Method for the preparation of compressible tuned high absorption porous polyurethane electromagnetic shielding composite foams

Abstract

The application discloses a preparation method of compressible and tunable high-absorption porous polyurethane electromagnetic shielding composite foam, and a composite foam of MXene-coated PA6 microspheres and thermoplastic polyurethane is prepared through an electrostatic self-assembly and freeze-drying process. The composite foam has compressible and tunable electromagnetic shielding efficiency and a high absorption power coefficient, can be applied to more complex application scenarios, and reduces the harm of secondary pollution to the environment.

Description

Technical Field

[0001] The invention belongs to the technical field of electromagnetic shielding composite materials, and in particular relates to a method for preparing a compressible and tunable high-absorption porous polyurethane electromagnetic shielding composite foam. Background Art

[0002] With the development of society and the advancement of science and technology, radio communications and information technology have flourished. The advent of the 5G era has further improved the efficiency of communication and transmission. The development and application of various fields such as national defense, medical care, education, and home appliances have been further enhanced. However, with the high-frequency operation and packaging density of electronic devices, the electromagnetic compatibility issues between electronic components have become increasingly prominent, and the accompanying electromagnetic radiation has become one of the hidden dangers to human health. Traditional electromagnetic shielding materials based on reflection loss as the dominant mechanism are generally metal materials, but their high density and susceptibility to chemical corrosion cannot be ignored. In addition, due to the skin effect of highly conductive metals, a large amount of electromagnetic waves are reflected at the material interface due to impedance mismatch, causing serious secondary pollution. This not only limits its application in electromagnetic shielding, but also poses a significant risk to the ecological environment.

[0003] In recent years, tunable electromagnetic shielding materials have attracted widespread attention because they can be modified according to specific application and environmental requirements. Patent CN115322442A designed a temperature-responsive, tunable intelligent electromagnetic shielding film. When the material is heated from room temperature to 80°C, the electromagnetic shielding effectiveness is increased from less than 20 dB to over 50 dB. However, the energy consumption caused by the temperature increase and the loss of the material itself limit the practical application of the material. Liu et al. prepared MXene aerogel with compressible tunable electromagnetic shielding effectiveness, which can be flexibly changed within the range of 2-25 dB. However, MXene aerogel is easily oxidized and is not conducive to long-term operation. Polymer foam is widely used by researchers to prepare high-absorption electromagnetic shielding materials because its porous structure increases the number of interfaces within the material, causing electromagnetic waves to undergo multiple reflection losses within the material. Patent CN116041780A designed a multi-layer porous composite foam. With increasing thickness, the electromagnetic shielding effectiveness increases from 23 dB to 40 dB. However, the absorption coefficient decreases from 0.55 to 0.15, failing to reconcile the contradiction between high electromagnetic shielding effectiveness and high absorption coefficient. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention provides a method for preparing a compressible and tunable, highly absorptive porous polyurethane composite foam for electromagnetic shielding. The polyurethane composite foam prepared by the present invention combines compressibility and tunability with a high absorption coefficient, making it suitable for more complex applications and effectively reducing secondary pollution. This provides a reference for a new generation of intelligent, green, and environmentally friendly electromagnetic shielding materials.

[0005] The technical solutions of the present invention are as follows:

[0006] A method for preparing a compressible and tunable high-absorption porous polyurethane electromagnetic shielding composite foam comprises the following steps:

[0007] (1) Etching the MAX phase precursor using lithium fluoride and concentrated hydrochloric acid to obtain a single layer or a few layers of MXene;

[0008] The specific operation is as follows: MAX phase precursor, lithium fluoride, concentrated hydrochloric acid (12 mol / L) and deionized water are mixed, stirred (500 rpm) at 30-40 ° C for 18-30 hours, then centrifuged at 3500 rpm for 5 minutes, washed with deionized water until the pH of the supernatant is neutral, collected and frozen, added with deionized water, ultrasonicated under N2 atmosphere for 30 minutes, and then centrifuged at 7000 rpm for 15 minutes. The supernatant is freeze-dried to obtain a single layer or few layers of MXene;

[0009] The preferred MAX phase precursor is Ti3AlC2;

[0010] The molar ratio of lithium fluoride to concentrated hydrochloric acid is 1:3 to 1:3, preferably 1:3;

[0011] Freeze drying temperature is -60 to -45°C and time is 24 to 72 hours;

[0012] (2) Nylon microspheres (PA6S) were added to a polydimethyldiallylammonium chloride (PDDA) aqueous solution and stirred at room temperature for 4 to 6 hours. The solution was then centrifuged and washed, and the precipitate was collected and vacuum-dried to obtain PDDA@PA6S.

[0013] The particle size of nylon microspheres is 2 to 10 microns;

[0014] The mass ratio of nylon microspheres to polydimethyldiallylammonium chloride is 1:1 to 1:3, preferably 1:2.1;

[0015] Preferably, the volume fraction of polydimethyldiallylammonium chloride in the polydimethyldiallylammonium chloride aqueous solution is 2%;

[0016] (3) adding the MXene obtained in step (1) and the PDDA@PA6S obtained in step (2) to deionized water, ultrasonically mixing them under nitrogen atmosphere at room temperature, continuing stirring for 4 to 6 hours, then centrifuging, collecting the precipitate and vacuum drying to obtain MXene@PA6S;

[0017] MXene@PA6S is obtained by electrostatic self-assembly; the mass ratio of MXene to PDDA@PA6S is 1:2 to 1:3, preferably 1:3;

[0018] (4) blending the polymer with the MXene@PA6S solution obtained in step (3) in an organic solvent, exchanging the solvent by a water solidification method, and freeze-drying to obtain a composite foam;

[0019] The specific operation is as follows: the polymer and MXene@PA6S are added to the organic solvent, and the resulting organic mixture is ultrasonically mixed under N2 atmosphere at room temperature. Stirring is continued for 4 to 6 hours. The thoroughly blended solution is then poured into a mold and placed in non-flowing deionized water for 3 hours. After solidification, it is taken out and freeze-dried to obtain a composite foam.

[0020] The polymer is selected from thermoplastic polyurethane (TPU); the organic solvent is selected from DMF; preferably, the total mass fraction of the polymer and MXene@PA6S in the organic mixture is 20%;

[0021] Based on the total mass of the composite foam, MXene@PA6S accounts for 5-20% by mass, preferably 15%;

[0022] The freeze-drying temperature is -60 to -45°C and the time is 48 to 72 hours.

[0023] The technical principle of the present invention is described as follows:

[0024] First, PDDA modifies the surface charge of PA6S, allowing it to electrostatically self-assemble with the oppositely charged MXene. PA6S exhibits a negative surface charge due to its amide groups, while the MXene surface, etched with lithium fluoride, exhibits a similarly negative charge due to its abundant hydroxyl and fluorine groups. Electrostatic repulsion prevents the two from binding. Therefore, PA6S is modified with a cationic surfactant to alter its original surface charge, giving it a positive charge, thereby enabling electrostatic self-assembly with the negatively charged MXene. The resulting MXene@PA6S composite foam effectively improves the overall absorption performance of the composite foam. The surface defects and functional groups created by etching the MXene generate dipoles in response to electromagnetic fields, increasing the material's dielectric loss capability. Furthermore, the nanometer-scale thickness of the MXene prevents electromagnetic waves from being fully reflected before reaching the skin depth, allowing them to penetrate the MXene@PA6S sphere and undergo multiple reflection losses.

[0025] On the other hand, MXene@PA6S was introduced into the TPU skeleton through solution blending and then prepared into a polyurethane electromagnetic shielding composite foam through water curing and freeze-drying processes. Due to the excellent conductivity and isolation structure of MXene@PA6S and the porous structure of the composite foam, the overall composite foam has both good electromagnetic shielding performance and absorption power coefficient. From a macroscopic perspective, the pores increase the number of interfaces within the material, causing electromagnetic waves to experience multiple reflection losses between the pores and the skeleton, thereby improving the material's absorption performance; from a microscopic perspective, electromagnetic waves can experience multiple reflection losses within the MXene@PA6S spheres. In addition, the porous structure expands the spacing of the internal skeletons, and the excellent resilience makes it easy to adjust the spacing of the skeletons inside the composite foam through compression, thereby adjusting the contact degree of the conductive network and tuning the electromagnetic shielding effectiveness.

[0026] The beneficial effects of the present invention are:

[0027] 1. Polyurethane composite foam can tune electromagnetic shielding effectiveness by simply compressing and releasing pressure. Compared to other stimulus response methods, pressure response is less damaging to the material, has a simpler tuning method, and is faster.

[0028] 2. A MXene@PA6S particle was designed from a microscopic perspective. Through a modified and electrostatic self-assembly process, a small MXene particle was coated on a larger PA6S particle. This exhibited a different coating and absorption mechanism than conventional MXene electrostatic self-assembly, resulting in excellent conductivity and absorption properties, lowering the percolation threshold while minimizing environmental pollution caused by secondary reflections.

[0029] 3. From a technological perspective, compared with the vacuum impregnation composite method, introducing MXene@PA6S particles into the TPU skeleton through solution blending and water curing reduces the contact area between the easily oxidized MXene and the air, which can effectively improve the working stability of the material.

[0030] 4. Overall, under the synergistic effect of MXene@PA6S particles, TPU and foam cells, electromagnetic waves can be reflected multiple times between the foam cells and the skeleton. The composite foam has excellent absorption performance due to the increase in propagation paths, reflection losses caused by impedance differences, and interface polarization losses. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 : Shielding mechanism of the compressible and tunable high-absorption electromagnetic shielding polymer composite foam of the present invention. DETAILED DESCRIPTION

[0032] The present invention is further described below by means of specific examples, but the protection scope of the present invention is not limited thereto.

[0033] In the present invention, unless otherwise specified, all equipment and raw materials can be purchased from the market or are commonly used in the industry. The raw materials and composite materials of all embodiments are vacuum dried and freeze-dried under the same conditions. The stirring method is magnetic stirring. The waveguide test is the average electromagnetic shielding effectiveness of the composite material in the X-band (8.2GHz-12.4GHz).

[0034] Unless otherwise specified, the methods in the following embodiments are all conventional methods in the art.

[0035] The PA6S used in the examples was laboratory-prepared. The raw materials included: caprolactam (technical grade, BASF), sodium hydroxide (AR, Xilong Chemical Company), toluene diisocyanate (AR, Alfa Aesar Chemical Co., Ltd.), and polyethylene glycol (Mn = 4000, Shanghai Aladdin Biochemical Co., Ltd.). The preparation method of PA6S was based on the method described by LIU Y, FU X, DUAN J, et al. (Self-assembly morphology evolution of the polyamide 6 (PA6) component in the PA6 / polyethylene glycol system by in situ polymerization of ε-caprolactammonomer). (Polymer International, 2018).

[0036] PDDA (20%, 600-900 cp, Shanghai BiDe Pharmaceutical Technology Co., Ltd.).

[0037] TPU (6065A, Covestro, Germany).

[0038] Ti3AlC2 (400 mesh, Forsman Technology Co., Ltd.).

[0039] Lithium fluoride (99.9%, Shandong Keyuan Biochemical Co., Ltd.).

[0040] Example 1

[0041] Composite foams with a MXene@PA6S:TPU ratio of 1:4 were prepared and subjected to vector network analysis in an uncompressed state. First, a single or few-layer MXene was prepared by weighing 0.5g of Ti3AlC2 and 0.75g of LiF. These chemicals were added to a mixture of 7.5ml of concentrated hydrochloric acid and 2.5ml of deionized water. The mixture was stirred at room temperature for 24 hours. After the reaction, the solution was centrifuged at 3500 rpm for 5 minutes, the supernatant was discarded, and the precipitate was washed with deionized water until the pH of the supernatant was neutral. The resulting precipitate was refrigerated for 12 hours, 20ml of deionized water was added, and ultrasonication was performed under a nitrogen atmosphere for 30 minutes. The solution was then centrifuged at 7000 rpm for 15 minutes, and the supernatant was poured into a Petri dish and refrigerated for 24 hours. The frozen sample was dried in a freeze dryer for 24 hours to obtain a single or few-layer MXene powder. Next, PDDA-modified PA6S was prepared. 0.5 g of PA6S was added to 50 ml of a 2 vol% PDDA aqueous solution and stirred at room temperature for 5 hours. The resulting solution was then centrifuged and washed with deionized water at 4500 rpm for 5 minutes, repeating this process three times. The precipitate was dried in a vacuum oven at 60°C for 12 hours to obtain PDDA@PA6S. Next, MXene@PA6S particles were prepared with a MXene:PDDA@PA6S ratio of 1:3. 0.1 g of MXene and 0.3 g of PDDA@PA6S were weighed. This sample was added to 50 ml of deionized water, ultrasonicated for 20 minutes at room temperature under a nitrogen atmosphere, and stirred for an additional 5 hours. The resulting solution was centrifuged at 4500 rpm for 5 minutes, the supernatant discarded, and the precipitate dried in a vacuum oven at 60°C for 12 hours to obtain MXene@PA6S powder. Finally, 0.25 g of MXene@PA6S and 1 g of TPU were weighed. The above-mentioned chemicals were added to 6.6 ml of DMF solvent and ultrasonicated at room temperature under an N2 atmosphere for half an hour, followed by stirring for 5 hours. The resulting solution was poured into a 30 mm inner diameter Petri dish and placed in stagnant deionized water for curing for 3 hours. The solution was then frozen for 12 hours. After freezing, the foam was freeze-dried at -60°C for 48 hours to obtain a polyurethane composite foam. Electromagnetic shielding tests were performed using a vector network analyzer. The electromagnetic shielding parameters are shown in Table 1.

[0042] Example 2

[0043] Composite foams with a ratio of MXene@PA6S:TPU = 1:9 were prepared and subjected to vector network analysis in an uncompressed state. First, a single or few-layer MXene was prepared by weighing 0.5g of Ti3AlC2 and 0.75g of LiF. These chemicals were added to a mixture of 7.5ml of concentrated hydrochloric acid and 2.5ml of deionized water. The mixture was stirred at room temperature for 24 hours. After the reaction, the solution was centrifuged at 3500 rpm for 5 minutes, the supernatant was discarded, and the precipitate was washed with deionized water until the pH of the supernatant was neutral. The resulting precipitate was refrigerated for 12 hours, 20ml of deionized water was added, and ultrasonication was performed under a nitrogen atmosphere for 30 minutes. The solution was then centrifuged at 7000 rpm for 15 minutes, and the supernatant was poured into a Petri dish and refrigerated for 24 hours. The frozen sample was dried in a freeze dryer for 24 hours to obtain a single or few-layer MXene powder. Next, PDDA-modified PA6S was prepared. 0.5 g of PA6S was added to 50 ml of a 2 vol% PDDA aqueous solution and stirred at room temperature for 5 hours. The resulting solution was then centrifuged and washed with deionized water at 4500 rpm for 5 minutes, repeating this process three times. The precipitate was dried in a vacuum oven at 60°C for 12 hours to obtain PDDA@PA6S. Next, MXene@PA6S particles were prepared with a MXene:PDDA@PA6S ratio of 1:3. 0.1 g of MXene and 0.3 g of PDDA@PA6S were weighed. This sample was added to 50 ml of deionized water, ultrasonicated for 20 minutes at room temperature under a nitrogen atmosphere, and stirred for an additional 5 hours. The resulting solution was centrifuged at 4500 rpm for 5 minutes, the supernatant discarded, and the precipitate dried in a vacuum oven at 60°C for 12 hours to obtain MXene@PA6S powder. Finally, 0.125 g of MXene@PA6S and 1.125 g of TPU were weighed. The above-mentioned chemicals were added to 6.6 ml of DMF solvent and ultrasonicated at room temperature under an N2 atmosphere for half an hour, followed by stirring for 5 hours. The resulting solution was poured into a 30 mm inner diameter Petri dish and placed in stagnant deionized water for curing for 3 hours. The solution was then frozen for 12 hours. After freezing, the foam was freeze-dried at -60°C for 48 hours to obtain a polyurethane composite foam. Electromagnetic shielding tests were performed using a vector network analyzer. The electromagnetic shielding parameters are shown in Table 1.

[0044] Example 3

[0045] Composite foams with a ratio of MXene@PA6S:TPU = 1:19 were prepared and subjected to vector network analysis in an uncompressed state. First, a single or few-layer MXene was prepared by weighing 0.5g of Ti3AlC2 and 0.75g of LiF. These chemicals were added to a mixture of 7.5ml of concentrated hydrochloric acid and 2.5ml of deionized water. The mixture was stirred at room temperature for 24 hours. After the reaction, the solution was centrifuged at 3500rpm for 5 minutes, the supernatant was discarded, and the precipitate was washed with deionized water until the pH of the supernatant was neutral. The resulting precipitate was refrigerated for 12 hours, 20ml of deionized water was added, and ultrasonication was performed under a nitrogen atmosphere for 30 minutes. The solution was then centrifuged at 7000rpm for 15 minutes, and the supernatant was poured into a Petri dish and refrigerated for 24 hours. The frozen sample was dried in a freeze dryer for 24 hours to obtain a single or few-layer MXene powder. Next, PDDA-modified PA6S was prepared. 0.5 g of PA6S was added to 50 ml of a 2 vol% PDDA aqueous solution and stirred at room temperature for 5 hours. The resulting solution was then centrifuged and washed with deionized water at 4500 rpm for 5 minutes, repeating this process three times. The precipitate was dried in a vacuum oven at 60°C for 12 hours to obtain PDDA@PA6S. Next, MXene@PA6S particles were prepared with a MXene:PDDA@PA6S ratio of 1:3. 0.1 g of MXene and 0.3 g of PDDA@PA6S were weighed and added to 50 ml of deionized water. After ultrasonication for 20 minutes at room temperature under a nitrogen atmosphere, stirring continued for 5 hours. The resulting solution was centrifuged at 4500 rpm for 5 minutes, the supernatant discarded, and the precipitate dried in a vacuum oven at 60°C for 12 hours to obtain MXene@PA6S powder. Finally, 0.0625g of MXene@PA6S and 1.1875g of TPU were weighed. These chemicals were added to 6.6ml of DMF solvent and ultrasonicated at room temperature under a nitrogen atmosphere for half an hour, followed by stirring for 5 hours. The resulting solution was poured into a 30mm inner diameter Petri dish and placed in stagnant deionized water for curing for 3 hours. The dish was then frozen for 12 hours. After freezing, the foam was freeze-dried at -60°C for 48 hours to produce a polyurethane composite foam. Electromagnetic shielding tests were performed using a vector network analyzer. The electromagnetic shielding parameters are shown in Table 1.

[0046] Comparative Example 1:

[0047] Prepare composite foams with a MXene:TPU ratio of 1:4. First, prepare a single or few-layer MXene. Weigh 0.5g of Ti3AlC2 and 0.75g of LiF. Add these chemicals to a mixed solution consisting of 7.5ml of concentrated hydrochloric acid and 2.5ml of deionized water. Stir at room temperature for 24 hours. Centrifuge the solution at 3500rpm for 5 minutes, discard the supernatant, and wash the precipitate with deionized water until the pH is neutral. Refrigerate the resulting precipitate for 12 hours, add 20ml of deionized water, and sonicate under a nitrogen atmosphere for 30 minutes. Then, centrifuge the solution at 7000rpm for 15 minutes, pour the supernatant into a Petri dish, and refrigerate for 24 hours. Dry the frozen sample in a freeze dryer for 24 hours to obtain a single or few-layer MXene powder. Finally, weigh 0.25g of MXene and 1g of TPU. The above-mentioned chemicals were added to 6.6 ml of DMF solvent and ultrasonicated at room temperature under an N2 atmosphere for half an hour, followed by stirring for 5 hours. The resulting solution was poured into a 30 mm inner diameter Petri dish and placed in stagnant deionized water for curing for 3 hours. The solution was then frozen for 12 hours. After freezing, the foam was freeze-dried at -60°C for 48 hours to obtain a polyurethane composite foam. Electromagnetic shielding tests were performed using a vector network analyzer. The electromagnetic shielding parameters are shown in Table 1.

[0048] Comparative Example 2:

[0049] A composite foam with a ratio of MXene@PA6S:TPU = 1:4 was prepared, and a vector network analysis test was performed under a compressive strain of 20%. The specific steps were the same as in Example 1.

[0050] Comparative Example 3:

[0051] A composite foam with a ratio of MXene@PA6S:TPU = 1:4 was prepared, and a vector network analysis test was performed under a compressive strain of 50%. The specific steps were the same as in Example 1.

[0052] Table 1

[0053] Total electromagnetic shielding effectiveness (dB) Absorption coefficient Example 1 38.42 0.61 Example 2 29.81 0.71 Example 3 8.24 0.19 Comparative Example 1 11.19 0.29 Comparative Example 2 24.41 0.55 Comparative Example 3 52.20 0.31

[0054] Comparative Examples 1, 2 and 3, the mass fraction of MXene@PA6S in the composite material decreases from 20wt% to 5wt%, and the electromagnetic shielding effectiveness and absorption coefficient of the composite material both show a downward trend. Because MXene@PA6S with a core-shell structure isolates the conductive particles from the periphery of the PA6 microspheres. On the one hand, MXene@PA6S effectively reduces the percolation threshold of the composite material under the synergistic effect of the pores, thereby more conducive to the construction of the conductive network, and the more perfect the conductive network, the better the electrical conductivity, which is a key factor affecting the electromagnetic shielding effectiveness. On the other hand, this structure is conducive to the multiple reflection loss of electromagnetic waves inside the PA6 microspheres, and converts energy into heat under the interface polarization, thereby improving the absorption coefficient. This also explains why, in Example 1 and Comparative Example 1, MXene@PA6S / TPU has more excellent electromagnetic shielding effectiveness and absorption coefficient than MXene / TPU under the same additive content.

[0055] In the composite material, MXene@PA6S is mainly loaded on the TPU skeleton and the pore wall, and the pore structure is conducive to increasing the multiple reflection loss, but also causes the conductive particles to be separated by the pores, resulting in uneven conductive network. Therefore, as can be seen from Comparative Example 1 and Comparative Example 2, as the compressive strain increases to 20%, the contact area of the conductive particles increases due to the compression of the pores to a certain extent, but the degree of multiple reflection loss is greater than the influence of the increase in electrical conductivity on the electromagnetic shielding effectiveness, and thus the electromagnetic shielding performance decreases under a 20% compressive strain. However, as the strain continues to increase, the influence of the integrity of the conductive network on the electromagnetic shielding effectiveness is gradually greater than the decrease in multiple reflection loss, which explains the significant increase in electromagnetic shielding effectiveness under a 50% strain in Comparative Example 3. At the same time, as the degree of pore compression increases, the internal multiple reflection loss decreases, which affects the absorption performance of the material. In addition, due to the increase in electrical conductivity of the composite material, the impedance difference increases, the proportion of the reflection coefficient increases, and the absorption coefficient shows a downward trend.

[0056] The principles and implementation modes of the present application are described by applying specific examples, but the implementation modes of the present application are not limited by the above examples, and any changes, modifications, substitutions, combinations and simplifications made without departing from the spirit and principles of the present application shall be equivalent replacement modes and shall be included in the protection scope of the present application.

Claims

1. A method for preparing a compressible and tunable high-absorption porous polyurethane electromagnetic shielding composite foam, characterized in that: The following steps are involved: (1) Etching the MAX phase precursor using lithium fluoride and concentrated hydrochloric acid to obtain a single layer or a few layers of MXene; (2) Adding nylon microspheres to a polydimethyldiallyl ammonium chloride aqueous solution, stirring at room temperature for 4 to 6 hours, then centrifuging and washing, collecting the precipitate and vacuum drying to obtain PDDA@PA6S; (3) adding the MXene obtained in step (1) and the PDDA@PA6S obtained in step (2) to deionized water, ultrasonically mixing them under nitrogen atmosphere at room temperature, continuing stirring for 4 to 6 hours, then centrifuging, collecting the precipitate and vacuum drying to obtain MXene@PA6S; (4) The polymer is blended with the MXene@PA6S solution obtained in step (3) in an organic solvent, and then the solvent is exchanged by a water solidification method and freeze-dried to obtain a composite foam.

2. The method for preparing the compressible and tunable high-absorption porous polyurethane electromagnetic shielding composite foam according to claim 1, characterized in that: Step (1) is as follows: MAX phase precursor, lithium fluoride, concentrated hydrochloric acid and deionized water are mixed, stirred at 30-40°C for 18-30h, then centrifuged at 3500rpm for 5min, and the precipitate is washed with deionized water until the pH of the supernatant is neutral. After the precipitate is collected and frozen, deionized water is added, ultrasonicated under N2 atmosphere for 30min, and then centrifuged at 7000rpm for 15min. The supernatant is freeze-dried to obtain a single layer or a few layers of MXene; The MAX phase precursor is Ti3AlC2; Concentrated hydrochloric acid is 12mol / L.

3. The method for preparing the compressible and tunable high-absorption porous polyurethane electromagnetic shielding composite foam according to claim 2, characterized in that: The molar ratio of lithium fluoride to concentrated hydrochloric acid is 1:3 to 1:

3.

4. The method for preparing the compressible and tunable high-absorption porous polyurethane electromagnetic shielding composite foam according to claim 1, characterized in that: In step (2), the particle size of the nylon microspheres is 2 to 10 microns.

5. The method for preparing the compressible and tunable high-absorption porous polyurethane electromagnetic shielding composite foam according to claim 1, characterized in that: In step (2), the mass ratio of nylon microspheres to polydimethyldiallylammonium chloride is 1:1 to 1:

3.

6. The method for preparing the compressible and tunable high-absorption porous polyurethane electromagnetic shielding composite foam according to claim 1, characterized in that: In step (2), the volume fraction of polydimethyldiallylammonium chloride in the polydimethyldiallylammonium chloride aqueous solution is 2%.

7. The method for preparing the compressible and tunable high-absorption porous polyurethane electromagnetic shielding composite foam according to claim 1, characterized in that: In step (3), the mass ratio of MXene to PDDA@PA6S is 1:2 to 1:

3.

8. The method for preparing the compressible and tunable high-absorption porous polyurethane electromagnetic shielding composite foam according to claim 1, characterized in that: Step (4) is as follows: the polymer and MXene@PA6S are added to the organic solvent, the resulting organic mixture is ultrasonically mixed under N2 atmosphere at room temperature, and stirring is continued for 4 to 6 hours. The thoroughly blended solution is then poured into a mold and placed in non-flowing deionized water for 3 hours. After solidification, it is taken out and freeze-dried to obtain a composite foam; The polymer is selected from thermoplastic polyurethane; The organic solvent is selected from DMF.

9. The method for preparing the compressible and tunable high-absorption porous polyurethane electromagnetic shielding composite foam according to claim 8, characterized in that: The total mass fraction of polymer and MXene@PA6S in the organic mixed solution is 20%.

10. The method for preparing the compressible and tunable high-absorption porous polyurethane electromagnetic shielding composite foam according to claim 8, characterized in that: Based on the total mass of the composite foam, MXene@PA6S accounts for 5-20% by mass.

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