Method, product and application for preparing carbon fiber paper with recycled carbon fiber

Abstract

The present invention relates to a method, product and application for preparing carbon fiber paper from recycled carbon fibers, which solves the technical problems of no pores and high conductivity of carbon fiber paper in the prior art, and comprises the following steps: adding recycled short carbon fibers into water added with a dispersant, stirring to obtain a recycled carbon fiber suspension, then adding an antifoaming agent and performing pneumatic dispersion, and finally obtaining a recycled carbon fiber pulp with good uniformity; obtaining a paper blank from the recycled short carbon fiber pulp by a wet papermaking method; dispersing functional nano-fillers in an adhesive resin solution, immersing the paper blank in the resin solution, taking it out and drying, and then performing staged curing to obtain a recycled carbon fiber paper precursor; performing carbonization and graphitization treatments on the recycled carbon fiber paper precursor to obtain a recycled carbon fiber paper. The carbon fiber paper prepared in the present invention can be used for preparing proton exchange membrane fuel cells.

Description

Technical Field

[0001] The present invention relates to a carbon fiber paper, a preparation method thereof and an application, and specifically to a method for preparing carbon fiber paper from recycled carbon fibers, a product thereof and an application. Background Art

[0002] Proton exchange membrane fuel cells (PEMFCs) have significant advantages in operating temperature and startup time and are widely used fuel cells. PEMFCs require three key materials: a proton exchange membrane, a catalyst, and a gas diffusion layer. A gas diffusion layer requires the use of carbon fiber paper. Carbon fiber paper is a conductive porous material formed by bonding and curing short carbon fibers with an adhesive and finally through carbonization and graphitization.

[0003] Currently, most of the raw material short carbon fibers for carbon fiber paper are products formed by cutting carbon fiber filaments, which have a high cost, and because the short carbon fibers lack continuity, it also has an adverse effect on the electrical conductivity of the carbon paper.

[0004] At the same time, the generation amount of carbon fiber composite waste is increasing day by day. The carbon fibers recovered by pyrolysis are difficult to ensure sufficient length and basically exist in the form of short cuts. Not only does their mechanical performance decline, but their surface also undergoes a certain degree of oxidation, and there are great limitations in using them again as a composite reinforcement. However, the short cut form of recycled carbon fibers is suitable as a raw material for carbon fiber paper, and the hydrophilic functional groups on the surface of recycled fibers are more than those of ordinary carbon fibers, making it easier to disperse. Since carbon fiber paper requires high-temperature graphitization treatment, the requirements for the surface state of carbon fibers are relatively low, and the mechanical properties of recycled fibers basically meet the overall performance requirements of fiber paper.

[0005] Chinese patent application with the application number CN202210472092.8 provides a method for preparing carbon fiber paper using recycled carbon fibers. It uniformly mixes recycled carbon fibers and recycled wood cellulose pulp, uses the wet papermaking process to make paper, and then uses resin impregnation molding.

[0006] The carbon fiber paper prepared by the above method has no pores, and its electrical conductivity is higher than the requirements of PEMFCs without carbonization and graphitization, so it is not suitable for application in PEMFCs. Summary of the Invention

[0007] The present invention is to solve the technical problems of the existing carbon fiber paper having no pores and high electrical conductivity, and provides a carbon fiber paper prepared from recycled carbon fibers, a preparation method thereof and an application, which have high electrical conductivity, moderate porosity, high mechanical strength, good flexibility and can meet the technical requirements of carbon fiber paper for PEMFCs.

[0008] To this end, the present invention provides a method for preparing carbon fiber paper from recycled carbon fibers, which comprises the following steps: S1. Add recycled short carbon fibers into water added with a dispersant, stir to obtain a recycled carbon fiber suspension, then add an antifoaming agent and perform pneumatic dispersion, and finally obtain a recycled carbon fiber pulp with good uniformity; S2. Obtain a paper blank from the recycled short carbon fiber pulp obtained in step S1 by wet papermaking; S3. Disperse functional nano-fillers in an adhesive resin solution, immerse the paper blank obtained in step S2 in the resin solution, take it out and dry it, and then perform staged curing to obtain a recycled carbon fiber paper precursor; S4. Perform carbonization and graphitization treatment on the recycled carbon fiber paper precursor obtained in step S3 to obtain recycled carbon fiber paper.

[0009] Preferably, the recycled short carbon fibers in step S1 include: viscose-based carbon fibers, pitch-based carbon fibers, and PAN-based carbon fibers recovered by pyrolysis; the resistivity of the recycled carbon fibers is ≤2.50 mΩ·cm, the tensile strength is ≥3.50 GPa, the length is 1 mm to 10 mm, and the diameter is 5 to 10 μm.

[0010] Preferably, in step S1, the dispersant is at least one of hydroxymethyl cellulose, sodium hydroxymethyl cellulose, hydroxyethyl cellulose, polyethylene oxide, sodium dodecylbenzenesulfonate, calcium dodecylbenzenesulfonate, polyvinyl alcohol, and silane coupling agent, and the concentration of the dispersant in the suspension is 0.5 to 10 g / L; the antifoaming agent is at least one of emulsified silicone oil, high-carbon alcohol fatty acid ester complex, polyoxyethylene polyoxypropylene pentaerythritol ether, polyoxyethylene polyoxypropylene alkanolamine ether, polyoxypropylene glycerol ether, polyoxypropylene polyoxyethylene glycerol ether, and polydimethylsiloxane; the concentration of the antifoaming agent is 1 to 10 g / L; the mass ratio of the recycled short carbon fibers to the dispersant is 1:(1 to 5). Using the above dispersant at the above concentration can make the short carbon fibers disperse evenly; using the antifoaming agent can eliminate a large number of bubbles generated in the pneumatic dispersion step, and these bubbles may affect the uniformity of fiber dispersion.

[0011] Preferably, in step S1, the stirring time for electric stirring dispersion is 10 to 60 min, and the stirring rate is 200 to 1200 rpm; after stirring dispersion, add an antifoaming agent and perform secondary dispersion on the dispersion liquid by pneumatic dispersion, and the blowing rate of the air pump is 20 L / min to 100 L / min; the types of the antifoaming agent include one or several of emulsified silicone oil, high-carbon alcohol fatty acid ester complex, polyoxyethylene polyoxypropylene pentaerythritol ether, polyoxyethylene polyoxypropylene alkanolamine ether, polyoxypropylene glycerol ether, polyoxypropylene polyoxyethylene glycerol ether, and polydimethylsiloxane; the concentration of the antifoaming agent is 1 to 10 g / L. Using the above dispersion process can ensure the uniform dispersion of fibers to the greatest extent.

[0012] Preferably, in step S3, the resin is at least one of polyvinyl alcohol, phenolic resin, epoxy resin, and polyurethane, and the mass fraction of the resin in the solution is 6% - 20%. The resin acts as an adhesive to bond the fibers together, imparting mechanical strength to the carbon fiber paper.

[0013] Preferably, in step S3, the functional nano-fillers include carbon nanotubes, carbon nanofibers, graphene, nano-scale conductive carbon black, and nano-scale graphite powder; the mass ratio of the functional nano-fillers to the resin is (1 - 3):(300 - 100). Adding the functional nano-fillers within the above proportion range can improve the conductivity, mechanical strength, and flexural strength performance.

[0014] Preferably, in step S3, hot pressing and curing are carried out in three stages: In the first stage, the impregnated paper blank is placed in a flat vulcanizing machine, and the paper blank is heated at a temperature of 80 - 110°C for 5 - 30 min under normal pressure; in the second stage, the following treatment is performed on the heated paper blank: The temperature is maintained at 80 - 110°C throughout. When pressurizing, the pressure is first increased from 0 MPa to 6 - 15 MPa, held for 5 - 20 min and then reduced to 0 MPa and left standing for 5 - 20 min, and the above operations are repeated; in the third stage, the pressure is increased to 15 - 30 MPa, and the temperature is increased to 130 - 230°C, held for 0.5 - 2 h for curing and shaping. Using the segmented curing method can enable the resin to infiltrate into the carbon fiber paper as much as possible, reducing its thickness and improving its uniformity and flatness.

[0015] Preferably, in step S4, the carbonization treatment conditions are: holding at 800 - 1200°C for 1.5 - 2 h, with a heating rate of 5 - 20°C / min; the graphitization treatment conditions are: holding at 1500 - 2500°C for 0.5 - 2 h, with a heating rate of 10 - 20°C / min. Carrying out carbonization and graphitization treatments on the carbon fiber paper can greatly improve the conductivity of the carbon fiber paper and increase the porosity.

[0016] The present invention also provides a carbon fiber paper prepared by a method for preparing carbon fiber paper using recycled carbon fibers.

[0017] The present invention further provides the application of the carbon fiber paper in the preparation of proton exchange membrane fuel cells.

[0018] The present invention has the following beneficial effects:

[0019] (1) The carbon fibers used in the present invention are recycled from waste carbon fiber products, providing a new idea for the application of recycled carbon fibers and reducing the cost of carbon fiber paper for PEMFC.

[0020] (2) The present invention uses a dispersion method combining electric dispersion and pneumatic dispersion, enabling the carbon fibers to achieve a more uniform dispersion effect, which greatly enhances the flatness and uniformity of the subsequent carbon fiber paper.

[0021] (3) In the present invention, the production of carbon fiber paper is carried out by means of staged curing. This staged curing method enables the binder to be more evenly distributed between the fibers, greatly improving the flatness of the carbon fiber paper and significantly reducing its thickness. The process of combining the two dispersion methods and the process of staged curing improve the flatness, uniformity, and thickness of the carbon fiber paper from two aspects: fiber dispersion and binder diffusion. Currently, the thickness of commercially available carbon fiber paper is 0.185 - 0.195 mm, and the thickness deviation is ≤ ±1.5%. After staged curing, the thickness can reach 0.120 - 0.150 mm, and the thickness deviation is ≤ ±0.8%.

[0022] (4) The recycled carbon fiber paper prepared by the present invention is added with functional nano-fillers, which can compensate for the local defects of the carbon fiber paper, improve the interfacial bonding between the recycled carbon fibers and the resin, and the conductivity of the carbon fiber paper. It reaches or even exceeds the commercially available carbon fiber paper in terms of conductivity, flexibility, and mechanical strength, has a high porosity and strong air permeability, and is suitable for application in PEMFC. Description of the Drawings

[0023] Figure 1 is a photograph of the recycled carbon fiber paper obtained in Example 1 of the present invention;

[0024] Figure 2 is an SEM image of the microscopic morphology and pore structure of the recycled carbon fiber paper obtained in Example 1 of the present invention. Detailed Embodiments

[0025] The following further describes the present invention in conjunction with embodiments.

[0026] In the embodiments of the present invention, the carbon fibers in the selected waste carbon fiber resin-based composites are Toray T700 carbon fibers, with a single fiber tensile strength of 4.90 GPa and a resistivity of 1.6 mΩ·cm. Recycled carbon fibers are obtained through pyrolysis recovery.

[0027] Example 1

[0028] The waste carbon fiber composite material is pyrolytically recovered in an air atmosphere, and finally short-cut recycled carbon fibers with a clean surface, a resistivity of 1.90 mΩ·cm, a tensile strength of 4.30 GPa, an average length of 10 mm, and a diameter of 5 μm are obtained.

[0029] Weigh 100 g of hydroxyethyl cellulose and dissolve it in 10 L of water to make a dispersion with a concentration of 10 g / L. Then weigh 20 g of recycled carbon fiber and put it into the dispersion. Use an electric stirrer to stir the mixture at a rate of 500 rpm for 20 min to obtain recycled carbon fiber pulp. Next, weigh 100 g of emulsified silicone oil and add it to the fiber suspension. Use pneumatic dispersion to perform secondary dispersion on the fiber suspension, and the air blowing volume of the air pump is 20 L / min. The pulp after secondary dispersion is filtered through a filter screen and dried in an oven to obtain a recycled carbon fiber paper blank.

[0030] Dissolve phenolic resin in ethanol to make a resin ethanol solution with a mass fraction of 20%. Immerse the paper blank in it for 1 h, take it out and dry it in an oven. Then use a flat vulcanizing machine for three-stage hot pressing and curing: In the first stage, place the impregnated paper blank in the flat vulcanizing machine and heat the paper blank at a temperature of 80 °C under normal pressure for 30 min; In the second stage, process the heated paper blank as follows: Keep the temperature at 80 °C throughout the process. When pressurizing, first increase the pressure from 0 MPa to 15 MPa, keep it for 5 min and then reduce it to 0 MPa and let it stand for 5 min. Repeat the above operation three times; In the third stage, increase the pressure to 15 MPa and increase the temperature to 130 °C, and keep it for 2 h for curing and shaping. After cooling, a recycled carbon fiber paper precursor is obtained.

[0031] Put the recycled carbon fiber paper precursor into a graphitization furnace and carry out carbonization and graphitization treatment in an argon atmosphere: Heat it to 800 °C at a heating rate of 5 °C / min and hold for 2 h, then heat it to 1500 °C at a heating rate of 10 °C / min and hold for 2 h. Take it out after cooling to obtain recycled carbon fiber paper.

[0032] As Figure 1 shown, the surface of the recycled carbon fiber paper is smooth and flat, and it has certain flexibility and mechanical strength.

[0033] As Figure 2 shown, the microscopic morphology of the recycled carbon fiber paper presents a porous morphology under a scanning electron microscope, and the fibers are randomly arranged to form a network structure. There is residual carbon formed after the carbonization of the binder phenolic resin between the fibers, and the residual carbon plays a role in connecting the fibers, enabling the carbon fiber paper to form a perfect conductive network structure and enhancing the mechanical properties and flexibility of the carbon fiber paper.

[0034] The conductive properties of the recycled carbon fiber paper obtained in Example 1 were tested. Referring to the test method in Standard GB / T20042.7—2014, its resistivity was tested using an RTS-8 four-probe tester. The resistivity of the recycled carbon fiber paper was 6.09 mΩ·cm. Similarly, referring to the test method in Standard GB / T20042.7—2014, the tensile strength, flexural strength, and flexural modulus of the recycled carbon fiber paper were tested using an INSTRON5567 high-temperature mechanical property tester. The tensile strength of the recycled carbon fiber paper was 38.02 MPa, the flexural strength was 51.54 MPa, and the flexural modulus was 11.45 GPa. The thickness of the recycled carbon fiber paper was measured with a thickness gauge to be 0.138 mm, and the thickness deviation value was 0.8%.

[0035] Example 2

[0036] The waste carbon fiber composite was pyrolytically recycled in an air atmosphere, and finally short-cut recycled carbon fibers with a clean surface, a resistivity of 2.50 mΩ·cm, a tensile strength of 3.50 GPa, an average length of 7 mm, and a diameter of 7 μm were obtained.

[0037] 30 g of polyethylene oxide was weighed and dissolved in 10 L of water to prepare a dispersion with a concentration of 3 g / L. Then, 15 g of recycled carbon fibers with a length of 7 mm and a diameter of 7 μm were weighed and put into the dispersion, and an electric stirrer was used to stir at a rate of 800 rpm for 30 min to obtain recycled carbon fiber pulp. Then, 30 g of emulsified silicone oil was weighed and added to the fiber suspension, and the fiber suspension was secondarily dispersed by pneumatic dispersion, and the air blowing volume of the air pump was 40 L / min. The secondarily dispersed pulp was filtered through a filter screen and dried in an oven to obtain a recycled carbon fiber paper blank.

[0038] Phenolic resin was dissolved in ethanol to prepare a resin ethanol solution with a mass fraction of 10%. Carbon nanotubes (with a mass ratio to phenolic resin of 3:100) were taken and put into the resin ethanol solution, and ultrasonic treatment was carried out with a power of 150 w for 1 h using an ultrasonic instrument. The paper blank was impregnated therein for 1 h, taken out, and dried in an oven. Then, three-stage hot pressing and curing were carried out with a flat vulcanizer: In the first stage, the impregnated paper blank was placed in the flat vulcanizer, and the paper blank was heated at a temperature of 110 °C under normal pressure for 5 min; in the second stage, the following treatment was carried out on the heated paper blank: The temperature was kept at 110 °C throughout the process. When pressurizing, the pressure was first increased from 0 MPa to 6 MPa, kept for 20 min, then reduced to 0 MPa and left standing for 10 min, and the above operation was repeated three times; in the third stage, the pressure was increased to 30 MPa and the temperature was increased to 200 °C, and kept for 0.5 h for curing and shaping. After cooling, a recycled carbon fiber paper precursor was obtained.

[0039] Put the recycled carbon fiber paper precursor into a graphitization furnace and carry out carbonization and graphitization treatment under an argon atmosphere: heat it to 1200 °C at a heating rate of 20 °C / min and hold for 1.5 h, then heat it to 2500 °C at a heating rate of 20 °C / min and hold for 0.5 h. After cooling, take it out to obtain the recycled carbon fiber paper.

[0040] Test the electrical conductivity of the recycled carbon fiber paper obtained in Example 2. Refer to the test method in Standard GB / T20042.7—2014 and use an RTS-8 type four-probe tester to test its resistivity. The resistivity of the recycled carbon fiber paper is 3.97 mΩ·cm. Also refer to the test method in Standard GB / T20042.7—2014 to test the tensile strength, flexural strength and flexural modulus of the recycled carbon fiber paper, and use an INSTRON5567 type high-temperature mechanical property tester for testing. The tensile strength of the recycled carbon fiber paper is 42.25 MPa, the flexural strength is 57.94 MPa, and the flexural modulus is 12.56 GPa. Use a thickness gauge to measure the thickness of the carbon fiber paper to be 0.150 mm, and the thickness deviation value is 0.5%.

[0041] Example 3

[0042] Carry out pyrolysis recovery of the waste carbon fiber composite material in an air atmosphere, and finally obtain short-cut recycled carbon fibers with a clean surface, a resistivity of 2.05 mΩ·cm, a tensile strength of 4.02 GPa, an average length of 7 mm and a diameter of 10 μm.

[0043] Weigh 20 g of polyethylene oxide and dissolve it in 10 L of water to make a dispersion with a concentration of 2 g / L. Then weigh 15 g of recycled carbon fibers and put them into the dispersion, and use an electric stirrer to stir at a rate of 400 rpm for 60 min to obtain recycled carbon fiber pulp. Then weigh 50 g of emulsified silicone oil and add it to the fiber suspension, and use pneumatic dispersion to carry out secondary dispersion of the fiber suspension. The air blowing volume of the air pump is 60 L / min. The pulp after secondary dispersion is filtered through a filter screen and dried in an oven to obtain a recycled carbon fiber paper blank.

[0044] Dissolve phenolic resin in ethanol to make a resin ethanol solution with a mass fraction of 6%. Take carbon nanofibers (the mass ratio to phenolic resin is 1:300) and put them into the resin ethanol solution. Use an ultrasonic instrument to perform ultrasonic treatment at a power of 150 w for 1 h, immerse the paper blank in it for 1 h, and then take it out and dry it in an oven. Then use a flat vulcanizing machine for three-stage hot pressing and curing: In the first stage, place the impregnated paper blank in the flat vulcanizing machine and heat the paper blank at a temperature of 100 °C under normal pressure for 30 min; In the second stage, perform the following treatment on the heated paper blank: Keep the temperature at 100 °C throughout. When pressurizing, first increase from 0 MPa to 10 MPa, keep it for 10 min and then reduce it to 0 MPa and let it stand for 10 min. Repeat the above operation three times; In the third stage, increase the pressure to 20 MPa and the temperature to 160 °C, and keep it for 1 h for curing and shaping. After cooling, a recycled carbon fiber paper precursor is obtained.

[0045] Put the recycled carbon fiber paper precursor into a graphitization furnace and carry out carbonization and graphitization treatment in an argon atmosphere: Heat it to 1000 °C at a heating rate of 5 °C / min and hold for 1 h, then heat it to 2500 °C at a heating rate of 20 °C / min and hold for 1 h. Take it out after cooling to obtain recycled carbon fiber paper.

[0046] Conduct electrical conductivity and mechanical property tests on the recycled carbon fiber paper obtained in Example 3: The resistivity of the recycled carbon fiber paper is 3.33 mΩ·cm, the tensile strength is 41.51 MPa, the flexural strength is 59.83 MPa, and the flexural modulus is 12.96 GPa. The thickness of the tested carbon fiber paper is 0.148 mm, and the thickness deviation value is 0.7%.

[0047] Example 4

[0048] Perform pyrolysis recovery on the waste carbon fiber composite material in an air atmosphere, and finally obtain short-cut recycled carbon fibers with a clean surface, a resistivity of 2.15 mΩ·cm, a tensile strength of 3.82 GPa, an average length of 1 mm, and a diameter of 7 μm.

[0049] Weigh 10 g of polyethylene oxide and dissolve it in 10 L of water to make a dispersion with a concentration of 1 g / L. Then weigh 10 g of recycled carbon fibers and put them into the dispersion. Use an electric stirrer to stir at a rate of 1000 rpm for 30 min to obtain recycled carbon fiber pulp. Then weigh 10 g of emulsified silicone oil and add it to the fiber suspension. Use pneumatic dispersion to perform secondary dispersion on the fiber suspension, and the air blowing volume of the air pump is 100 L / min. The pulp after secondary dispersion is filtered through a filter screen and dried in an oven to obtain a recycled carbon fiber paper blank.

[0050] Dissolve phenolic resin in ethanol to make a 10% resin ethanol solution by mass. Take graphite powder (with a mass ratio of 2:100 to phenolic resin) and put it into the resin ethanol solution. Use an ultrasonic instrument to perform ultrasonic treatment at a power of 100 w for 1 h, immerse the paper blank in it for 1 h, and then take it out and dry it in an oven. Then, use a flat vulcanizing machine for three-stage hot pressing and curing: In the first stage, place the impregnated paper blank in the flat vulcanizing machine and heat the paper blank at a temperature of 100 °C under normal pressure for 20 min; in the second stage, perform the following treatment on the heated paper blank: Keep the temperature at 100 °C throughout. When pressurizing, first increase from 0 MPa to 10 MPa, keep it for 10 min and then decrease to 0 MPa and let it stand for 5 min, and repeat the above operation three times; in the third stage, increase the pressure to 30 MPa and the temperature to 170 °C, and keep it for 1 h for curing and shaping. After cooling, a recycled carbon fiber paper precursor is obtained.

[0051] Put the recycled carbon fiber paper precursor into a graphitization furnace and carry out carbonization and graphitization treatment in an argon atmosphere: Heat it to 1200 °C at a heating rate of 20 °C / min and hold for 1 h, and then heat it to 2500 °C at a heating rate of 20 °C / min and hold for 1 h. After cooling, take it out to obtain recycled carbon fiber paper.

[0052] Conduct electrical conductivity and mechanical property tests on the recycled carbon fiber paper obtained in Example 4: The resistivity of the recycled carbon fiber paper is 2.93 mΩ·cm, the tensile strength is 36.20 MPa, the flexural strength is 50.72 MPa, and the flexural modulus is 11.23 GPa. The thickness of the tested carbon fiber paper is 0.144 mm, and the thickness deviation value is 0.5%.

[0053] Example 5

[0054] The carbon fiber paper prepared in the above examples can be applied to the preparation of proton exchange membrane fuel cells. The carbon fiber paper used in proton exchange membrane fuel cells should meet the following performance standards according to the requirements of Standard GB / T20042.7-2014: thickness 0.08 - 0.25 mm, thickness deviation value ≤ 1.5%, resistivity ≤ 7 mΩ·cm, tensile strength ≥ 10 MPa, flexural strength ≥ 8 MPa, flexural modulus ≥ 8 GPa.

[0055] Comparative Example 1

[0056] Take the commercial carbon fiber paper, the TGP-H-060 type carbon fiber paper produced by Toray Industries, Inc. of Japan as the comparative example. The test results of the commercial carbon paper under the same method and conditions are as follows: resistivity 7.00 mΩ·cm, tensile strength 36.62 MPa, flexural strength 50.24 MPa, flexural modulus 10.97 GPa, thickness 0.190 mm, and thickness deviation value 1.2%.

[0057] The performance test results of the examples and comparative examples are shown in Table 1 below:

[0058] Table 1

[0059] Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Thickness / mm 0.138 0.150 0.148 0.144 0.190 Thickness deviation value / % 0.8 0.5 0.7 0.5 1.2 Resistivity / mΩ·cm 6.09 3.97 3.33 2.93 7.00 Tensile strength / MPa 38.02 42.25 41.51 36.20 36.62 Flexural strength / MPa 51.54 57.94 59.83 50.72 50.24 Flexural modulus / GPa 11.45 12.56 12.96 11.23 10.97

[0060] As can be seen from Table 1, reducing the thickness of the carbon fiber paper can increase the volume specific power density of the carbon fiber paper in the fuel cell, thereby improving the power density of the fuel cell; the reduction of the thickness deviation value indicates that the flatness and uniformity of the carbon fiber paper are optimized, which improves the conductivity, mechanical properties, and bending properties of the carbon fiber paper. The improvement of conductivity will increase the power density of the fuel cell, and the improvement of mechanical properties and bending properties will make the carbon fiber paper easier to process and have a longer life in the fuel cell.

[0061] The recycled carbon fiber paper prepared by the present invention is slightly superior to the commercial carbon fiber paper in terms of resistivity, tensile strength, bending strength and modulus, thickness, and flatness.

[0062] However, the above are only specific embodiments of the present invention, and the scope of implementation of the present invention cannot be limited thereby. Therefore, the replacement of equivalent components or equivalent changes and modifications made according to the scope of protection of the present invention patent shall still fall within the scope covered by the claims of the present invention.

Claims

1. A method for preparing carbon fiber paper from recycled carbon fibers, characterized in that, it includes the following steps: S1. Add recycled short carbon fibers into water added with a dispersant, stir to obtain a recycled carbon fiber suspension, then add an antifoaming agent and perform pneumatic dispersion, and finally obtain a recycled carbon fiber pulp with good uniformity; the dispersant is at least one of carboxymethyl cellulose, sodium carboxymethyl cellulose, hydroxyethyl cellulose, polyethylene oxide, sodium dodecylbenzenesulfonate, calcium dodecylbenzenesulfonate, polyvinyl alcohol, and silane coupling agent; the concentration of the dispersant in the suspension is 0.5-10 g / L; the antifoaming agent is at least one of emulsified silicone oil, high-carbon alcohol fatty acid ester complex, polyoxyethylene polyoxypropylene pentaerythritol ether, polyoxyethylene polyoxypropylene alkanolamine ether, polypropylene glycerol ether, polypropylene polyoxyethylene glycerol ether, and polydimethylsiloxane; the concentration of the antifoaming agent is 1-10 g / L; the mass ratio of the recycled short carbon fibers to the dispersant is 1:(1-5); S2. Obtain a paper blank from the recycled short carbon fiber pulp obtained in step S1 by the wet papermaking method; S3. Disperse functional nano-fillers in an adhesive resin solution, place the paper blank obtained in step S2 into the resin solution for impregnation, take it out and dry it, and then perform staged curing to obtain a precursor of recycled carbon fiber paper; in step S3, hot pressing curing is carried out in three stages; in the first stage, place the impregnated paper blank in a flat vulcanizer and heat the paper blank at a temperature of 80-110 °C under normal pressure for 5-30 min; in the second stage, perform the following treatment on the heated paper blank: keep the temperature at 80-110 °C throughout the process, when pressurizing, first increase from 0 MPa to 6-15 MPa, keep it for 5-20 min and then reduce it to 0 MPa and let it stand for 5-20 min, and repeat the above operation; in the third stage, increase the pressure to 15-30 MPa and increase the temperature to 130-230 °C, and keep it for 0.5-2 h for curing and shaping; the resin is at least one of polyvinyl alcohol, phenolic resin, epoxy resin, and polyurethane; the mass fraction of the resin in the solution is 6%-20%; the functional nano-fillers include carbon nanotubes, carbon nanofibers, graphene, nano-scale conductive carbon black, and nano-scale graphite powder; the mass ratio of the functional nano-fillers to the resin is (1-3):(300-100); S4. Perform carbonization and graphitization treatment on the precursor of recycled carbon fiber paper obtained in step S3 to obtain recycled carbon fiber paper.

2. The method for preparing carbon fiber paper from recycled carbon fibers according to claim 1, characterized in that, the recycled short carbon fibers in step S1 include: viscose-based carbon fibers, pitch-based carbon fibers, and PAN-based carbon fibers recovered by pyrolysis; the resistivity of the recycled carbon fibers ≤ 2.50 mΩ·cm, the tensile strength ≥ 3.50 GPa, the length is 1 mm-10 mm, and the diameter is 5-10 μm.

3. The method for preparing carbon fiber paper from recycled carbon fibers according to claim 2, characterized in that, In the step S1, the stirring time for electric stirring and dispersion is 10 to 60 minutes, and the stirring rate is 200 to 1200 rpm; after stirring and dispersion, an antifoaming agent is added, and the dispersion liquid is secondarily dispersed by means of pneumatic dispersion, and the blowing rate of the air pump is 20 L / min to 100 L / min.

4. The carbon fiber paper prepared by the method according to claims 1 to 3.

5. The application of the carbon fiber paper according to claim 4 in the preparation of a proton exchange membrane fuel cell.

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