Method for preparing carbon fibers based on blending of nanocellulose and PAN

Abstract

The invention discloses a method for preparing carbon fibers based on blending of nanocellulose and PAN (polyacrylonitrile), which comprises the following steps: preparing the nanocellulose from biomass, then mixing the nanocellulose with polyacrylonitrile, carrying out dipping catalytic pretreatment and electrostatic spinning to obtain precursor fiber precursors, and finally, carrying out heat treatment on the precursor fiber precursors to obtain the carbon fibers. The interaction between the catalyst and the bamboo fibers is increased, the carbonization efficiency is accelerated, the original fiber network morphology can be maintained in the carbonization process, and the prepared carbon fiber material has high strength and modulus, light weight and high temperature resistance, and is suitable for being used in the field of carbon fiber materials. The problem that the fiber strength cannot meet the requirement due to the fact that the carbon fiber prepared from the cellulose nanocrystal-polyacrylonitrile composite fiber is poor in interfacial compatibility is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of carbon fibers, and more specifically, relates to a method for preparing carbon fibers based on blending of nanocellulose and PAN. Background Art

[0002] As the king of new materials in the 21st century, carbon fiber is a new type of fiber material with high strength and high modulus fiber with a carbon content of more than 95%. It is made of organic fibers such as flake graphite microcrystals stacked along the axial direction of the fiber. The microcrystalline graphite material obtained by carbonization and graphitization is lighter than metal aluminum, but stronger than steel, and has the characteristics of corrosion resistance and high modulus. It is widely used in high-tech fields such as national defense, aerospace, and wind power generation, and is known as the black gold in the material industry. At present, carbon fibers are commonly prepared from fossil resources, such as polyacrylonitrile (PAN), mesophase asphalt, etc., but because fossil resources are non-renewable and cause great pollution to the environment, there are also problems such as high preparation cost and the strength needs to be improved, which limits the application of carbon fibers.

[0003] Cellulose nanofibers have high Young's modulus, high strength and low thermal expansion coefficient, as well as low weight, biodegradability and renewability. In polymer composites, high hardness, high aspect ratio nanomaterials can provide the greatest mechanical reinforcement. In CN202010859083.5 Carbon fiber with cellulose nanocrystal-polyacrylonitrile composite fiber as precursor and its preparation method, it is disclosed that cellulose nanocrystals and acrylonitrile monomers are reacted in an organic solvent to obtain a cellulose nanocrystal-acrylonitrile polymer solution; (2) the cellulose nanocrystal-acrylonitrile polymer solution is filtered, degassed and spun to obtain a cellulose nanocrystal-polyacrylonitrile composite fiber; (3) the cellulose nanocrystal-polyacrylonitrile composite fiber is pre-oxidized and carbonized to obtain a carbon fiber with cellulose nanocrystal-polyacrylonitrile composite fiber as precursor. In this patent, the abundant chemical groups on the surface of cellulose nanocrystals, such as hydroxyl groups, can form strong hydrogen bonds with the nitrile groups in polyacrylonitrile, thereby improving the affinity with polyacrylonitrile and enhancing the interfacial bonding between the two. This also makes the cellulose nanocrystals evenly dispersed in the composite and has good interfacial bonding between the cellulose nanocrystals and the polymer, thereby obtaining a uniform cellulose nanocrystal-acrylonitrile polymer solution. However, there is still a problem of poor interfacial compatibility between cellulose nanocrystals and acrylonitrile, which results in certain limitations in the performance of carbon fibers and cannot meet existing requirements. Summary of the invention

[0004] In order to overcome the problem of poor interface compatibility in preparing carbon fibers from existing cellulose nanocrystal-polyacrylonitrile composite fibers, the present invention provides a method for preparing carbon fibers based on blending nanocellulose with PAN.

[0005] The present invention is achieved through the following technical solutions:

[0006] A method for preparing carbon fiber based on blending nanocellulose and PAN, comprising the following steps:

[0007] S1. extracting nanocellulose from biomass powder by enzymatic hydrolysis;

[0008] S2. blending the extracted nanocellulose with polyacrylonitrile to obtain an electrospinning solution, and electrospinning the solution to obtain a precursor fiber strand;

[0009] S3. Pre-treating the precursor fiber by impregnation catalysis;

[0010] S4. activating the pretreated precursor fiber precursor;

[0011] S5. The precursor fiber raw silk is heated to 400°C in a gradient manner at a heating rate of 2-5°C / min under a protective atmosphere for pre-oxidation and heat stabilization treatment;

[0012] S6. Heating from 400°C to 1800°C to remove non-carbon components and form a turbostratic graphite structure;

[0013] S7. Finally, the temperature is raised to 2000-2200° C. for graphitization to obtain carbon fibers.

[0014] Furthermore, the biomass includes one or more of bamboo powder, cotton fiber, and hemp fiber.

[0015] Furthermore, the enzymatic hydrolysis process in S1 includes:

[0016] S11. The biomass is dried and crushed into powder, soaked in ammonia water to soften, and then treated with alkali, ammonia pretreatment and acid to remove part of the lignin and hemicellulose;

[0017] S12. Then, a ligninase solution, a hemicellulase solution and a pectinase solution are added to the treated sample to remove the residual lignin and hemicellulose to obtain cellulose;

[0018] S13. Grind the cellulose, add cellulase solution and pectinase solution to remove the biological enzymes, and then wash and dry to obtain nanocellulose.

[0019] Furthermore, the mass ratio of nanocellulose to polyacrylonitrile is 0.5 to 1.5: 9. Preferably, the mass ratio of nanocellulose to polyacrylonitrile is 1: 9, and the obtained spinning solution has the best uniformity.

[0020] Furthermore, the impregnation catalytic pretreatment step in S3 includes:

[0021] The prepared precursor fiber filaments are added to a mixed aqueous solution of phosphoric acid and melamine for immersion, and then dried. The dried precursor fiber filaments are heated to 180-200°C and kept warm for 0.5-1h for calcination. Phosphoric acid and melamine are used as catalysts to be loaded on nanocellulose to control the dehydration of hydroxyl groups and prevent the formation of L-glucose, playing a key role in the oxidation and carbonization process.

[0022] Furthermore, the content of phosphoric acid and melamine in the mixed aqueous solution is 2-6 wt %, and the ratio of phosphoric acid to melamine is 1:1.

[0023] Furthermore, the activation treatment is: the precursor fiber raw silk is immersed in an alkaline solution and then dried, which can effectively improve the thermal stability of the raw silk in the subsequent pre-oxidation and accelerate the pyrolysis reaction.

[0024] Furthermore, the pre-oxidation and heat stabilization treatment in step S5 can prevent the precursor fibers from prematurely breaking and melting at a high temperature later, and the gradient heating step includes:

[0025] The first stage: heating from room temperature to 150°C, with a heating rate of 3-5°C / min;

[0026] The second stage: heating from 150℃ to 250℃, with a heating rate of 2-5℃ / min, and then keeping warm for 0.5-1h;

[0027] The third stage: heating from 250 to 400°C, with a heating rate of 2-5°C / min.

[0028] Furthermore, in step S6, the heating rate from 400°C to 1000°C is 5-7°C / min, and the holding time is 0-1.5h, so as to remove non-carbon elements and form a turbostratic graphite structure; the heating rate from 1000°C to 1800°C is 5-7°C / min, so as to further remove non-carbon components in the fiber, further enrich the carbon in the fiber, stabilize the turbostratic graphite structure, further reduce defects, and improve fiber performance.

[0029] Furthermore, the heating rate of heating to 2000-2200° C. in step S7 is 3-5° C. / min, and the carbonized fibers can be graphitized, which helps to form a more ordered carbon structure and further improve the mechanical properties and stability of the carbon fibers.

[0030] The present invention strictly controls the temperature rising gradient and the temperature rising rate. A too fast temperature rising rate will lead to incomplete reaction, insufficient time for recyclization, cracking of heteroelements and reorganization of carbon structure, and non-carbon atoms cannot be eliminated well, resulting in a decrease in carbon content; a too slow temperature rising rate will make defects easy to generate, reduce the strength of carbon fiber, and prolong the experimental cycle, resulting in a waste of resources.

[0031] Compared with the prior art, the beneficial effects are:

[0032] The present invention uses biomass as cellulose raw material and obtains nanocellulose through bio-enzyme extraction. This preparation method can be applied to most bio-based cellulose, which is then blended with polyacrylonitrile to prepare carbon fiber. On this basis, the pressure on fossil fuels is reduced, and the preparation of green, low-cost and continuous carbon fiber materials can be achieved, which greatly reduces energy consumption and production costs.

[0033] The present invention pre-impregnates the precursor prepared by blending nanocellulose and PAN with catalysis and NaOH activation treatment to shorten the carbonization time. The presence of alkali can reduce the step of thermal stabilization, accelerate the pyrolysis reaction, increase the interaction between the catalyst and the bamboo fiber, accelerate the carbonization efficiency, and save resources. The present invention controls the heating process of pre-oxidation, low-temperature carbonization and high-temperature carbonization, so that the original fiber network morphology can be maintained during the carbonization process. The obtained carbon fiber material has the characteristics of high strength and modulus, light weight, and high temperature resistance. DETAILED DESCRIPTION

[0034] The following is further explained and illustrated in conjunction with the examples, but the specific examples do not limit the present invention in any form. If not specifically stated, the methods and equipment used in the examples are conventional methods and equipment in the art, and the raw materials used are all conventional commercially available raw materials.

[0035] Example 1

[0036] This embodiment provides a method for preparing nanocellulose, the steps comprising:

[0037] S1. extracting nanocellulose from bamboo powder by enzymatic hydrolysis;

[0038] S11. Take fresh bamboo, peel off the outer layer of the bamboo, and then cut the bamboo into bamboo chips. After drying the bamboo chips in a hot air furnace at 85°C for 12 hours, grind the dried fibers into powder using a grinder. Continue to grind the powder with a high-speed mixer at a speed of 35,000 rpm for 15 minutes, and then pass through a 250-micron sieve and store it in a desiccator to maintain constant moisture.

[0039] S12. Take 10g of bamboo powder and add appropriate amount of NH3·H2O for pretreatment and soak for 24h, rinse with distilled water, filter until neutral, and dry at 105℃. Then, add appropriate amount of H2O2 and CH3COOH (volume ratio of 1:1) in a 70℃ constant temperature water bath and soak for 10h for bleaching and partial removal of lignin. After acid treatment, filter the sample, wash with distilled water until the filtrate is neutral, and dry at 105℃.

[0040] S13. Add appropriate amount of 10% ligninase solution, 5% hemicellulase solution and 5% pectinase solution (1:1:1) to the sample after ammonia pretreatment and acid treatment, and place it under magnetic stirring. Treat the sample at a constant temperature of 50°C and a stirring speed of 800-1200r / min for 240min to remove residual lignin, hemicellulose and impurities. Then, rinse the filtered sample with a large amount of distilled water until it is clean and dry it at a constant temperature of 105°C.

[0041] S14. Take 0.5g of the cellulose in S13 and place it in a beaker, and add 20g of zirconium oxide grinding beads. Configure and fix the volume of 5% cellulase solution and 5% pectinase solution, and add 15mL of cellulase solution and pectinase solution to the beaker. Then place it in a 100℃ water bath for 20min and ultrasonicate for 30min, the purpose of which is to remove the biological enzyme. Then, collect the precipitate and dilute it with distilled water by centrifugation at 8000r / min for 10min to wash away the biological enzyme impurities, and repeat 5 times. Finally, stir at room temperature (800-1200r / min) for 30min, ultrasonicate for 30min, and repeat several times until a suspension is formed. The suspension is freeze-dried into powder to obtain nanocellulose.

[0042] Example 2

[0043] This embodiment provides a method for preparing carbon fiber based on blending nanocellulose and PAN, the steps comprising:

[0044] S1. The nanocellulose obtained in Example 1 is dissolved with 1-ethyl-3-methylimidazole acetate and dimethyl sulfoxide, and the dissolved nanocellulose is blended with PAN at a ratio of 1:9, and a dimethylformamide solution is added to dissolve the raw materials. The nanocellulose and PAN are 12 wt %, so that the raw materials are fully contacted and reacted to prepare an electrospinning stock solution, and electrospinning is performed to prepare precursor fiber filaments.

[0045] S2. The precursor fiber raw silk is impregnated with a mixed aqueous solution of 2wt% phosphoric acid and melamine (1:1) as a catalyst. After the impregnation is completed, the precursor fiber raw silk is placed in a 105°C forced air drying oven for 3 hours. The dried raw silk is placed in a Ma Fuel furnace and heated to 200°C at 2°C / min and kept warm for 0.5 hours.

[0046] S3. The calcined precursor fiber raw silk is placed in a 2wt% NaOH aqueous solution for activation treatment for 2 hours and dried.

[0047] S4. Pre-oxidation and thermal stabilization treatment of the fiber precursors are performed in a gradient manner, while maintaining an argon atmosphere and heating in a gradient manner:

[0048] Stage 1: Heating from room temperature to 150°C at a rate of 3°C / min;

[0049] The second stage: heating from 150℃ to 250℃, heating rate is 2℃ / min, and then keeping warm for 0.5h;

[0050] The third stage: heating from 250 to 400°C at a heating rate of 2°C / min.

[0051] S5. Carbonize the fiber precursor at low temperature, and heat the temperature from 400°C to 1000°C at a heating rate of 5°C / min in an argon atmosphere without heat preservation. The main processes are dehydration, pyrolysis and aromatization, removing non-carbon elements and forming a turbostratic graphite structure.

[0052] S6. Continue to heat up from 1000°C to 1800°C at a heating rate of 5°C / min for high-temperature carbonization to remove non-carbon components in the fiber, further enrich the carbon in the fiber, stabilize the turbostratic graphite structure, further reduce defects, and improve fiber performance.

[0053] S7. Heating the carbonized fiber to 2200°C for graphitization helps to form a more ordered carbon structure and further improve the mechanical properties and stability of the carbon fiber.

[0054] Example 3

[0055] This embodiment provides a method for preparing carbon fiber based on blending nanocellulose and PAN, the steps comprising:

[0056] S1. The nanocellulose obtained in Example 1 is dissolved with 1-ethyl-3-methylimidazole acetate and dimethyl sulfoxide, and the dissolved nanocellulose is blended with PAN at a ratio of 1:9, and a dimethylformamide solution is added to dissolve the raw materials. The nanocellulose and PAN are 12 wt %, so that the raw materials are fully contacted and reacted to prepare an electrospinning stock solution, and electrospinning is performed to prepare precursor fiber filaments.

[0057] S2. The precursor fiber raw silk is impregnated with a mixed aqueous solution of 4wt% phosphoric acid and melamine (1:1) as a catalyst. After the impregnation is completed, the precursor fiber raw silk is placed in a 105°C forced air drying oven for 3 hours. The dried raw silk is placed in a Ma Fuel furnace and heated to 200°C at 2°C / min and kept warm for 0.5 hours.

[0058] S3. The calcined precursor fiber raw silk is placed in a 2wt% NaOH aqueous solution for activation treatment for 2 hours and dried.

[0059] S4. The fiber precursor is pre-oxidized and heat-stabilized in a gradient manner, maintained in an argon atmosphere, and heated in a gradient manner:

[0060] Stage 1: Heating from room temperature to 150°C at a rate of 3°C / min;

[0061] The second stage: heating from 150℃ to 250℃, heating rate is 2℃ / min, and then keeping warm for 0.5h;

[0062] The third stage: heating from 250 to 400°C at a heating rate of 2°C / min.

[0063] S5. Carbonize the fiber precursor at low temperature, and heat the temperature from 400°C to 1000°C at a heating rate of 5°C / min in an argon atmosphere without heat preservation. Mainly dehydration, pyrolysis and aromatization, remove non-carbon elements, and form a turbostratic graphite structure.

[0064] S6. Continue to heat up from 1000°C to 1800°C at a heating rate of 5°C / min for high-temperature carbonization to remove non-carbon components in the fiber, further enrich the carbon in the fiber, stabilize the turbostratic graphite structure, further reduce defects, and improve fiber performance.

[0065] S7. Heating the carbonized fiber to 2200°C for graphitization helps to form a more ordered carbon structure and further improve the mechanical properties and stability of the carbon fiber.

[0066] Example 4

[0067] This embodiment provides a method for preparing carbon fiber based on blending nanocellulose and PAN, the steps comprising:

[0068] S1. The nanocellulose obtained in Example 1 is dissolved with 1-ethyl-3-methylimidazole acetate and dimethyl sulfoxide, and the dissolved nanocellulose is blended with PAN at a ratio of 1:9, and a dimethylformamide solution is added to dissolve the raw materials. The nanocellulose and PAN are 12 wt %, so that the raw materials are fully contacted and reacted to prepare an electrospinning stock solution, and electrospinning is performed to prepare precursor fiber filaments.

[0069] S2. The precursor fiber raw silk is impregnated with a mixed aqueous solution of 6wt% phosphoric acid and melamine (1:1) as a catalyst. After the impregnation is completed, the precursor fiber raw silk is placed in a 105°C forced air drying oven for 3 hours. The dried raw silk is placed in a Ma Fuel furnace and heated to 200°C at 2°C / min and kept warm for 0.5 hours.

[0070] S3. The calcined precursor fiber raw silk is placed in a 2wt% NaOH aqueous solution for activation treatment for 2 hours and dried.

[0071] S4. The fiber precursor is pre-oxidized and heat-stabilized in a gradient manner, maintained in an argon atmosphere, and heated in a gradient manner:

[0072] Stage 1: Heating from room temperature to 150°C at a rate of 3°C / min;

[0073] The second stage: heating from 150℃ to 250℃, heating rate is 2℃ / min, and then keeping warm for 0.5h;

[0074] The third stage: heating from 250 to 400°C at a heating rate of 2°C / min.

[0075] S5. Carbonize the fiber precursor at low temperature, and heat the temperature from 400°C to 1000°C at a heating rate of 5°C / min in an argon atmosphere without heat preservation. Mainly dehydration, pyrolysis and aromatization, remove non-carbon elements, and form a turbostratic graphite structure.

[0076] S6. Continue to heat up from 1000°C to 1800°C at a heating rate of 5°C / min for high-temperature carbonization to remove non-carbon components in the fiber, further enrich the carbon in the fiber, stabilize the turbostratic graphite structure, further reduce defects, and improve fiber performance.

[0077] S7. Heating the carbonized fiber to 2200°C for graphitization helps to form a more ordered carbon structure and further improve the mechanical properties and stability of the carbon fiber.

[0078] Example 5

[0079] This embodiment provides a method for preparing carbon fiber based on blending nanocellulose and PAN, the steps comprising:

[0080] S1. The nanocellulose obtained in Example 1 is dissolved with 1-ethyl-3-methylimidazole acetate and dimethyl sulfoxide, and the dissolved nanocellulose is blended with PAN at a ratio of 1:9, and a dimethylformamide solution is added to dissolve the raw materials. The nanocellulose and PAN are 12 wt %, so that the raw materials are fully contacted and reacted to prepare an electrospinning stock solution, and electrospinning is performed to prepare precursor fiber filaments.

[0081] S2. The precursor fiber raw silk is impregnated with a mixed aqueous solution of 4wt% phosphoric acid and melamine (1:1) as a catalyst. After the impregnation is completed, the precursor fiber raw silk is placed in a 105°C forced air drying oven for 3 hours. The dried raw silk is placed in a Ma Fuel furnace and heated to 200°C at 2°C / min and kept warm for 0.5 hours.

[0082] S3. The calcined precursor fiber raw silk is placed in a 2wt% NaOH aqueous solution for activation treatment for 2 hours and dried.

[0083] S4. The fiber precursor is pre-oxidized and heat-stabilized in a gradient manner, maintained in an argon atmosphere, and heated in a gradient manner:

[0084] Stage 1: Heating from room temperature to 150°C at a rate of 3°C / min;

[0085] The second stage: heating from 150℃ to 250℃, heating rate is 2℃ / min, and then keeping warm for 0.5h;

[0086] The third stage: heating from 250 to 400°C at a heating rate of 2°C / min.

[0087] S5. Carbonize the fiber precursor at low temperature. In an argon atmosphere, increase the temperature from 400°C to 1000°C at a heating rate of 5°C / min and keep it warm for 0.5h. This is mainly for dehydration, pyrolysis and aromatization to remove non-carbon elements and form a turbostratic graphite structure.

[0088] S6. Continue to heat up from 1000°C to 1800°C at a heating rate of 5°C / min for high-temperature carbonization to remove non-carbon components in the fiber, further enrich the carbon in the fiber, stabilize the turbostratic graphite structure, further reduce defects, and improve fiber performance.

[0089] S7. Heating the carbonized fiber to 2200°C for graphitization helps to form a more ordered carbon structure and further improve the mechanical properties and stability of the carbon fiber.

[0090] Example 6

[0091] This embodiment provides a method for preparing carbon fiber based on blending nanocellulose and PAN, the steps comprising:

[0092] S1. The nanocellulose obtained in Example 1 is dissolved with 1-ethyl-3-methylimidazole acetate and dimethyl sulfoxide, and the dissolved nanocellulose is blended with PAN at a ratio of 1:9, and a dimethylformamide solution is added to dissolve the raw materials. The nanocellulose and PAN are 12 wt %, so that the raw materials are fully contacted and reacted to prepare an electrospinning stock solution, and electrospinning is performed to prepare precursor fiber filaments.

[0093] S2. The precursor fiber raw silk is impregnated with a mixed aqueous solution of 4wt% phosphoric acid and melamine (1:1) as a catalyst. After the impregnation is completed, the precursor fiber raw silk is placed in a 105°C forced air drying oven for 3 hours. The dried raw silk is placed in a Ma Fuel furnace and heated to 200°C at 2°C / min and kept warm for 0.5 hours.

[0094] S3. The calcined precursor fiber raw silk is placed in a 2wt% NaOH aqueous solution for activation treatment for 2 hours and dried.

[0095] S4. The fiber precursor is pre-oxidized and heat-stabilized in a gradient manner, maintained in an argon atmosphere, and heated in a gradient manner:

[0096] Stage 1: Heating from room temperature to 150°C at a rate of 3°C / min;

[0097] The second stage: heating from 150℃ to 250℃, heating rate is 3℃ / min, and then keeping warm for 0.5h;

[0098] The third stage: heating from 250 to 400°C at a heating rate of 3°C / min.

[0099] S5. Carbonize the fiber precursor at low temperature. In an argon atmosphere, increase the temperature from 400°C to 1000°C at a heating rate of 5°C / min and keep it warm for 1 hour. This is mainly for dehydration, pyrolysis and aromatization to remove non-carbon elements and form a turbostratic graphite structure.

[0100] S6. Continue to heat up from 1000°C to 1800°C at a heating rate of 5°C / min for high-temperature carbonization to remove non-carbon components in the fiber, further enrich the carbon in the fiber, stabilize the turbostratic graphite structure, further reduce defects, and improve fiber performance.

[0101] S7. Heating the carbonized fiber to 2200°C for graphitization helps to form a more ordered carbon structure and further improve the mechanical properties and stability of the carbon fiber.

[0102] Example 7

[0103] This embodiment provides a method for preparing carbon fiber based on blending nanocellulose and PAN, the steps comprising:

[0104] S1. The nanocellulose obtained in Example 1 is dissolved with 1-ethyl-3-methylimidazole acetate and dimethyl sulfoxide, and the dissolved nanocellulose is blended with PAN at a ratio of 1:9, and a dimethylformamide solution is added to dissolve the raw materials. The nanocellulose and PAN are 12 wt %, so that the raw materials are fully contacted and reacted to prepare an electrospinning stock solution, and electrospinning is performed to prepare precursor fiber filaments.

[0105] S2. The precursor fiber raw silk is impregnated with a mixed aqueous solution of 4wt% phosphoric acid and melamine (1:1) as a catalyst. After the impregnation is completed, the precursor fiber raw silk is placed in a 105°C forced air drying oven for 3 hours. The dried raw silk is placed in a Ma Fuel furnace and heated to 200°C at 2°C / min and kept warm for 0.5 hours.

[0106] S3. The calcined precursor fiber raw silk is placed in a 2wt% NaOH aqueous solution for activation treatment for 2 hours and dried.

[0107] S4. The fiber precursor is pre-oxidized and heat-stabilized in a gradient manner, maintained in an argon atmosphere, and heated in a gradient manner:

[0108] Stage 1: Heating from room temperature to 150°C at a rate of 3°C / min;

[0109] The second stage: heating from 150℃ to 250℃, heating rate is 5℃ / min, and then keeping warm for 0.5h;

[0110] The third stage: heating from 250 to 400°C at a heating rate of 5°C / min.

[0111] S5. Carbonize the fiber precursor at low temperature. In an argon atmosphere, increase the temperature from 400°C to 1000°C at a heating rate of 5°C / min and keep it warm for 1.5 hours. This is mainly for dehydration, pyrolysis and aromatization to remove non-carbon elements and form a turbostratic graphite structure.

[0112] S6. Continue to heat up from 1000°C to 1800°C at a heating rate of 5°C / min for high-temperature carbonization to remove non-carbon components in the fiber, further enrich the carbon in the fiber, stabilize the turbostratic graphite structure, further reduce defects, and improve fiber performance.

[0113] S7. Heating the carbonized fiber to 2200°C for graphitization helps to form a more ordered carbon structure and further improve the mechanical properties and stability of the carbon fiber.

[0114] The carbon fiber prepared from PAN without adding nanocellulose was used as the control group, and the mechanical properties of the precursor fiber and the carbon fiber prepared in Examples 2-7 were tested respectively. The test results are shown in the following table:

[0115] Table 1

[0116]

[0117] Table 2

[0118] Tensile strength(Gpa) Tensile modulus(Gpa) Pure PAN 4.18 235 Example 2 3.26 159 Example 3 4.01 215 Example 4 3.69 184 Example 5 4.09 219 Example 6 4.23 233 Example 7 3.63 177

[0119] It can be seen from Examples 2-4 that different contents of catalysts have different effects on the reaction of precursor fibers, and thus also affect the mechanical properties of the finished carbon fiber. The nanocellulose added to the electrostatically spun mixed PAN fiber causes the tensile modulus of the electrostatically spun precursor fiber precursor to increase by 19%, and the tensile strength to increase by 15%. When the content of the catalyst is 4wt%, the tensile strength and tensile modulus of the carbon fiber reach the optimal values ​​of 4.01Gpa and 215Gpa, respectively. It can be seen from Examples 5-7 that when the catalyst with the same content is kept at different insulation times, the extension of the insulation time will have a certain degree of influence on the strength and modulus of the generated carbon fiber. The extension of the insulation time will lead to the generation of defects during graphitization, and the defect growth is positively correlated with the extension of time, which will cause the quality and performance of the prepared carbon fiber to decline. The most suitable insulation time is 1h, which does not cause the generation of defects and improves the thermal stability of the carbon fiber, fully graphitizes, and improves the strength and modulus of the carbon fiber.

[0120] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for preparing carbon fiber based on blending nanocellulose and PAN, characterized in that the steps include: S1. extracting nanocellulose from biomass powder by enzymatic hydrolysis; S2. blending the extracted nanocellulose with polyacrylonitrile to obtain an electrospinning solution, and electrospinning the solution to obtain a precursor fiber strand; S3. Pre-treating the precursor fiber by impregnation catalysis; S4. activating the pretreated precursor fiber precursor; S5. The precursor fiber raw silk is heated to 400°C in a gradient manner at a heating rate of 2-5°C / min under a protective atmosphere for pre-oxidation and heat stabilization treatment; S6. Heating from 400°C to 1800°C to remove non-carbon components and form a turbostratic graphite structure; S7. Finally, the temperature is raised to 2000-2200° C. for graphitization to obtain carbon fibers.

2. The method for preparing carbon fiber based on blending nanocellulose and PAN according to claim 1, characterized in that: The biomass includes one or more of bamboo powder, cotton fiber and hemp fiber.

3. The method for preparing carbon fiber based on blending nanocellulose and PAN according to claim 1, characterized in that: The enzymatic hydrolysis process in S1 includes: S11. The biomass is dried and crushed into powder, soaked in ammonia water to soften, and then treated with alkali, ammonia pretreatment and acid to remove part of the lignin and hemicellulose; S12. Then, a ligninase solution, a hemicellulase solution and a pectinase solution are added to the treated sample to remove the residual lignin and hemicellulose to obtain cellulose; S13. Grind the cellulose, add cellulase solution and pectinase solution to remove the biological enzymes, and then wash and dry to obtain nanocellulose.

4. The method for preparing carbon fiber based on blending nanocellulose and PAN according to claim 1, characterized in that: The mass ratio of nanocellulose to polyacrylonitrile is 0.5-1.5:

9.

5. The method for preparing carbon fiber based on blending nanocellulose and PAN according to claim 1, characterized in that: S3 The impregnation catalytic pretreatment step comprises: The prepared precursor fiber raw silk is added into a mixed aqueous solution of phosphoric acid and melamine for immersion, and then dried. The dried precursor fiber raw silk is then heated to 180-200° C. and kept warm for 0.5-1 hour for calcination.

6. The method for preparing carbon fiber based on blending nanocellulose and PAN according to claim 5, characterized in that: The content of phosphoric acid and melamine in the mixed aqueous solution is 2-6 wt %, and the ratio of phosphoric acid to melamine is 1:

1.

7. The method for preparing carbon fiber based on blending nanocellulose and PAN according to claim 1, characterized in that: The activation treatment is as follows: the precursor fiber raw silk is immersed in an alkaline solution and then dried.

8. The method for preparing carbon fiber based on blending nanocellulose and PAN according to claim 1, characterized in that: The gradient temperature increase step of pre-oxidation and thermal stabilization treatment in step S5 includes: The first stage: room temperature is heated to 150°C, and the heating rate is 3-5°C / min; The second stage: heating from 150℃ to 250℃, with a heating rate of 2-5℃ / min, and then keeping warm for 0.5-1h; The third stage: heating from 250 to 400°C, with a heating rate of 2-5°C / min.

9. The method for preparing carbon fiber based on blending nanocellulose and PAN according to claim 1, characterized in that: In step S6, the heating rate from 400°C to 1000°C is 5-7°C / min, and the holding time is 0-1.5h; the heating rate from 1000°C to 1800°C is 5-7°C / min.

10. The method for preparing carbon fiber based on blending nanocellulose and PAN according to claim 1, characterized in that: The heating rate of heating to 2000-2200° C. in step S7 is 3-5° C. / min.

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