A wave-absorbing flame-retardant electromagnetic shielding fabric, its preparation method and application

Abstract

This invention relates to the field of multifunctional textile materials technology, and provides a microwave-absorbing flame-retardant electromagnetic shielding fabric, its preparation method, and its application. The fabric uses an aramid / stainless steel blended fabric as the substrate, and the substrate surface is coated with a functional coating. The functional coating consists of an aqueous polyurethane matrix, a NiZnFe2O4@MnO2 / GA composite microwave absorber dispersed in the aqueous polyurethane matrix, an ammonium polyphosphate flame retardant, and a catalyst, p-toluenesulfonic acid. Under the catalysis of p-toluenesulfonic acid, the ammonium polyphosphate undergoes an esterification reaction with the oxygen-containing functional groups in the aqueous polyurethane matrix and graphene aerogel, forming a phosphorus-oxygen-carbon covalent crosslinking network. This invention successfully solves the technical challenge of synergistic integration of microwave absorption and flame retardant properties, and features lightweight, flexibility, and environmental friendliness, making it suitable for high-end flexible electromagnetic protection and fire safety applications.

Description

Technical Field

[0001] This invention relates to the field of multifunctional textile materials technology, specifically to a wave-absorbing flame-retardant electromagnetic shielding fabric, its preparation method, and its application. Background Technology

[0002] With the rapid development and widespread adoption of 5G communication, the Internet of Things, and high-power electronic devices, electromagnetic radiation pollution has become a global environmental problem. Electromagnetic interference not only affects the normal operation of precision electronic equipment and leads to information leaks, but long-term exposure also poses potential health hazards. It is now widely recognized as the fourth major public health hazard after air, water, and noise pollution. Therefore, developing high-performance electromagnetic protection materials has become an important issue for ensuring electronic information security and human health.

[0003] As an emerging flexible electromagnetic shielding material, electromagnetic shielding fabrics have been widely used in health protection and military operations due to their advantages such as high shielding efficiency, flexible weaving, lightweight and durable. According to the process method, electromagnetic shielding fabrics mainly include: (1) Electromagnetic shielding fabrics made of conductive fiber blended yarns, such as stainless steel wire, silver wire, copper wire and other blended yarns. This method uses the conductivity of metal fibers to give the fabric electromagnetic shielding efficiency. For example, Yang Yang's master's thesis of Donghua University, "Study on the shielding performance of stainless steel blended fabrics with embedded copper-clad wires", prepared a multi-band electromagnetic shielding fabric with both comfort and functionality by embedding high conductivity copper-clad wires into a woven textile structure with stainless steel blended yarns as the main body. (2) Surface modified electromagnetic shielding fabrics, which use electroplating, chemical plating, magnetron sputtering, surface coating or in-situ polymerization and other methods to fix conductive particles on the surface of the fabric to improve the conductivity of the fabric and thus improve its loss of electromagnetic waves. Examples include the silver-nickel-copper three-layer chemical plating process for polyester fabrics researched by Liu Rongli et al. (Knitting Industry), and the technologies disclosed in patents such as CN104005224B and CN120537118A. The electromagnetic shielding fabrics described above primarily rely on the high conductivity of metal wires or coatings to create impedance mismatch, triggering a strong reflection mechanism to achieve electromagnetic shielding. While electromagnetic waves are strongly reflected on the fabric surface, the reflected waves easily cause secondary electromagnetic pollution, failing to fundamentally solve the problem of electromagnetic radiation hazards.

[0004] To overcome the drawbacks of reflective shielding, absorptive electromagnetic shielding materials have emerged. Their design philosophy is to enhance the electromagnetic loss capability of materials while optimizing impedance matching through electro-magnetic synergy, effectively converting electromagnetic energy into heat or other forms of energy dissipation. In recent years, researchers have attempted to introduce carbon materials (such as carbon nanotubes and graphene), conductive polymers (such as polypyrrole and polyaniline), and magnetic particles (such as ferrites) into fabrics. For example, patent CN118996836A discloses a super-dual-absorbent wave-absorbing fabric based on a molybdenum disulfide / reduced graphene oxide (MoS2 / RGO) composite material; another patent CN114351443B discloses a coating treatment on fabric with magnetic powders such as iron(III) oxide (Fe3O4) combined with a conductive polymer of polypyrrole (PPy) to achieve electromagnetic wave absorption characteristics in the low-frequency band. However, these studies still have significant limitations: First, most works still struggle to achieve efficient "absorption" shielding across a wide frequency band; second, the introduced functional fillers (such as Fe3O4 nanoparticles) are prone to oxidation and failure in the environment, resulting in insufficient stability; third, achieving sufficient performance often requires high filler loading, leading to thick coatings, loss of fabric flexibility, and decreased mechanical properties; fourth, and often overlooked, textile substrates generally suffer from poor thermal stability and flammability, limiting their application in high-security protection fields. Current research largely focuses on single electromagnetic shielding or flame-retardant properties, making it difficult to simultaneously achieve both "wave-absorbing electromagnetic shielding" and efficient flame-retardant performance. Therefore, there is an urgent need to develop a lightweight, flexible, multifunctional integrated fabric to achieve a synergistic improvement in electromagnetic absorption shielding and flame-retardant performance.

[0005] Graphene aerogel (GA) is an ideal material for constructing three-dimensional conductive loss networks due to its lightweight, high specific surface area, and excellent conductivity. The introduction of magnetic particles (such as ferrites) can improve magnetic loss capacity and impedance matching. Ammonium polyphosphate (APP), as a highly efficient halogen-free flame retardant, can exert flame-retardant effects in both the gas and condensed phases during combustion. However, how to integrate these components through ingenious structural design and synergistic effects to prepare multifunctional flexible fabrics that are thin, lightweight, wide, strong, and safe remains a key technical challenge in the field.

[0006] Therefore, in view of the above situation, there is an urgent need to provide a wave-absorbing flame-retardant electromagnetic shielding fabric, its preparation method and application, in order to overcome the shortcomings in current practical applications. Summary of the Invention

[0007] The purpose of this invention is to provide a wave-absorbing flame-retardant electromagnetic shielding fabric, its preparation method, and its application, effectively solving the problems in the background art.

[0008] The present invention is achieved as follows: a wave-absorbing flame-retardant electromagnetic shielding fabric, with aramid / stainless steel blended fabric as the base material, and the surface of the base material is coated with a functional coating.

[0009] The functional coating consists of an aqueous polyurethane matrix, a nickel-zinc ferrite@manganese dioxide / graphene aerogel (NiZnFe2O4@MnO2 / GA) composite microwave absorber dispersed in the aqueous polyurethane matrix, an ammonium polyphosphate flame retardant, and a catalyst p-toluenesulfonic acid.

[0010] The NiZnFe2O4@MnO2 / GA composite microwave absorber is a heterogeneous powder formed by loading core-shell structured nickel-zinc ferrite@manganese dioxide (NiZnFe2O4@MnO2) microspheres in a three-dimensional porous graphene aerogel network.

[0011] Ammonium polyphosphate undergoes an esterification reaction with oxygen-containing functional groups in an aqueous polyurethane matrix and graphene aerogel under the catalysis of p-toluenesulfonic acid, forming a phosphorus-oxygen-carbon covalent cross-linked network.

[0012] As a further aspect of the present invention: the mass of the NiZnFe2O4@MnO2 / GA composite microwave absorber accounts for 1-3% of the mass of the waterborne polyurethane matrix, the mass of ammonium polyphosphate accounts for 8-12% of the mass of the waterborne polyurethane matrix, and the mass of p-toluenesulfonic acid accounts for 0.3-0.7% of the mass of the waterborne polyurethane matrix.

[0013] As a further aspect of the present invention: the aramid / stainless steel blended fabric is subjected to low-temperature plasma treatment before coating.

[0014] As a further aspect of the present invention, the total thickness of the fabric is 0.8-1.2 mm.

[0015] The present invention also provides a method for preparing the above-mentioned microwave-absorbing flame-retardant electromagnetic shielding fabric, the method comprising the following steps:

[0016] S1. Substrate pretreatment: The aramid / stainless steel blended fabric is cleaned and surface etching activation is performed using low-temperature plasma.

[0017] S2. Preparation of NiZnFe2O4@MnO2 / GA composite microwave absorbing powder;

[0018] S3. Coating preparation: Using waterborne polyurethane as the base, add dispersant and defoamer, then add 1-3% of the NiZnFe2O4@MnO2 / GA composite microwave absorbing agent obtained in step S2, and stir at high speed to disperse it evenly to obtain the microwave absorbing coating.

[0019] Add 0.3-0.7% p-toluenesulfonic acid and 8-12% ammonium polyphosphate by mass of water-based polyurethane to the microwave absorbing coating, and stir at high speed again to disperse it evenly to obtain a flame-retardant microwave absorbing coating.

[0020] S4. Coating and curing: The coating prepared in step S3 is uniformly coated onto the surface of the fabric treated in step S1. The coating amount is controlled so that the total thickness of the fabric is 0.8-1.2 mm. Then, pre-curing and heat curing are performed to obtain a wave-absorbing flame-retardant electromagnetic shielding fabric.

[0021] As a further aspect of the present invention: in step S3, the speed of the two high-speed stirrings is 250-350 rpm and the time is 50-70 minutes.

[0022] As a further aspect of the present invention: in step S4, the pre-curing conditions are treatment at 50-70°C for 20-40 minutes;

[0023] The thermosetting conditions are 110-130℃ for 50-70 minutes.

[0024] As a further aspect of the present invention: In step S2, the preparation method of NiZnFe2O4@MnO2 / GA composite microwave absorbing powder includes:

[0025] a) Disperse nickel-zinc ferrite (NiZnFe2O4) microspheres, add potassium permanganate (KMnO4) and dissolve, add concentrated hydrochloric acid (HCl) dropwise and then hydrothermally react at 120℃ for 6 hours. After washing and drying, NiZnFe2O4@MnO2 core-shell microspheres are obtained.

[0026] b) Graphene oxide (GO) and the NiZnFe2O4@MnO2 core-shell microspheres obtained in step a) were mixed at a mass ratio of 75:25 and hydrothermally reacted at 180°C for 8 hours. The product was soaked in ammonia water, frozen, crushed, and freeze-dried, and then vacuum heat-treated at 400°C for 1 hour to obtain the NiZnFe2O4@MnO2 / GA composite microwave absorbing powder.

[0027] As a further aspect of the present invention: in step a), the mass ratio of nickel-zinc ferrite to potassium permanganate is 1:2.

[0028] The present invention also provides an application of the above-described wave-absorbing flame-retardant electromagnetic shielding fabric in flexible electromagnetic protection, military stealth, electronic equipment shielding, or fire safety materials.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] Superior absorption and shielding performance: The core absorbing agent, NiZnFe2O4@MnO2 / GA powder, achieves a minimum reflection loss of -55.78dB and an effective absorption bandwidth of 3.52GHz with a thickness of 2.45mm. When applied to the coating, the fabric exhibits an average total shielding effectiveness (SET) of 44.5dB, an average absorption shielding effectiveness (SEA) of 34.2dB, and an average reflection shielding effectiveness (SER) of 10.3dB in the X-band (8.2-12.4GHz), with an SEA / SET ratio of 77%. This achieves an absorption-dominated shielding mechanism, effectively preventing secondary pollution.

[0031] Excellent flame retardant properties: Ammonium polyphosphate and the waterborne polyurethane / graphene aerogel system produce a significant synergistic flame retardant effect. The limiting oxygen index (LOI) increases from 20.5% (pure waterborne polyurethane) to 32.0%, reaching a flame-retardant level. Cone calorimetry tests show that the peak heat release rate (pHRR), total heat release (THR), total smoke production (TSP), and peak CO production rate (pCO) are significantly reduced by 45.9%, 53.9%, 48.3%, and 85.2% respectively compared to pure waterborne polyurethane coated fabrics, effectively suppressing flame spread and smoke generation. Synergistic performance gains: This invention breaks through the bottleneck of mutual constraints between electromagnetic absorption and flame retardant functions in traditional technologies. Through material and structural design, the electromagnetic loss unit and flame retardant components produce a synergistic effect at the molecular and microscopic scale (such as POC bonding and enhanced interfacial polarization). It is not a simple superposition of functions, but achieves a "1+1>2" effect, that is, while achieving high absorption and shielding efficiency, it obtains excellent flame retardant performance, solving the problem of multifunctional integration.

[0032] Enhanced Functional Stability: The core-shell structure design (NiZnFe2O4@MnO2) employed in this invention is crucial for ensuring the long-term functional stability of the material. The manganese dioxide dielectric shell acts as a protective shield, effectively isolating the nickel-zinc ferrite magnetic core from the external environment. This prevents the magnetic core from being oxidized, corroded, or reduced by the graphene carbon source during heat treatment, thus ensuring the long-term stability and reliability of its magnetic loss capability and solving the common problem of easy failure in magnetic absorbing materials.

[0033] Practicality and Environmental Friendliness: Low loading of functional components (2wt% NiZnFe2O4@MnO2 / GA microwave absorber, 10wt% ammonium polyphosphate), maintaining the fabric's lightweight and flexibility. The preparation process is simple and mild, suitable for large-scale production. Utilizing a water-based system and halogen-free flame retardants, it is environmentally friendly. Attached Figure Description

[0034] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0035] Figure 1 This is a schematic diagram of the preparation process of the NiZnFe2O4@MnO2 / GA composite microwave absorber in an embodiment of the present invention.

[0036] Figure 2 Here is a SEM image of the NiZnFe2O4@MnO2 / GA composite microwave absorbing powder prepared in the examples;

[0037] in:

[0038] (a) is a three-dimensional porous network structure diagram of NiZnFe2O4@MnO2 / GA composite aerogel. It can be seen that the graphene sheets are interwoven to form a continuous porous framework, which provides stable support for the uniform loading of the microwave absorbing microspheres.

[0039] (b) is a morphology diagram of NiZnFe2O4@MnO2 microspheres dispersed on the surface of graphene aerogel, showing that the microspheres are uniformly distributed and tightly bonded to the matrix;

[0040] (c) is a magnified view of a single NiZnFe2O4@MnO2 microsphere, in which the MnO2 shell is composed of flower-like nanosheets, exhibiting typical core-shell structure characteristics.

[0041] Figure 3 The graph shows the microwave absorption performance data of the NiZnFe2O4@MnO2 / GA composite microwave absorber powder prepared in the examples;

[0042] in:

[0043] (a) is a two-dimensional curve showing the reflection loss (RL) of samples with different thicknesses as a function of frequency. It can be seen that the minimum reflection loss (RL) of the material is achieved at a thickness of 2.0 mm. min The impedance reaches -55.78 dB, with an effective absorption bandwidth (EAB) of 3.52 GHz;

[0044] (b) is a three-dimensional spatial distribution diagram of reflection loss as a function of thickness and frequency, showing that the material has strong electromagnetic wave absorption performance and continuous distribution.

[0045] Figure 4 This is a schematic diagram of the preparation process of the coated fabric in an embodiment of the present invention.

[0046] Figure 5The images shown are scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) images of the surface morphology and elemental distribution of the microwave-absorbing flame-retardant electromagnetic shielding fabric in the embodiment.

[0047] in:

[0048] (a) is a diagram of the overall morphology of the fabric surface, showing that the coating is uniformly covered on the surface of the aramid / stainless steel blended fabric.

[0049] (b) is a magnified view of a part of the fiber surface, showing that the functional coating is tightly bonded to the fiber and there is no peeling.

[0050] (c) is a microscopic morphology diagram of a local area on the coating surface, which shows that the NiZnFe2O4@MnO2 / GA composite microwave absorber is uniformly distributed and well bonded in the coating;

[0051] (d) is a high-magnification image of the coating surface, showing the typical layered wrinkles and three-dimensional porous structure of graphene aerogel;

[0052] The EDS image shows the morphology of the energy dispersive spectroscopy (EDS) test area, revealing the distribution characteristics of multiple elements in the coating.

[0053] The C, O, P, Mn, Fe, Ni, and Zn elemental maps show the elemental distribution mapping results for carbon, oxygen, phosphorus, manganese, iron, nickel, and zinc, respectively. The uniform elemental distribution and high signal overlap indicate that the NiZnFe2O4@MnO2 / GA composite microwave absorber and APP flame retardant components are uniformly dispersed in the WPU matrix and have good interfacial bonding.

[0054] Figure 6 The electromagnetic shielding performance curves of the wave-absorbing flame-retardant electromagnetic shielding fabric in the embodiment are shown in the 8–12.5 GHz frequency band.

[0055] Figure 7 This is a comparison chart showing the flame retardant properties of the coated fabrics prepared in the comparative example and the embodiment.

[0056] Figure 8 Macroscopic morphology and carbon layer structure of the coated fabrics prepared for comparative examples and embodiments after cone calorimetry (CCT) and scanning electron microscope (SEM) images.

[0057] in:

[0058] (a) to (c) are macroscopic morphology images of different samples (NMG / W, NMG / W-2, NMG / WP) after combustion;

[0059] (d) to (i) are magnified images of the char layer surface and local morphology of the samples corresponding to (a) to (c), respectively, reflecting the influence of the char layer structure difference under different formulations on flame retardant performance.

[0060] As can be seen from the figure, the carbon layer of the NMG / W (a,d,g) sample is dark brown, porous and broken, indicating that the carbonization is incomplete and the thermal insulation and protection effect is poor.

[0061] The NMG / W-2 (b,e,h) sample forms a uniform and dense gray-black carbon layer with a composite structure of lamellar and nanocrystal structures, which can effectively improve the density of the carbon layer and hinder heat and gas transport.

[0062] The formation of a dense, grayish-white carbon layer with very few microcracks on the surface of the NMG / WP (c,f,i) sample indicates that the phosphorus-containing intermediates promoted the cross-linking and structural strengthening of the carbon skeleton during carbonization, thereby significantly improving thermal stability and flame retardant properties.

[0063] Figure 9 A comparison diagram showing the flame retardant properties and pyrolysis behavior of the coated fabrics prepared in the comparative examples and embodiments;

[0064] in:

[0065] (a) is a bar chart of limiting oxygen index (LOI) for samples NMG / W, NMG / W-2 and NMG / WP. It can be seen that with the introduction of NiZnFe2O4@MnO2 / GA and APP, the LOI increased from 20.5% to 32.0%.

[0066] (b) shows the thermogravimetric analysis (TGA) curves of each sample, indicating that the NMG / WP sample has the highest char residue rate, reaching 50%, which shows that the composite flame retardant system can effectively promote char layer formation and inhibit thermal decomposition.

[0067] (c) shows the corresponding differential thermogravimetric (DTG) curve. The thermal decomposition peak of NMG / WP shifts to the high-temperature region, and the decomposition rate decreases, indicating that it has better thermal stability and thermal oxidation inhibition ability.

[0068] Figure 10 A comparison diagram showing the combustion heat release and flue gas release characteristics of the coated fabrics prepared in the comparative example and the embodiment;

[0069] in:

[0070] (a) shows the heat release rate (HRR) versus time. As can be seen from the figure, the NMG / W sample has the highest peak heat release rate (pHRR), while the pHRR of the NMG / WP sample is significantly reduced by 45.87%, indicating that the composite flame retardant system can effectively suppress the combustion rate and heat release.

[0071] (b) shows the total heat release (THR) curve over time. It can be seen that the THR of the NMG / WP sample is significantly lower than that of the matrix sample, with a cumulative release of 53.86%, indicating that the composite flame retardant system significantly reduces the overall heat release during combustion.

[0072] (c) shows the total smoke emission (TSP) curve. The peak TSP of the NMG / WP sample is significantly lower than that of other samples, and is 48.31% lower than that of the matrix sample, indicating that the composite system can significantly inhibit the generation and accumulation of smoke.

[0073] (d) shows the carbon monoxide (CO) release curve. The NMG / W sample had a higher peak CO concentration in the early stage of combustion, while the peak concentration of the NMG / WP sample decreased by about 85.19%, indicating that the system can effectively suppress the generation of toxic gases during combustion and has excellent fire safety performance. Detailed Implementation

[0074] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0075] The present invention will be further explained below with reference to specific embodiments.

[0076] Please see Figures 1-10 The present invention provides a wave-absorbing flame-retardant electromagnetic shielding fabric, which uses an aramid / stainless steel blended fabric as the base material and the surface of the base material is coated with a functional coating.

[0077] The functional coating consists of an aqueous polyurethane matrix, a nickel-zinc ferrite@manganese dioxide / graphene aerogel (NiZnFe2O4@MnO2 / GA) composite microwave absorber dispersed in the aqueous polyurethane matrix, an ammonium polyphosphate flame retardant, and a catalyst p-toluenesulfonic acid.

[0078] The mass of the NiZnFe2O4@MnO2 / GA composite microwave absorber accounts for 1-3% of the mass of the waterborne polyurethane matrix, the mass of ammonium polyphosphate accounts for 8-12% of the mass of the waterborne polyurethane matrix, and the mass of p-toluenesulfonic acid accounts for 0.3-0.7% of the mass of the waterborne polyurethane matrix.

[0079] The NiZnFe2O4@MnO2 / GA composite microwave absorber is a heterogeneous powder formed by loading core-shell structured nickel-zinc ferrite@manganese dioxide (NiZnFe2O4@MnO2) microspheres in a three-dimensional porous graphene aerogel network.

[0080] Ammonium polyphosphate undergoes an esterification reaction with oxygen-containing functional groups in an aqueous polyurethane matrix and graphene aerogel under the catalysis of p-toluenesulfonic acid, forming a phosphorus-oxygen-carbon covalent cross-linked network.

[0081] In this embodiment, the aramid / stainless steel blended fabric undergoes low-temperature plasma treatment before coating, and the total thickness of the fabric is 0.8-1.2 mm.

[0082] The present invention also provides a method for preparing the above-mentioned microwave-absorbing flame-retardant electromagnetic shielding fabric, the method comprising the following steps:

[0083] S1. Substrate pretreatment: The aramid / stainless steel blended fabric is cleaned and surface etching activation is performed using low-temperature plasma.

[0084] S2. Preparation of NiZnFe2O4@MnO2 / GA composite microwave absorbing powder, specifically:

[0085] a) Disperse nickel-zinc ferrite (NiZnFe2O4) microspheres, add potassium permanganate (KMnO4) and dissolve them, wherein the mass ratio of nickel-zinc ferrite to potassium permanganate is 1:2. After adding concentrated hydrochloric acid (HCl) dropwise, the reaction is carried out hydrothermally at 120℃ for 6 hours. After washing and drying, NiZnFe2O4@MnO2 core-shell microspheres are obtained.

[0086] b) Graphene oxide (GO) and the NiZnFe2O4@MnO2 core-shell microspheres obtained in step a) were mixed at a mass ratio of 75:25 and subjected to hydrothermal reaction at 180°C for 8 hours. The product was then soaked in ammonia water, frozen, crushed, and freeze-dried, followed by vacuum heat treatment at 400°C for 1 hour to obtain the NiZnFe2O4@MnO2 / GA composite microwave absorbing powder.

[0087] S3. Coating preparation: Using waterborne polyurethane as the base, add dispersant and defoamer, then add 1-3% of the NiZnFe2O4@MnO2 / GA composite microwave absorbing agent obtained in step S2, and stir at high speed to disperse it evenly to obtain the microwave absorbing coating.

[0088] Add 0.3-0.7% p-toluenesulfonic acid and 8-12% ammonium polyphosphate by mass of water-based polyurethane to the microwave absorbing coating, and stir at high speed again to disperse it evenly to obtain a flame-retardant microwave absorbing coating.

[0089] S4. Coating and curing: The coating prepared in step S3 is uniformly coated onto the surface of the fabric treated in step S1. The coating amount is controlled so that the total thickness of the fabric is 0.8-1.2 mm. Then, pre-curing and heat curing are performed to obtain the microwave-absorbing flame-retardant electromagnetic shielding fabric. The pre-curing conditions are 50-70℃ for 20-40 minutes, and the heat curing conditions are 110-130℃ for 50-70 minutes.

[0090] The present invention also provides an application of the above-described wave-absorbing flame-retardant electromagnetic shielding fabric in flexible electromagnetic protection, military stealth, electronic equipment shielding, or fire safety materials.

[0091] The synergistic effect described in this invention is mainly reflected in the following two aspects:

[0092] 1. PTSA-catalyzed esterification mechanism of APP and WPU / GA:

[0093] p-Toluenesulfonic acid (PTSA), as a strong acid catalyst, can provide protons (H+). + The phosphorus-oxygen double bond (P═O) in ammonium polyphosphate (APP) is attacked, activating it and making it easier for it to undergo esterification reactions with oxygen-containing functional groups such as hydroxyl groups (—OH) on the molecular chain of waterborne polyurethane (WPU) or carboxyl groups (—COOH) and hydroxyl groups (—OH) on the surface of graphene aerogel (GA). During this reaction, p-toluenesulfonic acid significantly increases the rate and extent of esterification by lowering the activation energy, ultimately forming a stable phosphorus-oxygen-carbon (P—O—C) covalent cross-linked network between the waterborne polyurethane macromolecular chain and the graphene aerogel.

[0094] 2. The enhancement mechanism of P-O-C network on microwave absorption performance, flame retardancy, and interfacial bonding:

[0095] The resulting P-O-C covalent cross-linked network exerts a synergistic effect in the following three aspects:

[0096] (a) Enhanced Absorption: The introduction of ammonium polyphosphate not only did not disrupt the conductive network and magnetic loss mechanism constructed by the NiZnFe2O4@MnO2 / GA composite absorber, but also introduced a large number of dipoles and defect sites at the interface through the cross-linking structure formed by P-O-C bonds and aqueous polyurethane / graphene aerogel. These sites, as polarization centers, significantly enhanced the interfacial polarization effect and related dielectric loss capability. At the same time, this cross-linking network optimized the multiple reflection and scattering paths of electromagnetic waves within the material, improving the efficiency of electromagnetic energy conversion into heat energy, thereby further increasing the absorption efficiency (SEA) ratio while maintaining high shielding effectiveness (SET).

[0097] (b) Enhanced flame retardancy: The P-O-C bond can decompose in advance during combustion to generate phosphates, promoting char formation on the fabric surface and forming a dense and stable expanded char layer. This char layer not only isolates oxygen and heat, inhibiting the escape of combustible gases, but also significantly reduces the heat release rate and the production of toxic smoke gases. At the same time, it captures free radicals in the gas phase, interrupting the combustion chain reaction, thus playing a dual flame retardant role in both the gas and condensed phases.

[0098] (c) Enhanced interfacial bonding: P-O-C covalent bonds tightly connect the waterborne polyurethane, graphene aerogel, and ammonium polyphosphate through chemical bonds, significantly improving the interfacial compatibility and bonding strength between the components, preventing phase separation, and improving the uniformity and stability of the coating. This strong interfacial bonding not only facilitates stress transfer and maintains the flexibility of the fabric, but also helps to construct a more continuous and stable electromagnetic loss / flame retardant network, achieving functional durability.

[0099] Example 1: Preparation of a microwave absorbing / flame retardant synergistic sample (NMG / WP)

[0100] This embodiment is the core of the present invention, which prepares a fabric that combines high-efficiency wave absorption and excellent flame retardant functions.

[0101] S1. Base fabric pretreatment: Take a 10cm×10cm aramid / stainless steel (80 / 20) blended fabric, ultrasonically clean it with ethanol for 15 minutes, and air dry. Treat the fabric surface with a low-temperature plasma treatment instrument (300W power, oxygen atmosphere) for 5 minutes.

[0102] S2. Preparation of microwave absorbing agent:

[0103] a) Preparation of NiZnFe2O4@MnO2 core-shell microspheres: 150 mg of nickel-zinc ferrite microspheres were dispersed in 40 mL of deionized water and mechanically stirred (150 rpm, 30 min) and sonicated (30 min) to ensure uniform dispersion. 300 mg of potassium permanganate was added and stirred to dissolve. Then, 0.5 mL of concentrated hydrochloric acid was added dropwise, and stirring was continued (150 rpm, 30 min). The resulting solution was transferred to a 50 mL hydrothermal reactor and reacted at 120 °C for 6 hours. After natural cooling, the microspheres were washed three times with anhydrous ethanol by centrifugation and dried in a vacuum drying oven at 60 °C for 10 hours to obtain NiZnFe2O4@MnO2 core-shell microspheres.

[0104] b) Preparation of NiZnFe2O4@MnO2 / GA powder: 170 mg of graphene oxide was dispersed in 35 mL of deionized water and stirred (150 rpm, 60 min) and sonicated (90 min) to form a homogeneous colloid. 56.7 mg of the microspheres obtained in step a) (accounting for 25 wt% of the final aerogel mass) was added and mechanically stirred (150 rpm, 60 min) to ensure uniform mixing. The mixture was transferred to a 50 mL hydrothermal reactor and reacted at 180 °C for 8 hours. The resulting product was soaked in ammonia water for 12 hours, frozen for 12 hours, crushed into powder, and then freeze-dried for 12 hours. Finally, it was heat-treated in a tube furnace under vacuum at 400 °C for 1 hour (heating rate 5 °C / min) to obtain NiZnFe2O4@MnO2 / GA composite microwave absorbing powder.

[0105] S3. Coating preparation:

[0106] Weigh 20g of waterborne polyurethane as the base, and add 0.2g of dispersant and 0.2g of defoamer (both 1% of the mass of waterborne polyurethane). Then add 0.4g (2wt%) of the microwave absorbing powder obtained in step S2, and stir at high speed at 300rpm for 60 minutes to obtain the microwave absorbing coating.

[0107] Add 0.1g (0.5wt%) p-toluenesulfonic acid and 2g (10wt%) ammonium polyphosphate to the above microwave absorbing coating, and continue to stir at high speed of 300rpm for 60 minutes to obtain a uniform flame-retardant microwave absorbing coating.

[0108] S4. Coating and Curing:

[0109] The fabric treated in step S1 is fixed on a coating machine and coated with the above-mentioned coating evenly, controlling the coating amount so that the total thickness of the fabric is (1.0±0.1) mm. The coated fabric is first placed in a 60℃ hot air oven for pre-curing for 30 minutes, and then transferred to a 120℃ oven for heat curing for 60 minutes to obtain the final product sample, named NMG / WP.

[0110] Example 2: Preparation of pure microwave absorbing sample (NMG / W-2)

[0111] This embodiment is used to illustrate the intrinsic properties of the core absorbing agent and to compare it with that of Example 1.

[0112] The preparation process was exactly the same as in Example 1, except that the steps of adding p-toluenesulfonic acid and ammonium polyphosphate were omitted in step S3. That is, after preparing the microwave absorbing coating, step S4 (coating and curing) was performed directly. The resulting sample was named NMG / W-2.

[0113] Comparative Example 1: Preparation of Blank Sample (NMG / W)

[0114] This comparative example serves as a benchmark for performance comparison, illustrating the state of the substrate without any added functional fillers.

[0115] The preparation process is similar to that of Example 1, but in step S3, neither microwave absorbing powder nor p-toluenesulfonic acid and ammonium polyphosphate are added. Instead, 20g of hydrogel polyurethane is mixed with 0.2g of dispersant and 0.2g of defoamer, stirred for 60 minutes, and then directly coated and cured. The resulting sample is named NMG / W.

[0116] Performance testing and results analysis:

[0117] In this invention, all tests on the various properties of the fabric are conducted in accordance with international or national standards, as detailed below:

[0118] Electromagnetic shielding effectiveness (SET, SEA, SER): The waveguide method was used to test the shielding effectiveness in the X-band (8.2-12.4 GHz) using a vector network analyzer (Agilent N5234A, USA), according to standard GB / T 30142-2013, "Measurement Method for Shielding Effectiveness of Planar Electromagnetic Shielding Materials". SET (Total Shielding Effectiveness) represents the overall attenuation capability of the material against electromagnetic waves; SEA (Absorption Shielding Effectiveness) represents the absorption loss of the material against electromagnetic waves; and SER (Reflection Shielding Effectiveness) represents the reflection loss of the material against electromagnetic waves.

[0119] Limiting Oxygen Index (LOI): Oxygen index tester (FTT0077, UK) was used, according to standard GB / T 5454-1997 "Test for Burning Performance of Textiles - Oxygen Index Method".

[0120] Thermogravimetric analysis (TGA): The thermal decomposition temperature and residual carbon content of the sample were determined using a thermogravimetric analyzer (TGA 8000, USA) in accordance with the standard GB / T 27761-2011 "Thermal Analyzer - Mass Differential Scanning Calorimetry" to evaluate its thermal stability.

[0121] Cone calorimetry (CCT): The test was conducted using a cone calorimeter (FTT0007, UK) at a thermal radiation intensity of 50 kW / m², in accordance with standard ISO 5660-1:2015 "Tests for reaction to fire – heat release, smoke production and mass loss".

[0122] All tests were conducted in a standard laboratory environment (temperature 23±2°C, relative humidity 50±5%).

[0123] The performance of the samples obtained from the above embodiments and control examples was tested, and the results are shown in the table below.

[0124] Table 1. Performance Comparison of Different Coated Fabrics

[0125]

[0126] Conclusion: The above data demonstrate that the NMG / WP sample (Example 1) provided by this invention successfully integrates efficient electromagnetic wave absorption with excellent flame retardant performance. Its performance is not a simple superposition of the effects of functional fillers, but rather stems from the synergistic effect of NiZnFe2O4@MnO2 / GA microwave absorber and ammonium polyphosphate flame retardant under the catalysis of p-toluenesulfonic acid, ultimately achieving a "1+1>2" effect and solving the technical challenge of multifunctional integrated design.

[0127] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A wave-absorbing flame-retardant electromagnetic shielding fabric, characterized in that, The substrate is made of aramid / stainless steel blended fabric, and the surface of the substrate is coated with a functional coating. The functional coating consists of an aqueous polyurethane matrix, a nickel-zinc ferrite@manganese dioxide / graphene aerogel NiZnFe2O4@MnO2 / GA composite microwave absorber dispersed in the aqueous polyurethane matrix, an ammonium polyphosphate flame retardant, and a catalyst p-toluenesulfonic acid. The NiZnFe2O4@MnO2 / GA composite microwave absorber is a heterogeneous powder formed by loading core-shell structured nickel-zinc ferrite@manganese dioxide NiZnFe2O4@MnO2 microspheres in a three-dimensional porous graphene aerogel network. Ammonium polyphosphate undergoes an esterification reaction with oxygen-containing functional groups in an aqueous polyurethane matrix and graphene aerogel under the catalysis of p-toluenesulfonic acid, forming a phosphorus-oxygen-carbon covalent cross-linked network. The mass of the NiZnFe2O4@MnO2 / GA composite microwave absorber accounts for 1-3% of the mass of the waterborne polyurethane matrix, the mass of ammonium polyphosphate accounts for 8-12% of the mass of the waterborne polyurethane matrix, and the mass of p-toluenesulfonic acid accounts for 0.3-0.7% of the mass of the waterborne polyurethane matrix. The aramid / stainless steel blended fabric is treated with low-temperature plasma before coating. The total thickness of the fabric is 0.8-1.2 mm.

2. A method for preparing the wave-absorbing flame-retardant electromagnetic shielding fabric as described in claim 1, characterized in that, The method includes the following steps: S1. Substrate pretreatment: The aramid / stainless steel blended fabric is cleaned and surface etching activation is performed using low-temperature plasma. S2. Preparation of NiZnFe2O4@MnO2 / GA composite microwave absorbing powder; S3. Coating preparation: Using waterborne polyurethane as the base, add dispersant and defoamer, then add 1-3% of the NiZnFe2O4@MnO2 / GA composite microwave absorbing agent obtained in step S2, and stir at high speed to disperse it evenly to obtain the microwave absorbing coating. Add 0.3-0.7% p-toluenesulfonic acid and 8-12% ammonium polyphosphate by mass of water-based polyurethane to the microwave absorbing coating, and stir at high speed again to disperse it evenly to obtain a flame-retardant microwave absorbing coating. S4. Coating and curing: The coating prepared in step S3 is uniformly coated onto the surface of the fabric treated in step S1. The coating amount is controlled so that the total thickness of the fabric is 0.8-1.2 mm. Then, pre-curing and heat curing are performed to obtain a wave-absorbing flame-retardant electromagnetic shielding fabric.

3. The method according to claim 2, characterized in that, In step S3, the speed of high-speed stirring is 250-350 rpm for both times, and the time is 50-70 minutes for both times.

4. The method according to claim 2, characterized in that, In step S4, the pre-curing conditions are treatment at 50-70℃ for 20-40 minutes; The thermosetting conditions are 110-130℃ for 50-70 minutes.

5. The method according to claim 2, characterized in that, In step S2, the preparation method of NiZnFe2O4@MnO2 / GA composite microwave absorbing powder includes: a) Disperse nickel-zinc ferrite NiZnFe2O4 microspheres, add potassium permanganate KMnO4 and dissolve them, add concentrated hydrochloric acid HCl dropwise and then hydrothermally react at 120℃ for 6 hours. After washing and drying, NiZnFe2O4@MnO2 core-shell microspheres are obtained. b) Graphene oxide (GO) and the NiZnFe2O4@MnO2 core-shell microspheres obtained in step a) were mixed at a mass ratio of 75:25 and hydrothermally reacted at 180°C for 8 hours. The product was soaked in ammonia water, frozen, crushed, and freeze-dried, and then vacuum heat-treated at 400°C for 1 hour to obtain the NiZnFe2O4@MnO2 / GA composite microwave absorbing powder.

6. The method according to claim 5, characterized in that, In step a), the mass ratio of nickel-zinc ferrite to potassium permanganate is 1:

2.

7. The application of the wave-absorbing flame-retardant electromagnetic shielding fabric as described in claim 1 in flexible electromagnetic protection, military stealth, electronic equipment shielding, or fire safety materials.

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