Ag / fe3o4 synergistically modified basalt fiber and pvdf composite material and preparation method

Abstract

The application discloses basalt fiber and PVDF composite material and a preparation method of Ag / Fe3O4 synergic modification, Ag nanoparticles and Fe3O4 nanoparticles are simultaneously modified on the basalt fiber, and the limitation of traditional single modification function is broken; and the modified basalt is used to prepare oriented PVDF composite material, so that the prepared PVDF composite material realizes synchronous improvement of piezoelectric performance and electromagnetic shielding performance, and can be directly used as a structural material of equipment shell, cabin, automobile and the like, realizes intelligent structure manufacturing of self-sensing and self-shielding, and has good application prospect and economic value as a new type of PVDF composite material product.

Description

Technical Field

[0001] This invention relates to the field of functional composite materials technology, specifically to an Ag / Fe3O4 synergistic modified basalt fiber and PVDF composite material and its preparation method. Background Technology

[0002] Polyvinylidene fluoride (PVDF)-based composites are composite materials prepared by adding various fillers, fibers, or other polymers to PVDF as the matrix. PVDF itself is a high-performance engineering plastic that has successfully achieved an excellent balance between chemical resistance, mechanical strength, ease of processing, and piezoelectric effectiveness, playing an indispensable role in modern industry and technology. However, although PVDF has good piezoelectric properties (the piezoelectric strain constant d33 of pure PVDF is 20 pC / N), its electromagnetic shielding effectiveness (SE) is low, only 5 dB. Therefore, existing technologies often improve the electromagnetic shielding effectiveness of PVDF materials by adding conductive fillers. For example, some studies have reported that by introducing carbon nanotubes (CNTs) as fillers, a conductive network can be formed in the composite material, increasing the material's conductivity and effectively improving the electromagnetic shielding performance of PVDF. However, introducing conductive materials disrupts the ordered arrangement of PVDF molecular chains, reducing the crystallinity of PVDF and leading to a decrease in the piezoelectric properties of the composite material. Simultaneously, the conductive network formed by the conductive material can short-circuit the piezoelectric potential, further degrading its piezoelectric properties. Furthermore, reports indicate that increasing the β-phase content of PVDF-based composites can enhance their electromagnetic shielding performance. For example, high-voltage polarization can cause a rearrangement of the charge distribution within the PVDF-based composite material, promoting the conversion of the α-phase to the β-phase, thus enhancing its electromagnetic shielding effectiveness. However, simply increasing the β-phase content has a limited contribution to electromagnetic shielding performance, typically <20 dB, which is insufficient to meet the broadband electromagnetic protection requirements of modern electronic equipment. Therefore, existing PVDF-based composites must sacrifice some of the piezoelectric properties of PVDF to achieve high electromagnetic shielding effectiveness.

[0003] Basalt fiber (BF), as a preferred reinforcement in PVDF-based composites, exhibits chemical inertness on its surface, resulting in poor interfacial bonding with the PVDF matrix and low stress transfer efficiency. Therefore, surface modification is necessary to improve interfacial adhesion. Traditional modification methods often employ coupling agents such as silanes to form a layer of chemical bonds on the fiber surface, thereby enhancing the interfacial bond between the fiber and the resin matrix. However, silane coupling agent treatment creates an insulating siloxane network on the fiber surface, which hinders electron transport and reduces the fiber's electrical conductivity.

[0004] Dopamine is a neurotransmitter that readily polymerizes into polydopamine (PDA) in a weakly alkaline environment at room temperature. PDA possesses excellent biocompatibility, environmental stability, and excellent dispersibility in water. Furthermore, it can deposit on the surface of almost any material to modify it, not only increasing the biomimetic properties of the material surface but also endowing it with abundant functional groups, such as amino and hydroxyl groups, significantly enhancing the active groups on the material surface. Therefore, PDA has become a novel fiber surface modifier. For example, Chinese patent application CN110258116A discloses a method for preparing a polydopamine-modified basalt fiber carrier. Basalt fibers, after being alkali-etched and dried, are immersed in a dopamine modification solution, shaken at room temperature, and then dried. This yields a basalt fiber carrier that simultaneously possesses abundant surface functional groups, exhibits good biocompatibility and hydrophilicity, promotes microbial adhesion to its surface, increases biofilm formation, and improves wastewater treatment efficiency. However, the fibers modified by this method are not suitable for the preparation of PVDF-based composites because alkali (NaOH solution) etching will damage the basalt fibers and destroy their performance as reinforcements.

[0005] Silver nanowires (AgNWs) commonly used in PVDF-based composites are one-dimensional nanomaterials with diameters typically in the nanoscale (1–100 nanometers) and lengths in the micrometer or millimeter range. Their role in PVDF-based composites is as a filler, similar to carbon nanotubes, primarily enhancing electromagnetic shielding effectiveness. Existing technologies have few reports on silver plating modification of basalt fibers, mainly aimed at coating the fiber surface with a more binding metal (Ag) element to increase compatibility with other metallic materials. For example, Chinese patent application CN117701962A discloses a method for preparing basalt fiber-reinforced magnesium alloy materials, which sequentially roughens, sensitizes, silver-plats, and nickel-plats the basalt fibers to obtain modified basalt fibers used in the preparation of basalt fiber-reinforced magnesium alloy materials, thereby improving the high-temperature resistance, specific strength, and specific modulus of the resulting basalt fiber-reinforced magnesium alloy materials. However, the roughening process here also involves treating the basalt fibers with an alkaline solution, damaging their surface and compromising the performance of the PVDF-based composite material.

[0006] Iron(III) oxide (Fe3O4) is paramagnetic, which can enable PVDF-based composite materials to achieve low-frequency electromagnetic wave shielding effectiveness. For example, Chinese patent application CN118185226A discloses a basalt fiber shielding material and its preparation method and application. Basalt fibers are dispersed in acetone, a silane coupling agent is added, and then a nano-silica suspension is added dropwise to obtain active fibers. Then, the active fibers, carbon nanotubes, dopamine, and magnetic iron(III) oxide nanoparticles are dispersed in a buffer solution to obtain a modified solution. Finally, glutaraldehyde solution is added dropwise to the modified solution to obtain modified basalt fibers with good mechanical and electromagnetic shielding properties, which can be well applied in high-voltage test chambers. However, in actual production, nanoparticles directly dispersed in solution are prone to agglomeration, resulting in unsatisfactory modification effects or even modification failure. Furthermore, Fe3O4 nanoparticles dispersed in solution can easily disrupt the PVDF polarization process, leading to a decrease in the piezoelectric properties of the resulting PVDF-based composite material.

[0007] Therefore, how to simultaneously improve the piezoelectric properties and electromagnetic shielding properties of polyvinylidene fluoride composite materials to meet the requirements of modern electronic equipment for broadband electromagnetic protection remains an urgent problem to be solved. Summary of the Invention

[0008] To address the aforementioned challenges in synergistically optimizing the piezoelectric and electromagnetic shielding properties of existing polyvinylidene fluoride (PVDF)-based composite materials, this invention provides an Ag / Fe3O4 synergistically modified basalt fiber and PVDF composite material, along with its preparation method. The method involves synergistically modifying basalt fibers with Ag and Fe3O4 nanoparticles through multi-level modification, combined with a magnetic field-induced orientation process, to prepare a PVDF-based composite material exhibiting both high piezoelectric properties and high electromagnetic shielding effectiveness. This material is suitable for flexible electronic devices, aerospace stealth structures, and intelligent electromagnetic protection equipment. The specific technical solution is as follows:

[0009] First, the present invention provides a basalt fiber synergistically modified with silver nanoparticles / Fe3O4, the modified basalt fiber comprising a basalt fiber body and Ag nanoparticles and Fe3O4 nanoparticles modified on its surface.

[0010] The aforementioned basalt fiber modified with silver nanoparticles / Fe3O4 has an amount of Ag nanoparticles of 1.5% to 3.5 wt% and an amount of Fe3O4 nanoparticles of 3% to 7 wt% on the basalt fiber body; and the mass ratio of the Ag nanoparticles to the Fe3O4 nanoparticles is 1 to 3: 1 to 3.

[0011] Secondly, the present invention provides a method for preparing the aforementioned modified basalt fiber, comprising the following steps:

[0012] 1) Preparation of BF@PDA: The cleaned and dried basalt fibers were dispersed in a dopamine buffer solution and reacted for 20-30 h; the basalt fiber sample was separated by filtration at room temperature, and then cleaned and dried; the above process was repeated 2-3 times; finally, the polydopamine-modified basalt fiber sample was obtained by drying and named BF@PDA.

[0013] 2) Preparation of BF@PDA@Ag: The BF@PDA prepared in step 1) was dispersed in anhydrous ethanol, a certain amount of formaldehyde solution was added, and the pH value was adjusted to weakly alkaline (between 8.5 and 9.5). Then, silver ammonia solution was added, and the reaction was stirred for 10 to 20 minutes under water bath heating. Then, the mixture was allowed to stand to precipitate, the solvent was removed, and the mixture was washed several times and dried to obtain the basalt fiber sample modified with Ag nanoparticles, which was named BF@PDA@Ag.

[0014] 3) Preparation of BF@PDA@Ag@Fe3O4: The BF@PDA@Ag prepared in step 2) was added to PEI solution, ultrasonically dispersed and mixed, and then stirred at room temperature for 10-15 h. Then FeCl2·4H2O solution and FeCl3·6H2O solution were added, and the mixture was stirred for another 20-40 min to form a suspension. The pH was then adjusted to 11-12 with ammonia water, and the suspension was stirred at 40-60°C for another 20-40 min to co-precipitate. Finally, the mixture was centrifuged, and the precipitate was washed several times with deionized water and ethanol. After drying, a basalt fiber sample modified with Ag nanoparticles and Fe3O4 nanoparticles was obtained and named BF@PDA@Ag@Fe3O4, which is a basalt fiber synergistically modified with silver nanoparticles and iron tetroxide.

[0015] As a preferred technical solution, in the aforementioned method for preparing modified basalt fiber, in step 1), the dopamine buffer solution is a dopamine-Tris hydrochloride buffer solution with a concentration of 0.001-0.003 g / mL; the material-to-liquid ratio of basalt fiber dispersed in the dopamine buffer solution is 0.02-0.03 g / mL.

[0016] As a preferred technical solution, in the aforementioned method for preparing modified basalt fiber, in step 2), the material-to-liquid ratio of BF@PDA dispersed in anhydrous ethanol is 0.005–0.02 g / mL; the concentration of the added formaldehyde solution is 0.1–0.5 mol / L, and the amount added is 1 / 10–1 / 2 of the volume of the silver ammonia solution; the concentration of the silver ammonia solution is 0.05–0.2 mol / L; the water bath heating temperature is 35–45°C; and the settling time is 1.5–3 h until the fiber is completely settled.

[0017] As a preferred technical solution, in the aforementioned method for preparing modified basalt fiber, in step 3), the concentration of the PEI solution is 1–5 mg / mL; the concentration or material-to-liquid ratio of BF@PDA@Ag dispersed in the PEI solution is 0.005–0.01 g / mL, and the dispersion time is 40–90 min; the concentrations of the FeCl2·4H2O solution and the FeCl3·6H2O solution are both 0.001–0.003 g / mL, and the volume ratio of the two added is 1:2.

[0018] Furthermore, the present invention provides an oriented PVDF composite material containing the aforementioned silver nanoparticle / Fe3O4 synergistic modified basalt fiber, wherein the total content of the silver nanoparticle modified basalt fiber and the silver nanoparticle / Fe3O4 synergistic modified basalt fiber is 5-35 wt% of the PVDF mass; and the respective contents of the silver nanoparticle modified basalt fiber and the silver nanoparticle / Fe3O4 synergistic modified basalt fiber are 5-20 wt% of the PVDF mass.

[0019] Finally, the present invention also provides a method for preparing the aforementioned oriented PVDF composite material, comprising the following steps:

[0020] A) Solution blending: Modified basalt fibers BF@PDA@Ag modified only with Ag nanoparticles were added to a PVDF / DMF solution to obtain suspension A; modified basalt fibers BF@PDA@Ag@Fe3O4 modified with silver ions and Fe3O4 nanoparticles were added to a PVDF / DMF solution to obtain suspension B; suspension A and suspension B were mixed to obtain the blended suspension required for preparing PVDF composite materials;

[0021] B) Magnetic field orientation molding: The obtained blend suspension is placed in a vertical magnetic field to induce the directional alignment of BF@PDA@Ag@Fe3O4. At the same time, a polarizing electric field is applied to activate the piezoelectric properties. After drying, the oriented PVDF composite material can be obtained.

[0022] As a preferred technical solution, in the aforementioned method for preparing oriented PVDF composite material, in step A), the mass concentration of the PVDF / DMF solution is 8-12 wt%; the amount of BF@PDA@Ag added to suspension A and the amount of BF@PDA@Ag@Fe3O4 added to suspension B are both 5-20 wt% of the mass of PVDF; and the blending ratio of suspension A to suspension B is 1:1.

[0023] As a preferred technical solution, in the aforementioned method for preparing oriented PVDF composite materials, in step B), the magnetic field orientation molding and the time for inducing oriented alignment is 35-45 min; the vertical magnetic field strength is 0.5-1.5 T, and the applied polarization electric field strength is 35-45 kV / mm.

[0024] The beneficial effects of this invention are:

[0025] 1) This invention innovatively performs synergistic modification of basalt fibers by simultaneously modifying their surface with Ag nanoparticles and Fe3O4 nanoparticles. This not only gives the modified basalt fibers good electrical conductivity, but also breaks through the limitations of traditional single modification functions, resulting in modified basalt fibers with a dual-functional interface of conductive and magnetic response. This allows the application fields of basalt fibers to leap from traditional structural reinforcement materials to high-tech fields such as electromagnetic shielding, wave absorption, and intelligent sensing, greatly enhancing their application and economic value.

[0026] 2) In the basalt fiber modification method of this invention, when using polydopamine to surface-activate the basalt fiber, the basalt fiber is directly dispersed in a hydrochloric acid dopamine buffer solution for multiple impregnations without alkaline etching or coarsening, thus avoiding fiber damage and ensuring its strength as a reinforcement in PVDF composite materials. During the modification of the basalt fiber, silver plating is performed first, followed by modification with Fe3O4 nanoparticles. The core of this design sequence is to prioritize ensuring the conductive foundation of the material before adding wave absorption enhancement functions to achieve synergistic effects. First, a three-dimensional conductive network of silver particles is constructed on the insulating basalt fiber, laying the foundation for the entire material's high-efficiency conductivity and electromagnetic wave reflection capabilities. If this structure is subsequently placed on a discontinuous layer of iron oxide particles, its conductive pathway will be severely damaged, leading to a sharp reduction in shielding effectiveness. Secondly, Fe3O4 nanoparticles are used as the outermost layer, cleverly forming a multi-layered "absorption-reflection-absorption" mechanism with the inner silver nanoparticles. The incident electromagnetic wave first encounters the magnetite layer, which has magnetic loss characteristics, resulting in partial energy absorption. Furthermore, the improved surface impedance reduces the amount of electromagnetic wave penetrating the interior. Subsequently, the electromagnetic wave is strongly reflected by the conductive silver particle layer inside, and the reflected wave is absorbed a second time when it passes through the magnetite layer again. This structure not only significantly improves the overall electromagnetic shielding effectiveness but also effectively reduces secondary electromagnetic pollution by enhancing the absorption mechanism, achieving a perfect balance between reflection and absorption.

[0027] 3) The PVDF composite material prepared using the modified basalt fiber of this invention not only endows the composite material with excellent mechanical strength and heat resistance, but the rigid basalt fiber also acts as a stress amplifier in the soft PVDF matrix. When the material is subjected to external force, the stress will preferentially concentrate at the interface between the fiber and the matrix, causing the PVDF in this region to undergo greater deformation, thereby significantly improving its piezoelectric output (voltage / current). This not only enables the prepared PVDF composite material to achieve simultaneous improvement in piezoelectric and electromagnetic shielding performance, but also allows it to be directly used as a material for preparing structural components such as equipment shells, cabins, and automobiles, realizing the manufacturing of self-sensing and self-shielding intelligent structures.

[0028] PVDF is a flexible polymer piezoelectric material whose piezoelectric properties primarily originate from the β phase in its crystal structure. When β-phase PVDF undergoes mechanical deformation (tension or bending), the electric dipoles distributed within its crystal lattice undergo directional deflection, generating charges on the material surface and resulting in voltage / current output. Therefore, under the same external force, the greater and more non-uniform the strain (deformation) generated within the PVDF matrix, the higher its piezoelectric output. Modified fibers themselves do not generate piezoelectricity, but they create significant strain non-uniformity. Through their rigid and robust interfaces, they "focus" and "amplify" macroscopic mechanical forces into massive microscopic strains within the PVDF matrix, thereby greatly stimulating the piezoelectric potential of PVDF itself. Furthermore, the three-dimensional conductive network formed by Ag nanoparticles can serve as highly efficient internal electrodes, more effectively collecting the charges generated by the β phase and reducing charge loss during transmission.

[0029] (4) The PVDF composite material preparation method of the present invention uses modified basalt fiber mixed with PVDF / DMF solution to achieve the process reform of "modification before composite". This firmly anchors functional nanomaterials (Ag nanoparticles and Fe3O4 nanoparticles) on the fiber surface, instead of directly blending them with PVDF. This effectively solves the problem of nanoparticle failure due to agglomeration and avoids the damage of magnetic particles to the polarization process of PVDF, ensuring the full utilization of the functions of each component. Furthermore, the modified basalt fiber can not only form good interfacial adhesion with PVDF / DMF and act as a reinforcement of the composite material, but also has dual functions of electrical conductivity and magnetic response. It not only does not sacrifice the piezoelectric properties of the material, but also improves the piezoelectric properties of the composite material while improving the electromagnetic shielding performance of the PVDF composite material.

[0030] (5) The method for preparing PVDF composite material of the present invention uses basalt fiber modified with silver nanoparticles / Fe3O4 as a skeleton. Through modification treatment, Ag nanoparticles with high conductivity and Fe3O4 with paramagnetism are combined together through the basalt fiber as a carrier. In a directional magnetic field, BF@PDA@Ag@Fe3O4 causes the prepared composite fiber skeleton to be oriented through the paramagnetism of Fe3O4; while BF@PDA@Ag interlocks the oriented fibers, forming a more efficient and continuous conductive path (provided by Ag nanoparticles) in a specific direction, which greatly improves the electromagnetic shielding effectiveness. Simultaneously applied polarized electric field activates the piezoelectric phase function of PVDF. When the material is under pressure, the oriented basalt fibers become concentrated stress transfer points, and the stress is highly concentrated on the PVDF matrix around the fibers, causing greater deformation in this area. This excites a piezoelectric output signal that is much higher than that of disordered composite materials, achieving unexpected results. As a new type of PVDF composite material, it lays the foundation for designing intelligent sensors with orientation recognition capabilities, and has good application prospects and economic value. Attached Figure Description

[0031] Figure 1 These are microscopic images of the unmodified basalt fiber (BF) used in Example 1 of this invention.

[0032] Figure 2 These are microscopic images of the BF@PDA modified fibers prepared in Example 1 of this invention.

[0033] Figure 3 These are microscopic images of the BF@PDA@Ag modified fibers prepared in Example 1 of this invention.

[0034] Figure 4 These are microscopic images of the BF@PDA@Ag@Fe3O4 modified fibers prepared in Example 1 of this invention.

[0035] Figure 5 The microscopic detection results of the oriented PVDF composite material prepared by the synergistic modification of silver nanoparticles and iron oxide basalt fibers in Example 2 of this invention;

[0036] Figure 6 The microscopic detection results are shown for the oriented PVDF composite material prepared by the synergistic modification of silver nanoparticles and iron tetroxide with basalt fibers in Comparative Example 4 of this invention. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with embodiments. The basalt fiber used in the following embodiments was purchased from Sichuan Fiberglass Group Co., Ltd., model 502-P1, with a single fiber diameter of 12.7 μm, an average length of 6 mm, and a linear density of 200 tex. Its microstructure is as follows... Figure 1 As shown; all other reagents not provided for reference are commercially available reagents; methods not described in detail in the examples are conventional and well-known experimental methods.

[0038] Example 1

[0039] This embodiment describes the preparation of a basalt fiber synergistically modified with silver nanoparticles and iron oxide, comprising the following steps:

[0040] 1) Preparation of BF@PDA: First, dissolve 0.4g Tris in 200mL of deionized water, and then use 0.5mol·L⁻¹ water. -1 The pH of the solution was adjusted to 8.5 with HCl, and then 0.4 g of dopamine hydrochloride was added to form a dopamine buffer solution. 5 g of washed and dried basalt fiber was added to the dopamine buffer solution and reacted for 24 h. BF was then separated by filtration at room temperature, washed with deionized water, and dried. The washed and dried BF was then added back to the dopamine buffer solution, and this process was repeated three times. Finally, the fiber was vacuum dried at 40 °C for 6 h to obtain a polydopamine-modified basalt fiber sample, named BF@PDA, whose microstructure is shown below. Figure 2 As shown;

[0041] 2) Preparation of BF@PDA@Ag: First, prepare a silver ammonia solution. Add 1g of AgNO3 to 50ml of deionized water, and add ~2.5% dilute ammonia solution dropwise to the AgNO3 solution while stirring continuously; a brown precipitate first appears, then disappears, at which point the addition is stopped to obtain a silver ammonia solution. Then, perform a silver mirror reaction. Disperse 1g of the modified BF@PDA from step 1) in 200ml of anhydrous ethanol, and add 4ml of formaldehyde solution, while adding a small amount of sodium hydroxide to adjust the pH to weakly alkaline (pH approximately 9). Then add the prepared silver ammonia solution, and react the mixture in a water bath at 40℃ for 15min while stirring slowly (stirring speed 500 rpm). Finally, let the silver-plated product stand for 2h to remove the upper solvent, then add deionized water, repeat the washing process 3 times, and vacuum dry at 40℃ for 6h to obtain a basalt fiber sample modified with Ag nanoparticles, named BF@PDA@Ag, whose microstructure is as follows. Figure 3 As shown.

[0042] 3) Preparation of BF@PDA@Ag@Fe3O4: Fe3O4 nanoparticles were decorated on the fiber surface using a one-pot simplified co-precipitation method. Polyethyleneimine (PEI) solution was selected as the modification solution system. Through PEI modification, the BF@PDA@Ag surface was transformed from a state unfavorable to iron ion adsorption into a positively charged, amino-rich viscous surface. This new surface can efficiently capture and fix the Fe3O4 precursor (iron ions) through electrostatic attraction and coordination, laying a solid foundation for the successful preparation of BF@PDA@Ag@Fe3O4 in the next step. Specifically, 0.2g of PEI (molecular weight of 10,000-70,000 g / mol) was first dissolved in water to form a PEI solution with a concentration of 2mg / mL. 0.2g of BF@PDA@Ag prepared in step 2) was dispersed in the prepared PEI solution and sonicated for 60min to ensure uniform dispersion. Then, the reaction was stirred at 500rpm for 12h at room temperature. During the process, 0.1 g of FeCl2·4H2O was added to 50 mL of deionized water, and 0.2 g of FeCl3·6H2O was added to 100 mL of deionized water to prepare solutions with a concentration of 0.002 g / mL. After BF@PDA@Ag reacted in PEI solution for 12 h, the prepared FeCl2·4H2O and FeCl3·6H2O solutions were added to the suspension solution, and the reaction was continued with stirring (500 rpm) for 30 min. Then, NH3·H2O was added to adjust the pH to between 11 and 12, and the suspension was stirred at 50 °C for another 30 min to co-precipitate, with the stirring speed remaining constant. Finally, the dark precipitate was separated by centrifugation, washed three times with deionized water and ethanol, and then vacuum dried at 40 °C for 6 h to obtain basalt fibers synergistically modified with silver nanoparticles / Fe3O4, named BF@PDA@Ag@Fe3O4, whose microstructure is as follows. Figure 4 As shown.

[0043] Example 2

[0044] This embodiment describes the preparation of an oriented PVDF composite material, including the following steps:

[0045] A) Solution blending: First, prepare 1000 mL of a 10 wt% PVDF / DMF solution and magnetically stir at 400 rpm until a transparent and homogeneous solution is formed. Divide the solution into two equal portions. Add the BF@PDA@Ag (10 wt% of PVDF mass) prepared in Example 1 to one portion of the PVDF / DMF solution and ultrasonically disperse at 60°C for 2 h to obtain suspension A. Simultaneously, add the BF@PDA@Ag@Fe3O4 (10 wt% of PVDF mass) prepared in Example 1 to the other portion of the PVDF / DMF solution and ultrasonically disperse at 60°C for 2 h to obtain suspension B. Then, mix suspension A and suspension B to obtain the blended suspension required for preparing the PVDF composite material (blending ratio 1:1).

[0046] B) Magnetic field orientation molding: The blend suspension obtained in step A) is placed in a 1.0T vertical magnetic field to induce the oriented alignment of BF@PDA@Ag@Fe3O4. Simultaneously, a 40kV / mm polarization electric field is applied to activate the piezoelectric phase function of PVDF. After treatment for 30 minutes, the mixture is dried at 60℃ to obtain the oriented PVDF composite material, denoted as the composite material of this invention. Its microstructure is as follows: Figure 5 As shown.

[0047] Comparative Example 1: Preparation of PVDF Composites from Unmodified BF

[0048] This embodiment describes the preparation of a PVDF composite material. The preparation method is as follows: First, a 10wt% PVDF / DMF solution is prepared and magnetically stirred at 400 rpm until a transparent and homogeneous solution is formed. Then, basalt fibers with a mass of 20% PVDF are added to the PVDF / DMF solution and ultrasonically dispersed at 60°C for 2 hours to obtain a suspension. The suspension is then placed in a 1.0T vertical magnetic field and a 40kV / mm polarization electric field is applied simultaneously. Finally, the suspension is dried at 60°C to obtain the PVDF material, which is designated as Comparative Composite 1.

[0049] Comparative Example 2: Only add BF@PDA@Ag

[0050] This embodiment describes the preparation of an Ag nanoparticle-modified basalt fiber PVDF composite material. The preparation method is as follows: First, a 10wt% PVDF / DMF solution is prepared and magnetically stirred at 400 rpm until a transparent and homogeneous solution is formed. Then, BF@PDA@Ag (20% of the PVDF mass) prepared in Example 1 is added to the PVDF / DMF solution and ultrasonically dispersed at 60℃ for 2 hours to obtain a suspension. The suspension is then placed in a 1.0T vertical magnetic field and a 40kV / mm polarization electric field is applied simultaneously. Finally, it is dried at 60℃ to obtain the PVDF material, which is designated as Comparative Composite 2.

[0051] Comparative Example 3: Only BF@PDA@Ag@Fe3O4 was added.

[0052] This embodiment describes the preparation of a composite material of Ag nanoparticles and iron tetroxide modified basalt fiber PVDF. The preparation method is as follows: First, a 10wt% PVDF / DMF solution is prepared and magnetically stirred at 400 rpm until a transparent and homogeneous solution is formed. Then, BF@PDA@Ag@Fe3O4 (20% of the PVDF mass) prepared in Example 1 is added to the PVDF / DMF solution and ultrasonically dispersed at 60℃ for 2 hours to obtain a suspension. The suspension is then placed in a 1.0T vertical magnetic field and a 40kV / mm polarization electric field is applied simultaneously. Finally, it is dried at 60℃ to obtain the PVDF material, which is designated as Comparative Composite 3.

[0053] Comparative Example 4: Orientation without applying a magnetic field

[0054] This embodiment also describes the preparation of a PVDF composite material, using the same method as in Example 2, but without the magnetic field orientation molding step. Specifically, suspension A and suspension B are mixed and directly dried at 60°C to obtain an oriented PVDF composite material, designated as control composite 4. Its microstructure is as follows: Figure 6 As shown.

[0055] Example 1

[0056] This example examines the piezoelectric properties (PE) and electromagnetic shielding properties (SE) of the composite material 1 of the present invention prepared in Example 2 and the comparative composite materials 1-4 prepared in Comparative Examples 1-4.

[0057] In this embodiment, the electrical conductivity, electromagnetic shielding, tensile properties, open-circuit voltage, and short-circuit current of each PVDF composite material are used as evaluation criteria.

[0058] Test method:

[0059] (1) Electrical conductivity

[0060] Each sample (sheet-shaped sample 10mm*20mm*2mm, prepared by hot pressing at 190℃ for 5 minutes and 20 MPa) was tested using a DC resistance meter at room temperature. To minimize error, each sample was tested 10 times, and the maximum and minimum values ​​were removed, with the average of the remaining data taken. The formulas for calculating volume resistivity and conductivity are as follows:

[0061] (1-1)

[0062] (1-2);

[0063] Where ρ is the volume resistivity of the material; R is the measured resistance of the sample; h is the width of the sample cross-section; d is the thickness of the sample cross-section; L is the distance between the two electrodes; and σ is the conductivity.

[0064] (2) Electromagnetic shielding performance

[0065] According to ASTM ES7-83 standard, EMI shielding performance was tested using a vector network analyzer (R&S ZNB20) in the frequency range of 8.2–12.4 GHz (X-band) via a coaxial method. The sample size was 20 mm × 20 mm × 2 mm (also made from hot-pressed sheet material, which can then be cut). Scattering parameters (S11 and S21), also known as S-parameters, can be obtained directly from the vector network analyzer. The power coefficients of the absorption coefficient (A), reflection coefficient (R), and transmission coefficient (T), as well as the total SE (SET), absorbed SE (SEA), and reflected SE (SER) values, were calculated using the following formulas:

[0066] (2-1)

[0067] (2-2)

[0068] (2-3);

[0069] (1-R) ​​is defined as the signal strength of the incident electromagnetic wave after reflection into the shielding material.

[0070] The effective absorption rate Aeff is:

[0071] (2-4);

[0072] Based on the definition of shielding effectiveness, the reflection shielding effectiveness and absorption shielding effectiveness can be obtained as follows:

[0073] (2-5)

[0074] (2-6);

[0075] When SEA > 10 dB, multiple reflection losses can be ignored; therefore, the total shielding effectiveness can be expressed as:

[0076] (2-7);

[0077] (3) Tensile properties

[0078] According to the national standard GB / T 528-2009, tensile strength was tested at room temperature.

[0079] (4) Open-circuit voltage and short-circuit current

[0080] First, the samples were cut into 5 cm × 5 cm square specimens and firmly adhered to a rigid acrylic (PMMA) substrate to prevent bending deformation during testing. A PMMA plate of the same material was selected as the moving layer, and the two friction layers were connected by a polyimide film to precisely control the testing height and ensure structural stability. During device assembly, copper wires were connected to the two electrode layers, with the other end connected to the positive probe of an electrometer to monitor the electrical output in real time. Finally, using a vertical-mode triboelectric nanogenerator testing platform, the output performance of the material was systematically evaluated under different operating conditions (operating frequency: 1–4 Hz; contact pressure: 4–16 kPa) to assess its energy harvesting efficiency and stability. The test results are shown in Table 1.

[0081] Table 1. Test results of piezoelectric properties and electromagnetic shielding properties of various PVDF composite materials

[0082]

[0083] As shown in Table 1, the unmodified BF-based comparative composite 1 has virtually no shielding performance and poor piezoelectric properties. Furthermore, due to the random arrangement of internal fibers, its improvement on the mechanical properties of PVDF is weak. Comparative composites 2 and 3, which incorporate BF@PDA@Ag or BF@PDA@Ag@Fe3O4 modified fibers alone, exhibit improved electromagnetic shielding effectiveness compared to the unmodified BF-based composite 1. However, the electromagnetic shielding effect of BF@PDA@Ag@Fe3O4 modified fibers alone is significantly better than that of BF@PDA@Ag modified fibers alone. This indicates that grafting Ag onto the BF surface is to transform BF from an insulating material into a conductive material, and the modification of Fe3O4 is primarily to obtain a highly efficient electromagnetic shielding material to prevent secondary electromagnetic pollution. Therefore, the addition of BF@PDA@Ag@Fe3O4 modified fibers can better absorb electromagnetic waves from the composite surface, thus improving the material's electromagnetic shielding effectiveness. However, adding BF@PDA@Ag@Fe3O4 alone is not as effective as simultaneously adding both BF@PDA@Ag modified fibers and BF@PDA@Ag@Fe3O4 modified fibers in improving electromagnetic shielding performance (the composite material of this invention). Furthermore, the composite material of this invention also shows significant improvements in conductivity, open-circuit voltage, and short-circuit current compared to comparative composites 2 and 3. This indicates that the simultaneous addition of both BF@PDA@Ag modified fibers and BF@PDA@Ag@Fe3O4 modified fibers synergistically enhances the electromagnetic shielding performance of the composite material while also strengthening its piezoelectric properties, achieving a "win-win" situation. Compared to comparative composite 4, because no magnetic field was applied for orientation, the BF@PDA@Ag@Fe3O4 modified fibers could not be oriented and remained in a random arrangement. Therefore, the mechanical properties of comparative composite 4 are relatively weak, while the mechanical properties of the oriented composite material of this invention are superior. Furthermore, comparing the test results of the composite material of this invention with those of comparative composite material 4, it can be seen that applying magnetic field orientation and high-voltage polarization are necessary means to simultaneously improve the electromagnetic shielding effectiveness and piezoelectric properties of the composite material, and can also further improve the tensile strength of the composite material. Therefore, the composite material of this invention has excellent comprehensive properties such as mechanical properties, electromagnetic shielding properties, and piezoelectric properties.

[0084] Example 2

[0085] This embodiment investigates the effects of the amount of basalt fiber synergistically modified with silver nanoparticles / Fe3O4 and the ratio of BF@PDA@Ag and BF@PDA@Ag@Fe3O4(g) on ​​the properties of the prepared PVDF composite material.

[0086] This embodiment is based on the preparation method of Example 2, except for the amount of silver nanoparticles / Fe3O4 synergistic modified basalt fibers and the ratio of BF@PDA@Ag and BF@PDA@Ag@Fe3O4(g). All other components and preparation methods are the same as in Example 2. In this embodiment, the electrical conductivity, electromagnetic shielding, tensile properties, open-circuit voltage, and short-circuit current of each PVDF composite material were used as evaluation criteria. The results are shown in Table 2.

[0087] Table 2. Modified basalt fiber content and properties in PVDF composites

[0088]

[0089] Table 2 shows that the electrical conductivity, electromagnetic shielding effectiveness, mechanical properties, and piezoelectric properties of the composite material all improve with increasing amounts of BF@PDA@Ag modified fibers and / or BF@PDA@Ag@Fe3O4 modified fibers. Furthermore, the absorption coefficient A of the material increases with increasing amounts of BF@PDA@Ag@Fe3O4 modified fibers, indicating that less electromagnetic wave is reflected from its surface, and thus, the shielding material exhibits better absorption performance. However, with the increase of modified fiber content, the tensile strength of the composite material shows a trend of first increasing and then decreasing, reaching its highest point when the total content of BF@PDA@Ag modified fiber and / or BF@PDA@Ag@Fe3O4 modified fiber reaches 20%. This is because excessive filler addition leads to fiber aggregation, reducing mechanical properties. Therefore, it is recommended that the total content of BF@PDA@Ag modified fiber and / or BF@PDA@Ag@Fe3O4 modified fiber in PVDF composite materials not exceed 35% of the PVDF weight, and the addition amount of BF@PDA@Ag and BF@PDA@Ag@Fe3O4 should be controlled between 5% and 20 wt% of the PVDF mass. Overall, formulation 6 (Example 2) has superior comprehensive performance, namely mechanical properties, high-absorption electromagnetic shielding, and piezoelectric properties.

[0090] In summary, this invention breaks through the limitations of traditional single-function modification, pioneering the synergistic modification of basalt fibers. By simultaneously modifying the surface of basalt fibers with Ag nanoparticles and Fe3O4 nanoparticles, the modified basalt fibers not only possess excellent conductivity but also exhibit a dual-functional interface of conductive and magnetic response. This allows basalt fibers to leap from traditional structural reinforcement materials to high-tech fields such as electromagnetic shielding, wave absorption, and intelligent sensing, significantly enhancing their application and economic value. In this invention's basalt fiber modification method, when surface-activating basalt fibers with polydopamine, the basalt fibers are directly dispersed in a dopamine hydrochloride buffer solution for multiple impregnations without alkaline etching or roughening, avoiding fiber damage and ensuring its strength as a reinforcement in PVDF composites. During basalt fiber modification, silver plating is performed before Fe3O4 nanoparticle modification. The core of this design sequence is to prioritize ensuring the material's conductive foundation before adding wave absorption enhancement functions to achieve synergistic effects. The PVDF composite material prepared using the modified basalt fiber of this invention not only endows the composite material with excellent mechanical strength and heat resistance, but the rigid basalt fiber also acts as a stress amplifier within the soft PVDF matrix. When the material is subjected to external force, the stress preferentially concentrates at the fiber-matrix interface, causing greater deformation of the PVDF in this region, thereby significantly improving its piezoelectric output (voltage / current). This not only enables the prepared PVDF composite material to simultaneously improve piezoelectric and electromagnetic shielding properties, but also allows it to be directly used as a material for manufacturing structural components such as equipment shells, cabins, and automobiles, realizing the manufacturing of self-sensing and self-shielding intelligent structures, with good application prospects and economic value.

[0091] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered exemplary and not restrictive in all respects. Furthermore, it should be understood that although this specification describes embodiments, it does not encompass only one technical solution. This descriptive method is merely for clarity, and those skilled in the art should consider the specification as a whole. The technical solutions in the embodiments can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A basalt fiber synergistically modified with silver nanoparticles and ferroferric oxide, characterized in that: The modified basalt fiber comprises a basalt fiber body and Ag nanoparticles and Fe3O4 nanoparticles decorated on the surface of the basalt fiber body; The amount of the decorated Ag nanoparticles is 1.5wt% to 3.5wt% of the mass of the basalt fiber body, and the amount of the decorated Fe3O4 nanoparticles is 3wt% to 7wt% of the mass of the basalt fiber body; and the mass ratio of the Ag nanoparticles to the Fe3O4 nanoparticles is 1 to 3:1 to 3. The preparation method of the modified basalt fiber comprises the following steps: 1) preparing BF@PDA: dispersing the cleaned and dried basalt fiber in a dopamine buffer solution, and reacting for 20 to 30 hours; separating the basalt fiber sample by suction filtration at room temperature, and cleaning and drying; then repeating the above process for 2 to 3 times; finally drying to obtain a polydopamine modified basalt fiber sample, which is named as BF@PDA; 2) preparing BF@PDA@Ag: dispersing the BF@PDA prepared in step 1) in anhydrous ethanol, adding a certain amount of formaldehyde solution, adjusting the pH value to 8.5 to 9.5, then adding a silver amine solution, and stirring and reacting for 10 to 20 minutes under water bath heating; then standing and precipitating, removing the solvent, and drying after multiple washing to obtain an Ag nanoparticle decorated basalt fiber sample, which is named as BF@PDA@Ag; 3) preparing BF@PDA@Ag@Fe3O4: adding the BF@PDA@Ag prepared in step 2) into a PEI solution, uniformly dispersing by ultrasonic, and stirring and reacting for 10 to 15 hours at room temperature; then adding FeCl2·4H2O solution and FeCl3·6H2O solution, continuing to stir and react for 20 to 40 minutes to form a suspension; then adjusting the pH value to 11 to 12 with ammonia water, and continuing to stir and precipitate the suspension at 40 to 60°C for 20 to 40 minutes; finally centrifuging, washing the precipitate with deionized water and ethanol for several times, and drying to obtain an Ag nanoparticle and Fe3O4 nanoparticle co-decorated basalt fiber sample, which is named as BF@PDA@Ag@Fe3O4, that is, a silver nanoparticle / ferroferric oxide synergistically modified basalt fiber.

2. Modified basalt fiber according to claim 1, characterized in that: In step 1), The dopamine buffer solution is a hydrochloric acid dopamine Tris buffer solution with a concentration of 0.001 to 0.003 g / mL; The basalt fiber is dispersed in the dopamine buffer solution at a ratio of 0.02 to 0.03 g / mL.

3. The modified basalt fiber according to claim 1, characterized in that: In step 2), The BF@PDA is dispersed in anhydrous ethanol at a ratio of 0.005 to 0.02 g / mL; The added formaldehyde solution has a concentration of 0.1 to 0.5 mol / L, and the amount is 1 / 10 to 1 / 2 of the volume of the silver amine solution; The silver amine solution has a concentration of 0.05 to 0.2 mol / L; The water bath heating temperature is 35 to 45°C; The standing and precipitating time is 1.5 to 3 hours until the fiber is completely settled.

4. The modified basalt fiber according to claim 1, characterized in that: In step 3), The PEI solution has a concentration of 1 to 5 mg / mL; The BF@PDA@Ag is dispersed in the PEI solution at a concentration or ratio of 0.005 to 0.01 g / mL, and the dispersion time is 40 to 90 minutes. The concentration of the FeCl2*4H2O solution and the FeCl3*6H2O solution is 0.001-0.003 g / mL, and the volume ratio of the two is 1:

2.

5. An oriented PVDF composite material characterized by: The PVDF composite material contains basalt fibers modified by silver nanoparticles and basalt fibers modified by silver nanoparticles / magnetite in coordination; The basalt fibers modified by silver nanoparticles / magnetite in coordination include a basalt fiber body and Ag nanoparticles and Fe3O4 nanoparticles modified on the surface of the basalt fiber body; the amount of the modified Ag nanoparticles is 1.5-3.5 wt% of the mass of the basalt fiber body, the amount of the modified Fe3O4 nanoparticles is 3-7 wt% of the mass of the basalt fiber body, and the mass ratio of the Ag nanoparticles to the Fe3O4 nanoparticles is 1-3:1-3. In the PVDF composite material, the content of the basalt fibers modified by silver nanoparticles and the basalt fibers modified by silver nanoparticles / magnetite in coordination is 5-20 wt% of the mass of PVDF.

6. The oriented PVDF composite of claim 5, wherein: In the PVDF composite material, the total content of the basalt fibers modified by silver nanoparticles and the basalt fibers modified by silver nanoparticles / magnetite in coordination is 5-35 wt% of the mass of PVDF.

7. A method of preparing an oriented PVDF composite according to claim 5 or 6, characterized in that: The method comprises the following steps: A) solution blending: adding the modified basalt fibers BF@PDA@Ag modified only with Ag nanoparticles into a PVDF / DMF solution to obtain a suspension A; adding the modified basalt fibers BF@PDA@Ag@Fe3O4 modified with silver ions and Fe3O4 nanoparticles into a PVDF / DMF solution to obtain a suspension B; and mixing the suspension A and the suspension B to obtain a blending suspension required for preparing the PVDF composite material; B) magnetic field directional forming: placing the obtained blending suspension in a vertical magnetic field to induce directional arrangement of BF@PDA@Ag@Fe3O4, simultaneously applying a polarization electric field to activate piezoelectric properties, and then drying to obtain the oriented PVDF composite material.

8. The method of preparing an oriented PVDF composite of claim 7, wherein: In step A), The mass concentration of the PVDF / DMF solution is 8-12 wt%; The addition amount of BF@PDA@Ag in the suspension A and the addition amount of BF@PDA@Ag@Fe3O4 in the suspension B are both 5-20 wt% of the mass of PVDF; The blending ratio of the suspension A to the suspension B is 1:

1.

9. The method of preparing an oriented PVDF composite of claim 7, wherein: In step B), the strength of the vertical magnetic field in the magnetic field directional forming is 0.5-1.5 T, and the time for inducing directional arrangement is 35-45 min; the strength of the applied polarization electric field is 35-45 kV / mm.

Images