Multifunctional nonwoven material and method of making same

Abstract

The present application relates to a kind of multifunctional nonwoven and its preparation method, belong to nonwoven technical field.The multifunctional nonwoven of the present application is composed of bottom layer fiber web, transition layer fiber web and surface layer fiber web in turn, wherein bottom layer fiber web is as mechanical support, insulation and flame retardant layer, with high proportion aramid fiber as main body, a small amount of lyocell fiber is used to realize good physical entanglement with transition layer fiber web, and the interlayer bonding force is significantly improved;Transition layer fiber web is structure and performance buffer transition layer, and lyocell fiber and aramid fiber are used in near equal proportion;Surface layer fiber web is electromagnetic shielding and heat conducting functional layer, and the supported catalytic lyocell fiber generated graphite microcrystal by in-situ catalytic graphitization is used as the main function, supplemented with a small amount of aramid fiber as skeleton, effectively prevent the brittle fracture and slagging of carbonized lyocell layer, and the obtained product has excellent electromagnetic shielding effectiveness, good in-plane thermal conductivity, higher mechanical strength, intrinsic flame retardancy and flexibility.

Description

Technical Field

[0001] This invention belongs to the field of nonwoven materials technology, and particularly relates to a multifunctional nonwoven material and its preparation method. Background Technology

[0002] With the rapid iteration of the new energy vehicle industry, the power battery, as the core energy unit of the vehicle, has become a key bottleneck restricting the upgrading of vehicle performance due to its operational safety, signal stability, and thermal management efficiency. The performance of the functional materials inside the battery pack directly determines the overall performance of the power battery system. To meet the urgent demand of the new energy vehicle industry for high-performance, highly integrated materials, there is a pressing need for an integrated functional material inside the battery pack that combines flexible adaptability, efficient electromagnetic shielding, rapid thermal conductivity, inherent flame retardancy, and lightweight properties. This material can replace the traditional multi-component stacking solution, fundamentally improving the integration, operational safety, and long-term reliability of the battery system.

[0003] Current mainstream solutions for the internal functional requirements of battery packs still suffer from numerous significant technical bottlenecks, making it difficult to meet the needs of industry development. These bottlenecks are manifested in the following aspects:

[0004] Firstly, traditional multi-material simple stacking schemes generally suffer from interface defects. Taking a representative cylindrical battery pack as an example, it typically uses insulating buffer materials such as polyester felt as spacers, combined with aluminum or copper foil to achieve electromagnetic shielding, and then supplemented with thermally conductive silicone pads to complete heat dissipation. This stacking method not only increases the weight and structural complexity of the battery system, but also easily causes interlayer impedance mismatch due to the differences in thermal expansion coefficients and electromagnetic properties between different materials, thereby weakening the overall heat dissipation efficiency and electromagnetic shielding effect of the system. Even if some advanced materials attempt to integrate electromagnetic shielding functions in thermally conductive substrates, their technical routes mostly rely on metal coatings such as silver and nickel. This not only significantly increases the material preparation cost, but also makes the metal coatings prone to oxidation and corrosion in complex automotive environments such as high humidity and salt spray, leading to performance degradation of the materials during long-term use and affecting the stability of the battery system.

[0005] Secondly, the low utilization rate of raw material resources and the prominent environmental pressure are also serious problems. The high cost of producing existing high-performance thermally conductive shielding fillers such as virgin carbon fiber and graphene limits their large-scale industrial application. Meanwhile, the textile industry generates a huge amount of waste lyocell fiber and industrial waste aramid fiber. It is estimated that tens of thousands of tons of waste aramid protective equipment and industrial scraps are generated globally each year. Currently, the main methods for handling these high-value polymer materials are landfilling, incineration, or downgrading, which not only fails to achieve high-value recycling of resources but also further exacerbates the environmental burden.

[0006] Thirdly, existing carbonization material technologies still have significant performance and process shortcomings. Traditional carbonized fiber materials with a single homogeneous structure are difficult to achieve multifunctional synergy. The high-temperature graphitization process without catalysis usually requires a processing temperature exceeding 2000℃, resulting in extremely high energy consumption. The products obtained by directly carbonizing waste fibers generally have poor thermal conductivity due to their low degree of graphitization, and their electromagnetic shielding effectiveness is also difficult to break through the 30dB bottleneck. For example, Chinese patent CN115850787A discloses recyclable aramid nanofiber aerogel, its preparation method and application. The prepared thermal insulation material with ultra-low thermal conductivity is not compatible with the application scenario of power battery packs that require efficient heat dissipation and electromagnetic shielding, and cannot meet the actual use requirements of battery packs. Patent CN107057338A discloses electromagnetic shielding high thermal conductivity nylon composite material for new energy vehicle battery boxes. Although the addition of indium metal or graphene improves some of the material's properties, it is difficult to meet the core requirements of the automotive industry for low cost and large-scale manufacturing due to excessive reliance on expensive fillers.

[0007] Based on this, the present invention is proposed. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention provides a multifunctional nonwoven material and its preparation method. Using waste lyocell fiber and waste aramid fiber as raw materials, a multifunctional nonwoven material is prepared through structural design and process optimization. This material is composed of a bottom fiber web, a transition layer fiber web, and a surface fiber web, sequentially composited. The bottom fiber web serves as a mechanical support, insulation, and flame-retardant layer, primarily composed of a high proportion of aramid fiber, supplemented with a small amount of lyocell fiber to achieve good physical entanglement with the transition layer fiber web, significantly improving interlayer bonding. The transition layer fiber web acts as a structural and performance buffer. The coating layer is made of a near-equal proportion of lyocell fiber and aramid fiber. The surface fiber mesh is an electromagnetic shielding and thermal conductive functional layer. The main functional component is supported catalytic lyocell fiber that has been catalytically graphitized in situ to form graphite microcrystals, supplemented by a small amount of aramid fiber as a skeleton. This effectively prevents the carbonized lyocell layer from becoming brittle and flaking. The resulting product has excellent electromagnetic shielding performance, good in-plane thermal conductivity, high mechanical strength, inherent flame retardancy, and flexibility. It can be used as a flexible electromagnetic shielding, thermal conductive, and flame retardant component in the power battery pack of new energy vehicles, achieving lightweight, high safety, and high integration applications.

[0009] The first objective of this invention is to provide a method for preparing a multifunctional nonwoven material, comprising the following steps:

[0010] S1. Lyocell fiber and aramid fiber are mixed at a mass ratio of (10-30):(70-90) and then formed into a web by airflow to obtain the bottom fiber web;

[0011] S2. Lyocell fiber and aramid fiber are mixed at a mass ratio of (45-55): (45-55) and formed into a transition layer fiber web on the surface of the bottom fiber web described in S1 by airflow.

[0012] S3. The supported catalytic lyocell fiber and aramid fiber are mixed at a mass ratio of (70-90):(10-30) and formed into a surface fiber web on the surface of the transition layer fiber web described in S2 by airflow forming, thus obtaining a multilayer fiber web preform. The supported catalytic lyocell fiber is prepared by sequentially pretreating lyocell fiber with an organic carboxylate solution and impregnating it with an iron salt solution. After pretreatment and impregnation, the lyocell fiber is loaded with an iron-based catalytic active component. During high-temperature carbonization, the catalytic component can guide the rearrangement of carbon atoms in the lyocell fiber, generating a graphite nanocrystal structure in situ inside the fiber. This allows the fiber to maintain its long, strip-shaped macroscopic morphology while achieving a highly graphitized microstructure, thereby endowing the material with excellent electrical conductivity.

[0013] S4. After hydroentangling and dehydration, the multilayer fiber web preform described in S3 is treated with hot air to obtain a nonwoven material.

[0014] S5. After performing embossing and heat treatment on the nonwoven material described in S4, the multifunctional nonwoven material is obtained.

[0015] In one embodiment of the present invention, in S1-S3, the process parameters for airflow web formation are independently: temperature of 20℃-25℃, humidity of 58%-62%, airflow velocity in the main duct of 18m / s-22m / s, web formation curtain velocity of 9m / min-11m / min, and vacuum degree of -0.7kPa to -0.9kPa.

[0016] In one embodiment of the present invention, in step S3, the concentration of the organic carboxylate solution is 0.05 mol / L to 0.2 mol / L; the organic carboxylate is selected from one or more of sodium citrate, sodium tartrate, and sodium gluconate.

[0017] And / or, the pretreatment temperature is 45℃-55℃ and the time is 55min-65min.

[0018] In one embodiment of the present invention, in step S3, the concentration of the iron salt solution is 0.05 mol / L to 0.2 mol / L; the iron salt is selected from one or more of ferric nitrate, ferric chloride, and ferric sulfate.

[0019] And / or, the impregnation reaction time is 55 min-65 min, and the system pH is 7.5-8.5.

[0020] In one embodiment of the present invention, in S4, the hydroentangling reinforcement is performed sequentially as 14bar-16bar pre-wetting, 68bar-72bar front hydroentangling, 88bar-92bar reverse hydroentangling and 48bar-52bar surface finishing.

[0021] And / or, the water needle diameter of the hydroentangled reinforcement is 0.1mm-0.15mm, and the fiber web conveying speed is 9m / min-11m / min.

[0022] In one embodiment of the invention, in S4, the dehydration is carried out under a negative pressure of -0.4 bar to -0.6 bar.

[0023] In one embodiment of the present invention, in S4, the temperature of the hot air treatment is 105°C-115°C and the time is 18 min-22 min.

[0024] In one embodiment of the present invention, in S5, the temperature of the embossing and wrinkling process is 75℃-85℃, and the linear pressure is 48N / mm-52N / mm. The embossing and wrinkling process reserves shrinkage space for high-temperature carbonization, avoiding structural cracking of the material due to stress concentration. At the same time, the non-planar structure formed by the wrinkles enhances the multiple reflections and scattering of electromagnetic waves, thereby synergistically improving the electromagnetic shielding performance of the material.

[0025] In one embodiment of the present invention, in S5, the heat treatment first involves pre-oxidation in air at a rate of 1.8℃ / min-2.2℃ / min to 280℃-320℃ and holding for 55min-65min, causing the lyocell fibers to dehydrate and crosslink to form a high-temperature resistant structure to stabilize the fiber morphology; then, in nitrogen atmosphere, the temperature is raised to 760℃-840℃ at a rate of 4.8℃ / min-5.2℃ / min and held for 28min-32min for pyrolysis carbonization, removing non-carbon elements from the fibers and converting them into an amorphous carbon network; then, the temperature is raised to 1100-1300℃ at a rate of 7.5℃ / min-8.5℃ / min and held for 55min-65min for in-situ catalytic graphitization, using pre-loaded nano-iron particles as catalytic centers to induce the amorphous carbon to transform into highly conductive graphite microcrystals.

[0026] A second objective of this invention is to provide a multifunctional nonwoven material prepared by the method described above.

[0027] The technical solution of the present invention has the following advantages compared with the prior art:

[0028] (1) The preparation method described in this invention introduces an iron-based catalyst in situ on the surface of the Lyocell fiber, which significantly reduces the activation energy of the conversion of amorphous carbon into graphite microcrystals, so that the fiber can form highly intact graphite nanocrystals and construct a highly efficient conductive network at a lower temperature. This low-temperature catalysis strategy can realize the simultaneous construction of conductive functional structure and mechanical load-bearing skeleton, so that the material has both excellent electromagnetic shielding performance and good mechanical support performance.

[0029] (2) The preparation method described in this invention introduces a crimping and pleating process, which can pre-form a geometric structure with a stretch margin at the microscopic level. This structure can expand and deform at high temperature, physically dissipating the severe stress generated by the shrinkage of Lyocell fibers and playing a buffering role. At the same time, the gradient layup of fibers is achieved through airflow web formation, and the fibers are deeply interlocked in the thickness direction by hydroentangling reinforcement. The two work together to construct a transition region with gradually changing modulus, effectively dispersing the interfacial stress, thereby producing a carbonized material with a complete structure, flat surface and tight interlayer bonding. In addition, the pleated structure formed by the crimping and pleating process constitutes a three-dimensional spring array with a high compression recovery rate on a macroscopic level. During battery pack assembly and driving, it can dynamically adapt to the breathing effect of battery cells and the small displacement caused by road vibration, continuously maintaining the tight fit between the material and the battery shell. This solves the problem of the shielding effectiveness decay caused by poor contact of traditional hard carbon plates, ensuring that the material maintains low contact resistance and stable thermal conductivity throughout its entire life cycle, providing continuous and reliable safety protection for the battery system.

[0030] (3) The multifunctional nonwoven material described in this invention adopts a three-layer structure design. The bottom fiber web is mainly composed of high proportion of aramid fibers, which can provide excellent mechanical strength, electrical insulation and inherent flame retardant properties. The transition layer fiber web is composed of lyocell fibers and aramid fibers in a near-equal proportion. As a functional and structural transition layer, it can ensure smooth connection of interlayer performance and avoid interface defects caused by sudden performance changes. The surface fiber web is constructed with in-situ catalytic graphitized supported catalytic lyocell fibers to build a highly conductive and thermally conductive three-dimensional network, realizing efficient electromagnetic shielding and in-plane rapid heat conduction. This self-integrated structure that integrates conductivity and insulation can completely eliminate the interface thermal resistance and contact resistance problems caused by traditional multilayer material stacking. At the same time, it eliminates the need for additional insulating patches and support components, significantly improving the integration and lightweight level of internal components of new energy vehicle battery packs, and realizing the integration of structure and function.

[0031] (4) The multifunctional nonwoven material described in this invention uses lyocell fiber and waste aramid fiber as raw materials to transform traditional textile waste that is difficult to separate and is often downgraded or landfilled into high-performance functional materials. It has both environmental benefits and cost advantages, opening up a new path for high-value-added applications of waste textiles. Detailed Implementation

[0032] The present invention will be further described below with reference to specific embodiments, so that those skilled in the art can better understand and implement the present invention, but the embodiments are not intended to limit the present invention.

[0033] In this invention, unless otherwise stated, the devices used in the embodiments are shown in Table 1:

[0034] Table 1

[0035]

[0036] In this invention, unless otherwise stated, the lyocell fibers and aramid fibers used in the embodiments need to be pretreated as follows: first, the waste fibers are mechanically opened using a porcupine-type cotton opener, then placed in a 3wt% sodium hydroxide aqueous solution at a bath ratio of 1:30, washed at 70°C for 45 minutes, then washed with deionized water until neutral, and finally vacuum dried at 60°C for 3 hours.

[0037] Example 1

[0038] The multifunctional nonwoven material and its preparation method in this embodiment specifically include the following steps:

[0039] S1. Preparation of supported catalytic lyocell fibers: Lyocell fibers were first immersed in a 0.05 mol / L sodium citrate aqueous solution at a bath ratio of 1:40 and shaken in a 50℃ constant temperature water bath shaker for 60 min. Then, the fibers were removed and immersed in a 0.05 mol / L ferric nitrate aqueous solution. Under continuous stirring, 1 mol / L sodium hydroxide solution was slowly added dropwise to adjust the pH of the system to 8.0, and the reaction was continued under this condition for 60 min. After the reaction was completed, the fibers were repeatedly washed with deionized water until the washing solution was neutral and no iron ions were detected. Finally, the fibers were dried in an 80℃ vacuum drying oven for 2 h to obtain supported catalytic lyocell fibers.

[0040] S2. Preparation of the fiber web preform: Three airflow web forming machines arranged in series were used to form the fiber web under the following process parameters: average fiber length of 40 mm, ambient temperature of 22℃, humidity of 60%, main airflow velocity of 20 m / s, web forming curtain speed of 10 m / min, and vacuum degree of -0.8 kPa in the web forming zone. Multilayer fiber web preforms were continuously prepared through three web forming units. In the first web forming unit, lyocell fiber and aramid fiber were mixed at a mass ratio of 20:80 to obtain a surface density of 50 g / m². 2 The bottom layer is a fiber web, and the second web-forming unit is a mixture of lyocell fiber and aramid fiber at a mass ratio of 50:50, resulting in an areal density of 50 g / m². 2The transition layer fiber web, the third web-forming unit is made by mixing supported catalytic lyocell fibers and aramid fibers at a mass ratio of 80:20, to obtain an areal density of 50 g / m². 2 Surface fiber web;

[0041] S3. Preparation of nonwoven materials: The multi-layer fiber web preform is reinforced by hydroentangling using a hydroentangling machine. It is then subjected to a series of processes, including pre-wetting at 15 bar pressure, front hydroentangling at 70 bar pressure, reverse hydroentangling at 90 bar pressure, and surface finishing at 50 bar pressure. The process is carried out with a water needle diameter of 0.13 mm and a fiber web conveying speed of 10 m / min. Dehydration is completed under a negative pressure of -0.5 bar. The preform is then introduced into a hot air circulating oven and treated at 110°C for 20 minutes to reduce its moisture content to below 8%, thus obtaining the nonwoven material.

[0042] S4. Preparation of Multifunctional Nonwoven Materials: The nonwoven material was embossed using a nonwoven embossing machine to create pleats with a depth of 1.0mm-2.0mm at 80℃ and 50N / mm. The material was then placed flat in a graphite boat and subjected to staged heat treatment in a tube furnace. First, pre-oxidation was performed by heating from room temperature to 300℃ at a rate of 2℃ / min in air atmosphere and holding for 60min. Then, the temperature was maintained at 300℃, and nitrogen gas was continuously purged at a flow rate of 300mL / min for 30min. Finally, nitrogen gas was purged at a flow rate of 100mL / min. The material was heated to 800℃ at a rate of 5℃ / min and held for 30 min under a nitrogen atmosphere for pyrolysis carbonization. Then, it was heated to 1200℃ at a rate of 8℃ / min and held for 60 min for in-situ catalytic graphitization. After the heat treatment, the heating was stopped, and the material was cooled to below 100℃ under a nitrogen atmosphere at a flow rate of 50 mL / min. The resulting material was then immersed in a 0.5 mol / L hydrochloric acid solution at a bath ratio of 1:25 for 2 h at room temperature. After that, it was repeatedly rinsed with deionized water until neutral and then dried in an 80℃ vacuum drying oven for 4 h to obtain a multifunctional nonwoven material.

[0043] Example 2

[0044] The method is basically the same as in Example 1, except that the concentration of sodium citrate aqueous solution is 0.1 mol / L and the concentration of ferric nitrate aqueous solution is 0.1 mol / L.

[0045] Example 3

[0046] The method is basically the same as in Example 1, except that the concentration of sodium citrate aqueous solution is 0.2 mol / L and the concentration of ferric nitrate aqueous solution is 0.2 mol / L.

[0047] Example 4

[0048] The process is basically the same as in Example 2, except that the temperature for in-situ catalytic graphitization is 1100°C.

[0049] Example 5

[0050] The process is basically the same as in Example 2, except that the temperature for in-situ catalytic graphitization is 1300°C.

[0051] Example 6

[0052] The process is basically the same as in Example 2, except that: in the bottom fiber web, the ratio of Lyocell fiber to aramid fiber is 30:70 by mass, and in the top fiber web, the ratio of supported catalytic Lyocell fiber to aramid fiber is 70:30 by mass.

[0053] Example 7

[0054] The process is basically the same as in Example 2, except that: in the bottom fiber web, the ratio of Lyocell fiber to aramid fiber is 10:90 by mass, and in the top fiber web, the ratio of supported catalytic Lyocell fiber to aramid fiber is 90:10 by mass.

[0055] Comparative Example 1

[0056] The process is basically the same as in Example 2, except that: in the bottom fiber web, the ratio of Lyocell fiber to aramid fiber is 50:50 by mass, and in the top fiber web, the ratio of supported catalytic Lyocell fiber to aramid fiber is 50:50 by mass.

[0057] Comparative Example 2

[0058] The method is basically the same as in Example 2, except that the supported catalytic lyocell fiber is replaced with lyocell fiber.

[0059] Comparative Example 3

[0060] It is basically the same as Example 2, except that no embossing or wrinkling process is performed.

[0061] Test case

[0062] The electrical properties and other characteristics of the multifunctional nonwoven materials prepared in the examples and comparative examples were tested:

[0063] (1) Surface resistivity: The four probes of the four-probe tester are vertically pressed onto the sample surface in a straight line. A constant current is passed through the two outer probes, and the potential difference between the two inner probes is measured. The surface resistivity of the sample is calculated accordingly.

[0064] (2) Electromagnetic shielding effectiveness: The waveguide method was used, and the test was completed in the frequency range of 8.2GHz-12.4GHz with the help of a vector network analyzer (VNA) and an X-band (WR-90) rectangular waveguide system.

[0065] (3) In-plane thermal conductivity: determined according to GB / T 22588-2008 "Measurement of thermal diffusivity or thermal conductivity by flash method";

[0066] (4) Tensile strength: The test was conducted in accordance with GB / T 3923.1-2013 "Textiles - Tensile properties of fabrics - Part 1: Determination of breaking strength and elongation at break (strip method)";

[0067] (5) Compression recovery rate: determined in accordance with GB / T 24442.1-2009 "Determination of compression properties of textiles - Part 1: Constant method";

[0068] (6) Limiting Oxygen Index (LOI): Determined according to GB / T 5454-1997 "Test for Burning Performance of Textiles - Oxygen Index Method";

[0069] Table 2 shows the final measured relevant performance:

[0070] Table 2

[0071]

[0072] As can be seen from Table 2, the multifunctional nonwoven material prepared in the examples achieves synergistic improvement in electromagnetic shielding, thermal conductivity, mechanical strength, compression recovery rate and flame retardant properties.

[0073] Comparing Examples 1 and 2-3, it can be seen that the concentrations of organic carboxylate and iron salt catalysts directly determine the degree of graphitization and functional performance of the material. As the catalyst concentration increases from 0.05 mol / L to 0.2 mol / L, the surface resistivity continuously decreases, while the electromagnetic shielding effectiveness and in-plane thermal conductivity gradually increase. However, excessive catalyst can damage the fiber structure, leading to a decrease in tensile strength. This is because an appropriate amount of iron-based catalyst can be uniformly loaded onto the fiber surface, efficiently inducing the transformation of amorphous carbon into graphite microcrystals at low temperatures, thus constructing a complete conductive and thermally conductive network. If the concentration is too low, there will be insufficient catalytic sites, resulting in incomplete graphitization; if the concentration is too high, it can easily cause nanoparticle aggregation, destroying the fiber structure and weakening mechanical properties.

[0074] A comparison of Examples 2 and 4-5 shows that the in-situ catalytic graphitization temperature is crucial for balancing electrical and thermal conductivity with mechanical strength. 1200℃ is the optimal temperature; too low a temperature results in insufficient graphitization and a significant decrease in functional properties; too high a temperature induces thermal corrosion of the aramid fiber, reducing mechanical strength and compression recovery. This is because 1200℃ protects the aramid's mechanical skeleton while allowing the catalytic graphitization reaction to proceed fully; below this temperature, carbon atom rearrangement is incomplete, leading to an imperfect conductive network; above this temperature, the fiber skeleton is ablated, destroying structural integrity.

[0075] A comparison of Examples 2 and 6-7 shows that the component ratio of the three-layer fiber web directly affects the balance between function and mechanical properties. A gradient ratio of 80:20 for the surface layer loaded with catalytic lyocell fiber / aramid fiber and 20:80 for the bottom layer of lyocell / aramid fiber achieves optimal synergy between electromagnetic shielding, thermal conductivity, and strength. This is because this gradient structure ensures both a high-density conductive network on the surface and sufficient mechanical support and flame retardancy from the high aramid fiber ratio in the bottom layer. Reducing the proportion of catalytic fiber on the surface layer weakens the conductive shielding performance, while increasing the proportion reduces the overall mechanical strength.

[0076] Comparing Example 2 and Comparative Example 1, it can be seen that the three-layer gradient structure has an overwhelming advantage over the uniform hybrid structure. The uniform structure causes a significant increase in surface resistivity and a comprehensive deterioration in electromagnetic shielding effectiveness, in-plane thermal conductivity, tensile strength, and compressive recovery rate. This is because the gradient structure can achieve a smooth transition between interlayer functions, eliminating the problem of interfacial stress and impedance mismatch, while the uniform hybrid structure cannot form directional functional layers and mechanical support layers, making it difficult to achieve multifunctional synergy.

[0077] Comparing Example 2 and Comparative Example 2, it can be seen that the supported iron-based catalyst is the core prerequisite for achieving high conductivity, high shielding, and high thermal conductivity of the material. The material without catalytic modification almost loses its conductivity and electromagnetic shielding capabilities, and its thermal conductivity decreases significantly. This is because the graphitization degree of uncatalyzed lyocell fibers after high-temperature carbonization is extremely low, making it impossible to form a continuous conductive network. It only has an amorphous carbon structure, and its functional performance cannot meet the requirements.

[0078] Comparing Example 2 and Comparative Example 3, it can be seen that crimping is a necessary process to ensure material structural stability and high compression recovery rate. The compression recovery rate of the uncrimpeded material drops sharply, and its electromagnetic shielding and thermal conductivity are also significantly reduced. This is because the crimped structure can release the thermal shrinkage stress during high-temperature carbonization, preventing the material from curling and delaminating. At the same time, the three-dimensional structure brought by the crimps can enhance electromagnetic wave reflection and scattering, improve the shielding effect, and give the material high resilience.

[0079] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a multifunctional nonwoven material, characterized in that, Includes the following steps: S1. Lyocell fiber and aramid fiber are mixed at a mass ratio of (10-30):(70-90) and then formed into a web by airflow to obtain the bottom fiber web; S2. Lyocell fiber and aramid fiber are mixed at a mass ratio of (45-55): (45-55) and formed into a transition layer fiber web on the surface of the bottom fiber web described in S1 by airflow. S3. The supported catalytic lyocell fiber and aramid fiber are mixed at a mass ratio of (70-90):(10-30), and the mixture is formed into a surface fiber web on the surface of the transition layer fiber web described in S2 by airflow forming, thereby obtaining a multilayer fiber web preform; the supported catalytic lyocell fiber is prepared by sequentially pretreating lyocell fiber with an organic carboxylate solution and then impregnating it with an iron salt solution. S4. After hydroentangling and dehydration, the multilayer fiber web preform described in S3 is treated with hot air to obtain a nonwoven material. S5. After performing embossing and heat treatment on the nonwoven material described in S4, the multifunctional nonwoven material is obtained.

2. The method for preparing the multifunctional nonwoven material according to claim 1, characterized in that, In S1-S3, the process parameters for airflow web formation are independently: temperature 20℃-25℃, humidity 58%-62%, main air duct airflow velocity 18m / s-22m / s, web formation curtain velocity 9m / min-11m / min, and vacuum degree -0.7kPa to -0.9kPa.

3. The method for preparing the multifunctional nonwoven material according to claim 1, characterized in that, In S3, the concentration of the organic carboxylate solution is 0.05 mol / L to 0.2 mol / L; the organic carboxylate is selected from one or more of sodium citrate, sodium tartrate, and sodium gluconate. And / or, the pretreatment temperature is 45℃-55℃ and the time is 55min-65min.

4. The method for preparing the multifunctional nonwoven material according to claim 1, characterized in that, In S3, the concentration of the iron salt solution is 0.05 mol / L to 0.2 mol / L; the iron salt is selected from one or more of ferric nitrate, ferric chloride, and ferric sulfate. And / or, the impregnation reaction time is 55 min-65 min, and the system pH is 7.5-8.

5.

5. The method for preparing the multifunctional nonwoven material according to claim 1, characterized in that, In S4, the hydroentangling reinforcement is performed sequentially as follows: 14bar-16bar pre-wetting, 68bar-72bar front hydroentangling, 88bar-92bar reverse hydroentangling, and 48bar-52bar surface finishing. And / or, the water needle diameter of the hydroentangled reinforcement is 0.1mm-0.15mm, and the fiber web conveying speed is 9m / min-11m / min.

6. The method for preparing the multifunctional nonwoven material according to claim 1, characterized in that, In S4, the dehydration is carried out under a negative pressure of -0.4 bar to -0.6 bar.

7. The method for preparing the multifunctional nonwoven material according to claim 1, characterized in that, In S4, the temperature of the hot air treatment is 105℃-115℃, and the time is 18min-22min.

8. The method for preparing the multifunctional nonwoven material according to claim 1, characterized in that, In S5, the temperature of the embossing and wrinkling process is 75℃-85℃, and the linear pressure is 48N / mm-52N / mm.

9. The method for preparing the multifunctional nonwoven material according to claim 1, characterized in that, In S5, the heat treatment involves first heating to 280℃-320℃ in air at a rate of 1.8℃ / min-2.2℃ / min and holding at that temperature for 55min-65min, then heating to 760℃-840℃ in nitrogen at a rate of 4.8℃ / min-5.2℃ / min and holding at that temperature for 28min-32min, and finally heating to 1100-1300℃ at a rate of 7.5℃ / min-8.5℃ / min and holding at that temperature for 55min-65min.

10. A multifunctional nonwoven material prepared by the method according to any one of claims 1-9.

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