Aramid nanofiber low-frequency wave-absorbing composite material and preparation method thereof

Abstract

The present invention relates to the technical field of polymer composite materials, and in particular to an aramid nanofiber low-frequency wave absorbing composite material and a preparation method thereof. The raw materials for preparing the aramid nanofiber low-frequency wave absorbing composite material include magnetic wave absorbing fibers and aromatic polyamide nanofibers; the magnetic wave absorbing fibers are prepared from a raw material system including FeCo magnetic wave absorbing fillers, aromatic polyamide fibers, and hyperbranched polysiloxane modifiers. The aramid nanofiber low-frequency wave absorbing composite material prepared by using magnetic wave absorbing fibers and aromatic polyamide nanofibers as raw materials has excellent mechanical properties (tensile strength can reach 133Mpa) and excellent wave absorbing performance (minimum reflection loss can reach ‑46.8dB, low-frequency effective absorption bandwidth (EAB) is 2.24GHz (5.52GHz~7.76GHz)), and can be widely used in fields such as communications and electronic equipment.

Description

Technical Field

[0001] The invention relates to the technical field of polymer composite materials, and in particular to an aramid nanofiber low-frequency wave-absorbing composite material and a preparation method thereof. Background Art

[0002] With the rapid development of 5G communications and electronic devices, the high power, high density and high integration of electronic components have made electromagnetic pollution problems such as electromagnetic radiation, electromagnetic interference and electromagnetic leakage increasingly prominent, which not only affects the normal operation of electronic equipment, but also may have a negative impact on human health. In order to solve the problem of electromagnetic pollution, the usual means is to use absorbing materials to effectively shield electromagnetic radiation, electromagnetic interference and electromagnetic leakage.

[0003] At present, the absorption range of most absorbing materials is mainly concentrated in the medium and high frequency microwave region (X band: 8~12GHz and Ku band: 12GHz~18GHz). With the rapid development of 5G communications and electronic equipment, the electromagnetic pollution problem in the low frequency microwave region (S band: 2GHz~4GHz and C band: 4GHz~8GHz) is becoming more and more serious. Therefore, it is urgent to explore efficient low frequency absorbing materials.

[0004] Aromatic polyamide nanofibers (aramid nanofibers, ANFs) have the advantages of light weight, high specific strength, easy processing, heat resistance, and corrosion resistance. They are widely used in high-tech fields such as aerospace and electronic equipment. However, their bulk absorption performance is poor, which limits their application in the preparation of absorbing materials.

[0005] The Chinese patent technology with publication number CN 115159500 A discloses a carbon nanofiber aerogel microsphere and a preparation method thereof, wherein the carbon nanofiber aerogel microsphere is obtained by aging, freeze-drying and heat-treating aramid nanofibers, and the carbon nanofiber aerogel microsphere has excellent wave absorption performance in the medium and high frequency microwave region (the minimum reflection loss can reach -51.89dB). However, the wave absorption performance of the carbon nanofiber aerogel microsphere in the low frequency microwave region is poor (the reflection loss is -20dB).

[0006] The Chinese patent technology with publication number CN 118994714 A discloses a method for preparing a black phosphorus-loaded aramid nanofiber aerogel electromagnetic shielding material, wherein the aramid nanofiber hydrogel is subjected to two solvent exchanges in a tert-butyl alcohol aqueous solution and then mixed with a black phosphorus dispersion, and then vacuum freeze-dried to obtain a black phosphorus / aramid nanofiber aerogel, which has excellent mechanical properties (tensile strength up to 1.43Mpa) and wave absorption properties (reflection loss up to -25.6dB). However, the black phosphorus / aramid nanofiber aerogel in the patent has the problem of poor mechanical properties.

[0007] Therefore, how to obtain an aramid nanofiber absorbing material that has excellent mechanical properties and absorbing properties in the low-frequency microwave region has become a technical problem that needs to be solved urgently. Summary of the invention

[0008] The invention provides an aramid nanofiber low-frequency wave-absorbing composite material, which has excellent mechanical properties and excellent wave-absorbing performance.

[0009] The present invention also provides a method for preparing an aramid nanofiber low-frequency wave-absorbing composite material, by which an aramid nanofiber low-frequency wave-absorbing composite material with excellent mechanical properties and wave-absorbing properties can be prepared.

[0010] The first aspect of the present invention provides an aramid nanofiber low-frequency wave absorbing composite material, wherein the raw materials for preparing the aramid nanofiber low-frequency wave absorbing composite material include magnetic wave absorbing fibers and aromatic polyamide nanofibers;

[0011] The magnetic wave-absorbing fiber is prepared from a raw material system comprising FeCo magnetic wave-absorbing filler, aromatic polyamide fiber and hyperbranched polysiloxane modifier.

[0012] In the aramid nanofiber low-frequency wave-absorbing composite material as described above, the FeCo magnetic wave-absorbing filler is in a core-shell spherical shape.

[0013] In the aramid nanofiber low-frequency wave absorbing composite material as described above, the weight ratio of the magnetic wave absorbing fiber to the aromatic polyamide nanofiber is (600-1500):(50-300).

[0014] In the aramid nanofiber low-frequency wave-absorbing composite material as described above, in the magnetic wave-absorbing fiber, the weight ratio of the FeCo magnetic wave-absorbing filler, the aromatic polyamide fiber and the hyperbranched polysiloxane modifier is (200-1000): (50-300): (2-30).

[0015] The second aspect of the present invention provides a method for preparing the aramid nanofiber low-frequency wave absorbing composite material, comprising:

[0016] Preparation of magnetic absorbing fiber:

[0017] The cobalt salt, the iron salt, the reducing agent and the organic solvent are mixed and then subjected to a reduction reaction to obtain the FeCo magnetic wave absorbing filler;

[0018] Mixing 3-aminopropyltriethoxysilane and diethylene glycol and performing an ester exchange polycondensation reaction to obtain the hyperbranched polysiloxane modifier;

[0019] The FeCo magnetic wave absorbing filler, the aromatic polyamide fiber and the hyperbranched polysiloxane modifier are mixed and then chemically cross-linked to prepare a magnetic wave absorbing fiber;

[0020] Preparation of aramid nanofiber low frequency absorbing composite materials:

[0021] Preparation of aromatic polyamide nanofibers;

[0022] The magnetic wave-absorbing fiber and the aromatic polyamide nanofiber are mixed, and then subjected to suction filtration, pressure-maintaining treatment and hot pressing treatment to obtain the aramid nanofiber low-frequency wave-absorbing composite material.

[0023] The method for preparing the aramid nanofiber low-frequency wave-absorbing composite material as described above, wherein the weight ratio of the cobalt salt, the iron salt, the reducing agent and the organic solvent in the FeCo magnetic wave-absorbing filler is (50-100): (10-50): (120-600): (1000-6000);

[0024] And / or, in the hyperbranched polysiloxane modifier, the weight ratio of the 3-aminopropyltriethoxysilane to the diethylene glycol is (500-1000): (500-1000).

[0025] The method for preparing the aramid nanofiber low-frequency wave absorbing composite material as described above, wherein the reduction reaction temperature is 140° C. to 240° C. and the time is 1 h to 24 h;

[0026] And / or, the temperature of the transesterification polycondensation reaction is 100°C to 160°C.

[0027] In the method for preparing the aramid nanofiber low-frequency wave-absorbing composite material as described above, the temperature of the chemical crosslinking is 80° C. to 140° C. and the time is 1 h to 6 h.

[0028] The method for preparing the aramid nanofiber low-frequency wave-absorbing composite material as described above, wherein the pressure of the suction filtration and pressure-maintaining treatment is 0.1Pa to 1.0Pa and the time is 0.5h to 3.0h;

[0029] And / or, the pressure of the hot pressing treatment is 0 MPa to 2.0 MPa, the temperature is 150 to 250° C., and the time is 0.1 h to 1.0 h.

[0030] In the method for preparing the aramid nanofiber low-frequency wave-absorbing composite material as described above, the cobalt salt is at least one of cobalt nitrate, cobalt chloride, and cobalt acetate, the iron salt is at least one of ferrous nitrate, ferrous chloride, and ferrous sulfate, the reducing agent is at least one of hydrazine hydrate and sodium borohydride, and the organic solvent includes ethylene glycol.

[0031] The aramid nanofiber low-frequency wave-absorbing composite material provided by the present invention comprises magnetic wave-absorbing fibers and aromatic polyamide nanofibers. The magnetic wave-absorbing fibers are prepared from a raw material system comprising core-shell spherical FeCo magnetic wave-absorbing fillers, aromatic polyamide fibers and a hyperbranched polysiloxane modifier. The aramid nanofiber low-frequency wave-absorbing composite material prepared by taking the magnetic wave-absorbing fibers and the aromatic polyamide nanofibers as raw materials has excellent mechanical properties (tensile strength can reach 133Mpa) and excellent wave-absorbing performance (minimum reflection loss can reach -46.8dB, and low-frequency effective absorption bandwidth (EAB) is 2.24GHz (5.52GHz-7.76GHz)), and can be widely used in the fields of communications and electronic equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0033] Figure 1 This is a scanning electron microscope (SEM) image of the spherical FeCo magnetic absorbing filler in Example 1 of the present invention;

[0034] Figure 2 This is a test result diagram of the wave absorbing performance of the spherical FeCo magnetic wave absorbing filler in Example 1 of the present invention;

[0035] Figure 3 This is a SEM image of the core-shell spherical FeCo magnetic wave absorbing filler in Example 2 of the present invention;

[0036] Figure 4 This is a graph showing the test results of the wave absorbing performance of the core-shell spherical FeCo magnetic wave absorbing filler in Example 2 of the present invention;

[0037] Figure 5 is a SEM image of poly(p-phenylene terephthalamide) fiber (PPTA fiber) in Example 3 of the present invention;

[0038] Figure 6 This is a SEM image of the PPTA@FeCo magnetic absorbing fiber in Example 3 of the present invention;

[0039] Figure 7 This is a SEM image of the PPTA@FeCo magnetic absorbing fiber in Example 4 of the present invention;

[0040] Figure 8 This is a SEM image of the PPTA@FeCo magnetic absorbing fiber in Comparative Example 1 of the present invention;

[0041] Fig. 9 This is a test result diagram of the wave absorbing performance of the aramid nanofiber low-frequency wave absorbing composite material in Example 3 of the present invention;

[0042] Fig.10 This is a test result diagram of the wave absorbing performance of the aramid nanofiber low-frequency wave absorbing composite material in Example 4 of the present invention;

[0043] Fig.11 This is a test result diagram of the wave absorbing performance of the aramid nanofiber low-frequency wave absorbing composite material in Example 5 of the present invention;

[0044] Fig.12 This is a test result diagram of the wave absorption performance of the aramid nanofiber composite material in Comparative Example 1 of the present invention;

[0045] Fig.13 This is a test result diagram of the wave absorption performance of the aramid nanofiber composite material in Comparative Example 2 of the present invention;

[0046] Fig.14 This is a graph showing the test results of the wave absorption performance of the aramid nanofiber composite material in Comparative Example 3 of the present invention. DETAILED DESCRIPTION

[0047] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0048] Unless otherwise specified, the raw materials and reagents used in the following examples can be obtained from commercial sources; the processes used, unless otherwise specified, are conventional processes in the art.

[0049] The first aspect of the present invention provides an aramid nanofiber low-frequency wave absorbing composite material, wherein the raw materials for preparing the aramid nanofiber low-frequency wave absorbing composite material include magnetic wave absorbing fibers and aromatic polyamide nanofibers;

[0050] The magnetic wave-absorbing fiber is prepared from a raw material system comprising FeCo magnetic wave-absorbing filler, aromatic polyamide fiber and hyperbranched polysiloxane modifier.

[0051] In the present invention, the aromatic polyamide nanofibers are referred to as aramid nanofibers (ANFs).

[0052] In the present invention, the aromatic polyamide fiber refers to poly(p-phenylene terephthalamide) fiber (PPTA fiber).

[0053] In the present invention, the aramid nanofiber low-frequency microwave absorbing composite material refers to a composite material having microwave absorbing properties in the low-frequency microwave region (S band: 2 GHz to 4 GHz and C band: 4 GHz to 8 GHz).

[0054] The aramid nanofiber low-frequency wave-absorbing composite material of the present invention is prepared by preparing magnetic wave-absorbing fibers from a raw material system including FeCo magnetic wave-absorbing fillers, aromatic polyamide fibers and a hyperbranched polysiloxane modifier, and then using the magnetic wave-absorbing fibers and aromatic polyamide nanofibers as raw materials. The aramid nanofiber low-frequency wave-absorbing composite material has excellent mechanical properties (tensile strength can reach 133Mpa) and excellent wave-absorbing performance (minimum reflection loss can reach -46.8dB, and low-frequency effective absorption bandwidth (EAB) is 2.24GHz (5.52GHz-7.76GHz)).

[0055] Furthermore, the FeCo magnetic absorbing filler is in the shape of a core-shell sphere.

[0056] When the FeCo magnetic absorbing filler is in the shape of a core-shell sphere, the FeCo magnetic absorbing filler has excellent saturation magnetization (121emu / g), coercive force (43Oe) and absorbing performance (minimum reflection loss can reach -42.1dB, and low-frequency effective absorption bandwidth is 1.36GHz (4.32GHz~5.68GHz)), which is conducive to the subsequent preparation of aramid nanofiber low-frequency absorbing composite materials with excellent mechanical properties and absorbing properties.

[0057] In a specific embodiment, in the above-mentioned aramid nanofiber low-frequency absorbing composite material, the weight ratio of the magnetic absorbing fiber to the aromatic polyamide nanofiber is (600-1500): (50-300).

[0058] When the weight ratio of the magnetic absorbing fiber to the aromatic polyamide nanofiber in the aramid nanofiber low-frequency absorbing composite material is within the above range, the magnetic absorbing fiber and the aromatic polyamide nanofiber can have a good synergistic effect, thereby preparing an aramid nanofiber low-frequency absorbing composite material with excellent mechanical properties and absorbing properties.

[0059] Exemplarily, in the aramid nanofiber low-frequency absorbing composite material, the weight ratio of the magnetic absorbing fiber to the aromatic polyamide nanofiber can be 600:50, 600:300, 700:50, 700:300, 800:50, 800:300, 1500:50, 1500:300 or a range consisting of any two of them.

[0060] In some embodiments, in the above-mentioned aramid nanofiber low-frequency absorbing composite material, the weight ratio of the magnetic absorbing fiber to the aromatic polyamide nanofiber may be preferably 800:300, and the synergistic effect of the magnetic absorbing fiber and the aromatic polyamide nanofiber is better, thereby preparing an aramid nanofiber low-frequency absorbing composite material with better mechanical properties and absorbing properties.

[0061] In a specific embodiment, in the above-mentioned magnetic absorbing fiber, the weight ratio of FeCo magnetic absorbing filler, aromatic polyamide fiber and hyperbranched polysiloxane modifier is (200-1000): (50-300): (2-30).

[0062] When the weight ratio of the FeCo magnetic absorbing filler, the aromatic polyamide fiber and the hyperbranched polysiloxane modifier in the magnetic absorbing fiber is within the above range, the FeCo magnetic absorbing filler, the aromatic polyamide fiber and the hyperbranched polysiloxane modifier can be better matched, thereby preparing a magnetic absorbing fiber in which the FeCo magnetic absorbing filler is uniformly coated on the surface of the aromatic polyamide fiber.

[0063] Exemplarily, in the magnetic absorbing fiber, the weight ratio of FeCo magnetic absorbing filler, aromatic polyamide fiber and hyperbranched polysiloxane modifier can be 200:50:2, 200:300:30, 200:50:30, 200:300:2, 1000:50:2, 1000:300:2, 1000:50:300, 500:200:5, 500:200:15 or a range of any three thereof.

[0064] In some embodiments, in the magnetic absorbing fiber, the weight ratio of the FeCo magnetic absorbing filler, the aromatic polyamide fiber and the hyperbranched polysiloxane modifier may preferably be 500:200:5.

[0065] The second aspect of the present invention provides a method for preparing an aramid nanofiber low-frequency wave absorbing composite material, comprising:

[0066] Preparation of magnetic absorbing fiber:

[0067] The cobalt salt, the iron salt, the reducing agent and the organic solvent are mixed and then subjected to reduction reaction to obtain the FeCo magnetic wave absorbing filler;

[0068] 3-aminopropyltriethoxysilane is mixed with diethylene glycol and subjected to transesterification polycondensation reaction to obtain a hyperbranched polysiloxane modifier;

[0069] The FeCo magnetic absorbing filler, aromatic polyamide fiber and hyperbranched polysiloxane modifier are mixed and then chemically cross-linked to prepare magnetic absorbing fiber;

[0070] Preparation of aramid nanofiber low frequency absorbing composite materials:

[0071] Preparation of aromatic polyamide nanofibers;

[0072] The magnetic wave-absorbing fiber and the aromatic polyamide nanofiber are mixed, and then subjected to suction filtration, pressure holding treatment and hot pressing treatment to obtain the aramid nanofiber low-frequency wave-absorbing composite material.

[0073] The present invention does not specifically limit the specific method for preparing the aromatic polyamide nanofibers, and the aromatic polyamide nanofibers can be prepared according to methods known in the art. For example, aromatic polyamide fibers, potassium hydroxide and dimethyl sulfoxide are mixed and then deprotonated and stripped, and then protonated by water to obtain aromatic polyamide nanofibers.

[0074] Specifically, the object prepared by the present invention is an aramid nanofiber low-frequency wave-absorbing composite material. First, cobalt salt, iron salt, a reducing agent and an organic solvent are mixed and then subjected to a reduction reaction to obtain a FeCo magnetic wave-absorbing filler; then 3-aminopropyl triethoxysilane and diethylene glycol are mixed and subjected to an ester exchange polycondensation reaction to obtain a hyperbranched polysiloxane modifier; then, the FeCo magnetic wave-absorbing filler, aromatic polyamide fiber and the hyperbranched polysiloxane modifier are mixed and then chemically cross-linked; the hyperbranched polysiloxane modifier can make the FeCo magnetic wave-absorbing filler and the aromatic polyamide fiber The fibers are well combined to prepare magnetic absorbing fibers in which FeCo magnetic absorbing filler is uniformly coated on the surface of aromatic polyamide fibers; finally, the magnetic absorbing fibers and aromatic polyamide nanofibers are mixed and filtered, pressurized and hot-pressed to obtain aramid nanofiber low-frequency absorbing composite materials with excellent mechanical properties (tensile strength can reach 133Mpa) and absorbing properties (minimum reflection loss can reach -46.8dB, and low-frequency effective absorption bandwidth (EAB) is 2.24GHz (5.52GHz~7.76GHz)).

[0075] In a specific embodiment, in the above-mentioned FeCo magnetic absorbing filler, the weight ratio of cobalt salt, iron salt, reducing agent and organic solvent is (50-100): (10-50): (120-600): (1000-6000).

[0076] When the weight ratio of the cobalt salt, the iron salt, the reducing agent and the organic solvent in the FeCo magnetic absorbing filler is within the above range, the cobalt salt, the iron salt, the reducing agent and the organic solvent can be mixed and then fully reduced, thereby obtaining a FeCo magnetic absorbing filler having excellent saturation magnetization, coercive force and absorbing performance. In the FeCo magnetic absorbing filler, the weight ratio of the cobalt salt, the iron salt, the reducing agent and the organic solvent can preferably be 90:10:600:6000, which can make the cobalt salt, the iron salt, the reducing agent and the organic solvent mixed and then fully reduced, thereby obtaining a core-shell spherical FeCo magnetic absorbing filler having more excellent saturation magnetization, coercive force and absorbing performance.

[0077] In a specific embodiment, in the hyperbranched polysiloxane modifier, the weight ratio of 3-aminopropyltriethoxysilane to diethylene glycol is (500-1000): (500-1000).

[0078] When the weight ratio of 3-aminopropyltriethoxysilane to diethylene glycol in the hyperbranched polysiloxane modifier is within the above range, 3-aminopropyltriethoxysilane and diethylene glycol can be mixed and then fully subjected to ester exchange polycondensation reaction to obtain a hyperbranched polysiloxane modifier capable of more fully combining the FeCo magnetic absorbing filler with the aromatic polyamide fiber, which is beneficial to the preparation of the magnetic absorbing fiber in which the FeCo magnetic absorbing filler is uniformly coated on the surface of the aromatic polyamide fiber.

[0079] For example, in the hyperbranched polysiloxane modifier, the weight ratio of 3-aminopropyltriethoxysilane to diethylene glycol may be 500:500, 500:1000, 1000:500, 1000:1000, 800:800 or a range consisting of any two thereof.

[0080] In a specific embodiment, the reduction reaction is carried out at a temperature of 140° C. to 240° C. and for a time of 1 h to 24 h.

[0081] When the temperature and time parameters of the reduction reaction are within the above ranges, the cobalt salt, iron salt, reducing agent and organic solvent can be mixed and then fully reduced to obtain FeCo magnetic wave absorbing filler with excellent saturation magnetization, coercive force and wave absorbing performance. The temperature of the reduction reaction may be preferably 200° C. and the time may be preferably 3 hours.

[0082] In a specific embodiment, the temperature of the transesterification polycondensation reaction is 100°C to 160°C.

[0083] When the temperature parameter of the transesterification polycondensation reaction is within the above range, 3-aminopropyltriethoxysilane and diethylene glycol can be mixed and then fully transesterified and polycondensed to prepare a hyperbranched polysiloxane modifier.

[0084] In a specific embodiment, the temperature of the chemical cross-linking is 80° C. to 140° C. and the time is 1 h to 6 h.

[0085] When the temperature and time parameters of chemical crosslinking are within the above ranges, the hyperbranched polysiloxane modifier can fully combine the FeCo magnetic absorbing filler with the aromatic polyamide fiber, thereby preparing a magnetic absorbing fiber in which the FeCo magnetic absorbing filler is uniformly coated on the surface of the aromatic polyamide fiber.

[0086] In a specific embodiment, the pressure of the suction filtration and pressure-maintaining treatment is 0.1Pa to 1.0Pa, and the time is 0.5h to 3.0h. Furthermore, the pressure of the suction filtration and pressure-maintaining treatment may preferably be 0.5Pa, and the time may preferably be 1h.

[0087] When the pressure and time parameters of the filtration and pressure-maintaining treatment are within the above ranges, the components in the aramid nanofiber low-frequency wave-absorbing composite material can be uniformly and tightly combined, thereby preparing an aramid nanofiber low-frequency wave-absorbing composite material with excellent mechanical properties and wave-absorbing properties.

[0088] In a specific embodiment, the pressure of the hot pressing treatment is 0 MPa to 2.0 MPa, the temperature is 150 to 250° C., and the time is 0.1 h to 1.0 h. Furthermore, the pressure of the hot pressing treatment may preferably be 1.5 MPa, the temperature may preferably be 200° C., and the time may preferably be 0.1 h.

[0089] When the parameters of pressure, temperature and time of the hot pressing treatment are within the above ranges, the close bonding of the components in the aramid nanofiber low-frequency wave-absorbing composite material can be further enhanced, thereby preparing an aramid nanofiber low-frequency wave-absorbing composite material with excellent mechanical properties and wave-absorbing properties.

[0090] In a specific embodiment, the cobalt salt is at least one of cobalt nitrate, cobalt chloride, and cobalt acetate. Further, the cobalt nitrate is preferably cobalt nitrate hexahydrate (Co(NO3)2·6H2O), the cobalt chloride is preferably cobalt chloride hexahydrate (CoCl2·6H2O), and the cobalt acetate is preferably cobalt acetate tetrahydrate ((CH3COO)2Co·4H2O); the iron salt is at least one of ferrous nitrate, ferrous chloride, and ferrous sulfate, further preferably ferrous chloride, and the ferrous chloride is preferably ferrous chloride tetrahydrate (FeCl2·4H2O); the reducing agent is at least one of hydrazine hydrate and sodium borohydride, further preferably hydrazine hydrate; the organic solvent includes ethylene glycol.

[0091] When the above substances are selected, FeCo magnetic wave-absorbing fillers having excellent saturation magnetization, coercive force and wave-absorbing performance can be prepared.

[0092] The present invention is further described below through specific embodiments.

[0093] Example 1

[0094] In this example, spherical FeCo magnetic wave absorbing filler is obtained by the following preparation method:

[0095] According to weight, 50 parts by weight of CoCl2·6H2O and 50 parts by weight of FeCl2·4H2O are added to 6000 parts by weight of ethylene glycol and mixed evenly, and then 600 parts by weight of hydrazine hydrate (N2H4·H2O) are added dropwise, and a mixed solution is obtained after stirring; the mixed solution is placed in a reactor at a temperature of 200°C for reduction reaction for 3 hours, and after the reduction reaction is completed and naturally cooled to room temperature, a precipitate is obtained; the precipitate is collected by a magnet, and is alternately washed with distilled water and anhydrous ethanol, and then placed in a vacuum drying oven at a temperature of 60°C for drying for 12 hours to obtain a spherical FeCo magnetic wave absorbing filler.

[0096] (1) Figure 1 This is a scanning electron microscope (SEM) image of the spherical FeCo magnetic absorbing filler in an embodiment of the present invention.

[0097] Depend on Figure 1 It can be seen that the average size of the spherical FeCo magnetic wave-absorbing filler provided in this embodiment is about 1.0 μm, and the size distribution is uniform.

[0098] (2) The saturation magnetization and coercivity of the spherical FeCo magnetic absorbing filler were tested using a vibrating sample magnetometer.

[0099] The test results show that the saturation magnetization intensity of the spherical FeCo magnetic absorbing filler is 99emu / g and the coercive force is 154Oe.

[0100] (3) The electromagnetic parameters of the spherical FeCo magnetic absorbing filler were tested using the ASTM D7449M-2014 / coaxial method. The minimum reflection loss and low-frequency effective absorption bandwidth of the spherical FeCo magnetic absorbing filler were calculated. The results are as follows: Figure 2 shown.

[0101] Depend on Figure 2 The results show that when the thickness of the spherical FeCo magnetic absorbing filler is 5.0 mm, the minimum reflection loss (RLmin) is -29.1 dB and the low-frequency effective absorption bandwidth (EAB) is 0.16 GHz (7.76 GHz to 7.92 GHz).

[0102] Example 2

[0103] In this example, the core-shell spherical FeCo magnetic wave absorbing filler is prepared by the following preparation method:

[0104] According to weight, 90 parts by weight of CoCl2·6H2O and 10 parts by weight of FeCl2·4H2O are added to 6000 parts by weight of ethylene glycol and mixed evenly, and then 600 parts by weight of hydrazine hydrate (N2H4·H2O) are added dropwise, and a mixed solution is obtained after stirring; the mixed solution is placed in a reactor at a temperature of 200°C for reduction reaction for 3 hours, and after the reduction reaction is completed and naturally cooled to room temperature, a precipitate is obtained; the precipitate is collected by a magnet, and is alternately washed with distilled water and anhydrous ethanol, and then placed in a vacuum drying oven at a temperature of 60°C for drying for 12 hours to obtain a core-shell spherical FeCo magnetic wave-absorbing filler.

[0105] (1) Figure 3 : This is a SEM image of the core-shell spherical FeCo magnetic absorbing filler in an embodiment of the present invention.

[0106] Depend on Figure 3 It can be seen that the average size of the core-shell spherical FeCo magnetic wave-absorbing filler provided in this embodiment is about 0.5 μm, and the size distribution is uniform.

[0107] (2) The saturation magnetization and coercivity of the core-shell spherical FeCo magnetic absorbing filler were tested using a vibrating sample magnetometer.

[0108] The test results show that the saturation magnetization intensity of the core-shell spherical FeCo magnetic absorbing filler is 121emu / g and the coercive force is 43Oe.

[0109] (3) The electromagnetic parameters of the core-shell spherical FeCo magnetic absorbing filler were tested using the ASTM D7449M-2014 / coaxial method. The minimum reflection loss and low-frequency effective absorption bandwidth of the core-shell spherical FeCo magnetic absorbing filler were calculated. The results are as follows: Figure 4 shown.

[0110] Depend on Figure 4 The results show that when the thickness of the core-shell spherical FeCo magnetic absorbing filler is 2.6 mm, the minimum reflection loss (RLmin) is -42.1 dB and the low-frequency effective absorption bandwidth (EAB) is 1.36 GHz (4.32 GHz to 5.68 GHz).

[0111] Example 3

[0112] In this embodiment, the aramid nanofiber low-frequency wave absorbing composite material is prepared by the following process:

[0113] Preparation of magnetic absorbing fiber:

[0114] (1) A core-shell spherical FeCo magnetic wave absorbing filler was prepared according to the preparation method of Example 2;

[0115] (2) adding 800 parts by weight of 3-aminopropyltriethoxysilane and 800 parts by weight of diethylene glycol into a four-necked flask equipped with a thermometer, an overhead stirrer, an air inlet and a room temperature distillation device and mixing them uniformly at a speed of 200 rpm to obtain a reaction mixture, heating the reaction mixture to 110° C. under a nitrogen atmosphere and keeping the temperature to carry out an ester exchange polycondensation reaction until a distillate evaporates, continuing to heat the reaction mixture to 160° C. and keeping the temperature until the temperature of the distillate drops to 55° C., collecting the distillate to obtain a hyperbranched polysiloxane modifier;

[0116] (3) In parts by weight, 500 parts by weight of core-shell spherical FeCo magnetic absorbing filler, 200 parts by weight of poly(p-phenylene terephthalamide) fiber (PPTA fiber) and 5 parts by weight of hyperbranched polysiloxane modifier were added to 5000 parts by weight of water and mixed evenly to obtain a mixture, the mixture was stirred at 80°C for 3 h for chemical crosslinking to obtain a product, and the product was dialyzed and purified in water (cutoff molecular weight of 1000) to obtain PPTA@FeCo magnetic absorbing fiber.

[0117] Preparation of aramid nanofiber low frequency absorbing composite materials:

[0118] (1) By weight, 10 parts by weight of PPTA fiber and 20 parts by weight of potassium hydroxide are added to 500 parts by weight of dimethyl sulfoxide to obtain a mixture; the mixture is stirred at 35° C. for 7 days for deprotonation reaction and exfoliation to obtain a reddish brown aramid nanofiber (ANFs) dispersion; the ANFs dispersion is poured into 4000 parts by weight of water, mechanically stirred, filtered and washed with deionized water until neutral, and then poured into 2500 parts by weight of water for protonation, and dispersed evenly with a homogenizer to obtain aramid nanofibers (ANFs);

[0119] (2) According to weight, 800 parts by weight of PPTA@FeCo magnetic absorbing fibers and 300 parts by weight of aramid nanofibers (ANFs) were mixed evenly, and then subjected to vacuum filtration and pressure treatment at a pressure of 0.5 Pa for 1 h. Subsequently, they were hot-pressed at a pressure of 1.5 MPa and a temperature of 200°C for 0.1 h to obtain an aramid nanofiber low-frequency absorbing composite material.

[0120] Example 4

[0121] The preparation of the aramid nanofiber low-frequency wave absorbing composite material provided in this embodiment is basically the same as that in embodiment 3, except that:

[0122] Preparation of magnetic absorbing fiber:

[0123] (3) 5 parts by weight of the hyperbranched polysiloxane modifier was replaced with 15 parts by weight of the hyperbranched polysiloxane modifier.

[0124] Preparation of aramid nanofiber low frequency absorbing composite materials:

[0125] (2) The PPTA@FeCo magnetic absorbing fiber in this embodiment is used to prepare an aramid nanofiber low-frequency absorbing composite material.

[0126] Example 5

[0127] The preparation of the aramid nanofiber low-frequency wave absorbing composite material provided in this embodiment is basically the same as that in embodiment 3, except that:

[0128] Preparation of aramid nanofiber low frequency absorbing composite materials:

[0129] (2) 800 parts by weight of PPTA@FeCo magnetic absorbing fiber was replaced with 700 parts by weight of PPTA@FeCo magnetic absorbing fiber.

[0130] Comparative Example 1

[0131] The preparation of the aramid nanofiber composite material provided in this comparative example is basically the same as that in Example 3, except that:

[0132] Preparation of magnetic absorbing fiber:

[0133] (3) 500 parts by weight of the core-shell spherical FeCo magnetic absorbing filler was replaced with 1500 parts by weight of the core-shell spherical FeCo magnetic absorbing filler.

[0134] Preparation of aramid nanofiber composites:

[0135] (2) Aramid nanofiber composite materials were prepared using the PPTA@FeCo magnetic absorbing fibers in this comparative example.

[0136] Comparative Example 2

[0137] The preparation of the aramid nanofiber composite material provided in this comparative example is basically the same as that in Example 3, except that:

[0138] Preparation of aramid nanofiber composites:

[0139] (2) 800 parts by weight of PPTA@FeCo magnetic absorbing fiber was replaced with 2000 parts by weight of PPTA@FeCo magnetic absorbing fiber.

[0140] Comparative Example 3

[0141] In this comparative example, an aramid nanofiber composite material was prepared by the following process:

[0142] (1) By weight, 10 parts by weight of PPTA fiber and 20 parts by weight of potassium hydroxide are added to 500 parts by weight of dimethyl sulfoxide to obtain a mixture; the mixture is stirred at 35° C. for 7 days for deprotonation reaction and exfoliation to obtain a reddish brown aramid nanofiber (ANFs) dispersion; the ANFs dispersion is poured into 4000 parts by weight of water, mechanically stirred, filtered and washed with deionized water until neutral, and then poured into 2500 parts by weight of water for protonation, and dispersed evenly with a homogenizer to obtain aramid nanofibers (ANFs);

[0143] (2) 1100 parts by weight of aramid nanofibers (ANFs) were subjected to vacuum filtration and pressure-maintaining treatment at a pressure of 0.5 Pa for 1 h, and then subjected to hot pressing treatment at a pressure of 1.5 MPa and a temperature of 200°C for 0.1 h to obtain an aramid nanofiber composite material.

[0144] Performance Testing

[0145] 1. Scanning electron microscope (SEM) test

[0146] Figure 5 is a SEM image of poly(p-phenylene terephthalamide) fiber (PPTA fiber) in Example 3 of the present invention; Figure 6 This is a SEM image of the PPTA@FeCo magnetic absorbing fiber in Example 3 of the present invention; Figure 7 This is a SEM image of the PPTA@FeCo magnetic absorbing fiber in Example 4 of the present invention; Figure 8 This is the SEM image of the PPTA@FeCo magnetic absorbing fiber in Comparative Example 1 of the present invention.

[0147] Depend on Figure 5 and Figure 6 It can be seen that in the PPTA@FeCo magnetic absorbing fiber of Example 3 of the present invention, the core-shell spherical FeCo magnetic absorbing filler is uniformly coated on the surface of the PPTA fiber, and the PPTA fiber and the core-shell spherical FeCo magnetic absorbing filler are not damaged during the coating process.

[0148] Depend on Figure 5 and Figure 7 It can be seen that in the PPTA@FeCo magnetic absorbing fiber of Example 4 of the present invention, the core-shell spherical FeCo magnetic absorbing filler is uniformly coated on the surface of the PPTA fiber, and the PPTA fiber and the core-shell spherical FeCo magnetic absorbing filler are not damaged during the coating process.

[0149] Depend on Figure 5 and Figure 8 It can be seen that in the PPTA@FeCo magnetic absorbing fiber of Comparative Example 1 of the present invention, the core-shell spherical FeCo magnetic absorbing filler is agglomerated and coated on the surface of the PPTA fiber.

[0150] 2. Mechanical properties and microwave absorption performance test

[0151] (1) The tensile strength of the aramid nanofiber low-frequency wave absorbing composite materials in Examples 3-5 and the aramid nanofiber composite materials in Comparative Examples 1-3 were tested using a universal testing machine. The test results are shown in Table 1.

[0152] Table 1 Test results

[0153]

[0154] It can be seen from Table 1 that the aramid nanofiber low-frequency wave-absorbing composite materials provided in Examples 3-5 of the present invention have excellent mechanical properties (tensile strength can reach up to 134 MPa).

[0155] (2) The electromagnetic parameters of the aramid nanofiber low-frequency absorbing composite materials in Examples 3 to 5 and the aramid nanofiber composite materials in Comparative Examples 1 to 3 were tested respectively by ASTM D7449M-2014 / coaxial method, and the minimum reflection loss and low-frequency effective absorption bandwidth of the aramid nanofiber low-frequency absorbing composite materials in each example and the aramid fiber composite materials in each comparative example were obtained by calculation.

[0156] Fig. 9 This is a test result diagram of the wave absorbing performance of the aramid nanofiber low-frequency wave absorbing composite material in Example 3 of the present invention; Fig.10 This is a test result diagram of the wave absorbing performance of the aramid nanofiber low-frequency wave absorbing composite material in Example 4 of the present invention; Fig.11 This is a test result diagram of the wave absorbing performance of the aramid nanofiber low-frequency wave absorbing composite material in Example 5 of the present invention; Fig.12 This is a test result diagram of the wave absorption performance of the aramid nanofiber composite material in Comparative Example 1 of the present invention; Fig.13 This is a test result diagram of the wave absorption performance of the aramid nanofiber composite material in Comparative Example 2 of the present invention; Fig.14 This is a graph showing the test results of the wave absorption performance of the aramid nanofiber composite material in Comparative Example 3 of the present invention.

[0157] Depend on Fig. 9 It can be seen that when the thickness of the aramid nanofiber low-frequency absorbing composite material in Example 3 of the present invention is 2.5 mm, the minimum reflection loss (RLmin) is -46.8 dB and the low-frequency effective absorption bandwidth (EAB) is 2.24 GHz (5.52 GHz to 7.76 GHz).

[0158] Depend on Fig.10 It can be seen that when the thickness of the aramid nanofiber low-frequency absorbing composite material in Example 4 of the present invention is 3.2 mm, the minimum reflection loss (RLmin) is -34.5 dB and the low-frequency effective absorption bandwidth (EAB) is 0.8 GHz (2.24 GHz to 3.04 GHz).

[0159] Depend on Fig.11 It can be seen that when the thickness of the aramid nanofiber low-frequency absorbing composite material in Example 5 of the present invention is 2.7 mm, the minimum reflection loss (RLmin) is -39.7 dB and the low-frequency effective absorption bandwidth (EAB) is 1.52 GHz (4.32 GHz to 5.84 GHz).

[0160] Depend on Fig.12 It can be seen that when the thickness of the aramid nanofiber composite material in Comparative Example 1 of the present invention is 3.4 mm, the minimum reflection loss (RLmin) is -39.0 dB and the low-frequency effective absorption bandwidth (EAB) is 0.64 GHz (2.48 GHz to 3.12 GHz).

[0161] Depend on Fig.13 It can be seen that when the thickness of the aramid nanofiber composite material in Comparative Example 2 of the present invention is 1.7 mm, the minimum reflection loss (RLmin) is -8.0 dB and the low-frequency effective absorption bandwidth (EAB) is 0 GHz.

[0162] Depend on Fig.14 It can be seen that when the thickness of the aramid nanofiber composite material in Comparative Example 3 of the present invention is 5.0 mm, the minimum reflection loss (RLmin) is -1.3 dB and the low-frequency effective absorption bandwidth (EAB) is 0 GHz.

[0163] From Table 1 and Figure 9-14 It can be seen that, by comparing Example 3 with Comparative Example 1, it is found that when the weight ratio of the core-shell spherical FeCo magnetic absorbing filler, the PPTA fiber and the hyperbranched polysiloxane modifier in the PPTA@FeCo magnetic absorbing fiber is 500:200:5, the prepared aramid nanofiber low-frequency absorbing composite material has excellent mechanical properties and absorbing properties; by comparing Example 3 with Comparative Example 2, it is found that when the weight ratio of the PPTA@FeCo magnetic absorbing fiber and the aramid nanofiber in the aramid nanofiber low-frequency absorbing composite material is 800:300, the prepared aramid nanofiber low-frequency absorbing composite material has excellent mechanical properties and also has excellent absorbing properties; by comparing Example 3 with Comparative Example 3, it is found that although Although the aramid nanofiber composite material in comparative example 3 has excellent mechanical properties (tensile strength of 140 MPa), its wave absorption performance is extremely poor (when its thickness is 5.0 mm, the minimum reflection loss (RLmin) is only -1.3 dB, and the low-frequency effective absorption bandwidth (EAB) is 0 GHz), the aramid nanofiber low-frequency wave absorbing composite material in Example 3 of the present invention has excellent mechanical properties (tensile strength can reach 133 MPa) and excellent wave absorption performance (when its thickness is 2.5 mm, the minimum reflection loss (RLmin) can reach -46.8 dB, and the low-frequency effective absorption bandwidth (EAB) is 2.24 GHz (5.52 GHz~7.76 GHz)).

[0164] In summary, the aramid nanofiber low-frequency absorbing composite material prepared in the embodiment of the present invention has excellent mechanical properties and absorbing properties in the low-frequency microwave region (S band: 2GHz~4GHz and C band: 4GHz~8GHz), and can be widely used in the fields of communications and electronic equipment.

[0165] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An aramid nanofiber low-frequency wave absorbing composite material, characterized in that: The raw materials for preparing the aramid nanofiber low-frequency wave absorbing composite material include magnetic wave absorbing fibers and aromatic polyamide nanofibers; the magnetic wave absorbing fibers are prepared from a raw material system including FeCo magnetic wave absorbing fillers, aromatic polyamide fibers and hyperbranched polysiloxane modifiers; The FeCo magnetic wave absorbing filler is in the shape of a core-shell sphere; The preparation method of the FeCo magnetic wave absorbing filler comprises: mixing cobalt salt, iron salt, reducing agent and organic solvent and performing reduction reaction to obtain the FeCo magnetic wave absorbing filler; The iron salt is at least one of ferrous nitrate, ferrous chloride, and ferrous sulfate, and the reducing agent is at least one of hydrazine hydrate and sodium borohydride; In the aramid nanofiber low-frequency wave-absorbing composite material, the weight ratio of the magnetic wave-absorbing fiber to the aromatic polyamide nanofiber is (600-1500):(50-300).

2. The aramid nanofiber low-frequency wave absorbing composite material according to claim 1, characterized in that: In the magnetic wave-absorbing fiber, the weight ratio of the FeCo magnetic wave-absorbing filler, the aromatic polyamide fiber and the hyperbranched polysiloxane modifier is (200-1000): (50-300): (2-30).

3. A method for preparing the aramid nanofiber low-frequency wave absorbing composite material according to any one of claims 1 to 2, characterized in that: include: Preparation of magnetic absorbing fiber: The cobalt salt, the iron salt, the reducing agent and the organic solvent are mixed and then subjected to a reduction reaction to obtain the FeCo magnetic wave absorbing filler; Mixing 3-aminopropyltriethoxysilane and diethylene glycol and performing an ester exchange polycondensation reaction to obtain the hyperbranched polysiloxane modifier; The FeCo magnetic wave absorbing filler, the aromatic polyamide fiber and the hyperbranched polysiloxane modifier are mixed and then chemically cross-linked to prepare a magnetic wave absorbing fiber; Preparation of aramid nanofiber low frequency absorbing composite materials: Preparation of aromatic polyamide nanofibers; The magnetic wave-absorbing fiber and the aromatic polyamide nanofiber are mixed, and then subjected to suction filtration, pressure-maintaining treatment and hot pressing treatment to obtain the aramid nanofiber low-frequency wave-absorbing composite material.

4. The method for preparing the aramid nanofiber low-frequency wave absorbing composite material according to claim 3, characterized in that: In the FeCo magnetic wave absorbing filler, the weight ratio of the cobalt salt, the iron salt, the reducing agent and the organic solvent is (50-100): (10-50): (120-600): (1000-6000); And / or, in the hyperbranched polysiloxane modifier, the weight ratio of the 3-aminopropyltriethoxysilane to the diethylene glycol is (500-1000): (500-1000).

5. The method for preparing the aramid nanofiber low-frequency wave absorbing composite material according to claim 3, characterized in that: The reduction reaction temperature is 140°C to 240°C and the time is 1h to 24h; And / or, the temperature of the transesterification polycondensation reaction is 100°C to 160°C.

6. The method for preparing the aramid nanofiber low-frequency wave absorbing composite material according to claim 3, characterized in that: The temperature of the chemical cross-linking is 80° C. to 140° C., and the time is 1 h to 6 h.

7. The method for preparing the aramid nanofiber low-frequency wave absorbing composite material according to claim 3, characterized in that: The pressure of the suction filtration and pressure-maintaining treatment is 0.1Pa to 1.0Pa, and the time is 0.5h to 3.0h; And / or, the pressure of the hot pressing treatment is 0 MPa to 2.0 MPa, the temperature is 150 to 250° C., and the time is 0.1 h to 1.0 h.

8. The method for preparing the aramid nanofiber low-frequency wave absorbing composite material according to claim 3, characterized in that: The cobalt salt is at least one of cobalt nitrate, cobalt chloride and cobalt acetate; the iron salt is at least one of ferrous nitrate, ferrous chloride and ferrous sulfate; the reducing agent is at least one of hydrazine hydrate and sodium borohydride; and the organic solvent includes ethylene glycol.

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