Flexible electromagnetic shielding film and preparation method and application thereof

Abstract

The invention relates to the technical field of composite materials, in particular to a flexible electromagnetic shielding film and a preparation method and application thereof. The invention relates to a flexible electromagnetic shielding film, which takes bamboo charcoal as conductive particles, liquid metal as conductive filler and bamboo nano cellulose as a binder. The flexible electromagnetic shielding film provided by the invention has excellent conductivity and electromagnetic shielding performance, and is environment-friendly.

Description

Technical Field

[0001] The present invention relates to the technical field of composite materials, and in particular to a flexible electromagnetic shielding film and a preparation method and application thereof. Background Art

[0002] In the rapidly developing modern society, the extensive use of electronic devices has greatly increased the convenience of people's lives, but it has also caused serious electromagnetic pollution. Long-term exposure to electromagnetic wave environment will endanger human health or interfere with the normal operation of electronic equipment. Therefore, the research on electromagnetic interference shielding materials has become an important emerging research topic. In the past few decades, carbon-based materials, polymer-based composite materials, metals and their oxides have developed rapidly in the field of electromagnetic shielding. With the improvement of environmental awareness and the concept of sustainable development, it is of great significance to study the use of renewable resources to replace non-renewable materials.

[0003] In recent years, biomass materials, as the main source of natural carbon-based materials, have gradually become a research hotspot in the field of EMI shielding. However, biomass materials have poor electrical conductivity and do not have excellent EMI shielding effects. Therefore, they often need to be compounded with other functional materials, such as highly conductive materials (such as MXene, carbon nanotubes, graphene, etc.) and metal oxides (Fe3O4, Ni, Co, etc.) to enhance their EMI shielding effectiveness. These cumbersome processing steps increase costs and are not environmentally friendly, limiting the practical application of biomass materials. Summary of the invention

[0004] The present invention provides a flexible electromagnetic shielding film and a preparation method and application thereof, which are used to solve the problems of complicated processing and environmental unfriendliness in the existing electromagnetic shielding material prepared with biomass materials as raw materials.

[0005] According to a first aspect of the present invention, the present invention provides a flexible electromagnetic shielding film, which uses bamboo charcoal as conductive particles, liquid metal as conductive filler, and bamboo nanocellulose as a binder.

[0006] The pore structure and high specific surface area of ​​bamboo charcoal enable it to effectively absorb electromagnetic waves. Using bamboo charcoal as conductive particles can improve the electromagnetic shielding performance of flexible electromagnetic shielding films. Bamboo charcoal has a low density and good chemical stability, and can be used as a lightweight electrostatic shielding material. Bamboo charcoal is a renewable resource. Its application in electromagnetic shielding materials helps to reduce the impact on the environment and is in line with the development trend of green materials. Liquid metal has excellent conductivity and can form a continuous conductive network to effectively shield electromagnetic interference. The fluidity of liquid metal enables it to construct a conductive network with dynamic response characteristics, which helps to solve the problem of electromagnetic sealing at the contact interface. Liquid metal-based electromagnetic shielding materials can have the characteristics of being cuttable, low density, high compression, and super resilience. These characteristics make the material more flexible and adaptable in practical applications. After heat treatment, the electromagnetic shielding effectiveness of liquid metal-based electromagnetic shielding materials can still remain stable. However, liquid metal has ultra-high surface tension, poor compatibility with other materials, and is easily oxidized, reducing conductivity. As a renewable biomass material with good biocompatibility, the application of bamboo nanocellulose in electromagnetic shielding materials meets the requirements of sustainable development and is of great significance to "low-carbon" development. Bamboo nanocellulose has a high aspect ratio and excellent mechanical properties. These characteristics enable it to be used as a reinforcing phase in composite materials to improve the mechanical strength of the material. The surface of bamboo nanocellulose contains a large number of hydroxyl groups and has a high specific surface area, which allows it to form a stable composite material with other materials through hydrogen bonding to improve the electromagnetic shielding effect. The present invention uses bamboo charcoal as conductive particles, liquid metal as conductive filler, and bamboo nanocellulose as a binder for compounding, which can obtain a composite material with excellent electrical conductivity and electromagnetic shielding performance and environmental protection.

[0007] Furthermore, the weight ratio of the bamboo charcoal, the liquid metal and the bamboo nanocellulose is (2-12):1:(0-2.5). Within the above raw material ratio range, the bamboo charcoal, the liquid metal and the bamboo nanocellulose can have a better synergistic effect, thereby improving the conductivity and electromagnetic shielding performance of the flexible electromagnetic shielding film.

[0008] Preferably, the weight ratio of the bamboo charcoal, the liquid metal and the bamboo nanocellulose is (2-6):1:(0.2-0.6), more preferably (2-3):1:(0.2-0.3).

[0009] Further, the carbonization temperature of the bamboo charcoal is 600-1400°C, the particle size is 200-2000 mesh, and the conductivity is 2-5000 S / m. In some specific embodiments, the carbonization temperature of the bamboo charcoal is 1000-1200°C, the particle size is 300-500 mesh, and the conductivity is 3000-4500 S / m.

[0010] Furthermore, the liquid metal is a gallium-indium-tin alloy with a melting point of 8-30° C. The conductivity and electromagnetic shielding performance of the flexible electromagnetic shielding film can be improved by using a suitable type of liquid metal.

[0011] Furthermore, the diameter of the bamboo nanocellulose is 10-90 nm and the length is greater than 100 μm. By selecting bamboo nanocellulose of appropriate size, a better bonding effect can be achieved, and the conductivity and electromagnetic shielding performance of the flexible electromagnetic shielding film can be improved.

[0012] Furthermore, the electrical conductivity of the flexible electromagnetic shielding film is 10-4000 S / m, and the electromagnetic shielding performance is 10-70 dB. In some specific embodiments, the electrical conductivity of the flexible electromagnetic shielding film is 60-500 S / m, and the electromagnetic shielding performance is 20-35 dB.

[0013] According to a second aspect of the present invention, the present invention also provides a method for preparing the above-mentioned flexible electromagnetic shielding film, comprising the following steps: preparing bamboo charcoal powder; nano-processing bamboo cellulose to obtain bamboo nanofiber suspension; Adding a cationic surfactant to the bamboo nanofiber suspension and stirring evenly; then adding bamboo charcoal powder and stirring evenly; then adding liquid metal and performing ultrasonic dispersion treatment for 5-30 minutes to obtain a stable bamboo nanocellulose-bamboo charcoal powder-liquid metal solution; The obtained bamboo nanocellulose-bamboo charcoal powder-liquid metal solution is subjected to suction filtration, pressed, and dried to obtain a flexible electromagnetic shielding film.

[0014] Bamboo nanocellulose has abundant negatively charged groups, which keeps the fibers dispersed through electrostatic repulsion and prevents them from aggregating with each other. Bamboo charcoal powder and liquid metal have poor compatibility with bamboo nanocellulose, and they are easily agglomerated and precipitated when added directly. Therefore, adding cationic surfactants to bamboo nanocellulose solution can improve the compatibility between bamboo nanocellulose, bamboo charcoal powder and liquid metal. The above solution is ultrasonically treated to break the liquid metal into small droplets. After a certain period of ultrasound, bamboo charcoal powder and liquid metal are evenly dispersed in the bamboo nanocellulose solution and can exist stably for several months without precipitation. Bamboo nanocellulose is usually hydrophilic, while liquid metal, due to its metallic nature, often exhibits hydrophobicity or is difficult to be compatible with organic materials. Cationic surfactants can interact with the surfaces of liquid metal and bamboo charcoal powder to improve interfacial compatibility. A certain amount of prepared bamboo nanocellulose-bamboo charcoal powder-liquid metal solution is added to a vacuum filter and vacuum filtered to form a film. The filtered membrane is then pressed, the liquid metal is sintered, and a continuous conductive network is formed in the flexible membrane. Finally, drying is performed to obtain a flexible bamboo charcoal-based electromagnetic shielding film. A flexible film with good softness and high conductivity is prepared by using high-temperature bamboo charcoal as conductive particles, liquid metal to construct a continuous conductive network, and bamboo-based nanocellulose with a high aspect ratio as a flexible substrate. The preparation method of the present invention is simple and the conditions are mild. The prepared flexible electromagnetic shielding film has broad application prospects in flexible electronic devices, wearable devices and other fields with high demands for electromagnetic shielding.

[0015] Further, the preparation method of bamboo charcoal powder is as follows: Using 1-5 year old bamboo as raw material, cut the bamboo into bamboo pieces with a length of 4-5 cm and a width of 1-2 cm; The cut bamboo pieces are carbonized to obtain bamboo charcoal; the carbonization temperature is 600-1400°C, the insulation time is 1-5 h, the heating rate is 1-10°C / min, and the carbonization process is carried out under nitrogen protection with a gas flow rate of 0.2-1 L / min; The obtained bamboo charcoal is ball-milled to obtain bamboo charcoal powder; the rotation speed of the ball mill is 400-600 prm, and the time is 10-30 min.

[0016] By specially setting the preparation method of bamboo charcoal powder, bamboo charcoal powder with suitable particle size and high conductivity can be obtained.

[0017] Furthermore, in the bamboo nanofiber suspension, the mass percentage of the bamboo nanofiber is 0.5-1.5%. In some specific embodiments, in the bamboo nanofiber suspension, the mass percentage of the bamboo nanofiber is 0.9-1.1%.

[0018] Furthermore, the cationic surfactant is hexadecyltrimethylammonium bromide; bamboo nanocellulose is usually hydrophilic, while liquid metal, due to its metallic nature, often exhibits hydrophobicity or is difficult to be compatible with organic materials. The hydrophobic tail of CTAB can interact with the surface of liquid metal and bamboo charcoal powder, while its hydrophilic head can combine with nanocellulose, thereby improving interfacial compatibility. In addition, the positive charge of CTAB can neutralize the negative charge on nanocellulose, and improve the dispersion of liquid metal droplets and bamboo charcoal powder in nanocellulose solution. More uniform. In particular, in a liquid metal particle suspension system, CTAB can help improve the stability of particle dispersion, thereby preventing the agglomeration of liquid metal.

[0019] Furthermore, the volume mass ratio of the bamboo nanofiber suspension to the cationic surfactant is (80-120) ml: (0.9-5) g. By limiting the volume mass ratio of the bamboo nanofiber suspension to the cationic surfactant to a reasonable range, it is more conducive to improving the interfacial compatibility between materials. Preferably, the volume mass ratio of the bamboo nanofiber suspension to the cationic surfactant is (90-110) ml: (4-5) g.

[0020] Furthermore, the pressing pressure is 2-10 MPa and the pressing time is 1-30 min. By limiting the pressing pressure and time within a reasonable range, it is more conducive to forming a continuous conductive network in the flexible film. In some specific embodiments, the pressing pressure is 5-8 MPa and the pressing time is 5-15 min.

[0021] According to a third aspect of the present invention, the present invention also provides an application of the above-mentioned flexible electromagnetic shielding film in the field of electromagnetic shielding. The field of electromagnetic shielding involves flexible electronic devices, wearable devices, and the like.

[0022] The invention provides a flexible electromagnetic shielding film, which uses bamboo charcoal as conductive particles, liquid metal as conductive filler, and bamboo nanocellulose as a binder. The film has excellent electrical conductivity and electromagnetic shielding performance and is environmentally friendly.

[0023] The present invention provides a method for preparing a flexible electromagnetic shielding film, which is simple and requires mild conditions. The prepared flexible electromagnetic shielding film has broad application prospects in flexible electronic devices, wearable devices and other fields with high demands for electromagnetic shielding. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 This is the surface SEM image of the bamboo charcoal-based flexible electromagnetic shielding film of Experimental Example 1 of the present invention.

[0026] Figure 2 This is a SEM image of the longitudinal section of the bamboo charcoal-based flexible electromagnetic shielding film according to Example 1 of the present invention.

[0027] Figure 3 This is a surface SEM image of the bamboo charcoal-based flexible electromagnetic shielding film according to Example 3 of the present invention. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] Example 1 This embodiment provides a bamboo charcoal-based flexible electromagnetic shielding film, which uses bamboo charcoal as conductive particles, liquid metal as conductive filler, and bamboo nanocellulose as a binder, wherein the weight ratio of bamboo charcoal, liquid metal and bamboo nanocellulose is 2.25:0.2:0.45. The carbonization temperature of bamboo charcoal is 1000 ° C, the particle size is 400 mesh, and the conductivity is 3000 S / m. The liquid metal is a gallium indium tin alloy with a melting point of 30 ° C. The diameter of bamboo nanocellulose is 10-90nm and the length is greater than 100 μm.

[0030] A method for preparing a flexible electromagnetic shielding film comprises the following steps: 1. Preparation of Bamboo Charcoal Powder 1.1: Use 4-year-old bamboo as raw material and cut it into bamboo strips with a length of 4-5 cm and a width of 1-2 cm.

[0031] 1.2: Place the bamboo strips sawn in step 1.1 in a tubular furnace for carbonization. The carbonization temperature is 1400 °C, the holding time is 2 h, the heating rate is 5 °C / min, and nitrogen is passed for 30 min before carbonization. The carbonization process is carried out under nitrogen protection with a gas flow rate of 0.2 L / min.

[0032] 1.3: Use a planetary ball mill to ball mill the bamboo charcoal in step 1.2 at a speed of 500 rpm for 10 min.

[0033] 2. Preparation of bamboo nanocellulose-bamboo charcoal powder-liquid metal solution 2.1: Use a high-pressure homogenizer to nano-process bamboo cellulose to obtain bamboo nanofiber suspension.

[0034] 2.2: Prepare the above bamboo nanocellulose solution into a solution with a bamboo nanocellulose mass fraction of 0.9%, take 50 ml, then add 0.45 g of hexadecyltrimethylammonium bromide and stir evenly.

[0035] 2.3: Add 2.25 g bamboo charcoal powder as a conductive agent to the above solution and stir evenly.

[0036] 2.4: Take 0.2 g of liquid metal with a melting point of 30 °C and add it to the above solution. Perform ultrasonic dispersion for 20 min to obtain a stable bamboo nanocellulose-bamboo charcoal powder-liquid metal solution.

[0037] 3. Preparation of bamboo charcoal-based flexible electromagnetic shielding film 3.1: Take 10 ml of bamboo nanocellulose-bamboo charcoal powder-liquid metal solution and use a vacuum filter to filter it to obtain a bamboo charcoal-based flexible film.

[0038] 3.2: Use a hydraulic press to press the flexible film for 5 min to mechanically sinter the liquid metal at a pressure of 5 MPa.

[0039] 3.3: The flexible film after mechanical sintering is placed in an oven for drying to obtain a bamboo charcoal-based flexible electromagnetic shielding film. Figure 1 This is the surface of the bamboo charcoal-based flexible electromagnetic shielding film of Experimental Example 1 of the present invention. It can be seen that the bamboo nanofibers evenly wrap the bamboo charcoal particles, and the liquid metal liquid forms a conductive network. Figure 2 This is a longitudinal section of the bamboo charcoal-based flexible electromagnetic shielding film of Example 1 of the present invention. It can be seen that the bamboo charcoal powder particles are evenly dispersed in the entire film and are densely adhered together.

[0040] The conductivity of the bamboo charcoal-based flexible electromagnetic shielding film obtained in this example is 60 S / m, and the electromagnetic shielding performance is 22 dB.

[0041] Example 2 This embodiment provides a bamboo charcoal-based flexible electromagnetic shielding film, which uses bamboo charcoal as conductive particles, liquid metal as conductive filler, and bamboo nanocellulose as a binder, wherein the weight ratio of bamboo charcoal, liquid metal and bamboo nanocellulose is 5.5:1:0.55. The carbonization temperature of bamboo charcoal is 1200 ° C, the particle size is 300 mesh, and the conductivity is 4500 S / m. The liquid metal is a gallium indium tin alloy with a melting point of 20 ° C. The diameter of bamboo nanocellulose is 10-90 nm and the length is greater than 100 μm.

[0042] A method for preparing a flexible electromagnetic shielding film comprises the following steps: 1. Preparation of Bamboo Charcoal Powder 1.1: Use 3-year-old bamboo as raw material and cut it into bamboo strips with a length of 4-5 cm and a width of 1-2 cm.

[0043] 1.2: Place the bamboo strips sawn in step 1 in a tubular furnace for carbonization. The carbonization temperature is 1000 °C, the holding time is 2 h, the heating rate is 10 °C / min, and nitrogen is passed for 30 min before carbonization. The carbonization process is carried out under nitrogen protection with a gas flow rate of 0.1 L / min.

[0044] 1.3: Use a planetary ball mill to ball mill the bamboo charcoal in step 2 at a speed of 1000 prm for 10 min.

[0045] 2. Preparation of bamboo nanocellulose-bamboo charcoal powder-liquid metal solution 2.1: Use a high-pressure homogenizer to nano-process bamboo cellulose to obtain bamboo nanofiber suspension.

[0046] 2.2: Prepare the above bamboo nanocellulose solution into a solution with a bamboo nanocellulose mass fraction of 1.1%, take 50 ml, then add 2 g of hexadecyltrimethylammonium bromide and stir evenly.

[0047] 2.3: Add 5.5 g bamboo charcoal powder as a conductive agent to the above solution and stir evenly.

[0048] 2.4: Take 1 g of liquid metal with a melting point of 20 °C and add it to the above solution. Perform ultrasonic dispersion for 30 min to obtain a stable bamboo nanocellulose-bamboo charcoal powder-liquid metal solution.

[0049] 3. Preparation of bamboo charcoal-based flexible electromagnetic shielding film 3.1: Take 15 ml of bamboo nanocellulose-bamboo charcoal powder-liquid metal solution and use a vacuum filter to filter it to obtain a bamboo charcoal-based flexible film.

[0050] 3.2: Use a hydraulic press to press the flexible film for 10 min to mechanically sinter the liquid metal at a pressure of 5 MPa.

[0051] 3.3: The flexible film after mechanical sintering is pressed by a mold and then naturally air-dried to obtain a bamboo charcoal-based flexible electromagnetic shielding film.

[0052] The conductivity of the bamboo charcoal-based flexible electromagnetic shielding film obtained in this embodiment is 320 S / m, and the electromagnetic shielding performance is 30 dB.

[0053] Example 3 This embodiment provides a bamboo charcoal-based flexible electromagnetic shielding film, which uses bamboo charcoal as conductive particles, liquid metal as conductive filler, and bamboo nanocellulose as a binder, wherein the weight ratio of bamboo charcoal, liquid metal and bamboo nanocellulose is 5:2:0.5. The carbonization temperature of bamboo charcoal is 1100 ° C, the particle size is 500 mesh, and the conductivity is 3500 S / m. The liquid metal is a gallium indium tin alloy with a melting point of 20 ° C. The diameter of bamboo nanocellulose is 10-90 nm and the length is greater than 100 μm.

[0054] A method for preparing a flexible electromagnetic shielding film comprises the following steps: 1. Preparation of Bamboo Charcoal Powder 1.1: Use 2-year-old tea bamboo as raw material and cut the bamboo into bamboo strips with a length of 4-5 cm and a width of 1-2 cm.

[0055] 1.2: Place the bamboo strips sawn in step 1 in a tubular furnace for carbonization. The carbonization temperature is 1200 °C, the holding time is 3 h, the heating rate is 15 °C / min, and nitrogen is passed for 30 min before carbonization. The carbonization process is carried out under nitrogen protection with a gas flow rate of 0.1 L / min.

[0056] 1.3: Use a planetary ball mill to ball mill the bamboo charcoal in step 1.2 at a speed of 800 rpm for 15 min.

[0057] 2. Preparation of bamboo nanocellulose-bamboo charcoal powder-liquid metal solution 2.1: Use a high-pressure homogenizer to nano-process bamboo cellulose to obtain bamboo nanofiber suspension.

[0058] 2.2: Prepare the above bamboo nanocellulose solution into a solution with a bamboo nanocellulose mass fraction of 1%, take 50 ml, then add 2.5 g of hexadecyltrimethylammonium bromide and stir evenly.

[0059] 2.3: Add 5 g of bamboo charcoal powder as a conductive agent to the above solution and stir evenly.

[0060] 2.4: Take 2 g of liquid metal with a melting point of 20 °C and add it to the above solution. Perform ultrasonic dispersion for 40 min to obtain a stable nanocellulose / bamboo charcoal powder / liquid metal solution.

[0061] 3. Preparation of bamboo charcoal-based flexible electromagnetic shielding film 3.1: Take 12 ml of bamboo charcoal powder / liquid metal / nanocellulose solution and filter it using a vacuum filter to obtain a bamboo charcoal-based flexible film.

[0062] 3.2: Use a hydraulic press to press the flexible film for 15 min to mechanically sinter the liquid metal at a pressure of 8 MPa.

[0063] 3.3: The flexible film after mechanical sintering is pressed by a mold and then naturally air-dried to obtain a bamboo charcoal-based flexible electromagnetic shielding film. Figure 3 This is the surface of the bamboo charcoal-based flexible electromagnetic shielding film of Example 3 of the present invention. It can be seen that the bamboo nanocellulose wraps the bamboo charcoal more evenly, and the liquid metal forms a continuous conductive network.

[0064] The conductivity of the bamboo charcoal-based flexible electromagnetic shielding film obtained in this example is 500 S / m, and the electromagnetic shielding performance is 35 dB.

[0065] Comparative Example 1 This comparative example provides a flexible electromagnetic shielding film, which uses bamboo charcoal as conductive particles and nanocellulose as a binder, and the ratio of the raw materials is 8:2. The rest of the preparation method is the same as that of Example 1.

[0066] The conductivity of the flexible electromagnetic shielding film obtained in this comparative example is 0 S / m, and the electromagnetic shielding performance is 0 dB.

[0067] Comparative Example 2 This comparative example provides a flexible electromagnetic shielding film, which is different from Example 1 in that it does not contain liquid metal, and its preparation method is different from that of Example 1 in that the mass fraction of liquid metal is 0%, and the rest of the preparation method and parameters are the same as those of Example 1.

[0068] The conductivity of the flexible electromagnetic shielding film obtained in this comparative example is 0 S / m, and the electromagnetic shielding performance is 0 dB.

[0069] Comparative Example 3 This comparative example provides a flexible electromagnetic shielding film, and its preparation method is different from that of Example 3, except that the mass of hexadecyltrimethylammonium bromide is 0 g.

[0070] The flexible electromagnetic shielding film obtained in this comparative example has poor interface compatibility, is easy to crack, has an electrical conductivity of 5 S / m, and has an electromagnetic shielding performance of 2 dB.

[0071] Comparative Example 4 This comparative example provides a flexible electromagnetic shielding film, which is different from Example 2 in that it does not contain bamboo charcoal; the preparation method is different from Example 2 in that the mass fraction of bamboo charcoal powder is 0%, and the rest of the preparation method and parameters are the same as Example 2.

[0072] The conductivity of the flexible electromagnetic shielding film obtained in this comparative example is 12 S / m, and the electromagnetic shielding performance is 4 dB.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A flexible electromagnetic shielding film, characterized in that: Bamboo charcoal is used as conductive particles, liquid metal is used as conductive filler, and bamboo nanocellulose is used as a binder.

2. The flexible electromagnetic shielding film according to claim 1, characterized in that: The weight ratio of the bamboo charcoal, the liquid metal and the bamboo nanocellulose is (2-12):1:(0-2.5).

3. The flexible electromagnetic shielding film according to claim 1 or 2, characterized in that: The carbonization temperature of the bamboo charcoal is 600-1400°C, the particle size is 200-2000 meshes, and the conductivity is 2-5000 S / m.

4. The flexible electromagnetic shielding film according to any one of claims 1 to 3, characterized in that: The liquid metal is a gallium-indium-tin alloy with a melting point of 8-30°C.

5. The flexible electromagnetic shielding film according to any one of claims 1 to 4, characterized in that: The bamboo nanocellulose has a diameter of 10-90 nm and a length of more than 100 μm.

6. The flexible electromagnetic shielding film according to any one of claims 1 to 5, characterized in that: The electrical conductivity of the flexible electromagnetic shielding film is 10-4000 S / m, and the electromagnetic shielding performance is 10-70 dB.

7. The method for preparing the flexible electromagnetic shielding film according to any one of claims 1 to 6, characterized in that: The steps include: preparing bamboo charcoal powder; nano-processing bamboo cellulose to obtain bamboo nanofiber suspension; Adding a cationic surfactant to the bamboo nanofiber suspension and stirring evenly; then adding bamboo charcoal powder and stirring evenly; then adding liquid metal and performing ultrasonic dispersion treatment for 5-30 minutes to obtain a stable bamboo nanocellulose-bamboo charcoal powder-liquid metal solution; The obtained bamboo nanocellulose-bamboo charcoal powder-liquid metal solution is subjected to suction filtration, pressed, and dried to obtain a flexible electromagnetic shielding film.

8. The preparation method according to claim 7, characterized in that: The preparation method of bamboo charcoal powder is as follows: Using 1-5 year old bamboo as raw material, cut the bamboo into bamboo pieces with a length of 4-5 cm and a width of 1-2 cm; The cut bamboo pieces are carbonized to obtain bamboo charcoal; the carbonization temperature is 600-1400°C, the insulation time is 1-5 h, the heating rate is 1-10°C / min, and the carbonization process is carried out under nitrogen protection with a gas flow rate of 0.2-1 L / min; The obtained bamboo charcoal is ball-milled to obtain bamboo charcoal powder; the rotation speed of the ball mill is 400-600 prm, and the time is 10-30 min.

9. The preparation method according to claim 7, characterized in that: In the bamboo nanofiber suspension, the mass percentage of the bamboo nanofiber is 0.5-1.5%; and / or, the cationic surfactant is hexadecyltrimethylammonium bromide; and / or, the volume mass ratio of the bamboo nanofiber suspension to the cationic surfactant is (80-120) ml: (0.9-5) g; and / or, the pressing pressure is 2-10 MPa and the pressing time is 1-30 min.

10. Use of the flexible electromagnetic shielding film according to any one of claims 1 to 6 in the field of electromagnetic shielding.

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