Preparation method of aramid for electromagnetic shielding

Abstract

The present application relates to a kind of preparation methods of aramid for electromagnetic shielding.The method includes: by interfacial polymerization reaction on the surface of commercial meta-aramid, a layer of ultrathin crosslinking layer containing active carboxyl, pyridine or imidazole unit is constructed, at the same time, by the coordination of active group and metal ion in the reaction solution, Cu2+, Ag+, Ni2+ and other metal ions are introduced synchronously, after in-situ reduction, metal nanoparticles are formed on the surface of aramid to serve as "seed", and then a thin and uniform continuous metal conductive coating is efficiently constructed on the surface of aramid by subsequent metal electroless plating.The method is based on interfacial polymerization reaction to synchronously form crosslinked ultrathin layer on the surface of aramid and introduce metal nanoparticle "seed".The ultrathin crosslinking layer does not affect the excellent flexibility of aramid and does not damage the mechanical properties of aramid.The coordination of active group and metal ion based on ultrathin crosslinking layer can realize the strong interfacial composite of metal particles and fiber and improve the adhesion of metal conductive layer on the surface of fiber.

Description

Technical Field

[0001] This invention belongs to the field of high-performance fiber preparation technology, and specifically relates to a method for preparing high-performance aramid fibers that can meet electromagnetic shielding applications. Background Technology

[0002] Aramid, as a type of high-performance organic fiber, possesses excellent properties such as high strength, high modulus, excellent heat resistance, intrinsic flame retardancy, and corrosion resistance, making it widely used in aerospace, military equipment, information communication, and transportation. Conductive aramid, prepared by constructing a continuous conductive coating on its surface through chemical or physical modification, has attracted widespread attention in the field of electromagnetic shielding. However, the smooth surface and strong chemical inertness of aramid make it difficult to bond with other materials. Continuous and stable metal layers cannot be obtained on its surface through methods such as physical sputtering or conventional chemical plating. Therefore, surface modification of aramid fibers to enhance their reactivity is crucial for obtaining high-performance conductive aramid fabrics.

[0003] To improve the adhesion between aramid and conductive coatings, current surface treatment methods for aramid mainly include plasma etching, acid-base etching, and chemical grafting. Taking acid-base etching as an example, the main process involves using strong acid or alkali solutions to etch the fiber surface, forming a rough groove structure or destroying the amide units on the surface to form active carboxyl groups. Then, through mechanical meshing or ionic coordination, active sites of metal nanoparticles are formed on the fiber surface, followed by the formation of a conductive metal coating on the fiber surface through chemical metal plating. For example, national invention patent application number CN202010242357.6 discloses a method for preparing conductive aramid paper by first cleaning the aramid and then using plasma etching to improve the adhesion between the aramid and the silver coating. National invention patent application number CN201911326096.X discloses a method for preparing aramid with a composite metal coating structure. Its core process also includes pre-treating the fiber with a dimethyl sulfoxide (DMSO) solution containing sulfuric acid and calcium chloride to improve surface activity and achieve efficient composite of metal and fiber. National invention patent application number CN201310685423.7 discloses a method for preparing conductive aramid by first roughening the surface of aramid with NaOH etching, followed by palladium metal activation and chemical silver plating. However, both physical and chemical etching always come at the cost of damaging the physical morphology or chemical structure of the fiber, easily leading to a decrease in the fiber's mechanical properties. In addition, the formation of metal nanoparticle "seeds" in the above process is separate from the fiber pretreatment, making the process cumbersome.

[0004] In common organic functional groups (such as carboxyl, imidazole, pyridine, 1,2,4-triazole, etc.), the lone pair electrons on oxygen or nitrogen atoms have a strong coordination ability with metal ions (Macromolecular Rapid Communications, 2022, 43(3):2100643; Polymers, 2020, 12(2):442). This special interaction can be used to achieve strong interfacial composites between polymers and metal nanoparticles. However, how to efficiently construct continuous conductive metal coatings on the surface of aramid fibers by building such special interactions without compromising their inherent mechanical properties and flexibility remains a significant challenge in this field. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing conductive aramid for electromagnetic shielding, so as to overcome the problems of damage to the mechanical properties of fibers by physical or chemical etching and low efficiency caused by complex process flow in the prior art.

[0006] This invention provides a method for preparing aramid for electromagnetic shielding. The main process includes immersing meta-aramid in a mixed solution of diamine monomer / ethanol / metal salt containing active carboxyl groups, pyridine or imidazole units for a period of time, then transferring it to a trimesoyl chloride (TMC) / n-hexane solution and maintaining it at room temperature for a period of time; treating the obtained aramid with a reducing agent to form metal nanoparticles on the fiber surface, then performing metal electroless plating on the fiber to construct a continuous metal conductive layer on the surface; finally washing and drying with deionized water to prepare aramid for electromagnetic shielding.

[0007] The diamine containing an active carboxyl group, pyridine, or imidazole unit has one of the following chemical structures:

[0008]

[0009] The metal salt is one of copper chloride, silver nitrate, nickel nitrate, or nickel sulfate.

[0010] The composition of the mixed solution of diamine monomer / ethanol / metal salt containing active carboxyl groups, pyridine or imidazole units is as follows: (3-5)wt%: (90-92)wt%: (3-7)wt%. The aramid is treated in the mixed solution of diamine monomer / ethanol / metal salt containing active carboxyl groups, pyridine or imidazole units for (10-15) min at room temperature.

[0011] The concentration of the TMC / n-hexane solution is (10-25) mmol / L, and the treatment time of aramid in the solution is (1-3) min at room temperature.

[0012] The reducing agent used is one of sodium borohydride (NaBH4), hypophosphite (H3PO2), or sodium hypophosphite (NaH2PO2) aqueous solution, and the concentration of the reducing agent is (0.1-0.5) mol / L.

[0013] The chemical plating solution used is a commercially available chemical plating solution containing silver, copper, and nickel metal salts.

[0014] This invention utilizes an interfacial polymerization reaction between trimesoyl chloride and a diamine monomer containing active groups on the surface of aramid fiber to form an ultrathin cross-linked layer. This enhances the surface activity of aramid fiber and simultaneously fosters metal coordination, thereby anchoring metal nanoparticles. Furthermore, the formed ultrathin cross-linked layer helps protect the aramid fiber from chemical corrosion during subsequent electroless metal plating, preventing degradation of its mechanical properties. This invention enables the efficient and continuous preparation of conductive aramid fiber, meeting current electromagnetic shielding application requirements.

[0015] Beneficial effects

[0016] (1) The present invention constructs an ultra-thin cross-linked layer on the surface of aramid by means of diamine and pyromellitic chloride without affecting the excellent flexibility of aramid or damaging the mechanical properties of aramid itself. It is a non-destructive surface modification method.

[0017] (2) Based on the coordination of active groups and metal ions in the ultrathin cross-linked layer, strong interfacial composite between metal particles and fibers can be achieved, which enhances the adhesion of the metal conductive layer on the fiber surface and provides more outstanding conductivity stability in harsh environments such as repeated bending and chemical corrosion.

[0018] (3) The ultrathin cross-linked layer is formed simultaneously with the metal coordination, which simplifies the preparation process and is more conducive to large-scale development;

[0019] (4) The formation of an ultra-thin cross-linked layer on the surface of aramid can fully protect aramid from chemical erosion in subsequent metal plating solutions. Attached Figure Description

[0020] Figure 1 This is a SEM image of the unmodified aramid surface in this invention. Figure 2 This is a SEM image of the aramid surface containing the metallic silver conductive layer in Example 1. Figure 3 This is an EDS image of the silver element on the surface of the aramid fiber containing the metallic silver conductive layer in Example 1. Figure 4 The resistance of the aramid fabric containing a conductive silver layer in Example 1 after ultrasonic cleaning in different solvents is shown. Detailed Implementation

[0021] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0022] The sources of fiber materials, sample processing, and testing conditions in the embodiments of this invention are as follows:

[0023] The meta-aramid fiber was purchased from Dongguan Tekelun New Material Application Co., Ltd., and its specification is 200D.

[0024] Carboxydiamine: Purchased from Zhengzhou Huiju Chemical Co., Ltd.;

[0025] Pyridine diamine: Purchased from Shanghai Qiao Chemical Technology Co., Ltd.;

[0026] Imidazolidine: Purchased from Changzhou Sunshine Pharmaceutical Co., Ltd.;

[0027] Nickel nitrate: Purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0028] Fiber bending treatment: The fibers with metal coating are repeatedly bent using self-made equipment, 1000 times.

[0029] Corrosion resistance test of fibers: The fibers with metal coatings were treated with water, HCl (0.1 mol / L), NaOH (0.1 mol / L), sodium chloride (0.1 mol / L) and acetone solution.

[0030] Mechanical properties: tested using Instron 3300, tensile rate 5cm / min, clamp distance 2cm;

[0031] Fiber resistance test: The resistance of the fiber was tested at room temperature using a Kaisi DT-9205A high-precision multimeter. The length was controlled at 20cm. Ten sets of data were tested for each sample, and the average value was taken.

[0032] Example 1

[0033] A suitable amount of commercially available meta-aramid fiber, without pretreatment, was directly immersed in a mixed solution of carboxydiamine monomer / ethanol / AgNO3, where the mass fractions of carboxydiamine, ethanol, and AgNO3 were 4%, 90%, and 6%, respectively, and kept at room temperature for 15 minutes. The diamine-treated aramid fiber was then immersed in a TMC / n-hexane solution, where the TMC concentration was 20 mol / L, for 3 minutes. The treated fiber was then removed and immersed in a sodium borohydride (NaBH4) solution for 2 minutes at 40°C. Finally, the fiber was continuously passed through a commercially available electroless plating solution containing silver salt (3.5 g AgNO3, 5 mL ammonia, 60 mL water) and a reducing solution (45 g glucose, 4 g tartaric acid, 10 mL ethanol, and 1 L water), with the electroless plating time controlled at 2 minutes. Finally, the fiber was washed with deionized water and dried at 60°C to obtain aramid fiber with a silver conductive layer on its surface.

[0034] Example 2

[0035] A suitable amount of commercially available meta-aramid fiber, without pretreatment, was directly immersed in a mixed solution of pyridine diamine-II monomer / ethanol / AgNO3, wherein the mass fractions of carboxydiamine, ethanol, and AgNO3 were 4%, 90%, and 6%, respectively, and kept at room temperature for 15 min. Then, the diamine-treated aramid fiber was immersed in a TMC / n-hexane solution, where the TMC concentration was 20 mol / L, for 3 min. The treated fiber was then removed and immersed in a sodium borohydride (NaBH4) solution for 2 min at 40℃. Finally, the fiber was continuously passed through a commercially available chemical plating solution containing silver salt (3.5 g AgNO3, 5 mL ammonia, 60 mL water) and a reducing solution (45 g glucose, 4 g tartaric acid, 10 mL ethanol, and 1 L water), with the metal plating time controlled at 2 min. Finally, the fiber was washed with deionized water and dried at 60℃ to obtain aramid fiber with a silver conductive layer on its surface.

[0036] Example 3

[0037] A suitable amount of commercially available meta-aramid fiber was directly immersed in a mixed solution of imidazole diamine-1 / ethanol / CuCl2 without pretreatment, wherein the mass fractions of carboxydiamine, ethanol, and CuCl2 were 5%:90%:5%, respectively, and kept at room temperature for 15 min. Then, the diamine-treated aramid fiber was immersed in a TMC / n-hexane solution, wherein the concentration of TMC was 22 mol / L, and the treatment time was 3 min. The treated fiber was then removed and immersed in a sodium borohydride (NaBH4) solution for 2 min at a temperature of 40℃. Finally, the fiber was continuously passed through a commercially available electroless plating solution containing copper salts (10g copper chloride, 2g N-methylmorpholine, 4g formaldehyde, 13g sodium hydroxide, 10g sodium tartrate, 20g EDTA·2Na, 0.1g potassium ferrocyanide, 0.01g bipyridine, 50mL methanol, 1L water), with the electroless plating time controlled at 2 min. Finally, the fibers are washed with deionized water and dried at 60°C to obtain aramid fibers with a copper conductive layer on the surface.

[0038] Example 4

[0039] A suitable amount of commercially available meta-aramid fiber, without pretreatment, was directly immersed in a mixed solution of imidazole diamine-I / ethanol / Ni(NO3)2, wherein the mass fractions of carboxydiamine, ethanol, and AgNO3 were 5%:90%:5%, respectively, and kept at room temperature for 15 min. Then, the diamine-treated aramid fiber was immersed in a TMC / n-hexane solution, where the TMC concentration was 25 mol / L, for 3 min. The treated fiber was then removed and immersed in a sodium borohydride (H3PO2) solution for 5 min at 40℃. Finally, the fiber was continuously passed through a commercially available electroless plating solution containing nickel salts (NiCl2·6H2O: 20 g / L, NaH2PO2·H2O: 30 g / L, Na3C6H5O7·2H2O: 10 g / L, NH4Cl: 30 g / L, pH = 8.5-9.5), with the electroless plating time controlled at 3 min. Finally, the fibers are washed with deionized water and dried at 60°C to obtain aramid fibers with a silver conductive layer on the surface.

[0040] Comparative Example 1

[0041] A suitable amount of commercially available meta-aramid fiber was taken and pretreated according to the method reported in application number CN201310685423.7. First, the aramid fiber was roughened using a NaOH solution (200g NaOH, 50g anhydrous ethanol, and 950mL water). Then, the aramid fiber was immersed in an AgNO3 / ethanol solution (6wt%) at room temperature for 15 minutes. The treated fiber was then removed and immersed in a sodium borohydride (NaBH4) solution for 2 minutes at 40℃. Finally, the fiber was continuously passed through a commercially available electroless plating solution containing silver salt (3.5g AgNO3, 5mL ammonia, and 60mL water) and a reducing solution (45g glucose, 4g tartaric acid, 10mL ethanol, and 1L water) for 2 minutes. The electroless plating time was controlled to be 2 minutes. Finally, the fiber was washed with deionized water and dried at 60℃ to obtain aramid fiber with a silver conductive layer on its surface.

[0042] Comparative Example 2

[0043] A suitable amount of commercially available meta-aramid fiber, without pretreatment, was directly immersed in a mixed solution of carboxydiamine monomer / ethanol / AgNO3, where the mass fractions of carboxydiamine, ethanol, and AgNO3 were 4%, 90%, and 6%, respectively, and kept at room temperature for 15 minutes. Then, the diamine-treated aramid fiber was immersed in a terephthaloyl chloride / n-hexane solution with a TMC concentration of 20 mol / L for 3 minutes. At this point, a linear molecular chain polymer film, rather than a cross-linked film, was formed on the aramid surface. The treated fiber was then removed and immersed in a sodium borohydride (NaBH4) solution for 2 minutes at 40°C. Finally, the fiber was continuously passed through a commercially available electroless plating solution containing silver salt (3.5 g AgNO3, 5 mL ammonia, 60 mL water) and a reducing solution (45 g glucose, 4 g tartaric acid, 10 mL ethanol, and 1 L water), with the electroless plating time controlled at 2 minutes. Finally, the fiber was washed with deionized water and dried at 60°C to obtain aramid fiber with a silver conductive layer on its surface.

[0044] Table 1 compares the electrical conductivity and mechanical properties of the modified aramid prepared by this invention with those reported in invention patents CN202010242357.6, CN202110126531.5 and research literature Adv. Eng. Mater. 2019, 21, 1801041 (Reference 1).

[0045] Table 1

[0046]

[0047]

[0048] As can be seen from Comparative Example 1, this process uses strong alkali NaOH to pretreat the surface of aramid, forming active sites on the surface of aramid, which is conducive to the complexation of metallic silver ions. However, in terms of the final effect, on the one hand, the strong alkali treatment seriously damages the mechanical properties of the fiber, and on the other hand, the electromagnetic shielding effectiveness of the fabric prepared is still lower than that of this invention.

[0049] As can be seen from Comparative Example 2, replacing TMC with terephthaloyl chloride results in the formation of a linear polymer film on the aramid surface. The resistance change rate after 1000 bends is higher than that of the present invention, and the structure of the conductive metal layer on the surface is unstable.

Claims

1. A method for preparing aramid fiber for electromagnetic shielding, characterized in that, Meta-aramid fibers are first immersed in a mixed solution of a diamine monomer / ethanol / metal salt containing active carboxyl groups, pyridine, or imidazole units, and kept for a period of time. Then, they are transferred to a trimesoyl chloride / n-hexane solution and kept at room temperature for a period of time. The resulting aramid fibers are treated with a reducing agent to form metal nanoparticles on the fiber surface. The fibers are then subjected to electroless metal plating to construct a continuous conductive metal layer on the surface. Finally, the fibers are washed and dried with deionized water to prepare electromagnetic shielding aramid fibers. The diamine containing active carboxyl groups, pyridine, or imidazole units has one of the following chemical structures: 。 2. The method for preparing aramid fiber for electromagnetic shielding according to claim 1, characterized in that, The metal salt is one of copper chloride, silver nitrate, nickel nitrate, or nickel sulfate.

3. The method for preparing aramid for electromagnetic shielding according to claim 1, wherein the composition of the mixed solution of diamine monomer / ethanol / metal salt containing active carboxyl groups, pyridine or imidazole units is: (3-5) wt% : (90-92) wt% : (3-7) wt%, and the aramid is treated in the mixed solution of diamine monomer / ethanol / metal salt containing active carboxyl groups, pyridine or imidazole units for (10-15) min at room temperature.

4. The method for preparing aramid for electromagnetic shielding according to claim 1, wherein the concentration of the pyromellitic chloride / n-hexane solution is (10-25) mmol / L, the treatment time of the aramid in the solution is (1-3) min, and the room temperature is used.

5. The method for preparing aramid for electromagnetic shielding according to claim 1, wherein the reducing agent used is one of sodium borohydride, hypophosphite, or an aqueous solution of sodium hypophosphite, and the concentration of the reducing agent is (0.1-0.5) mol / L.

6. The method for preparing aramid for electromagnetic shielding according to claim 1, wherein the chemical plating solution used is a commercially available chemical plating solution containing silver, copper, and nickel metal salts.

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