A ramie fiber diaphragm based on fiber crystalline domain entropy regulation and a preparation method and application thereof

Abstract

The application discloses a ramie fiber diaphragm based on fiber crystalline domain entropy regulation and a preparation method and application thereof, and belongs to the technical field of preparation of cellulose diaphragms for capacitors. The preparation method comprises the following steps: pretreating ramie raw materials by soaking, cooking and cutting to obtain ramie sections, then performing low-temperature beating to maintain high crystallinity of the fibers and realize refinement, forming a suspension slurry, then performing ultrasonic dispersion, screening and dissociation dispersion to obtain uniform fine slurry, and finally performing wet laying molding and freeze drying to obtain the ramie fiber diaphragm which has a three-dimensional interconnected porous structure and high tough mechanical properties. The application fully utilizes the alkaloid characteristics of the ramie fiber to realize alkali-free cooking, and the process is environmentally friendly. Through the synergistic effect of low-temperature beating and freeze drying, the fiber intrinsic toughness is maintained while the multi-stage ion transmission channel is constructed. The obtained diaphragm has excellent air permeability, porosity and mechanical strength.

Description

Technical Field

[0001] This invention belongs to the field of cellulose membrane preparation technology for capacitors, specifically relating to a ramie fiber membrane based on the entropy regulation of fiber crystallization domains, its preparation method, and its application. Background Technology

[0002] With the rapid development of fields such as flexible electronics, wearable devices, and urban rail transit, the market demand for supercapacitors that combine high power density, fast charging and discharging capabilities, and long cycle life is becoming increasingly urgent. Among the core components of supercapacitors, although the separator does not directly participate in energy storage, its pore structure, mechanical strength, and electrolyte affinity profoundly affect the ion transport efficiency and the overall performance and safety of the device.

[0003] Currently, the separators widely used in commercial supercapacitors mainly include polyolefin microporous membranes (such as Celgard) and various nonwoven fabric separators. While these traditional materials are mature, they still have significant shortcomings when facing the demands of high-performance, especially flexible, applications. Polyolefin microporous membranes have advantages such as high mechanical strength and good dimensional stability, but their porosity and hydrophilicity are poor, limiting their ionic conductivity. They are also prone to shrinkage at high temperatures, posing safety hazards. Nonwoven fabric and regenerated cellulose separators have high porosity and good electrolyte wettability, but their mechanical strength is usually insufficient. They are prone to plastic deformation, fraying, wrinkling, and breakage during assembly or use, affecting device reliability. Furthermore, these two types of commercial separators—polyolefin microporous membranes and nonwoven fabric separators—rely on petrochemical resources for raw materials, which is insufficient in terms of environmental protection and sustainability, making it difficult to achieve a balance between overall performance (strength, toughness, and porosity).

[0004] Ramie fiber, as a natural cellulose fiber, exhibits unique potential. Its internal structure contains natural grooves and hollow cavities, making it easier to construct hierarchical channels that facilitate rapid ion transport compared to common fibers such as dense bamboo or cotton. With fiber lengths ranging from 127 to 250 mm and high crystallinity (approximately 90%), it provides a foundation for excellent mechanical properties. Currently, significant progress has been made in the research of preparing porous carbon electrodes for supercapacitors using ramie as a precursor, verifying the porosity of ramie and its feasibility for application in this field.

[0005] However, most existing research focuses on high-temperature carbonization of ramie for use in electrodes, a process that completely destroys its natural fiber morphology and mechanical toughness. Directly developing ramie fibers into membrane materials with both excellent mechanical properties and ion transport channels is currently a blank area of ​​research. How to maintain the high strength and toughness of ramie fibers during pulping and construct a continuous, stable, three-dimensional interconnected porous network structure through controllable physical or chemical methods to prepare a novel type of high-performance ramie biomass-based membrane has become an urgent technical problem to be solved. This type of membrane is expected to significantly enhance the mechanical reliability and environmental friendliness of supercapacitors while improving their electrochemical performance. Summary of the Invention

[0006] In view of the above-mentioned prior art, the present invention discloses a ramie fiber diaphragm based on the entropy regulation of fiber crystal domain, its preparation method and application, so as to solve the comprehensive technical problem that the diaphragms prepared in the prior art are difficult to simultaneously achieve high strength and toughness mechanical properties and efficient ion transport channels.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is to provide a method for preparing a ramie fiber diaphragm based on the entropy regulation of fiber crystallization domains, which includes the following steps: S1: The ramie raw material is soaked, cooked, filtered, squeezed and cut in sequence to obtain pretreated ramie segments. The pretreated ramie segments are then subjected to low-temperature pulping to obtain a suspension slurry. S2: The suspension slurry is ultrasonically dispersed and screened to obtain a fine slurry; S3: The fine pulp is dissociated and dispersed, and the pulp concentration is adjusted to 0.5~1.5wt%. Then, a wet forming and papermaking process is used to obtain ramie wet film. S4: The ramie wet film is freeze-dried to obtain the product.

[0008] Based on the above technical solution, the present invention can be further improved as follows: Furthermore, in step S1, the soaking temperature is 50~60℃ and the soaking time is 6~7h; the cooking temperature is 120~160℃, the cooking pressure is 0.4~0.6MPa, and the cooking time is 12~24h; the length of the pretreated ramie segments is 1.5~3cm.

[0009] Furthermore, the conditions for low-temperature pulping in step S1 are as follows: prepare a pulp with a pretreated ramie content of 2~4wt% for pulping, the pulping blade pressure is 1.5~3N, the pulping time is 120~360min, the degree of freeness of the pulp after pulping is 75~85°SR, and the pulp temperature is controlled below 20℃ during the pulping process.

[0010] Furthermore, in step S2, the ultrasonic dispersion power is 300~400W, and the ultrasonic dispersion time is 30~60min.

[0011] Furthermore, in step S2, a flat plate slurry screener is used for slurry screening at a frequency of 900~1000Hz.

[0012] Furthermore, in step S3, the dissociation and dispersion are carried out in a dissociation machine at a speed of 7000~8000 r / min and a dissociation time of 2~4 min.

[0013] Furthermore, the wet forming and papermaking process in step S3 includes: pneumatically stirring the slurry for 5-10 seconds, letting it stand for 5-8 seconds, then filtering it by drainage for 50-100 seconds, and then vacuum dewatering for 50-80 seconds to obtain a wet film with a moisture content of 10-30%, and then demolding it to obtain ramie wet film.

[0014] Furthermore, in step S4, the freeze-drying temperature is -30 to -40°C, and the freeze-drying time is 12 to 24 hours.

[0015] The present invention also discloses the application of the above-mentioned ramie fiber diaphragm in the preparation of capacitor diaphragms.

[0016] The beneficial effects of this invention are: 1. Ramie is selected as the pulping raw material for the membrane. Utilizing the inherent alkaloid properties of this bast fiber, no additional alkaline reagent treatment is required during the high-temperature cooking process. Compared to other fiber treatments, this effectively saves costs and reduces the difficulty of wastewater treatment, which is beneficial to environmental protection. An "entropy regulation" strategy is proposed, which stabilizes the ordered molecular structure of cellulose through intermittent low-temperature pulping, thereby controlling the fiber crystallinity and resulting in a membrane with high strength and toughness. Simultaneously, the ultra-high aspect ratio ramie fibers with their natural structure not only form an interwoven network structure to enhance mechanical properties during fiber refinement, but also further form a three-dimensional porous structure after vacuum freeze-drying, greatly increasing the membrane's air permeability and ion transport rate, thus achieving a balance between the membrane's high strength and toughness and its interconnected porous properties.

[0017] 2. The diaphragm prepared in this invention has excellent mechanical properties, porosity and air permeability. In addition, after 12,000 cycles in the constant current charge-discharge test, it still has 84% ​​capacity retention and 99.52% charge-discharge efficiency, indicating that the prepared diaphragm can be successfully and effectively applied to supercapacitors. Attached Figure Description

[0018] Figure 1 Electron micrograph of ramie raw material in Example 1; Figure 2 This is an electron microscope image of the ramie cellulose membrane prepared in Example 1; Figure 3X-ray diffraction pattern of the ramie cellulose membrane prepared in Example 1; Figure 4 The figure shows the tensile properties test results of the ramie cellulose membrane prepared in Example 1; Figure 5 The image shows the puncture strength test results of the ramie cellulose diaphragm prepared in Example 1. Figure 6 The graph shows the ionic conductivity test results of the ramie cellulose membrane prepared in Example 1. Figure 7 The graph shows the electrochemical cycling test results of the ramie cellulose membrane prepared in Example 1. Detailed Implementation

[0019] The specific embodiments of the present invention will be described in detail below with reference to examples.

[0020] Example 1 A ramie fiber membrane based on the entropy regulation of fiber crystallization domains is prepared by the following steps: S1: Weigh 420g of dried ramie and measure 2000mL of deionized water. Add the deionized water and dried ramie to a high-pressure steam reactor and stir well to completely submerge the ramie in the water. Then, set a gradient heating step, first heating to 60℃ and holding for 6 hours to ensure the ramie is completely soaked, allowing its alkaloids to gradually dissolve into the water, thus raising the pH value in preparation for degumming at high temperature. Then, heat to 150℃ and hold for 12 hours, controlling the cooking pressure at 0.45MPa. After cooking, filter out the ramie after alkali degumming and swelling. Use a flatbed hydraulic press to compress the ramie. Under pressure, the swollen ramie begins to split from a single fiber into multiple fine fibers. At the same time, under pressure, most of the water inside the fiber is removed, increasing the fiber's internal dehydration toughness. Then, using a guillotine cutter, the compressed finely fiberized ramie was cut into uniform 1.5cm segments to obtain pretreated ramie segments. These pretreated ramie segments were then fed into a pulping machine, and 15000mL of frozen deionized water was added to prepare a pulp with a solid content of 2.3%. The pulping machine was started for dissociation. After the ramie fibers were completely dispersed, the blade pressure was set to 2N, and the pulping time to 160min, initiating gradient pulping. During pulping, the temperature change of the pulp was observed using a thermometer. When the temperature exceeded 20℃, pulping was stopped, and 500mL of water was filtered out using a filter bag. Then, 500mL of frozen deionized water was added to the pulp tank to buffer the pulp temperature and ensure the stable crystallinity of the ramie fibers. Simultaneously, according to the national standard GB / T3332-2004, the pulp freeness was measured to be 80. oPulping is stopped at SR (Solid Reduction). By controlling the temperature changes caused by mechanical friction during pulping, the damage to the crystallinity of ramie cellulose caused by heat under strong mechanical force is reduced, thereby ensuring the strength and toughness of ramie fibers. A suspension pulp is obtained after pulping.

[0021] S2: Use an ultrasonic machine to sonicate the suspended slurry. Set the power to 300W and the sonication time to 40min. Stir continuously to ensure that the entangled fibers are evenly dispersed. After sonication, pour the slurry into a flat plate sieve and set the sieve frequency to 990Hz to remove impurities and undissolved fiber clumps from the slurry. After sieve, take the fine slurry as the molding slurry.

[0022] S3: Disperse the fine slurry in a fiber dissociation disperser at a speed of 7000 r / min for 2 min; prepare the dissociated slurry to a concentration of 0.5 wt%, take 200 mL of the slurry for sheet forming, and control the weight of the diaphragm to be 10~12 g / m. 2 The thickness is 40±2μm. The pneumatic stirring time is set to 8s, the settling time is 6s, the rapid drainage filtration is 80s, and then vacuum dehydration is started. After dehydration for 60s, the film is removed by extrusion with rollers to obtain ramie wet film.

[0023] S4: Place the ramie wet film in a vacuum freeze dryer, set the freezing temperature to -40℃, and dry for 12 hours to obtain the product.

[0024] Example 2 A ramie fiber membrane based on the entropy regulation of fiber crystallization domains is prepared by the following steps: S1: Weigh 420g of dried ramie and measure 2000mL of deionized water. Add the deionized water and dried ramie to a high-pressure steam reactor and stir well to completely submerge the ramie in the water. Then, set a gradient heating step, first heating to 50℃ and holding for 7 hours to ensure the ramie is completely soaked, allowing its alkaloids to gradually dissolve into the water, thus raising the pH value in preparation for degumming at high temperature. Then, heat to 120℃ and hold for 24 hours, controlling the cooking pressure at 0.4MPa. After cooking, filter and remove the ramie after alkali degumming and swelling. Use a flatbed hydraulic press to compress the ramie. Under pressure, the swollen ramie begins to split from a single fiber into multiple fine fibers. At the same time, under pressure, most of the water inside the fiber is removed, increasing the fiber's internal dehydration toughness. Then, using a guillotine cutter, the compressed finely fibrous ramie was cut into uniform 3cm segments to obtain pretreated ramie segments. These pretreated ramie segments were then fed into a pulping machine, and 15000mL of frozen deionized water was added to prepare a pulp with a solid content of 2%. The pulping machine was started for dissociation. After the ramie fibers were completely dispersed, the blade pressure was set to 1.5N, and the pulping time was set to 360min for gradient pulping. During pulping, the temperature change of the pulp was observed using a thermometer. When the temperature exceeded 20℃, pulping was stopped, and 500mL of water was filtered out of the pulp using a filter bag. Then, 500mL of frozen deionized water was added to the pulp tank to buffer the pulp temperature and ensure the stable crystallinity of the ramie fibers. Simultaneously, the freeness of the pulp was measured to be 85 according to the national standard GB / T3332-2004. o Pulping is stopped at SR (Solid Reduction). By controlling the temperature changes caused by mechanical friction during pulping, the damage to the crystallinity of ramie cellulose caused by heat under strong mechanical force is reduced, thereby ensuring the strength and toughness of ramie fibers. A suspension pulp is obtained after pulping.

[0025] S2: Use an ultrasonic machine to sonicate the suspended slurry. Set the power to 400W and the sonication time to 30min. Stir continuously to ensure that the entangled fibers are evenly dispersed. After sonication, pour the slurry into a flat plate sieve and set the sieve frequency to 900Hz to remove impurities and undissolved fiber clumps from the slurry. After sieve, take the fine slurry as the molding slurry.

[0026] S3: Disperse the fine slurry in a fiber dissociation disperser at a speed of 8000 r / min for 2 min; prepare the dissociated slurry to a concentration of 1.5 wt%, take 200 mL of the slurry for sheet forming, and control the weight of the diaphragm to be 10~12 g / m³. 2 The thickness is 40±2μm. The pneumatic stirring time is set to 5s, the settling time is set to 5s, the rapid drainage and filtration is set to 100s, and then the vacuum dehydration is started. After dehydration for 50s, the film is removed by extrusion with rollers to obtain ramie wet film.

[0027] S4: Place the ramie wet film in a vacuum freeze dryer, set the freezing temperature to -30℃, and dry for 24 hours to obtain the product.

[0028] Example 3 A ramie fiber membrane based on the entropy regulation of fiber crystallization domains is prepared by the following steps: S1: Weigh 420g of dried ramie and measure 2000mL of deionized water. Add the deionized water and dried ramie to a high-pressure steam reactor and stir well to completely submerge the ramie in the water. Then, set a gradient heating step, first heating to 55℃ and holding for 6.5h to ensure the ramie is completely soaked, allowing its alkaloids to gradually dissolve into the water, thus raising the pH value in preparation for degumming at high temperature. Then, heat to 160℃ and hold for 20h, controlling the cooking pressure at 0.46MPa. After cooking, filter out the ramie after alkali degumming and swelling. Use a flatbed hydraulic press to compress the ramie. Under pressure, the swollen ramie begins to split from a single fiber into multiple fine fibers. At the same time, under pressure, most of the water inside the fiber is removed, increasing the fiber's internal dehydration toughness. Then, using a guillotine cutter, the compressed finely fiberized ramie was cut into uniform 2cm segments to obtain pretreated ramie segments. These pretreated ramie segments were then fed into a pulping machine, and 15000mL of frozen deionized water was added to prepare a pulp with a solid content of 4%. The pulping machine was started for dissociation. After the ramie fibers were completely dispersed, the blade pressure was set to 3N, and the pulping time to 120min, initiating gradient pulping. During pulping, the temperature change of the pulp was observed using a thermometer. When the temperature exceeded 20℃, pulping was stopped, and 500mL of water was filtered out of the pulp using a filter bag. Then, 500mL of frozen deionized water was added to the pulp tank to buffer the pulp temperature and ensure the stable crystallinity of the ramie fibers. Simultaneously, the pulp freeness was measured to be 75 according to the national standard GB / T3332-2004. o Pulping is stopped at SR (Solid Reduction). By controlling the temperature changes caused by mechanical friction during pulping, the damage to the crystallinity of ramie cellulose caused by heat under strong mechanical force is reduced, thereby ensuring the strength and toughness of ramie fibers. A suspension pulp is obtained after pulping.

[0029] S2: Use an ultrasonic machine to sonicate the suspended slurry, set the power to 350W, the sonication time to 60min, and continuously stir to ensure that the entangled fibers are evenly dispersed; after sonication, pour the slurry into a flat plate sieve and set the sieve frequency to 1000Hz to remove impurities and undissolved fiber clumps from the slurry. After sieve, take the fine slurry as the molding slurry.

[0030] S3: Disperse the fine slurry in a fiber dissociation disperser at a speed of 8000 r / min for 4 min; prepare the dissociated slurry to a concentration of 1 wt%, take 200 mL of the slurry for sheet forming, and control the weight of the diaphragm to be 10~12 g / m³. 2 The thickness is 40±2μm. The pneumatic stirring time is set to 10s, the standing time is 8s, the rapid drainage and filtration is 50s, and then vacuum dehydration is started. After dehydration for 80s, the film is removed by extrusion with rollers to obtain ramie wet film.

[0031] S4: Place the ramie wet film in a vacuum freeze dryer, set the freezing temperature to -30℃, and dry for 20 hours to obtain the product.

[0032] Comparative Example 1 A ramie fiber diaphragm, the difference between its preparation method and that of Example 1 is that the pulping process in step S1 does not involve low-temperature control of the pulping solution, and the deionized water is at room temperature.

[0033] Comparative Example 2 A ramie fiber diaphragm, the preparation method of which differs from that of Example 1, is that the wet membrane is vacuum dried in step S4, and no freeze-drying is performed.

[0034] The preparation methods of the plant fiber membranes in Comparative Examples 3-6 are the same as those in Example 1, the difference being the different raw materials, as shown in Table 1.

[0035] Table 1

[0036] Test case The ramie fiber membranes prepared in the embodiments of the present invention have similar properties. Taking Example 1 as an example, the performance of the related products will be described.

[0037] Characterization analysis was performed using scanning electron microscopy and X-ray diffraction. Figure 1 The image shows an electron microscope (EM) image of ramie raw material, revealing numerous grooves on the surface of the ramie fibers, with the fibers tightly packed together. The diaphragm EEM image is shown below. Figure 2 As shown, after pulping, ramie fibers form an interwoven, interconnected three-dimensional porous network structure. This structure facilitates the migration of electrolytes and ions, while also providing higher elongation at break. Figure 3As shown, X-ray diffraction results indicate that the ramie cellulose membrane exhibits sharp characteristic peaks. Crystallinity, expressed by the empirical crystallinity index CrI, is calculated using the formula CrI=(I002-Iam) / I002, resulting in a crystallinity of 79.68%. This indicates that the entropy-regulated fiber effectively retains the stability of the crystalline domains, and the prepared ramie fiber membrane possesses high crystallinity. The arrangement of its cellulose molecular chains exhibits a high degree of order. High crystallinity can effectively improve the melting point, strength, and mechanical properties of the material.

[0038] The mechanical tensile properties of the prepared diaphragm were tested according to GB / T 1040.3-2006 standard. The puncture strength, air permeability, and ionic conductivity of the prepared fiber diaphragm were tested according to GB / T 36363-2018 standard. The porosity and thermal shrinkage rate of the diaphragm were tested according to GB / T 6672-2001 and GB / T 33818-2017. The results of the tensile properties, puncture strength, and ionic conductivity tests of the diaphragm prepared in Example 1 are as follows: Figures 4-6 As shown. The supercapacitor assembled into a button from the diaphragm prepared in Example 1 was tested using the Xinwei CT-4008T testing equipment. A constant current charge-discharge test method was employed, with the test current density set at 1 A / g and the voltage range at 0–2.7 V. The test was conducted in a constant temperature environment of 25°C. The results are as follows. Figure 7 As shown, the prepared high-toughness interconnected porous ramie membrane still retains 84% ​​capacity retention and 99.52% charge-discharge efficiency after 12,000 cycles, indicating that the prepared membrane can be successfully and effectively applied to supercapacitors. The test results of all samples are summarized in Table 2.

[0039] Table 2

[0040] The ramie cellulose membrane prepared in Comparative Example 1 had a crystallinity of 66.35%, which is lower than that of ramie cellulose membranes suitable for low-temperature pulping. This is because the heat generated by mechanical friction during pulping destroys the crystallinity of the fibers, thus affecting their mechanical properties. The ramie fiber membrane in Comparative Example 2, which was not vacuum freeze-dried, had lower porosity and air permeability, indicating a reduction in its internal interconnected porous network structure. Such a structure is not conducive to ion transfer, resulting in an ionic conductivity of only 4.89 mS / cm. Comparative Example 3 used jute with a shorter aspect ratio as the membrane material, and the jute cellulose membrane had a crystallinity of 58.32%. The network structure constructed by these shorter fibers has a higher ionic conductivity, but its mechanical properties are far inferior to those of ramie fibers. Comparative Example 4 used cotton as the membrane material, and the cotton cellulose membrane had a crystallinity of 60.21%. Although it maintained the crystallinity of cotton fibers, its mechanical properties and heat shrinkage rate were far inferior to those of ramie fibers. Comparative Example 5 uses short-fiber sugarcane bagasse as raw material, which can achieve high ionic conductivity, but it is difficult to compensate for the lack of mechanical properties. Comparative Example 6 uses bamboo fiber as membrane raw material, and the porosity and thermal shrinkage rate of the prepared membrane are 18.36% and 1.43%, respectively. This indicates that it is difficult to remove the impurities of cellulose contained in bamboo fiber without the addition of alkaline chemical reagents. It is difficult to remove and soften the impurities of cellulose through its own alkaloids, as is the case with ramie, thus making it difficult to form an interconnected porous structure during freeze-drying.

[0041] While specific embodiments of the present invention have been described in detail, they should not be construed as limiting the scope of protection of the present invention. Various modifications and variations that can be made by those skilled in the art without inventive effort within the scope described in the claims are still within the scope of protection of the present invention.

Claims

1. A method for preparing a ramie fiber diaphragm, characterized in that, Includes the following steps: S1: The ramie raw material is soaked, cooked, filtered, squeezed and cut in sequence to obtain pretreated ramie segments. The pretreated ramie segments are then subjected to low-temperature pulping to obtain a suspension slurry. S2: The suspension slurry is ultrasonically dispersed and screened to obtain a fine slurry; S3: The fine pulp is dissociated and dispersed, the pulp concentration is adjusted to 0.5~1.5wt%, and then a wet forming and papermaking process is used to obtain ramie wet film; S4: The ramie wet film is freeze-dried to obtain the final product.

2. The method for preparing the ramie fiber diaphragm according to claim 1, characterized in that: In step S1, the soaking temperature is 50~60℃ and the soaking time is 6~7h; the cooking temperature is 120~160℃, the cooking pressure is 0.4~0.6MPa, and the cooking time is 12~24h; the length of the pretreated ramie segments is 1.5~3cm.

3. The method for preparing the ramie fiber diaphragm according to claim 1, characterized in that, The conditions for low-temperature pulping in step S1 are as follows: prepare a pulp with a pretreated ramie content of 2~4wt% for pulping, the pulping blade pressure is 1.5~3N, the pulping time is 120~360min, the freeness of the pulp after pulping is 75~85°SR, and the pulp temperature is controlled below 20℃ during the pulping process.

4. The method for preparing the ramie fiber diaphragm according to claim 1, characterized in that: In step S2, the ultrasonic dispersion power is 300~400W and the ultrasonic dispersion time is 30~60min.

5. The method for preparing the ramie fiber diaphragm according to claim 1, characterized in that: In step S2, a flat plate slurry screener is used for slurry screening at a frequency of 900~1000Hz.

6. The method for preparing the ramie fiber diaphragm according to claim 1, characterized in that: The dissociation and dispersion described in step S3 is carried out in a dissociation machine at a speed of 7000~8000 r / min and a dissociation time of 2~4 min.

7. The method for preparing the ramie fiber diaphragm according to claim 1, characterized in that, The wet forming and papermaking process described in step S3 includes: pneumatically stirring the slurry for 5-10 seconds, letting it stand for 5-8 seconds, then filtering it by drainage for 50-100 seconds, and then vacuum dehydrating it for 50-80 seconds to obtain a wet film with a moisture content of 10-30%. After demolding, the ramie wet film is obtained.

8. The method for preparing the ramie fiber diaphragm according to claim 1, characterized in that: In step S4, the freeze-drying temperature is -30~-40℃ and the freeze-drying time is 12~24h.

9. The ramie fiber diaphragm prepared by the preparation method according to any one of claims 1 to 8.

10. The use of the ramie fiber diaphragm according to claim 9 in the preparation of capacitor diaphragms.

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