Preparation method of modified aramid fiber electromagnetic shielding flexible composite film

Abstract

The invention relates to functional composite fibers, and discloses a preparation method of a modified aramid fiber electromagnetic shielding flexible composite film, which comprises the following steps: firstly adding aramid fiber short fibers into a potassium hydroxide solution, then adding dimethyl sulfoxide, fully stirring to obtain an aramid nanofiber dispersion, diluting, then carrying out vacuum filtration, and drying to obtain the modified aramid fiber electromagnetic shielding flexible composite film. And repeatedly washing to obtain aramid nanofiber gel, adding the aramid nanofiber gel into an ethanol solution of hyperbranched polyamide-amine, heating and stirring, carrying out vacuum suction filtration to obtain a modified aramid nanofiber film, plating silver on the surface of the modified aramid nanofiber film, and carrying out vacuum suction filtration after the reaction is completed. The hyperbranched polymer in the flexible composite film can be effectively bonded with silver through coordination or chelation due to a three-dimensional molecular structure, a large intermolecular space and an adjustable terminal functional group, and can be combined with the aramid nanofibers through the interaction of hydrogen bonds and static electricity to form a continuous conductive network, so that electromagnetic waves are repeatedly lost, and the electromagnetic wave absorption performance is improved. And a high shielding effect is achieved.

Description

Technical Field

[0001] The present invention relates to the field of electromagnetic shielding materials, and particularly to a preparation method of a modified aramid fiber electromagnetic shielding flexible composite film. Background Art

[0002] Electronic instruments that communicate using X-band (8.2 - 12.4 GHz) electromagnetic waves are now ubiquitous in satellites, airplanes, wireless computer networks, portable devices, etc. Although this technology has brought great convenience to life, interference between electromagnetic waves from different instruments will reduce the safety, stability, reliability, and lifespan of their respective applications. In addition, electromagnetic waves have been considered as a factor leading to health conditions such as cancer, headache, insomnia, immune deficiency, depression, sleep disorders, anxiety, etc., causing great harm to human health. Therefore, further research on materials for shielding X-band electromagnetic interference is urgent. Among them, electromagnetic wave absorption and electromagnetic interference shielding are effective strategies for controlling electromagnetic pollution and radiation. Therefore, in order to solve electromagnetic pollution (or radiation) and meet daily needs, electromagnetic shielding materials need to have the characteristics of light weight, ultrathin, good flexibility, simple manufacturing, EMI shielding performance, and multifunctionality. Traditional metal-based electromagnetic shielding materials have a single shielding mechanism, mainly based on reflection, are prone to corrosion, have a large density, and have many limitations.

[0003] Currently, due to their excellent mechanical properties, gas permeability, chemical stability, high temperature resistance, low cost, etc., conductive polymer composites have become a practical solution for electromagnetic interference shielding. They are usually composed of a non-conductive polymer matrix and a surface conductive layer (such as metal particles and nanowires, carbon nanotubes, reduced graphene oxide, Mxene, and intrinsically conductive polymers). Among them, the non-conductive polymer matrix selects aramid nanofibers, which not only maintain the excellent properties of aramid fibers but also have a large specific surface area and high surface energy due to their nanoscale size and large aspect ratio, enabling better combination with conductive fillers. At the same time, it performs well in terms of dispersibility, film-forming property, etc., and can form a uniform and dense film. However, since conductive polymer composites generally have a relatively high percolation threshold, in order to obtain ideal electromagnetic shielding performance, high filler content and large thickness are required, resulting in a significant decline in their mechanical properties.

[0004] Hyperbranched polymers (HBPs) have been developed as new high-performance materials and have attracted much attention due to their three-dimensional molecular structure, large intermolecular space and adjustable terminal functional groups. In addition, their unique physical and chemical properties, such as low viscosity, good solubility, excellent thermal and chemical stability, and encapsulation effect, have led to various applications. Compared with other dendritic polymers, they can effectively bond to metals through coordination or chelation, and can also be combined with aramid nanofibers through hydrogen bonding and electrostatic interactions. The shortcomings of conductive polymer composites can be solved to a certain extent. Therefore, the present invention provides a method for preparing a composite electromagnetic shielding film to meet the growing needs of emerging fields such as flexible electronic devices. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a method for preparing a modified aramid fiber electromagnetic shielding flexible composite film, comprising the following steps: 1) Preparation of aramid nanofiber gel Aramid fiber staple fibers are first added to a potassium hydroxide solution, followed by dimethyl sulfoxide, and the mixture is stirred thoroughly to obtain an aramid nanofiber dispersion. The dispersion is diluted and then vacuum filtered, and the aramid nanofiber gel is obtained after repeated washing. 2) Modified aramid nanofiber The aramid nanofiber gel obtained in step 1) is added to an ethanol solution of a hyperbranched polyamide-amine, heated and stirred, and vacuum filtered to obtain a modified aramid nanofiber film; 3) Surface silver plating The modified aramid nanofiber film obtained in step 2) is added to the silver ammonia solution, and the reducing solution is added dropwise under heating and ultrasonic treatment. After the reaction is completed, vacuum filtration is performed to obtain a composite film.

[0006] Further, in the method of the present invention, in step 1), potassium hydroxide is difficult to dissolve in dimethyl sulfoxide, and it takes a long time to prepare aramid nanofibers in a potassium hydroxide and dimethyl sulfoxide system, but potassium hydroxide is very soluble in water, so potassium hydroxide is dissolved in ultrapure water to construct an alkaline environment, added to the aramid fiber for pretreatment, and finally dimethyl sulfoxide is added to prepare the aramid nanofiber, wherein the ultrapure water can serve as a proton donor and can dissolve potassium hydroxide, which greatly shortens the preparation cycle. The concentration of the potassium hydroxide solution is 5-10wt%, the weight ratio of potassium hydroxide to aramid fiber is (1-3):1, and the specification fineness of the aramid fiber is 100-3000D and the length is 1-3cm; in step 2), the amount of hyperbranched polyamide-amine used is 5-20% of the weight of the aramid nanofiber in step 1), and the molecular structure of the hyperbranched polyamide-amine is as follows Figure 1 shown.

[0007] In step 3), the preparation method of the silver ammonia solution is as follows: add AgNO3 Ammonia water was added dropwise to the aqueous solution until the solution became clear and transparent. The pH of the solution was adjusted to 11.0 with 5 - 10 g / L KOH solution, and then ammonia water was continuously added dropwise until the solution became clear again. 0.3 - 1 g of PVP was added to obtain a silver ammonia solution. The preparation method of the reducing solution was as follows: absolute ethanol and polyethylene glycol were added to a glucose solution with a concentration of 20 - 40 g / L, and they were fully stirred and dissolved. The concentration of absolute ethanol was 30 - 50 mL / L, and the concentration of polyethylene glycol was 60 - 80 mg / L. Before reducing with glucose, it was necessary to ultrasonicate (252 W, 40 KHz) at 30 °C for 30 min, and then it was dropped into the mixture at a rate of 1 - 3 drops per second. At the same time, it was ultrasonically treated at 10 - 50 °C under the same ultrasonic conditions for 60 min. After dropping the glucose suspension, it was left standing for 4 - 10 h. When the dropping rate was controlled at 1 drop per second, Ag + The particle size of Ag NPs reduced from Ag was smaller, and with the prolongation of the standing time, Ag in the solution + was reduced as much as possible. Ag NPs combined with each other to form a continuous, dense and uniform silver layer on the surface of aramid nanofibers. The ultrasonic temperature during the chemical reduction method for silver plating was 10 °C - 50 °C; the standing time was 4 h - 10 h.

[0008] The modified aramid fiber electromagnetic shielding flexible composite film of the present invention is a flexible ANFs - HBPs - Ag composite film. Due to its three - dimensional molecular structure, large intermolecular space and adjustable terminal functional groups, hyperbranched polymer has low viscosity, good solubility, excellent thermal stability and chemical stability, as well as encapsulation effect. In the present invention, by adding hyperbranched polymer to the composite material of aramid nanofibers and silver, silver can be effectively bonded through coordination or chelation, and it can also be combined with aramid nanofibers through hydrogen bonding and electrostatic interaction, thereby forming a continuous conductive network, enabling electromagnetic waves to undergo multiple losses, and thus achieving a high shielding effect. Compared with the existing traditional electromagnetic shielding materials, the modified aramid fiber electromagnetic shielding flexible composite film of the present invention has higher electromagnetic shielding performance and good mechanical properties, providing favorable technical support for the commercial application of thin film materials in electronic devices. In addition, the processes such as suction filtration and hot pressing in the method of the present invention are simple and low - cost, and have the potential for industrialization. Description of the Drawings

[0009] Figure 1 It is the molecular structure diagram of the hyperbranched polyamide - amine of the present invention.

[0010] Figure 2 It is the transmission electron microscope image of the aramid nanofibers obtained after subsequent treatment of the aramid nanofiber dispersion prepared in step 1 of Example 1.

[0011] Figure 3 It is the cross - sectional scanning electron microscope image of the modified aramid nanofiber film obtained in step 2 of Example 1.

[0012] Figure 4 Cross-sectional scanning electron micrograph of the modified aramid fiber electromagnetic shielding flexible composite film obtained in step 3 of Example 1.

[0013] Figure 5 Total shielding effectiveness SE of the modified aramid fiber electromagnetic shielding flexible composite films obtained in Examples 1 to 4 for electromagnetic waves in the frequency range from 8.2 to 12.4 GHz.

[0014] Figure 6 Comparison of reflection loss SER, absorption loss SEA, and total shielding effectiveness SE of the modified aramid fiber electromagnetic shielding flexible composite films obtained in Examples 1 to 4 for electromagnetic waves in the frequency range from 8.2 to 12.4 GHz.

[0015] Figure 7 Total shielding effectiveness SE of the modified aramid fiber electromagnetic shielding flexible composite films obtained in Examples 1, 5, and 6 for electromagnetic waves in the frequency range from 8.2 to 12.4 GHz.

[0016] Figure 8 Comparison of reflection loss SER, absorption loss SEA, and total shielding effectiveness SE of the modified aramid fiber electromagnetic shielding flexible composite films obtained in Examples 1, 5, and 6 for electromagnetic waves in the frequency range from 8.2 to 12.4 GHz.

[0017] Figure 9 Stress-strain diagram of the modified aramid fiber electromagnetic shielding flexible composite films obtained in Examples 1 to 4.

[0018] Figure 10 Stress-strain diagram of the modified aramid fiber electromagnetic shielding flexible composite films obtained in Examples 1, 5, and 6. Detailed implementation manners

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0020] Example 1 A preparation method of a modified aramid fiber electromagnetic shielding flexible composite film includes the following steps: 1. Preparation of aramid nanofiber gel Weigh 1.5 g of potassium hydroxide with a beaker, pour it into 20 mL of ultrapure water, and stir until the potassium hydroxide is completely dissolved. Then weigh 1 g of aramid fiber, cut it into short fibers about 2 cm long with scissors, and add it to the flask. Add the potassium hydroxide solution to the flask, and add 480 mL of dimethyl sulfoxide after 15 s. Stir magnetically at room temperature for 4 h until the fiber is completely dissolved, and finally obtain a dark red aramid nanofiber dispersion with a concentration of 2 g / L. Take 50 mL of the aramid nanofiber dispersion in a beaker, add 200 mL of ultrapure water, and use the method of vacuum-assisted filtration to wash the aramid nanofiber dispersion repeatedly with ultrapure water and absolute ethanol until it is neutral, removing dimethyl sulfoxide and potassium hydroxide in the aramid nanofibers, and finally obtain a transparent aramid nanofiber gel. 2. Preparation of hyperbranched polyamide-amine modified aramid nanofibers Weigh 0.1 g of hyperbranched polyamide-amine and dissolve it in absolute ethanol. Stir magnetically at 60 °C for 30 min until it is completely dissolved. Add the aramid nanofiber gel to the beaker, and use an ultrasonic cell disruptor to ultrasonically mix it evenly. The mixture is stirred magnetically at 60 °C for 1 h, and then vacuum-assisted filtration is used to remove absolute ethanol to obtain a modified aramid nanofiber film. 3. Preparation of modified aramid fiber electromagnetic shielding flexible composite film Dropwise add ammonia water to 100 mL of AgNO 3 aqueous solution (20 g / L) until the solution becomes clear and transparent. Then adjust the pH of the solution to 11.0 with 6 g / L KOH solution, and continue to add ammonia water until the solution becomes clear again. Finally, add 0.5 g of PVP (0.5 wt%) to the solution to obtain a silver ammonia solution. Weigh 3 g of glucose (30 g / L), add 4 mL of absolute ethanol (40 mL / L) and 7.5 mg of polyethylene glycol (75 mg / L), dissolve and make up the volume to 100 mL with water. Add the modified aramid nanofiber film to the above silver ammonia solution, and ultrasonically mix it for 3 min in an ultrasonic cell disruptor (500 W). Ultrasonically mix the mixture at 30 °C (252 W, 40 KHz) for 30 min. After that, slowly add the glucose solution (1 drop / second), and perform ultrasonication under the same conditions for 60 min to ensure that Ag + is completely converted to AgNPs. Let the system stand for 10 h to make the solution clear to ensure high silver utilization rate. After that, use the method of vacuum-assisted filtration to obtain a composite film, and hot press it at 100 °C for 5 min with a hot press to prepare a modified aramid fiber electromagnetic shielding flexible composite film, denoted as ANFs-HP 1 -Ag 20 composite film with a thickness of 0.13 mm.

[0021] Example 2 The difference from Example 1 is that the concentration of silver nitrate is 15 g / L, and ANFs-HP 1 -Ag 15 The thickness of the composite film is 0.12 mm.

[0022] Example 3 The difference from Example 1 is that the concentration of silver nitrate is 10 g / L, and ANFs-HP 1 -Ag 10 The thickness of the composite film is 0.11 mm.

[0023] Example 4 The difference from Example 1 is that the concentration of silver nitrate is 5 g / L, and ANFs-HP 1 -Ag 5 The thickness of the composite film is 0.09 mm.

[0024] Example 5 The difference from Example 1 is that the concentration of hyperbranched polyamide-amine is 10 g / L, and ANFs-HP 0.5 -Ag 1 The thickness of the composite film is 0.13 mm.

[0025] Example 6 The difference from Example 1 is that the concentration of hyperbranched polyamide-amine is 20 g / L, and ANFs-HP 1 -Ag 1 The thickness of the composite film is 0.13 mm.

[0026] Figure 2 It is the transmission electron microscopy image of the aramid nanofibers obtained after the subsequent treatment of the aramid nanofiber dispersion prepared in Step 1 of Example 1. The specific treatment process is as follows: The aramid nanofiber dispersion in Step (1) is rinsed repeatedly with ultrapure water and absolute ethanol by vacuum-assisted filtration until it is washed to neutral to remove potassium hydroxide and dimethyl sulfoxide in the solution. Then, the aramid nanofiber solution is poured from the filter cup into a beaker, sonicated with a cell crusher for 10 min, diluted with 100 mL of deionized water, and the diluted aramid nanofiber solution is repeatedly dropped on the copper grid five times with a dropper for transmission electron microscopy. It can be seen from the figure that the prepared aramid nanofibers have a high aspect ratio, proving the successful preparation of aramid nanofibers.

[0027] Figure 3 、 Figure 4Cross-sectional scanning electron micrographs of the aramid nanofiber gel obtained in Step 1 of Example 1, the modified aramid nanofiber film obtained in Step 2, and the modified aramid fiber electromagnetic shielding flexible composite film obtained in Step 3, respectively. It can be seen that with the addition of hyperbranched polyamide-amine, hydrogen bonding is formed with aramid nanofibers, reducing the interlayer spacing. However, with the addition of silver, the interaction force is weakened, and thus Figure 3 compared with that, the interlayer spacing is increased.

[0028] Figure 5 and Figure 7 For the total electromagnetic shielding performance test of the composite electromagnetic shielding films with different mass ratios of hyperbranched polyamide-amine and silver nitrate, six samples were tested by a vector network analyzer. Under the condition of a frequency of 8.2 - 12.4 GHz, the reflection loss SER, absorption loss SEA, and total shielding effectiveness SE were obtained using the data of S11 and S21. Through Figure 3 and Figure 5 it can be seen that with the increase of silver content, the total shielding effectiveness of the composite film also increases significantly. Among them, the content of hyperbranched polyamide-amine also has a certain influence on the electromagnetic shielding effectiveness.

[0029] Figure 6 For the comparison of the reflection loss SER, absorption loss SEA, and total shielding effectiveness SE at a frequency of 8.2 - 12.4 GHz when the mass ratio of hyperbranched polyamide-amine to silver nitrate is 1:5, 1:10, 1:15, and 1:20. Figure 8 For the comparison of the reflection loss SER, absorption loss SEA, and total shielding effectiveness SE at a frequency of 8.2 - 12.4 GHz when the mass ratio of hyperbranched polyamide-amine to silver nitrate is 0.05:1, 0.5:1, and 1:1. Figures 5 to 8 It shows that the electromagnetic shielding material SE provided by the present invention includes two shielding mechanisms, SEA and SER. The increase in silver content leads to a sharp increase in the values of SE and SEA, indicating that the increase in the area density of silver makes the conductive network more perfect. At the same time, it can also increase the SEA and SER of the composite film. Electromagnetic waves will be dissipated or absorbed in the form of heat inside the composite film, thereby greatly improving the overall shielding performance of the composite film.

[0030] Figure 9 and Figure 10 Are the stress-strain diagrams of the composite films prepared in Examples 1 - 4 and Examples 1, 5, and 6, respectively. It can be seen from the figure that with the increase of silver content, the mechanical properties decrease, but still have good mechanical properties.

[0031] The foregoing description of the disclosed embodiments enables those skilled in the art to practice or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a modified aramid fiber electromagnetic shielding flexible composite film, characterized in that: The following steps are involved: 1) Preparation of aramid nanofiber gel Aramid fiber staple fibers are first added to a potassium hydroxide solution, followed by dimethyl sulfoxide, and the mixture is stirred thoroughly to obtain an aramid nanofiber dispersion. The dispersion is diluted and then vacuum filtered, and the aramid nanofiber gel is obtained after repeated washing. 2) Modified aramid nanofiber The aramid nanofiber gel obtained in step 1) is added to an ethanol solution of a hyperbranched polyamide-amine, heated and stirred, and vacuum filtered to obtain a modified aramid nanofiber film; 3) Surface silver plating The modified aramid nanofiber film obtained in step 2) is added to the silver ammonia solution, and the reducing solution is added dropwise under heating and ultrasonic treatment. After the reaction is completed, vacuum filtration is performed to obtain a composite film.

2. The method for preparing the modified aramid fiber electromagnetic shielding flexible composite film according to claim 1, characterized in that: In step 1), the concentration of the potassium hydroxide solution is 5-10wt%, the weight ratio of potassium hydroxide to aramid fiber is (1-3):1, and the specification fineness of the aramid fiber is 100-3000D and the length is 1-3cm.

3. The method for preparing the modified aramid fiber electromagnetic shielding flexible composite film according to claim 1, characterized in that: In step 2), the amount of the hyperbranched polyamide-amine used is 5-20% of the weight of the aramid nanofibers in step 1).

4. The method for preparing the modified aramid fiber electromagnetic shielding flexible composite film according to claim 1, characterized in that: In step 3), the preparation method of the silver ammonia solution is as follows: add ammonia water drop by drop into a 10-30 g / L AgNO3 aqueous solution until the solution becomes clear and transparent, adjust the pH of the solution to 11.0 with a 5-10 g / L KOH solution, continue to add ammonia water until the solution becomes clear again, add 0.3-1 g PVP to obtain a silver ammonia solution; the preparation method of the reducing solution is as follows: add anhydrous ethanol and polyethylene glycol to a 20-40 g / L glucose solution, stir thoroughly to dissolve, the concentration of anhydrous ethanol is 30-50 mL / L, and the concentration of polyethylene glycol is 60-80 mg / L.

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