Preparation method of cellulose acetate self-supporting carbonized membrane

Abstract

The invention discloses a preparation method of a cellulose acetate self-supporting carbonized membrane, which comprises the following steps: preparing a cellulose acetate membrane by taking cellulose acetate as a precursor and adopting an electrostatic spinning technology, sequentially carrying out deacetylation, metal crosslinking and Lewis acid activation treatment on the membrane, cleaning and drying, and carbonizing in a nitrogen atmosphere to obtain the cellulose acetate self-supporting carbonized membrane. And finally obtaining the cellulose acetate self-supporting carbonized membrane. The cellulose acetate self-supporting film is prepared by adopting a metal crosslinking and Lewis acid activation method, so that a pre-oxidation step in an existing CA carbonized film technology is omitted, the energy loss is reduced, and the method has more advantages in the aspects of economy and environmental protection.

Description

Technical Field

[0001] The invention belongs to the technical field of carbonized film preparation, and in particular relates to a method for preparing a cellulose acetate self-supporting carbonized film. Background Art

[0002] Carbonized membranes, due to their unique physical and chemical properties, including high flexibility, excellent electrical properties, thermal stability, and high specific surface area, hold great promise for applications in a variety of fields, including electronics, sensors, energy storage devices, and smart fabrics. Polyacrylonitrile (PAN) is the most commonly used precursor material for carbonized membranes, but its production cost is high, and the carbonization process produces toxic gases such as ammonia and hydrogen cyanide, requiring extensive waste gas treatment.

[0003] In recent years, cellulose acetate (CA), a naturally derived biopolymer, has been considered a potential alternative to PAN due to its low cost, renewability, biocompatibility, and environmental friendliness. However, CA has difficulty forming a stable, self-supporting membrane structure during carbonization.

[0004] Meanwhile, researchers have successfully synthesized polyvinylpyrrolidone (PVP) self-supporting carbonized membranes using metal coordination crosslinking. Currently, metal crosslinking has not been applied to the preparation of CA self-supporting carbonized membranes. Developing a method for preparing CA self-supporting carbonized membranes using metal crosslinking technology is of great significance for reducing costs and producing environmentally friendly CA-based carbonized membranes. Summary of the Invention

[0005] In order to solve the problems existing in the prior art, one of the objects of the present invention is to provide a method for preparing a cellulose acetate self-supporting carbonized film, the method comprising the following steps:

[0006] (1) Preparation of electrospinning solution: Cellulose acetate (CA), acetone and N,N-dimethylacetamide (DMAC) were mixed and stirred at room temperature for 3-12 h. After stirring evenly, the mixture was allowed to stand for 12 h to obtain the precursor spinning solution.

[0007] (2) Preparation of cellulose acetate membrane using electrospinning technology;

[0008] (3) Soak the fiber membrane in 0.1 M NaOH methanol solution for deacetylation. After deacetylation, wash with ultrapure water until neutral and dry.

[0009] (4) soaking the fiber membrane in a metal salt solution to react, and after the reaction is completed, washing and drying to obtain a cellulose acetate cross-linked membrane;

[0010] (5) immersing the cross-linked membrane in a Lewis acid solution to react, and after the reaction is completed, washing and drying to obtain an activated cellulose acetate cross-linked membrane;

[0011] (6) The activated cellulose acetate cross-linked membrane is placed in a tubular furnace and carbonized in a nitrogen atmosphere to obtain a cellulose acetate self-supporting carbonized membrane.

[0012] In step (1), the volume ratio of acetone to DMAC is 2:1; the concentration of the electrospinning solution is 10-20 wt / v%.

[0013] In step (2), the process parameters of electrospinning are: spinning voltage of 10-35 kV, feed rate of 0.1-0.3 mm / min, spinning temperature of 18-30 °C, relative humidity of 35-60%, and injection distance of 10-30 cm.

[0014] The degree of deacetylation in step (3) is 25%-65%.

[0015] The metal salt solution in step (4) is one or more of Co(NO3)2, Cu(NO3)2, and Fe(NO3)3, with a solution concentration of 3-6 wt / v%, and the reaction conditions are heating in a water bath at 60°C for 5-8 h.

[0016] The metal ions in the metal salt solution can undergo a coordination reaction with the carbonyl groups in cellulose acetate to form a cross-linked structure. This cross-linked structure can effectively increase the interaction force between cellulose acetate molecular chains and effectively limit the movement of cellulose acetate molecular chains at high temperatures, thereby slowing down its thermal decomposition process and providing conditions for the formation of a self-supporting carbonized film.

[0017] In step (5), the Lewis acid solution is one or more of NH4Cl, ZnCl2, and AlCl3, and the solution concentration is 3-6 wt / v%. The reaction conditions are heating in a water bath at 60 °C for 5-8 h.

[0018] The decomposition of cellulose is primarily related to dehydrogenation and depolymerization. Depolymerization primarily forms L-glucose, which further decomposes to produce volatile carbon compounds and tar. The relatively low carbon residue after cellulose decomposition is primarily due to the dominance of depolymerization. Dehydrogenation inhibits the formation of L-glucose, leading to an increase in solid residues, a reduction in the formation of volatile substances and tar, and ultimately an increase in carbon residue. The presence of Lewis acids such as ZnCl2 and NH4Cl facilitates dehydrogenation, leading to cyclization of cellulose and a greater tendency to form self-supporting films after carbonization.

[0019] The carbonization treatment conditions in step (6) include: the initial temperature of the tube furnace is 25 °C, the temperature is increased to 700 °C at 2.5 °C / min, and the temperature is kept at this temperature for 2 h before natural cooling.

[0020] A second object of the present invention is to provide a cellulose acetate carbonized film prepared by the above method.

[0021] Compared with the prior art, the technical solution of the present invention has the following advantages:

[0022] (1) The present invention uses a metal coordination method to crosslink CA, solving the problem of difficulty in forming a stable self-supporting membrane structure during CA carbonization. This improvement strengthens the intermolecular forces of CA, effectively restricting the movement of CA molecular chains at high temperatures, thereby slowing its thermal decomposition process and providing favorable conditions for the preparation of CA self-supporting carbonized membranes.

[0023] (2) The present invention uses Lewis acid to activate the CA membrane, reducing the formation of volatile substances and tar during the decomposition of CA, and successfully prepares cellulose acetate self-supporting carbonized membrane, providing a new method for the development of cellulose acetate self-supporting carbonized membrane

[0024] (3) Conventional knowledge suggests that CA has poor thermal stability and is easily decomposed at high temperatures. Pre-oxidation is a key step in the preparation of carbonized films from CA. Pre-oxidation can partially convert CA into a thermally stable intermediate, preventing excessive decomposition or combustion during the subsequent high-temperature carbonization process. In addition, pre-oxidation can ensure that CA is uniformly converted into carbon during the carbonization process, avoiding local overheating or incomplete carbonization, and forming a self-supporting membrane structure. However, the present invention discovered that the thermal stability of CA can be significantly improved through metal coordination cross-linking, Lewis acid activation, and other methods, eliminating the pre-oxidation step, and being more energy-efficient and environmentally friendly, overcoming previous technical prejudices. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The cellulose acetate self-supporting carbonized film prepared in Example 1 of the present invention;

[0026] Figure 2 The carbonized cellulose acetate film prepared in Comparative Example 1 of the present invention;

[0027] Figure 3 The carbonized product of the cellulose acetate cross-linked membrane prepared in Comparative Example 2 of the present invention;

[0028] Figure 4 The cellulose acetate self-supporting carbonized film prepared in Comparative Example 3 of the present invention;

[0029] Figure 5Thermogravimetric curves of the Lewis acid-treated and metal-crosslinked cellulose acetate films, the original cellulose acetate film, and the metal-crosslinked cellulose acetate films prepared in Example 1, Comparative Example 1, and Comparative Example 2 of the present invention, respectively, during heating from room temperature to 800°C at a rate of 10°C / min in an N2 atmosphere;

[0030] Figure 6 Flowchart of the present invention DETAILED DESCRIPTION

[0031] For a further understanding of the present invention, the present invention will be further described below with reference to the accompanying drawings and examples, but the present invention is not limited to the following examples.

[0032] Example 1:

[0033] This embodiment provides a method for preparing a carbonized cellulose acetate film, the method comprising the following steps:

[0034] (1) Preparation of electrospinning solution:

[0035] 1.53 g of CA was dissolved in 9 ml of a mixed solution of acetone / DMAC, where the volume ratio of acetone to DMAC was 2:1. The solution was stirred at room temperature for 6 h to completely dissolve the CA, and then allowed to stand for 12 h for degassing to obtain a CA spinning solution.

[0036] (2) Preparation of cellulose acetate film using electrospinning technology:

[0037] The CA spinning solution obtained in step (1) was transferred to a 10 ml disposable syringe. The relative humidity of the environment in the spinning apparatus was controlled to 50%, the voltage of the spinning apparatus was adjusted to 21 kV, the injection speed was adjusted to 0.1 mm / min, the distance between the needle and the receiver was adjusted to 20 cm, the receiver speed was adjusted to 120 r / h, and the release paper was wrapped on the roller receiver to receive the electrospun fibers. The drum receiver was dried under vacuum conditions at 60 °C for 12 h to obtain a cellulose acetate film.

[0038] (3) Deacetylation treatment of fiber membrane:

[0039] Weigh 0.21 g of NaOH powder and dissolve it in 50 ml of methanol solution. Soak the cellulose acetate film obtained in step (2) in the above-mentioned NaOH methanol solution and let it stand at room temperature for 24 h for deacetylation treatment. After treatment, rinse with ultrapure water until neutral and dry at 60 °C for 12 h to obtain a deacetylated cellulose acetate film.

[0040] (4) Weigh 1.51 g of Co(NO3)2 powder and dissolve it in 50 ml of methanol solution to prepare a metal salt solution. Immerse the deacetylated cellulose acetate film obtained in step (3) in the above metal salt solution and heat it in a water bath at 60°C for 6 h to react. After the reaction is completed, wash it with methanol and dry it under vacuum at 60°C for 12 h to obtain a cellulose acetate cross-linked film.

[0041] (5) Weigh 0.75 g of NH4Cl powder and dissolve it in 25 ml of ultrapure water to prepare a Lewis acid solution. Immerse the cellulose acetate cross-linked membrane obtained in step (4) in the above Lewis acid solution and heat it in a water bath at 60 °C for 6 h to react. After the reaction is completed, wash it with ultrapure water and dry it under vacuum at 60 °C for 12 h to obtain an activated cellulose acetate cross-linked membrane.

[0042] (6) The composite fiber membrane was placed in a tubular furnace for carbonization treatment. The initial temperature of the tubular furnace was 25 °C, and the temperature was increased to 700 °C at a rate of 2.5 °C / min. The temperature was kept at this temperature for 2 h, and the membrane was naturally cooled to room temperature to obtain a cellulose acetate self-supporting carbonized membrane.

[0043] Example 1: Product of cellulose acetate carbonized film Figure 1 shown.

[0044] Comparative Example 1:

[0045] In this comparative example, steps (4) and (5) were omitted, metal cross-linking and Lewis acid activation treatment were not performed, and a pre-oxidation step was added before step (6). Other conditions were the same as those in Example 1.

[0046] Pre-oxidation: The CA membrane prepared in the above steps was placed in a tube furnace for carbonization treatment. The initial temperature of the tube furnace was 25°C, and the temperature was increased to 240°C at a rate of 1°C / min, kept at this temperature for 2 h, and naturally cooled to room temperature to obtain a cellulose acetate pre-oxidation product.

[0047] Figure 2 It is a carbonized product of cellulose acetate that has not been treated with metal cross-linking and Lewis acid activation. The obtained product is black and does not form a film. Figure 2 It can be seen that the CA film without metal cross-linking and Lewis acid activation treatment has poor thermal stability and is difficult to form a free-standing film.

[0048] Comparative Example 2:

[0049] In this comparative example, step (5) was omitted, Lewis acid activation treatment was not performed, and a pre-oxidation step was added before step (6). Other conditions were the same as those in Example 1.

[0050] Pre-oxidation: The CA cross-linked membrane prepared in the above steps was placed in a tube furnace for carbonization treatment. The initial temperature of the tube furnace was 25°C, and the temperature was increased to 240°C at a rate of 1°C / min, kept at this temperature for 2 h, and naturally cooled to room temperature to obtain a pre-oxidized product of cellulose acetate cross-linked membrane.

[0051] The cross-linked film carbonized product prepared in Comparative Example 2 of the present invention is as follows Figure 3 As shown, the product is black and has a high shrinkage rate. Figure 3 It can be seen that the film-forming effect of cellulose acetate after metal cross-linking treatment is improved compared with Comparative Example 1.

[0052] Comparative Example 3:

[0053] In this comparative example, a pre-oxidation step was added before step (6), and other conditions were the same as those in Example 1.

[0054] Pre-oxidation: The CA cross-linked membrane prepared in the above steps was placed in a tube furnace for carbonization treatment. The initial temperature of the tube furnace was 25°C, and the temperature was increased to 240°C at a rate of 1°C / min, kept at this temperature for 2 h, and naturally cooled to room temperature to obtain a pre-oxidized product of cellulose acetate cross-linked membrane.

[0055] The cross-linked film carbonized product prepared in Comparative Example 3 of the present invention is as follows Figure 4 As shown, the carbonized film is black, similar to the carbonized film obtained in Example. Figure 4 It can be seen that cellulose acetate after metal cross-linking and Lewis acid activation can form a stable self-supporting structure during the carbonization process. In addition, the pre-oxidation step can be omitted, thereby reducing energy consumption.

[0056] Figure 5 Thermogravimetric test curves of the Lewis acid treated and metal cross-linked cellulose acetate film, the original cellulose acetate film, and the metal cross-linked cellulose acetate film prepared in Example 1, Comparative Example 1, and Comparative Example 2 of the present invention, respectively, during heating from room temperature to 800°C at a rate of 10°C / min in a N2 atmosphere. Figure 5The carbon residue rate of the metal-crosslinked cellulose acetate film after decomposition was significantly higher than that of the original cellulose acetate film. This indicates that the crosslinked structure formed by the metal ions and the carbonyl groups in the cellulose acetate effectively increases the interaction between the cellulose acetate molecular chains, restricting their movement at high temperatures. The cellulose acetate film treated with metal crosslinking and Lewis acid activation exhibited the highest carbon residue rate. This is primarily because the presence of Lewis acid facilitates the dehydrogenation of cellulose, reducing the formation of volatile substances and tar. These results demonstrate that metal crosslinking and Lewis acid activation significantly enhance the thermal stability of the cellulose acetate film, allowing for the formation of a stable, self-supporting membrane structure during the carbonization process.

Claims

1. A method for preparing a cellulose acetate self-supporting carbonized film, characterized in that : It includes the following steps: (1) Preparation of electrospinning solution: Cellulose acetate (CA), acetone, and N,N-dimethylacetamide (DMAC) were mixed and stirred at room temperature for 3-12 h. After stirring evenly, the mixture was allowed to stand for 12 h to obtain a precursor spinning solution. (2) Preparation of cellulose acetate membrane using electrospinning technology; (3) Soak the fiber membrane in 0.1 M NaOH methanol solution for deacetylation. After deacetylation, wash with ultrapure water until neutral and dry. (4) soaking the fiber membrane in a methanol solution of a metal salt to react, and after the reaction is completed, washing and drying to obtain a cellulose acetate cross-linked membrane; (5) immersing the cross-linked membrane in a Lewis acid aqueous solution for reaction, and after the reaction is completed, washing and drying to obtain an activated cellulose acetate cross-linked membrane; (6) The activated cellulose acetate cross-linked membrane is placed in a tubular furnace and carbonized in a nitrogen atmosphere to obtain a cellulose acetate self-supporting carbonized membrane.

2. The method for preparing a cellulose acetate self-supporting carbonized film according to claim 1, wherein: In step (1), the volume ratio of acetone to DMAC is 2:1; the concentration of the electrospinning solution is 10-20 wt / v%.

3. The method for preparing a cellulose acetate self-supporting carbonized film according to claim 1, wherein: In step (2), the process parameters of electrospinning are: spinning voltage of 10-35 kV, feed rate of 0.1-0.3 mm / min, spinning temperature of 18-30 °C, relative humidity of 35-60%, and injection distance of 10-30 cm.

4. The method for preparing a cellulose acetate self-supporting carbonized film according to claim 1, wherein: The degree of deacetylation in step (3) is 25%-65%.

5. The method for preparing a cellulose acetate self-supporting carbonized film according to claim 1, wherein: The metal salt in step (4) is one or more of Co(NO3)2, Cu(NO3)2, and Fe(NO3)3, the solution concentration is 3-6 wt / v%, and the reaction conditions are heating in a water bath at 60°C for 5-8 h.

6. The method for preparing a cellulose acetate self-supporting carbonized film according to claim 1, wherein: In step (5), the Lewis acid is one or more of NH4Cl, ZnCl2, and AlCl3, the solution concentration is 3-6 wt / v%, and the reaction conditions are heating in a water bath at 60°C for 5-8 h.

7. The method for preparing a cellulose acetate self-supporting carbonized film according to claim 1, wherein: The carbonization treatment conditions in step (6) include: the initial temperature of the tube furnace is 25 °C, the temperature is increased to 700 °C at 2.5 °C / min, and the temperature is kept at this temperature for 2 h before natural cooling.

8. A cellulose acetate self-supporting carbonized film, characterized in that: Prepared according to the method according to any one of claims 1 to 7.

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