Carbon fiber paper based on composite carbon fiber preoxidized yarn and its preparation method and application

Abstract

The present invention belongs to the field of fuel cell technology, and provides a carbon fiber paper based on composite carbon fiber preoxidized yarn, and its preparation method and application. The method of the present invention comprises: mixing a soluble asphalt solution and a polyacrylonitrile resin solution, sequentially wet-spinning and coagulation molding the spinning stock solution, sequentially washing the primary fibers with water, hot water drawing, and heat setting, sequentially pre-oxidizing and chopping the composite carbon fiber precursors, mixing the chopped preoxidized yarns with a dispersant solution, sequentially wet-papermaking, impregnating in a resin solution, and hot-pressing and curing to obtain preoxidized fiber paper; the preoxidized fiber paper is sequentially carbonized and graphitized to obtain carbon fiber paper based on composite carbon fiber preoxidized yarn. The present invention introduces soluble asphalt into the polyacrylonitrile wet spinning stock solution, increases the content of active groups on the fiber surface in the preoxidation stage, and regulates the formation and distribution of graphite crystallites in the carbonization and graphitization stage, thereby expanding the types of raw materials for carbon fiber paper used in fuel cell gas diffusion layers.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cells, and in particular to a carbon fiber paper based on composite carbon fiber pre-oxidized yarns, and a preparation method and application thereof. Background Art

[0002] Carbon fiber paper is the base material for the gas diffusion layer of commercial proton exchange membrane fuel cells (PEMFCs). It's typically made from chopped carbon fibers randomly interwoven in three dimensions through a papermaking process. The fibers are then bonded with a resin solution at their joints. The resulting porous fiber paper is then cured by hot pressing, carbonized, and graphitized. During PEMFC service, carbon fiber paper serves as a supporting structure while also performing multiple functions, including mass transfer (heat transfer) and electrical conductivity.

[0003] Due to the dipole effect within and between the molecular chains, the polyacrylonitrile molecular chain presents an irregular helical conformation in the state of lowest potential energy, showing difficult graphitization characteristics during the carbonization and graphitization process. The resulting carbon fiber presents a disordered layered graphite structure, so its mechanical properties are outstanding but its electrical and thermal conductivity is weak; increasing the graphitization temperature can promote the formation of regular graphite lattice, but it will also cause the carbon fiber paper to become brittle and the mechanical properties to decrease. The electrical conductivity and thermal conductivity of carbon fiber paper are important parameters to ensure the efficient operation of PEMFC. Chinese invention patent 202110706943.6 uses a melt-blowing method to construct an intermediate phase asphalt fiber layer on the surface of carbon fiber base paper, which not only improves the electrical conductivity of the carbon fiber paper, but also increases the tensile strength; Chinese invention patent 201810741949.5 introduces intermediate phase asphalt-based carbon fibers as functional additives into the polyacrylonitrile-based carbon fiber papermaking system, and wet-mixes the paper in proportion to improve the electrical conductivity of the carbon fiber paper; the invention patent with application number CN202211025524.7, entitled "A method for preparing highly conductive and thermally conductive graphite fiber paper," uses ultrafine diameter intermediate phase asphalt-based graphite fibers and polyacrylonitrile-based carbon fibers as raw materials to produce a graphite fiber paper with good electrical conductivity, thermal conductivity and processing properties.

[0004] Abundant sources, low cost, easy graphitization, and electrical and thermal conductivity are the inherent advantages of asphalt-based carbon fibers, which are in line with the performance requirements and development trends of high-performance carbon fiber paper. The core of the above-mentioned existing technologies is to achieve uniform mixing of carbon fiber raw materials or the construction of conductive and thermal conductive layers to enhance the rapid transfer of electrons / heat by carbon fiber paper. However, asphalt-based carbon fibers are brittle and can easily break due to dynamic thermal fields during service, destroying the effective mass transfer path and thus reducing battery performance. How to better balance the mechanical properties of polyacrylonitrile-based carbon fibers with the electrical and thermal conductivity of asphalt-based carbon fibers is a difficult problem that needs to be solved urgently. Summary of the Invention

[0005] The purpose of the present invention is to provide a carbon fiber paper based on composite carbon fiber pre-oxidized yarn and a preparation method and application thereof in order to overcome the deficiencies of the prior art.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing carbon fiber paper based on composite carbon fiber pre-oxidized yarn, comprising the following steps:

[0008] 1) Mixing a soluble asphalt solution and a polyacrylonitrile resin solution to obtain a spinning solution;

[0009] 2) The spinning solution is sequentially wet-spun and coagulated to obtain primary fibers; the primary fibers are sequentially washed, hot-water drawn, and heat-set to obtain composite carbon fiber precursors;

[0010] 3) The composite carbon fiber precursor is sequentially pre-oxidized and chopped to obtain chopped pre-oxidized fibers; the chopped pre-oxidized fibers are mixed with a dispersant solution, and sequentially subjected to wet papermaking, impregnation in a resin solution, and hot pressing to obtain pre-oxidized fiber paper;

[0011] 4) The preoxidized fiber paper is sequentially carbonized and graphitized to obtain carbon fiber paper based on composite carbon fiber preoxidized filaments;

[0012] The solvent of the polyacrylonitrile resin solution is N,N-dimethylformamide, and the polyacrylonitrile resin is acrylonitrile-itaconic acid copolymer; the mass fraction of the polyacrylonitrile resin solution is 15-30%;

[0013] The soluble asphalt solution consists of a soluble asphalt extract and an organic solvent, and the mass ratio of the polyacrylonitrile resin to the soluble asphalt extract is 1:0.1~1.5.

[0014] Preferably, the mass fraction of the soluble asphalt solution in step 1) is 5-45%; and the intrinsic viscosity of the spinning solution is 1.0-2.0 dL / g.

[0015] Preferably, the preparation method of the soluble asphalt extract in step 1) is: mixing asphalt and an organic solvent, extracting, centrifuging, rotary evaporating, and drying in sequence to obtain a soluble asphalt extract;

[0016] The asphalt is one or more of naphthalene asphalt, petroleum asphalt and coal asphalt; the organic solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, tetrahydrofuran, pyridine, quinoline and dimethyl sulfoxide; the extraction method is ultrasonic-assisted extraction, Soxhlet extraction or magnetic stirring.

[0017] Preferably, the coagulation bath for the coagulation molding in step 2) consists of water and an organic solvent, the mass fraction of the organic solvent in the coagulation bath is 20-70%, and the coagulation molding temperature is 0-70°C.

[0018] Preferably, in step 2), the water washing temperature is 10-70°C, the hot water stretching temperature is 50-90°C, and the heat setting temperature is 100-180°C.

[0019] Preferably, in step 3), the mass fraction of the dispersant solution is 0.01-0.3%, and the dispersant is one or more of hydroxymethyl cellulose, sodium dodecylbenzene sulfonate, polyacrylamide and polyethylene oxide; and the resin solution is an alcohol solution of boron phenolic resin;

[0020] The length of the chopped pre-oxidized yarn is 5-23 mm, and the cyclization degree is ≥85%.

[0021] Preferably, the pre-oxidation process in step 3) comprises three stages of pre-oxidation, wherein the first stage of pre-oxidation is performed at a temperature of 200-250° C. and a duration of 15-24 minutes, the second stage of pre-oxidation is performed at a temperature of 250-300° C. and a duration of 30-60 minutes, and the third stage of pre-oxidation is performed at a temperature of 240-270° C. and a duration of 30-45 minutes.

[0022] The temperature of the hot pressing curing is 110-150° C., the time is 10-20 min, and the pressure is 0.5-6 MPa.

[0023] Preferably, in step 4), the carbonization temperature is 600-1200° C., the time is 0.8-1.2 h, the graphitization temperature is 2000-2600° C., the time is 0.3-1 h, and the carbonization and graphitization are carried out under a protective atmosphere.

[0024] The present invention also provides carbon fiber paper based on composite carbon fiber preoxidized yarn prepared by the preparation method, wherein the carbon fiber paper has a thickness of 120-210 μm, a tensile strength of 16.3-30.2 MPa, a resistivity of 3.5-8.7 mΩ·cm, and a thermal conductivity of 17.2-26.7 W / m·K.

[0025] The present invention also provides the use of the carbon fiber paper based on the composite carbon fiber preoxidized yarn in the gas diffusion layer of a proton exchange membrane fuel cell.

[0026] The beneficial effects of the present invention include the following:

[0027] 1) The present invention introduces soluble asphalt into polyacrylonitrile spinning solution, and after wet spinning and programmed pre-oxidation treatment, produces a composite carbon fiber pre-oxidized yarn that can be used as a raw material for carbon fiber paper making, expanding the raw material types of carbon fiber paper for fuel cell gas diffusion layers.

[0028] 2) The present invention uses pre-oxidized fibers as the raw material for papermaking. The polyacrylonitrile molecular chains or asphalt components are pre-oxidized in an air atmosphere to form active hydrophilic groups such as -OH, -COOH, and -C=O. Their dispersion in the aqueous phase is better than that of chopped carbon fibers, which is beneficial for the full random interweaving of the fibers in three-dimensional space during papermaking, thereby improving the mechanical properties of the base paper and constructing a path for electrical and thermal conductivity.

[0029] 3) Based on the fact that the polycyclic aromatic hydrocarbons and alkyl side chain structures of the soluble asphalt components easily form carbon crystals under high temperature conditions, the present invention achieves differentiated preparation of electron / heat transfer performance by regulating the content and distribution differences of graphite microcrystals inside the fiber.

[0030] 4) The present invention prepares high-performance carbon fiber paper based on pre-oxidized fiber paper, which only requires one carbonization and graphitization process; the asphalt raw material is abundant in source and has a greater price advantage, which helps to reduce the overall production cost.

[0031] 5) The present invention introduces soluble pitch into the polyacrylonitrile wet spinning solution, increases the content of active groups on the fiber surface during the pre-oxidation stage, and regulates the formation and distribution of graphite crystallites during the carbonization and graphitization stage. This expands the preparation process and raw material types of carbon fiber paper for fuel cell gas diffusion layers, and achieves the preparation of "low-cost, high-electrical conductivity, and high-thermal conductivity" functional carbon fiber paper based on good mechanical properties, providing a new strategy for the industrial production of high-performance carbon fiber paper for fuel cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a scanning electron microscope image of the fiber paper after carbonization treatment in Example 1;

[0033] Figure 2 This is a scanning electron microscope image of the fiber paper after graphitization treatment in Example 2;

[0034] Figure 3 IR spectra of the as-spun fibers of Example 5 and Comparative Example 1;

[0035] Figure 4 This is a scanning electron microscope image of the fiber paper after carbonization treatment in Comparative Example 3. DETAILED DESCRIPTION

[0036] The present invention provides a method for preparing carbon fiber paper based on composite carbon fiber pre-oxidized yarn, comprising the following steps:

[0037] 1) Mixing a soluble asphalt solution and a polyacrylonitrile resin solution to obtain a spinning solution;

[0038] 2) The spinning solution is sequentially wet-spun and coagulated to obtain primary fibers; the primary fibers are sequentially washed, hot-water drawn, and heat-set to obtain composite carbon fiber precursors;

[0039] 3) The composite carbon fiber precursor is sequentially pre-oxidized and chopped to obtain chopped pre-oxidized fibers; the chopped pre-oxidized fibers are mixed with a dispersant solution, and sequentially subjected to wet papermaking, impregnation in a resin solution, and hot pressing to obtain pre-oxidized fiber paper;

[0040] 4) The preoxidized fiber paper is sequentially carbonized and graphitized to obtain carbon fiber paper based on composite carbon fiber preoxidized filaments;

[0041] The solvent of the polyacrylonitrile resin solution is N,N-dimethylformamide, and the polyacrylonitrile resin is acrylonitrile-itaconic acid copolymer; the mass fraction of the polyacrylonitrile resin solution is 15-30%;

[0042] The soluble asphalt solution consists of a soluble asphalt extract and an organic solvent, and the mass ratio of the polyacrylonitrile resin to the soluble asphalt extract is 1:0.1~1.5.

[0043] In the present invention, the mass fraction of the polyacrylonitrile resin solution is preferably 18-27%, more preferably 20-25%, and more preferably 22-23%; the mass ratio of the polyacrylonitrile resin to the soluble asphalt extract is preferably 1:0.4-1.2, more preferably 1:0.8-1.0.

[0044] In the present invention, the mass fraction of the soluble asphalt solution in step 1) is preferably 5-45%, more preferably 10-38%, and more preferably 18-32%; the intrinsic viscosity of the spinning solution is preferably 1.0-2.0 dL / g, more preferably 1.2-1.8 dL / g, and more preferably 1.3-1.6 dL / g.

[0045] In the present invention, the method for preparing the soluble asphalt extract in step 1) is preferably: mixing asphalt and an organic solvent, followed by extraction, centrifugation, rotary evaporation, and drying to obtain a soluble asphalt extract;

[0046] The asphalt is preferably one or more of naphthalene asphalt, petroleum asphalt and coal asphalt, and the organic solvent is preferably one or more of N,N-dimethylformamide, N,N-dimethylacetamide, tetrahydrofuran, pyridine, quinoline and dimethyl sulfoxide; the extraction method is preferably ultrasonic-assisted extraction, Soxhlet extraction or magnetic stirring.

[0047] In the present invention, the mass ratio of the asphalt and the organic solvent in step 1) is preferably 1:3~8, more preferably 1:4~7, and more preferably 1:5~6; the temperature of the magnetic stirring is preferably 20~70°C, more preferably 30~60°C, more preferably 40~50°C, the time of the magnetic stirring is preferably 10~14h, more preferably 12h, the speed of the centrifugation is preferably 7000~9000rpm, more preferably 7500~8500rpm, more preferably 8000rpm, and the time of the centrifugation is preferably 8~12min, more preferably 10min; the speed of the rotary evaporation is preferably 80~150rpm, more preferably 100~120rpm; the drying temperature is preferably 50~70°C, more preferably 55~65°C, more preferably 60°C, and the drying time is preferably 20~26h, more preferably 22~24h.

[0048] In the present invention, in step 1), the soluble asphalt solution and the polyacrylonitrile resin solution are mixed, and the obtained mixture is stirred, filtered, and vacuum degassed to obtain a spinning solution.

[0049] In the present invention, the preparation process of the spun fiber in step 2) is as follows: the spinning solution is delivered to the spinneret via a metering pump, and enters the coagulation bath directly from the spinneret at a speed of preferably 1 to 20 m / min, more preferably 5 to 16 m / min, and more preferably 10 to 13 m / min; after the guide roller is adjusted, it preferably enters the second roller at a speed of 0.5 to 50 m / min to form the spun fiber, more preferably 1 to 30 m / min, and more preferably 1.5 to 20 m / min.

[0050] In the present invention, the coagulation bath for the coagulation molding in step 2) is preferably composed of water and an organic solvent. The mass fraction of the organic solvent in the coagulation bath is preferably 20-70%, more preferably 30-60%, and more preferably 40-50%. The coagulation molding temperature is preferably 0-70°C, more preferably 10-60°C, and more preferably 20-50°C.

[0051] In the present invention, the temperature of the water washing in step 2) is preferably 10-70°C, more preferably 20-60°C, more preferably 30-50°C; the temperature of the hot water drawing is preferably 50-90°C, more preferably 60-80°C, more preferably 70°C; and the temperature of the heat setting is preferably 100-180°C, more preferably 110-160°C, more preferably 130-150°C.

[0052] In the present invention, the mass fraction of the dispersant solution in step 3) is preferably 0.01-0.3%, more preferably 0.05-0.25%, and more preferably 0.1-0.2%. The dispersant is preferably one or more of hydroxymethyl cellulose, sodium dodecylbenzene sulfonate, polyacrylamide, and polyethylene oxide.

[0053] In the present invention, the resin solution is preferably an alcohol solution of boron phenolic resin; the mass fraction of the resin solution is preferably 5-18%, more preferably 8-12%, and more preferably 10%; the solvent in the alcohol solution of boron phenolic resin is preferably methanol or ethanol; the preparation method of boron phenolic resin adopts a method well known in the art, boron phenolic resin is a resin with a high residual carbon rate, which can improve the bonding performance of the overlap between single fibers; the impregnation method in the resin solution is preferably vacuum impregnation or normal pressure impregnation, the vacuum degree is preferably 120-140 Pa, more preferably 125-135 Pa, and more preferably 130 Pa, and the impregnation time is preferably 30-70 min, more preferably 40-60 min, and more preferably 50 min.

[0054] In the present invention, the length of the chopped pre-oxidized yarn is preferably 5-23 mm, more preferably 8-20 mm, more preferably 10-18 mm, and the degree of cyclization is preferably ≥85%, more preferably ≥88%, and more preferably ≥90%.

[0055] In the present invention, the process pre-oxidation in step 3) preferably comprises three stages of pre-oxidation, and the temperature of the first stage of pre-oxidation is preferably 200-250°C, more preferably 210-240°C, and more preferably 220- The pre-oxidation temperature of the second stage is preferably 250-300°C, more preferably 260-290°C, more preferably 270-280°C, and the pre-oxidation time of the second stage is preferably 30-60min, more preferably 35-55min, more preferably 40-50min; the pre-oxidation temperature of the third stage is preferably 240-270°C, more preferably 250-260°C, more preferably 255°C, and the pre-oxidation time of the third stage is preferably 30-45min, more preferably 33-42min, more preferably 35-40min; the heating rate of the programmed pre-oxidation is preferably 3-7°C / min, more preferably 4-6°C / min, more preferably 5°C / min.

[0056] The pre-oxidation of the present invention includes two heating steps and one cooling step. The purpose of cooling is to buffer and release the thermal stress inside the fiber during the high temperature stage.

[0057] In the present invention, the temperature of the hot pressing curing in step 3) is preferably 110-150°C, more preferably 120-140°C, and more preferably 130°C; the time of the hot pressing curing is preferably 10-20 min, more preferably 12-18 min, and more preferably 15-16 min; and the pressure of the hot pressing curing is preferably 0.5-6 MPa, more preferably 1-5 MPa, and more preferably 2-4 MPa.

[0058] In the present invention, in step 3), the chopped pre-oxidized fibers are mixed with a dispersant solution, and are sequentially subjected to wet papermaking, a first drying step, impregnation in a resin solution, a second drying step, and hot pressing and curing to obtain pre-oxidized fiber paper. The chopped pre-oxidized fibers and the dispersant solution are preferably mixed by ultrasonic stirring. The vacuum degree of the wet papermaking is preferably 0.04-0.06 MPa, more preferably 0.05 MPa, and the dehydration time is preferably 80-100 s, more preferably 85-95 s, and more preferably 90 s.

[0059] In the present invention, the polyacrylonitrile molecular chain and the asphalt component are pre-oxidized in an air atmosphere to form active hydrophilic groups such as -OH, -COOH, and -C=O, which promotes the rapid and uniform dispersion of the chopped pre-oxidized fibers in the dispersant solution, and is beneficial to the full random interweaving of the fibers in three-dimensional space during papermaking, thereby improving the mechanical properties of the pre-oxidized fiber paper.

[0060] In the present invention, the carbonization temperature in step 4) is preferably 600-1200° C., more preferably 800-1100° C., more preferably 900-1000° C., and the carbonization time is preferably 0.8-1.2 h, more preferably 1 h; the graphitization temperature is preferably 2000-2600° C., more preferably 2100-2500° C., more preferably 2200-2300° C., and the graphitization time is preferably 0.3-1 h, more preferably 0.5 h. Carbonization and graphitization are preferably carried out under a protective atmosphere.

[0061] In the present invention, the carbonization and graphitization treatment is preferably carried out in a multi-stage step-by-step programmed temperature-controlled tubular furnace to perform one-step carbonization and graphitization.

[0062] The present invention also provides carbon fiber paper based on composite carbon fiber preoxidized yarn prepared by the preparation method, wherein the carbon fiber paper has a thickness of 120-210 μm, a tensile strength of 16.3-30.2 MPa, a resistivity of 3.5-8.7 mΩ·cm, and a thermal conductivity of 17.2-26.7 W / m·K.

[0063] The present invention also provides the use of the carbon fiber paper based on the composite carbon fiber preoxidized yarn in the gas diffusion layer of a proton exchange membrane fuel cell.

[0064] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0065] The model of the multi-stage step-by-step program temperature-controlled tube furnace used in the examples and comparative examples is KSL-1700X-GS;

[0066] Polyethylene oxide: Shanghai Aladdin Biochemical Technology Co., Ltd., CAS-68441-17-8, viscosity-average molecular weight Mv=5 million; hydroxymethyl cellulose: Shanghai Yuanye Biotechnology Co., Ltd., S14014-500g, viscosity is 100,000; polyacrylonitrile resin is acrylonitrile-itaconic acid copolymer, Shanghai Yuanye Biotechnology Co., Ltd., CAS-25014-41-9, weight-average molecular weight Mw=150,000; boron phenolic resin: boron-modified phenolic resin, Jining Tangyi Chemical Co., Ltd.; coal tar: Tangshan Kailuan Carbon Chemical Co., Ltd., 17501; naphthalene pitch: Jining Carbon Group Co., Ltd., naphthalene asphalt; mesophase pitch-based carbon fiber: Mitsubishi Chemical Corporation of Japan, K63B; polyacrylonitrile-based carbon fiber: Jiangsu Hengshen Co., Ltd., HF40.

[0067] Example 1

[0068] The coal tar raw material was mechanically ground and sieved with a 200-mesh sieve. The sieved powder was mixed with tetrahydrofuran in a mass ratio of 1:7, and magnetically stirred at 600 rpm at 30°C for 12 hours. The mixture was then centrifuged in a centrifuge at 8000 rpm for 10 minutes. The filtrate was filtered in two steps (first through a 5-μm filter and then through a 1-μm filter) to remove the solvent tetrahydrofuran in a vacuum rotary evaporator at 100 rpm (vacuum degree of 0.08 MPa), and then dried in a 60°C forced air drying oven for 24 hours to obtain a soluble asphalt extract. The tetrahydrofuran and soluble asphalt extract were evenly mixed to obtain a soluble asphalt solution with a mass fraction of 42%.

[0069] At 120 rpm and room temperature, polyacrylonitrile resin was fully dissolved with N,N-dimethylformamide to obtain a polyacrylonitrile resin solution with a mass fraction of 25%; the soluble asphalt solution was slowly added to the polyacrylonitrile resin solution (the mass ratio of polyacrylonitrile resin and soluble asphalt extract was 1:0.8), stirred at 60°C and 300 rpm for 360 minutes, and then filtered in two steps (first filtered through a 5 μm filter and then filtered through a 1 μm filter), followed by vacuum degassing at room temperature and a vacuum degree of -0.7 bar to obtain a spinning solution.

[0070] The spinning solution is transported to the spinneret assembly through a metering pump, and a spinning stream is extruded from the spinneret. It enters the coagulation bath at a rate of 2m / min (the coagulation bath consists of water and N,N-dimethylformamide, and the mass fraction of N,N-dimethylformamide is 40%), and is coagulated and formed at 20°C. After the guide roller is adjusted, it enters the second roller at a rate of 1.8m / min to form primary fibers; the primary fibers are washed with water at 50°C, stretched with hot water at 80°C, and heat-set at 130°C to obtain composite carbon fiber precursors.

[0071] In a purified air atmosphere, the composite carbon fiber precursor was pre-oxidized by heating to 210°C (holding for 20 minutes) and 270°C (holding for 40 minutes) at a rate of 5°C / min, and then cooled to 250°C (holding for 20 minutes) at a rate of 5°C / min to obtain a composite carbon fiber pre-oxidized yarn with a cyclization degree of 87%, which was then chopped into 8 mm long short pre-oxidized yarns using a fiber cutting machine.

[0072] Short-cut pre-oxidized fibers were added to a 0.05% by mass polyethylene oxide aqueous solution, and stirred at a rate of 400 rpm for 3 minutes under 40kHz ultrasonic synergy to obtain a uniformly dispersed pre-oxidized fiber papermaking pulp; the pulp was added to a wet former and dehydrated at a vacuum of 0.05 MPa for 90 seconds, and the fibers formed pre-oxidized fiber paper with uniform thickness on the filter screen; the pre-oxidized fiber paper was dried at 60°C for 6 hours, and then slowly placed in a methanol solution of boron phenolic resin (the mass fraction of boron phenolic resin in methanol solution was 10%), and impregnated at a vacuum of 130 Pa for 40 minutes. After the impregnation was completed, the pulp was dried at 60°C for 1 hour; and then hot-pressed and cured at 140°C and 4 MPa for 20 minutes to obtain resin-impregnated pre-oxidized fiber paper.

[0073] The resin-impregnated preoxidized fiber paper was transferred into a multi-stage step-by-step temperature-controlled tubular furnace. Under a nitrogen atmosphere, the temperature was raised from room temperature to 900°C at a rate of 5°C / min and kept warm for 60 minutes. Then, under an argon atmosphere, the temperature was raised to 2300°C at a rate of 10°C / min and kept warm for 30 minutes to obtain carbon fiber paper based on composite carbon fiber preoxidized yarn.

[0074] The microstructure of the fiber paper after carbonization treatment in this embodiment is as follows: Figure 1 As shown by Figure 1 It can be seen that in three-dimensional space, the fibers are intertwined and connected with each other, and the resin carbon is mainly concentrated at the overlapping points between the fibers, which plays a role in strengthening the fiber bonding without blocking the pore structure inside the fiber paper.

[0075] Example 2

[0076] The mass ratio of polyacrylonitrile resin and soluble asphalt extract in the spinning solution of Example 1 was adjusted to 1:0.4, the length of the chopped pre-oxidized yarn was adjusted to 14 mm, and the dispersion was adjusted to an aqueous solution of hydroxymethyl cellulose with a mass fraction of 0.1%; the other preparation methods were the same as in Example 1.

[0077] The microstructure of the fiber paper after graphitization treatment in this embodiment is as follows Figure 2 As shown by Figure 2 It can be seen that the resin carbon is tightly adhered to the fiber overlap and does not separate from the fiber surface. At the same time, it shows a regular graphite layer morphology and also reflects the graphite orientation characteristics in the local area of the fiber cross section.

[0078] Example 3

[0079] The naphthalene asphalt raw material was mechanically ground and sieved with a 200-mesh sieve. The sieved powder was mixed with dimethyl sulfoxide at a mass ratio of 1:5, and magnetically stirred at 800 rpm at 60°C for 12 hours. Then, the mixture was centrifuged in a centrifuge at 8000 rpm for 10 minutes. The filtrate was filtered in two steps (first through a 5-μm filter and then through a 1-μm filter) to remove the solvent dimethyl sulfoxide in a vacuum rotary evaporator at 120 rpm (vacuum degree of 0.08 MPa), and then dried in a 60°C forced air drying oven for 24 hours to obtain a soluble asphalt extract. The dimethyl sulfoxide and the soluble asphalt extract were evenly mixed to obtain a soluble asphalt solution with a mass fraction of 20%.

[0080] At 120 rpm and room temperature, polyacrylonitrile resin was fully dissolved with N,N-dimethylformamide to obtain a polyacrylonitrile resin solution with a mass fraction of 30%; the soluble asphalt solution was slowly added to the polyacrylonitrile resin solution (the mass ratio of polyacrylonitrile resin and soluble asphalt extract was 1:1.1), stirred at 60°C and 300 rpm for 360 minutes, and then filtered in two steps (first filtered through a 5 μm filter and then filtered through a 1 μm filter), followed by vacuum degassing at room temperature and a vacuum degree of -0.7 bar to obtain a spinning solution.

[0081] The spinning solution is transported to the spinneret assembly through a metering pump, and a spinning stream is extruded from the spinneret. It enters the coagulation bath at a rate of 1 m / min (the coagulation bath consists of water and N,N-dimethylformamide, and the mass fraction of N,N-dimethylformamide is 30%), and is coagulated and formed at 50°C. After the guide roller is adjusted, it enters the second roller at a rate of 1.2 m / min to form primary fibers; the primary fibers are washed with water at 60°C, stretched with hot water at 70°C, and heat-set at 140°C to obtain composite carbon fiber precursors.

[0082] In a purified air atmosphere, the composite carbon fiber precursor was pre-oxidized by heating to 220°C (holding for 20 min) and 290°C (holding for 60 min) at a rate of 5°C / min, and then cooled to 260°C (holding for 30 min) at a rate of 5°C / min to obtain a composite carbon fiber pre-oxidized yarn with a cyclization degree of 88%, which was then chopped into 12 mm long short pre-oxidized yarns using a fiber cutting machine.

[0083] Short-cut pre-oxidized fibers were added to a 0.15% by mass polyethylene oxide aqueous solution, and stirred at a rate of 400 rpm for 3 minutes under 40kHz ultrasonic synergy to obtain a uniformly dispersed pre-oxidized fiber papermaking pulp; the pulp was added to a wet former and dehydrated at a vacuum of 0.05 MPa for 90 seconds, and the fibers formed pre-oxidized fiber paper with uniform thickness on the filter screen; the pre-oxidized fiber paper was dried at 60°C for 6 hours, and then slowly placed in a methanol solution of boron phenolic resin (the mass fraction of boron phenolic resin in methanol solution was 9%), and impregnated at a vacuum of 130 Pa for 40 minutes. After the impregnation was completed, the pulp was dried at 60°C for 1 hour; and then hot-pressed and cured at 140°C and 4 MPa for 20 minutes to obtain resin-impregnated pre-oxidized fiber paper.

[0084] The resin-impregnated preoxidized fiber paper was transferred into a multi-stage step-by-step temperature-controlled tubular furnace. Under a nitrogen atmosphere, the temperature was raised from room temperature to 1000°C at a rate of 5°C / min and kept warm for 60 minutes. Then, under an argon atmosphere, the temperature was raised to 2200°C at a rate of 10°C / min and kept warm for 30 minutes to obtain carbon fiber paper based on composite carbon fiber preoxidized yarn.

[0085] Example 4

[0086] The mass ratio of polyacrylonitrile resin and soluble asphalt extract in Example 3 was adjusted to 1:0.7, the length of the chopped pre-oxidized fibers was adjusted to 18 mm, and the dispersion was adjusted to a 0.2% by mass hydroxymethyl cellulose aqueous solution; the other preparation methods were the same as in Example 3.

[0087] Example 5

[0088] The coal tar raw material was mechanically ground and sieved with a 200-mesh sieve. The sieved powder was mixed with tetrahydrofuran in a mass ratio of 1:4, and magnetically stirred at 600 rpm at 50°C for 12 hours. The mixture was then centrifuged in a centrifuge at 8500 rpm for 9 minutes. The filtrate was filtered in two steps (first through a 5-μm filter and then through a 1-μm filter) to remove the solvent tetrahydrofuran in a vacuum rotary evaporator at 120 rpm (vacuum degree of 0.08 MPa), and then dried in a 65°C forced air drying oven for 22 hours to obtain a soluble asphalt extract. The tetrahydrofuran and soluble asphalt extract were evenly mixed to obtain a soluble asphalt solution with a mass fraction of 15%.

[0089] At 120 rpm and room temperature, polyacrylonitrile resin was fully dissolved in N,N-dimethylformamide to obtain a polyacrylonitrile resin solution with a mass fraction of 20%; the soluble asphalt solution was slowly added to the polyacrylonitrile resin solution (the mass ratio of polyacrylonitrile resin and soluble asphalt extract was 1:0.9), stirred at 60°C and 300 rpm for 360 minutes, and then filtered in two steps (first filtered through a 5 μm filter and then filtered through a 1 μm filter), followed by vacuum degassing at room temperature and a vacuum degree of -0.7 bar to obtain a spinning solution.

[0090] The spinning solution is transported to the spinneret assembly through a metering pump, and a spinning stream is extruded from the spinneret. It enters the coagulation bath at a rate of 0.8 m / min (the coagulation bath consists of water and N,N-dimethylformamide, and the mass fraction of N,N-dimethylformamide is 60%), and is coagulated and formed at 30°C. After the guide roller is adjusted, it enters the second roller at a rate of 0.72 m / min to form nascent fibers; the nascent fibers are washed with water at 30°C, stretched with hot water at 60°C, and heat-set at 160°C to obtain composite carbon fiber precursors.

[0091] In a purified air atmosphere, the composite carbon fiber precursor was pre-oxidized by heating to 210°C (keeping temperature for 20 min) and 280°C (keeping temperature for 50 min) at a rate of 5°C / min, and then cooled to 250°C (keeping temperature for 40 min) at a rate of 5°C / min to obtain a composite carbon fiber pre-oxidized yarn with a cyclization degree of 87%, which was then chopped into 20 mm long short pre-oxidized yarns using a fiber cutting machine.

[0092] A sodium dodecylbenzenesulfonate aqueous solution (mass fraction 0.25%) and a polyethylene oxide aqueous solution (mass fraction 0.05%) in a volume ratio of 1:1 were evenly mixed, short-cut pre-oxidized fibers were added, and the mixture was stirred at a rate of 400 rpm for 3 minutes under 40kHz ultrasonic assisted conditions to obtain a uniformly dispersed pre-oxidized fiber papermaking pulp; the pulp was added to a wet former and dehydrated at a vacuum degree of 0.06 MPa for 85 seconds, and the fibers formed pre-oxidized fiber paper with uniform thickness on the filter screen; the pre-oxidized fiber paper was dried at 60°C for 6 hours, and then slowly placed in an ethanol solution of boron phenolic resin (the mass fraction of boron phenolic resin in the ethanol solution was 11%), and impregnated at a vacuum degree of 130 Pa for 40 minutes. After the impregnation was completed, the pulp was dried at 60°C for 1 hour; and then hot-pressed and cured at 150°C and 4 MPa for 10 minutes to obtain resin-impregnated pre-oxidized fiber paper.

[0093] The resin-impregnated preoxidized fiber paper was transferred into a multi-stage step-by-step temperature-controlled tubular furnace. Under a nitrogen atmosphere, the temperature was raised from room temperature to 1200°C at a rate of 5°C / min and kept warm for 60 minutes. Then, under an argon atmosphere, the temperature was raised to 2400°C at a rate of 10°C / min and kept warm for 30 minutes to obtain carbon fiber paper based on composite carbon fiber preoxidized yarn.

[0094] Comparative Example 1

[0095] The difference from Example 1 is that only an equal amount of tetrahydrofuran is added to the spinning solution, and no soluble asphalt extract is added. Tetrahydrofuran is slowly added to the polyacrylonitrile resin solution to prepare carbon fiber paper. Other process conditions are the same as in Example 1.

[0096] The infrared spectra of the as-spun fibers of Example 5 and Comparative Example 1 are as follows: Figure 3 As shown, wherein asphalt-PAN is Example 5, PAN is Comparative Example 1; Figure 3 It can be seen that the as-spun fibers of Example 5 are 600~750cm -1 The presence of CH absorption peaks characteristic of aromatic hydrocarbon molecules indicates that the as-spun fibers contain aromatic compounds with short aliphatic side chains. This indicates that the introduction of soluble pitch significantly impacts the internal chemical composition of the fibers. The as-spun fibers of Comparative Example 1 lack the typical absorption peaks characteristic of the chemical structure of soluble pitch. Under identical wet spinning, pre-oxidation, resin impregnation, hot pressing, and carbonization and graphitization conditions, the carbon fiber paper produced in Comparative Example 1 exhibits weaker tensile strength, electrical conductivity, and thermal conductivity than those of Example 1.

[0097] Comparative Example 2

[0098] The difference from Comparative Example 1 is that only the graphitization temperature is adjusted from 2300°C to 2800°C to prepare carbon fiber paper, and the other process conditions are the same as those in Comparative Example 1.

[0099] In this comparative example, a higher temperature graphitization treatment was performed. Due to the inherent difficulty in graphitization of polyacrylonitrile-based carbon fibers and phenolic resin, the electrical and thermal conductivity of the carbon fiber paper in this comparative example was not significantly improved compared to comparative example 1.

[0100] Comparative Example 3

[0101] The difference from Example 5 is that this comparative example uses mesophase pitch-based carbon fiber and polyacrylonitrile-based carbon fiber as fiber raw materials for papermaking (the mass ratio of mesophase pitch-based carbon fiber to polyacrylonitrile-based carbon fiber is 0.9:1). The specific steps are as follows: a sodium dodecylbenzenesulfonate aqueous solution (mass fraction 0.25%) and a polyethylene oxide aqueous solution (mass fraction 0.05%) in a volume ratio of 1:1 are evenly mixed, and mesophase pitch-based carbon fibers (length 5 mm) and polyacrylonitrile-based carbon fibers (length 8 mm) in a mass ratio of 0.9:1 are added, and stirred at a speed of 400 rpm for 10 minutes under 40kHz ultrasonic synergy to obtain a papermaking slurry; the slurry is added to a wet former for papermaking, and dehydrated at a vacuum degree of 0.05 MPa for 90 seconds, and the fibers form a base paper with uniform thickness on the filter screen; the base paper is dried at 60°C for 6 hours, and then slowly placed in an ethanol solution of 11% boron phenolic resin, and impregnated at a vacuum degree of 130 Pa for 40 minutes. After the impregnation is completed, it is dried at 60°C for 1 hour; and then hot-pressed and cured at 150°C and 4 MPa for 10 minutes to obtain resin-impregnated pre-oxidized fiber paper.

[0102] The resin-impregnated preoxidized fiber paper was transferred into a multi-stage step-by-step temperature-controlled tubular furnace. Under a nitrogen atmosphere, the temperature was raised from room temperature to 1200°C at a rate of 5°C / min and kept warm for 60 minutes. Then, under an argon atmosphere, the temperature was raised to 2300°C at a rate of 10°C / min and kept warm for 30 minutes to obtain the corresponding carbon fiber paper.

[0103] Other process conditions are the same as those in Example 5.

[0104] Compared with Comparative Examples 1 and 2, the electrical and thermal conductivity of this comparative example is significantly improved; compared with Example 5, the thermal conductivity is close, but the strength and conductivity are quite different, and secondary carbonization and graphitization are required, which is costly.

[0105] The microstructure of the fiber paper after carbonization treatment in this comparative example is as follows Figure 4 As shown in the figure, due to the lack of active groups on the surface of carbon fiber, the hydrophilicity is poor. After the dispersion liquid is ultrasonically stirred, small fiber bundles will still agglomerate, affecting the uniform dispersion of the fiber in water. Figure 4 It can be seen that the agglomerated fiber bundles affect the aggregation of resin carbon at the fiber overlap and do not play a good bonding role.

[0106] The performance test results of the carbon fiber papers prepared in the examples and comparative examples are shown in Table 1. The detection method for the carbon fiber paper performance test is based on GB / T 20042.7-2014.

[0107] Table 1 Performance data of carbon fiber paper prepared in different embodiments and comparative examples

[0108]

[0109] As can be seen from Table 1, after the soluble asphalt component is introduced into the spinning solution, the tensile strength, electrical conductivity and thermal conductivity of the carbon fiber paper prepared with the composite carbon fiber pre-oxidized yarn are better than those of the carbon fiber paper made from polyacrylonitrile-based carbon fiber; compared with the 2800°C graphitized carbon fiber paper, the performance of the composite carbon fiber paper treated only at 2300°C is also excellent.

[0110] The present invention introduces soluble asphalt into polyacrylonitrile spinning solution, adopts wet spinning process to prepare composite carbon fiber precursor, and performs pre-oxidation and short-cut treatment to obtain composite carbon fiber pre-oxidized yarn. After wet papermaking, impregnation in resin solution, hot pressing and curing, the large-layer graphite microcrystals formed by the asphalt polycyclic aromatic hydrocarbon components regulate the growth, formation and stacking of graphite microcrystals in the polyacrylonitrile fiber matrix, and a rich conductive network structure is constructed inside the fiber. On the basis of good mechanical properties, the preparation of "low-cost-high-conductivity-high-thermal conductivity" functional carbon fiber paper is achieved, which solves the problems in the prior art of limited sources of carbon fiber raw materials used in carbon fiber paper, poor electrical and thermal conductivity, and high cost.

[0111] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing carbon fiber paper based on composite carbon fiber pre-oxidized yarn, characterized in that: The following steps are included: 1) mixing a soluble asphalt solution and a polyacrylonitrile resin solution to obtain a spinning solution; 2) The spinning solution is sequentially wet-spun and coagulated to obtain spun fibers; the spun fibers are sequentially washed, hot-water drawn, and heat-set to obtain composite carbon fiber precursors; 3) The composite carbon fiber precursor is sequentially pre-oxidized and chopped to obtain chopped pre-oxidized fibers; The chopped pre-oxidized fibers are mixed with a dispersant solution, and are sequentially subjected to wet papermaking, impregnation in a resin solution, and hot pressing to obtain pre-oxidized fiber paper. 4) The preoxidized fiber paper is sequentially carbonized and graphitized to obtain carbon fiber paper based on composite carbon fiber preoxidized filaments; The solvent of the polyacrylonitrile resin solution is N,N-dimethylformamide, and the polyacrylonitrile resin is acrylonitrile-itaconic acid copolymer; the mass fraction of the polyacrylonitrile resin solution is 15-30%; The soluble asphalt solution is composed of a soluble asphalt extract and an organic solvent, wherein the mass ratio of polyacrylonitrile resin to the soluble asphalt extract is 1:0.1-1.

5. The preparation method of the soluble asphalt extract comprises: mixing asphalt and the organic solvent, extracting, centrifuging, rotary evaporating, and drying in sequence to obtain the soluble asphalt extract; Step 2) the coagulation bath for coagulation molding is composed of water and an organic solvent; Step 4) The carbonization temperature is 600-1200° C., the time is 0.8-1.2 h, the graphitization temperature is 2000-2600° C., the time is 0.3-1 h, and the carbonization and graphitization are carried out under a protective atmosphere.

2. The method for preparing carbon fiber paper based on composite carbon fiber preoxidized yarn according to claim 1, characterized in that: In step 1), the mass fraction of the soluble asphalt solution is 5-45%; the intrinsic viscosity of the spinning solution is 1.0-2.0 dL / g.

3. The method for preparing carbon fiber paper based on composite carbon fiber preoxidized yarn according to claim 1 or 2, characterized in that: In step 1), the asphalt is one or more of naphthalene asphalt, petroleum asphalt and coal asphalt, and the organic solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, tetrahydrofuran, pyridine, quinoline and dimethyl sulfoxide; and the extraction method is ultrasonic-assisted extraction, Soxhlet extraction or magnetic stirring.

4. The method for preparing carbon fiber paper based on composite carbon fiber preoxidized yarn according to claim 3, characterized in that: In step 2), the mass fraction of the organic solvent in the coagulation bath is 20-70%, and the coagulation temperature is 0-70°C.

5. The method for preparing carbon fiber paper based on composite carbon fiber preoxidized yarn according to claim 4, characterized in that: Step 2) the water washing temperature is 10-70°C, the hot water drawing temperature is 50-90°C, and the heat setting temperature is 100-180°C.

6. The method for preparing carbon fiber paper based on composite carbon fiber preoxidized yarn according to claim 4 or 5, characterized in that: Step 3) the mass fraction of the dispersant solution is 0.01-0.3%, the dispersant is one or more of hydroxymethyl cellulose, sodium dodecylbenzene sulfonate, polyacrylamide and polyethylene oxide; the resin solution is an alcohol solution of boron phenolic resin; The length of the chopped pre-oxidized yarn is 5 to 23 mm, and the cyclization degree is ≥85%.

7. The method for preparing carbon fiber paper based on composite carbon fiber preoxidized yarn according to claim 6, characterized in that: Step 3) The program pre-oxidation includes three stages of pre-oxidation, the first stage of pre-oxidation temperature is 200-250 ° C, the time is 15-24 minutes, the second stage of pre-oxidation temperature is 250-300 ° C, the time is 30-60 minutes, and the third stage of pre-oxidation temperature is 240-270 ° C, the time is 30-45 minutes; The temperature of the hot pressing curing is 110-150° C., the time is 10-20 minutes, and the pressure is 0.5-6 MPa.

8. The carbon fiber paper based on composite carbon fiber preoxidized yarn prepared by the preparation method according to any one of claims 1 to 7, characterized in that: The carbon fiber paper has a thickness of 120 to 210 μm, a tensile strength of 16.3 to 30.2 MPa, a resistivity of 3.5 to 8.7 mΩ·cm, and a thermal conductivity of 17.2 to 26.7 W / m·K.

9. Use of the carbon fiber paper based on composite carbon fiber preoxidized yarn according to claim 8 in a gas diffusion layer of a proton exchange membrane fuel cell.

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