Wave-absorbing flame-retardant electromagnetic shielding fabric as well as preparation method and application thereof

Abstract

The invention is suitable for the technical field of multifunctional textile materials, and provides a wave-absorbing type flame-retardant electromagnetic shielding fabric and a preparation method and application thereof.The wave-absorbing type flame-retardant electromagnetic shielding fabric takes aramid fiber / stainless steel blended fabric as a base material, and the surface of the base material is coated with a functional coating; the functional coating is composed of a waterborne polyurethane matrix, a NiZnFe2O4 and MnO2 / GA composite wave absorbing agent dispersed in the waterborne polyurethane matrix, an ammonium polyphosphate flame retardant and a catalyst p-toluenesulfonic acid; under the catalysis of p-toluenesulfonic acid, carrying out esterification reaction on ammonium polyphosphate, the waterborne polyurethane matrix and oxygen-containing functional groups in the graphene aerogel to form a phosphorus-oxygen-carbon covalent cross-linked network; the invention successfully solves the technical problem of collaborative integration of wave-absorbing and flame-retardant properties, has the characteristics of light weight, flexibility, environmental friendliness and the like, and is suitable for the field of high-end flexible electromagnetic protection and fireproof safety.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of multifunctional textile materials, and particularly relates to a wave-absorbing flame-retardant electromagnetic shielding fabric as well as a preparation method and application thereof. BACKGROUND

[0002] With the rapid development and popularization 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 devices, leading to information leakage, but also causes potential harm to human health in the long term, and has been recognized as the fourth major public hazard after air, water and noise pollution. Therefore, the development of high-performance electromagnetic shielding materials has become an important issue to protect electronic information security and human health.

[0003] As an emerging flexible electromagnetic shielding material, electromagnetic shielding fabric is widely used in health protection and military operations due to its high shielding efficiency, flexible weaving, lightweight and durability. According to the process method, electromagnetic shielding fabric mainly includes: (1) conductive fiber blended electromagnetic shielding fabric, such as stainless steel wire, silver wire, copper wire and other blended yarns. This method imparts electromagnetic shielding efficiency to the fabric through the electrical conductivity of metal fibers. For example, Yang Yang's master's thesis "Shielding Performance Research of Stainless Steel Blended Fabric Embedded with Copper Coated Filament" of Donghua University embeds high electrical conductivity copper coated filament into the woven textile structure mainly composed of stainless steel blended yarn to prepare a multi-band electromagnetic shielding fabric with comfort and functionality. (2) Surface modification type electromagnetic shielding fabric, which uses electroplating, chemical plating, magnetron sputtering, surface coating or in-situ polymerization to fix conductive particles on the surface of the fabric to improve the electrical conductivity of the fabric and thus improve its loss to electromagnetic waves. For example, Liu Rongli et al. (Knitting Industry) studied the silver-nickel-copper three-layer chemical plating process of polyester fabric, and the technologies disclosed in patents CN104005224B and CN120537118A. The above-mentioned electromagnetic shielding fabric mainly relies on the high electrical conductivity of metal wires or coatings, causing impedance mismatch and triggering strong reflection mechanism to achieve electromagnetic shielding. Electromagnetic waves are strongly reflected on the surface of the fabric, but the reflected waves easily cause secondary electromagnetic pollution, which cannot fundamentally solve the harm of electromagnetic radiation.

[0004] To overcome the disadvantages of reflective shielding, absorptive electromagnetic shielding materials emerged as the times require. The design concept is to enhance the material's electromagnetic loss capacity through the synergistic effect of electricity-magnetism, optimize impedance matching, and effectively convert electromagnetic energy into heat energy or other forms of energy dissipation. In recent years, researchers have tried to introduce carbon materials (such as carbon nanotubes, graphene), conductive polymers (such as polypyrrole, polyaniline) and magnetic particles (such as ferrite) into fabrics. For example, patent CN118996836A discloses a super-amphiphobic wave-absorbing fabric based on molybdenum disulfide / reduced graphene oxide (MoS2 / RGO) composite material; another patent CN114351443B discloses adding magnetic powder such as ferroferric oxide (Fe3O4) and polypyrrole (PPy) conductive polymer to the coating finish on the fabric, in order to achieve electromagnetic wave absorption characteristics in the low frequency band. However, these studies still have obvious limitations: first, most of the work still cannot achieve efficient "absorption" shielding in a wide frequency band; second, the functional fillers (such as Fe3O4 nanoparticles) introduced are easy to oxidize and fail in the environment, and have insufficient stability; third, in order to achieve sufficient performance, high filler loading is often required, resulting in thick and heavy coatings, loss of fabric flexibility, and decline in mechanical properties; fourth, and often overlooked, the textile substrate generally has poor thermal stability and is prone to burning, limiting its application in high safety level protection fields. Current researches mainly focus on single electromagnetic shielding or flame retardant performance, and it is difficult to balance "wave-absorbing electromagnetic shielding" and efficient flame retardant performance. Therefore, it is urgent to develop a lightweight, flexible, multifunctional integrated fabric to achieve synergistic improvement of electromagnetic absorption shielding and flame retardant performance.

[0005] Graphene aerogel (GA) is an ideal material for building a three-dimensional conductive loss network due to its lightweight, high specific surface area and excellent electrical conductivity. The introduction of magnetic particles (such as ferrite) can provide magnetic loss capacity and improve impedance matching. Ammonium polyphosphate (APP) is a high-efficiency halogen-free flame retardant that can play a gas phase and condensed phase flame-retardant role during combustion. However, how to integrate these components through sophisticated structural design and synergistic effect to prepare a multifunctional flexible fabric that is "thin, light, wide, strong and safe" is still a technical difficulty in the current field.

[0006] Therefore, in view of the above status, it is urgent to provide a wave-absorbing flame-retardant electromagnetic shielding fabric, a preparation method and application thereof, to overcome the deficiencies in current practical applications. SUMMARY

[0007] The purpose of the present application is to provide a wave-absorbing flame-retardant electromagnetic shielding fabric, a preparation method and application thereof, which effectively solve the problems in the background art.

[0008] The present application is realized as follows: a wave-absorbing flame-retardant electromagnetic shielding fabric, which takes aramid / stainless steel blended fabric as a substrate, and the surface of the substrate is coated with a functional coating; The functional coating is composed of a water-based polyurethane matrix, a nickel-zinc ferrite@ manganese dioxide / graphene aerogel (NiZnFe2O4@MnO2 / GA) composite wave-absorbing agent dispersed in the water-based polyurethane matrix, an ammonium polyphosphate flame retardant, and a catalyst p-toluenesulfonic acid; The NiZnFe2O4@MnO2 / GA composite wave-absorbing agent is a heterogeneous structure powder formed by loading nickel-zinc ferrite@ manganese dioxide (NiZnFe2O4@MnO2) microspheres with a core-shell structure in a three-dimensional porous graphene aerogel network. The ammonium polyphosphate reacts with the oxygen-containing functional groups in the water-based polyurethane matrix and the graphene aerogel to form a phosphorus-oxygen-carbon covalent crosslinking network under the catalysis of p-toluenesulfonic acid.

[0009] As a further scheme of the present application, the mass of the NiZnFe2O4@MnO2 / GA composite wave-absorbing agent accounts for 1-3% of the mass of the water-based polyurethane matrix, the mass of the ammonium polyphosphate accounts for 8-12% of the mass of the water-based polyurethane matrix, and the mass of the p-toluenesulfonic acid accounts for 0.3-0.7% of the mass of the water-based polyurethane matrix.

[0010] As a further scheme of the present application, the aramid / stainless steel blended fabric is subjected to low-temperature plasma treatment before coating.

[0011] As a further scheme of the present application, the total thickness of the fabric is 0.8-1.2 mm.

[0012] The present application also provides a method for preparing the wave-absorbing type flame-retardant electromagnetic shielding fabric as described above, which comprises the following steps: S1. Substrate pretreatment: clean the aramid / stainless steel blended fabric and perform surface etching activation treatment by using low-temperature plasma; S2. Preparation of NiZnFe2O4@MnO2 / GA composite wave-absorbing powder; S3. Preparation of coating: take water-based polyurethane as a base, add a dispersing agent and a defoaming agent, then add the NiZnFe2O4@MnO2 / GA composite wave-absorbing agent prepared in step S2, which accounts for 1-3% of the mass of the water-based polyurethane, and perform high-speed stirring to make it uniformly dispersed, to obtain wave-absorbing coating; Add p-toluenesulfonic acid, which accounts for 0.3-0.7% of the mass of the water-based polyurethane, and ammonium polyphosphate, which accounts for 8-12% of the mass of the water-based polyurethane, to the wave-absorbing coating, and perform high-speed stirring again to make it uniformly dispersed, to obtain flame-retardant wave-absorbing coating; S4. Coating and curing: uniformly coat the coating prepared in step S3 on the surface of the fabric treated in step S1, control the coating amount to make the total thickness of the fabric 0.8-1.2 mm, and then perform pre-curing and thermal curing, to obtain the wave-absorbing type flame-retardant electromagnetic shielding fabric.

[0013] As a further scheme of the present application: in step S3, the rotating speed of the two high-speed stirring is 250-350 rpm, and the time is 50-70 minutes.

[0014] As a further scheme of the present application: in step S4, the pre-curing condition is 50-70℃ for 20-40 minutes. The heat curing condition is 110-130℃ for 50-70 minutes.

[0015] As a further scheme of the present application: in step S2, the preparation method of the NiZnFe2O4@MnO2 / GA composite wave-absorbing powder comprises: a) dispersing nickel-zinc ferrite (NiZnFe2O4) microspheres, adding potassium permanganate (KMnO4) and dissolving, adding concentrated hydrochloric acid (HCl) dropwise, and then hydrothermal reaction at 120℃ for 6 hours, washing and drying to obtain NiZnFe2O4@MnO2 core-shell microspheres; b) mixing graphene oxide (GO) with the NiZnFe2O4@MnO2 core-shell microspheres obtained in step a) at a mass ratio of 75:25, hydrothermal reaction at 180℃ for 8 hours, and then the product is soaked in ammonia water, frozen, broken, and freeze-dried, and then vacuum heat treated at 400℃ for 1 hour to obtain the NiZnFe2O4@MnO2 / GA composite wave-absorbing powder.

[0016] As a further scheme of the present application: in step a), the mass ratio of nickel-zinc ferrite to potassium permanganate is 1:2.

[0017] The present application also provides an application of the wave-absorbing type flame-retardant electromagnetic shielding fabric as described above in flexible electromagnetic protection, military stealth, electronic device shielding or fire safety materials.

[0018] Compared with the prior art, the present application has the following advantages: Excellent wave-absorbing and shielding performance: the core wave-absorbing agent NiZnFe2O4@MnO2 / GA powder itself can achieve a minimum reflection loss of -55.78 dB and an effective absorption bandwidth of 3.52 GHz at a thickness of 2.45 mm. After applying it to the coating, the fabric has an average total shielding effectiveness (SET) of 44.5 dB, an average absorption shielding effectiveness (SEA) of 34.2 dB, and an average reflection shielding effectiveness (SER) of 10.3 dB in the X-band (8.2-12.4 GHz), wherein SEA / SET=77%, realizing an absorption-dominant shielding mechanism and effectively avoiding secondary pollution.

[0019] Excellent flame retardant performance: The ammonium polyphosphate and the waterborne polyurethane / graphene aerogel system produce a significant synergistic flame-retardant effect. The limiting oxygen index (LOI) is increased from 20.5% (pure waterborne polyurethane) to 32.0%, reaching the difficultly flammable level. The cone calorimeter test shows 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 with the pure waterborne polyurethane coating fabric, effectively inhibiting the spread of the flame and the generation of smoke. Performance synergistic gain: The application breaks through the bottleneck of mutual restriction between wave-absorbing function and flame-retardant function in traditional technology, and through material and structure design, the electromagnetic loss unit and the flame-retardant component produce a synergistic effect (such as P-O-C bonding, interface polarization enhancement) at the molecular and microscale. It is not a simple superposition of functions, but achieves the effect of "1+1>2", that is, while achieving high absorption and shielding efficiency, excellent flame retardant performance is also achieved, solving the problem of multi-functional integration.

[0020] Functional stability enhancement: The core-shell structure design (NiZnFe2O4@MnO2) adopted in the application is the key to ensuring the long-term functional stability of the material. The manganese dioxide dielectric shell layer effectively isolates the nickel-zinc ferrite magnetic core from the external environment, avoiding oxidation and corrosion of the magnetic core, as well as reduction by the graphene carbon source during the heat treatment stage, thereby ensuring the long-term stability and reliability of its magnetic loss capability, solving the common problem of magnetic wave-absorbing material failure.

[0021] Practicality and environmental friendliness: The functional component load is low (NiZnFe2O4@MnO2 / GA wave-absorbing agent 2wt%, ammonium polyphosphate 10wt%), and the fabric remains lightweight and flexible. The preparation process is simple and the conditions are mild, suitable for large-scale production. The water-based system and halogen-free flame retardant are used, which is environmentally friendly. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the specific embodiments of the application or the technical solutions in the prior art, the following will briefly introduce the drawings needed to be used in the description of the specific embodiments or the prior art. Obviously, the drawings described below are some embodiments of the application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0023] Figure 1 The preparation process flowchart of the NiZnFe2O4@MnO2 / GA composite wave-absorbing agent in the embodiments of the application.

[0024] Figure 2 SEM photos of the NiZnFe2O4@MnO2 / GA composite wave-absorbing agent powder prepared in the embodiments. Wherein: (a) is a three-dimensional porous network structure diagram of NiZnFe2O4@MnO2 / GA composite aerogel, and it can be seen that graphene sheets interweave to form a continuous porous skeleton, which provides stable support for uniform loading of wave-absorbing microspheres; (b) is a morphology diagram of NiZnFe2O4@MnO2 microspheres dispersed on the surface of graphene aerogel, which shows that the microspheres are uniformly distributed and closely combined with the matrix; (c) is a local magnification diagram of a single NiZnFe2O4@MnO2 microsphere, and it can be observed that the MnO2 shell is composed of flower-like nanosheets, showing typical core-shell structure characteristics.

[0025] Figure 3 It is a wave-absorbing performance data diagram of the NiZnFe2O4@MnO2 / GA composite wave-absorbing agent powder prepared in the examples; Wherein: (a) is a two-dimensional curve diagram of the reflection loss (RL) of samples with different thicknesses with respect to frequency, and it can be seen that the minimum reflection loss (RL min ) of the material reaches -55.78 dB at a thickness of 2.0 mm, and the effective absorption bandwidth (EAB) is 3.52 GHz; (b) is a three-dimensional spatial distribution diagram of the reflection loss with respect to thickness and frequency, which shows that the material has strong electromagnetic wave absorption performance and continuous distribution.

[0026] Figure 4 It is a preparation process flow diagram of the coated fabric in the examples.

[0027] Figure 5 It is a scanning electron microscope (SEM) and energy spectrum (EDS) image of the surface morphology and element distribution of the wave-absorbing type flame-retardant electromagnetic shielding fabric in the examples; Wherein: (a) is a whole surface morphology diagram of the fabric, and it can be seen that the coating is uniformly covered on the aramid / stainless steel blended fabric surface; (b) is a local magnification diagram of the fiber surface, which shows that the functional coating is closely combined with the fiber without falling off; (c) is a micro-morphology diagram of a local area on the coating surface, which can be observed that the NiZnFe2O4@MnO2 / GA composite wave-absorbing agent is uniformly distributed and well combined in the coating; (d) is a high magnification diagram of the coating surface, which shows the typical layered wrinkles and three-dimensional porous structure of graphene aerogel; The EDS diagram is the morphology of the energy spectrum test area, which shows the distribution characteristics of multiple elements in the coating; C, O, P, Mn, Fe, Ni, Zn element maps are element distribution mapping results of carbon, oxygen, phosphorus, manganese, iron, nickel and zinc, the element distribution is uniform and the signal overlapping degree is high, which indicates that the NiZnFe2O4@MnO2 / GA composite wave-absorbing agent and the APP flame-retardant component are uniformly dispersed in the WPU matrix, and the interface is well combined.

[0028] Figure 6 The electromagnetic shielding performance curve of the wave-absorbing type flame-retardant electromagnetic shielding fabric in the 8-12.5 GHz frequency band in the examples.

[0029] Figure 7 The flame-retardant performance comparison chart of the coated fabrics prepared in the comparative examples and the examples.

[0030] Figure 8 The macroscopic morphology and carbon layer structure scanning electron microscope (SEM) images of the coated fabrics prepared in the comparative examples and the examples after the cone calorimeter test (CCT); Wherein: (a)-(c) are macroscopic morphology charts of different samples (NMG / W, NMG / W-2, NMG / W-P) after combustion, respectively; (d)-(i) are carbon layer surface and local magnification morphology charts of the samples corresponding to (a)-(c), respectively, reflecting the influence of carbon layer structure difference under different formulations on the flame-retardant performance; 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 heat shielding and protection effect is poor; The NMG / W-2 (b, e, h) sample forms a uniform and dense gray-black carbon layer, which has a lamellar and nanocrystalline composite structure inside, which can effectively improve the density of the carbon layer and hinder the transmission of heat and gas; The NMG / W-P (c, f, i) sample generates a gray and white dense carbon layer on the surface, with very few micro-cracks, indicating that the phosphorus-containing intermediate promotes the cross-linking of the carbon skeleton and the strengthening of the structure during the carbonization process, thereby significantly improving the thermal stability and flame-retardant performance.

[0031] Figure 9 The flame-retardant performance and pyrolysis behavior comparison chart of the coated fabrics prepared in the comparative examples and the examples; Wherein: (a) is a column chart of the limiting oxygen index (LOI) of the samples NMG / W, NMG / W-2 and NMG / W-P, it can be seen that with the introduction of NiZnFe2O4@MnO2 / GA and APP, the LOI is increased from 20.5% to 32.0%; (b) is the thermogravimetric analysis (TGA) curve of each sample, indicating that the carbon residue rate of the NMG / W-P sample is the highest, which can reach 50%, indicating that the composite flame-retardant system can effectively promote the formation of carbon layer and inhibit thermal decomposition; (c) is the corresponding differential thermal gravimetric (DTG) curve, the thermal decomposition peak of NMG / W-P shifts to the high temperature zone, and the decomposition rate decreases, indicating that it has more excellent thermal stability and thermal oxidative inhibition ability.

[0032] Figure 10 Comparison of the combustion heat release and smoke release characteristics of the coated fabrics prepared in the comparative examples and the examples; Wherein: (a) is the heat release rate (HRR) curve with time. As can be seen from the figure, the peak heat release rate (pHRR) of the NMG / W sample is the highest, and the pHRR of the NMG / W-P sample is significantly reduced by 45.87%, indicating that the composite flame retardant system can effectively inhibit the burning rate and heat release.

[0033] (b) is the total heat release (THR) curve with time, and it can be seen that the THR of the NMG / W-P sample is significantly lower than that of the substrate sample, and the cumulative release amount is reduced by 53.86%, indicating that the composite flame retardant system significantly reduces the overall combustion heat release.

[0034] (c) is the total smoke release (TSP) curve, and the TSP peak of the NMG / W-P sample is significantly lower than that of the other samples, which is reduced by 48.31% compared with the substrate sample, indicating that the composite system can significantly inhibit the generation and accumulation of smoke.

[0035] (d) is the carbon monoxide (CO) release curve, and the CO peak concentration of the NMG / W sample is higher in the early stage of combustion, while the peak concentration of the NMG / W-P sample is reduced by about 85.19%, indicating that the system can effectively inhibit the generation of toxic gases in the combustion process and has excellent fire safety performance. DETAILED DESCRIPTION

[0036] The technical solutions of the present application will be described clearly and completely below in combination with the drawings. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0037] The present application will be further explained and described below in combination with specific embodiments.

[0038] Please refer to Figures 1-10 The wave-absorbing flame-retardant electromagnetic shielding fabric provided by the embodiments of the present application takes aramid / stainless steel blended fabric as the substrate, and the surface of the substrate is coated with a functional coating. The functional coating is composed of a water-based polyurethane matrix, a nickel-zinc ferrite@ manganese dioxide / graphene aerogel (NiZnFe2O4@MnO2 / GA) composite wave-absorbing agent dispersed in the water-based polyurethane matrix, an ammonium polyphosphate flame retardant, and a catalyst p-toluenesulfonic acid; The mass of the NiZnFe2O4@MnO2 / GA composite wave-absorbing agent accounts for 1-3% of the mass of the water-based polyurethane matrix, the mass of the ammonium polyphosphate accounts for 8-12% of the mass of the water-based polyurethane matrix, and the mass of the p-toluenesulfonic acid accounts for 0.3-0.7% of the mass of the water-based polyurethane matrix. The NiZnFe2O4@MnO2 / GA composite wave-absorbing agent is a heterogeneous structure powder formed by loading nickel-zinc ferrite@ manganese dioxide (NiZnFe2O4@MnO2) microspheres with a core-shell structure in a three-dimensional porous graphene aerogel network. Under the catalysis of the p-toluenesulfonic acid, the ammonium polyphosphate reacts with the oxygen-containing functional groups in the water-based polyurethane matrix and the graphene aerogel to form a phosphorus-oxygen-carbon covalent crosslinking network.

[0039] In this embodiment, the aramid / stainless steel blended fabric is subjected to low-temperature plasma treatment before coating, and the total thickness of the fabric is 0.8-1.2 mm.

[0040] The application also provides a method for preparing the wave-absorbing flame-retardant electromagnetic shielding fabric as described above, which comprises the following steps: S1. Substrate pretreatment: clean the aramid / stainless steel blended fabric and perform surface etching activation treatment by using low-temperature plasma; S2. Preparation of the NiZnFe2O4@MnO2 / GA composite wave-absorbing powder, specifically: a) Disperse nickel-zinc ferrite (NiZnFe2O4) microspheres, add potassium permanganate (KMnO4) and dissolve, wherein the mass ratio of nickel-zinc ferrite to potassium permanganate is 1:2, add concentrated hydrochloric acid (HCl) dropwise, and then perform hydrothermal reaction at 120℃ for 6 hours, and then wash and dry to obtain NiZnFe2O4@MnO2 core-shell microspheres; b) Mix graphene oxide (GO) with the NiZnFe2O4@MnO2 core-shell microspheres obtained in step a) at a mass ratio of 75:25, perform hydrothermal reaction at 180℃ for 8 hours, and then perform ammonia immersion, freezing, crushing, and freeze-drying on the product, and then perform vacuum heat treatment at 400℃ for 1 hour to obtain the NiZnFe2O4@MnO2 / GA composite wave-absorbing powder S3. Preparation of the coating: take water-based polyurethane as the base, add a dispersing agent and a defoaming agent, and then add the NiZnFe2O4@MnO2 / GA composite wave-absorbing agent prepared in step S2, which accounts for 1-3% of the mass of the water-based polyurethane, and then perform high-speed stirring to make it uniformly dispersed, so as to obtain a wave-absorbing coating. The p-toluenesulfonic acid accounts for 0.3-0.7% of the mass of the water-based polyurethane, and the ammonium polyphosphate accounts for 8-12% of the mass of the water-based polyurethane, and the mixture is stirred again at high speed to make the mixture uniformly dispersed, so that the flame-retardant wave-absorbing coating is obtained; S4. Coating and curing: the coating prepared in step S3 is uniformly coated on 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, and then pre-curing and thermal curing are performed, so that the wave-absorbing flame-retardant electromagnetic shielding fabric is obtained; wherein the pre-curing condition is 50-70 DEG C for 20-40 minutes, and the thermal curing condition is 110-130 DEG C for 50-70 minutes.

[0041] The application also provides a use of the wave-absorbing flame-retardant electromagnetic shielding fabric in flexible electromagnetic protection, military stealth, electronic device shielding or fire safety materials.

[0042] The synergistic effect of the application mainly embodies in the following two aspects: 1. The esterification reaction mechanism of PTSA catalyzing APP and WPU / GA: The p-toluenesulfonic acid (PTSA) as a strong acid catalyst can provide protons (H + ) to attack the phosphorus-oxygen double bond (P=O) in the ammonium polyphosphate (APP), so that the APP is activated and more easily reacts with the hydroxyl groups (-OH) on the molecular chain of the water-based polyurethane (WPU) or the carboxyl groups (-COOH) and hydroxyl groups (-OH) on the surface of the graphene aerogel (GA). In the reaction process, the p-toluenesulfonic acid significantly improves the esterification reaction rate and degree by reducing the reaction activation energy, and finally forms a stable phosphorus-oxygen-carbon (P-O-C) covalent crosslinking network between the water-based polyurethane macromolecular chain and the graphene aerogel.

[0043] 2. The enhancement mechanism of the P-O-C network to the wave-absorbing performance, the flame retardancy and the interfacial bonding force: The formed P-O-C covalent crosslinking network plays a synergistic effect in the following three aspects: (a) wave-absorbing enhancement: the introduction of the ammonium polyphosphate does not destroy the conductive network and the magnetic loss mechanism constructed by the NiZnFe2O4@MnO2 / GA composite wave-absorbing agent, but introduces a large number of dipoles and defect sites at the interface through the crosslinking structure of the P-O-C bond and the water-based polyurethane / graphene aerogel. These sites as polarization centers significantly enhance the interface polarization effect and the related dielectric loss ability. At the same time, the crosslinking network optimizes the multiple reflection and scattering paths of electromagnetic waves in the material, improves the efficiency of the conversion of electromagnetic energy into heat energy, and thus further improves the proportion of the absorption efficiency (SEA) while maintaining the high shielding efficiency (SET).

[0044] (b) Flame-retardant enhancement: P—O—C bonds can decompose to generate phosphoric acid substances in advance during the combustion process, promoting the formation of carbon on the fabric surface, forming a dense and stable intumescent carbon layer. This carbon layer not only insulates oxygen and heat and inhibits the escape of flammable gas, but also significantly reduces the heat release rate and smoke gas production, while capturing free radicals in the gas phase and interrupting the combustion chain reaction, thereby playing a dual flame-retardant role in the gas and condensed phases.

[0045] (c) Interfacial bonding force enhancement: P—O—C covalent bonds chemically connect the waterborne polyurethane, graphene aerogel, and ammonium polyphosphate, significantly improving the interfacial compatibility and bonding force between the components, avoiding phase separation, and improving the uniformity and stability of the coating. This strong interfacial bonding not only facilitates stress transfer, maintaining the flexibility of the fabric, but also helps to build a more continuous and stable electromagnetic loss / flame-retardant network, achieving functional durability.

[0046] Example 1: Preparation of wave-absorbing-flame-retardant synergistic sample (NMG / W-P) This example is the core of the present application, and a fabric with high-efficiency wave absorption and excellent flame-retardant function is prepared.

[0047] S1. Pre-treatment of the base fabric: Take a 10 cm x 10 cm aramid / stainless steel (80 / 20) blended fabric and ultrasonically clean it with ethanol for 15 minutes, then air dry. Use a low-temperature plasma treatment instrument (power 300 W, oxygen atmosphere) to treat the surface of the fabric for 5 minutes.

[0048] S2. Preparation of wave-absorbing agent: a) Preparation of NiZnFe2O4@MnO2 core-shell microspheres: Disperse 150 mg of nickel-zinc ferrite microspheres in 40 ml of deionized water, and uniformly disperse them by mechanical stirring (150 rpm, 30 min) and ultrasonication (30 min). Add 300 mg of potassium permanganate, stir to dissolve, then add 0.5 mL of concentrated hydrochloric acid, and continue stirring (150 rpm, 30 min). Transfer the resulting solution to a 50 mL hydrothermal reactor, and react at 120°C for 6 hours. After natural cooling, wash with anhydrous ethanol by centrifugation 3 times, and dry in a vacuum drying oven at 60°C for 10 hours to obtain NiZnFe2O4@MnO2 core-shell microspheres.

[0049] b) Preparation of NiZnFe2O4@MnO2 / GA powder: 170 mg of graphene oxide was dispersed in 35 ml of deionized water to form a homogeneous colloid by stirring (150 rpm, 60 min) and ultrasonicating (90 min). 56.7 mg of the microspheres prepared in step a) (25 wt% of the final aerogel) was added and mixed uniformly by mechanical stirring (150 rpm, 60 min). 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 in a freeze dryer for 12 hours. Finally, the NiZnFe2O4@MnO2 / GA composite wave-absorbing powder was obtained by heat treatment at 400 °C in a tube furnace under vacuum for 1 hour (heating rate 5 °C / min).

[0050] S3. Preparation of paint: 20 g of waterborne polyurethane was weighed as the base, and 0.2 g of dispersant and 0.2 g of defoaming agent (1% of the mass of waterborne polyurethane) were added. Then 0.4 g (2 wt%) of the wave-absorbing powder prepared in step S2 was added, and high-speed stirring was carried out at a speed of 300 rpm for 60 minutes to obtain a wave-absorbing paint.

[0051] 0.1 g (0.5 wt%) of p-toluenesulfonic acid and 2 g (10 wt%) of ammonium polyphosphate were added to the above wave-absorbing paint, and high-speed stirring was continued at a speed of 300 rpm for 60 minutes to obtain a uniform flame-retardant wave-absorbing paint.

[0052] S4. Coating and curing: The fabric treated in step S1 was fixed on a coating machine, and the above paint was uniformly coated, with the coating amount controlled to make the total thickness of the fabric (1.0 ± 0.1) mm. The coated fabric was first placed in a hot air oven at 60 °C for pre-curing for 30 minutes, and then transferred to an oven at 120 °C for heat curing for 60 minutes to obtain the final product sample, named NMG / W-P.

[0053] Example 2: Preparation of pure wave-absorbing sample (NMG / W-2) This example is used to illustrate the intrinsic performance of the core wave-absorbing agent and the comparison with Example 1.

[0054] The preparation process is exactly the same as that of Example 1, except that the step of adding p-toluenesulfonic acid and ammonium polyphosphate in step S3 is omitted. That is, after the wave-absorbing paint is prepared, step S4 of coating and curing is directly performed. The obtained sample is named NMG / W-2.

[0055] Comparative Example 1: Preparation of blank sample (NMG / W) This comparative example is used as a benchmark for performance comparison to illustrate the state of the substrate without adding any functional filler.

[0056] The preparation process is similar to Example 1, but in step S3, neither absorbing powder nor p-toluenesulfonic acid and ammonium polyphosphate is added. That is, only 20 g of water-borne polyurethane is mixed with 0.2 g of dispersant and 0.2 g of defoaming agent, and after stirring for 60 minutes, it is directly coated and cured. The obtained sample is named NMG / W.

[0057] Performance test and result analysis: In the present application, the test of each performance of the fabric is carried out according to the international or national general standard, which is as follows: Electromagnetic shielding effectiveness (SET, SEA, SER): Waveguide method is used to test in X waveband (8.2-12.4 GHz) using a vector network analyzer (Agilent N5234A, USA), according to the standard GB / T 30142-2013 “Measurement method of shielding effectiveness of planar electromagnetic shielding materials”. Among them, SET (total shielding effectiveness) represents the overall attenuation ability of the material to electromagnetic waves; SEA (absorbing shielding effectiveness) represents the absorption loss of the material to electromagnetic waves; SER (reflective shielding effectiveness) represents the reflection loss of the material to electromagnetic waves.

[0058] Limiting oxygen index (LOI): Oxygen index tester (FTT0077, UK) is used, according to the standard GB / T 5454-1997 “Textile burning performance test oxygen index method”.

[0059] Thermogravimetric analysis (TGA): Thermogravimetric analyzer (TGA 8000, USA) is used, according to the standard GB / T 27761-2011 “Thermal analyzer mass differential scanning calorimetry method”, to determine the thermal decomposition temperature and carbon residue of the sample, so as to evaluate its thermal stability.

[0060] Cone calorimeter test (CCT): Cone calorimeter (FTT0007, UK) is used to test under the heat radiation intensity of 50 kW / m², according to the standard ISO 5660-1:2015 “Reaction to fire test-heat release, smoke production and mass loss rate”.

[0061] All tests are carried out in standard laboratory environment (temperature 23±2°C, relative humidity 50±5%).

[0062] The performance of the samples obtained in the above examples and control examples is tested, and the results are shown in the following table.

[0063] Table 1 Comparison table of properties of different coated fabrics

[0064] Conclusion: The above data show that the NMG / W-P sample (Example 1) provided by the application successfully integrates high-efficiency electromagnetic wave absorption and excellent flame retardation. The performance is not a simple superposition of the effect of functional fillers, but is derived from the synergistic effect of the NiZnFe2O4@MnO2 / GA wave-absorbing agent and the ammonium polyphosphate flame retardant under the catalysis of p-toluenesulfonic acid, ultimately achieving the effect of "1+1>2" and solving the technical problem of multifunctional integration.

[0065] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

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.

2. The wave-absorbing flame-retardant electromagnetic shielding fabric according to claim 1, characterized in that, 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.

3. The wave-absorbing flame-retardant electromagnetic shielding fabric according to claim 1, characterized in that, The aramid / stainless steel blended fabric undergoes low-temperature plasma treatment before coating.

4. The wave-absorbing flame-retardant electromagnetic shielding fabric according to claim 1, characterized in that, The total thickness of the fabric is 0.8-1.2 mm.

5. A method for preparing a wave-absorbing, flame-retardant electromagnetic shielding fabric as described in any one of claims 1-4, 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.

6. The method according to claim 5, 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.

7. The method according to claim 5, 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.

8. The method according to claim 5, 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.

9. The method according to claim 8, characterized in that, In step a), the mass ratio of nickel-zinc ferrite to potassium permanganate is 1:

2.

10. The application of a wave-absorbing flame-retardant electromagnetic shielding fabric as described in any one of claims 1-4 in flexible electromagnetic protection, military stealth, electronic equipment shielding, or fire safety materials.

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