Polyaniline / polyisophthaloyl metaphenylene diamine electromagnetic shielding material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of electromagnetic shielding materials, and relates to a polyaniline / polyisophthaloyl metaphenylene diamine electromagnetic shielding material as well as a preparation method and application thereof. The method comprises the following steps: respectively preparing polyisophthaloyl metaphenylene diamine short fibers and polyaniline into solutions, mixing the two solutions to obtain a spinning solution, then carrying out electrostatic spinning on the spinning solution to prepare a PANI / PMIA fiber membrane, putting the prepared PANI / PMIA fiber membrane into an aniline solution, and adding an oxidizing agent to carry out in-situ polymerization reaction to obtain the electromagnetic shielding material. The method is based on an electrostatic spinning technology and a seed effect assisted in-situ polymerization strategy, PMIA is used as a matrix of a material, a PANI core-shell dual structure is constructed, penetration of PANI molecular chains in a core-shell dual-phase system is achieved, and then the PANI loading capacity of a single nanofiber is improved. Meanwhile, through the acting force between PANI and aniline molecules, the bonding strength between core-shell interfaces is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electromagnetic shielding materials, and particularly relates to a polyaniline / poly-m-phenylene isophthalamide electromagnetic shielding material and a preparation method and application thereof. BACKGROUND

[0002] Under the background of the continuous expansion of the fifth generation mobile communication technology (5G) and subsequent evolution standards (6G) to the GHz frequency band, along with the popularization of wearable devices, electromagnetic wave radiation pollution problems are increasingly prominent. Electromagnetic shielding materials not only need to have excellent electromagnetic wave attenuation ability in actual use, but also need to be able to withstand the heat generated in the process of electromagnetic wave energy conversion, so as to ensure the stability and reliability of long-term use in high temperature environment. The traditional electromagnetic shielding materials using polymers (such as polyester, polyurethane, polypropylene, polyethylene, etc.) as the matrix often have insufficient thermal stability and are difficult to meet this demand, especially in high temperature or extreme environment, which is prone to thermal degradation, resulting in significant performance decline. Therefore, for the application scenarios of flexible electronic devices, it is urgent to break through the technical bottleneck of simultaneous optimization of multiple performance indicators such as lightweight, heat resistance, high-efficiency electromagnetic shielding performance and long-term stability.

[0003] The amide bond (-CONH-) and benzene ring structure in the molecular chain of poly-m-phenylene isophthalamide (PMIA) endow the material with excellent thermal stability, high mechanical strength, flame retardance and chemical stability, which can maintain stable performance in harsh environments such as high temperature, strong acid and strong base. PMIA fibers have been widely used in high temperature filtration, transportation and flame retardant protection fields. However, there is no electromagnetic shielding PMIA film on the market.

[0004] Traditional metal-based shielding materials have ideal conductive properties, but their inherent high density, rigid structure and corrosion resistance defects make it difficult to meet the integration needs of modern miniaturized electronic devices. Carbon nanotubes and graphene are also common electromagnetic shielding materials, but they are difficult to mass-produce and very expensive. Polyaniline (PANI) as a typical intrinsic conductive polymer can realize wide-range conductive regulation from insulating state to metallic state through molecular doping mechanism, and its synthesis process is simple, low in cost, low in density and resistant to corrosion and oxidation, which can not only build a continuous conductive network to enhance the electromagnetic performance of composite materials, but also can be used as a functional additive to improve the shielding efficiency of non-conductive systems.

[0005] At present, different structures of PANI composites have been developed, and the common method is to mix PANI with other materials. However, PANI as a functional filler is usually randomly distributed in the composite material, and the physical barrier effect of the matrix on the conductive path significantly reduces the conductive continuity of the composite material, which forces the material to increase the thickness or increase the filler load ratio to meet the electromagnetic shielding efficiency requirement, but this often leads to problems such as the decrease of material flexibility and mechanical properties, which restricts its application in precision flexible equipment. In order to solve this problem, many developers directly perform in-situ polymerization of aniline (ANI) monomer or PANI coating on the surface of the substrate to establish a continuous conductive network. However, the coating process easily leads to an ideal interface interaction between PANI and the substrate, which causes the PANI coating to easily peel off under mechanical deformation, thereby affecting the stability of the electromagnetic shielding performance, etc., and the in-situ polymerization of ANI monomer on the surface of the substrate will result in a stronger interface interaction between the obtained PANI composites.

[0006] A Chinese patent application with publication number CN119956612A discloses a CA / MWCNTs / PANI electromagnetic shielding film and a preparation method thereof. The electromagnetic shielding film is composed of cellulose acetate and multi-walled carbon nanotubes as electrostatic spinning precursors, combined with in-situ polymerized polyaniline. However, cellulose acetate is not acid-resistant, resulting in a short polymerization time (1.5 h) and a limited PANI layer. In addition, carbon nanotubes are prone to agglomeration, and the spinning process often occurs a needle blockage phenomenon, making it difficult to spin. Moreover, the carbon nanotubes exist in the form of dispersed particles in the electrostatic spinning precursor and are not soluble, which can easily lead to fiber breakage and poor mechanical properties when mixed with cellulose acetate.

[0007] A Chinese patent with publication number CN116676782B discloses a preparation method of a flexible PANI / biomass carbon electromagnetic shielding material. Pure cotton fabric and linen fabric are carbonized at high temperature to obtain a biomass carbon matrix, and a flexible wearable electronic device electromagnetic shielding material is prepared on the surface of the biomass carbon matrix by chemical oxidation. However, the material prepared by this method has weak mechanical properties, and the biomass carbon matrix prepared by carbonizing the fabric at high temperature is prone to carbon powder falling, which will affect the subsequent practical application.

[0008] Chinese patent application CN115110344A discloses a cellulose-PANI electromagnetic shielding composite paper and its preparation method. Wood is processed to form a cellulose skeleton, and PANI is polymerized in situ on the surface of the cellulose skeleton. Finally, the electromagnetic shielding composite paper is obtained through washing, rolling, and air drying. Chinese patent application CN106589938A discloses a bamboo fiber-doped PANI electromagnetic shielding material and its preparation method, using an in-situ chemical oxidation polymerization method to coat PANI onto the surface of bamboo fibers of different sizes. However, in the above materials, the core material for electromagnetic shielding is PANI, which only remains on the fiber surface. The core material is limited, and the electromagnetic shielding performance can only be improved by increasing the thickness of the surface PANI, which often sacrifices the material's thickness advantage. Summary of the Invention

[0009] To address the limitations of existing technologies that directly polymerize ANI monomers on substrate surfaces to produce PANI shells with limited quantity and generally poor conductivity, the primary objective of this invention is to provide a method for preparing polyaniline / poly(m-phenylene isophthalamide) electromagnetic shielding materials. This method utilizes electrospinning technology and a seed-effect-assisted in-situ polymerization strategy, using PMIA as the material matrix to construct a PANI core-shell dual-phase structure. This achieves the interconnection of PANI molecular chains within the core-shell dual-phase system, thereby increasing the PANI loading of individual nanofibers. Simultaneously, the intermolecular forces between PANI and aniline molecules enhance the bonding strength at the core-shell interface.

[0010] Another object of the present invention is to provide a polyaniline / polyisophthaloylm-phenylenediamine electromagnetic shielding material prepared by the above method.

[0011] Another object of the present invention is to provide the application of the above-mentioned polyaniline / polyisophthaloylm-phenylenediamine electromagnetic shielding material.

[0012] The objective of this invention is achieved through the following technical solution: A method for preparing a polyaniline / poly(m-phenylene isophthalamide) electromagnetic shielding material includes the following steps: (1) After preparing solutions of poly(m-phenylene isophthalamide) short fibers and polyaniline (PANI) respectively, the two solutions are mixed to obtain a spinning solution, and then the spinning solution is electrospun to obtain a PANI / PMIA fiber membrane. (2) Place the PANI / PMIA fiber membrane in an aniline (ANI) solution and let it stand so that ANI is evenly adsorbed on the fiber membrane. Then add an oxidant to carry out an in-situ polymerization reaction. After the reaction is completed, take out the membrane, wash and dry it to obtain a nanofiber membrane with PANI / PMIA core and PANI shell, which is the polyaniline / polyisophthaloylm-phenylenediamine electromagnetic shielding material.

[0013] Preferably, the length of the poly(m-phenylene isophthalamide) short fiber in step (1) is 20-50 mm; the polyaniline is intrinsic polyaniline.

[0014] Preferably, in step (1), the poly(m-phenylene isophthalamide) short fibers are dissolved in a mixed solvent of N,N-dimethylacetamide / lithium chloride (DMAc / LiCl), and then heated and stirred at 60-90 °C for 24-72 h to obtain a PMIA solution; the polyaniline is dissolved in a mixed solution of pyrrolidine (THP) and N-methylpyrrolidone (NMP), and stirred at room temperature for 6-12 h to obtain a PANI solution.

[0015] More preferably, in the N,N-dimethylacetamide / lithium chloride mixed solvent, the mass fraction of LiCl is 2 wt%; in the mixed solution of pyrrolidine and N-methylpyrrolidone, the mass fraction of pyrrolidine is 2 wt% and the mass fraction of N-methylpyrrolidone is 98 wt%.

[0016] Preferably, the mass ratio of poly(m-phenylene isophthalamide) to polyaniline in the spinning solution in step (1) is (1~9):(9~1), more preferably (1~4):(6~9), and in specific embodiments it can be 1:9, 2:8, 3:7, 4:6, etc.

[0017] Preferably, the parameters for electrospinning in step (1) are: spinning time of 2-6 h and liquid supply rate of 0.4-1 mL·h. -1 The receiving distance is 15-18 cm, the output high voltage of the spinning machine is controlled at 16-20 kV, the collector cylinder speed is 170-200 rpm, and the humidity of the electrospinning process is controlled within 50-60%.

[0018] Preferably, in step (2), the PANI / PMIA fiber membrane is left to stand in the aniline solution for 1-3 hours at a temperature of 0 to -5 °C. More preferably, the standing time is 2 hours at a temperature of 0 °C.

[0019] Preferably, the in-situ polymerization reaction in step (2) is carried out at a temperature of 0 °C for 6-12 h.

[0020] Preferably, the washing in step (2) refers to rinsing the membrane surface with ethanol and water, and the drying is vacuum drying at 60 °C for 24 h.

[0021] Preferably, the oxidant in step (2) is ammonium persulfate (APS) or hydrogen peroxide (H2O2). More preferably, the mass ratio of the ANI monomer to APS is 1:1.28-2.56, and the mass-volume ratio of the ANI monomer to H2O2 is 1 g:0.55-1.65 mL.

[0022] Preferably, the solvent in the aniline solution in step (2) is a mixed solution of water, anhydrous ethanol and hydrochloric acid, with a volume ratio of water:anhydrous ethanol:hydrochloric acid of 1:1:0.1 and a concentration of hydrochloric acid of 1-1.5 mol / L.

[0023] The polyaniline / polyisophthalamide electromagnetic shielding material prepared by the method of the present invention can be used to prepare protective fabrics, wearable protective equipment, and flexible electronic devices or communication equipment housings.

[0024] This invention combines electrospinning technology with a seed-effect assisted in-situ polymerization strategy to prepare a PANI-based nanofiber composite membrane with a core-shell dual structure. The method first uses electrospinning to uniformly disperse PANI within PMIA nanofibers to obtain a PANI / PMIA fiber membrane. PANI acts as a "seed" to induce subsequent ANI polymerization, while PMIA serves as the substrate, exhibiting not only high thermal stability but also excellent acid resistance and structural stability. Next, the obtained PANI / PMIA fiber membrane is immersed in a solution of ANI and hydrochloric acid (HCl), utilizing the seed effect to enhance the adsorption capacity of ANI monomers on the fiber surface, forming a high-concentration ANI layer. Finally, upon introduction of the oxidant APS, ANI monomers undergo oxidative polymerization on the fiber surface, forming a continuous and interconnected PANI shell, achieving the interconnection of PANI molecular chains in the core-shell dual-phase system, thereby increasing the PANI loading of individual nanofibers. In this method, the π-π stacking interaction between ANI and PANI seeds not only provides the driving force for polymerization, but also provides abundant active sites for subsequent in-situ polymerization, improves the utilization rate of ANI monomers in solution, and enhances the binding strength between the core and shell interfaces.

[0025] Compared with the prior art, the present invention has the following advantages and beneficial effects: (1) Compared with the traditional method of in-situ polymerization on the template surface to form only a limited PMIA surface layer, the present invention uses electrospinning process and seed induction effect to make both the core layer and the shell layer contain PMIA, realize the connection of PANI molecular chains in the core-shell biphase system, and thus increase the PANI loading of a single nanofiber.

[0026] (2) Based on density functional theory, the interaction force at the core-shell interface was simulated and calculated. The seed-induced effect comes from the π-π stacking interaction between the ANI monomer and the PANI molecular chain, with a binding energy of -79.47 kJ·mol⁻¹. -1This indicates that there is a stronger interaction between the ANI monomer and the PANI seed, which promotes the adsorption of more ANI monomer in solution on the fiber surface containing PANI seed. This not only improves the utilization rate of aniline monomer in the polymerization process, but also improves the stability of the fiber core-shell structure.

[0027] (3) PANI is uniformly dispersed inside PMIA fibers through electrospinning technology to form a "seed" structure. These PANI seeds provide abundant active sites on the fiber surface and inside, enhancing the adsorption capacity of ANI monomers on the fiber surface, thereby forming a high-concentration ANI monomer adsorption layer. Under the action of the oxidant APS, the ANI monomers adsorbed on the fiber surface undergo chemical oxidation polymerization, thereby forming a dense PANI shell on the fiber surface, ensuring that the material has a good conductive network.

[0028] (4) A large number of interfacial dipoles are formed at the heterogeneous interface of the composite film. The interfacial polarization further absorbs and attenuates the incident electromagnetic waves. This unique structural design significantly improves the electromagnetic wave loss efficiency. The layered fiber structure and pore distribution cause electromagnetic waves to be reflected multiple times inside the material, thereby extending the propagation path. Multiple reflections help to further dissipate electromagnetic wave energy.

[0029] (5) Using PMIA as the matrix of the composite material, it is further processed by electrospinning and uniformly blended with PANI seeds to improve the thermal stability of the composite material and ensure that it can maintain long-term performance stability even when a large amount of heat is generated by electromagnetic wave energy conversion. Attached Figure Description

[0030] Figure 1 SEM image of the electromagnetic shielding film prepared in Comparative Example 1; Figure 2 SEM image of the electromagnetic shielding film prepared in Example 4; Figure 3 SEM image of the electromagnetic shielding film prepared in Example 3; Figure 4 SEM image of the electromagnetic shielding film prepared in Example 2; Figure 5 SEM image of the electromagnetic shielding film prepared in Example 1; Figure 6 A physical image and a demonstration of the flexibility of the electromagnetic shielding film prepared in Example 1; Figure 7 This demonstrates that the electromagnetic shielding film prepared in Example 1 does not break when a 500 g weight is suspended from it. Figure 8 Thermogravimetric (TGA) curves of the electromagnetic shielding films prepared in Examples 1-3. Figure 9Thermogravimetric (TGA) curves of the electromagnetic shielding films prepared in Examples 4-6. Figure 10 Thermogravimetric (TGA) curves of the electromagnetic shielding films prepared for comparative examples 1-3. Figure 11 The electromagnetic shielding efficiencies are those of the electromagnetic shielding films prepared in Examples 1-4, where 4PANI / 6PMIA, 3PANI / 7PMIA, 2PANI / 8PMIA, and 1PANI / 9PMIA represent the electromagnetic shielding films prepared in Examples 1-4, respectively. Detailed Implementation

[0031] The present invention will be further described in detail below with reference to embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. All raw materials involved in the present invention can be purchased directly from the market. For process parameters not specifically specified, conventional techniques can be referred to.

[0032] The length of the PMIA short fibers used in the following examples and comparative examples is 20-50 mm.

[0033] In the following embodiments and comparative examples, the performance of the composite membrane was tested according to the following methods: Microscopic morphology testing: The microstructure of the samples was observed using a field emission scanning electron microscope (FE-SEM, Hitachi S4800). The samples were fixed to the stage with conductive adhesive and dried, followed by gold sputtering using an ion sputtering system. The scanning voltage was set to 10 kV during testing. The microstructure of the samples was then observed at high magnification using a transmission electron microscope (TEM, FEI Tecnai F20) with energy-dispersive X-ray spectroscopy (EDS).

[0034] Thermogravimetric analysis (TGA): The thermal stability of the composite membrane was studied using a thermogravimetric analyzer (TG-2, Mettler, Switzerland). The gas flow rate was set to 50 mL / min. -1 The test temperature range was 25 ℃ to 800 ℃. The heating rate was 10 ℃·min. -1 When the temperature is raised to 105 °C, it is held at that temperature for 2 min to remove moisture from the sample, and then heated for another 10 °C·min. -1 Cool down to 25 °C, and finally at 10 °C·min. -1 The temperature was continuously increased to 800 ℃, and the sample mass loss during the heating process was observed and analyzed.

[0035] Tensile property testing: The tensile properties of the membrane were characterized using the Instron 3000 universal testing system. The composite membrane was cut into regular shapes, and the initial specifications of the samples (including initial length, thickness, and width) were recorded. With both ends of the composite membrane fixed, the maximum stress and strain were measured by applying tension. The tensile strength was calculated using the following formula:

[0036] Where F(N), L(m), and D(m) represent the pressure, initial width, and thickness of the composite membrane, respectively.

[0037] Shielding effectiveness testing: Using an Agilent E5071C vector network analyzer, the EMI shielding performance of the samples was measured in the 8.2–12.4 GHz (X-band) range using the waveguide method. Samples were cut into 22.5 mm × 10.2 mm pieces, stacked to a thickness of 1 mm, and compacted. Electromagnetic shielding effectiveness was measured. The electromagnetic absorption loss (SE) of the samples was calculated using the measured scattering parameters (S11 and S21). A ), reflection loss (SE) R ) and total shielding (SE) T ).

[0038] Example 1 (1) Preparation of electrospinning precursor: 1.37 g of PMIA short fibers were dissolved in 11.37 g of DMAc / LiCl (2 wt% LiCl) mixed solvent and heated and stirred in a 90 °C water bath for 24 h to prepare a 12 wt% PMIA solution. After complete dissolution, the solution was allowed to cool. 0.5 g of intrinsic PANI was dissolved in 0.1 g of THP and 4.4 g of NMP solution and stirred with a magnetic stirrer at room temperature for 6 h to prepare a 15 wt% PANI solution. The PANI solution and PMIA solution were mixed at a solid mass ratio of 4:6 and magnetically stirred at 500 r / min for 4 h at room temperature to obtain a 4PANI / 6PMIA electrospinning hybrid precursor.

[0039] (2) Preparation of electrospun PANI / PMIA fiber membrane: The PANI / PMIA electrospinning precursor obtained in step (1) was injected into a 5 mL syringe, the spinning time was set to 4 h, and the liquid supply rate was 0.5 mL·h. -1 The receiving distance is 17cm, the output high voltage of the spinning machine is controlled at 19 kV, the collector cylinder speed is 170 rpm, and the humidity of the electrospinning process is controlled within 50%.

[0040] (3) Solution impregnation of PANI / PMIA fiber membrane template: Prepare a 630 mL mixed solution of deionized water, anhydrous ethanol and hydrochloric acid (the volume ratio of water: anhydrous ethanol: hydrochloric acid is 1:1:0.1, and the concentration of hydrochloric acid is 1 mol / L), and divide it into solution A and solution B. Take 1 g of ANI monomer and add it to solution A and mix well. Fix the PANI / PMIA composite nanofiber membrane obtained in step (2) on the plastic mesh, put it in solution A and let it stand for 2 h to allow the ANI monomer to be evenly adsorbed on the fiber membrane.

[0041] (4) Add 2.45 g of APS to solution B, sonicate for 2 min to dissolve it completely, then pour in solution A and mix. Finally, place the reactor in an ice-water bath at 0 °C for in-situ polymerization for 12 h and then remove it. Rinse the membrane surface with ethanol and deionized water, and finally vacuum dry at 60 °C for 24 h to obtain a nanofiber composite membrane with a core of PANI / PMIA and a shell of PANI.

[0042] Electromagnetic shielding effectiveness: The PANI / PMIA electromagnetic shielding material prepared in this embodiment was tested and found to have an electromagnetic shielding effectiveness of approximately 28 dB in the X-band (8.2-12.4 GHz). After more than 2000 bending cycles, the material's structure remained undamaged and its electromagnetic shielding performance remained almost unchanged, with a tensile strength of 31.1 MPa, demonstrating good flexibility and mechanical properties.

[0043] Thermal stability: The composite membrane only showed significant weight loss after 400 ℃, indicating that the composite membrane has excellent thermal stability.

[0044] Example 2 The difference between Example 2 and Example 1 is that in step (1) of Example 2, the PANI solution and PMIA solution are mixed in a solid mass ratio of 3:7 to prepare a 3PANI / 7PMIA electrospinning hybrid precursor. Other operation steps and working conditions are the same.

[0045] Electromagnetic shielding effectiveness: The PANI / PMIA electromagnetic shielding material prepared in this embodiment was tested and found to have an electromagnetic shielding effectiveness of approximately 24 dB in the X-band (8.2-12.4 GHz). After more than 2000 bending cycles, the material's structure remained undamaged and its electromagnetic shielding performance remained almost unchanged, with a tensile strength of 29.5 MPa, demonstrating good flexibility and mechanical properties.

[0046] Thermal stability: The composite membrane only showed significant weight loss after 400 ℃, indicating that the composite membrane has excellent thermal stability.

[0047] Based on the density functional theory (DFT) framework, the core-shell interface interaction force of the PANI / PMIA electromagnetic shielding material prepared in this embodiment was simulated and calculated. The seed-induced effect originates from the π-π stacking interaction between the ANI monomer and the PANI molecular chain, with a binding energy of -79.47 kJ·mol⁻¹. -1 As shown in Table 1.

[0048] Table 1. Binding energy between molecules in the optimized model

[0049] Example 3 The difference between Example 3 and Example 1 is that in step (1) of Example 3, the PANI solution and PMIA solution are mixed at a solid mass ratio of 2:8 to prepare a 2PANI / 8PMIA electrospinning hybrid precursor. Other operation steps and working conditions are the same.

[0050] Electromagnetic shielding effectiveness: The PANI / PMIA electromagnetic shielding material prepared in this embodiment was tested and found to have an electromagnetic shielding effectiveness of approximately 21 dB in the X-band (8.2-12.4 GHz). After more than 2000 bending cycles, the material's structure remained undamaged and its electromagnetic shielding performance remained almost unchanged, with a tensile strength of 27.3 MPa, demonstrating good flexibility and mechanical properties.

[0051] Thermal stability: The composite membrane only showed significant weight loss after 400 ℃, indicating that the composite membrane has excellent thermal stability.

[0052] Example 4 The difference between Example 4 and Example 1 is that in step (1) of Example 4, the PANI solution and PMIA solution are mixed at a solid mass ratio of 1:9 to prepare a 1PANI / 9PMIA electrospinning hybrid precursor. Other operation steps and working conditions are the same.

[0053] Electromagnetic shielding effectiveness: The PANI / PMIA electromagnetic shielding material prepared in this embodiment was tested and found to have an electromagnetic shielding effectiveness of approximately 19.8 dB in the X-band (8.2-12.4 GHz). After more than 2000 bending cycles, the material's structure remained undamaged and its electromagnetic shielding performance remained almost unchanged, with a tensile strength of 21.2 MPa, demonstrating good flexibility and mechanical properties.

[0054] Thermal stability: The composite membrane only showed significant weight loss after 400 ℃, indicating that the composite membrane has excellent thermal stability.

[0055] Example 5 The difference between Example 5 and Example 1 is that in step (4) of Example 5, the polymerization was carried out in situ in an ice-water bath at 0 °C for 8 h and then dried. Other operation steps and working conditions are the same.

[0056] Electromagnetic shielding effectiveness: The PANI / PMIA electromagnetic shielding material prepared in this embodiment was tested and found to have an electromagnetic shielding effectiveness of approximately 25 dB in the X-band (8.2-12.4 GHz). After more than 2000 bending cycles, the material's structure remained undamaged and its electromagnetic shielding performance remained almost unchanged, with a tensile strength of 29 MPa, demonstrating good flexibility and mechanical properties.

[0057] Thermal stability: The composite membrane only showed significant weight loss after 400 ℃, indicating that the composite membrane has excellent thermal stability.

[0058] Example 6 The difference between Example 6 and Example 1 is that in step (4) of Example 6, the polymerization was carried out in situ in an ice-water bath at 0 °C for 6 h and then dried. Other operation steps and working conditions are the same.

[0059] Electromagnetic shielding effectiveness: The PANI / PMIA electromagnetic shielding material prepared in this embodiment was tested and found to have an electromagnetic shielding effectiveness of approximately 22 dB in the X-band (8.2-12.4 GHz). After more than 2000 bending cycles, the material's structure remained undamaged and its electromagnetic shielding performance remained almost unchanged, with a tensile strength of 27 MPa, demonstrating good flexibility and mechanical properties.

[0060] Thermal stability: The composite membrane only showed significant weight loss after 400 ℃, indicating that the composite membrane has excellent thermal stability.

[0061] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that in step (1) of Comparative Example 1, the electrospinning precursor is only PMIA solution and no PANI solution is mixed in. The PMIA nanofiber membrane is used as a template and is soaked in step (3). Other operation steps and working conditions are the same.

[0062] Electromagnetic shielding effectiveness: The prepared PANI / PMIA electromagnetic shielding material was tested and found to have an electromagnetic shielding effectiveness of approximately 17.8 dB in the X-band (8.2-12.4 GHz), a tensile strength of 18.3 MPa, and thermal stability similar to that of Example 1. The core of this composite fiber is PMIA, and the shell is PANI, while the core of the composite fibers in Examples 1-6 is PANI / PMIA. Clearly, Comparative Example 1 reduced the PANI loading and lacked the interconnected PANI molecular chains in the core-shell system, thus weakening its electromagnetic shielding performance. Compared to Examples 1-6, the tensile strength of Comparative Example 1 also decreased significantly, indicating that the interfacial bonding force between the PANI seed core layer and the PANI shell layer in Examples 1-6 plays a crucial role in the mechanical properties of the membrane.

[0063] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that in step (1) of Comparative Example 1, the electrospinning precursor is only thermoplastic polyurethane (TPU) solution and no PANI solution is mixed in. The prepared TPU nanofiber membrane is used as a template for immersion in step (3). Other operation steps and working conditions are the same.

[0064] Electromagnetic shielding effectiveness: The prepared PANI / TPU electromagnetic shielding material was tested and found to have an electromagnetic shielding effectiveness of approximately 17.5 dB in the X-band (8.2-12.4 GHz) and a tensile strength of 20.2 MPa. The material showed significant weight loss after 120 ℃. Since TPU has a low glass transition temperature, this indicates that the material does not have high-temperature resistance.

[0065] Comparative Example 3 Preparation of CA / MWCNTs / PANI electromagnetic shielding material: 1 g of cellulose acetate powder (CA) was added to 6 g of dimethylacetamide (DMAc) and 3 g of acetone (AC) solution and magnetically stirred until dissolved to form a colloid. Then, 0.1 g of MWCNTs was added and ultrasonically treated. After stirring for 2 h, a CA / MWCNTs electrospinning precursor solution was obtained. The precursor solution was poured into a 5 mL syringe, and the spinning time was set to 4 h with a solution supply rate of 0.8 mL·h. -1 The receiving distance was 12 cm, the output high voltage of the spinning machine was controlled at 18 kV, the collector cylinder speed was 170 rpm, and the humidity of the electrospinning process was controlled within 50%. The subsequent polymerization experiment was the same as steps (3) and (4) of Example 1, and the polymerization time was 1.5 h.

[0066] Electromagnetic shielding effectiveness: The prepared CA / MWCNTs / PANI electromagnetic shielding material was tested and found to have an electromagnetic shielding effectiveness of approximately 30 dB in the X-band (8.2-12.4 GHz), but its fracture strength was only 3 MPa.

[0067] Figures 1-5 The figures show SEM images of the electromagnetic shielding films prepared in Comparative Example 1, Example 4, Example 3, Example 2, and Example 1, respectively. As can be seen from the figures, after immersing the PMIA nanofiber membrane in the ANI monomer growth solution, SEM characterization confirmed that the fiber surface was successfully coated with a PANI conductive shell. With the increase of PANI seed content in the fiber, the PANI shell thickness showed a significant gradient change. This is because a higher PANI content in the fiber results in more surface active sites, which is more conducive to the adsorption of ANI monomer and subsequent oxidative polymerization reactions, thus forming a thicker PANI conductive layer.

[0068] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a polyaniline / poly(m-phenylene isophthalamide) electromagnetic shielding material, characterized in that, Includes the following steps: (1) After preparing solutions of poly(m-phenylene isophthalamide) short fibers and polyaniline respectively, the two solutions are mixed to obtain a spinning solution, and then the spinning solution is electrospun to obtain a PANI / PMIA fiber membrane. (2) The PANI / PMIA fiber membrane was placed in an aniline solution and allowed to stand. Then an oxidant was added to carry out an in-situ polymerization reaction. After the reaction was completed, the membrane was taken out, washed and dried to obtain the polyaniline / polyisophthaloylm-phenylenediamine electromagnetic shielding material.

2. The preparation method according to claim 1, characterized in that, In step (1), the poly(m-phenylene isophthalamide) short fibers are dissolved in a mixed solvent of N,N-dimethylacetamide / lithium chloride, and then heated and stirred at 60-90 °C for 24-72 h to obtain a PMIA solution; the polyaniline is dissolved in a mixed solution of pyrrolidine and N-methylpyrrolidone, and stirred at room temperature for 6-12 h to obtain a PANI solution.

3. The preparation method according to claim 1, characterized in that, In step (1), the mass ratio of poly(m-phenylene isophthalamide) to polyaniline in the spinning solution is (1~9):(9~1).

4. The preparation method according to claim 3, characterized in that, The mass ratio of poly(m-phenylene isophthalamide) to polyaniline in the spinning solution is (1~4):(6~9).

5. The preparation method according to claim 1, characterized in that, The electrospinning parameters in step (1) are: spinning time of 2-6 h and liquid supply rate of 0.4-1 mL·h. -1 The receiving distance is 15-18 cm, the output high voltage of the spinning machine is controlled at 16-20 kV, the collector cylinder speed is 170-200 rpm, and the humidity of the electrospinning process is controlled within 50-60%.

6. The preparation method according to claim 1, characterized in that, The standing time mentioned in step (2) refers to standing the PANI / PMIA fiber membrane in an aniline solution for 1-3 h at 0 ~ -5 ℃.

7. The preparation method according to claim 1, characterized in that, The in-situ polymerization reaction in step (2) is carried out at a temperature of 0°C for 6-12 hours.

8. The preparation method according to claim 1, characterized in that, The oxidant in step (2) is ammonium persulfate or hydrogen peroxide.

9. A polyaniline / poly(m-phenylene isophthalamide) electromagnetic shielding material prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the polyaniline / polyisophthalamide electromagnetic shielding material of claim 9 in the fields of protective fabrics, wearable protective equipment, textile flexible electronic devices or communication equipment housings.

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