Preparation method and application of high-thermal-stability nanoscale magnetic conductive PA6 microspheres

Abstract

The invention discloses a preparation method and application of high-thermal-stability nanoscale magnetic conductive PA6 microspheres, and the preparation method comprises the following steps: introducing polypyrrole-coated magnetic particles into a caprolactam in-situ polymerization system in situ by adopting a reaction induced phase inversion method to prepare nanoscale PA6 microspheres with conductivity and magnetism; functionalized PA6 microspheres are uniformly dispersed in a PVDF electrostatic spinning film through an electrostatic spinning technology to serve as a middle layer, SiCw and AgNWs are deposited on the upper layer and the lower layer respectively through a vacuum-assisted suction filtration technology, and the prepared composite film has excellent electromagnetic shielding performance, mechanical performance and thermal stability and is suitable for large-scale production. The method is suitable for the fields of electronic equipment, electromagnetic shielding materials, high-performance composite materials and the like.

Description

Technical Field

[0001] The present invention relates to the field of high-performance composite films for electromagnetic shielding, and particularly relates to a preparation method and application of nano-scale magnetic conductive PA6 microspheres with high thermal stability. Background Art

[0002] Electromagnetic pollution has become increasingly serious with the popularization and application of modern electronic devices. Therefore, electromagnetic shielding materials have become a research hotspot. Although traditional metal shielding materials have significant effects, they are heavy and have poor flexibility, which do not meet the requirements of lightweight and flexibility for modern electronic devices. In recent years, polymer-based composite materials have become an important development direction for new electromagnetic shielding materials due to their excellent mechanical properties, low density, and good designability. However, how to improve the electromagnetic shielding efficiency and mechanical properties while ensuring the lightweight of the materials remains the focus and difficulty of current research. In most current studies on polymer-based electromagnetic shielding materials, fillers are usually used to construct a separated structure in the polymer matrix to form an effective conductive network, which is the basis for high electromagnetic shielding. However, this segregation structure causes the fillers to be distributed at the polymer micro-region interface, generating stress defects and reducing the mechanical strength of the materials. Therefore, there is an urgent need to develop an electromagnetic interference shielding material with high strength and high absorption rate to meet the requirements of industrial applications.

[0003] Magnetic metal micro-powders are a very important type of electromagnetic shielding materials, which mainly absorb and attenuate electromagnetic waves through mechanisms such as hysteresis loss, eddy current loss, and natural resonance loss. For magnetic materials with high magnetic permeability, absorption shielding plays a major role; for materials with relatively high conductivity, reflection shielding plays a major role. Polypyrrole, as a common conductive polymer, has the advantages of high conductivity, easy processing, and corrosion resistance. Therefore, to achieve multi-band high-efficiency shielding of shielding materials for low-frequency and high-frequency bands, compounding magnetic materials with conductive materials is an ideal method. PA6 microspheres have high strength, wear resistance, high thermal stability, and excellent anti-chemical properties. Introducing metal magnetic particles coated with polypyrrole into the in-situ polymerization process of caprolactam can prepare functional fillers with both magnetic, conductive, and high strength. Polyvinylidene fluoride (PVDF) has good mechanical properties, thermal stability, and chemical resistance. The PVDF film prepared by electrospinning technology can provide high strength and ductility, and can maintain its mechanical and electrical properties at high temperatures. Silicon carbide whiskers (SiCw), as a semiconductor material, are a type of dielectric wave-absorbing material with characteristics such as low density and high strength, and are easy to be used in lightweight, flexible, and thin-layer application materials. Silver nanowires (AgNWs) are a type of conductive nanomaterial that can increase the reflection electromagnetic shielding efficiency while improving the electrical conductivity of the material.

[0004] Patent CN117363010A discloses a polymer electromagnetic shielding material with high temperature resistance. By in-situ growing polypyrrole on the surface of magnetic metal powder, the purpose of electromagnetic shielding is achieved. However, its material structure is single, without structural design, and the shielding mechanism is mainly reflection-based, which is likely to cause secondary pollution to the environment. Patent CN118110028A discloses a flexible high-absorption electromagnetic shielding composite film based on a multi-layer structure and its preparation method. Due to its "absorption-reflection-reabsorption" mechanism, the composite film has high-absorption electromagnetic shielding and good absorption coefficient. However, the low melting point of TPU and its long-term service temperature within 80 °C limit its application in high-temperature environments. The present invention uses high-temperature-resistant PVDF as the matrix, and through reasonable material design and structural design, a composite material with high-temperature use, better absorption performance for unidirectional incidence is obtained. The prepared composite film has excellent electromagnetic shielding performance, mechanical properties and thermal stability, and is suitable for fields such as electronic devices, electromagnetic shielding materials and high-performance composite materials. Summary of the Invention

[0005] The present invention aims to provide a preparation method and application of a nano-sized magnetic conductive PA6 microsphere with high thermal stability, overcome the deficiencies in the prior art, and provide a lightweight, efficient and flexible electromagnetic shielding material. By compounding magnetic metal particles coated with polypyrrole with nano-sized PA6 microspheres, and combining with an asymmetric multi-layer structure prepared from a PVDF electrospun membrane, AgNWs and SiCw, a composite film with excellent electromagnetic shielding performance and mechanical strength is prepared.

[0006] The technical solution of the present invention is as follows:

[0007] A preparation method and application of a nano-sized magnetic conductive PA6 microsphere with high thermal stability, including the following process: magnetic metal particles coated with polypyrrole are used as the core, and PA6 microspheres are used as the shell. Through in-situ polymerization, nano-sized functionalized PA6 microspheres with a core-shell structure are formed. The magnetoelectric microspheres are uniformly dispersed in the PVDF electrospun membrane by electrospinning technology, and SiCw and AgNWs are deposited on the upper and lower layers of the Ni@PPY@PA6-PVDF composite membrane through a vacuum-assisted device to form a composite film with high thermal stability, high mechanical properties and high electromagnetic shielding.

[0008] The present invention uses the reaction-induced phase inversion method to in-situ introduce magnetic particles coated with polypyrrole into the ε-caprolactam in-situ polymerization system to prepare nano-sized PA6 microspheres with both conductivity and magnetism. The functionalized PA6 microspheres are uniformly dispersed in the PVDF electrospun membrane by electrospinning technology as the intermediate layer. SiCw and AgNWs are respectively deposited on the upper and lower layers through vacuum-assisted filtration technology. The prepared composite film has excellent electromagnetic shielding performance, mechanical properties and thermal stability, and is suitable for fields such as electronic devices, electromagnetic shielding materials and high-performance composite materials.

[0009] Preparation method and application of a nano-sized magnetic conductive PA6 microsphere with high thermal stability. The preparation method includes the following steps:

[0010] (1)Disperse magnetic metal particles and pyrrole monomers in an ethanol aqueous solution to prepare a mixed solution. Then add ammonium persulfate to the mixed solution, and under the condition of ice bath at 0 °C, mechanically stir and react for 12 - 20 h. After that, filter, wash, and vacuum dry the obtained product to obtain a composite filler Ni@PPY with magnetic metal particles coated with polypyrrole. The magnetic metal particles are one or more of hydroxyl Fe powder, hydroxyl Co powder, and hydroxyl Ni powder.

[0011] (2)Ultrasonically disperse the composite filler Ni@PPY obtained in step (1) in caprolactam monomer to obtain a caprolactam / composite filler suspension; in the presence of vacuum or protective atmosphere, add polyethylene glycol to the caprolactam / composite filler suspension, and keep stirring at 120 - 140 °C for 2 - 4 h to obtain a mixed solution; the mass ratio of Ni@PPY, polyethylene glycol, and caprolactam is 1 - 8:15 - 20:75 - 85. The protective atmosphere is at least one of hydrogen, argon, methane, and nitrogen.

[0012] (3)Add an initiator to the mixed solution obtained in step (2), and then remove water under vacuum at 130 - 160 °C; the initiator is an alkali metal hydride, alkali metal hydroxide, alkali metal alkoxide, or alkali metal carbonate; the addition amount of the initiator is 0.1 - 1 wt% of the total mass of Ni@PPY, polyethylene glycol, and caprolactam.

[0013] (4)Add an activator, and caprolactam undergoes anionic ring-opening polymerization. Polymerize at 150 - 200 °C for 20 - 60 min, and the experimental system undergoes an inversion to obtain a Ni@PPY@PA6 / PEG alloy; the activator is an isocyanate, acyl chloride, acid anhydride, or acyl caprolactam; the addition amount of the activator is 0.1 - 1 wt% of the total mass of Ni@PPY, polyethylene glycol, and caprolactam.

[0014] (5)High-speed crush and wash the PA6 alloy obtained in step (4) to obtain a nano-sized magnetic and electrical functional Ni@PPY@PA6 microsphere with high thermal stability; the washing time is 24 - 48 h, and the size of the nano-sized magnetic and electrical functional Ni@PPY@PA6 microsphere is 200 - 500 nm.

[0015] (6) Dissolve PVDF powder in a solvent, and after magnetic stirring for 1 h, obtain a PVDF electrospinning solution. Add a certain amount of the Ni@PPY@PA6 microspheres obtained in step (5) to the PVDF electrospinning solution, and after ultrasonic dispersion, obtain a Ni@PPY@PA6-PVDF electrospinning solution. Using fixed electrospinning parameters, prepare a Ni@PPY@PA6-PVDF electrospinning membrane, and reserve it after vacuum drying;

[0016] (7) Add AgNWs to a solvent, stir for 0.5 - 1 h, to obtain an AgNWs dispersion liquid, and the mass fraction of AgNWs in the AgNWs dispersion liquid is 0.5 - 3%;

[0017] (8) Add SiCw to a solvent, perform ultrasonic treatment for 0.5 - 1 h, to obtain a SiCw dispersion liquid, and the mass fraction of SiCw in the SiCw dispersion liquid is 0.5 - 3%;

[0018] The solvent used in steps (7) and (8) is one of water and ethanol.

[0019] (9) Place the Ni@PPY@PA6-PVDF electrospinning membrane prepared in step (6) on a vacuum filtration device, pour the AgNWs dispersion liquid in step (7), and through suction filtration, make the AgNWs deposit and adhere to the Ni@PPY@PA6-PVDF spinning membrane. Deposit and adhere SiCw on the other side of the Ni@PPY@PA6-PVDF spinning membrane in the same way, and after drying, obtain an AgNWs / Ni@PPY@PA6-PVDF / SiCw composite film with an asymmetric multi-layer structure; the suction filtration time is 10 - 30 min.

[0020] Further preferably, a preparation method and application of a nano-level magnetic conductive PA6 microsphere with high thermal stability, the preparation method includes the following steps:

[0021] (1) Disperse 10 g of magnetic metal particles and 10 - 30 mL of pyrrole monomer in 20 - 30 mL of an ethanol aqueous solution (volume ratio 1:1) to prepare a mixed solution, then add 4 - 6 g of ammonium persulfate to the mixed solution, and under the condition of an ice bath at 0 °C, mechanically stir and react for 12 - 20 h, then filter, wash the obtained product, and vacuum dry it at 50 - 60 °C to obtain a polypyrrole-coated magnetic metal particle composite filler Ni@PPY.

[0022] (2) Ultrasonically disperse the composite filler obtained in step (1) in caprolactam monomer to obtain a caprolactam / composite filler suspension; in the presence of vacuum or protective atmosphere, add polyethylene glycol to the caprolactam / composite filler suspension, keep stirring at 120 - 140 °C for 2 - 4 h to obtain a mixed solution; add an initiator to the mixed solution, then remove water under vacuum at 130 - 160 °C for 20 - 40 min, add an activator, and polymerize at 150 - 200 °C for 20 - 60 min. The experimental system undergoes an inverse transition to obtain Ni@PPY@PA6 / PEG alloy. After crushing the alloy, wash it with water for 24 - 48 h, then vacuum filter and dry to obtain nanoscale magnetoelectric Ni@PPY@PA6 microspheres.

[0023] (3) Dissolve 3 g of PVDF powder in a mixed solvent of 30 mL of N,N - dimethylformamide (DMF) and acetone (volume ratio 2:1), stir magnetically for 1 h to obtain a PVDF electrospinning solution. Add a certain amount of the Ni@PPY@PA6 microspheres obtained in step (2) to the PVDF electrospinning solution, ultrasonically disperse it to obtain a Ni@PPY@PA6 - PVDF electrospinning solution, and use fixed electrospinning parameters to prepare a Ni@PPY@PA6 - PVDF electrospinning membrane, which is dried in vacuum for later use;

[0024] (4) Place the Ni@PPY@PA6 - PVDF electrospinning membrane prepared in step (3) on a vacuum filtration device, pour in the AgNWs aqueous dispersion, and deposit AgNWs on the Ni@PPY@PA6 - PVDF electrospinning membrane by filtration. Deposit SiCw on the other side of the Ni@PPY@PA6 - PVDF electrospinning membrane in the same way, and dry to obtain an asymmetric multi - layer structured AgNWs / Ni@PPY@PA6 - PVDF / SiCw composite film;

[0025] Further, the magnetic metal particles include one or more of nickel carbonyl powder, iron carbonyl powder, and cobalt carbonyl powder

[0026] Further, the dosages of the magnetic metal particles, polyethylene glycol, and caprolactam are 1 - 8%, 15 - 20%, and 75 - 85% of the total mass of the magnetic metal particles, polyethylene glycol, and caprolactam, respectively.

[0027] Further, the initiator is an alkali metal hydride, alkali metal hydroxide, alkali metal alkoxide, or alkali metal carbonate, preferably sodium hydroxide.

[0028] Further, the activator is an isocyanate, acyl chloride, acid anhydride, or acyl caprolactam, preferably toluene diisocyanate.

[0029] Further, the addition amount of the initiator is 0.1 - 1 wt% of the total mass of caprolactam, polyethylene glycol and polystyrene-block copolymer;

[0030] Further, the addition amount of the activator is 0.1 - 1 wt% of the total mass of caprolactam, polyethylene glycol and polystyrene-block copolymer.

[0031] Further, the protective atmosphere is at least one of hydrogen, argon, methane and nitrogen.

[0032] Further, the solvent is one of DMF (N,N-dimethylformamide), acetone, and a mixed solvent of DMF (N,N-dimethylformamide) and acetone.

[0033] Further, the electrospinning parameters are: spinning voltage 8 - 15 kV, receiving distance 10 - 15 cm, collector speed 150 - 300 rpm, spinning speed 0.5 - 2.0 mL / h, spinning time 4 - 6 h, spinning environment temperature 15 - 30 °C, relative humidity 25 - 50%.

[0034] Compared with the prior art, the present invention has the following advantages:

[0035] 1. Method innovation: The present invention combines the anion reaction-induced phase inversion method and electrospinning technology to prepare a composite film with high thermal stability, high electromagnetic absorption shielding and excellent mechanical properties. The anion reaction-induced phase inversion method is used to introduce metal magnetic particles coated with polypyrrole into the in-situ polymerization system of caprolactam monomer. In the presence of polyethylene glycol, the caprolactam monomer undergoes phase inversion to obtain uniformly sized nano-PA6 microspheres with both magnetic and conductive functions, namely Ni@PPY@PA6 microspheres. The improvement of the overall performance of the polymer-based composite film depends on the dispersion state and synergistic effect of the filler in the polymer matrix. The problem of uneven dispersion of Ni@PPY@PA6 microspheres is solved by electrospinning technology. The uniformly dispersed Ni@PPY@PA6 microspheres generate rich heterogeneous interfaces inside the composite material, enhancing the multiple reflections of electromagnetic waves inside the material. Combining the high strength, magnetic and conductive properties of Ni@PPY@PA6 microspheres themselves, the synergistic effect not only enhances the mechanical properties of the composite film but also improves the electromagnetic wave absorption efficiency of the composite film.

[0036] 2. Structural innovation: The asymmetric multilayer structure designed by the present invention, which combines the electrospinning membrane with PVDF as the matrix, silver nanowires (AgNWs) and silicon carbide fibers (SiCw), achieves a more efficient electromagnetic shielding effect through the synergistic effect of the multilayer structure and nanomaterials, while maintaining excellent mechanical strength to meet the requirements of high-performance composite materials. The SiCw layer and a layer of AgNWs are vacuum-assisted filtered on the upper and lower surfaces of the Ni@PPY@PA6-PVDF film material, respectively. The SiCw gives the composite material super strong electromagnetic wave absorption performance, and the AgNWs give the composite material electromagnetic wave reflection performance. Through reasonable asymmetric structural design, the electromagnetic shielding mechanism of "absorption-reflection-reabsorption" is achieved, and finally a high-absorption electromagnetic shielding composite film is obtained.

[0037] 3. Material innovation: The present invention uses PVDF with high temperature resistance and excellent piezoelectric properties as the matrix, combines magnetoelectric Ni@PPY@PA6 microspheres with PVDF spinning membrane, further improves the impedance matching of PVDF spinning membrane, and gives the composite film good high temperature resistance and better electromagnetic wave absorption performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 Schematic diagram of the structure of SiCw / Ni@PPY@PA6-PVDF / AgNWs electromagnetic shielding film;

[0039] Figure 2 Schematic diagram of the electromagnetic shielding effect of SiCw / Ni@PPY@PA6-PVDF / AgNWs electromagnetic shielding film;

[0040] Figure 3 The SEM morphology and particle size distribution diagram of Ni@PPY@PA6 composite microspheres in the embodiment of the present invention;

[0041] Figure 4 This is the XRD crystal structure characterization diagram of Ni@PPY@PA6 composite microspheres in the embodiment of the present invention;

[0042] Figure 5 This is the TGA comparison chart of PA6 microspheres and Ni@PPY@PA6 composite microspheres. DETAILED DESCRIPTION

[0043] The present invention is further described below by means of specific embodiments, but the protection scope of the present invention is not limited thereto.

[0044] Example 1

[0045] A preparation method and application of nano-scale magnetic conductive PA6 microspheres with high thermal stability, specifically comprising:

[0046] Disperse 10 g of hydroxyl Ni powder (40 nm) and 10 mL of pyrrole monomer in 20 mL of an ethanol aqueous solution to prepare a mixed solution. Then, add 4 g of ammonium persulfate to the mixed solution, and under the condition of an ice bath at 0 °C, mechanically stir and react for 12 h. After that, filter, wash the obtained product, and vacuum dry it at 60 °C to obtain a polypyrrole-coated magnetic metal particle composite filler. Add 8 g of the composite filler to 80 g of caprolactam monomer, and perform ultrasonic treatment in a water bath at 85 °C for 45 min to obtain a suspension; under a nitrogen atmosphere, add 20 g of PEG 6k to the suspension, and keep stirring at 120 °C for 2 - 4 h to obtain a mixed solution. Place the mixed solution in a heating jacket at 150 °C to remove water under vacuum for 30 min, add zeolite and 0.4 g of NaOH, continue to remove water for 30 min, add 0.6 g of TDI (toluene diisocyanate), quickly shake violently, and then pour it into a mold at 180 °C to polymerize for 30 min. Use a high-speed crusher to crush the Ni@PPY@PA6 / PEG alloy, soak it in water for 48 h to etch the PEG phase, vacuum filter to remove the PEG dissolved in water, and dry it in an oven at 120 °C for 48 h to obtain Ni@PPY@PA6 functional microspheres. As Figure 3 shown, the average particle size of the Ni@PPY@PA6 composite microspheres is 500 nm, and the Ni@PPY@PA6 composite microspheres have good sphericity and a smooth surface. In Figure 4 , the XRD pattern of the Ni@PPY@PA6 composite microspheres includes the characteristic diffraction peaks of PPY (30.4° corresponding to the (002) crystal plane), the characteristic diffraction peaks of PA6 (20.2° and 23.8°, corresponding to the (200) and (002) crystal planes), and the characteristic diffraction peaks of Ni nanoparticles (44.5°, corresponding to the (111), (200), and (220) crystal planes of face-centered cubic Ni), indicating that the Ni@PPY particles are successfully wrapped inside the PA6 microspheres. From Figure 5 it can be seen that the temperatures at which PPY and PA6 are completely decomposed are 390 °C and 460 °C respectively, further confirming the successful preparation of the Ni@PPY@PA6 composite microspheres and the high thermal stability of the Ni@PPY@PA6 composite microspheres.

[0047] Dissolve 3 g of PVDF powder in a mixed solvent of 30 mL of DMF and acetone. After magnetic stirring for 1 h, add 0.15 g of Ni@PPY@PA6 microspheres and ultrasonically disperse for 30 min to obtain a Ni@PPY@PA6 / PVDF electrospinning solution. Place the electrospinning solution in a 10 ml syringe. The parameters of electrospinning are as follows: electrospinning for 8 h, electrospinning speed 1 ml / h; electrospinning voltage 12 kV; humidity: <50%. Place the obtained electrospun membrane in an oven at 60 °C and dry for 4 h to obtain a Ni@PPY@PA6 / PVDF electrospun membrane. Take 5 g of SiCw aqueous dispersion (3 wt%) and filter it on the front side of the Ni@PPY@PA6 / PVDF electrospun membrane. Then take 5 g of AgNWs aqueous dispersion (3 wt%) and filter it on the reverse side of the Ni@PPY@PA6 / PVDF electrospun membrane. Take it out and dry it at 50 °C for 2 h to obtain an asymmetric multi-layer structured SiCw / Ni@PPY@PA6-PVDF / AgNWs electromagnetic shielding thin film. Use a vector network analyzer to conduct electromagnetic shielding tests on it, and the relevant parameters of electromagnetic shielding are shown in Table 1.

[0048] Figure 1 Show a schematic diagram of the overall structure of the SiCw / Ni@PPY@PA6-PVDF / AgNWs electromagnetic shielding thin film, which is an asymmetric structure as a whole. Figure 2 It is a schematic diagram of the electromagnetic shielding effect. Electromagnetic waves enter from the impedance matching layer (SiCw layer). After reaching the silver nanowire layer, due to high conductivity, the electromagnetic waves are reflected back into the material interior. The addition of Ni@PPY@PA6 microspheres introduces more heterogeneous interfaces, increasing the paths of multiple reflections of electromagnetic waves inside the material and the magnetic loss mechanism, further enhancing the absorption efficiency of the composite material for electromagnetic waves.

[0049] Example 2

[0050] A preparation method and application of high thermal stability nano-scale magnetic conductive PA6 microspheres, specifically including:

[0051] Disperse 10 g of hydroxyl Ni powder (40 nm) and 10 mL of pyrrole monomer in 20 mL of an ethanol-water solution to prepare a mixed solution. Then, add 4 g of ammonium persulfate to the mixed solution. After mechanically stirring and reacting for 12 h under an ice bath condition at 0 °C, filter, wash the obtained product, and vacuum dry it at 60 °C to obtain a polypyrrole-coated magnetic metal particle composite filler. Add 8 g of the composite filler to 80 g of caprolactam monomer, and ultrasonically bath at 85 °C for 45 min to obtain a suspension. Under a nitrogen atmosphere, add 20 g of PEG4k to the suspension, keep stirring at 120 °C for 2 - 4 h to obtain a mixed solution. Place the mixed solution in a 150 °C heating jacket to remove water under vacuum for 30 min, add zeolite and 0.4 g of NaOH, continue to remove water for 30 min, add 0.6 g of TDI, quickly shake vigorously, and then pour it into a mold at 180 °C for polymerization for 30 min. Use a high-speed crusher to crush the Ni@PPY@PA6 / PEG alloy, soak it in water for 48 h to etch the PEG phase, vacuum filter to remove the PEG dissolved in water, and dry it in an oven at 120 °C for 48 h to obtain Ni@PPY@PA6 functional microspheres.

[0052] Dissolve 3 g of PVDF powder in a mixed solvent of 30 mL of DMF and acetone, magnetically stir for 1 h, then add 0.3 g of Ni@PPY@PA6 microspheres, and ultrasonically disperse for 30 min to obtain a Ni@PPY@PA6 / PVDF electrospinning solution. Place the electrospinning solution in a 10 ml syringe. The parameters of electrospinning are: electrospinning for 8 h, electrospinning speed 1 ml / h; electrospinning voltage 12 kV; humidity: <50%. Place the obtained electrospun membrane in an oven at 60 °C and dry for 4 h to obtain a Ni@PPY@PA6 / PVDF electrospun membrane. Take 5 g of SiCw aqueous dispersion (3 wt%), filter it on the front side of the Ni@PPY@PA6 / PVDF electrospun membrane by suction filtration, then take 5 g of AgNWs aqueous dispersion (3 wt%), filter it on the reverse side of the Ni@PPY@PA6 / PVDF electrospun membrane by suction filtration, take it out, and dry it at 50 °C for 2 h to obtain an asymmetric multi-layer structured SiCw / Ni@PPY@PA6-PVDF / AgNWs electromagnetic shielding thin film. Use a vector network analyzer to conduct electromagnetic shielding tests on it, and the relevant parameters of electromagnetic shielding are shown in Table 1.

[0053] Example 3

[0054] A preparation method and application of a high thermal stability nano-scale magnetic conductive PA6 microsphere, specifically including:

[0055] Disperse 10 g of hydroxyl Ni powder (40 nm) and 10 mL of pyrrole monomer in 20 mL of an ethanol aqueous solution to prepare a mixed solution. Then, add 4 g of ammonium persulfate to the mixed solution. After mechanically stirring and reacting for 12 h under an ice bath condition at 0 °C, filter, wash the obtained product, and vacuum dry it at 60 °C to obtain a polypyrrole-coated magnetic metal particle composite filler. Add 8 g of the composite filler to 80 g of caprolactam monomer, and ultrasonically bath it at 85 °C for 45 min to obtain a suspension; under a nitrogen atmosphere, add 20 g of PEG6K to the suspension, keep it warm and stir at 120 °C for 2 - 4 h to obtain a mixed solution. Place the mixed solution in a heating jacket at 150 °C to remove water under vacuum for 30 min, add zeolite and 0.4 g of NaOH, continue to remove water for 30 min, add 0.6 g of TDI, quickly shake it violently, and then pour it into a mold at 180 °C to polymerize for 30 min. Use a high-speed crusher to crush the Ni@PPY@PA6 / PEG alloy, soak it in water for 48 h to etch the PEG phase, vacuum filter to remove the PEG dissolved in water, and dry it in an oven at 120 °C for 48 h to obtain Ni@PPY@PA6 functional microspheres.

[0056] Dissolve 3 g of PVDF powder in a mixed solvent of 30 mL of DMF and acetone, magnetically stir for 1 h, then add 0.45 g of Ni@PPY@PA6 microspheres, and ultrasonically disperse for 30 min to obtain a Ni@PPY@PA6 / PVDF electrospinning solution. Place the electrospinning solution in a 10 ml syringe. The parameters of electrospinning are: electrospinning for 8 h, electrospinning speed 1 ml / h; electrospinning voltage 12 kV; humidity: <50%. Place the obtained electrospun membrane in an oven at 60 °C and dry for 4 h to obtain a Ni@PPY@PA6 / PVDF electrospun membrane. Take 5 g of SiCw aqueous dispersion (3 wt%), filter it on the front side of the Ni@PPY@PA6 / PVDF electrospun membrane by suction filtration, then take 5 g of AgNWs aqueous dispersion (3 wt%), filter it on the reverse side of the Ni@PPY@PA6 / PVDF electrospun membrane by suction filtration, take it out, and dry it at 50 °C for 2 h to obtain an asymmetric multi-layer structure of SiCw / Ni@PPY@PA6 - PVDF / AgNWs electromagnetic shielding thin film. Use a vector network analyzer to conduct electromagnetic shielding tests on it, and the relevant parameters of electromagnetic shielding are shown in Table 1.

[0057] Example 4

[0058] A preparation method and application of a high thermal stability nanoscale magnetic conductive PA6 microsphere, specifically including:

[0059] Disperse 10 g of hydroxy nickel powder (40 nm) and 10 mL of pyrrole monomer in 20 mL of an ethanol aqueous solution to prepare a mixed solution. Then, add 4 g of ammonium persulfate to the mixed solution. After mechanical stirring and reacting for 12 h under an ice bath condition at 0 °C, filter, wash the obtained product, and vacuum dry it at 60 °C to obtain a polypyrrole-coated magnetic metal particle composite filler. Add 8 g of the composite filler to 80 g of caprolactam monomer, and perform ultrasonic treatment in a water bath at 85 °C for 45 min to obtain a suspension. Under a nitrogen atmosphere, add 20 g of PEG6K to the suspension, keep stirring at 120 °C for 2 - 4 h to obtain a mixed solution. Place the mixed solution in a heating jacket at 150 °C to remove water under vacuum for 30 min, add zeolite and 0.4 g of NaOH, continue to remove water for 30 min, add 0.6 g of TDI, quickly shake vigorously, and then pour it into a mold at 180 °C for polymerization for 30 min. Use a high-speed crusher to crush the Ni@PPY@PA6 / PEG alloy, soak it in water for 48 h to etch the PEG phase, vacuum filter to remove the PEG dissolved in water, and dry it in an oven at 120 °C for 48 h to obtain Ni@PPY@PA6 functional microspheres.

[0060] Dissolve 3 g of PVDF powder in a mixed solvent of 30 mL of DMF and acetone, magnetically stir for 1 h, then add 0.45 g of Ni@PPY@PA6 microspheres, and ultrasonically disperse for 30 min to obtain a Ni@PPY@PA6 / PVDF electrospinning solution. Place the electrospinning solution in a 10 ml syringe. The electrospinning parameters are: electrospinning for 8 h, electrospinning speed 1 ml / h; electrospinning voltage 12 kV; humidity: <50%. Place the obtained electrospun membrane in an oven at 60 °C and dry for 4 h to obtain a Ni@PPY@PA6 / PVDF electrospun membrane. Take 10 g of SiCw aqueous dispersion (3 wt%), filter it on the front side of the Ni@PPY@PA6 / PVDF electrospun membrane by suction filtration, then take 8 g of AgNWs aqueous dispersion (3 wt%), filter it on the reverse side of the Ni@PPY@PA6 / PVDF electrospun membrane by suction filtration, take it out, and dry it at 50 °C for 2 h to obtain an asymmetric multi-layer structured SiCw / Ni@PPY@PA6 - PVDF / AgNWs electromagnetic shielding film. Use a vector network analyzer to perform electromagnetic shielding tests on it, and the relevant electromagnetic shielding parameters are shown in Table 1.

[0061] Table 1

[0062] Total electromagnetic shielding effectiveness (dB) Absorption coefficient Example 1 48.93 0.12 Example 2 49.19 0.26 Example 3 49.86 0.31 Example 4 82.45 0.56

Claims

1. A method for preparing nanoscale magnetic conductive PA6 microspheres with high thermal stability, characterized in that: The following steps are involved: (1) dispersing hydroxy Ni powder and pyrrole monomer in an ethanol aqueous solution to prepare a mixed solution, then adding ammonium persulfate to the mixed solution, mechanically stirring the mixture in an ice bath for 12-20 hours, filtering, washing and vacuum drying the obtained product to obtain a polypyrrole-coated magnetic metal particle composite filler, namely Ni@PPY; (2) ultrasonically dispersing the Ni@PPY obtained in step (1) in caprolactam to obtain a caprolactam / composite filler suspension, adding polyethylene glycol to the caprolactam / composite filler suspension in a vacuum or protective atmosphere, and stirring at 120 to 140° C. for 2 to 4 hours to obtain a mixed solution; (3) adding an initiator to the mixed solution obtained in step (2), and then removing water under vacuum at 130-160° C.; (4) After vacuum dehydration, an activator is added to allow caprolactam to undergo anionic ring-opening polymerization to achieve phase inversion, thereby obtaining a Ni@PPY@PA6 / PEG alloy; The conditions for anionic ring-opening polymerization are: polymerization at 150-200°C for 20-60 min; (5) The Ni@PPY@PA6 / PEG alloy obtained in step (4) is crushed and washed to obtain high thermal stability nanoscale magnetoelectric functional Ni@PPY@PA6 microspheres, that is, high thermal stability nanoscale magnetic conductive PA6 microspheres.

2. The method for preparing nanoscale magnetic conductive PA6 microspheres with high thermal stability according to claim 1, characterized in that: In step (1), the hydroxy Ni powder is replaced by hydroxy Fe powder or hydroxy Co powder.

3. The method for preparing nanoscale magnetic conductive PA6 microspheres with high thermal stability according to claim 1, characterized in that: In step (2), the mass ratio of Ni@PPY, polyethylene glycol and caprolactam is 1-8:15-20:75-85.

4. The method for preparing nanoscale magnetic conductive PA6 microspheres with high thermal stability according to claim 1, characterized in that: In step (2), the protective atmosphere is at least one of hydrogen, argon, methane and nitrogen.

5. The method for preparing nanoscale magnetic conductive PA6 microspheres with high thermal stability according to claim 1, characterized in that: In step (3), the initiator is an alkali metal hydride, an alkali metal hydroxide, an alkali metal alkoxide or an alkali metal carbonate; The added amount of the initiator is 0.1-1 wt % of the total mass of Ni@PPY, polyethylene glycol and caprolactam.

6. The method for preparing nanoscale magnetic conductive PA6 microspheres with high thermal stability according to claim 1, characterized in that: In step (4), the activator is isocyanate, acyl chloride, acid anhydride or acyl caprolactam; The amount of the activator added is 0.1-1 wt % of the total mass of Ni@PPY, polyethylene glycol and caprolactam.

7. Use of high thermal stability nanoscale magnetic conductive PA6 microspheres prepared by the preparation method according to any one of claims 1 to 6 in the preparation of composite films.

8. The use according to claim 7, characterized in that: Specifically include: (6) dissolving PVDF powder in a solvent, and obtaining a PVDF electrospinning solution after magnetic stirring, adding the obtained high thermal stability nanoscale magnetic conductive PA6 microspheres to the PVDF electrospinning solution, and obtaining a Ni@PPY@PA6-PVDF electrospinning solution after ultrasonic dispersion, and preparing a Ni@PPY@PA6-PVDF electrospinning membrane using fixed electrospinning parameters, and vacuum drying it for later use; (7) adding AgNWs into a solvent and stirring to obtain an AgNWs dispersion; (8) Adding SiCw into a solvent and subjecting it to ultrasonic treatment to obtain a SiCw dispersion; (9) The Ni@PPY@PA6-PVDF electrospun membrane prepared in step (6) is placed on a vacuum filtration device, and the AgNWs dispersion prepared in step (7) is poured onto one side of the Ni@PPY@PA6-PVDF electrospun membrane, and AgNWs are deposited and attached to the Ni@PPY@PA6-PVDF electrospun membrane by filtration. SiCw is deposited and attached to the other side of the Ni@PPY@PA6-PVDF electrospun membrane by pouring the SiCw dispersion prepared in step (8) and then filtering and depositing SiCw, and after drying, an AgNWs / Ni@PPY@PA6-PVDF / SiCw composite film having an asymmetric multilayer structure is obtained.

9. The use according to claim 8, characterized in that: In step (6), the solvent is one of DMF, acetone, and a mixed solvent of DMF and acetone; The mass ratio of the high thermal stability nano-scale magnetic conductive PA6 microspheres to the PVDF powder is 5 to 15:

100.

10. The use according to claim 9, characterized in that: In step (7), the mass fraction of AgNWs in the AgNWs dispersion is 0.5-3%; In step (8), the mass fraction of SiCw in the SiCw dispersion is 0.5-3%.

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