Modified bamboo charcoal powder, modified bamboo charcoal powder / polyacrylonitrile composite film and preparation method of modified bamboo charcoal powder / polyacrylonitrile composite film

Abstract

The invention discloses modified bamboo charcoal powder, a modified bamboo charcoal powder / polyacrylonitrile composite film and a preparation method thereof, and relates to the technical field of polymer composite films. The preparation method comprises the following steps: firstly, carrying out ball milling treatment on bamboo charcoal fibers to prepare superfine bamboo charcoal powder with nanoscale particle size, cleaning, oxidizing and modifying the superfine bamboo charcoal powder to obtain modified bamboo charcoal powder, and then jointly dispersing the modified bamboo charcoal powder and PAN in a DMF (Dimethyl Formamide) solvent, stirring and dissolving to prepare a uniform membrane casting solution. A wet film is formed on a glass substrate in a film coating mode, and the superfine modified bamboo charcoal powder / PAN composite film is finally obtained through the steps of solidification, cleaning and drying. The film has the good film-forming property of PAN and the excellent adsorption property of bamboo charcoal, and shows good mechanical strength and high thermal stability and adsorption efficiency. The method is simple in process and wide in material source, has a good industrialization prospect, and is suitable for the fields of environment-friendly filtering materials, energy storage and high-temperature-resistant materials and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer composite films, and particularly relates to a modified bamboo charcoal powder, a modified bamboo charcoal powder / polyacrylonitrile composite film and a preparation method thereof. Background Art

[0002] Polyacrylonitrile (PAN) is a linear polymer material polymerized from acrylonitrile monomers. Its molecular chain contains strong polar cyano groups (-C≡N), which endow the material with high chemical stability, excellent film-forming properties, controllable mechanical properties, functionalization potential, etc. Therefore, it has been widely used in fields such as gas separation, liquid filtration, and electrochemical energy storage. However, although PAN-based materials have excellent film-forming properties and functionalization potential, when compounded with inorganic fillers (such as bamboo charcoal powder), due to the significant difference in surface energy between the strong polar cyano groups (-C≡N) in the PAN molecular chain and the filler, the interfacial compatibility between the two is poor, easily leading to uneven dispersion of the filler and weak interfacial binding force, thereby affecting the mechanical properties and functional stability of the composite film.

[0003] In addition, traditional PAN film preparation methods mainly include non-solvent induced phase separation (NIPS), thermally induced phase separation (TIPS), and solvent evaporation methods, etc. Although these methods are mature, they generally have many deficiencies: on the one hand, the film preparation process highly depends on toxic polar solvents (such as DMAc, DMSO), which have an adverse impact on the environment and the health of operators, and the solvent recovery is difficult and costly; on the other hand, in traditional processes, the pore structure of the film is mainly determined by the phase separation behavior, which is easily affected by factors such as temperature, humidity, and ratio, and it is difficult to regulate the film structure, resulting in uneven pore distribution of the prepared film materials, poor mechanical properties and functional adaptability. In addition, most traditional methods have complex processes and high energy consumption, and it is difficult to meet the requirements of the current coordinated development of green, low-consumption, and multi-functional film materials. Summary of the Invention

[0004] One of the purposes of the present invention is to provide a preparation method of modified bamboo charcoal powder. By blending the prepared modified bamboo charcoal powder with polyacrylonitrile to prepare a composite film, the problem of poor interfacial compatibility existing in the preparation of the film by using existing bamboo charcoal powder and polyacrylonitrile can be improved.

[0005] In order to achieve the above purpose, the present invention adopts the following technical scheme: A preparation method of modified bamboo charcoal powder, comprising the following steps:

[0006] S1-1. Preparation of bamboo charcoal fibers:

[0007] Carbonize bamboo fibers at high temperature to obtain bamboo charcoal fibers;

[0008] S1-2. Preparation of nano bamboo charcoal powder:

[0009] Perform ball milling on the bamboo charcoal fibers to obtain nano bamboo charcoal powder;

[0010] S1-3. Modification treatment:

[0011] S1-3-1. Mix nano bamboo charcoal powder and hydrogen peroxide, and let it stand for oxidation;

[0012] S1-3-2. Mix the oxidized nano bamboo charcoal powder with phytic acid, and perform staged heat treatment:

[0013] First, stir at 75°C for 0.5 hours; then raise the temperature to 100°C and stir for another 0.5 hours; then add urea solution to the mixture; continue to heat to 120°C and stir for 0.5 hours; finally, heat to 160°C until the mixture foams;

[0014] S1-3-3. Dry and ball-mill the foamed mixture to obtain modified bamboo charcoal powder.

[0015] Furthermore, in step S1-1, the bamboo fiber is selected from at least one of bamboo raw fiber and bamboo pulp fiber (for example, one of them). Preferably, the bamboo fiber is bamboo raw fiber.

[0016] Furthermore, in step S1-1, the temperature of the high-temperature treatment is 600 - 1200°C (preferably 1200°C), and the time is 150 - 270 min.

[0017] Furthermore, in step S1-2, the ball-milling treatment includes the following steps:

[0018] Put the bamboo charcoal fiber into a ball mill, and ball-mill at a rotation speed of 750 - 950 rpm (preferably 750 rpm) for 10 - 16 hours (for example, 10 hours, 13 hours, 16 hours, preferably 13 hours), and the ball-to-material ratio is 1:100 to obtain nano bamboo charcoal powder.

[0019] Furthermore, before the modification treatment in step S1-3, the nano bamboo charcoal powder is washed to remove impurities. For example, ultrasonic cleaning with ethanol is performed more than three times.

[0020] Furthermore, in step S1-3-1, the mass ratio of nano bamboo charcoal powder to hydrogen peroxide is 1:(1 - 3), preferably 1:3.

[0021] Furthermore, in step S1-3-1, the time for standing oxidation is 6 - 10 hours, preferably 8 hours.

[0022] Through standing oxidation, functional groups such as hydroxyl and carboxyl can be introduced on the surface of the nano bamboo charcoal powder.

[0023] Furthermore, in step S1-3-2, the mass ratio of the oxidized nano bamboo charcoal powder to phytic acid is 1:(1 - 3), preferably 1:3; the mass ratio of phytic acid to urea is 1:(0.5 - 1.5), preferably 1:1.

[0024] Further, in step S1-3-3, the particle size of the modified bamboo charcoal powder does not exceed 300 nm, for example, within 300 nm.

[0025] By controlling the particle size of the modified bamboo charcoal powder at the nanoscale, the interfacial bonding ability between the modified bamboo charcoal powder and PAN can be increased.

[0026] Further, in step S1-3-3, the drying temperature is 110 °C.

[0027] It should be noted that the staged heating divides the heating process into multiple temperature platforms. Each stage maintains a certain temperature and time, enabling different reactions and physical processes to occur sequentially. As a multifunctional phosphate ester, phytic acid has different degrees of condensation, hydrogen bonding, or coordination with urea and other organic components at different temperatures. The staged temperature increase allows weak interactions (such as physical adsorption and hydrogen bond formation) to occur prior to strong interactions (such as condensation and crosslinking), which is conducive to the orderly construction of the internal structure of the system and improves the uniformity and controllability of the modification effect; at each stage, the components have more sufficient time for intermolecular diffusion and uniform distribution. In particular, the subsequent addition of urea can avoid the violent reaction with phytic acid at high temperature, resulting in agglomeration. Thermal-induced structure construction mechanism: At the 75 °C and 100 °C stages, the interaction between phytic acid and other components may mainly be hydrogen bonding and van der Waals forces, accompanied by some weak condensation reactions; after adding urea, amidation or weak condensation reactions may occur at 120 °C, and a preliminary three-dimensional network structure begins to form; at 160 °C, the urea and phytic acid in the system may undergo a strong condensation reaction and release gases (such as NH3 or CO2), triggering foaming and forming a porous structure, while the system completes crosslinking.

[0028] The second object of the present invention is to provide a modified bamboo charcoal powder, which is prepared by the above-mentioned preparation method of the modified bamboo charcoal powder.

[0029] The third object of the present invention is to provide a method for preparing a composite film based on the blending of modified bamboo charcoal powder and polyacrylonitrile, so as to overcome the problem of poor interfacial compatibility existing in the preparation of the film by the composite of existing bamboo charcoal powder and polyacrylonitrile.

[0030] Specifically, the preparation method of the modified bamboo charcoal powder / polyacrylonitrile composite film includes the following steps:

[0031] S2-1. Dissolve the above-mentioned modified bamboo charcoal powder and polyacrylonitrile (PAN) in N,N-dimethylformamide (DMF), and stir evenly at 50-80 °C (preferably 60 °C) to obtain a mixed solution;

[0032] S2-2. Perform ultrasonic degassing treatment on the mixed solution, and then coat the film on a glass plate by the doctor blade method;

[0033] S2-3. Heat-cure the coated glass plate at 50-70 °C (preferably 60 °C), soak it in deionized water to remove the film after curing, and obtain the modified bamboo charcoal powder / polyacrylonitrile composite film after drying.

[0034] Furthermore, in step S2-1, the mass ratio of the modified bamboo charcoal powder to polyacrylonitrile is (1-3):(7-9), such as 1:9, 2:8, 3:7, preferably 1:9.

[0035] Furthermore, in step S2-1, the mass ratio of the total mass of the modified bamboo charcoal powder and polyacrylonitrile to the mass of N,N-dimethylformamide is 1.5:8.5. For example, the total mass of the modified bamboo charcoal powder and polyacrylonitrile is 1.5 g, and the mass of N,N-dimethylformamide is 8.5 g.

[0036] Furthermore, in step S2-1, stir at a speed of 100-300 rpm (preferably 200 rpm), and the stirring time is 1-4 hours (preferably 1 hour).

[0037] Furthermore, in step S2-2, the time for ultrasonic degassing treatment is 0.25-1 hour, preferably 0.25 hour.

[0038] Through ultrasonic degassing treatment, air bubbles can be eliminated and the solution homogeneity can be improved.

[0039] Furthermore, in step S2-2, the steps of coating the solution on the glass plate by the doctor blade method include: using a four-sided coater (doctor blade gap 100 μm) to uniformly coat the solution on the glass plate to form a film. Note: Each glass plate can only be coated once.

[0040] Furthermore, in step S2-3, the heat-curing treatment time is 0.5-2 hours, preferably 1 hour.

[0041] Furthermore, in step S2-3, the soaking time of the cured glass plate in deionized water is 0.5-2 hours, preferably 1 hour.

[0042] Furthermore, in step S2-3, the drying time after film removal is 0.5-2 hours, preferably 1 hour.

[0043] The fourth object of the present invention is to provide a modified bamboo charcoal powder / polyacrylonitrile composite film, which is prepared by the above-mentioned preparation method of the modified bamboo charcoal powder / polyacrylonitrile composite film.

[0044] After the present invention modifies the bamboo charcoal powder with phytic acid and urea, bamboo charcoal powder with a uniform and dense nanoscale agglomerated structure can be obtained. The surface of the modified bamboo charcoal powder particles is smooth, the particle size is uniform and regularly distributed, and the microstructure is ordered and dense. This structural change is attributed to the phosphate groups (-PO43 -), and the synergistic effect of the nitrogen doping effect effectively reduces the interfacial defects, enhances the bonding strength between particles, and improves the surface activity and stability. The modification treatment also improves the interfacial compatibility between the bamboo charcoal powder and the polyacrylonitrile (PAN) matrix, providing a structural basis for the improvement of the composite material properties.

[0045] In addition, using the modified bamboo charcoal powder prepared by the present invention to blend with polyacrylonitrile (PAN) to prepare a composite membrane can reduce the dependence on petrochemical resources and toxic polar solvents, and realize the continuous production of the green and low-consumption modified bamboo charcoal powder / polyacrylonitrile composite film, reducing energy consumption and production costs. At the same time, by virtue of the porous large specific surface area and rich functional groups of the bamboo charcoal powder, the composite membrane can not only improve the thermal stability, but also exhibit excellent molecular sieving and adsorption properties, with good environmental friendliness and sustainable application potential, providing an efficient and feasible new path for the industrial preparation of high-performance functional membrane materials. Description of the Drawings

[0046] Figure 1 SEM images of bamboo charcoal fibers carbonized at different temperatures in Examples 1-4;

[0047] Figure 2 SEM comparison images of the bamboo charcoal powder before and after modification prepared in Example 5;

[0048] Figure 3 SEM comparison images of the composite films and pure PAN films prepared in Examples 7-10;

[0049] Figure 4 TG comparison images of the composite films and pure PAN films prepared in Examples 7-10;

[0050] Figure 5 DTG comparison images of the composite films and pure PAN films prepared in Examples 7-10;

[0051] Figure 6 Physical sample images of the composite films and pure PAN films prepared in Examples 7-10. Detailed Embodiments

[0052] For the convenience of understanding by those skilled in the art, the present invention will be further described below in conjunction with examples. The content mentioned in the examples does not limit the present invention. It should be noted in advance that the following examples were completed in the laboratory. Those skilled in the art should understand that the dosage of each component given in the examples only represents the ratio relationship between the components, rather than specific limitations.

[0053] Aiming at the problem of poor interfacial compatibility existing in the preparation of films by compounding bamboo charcoal powder and polyacrylonitrile, the present invention first conducts specific modification treatment on the bamboo charcoal powder, and then prepares a modified bamboo charcoal powder / PAN composite film with it and a PAN matrix, which can effectively improve the interfacial compatibility problem existing between them. Specifically, first, phytic acid / urea co-modified bamboo charcoal powder is prepared (the modification method is also applicable to other biomass fibers), and then, with the modified bamboo charcoal powder as a functional filler, a modified bamboo charcoal powder / PAN composite film is prepared with a PAN matrix. By blending the modified bamboo charcoal powder and PAN in DMF, fully mixing them under mild temperature and stirring conditions, and performing ultrasonic degassing to improve the homogeneity of the solution, and then adopting the process of film coating - thermal curing - demoulding - drying, the efficient and low-consumption preparation of the film material is realized. This method simplifies the technological process, improves the environmental friendliness and operation safety. And the introduction of the modified bamboo charcoal powder can ensure that the film material has better mechanical properties. At the same time, relying on its rich pore structure, high specific surface area and excellent adsorption properties, the thermal stability, molecular sieving ability, surface activity and functionalization potential of the composite film can be significantly improved. The uniform distribution of the modified bamboo charcoal powder in the film can also effectively regulate the microstructure of the film, endowing the composite film material with more excellent thermal management characteristics and multifunctional application value. Compared with the traditional film-making method, this process has the advantages of strong structure controllability, environmental protection in the process and wide adaptability, providing a feasible and efficient new path for the preparation of high-performance and multifunctional PAN-based composite film materials.

[0054] In addition, the present invention composites ultrafine modified bamboo charcoal powder and a PAN matrix by physical means (such as physical blending method) to prepare a film, which can keep the thermal performance of the composite material stable, and the melting temperature of PAN will not change, ensuring that when the composite material needs to be heated for processing or modification treatment subsequently, there is no need to consider the problem of premature melting of the PAN film. This not only ensures the smooth progress of the modification process, but also improves the adaptability and reliability of the composite film in the hot processing process, thus contributing to its stable application in industrial production.

[0055] The following is further illustrated by specific examples.

[0056] Example 1

[0057] The following method is adopted in this example to prepare modified bamboo charcoal powder (also called "modified nano bamboo charcoal fiber"):

[0058] I. High-temperature carbonize bamboo raw fiber at 600 °C to obtain bamboo charcoal fiber;

[0059] II. Place the bamboo charcoal fiber in a ball mill, ball mill it at a rotation speed of 750 rpm for 10 hours, and the ball-to-material ratio is 1:100 to obtain nano bamboo charcoal powder;

[0060] III. Use ethanol to perform ultrasonic cleaning on the nano bamboo charcoal powder 3 times to remove impurities;

[0061] IV. Mix the cleaned nano bamboo charcoal powder and hydrogen peroxide in a mass ratio of 1:3, and carry out static oxidation treatment for 8 hours to introduce functional groups such as hydroxyl and carboxyl groups on the surface of the nano bamboo charcoal powder;

[0062] V. Mix the oxidized nano bamboo charcoal powder and phytic acid in a mass ratio of 1:3 in a three-necked flask and carry out staged heating treatment. First, stir at 75 °C for 0.5 hours, then raise the temperature to 100 °C and continue stirring for 0.5 hours. Subsequently, add a urea solution (the mass ratio of phytic acid to urea is 1:1) to the mixture, continue heating to 120 °C and stir for 0.5 hours, and finally heat to 160 °C until the mixture foams. Dry the generated foam in an oven at 110 °C, and then use a ball mill to grind it into a powder with a particle size less than 300 nm. Finally, rinse it with ethanol at least 3 times to obtain phytic acid / urea co-modified bamboo charcoal powder (m-BC). Dry the m-BC for later use.

[0063] Example 2

[0064] This example prepares modified bamboo charcoal powder (also called "modified nano bamboo charcoal fiber") by the following method:

[0065] I. High-temperature carbonize bamboo raw fibers at 800 °C to obtain bamboo charcoal fibers;

[0066] II. Place the bamboo charcoal fibers in a ball mill and ball mill at a speed of 750 rpm for 10 hours, with a ball-to-material ratio of 1:100 to obtain nano bamboo charcoal powder;

[0067] III. Use ethanol to ultrasonically clean the nano bamboo charcoal powder 3 times to remove impurities;

[0068] IV. Mix the cleaned nano bamboo charcoal powder and hydrogen peroxide in a mass ratio of 1:3, and carry out static oxidation treatment for 8 hours to introduce functional groups such as hydroxyl and carboxyl groups on the surface of the nano bamboo charcoal powder;

[0069] V. Mix the oxidized nano bamboo charcoal powder and phytic acid in a mass ratio of 1:3 in a three-necked flask and carry out staged heating treatment. First, stir at 75 °C for 0.5 hours, then raise the temperature to 100 °C and continue stirring for 0.5 hours. Subsequently, add a urea solution (the mass ratio of phytic acid to urea is 1:1) to the mixture, continue heating to 120 °C and stir for 0.5 hours, and finally heat to 160 °C until the mixture foams. Dry the generated foam in an oven at 110 °C, and then use a ball mill to grind it into a powder with a particle size less than 300 nm. Finally, rinse it with ethanol at least 3 times to obtain phytic acid / urea co-modified bamboo charcoal powder (m-BC). Dry the m-BC for later use.

[0070] Example 3

[0071] In this embodiment, the following method is used to prepare modified bamboo charcoal powder (also known as "modified nano bamboo charcoal fiber"):

[0072] I. Pyrolyze bamboo fiber at 1000 °C to obtain bamboo charcoal fiber;

[0073] II. Place the bamboo charcoal fiber in a ball mill and ball mill it at a speed of 750 rpm for 10 hours with a ball-to-material ratio of 1:100 to obtain nano bamboo charcoal powder;

[0074] III. Use ethanol to ultrasonically clean the nano bamboo charcoal powder 3 times to remove impurities;

[0075] IV. Mix the cleaned nano bamboo charcoal powder and hydrogen peroxide in a mass ratio of 1:3, and carry out a static oxidation treatment for 8 hours to introduce functional groups such as hydroxyl and carboxyl groups on the surface of the nano bamboo charcoal powder;

[0076] V. Mix the oxidized nano bamboo charcoal powder and phytic acid in a mass ratio of 1:3 in a three-necked flask and carry out staged heating treatment. First, stir at 75 °C for 0.5 hours, then raise the temperature to 100 °C and continue stirring for 0.5 hours. Subsequently, add a urea solution (the mass ratio of phytic acid to urea is 1:1) to the mixture, continue heating to 120 °C and stir for 0.5 hours, and finally heat to 160 °C until the mixture foams. Dry the generated foam in an oven at 110 °C, and then use a ball mill to grind it into a powder with a particle size less than 300 nm. Finally, rinse it with ethanol at least 3 times to obtain phytic acid / urea co-modified bamboo charcoal powder (m-BC). Dry the m-BC for later use.

[0077] Example 4

[0078] In this embodiment, the following method is used to prepare modified bamboo charcoal powder (also known as "modified nano bamboo charcoal fiber"):

[0079] I. Pyrolyze bamboo fiber at 1200 °C to obtain bamboo charcoal fiber;

[0080] II. Place the bamboo charcoal fiber in a ball mill and ball mill it at a speed of 750 rpm for 10 hours with a ball-to-material ratio of 1:100 to obtain nano bamboo charcoal powder;

[0081] III. Use ethanol to ultrasonically clean the nano bamboo charcoal powder 3 times to remove impurities;

[0082] IV. Mix the cleaned nano bamboo charcoal powder and hydrogen peroxide in a mass ratio of 1:3, and carry out a static oxidation treatment for 8 hours to introduce functional groups such as hydroxyl and carboxyl groups on the surface of the nano bamboo charcoal powder;

[0083] V. Mix the oxidized nano bamboo charcoal powder and phytic acid in a mass ratio of 1:3 in a three-necked flask and perform staged heat treatment. First, stir at 75 °C for 0.5 hours, then raise the temperature to 100 °C and continue stirring for 0.5 hours. Subsequently, add a urea solution (the mass ratio of phytic acid to urea is 1:1) to the mixture, continue heating to 120 °C and stir for 0.5 hours, and finally heat to 160 °C until the mixture foams. Dry the generated foam in an oven at 110 °C, and then use a ball mill to grind it into a powder with a particle size less than 300 nm. Finally, rinse it with ethanol at least 3 times to obtain phytic acid / urea co-modified bamboo charcoal powder (m-BC). Dry the m-BC for later use.

[0084] Example 5

[0085] In this example, the following method was used to prepare modified bamboo charcoal powder (also known as "modified nano bamboo charcoal fiber"):

[0086] I. Subject bamboo raw fibers to high-temperature carbonization at 1200 °C to obtain bamboo charcoal fibers;

[0087] II. Place the bamboo charcoal fibers in a ball mill and ball mill at a speed of 750 rpm for 13 hours, with a ball-to-material ratio of 1:100, to obtain nano bamboo charcoal powder;

[0088] III. Use ethanol to ultrasonically clean the nano bamboo charcoal powder 3 times to remove impurities;

[0089] IV. Mix the cleaned nano bamboo charcoal powder and hydrogen peroxide in a mass ratio of 1:3, and perform a static oxidation treatment for 8 hours to introduce functional groups such as hydroxyl and carboxyl groups on the surface of the nano bamboo charcoal powder;

[0090] V. Mix the oxidized nano bamboo charcoal powder and phytic acid in a mass ratio of 1:3 in a three-necked flask and perform staged heat treatment. First, stir at 75 °C for 0.5 hours, then raise the temperature to 100 °C and continue stirring for 0.5 hours. Subsequently, add a urea solution (the mass ratio of phytic acid to urea is 1:1) to the mixture, continue heating to 120 °C and stir for 0.5 hours, and finally heat to 160 °C until the mixture foams. Dry the generated foam in an oven at 110 °C, and then use a ball mill to grind it into a powder with a particle size less than 300 nm. Finally, rinse it with ethanol at least 3 times to obtain phytic acid / urea co-modified bamboo charcoal powder (m-BC). Dry the m-BC for later use.

[0091] Example 6

[0092] In this example, the following method was used to prepare modified bamboo charcoal powder (also known as "modified nano bamboo charcoal fiber"):

[0093] I. Subject bamboo raw fibers to high-temperature carbonization at 1200 °C to obtain bamboo charcoal fibers;

[0094] II. Place the bamboo charcoal fiber in a ball mill and mill it at a speed of 750 rpm for 16 hours with a ball-to-material ratio of 1:100 to obtain nano bamboo charcoal powder;

[0095] III. Use ethanol to ultrasonically clean the nano bamboo charcoal powder three times to remove impurities;

[0096] IV. Mix the cleaned nano bamboo charcoal powder and hydrogen peroxide in a mass ratio of 1:3, and perform a static oxidation treatment for 8 hours to introduce functional groups such as hydroxyl groups and carboxyl groups on the surface of the nano bamboo charcoal powder;

[0097] V. Mix the oxidized nano bamboo charcoal powder and phytic acid in a mass ratio of 1:3 in a three-necked flask and perform a staged heating treatment. First, stir at 75 °C for 0.5 hours, then raise the temperature to 100 °C and continue stirring for 0.5 hours. Subsequently, add a urea solution (the mass ratio of phytic acid to urea is 1:1) to the mixture, continue heating to 120 °C and stir for 0.5 hours, and finally heat to 160 °C until the mixture foams. Dry the generated foam in an oven at 110 °C, and then use a ball mill to grind it into a powder with a particle size less than 300 nm. Finally, rinse it with ethanol at least three times to obtain phytic acid / urea co-modified bamboo charcoal powder (m-BC). Dry the m-BC for later use.

[0098] Example 7

[0099] This example prepares the m-BC / PAN composite film by the following method:

[0100] I. Mix the modified bamboo charcoal powder (m-BC) prepared in Example 5 and polyacrylonitrile (PAN) in a mass ratio of 1:9, with a total mass of 1.5 g. Add the mixed material to 8.5 g of N,N-dimethylformamide (DMF), and perform magnetic stirring at a speed of 200 rpm for 1 hour at 60 °C to obtain a uniform mixed solution.

[0101] II. Perform an ultrasonic degassing treatment on the mixed solution for a duration of 0.25 hours to eliminate bubbles and improve the uniformity of the solution. Subsequently, use a four-sided film applicator (blade gap 100 μm) to uniformly scrape and coat the solution on a glass plate to form a film. Note that each glass plate can only be scraped and coated once.

[0102] III. Transfer the glass plate with the coated film to a forced-air drying oven at 60 °C for thermal curing treatment for 1 hour.

[0103] IV. After the thermal curing is completed, place the sample in deionized water and soak it statically for 1 hour to complete the film stripping operation. Subsequently, place the film-stripped sample in a forced-air drying oven at 40 °C and dry it for 1 hour to finally obtain the m-BC / PAN composite film material.

[0104] Example 8

[0105] In this example, the m-BC / PAN composite film was prepared by the following method:

[0106] I. The modified bamboo charcoal powder (m-BC) prepared in Example 5 and polyacrylonitrile (PAN) were mixed at a mass ratio of 2:8, and the total mass was 1.5 g. The mixed material was added to 8.5 g of N,N-dimethylformamide (DMF), and under the condition of 60 °C, magnetic stirring was carried out at a speed of 200 rpm for 1 hour to obtain a uniform mixed solution.

[0107] II. The mixed solution was subjected to ultrasonic degassing treatment for 0.25 hours to eliminate bubbles and improve the uniformity of the solution. Subsequently, a four-sided film applicator (doctor blade gap 100 μm) was used to uniformly scrape the solution onto a glass plate to form a film. Note that each glass plate can only be scraped once.

[0108] III. The glass plate with the film was transferred to a forced-air drying oven at 60 °C for heat curing treatment for 1 hour.

[0109] IV. After the heat curing was completed, the sample was placed in deionized water and soaked statically for 1 hour to complete the film stripping operation. Subsequently, the film-stripped sample was placed in a forced-air drying oven at 40 °C and dried for 1 hour to finally obtain the m-BC / PAN composite film material.

[0110] Example 9

[0111] In this example, the m-BC / PAN composite film was prepared by the following method:

[0112] I. The modified bamboo charcoal powder (m-BC) prepared in Example 5 and polyacrylonitrile (PAN) were mixed at a mass ratio of 3:7, and the total mass was 1.5 g. The mixed material was added to 8.5 g of N,N-dimethylformamide (DMF), and under the condition of 60 °C, magnetic stirring was carried out at a speed of 200 rpm for 1 hour to obtain a uniform mixed solution.

[0113] II. The mixed solution was subjected to ultrasonic degassing treatment for 0.25 hours to eliminate bubbles and improve the uniformity of the solution. Subsequently, a four-sided film applicator (doctor blade gap 100 μm) was used to uniformly scrape the solution onto a glass plate to form a film. Note that each glass plate can only be scraped once.

[0114] III. The glass plate with the film was transferred to a forced-air drying oven at 60 °C for heat curing treatment for 1 hour.

[0115] IV. After the thermal curing is completed, the sample is placed in deionized water and soaked statically for 1 hour to complete the demoulding operation. Subsequently, the demoulded sample is dried in a blast drying oven at 40 °C for 1 hour, and finally the m-BC / PAN composite membrane material is obtained.

[0116] Example 10

[0117] In this example, the BC / PAN composite thin film was prepared by the following method:

[0118] I. Pure bamboo charcoal powder (BC) without oxidation and modification and polyacrylonitrile (PAN) were mixed at a mass ratio of 1:9, and the total mass was 1.5 g. The mixed materials were added to 8.5 g of N,N-dimethylformamide (DMF), and under the condition of 60 °C, magnetic stirring was carried out at a speed of 200 rpm for 1 hour to obtain a uniform mixed solution.

[0119] II. The mixed solution was subjected to ultrasonic degassing treatment for 0.25 hours to eliminate bubbles and improve the uniformity of the solution. Subsequently, a four-sided film applicator (doctor blade gap 100 μm) was used to uniformly scrape and coat the solution on a glass plate to form a film. Note that each glass plate can only be scraped and coated once.

[0120] III. The glass plate coated with the film was transferred to a blast drying oven at 60 °C for thermal curing treatment for 1 hour.

[0121] IV. After the thermal curing is completed, the sample is placed in deionized water and soaked statically for 1 hour to complete the demoulding operation. Subsequently, the demoulded sample is dried in a blast drying oven at 40 °C for 1 hour, and finally the BC / PAN composite membrane material is obtained.

[0122] The following is a specific analysis.

[0123] In Examples 1-6, the high-temperature treatment time in Step I was controlled within 150 - 270 minutes. During the actual preparation process, the change in the treatment time within this time range had little impact on the preparation of the target product, and the target product could be successfully prepared.

[0124] Among them, the nanoscale bamboo charcoal powder obtained by ball milling treatment can also be named "ultrafine bamboo charcoal powder" due to its extremely fine particle size characteristics.

[0125] In Examples 1-6, the particle size of the powder after ball milling in Step II was controlled at the nanoscale. In the subsequent modification treatment (Step V), the particle size of the powder was further controlled below 300 nm by ball milling treatment. In order to verify the influence of the ball milling time on the particle size of the powder, a comparative test was carried out on the ball milling treatment in Step II of Examples 4-6. The test results are shown in Table 1 below:

[0126] Table 1 Particle diameters of bamboo charcoal powder obtained under different ball milling times

[0127]

[0128] Different ball milling times have a significant impact on the particle size of bamboo charcoal powder, which directly affects its dispersion performance and composite effect in the polyacrylonitrile (PAN) matrix. The experimental results show that with the increase of ball milling time, the particle size of bamboo charcoal powder gradually decreases, and its particle size distribution also tends to be uniform, which is conducive to its uniform dispersion and interfacial bonding in the polymer matrix, and improves the structural compactness and comprehensive performance of the composite material.

[0129] In the actual process, after 13 hours of ball milling treatment, bamboo charcoal powder can stably obtain nanoscale particles with a particle size distribution in the range of about 10 - 300 nm, and already has good dispersibility and composite compatibility. Although further extending the ball milling time to 16 hours can further refine the particle size of bamboo charcoal powder, its marginal improvement effect is relatively limited, and it will significantly increase the equipment operation time and energy consumption, reduce the overall production efficiency, and is not conducive to industrial cost control.

[0130] Therefore, considering the particle size control effect and process economy comprehensively, 13 hours of ball milling treatment is determined as a more reasonable process parameter to achieve an optimal balance between preparation cost and efficiency while ensuring the material performance.

[0131] Next, taking the film prepared from pure PAN as the control group, the mechanical properties of the pure PAN film and the composite films prepared in Examples 7 - 10 were respectively detected. The raw material ratios of the PAN film and the composite films are shown in Table 2 below, and the test results are shown in Table 3 below:

[0132] Table 2 Raw material ratios of PAN film and composite films

[0133]

[0134] Table 3 Test results of mechanical properties of pure PAN film and composite films

[0135]

[0136] The test results of Examples 7-10 show that as the content of modified bamboo charcoal powder increases, the tensile strength and elongation at break of the composite films gradually decrease inversely. However, comparing the composite films prepared in Examples 7 and 10, the tensile strength and elongation at break of Example 10 decreased by 24.18% and 0.13 percentage points, respectively, compared to those prepared in Example 7. This demonstrates that the modified bamboo charcoal powder has better compatibility with the PAN matrix. This suggests that the surface of the bamboo charcoal powder, modified by oxidation and phytic acid / urea, possesses more polar functional groups, forming stronger interfacial interactions with the PAN molecular chains. This allows for more effective stress transfer and dispersion under load, reducing stress concentration. In contrast, the lack of polar groups on the surface of BC makes it difficult to form a stable interface with the PAN matrix, resulting in weaker interfacial bonding and greater susceptibility to internal stress concentration, which reduces the overall tensile properties of the composite film. This demonstrates the importance of the modification treatment in improving the interfacial bonding and mechanical properties of BC with the PAN matrix.

[0137] The following is a further analysis with reference to the accompanying drawings.

[0138] Figure 1 The morphological evolution of bamboo charcoal fibers at different carbonization temperatures is demonstrated. SEM results show that as the temperature increases, the surface of the bamboo charcoal fibers gradually shrinks and densifies, significantly increasing the degree of graphitization. At 600°C, the bamboo charcoal fibers retain their precursor morphology and have a smooth surface, indicating that the decomposition of the organic precursor is not complete at this temperature, forming only a preliminary carbon skeleton. At 800°C, the fiber surface begins to shrink slightly and becomes rough, further decomposing volatile small molecules and initially reconstructing the carbon skeleton. At 1000°C, the fiber structure becomes dense, and the regularity of the carbon layer increases. Finally, at 1200°C, the fiber structure becomes further ordered, the surface becomes smooth, and the degree of graphitization reaches its optimal level. This further demonstrates that high-temperature carbonization can accelerate the graphitization process of bamboo charcoal, making the fiber structure more dense and ordered. Therefore, the optimal carbonization temperature is 1200°C.

[0139] By comparison Figure 2 The SEM images of bamboo charcoal powder before and after modification show that the chemical modification treatment significantly optimized the microstructure of the material. Figure 2 (a) and (b) are unmodified samples BC, which show a relatively loose particle aggregation state, a rough surface and a relatively dispersed pore structure, and uneven particle distribution, indicating that its degree of graphitization is low and the content of surface polar functional groups is small. Figure 2 (c) and (d) are samples after modification, showing a more uniform and dense nano-scale agglomerate structure, with smooth particle surface, uniform particle size and regular distribution, and the gaps between particles are reduced and closely arranged. The microstructure shows a higher order and density. This change in microstructure can be attributed to the phosphate group (-PO4 3(-) and the synergistic effect of nitrogen doping can effectively reduce interface defects, enhance the bonding strength between particles, and improve their surface activity and stability. It shows that the synergistic grafting of phytic acid and urea on the BC substrate can provide a wide range of active sites, thereby optimizing the interfacial compatibility with the PAN matrix and providing a structural basis for the improvement of the properties of the composite material.

[0140] Figure 3 SEM images of the cross-sections of pure PAN, m-BC / PAN composites with different ratios, and 10 wt% BC / PAN composites. As Figure 3 shown in (a), the cross-section of pure PAN presents a uniform and dense structure with a smooth surface and no defects, indicating that a complete and continuous microstructure is formed during the film-forming process of PAN. With the addition of m-BC, Figure 3 the cross-section of the 10 wt% m-BC / PAN composite in (b) has no obvious agglomeration, and the interface is tightly bonded, still maintaining good integrity. This shows that the phosphate groups on the surface of m-BC and the cyano groups (-CN) in the PAN molecular chain form strong interfacial interactions through hydrogen bonds and partial chemical bonding, increasing the interfacial compatibility, and the addition of a small amount of m-BC has limited influence on the matrix structure; as the m-BC content increases to 20 wt% ( Figure 3 in (c)) and 30 wt% ( Figure 3 in (d)), the cross-sections of the composite materials become rough, with obvious particle agglomeration and increased porosity locally. Although the phosphorus-nitrogen co-doping improves the surface activity of m-BC, the introduction of excessive fillers leads to an increase in the van der Waals force between particles, exceeding the dispersion ability of the PAN matrix, forming a discontinuous phase, resulting in internal defects and an increase in microcracks at the interface, causing poor interfacial bonding. Therefore, the preferred m-BC content in m-BC / PAN is 10 wt%.

[0141] Comparing with the unmodified BC composite material ( Figure 3 in (e)), due to the extremely few polar functional groups on the surface of unmodified BC, the compatibility with the PAN matrix is poor, and the interfacial bonding is mainly weak physical adsorption with low interfacial bonding strength. Therefore, the cross-section of the 10 wt% BC / PAN composite material has obvious particle agglomeration, a higher porosity, and is prone to form large particle agglomerations.

[0142] From Figure 4 , 5It can be seen from the TGA and DTG curves that PAN and its composite films underwent obvious thermal decomposition during heating. The pure PAN film experienced a large mass loss in the range of about 250–400 °C, and the DTG peak was at about 320 °C. This is because PAN underwent thermal degradation processes such as de-cyanation, cyclization, and cracking in this temperature range, and the final mass loss was 49.44%. After adding 10 wt% m-BC, the mass loss decreased to 46.31%, and the DTG peak shifted to a higher temperature of 335 °C, indicating that the addition of m-BC can delay the thermal decomposition of the composite material and improve the overall thermal stability. As the m-BC content increased to 20 wt% and 30 wt%, the mass loss further decreased to 42.84% and 37.90%, respectively, and the DTG peak width gradually increased. This phenomenon is attributed to the high thermal stability of m-BC, which can act as a carbon source and a thermal barrier at high temperatures to inhibit the thermal decomposition of PAN.

[0143] However, the final char yield of 10 wt% BC / PAN is higher than that of 10 wt% m-BC / PAN. This is because BC is unmodified and retains more inorganic minerals and ash, which act as solid-phase residues. At the same time, the functional groups introduced during the modification process make the composite material more prone to thermal degradation, further reducing the final solid-phase residue amount. Therefore, the final remaining amount of 10 wt% BC / PAN is higher than that of 10 wt% m-BC / PAN.

[0144] In summary, in the present invention, bamboo charcoal fibers are first prepared into ultrafine bamboo charcoal powder with a nanoscale particle size through ball milling treatment. After cleaning, oxidizing, and modifying it, modified bamboo charcoal powder is obtained. Then, the modified bamboo charcoal powder and PAN are jointly dispersed in N,N-dimethylformamide (DMF) solvent and stirred to dissolve to prepare a uniform casting solution. A wet film is formed on a glass substrate by the coating method, and through the steps of coagulation, cleaning, and drying, an ultrafine modified bamboo charcoal powder / PAN composite film is finally obtained. This film combines the good film-forming property of PAN and the excellent adsorption performance of bamboo charcoal, showing good mechanical strength, high thermal stability, and adsorption efficiency. This method has a simple process and wide material sources, and has good industrialization prospects, and is applicable to fields such as environmental protection filter materials, energy storage, and high-temperature resistant materials.

[0145] The above embodiments are preferred implementation schemes of the present invention. In addition, the present invention can also be implemented in other ways. Any obvious substitution without departing from the concept of the present technical solution is within the protection scope of the present invention.

[0146] Finally, it should be emphasized that in order to make it more convenient for those skilled in the art to understand the improvements of the present invention over the prior art, some descriptions of the present invention have been simplified, and for the sake of clarity, some other elements have also been omitted in this application document. Those skilled in the art should be aware that these omitted elements can also constitute the content of the present invention.

Claims

1. A preparation method of modified bamboo charcoal powder, characterized in that, It includes the following steps: S1-1. Preparation of bamboo charcoal fiber: Carbonize bamboo fiber at high temperature to obtain bamboo charcoal fiber; S1-2. Preparation of nano bamboo charcoal powder: Perform ball milling on the bamboo charcoal fiber to obtain nano bamboo charcoal powder; S1-3. Modification treatment: S1-3-1. Mix the nano bamboo charcoal powder and hydrogen peroxide, and let it stand for oxidation; S1-3-2. Mix the oxidized nano bamboo charcoal powder with phytic acid, and perform staged heat treatment: First, stir at 75°C for 0.5 hours; then raise the temperature to 100°C and stir for another 0.5 hours; then add urea solution to the mixture; continue to heat to 120°C and stir for 0.5 hours; finally, heat to 160°C until the mixture foams; S1-3-3. Dry and ball mill the foamed mixture to obtain modified bamboo charcoal powder.

2. The preparation method of the modified bamboo charcoal powder according to claim 1, characterized in that: In step S1-1, the temperature of the high-temperature treatment is 600-1200°C, and the time is 150-270 min.

3. The preparation method of the modified bamboo charcoal powder according to claim 1, wherein: In step S1-3-1, the mass ratio of the nano bamboo charcoal powder to hydrogen peroxide is 1:(1-3).

4. The preparation method of the modified bamboo charcoal powder according to claim 1, wherein: In step S1-3-2, the mass ratio of the oxidized nano bamboo charcoal powder to phytic acid is 1:(1-3); the mass ratio of phytic acid to urea is 1:(0.5-1.5).

5. The preparation method of the modified bamboo charcoal powder according to claim 1, wherein: In step S1-3-3, the particle size of the modified bamboo charcoal powder does not exceed 300 nm.

6. A modified bamboo charcoal powder, characterized in that: It is prepared by the preparation method of the modified bamboo charcoal powder described in any one of claims 1-5.

7. A preparation method of a modified bamboo charcoal powder / polyacrylonitrile composite film, characterized in that, It includes the following steps: S2-1. Dissolve the modified bamboo charcoal powder described in claim 6 and polyacrylonitrile in N,N-dimethylformamide, and stir evenly at 50-80°C to obtain a mixed solution; S2-2. Perform ultrasonic degassing treatment on the mixed solution, and then coat the film on a glass plate by the doctor blade method; S2-3. Perform thermal curing treatment on the glass plate coated with the film at 50-70°C, soak and demold it in deionized water after curing, and dry to obtain a modified bamboo charcoal powder / polyacrylonitrile composite film.

8. The preparation method of the modified bamboo charcoal powder / polyacrylonitrile composite film according to claim 7, wherein: In step S2-1, the mass of the modified bamboo charcoal powder and polyacrylonitrile is (1-3):(7-9).

9. The preparation method of the modified bamboo charcoal powder / polyacrylonitrile composite film according to claim 7, characterized in that: In step S2-1, the mass ratio of the total mass of the modified bamboo charcoal powder and polyacrylonitrile to N,N-dimethylformamide is 1.5:8.

5.

10. A modified bamboo charcoal powder / polyacrylonitrile composite film, characterized in that: It is prepared by the preparation method of the modified bamboo charcoal powder / polyacrylonitrile composite film described in any one of claims 7-9.

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