Ultralight microwave absorption nanofiber material and preparation method thereof

Abstract

The invention provides an ultralight microwave absorbing nanofiber material and a preparation method thereof, and relates to the technical field of wave absorbing materials. The preparation method comprises the following steps: S1, immersing a polyurethane fiber membrane into a mixed solution of dopamine and a buffer solution for polymerization reaction to obtain a polydopamine-polyurethane fiber membrane; s2, dispersing the modified carbon nanotubes in a solvent, then adding a polydopamine-polyurethane fiber membrane, applying a vertical electric field, performing ultrasonic treatment, then immersing into a reducing agent, and drying to obtain a carbon nanotube coated polydopamine-polyurethane fiber membrane; and S3, carrying out hot pressing treatment on the carbon nanotube coated polydopamine-polyurethane fiber membrane to obtain the ultralight microwave absorption nanofiber material. The fiber material meets the requirements of efficient wave absorption, mechanical property improvement and absorption frequency stability under the condition of low filler addition.

Description

Technical Field

[0001] The present invention relates to the technical field of microwave absorbing materials, and more particularly, to an ultra-light microwave absorbing nanofiber material and a preparation method thereof. Background Art

[0002] With the widespread popularity of electronic devices and wireless communication systems, electromagnetic interference (EMI) has become an increasingly serious environmental problem. To effectively reduce or eliminate this interference, various types of microwave absorbing materials have been developed to absorb and attenuate unnecessary electromagnetic radiation. These materials play a crucial role in military stealth technology, civilian electronic products, and electromagnetic compatibility, etc.

[0003] A common method for preparing microwave absorbing materials is direct polymerization of monomers. This method results in a relatively dense structure, which affects the microwave absorbing performance because microwave absorbing materials require a porous or layered structure to effectively absorb electromagnetic waves of different frequencies. In terms of strength, the materials prepared by direct polymerization may be relatively hard, lack toughness, and are prone to cracking. Additionally, there is the method of preparing microwave absorbing materials by electrospinning, where a polymer solution or melt is stretched into nanofibers through a high-voltage electric field to form a non-woven fabric or a porous structure. This structure has a high specific surface area and porosity, which may be more conducive to multiple reflections and absorption of electromagnetic waves, thereby improving the microwave absorbing performance.

[0004] In electrospinning technology, increasing the filler amount is often used to meet the high microwave absorbing requirements of the material. Carbon nanotubes have a low density and excellent conductivity, and are one of the commonly used fillers. However, when the amount of carbon nanotubes added is increased to improve the microwave absorbing efficiency, carbon nanotubes are prone to agglomeration due to van der Waals forces in the spinning solution, resulting in uneven distribution in the matrix and forming local conductive regions, reducing the microwave absorbing efficiency. The high conductivity of carbon nanotubes will form a continuous conductive network inside the material, causing electromagnetic wave reflection rather than absorption, leading to impedance mismatch and weakening the microwave absorbing performance. In addition, carbon nanotubes may be damaged during the electrospinning process due to high voltage or shear force, and their structure is destroyed, affecting their performance. At the same time, it will also affect the interfacial bonding with the matrix and reduce the mechanical properties of the material. Summary of the Invention

[0005] The purpose of the present invention is to provide a preparation method of an ultra-light microwave absorbing nanofiber material, which can make the material light in weight, have a low filler addition amount, high modulus, and high microwave absorbing intensity.

[0006] Another purpose of the present invention is to provide an ultra-light microwave absorbing nanofiber material, which has excellent microwave absorbing performance and good mechanical properties.

[0007] The present invention is achieved through the following technical solutions:

[0008] On the one hand, a method for preparing an ultra-light microwave-absorbing nanofiber material is provided, including the following steps:

[0009] S1. Immerse a polyurethane fiber membrane in a mixed solution of dopamine and a buffer solution for polymerization reaction to obtain a polydopamine-polyurethane fiber membrane;

[0010] S2. Disperse modified carbon nanotubes in a solvent, then add the polydopamine-polyurethane fiber membrane, apply a vertical electric field, perform ultrasonic treatment, and then immerse it in a reducing agent and dry it to obtain carbon nanotube@polydopamine-polyurethane fiber membrane;

[0011] S3. Thermally press the carbon nanotube@polydopamine-polyurethane fiber membrane to obtain an ultra-light microwave-absorbing nanofiber material.

[0012] On the other hand, an ultra-light microwave-absorbing nanofiber material prepared by the above method is provided.

[0013] Mechanism of the present invention:

[0014] Construct a nanofiber porous network skeleton through electrospinning technology, and use the elastic segments (polyester / polyether) of thermoplastic polyurethane to improve the fiber toughness, reduce the fiber brittleness, prevent fiber breakage, and improve the strength of the nanofiber skeleton.

[0015] Modify the surface of the polyurethane fiber membrane with polydopamine. On the one hand, use the adhesion effect of polydopamine to make the carbon nanotubes adhere to the fiber skeleton and be fixed in the holes of the network structure, which not only reduces the filler addition amount but also ensures the wave absorption performance; on the other hand, the amino group of polydopamine forms a covalent bond with the functional groups on the surface of the modified carbon nanotubes to realize the pre-dispersion of the modified carbon nanotubes and inhibit the filler aggregation; on the third hand, the catechol group of polydopamine forms a hydrogen bond with the amino group of polyurethane to enhance the interfiber binding force and improve the fiber mechanical properties.

[0016] Apply a vertical electric field. During the attachment process of the carbon nanotubes, use the conductivity of the carbon nanotubes to induce their alignment along the electric field direction, reduce the lateral aggregation, prevent wave absorption anisotropy while improving the uniformity of the carbon nanotube distribution. Use a reducing agent to initiate a mild reduction reaction of the polydopamine on the surface of the carbon nanotubes to enhance the interfacial binding between the carbon nanotubes and the fibers.

[0017] Through thermocompression treatment, the surface fibers are partially melted to form a dense protective layer, and the inner layer retains a porous structure. At the same time, the alignment of the carbon nanotubes compensates for the dielectric loss, taking into account both the material strength and the wave absorption performance.

[0018] The conductive network connected by carbon nanotubes with a high aspect ratio provides more paths for the migration and transition of free electrons, resulting in effective conductive losses. Reasonably constructing a porous structure and introducing air into the pores can not only significantly reduce the density of the filler, but also optimize the impedance matching, increase the incidence of electromagnetic waves, and thus effectively improve the wave absorption performance. In addition, the multi-level heterointerfaces and numerous functional groups in polydopamine and polyurethane cause strong polarization losses, enabling the nanofiber material to exhibit excellent loss and EAB values across the entire frequency and thickness range.

[0019] The technical solution of the present invention has at least the following advantages and beneficial effects:

[0020] A porous nanofiber framework was prepared by electrospinning, and then the surface of the polyurethane fiber membrane was modified with polydopamine to optimize the binding ability between polyurethane and carbon nanotubes, enabling the carbon nanotubes to enter and adhere inside the network under ultrasonic action. The porous network structure not only reduces the material mass but also introduces air and optimizes the impedance performance. The heteroatoms and functional groups in polydopamine and polyurethane can serve as polarization centers, resulting in significant polarization losses, making the obtained nanofiber material have excellent microwave absorption performance of -63.5 dB and an optimal effective absorption bandwidth of 8.6 GHz, meeting the requirements of achieving high-efficiency wave absorption, improving mechanical properties, and maintaining the stability of absorption frequency with low filler addition. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a flowchart of the ultra-light microwave-absorbing nanofiber material provided by the present invention;

[0022] Figure 2 It is a schematic diagram of the wave absorption performance of the ultra-light microwave-absorbing nanofiber material obtained in Example 1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention will be further described below in conjunction with specific embodiments, but the embodiments do not impose any form of limitation on the present invention. Unless otherwise specified, the raw material reagents used in the embodiments of the present invention are conventionally purchased raw material reagents.

[0024] A preparation method of an ultra-light microwave-absorbing nanofiber material includes the following steps:

[0025] S1. Immerse the polyurethane fiber membrane in a mixed solution of dopamine and buffer solution for polymerization reaction to obtain a polydopamine-polyurethane fiber membrane;

[0026] S2. Disperse the modified carbon nanotubes in a solvent, then add the polydopamine-polyurethane fiber membrane, apply a vertical electric field, perform ultrasonic treatment, and then immerse it in a reducing agent and dry to obtain a carbon nanotube@polydopamine-polyurethane fiber membrane;

[0027] S3. Thermally press the carbon nanotube@polydopamine-polyurethane fiber membrane to obtain an ultra-light microwave-absorbing nanofiber material.

[0028] In the present invention, the polyurethane fiber membrane is prepared by dissolving thermoplastic polyurethane in an organic solvent to form a spinning solution, and then electrospinning. The mass fraction of the thermoplastic polyurethane is 5-10 wt%, and the thickness of the polyurethane fiber membrane is 180-220 μm. By adjusting the spinning process and increasing the thickness of the spinning membrane (including directly preparing a thick membrane or multi-layer stacking), the mechanical strength and toughness of the composite material can be further improved, while maintaining excellent microwave absorption performance, so that the microwave-absorbing material can achieve the purpose of being lightweight, having a low filler addition amount, high modulus, and high microwave absorption intensity.

[0029] In the present invention, the organic solvent is a mixed solution of N,N-dimethylformamide and tetrahydrofuran, and the mass ratio of N,N-dimethylformamide to tetrahydrofuran is 1.

[0030] In the present invention, the electrospinning voltage is 16-20 kV, the receiving distance is 12-16 cm, and the roller rotation speed is 1500-2500 r / min.

[0031] In the present invention, before electrospinning, it also includes adding cellulose nanocrystals accounting for 2-5% of the mass of the spinning solution and a photoinitiator accounting for 1-2% of the mass of the spinning solution to the spinning solution, and ultrasonically dispersing for 4-5 h; after electrospinning, it also includes irradiating under ultraviolet light for 10-15 min. The high modulus and rigid network of cellulose nanocrystals are used to enhance the mechanical properties of the fibers. Ultraviolet light irradiation is used to initiate the cross-linking of polyurethane molecular chains to achieve multi-stage cross-linking strengthening and improve the material strength. The photoinitiator is benzotriazole-based formate (BAPO) or a stilbene compound.

[0032] In the present invention, the mass fraction of the dopamine is 0.5-2 wt%, the buffer solution is a 0.01-1 M Tris-HCl buffer solution, and the mass ratio of the dopamine to the Tris-HCl buffer solution is 1:40-50, and the polymerization reaction is carried out for 10-15 h.

[0033] In the present invention, the mass fraction of the modified carbon nanotubes is 0.1-0.8 wt%, and the modified carbon nanotubes are carbon nanotubes treated by oxidation. Specifically: the carbon nanotubes are placed in a mixed solution of concentrated sulfuric acid and nitric acid, and ultrasonically treated for 2-3 h, and the mass ratio of the concentrated sulfuric acid to the nitric acid is 3:1. Carboxyl groups are introduced onto the carbon nanotubes to enhance hydrophilicity and the bonding ability with polydopamine, and the agglomeration is inhibited by the chemical bonding of carboxylated carbon nanotubes and polydopamine. Preferably, in step S2, the solvent of the modified carbon nanotubes is an ethanol aqueous solution, and the concentration of the ethanol aqueous solution is 1-2 mg / mL.

[0034] In the present invention, the reducing agent is ascorbic acid solution, glutathione solution or tannic acid solution. The concentration of the ascorbic acid solution is 0.08 - 0.15 M, the concentration of the glutathione solution is 1 - 10 mM, and the concentration of the tannic acid solution is 0.1 - 1% w / v. The vertical electric field voltage is 1 - 3 kV, and the application time is 1 - 2 h. Preferably, the treatment time of the ascorbic acid solution is less than 2 h to avoid carboxylation from damaging the sp 2 structure and reducing the dielectric loss. The reducing agent can also regulate the oxidized state structure of polydopamine (such as quinone groups) to optimize the wave absorption performance of the material and enhance the antioxidant property of the material. The tannic acid solution can also improve the corrosion resistance of the material.

[0035] In the present invention, the hot pressing treatment is divided into two stages. The first stage is hot pressed at 80 - 90°C and 5 MPa for 2 - 5 min, and the second stage is hot pressed at 110 - 130°C and 10 MPa for 1 - 4 min. Under the above conditions, 50% porosity can be retained inside the fiber to avoid excessive densification and reduce the multiple reflection paths of electromagnetic waves.

[0036] In the present invention, through multi-level fiber reinforcement: cellulose nanocrystals enhance rigidity, thermoplastic polyurethane improves toughness, and photo-crosslinking + hot pressing optimize the interface to achieve the balance of strength and flexibility; through the dual strategies of chemical bonding + electric field orientation: covalent bonding between polydopamine and carbon nanotubes inhibits agglomeration, and electric field induction enhances directional wave absorption; through gradient structure to retain functions: surface densification protects carbon nanotubes, and internal porous structure maintains wave absorption performance. Through multi-scale collaborative regulation, a multi-layer and gradient structure of the material is constructed, systematically solving the contradiction between carbon nanotube dispersion and material strength, and enabling the material to achieve light weight, low filler addition, high modulus, and high microwave absorption intensity.

[0037] An ultra-light microwave-absorbing nanofiber material prepared by the above method has excellent microwave absorption performance of -63.5 dB and an optimal effective absorption bandwidth of 8.6 GHz, meeting the requirements of achieving high-efficiency wave absorption, improving mechanical properties, and maintaining absorption frequency stability with low filler addition.

[0038] Example 1

[0039] A preparation method of an ultra-light microwave-absorbing nanofiber material, comprising the following steps:

[0040] S1. Dissolve thermoplastic polyurethane in a mixed solution of N,N-dimethylformamide and tetrahydrofuran to prepare a spinning solution. The mass fraction of thermoplastic polyurethane is 6 wt%, and the mass ratio of N,N-dimethylformamide to tetrahydrofuran is 1; add cellulose nanocrystals accounting for 4% of the mass of the spinning solution and benzotriazole-based formate accounting for 2% of the mass of the spinning solution to the spinning solution, ultrasonically disperse for 4 h, and perform electrospinning under the conditions of a voltage of 18 kV, a receiving distance of 15 cm, and a roller rotation speed of 2000 r / min. After electrospinning, irradiate under ultraviolet light for 10 min to obtain a polyurethane fiber membrane with a thickness of 200 μm;

[0041] S2. Immerse the polyurethane fiber membrane in a mixed solution of dopamine and Tris-HCl buffer with a mass ratio of 1:40. The mass fraction of dopamine is 1 wt%, and the concentration of Tris-HCl buffer is 0.1 M. Carry out a polymerization reaction for 12 h and place it in an oven to dry for 2 h to obtain a polydopamine-polyurethane fiber membrane;

[0042] S3. Disperse the modified carbon nanotubes in an ethanol aqueous solution with a concentration of 1 mg / mL, and the mass fraction of the modified carbon nanotubes in the solution is 0.3 wt%. Then add the polydopamine-polyurethane fiber membrane, apply a vertical electric field with a voltage of 3 kV for 1 h, ultrasonically treat for 20 min, then immerse it in an ascorbic acid solution and ultrasonically treat for 1 h. The concentration of the ascorbic acid solution is 0.1 M, and then dry to obtain a carbon nanotube@polydopamine-polyurethane fiber membrane;

[0043] S4. Perform gradient hot pressing on the carbon nanotube@polydopamine-polyurethane fiber membrane. In the first stage, hot press at 80 °C and 5 MPa for 2 min, and in the second stage, hot press at 120 °C and 10 MPa for 1 min to obtain an ultra-light microwave absorption nanofiber material.

[0044] Among them, the modification method of the modified carbon nanotubes is: place the carbon nanotubes in a mixed solution of concentrated sulfuric acid and nitric acid, ultrasonically treat for 2 h, and the mass ratio of concentrated sulfuric acid to nitric acid is 3:1.

[0045] Example 2

[0046] A preparation method of an ultra-light microwave absorption nanofiber material, comprising the following steps:

[0047] S1. Dissolve thermoplastic polyurethane in a mixed solution of N,N-dimethylformamide and tetrahydrofuran to prepare a spinning solution. The mass fraction of thermoplastic polyurethane is 5 wt%, and the mass ratio of N,N-dimethylformamide to tetrahydrofuran is 1. Add cellulose nanocrystals accounting for 5% of the mass of the spinning solution and benzotriazole-based formate accounting for 1% of the mass of the spinning solution to the spinning solution, and ultrasonically disperse for 5 h. Electrospinning is carried out under the conditions of a voltage of 16 kV, a receiving distance of 12 cm, and a roller rotation speed of 1500 r / min. After spinning, irradiate under ultraviolet light for 10 min to obtain a polyurethane fiber membrane with a thickness of 180 μm;

[0048] S2. Immerse the polyurethane fiber membrane in a mixed solution of dopamine and Tris-HCl buffer with a mass ratio of 1:45. The mass fraction of dopamine is 0.5 wt%, and the concentration of Tris-HCl buffer is 0.01 M. Carry out a polymerization reaction for 10 h and place it in an oven to dry for 2 h to obtain a polydopamine-polyurethane fiber membrane;

[0049] S3. Disperse the modified carbon nanotubes in an ethanol solution. The concentration of the ethanol solution is 2 mg / mL, and the mass fraction of the modified carbon nanotubes in the solution is 0.1 wt%. Then add the polydopamine-polyurethane fiber membrane, apply a vertical electric field with a voltage of 1 kV for 2 h, carry out ultrasonic treatment for 40 min, and then immerse it in a glutathione solution for ultrasonic treatment for 0.5 h. The concentration of the glutathione solution is 5 mM, and dry it to obtain a carbon nanotube@polydopamine-polyurethane fiber membrane;

[0050] S4. Carry out gradient hot pressing treatment on the carbon nanotube@polydopamine-polyurethane fiber membrane. The first stage is hot pressing at 90 °C and 5 MPa for 5 min, and the second stage is hot pressing at 110 °C and 10 MPa for 4 min to obtain an ultra-light microwave absorption nanofiber material.

[0051] Among them, the modification method of the modified carbon nanotubes is: place the carbon nanotubes in a mixed solution of concentrated sulfuric acid and nitric acid, ultrasonically disperse for 3 h, and the mass ratio of concentrated sulfuric acid to nitric acid is 3:1.

[0052] Example 3

[0053] S1. Dissolve thermoplastic polyurethane in a mixed solution of N,N-dimethylformamide and tetrahydrofuran to prepare a spinning solution. The mass fraction of thermoplastic polyurethane is 10 wt%, and the mass ratio of N,N-dimethylformamide to tetrahydrofuran is 1. Add cellulose nanocrystals accounting for 2% of the mass of the spinning solution and a stilbene compound accounting for 1% of the mass of the spinning solution to the spinning solution, and ultrasonically disperse for 4 h. Electrospinning is carried out under the conditions of a voltage of 20 kV, a receiving distance of 16 cm, and a roller rotation speed of 2500 r / min. After spinning, irradiate under ultraviolet light for 15 min to obtain a polyurethane fiber membrane with a thickness of 220 μm;

[0054] S2. Immerse the polyurethane fiber membrane in a mixed solution of dopamine and Tris-HCl buffer with a mass ratio of 1:50. The mass fraction of dopamine is 2 wt%, the concentration of Tris-HCl buffer is 1 M, carry out the polymerization reaction for 15 h, place it in an oven to dry for 2 h to obtain a polydopamine-polyurethane fiber membrane;

[0055] S3. Disperse the modified carbon nanotubes in an ethanol aqueous solution with a concentration of 1.5 mg / mL. The mass fraction of the modified carbon nanotubes in the solution is 0.8 wt%. Then add the polydopamine-polyurethane fiber membrane, apply a vertical electric field with a voltage of 3 kV and an application time of 1 h, carry out ultrasonic treatment for 20 min, and then immerse it in a tannic acid solution for ultrasonic treatment for 1.5 h. The concentration of the tannic acid solution is 0.5% w / v, and dry it to obtain a carbon nanotube@polydopamine-polyurethane fiber membrane;

[0056] S4. Carry out gradient hot pressing treatment on the carbon nanotube@polydopamine-polyurethane fiber membrane. In the first stage, hot press at 85 °C and 5 MPa for 3 min, and in the second stage, hot press at 110 °C and 10 MPa for 2 min to obtain an ultra-light microwave absorption nanofiber material.

[0057] Among them, the modification method of the modified carbon nanotubes is: place the carbon nanotubes in a mixed solution of concentrated sulfuric acid and nitric acid, carry out ultrasonic treatment for 2 h, and the mass ratio of concentrated sulfuric acid to nitric acid is 3:1.

[0058] Example 4

[0059] In this example, the preparation process of the polyurethane fiber membrane is as follows: dissolve thermoplastic polyurethane in a mixed solution of N,N-dimethylformamide and tetrahydrofuran to make a spinning solution. The mass fraction of thermoplastic polyurethane is 6 wt%, and the mass ratio of N,N-dimethylformamide to tetrahydrofuran is 1; carry out electrospinning under the conditions of a voltage of 18 kV, a receiving distance of 15 cm, and a roller rotation speed of 2000 r / min. After electrospinning, irradiate it under ultraviolet light for 10 min to obtain a polyurethane fiber membrane with a thickness of 200 μm. The rest is the same as in Example 1.

[0060] Comparative Example 1

[0061] The difference between this comparative example and Example 1 is that: the mass fraction of the modified carbon nanotubes is 5 wt%. The rest are the same as in Example 1.

[0062] Comparative Example 2

[0063] The difference between this comparative example and Example 1 is that: the mass fraction of the modified carbon nanotubes is 0.05 wt%. The rest are the same as in Example 1.

[0064] Comparative Example 3

[0065] The difference between this comparative example and Example 1 is that the carbon nanotubes are not modified. The rest are the same as in Example 1.

[0066] Comparative Example 4

[0067] The difference between this comparative example and Example 1 is that no vertical electric field is applied. The rest are the same as in Example 1.

[0068] Comparative Example 5

[0069] The difference between this comparative example and Example 1 is that treatment with ascorbic acid solution is not used. The rest are the same as in Example 1.

[0070] Comparative Example 6

[0071] The difference between this comparative example and Example 1 is that hot pressing treatment is not carried out. The rest are the same as in Example 1.

[0072] Test Example

[0073] The nanofiber materials obtained in the examples and comparative examples were tested, and the test indexes included the dispersion of carbon nanotubes, tensile strength, wave absorption efficiency, and flexibility. The results are shown in Table 1.

[0074] Dispersion detection of carbon nanotubes (CNTs) - Observed by scanning electron microscope, the steps are as follows:

[0075] 1. Sample preparation: Cut the material sample into 5×5 mm thin slices and perform gold spraying treatment (thickness 5 mm);

[0076] 2. Observation conditions: Accelerating voltage 5 kV, working distance 8 mm, select backscattered electron mode;

[0077] 3. Data analysis: Randomly select 5 regions (≥100 carbon nanotubes in each region), measure the diameter and spacing of carbon nanotubes. If the diameter of more than 90% of the carbon nanotubes is <100 nm and there are no aggregates, it is determined to be uniformly dispersed.

[0078] The tensile strength was detected according to ASTM D638 (Tensile Properties of Plastics). The wave absorption efficiency was detected according to GJB 9885-2020 "Test Method for Surface Wave Attenuation Rate of Radar Absorbing Materials". The flexibility was detected according to STM D522 (Flexural Properties).

[0079] Table 1

[0080]

[0081]

[0082] As can be seen from Table 1, compared with the comparative examples, the carbon nanotubes of the nanofiber materials in Examples 1-4 have good dispersibility and exhibit better tensile strength, wave absorption efficiency, and flexibility. This indicates that the nanofiber material of the present invention meets the requirements of achieving high-efficiency wave absorption, improving mechanical properties, and maintaining the stability of absorption frequency with low filler addition.

[0083] When comparing Example 1 with Comparative Examples 1-2, in Comparative Example 1, the amount of modified carbon nanotubes is relatively large, but the dispersibility, tensile strength, wave absorption performance, and flexibility of CNTs are all poor. In Comparative Example 2, the amount of modified carbon nanotubes is relatively small, and the tensile strength and wave absorption performance are poor. Thus, it can be seen that appropriately reducing the filler can endow the material with high wave absorption and excellent mechanical properties.

[0084] When comparing Example 1 with Comparative Examples 3-4, in Comparative Examples 3 and 4, CNTs agglomerate severely, resulting in a significant reduction in the tensile strength and flexibility of the material, and a certain decrease in the wave absorption performance. In Comparative Example 3, it is because the amino group of polydopamine cannot form a covalent bond with the carboxyl group of the modified CNTs, affecting the dispersion of CNTs. In Comparative Example 4, it is because CNTs cannot be aligned directionally, leading to lateral agglomeration of CNTs. Thus, it can be seen that the modification of carbon nanotubes and the vertical electric field can act synergistically to achieve the directional alignment of carbon nanotubes and improve the dispersibility of carbon nanotubes.

[0085] When comparing Examples 1-4 with Comparative Examples 5-6, the materials obtained in Comparative Examples 5 and 6 have poor tensile strength and flexibility. Thus, it can be seen that the strength of the material can be improved through ascorbic acid solution and hot pressing treatment, and the strength of the material can be improved by combining hot pressing and ultraviolet cross-linking.

[0086] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, various modifications and changes can be made to the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing an ultralight microwave absorbing nanofiber material, characterized in that: The following steps are involved: S1. Immersing the polyurethane fiber membrane in a mixed solution of dopamine and buffer for polymerization reaction to obtain a polydopamine-polyurethane fiber membrane; S2. The modified carbon nanotubes are dispersed in a solvent, and then a polydopamine-polyurethane fiber membrane is added, a vertical electric field is applied, ultrasonic treatment is performed, and then the membrane is immersed in a reducing agent and dried to obtain a carbon nanotube@polydopamine-polyurethane fiber membrane; S3. The carbon nanotube@polydopamine-polyurethane fiber membrane is subjected to hot pressing to obtain an ultra-light microwave absorbing nanofiber material.

2. The method for preparing the ultralight microwave absorbing nanofiber material according to claim 1, characterized in that: The polyurethane fiber membrane is prepared by dissolving thermoplastic polyurethane in an organic solvent to form a spinning solution and then electrospinning the solution. The mass fraction of the thermoplastic polyurethane is 5-10wt%, and the thickness of the polyurethane fiber membrane is 180-220μm.

3. The method for preparing the ultralight microwave absorbing nanofiber material according to claim 2, characterized in that: The organic solvent is a mixed solution of N,N-dimethylformamide and tetrahydrofuran, and the mass ratio of N,N-dimethylformamide to tetrahydrofuran is 1.

4. The method for preparing the ultralight microwave absorbing nanofiber material according to claim 3, characterized in that: The electrospinning voltage is 16-20 kV, the receiving distance is 12-16 cm, and the drum speed is 1500-2500 r / min.

5. The method for preparing the ultralight microwave absorbing nanofiber material according to claim 2, characterized in that: Before electrospinning, the method further includes adding 2-5% of cellulose nanocrystals and 1-2% of photoinitiator to the spinning solution, and ultrasonically dispersing for 4-5 hours. After electrospinning, the method further includes irradiating the solution under ultraviolet light for 10-15 minutes.

6. The method for preparing the ultralight microwave absorbing nanofiber material according to claim 1, characterized in that: The mass fraction of the dopamine is 0.5-2wt%, the buffer is a Tris-HCl buffer with a concentration of 0.01-1M, the mass ratio of the dopamine to the Tris-HCl buffer is 1:40-50, and the polymerization reaction takes 10-15h.

7. The method for preparing the ultralight microwave absorbing nanofiber material according to claim 1, characterized in that: The mass fraction of the modified carbon nanotubes is 0.1-0.8wt%, and the modified carbon nanotubes are carbon nanotubes that have been oxidized.

8. The method for preparing the ultralight microwave absorbing nanofiber material according to claim 1, characterized in that: The reducing agent is ascorbic acid solution, glutathione solution or tannic acid solution, the concentration of the ascorbic acid solution is 0.08-0.15M, the concentration of the glutathione solution is 1-10mM, the concentration of the tannic acid solution is 0.1-1% w / v, the vertical electric field voltage is 1-3kV, and the application time is 1-2h.

9. The method for preparing the ultralight microwave absorbing nanofiber material according to claim 1, characterized in that: The hot pressing treatment is divided into two stages. The first stage is hot pressing at 80-90°C and 5MPa for 2-5min, and the second stage is hot pressing at 110-130°C and 10MPa for 1-4min.

10. An ultralight microwave absorbing nanofiber material obtained by the preparation method according to any one of claims 1 to 9.

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