Preparation method of carbon fiber cloth

Abstract

The invention belongs to the field of carbon fiber reinforced composite materials, and provides a preparation method of carbon fiber cloth, which comprises the following steps: depolymerizing lignin into a micromolecular aromatic compound, and collecting a lignin depolymerization liquid phase product; dispersing carbon fibers in an aqueous solution containing a dispersing agent to obtain a carbon fiber solution; preparing the carbon fiber solution into a fiber felt by adopting a wet forming method; taking a diluted solution of the lignin depolymerization liquid phase product as an adhesive, dipping the fibrofelt in the adhesive, performing hot pressing, and carbonizing in an oxygen-free environment; and repeating the dipping, hot pressing and carbonization processes for multiple times until the carbon fibers meet the expected performance requirements, and then performing graphitization treatment to obtain the carbon fiber cloth. The invention provides the preparation method of the carbon fiber cloth by using the lignin depolymerization liquid phase product as the adhesive, the use of phenolic resin is reduced, the influence of formaldehyde and phenol on the environment is reduced, and the carbon fiber cloth with excellent conductivity is obtained.

Description

Technical Field

[0001] The invention belongs to the field of carbon fiber reinforced composite materials and relates to a method for preparing carbon fiber cloth. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

[0003] Carbon fiber cloth's exceptional mechanical, electrical, and structural properties have led to its widespread application in a variety of fields, including aerospace, automotive, energy storage, and environmental protection. Traditional carbon fiber cloth production processes use thermosetting resins such as phenolic and epoxy as adhesives. During the prepreg hot pressing or hand lay-up curing stages, phenolic resins release carcinogens such as free formaldehyde and phenol, resulting in excessive VOC levels in the workshop, high post-processing costs, and significant harm to the environment and human health.

[0004] Although some researchers have tried to replace petroleum-based resins with renewable biomass adhesives (such as lignin, tannin, soy protein or cellulose derivatives), these natural macromolecules generally have inherent defects such as wide molecular weight distribution, low reactivity and poor thermal stability. Currently, they are only pressed into low-end materials such as low-density particleboard and paper-based composite films that do not require high mechanical properties. It is difficult to meet the requirements of the field of carbon fiber reinforced composite materials for high residual carbon rate and suitable rheological properties of adhesives. Therefore, large-scale application has not been achieved. Summary of the Invention

[0005] In order to solve the above problems, the present invention provides a method for preparing carbon fiber cloth using a liquid phase product of lignin depolymerization as a binder, reducing the use of phenolic resin, reducing the impact of formaldehyde and phenol on the environment, and obtaining a carbon fiber cloth with excellent conductivity.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: A first aspect of the present invention provides a method for preparing a carbon fiber cloth, comprising: Depolymerizing lignin into small molecular aromatic compounds and collecting lignin depolymerization liquid products; dispersing carbon fibers in an aqueous solution containing a dispersant to obtain a carbon fiber solution; The carbon fiber solution is formed into a fiber mat by a wet forming method; Using the diluted solution of the lignin depolymerization liquid phase product as an adhesive, impregnating the fiber felt in the adhesive, hot pressing, and carbonizing in an oxygen-free environment; The above impregnation, hot pressing and carbonization processes are repeated many times until the carbon fiber reaches the expected performance requirements, and then graphitization treatment is performed to obtain carbon fiber cloth.

[0007] The second aspect of the present invention provides a carbon fiber cloth prepared by the above method.

[0008] The third aspect of the present invention provides applications of the above-mentioned carbon fiber cloth in the fields of aerospace, automobiles, energy storage, and environmental protection.

[0009] Beneficial effects of the present invention (1) The present invention uses biomass components to replace traditional petroleum-based resins, reducing the release of phenol and formaldehyde and lowering carbon emissions.

[0010] (2) The present invention found that the lignin depolymerization liquid product obtained under a specific depolymerization process has good fluidity at room temperature and a high residual carbon rate after high-temperature carbonization, which can meet the requirements of carbon fiber production. The carbon fiber cloth prepared by using the lignin depolymerization liquid product instead of phenolic resin has excellent mechanical strength, and no free formaldehyde escape is detected.

[0011] (3) The preparation method of the present invention is simple, practical, and easy to promote. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their description are used to explain the present invention and do not constitute improper limitations on the present invention.

[0013] Figure 1 The microstructure of the carbon fiber cloth prepared in Example 2 was observed under a scanning electron microscope. DETAILED DESCRIPTION

[0014] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0015] Unless otherwise defined, all professional and scientific terms used herein have the same meaning as those familiar to those skilled in the art. The reagents or raw materials used in the present invention can be purchased through conventional channels. Unless otherwise specified, the reagents or raw materials used in the present invention are used in accordance with conventional methods in the art or according to product specifications. Similarly, unless otherwise specified, the test methods of the present invention are also tested in accordance with conventional methods in the art or the common methods or standards in the industry. In addition, any methods and materials similar to or equivalent to the described contents can be applied to the inventive method. The preferred embodiments and materials described herein are for demonstration purposes only.

[0016] As described in the background art, the use of phenolic resin as an impregnating agent to prepare carbon fiber cloth has the problem of formaldehyde and phenol volatilization, and both phenol and formaldehyde are non-renewable resources. Renewable biomass adhesives generally have the problems of low carbon residue rate and poor rheological properties. Therefore, the industry has not yet found a renewable resource to prepare carbon fiber cloth that can meet the requirements of the field of carbon fiber reinforced composite materials for high carbon residue rate and suitable rheological properties of adhesives. To this end, the present invention provides a method for preparing carbon fiber cloth, comprising: Depolymerizing lignin into small molecular aromatic compounds and collecting lignin depolymerization liquid products; dispersing carbon fibers in an aqueous solution containing a dispersant to obtain a carbon fiber solution; The carbon fiber solution is formed into a fiber mat by a wet forming method; Using the diluted solution of the lignin depolymerization liquid phase product as an adhesive, impregnating the fiber felt in the adhesive, hot pressing, and carbonizing in an oxygen-free environment; The above impregnation, hot pressing and carbonization processes are repeated many times until the carbon fiber reaches the expected performance requirements, and then graphitization treatment is performed to obtain carbon fiber cloth.

[0017] The present invention does not impose any particular limitation on the method of lignin depolymerization, as long as the small molecule aromatic compounds obtained after depolymerization have excellent fluidity and high residual carbon rate. Therefore, in some embodiments, the depolymerization method is selected from at least one of thermochemical depolymerization, liquefaction degradation, oxidative degradation, hydrogenation degradation, and enzymatic hydrolysis.

[0018] In order to obtain a lignin depolymerization liquid product with excellent fluidity and a high residual carbon rate, the present invention studied the depolymerization method and found that when oxidative depolymerization is carried out in the presence of an oxidant H2O2 and an alkaline environment, the obtained lignin depolymerization liquid product has excellent fluidity and a high residual carbon rate. Therefore, in some embodiments, the specific step of the oxidative degradation includes: oxidatively degrading lignin in the presence of an oxidant H2O2 and an alkaline environment at a preset temperature.

[0019] The type and amount of oxidant affect the composition and content of the liquid phase product of lignin depolymerization, which in turn affects its fluidity and high carbon residue as an adhesive. Therefore, the present invention has studied the type and amount of oxidant. In some embodiments, the mass ratio of lignin to the oxidant H2O2 is 1:0.8-5 to achieve optimal fluidity and high carbon residue.

[0020] The temperature and duration of oxidative degradation also affect the composition and content of the liquid phase product of lignin depolymerization, which in turn affects its fluidity and high carbon residue rate as an adhesive. Therefore, the present invention has studied the temperature and duration of oxidative degradation. In some embodiments, the preset temperature is 140°C-160°C; in some embodiments, the depolymerization time is 4-6 hours to achieve better fluidity and high carbon residue rate.

[0021] The present invention has found that at a specific temperature, the lignin depolymerization liquid phase product obtained by thermochemical depolymerization has excellent fluidity and a high residual carbon rate. Therefore, in some embodiments, the conditions of the thermochemical depolymerization are: pyrolysis at 600°C-650°C for 10 min-20 min to obtain a lignin depolymerization liquid phase product with excellent fluidity and a high residual carbon rate.

[0022] It should be noted that due to the different uses of pyrolysis oil, its collection method will be different. In the present invention, nitrogen is used to blow the volatiles into the condenser for condensation to obtain lignin pyrolysis oil.

[0023] In order to ensure that the carbon fiber can be completely dispersed in the solution, the present invention studies the concentration of the carbon fiber. In some embodiments, the concentration of the carbon fiber in the carbon fiber solution is 0.1%-1%, so that the carbon fiber can have better dispersibility in the solution.

[0024] Dispersants can act directly on the surface of carbon fibers, reducing their surface energy and preventing agglomeration. To this end, the present invention has studied the type and dosage of dispersants. In some embodiments, the concentration of the dispersant in the carbon fiber solution is 1%-2%; in some embodiments, the dispersant is selected from at least one of sodium carboxymethyl cellulose, hydroxyethyl cellulose, polyvinyl pyrrolidone, and sodium dodecylbenzene sulfonate to obtain a better carbon fiber dispersion effect.

[0025] In the present application, there is no special limitation on the type of solvent for the dilution solution of the lignin depolymerization liquid phase product, as long as it can effectively dissolve the lignin depolymerization liquid phase product and meet the subsequent carbon fiber cloth production requirements. Therefore, in some embodiments, the solvent of the dilution solution of the lignin depolymerization liquid phase product is selected from a mixture of one or more of ethyl acetate, methanol, acetonitrile, tetrahydrofuran, acetic acid, ethanol, water, chloroform, toluene, and acetone to prepare a carbon fiber adhesive.

[0026] The dilution ratio affects the bonding performance of the adhesive. Therefore, the present invention studies the dilution ratio of the diluted solution of the lignin depolymerization liquid phase product. In some embodiments, the dilution ratio of the diluted solution of the lignin depolymerization liquid phase product is 0-15 times to ensure that the adhesive has better bonding performance and can meet the production requirements of carbon fiber cloth.

[0027] In order to ensure that the carbon fiber cloth has better mechanical strength, the present invention studies the amount of adhesive used. In some embodiments, the amount of the adhesive used is 1-1.5 g / g fiber felt, preferably 1.2 g / g fiber felt. At this ratio, the prepared carbon fiber cloth has better conductivity and mechanical properties.

[0028] Hot pressing can make the carbon fiber cloth more compact and improve its density and strength. Therefore, the present invention studies the temperature and time of hot pressing. In some embodiments, the hot pressing temperature is 140-200°C and the hot pressing time is 30-90 min to make the carbon fiber cloth have higher density and mechanical strength.

[0029] The carbonization temperature affects the mechanical properties and electrical conductivity of the carbon fiber cloth. Therefore, the present invention studies the carbonization temperature. In some embodiments, the carbonization temperature is 800-1200° C. to obtain better mechanical properties and electrical conductivity.

[0030] Graphitization is a process of high-temperature treatment that causes carbon atoms to rearrange to form a layered structure similar to graphite. This can effectively increase the carbon content of carbon fibers while reducing the content of impurities such as hydrogen and nitrogen. Therefore, the present invention studies the graphitization temperature. In some embodiments, the graphitization temperature is 2000-2600°C to obtain better mechanical properties and conductivity.

[0031] The present application does not impose any particular limitation on the type of lignin. In some embodiments, the lignin is selected from at least one of sulfate lignin, alkali lignin, hydrolyzed lignin, enzymatic lignin, and organic solvent lignin. The present application does not impose any particular limitation on the preparation method of lignin. In some embodiments, the preparation method of lignin comprises: subjecting biomass to acid, alkali, supercritical, aqueous two-phase, ionic liquid, organic solvent or enzyme treatment; The present invention does not impose any special limitation on the source of lignin. In some embodiments, the biomass is selected from at least one of woody plants, herbaceous plants, and vascular plants. The prepared lignin is more conducive to the subsequent preparation of carbon fibers.

[0032] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments are intended to explain the present invention rather than to limit it.

[0033] In the following examples, the tensile strength test method is as follows: ASTM standard: ASTM D3039.

[0034] Volume resistivity test method: Group standard T CSTM 00252—2020.

[0035] Example 1 Ten grams of kraft lignin were added to 470 mL of water, oxidized with 30 mL of H₂O₂ (30 wt%) as the oxidant, and sodium hydroxide was used to adjust the pH to 12. Oxidative depolymerization was performed at 140°C for 4 h. After extraction with ethyl acetate three times, the extracts were collected and rotary evaporated to obtain the oxidative depolymerization liquid phase of the kraft lignin. 3 mm PAN-based chopped carbon fibers were ultrasonically cleaned with ethanol for 10 min and added to a 0.5 wt% water-sodium carboxymethyl cellulose suspension. High-speed shearing was performed for 15 min to obtain a dispersed carbon fiber solution. The dispersed carbon fiber solution was poured into a 100-mesh stainless steel mesh mold, vacuum-dehydrated for 2 min, and oriented by roller pressing at 0.3 MPa to obtain a fiber mat. The lignin depolymerization liquid phase was diluted three-fold with ethanol and slowly added dropwise to the fiber mat at a rate of 1.2 g solution / g of fiber mat. The mixture was vacuum-impregnated for 30 min. The mixture was then hot-pressed at 180°C and 2 MPa for 60 min. The hot-pressed fiber mat was carbonized at 1000°C for 30 minutes under an argon atmosphere at a heating rate of 5°C / min. Following carbonization, it was graphitized at 2400°C for 20 minutes under an argon atmosphere to produce a carbon fiber cloth. The resulting carbon fiber cloth had a volume resistivity of 28 mΩ·cm, a tensile strength of 36 MPa, and undetectable formaldehyde emission.

[0036] Example 2 Lignin was added to a quartz tube, and the air in the tube furnace was purged with nitrogen. After the pyrolysis furnace was heated to 650°C, the tube was placed in the tube furnace and pyrolyzed for 10 minutes. Nitrogen was then introduced at a flow rate of 100 mL / min to sweep the volatiles into a condenser for condensation, yielding lignin pyrolysis oil. 5 mm PAN-based chopped carbon fibers were ultrasonically cleaned with ethanol for 10 minutes and added to a 1 wt% water-sodium carboxymethyl cellulose suspension. High-speed shearing was performed for 15 minutes to obtain a dispersed carbon fiber solution. The dispersed carbon fiber solution was poured into a 100-mesh stainless steel mesh mold, vacuum-dehydrated for 2 minutes, and oriented by roller pressing at 0.3 MPa to obtain a fiber mat. The lignin depolymerization liquid phase was diluted 1 / 100 with ethanol and slowly added dropwise to the fiber mat at a rate of 1.2 g solution / g fiber mat. The mixture was vacuum-impregnated for 30 minutes. The mixture was then hot-pressed at 180°C and 2 MPa for 60 minutes. The hot-pressed fiber mat was carbonized at 1000°C for 30 minutes under an argon atmosphere at a heating rate of 5°C / min. Following carbonization, it was graphitized at 2400°C for 20 minutes under an argon atmosphere to produce a carbon fiber cloth. The resulting carbon fiber cloth had a volume resistivity of 31 mΩ·cm, a tensile strength of 42 MPa, and undetectable formaldehyde emissions.

[0037] Example 3 Lignin was added to a quartz tube, and nitrogen was used to expel air from the tube furnace. After the pyrolysis furnace was heated to 650°C, the tube was placed in the tube furnace and pyrolyzed for 10 minutes. Nitrogen was then introduced at a flow rate of 100 mL / min to sweep volatiles into a condenser for condensation, yielding lignin pyrolysis oil. 5 mm PAN-based chopped carbon fibers were ultrasonically cleaned with ethanol for 10 minutes and added to a 1 wt% water-sodium carboxymethyl cellulose suspension. High-speed shearing was performed for 15 minutes to obtain a dispersed carbon fiber solution. The dispersed carbon fiber solution was poured into a 100-mesh stainless steel mesh mold, vacuum-dehydrated for 2 minutes, and oriented by roller pressing at 0.3 MPa to obtain a fiber mat. The lignin depolymerization liquid phase was diluted 100% with ethanol and slowly added dropwise at a rate of 1.2 g solution / g fiber mat. Vacuum impregnation was performed for 30 minutes. The fiber mat was then hot-pressed at 180°C and 2 MPa for 60 minutes. The hot-pressed fiber mat was carbonized at 1000°C for 30 minutes under an argon atmosphere at a heating rate of 5°C / min. The carbonized fiber cloth was impregnated again (under the same conditions as before) and carbonized (under the same conditions as before). The carbonized fiber cloth was graphitized at 2400°C for 20 minutes under an argon atmosphere to produce a carbon fiber cloth. The resulting carbon fiber cloth had a volume resistivity of 23 mΩ·cm, a tensile strength of 55 MPa, and undetectable formaldehyde emission.

[0038] Comparative Example 1 The difference from Example 2 is that the pyrolysis temperature is 700°C.

[0039] The test results show that the obtained carbon fiber cloth has a volume resistivity of 67 mΩ·cm, a tensile strength of 28 MPa, and no formaldehyde emission is detected.

[0040] Comparative Example 2 The difference from Example 2 is that the pyrolysis temperature is 450°C.

[0041] The test results show that the obtained carbon fiber cloth has a volume resistivity of 61 mΩ·cm, a tensile strength of 31 MPa, and no formaldehyde emission is detected.

[0042] As described in Examples 1 and 2, a binder with good fluidity and a high carbon residue rate can be obtained by adopting a specific oxidative degradation or pyrolysis process.

[0043] From the comparison between Example 2 and Example 3, it can be seen that the electrical conductivity and mechanical properties of the carbon fiber cloth can be further improved through multiple impregnation and carbonization treatments.

[0044] From the comparison between Example 2 and Comparative Examples 1 and 2, it can be seen that a pyrolysis temperature that is too high or too low will affect the yield and composition of the pyrolysis oil, thereby affecting the fluidity and residual carbon rate of the adhesive, resulting in a decrease in the conductivity and mechanical properties of the carbon fiber cloth.

[0045] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing carbon fiber cloth, characterized in that: include: Depolymerizing lignin into small molecular aromatic compounds and collecting lignin depolymerization liquid products; dispersing carbon fibers in an aqueous solution containing a dispersant to obtain a carbon fiber solution; The carbon fiber solution is formed into a fiber mat by a wet forming method; Using the diluted solution of the lignin depolymerization liquid phase product as an adhesive, impregnating the fiber felt in the adhesive, hot pressing, and carbonizing in an oxygen-free environment; The above impregnation, hot pressing and carbonization processes are repeated many times until the carbon fiber reaches the expected performance requirements, and then graphitization treatment is performed to obtain carbon fiber cloth.

2. The method for preparing carbon fiber cloth according to claim 1, wherein: The depolymerization method is selected from at least one of thermochemical depolymerization, liquefaction degradation, oxidative degradation, hydrogenation degradation, and enzymatic degradation.

3. The method for preparing carbon fiber cloth according to claim 2, wherein: The specific steps of the oxidative degradation include: oxidatively degrading lignin in the presence of an oxidant H2O2 in an alkaline environment at a preset temperature.

4. The method for preparing carbon fiber cloth according to claim 3, wherein: The mass ratio of the lignin to the oxidant H2O2 is 1: 0.8-5; Alternatively, the preset temperature is 140° C.-160° C.; Alternatively, the depolymerization time is 4 h-6 h.

5. The method for preparing the carbon fiber cloth according to claim 2, wherein: The conditions for the thermochemical depolymerization are: pyrolysis at 600° C.-650° C. for 10 min-20 min.

6. The method for preparing carbon fiber cloth according to claim 1, wherein: In the carbon fiber solution, the concentration of carbon fiber is 0.1%-1%; Alternatively, the concentration of the dispersant in the carbon fiber solution is 1%-2%; Or, the dispersant is sodium carboxymethyl cellulose; Alternatively, the solvent of the diluted solution of the lignin depolymerization liquid phase product is selected from a mixture of one or more of ethyl acetate, methanol, acetonitrile, tetrahydrofuran, acetic acid, ethanol, water, chloroform, toluene, and acetone; Alternatively, the dilution ratio of the diluted solution of the lignin depolymerization liquid phase product is 0-15 times; Alternatively, the amount of the binder is 1-1.5 g / g fiber mat, preferably 1.2 g / g fiber mat.

7. The method for preparing carbon fiber cloth according to claim 1, wherein: The hot pressing temperature is 140-200°C and the hot pressing time is 30-90 min; Alternatively, the carbonization temperature is 800-1200°C; Alternatively, the graphitization temperature is 2000-2600°C.

8. The method for preparing carbon fiber cloth according to claim 1, wherein: The lignin is selected from at least one of sulfate lignin, alkali lignin, hydrolyzed lignin, enzymatic lignin, and organic solvent lignin; Alternatively, the method for preparing the lignin comprises: subjecting biomass to acid, alkali, supercritical, aqueous two-phase, ionic liquid, organic solvent or enzyme treatment to obtain the lignin; Alternatively, the biomass is selected from at least one of woody plants, herbaceous plants, and vascular plants.

9. Carbon fiber cloth prepared by the method according to any one of claims 1 to 8.

10. Application of the carbon fiber cloth according to claim 9 in the fields of aerospace, automobile, energy storage, and environmental protection.

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