Wave-absorbing fiber with porous structure as well as preparation method and application of wave-absorbing fiber

Abstract

The invention discloses a wave-absorbing fiber with a porous structure as well as a preparation method and application of the wave-absorbing fiber. The wave-absorbing fiber with the porous structure comprises a carbon nano tube and an aramid nano fiber, the wave-absorbing fiber with the porous structure has a porous structure, and the pore size of pores in the wave-absorbing fiber is gradually reduced from a surface layer to a core layer in the radial direction. The preparation method comprises the following steps: mixing a carbon nanotube dispersion liquid, an aramid nanofiber solution and a polyvinyl alcohol solution to form a homogeneous spinning solution; and extruding the homogeneous spinning solution through a spinning nozzle by adopting a wet spinning technology, enabling the homogeneous spinning solution to enter a coagulating bath, carrying out a differentiated phase separation process on the obtained fiber along the radial direction to form a porous structure of which the aperture is gradually reduced from the surface layer to the core layer along the radial direction, and drying to obtain the wave-absorbing fiber with the porous structure. According to the invention, the dielectric constant is regulated and controlled by introducing the aramid nanofiber as a nano element material, and the impedance matching characteristic of the fiber is improved by constructing a radial porous structure of the fiber, so that the electromagnetic wave absorption performance of the material is improved, and ultra-wideband electromagnetic microwave absorption is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to a preparation method of a porous fiber, in particular to a porous structure wave-absorbing fiber with a pore size gradually decreasing from the surface layer to the core layer and a preparation method and application thereof, and belongs to the technical field of new materials. BACKGROUND

[0002] At present, existing electromagnetic wave absorbing fibers mainly adopt porous fibers or hollow fibers. For example, the published patent CN119321009A discloses a super-light hollow carbon nanotube composite fiber, an electromagnetic shielding material based on a shuttle-shaped supramolecular structure and a preparation method thereof. The carbon nanotube-PBIA polymer supramolecule is prepared by centrifugal separation and freeze-drying, and is prepared into a spinning solution. The super-light hollow carbon nanotube composite fiber is prepared by wet spinning. However, the porous fiber or hollow fiber is difficult to effectively control the impedance matching of the electromagnetic microwave interface, and the electromagnetic loss capacity is weak.

[0003] Carbon nanotubes can be used for electromagnetic microwave high-frequency band absorbing materials due to their high and controllable electrical conductivity, low density, large specific surface area and other characteristics. However, due to the high electrical conductivity and lack of magnetic loss, the impedance matching is poor, and the effect is not good when used alone. Therefore, how to optimize the structure and preparation process of the fiber, and seek a new technology that can improve the impedance matching characteristics of the fiber and improve the electromagnetic wave absorbing performance of the material, has been the long-term effort of researchers in the industry. SUMMARY

[0004] The main purpose of the present application is to provide a porous structure wave-absorbing fiber and a preparation method thereof to overcome the shortcomings of the prior art.

[0005] Another purpose of the present application is to provide the application of the porous structure wave-absorbing fiber in the field of electromagnetic microwave absorption.

[0006] In order to achieve the above-mentioned purposes, the technical scheme adopted by the present application comprises:

[0007] The present application provides a porous structure wave-absorbing fiber, which comprises carbon nanotubes and aramid nanofibers. The porous structure wave-absorbing fiber has a porous structure, and the pore size of the pores contained in the porous structure wave-absorbing fiber gradually decreases from the surface layer to the core layer in the radial direction of the porous structure wave-absorbing fiber.

[0008] The present application provides a preparation method of a porous structure wave-absorbing fiber, which comprises:

[0009] Mixing carbon nanotube dispersion liquid, aramid nanofiber solution and polyvinyl alcohol solution to form a homogeneous spinning solution;

[0010] The homogeneous spinning solution is extruded through a spinneret into a first coagulation bath and a second coagulation bath, respectively, to obtain the fiber which experiences a differential phase separation process along the radial direction to form a porous structure with a pore size gradually decreasing from the surface layer to the core layer; wherein the first coagulation bath is water, and the second coagulation bath is a mixture of water and a specified organic solvent, wherein the volume ratio of water to the specified organic solvent is 1:4-4:1.

[0011] The as-spun fiber obtained in the coagulation bath is dried to obtain the porous structure wave-absorbing fiber.

[0012] The application provides an application of the porous structure wave-absorbing fiber in the field of electromagnetic microwave absorption.

[0013] Compared with the prior art, the application has at least the following beneficial effects:

[0014] The application provides a method for preparing a porous structure wave-absorbing fiber with a radial pore size gradually decreasing by using a wet spinning method combined with a freeze-drying technology, the dielectric constant of the fiber is regulated by introducing insulating aramid nanofiber as a nanometer base material, the impedance matching property of the fiber is improved by constructing a radial porous structure of the fiber, the electromagnetic wave absorption performance of the material is improved, and super-wideband electromagnetic microwave absorption is realized. BRIEF DESCRIPTION OF DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are only some embodiments of the application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0016] Figure 1 And Figure 2 FIG. 1 is a schematic diagram of the microstructure of the porous structure wave-absorbing fiber prepared in Embodiment 1 of the application;

[0017] Figure 3 FIG. 2 is a test result diagram of the electromagnetic microwave absorption performance of the porous structure wave-absorbing fiber prepared in Embodiment 1 of the application;

[0018] Figure 4 And Figure 5 FIG. 3 is a schematic diagram of the microstructure of the porous structure wave-absorbing fiber prepared in Embodiment 2 of the application;

[0019] Figure 6 FIG. 4 is a test result diagram of the electromagnetic microwave absorption performance of the porous structure wave-absorbing fiber prepared in Embodiment 2 of the application;

[0020] Figure 7 And Figure 8A schematic diagram of the microstructure of the porous structure wave-absorbing fiber prepared in Example 3 of the present application;

[0021] Figure 9 A graph of the electromagnetic microwave absorption performance test results of the porous structure wave-absorbing fiber prepared in Example 3 of the present application;

[0022] Figure 10 A graph of the electromagnetic microwave absorption performance test results of the fiber obtained in Comparative Example 1;

[0023] Figure 11 A graph of the electromagnetic microwave absorption performance test results of the fiber obtained in Comparative Example 2;

[0024] Figure 12 A graph of the electromagnetic microwave absorption performance test results of the fiber obtained in Comparative Example 7. DETAILED DESCRIPTION

[0025] In view of the limitations of existing porous fibers or hollow fibers, it is difficult to effectively control the electromagnetic microwave interface impedance matching and electromagnetic microwave effective attenuation. The present inventors have long-term research and a large number of practices, and have proposed the technical solution of the present application, which mainly provides a different porous structure fiber preparation by using wet spinning combined with freeze drying, and proposes a porous structure with gradually decreasing radial porosity to improve the fiber interface impedance matching.

[0026] The technical solution, its implementation process and principles will be further explained and described as follows. However, it should be understood that within the scope of the present application, the above-mentioned technical features of the present application and the technical features specifically described in the following (Examples) can be combined with each other to form new or preferred technical solutions. Due to the limited space, they will not be listed one by one here.

[0027] As an aspect of the technical solution of the present application, a porous structure wave-absorbing fiber includes carbon nanotubes and aramid nanofibers, the porous structure wave-absorbing fiber has a porous structure, and in the radial direction of the porous structure wave-absorbing fiber, the pore size of the pores contained in the porous structure wave-absorbing fiber gradually decreases from the surface layer to the core layer, preferably decreases in gradient.

[0028] In some embodiments, the pores contained in the porous structure wave-absorbing fiber include elliptical pores distributed in the surface layer in the radial direction of the porous structure wave-absorbing fiber, and nanopores in the core of the porous structure wave-absorbing fiber.

[0029] In some embodiments, the pore size of the surface layer of the porous structure wave-absorbing fiber is defined as a first pore size, and the pore size of the core layer is defined as a second pore size, the first pore size is 5-100 μm, and the second pore size is 100-1000 nm.

[0030] In some embodiments, the porosity of the porous structure wave-absorbing fiber is 60-90%.

[0031] Further, the cross-sectional shape of the pores of the porous structure wave-absorbing fiber is radial ellipse.

[0032] In some embodiments, the diameter of the porous structure wave-absorbing fiber is 300-600 μm.

[0033] In some embodiments, the electromagnetic microwave reflectivity of the porous structure wave-absorbing fiber is better than -10 dB in the range of 5-18 GHz, the mechanical strength is 50-200 MPa, the impedance matching value is between 0.5-1 in the range of 5-18 GHz, and the fiber has good matching characteristics.

[0034] As another aspect of the technical solution of the present application, a method for preparing a porous structure wave-absorbing fiber comprises:

[0035] Mixing a carbon nanotube dispersion liquid, an aramid nanofiber solution, and a polyvinyl alcohol solution to form a homogeneous spinning solution;

[0036] Using a wet spinning technology, extruding the homogeneous spinning solution through a spinneret into a first coagulation bath and a second coagulation bath, respectively, so that the obtained fiber undergoes a differential phase separation process along the radial direction to form a porous structure with a pore size gradually decreasing from the surface layer to the core layer along the radial direction; wherein the first coagulation bath is water, and the second coagulation bath is a mixture of water and a specified organic solvent, wherein the volume ratio of water to the specified organic solvent is 1:4-4:1;

[0037] Drying the as-spun fiber obtained in the coagulation bath to obtain the porous structure wave-absorbing fiber.

[0038] In some embodiments, the component of the first coagulation bath is water (preferably deionized water), and the component of the second coagulation bath is a mixture of water (preferably deionized water) and a specified organic solvent (preferably dimethyl sulfoxide). By changing the composition of the spinning solution and the composition ratio of the coagulation liquid in this process, fibers with different pore structures can be obtained.

[0039] In some embodiments, the preparation method specifically comprises: mixing a carbon nanotube dispersion liquid, an aramid nanofiber solution and a polyvinyl alcohol solution according to a mass ratio of 8:4:1-4:8:5, and then ultrasonic treatment for 30-60 min to form a homogeneous spinning solution. If the mass ratio of the carbon nanotube dispersion liquid to the aramid nanofiber solution is higher than 2:1, the content of aramid nanofiber is too low to effectively adjust the impedance matching, and it will seriously affect the fiber forming, and the mechanical properties of the obtained fiber are extremely low, and it is basically impossible to be practically applied. If the mass ratio of the carbon nanotube dispersion liquid to the aramid nanofiber solution is lower than 1:2, the content of carbon nanotube is too low to seriously reduce the electromagnetic microwave loss capacity of the obtained fiber, and the wave absorption performance is significantly reduced.

[0040] In some embodiments, the carbon nanotube dispersion liquid comprises carbon nanotubes and a specified organic solvent, and the specified organic solvent is dimethyl sulfoxide.

[0041] In some embodiments, the aramid nanofiber solution comprises aramid nanofibers and a specified organic solvent, and the specified organic solvent is dimethyl sulfoxide.

[0042] In some embodiments, the polyvinyl alcohol solution comprises polyvinyl alcohol and a specified organic solvent, and the specified organic solvent is dimethyl sulfoxide. The polyvinyl alcohol is dissolved in water, and the aramid nanofibers and the carbon nanotubes are not dissolved in water, so that the pore structure is formed in the fiber during the fiber setting process due to the dissolution in water.

[0043] In some more preferred embodiments, the preparation method specifically comprises:

[0044] mixing the carbon nanotube / dimethyl sulfoxide dispersion liquid, the aramid nanofiber / dimethyl sulfoxide solution and the polyvinyl alcohol / dimethyl sulfoxide solution to form a homogeneous spinning solution;

[0045] using a wet spinning technology, extruding the homogeneous spinning solution through a spinneret, and then sequentially entering a first coagulation bath and a second coagulation bath, respectively, so that the obtained fiber experiences a differential phase separation process along the radial direction, the spinning solution is quickly coagulated into a gel fiber after passing through the deionized water first coagulation liquid, and then enters a mixed coagulation liquid tank with different volume ratios of deionized water and dimethyl sulfoxide, and the volume ratio of deionized water to dimethyl sulfoxide in the coagulation liquid tank can be 4:1, 1:1 and 1:4 in sequence, and the difference in the solubility of polyvinyl alcohol in different proportion mixed coagulation liquid is used to form a porous structure with a pore size gradually decreasing from the surface layer to the core layer along the radial direction in the fiber;

[0046] freezing and drying the as-spun fiber obtained in the coagulation bath to obtain the porous structure wave-absorbing fiber.

[0047] Further, the content of the carbon nanotubes in the carbon nanotube / dimethyl sulfoxide dispersion liquid is 1-5 wt%. If the content exceeds 5 wt%, the carbon nanotube dispersion liquid is too concentrated to be uniformly mixed with aramid nanofibers during preparation of the spinning solution, affecting the preparation of the fiber; if the content is less than 1 wt%, it is difficult to effectively adjust the concentration of the carbon nanotubes in the mixed spinning solution under the premise of meeting the proportion of the mixed solution, and it is difficult to meet the viscosity requirements of the spinning solution.

[0048] Further, the content of the aramid nanofiber in the aramid nanofiber / dimethyl sulfoxide solution is 0.2-4 wt%. If the content exceeds 4 wt%, it is difficult to effectively dissolve Kevlar to obtain a Kevlar nanofiber solution; if the content is less than 0.2 wt%, it is difficult to effectively adjust the content of the Kevlar nanofiber in the mixed spinning solution under the premise of meeting the proportion of the mixed solution, and it is difficult to effectively control the dielectric constant of the fiber.

[0049] Further, the carbon nanotubes and aramid nanofibers used in the present application can be commonly used or commercially available products in the industry. For example, the diameter of the aramid nanofiber can be 30-100 nm.

[0050] Further, the content of the polyvinyl alcohol in the polyvinyl alcohol / dimethyl sulfoxide solution is 0.1-10 wt%. If the content exceeds 10 wt%, the spinning solution is difficult to form a fiber in the coagulation liquid due to the dissolution of the polyvinyl alcohol; if the content is less than 0.1 wt%, the effect of the fiber pore control is limited.

[0051] In some embodiments, the process conditions of the wet spinning technology include: the diameter of the circular spinning hole of the spinneret is 300-700 μm, and the spinning speed is 1-15 m / min.

[0052] In some embodiments, the drying includes natural drying and / or freeze drying, etc.

[0053] In some preferred embodiments, the freeze drying specifically includes: first, the nascent fiber is rapidly frozen in a liquid nitrogen environment ≤-196 ℃ for 10-15 s, and then is freeze-dried under the condition of ≤-5 ℃ and a vacuum degree ≤5 Pa for 24-48 h to obtain the porous structure wave-absorbing fiber. The present application preferably uses rapid freezing to make the water in the fiber rapidly freeze, thereby reducing the damage of the slow growth process of ice crystals to the porous structure with gradually decreasing pore size, better preserving the integrity of the porous structure, and improving the structural stability and electromagnetic microwave absorption performance of the fiber.

[0054] In some more specific embodiments, a method for preparing a porous structure wave-absorbing fiber according to the present application specifically includes the following steps:

[0055] 1. Spinning solution preparation:

[0056] The carbon nanotube (CNT) dispersion liquid (1-5wt%) is mixed with aramid nanofiber (ANF) solution (0.2-4wt%) and polyvinyl alcohol solution (0.1-1wt%) in a mass ratio of 8:4:1-4:8:5, and ultrasonic treatment is performed for 30-60min to form a homogeneous spinning solution.

[0057] 2. Wet spinning:

[0058] After the homogeneous spinning solution is extruded through a spinneret (pore size 300-700μm), it enters a deionized water bath and a deionized water and dimethyl sulfoxide mixed coagulation bath, respectively, and the fiber undergoes a differential phase separation process along the radial direction to form a porous structure with a pore size gradually decreasing from the surface to the core layer, and a primary fiber is obtained.

[0059] 3. Freeze-drying:

[0060] After the primary fiber is rapidly frozen in liquid nitrogen (≤-196℃, 10-15s), it is transferred to a freeze dryer (≤-5℃, vacuum degree ≤5Pa) for drying for 24-48h, thereby retaining the integrity of the porous structure.

[0061] As another aspect of the technical solution of the present application, it relates to the application of the porous structure wave-absorbing fiber in the field of electromagnetic microwave absorption.

[0062] In summary, the present application introduces insulating aramid nanofiber as a nanometer unit material to regulate its dielectric constant, and constructs a radial porous structure wave-absorbing fiber, which utilizes the gradually decreasing porous structure to improve the impedance matching characteristics of the composite fiber and the multiple reflection of electromagnetic waves inside the fiber, significantly improving the fiber's ability to absorb electromagnetic waves and realizing ultra-wideband electromagnetic microwave absorption.

[0063] The technical solutions of the present application will be further described in detail below in conjunction with several preferred embodiments and the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. It should be noted that the following embodiments are intended to facilitate the understanding of the present application, and do not have any limiting effect on it. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application. The experimental methods not specified in the following examples are usually carried out under conventional conditions or under the conditions recommended by the manufacturer.

[0064] Example 1

[0065] 1. Spinning solution preparation:

[0066] 1g of single-walled carbon nanotubes (purchased from Shenzhen Liren Handi Trade Co., Ltd.) is dispersed in 99g of dimethyl sulfoxide to form a 1wt% carbon nanotube dispersion liquid;

[0067] 0.4 g aramid nanofiber (purchased from Yantai Taihe New Material Sales Co., Ltd.) was dispersed in 99.6 g dimethyl sulfoxide to form a 0.4 wt% aramid nanofiber solution;

[0068] 0.2 g polyvinyl alcohol (purchased from Sinopec Chongqing Chuanwei Chemical Co., Ltd.) was dispersed in 99.8 g dimethyl sulfoxide to form a 0.2 wt% polyvinyl alcohol solution;

[0069] The carbon nanotube dispersion prepared above, the aramid nanofiber solution, and the polyvinyl alcohol solution were mixed in a mass ratio of 8:8:2, and ultrasonic treatment was performed for 60 min at an ultrasonic power of 500 W to form a homogeneous spinning solution.

[0070] 2. Wet spinning:

[0071] After the homogeneous spinning solution was extruded through a spinneret (pore size 500 μm) at a spinning speed of 5-15 m / min, it entered a deionized water bath, and then entered a coagulating liquid with a volume ratio of deionized water to dimethyl sulfoxide of 4:1. The fiber underwent a differential phase separation process along the radial direction, forming a porous structure with a pore size gradually decreasing from the surface to the core layer along the radial direction, and a primary fiber was obtained.

[0072] 3. Freeze-drying:

[0073] After the primary fiber was rapidly frozen in liquid nitrogen (-196 ℃, 15 s), it was transferred to a freeze dryer (≤-5 ℃, vacuum degree ≤5 Pa) for drying for 36 h, thereby retaining the integrity of the porous structure, and a porous wave-absorbing fiber was prepared.

[0074] Example 2

[0075] 1. Spinning solution preparation:

[0076] 5 g carbon nanotubes (purchased from Shenzhen Liren Artificial Trade Co., Ltd.) were dispersed in 95 g DMSO to form a 5 wt% carbon nanotube dispersion;

[0077] 4 g aramid nanofiber (purchased from Yantai Taihe New Material Sales Co., Ltd.) was dispersed in 96 g DMSO to form a 4 wt% aramid nanofiber solution;

[0078] 0.2 g polyvinyl alcohol (purchased from Sinopec Chongqing Chuanwei Chemical Co., Ltd.) was dispersed in 99.8 g DMSO to form a 0.2 wt% polyvinyl alcohol solution;

[0079] The carbon nanotube dispersion prepared above, the aramid nanofiber solution, and the polyvinyl alcohol solution were mixed in a mass ratio of 8:8:5, and ultrasonic treatment was performed for 60 min to form a homogeneous spinning solution.

[0080] 2. Wet spinning:

[0081] After the homogeneous spinning solution is extruded through a spinneret (orifice size of 700 μm) at a spinning speed of 3–10 m / min, it enters a deionized water bath and then a coagulation solution with a volume ratio of deionized water to dimethyl sulfoxide of 1:1. The fiber undergoes a differentiated phase separation process in the radial direction, forming a porous structure in which the pore size gradually decreases from the surface to the core layer in the radial direction, thus obtaining nascent fiber.

[0082] 3. Freeze-drying:

[0083] After the nascent fibers are quick-frozen with liquid nitrogen (-196℃, 15s), they are transferred to a freeze dryer (≤-5℃, vacuum degree ≤5Pa) for 48h to dry, thereby preserving the integrity of the porous structure and producing porous structure microwave absorbing fibers.

[0084] Example 3

[0085] 1. Preparation of spinning solution:

[0086] 3g of carbon nanotubes (purchased from Shenzhen Liren Trade Co., Ltd.) were dispersed in 97g of DMSO to form a 3wt% carbon nanotube dispersion.

[0087] 1g of aramid nanofibers (purchased from Yantai Taihe New Material Sales Co., Ltd.) was dispersed in 99g of DMSO to form a 1wt% aramid nanofiber solution.

[0088] 0.2 g of polyvinyl alcohol (purchased from Chongqing Chuanwei Chemical Co., Ltd. of China Petrochemical Corporation) was dispersed in 99.8 g of DMSO to form a 0.2 wt% polyvinyl alcohol solution;

[0089] The carbon nanotube dispersion prepared above was mixed with aramid nanofiber solution and polyvinyl alcohol solution at a mass ratio of 8:8:4, and ultrasonically treated for 60 min to form a homogeneous spinning solution.

[0090] 2. Wet spinning:

[0091] After the homogeneous spinning solution is extruded through a spinneret (orifice size of 500 μm) at a spinning speed of 5–15 m / min, it first enters a deionized water bath, and then enters a coagulation solution with a volume ratio of deionized water to dimethyl sulfoxide of 1:4. The fiber undergoes a differentiated phase separation process in the radial direction, forming a porous structure in which the pore size gradually decreases from the surface to the core layer in the radial direction, thus obtaining nascent fiber.

[0092] 3. Freeze-drying:

[0093] After the nascent fibers are quick-frozen in liquid nitrogen (-196℃, 15s), they are transferred to a freeze dryer (≤-5℃, vacuum degree ≤5Pa) for 36h to dry, thereby preserving the integrity of the porous structure and producing porous structure microwave absorbing fibers.

[0094] Example 4

[0095] 1. Spinning solution preparation:

[0096] 5 g of carbon nanotubes (purchased from Guangzhou Tengyan Cloud Technology Co., Ltd.) were dispersed in 95 g of DMSO to form a 5 wt% carbon nanotube dispersion;

[0097] 0.2 g of aramid nanofiber (purchased from Yantai Taihe New Material Sales Co., Ltd.) was dispersed in 99.8 g of DMSO to form a 0.2 wt% aramid nanofiber solution;

[0098] 0.1 g of polyvinyl alcohol (purchased from Sinopec Chongqing Chuanwei Chemical Co., Ltd.) was dispersed in 99.9 g of DMSO to form a 0.1 wt% polyvinyl alcohol solution;

[0099] The carbon nanotube dispersion, aramid nanofiber solution, and polyvinyl alcohol solution prepared above were mixed in a mass ratio of 8:4:1, ultrasonically treated for 30 min, and a homogeneous spinning solution was formed.

[0100] 2. Wet spinning:

[0101] The homogeneous spinning solution was extruded through a spinneret (pore size 700 pm) at a spinning speed of 3-10 m / min, entered a deionized water bath, and then entered a coagulation liquid of deionized water and dimethyl sulfoxide in a volume ratio of 1:1. The fiber underwent a differential phase separation process along the radial direction, forming a porous structure with a pore size gradually decreasing from the surface to the core layer along the radial direction, and a nascent fiber was obtained.

[0102] 3. Freeze-drying:

[0103] The nascent fiber was rapidly frozen in liquid nitrogen (-196 °C, 12 s), then transferred to a freeze dryer (≤-5 °C, vacuum degree ≤5 Pa) for drying for 48 h, thereby retaining the integrity of the porous structure, and a porous wave-absorbing fiber was prepared.

[0104] Example 5

[0105] 1. Spinning solution preparation:

[0106] 5 g of carbon nanotubes (purchased from Shenzhen Liren Trading Co., Ltd.) were dispersed in 95 g of DMSO to form a 5 wt% carbon nanotube dispersion;

[0107] 2 g of aramid nanofiber (purchased from Yantai Taihe New Material Sales Co., Ltd.) was dispersed in 98 g of DMSO to form a 2 wt% aramid nanofiber solution;

[0108] 10 g of polyvinyl alcohol (purchased from Sinopec Chongqing Chuanwei Chemical Co., Ltd.) was dispersed in 90 g of DMSO to form a 10 wt% polyvinyl alcohol solution;

[0109] The carbon nanotube dispersion solution prepared above is mixed with aramid nanofiber solution and polyvinyl alcohol solution at a mass ratio of 4:8:5, and ultrasonic treatment is performed for 50 min to form a homogeneous spinning solution.

[0110] 2. Wet spinning:

[0111] After the homogeneous spinning solution is extruded through a spinneret (pore size 300 μm) at a spinning speed of 8-15 m / min, it enters a deionized water bath, and then enters a coagulating liquid of deionized water and dimethyl sulfoxide at a volume ratio of 1:1. The fiber undergoes a differential phase separation process along the radial direction, forming a porous structure with a pore size gradually decreasing from the surface to the core layer along the radial direction, and obtaining a nascent fiber.

[0112] 3. Freeze drying:

[0113] After the nascent fiber is rapidly frozen in liquid nitrogen (-196℃, 10 s), it is transferred to a freeze dryer (≤-5℃, vacuum degree ≤5 Pa) for drying for 24 h, thereby retaining the integrity of the porous structure, and a porous structure wave-absorbing fiber is prepared.

[0114] The inventors of the present case characterized the porous structure wave-absorbing fiber prepared in Examples 1-3 in terms of structure and performance, as follows:

[0115] As shown in FIGS. 1-3, the SEM images of the porous structure wave-absorbing fiber prepared in Example 1 can be seen to have a pore size of 5-40 μm in the surface layer and a pore size of 100-200 nm in the core layer. Figure 1 Figure 2 As shown in FIG. 4, the wave-absorbing performance test results of the porous structure wave-absorbing fiber prepared in Example 1 can be seen to have an effective absorption bandwidth of 6 GHz (7-18 GHz) for a fiber-paraffin mixture sample at a thickness of 3.5 mm, a widest absorption bandwidth of 10 GHz (8-18 GHz), and a boundary formed by the black line in the figure to have an RL=-10 dB. The impedance matching value is 0.25-1.5, and the tensile breaking strength of the fiber sample is about 110 MPa.

[0116] As shown in FIGS. 5-7, the SEM images of the porous structure wave-absorbing fiber prepared in Example 2 can be seen to have a pore size of 20-40 μm in the surface layer and a pore size of 100-200 nm in the core layer, with a gradually decreasing trend in pore size from the surface layer to the core layer. Figure 3 As shown in FIGS. 8-10, the SEM images of the porous structure wave-absorbing fiber prepared in Example 3 can be seen to have a pore size of 5-20 μm in the surface layer and a pore size of 100-200 nm in the core layer, with a gradually decreasing trend in pore size from the surface layer to the core layer.

[0117] Figure 4 As shown in FIG. 11, the wave-absorbing performance test results of the porous structure wave-absorbing fiber prepared in Example 3 can be seen to have an effective absorption bandwidth of 6 GHz (7-18 GHz) for a fiber-paraffin mixture sample at a thickness of 3.5 mm, a widest absorption bandwidth of 10 GHz (8-18 GHz), and a boundary formed by the black line in the figure to have an RL=-10 dB. The impedance matching value is 0.25-1.5, and the tensile breaking strength of the fiber sample is about 110 MPa. Figure 5 As shown in FIG. 12, the wave-absorbing performance test results of the porous structure wave-absorbing fiber prepared in Example 3 can be seen to have an effective absorption bandwidth of 6 GHz (7-18 GHz) for a fiber-paraffin mixture sample at a thickness of 3.5 mm, a widest absorption bandwidth of 10 GHz (8-18 GHz), and a boundary formed by the black line in the figure to have an RL=-10 dB. The impedance matching value is 0.25-1.5, and the tensile breaking strength of the fiber sample is about 110 MPa.

[0118] Figure 6 ​​​The wave-absorbing performance test results of the porous structure wave-absorbing fiber prepared in Example 2 are shown in Figure 2, and it can be seen that the effective absorption bandwidth is 13 GHz (5.0-18 GHz), which is the widest among the three examples. The impedance matching value is 0.35-1.25, and the tensile breaking strength of the fiber sample is about 45 MPa.

[0119] As shown in Figure 3, it is the SEM image of the porous structure wave-absorbing fiber prepared in Example 3, and it can be seen that the pore size of the surface layer is 40-100 μm, and the pore size of the core layer is 100-1000 nm. Figure 7 Figure 8 The wave-absorbing performance test results of the porous structure wave-absorbing fiber prepared in Example 3 are shown in Figure 4, and it can be seen that the effective absorption bandwidth is 6.5 GHz (11.5-18 GHz). The impedance matching value is 0.15-2, and the tensile breaking strength of the fiber sample is about 45 MPa.

[0120] As shown in Figure 5, it is the SEM image of the porous structure wave-absorbing fiber prepared in Example 4, and it can be seen that the pore size of the surface layer is 40-100 μm, and the pore size of the core layer is 100-1000 nm. Figure 9 The wave-absorbing performance test results of the porous structure wave-absorbing fiber prepared in Example 4 are shown in Figure 6, and it can be seen that the effective absorption bandwidth is 6.5 GHz (11.5-18 GHz). The impedance matching value is 0.15-2, and the tensile breaking strength of the fiber sample is about 45 MPa.

[0121] Comparative Example 1

[0122] Figure 10 The difference between this comparative example and Example 1 is that no aramid nanofiber is added to the spinning solution. Although the finally obtained fiber has a porous structure, its wave-absorbing performance is poorer than that of Example 1 (11-18 GHz), as shown in Figure 7.

[0123] Comparative Example 2

[0124] The difference between this comparative example and Example 1 is that no polyvinyl alcohol solution is added to the spinning solution, and the content of carbon nanotubes is increased. The finally obtained fiber does not have a pore structure with gradually decreasing pore size, but is uniformly distributed. Its wave-absorbing performance is poorer than that of Example 1 (13-18 GHz), as shown in Figure 8. Figure 11 Comparative Example 3

[0125] The difference between this comparative example and Example 1 is that only deionized water is used in the coagulation bath, and the finally obtained fiber generally has a large pore size, and the pore size does not have a significant gradual decrease. The maximum absorption bandwidth of the fiber is about 4.5 GHz (13.5-18 GHz).

[0126] Comparative Example 4

[0127] The difference between this comparative example and Example 1 is that only deionized water + dimethyl sulfoxide is used in the coagulation bath, and the finally obtained fiber generally has a small pore size, and the pore size does not have a significant gradual decrease. The maximum absorption bandwidth of the fiber is about 5.5 GHz (12.5-18 GHz).

[0128] Comparative Example 5

[0129] ​​​

[0130] The comparative example is different from example 1 in that the volume ratio of deionized water to dimethyl sulfoxide in the second coagulation bath is 1:5, the larger pore size of the outer layer of the final obtained fiber is smaller than that of example 1, and the maximum absorption bandwidth of the fiber is about 8 GHz (10-18 GHz).

[0131] Comparative example 6

[0132] The comparative example is different from example 1 in that the volume ratio of deionized water to dimethyl sulfoxide in the second coagulation bath is 5:1, the larger pore size of the outer layer of the final obtained fiber is larger than that of example 1, and the maximum absorption bandwidth of the fiber is about 6 GHz (12-18 GHz).

[0133] Comparative example 7

[0134] The comparative example is different from example 1 in that it is not quick-frozen in liquid nitrogen, but directly dried in a freeze dryer. The final obtained fiber is in a flat strip shape, does not have a pore structure with gradually decreasing pore size, and has a poorer wave absorption test performance (14-18 GHz) than example 1, as shown in Figure 12

[0135] In addition, the inventors of the present application have also conducted tests with other raw materials, process operations, and process conditions described in the specification with reference to the foregoing examples, and all have obtained relatively ideal results.

[0136] It should be understood that the above examples and features are only for illustrating the technical concepts and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and implement it, and cannot limit the protection scope of the present application. Any equivalent transformation or modification made according to the spirit and essence of the present application should be covered within the protection scope of the present application.​

Claims

1. A porous structure wave-absorbing fiber, characterized by: The porous structure absorbing wave fiber comprises carbon nanotubes and aramid nanofibers, has a porous structure, and the pore size of the pores contained in the porous structure absorbing wave fiber gradually decreases from the surface layer to the core layer in the radial direction of the porous structure absorbing wave fiber.

2. The porous structure wave-absorbing fiber according to claim 1, characterized in that: The pores contained in the porous structure absorbing wave fiber comprise elliptical holes radially distributed in the surface layer of the porous structure absorbing wave fiber and nanopores in the core of the porous structure absorbing wave fiber.

3. The porous structure wave-absorbing fiber according to claim 2, characterized in that: The pore size of the surface layer of the porous structure absorbing wave fiber is defined as a first pore size, and the pore size of the core layer is defined as a second pore size, the first pore size is 5-100 μm, and the second pore size is 100-1000 nm.

4. The porous structure wave-absorbing fiber according to claim 1, characterized in that: The porosity of the porous structure absorbing wave fiber is 60%-90%; and / or, the cross-sectional shape of the pores contained in the porous structure absorbing wave fiber is a radial ellipse; and / or, the diameter of the porous structure absorbing wave fiber is 300-600 μm; and / or, the electromagnetic microwave reflectivity of the porous structure absorbing wave fiber is better than -10 dB in the range of 5-18 GHz, the mechanical strength is 50-200 MPa, and the impedance matching value is between 0.5 and 1 in the range of 5-18 GHz.

5. The method of claim 1-4, wherein the porous structure wave absorbing fiber is prepared by the steps of: a) mixing the carbon nanotubes and the polymer to form a mixture; b) extruding the mixture to form a fiber; c) heating the fiber to form a porous structure wave absorbing fiber. Comprising: Mixing carbon nanotube dispersion, aramid nanofiber solution and polyvinyl alcohol solution to form a homogeneous spinning solution; Using a wet spinning technology, the homogeneous spinning solution is extruded through a spinneret and then enters a first coagulation bath and a second coagulation bath, respectively, and the obtained fiber undergoes a differential phase separation process along the radial direction to form a porous structure with a pore size gradually decreasing from the surface layer to the core layer; wherein the first coagulation bath is water, and the second coagulation bath is a mixture of water and a specified organic solvent, wherein the volume ratio of water to the specified organic solvent is 1:4-4:1; Drying the as-spun fiber obtained in the coagulation bath to obtain the porous structure absorbing wave fiber.

6. The production method according to claim 5, characterized by, Comprising: Mixing carbon nanotube dispersion, aramid nanofiber solution and polyvinyl alcohol solution in a mass ratio of 8:4:1-4:8:5, and then ultrasonic treatment for 30-60 min to form a homogeneous spinning solution.

7. The method of manufacturing according to claim 5 or 6, characterized in that: The carbon nanotube dispersion comprises carbon nanotubes and a specified organic solvent; preferably, the content of carbon nanotubes in the carbon nanotube dispersion is 1-5 wt%; and / or, the aramid nanofiber solution comprises aramid nanofibers and a specified organic solvent; preferably, the content of aramid nanofibers in the aramid nanofiber solution is 0.2-4 wt%, and preferably, the diameter of the aramid nanofibers is 30-100 nm; and / or, the polyvinyl alcohol solution comprises polyvinyl alcohol and a specified organic solvent, and preferably, the content of polyvinyl alcohol in the polyvinyl alcohol solution is 0.1-10 wt%; and / or, the specified organic solvent comprises dimethyl sulfoxide; and / or, the water comprises deionized water.

8. The preparation method according to claim 5, characterized in that, The process conditions of the wet spinning technology include: the pore size of the spinneret is 300-700 μm, and the spinning speed is 1-15 m / min.

9. The method of claim 5, wherein: The drying comprises natural drying and / or freeze drying; Preferably, the freeze-drying comprises: first freezing the nascent fiber in liquid nitrogen environment of ≤-196 ℃ for 10-15 s, and then freeze-drying in a condition of ≤-5 ℃ and a vacuum degree of ≤5 Pa for 24-48 h to obtain the porous structure wave-absorbing fiber.

10. Application of the porous structure wave-absorbing fiber in any one of claims 1-4 in the field of electromagnetic microwave absorption.

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