Electromagnetic shielding nanofiber composite film and its preparation method

Abstract

This application provides an electromagnetic shielding nanofiber composite membrane and its preparation method, belonging to the field of electromagnetic shielding material preparation technology. The electromagnetic shielding nanofiber composite membrane provided in this application includes a three-dimensional framework substrate, and conductive and magnetic media uniformly dispersed in the three-dimensional framework substrate. The substrate and the conductive and magnetic media form a special three-dimensional network porous structure through overlap and adsorption. The composite membrane provided in this application has a thickness of 20-30 μm, an electromagnetic shielding effectiveness of 59 dB, and a maximum tensile stress of 12 MPa. The preparation method of this composite membrane is as follows: carboxylated carbon nanotubes, copper nanowires, and nickel ferrite are uniformly loaded into PVA-co-PE nanofibers through vacuum-assisted filtration, cross-linking, and hot pressing processes. The membrane can be formed in a single filtration step. The preparation method is simple and has good repeatability.

Description

Technical Field

[0001] This application relates to the field of electromagnetic shielding material preparation technology, specifically to an electromagnetic shielding nanofiber composite membrane and its preparation method. Background Technology

[0002] The rapid development of electronic information technology has brought numerous conveniences to society, but the resulting excessive electromagnetic radiation not only affects human health but also the normal operation of equipment or electronic systems. Therefore, electromagnetic shielding materials are needed in nuclear power plants, transformers, aerospace systems, aircraft, ships, 5G communications, and medical equipment to block the propagation of electromagnetic waves and reduce electromagnetic interference. According to the transmission line theory of electromagnetic shielding mechanisms, the attenuation of electromagnetic waves by an electromagnetic shield is mainly based on its reflection and absorption. The attenuation of electromagnetic waves is often achieved through electrical loss, magnetic loss, and dielectric loss during reflection and absorption. Good electromagnetic interference shielding materials, in addition to having good electromagnetic shielding performance, should also be lightweight, flexible, chemically stable, and possess excellent mechanical properties to be suitable for different scenarios and fields.

[0003] Metallic electromagnetic shielding materials possess excellent conductivity, electromagnetic interference shielding performance, and thermal management properties, making them widely used in industry. However, their high density, low flexibility, poor mechanical properties, and poor chemical corrosion resistance limit their application in many situations. Conductive polymer composites (CPCs), composed of a polymer matrix and conductive fillers, are easy to mold, corrosion-resistant, and possess good mechanical properties, making them widely used for lightweight electromagnetic interference shielding and thermal management. Currently, introducing magnetic media into CPCs to enhance the interference shielding performance of electromagnetic shielding materials through the synergistic effect of magneto-electricity has become a new key research direction.

[0004] In existing technologies, most electromagnetic shielding materials are designed as multi-layered structures, such as gradient-distributed multi-layered structures. By stacking composite material layers containing different fillers, electromagnetic shielding over a wider frequency range can be achieved; by stacking composite material layers with the same filler but gradually increasing filler content, interface differences can be reduced, reflectivity limited, and electromagnetic shielding performance improved. However, because these electromagnetic shielding materials are assembled through stacking, their mechanical properties still deviate, making them prone to slippage or cracking during use. How to simultaneously improve the electromagnetic interference shielding performance and mechanical properties of the material is a pressing technical challenge that needs to be addressed.

[0005] In view of this, it is necessary to design an improved electromagnetic shielding nanofiber composite membrane and its preparation method to solve the above problems. Summary of the Invention

[0006] In view of the technical problems existing in the background art, this application provides an electromagnetic shielding nanofiber composite membrane and its preparation method. This application uses PVA-co-PE as the substrate and carboxylated carbon nanotubes, copper nanowires and nickel ferrite as fillers. The fillers are uniformly loaded into the substrate through vacuum-assisted filtration, cross-linking and hot pressing processes. The substrate and the three fillers overlap and adsorb to form a three-dimensional network porous structure. The prepared nanofiber composite membrane has excellent electromagnetic shielding performance and mechanical properties. The electromagnetic shielding effectiveness of the composite membrane reaches 59dB and the maximum tensile stress reaches 12MPa.

[0007] In a first aspect, embodiments of this application provide an electromagnetic shielding nanofiber composite membrane, comprising a three-dimensional framework substrate, and a conductive medium and a magnetic medium uniformly dispersed in the three-dimensional framework substrate; the electromagnetic shielding nanofiber composite membrane has a three-dimensional network porous structure; the thickness of the electromagnetic shielding nanofiber composite membrane is 20-30 μm, the electromagnetic shielding effectiveness reaches 59 dB, and the maximum tensile stress reaches 12 MPa. The three-dimensional framework substrate accounts for 94-99% of the mass of the electromagnetic shielding nanofiber composite membrane.

[0008] In some embodiments, the conductive medium includes carboxylated carbon nanotubes and copper nanowires, and the magnetic medium includes nickel ferrite.

[0009] In some embodiments, the mass ratio of the carboxylated carbon nanotubes, the copper nanowires, and the nickel ferrite is (1-2.5):(1-1.5):1.

[0010] In some embodiments, the electromagnetic shielding nanofiber composite film uses PVA-co-PE nanofibers as a three-dimensional skeleton substrate, and the carboxylated carbon nanotubes, copper nanowires and nickel ferrite are uniformly loaded into the PVA-co-PE nanofibers through vacuum-assisted filtration, cross-linking and hot pressing processes.

[0011] In some embodiments, the PVA-co-PE nanofibers, carboxylated carbon nanotubes, and copper nanowires overlap to form a three-dimensional network porous structure.

[0012] Secondly, embodiments of this application provide a method for preparing the aforementioned electromagnetic shielding nanofiber composite film, comprising the following steps:

[0013] S1, Isopropanol, deionized water and PVA-co-PE nanofibers were uniformly mixed using a high-speed shearing machine to prepare a PVA-co-PE nanofiber suspension with a fiber content of 1wt%.

[0014] S2, the PVA-co-PE nanofiber suspension prepared in step S1 is mixed with carboxylated carbon nanotubes, copper nanowires and nickel ferrite, stirred for 0.5-1 h, and vacuum-assisted filtration is performed to obtain a nanofiber composite membrane; the PVA-co-PE nanofibers account for 94-99% of the mass of the nanofiber composite membrane; the mass ratio of the carboxylated carbon nanotubes to the copper nanowires and the nickel ferrite is (1-2.5):(1-1.5):1;

[0015] S3, the nanofiber composite membrane is immersed in glutaraldehyde crosslinking agent with a concentration of 1.5wt%, crosslinked by ultraviolet light irradiation, then naturally air-dried and hot-pressed to obtain the electromagnetic shielding nanofiber composite membrane.

[0016] In some embodiments, in step S2, the method for preparing the carboxylated carbon nanotubes is as follows: multi-walled carbon nanotubes are mixed with concentrated nitric acid and sonicated for 1-2 hours, concentrated sulfuric acid is added, the mixture is left at 55-65°C overnight, then diluted with 2 times the volume of deionized water, and freeze-dried to obtain carboxylated carbon nanotube powder.

[0017] In some embodiments, in the method for preparing carboxylated carbon nanotubes, the volume ratio of concentrated sulfuric acid to concentrated nitric acid is 1:3.

[0018] In some embodiments, in step S3, the hot pressing method is to sandwich the air-dried nanofiber composite film between two polyimide films and place them together in a hot press at 100-105°C for 60-65 seconds.

[0019] In some embodiments, in step S3, the crosslinking time under ultraviolet light irradiation is 3-3.5 h.

[0020] The beneficial effects of this application are:

[0021] This application uses PVA-co-PE as the substrate, and carboxylated carbon nanotubes (HOOC-MWCNT), copper nanowires (CuNWs), and nickel ferrite (NiFe2O4) are uniformly loaded into the substrate through vacuum-assisted filtration, cross-linking, and hot pressing processes. The substrate and the three fillers overlap and adsorb to form a three-dimensional network porous structure. The prepared nanofiber composite membrane has excellent electromagnetic shielding performance and mechanical properties. The electromagnetic shielding effectiveness of the composite membrane reaches 59dB, and the maximum tensile stress reaches 12MPa.

[0022] (1) This application modifies carbon nanotubes by introducing carboxyl functional groups, so that the modified carbon nanotubes can generate hydrogen bonds with functional groups such as hydroxyl groups on PVA-co-PE nanofibers through cross-linking reaction, thereby increasing the mechanical properties of the composite film.

[0023] (2) This application combines three fillers: HOOC-MWCNTs, CuNWs, and NiFe2O4. A unique three-dimensional network porous structure is formed through the interlocking and adsorption between the substrate and the three fillers. The tubular and linear structures of the carbon nanomaterials and copper nanomaterials effectively prevent agglomeration during membrane preparation. NiFe2O4, with its anti-spinel structure, adsorbs onto HOOC-MWCNTs and CuNWs, significantly increasing the heterogeneous contact area between the three fillers. This enhances the dipole polarization effect, optimizes impedance matching, and gives the composite membrane excellent electromagnetic shielding performance. When electromagnetic waves are incident on the composite membrane, the dielectric loss effect of HOOC-MWCNTs, the dielectric shielding effect of CuNWs, and the magnetic loss effect of NiFe2O4 work together to form a "magnetic-electric" synergistic effect. This causes the electromagnetic waves to be repeatedly scattered and absorbed on the uneven surface of the composite membrane, achieving a good shielding effect.

[0024] (3) The electromagnetic shielding nanofiber composite membrane provided in this application has a single-layer uniform filling structure, which makes it easier to control product quality in actual production, and can be formed by one-time filtration, making the preparation method simpler.

[0025] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0027] Figure 1 This is a flowchart illustrating the preparation process of electromagnetic shielding nanofiber composite films.

[0028] Figure 2 The surface microstructure of PVA-co-PE nanofibers when magnified 1000 times;

[0029] Figure 3 The surface microstructure of the electromagnetic shielding nanofiber composite film prepared in Example 1 is shown at 10,000x magnification.

[0030] Figure 4 The surface microstructure of the electromagnetic shielding nanofiber composite film prepared in Example 1 is shown at 1000x magnification.

[0031] Figure 5Electromagnetic shielding effectiveness diagrams of the composite membranes prepared in Example 1 and Comparative Examples 5-6, as well as the PVA-co-PE nanofiber membranes;

[0032] Figure 6 The mechanical properties of the composite membranes prepared in Example 1 and Comparative Examples 7-8, as well as the PVA-co-PE nanofiber membranes, are shown in the diagram. Detailed Implementation

[0033] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0035] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0036] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0037] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0038] In existing technologies, most electromagnetic shielding materials are designed as multi-layered structures, such as gradient-distributed multi-layered structures. By stacking composite material layers containing different fillers, electromagnetic shielding over a wider frequency range can be achieved; by stacking composite material layers with the same filler but gradually increasing filler content, interface differences can be reduced, reflectivity limited, and electromagnetic shielding performance improved. However, because these electromagnetic shielding materials are assembled through stacking, their mechanical properties still deviate, making them prone to slippage or cracking during use. How to simultaneously improve the electromagnetic interference shielding performance and mechanical properties of the material is a pressing technical challenge that needs to be addressed.

[0039] To address the aforementioned technical problems, this application provides an electromagnetic shielding nanofiber composite membrane and its preparation method. PVA-co-PE nanofibers are used as the substrate, and carboxylated carbon nanotubes (HOOC-MWCNT), copper nanowires (CuNWs), and nickel ferrite (NiFe2O4) are used as fillers. The fillers are uniformly loaded into the substrate through vacuum-assisted filtration, cross-linking, and hot pressing processes. The substrate and the three fillers overlap and adsorb to form a three-dimensional network porous structure, thus preparing a nanofiber composite membrane with excellent electromagnetic shielding and mechanical properties. The electromagnetic shielding effectiveness of this composite membrane reaches 59 dB, and the maximum tensile stress reaches 12 MPa.

[0040] Please refer to Figure 1 In a first aspect, embodiments of this application provide an electromagnetic shielding nanofiber composite film, comprising a three-dimensional framework substrate, and a conductive medium and a magnetic medium uniformly dispersed in the three-dimensional framework substrate. The conductive medium includes carboxylated carbon nanotubes and copper nanowires, and the magnetic medium includes nickel ferrite. The three-dimensional framework substrate accounts for 94-99% of the mass of the electromagnetic shielding nanofiber composite film, and the mass ratio of carboxylated carbon nanotubes, copper nanowires, and nickel ferrite is (1-2.5):(1-1.5):1.

[0041] Furthermore, the electromagnetic shielding nanofiber composite membrane uses PVA-co-PE nanofibers as a three-dimensional framework substrate. Carboxylated carbon nanotubes, copper nanowires, and nickel ferrite are uniformly loaded onto the PVA-co-PE nanofibers through vacuum-assisted filtration, cross-linking, and hot-pressing processes. The PVA-co-PE nanofibers, carboxylated carbon nanotubes, and copper nanowires interlock to form a three-dimensional network, giving the electromagnetic shielding nanofiber composite membrane a three-dimensional porous network structure. The nickel ferrite adheres to the copper nanowires and PVA-co-PE nanofibers, increasing the heterogeneous contact area and achieving the effects of reducing magnetic force and increasing electromagnetic wave scattering.

[0042] Furthermore, the thickness of the electromagnetic shielding nanofiber composite film is 20-30 μm, the electromagnetic shielding effectiveness reaches 59 dB, and the maximum tensile stress reaches 12 MPa.

[0043] Secondly, embodiments of this application provide a method for preparing the aforementioned electromagnetic shielding nanofiber composite film, comprising the following steps:

[0044] S1. Isopropanol, deionized water and PVA-co-PE nanofibers are uniformly mixed using a high-speed shearing machine to prepare a PVA-co-PE nanofiber suspension with a fiber content of 1 wt%.

[0045] S2, the PVA-co-PE nanofiber suspension prepared in step S1 is mixed with carboxylated carbon nanotubes, copper nanowires and nickel ferrite, stirred for 0.5-1 h, and vacuum-assisted filtration is performed to obtain a nanofiber composite membrane.

[0046] S3. The nanofiber composite membrane was immersed in glutaraldehyde crosslinking agent with a concentration of 1.5wt%, and crosslinked by ultraviolet light irradiation for 3-3.5h. Then it was naturally air-dried and hot-pressed to obtain electromagnetic shielding nanofiber composite membrane (PVA-co-PE / HOOC-MWCNTs / CuNWs / NiFe2O4).

[0047] Further, in step S2, PVA-co-PE nanofibers account for 94-99% of the mass of the nanofiber composite membrane, and the mass ratio of carboxylated carbon nanotubes to copper nanowires and nickel ferrite is (1-2.5):(1-1.5):1.

[0048] Further, in step S2, the preparation method of carboxylated carbon nanotubes is as follows: multi-walled carbon nanotubes are added to concentrated nitric acid, sonicated for 1-2 hours, then an appropriate amount of concentrated sulfuric acid is added, and the mixture is left to stand overnight at 55-65℃. After dilution with twice the volume of deionized water, the mixture is freeze-dried to obtain carboxylated carbon nanotube powder. Specifically, 1-1.2 g of multi-walled carbon nanotubes are added to every 50 mL of concentrated nitric acid, and the volume ratio of concentrated sulfuric acid to concentrated nitric acid is 1:3. The carboxylated carbon nanotubes have an inner diameter of 5-6 nm, an outer diameter of 15-16 nm, and a length of 10-11 μm.

[0049] Further, in step S2, the copper nanowires are prepared by reacting copper chloride, octadecylamine, and anhydrous glucose in a hydration reactor at a mass ratio of 1:1:(1.8-2.0) at 120°C for 8-9 hours. The copper nanowires have a diameter of 100-105 nm and a length of 10-11 μm.

[0050] Further, in step S2, the preparation method of nickel ferrite is as follows: nickel nitrate nonahydrate and ferric nitrate hexahydrate are reacted at 180℃ for 12-14h in a mass ratio of 1:(1-1.2) to obtain nickel ferrite with spinel structure and particle size of 30-35nm.

[0051] Furthermore, in step S3, the solvent for the glutaraldehyde crosslinking agent is anhydrous ethanol.

[0052] Further, in step S3, the hot pressing method is to sandwich the air-dried nanofiber composite film between two polyimide films, and then place them together in a hot press at 100-105°C for 60-65 seconds.

[0053] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0054] I. Preparation Method

[0055] In the embodiments provided in this application, the carboxylated carbon nanotubes have an inner diameter of 5 nm, an outer diameter of 15 nm, and a length of 10 μm; the copper nanowires have a diameter of 100 nm and a length of 10 μm; and the nickel ferrite has a particle size of 30 nm. The preparation methods for the three are as follows:

[0056] (1) Carboxylated carbon nanotubes (HOOC-MWCNTs): Mix 1g of multi-walled carbon nanotubes (MWCNTs) with 50mL of concentrated nitric acid and sonicate for 1.5h. Add concentrated sulfuric acid (the volume ratio of concentrated sulfuric acid to concentrated nitric acid is 1:3), place at 60℃ overnight, dilute with 2 times the volume of deionized water, and freeze dry.

[0057] (2) Copper nanowires (CuNWs): Copper chloride, octadecylamine and anhydrous glucose were reacted in a hydration reactor at 120°C for 8 hours in a mass ratio of 1:1:1.8;

[0058] (3) Nickel ferrite (NiFe2O4): Nickel nitrate nonahydrate and ferric nitrate hexahydrate were reacted at 180℃ for 12h in a mass ratio of 1:1.

[0059] Example 1

[0060] Example 1 provides a method for preparing an electromagnetic shielding nanofiber composite film, the specific steps of which are as follows:

[0061] S1. Isopropanol, deionized water and PVA-co-PE nanofibers were dispersed and mixed using a high-speed shearing machine to obtain a PVA-co-PE nanofiber suspension with a fiber content of 1 wt%.

[0062] S2, the PVA-co-PE nanofiber suspension prepared in step S1 is mixed with HOOC-MWCNTs, CuNWs and NiFe2O4 in a mass ratio of 10:0.05:0.05:0.05 and stirred for 0.5 h to obtain a multi-component suspension. The nanofiber composite membrane is obtained by vacuum-assisted filtration at 0.1 MPa.

[0063] S3. The nanofiber composite membrane prepared in step S4 is immersed in glutaraldehyde crosslinking agent with a concentration of 1.5wt% (solvent is anhydrous ethanol). The immersed nanofiber composite membrane is placed under ultraviolet radiation for crosslinking for 3 hours. It is carefully removed with tweezers and air-dried naturally. The air-dried composite membrane is clamped with a polyimide film and placed in a hot press at 105°C for 60 seconds to obtain an electromagnetic shielding nanofiber composite membrane.

[0064] Example 2 and Comparative Examples 1-2

[0065] The difference between Example 2 and Comparative Examples 1-2 and Example 1 is that the mass ratio of the magnetic medium and the conductive medium was changed, as shown in the table below. Other contents are roughly the same as in Example 1, and will not be repeated here.

[0066]

[0067]

[0068] Examples 3-5 and Comparative Examples 3-4

[0069] The difference between Examples 4-6 and Comparative Examples 1-3 and Example 1 is that the mass ratio of PVA-co-PE nanofibers was changed, as shown in the table below. Other contents are roughly the same as in Example 1 and will not be repeated here.

[0070] project <![CDATA[Mass ratio (PVA-co-PE: HOOC-MWCNTs: CuNWs: NiFe2O4)]]> Example 1 10：0.25：0.15：0.10 Comparative Example 3 4：0.25：0.15：0.10 Example 3 8：0.25：0.15：0.10 Example 4 12：0.25：0.15：0.10 Example 5 15：0.25：0.15：0.10 Comparative Example 4 20：0.25：0.15：0.10

[0071] Comparative Example 5

[0072] The difference between Comparative Example 5 and Example 1 is that, in step S2, the conductive medium CuNWs and the magnetic medium NiFe2O4 are not added, and the mass ratio of the substrate PVA-co-PE to the conductive medium HOOC-MWCNTs is 10:0.25. Other contents are roughly the same as in Example 1, and will not be repeated here.

[0073] Comparative Example 6

[0074] The difference between Comparative Example 6 and Example 1 is that, in step S2, the magnetic medium NiFe2O4 is not added, and the mass ratio of the substrate PVA-co-PE to the conductive media HOOC-MWCNTs and CuNWs is 10:0.25:0.15. Other contents are roughly the same as in Example 1, and will not be repeated here.

[0075] Comparative Example 7

[0076] The difference between Comparative Example 7 and Example 1 is that in step S2, the carboxylated carbon nanotube (HOOC-MWCNTs) powder is replaced with multi-walled carbon nanotubes (MWCNTs). That is, the nanofiber composite membrane is prepared by mixing PVA-co-PE nanofiber suspension with MWCNTs, CuNWs and NiFe2O4 in a mass ratio of 10:0.25:0.15:0.10. Other contents are roughly the same as in Example 1, and will not be repeated here.

[0077] Comparative Example 8

[0078] The difference between Comparative Example 8 and Example 1 is that, in step S3, no glutaraldehyde crosslinking agent is added, and the nanofiber composite membrane prepared in step S2 is directly placed under ultraviolet radiation for 30 minutes to obtain the nanofiber composite membrane. Other contents are roughly the same as in Example 1, and will not be repeated here.

[0079] Comparative Example 9

[0080] The difference between Comparative Example 9 and Example 1 lies in the alteration of the structure of the electromagnetic shielding nanofiber composite membrane. Specifically, in step S2, PVA-co-PE nanofibers, HOOC-MWCNTs, and CuNWs are first mixed to prepare suspension A, and then NiFe2O4 is prepared to prepare suspension B. Vacuum-assisted filtration is then performed at 0.1 MPa in the order of suspension A-suspension B-suspension A, resulting in a sandwich-layered structure for the prepared nanofiber composite membrane. PVA-co-PE / HOOC-MWCNTs / CuNWs form the outer layer, and NiFe2O4 forms the middle layer. Other aspects are largely the same as in Example 1 and will not be repeated here.

[0081] Comparative Example 10

[0082] The difference between Comparative Example 10 and Example 1 is that the hot pressing step is omitted in step S3. Instead, the nanofiber membrane obtained in step S2 is immersed in glutaraldehyde crosslinking agent, crosslinked by ultraviolet radiation, picked up with tweezers and air-dried to directly obtain an electromagnetic shielding nanofiber composite membrane. Other contents are roughly the same as in Example 1, and will not be repeated here.

[0083] II. Testing Methods

[0084] 1. Observe the surface morphology and microstructure.

[0085] The surface morphology and microstructure of the sample were observed using a thermal scanning electron microscope (SU5000). Specifically, the sample was cut into small pieces of 0.5cm*0.5cm, attached to the electron microscope stage with conductive adhesive, vacuum sputtered with gold for 120s, and then placed in the electron microscope for testing.

[0086] 2. Electromagnetic shielding performance test

[0087] (1) Resistivity and conductivity testing

[0088] The resistivity and conductivity at different locations of the sample were tested using an RTS-9 dual-electrical-measurement four-probe tester, and the average value was calculated to obtain the final result.

[0089] (2) Electromagnetic shielding effectiveness (EMI SE) test

[0090] The electromagnetic shielding effectiveness of the sample was tested using a ZNB-20 vector network analyzer with a test bandwidth of 8.12-12.5 GHz.

[0091] 3. Mechanical property testing

[0092] The mechanical properties of the sample were tested using an INSTRON 68TM-10 electronic universal testing machine. The sample was cut to a size of 2cm*0.5cm, and the tensile speed was set to 50mm / s. The test ended when the sample broke.

[0093] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0094] The surface morphology and microstructure of the electromagnetic shielding nanofiber composite film prepared in Example 1 were tested using test method 1 and compared with PVA-co-PE nanofibers.

[0095] Please see Figures 2 to 4 As shown, Figure 2 The surface microstructure of PVA-co-PE nanofibers when magnified 1000 times. Figure 3 The surface microstructure of the electromagnetic shielding nanofiber composite film prepared in Example 1 is shown at 10,000x magnification. Figure 4The image shows the surface microstructure of the electromagnetic shielding nanofiber composite film prepared in Example 1 at 1000x magnification. As can be seen, PVA-co-PE nanofibers provide a three-dimensional network substrate for the electromagnetic shielding nanofiber composite film. HOOC-MWCNTs, NiFe2O4, and CuNWs are uniformly distributed within the nanofibers. PVA-co-PE, HOOC-MWCNTs, and CuNWs overlap to form a unique three-dimensional network structure, giving the composite film a good porous structure. NiFe2O4 is tightly adhered to the three-dimensional network structure, forming a large-area heterostructure with the rod-shaped CuNWs and HOOC-MWCNTs. When electromagnetic waves are incident on the surface of this composite film, they are repeatedly scattered and absorbed on the heterostructure surface, achieving electromagnetic wave attenuation.

[0096] The electromagnetic shielding performance and mechanical properties of the composite films prepared in Examples 1-5 and Comparative Examples 1-4 were tested using test methods 2 and 3. The results are shown in the table below.

[0097]

[0098]

[0099] Please refer to the table above. It can be seen that the optimal electromagnetic shielding effect (59 dB) and mechanical properties (12 MPa) are achieved when the ratio of fillers (HOOC-MWCNTs, CuNWs, and NiFe2O4) is 0.25:0.15:0.10. This is because the modified carbon nanotubes contain a large number of carboxyl groups, which can form hydrogen bonds with PVA-co-PE, improving the mechanical properties of the composite film. Simultaneously, the tubular and linear structures of the carbon and copper nanomaterials effectively prevent agglomeration during film preparation, facilitating their uniform dispersion in the substrate. Furthermore, the carbon-copper composite exhibits superior electrical conductivity, and when mixed with NiFe2O4, which has an anti-spinel structure, it forms a "magnetic-electric" synergistic effect, enhancing the electromagnetic shielding performance of the film. When the content of HOOC-MWCNTs and CuNWs is too low, most of the NiFe2O4 is adsorbed on PVA-co-PE and does not contact HOOC-MWCNTs and CuNWs, making it difficult to form a heterogeneous structure, thus reducing the electromagnetic shielding performance of the composite film.

[0100] It can also be observed that increasing the mass ratio of the substrate (PVA-co-PE) leads to an initial increase followed by a decrease in the electromagnetic shielding performance and mechanical properties of the composite membrane. This is because when the substrate content is too high, the nanofiber slurry becomes too viscous, making it difficult to filter during preparation, resulting in poor film formation. Furthermore, the pores in the composite membrane are easily blocked by coarse fibers or viscous slurry, reducing the number of pores available for electromagnetic waves to enter and thus impairing the scattering effect. Conversely, when the substrate content is too low and there is too much dielectric filler, the substrate is insufficient to provide adequate three-dimensional structural support, resulting in a loose overall structure and poor mechanical properties in the composite membrane, making it prone to cracking during use. Additionally, excessive filler can cause it to stack, agglomerate, and distribute unevenly within the substrate, leading to poor shielding performance.

[0101] The electromagnetic shielding performance and mechanical properties of the nanofiber composite membranes prepared in Comparative Examples 5-10 were tested using the methods in Test Methods 2 and 3. The results are shown in the table below.

[0102]

[0103]

[0104] Please see Figure 5 As shown in the table above, and in conjunction with the data from Example 1 and Comparative Examples 5-6, it can be seen that the absence of NiFe2O4 and CuNWs, or even the absence of only CuNWs, in the filler reduces the electromagnetic shielding performance of the composite film, further illustrating the synergistic effect among the three fillers.

[0105] Please see Figure 6 As shown, and in conjunction with the data from Example 1 and Comparative Examples 7-8 in the table above, it can be seen that using unmodified carbon nanotubes (MWCNTs) or not adding a crosslinking agent will lead to a decrease in the mechanical properties of the composite film. This is because modified carbon nanotubes (HOOC-MWCNTs) have a large number of carboxyl functional groups, which need to form hydrogen bonds with the PVA-co-PE molecular chains through a crosslinking reaction to improve the mechanical properties of the composite film.

[0106] Please refer to the table above. By comparing the data of Comparative Example 9 with that of Example 1, it can be seen that the electromagnetic shielding performance and mechanical properties of the nanofiber composite membrane prepared in Comparative Example 9 are both poor. This is because NiFe2O4, as the intermediate layer alone, is not tightly integrated with the upper and lower layers, and cannot uniformly contact the other three raw materials to form a large number of heterogeneous interfaces. This indicates that the improvement of the composite membrane structure in this application significantly improves the electromagnetic shielding performance and mechanical properties of the membrane.

[0107] Referring to the table above, comparing the data of Comparative Example 10 with that of Example 1, it can be seen that the electromagnetic shielding performance and mechanical properties of the nanofiber composite membrane prepared in Comparative Example 10 are slightly lower. This is because hot pressing can squeeze out excess solvent from the composite membrane, accelerate the formation of hydrogen bonds between raw materials, and make its internal structure more compact, which is beneficial to improving electromagnetic shielding performance and mechanical properties.

[0108] In summary, this application uses PVA-co-PE as the substrate and HOOC-MWCNT, CuNWs, and NiFe2O4 as fillers. The fillers are uniformly loaded into the substrate through vacuum-assisted filtration, cross-linking, and hot pressing processes. The substrate and the three fillers overlap and adsorb to form a three-dimensional porous network structure, resulting in a nanofiber composite membrane with excellent electromagnetic shielding and mechanical properties. The porous structure promotes the scattering and absorption of electromagnetic waves by the composite membrane. The numerous heterogeneous contact surfaces formed by the uniform dispersion of the three fillers in the substrate increase the dipole polarization effect, optimize impedance matching, and enable the composite membrane to exhibit better electromagnetic attenuation and shielding performance. Furthermore, the HOOC-MWCNT obtained by modifying carbon nanotubes can form numerous hydrogen bonds with PVA-co-PE through cross-linking, improving the mechanical properties of the composite membrane.

[0109] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. An electromagnetic shielding nanofiber composite membrane, characterized in that: It includes a three-dimensional skeleton substrate, and a conductive medium and a magnetic medium uniformly dispersed in the three-dimensional skeleton substrate; the electromagnetic shielding nanofiber composite film has a three-dimensional network porous structure; the thickness of the electromagnetic shielding nanofiber composite film is 20-30μm, the electromagnetic shielding effectiveness reaches 59dB, and the maximum tensile stress reaches 12MPa; The conductive medium includes carboxylated carbon nanotubes and copper nanowires, and the magnetic medium includes nickel ferrite. The mass ratio of the carboxylated carbon nanotubes, copper nanowires, and nickel ferrite is (1-2.5):(1-1.5):

1. The electromagnetic shielding nanofiber composite film uses PVA-co-PE nanofibers as a three-dimensional framework substrate. The carboxylated carbon nanotubes, copper nanowires, and nickel ferrite are uniformly loaded into the PVA-co-PE nanofibers through vacuum-assisted filtration, cross-linking, and hot-pressing processes. The three-dimensional framework substrate accounts for 94-99% of the mass of the electromagnetic shielding nanofiber composite film.

2. The electromagnetic shielding nanofiber composite membrane according to claim 1, characterized in that: The PVA-co-PE nanofibers, carboxylated carbon nanotubes, and copper nanowires overlap to form a three-dimensional network porous structure.

3. A method for preparing the electromagnetic shielding nanofiber composite film according to any one of claims 1 to 2, characterized in that, Includes the following steps: S1, Isopropanol, deionized water and PVA-co-PE nanofibers were uniformly mixed using a high-speed shearing machine to prepare a PVA-co-PE nanofiber suspension with a fiber content of 1 wt%. S2, the PVA-co-PE nanofiber suspension prepared in step S1 is mixed with carboxylated carbon nanotubes, copper nanowires and nickel ferrite, stirred for 0.5-1 h, and vacuum-assisted filtration is performed to obtain a nanofiber composite membrane; the PVA-co-PE nanofibers account for 94-99% of the mass of the nanofiber composite membrane; the mass ratio of the carboxylated carbon nanotubes to the copper nanowires and the nickel ferrite is (1-2.5): (1-1.5): 1; S3, the nanofiber composite membrane is immersed in glutaraldehyde crosslinking agent with a concentration of 1.5wt%, crosslinked by ultraviolet light irradiation, then naturally air-dried and hot-pressed to obtain the electromagnetic shielding nanofiber composite membrane.

4. The method for preparing the electromagnetic shielding nanofiber composite film according to claim 3, characterized in that: In step S2, the method for preparing the carboxylated carbon nanotubes is as follows: multi-walled carbon nanotubes are mixed with concentrated nitric acid and sonicated for 1-2 hours, concentrated sulfuric acid is added, and the mixture is left overnight at 55-65°C. Then, twice the volume of deionized water is added for dilution, and the mixture is freeze-dried to obtain carboxylated carbon nanotube powder.

5. The method for preparing the electromagnetic shielding nanofiber composite film according to claim 4, characterized in that: In the preparation method of carboxylated carbon nanotubes, the volume ratio of concentrated sulfuric acid to concentrated nitric acid is 1:

3.

6. The method for preparing the electromagnetic shielding nanofiber composite film according to claim 3, characterized in that: In step S3, the hot pressing method is to sandwich the air-dried nanofiber composite film between two polyimide films and place them together in a hot press at 100-105°C for 60-65 seconds.

7. The method for preparing the electromagnetic shielding nanofiber composite film according to claim 6, characterized in that, In step S3, the crosslinking time under ultraviolet light irradiation is 3-3.5 hours.

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