Flexible nanofiber membrane with electromagnetic wave protection function as well as preparation method and application of flexible nanofiber membrane

Abstract

The invention belongs to the field of functional materials, and relates to a flexible nanofiber membrane with an electromagnetic wave protection function as well as a preparation method and application thereof. The preparation method provided by the invention comprises the following steps: S1, taking a polyacrylonitrile solution as a core layer spinning solution, taking a polyacrylonitrile solution containing acetylacetone metal salt and polymethyl methacrylate as a skin layer spinning solution, and carrying out electrostatic spinning by using coaxial spinning equipment to prepare a fiber membrane; performing pre-oxidation treatment on the fiber membrane under the control of first preset tension to obtain a pre-oxidized fiber membrane with micropores; and carrying out carbonization treatment on the pre-oxidized fiber membrane under the control of second preset tension to obtain the flexible nanofiber membrane with the electromagnetic wave protection function. The flexible nanofiber membrane is excellent in electromagnetic wave absorption performance and mechanical performance and can be widely applied to preparation of electromagnetic wave shielding materials and wave absorbing materials.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of functional materials, and relates to a flexible nanofiber membrane with electromagnetic wave protection function, a preparation method and application thereof. BACKGROUND

[0002] With the development of electronic information industry, electromagnetic wave absorbing and shielding materials are widely used in the fields of anti-electromagnetic interference, electromagnetic wave pollution control, etc., and fibrous flexible electromagnetic wave absorbing materials show broad application prospects due to their light weight, strong processability and easy molding.

[0003] Among many research systems, carbon-based fibrous wave-absorbing materials have become a research hotspot due to their excellent electromagnetic properties, but the existing technology has always failed to break through a key technical bottleneck, i.e., the brittleness problem caused by insufficient mechanical strength of the material. For example, patents CN102762784A, CN103422192A, CN116641160B and CN118704120A all study the addition of metal salt in polyacrylonitrile (PAN) spinning solution, and then spinning, pre-oxidation, carbonization and other processes to prepare fibrous wave-absorbing materials with electromagnetic wave absorption function. However, the fibrous materials prepared in these patents are brittle and cannot be directly used as wave-absorbing materials, but can only be used after being crushed and compounded with other materials, which leads to problems such as easy performance degradation, easy damage during processing, and short service life, seriously restricting the industrial application of the materials in high-end fields such as flexible electronic devices and wearable protective equipment.

[0004] Therefore, it is necessary to innovate in the preparation process and fiber structure, and to develop a flexible nanofiber membrane with excellent mechanical properties and certain strength for electromagnetic wave absorption. SUMMARY

[0005] In view of the defects of poor mechanical properties and narrow absorption frequency band of existing carbon-based flexible wave-absorbing fiber materials, the present application provides a flexible nanofiber membrane with electromagnetic wave protection function, a preparation method and application thereof, which has excellent electromagnetic wave absorption performance and mechanical properties.

[0006] In a first aspect, the present application provides a preparation method of a flexible nanofiber membrane with electromagnetic wave protection function, which comprises:

[0007] S1. Using polyacrylonitrile (PAN) solution as core layer spinning solution, polyacrylonitrile solution containing acetylacetone metal salt and polymethyl methacrylate as skin layer spinning solution, and using coaxial spinning equipment for electrospinning to prepare a fibrous membrane; the fibers in the fibrous membrane are of skin-core structure.

[0008] S2. Pre-oxidizing the fiber membrane under control of a first preset tension to obtain a pre-oxidized fiber membrane with micropores;

[0009] S3. Carbonizing the pre-oxidized fiber membrane under control of a second preset tension to obtain the flexible nanofiber membrane with electromagnetic wave protection function.

[0010] In some embodiments, the method for preparing the sheath layer spinning solution is as follows: adding acetylacetone metal salt into polyacrylonitrile (PAN) solution, then adding PMMA, and stirring at a temperature of 35-45℃ for 2-4 hours to prepare the sheath layer spinning solution.

[0011] In some embodiments, the solvent of the polyacrylonitrile (PAN) solution is N,N-dimethylformamide (DMF).

[0012] In some embodiments, in the polyacrylonitrile solution containing acetylacetone metal salt and polymethyl methacrylate, the concentration of polyacrylonitrile is 8wt%-10wt%, the concentration of polymethyl methacrylate is 2wt%-5wt%, and the concentration of acetylacetone metal salt is 1wt%-2wt%.

[0013] In some embodiments, the acetylacetone metal salt is one or more of acetylacetone iron, acetylacetone nickel and acetylacetone cobalt.

[0014] When the acetylacetone metal salt is a mixture of two or three of acetylacetone iron, acetylacetone nickel and acetylacetone cobalt, the amount of substance of each component in the mixture is the same.

[0015] In some embodiments, the electrospinning condition is that the voltage is 15-25V, the core layer spinning speed is 1-3ml / h, and the sheath layer spinning speed is 0.5-2ml / h.

[0016] In some embodiments, the first preset tension is 10-30N / 10cm, the second preset tension is 5-20N / 10cm, and the second preset tension is less than the first preset tension.

[0017] In some embodiments, the pre-oxidation treatment adopts a stepwise heating mode.

[0018] In some embodiments, the pre-oxidation treatment is specifically as follows: pre-oxidizing at 150℃ for 30min, pre-oxidizing at 200℃ for 30min, and pre-oxidizing at 300℃ for 180min in an air environment.

[0019] In some embodiments, the carbonization treatment is specifically as follows: carbonizing at 600-900℃ for 1-2 hours in an N2 environment.

[0020] In a second aspect of the present application, the flexible nanofiber membrane with electromagnetic wave protection function prepared by the preparation method is provided.

[0021] In a third aspect of the present application, the flexible nanofiber membrane with electromagnetic wave protection function is applied to electromagnetic wave shielding materials or wave absorbing materials.

[0022] Compared with the prior art, the fiber in the flexible nanofiber membrane provided by the present application is in a skin-core structure, the core layer of the fiber is a pure PAN-based carbon fiber, and the skin layer is a porous fiber flexible nanofiber membrane containing metal or metal oxide. In the fiber membrane, the PAN-based carbon fiber can provide certain strength support, and has excellent electrical conductivity. The fiber containing metal or metal oxide is designed as a porous fiber. The porous design improves the wave absorbing performance, and because the electrical conductivity of the fiber is lower than that of the solid carbon fiber in the core layer, the difference in electrical conductivity of the fiber skin and core layers can increase the impedance matching, which is beneficial to the entry of electromagnetic waves into the inside of the fiber, thereby effectively enhancing the electromagnetic wave loss. BRIEF DESCRIPTION OF DRAWINGS

[0023] These and / or other aspects and advantages of the present application will become apparent and readily understood from the following description, by way of example only, of preferred embodiments with reference to the accompanying drawings in which:

[0024] Figure 1 A schematic diagram for giving the fixed tension to the fiber membrane to be treated by using a tension clip;

[0025] Figure 2 A schematic diagram of the nanofiber structure in the flexible nanofiber membrane provided by the present application;

[0026] Figure 3 A flexibility test photo of the flexible nanofiber membrane prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0027] The technical solutions of the present application will be further specifically described below by way of examples and in conjunction with the accompanying drawings. In the description, the same or similar reference numerals indicate the same or similar components. The following description of the embodiments of the present application with reference to the accompanying drawings is intended to explain the general inventive concept of the present application, and should not be understood as a limitation of the present application.

[0028] In an embodiment of the first aspect of the present application, a preparation method of a flexible nanofiber membrane with electromagnetic wave protection function is provided, and the preparation method comprises:

[0029] S1. Using polyacrylonitrile (PAN) solution as a core layer spinning solution, using polyacrylonitrile solution containing acetylacetone metal salt and polymethyl methacrylate (PMMA) as a skin layer spinning solution, and using coaxial spinning equipment to perform electrospinning, a fiber membrane is prepared. The fiber in the fiber membrane is in a skin-core structure.

[0030] S2. Pre-oxidizing the fiber membrane under control of a first preset tension to obtain a pre-oxidized fiber membrane with micropores.

[0031] S3. Carbonizing the pre-oxidized fiber membrane under control of a second preset tension to obtain the flexible nanofiber membrane with electromagnetic wave protection function.

[0032] The fiber in the flexible nanofiber membrane prepared by the preparation method provided in the embodiments of the present application is in a skin-core structure, and a structural schematic diagram is shown in Figure 2 The left drawing is a three-dimensional structural schematic diagram of the fiber, and the right drawing is a cross-sectional schematic diagram of the fiber. As can be seen from Figure 2 The core layer of the fiber is a pure PAN-based carbon fiber, and the skin layer is a fiber (porous fiber) containing magnetic particles (metal or metal oxide) and having micropores. In the fiber membrane, the PAN-based carbon fiber in the core layer can provide certain strength support and has excellent electrical conductivity. The fiber containing metal or metal oxide in the skin layer is designed as a porous fiber. The porous design improves the wave absorption performance, and because the electrical conductivity of the fiber is lower than that of the solid carbon fiber in the core layer, the difference in electrical conductivity between the fiber skin and core layers can increase impedance matching, which is beneficial to the entry of electromagnetic waves into the inside of the fiber and thus effectively enhances electromagnetic wave loss. Based on this design, the strength and electromagnetic wave absorption performance of the flexible nanofiber membrane obtained by the present application are both improved.

[0033] In the preparation method provided by the present application, although both PMMA and metal organic salt can increase the electromagnetic wave absorption effect of the material, they will weaken the mechanical properties of the fiber membrane. The micropores and the pre-tension in the pre-oxidation and carbonization processes can control the shrinkage rate and crystallization reconstruction order of the nanofiber membrane and increase the mechanical properties of the fiber.

[0034] In some embodiments, the preparation method of the skin layer spinning solution is as follows: acetylacetone metal salt is added to a polyacrylonitrile (PAN) solution, then PMMA is added, and stirring is performed at a temperature of 35-45°C for 2-4 hours to prepare the skin layer spinning solution.

[0035] In some embodiments, the solvent of the polyacrylonitrile (PAN) solution is N,N-dimethylformamide (DMF).

[0036] The mass fraction of PAN in the polyacrylonitrile (PAN) solution is too large to be easily spun. When the concentration is too low, it is not easy to form a film. Therefore, in some embodiments, the concentration of the polyacrylonitrile (PAN) solution is preferably 8wt%-10wt%.

[0037] In some embodiments, the polyacrylonitrile solution containing the acetylacetone metal salt and the polymethyl methacrylate has a polyacrylonitrile concentration of 8wt%-10wt%, a polymethyl methacrylate concentration of 2wt%-5wt%, and an acetylacetone metal salt concentration of 1wt%-2wt%. If the acetylacetone metal salt is too large, the solution cannot be spun.

[0038] In some embodiments, the acetylacetone metal salt is one or more of acetylacetone iron, acetylacetone nickel, and acetylacetone cobalt. Preferably, a mixture of acetylacetone iron, acetylacetone nickel, and acetylacetone cobalt is used, which is conducive to the absorption of electromagnetic waves by the hybrid metal fiber skin layer. When the molar mass ratio of acetylacetone iron, acetylacetone nickel, and acetylacetone cobalt is 1:1:1, the electromagnetic wave absorption effect of the prepared sample is the best.

[0039] In some embodiments, the electrospinning conditions are as follows: the voltage is 15-25V, the core layer spinning speed is 1-3ml / h, and the skin layer spinning speed is 0.5-2ml / h.

[0040] In some embodiments, the first preset tension is 10-30N / 10cm, and the second preset tension is 5-20N / 10cm, and the second preset tension is less than the first preset tension. Too large tension will cause the nanofiber membrane to break during the pre-oxidation or carbonization process, and too small tension will cause the nanofiber membrane to shrink severely.

[0041] In some embodiments, the fixed tension can be applied by clamping the fiber with a tension clamp as shown in Figure 1 The tension clamp can move with the shrinkage of the fiber membrane.

[0042] In some embodiments, the pre-oxidation treatment is performed in a stepwise heating manner.

[0043] In some embodiments, the pre-oxidation treatment is performed in an air environment at 150℃ for 30min, at 200℃ for 30min, and at 300℃ for 180min.

[0044] By taking advantage of the characteristics of the core layer PMMA that it will thermally crack and volatilize at high temperatures, and by using gradient pre-oxidation temperature and pre-tension auxiliary processes, the shrinkage rate and crystallization reconstruction order of the nanofiber membrane can be controlled, which can effectively form micropores, on the one hand facilitating the removal of tar during the PAN carbonization process, and on the other hand being conducive to enhancing the ability of the fiber membrane to absorb electromagnetic waves.

[0045] In some embodiments, the carbonization treatment is specifically: carbonization in N2 environment at 750-850℃ for 1-2 hours. Corresponding to the fiber membrane formed by the core-sheath structure fiber provided in the present application, the carbonization temperature can prepare a nanofiber membrane with optimal electromagnetic wave absorption function and flexibility. The pre-tension can make the fibers further orderly arrange in the crystallization process during carbonization, and better increase the strength of the fibers.

[0046] In a second aspect of the present application, a flexible nanofiber membrane with electromagnetic wave protection function prepared by the preparation method is provided.

[0047] In a third aspect of the present application, the application of the flexible nanofiber membrane with electromagnetic wave protection function in electromagnetic wave shielding materials or wave absorbing materials is provided.

[0048] Example 1

[0049] (1) Prepare a PAN (DMF solvent) solution with a concentration of 8% as the core layer;

[0050] (2) Add 2% mass fraction of iron acetylacetonate, nickel acetylacetonate and cobalt acetylacetonate (molar mass ratio of 1:1:1) in sequence to the PAN solution with a concentration of 8%, uniformly stir at 40℃ for 20 min, then add 2% mass fraction of PMMA, and stir at 40℃ for 2 hours, to prepare a solution as the sheath layer;

[0051] (3) Use a coaxial spinning device to perform electrospinning, the voltage is 20V, the spinning speed of the core layer is 1ml / h, and the spinning speed of the sheath layer is 0.5ml / h, to prepare a fiber membrane with a thickness of 0.5mm; the core layer is a pure PAN-based carbon fiber, which can provide certain strength support, and the sheath layer is a magnetic particle hybrid porous fiber, which has lower conductivity than the solid carbon fiber of the core layer, and can effectively enhance electromagnetic wave loss.

[0052] (4) Pre-oxidize the fiber membrane at 150℃ for 30min, at 200℃ for 30min, and at 300℃ for 180min, and introduce air during the pre-oxidation process, and give the fiber membrane a fixed tension of 10 N / 10cm on four sides, the tension is a constant value, and the tension clamp (as shown in Figure 1 The developed gradient pre-oxidation temperature and pre-tension auxiliary process can control the shrinkage rate and crystallization reconstruction ordering of the nanofiber membrane, which can effectively form micropores, facilitate the removal of tar during the carbonization process of PAN, and improve the fiber strength.

[0053] (5) The pre-oxidized fiber membrane was carbonized in a N2 environment at 800℃ for 1 hour. During the carbonization process, a tension of 5 N / 10 cm was applied to all four sides to prepare a flexible nanofiber membrane with electromagnetic wave absorption function. The pre-tension can further arrange the fibers in an orderly manner during the carbonization process, which can better increase the strength of the fibers.

[0054] The prepared flexible nanofiber membrane was tested and found to have a specific surface area of ​​876.67 m². 2 / g. The bandwidth with electromagnetic wave loss <-10dB reached 4.65GHz, and the electromagnetic wave loss reached -35.23dB at 12.04GHz; the breaking strength was 10N / 5cm. The flexibility test (bending the flexible nanofiber membrane) of the flexible nanofiber membrane prepared in Example 1 is shown in the following image. Figure 3 As shown.

[0055] Example 2

[0056] (1) Prepare an 8% concentration PAN (DMF solvent) solution as the core layer;

[0057] (2) Add 2% by mass of iron acetylacetone, nickel acetylacetone, and cobalt acetylacetone (molar mass ratio of 1:1:1) to an 8% PAN solution, and then add 2% by mass of PMMA. Stir at 40°C for 2 hours to prepare solution A2 as the skin layer.

[0058] (3) Electrospinning was carried out using a coaxial spinning device with a voltage of 20V and a spinning speed of 1 ml / h for the core layer and 0.5 ml / h for the sheath layer to prepare a fiber membrane with a thickness of 0.5 mm. The core layer is pure PAN-based carbon fiber, which can provide a certain strong support. In addition, the sheath layer is a magnetic particle hybrid porous fiber with a lower conductivity than the solid carbon fiber in the core layer, which can effectively enhance electromagnetic wave loss.

[0059] (4) Pre-oxidize the fiber membrane at 150℃ for 30 min, at 200℃ for 30 min, and at 300℃ for 180 min. During the pre-oxidation process, air is introduced, and a fixed tension of 20 N / 10 cm is applied to the four sides of the fiber membrane. The tension is constant. Tension clamps (such as...) Figure 1 (As shown) can move as the fiber membrane shrinks; a gradient pre-oxidation temperature and pre-tension assisted process were developed to control the shrinkage rate and crystal reconstruction sorting of the nanofiber membrane, which can effectively form micropores, facilitate the removal of tar during PAN carbonization, and improve fiber strength.

[0060] (3) The pre-oxidized fiber membrane is carbonized in N2 environment at 800°C for 1 hour, and a flexible nanofiber membrane with electromagnetic wave absorption function is prepared by giving a tension of 15N / 10cm to the four sides during the carbonization process. The pre-tension can make the fibers further orderly arrange and crystallize during the carbonization process, and better increase the strength of the fibers.

[0061] The specific surface area of the prepared flexible nanofiber membrane reaches 923.32 m 2 / g. The frequency width of electromagnetic wave loss <-10dB reaches 5.21GHz, and the electromagnetic wave loss reaches -49.25dB at 13.27GHz; the breaking strength is 18.5N / 2cm.

[0062] Example 3

[0063] (1) The PAN (DMF solvent) solution with a concentration of 8wt% is used as the spinning solution to perform electrostatic spinning by using a spinning device, the voltage is 20V, the spinning speed of the core layer is 1ml / h, and the spinning speed of the skin layer is 0.5ml / h, and a fiber membrane with a thickness of 0.5mm is prepared.

[0064] (2) The fiber membrane is pre-oxidized at 150°C for 30min, at 200°C for 30min, and at 300°C for 180min, air is introduced during the pre-oxidation process, and a fixed tension of 20N / 10cm is given to the fiber membrane on the four sides, the tension is a constant value, and the tension clamp (as shown in Figure 1 ) can move with the shrinkage of the fiber membrane; a gradient pre-oxidation temperature and pre-tension auxiliary process is developed, which can control the shrinkage rate, crystallization reconstruction ordering of the nanofiber membrane, so as to effectively form micropores, facilitate the removal of tar during the carbonization process of PAN, and improve the fiber strength.

[0065] (3) The pre-oxidized fiber membrane is carbonized in N2 environment at 800°C for 1 hour, and a flexible nanofiber membrane with electromagnetic wave absorption function is prepared by giving a tension of 15N / 10cm to the four sides during the carbonization process. The pre-tension can make the fibers further orderly arrange and crystallize during the carbonization process, and better increase the strength of the fibers.

[0066] The specific surface area of the prepared flexible nanofiber membrane reaches 923.32 m 2 / g. The frequency width of electromagnetic wave loss <-10dB reaches 5.21GHz, and the electromagnetic wave loss reaches -49.25dB at 13.27GHz; the breaking strength is 18.5N / 2cm.

[0067] Example 4

[0068] (1) In the 8wt% concentration of PAN solution, then add the mass fraction of 2% acetylacetone iron, acetylacetone nickel, acetylacetone cobalt (molar mass ratio of 1:1:1) in turn, and finally add 2% mass fraction of PMMA, stirring at 40℃ for 2 hours, to prepare solution A2;

[0069] (2) Using the spinning equipment to perform electrospinning, the voltage is 20V, the spinning speed is 0.5 ml / h, to prepare the fiber membrane, the thickness is 0.5mm.

[0070] (3) The fiber membrane is pre-oxidized at 150℃ for 30min, at 200℃ for 30min, and at 300℃ for 180min, air is introduced during the pre-oxidation process, and the fiber membrane is given a fixed tension of 20N / 10cm on four sides, the tension is a constant value, and the tension clamp (as shown in Figure 1 ) can move with the shrinkage of the fiber membrane; the gradient pre-oxidation temperature and pre-tension auxiliary process is developed, which can control the shrinkage rate and crystallization reconstruction ordering of the nanofiber membrane, so that micropores can be effectively formed, the tar removal during the carbonization of PAN is facilitated, and the fiber strength is improved.

[0071] (4) The pre-oxidized fiber membrane is carbonized at 800℃ in N2 environment for 1 hour, and a tension of 15N / 10cm is given on four sides during the carbonization process, to prepare a flexible nanofiber membrane with electromagnetic wave absorption function. The pre-tension can make the fiber further orderly arrange the crystallization during the carbonization process, and better increase the strength of the fiber.

[0072] The prepared flexible nanofiber membrane is tested, and the specific surface area reaches 1074.36 m 2 / g. The frequency width of electromagnetic wave loss <-10dB reaches 5.97GHz, and the electromagnetic wave loss at 10.14GHz reaches -57.26dB; the average breaking strength is only 3.2N / 5cm, and the fiber membrane is brittle.

[0073] Although some embodiments of the general inventive concept have been shown and described, those of ordinary skill in the art will understand that changes can be made in these embodiments without departing from the principles and spirit of the general inventive concept, and the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A method for preparing a flexible nanofiber membrane having an electromagnetic wave shielding function, characterized by, The preparation method comprises: S1. Using a polyacrylonitrile solution as a core layer spinning solution, using a polyacrylonitrile solution containing an acetylacetone metal salt and polymethyl methacrylate as a skin layer spinning solution, and using a coaxial spinning device to perform electrospinning to obtain a fiber membrane; S2. Pre-oxidizing the fiber membrane under control of a first preset tension to obtain a pre-oxidized fiber membrane with micropores; S3. Carbonizing the pre-oxidized fiber membrane under control of a second preset tension to obtain the flexible nanofiber membrane with electromagnetic wave shielding function.

2. The production method according to claim 1, characterized by, In the polyacrylonitrile solution containing the acetylacetone metal salt and the polymethyl methacrylate, the concentration of the polyacrylonitrile is 8-10 wt%, the concentration of the polymethyl methacrylate is 2-5 wt%, and the concentration of the acetylacetone metal salt is 1-2 wt%.

3. The production method according to claim 1, characterized by, The acetylacetone metal salt is one or more of acetylacetone iron, acetylacetone nickel and acetylacetone cobalt.

4. The method of claim 1, wherein, The electrospinning condition is that the voltage is 15-25 V, the core layer spinning speed is 1-3 ml / h, and the skin layer spinning speed is 0.5-2 ml / h.

5. The preparation method according to claim 1, characterized in that, The first preset tension is 10-30 N / 10 cm, and the second preset tension is 5-20 N / 10 cm, and the second preset tension is less than the first preset tension.

6. The method of claim 1, wherein, The pre-oxidation treatment adopts a stepwise heating mode.

7. The preparation method according to claim 1, characterized in that, The pre-oxidation treatment specifically comprises pre-oxidizing at 150 DEG C for 30 min, pre-oxidizing at 200 DEG C for 30 min, and pre-oxidizing at 300 DEG C for 180 min in an air environment.

8. The method of claim 1, wherein, The carbonization treatment specifically comprises carbonizing at 600-900 DEG C for 1-2 hours in an N2 environment.

9. A flexible nanofiber membrane with electromagnetic wave shielding function prepared by the preparation method in any one of claims 1-8.

10. Application of the flexible nanofiber membrane with electromagnetic wave shielding function in claim 9 to electromagnetic wave shielding materials or wave absorbing materials.

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