A waste biomass-based carbon fiber and a method for preparing the same

Abstract

The application relates to the technical field of carbon fibers, in particular to a waste biomass-based carbon fiber and a preparation method thereof. Reinforced carbon materials are added into N,N-dimethylformamide, a mixture of hydrothermal straws and polyacrylonitrile is added after uniform dispersion, stirring and standing are carried out, and a spinning solution is obtained. The spinning solution is subjected to electrostatic spinning and vacuum drying, and a nanofiber membrane is obtained; the nanofiber membrane is subjected to pre-oxidation cooling, cutting, carbonization, cooling, alkali activation, washing and drying, and a straw-based carbon fiber is obtained. The straw-based carbon fiber prepared by the application uses waste biomass as raw material, and green carbon fibers with excellent mechanical properties and specific surface area are prepared, so that the application has a wide application prospect in the technical field of carbon fibers.

Description

Technical Field

[0001] This invention relates to the field of carbon fiber technology, specifically to a waste biomass-based carbon fiber and its preparation method. Background Technology

[0002] Carbon fiber is a type of fibrous material with a carbon content exceeding 90%. Its density is only one-quarter that of steel, yet its strength is seven to nine times greater, while also possessing excellent modulus, fatigue resistance, and a low coefficient of thermal expansion. Carbon fiber has had a profound impact on many major fields, including aerospace, transportation, and energy, by providing excellent lightweight solutions. However, the traditional carbon fiber industry heavily relies on petroleum-based precursors made from polyacrylonitrile (PAN), pitch, or viscose. Among these, the PAN-based route, due to its ability to achieve the optimal balance between high strength and high modulus, occupies over 90% of the commercial market. However, this technological path faces significant challenges: its core raw material, acrylonitrile, is derived from non-renewable fossil resources, resulting in high energy consumption and emissions during production; furthermore, the preparation of PAN precursor fibers is complex and costly. These factors restrict the large-scale application of carbon fiber in a wider range of fields and inherently contradict the sustainable development goals of the green industries it serves, such as wind power and transportation. Therefore, this application proposes an innovative route using waste biomass as raw material, supplemented by modified polyacrylonitrile, aiming to develop a green carbon fiber preparation technology.

[0003] To overcome the shortcomings of existing technologies, this invention provides a waste biomass-based carbon fiber and its preparation method. Summary of the Invention

[0004] The purpose of this invention is to provide a waste biomass-based carbon fiber and its preparation method to solve the problems raised in the prior art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing waste biomass-based carbon fiber includes the following steps: Step 1: Mix deionized water and straw, and after hydrothermal reaction, cool, wash, dry and grind to obtain hydrothermal straw; mix hydrothermal straw and polyacrylonitrile in a certain proportion, then add N,N-dimethylformamide, stir and let stand to defoam to obtain spinning solution; Step 2: Electrospinning and vacuum drying of the spinning solution yields a nanofiber membrane; pre-oxidation, cooling, and cutting of the nanofiber membrane yields a strip-shaped fiber membrane; carbonization, cooling, activation with KOH solution, washing, and drying of the strip-shaped fiber membrane yields straw-based carbon fiber.

[0006] In a more optimized manner, hydrothermal straw and polyacrylonitrile are mixed in a certain proportion, then added to N,N-dimethylformamide, stirred for 24-28 hours, and allowed to stand to defoam, to obtain the spinning solution.

[0007] In a more optimized manner, the reaction mass ratio of deionized water to straw is (5.0-6.0):1; the mixing mass ratio of hydrothermal straw and polyacrylonitrile is (0.9-1.1):(1.0-1.3).

[0008] In a more optimized manner, the temperature is increased to 750-850℃ under N2 atmosphere at a heating rate of 5℃ / min for carbonization for 2.0-2.5h.

[0009] The optimized electrospinning parameters are as follows: positive voltage 17-18kV, negative voltage 3.0-3.2kV, receiving speed 100-110rpm, injection speed 0.10-0.12mm / min, receiving distance 15-18cm; translational speed of the injector 300-350mm / min, stroke 60-70mm, ambient temperature 25-30℃, humidity 35-45%, and electrospinning time 12-14h.

[0010] The optimal size of the strip fiber membrane is 2×5cm; activation parameters: activation in 2MKOH solution for 2-3h; hydrothermal reaction at 180-200℃ for 10-11h.

[0011] In a more optimized manner, the temperature is increased to 200-220℃ in an air atmosphere at a heating rate of 1℃ / min for 2.0-2.5h for pre-oxidation.

[0012] In a more optimized manner, in step one, the polyacrylonitrile is modified to obtain a modified polyacrylonitrile. Specifically, the reinforcing carbon material and polyacrylonitrile are stirred and mixed to obtain the modified polyacrylonitrile; the mixing mass ratio of the reinforcing carbon material and polyacrylonitrile is (0.02-0.03):1.

[0013] A more optimized preparation process for reinforced carbon materials is as follows: Step S1: Add graphene oxide to a mixed solution of anhydrous ethanol and deionized water, disperse it evenly, then add γ-glycidyl etheroxypropyltrimethoxysilane, and then add triethylamine to adjust the pH to 4.5-4.7. After dispersion, stir and react at 70-75℃ for 3.5-4.5h. After the reaction is completed, centrifuge, wash and dry to obtain epoxide graphene. Step S2: Add graphene epoxide to deionized water, stir evenly, then add dopamine, Tris buffer and hydrochloric acid to adjust the pH to 8.5-8.7, stir and react at 25-30℃ for 2.5-3.0h, then raise the temperature to 40-45℃ and continue stirring and reacting for 2.5-3.5h, then stir and react at 25-30℃ for 8-10h to obtain modified graphene; Step S3: Add polyethyleneimine to deionized water to obtain a polyethyleneimine solution; then add carboxylated carbon nanotubes to the polyethyleneimine solution and reflux at 100-110℃ for 10-15 h. After the reaction is completed, filter, wash and freeze dry to obtain modified carbon nanotubes. Step S4: Add 2,5-dihydroxyterephthalaldehyde, modified graphene, and modified carbon nanotubes to anhydrous ethanol, disperse them evenly, and then add acetic acid dropwise. React at 70-75℃ for 9-10 hours. After the reaction is completed, filter, wash, and vacuum dry to obtain the reinforced carbon material.

[0014] In a more optimized manner, in step S1, the volume ratio of anhydrous ethanol to deionized water is (2-3):1; the reaction mass ratio of graphene oxide to γ-glycidyl etheroxypropyltrimethoxysilane is 1:(0.7-1.0).

[0015] In a more optimized manner, in step S2, the reaction mass ratio of graphene epoxide, dopamine, and Tris buffer is (0.05-0.07):0.4:0.5.

[0016] In a more optimized manner, in step S3, the concentration of the polyethyleneimine solution is 45-55 mg / mL; the reaction mass ratio of polyethyleneimine to carboxylated carbon nanotubes is (10-15):1.

[0017] In a more optimized manner, in step S4, the reaction mass ratio of 2,5-dihydroxyterephthalaldehyde, modified graphene, and modified carbon nanotubes is (0.8-1.0):3:3.

[0018] The beneficial effects of this invention are: SEM chart analysis: From Figure 1 (ad) shows that the surface color of the straw turned dark brown after hydrothermal treatment, indicating that the straw's structure was destroyed under high temperature and pressure, and impurities were decomposed. Microscopic images show that the surface of the straw became smoother after hydrothermal treatment, further demonstrating that the straw's morphological structure changed and rough surface impurities were decomposed. The carbon fibers before and after calcination show that before calcination, the fibers were interwoven to form a network structure with a diameter of approximately 500 nm, indicating the effectiveness of current electrospinning technology using waste biomass. Figure 1 (h), (i) and (j) show that the surface of the straw-based carbon fiber is rough and the fiber diameter is about 100 nm.

[0019] Analysis of specific surface area and iodine value of carbon fiber: The effects of different carbonization temperatures and raw material ratios on the specific surface area and iodine value of carbon fiber were investigated. The best results were observed at 800°C and a 1:1 ratio, with the values ​​reaching 2691.5 m². 2 / g and 2518.3mg / g. From Figure 2(a) It can be seen that the changes in specific surface area and iodine value follow a basically similar pattern. Specific surface area decreases between 500°C and 600°C, then increases again with rising temperature, reaching its maximum at 800°C. Then, when the temperature rises to 900 and 1000°C, the specific surface area decreases significantly. Iodine value, on the other hand, shows an increasing trend from 500°C to 800°C, decreases at 900°C, and increases slightly at 1000°C. Figure 2 (b) It can be seen that the increase in straw content leads to a trend of first increasing and then decreasing specific surface area and iodine value. The effect is best when the addition amount is 50%. When the addition amount is 66.7%, the viscosity of the spinning solution is relatively high. Although it can produce carbon fibers with better performance, it reduces the performance of the material to a certain extent.

[0020] Pore ​​size distribution of carbon fibers: Figure 3 Analysis of the pore size distribution under varying temperature and ratio revealed that the pore structure of carbon fibers prepared under all conditions was predominantly micropores, mainly distributed in the 0.5-2 nm size range, with a small number of mesopores distributed in the 2-10 nm size range, and almost no macropores. This result is consistent with the characteristics of carbon fibers. Comparison showed that the micropore effect was most pronounced at 800°C and a 1:1 ratio. This may be because combustion was not complete during low-temperature carbonization, especially since the lignin-based components required sufficient pyrolysis after 600°C. With increasing straw addition, the exposed microstructures on the surface after hydrothermal pretreatment facilitated thorough KOH impregnation, leading to a more complete activation reaction and promoting microstructure development. Therefore, 800°C and a 1:1 ratio were chosen for further research to investigate the pyrolysis process of the straw-based carbon fiber precursor.

[0021] Thermogravimetric analysis of carbon fiber: Figure 4 The lignocellulose composition of straw and hydrothermal straw was analyzed, along with their pyrolysis curves at 800°C. From... Figure 4 (a) It can be seen that the original straw has the highest cellulose content. After hydrothermal treatment, the relative content of lignin increases, while the relative content of cellulose and hemicellulose decreases. From Figure 4 (b) It can be seen that the carbon yield of the original straw is 27.0%, the carbon yield of the hydrothermal straw is 38.4%, the carbon yield of the hydrothermal straw with PAN is 39.2%, and the carbon yield of PAN is 41.3%. The increase in carbon yield indicates that the hydrothermal straw is more conducive to the preparation of carbon fibers. From the decomposition trend, it can be seen that the hydrothermal straw mixed with PAN can slow down the decomposition rate of cellulose and hemicellulose. This decomposition trend is more conducive to the preparation of carbon fibers with high surface area.

[0022] Mechanical property analysis of carbon fiber: Figure 5The mechanical properties of hydrothermal straw-based carbon fibers prepared under different ratios were tested. It can be seen that the elastic modulus of pure PAN-based carbon fibers is relatively the largest. When different contents of hydrothermal straw are added, the elastic modulus of the carbon fibers prepared at a ratio of 1:2 is close to that of pure PAN-based carbon fibers, indicating that biomass-based carbon fibers have the potential to replace PAN in the preparation of carbon fibers.

[0023] The key feature of this invention is that it modifies graphene oxide by adding γ-glycidyl etheroxypropyltrimethoxysilane to obtain epoxidized graphene. Then, the epoxidized graphene, dopamine, Tris buffer, and hydrochloric acid are mixed. On one hand, dopamine undergoes crosslinking and polymerization to form a polydopamine structure; on the other hand, the primary or secondary amino groups on the polydopamine chain undergo a nucleophilic ring-opening reaction with the epoxy groups on the surface of the epoxidized graphene, anchoring the polydopamine to the graphene surface, thus obtaining modified graphene. Polyethyleneimine and carboxylated carbon nanotubes are then mixed and an amidation reaction occurs to obtain modified carbon nanotubes. Since both the modified graphene and the modified carbon nanotubes have active amino groups on their surfaces, further, 2,5-dihydroxyterephthalaldehyde is mixed with the modified graphene and modified carbon nanotubes containing active amino groups to undergo a Schiff base reaction, resulting in reinforced carbon materials.

[0024] The present invention is characterized by adding reinforcing carbon material to N,N-dimethylformamide, dispersing it evenly, then adding a mixture of hydrothermal straw and polyacrylonitrile, stirring and allowing it to stand to obtain a spinning solution. The spinning solution is then subjected to electrospinning and vacuum drying to obtain a nanofiber membrane; the nanofiber membrane is then subjected to pre-oxidation cooling, cutting, carbonization, cooling, alkali activation, washing, and drying to obtain straw-based carbon fibers.

[0025] In this study, both modified graphene (surface-anchored with polydopamine) and modified carbon nanotubes (surface-grafted with polyethyleneimine) are rich in active amino groups. These groups react with 2,5-dihydroxyterephthalaldehyde via a Schiff base reaction to form a stable three-dimensional covalently cross-linked network connected by imine bonds (-C=N-). Compared to physical mixing or van der Waals force bonding, this continuous covalent network can more effectively transfer and disperse stress under external loads, greatly improving the intrinsic stiffness and structural integrity of the reinforced carbon material. Furthermore, graphene, as a two-dimensional sheet material, possesses extremely high intrinsic modulus; carbon nanotubes, as one-dimensional nanomaterials, have high aspect ratios and excellent mechanical properties. Therefore, the covalent bonds between graphene and carbon nanotubes effectively prevent agglomeration and allow them to interweave and support each other in three-dimensional space, forming a strong and tough reinforcing framework at the nano / micro scale. When this framework is embedded in the carbon fiber matrix, it significantly constrains the deformation of the matrix material, resulting in a significant increase in the elastic modulus of the carbon fiber. Meanwhile, the three-dimensional network formed by covalently connecting two-dimensional graphene sheets and one-dimensional carbon nanotubes naturally contains a large number of nanoscale gaps and pores. These pores are retained after carbonization, providing a large specific surface area.

[0026] The key feature of this invention is the addition of reinforcing carbon materials to N,N-dimethylformamide, followed by uniform dispersion and the addition of a mixture of hydrothermal straw and polyacrylonitrile. The mixture is then stirred and allowed to stand to obtain a spinning solution. This solution is then subjected to electrospinning and vacuum drying to obtain a nanofiber membrane. The nanofiber membrane is then subjected to pre-oxidation cooling, cutting, carbonization, cooling, alkali activation, washing, and drying to obtain straw-based carbon fibers. Compared to the traditional PAN-based route, this application achieves a fundamental substitution of raw materials, shifting the "carbon source" of carbon fibers from fossil fuels to a renewable biomass recycling system. Simultaneously, the utilization of waste biomass has both environmental and economic value, reducing waste disposal pressure and significantly lowering raw material costs. Attached Figure Description

[0027] Figure 1 (a) Physical image of straw, (c) Physical image of hydrothermal straw, (b) SEM image of straw, (d) SEM image of hydrothermal straw, (e, f) Fiber without pre-oxidation and carbonization, (g) SEM image of product obtained by mixing hydrothermal straw and PAN at a ratio of 0:1, (h) SEM image of product obtained by mixing hydrothermal straw and PAN at a ratio of 1:2, (i) SEM image of product obtained by mixing hydrothermal straw and PAN at a ratio of 1:1, (j) SEM image of product obtained by mixing hydrothermal straw and PAN at a ratio of 2:1; Figure 2 (a) Iodine value and specific surface area of ​​ACF prepared at different carbonization temperatures, with a hydrothermal straw to PAN mixing ratio of 1:1; (b) Iodine value and specific surface area of ​​ACF prepared at different hydrothermal straw ratios, with a carbonization temperature of 800℃. Figure 3 (a) Pore size distribution of carbon fibers prepared at different carbonization temperatures, (b) Pore size distribution of carbon fibers prepared with different straw ratios. Figure 4 (a) Composition diagram of straw and hydrothermal straw; (b) Pyrolysis analysis diagram of straw, hydrothermal straw and PAN / hydrothermal straw; Figure 5 This is a graph showing the carbon fiber elastic modulus test results of the present invention. Detailed Implementation

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Raw material source: Tris buffer solution, supplied by Sinopharm Chemical Reagent Co., Ltd., specification RG; graphene oxide, supplied by Beijing Meiston Technology Development Co., Ltd., model SY-GO-S; polyethyleneimine, supplied by Shanghai Aladdin, MW 70000; carboxylated carbon nanotubes, diameter 5nm; polyacrylonitrile, supplied by Hubei Great Biomedical Technology Co., Ltd., model GREAT5777.

[0030] Example 1: Step S1: Deionized water and straw were mixed and hydrothermally reacted at 200℃ for 10 hours. After the reaction, the mixture was cooled, washed, dried, and ground to obtain hydrothermal straw. The hydrothermal straw and polyacrylonitrile were mixed in a certain proportion and then added to N,N-dimethylformamide. After stirring for 24 hours, the mixture was allowed to stand to defoam and obtain spinning solution. The reaction mass ratio of deionized water to straw was 6:1; the mixing mass ratio of hydrothermal straw to polyacrylonitrile was 1:1. Step S2: Electrospinning and vacuum drying of the spinning solution yields a nanofiber membrane; pre-oxidation of the nanofiber membrane at 200℃ for 2 hours, followed by cooling and cutting to obtain a strip-shaped fiber membrane; carbonization of the strip-shaped fiber membrane at 800℃ for 2 hours, followed by cooling, activation with KOH solution, washing, and drying to obtain straw-based carbon fiber. Electrospinning parameters: positive voltage 17kV, negative voltage 3.0kV, receiving speed 100rpm, injection speed 0.10mm / min, receiving distance 15cm; translational speed of the injector 300mm / min, stroke 60mm, ambient temperature 30℃, humidity 40%, electrospinning time 12h; size of the strip fiber membrane 2×5cm; activation parameters: activation in 2MKOH solution for 2h.

[0031] Example 2: Step S1: Graphene oxide was added to a mixed solution of anhydrous ethanol and deionized water. After being dispersed evenly, γ-glycidoxypropyltrimethoxysilane was added, and then triethylamine was added to adjust the pH to 4.6. After being dispersed evenly, the mixture was stirred at 73°C for 4 hours. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain epoxide graphene. The volume ratio of anhydrous ethanol to deionized water was 2.5:1; the mass ratio of graphene oxide to γ-glycidoxypropyltrimethoxysilane was 1:0.8. Step S2: Add graphene oxide to deionized water, stir well, then add dopamine, Tris buffer, and hydrochloric acid to adjust the pH to 8.6. Stir and react at 27°C for 2.7 h, then raise the temperature to 43°C and continue stirring for 3 h, then stir and react at 27°C for 9 h to obtain modified graphene; the mass ratio of graphene oxide, dopamine, and Tris buffer is 0.06:0.4:0.5. Step S3: Polyethyleneimine was added to deionized water to obtain a polyethyleneimine solution; then carboxylated carbon nanotubes were added to the polyethyleneimine solution, and the mixture was refluxed at 105°C for 12 hours. After the reaction was completed, the mixture was filtered, washed, and freeze-dried to obtain modified carbon nanotubes; the concentration of the polyethyleneimine solution was 50 mg / mL; the mass ratio of polyethyleneimine to carboxylated carbon nanotubes was 12:1. Step S4: 2,5-Dihydroxyterephthalaldehyde, modified graphene, and modified carbon nanotubes were added to anhydrous ethanol, dispersed evenly, and then acetic acid was added dropwise. The reaction was carried out at 73°C for 9.5 h. After the reaction was completed, the mixture was filtered, washed, and vacuum dried to obtain the reinforced carbon material. The mass ratio of 2,5-dihydroxyterephthalaldehyde, modified graphene, and modified carbon nanotubes was 0.9:3:3. Step S5: Deionized water and straw are mixed and hydrothermally reacted at 200℃ for 10 hours. After the reaction, the mixture is cooled, washed, dried, and ground to obtain hydrothermal straw. Reinforcing carbon material and polyacrylonitrile are stirred and mixed to obtain modified polyacrylonitrile. Hydrothermal straw and modified polyacrylonitrile are mixed in a certain proportion and then added to N,N-dimethylformamide. After stirring for 24 hours, the mixture is allowed to stand to defoam, resulting in a spinning solution. The reaction mass ratio of deionized water to straw is 6:1; the mixing mass ratio of reinforcing carbon material to polyacrylonitrile is 0.025:1; and the mixing mass ratio of hydrothermal straw to modified polyacrylonitrile is 1:1. Step S6: Electrospinning and vacuum drying of the spinning solution yields a nanofiber membrane; pre-oxidation of the nanofiber membrane at 200℃ for 2 hours, followed by cooling and cutting to obtain a strip-shaped fiber membrane; carbonization of the strip-shaped fiber membrane at 800℃ for 2 hours, followed by cooling, activation with KOH solution, washing, and drying to obtain straw-based carbon fiber. Electrospinning parameters: positive voltage 17kV, negative voltage 3.0kV, receiving speed 100rpm, injection speed 0.10mm / min, receiving distance 15cm; translational speed of the injector 300mm / min, stroke 60mm, ambient temperature 30℃, humidity 40%, electrospinning time 12h; size of the strip fiber membrane 2×5cm; activation parameters: activation in 2MKOH solution for 2h.

[0032] Comparative Example 1: The ratio of hydrothermal straw to PAN was adjusted to 0:1, and the rest was the same as in Example 1. The specific steps are as follows: Step S1: Polyacrylonitrile and N,N-dimethylformamide were mixed and stirred for 24 hours. After standing to defoam, the spinning solution was obtained. The mass ratio of hydrothermal straw to polyacrylonitrile was 0:1. Step S2: Electrospinning and vacuum drying of the spinning solution yields a nanofiber membrane; pre-oxidation of the nanofiber membrane at 200℃ for 2 hours, followed by cooling and cutting to obtain a strip-shaped fiber membrane; carbonization of the strip-shaped fiber membrane at 800℃ for 2 hours, followed by cooling, activation with KOH solution, washing, and drying to obtain straw-based carbon fiber. Electrospinning parameters: positive voltage 17kV, negative voltage 3.0kV, receiving speed 100rpm, injection speed 0.10mm / min, receiving distance 15cm; translational speed of the injector 300mm / min, stroke 60mm, ambient temperature 30℃, humidity 40%, electrospinning time 12h; size of the strip fiber membrane 2×5cm; activation parameters: activation in 2MKOH solution for 2h.

[0033] Comparative Example 2: The ratio of hydrothermal straw to PAN was adjusted to 1:2, and the rest was the same as in Example 1. The specific steps are as follows: Step S1: Deionized water and straw were mixed and hydrothermally reacted at 200℃ for 10 hours. After the reaction, the mixture was cooled, washed, dried, and ground to obtain hydrothermal straw. The hydrothermal straw and polyacrylonitrile were mixed in a certain proportion and then added to N,N-dimethylformamide. After stirring for 24 hours, the mixture was allowed to stand to defoam and obtain spinning solution. The reaction mass ratio of deionized water to straw was 6:1; the mixing mass ratio of hydrothermal straw and polyacrylonitrile was 1:2. Step S2: Electrospinning and vacuum drying of the spinning solution yields a nanofiber membrane; pre-oxidation of the nanofiber membrane at 200℃ for 2 hours, followed by cooling and cutting to obtain a strip-shaped fiber membrane; carbonization of the strip-shaped fiber membrane at 800℃ for 2 hours, followed by cooling, activation with KOH solution, washing, and drying to obtain straw-based carbon fiber. Electrospinning parameters: positive voltage 17kV, negative voltage 3.0kV, receiving speed 100rpm, injection speed 0.10mm / min, receiving distance 15cm; translational speed of the injector 300mm / min, stroke 60mm, ambient temperature 30℃, humidity 40%, electrospinning time 12h; size of the strip fiber membrane 2×5cm; activation parameters: activation in 2MKOH solution for 2h.

[0034] Comparative Example 3: The ratio of hydrothermal straw to PAN was adjusted to 2:1, and the rest was the same as in Example 1. The specific steps are as follows: Step S1: Deionized water and straw were mixed and hydrothermally reacted at 200℃ for 10 hours. After the reaction, the mixture was cooled, washed, dried, and ground to obtain hydrothermal straw. The hydrothermal straw and polyacrylonitrile were mixed in a certain proportion and then added to N,N-dimethylformamide. After stirring for 24 hours, the mixture was allowed to stand to defoam and obtain spinning solution. The reaction mass ratio of deionized water to straw was 6:1; the mixing mass ratio of hydrothermal straw and polyacrylonitrile was 2:1. Step S2: Electrospinning and vacuum drying of the spinning solution yields a nanofiber membrane; pre-oxidation of the nanofiber membrane at 200℃ for 2 hours, followed by cooling and cutting to obtain a strip-shaped fiber membrane; carbonization of the strip-shaped fiber membrane at 800℃ for 2 hours, followed by cooling, activation with KOH solution, washing, and drying to obtain straw-based carbon fiber. Electrospinning parameters: positive voltage 17kV, negative voltage 3.0kV, receiving speed 100rpm, injection speed 0.10mm / min, receiving distance 15cm; translational speed of the injector 300mm / min, stroke 60mm, ambient temperature 30℃, humidity 40%, electrospinning time 12h; size of the strip fiber membrane 2×5cm; activation parameters: activation in 2MKOH solution for 2h.

[0035] Comparative Example 4: The carbonization temperature was adjusted to 500℃, and the rest was the same as in Example 1. The specific steps are as follows: Step S1: Deionized water and straw were mixed and hydrothermally reacted at 200℃ for 10 hours. After the reaction, the mixture was cooled, washed, dried, and ground to obtain hydrothermal straw. The hydrothermal straw and polyacrylonitrile were mixed in a certain proportion and then added to N,N-dimethylformamide. After stirring for 24 hours, the mixture was allowed to stand to defoam and obtain spinning solution. The reaction mass ratio of deionized water to straw was 6:1; the mixing mass ratio of hydrothermal straw and polyacrylonitrile was 1:1. Step S2: Electrospinning and vacuum drying of the spinning solution yields a nanofiber membrane; pre-oxidation of the nanofiber membrane at 200℃ for 2 hours, followed by cooling and cutting to obtain a strip-shaped fiber membrane; carbonization of the strip-shaped fiber membrane at 500℃ for 2 hours, followed by cooling, activation with KOH solution, washing, and drying to obtain straw-based carbon fiber. Electrospinning parameters: positive voltage 17kV, negative voltage 3.0kV, receiving speed 100rpm, injection speed 0.10mm / min, receiving distance 15cm; translational speed of the injector 300mm / min, stroke 60mm, ambient temperature 30℃, humidity 40%, electrospinning time 12h; size of the strip fiber membrane 2×5cm; activation parameters: activation in 2MKOH solution for 2h.

[0036] Comparative Example 5: The carbonization temperature was adjusted to 600℃, and the rest was the same as in Example 1. The specific steps are as follows: Step S1: Deionized water and straw were mixed and hydrothermally reacted at 200℃ for 10 hours. After the reaction, the mixture was cooled, washed, dried, and ground to obtain hydrothermal straw. The hydrothermal straw and polyacrylonitrile were mixed in a certain proportion and then added to N,N-dimethylformamide. After stirring for 24 hours, the mixture was allowed to stand to defoam and obtain spinning solution. The reaction mass ratio of deionized water to straw was 6:1; the mixing mass ratio of hydrothermal straw and polyacrylonitrile was 1:1. Step S2: Electrospinning and vacuum drying of the spinning solution yields a nanofiber membrane; pre-oxidation of the nanofiber membrane at 200℃ for 2 hours, followed by cooling and cutting to obtain a strip-shaped fiber membrane; carbonization of the strip-shaped fiber membrane at 600℃ for 2 hours, followed by cooling, activation with KOH solution, washing, and drying to obtain straw-based carbon fiber. Electrospinning parameters: positive voltage 17kV, negative voltage 3.0kV, receiving speed 100rpm, injection speed 0.10mm / min, receiving distance 15cm; translational speed of the injector 300mm / min, stroke 60mm, ambient temperature 30℃, humidity 40%, electrospinning time 12h; size of the strip fiber membrane 2×5cm; activation parameters: activation in 2MKOH solution for 2h.

[0037] Comparative Example 6: The carbonization temperature was adjusted to 700℃, and the rest was the same as in Example 1. The specific steps are as follows: Step S1: Deionized water and straw were mixed and hydrothermally reacted at 200℃ for 10 hours. After the reaction, the mixture was cooled, washed, dried, and ground to obtain hydrothermal straw. The hydrothermal straw and polyacrylonitrile were mixed in a certain proportion and then added to N,N-dimethylformamide. After stirring for 24 hours, the mixture was allowed to stand to defoam and obtain spinning solution. The reaction mass ratio of deionized water to straw was 6:1; the mixing mass ratio of hydrothermal straw and polyacrylonitrile was 1:1. Step S2: Electrospinning and vacuum drying of the spinning solution yields a nanofiber membrane; pre-oxidation of the nanofiber membrane at 200℃ for 2 hours, followed by cooling and cutting to obtain a strip-shaped fiber membrane; carbonization of the strip-shaped fiber membrane at 700℃ for 2 hours, followed by cooling, activation with KOH solution, washing, and drying to obtain straw-based carbon fiber. Electrospinning parameters: positive voltage 17kV, negative voltage 3.0kV, receiving speed 100rpm, injection speed 0.10mm / min, receiving distance 15cm; translational speed of the injector 300mm / min, stroke 60mm, ambient temperature 30℃, humidity 40%, electrospinning time 12h; size of the strip fiber membrane 2×5cm; activation parameters: activation in 2MKOH solution for 2h.

[0038] Comparative Example 7: The carbonization temperature was adjusted to 900℃, and the rest was the same as in Example 1. The specific steps are as follows: Step S1: Deionized water and straw were mixed and hydrothermally reacted at 200℃ for 10 hours. After the reaction, the mixture was cooled, washed, dried, and ground to obtain hydrothermal straw. The hydrothermal straw and polyacrylonitrile were mixed in a certain proportion and then added to N,N-dimethylformamide. After stirring for 24 hours, the mixture was allowed to stand to defoam and obtain spinning solution. The reaction mass ratio of deionized water to straw was 6:1; the mixing mass ratio of hydrothermal straw and polyacrylonitrile was 1:1. Step S2: Electrospinning and vacuum drying of the spinning solution yields a nanofiber membrane; pre-oxidation of the nanofiber membrane at 200℃ for 2 hours, followed by cooling and cutting to obtain a strip-shaped fiber membrane; carbonization of the strip-shaped fiber membrane at 900℃ for 2 hours, followed by cooling, activation with KOH solution, washing, and drying to obtain straw-based carbon fiber. Electrospinning parameters: positive voltage 17kV, negative voltage 3.0kV, receiving speed 100rpm, injection speed 0.10mm / min, receiving distance 15cm; translational speed of the injector 300mm / min, stroke 60mm, ambient temperature 30℃, humidity 40%, electrospinning time 12h; size of the strip fiber membrane 2×5cm; activation parameters: activation in 2MKOH solution for 2h.

[0039] Comparative Example 8: The carbonization temperature was adjusted to 1000℃, and the rest was the same as in Example 1. The specific steps are as follows: Step S1: Deionized water and straw were mixed and hydrothermally reacted at 200℃ for 10 hours. After the reaction, the mixture was cooled, washed, dried, and ground to obtain hydrothermal straw. The hydrothermal straw and polyacrylonitrile were mixed in a certain proportion and then added to N,N-dimethylformamide. After stirring for 24 hours, the mixture was allowed to stand to defoam and obtain spinning solution. The reaction mass ratio of deionized water to straw was 6:1; the mixing mass ratio of hydrothermal straw and polyacrylonitrile was 1:1. Step S2: Electrospinning and vacuum drying of the spinning solution yields a nanofiber membrane; pre-oxidation of the nanofiber membrane at 200℃ for 2 hours, followed by cooling and cutting to obtain a strip-shaped fiber membrane; carbonization of the strip-shaped fiber membrane at 1000℃ for 2 hours, followed by cooling, activation with KOH solution, washing, and drying to obtain straw-based carbon fiber. Electrospinning parameters: positive voltage 17kV, negative voltage 3.0kV, receiving speed 100rpm, injection speed 0.10mm / min, receiving distance 15cm; translational speed of the injector 300mm / min, stroke 60mm, ambient temperature 30℃, humidity 40%, electrospinning time 12h; size of the strip fiber membrane 2×5cm; activation parameters: activation in 2MKOH solution for 2h.

[0040] Testing and experimentation: Elastic modulus test: The prepared unactivated carbon fibers were pressed into a 3mm × 10mm barbell-shaped specimen using a mold and hydraulic press. The material was placed on a support and a force was applied to make it bend. The deformation and stress after bending were measured, and the elastic modulus was calculated.

[0041] Nitrogen adsorption and specific surface area tests: The prepared carbon fibers were used as samples. First, they were placed in sample tubes and then pretreated in a vacuum at 200℃ for 5 hours to remove impurities from the carbon fiber surface. Then, high-purity nitrogen was used as the adsorption medium for the carbon fibers. The N2 desorption isotherm of the samples was measured under liquid nitrogen conditions. The specific surface area of ​​the samples was calculated using the Brunauer-Emmett-Teller equation (BET), and the pore size distribution was calculated using the Barrett-Joyner-Halenda model. The results are shown in the table below: Conclusion: By testing the specific surface area of ​​hydrothermal straw-based carbon fibers prepared under different ratios and at different carbonization temperatures, it can be seen that the carbon fibers with the best specific surface area (2691.5 m²) are obtained at 800°C and a 1:1 ratio. 2 / g. By testing the elastic modulus of hydrothermal straw-based carbon fibers prepared under different ratios, it can be seen that the elastic modulus of pure PAN-based carbon fibers is relatively the largest. When different contents of hydrothermal straw are added, the elastic modulus of the carbon fibers prepared at a ratio of 1:2 is close to that of pure PAN-based carbon fibers, indicating that biomass-based carbon fibers have the potential to replace PAN in the preparation of carbon fibers. Furthermore, in Example 2, reinforcing carbon materials and polyacrylonitrile were mixed to obtain modified polyacrylonitrile. Straw-based carbon fibers were further prepared using modified polyacrylonitrile, achieving an elastic modulus of 2351.7 MPa and a specific surface area of ​​3323.4 m². 2 / g indicates that by adding reinforcing carbon materials, the mechanical properties and specific surface area of ​​carbon fibers can be effectively improved.

[0042] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process method article or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process method article or apparatus.

[0043] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing waste biomass-based carbon fiber, characterized in that: Includes the following steps: Step 1: Mix deionized water and straw, and after hydrothermal reaction, cool, wash, dry and grind to obtain hydrothermal straw; mix hydrothermal straw and polyacrylonitrile in a certain proportion, then add N,N-dimethylformamide, stir and let stand to defoam to obtain spinning solution; Step 2: Electrospinning and vacuum drying of the spinning solution yields a nanofiber membrane; pre-oxidation, cooling, and cutting of the nanofiber membrane yields a strip-shaped fiber membrane; carbonization, cooling, activation with KOH solution, washing, and drying of the strip-shaped fiber membrane yields straw-based carbon fiber.

2. The method for preparing waste biomass-based carbon fiber according to claim 1, characterized in that: The reaction mass ratio of deionized water to straw is (5.0-6.0):1; the mixing mass ratio of hydrothermal straw and polyacrylonitrile is (0.9-1.1):(1.0-1.3); the carbonization temperature is 750-850℃, and the carbonization time is 2.0-2.5h.

3. The method for preparing waste biomass-based carbon fiber according to claim 1, characterized in that: Electrospinning parameters: positive voltage 17-18kV, negative voltage 3.0-3.2kV, receiving speed 100-110rpm, injection speed 0.10-0.12mm / min, receiving distance 15-18cm; translational speed of the injector 300-350mm / min, stroke 60-70mm, ambient temperature 25-30℃, humidity 35-45%, electrospinning time 12-14h.

4. The method for preparing waste biomass-based carbon fiber according to claim 1, characterized in that: The strip-shaped fiber membrane has a size of 2×5cm; activation parameters: activation in 2MKOH solution for 2-3h; hydrothermal reaction at 180-200℃ for 10-11h; pre-oxidation at 200-220℃ for 2.0-2.5h.

5. The method for preparing waste biomass-based carbon fiber according to claim 1, characterized in that: In step one, the polyacrylonitrile is modified to obtain a modified polyacrylonitrile. Specifically, the reinforcing carbon material and polyacrylonitrile are stirred and mixed to obtain the modified polyacrylonitrile. The mixing mass ratio of the reinforcing carbon material and polyacrylonitrile is (0.02-0.03):

1.

6. The method for preparing waste biomass-based carbon fiber according to claim 5, characterized in that: The preparation process of reinforced carbon materials is as follows: Step S1: Add graphene oxide to a mixed solution of anhydrous ethanol and deionized water, disperse it evenly, then add γ-glycidyl etheroxypropyltrimethoxysilane, and then add triethylamine to adjust the pH to 4.5-4.

7. After dispersion, stir and react at 70-75℃ for 3.5-4.5h. After the reaction is completed, centrifuge, wash and dry to obtain epoxide graphene. Step S2: Add graphene epoxide to deionized water, stir evenly, then add dopamine, Tris buffer and hydrochloric acid to adjust the pH to 8.5-8.7, stir and react at 25-30℃ for 2.5-3.0h, then raise the temperature to 40-45℃ and continue stirring and reacting for 2.5-3.5h, then stir and react at 25-30℃ for 8-10h to obtain modified graphene; Step S3: Add polyethyleneimine to deionized water to obtain a polyethyleneimine solution; then add carboxylated carbon nanotubes to the polyethyleneimine solution and reflux at 100-110℃ for 10-15 h. After the reaction is completed, filter, wash and freeze dry to obtain modified carbon nanotubes. Step S4: Add 2,5-dihydroxyterephthalaldehyde, modified graphene, and modified carbon nanotubes to anhydrous ethanol, disperse them evenly, and then add acetic acid dropwise. React at 70-75℃ for 9-10 hours. After the reaction is completed, filter, wash, and vacuum dry to obtain the reinforced carbon material.

7. The method for preparing waste biomass-based carbon fiber according to claim 6, characterized in that: In step S1, the volume ratio of anhydrous ethanol to deionized water is (2-3):1; the mass ratio of graphene oxide to γ-glycidyl etheroxypropyltrimethoxysilane is 1:(0.7-1.0).

8. The method for preparing waste biomass-based carbon fiber according to claim 6, characterized in that: In step S2, the mass ratio of graphene epoxide, dopamine, and Tris buffer is (0.05-0.07):0.4:0.

5.

9. The method for preparing waste biomass-based carbon fiber according to claim 6, characterized in that: In step S3, the concentration of the polyethyleneimine solution is 45-55 mg / mL; the reaction mass ratio of polyethyleneimine to carboxylated carbon nanotubes is (10-15):1; in step S4, the reaction mass ratio of 2,5-dihydroxyterephthalaldehyde, modified graphene, and modified carbon nanotubes is (0.8-1.0):3:

3.

10. A waste biomass-based carbon fiber, characterized in that, Prepared by the preparation method according to any one of claims 1-9.

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