Aramid nanofiber-based gradient structure composite electromagnetic shielding material and preparation method thereof

Abstract

The invention discloses an aramid nanofiber-based gradient structure composite electromagnetic shielding material and a preparation method thereof, and belongs to the technical field of electromagnetic shielding materials. Comprising an impedance matching layer, an electromagnetic absorption layer and an electromagnetic reflection layer which are stacked from top to bottom; wherein the material of the impedance matching layer comprises aramid nanofiber and Fe3O4; the electromagnetic absorption layer is made of aramid nanofibers and carbon nanotubes; and the electromagnetic reflecting layer is made of aramid nanofibers, polypyrrole and carbon nanotubes. According to the invention, an aramid polymer solution is used as an adhesive and gradient structure design is carried out, a magnetic material is introduced to promote electromagnetic wave incidence and reduce surface reflection, efficient attenuation of electromagnetic waves is realized through a continuous conductive network constructed by carbon nanotubes, and a strong reflection layer is formed by polypyrrole coated aramid nanofibers with a core-shell structure and the carbon nanotubes, so that the electromagnetic wave attenuation is improved. Therefore, the problems of poor mechanical property and insufficient electromagnetic shielding property of the composite electromagnetic shielding material are solved.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic shielding materials technology, specifically to an aramid nanofiber-based gradient structure composite electromagnetic shielding material and its preparation method. Background Technology

[0002] With the rapid development of highly integrated electronic systems, electromagnetic radiation interference and pollution have become serious problems in many fields such as wearable electronic devices, aerospace, and military. Therefore, electromagnetic interference shielding technology has emerged as a feasible way to effectively eliminate electromagnetic pollution.

[0003] The electromagnetic attenuation mechanism of electromagnetic shielding materials mainly relies on the reflection and absorption of incident electromagnetic waves. To effectively suppress the problem of secondary reflection of electromagnetic waves, it is necessary to develop new shielding materials with low reflection and high absorption characteristics. Through innovative structural design, combined with the introduction of new functional components and the synergistic control of electromagnetic parameters, a high-performance electromagnetic shielding film integrating structure and function can be constructed.

[0004] Although traditional metal-based shielding materials have high conductivity, their large mass, high density, poor mechanical properties, and poor corrosion resistance limit their ability to meet the requirements of the electronics and aerospace industries for materials to combat electromagnetic interference.

[0005] Polymer-based electromagnetic shielding materials have attracted widespread attention in the field of electromagnetic shielding due to their advantages such as light weight, excellent processing performance, good corrosion resistance, and adjustable electromagnetic parameters. Traditional conductive polymer composite materials are ideal materials that combine lightweight, flexibility, and electromagnetic shielding performance, but the distribution of fillers in the polymer matrix and high percolation value must be considered, and the conductivity and mechanical properties of the materials are not ideal. Aramid nanofibers (ANFs), with their high aspect ratio and high specific surface area, and surface rich in amide groups, can significantly enhance the interfacial interaction with conductive fillers. They also possess excellent mechanical properties, chemical stability, and heat resistance. Using ANFs as a polymer matrix and combining them with highly conductive fillers can effectively promote electromagnetic wave dissipation while maintaining good mechanical strength. Carbon nanotubes, as ideal conductive fillers, possess excellent flexibility, high conductivity, and good chemical stability. Furthermore, introducing magnetic materials into the polymer matrix can enhance the material's absorption capacity for incident electromagnetic waves. By constructing multilayer structures with gradient distributions, the synergistic effect of electrical and magnetic losses can be achieved, thereby significantly improving the overall shielding effectiveness of shielding materials. However, existing multilayer composite materials are mostly prepared using simple stacking assembly methods, resulting in poor mechanical properties. In addition, existing conductive-magnetic filler blends are prone to agglomeration and it is difficult to construct ordered gradient structures in three-dimensional space. Summary of the Invention

[0006] To address the aforementioned technical problems, the present invention aims to provide an aramid nanofiber-based gradient structure composite electromagnetic shielding material and its preparation method, thereby solving the problem of insufficient mechanical and electromagnetic shielding performance of existing aramid nanofiber composite electromagnetic shielding materials.

[0007] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: In a first aspect, the present invention provides an aramid nanofiber-based gradient structure composite electromagnetic shielding material, characterized in that it comprises an impedance matching layer, an electromagnetic absorption layer, and an electromagnetic reflection layer stacked from top to bottom; The impedance matching layer is composed of aramid nanofibers and Fe3O4. The electromagnetic absorption layer is composed of aramid nanofibers and carbon nanotubes. The electromagnetic reflective layer is composed of aramid nanofibers, polypyrrole, and carbon nanotubes.

[0008] The beneficial effects of this invention are as follows: the impedance matching layer, electromagnetic absorption layer, and electromagnetic reflection layer of the composite material are all based on aramid nanofibers, giving the material excellent mechanical properties. In the impedance matching layer, the introduction of magnetic Fe3O4 nanoparticles gives the material surface low conductivity, forming a good impedance match with the environment, effectively promoting electromagnetic wave incidentness and reducing surface reflection. In the electromagnetic absorption layer, the introduction of carbon nanotubes as fillers constructs a continuous conductive network, achieving efficient attenuation of electromagnetic waves through dielectric loss and conduction loss mechanisms. In the electromagnetic reflection layer, the introduction of polypyrrole-coated aramid nanofibers with a core-shell structure synergistically composites with carbon nanotubes to form a strong reflection layer with multiple reflection absorption effects, further attenuating and reflecting electromagnetic waves. This solves the problem that traditional multilayer aramid nanofiber-based composite materials, prepared using simple mixing methods, are difficult to form an ordered gradient structure, resulting in insufficient electromagnetic shielding performance.

[0009] Furthermore, the method for preparing the impedance matching layer includes the following steps: mixing Fe3O4 and aramid nanofiber dispersion to prepare an ANF / Fe3O4 mixture, and then performing vacuum filtration to obtain the desired solution; The preparation method of the electromagnetic absorption layer includes the following steps: mixing aramid nanofiber dispersion and carbon nanotubes to prepare ANF / Fe3O4 mixture, and then performing vacuum filtration to obtain the desired solution; The preparation method of the electromagnetic reflection layer includes the following steps: in-situ polymerization of aramid nanofiber dispersion, pyrrole and anhydrous iron chloride, then adding carbon nanotube dispersion and stirring to prepare ANF@PPy / CNT mixture, and finally vacuum filtration to obtain the final product.

[0010] The beneficial effects of adopting the above-mentioned further technical solutions are as follows: the present invention achieves good impedance matching between the material surface and the environment through the impedance matching layer, effectively promoting the incidence of electromagnetic waves and reducing surface reflection; through the dielectric loss and conduction loss mechanism of the electromagnetic absorption layer, the electromagnetic waves are attenuated efficiently; through the strong reflection effect of the electromagnetic reflection layer, the residual electromagnetic waves are reflected back into the material for multiple attenuations, thereby achieving further attenuation of electromagnetic waves.

[0011] Furthermore, an aramid polymer liquid is added as an interface adhesive between the impedance matching layer, the electromagnetic absorption layer, and the electromagnetic reflection layer; The aramid polymerization solution is prepared by mixing and stirring poly(p-phenylene terephthalamide), potassium hydroxide, dimethyl sulfoxide and deionized water.

[0012] The beneficial effects of adopting the above-mentioned further technical solutions are as follows: By using aramid polymer liquid as an interface adhesive, the present invention achieves molecular-level fusion between the impedance matching layer, electromagnetic absorption layer and electromagnetic reflection layer of the composite material, imparting structural stability, preventing interlayer delamination, and not introducing foreign impurities.

[0013] Furthermore, the mass-to-volume ratio of poly(p-phenylene terephthalamide), potassium hydroxide, dimethyl sulfoxide, and deionized water in the aramid polymerization solution is 0.5-2 g: 1-2 g: 400-500 mL: 10-30 mL.

[0014] A second aspect of the present invention provides a method for preparing the above-mentioned aramid nanofiber-based gradient structure composite electromagnetic shielding material, comprising the following steps: S1. First, mix and stir poly(p-phenylene terephthalamide), potassium hydroxide, dimethyl sulfoxide and deionized water to prepare aramid polymer solution, and then add deionized water to dissolve and prepare aramid nanofiber dispersion. S2. First, the aramid nanofiber dispersion, pyrrole and anhydrous iron chloride are polymerized in situ, and then carbon nanotube dispersion is added and stirred to prepare ANF@PPy / CNT mixture. S3. Prepare an ANF / Fe3O4 mixture by mixing Fe3O4 and aramid nano-dispersion; S4. Mix the aramid nanofiber dispersion and the carbon nanotube dispersion to prepare an ANF / CNT mixture; S5. Vacuum filter the ANF@PPy / CNT mixture, ANF / Fe3O4 mixture and ANF / CNT mixture respectively to prepare ANF@PPy / CNT wet membrane, ANF / Fe3O4 wet membrane and ANF / CNT wet membrane; S6. First, coat the upper and lower sides of the ANF / CNT wet film with aramid polymer liquid. Then, laminate the ANF / Fe3O4 wet film and the ANF@PPy / CNT wet film onto the upper and lower sides of the ANF / CNT wet film respectively. Finally, cure and hot press to obtain the aramid nanofiber-based gradient structure composite electromagnetic shielding material.

[0015] The beneficial effects of this invention are as follows: Using common poly(p-phenylene terephthalamide) as a raw material, the preparation cost is low; the preparation method is simple and the process is short; the content of conductive and magnetic nanomaterials in each layer can be quickly and accurately controlled according to requirements, resulting in a multi-layered gradient structure. Through vacuum filtration, the impedance matching layer's ANF densely coats Fe3O4 magnetic particles, forming a good impedance match with the environment, which helps electromagnetic waves transmit into the material's interior. The resulting hysteresis and eddy current losses effectively dissipate electromagnetic wave energy. The electromagnetic absorption layer's ANF and CNTs construct a conductive network structure, extending the electromagnetic wave transmission path and enhancing dielectric loss. The electromagnetic reflection layer's ANF@PPy core-shell structure and CNTs generate strong interfacial coupling and π-π conjugation effects, forming a high-density, highly conductive network. This not only improves conductivity but also reflects residual electromagnetic waves back into the material for multiple attenuations, thereby achieving highly efficient electromagnetic shielding performance.

[0016] Furthermore, in S1, the mass-to-volume ratio of poly(p-phenylene terephthalamide), potassium hydroxide, dimethyl sulfoxide, and deionized water in the aramid polymerization solution is 0.5-2 g: 1-2 g: 400-500 mL: 10-30 mL; the stirring time is 6-10 h; and the concentration of the aramid nanofiber dispersion is 1-3 mg / mL.

[0017] Preferably, in S1, the mass-to-volume ratio of poly(p-phenylene terephthalamide), potassium hydroxide, dimethyl sulfoxide, and deionized water in the aramid polymerization solution is 1 g: 1.5 g: 480 mL: 20 mL; the stirring time is 6 h; and the concentration of the aramid nanofiber dispersion is 2 mg / mL.

[0018] Furthermore, the mass-to-volume ratio of aramid nanofiber dispersion, pyrrole, and anhydrous ferric chloride in S2 is 10-30 mL: 1-2 mL: 500-800 mg.

[0019] Preferably, the mass-to-volume ratio of aramid nanofiber dispersion, pyrrole, and anhydrous ferric chloride in S2 is 20 mL: 1.68 mL: 672 mg.

[0020] Furthermore, the volume ratio of the in-situ polymerization product to the carbon nanotube dispersion in S2 is 10-30:1-3; the concentration of the carbon nanotube dispersion is 1-3 mg / mL.

[0021] Preferably, the volume ratio of the in-situ polymerization product to the carbon nanotube dispersion in S2 is 20:1-3; and the concentration of the carbon nanotube dispersion is 2 mg / mL.

[0022] Furthermore, the mass-to-volume ratio of Fe3O4 and aramid nano-dispersion in S3 is 10-25 g: 20-30 mL.

[0023] Preferably, the mass-to-volume ratio of Fe3O4 and aramid nano-dispersion in S3 is 12.5-21.43 g: 25 mL.

[0024] Furthermore, the volume ratio of the aramid nanofiber dispersion to the carbon nanotube dispersion in S4 is 10-30:1-3; the concentration of the carbon nanotube dispersion is 1-3 mg / mL.

[0025] Preferably, the volume ratio of aramid nanofiber dispersion to carbon nanotube dispersion in S4 is 20:1-3; the concentration of carbon nanotube dispersion is 2 mg / mL.

[0026] Furthermore, the curing temperature in S6 is room temperature, and the time is 30-90 min; the hot pressing temperature is 100-150℃, the pressure is 8-12 MPa, and the time is 1-5 min.

[0027] Preferably, the curing temperature in S6 is room temperature and the time is 60 min; the hot pressing temperature is 120 ℃, the pressure is 10 MPa, and the time is 3 min.

[0028] A third aspect of the present invention provides the application of the above-mentioned aramid nanofiber-based gradient structure composite electromagnetic shielding material in electromagnetic interference shielding.

[0029] The present invention has the following beneficial effects: 1. This invention uses common poly(p-phenylene terephthalamide) as raw material, which has low preparation cost, simple process, and short preparation process. It can quickly and accurately control the content of conductive and magnetic nanomaterials in each layer according to the requirements.

[0030] 2. This invention uses aramid polymer liquid as an interface adhesive to achieve molecular-level fusion between the impedance matching layer, electromagnetic absorption layer and electromagnetic reflection layer of the composite material, thereby giving structural stability, preventing interlayer delamination, and not introducing foreign impurities.

[0031] 3. In this invention, the impedance matching layer, electromagnetic absorption layer and electromagnetic reflection layer of the composite material are all based on aramid nanofibers, which gives the material excellent mechanical properties.

[0032] 4. This invention employs a multi-layered gradient structure, exhibiting strong electromagnetic wave absorption and effectively reducing secondary electromagnetic wave pollution. Magnetic Fe3O4 nanoparticles are introduced through an impedance matching layer, achieving excellent impedance matching between the material surface and the environment, effectively promoting electromagnetic wave incidence and reducing surface reflection. Carbon nanotubes introduced through an electromagnetic absorption layer construct a continuous conductive network, achieving efficient attenuation of electromagnetic waves through dielectric and conduction loss mechanisms. Furthermore, the introduction of polypyrrole-coated aramid nanofibers with a core-shell structure synergistically forms a strong reflective layer with multiple reflection and absorption effects, further attenuating and reflecting electromagnetic waves. Attached Figure Description

[0033] Figure 1 The image shows a photograph of the composite material prepared in Example 1, where (a) is the impedance matching layer and (b) is the electromagnetic reflection layer. Figure 2 The images show scanning electron microscope (SEM) images and energy dispersive spectroscopy (EDS) analysis diagrams of the impedance matching layer of the composite material prepared in Example 1. In the SEM image, (a) is the impedance matching layer, and (b)-(d) are the elemental distribution diagrams of C, O and Fe obtained by EDS analysis, respectively. Figure 3 The images shown are scanning electron microscope (SEM) images and energy dispersive spectroscopy (EDS) analysis diagrams of the electromagnetic reflective layer of the composite material prepared in Example 1. (a) is a scanning electron microscope image of the electromagnetic reflective layer, and (b)-(d) are the elemental distribution diagrams of C, O and Fe obtained by EDS analysis, respectively. Figure 4 The images show scanning electron microscope (SEM) images and energy dispersive spectroscopy (EDS) analysis diagrams of the cross-section of the composite material prepared in Example 1. In the images, (a) is a cross-sectional SEM image, and (b)-(d) are the elemental distribution diagrams of C, O and Fe obtained by EDS analysis, respectively. Figure 5 The diagram shows the total electromagnetic shielding effectiveness of the composite material prepared in Example 1; Figure 6 The overall electromagnetic shielding effectiveness of the composite material prepared in Comparative Example 1 is shown in the diagram. Figure 7 The diagram shows the overall electromagnetic shielding effectiveness of the composite material prepared for Comparative Example 2. Detailed Implementation

[0034] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer should be followed. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0035] Example 1: An aramid nanofiber-based gradient structure composite electromagnetic shielding material, characterized in that it comprises an impedance matching layer, an electromagnetic absorption layer, and an electromagnetic reflection layer stacked from top to bottom; The impedance matching layer is composed of aramid nanofibers and Fe3O4. The electromagnetic absorption layer is composed of aramid nanofibers and carbon nanotubes. The electromagnetic reflective layer is composed of aramid nanofibers, polypyrrole, and carbon nanotubes.

[0036] The preparation method of the above-mentioned aramid nanofiber-based gradient structure composite electromagnetic shielding material includes the following steps: S1. First, mix 1 g of poly(p-phenylene terephthalamide), 1.5 g of potassium hydroxide, 480 mL of dimethyl sulfoxide and 20 mL of deionized water and stir in a sealed container for 4 h to obtain an aramid polymer solution; then add deionized water to dissolve and obtain an aramid nanofiber dispersion with a concentration of 2 mg / mL.

[0037] S2. First, 20 mL of aramid nanofiber dispersion, 1.68 mL of pyrrole, and 672 mg of anhydrous ferric chloride were mixed and polymerized in situ to prepare ANF@PPy. Then, 2 mL of carbon nanotube dispersion was added and magnetically stirred to prepare ANF@PPy / CNT mixture. The carbon nanotube dispersion was prepared by mixing 0.2 g of single-walled carbon nanotubes, 0.5 g of sodium dodecylbenzenesulfonate, and 100 mL of deionized water, and then treating with ultrasound at 600 W for 2 h, with a concentration of 2 mg / mL.

[0038] S3. Mix 17.5 mg Fe3O4 and 25 mL aramid nano-dispersion and ultrasonically disperse to obtain ANF / Fe3O4 mixture.

[0039] S4. Add 2 mL of carbon nanotube dispersion to 20 mL of aramid nanofiber dispersion and magnetically stir to obtain ANF / CNT mixture; wherein, the carbon nanotube dispersion is obtained by mixing 0.2 g of single-walled carbon nanotubes, 0.5 g of sodium dodecylbenzenesulfonate and 100 mL of deionized water and treating with ultrasound at 600 W for 2 h, with a concentration of 2 mg / mL.

[0040] S6. Vacuum filter the ANF@PPy / CNT mixture, ANF / Fe3O4 mixture, and ANF / CNT mixture respectively to prepare ANF@PPy / CNT wet membrane, ANF / Fe3O4 wet membrane, and ANF / CNT wet membrane.

[0041] S7. Using the ANF / CNT wet film as the electromagnetic absorption layer, aramid polymer liquid is uniformly coated on its upper and lower sides as an adhesive. Then, the ANF / Fe3O4 wet film as the impedance matching layer and the ANF@PPy / CNT wet film as the electromagnetic reflection layer are respectively laminated on the upper and lower sides of the ANF / CNT wet film. After being dried and cured at room temperature for 1 h, it is hot-pressed at 120 ℃ and 10 MPa for 3 min to obtain the aramid nanofiber-based gradient structure composite electromagnetic shielding material (actual photo as shown). Figure 1 (As shown).

[0042] Example 2: An aramid nanofiber-based gradient structure composite electromagnetic shielding material, characterized in that it comprises an impedance matching layer, an electromagnetic absorption layer, and an electromagnetic reflection layer stacked from top to bottom; The impedance matching layer is composed of aramid nanofibers and Fe3O4. The electromagnetic absorption layer is composed of aramid nanofibers and carbon nanotubes. The electromagnetic reflective layer is composed of aramid nanofibers, polypyrrole, and carbon nanotubes.

[0043] The preparation method of the above-mentioned aramid nanofiber-based gradient structure composite electromagnetic shielding material includes the following steps: S1. First, mix 1 g of poly(p-phenylene terephthalamide), 1.5 g of potassium hydroxide, 480 mL of dimethyl sulfoxide and 20 mL of deionized water and stir in a sealed container for 4 h to obtain an aramid polymer solution; then add deionized water to dissolve and obtain an aramid nanofiber dispersion with a concentration of 2 mg / mL.

[0044] S2. First, 20 mL of aramid nanofiber dispersion, 1.68 mL of pyrrole, and 672 mg of anhydrous ferric chloride were mixed and polymerized in situ to prepare ANF@PPy. Then, 1 mL of carbon nanotube dispersion was added and magnetically stirred to prepare ANF@PPy / CNT mixture. The carbon nanotube dispersion was prepared by mixing 0.2 g of single-walled carbon nanotubes, 0.5 g of sodium dodecylbenzenesulfonate, and 100 mL of deionized water, and then treating with ultrasound at 600 W for 2 h, with a concentration of 2 mg / mL.

[0045] S3. Mix 12.5 mg Fe3O4 and 25 mL aramid nano-dispersion and ultrasonically disperse to obtain ANF / Fe3O4 mixture.

[0046] S4. Add 2 mL of carbon nanotube dispersion to 20 mL of aramid nanofiber dispersion and magnetically stir to obtain ANF / CNT mixture; wherein, the carbon nanotube dispersion is obtained by mixing 0.2 g of single-walled carbon nanotubes, 0.5 g of sodium dodecylbenzenesulfonate and 100 mL of deionized water and treating with ultrasound at 600 W for 2 h, with a concentration of 2 mg / mL.

[0047] S6. Vacuum filter the ANF@PPy / CNT mixture, ANF / Fe3O4 mixture, and ANF / CNT mixture respectively to prepare ANF@PPy / CNT wet membrane, ANF / Fe3O4 wet membrane, and ANF / CNT wet membrane.

[0048] S7. Using the ANF / CNT wet film as the electromagnetic absorption layer, aramid polymer liquid is uniformly coated on its upper and lower sides as an adhesive. Then, the ANF / Fe3O4 wet film as the impedance matching layer and the ANF@PPy / CNT wet film as the electromagnetic reflection layer are respectively laminated on the upper and lower sides of the ANF / CNT wet film. After being placed at room temperature to dry and cure for 1 h, it is hot-pressed at 120 ℃ and 10 MPa for 3 min to obtain the aramid nanofiber-based gradient structure composite electromagnetic shielding material.

[0049] Example 3: An aramid nanofiber-based gradient structure composite electromagnetic shielding material, characterized in that it comprises an impedance matching layer, an electromagnetic absorption layer, and an electromagnetic reflection layer stacked from top to bottom; The impedance matching layer is composed of aramid nanofibers and Fe3O4. The electromagnetic absorption layer is composed of aramid nanofibers and carbon nanotubes. The electromagnetic reflective layer is composed of aramid nanofibers, polypyrrole, and carbon nanotubes.

[0050] The preparation method of the above-mentioned aramid nanofiber-based gradient structure composite electromagnetic shielding material includes the following steps: S1. First, mix 1 g of poly(p-phenylene terephthalamide), 1.5 g of potassium hydroxide, 480 mL of dimethyl sulfoxide and 20 mL of deionized water and stir in a sealed container for 4 h to obtain an aramid polymer solution; then add deionized water to dissolve and obtain an aramid nanofiber dispersion with a concentration of 2 mg / mL.

[0051] S2. First, 20 mL of aramid nanofiber dispersion, 1.68 mL of pyrrole, and 672 mg of anhydrous ferric chloride were mixed and polymerized in situ to prepare ANF@PPy. Then, 3 mL of carbon nanotube dispersion was added and magnetically stirred to prepare ANF@PPy / CNT mixture. The carbon nanotube dispersion was prepared by mixing 0.2 g of single-walled carbon nanotubes, 0.5 g of sodium dodecylbenzenesulfonate, and 100 mL of deionized water, and then treating with ultrasound at 600 W for 2 h, with a concentration of 2 mg / mL.

[0052] S3. Mix 21.43 mg Fe3O4 and 25 mL aramid nano-dispersion and ultrasonically disperse to obtain ANF / Fe3O4 mixture.

[0053] S4. Add 3 mL of carbon nanotube dispersion to 20 mL of aramid nanofiber dispersion and stir magnetically to obtain ANF / CNT mixture; wherein, the carbon nanotube dispersion is prepared by mixing 0.2 g of single-walled carbon nanotubes, 0.5 g of sodium dodecylbenzenesulfonate and 100 mL of deionized water and treating with ultrasound at 600 W for 2 h, with a concentration of 2 mg / mL.

[0054] S6. Vacuum filter the ANF@PPy / CNT mixture, ANF / Fe3O4 mixture, and ANF / CNT mixture respectively to prepare ANF@PPy / CNT wet membrane, ANF / Fe3O4 wet membrane, and ANF / CNT wet membrane.

[0055] S7. Using the ANF / CNT wet film as the electromagnetic absorption layer, aramid polymer liquid is uniformly coated on its upper and lower sides as an adhesive. Then, the ANF / Fe3O4 wet film as the impedance matching layer and the ANF@PPy / CNT wet film as the electromagnetic reflection layer are respectively laminated on the upper and lower sides of the ANF / CNT wet film. After being placed at room temperature to dry and cure for 1 h, it is hot-pressed at 120 ℃ and 10 MPa for 3 min to obtain the aramid nanofiber-based gradient structure composite electromagnetic shielding material.

[0056] Comparative Example 1: A method for preparing an aramid nanofiber-based composite electromagnetic shielding material includes the following steps: S1. First, mix 1 g of poly(p-phenylene terephthalamide), 1.5 g of potassium hydroxide, 480 mL of dimethyl sulfoxide and 20 mL of deionized water and stir in a sealed container for 4 h to obtain an aramid polymer solution; then add deionized water to dissolve and obtain an aramid nanofiber dispersion with a concentration of 2 mg / mL.

[0057] S2. Mix 0.2 g of single-walled carbon nanotubes, 0.5 g of sodium dodecylbenzenesulfonate and 100 mL of deionized water, and treat with ultrasound at 600 W for 2 h to obtain a carbon nanotube dispersion with a concentration of 2 mg / mL.

[0058] S3. Add 4 mL of carbon nanotube dispersion to 60 mL of aramid nanofiber dispersion and stir magnetically to obtain ANF / CNT mixture.

[0059] S4. Prepare an ANF / CNT wet membrane by vacuum filtration of the ANF / CNT mixture.

[0060] S6. Place the ANF / CNT wet film in a vacuum drying oven at 70 °C and dry overnight to cure, thus obtaining the aramid nanofiber-based composite electromagnetic shielding material.

[0061] Comparative Example 2: A method for preparing an aramid nanofiber-based composite electromagnetic shielding material includes the following steps: S1. First, mix 1 g of poly(p-phenylene terephthalamide), 1.5 g of potassium hydroxide, 480 mL of dimethyl sulfoxide and 20 mL of deionized water and stir in a sealed container for 4 h to obtain an aramid polymer solution; then add deionized water to dissolve and obtain an aramid nanofiber dispersion with a concentration of 2 mg / mL.

[0062] S2. ANF@PPy was prepared by in-situ polymerization of 20 mL of aramid nanofiber dispersion, 1.68 mL of pyrrole and 672 mg of anhydrous ferric chloride. Then, 2 mL of carbon nanotube dispersion was added and mixed to obtain ANF@PPy / CNT mixture.

[0063] S3. Mix 21.43 mg Fe3O4 and 20 mL aramid nano-dispersion and ultrasonically disperse to obtain ANF / Fe3O4 mixture.

[0064] S4. Add 2 mL of carbon nanotube dispersion to 20 mL of aramid nanofiber dispersion and magnetically stir to obtain ANF / CNT mixture. The carbon nanotube dispersion is prepared by mixing 0.2 g of single-walled carbon nanotubes, 0.5 g of sodium dodecylbenzenesulfonate and 100 mL of deionized water and treating with ultrasound at 600 W for 2 h, with a concentration of 2 mg / mL.

[0065] S3. Mix and stir the above three mixtures of ANF@PPy / CNT, ANF / Fe3O4 and ANF / CNT, and then filter under vacuum to obtain a wet film of ANF@PPy / CNT / Fe3O4.

[0066] S4. After the ANF@PPy / CNT / Fe3O4 wet film is dried and cured at room temperature for 1 h, it is hot-pressed at 120 ℃ and 10 MPa for 3 min to obtain the aramid nanofiber-based composite electromagnetic shielding material.

[0067] Experimental example: The aramid nanofiber-based composite electromagnetic shielding materials prepared in Example 1 and Comparative Examples 1-2 were characterized, including SEM characterization, electromagnetic shielding performance characterization, and mechanical property characterization.

[0068] Test method: In this experiment, a German ZEISS Sigma 300 scanning electron microscope was used to characterize the material morphology, with an accelerating voltage of 3 kV-10 kV. During characterization, the sample was fixed to the sample stage with conductive tape. For cross-sectional SEM characterization, the material was cut into a flat section and then fixed on both sides with conductive tape. For samples with poor conductivity, gold sputtering was performed before characterization.

[0069] In this experimental example, an E5071C vector network analyzer was used to test the electromagnetic shielding performance of the composite material in the X-band (8.2-12.4 GHz). The waveguide method was used to test the S-parameters. During testing, the sample under test was clamped in the middle of a waveguide, ensuring the sample completely covered the waveguide openings for measurement. The scattering parameters (S...) were measured... 11 and S 21 or S 22 and S 12 This is used to reflect the electromagnetic shielding performance of a material.

[0070] In this experiment, a C610 intelligent electronic tensile testing machine was used to test the mechanical properties of the composite material. The samples were uniformly cut into strips of 30 mm × 5 mm. A film thickness gauge was used to measure the sample thickness. The samples were placed on both sides of the mechanical property testing machine fixtures to ensure they were under tension, and the gauge length was measured. The testing speed for all samples was 1 mm / min. -1 To ensure the accuracy of the test results, five samples were tested and the average value was taken.

[0071] The experimental results are shown in Table 1 and Figures 2 to 7 As shown.

[0072] Table 1 Performance Characterization

[0073] As shown in Table 1, the aramid nanofiber-based composite electromagnetic shielding material prepared in the embodiments of the present invention has excellent electromagnetic shielding ability, with an electromagnetic shielding efficiency of 41 dB. It also has excellent mechanical properties, with a tensile strength of 75 MPa, which is significantly better than that of the homogeneous structures in Comparative Examples 1 and 2.

[0074] like Figure 2 As shown in the figure, the impedance matching layer ANF / Fe3O4 film prepared in Example 1 exhibits a dense and horizontal morphology, with Fe elements uniformly distributed and completely covering the experimental area, indicating that Fe3O4 has good encapsulation properties in ANF. The strong van der Waals forces between CNTs and the strong hydrogen bonds between ANF molecules were successfully overcome through ultrasonic-shear synergistic dispersion, achieving uniform dispersion of both at the micro-nano scale, forming a homogeneous, randomly arranged nanofiber conductive network. Figure 3 As shown, the surface of the electromagnetic reflection layer ANF@PPy / CNT film is dense and flat. By in-situ polymerization of polypyrrole on ANF, the ANF@PPy core-shell structure is constructed, which generates a strong interfacial coupling and π-π conjugation effect with CNT, effectively reducing the interfacial contact resistance and promoting an efficient electron transport path. Figure 4 The image shows the morphology of the composite material cross-section. Through vacuum filtration, the surface layer of ANF densely coats Fe3O4 magnetic particles, effectively dissipating electromagnetic wave energy through hysteresis and eddy current losses. The electromagnetic absorption layer, consisting of ANF and CNTs, forms a conductive network; its porous internal structure extends the electromagnetic wave transmission path and enhances dielectric loss. The electromagnetic reflection layer, with its ANF@PPy core-shell structure, exhibits strong interfacial coupling and π-π conjugation effects with the CNTs, forming a high-density conductive network. This not only improves conductivity but also reflects residual electromagnetic waves back into the material for multiple attenuations, achieving highly efficient electromagnetic shielding. This invention uses aramid polymer as an interlayer binder. During coating and curing, the oligomeric molecular chains in the polymer effectively penetrate into the ANF network and interpenetrate and diffuse with the molecular chains on the ANF surface, forming a high-density hydrogen bond network at the interface. This avoids phase separation caused by differences in chemical structure, significantly improving the overall mechanical properties of the ANF-based multilayer composite material and greatly enhancing its electromagnetic shielding performance.

[0075] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An aramid nanofiber-based gradient structure composite electromagnetic shielding material, characterized in that, The gradient structure composite electromagnetic shielding material comprises an impedance matching layer, an electromagnetic absorption layer and an electromagnetic reflection layer which are stacked from top to bottom. The constituting material of the impedance matching layer comprises aramid nanofiber and Fe3O4. The constituting material of the electromagnetic absorption layer comprises aramid nanofiber and carbon nanotube. The constituting material of the electromagnetic reflection layer comprises aramid nanofiber, polypyrrole and carbon nanotube.

2. The aramid nanofiber-based gradient structured composite electromagnetic shielding material according to claim 1, characterized in that, The preparation method of the impedance matching layer comprises the following steps: mixing Fe3O4 and aramid nanofiber dispersion liquid to prepare ANF / Fe3O4 mixed liquid, and then performing vacuum filtration to prepare the impedance matching layer. The preparation method of the electromagnetic absorption layer comprises the following steps: mixing aramid nanofiber dispersion liquid and carbon nanotube to prepare ANF / Fe3O4 mixed liquid, and then performing vacuum filtration to prepare the electromagnetic absorption layer. The preparation method of the electromagnetic reflection layer comprises the following steps: in-situ polymerization of aramid nanofiber dispersion liquid, pyrrole and anhydrous ferric chloride, then adding carbon nanotube dispersion liquid for stirring to prepare ANF@PPy / CNT mixed liquid, and finally performing vacuum filtration to prepare the electromagnetic reflection layer.

3. The aramid nanofiber-based gradient structured composite electromagnetic shielding material according to claim 1, characterized in that, The aramid polymer liquid is added between the impedance matching layer, the electromagnetic absorption layer and the electromagnetic reflection layer as an interface adhesive. The aramid polymer liquid is prepared by mixing and stirring poly-p-phenyleneterephthalamide, potassium hydroxide, dimethyl sulfoxide and deionized water.

4. The method of producing aramid nanofiber-based gradient structure composite electromagnetic shielding material according to any one of claims 1 to 3, characterized in that, The method comprises the following steps: S1, first mixing and stirring poly-p-phenyleneterephthalamide, potassium hydroxide, dimethyl sulfoxide and deionized water to prepare aramid polymer liquid, and then adding deionized water for defibration to prepare aramid nanofiber dispersion liquid; S2, first in-situ polymerization of aramid nanofiber dispersion liquid, pyrrole and anhydrous ferric chloride, then adding carbon nanotube dispersion liquid for stirring to prepare ANF@PPy / CNT mixed liquid; S3, mixing Fe3O4 and aramid nanofiber dispersion liquid to prepare ANF / Fe3O4 mixed liquid; S4, mixing aramid nanofiber dispersion liquid and carbon nanotube dispersion liquid to prepare ANF / CNT mixed liquid; S5, vacuum filtration of the above ANF@PPy / CNT mixed liquid, ANF / Fe3O4 mixed liquid and ANF / CNT mixed liquid to prepare ANF@PPy / CNT wet film, ANF / Fe3O4 wet film and ANF / CNT wet film; S6, first coating aramid polymer liquid on the upper and lower sides of the ANF / CNT wet film, then laminating the ANF / Fe3O4 wet film and the ANF@PPy / CNT wet film on the upper and lower sides of the ANF / CNT wet film respectively, and finally curing and hot pressing to prepare the aramid nanofiber-based gradient structure composite electromagnetic shielding material.

5. The preparation method of the aramid nanofiber-based gradient structure composite electromagnetic shielding material according to claim 4, characterized in that, In S1, the mass-volume ratio of poly-p-phenyleneterephthalamide, potassium hydroxide, dimethyl sulfoxide and deionized water in the aramid polymer liquid is 0.5-2 g:1-2 g:400-500 mL:10-30 mL; the stirring time is 6-10 h; and the concentration of the aramid nanofiber dispersion liquid is 1-3 mg / mL.

6. The method for preparing the aramid nanofiber-based gradient structure composite electromagnetic shielding material according to claim 4, characterized in that, The mass-volume ratio of aramid nanofiber dispersion, pyrrole and anhydrous ferric chloride in S2 is 10-30 mL: 1-2 mL: 300-800 mg; the volume ratio of in-situ polymerization product and carbon nanotube dispersion is 10-30: 1-3; the concentration of carbon nanotube dispersion is 1-3 mg / mL.

7. The method for preparing the aramid nanofiber-based gradient structure composite electromagnetic shielding material according to claim 4, characterized in that, The mass-volume ratio of Fe3O4 and aramid nanometer dispersion in S3 is 10-25 g: 20-30 mL.

8. The method for preparing the aramid nanofiber-based gradient structure composite electromagnetic shielding material according to claim 4, characterized in that, The volume ratio of aramid nanofiber dispersion and carbon nanotube dispersion in S4 is 10-30: 1-3; the concentration of carbon nanotube dispersion is 1-3 mg / mL. 9.The method of claim 4, wherein the aramid nanofiber-based gradient structure composite electromagnetic shielding material is prepared by the steps of, The temperature of the curing treatment in S6 is room temperature, and the time is 30-90 min; the temperature of the hot pressing is 100-150 ℃, the pressure is 8-12 MPa, and the time is 1-5 min.

10. The application of aramid nanofiber-based gradient structure composite electromagnetic shielding material in electromagnetic interference shielding according to any one of claims 1-3.

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