances; Manufacture thereof; Apparatus specially adapted for the manufacture of carbon filaments of inorganic material
    • D01F9/12—Carbon filaments; Apparatus specially adapted for the manufacture thereof
    • D01F9/14—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments
    • D01F9/20—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments from polyaddition, polycondensation or polymerisation products
    • D01F9/24—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments from polyaddition, polycondensation or polymerisation products from macromolecular compounds obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds

Definitions

  • the invention relates to the field of nanometer materials, in particular to a method for preparing large-crystal region-oriented high-crystallinity carbonaceous fibers.
  • One-dimensional linear polymers are cheap and easy to obtain.
  • they are mainly obtained through high-temperature carbonization and crystallization of one-dimensional linear polymer precursors.
  • the commercial polyacrylonitrile carbon fiber is carbonized at 1300 degrees, its mechanical strength is high, but the size of the internal graphite crystal region is small and the arrangement is disordered, resulting in poor electrical and thermal conductivity, and the thermal conductivity is 60W/mK.
  • the size of the graphite crystal region is slightly increased, but it is still unable to generate large-sized graphite crystal regions, and the highest thermal conductivity is only 300W/mK.
  • the essential reason is that the one-dimensional polymer chain and the two-dimensional graphene sheet have an essential topological geometric dimension mismatch, and the one-dimensional polymer molecular chain spontaneously undergoes carbonization and crystallization, and the crystallization of the graphite crystal region is disordered crystallization, resulting in Finally, the size of the three-dimensional carbonaceous crystal domain is small and the degree of orientation is low, which finally makes the electron/phonon scattering centers inside the fiber more. Therefore, it is impossible to have carbon fiber with high strength, high electrical conductivity and high thermal conductivity at the same time.
  • Graphene is a two-dimensional honeycomb single-layer carbon atom crystal formed by carbon atoms connected to each other through sp 2 covalent bonds. It has a mechanical strength of up to 120GPa and a Young's modulus of up to 1.0TPa.
  • the carrier mobility can reach 15000cm 2 /(V ⁇ s), and the thermal conductivity can reach 5300W/mK.
  • Graphene as the basic constituent unit of graphite crystal region, can provide the best constituent unit for macroscopic carbon materials with high strength, high electrical conductivity and high thermal conductivity.
  • a large number of defects and voids will inevitably be introduced, which eventually leads to a gap between the properties of macroscopic materials and those of monolithic materials.
  • How to prepare low-cost high thermal conductivity carbon fiber by combining it with existing commercial polymers while ensuring high-performance carbon fiber has always been a difficult problem.
  • the existing graphene/polymer composite materials mainly have the following problems:
  • the graphene sheet diameter is small, because the raw materials for the preparation of graphene or graphene oxide with small sheet diameter are easier to obtain, so most graphene/polymer composites
  • the size of the graphene sheets in the compound composites is less than 10 microns, which cannot give full play to the advantages of graphene as a two-dimensional topological geometric planar structure.
  • the second is that graphene is disorderly arranged in the polymer and is difficult to orientate. Due to the small diameter of the graphene used, it is difficult for graphene to form a liquid crystal phase in the dispersion and polymer solution.
  • graphene cannot form a continuous network in the polymer system, and it is a composite structure of sea-island phases, and the interlayer confinement of graphene is limited, so the molecular arrangement of the polymer body is highly disordered, and the crystallization region The degree of crystallinity is low, and the polymer molecular chain needs to be improved through subsequent processes such as multiple stretches, resulting in complicated processes and increased costs.
  • the third is that the low degree of oxidation and structural defects of graphene are not high. Since most of the existing graphene is added to the polymer system as a physical filler, the oxygen-containing functional groups and structural defects of graphene itself are ignored as chemical groups. chemical catalysis. Therefore, the chemical properties of graphene itself have not been fully exploited.
  • the present invention forms a liquid crystal composite solution and post-carbonization treatment by liquid-phase compounding a single-layer graphene oxide sheet with a large size and a high degree of oxidation and a polymer precursor, and by virtue of the unique two-dimensional topological geometry of graphene, through graphene
  • the "two-dimensional structural template effect" of the large sheet and the "induced graphitization effect" of the oxygen-containing functional group solved the problem of the mismatch between the one-dimensional linear polymer and the two-dimensional graphite sheet and the three-dimensional graphite crystal region in the topological geometric dimension, and successfully prepared Low-cost graphene carbon fiber with high crystallinity.
  • the purpose of the present invention is to improve the traditional industrialized preparation process of carbon fiber, and provide a preparation process for obtaining large crystal region and high crystallinity carbon fiber with cheap and easy-to-obtain one-dimensional linear polymer, which has high thermal conductivity.
  • a two-dimensional flaky seed (graphene oxide) is added to a one-dimensional linear polymer, and the composite precursor obtained after wet spinning is heated to above 2000° C. for 0.5-3 hours.
  • large sheets of graphene oxide align and align the one-dimensional molecular chains of carbonizable polymers through strong interlayer confinement, that is, through the "structural template effect" of graphene oxide for directional crystallization, thereby preparing a highly crystalline degree of composite precursors.
  • graphitization induction is achieved by using the edge defects and surface oxygen-containing functional groups of graphene oxide as catalytic sites to efficiently convert 1D carbonizable polymers into 2D graphene-like carbon layers.
  • the size of the graphene oxide sheet is more than 30 microns, and the carbon-to-oxygen ratio is greater than 0.5;
  • the one-dimensional linear polymer molecule is a carbonizable polymer, the residual carbon rate is above 20%, and the aromatization index is above 0.8;
  • the solid content of the mixed solution is 3mg/g-30mg/g.
  • the above four conditions are complementary and indispensable. If the graphene oxide sheet size is less than 30 microns and the addition amount is low (less than 30%), it is difficult to form a continuous two-dimensional network sheet structure in the polymer matrix, and the crystal template effect and spatial confinement effect cannot be effectively realized; if If the size is greater than 100 microns, the excessively large two-dimensional graphene oxide sheet is easy to form a folded conformation, hindering the formation of a continuous seed plane, and to a certain extent will affect the display of subsequent graphitization induction.
  • the carbon residue rate of one-dimensional linear polymer molecules needs to be above 20% and the aromatization index is greater than 0.8; if the carbon residue rate is too low, the one-dimensional linear polymer cannot form an effective intermediate phase for topology transformation, thus decomposing A large amount of gas products are generated, graphitization induction cannot be realized, and porous structures are easily formed inside the fibers.
  • the concentration of the mixed solution needs to be controlled at 3mg/g-30mg/g, this concentration range is beneficial to the actual spinning operation, too low and too high will greatly increase the difficulty of spinning.
  • the high crystallinity of the obtained fiber material can not only improve its mechanical strength, but also reduce the internal defects and disorder of the material, and can promote the internal transmission of phonon electrons, thereby improving electrical and thermal conductivity.
  • the high-crystallinity graphene fiber is composed of multiple graphene sheets and graphene-like carbon layers, the degree of graphitization is greater than 80%, the density is greater than or equal to 1.8g/cm 3 , and the carbon content reaches 80wt%.
  • a plurality of graphite crystals in the fiber constitute electron and phonon paths, and the orientation degree of the graphite crystals is above 80%, and the lateral size of the graphite crystals is larger than 100nm.
  • the fiber material can have higher electrical and thermal conductivity; at the same time, the internal graphite crystal stacking mode of the high-crystallinity graphene fiber is mainly AB orderly stacking, which accounts for The proportion is not less than 50% of the overall graphite crystal area inside the fiber, the internal structure of the material is more uniform, the stress concentration points are less, and the material can achieve higher mechanical strength.
  • the method includes the following steps:
  • the liquid crystal composite spinning solution is spun through a liquid crystal wet spinning process, and an appropriate draft force is maintained during the spinning process, and the force value ranges from 0 to 100 MPa, and the fiber is not broken.
  • the one-dimensional linear polymer molecules use the two-dimensional graphene oxide molecules as structural templates to undergo directional crystallization, realizing the "structural template effect" of graphene oxide, and preparing polymers with high Crystalline composite precursors.
  • the polymers inside the fibers have low crystallinity, are not oriented, and have a low degree of orientation. Wherein the crystallinity of the polymer in the precursor is 40%-100%.
  • the high-crystallinity composite precursor after drying is subjected to high-temperature heat treatment. Specifically, in a tube furnace, the temperature is raised to above 2000°C and maintained at 0.5-3h.
  • the graphene assembly material is crystallized to obtain the aforementioned structure-function integrated graphene material.
  • polymer molecules produce small molecular carbon sources during pyrolysis, and two-dimensional graphene oxide can evolve into two-dimensional graphene sheets by removing surface functional groups and repairing defects.
  • Two-dimensional graphene sheets undergo directional assembly by inducing catalytic polymer cracking molecules at the edge of the sheet and on the surface of the sheet, thereby generating a highly oriented graphene-like layer, exhibiting "induced graphitization" to achieve high quality, large size and high crystallinity Degree of graphite crystal region.
  • the graphite domains generated inside have low crystallinity and extremely small size (less than 8nm).
  • an external drawing force can be applied, the force value ranges from 0-100MPa, and the fiber is not broken.
  • the polymer means that the polymer molecule is a carbonizable polymer.
  • the carbonizable polymer is composed of one or more of polyacrylonitrile (PAN), polyimide (PI), polyacrylamide, lignin, pitch, phenolic resin, etc. with different molecular weights mixed in any proportion .
  • the present invention also relates to the application of the above-mentioned high crystallinity graphene fiber material with two-dimensional induction effect in graphene materials with high strength, high modulus, high electrical conductivity and high thermal conductivity.
  • the thermally conductive filler is used as a high thermal conductivity composite material or as a high electrical conductivity composite material to make composite structural parts with high strength.
  • the beneficial effect of the present invention is that: the present invention utilizes the "structural template effect" and "induced graphitization effect" of large-scale graphene oxide to improve the residual carbon rate, graphitization degree and crystallinity of the polymer.
  • the geometric structure of two-dimensional graphene oxide sheets is used to induce one-dimensional polymers to generate two-dimensional graphene-like sheets. It makes it possible to obtain a graphene fiber material with high crystallinity by adding a small amount of large-size two-dimensional graphene oxide (higher polymer ratio), which is very rare for reducing the production cost and performance improvement of graphene fibers.
  • the graphene-like layer induced by the polymer catalyzed by graphene can regulate the AB stacking mode of the graphite crystal inside the fiber, increase the density of the graphene fiber, promote the orderly arrangement of the graphite crystal region, and reduce the internal defects of the fiber, thus obtaining High crystallinity graphene fiber material integrating high strength, high modulus, high electrical conductivity, and high thermal conductivity.
  • Fig. 1 is the data of fiber strength, modulus, electrical conductivity, thermal conductivity that embodiment 1 and embodiment 2 obtain, and wherein blue ball refers to pure polymer fiber (polyacrylonitrile), and red color ball refers to high crystallinity graphene fiber.
  • Fig. 2 is the internal graphite crystal region structure and the selected area electron diffraction diagram of the high crystallinity graphene fiber obtained in embodiment 2.
  • the present invention provides a preparation method of large crystal region high crystallinity carbonaceous fiber.
  • the method combines two-dimensional graphene oxide sheets with one-dimensional linear polymers, with the help of the unique two-dimensional topological geometry structure of large-scale graphene oxide , the one-dimensional linear polymer uses it as a geometric template, and realizes the directional assembly and crystallization of the polymer through the "structural template effect", and obtains a composite filament with high crystallinity; and then through the "induced graphitization effect" of graphene during the heat treatment process,
  • the polymer precursor can form a highly oriented two-dimensional graphene-like layer, thereby solving the problem of mismatching one-dimensional and two-dimensional topological geometric dimensions, which is conducive to the formation of large-sized graphite crystals, and at the same time adjusting the stacking method of graphene sheets Increasing the ratio of AB ordered stacking, thereby obtaining graphene fibers with high graphite crystallinity.
  • the orientation degree of graphite crystals is above 80%, and the density is greater than or equal to 1.8g/cm 3 .
  • the size (Lc) ranges from 10-30nm, and the internal graphite crystal stacking method is mainly AB orderly stacking, and its proportion is not less than 50% of the overall graphite crystal area inside the fiber.
  • the present embodiment adopts one-dimensional linear polymer polyacrylonitrile (its residual carbon rate is 30%, aromatization index is 0.8) to prepare carbon fiber, has studied the parameter (see table 1) of the two-dimensional lamellar seed crystal used for induction The impact on its performance is as follows:
  • the crystallinity of the composite precursor and the degree of graphitization of the graphene fiber, the size of the graphite crystal, and the degree of AB order stacking in the graphite crystal region are obtained, as shown in Table 2, and the layer spacing of the graphite crystal region is 0.35nm the following.
  • Analyzing sample 2 and sample 3 in Example 1 can find that, along with the carbon-oxygen ratio of two-dimensional graphene oxide increases gradually, the performance of the graphene fiber that finally obtains improves, and this is due to the content of the graphene oxide/polypropylene composite system
  • the carbon ratio is increased, the final carbon residue rate is improved to a certain extent, and the graphitization induction effect of graphene oxide is more obvious.
  • graphene oxide still has liquid crystal properties, which can ensure the smooth progress of the liquid crystal spinning process.
  • the crystallinity of the composite precursors, the degree of graphitization of the graphene fibers, the size of the graphite crystals, and the orderly stacking degree of AB in the graphite crystal region are obtained, as shown in Table 4, and the layer spacing of the graphite crystal region is 0.35nm the following.
  • Example 2 Analyze the sample in Example 2 to find that graphene oxide can be used as a two-dimensional seed crystal to induce graphitization for polymers (polyimide, lignin, pitch, phenolic resin) with a carbon residue rate higher than 50%. function, and finally obtain graphene fibers with high crystallinity and high thermal conductivity.
  • polymers polyimide, lignin, pitch, phenolic resin

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Abstract

本发明公开了大晶区化高结晶度碳质纤维的制备方法，主要采用湿法纺丝的方式将氧化石墨烯和其它聚合物材料进行液相复合组装，二维氧化石墨烯片对聚合物分子进行"模板取向化作用"，使得聚合物分子在二维氧化石墨烯片上定向结晶，从而制得高取向度和结晶度的复合原丝。高温处理，二维拓扑结构的墨烯片通过"诱导石墨化作用"催化热解分子以单层石墨烯片为模板定向生成类石墨烯的碳层，促进了石墨烯片层的堆叠行为，从而制得具有最佳石墨晶体结构的复合碳质纤维。该法制备得到的石墨烯纤维材料具有低成本，高结晶度和高性能的特点，可应用于轻质高强结构材料领域。本发明是一种具备二维诱导效应的高结晶度石墨烯纤维材料及其制备方法。

Description

大晶区化高结晶度碳质纤维的制备方法 技术领域
本发明涉及纳米材料领域，特别是一种大晶区化高结晶度碳质纤维的制备方法。
背景技术
一维线形聚合物廉价易得，在碳纤维的工业化生产中，主要是通过一维线形聚合物前驱体通过高温碳化结晶而得。商业聚丙烯腈碳纤维经过1300度碳化处理后，其力学强度高，但内部石墨晶区尺寸小且排列无序，导致其导电导热性能差，导热率为60W/mK。即使经过2800度高温石墨化处理后，其石墨晶区尺寸略有提升，但依旧无法生成大尺寸的石墨晶区，导热率最高仅仅为300W/mK。其本质原因是由于一维聚合物链与二维石墨烯片层存在着本质上的拓扑几何维度不匹配，一维聚合物分子链自发进行碳化结晶，其石墨晶区结晶为无序结晶，导致最终生成三维碳质晶区尺寸较小且取向度低，最终使得纤维内部的电子/声子散射中心多。因此，无法同时具备高强度、高导电和高导热性能的碳质纤维。
自2004年起，由英国曼彻斯特大学的A.K.Geim教授课题组发现了石墨烯，证明了完美的二维晶体结构也可以在非绝对零度下稳定存在，由此获得了诺贝尔物理学奖。具体而言，石墨烯(Graphene)是由碳原子通过sp 2共价键相互连接成的二维蜂窝状单层碳原子晶，其具有力学强度可达120GPa,杨氏模量可达1.0TPa，载流子迁移率可达15000cm 2/(V·s)，导热系数可达5300W/mK。因此，通过将二维的石墨烯片层作为宏观材料的组成基元，成为了研制新型碳质宏观材料的一条新途径。其可将石墨烯各项优异的物理化学性质，通过可控制备的方式传承至其宏观组装体中，实现碳质宏观材料的各方面性能得到提升。
石墨烯作为石墨晶区的基本组成基元，可为高强度、高导电和高导热的宏观碳材料提供最佳的组成基元。但是由于纳米材料在组装成宏观材料的过程中，难免会引入大量缺陷和空洞，最终导致宏观材料的各项性能与单片材料的性能存在差距。如何在保证制得高性能碳质纤维的同时，采用与现有商业化聚合物 相结合制备低成本的高导热碳质纤维一直是个难题。现有的石墨烯/聚合物复合材料主要存在以下几个问题：一是石墨烯片径较小，由于小片径的石墨烯或者氧化石墨烯的制备原料较易获得，所以大部分石墨烯/聚合物复合物中石墨烯的片径尺寸均小于10微米，无法充分发挥石墨烯作为二维拓扑几何平面结构的优势。二是石墨烯在聚合物中为无序排列且难以取向，由于采用的石墨烯片径较小，导致石墨烯在分散液和聚合物溶液中不易形成液晶相。若想形成液晶相，则需要大幅提高石墨烯在聚合物中的含量，但提高石墨烯在聚合物中的比例，由于石墨烯的二维屏蔽效应，会降低聚合物在复合体系中的链缠结密度。因此，复合溶液的流动性会大大减弱，不利于后续的成型加工。综合一二两点，石墨烯在聚合物体系中无法形成连续网络，为海岛相复合结构，且石墨烯的层间限域作用有限，故聚合物本体的分子排列无序度高，结晶区的结晶度较低，聚合物分子链需通过后续多次拉伸等工艺才能得到提高，导致流程复杂和增加成本。此外，三是石墨烯的低氧化度和结构缺陷度不高，由于现有的石墨烯大多数作为物理填料加入到聚合物体系中，忽略了石墨烯本身含氧官能团和结构缺陷作为化学基团的化学催化作用。因此，石墨烯本身的化学性质没有得到充分的发挥。
因此本发明通过将大尺寸和高氧化度的单层氧化石墨烯片与聚合物前驱体进行液相复合形成液晶复合溶液和碳化后处理，借助石墨烯独特的二维拓扑几何结构，通过石墨烯大片的“二维结构模板作用”和含氧官能团的“诱导石墨化作用”解决了一维线形聚合物与二维石墨片层和三维石墨晶区在拓扑几何维度上的不匹配难题，成功制备了低成本的具有高结晶度石墨烯碳质纤维。
发明内容
本发明的目的在于改进传统的碳纤维工业化制备流程，提供一种利用廉价易得的一维线形聚合物获得大晶区化高结晶度碳质纤维的制备工艺，其具有高导热性能。
具体的，本发明是在一维线形聚合物中加入二维片状晶种(氧化石墨烯)，湿法纺丝后得到的复合原丝升温至2000℃以上高温处理0.5-3h。一方面，大片 氧化石墨烯通过强的层间限域作用将可碳化聚合物一维分子链排列取向，即，通过氧化石墨烯的“结构模板作用”进行定向取向结晶，从而制备得到具有高结晶度的复合原丝。另一方面，通过氧化石墨烯的边缘缺陷和表面含氧官能团作为催化位点，实现石墨化诱导作用，将一维可碳化聚合物高效地转化为二维类石墨烯碳层。
为了实现上述结构模板作用和石墨化诱导作用，需满足：
(1)氧化石墨烯片尺寸为30微米以上,碳氧比大于0.5；
(2)一维线形聚合物分子为可碳化聚合物，残碳率在20％以上，芳香化指数在0.8以上；
(3)二维片状晶种的含碳量与聚合物的碳含量之比在1：8.3以上；
(4)混合溶液的固含量为3mg/g-30mg/g。
以上四个条件相辅相成，缺一不可。若氧化石墨烯片层尺寸小于30微米且低添加量(小于30％)时，在聚合物基质中难以形成连续二维网络片层结构，无法有效地实现晶体模板作用和空间限域作用；若尺寸大于100微米，则由于过大的二维氧化石墨烯片易形成折叠构象，阻碍连续晶种平面的形成，一定程度上会影响后续石墨化诱导作用的展现。一维线形聚合物分子的残碳率需在20％以上且芳香化指数大于0.8即可；若残碳率过低，则一维线形高分子无法形成有效的中间相进行拓扑结构转变，从而分解生成大量气体产物，无法实现石墨化诱导作用，易造成纤维内部生成多孔结构。二维片状晶种和聚合物基质的碳含量之比越高，其石墨化诱导作用和最终热处理纤维的碳收率越高，石墨化诱导作用越容易发生。混合溶液的浓度需控制在3mg/g-30mg/g，此浓度范围有利于实际纺丝操作，过低和过高将大大提高纺丝难度。所得到的纤维材料具备高结晶度既可提高其力学强度，同时减小材料内部缺陷和无序度，可促进声子电子的内部传输，从而提高导电导热。高结晶度石墨烯纤维由多个由石墨烯片和类石墨烯碳层构成，其石墨化程度大于80％，密度大于等于1.8g/cm 3，含碳量达80wt％。纤维中多个石墨晶体构成电子和声子路径，其组成的石墨晶体的取向度在80％以上，石墨晶体的横向尺寸大于100nm。石墨晶体的尺寸越大，电子 和声子自由程越长，纤维材料可具有更高的导电导热性能；同时高结晶度石墨烯纤维的内部石墨晶体堆叠方式主要为AB有序堆叠，其所占比例不低于纤维内部整体石墨晶区的50％，材料内部结构更加均匀，应力集中点较少，材料可实现更高的力学强度。
具体的，该方法包括如下步骤：
(1)将氧化石墨烯溶液与聚合物分子溶液进行均匀混合；其中氧化石墨烯与聚合物的质量比例为0.1-50:100，混合溶液的固含量为3mg/g-30mg/g。控制氧化石墨烯与聚合物的比例，确保混合溶液具备典型的液晶性质，同时混合溶液具备可纺性。氧化石墨烯与聚合物比例过低，则纤维最终的结晶度不高且石墨晶区较小；比例过高，则纤维最终的密度较低且成本提高。
(2)将液晶复合纺丝液通过液晶湿法纺丝工艺进行纺丝，在纺丝过程中保持适当的牵伸力，其力值范围为0-100MPa，且确保纤维不发生断裂。在挤出流场的剪切作用下，一维线形聚合物分子以二维氧化石墨烯分子作为结构模板，进行定向取向结晶，实现氧化石墨烯的“结构模板作用”，制备得到具有高聚合物结晶度的复合原丝。与无二维氧化石墨烯模板的聚合物纤维相比，纤维内部聚合物结晶度低，且无定向排列，取向度较低。其中原丝中聚合物的结晶度为40％-100％。
(3)干燥后的高结晶度复合原丝进行高温热处理。具体而言，在管式炉中，升温至2000℃以上，维持在0.5-3h。使石墨烯组装材料进行结晶，得到前述的结构功能一体化石墨烯材料。在热处理过程中，聚合物分子在热裂解过程中产生小分子碳源，二维氧化石墨烯通过去除表面官能团和缺陷修复作用，可演变为二维石墨烯片层。二维石墨烯片通过片层边缘和片层表面诱导催化聚合物裂解分子进行定向组装，从而生成高定向的类石墨烯层，表现出“诱导石墨化作用”实现高质量、大尺寸和高结晶度的石墨晶区。与无氧化石墨烯片层的纯聚合物纤维相比，其内部生成的石墨晶区结晶度低和尺寸极小(小于8nm)。
高温处理过程中，可通过外加牵伸力，其力值范围为0-100MPa，且确保纤维不发生断裂。
本申请中，所述聚合物为所述聚合物分子为可碳化聚合物。所述可碳化聚合物为不同分子量大小的聚丙烯腈(PAN)、聚酰亚胺(PI)、聚丙烯酰胺、木质素、沥青、酚醛树脂等中的一种或几种按任意比例混合组成。
本发明还涉及上述一种具备二维诱导效应的高结晶度石墨烯纤维材料在高强度、高模量、高导电和高导热的石墨烯材料中的应用。例如，导热填料作为高导热复合材料或者作为高导电复合材料，利用高强度做复合结构件。
本发明的有益效果在于：本发明利用大尺寸氧化石墨烯的“结构模板作用”和“诱导石墨化作用”，提升了聚合物的残碳率、石墨化度和结晶度。通过解决一维线形聚合物与二维石墨片层在拓扑几何维度上的不匹配问题，利用二维氧化石墨烯片的几何结构，诱导一维聚合物生成二维类石墨烯片层。使得实现少量添加大尺寸二维氧化石墨烯(聚合物比例更高)即可得到高结晶度的石墨烯纤维材料，这对于降低石墨烯纤维的生成成本和性能提升方面是非常难得的。同时聚合物被石墨烯催化诱导的类石墨烯层可以调控纤维内部石墨晶体的AB堆叠方式，增加了石墨烯纤维的密度，促进了石墨晶区的有序排列，减少纤维内部缺陷，从而得到了集高强度、高模量、高导电、高导热为一体的高结晶度石墨烯纤维材料。
附图说明
图1为实施例1和实施例2得到的纤维强度、模量、导电率、导热率的数据，其中蓝色球指纯聚合物纤维(聚丙烯腈)，红颜色球指高结晶度石墨烯纤维。
图2为实施例2得到的高结晶度石墨烯纤维的内部石墨晶区结构及选区电子衍射图。
具体实施方式
本发明提供一种大晶区化高结晶度碳质纤维的制备方法，该方法通过二维氧化石墨烯片与一维线形聚合物复合，借助于大尺寸氧化石墨烯独特的二维拓扑几何结构，一维线形聚合物将其作为几何模板，通过“结构模板作用”实现了聚合物定向组装结晶，得到高结晶度的复合原丝；再通过热处理过程中石墨烯的“诱导石墨化作用”，聚合物前驱体可形成高定向的二维类石墨烯层，从而解决了 一维与二维的拓扑几何维度不匹配问题，有利于大尺寸的石墨晶体的形成，同时调整石墨烯片层堆叠方式增加AB有序堆叠比例，由此得到具有高石墨结晶度的石墨烯纤维。最终得到具有高结晶度的石墨烯材料，石墨晶体的取向度在80％以上，密度大于等于1.8g/cm 3，每个石墨晶体的横向尺寸(La)范围为60-200nm,石墨晶体的纵向尺寸(Lc)范围为10-30nm，内部石墨晶体堆叠方式主要为AB有序堆叠，其所占比例不低于纤维内部整体石墨晶区的50％。
实施例1：
本实施例采用一维线形聚合物聚丙烯腈(其残碳率为30％，芳香化指数为0.8)来制备碳纤维，研究了诱导用的二维片层晶种的参数(见表1)对于其性能的影响，具体如下：
(1)将聚丙烯腈在纯DMF溶液中进行均匀分散，加入氧化石墨烯，形成纺丝溶液，体系的固含量为5％。
(2)将液晶复合纺丝液挤出进入纯乙酸乙酯的凝固浴中，经过湿法液晶纺丝工艺得到高结晶度复合原丝纤维。纺丝过程中保持适当的牵伸力5N。
(3)将原丝至于管式炉中，升温至2000℃热处理3h、气压压强10MPa。
表1
Figure PCTCN2022085936-appb-000001
通过广角X射线衍射测试获得复合原丝的结晶度和石墨烯纤维的石墨化程度、石墨晶体尺寸、石墨晶区内AB有序堆叠度，见表2，且石墨晶区的层间距在0.35nm以下。
通过Keysight T150U仪器测试，获得产物的力学强度，通过纤维四线法对 导电率进行测试，获得产物石墨烯纤维的导电率；通过导热率测试T形法，得产物石墨烯纤维的导热率，结果见表2。
表2
Figure PCTCN2022085936-appb-000002
分析实施例1中的样品2和样品1可以发现，通过添加二维氧化石墨烯晶种可以大幅提高原丝纤维的结晶度，并且生成具备更完美的石墨化程度和石墨晶区尺寸，从而得到具备高结晶度和高导热的石墨烯纤维。
分析实施例1中的样品2和样品3可以发现，随着二维氧化石墨烯的碳氧比逐渐提高，最终得到的石墨烯纤维性能提高，这是由于氧化石墨烯/聚丙烯复合体系的含碳量比提高，最终残碳率得到一定提高，氧化石墨烯的石墨化诱导效应更加明显，同时氧化石墨烯仍具有液晶性质，可保证液晶纺丝过程的顺利进行。
分析实施例1中的样品2和样品4可以发现，聚丙烯腈的残碳率和芳香化指数增加，二维拓扑晶种诱导的石墨化效应越强，最终得到的石墨烯纤维性能逐渐增强。当聚合物的残碳率过低时，导致氧化石墨烯进行石墨化诱导时，无法形成有效的中间相固态碳质产物，最终聚合物已碳质气态小分子逸出，造成纤维内部多孔，最终无法达到高结晶度高导热的石墨烯纤维。
分析实施例1中的样品2和样品5可以发现，二维氧化石墨烯的添加量增加，二维拓扑晶种诱导的石墨化效应越强，最终得到的石墨烯纤维性能逐渐增 强。但复合添加量过少时，导致氧化石墨烯在聚合物溶液中不易形成液晶相，聚合物基质中无法形成连续二维结构导致原丝的结晶度和石墨烯纤维石墨化度无法提高，最终无法达到高结晶度高导热的石墨烯纤维。
分析实施例1中的样品2、样品6、样品7和样品8可以发现，随着二维氧化石墨烯的尺寸从小到大，二维石墨烯晶种的诱导石墨化效果逐渐提高。片径尺寸过小时，无法充分发挥石墨烯作为二维拓扑几何平面结构的优势，但当氧化石墨烯的尺寸超过150μm，由于大尺寸的单层氧化石墨烯片在纺丝过程中易产生褶皱结构在热处理后不利于诱导生成完美的石墨晶体，从而一定程度上导致原丝结晶度和石墨烯石墨化度反而下降，石墨烯纤维的最终力学性能和导热性能有所下降。
实施例2：
本实施例采用了不同的一维线形聚合物(具有不同残碳率和芳香化指数)来制备碳纤维，见表3，具体如下：
(1)将一维线形聚合物在纯DMSO溶液中进行均匀分散，加入氧化石墨烯，形成纺丝溶液，体系的固含量为10％。氧化石墨烯尺寸为45±20微米,碳氧比2.5；二维片状晶种的含碳量与聚合物的碳含量之比控制在0.76±0.02；混合溶液的固含量为5mg/g。
(2)将液晶复合纺丝液挤出进入纯乙酸乙酯的凝固浴中，经过湿法液晶纺丝工艺得到高结晶度复合原丝纤维。
(3)将原丝至于管式炉中，升温至2000℃以上进行热处理，气压压强5MPa。
表3
样品编号 聚合物 残碳率 芳香化指数 热处理温度(℃) 时间(h)
1 聚酰亚胺 80％ 2.1 2000 0.5
2 木质素 55％ 1.2 3000 0.5
3 沥青 70％ 1.7 2400 1.5
4 酚醛树脂 60％ 1.4 2500 3
通过广角X射线衍射测试获得复合原丝的结晶度和石墨烯纤维的石墨化程度、石墨晶体尺寸、石墨晶区内AB有序堆叠度，见表4，且石墨晶区的层间距在0.35nm以下。
通过Keysight T150U仪器测试，获得产物的力学强度，通过纤维四线法对导电率进行测试，获得产物石墨烯纤维的导电率；通过导热率测试T形法，得产物石墨烯纤维的导热率，结果见表4。
表4
Figure PCTCN2022085936-appb-000003
分析实施例2中的样品以发现，氧化石墨烯可作为二维晶种对残碳率高于50％的聚合物(聚酰亚胺、木质素、沥青、酚醛树脂)均可发生诱导石墨化作用，最终得到高结晶度和高导热石墨烯纤维。

Claims (6)

  1. 大晶区化高结晶度碳质纤维的制备方法，其特征在于，该方法为：在一维线形聚合物溶液中加入二维片状晶种，混合均匀后，进行湿法纺丝；将纺丝得到的复合原丝升温至2000℃以上高温处理0.5-3h后，得到具有大晶区化高结晶度碳质纤维；所述二维片状晶种为氧化石墨烯片，尺寸为30微米以上,碳氧比大于0.5；一维线形聚合物分子为可碳化聚合物，残碳率在20％以上，芳香化指数在0.8以上；二维片状晶种的含碳量与聚合物的碳含量之比在1：8.3以上；混合溶液的固含量为3mg/g-30mg/g。
  2. 根据权利要求1所述的制备方法，其特征在于，湿法纺丝所采用的凝固浴的极性参数为0.3～0.5，凝固浴温度控制为40～70摄氏度。
  3. 根据权利要求1所述的制备方法，其特征在于，混合溶液的溶剂为水、N,N-二甲基甲酰胺(DMF)、N,N-二甲基乙酰胺(DMAC)、N-甲基吡咯烷酮(NMP)、二甲基亚砜(DMSO)、乙醇、甘油等中的一种或几种按任意比例混合组成。
  4. 根据权利要求1所述的制备方法，其特征在于，一维线形聚合物分子选自聚丙烯腈(PAN)、聚酰亚胺(PI)、聚丙烯酰胺(PAM)、木质素、沥青、酚醛树脂等中的一种或几种按任意比例混合组成。
  5. 根据权利要求1所述的制备方法，其特征在于，湿法纺丝过程和高温处理过程均保持牵伸力。
  6. 如权利要求1所述方法制备的高结晶度石墨烯纤维在高强度、高模量、高导电和高导热的石墨烯材料中的应用。
PCT/CN2022/085936 2022-02-16 2022-04-08 大晶区化高结晶度碳质纤维的制备方法 WO2023155282A1 (zh)

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