Polypropylene composite material, and preparation method and application thereof

Abstract

The application provides a polypropylene composite material and a preparation method and application thereof, and relates to the technical field of electrical materials. The application comprises the following steps: S1: dissolving polyetherimide in a solvent to form an electrospinning solution; S2: adding nano magnetic particles into the electrospinning solution to perform electrospinning; S3: collecting the same-direction nano fibers to perform hot pressing to form a functional layer; S4: hot pressing the functional layer and a polypropylene film in the order of functional layer-polypropylene film layer-functional layer to form a composite layer; and S5: performing directional magnetization on the composite layer to obtain the polypropylene composite material. The electrospinning technology is used to prepare the functional layer, which not only solves the problem of uniform dispersion of the magnetic particles in the polymer, but also provides abundant interface areas for charge capture through the construction of the nano fiber network. The problem of space charge accumulation in the polypropylene material under a high-voltage direct-current system is solved.

Description

Technical Field

[0001] This invention relates to the field of electrical materials technology, and more specifically, to a polypropylene composite material, its preparation method, and its application. Background Technology

[0002] Space charge in polypropylene materials has become a significant factor hindering the development of higher electric fields in power systems. The presence, migration, and dissipation of space charge directly affect the internal electric field distribution of insulating materials. This problem is particularly pronounced in DC systems. Prolonged space charge can cause partial discharge, decreased insulation performance, and even breakdown failure in polypropylene materials, severely threatening their long-term stability. Reducing space charge effects is crucial for improving the voltage rating of polypropylene materials and enhancing power transmission efficiency.

[0003] Existing patents such as CN114261036A and CN115044994A focus on how to reflect or absorb electromagnetic waves to prevent external electromagnetic interference or harvest energy from human movement. Their core lies in the macroscopic electromagnetic wave response of the material, rather than suppressing the microscopic charge transport within the material. For example, CN113718368B focuses on developing a universal, scalable method for preparing magnetic fibers, integrating magnetic particles uniformly and at high concentrations into the fibers. Its applications are broad, including flexible actuation and biomedicine, but it does not offer a specific solution to the space charge problem in capacitors or cable insulation.

[0004] Furthermore, existing studies often employ melt blending of inorganic particles (such as nano-silica and alumina) with polypropylene for modification. This method suffers from poor particle dispersibility and easy agglomeration, and often requires high filler content to achieve certain effects, which leads to increased dielectric loss and decreased mechanical properties of the material.

[0005] Existing research on space charge issues has largely focused on cable insulation layers, with fewer reports on methods for suppressing space charge in capacitors. Capacitors operate differently (charge-discharge cycles) and have different structures than cables, requiring specially designed solutions. Summary of the Invention

[0006] To address the space charge problem caused by long-term charging and discharging in polypropylene capacitors, this invention provides a polypropylene composite material that creatively constructs a sandwich structure of a functional layer-polypropylene film layer-functional layer. The functional layer, constructed with a small number of magnetic particles, reduces the overall amount of charge flowing through the dielectric, thereby reducing the possibility of charge accumulation. The functional layer is prepared using electrospinning technology, which not only solves the problem of uniform dispersion of magnetic particles in the polymer but also provides abundant interface regions for charge trapping by constructing a nanofiber network. This solves the problem of space charge accumulation in polypropylene materials under high-voltage direct current systems.

[0007] The first aspect of this invention provides a method for preparing a polypropylene composite material, the method comprising the following steps: S1: Dissolve polyetherimide in a solvent to form an electrospinning solution; S2: Add nano-magnetic particles to the electrospinning solution and perform electrospinning; S3: Collect unidirectional nanofibers and hot-press them to form a functional layer; S4: Hot-press the functional layer and the polypropylene film in the order of functional layer-polypropylene film layer-functional layer to form a composite layer; S5: The composite layer is directionally magnetized to obtain a polypropylene composite material; By mass, the composition is 15-25 parts polyetherimide, 75-85 parts solvent, and 0.1-5 parts nano-magnetic particles.

[0008] In the polypropylene composite material prepared in this application, a charge injection suppression functional layer is constructed through electrospinning and magnetic particle modification, forming a ground terminal-functional layer-insulating material-functional layer-electrode structure. The functional layer contains nano-magnetic particles, which can generate a directional magnetic field in the medium through directional magnetization. The injected charge is deflected under the Lorentz force, and with the time remaining constant, the time for the charge to reach the opposite electrode is prolonged, thereby reducing leakage current. Simultaneously, the charge accumulated at the interface generates a reverse interfacial electric field, which helps to reduce further charge injection. (See schematic diagram of the effect of magnetic particles on charge migration for reference.) Figure 1 As shown.

[0009] Furthermore, the functional layer is composed of polyetherimide, forming a three-layer structure with polypropylene, introducing an interface region to improve the dielectric constant. Simultaneously, it reduces space charge accumulation and improves breakdown performance.

[0010] Optionally, in step S5, the composite layer is directionally magnetized to form a magnetic field perpendicular to the direction of the electric field. The directional magnetic field generated by the nano-magnetic particles is perpendicular to the applied electric field, exerting a force perpendicular to the direction of the electric field on the moving charges. This has the effect of deflecting the moving charges.

[0011] Optionally, in step S3, nanofibers arranged along the same axis are collected and hot-pressed to form a functional layer.

[0012] Optionally, by weight, the composition includes 15-25 parts polyetherimide, 75-85 parts solvent, and 0.5-3 parts nano-magnetic particles.

[0013] Optionally, by weight, the composition includes 18-22 parts polyetherimide, 78-82 parts solvent, and 0.5-2 parts nano-magnetic particles.

[0014] Optionally, the concentration of the electrospinning solution is 15-25 wt%.

[0015] Optionally, the solvent is N-methylpyrrolidone.

[0016] Optionally, the nanomagnetic particles are permanent magnet nanomagnetic particles that are not easily demagnetized and have high remanent magnetic induction. Optionally, the nanomagnetic particles are single-domain particles; further, the nanomagnetic particles are strontium ferrite or barium ferrite. For single-domain materials, there are no domain walls inside. When a strong magnetic field is applied, the domains turn. After the external magnetic field is removed, due to the magnetocrystalline anisotropy, the domains cannot return to their original direction and remain aligned along the direction of the applied magnetic field.

[0017] Optionally, the particle size of the magnetic nanoparticles is tens to hundreds of nanometers. Optionally, the particle size of the magnetic nanoparticles is 50nm-500nm. Optionally, the particle size of the magnetic nanoparticles is 50nm-100nm.

[0018] Optionally, the mass of the nanomagnetic particles accounts for 0.1-5% of the total mass of the functional layer. Optionally, the mass fraction of the nanomagnetic particles can account for 0.5-2% of the total mass of the functional layer. For example, the mass fraction of the nanomagnetic particles can be any value or a range between any two points from 0.1%, 0.3%, 0.5%, 0.7%, 0.9%, 1.1%, 1.3%, 1.5%, 1.7%, 1.9%, 2.1%, 2.3%, 2.5%, 2.7%, 2.9%, 3.1%, 3.3%, 3.5%, 3.7%, 3.9%, 4.1%, 4.3%, 4.5%, 4.7%, 4.9%, or 5.0% of the total mass of the functional layer. The content of nanomagnetic particles mainly affects the magnitude of the Lorentz force generated inside the medium. When the content of nanomagnetic particles is high, the corresponding Lorentz force is large, and the charge is greatly affected by the Lorentz force, which may cause it to move in a circular motion inside the medium, which is not conducive to the coordinated improvement of breakdown with the interfacial barrier.

[0019] Optionally, the electrospinning voltage is 15-20 kV / mm, and the feed rate is 1-2 ml / h. Under these electrospinning conditions, stable fibers can be formed. If the electrospinning voltage is too high, the following problems mainly exist: 1. The electric field force far exceeds the surface tension of the solution, making the fibers prone to splitting. 2. The electric field force easily leads to the aggregation of magnetic particles. 3. It causes air discharge, affecting the surface morphology of the fibers.

[0020] Optionally, in step S4, the hot-pressing temperature is 160-200℃, and the hot-pressing pressure is 10-15MPa. By adjusting the hot-pressing temperature and pressure, a microscopic interface is formed between the functional layer and the polypropylene, further inhibiting charge movement. The hot-pressing time is 2-5 minutes. This application selects a hot-pressing temperature higher than the melting temperature of polypropylene, allowing the amorphous regions of the polypropylene to melt rapidly in a short time, bonding with the functional layer without completely destroying the internal crystalline structure. Sufficient crystallization points are available during cooling to ensure complete crystallization. If the temperature is too low, sufficient heat conduction will lead to excessive melting of the crystalline regions, affecting performance. Excessively high temperatures will also cause excessively rapid heat conduction, resulting in over-melting.

[0021] Optionally, in step S3, the hot pressing temperature is 220-230℃ and the hot pressing pressure is 10-15MPa.

[0022] A second aspect of the present invention provides a polypropylene composite material, wherein the thickness of the functional layer is 10-50 μm and the thickness of the polypropylene film layer is 10-50 μm.

[0023] A third aspect of the present invention provides a capacitor comprising the aforementioned polypropylene composite material.

[0024] Compared with the prior art, the present invention achieves at least one of the following beneficial effects: (1) In the preparation method of the polypropylene composite material of the present invention, the number of charges flowing through the medium is reduced by constructing a functional layer with a small number of magnetic particles, thereby reducing the possibility of charge accumulation. The moving electrons are subjected to the Lorentz force, and their direction of motion is deflected. Furthermore, through reasonable structural design and adjustment of magnetic force, the space charge effect is suppressed, thereby achieving the purpose of improving electrical performance.

[0025] (2) The present invention uses a modification method of magnetic particles + interface. On the one hand, the Lorentz force only changes the direction of charge movement and does not cause additional loss of work done on the charge. On the other hand, the amount of magnetic particles used is small and will not have a significant impact on mechanical properties.

[0026] (3) The main advantages of using electrospinning to prepare polypropylene composite materials in this invention are as follows: ① Polypropylene has stable physical properties and is difficult to dissolve. Polyetherimide is easily soluble in organic solvents and is suitable for electrospinning. Moreover, polyetherimide has stable high-temperature properties and a high relative permittivity, which is beneficial to improving the high-temperature performance of polypropylene after being combined with polypropylene. The difference in relative permittivity between polyetherimide and polypropylene is also beneficial to disperse voltage and improve breakdown strength. ② The micron / nano-scale fibers prepared have a large specific surface area and can form more interface regions with polypropylene, which can act as traps for capturing charges, thereby improving insulation performance. ③ By adjusting the solution formulation, process parameters and other conditions during electrospinning, the diameter of the fibers and the distribution of particles in the fibers can be controlled to form fibers with uniform particle dispersion. ④ The voltage applied during electrospinning is beneficial to the pre-orientation of magnetic particles in the solution. ⑤ The directional collection of fibers generated by electrospinning is beneficial to the arraying of particles throughout the composite material, which facilitates further adjustment of magnetic force to adapt to different voltage levels. Attached Figure Description

[0027] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings: Figure 1 A schematic diagram illustrating the effect of magnetic particles on charge migration according to the present invention is shown. Detailed Implementation To more clearly illustrate the overall concept of the present invention, a detailed description will be provided below with reference to the accompanying drawings and examples.

[0028] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0029] Example 1 In an exemplary embodiment of the present invention, the method for preparing the polypropylene composite material includes the following steps: S1: Polyetherimide (PEI) particles were vacuum dried at 80°C for 12 hours to remove moisture. 15 parts of the dried polyetherimide particles were dissolved in 85 parts of N-methylpyrrolidone and stirred for 12 hours to form a 15 wt% electrospinning solution. S2: Add 0.5 parts of strontium ferrite nanoparticles with a particle size of 80 nm to the electrospinning solution, ultrasonically disperse for 30 min, and then perform electrospinning; the electrospinning voltage is controlled at 18 kV / mm, and the feed rate is 1 ml / h.

[0030] S3: After collecting unidirectional nanofibers using a roller and hot-pressing them, a functional layer is formed; the hot-pressing temperature is 220℃ and the hot-pressing pressure is 15MPa.

[0031] S4: Hot-press the functional layer and the polypropylene film in the order of functional layer-polypropylene film layer-functional layer, control the hot-pressing temperature at 180℃, the hot-pressing pressure at 15MPa, and the hot-pressing time at 2 minutes, so as to form a good interface between the polypropylene and the functional layer and form a composite layer; in the polypropylene composite material, the thickness of each functional layer is 50μm, and the thickness of the polypropylene film layer is 50μm.

[0032] S5: The hot-pressed composite layer is directionally magnetized using a magnetizer to make the magnetic particles reach magnetic saturation, forming a magnetic field perpendicular to the electric field direction, thus obtaining a polypropylene composite material.

[0033] Example 2 In an exemplary embodiment of the present invention, the method for preparing the polypropylene composite material includes the following steps: S1: Polyetherimide (PEI) particles were vacuum dried at 80°C for 12 hours to remove moisture. 25 parts of the dried polyetherimide particles were dissolved in 75 parts of N-methylpyrrolidone and stirred for 12 hours to form a 25 wt% electrospinning solution. S2: Add 5 parts of barium ferrite nanoparticles with a particle size of 80 nm to the electrospinning solution, ultrasonically disperse for 30 min, and then perform electrospinning; the electrospinning voltage is controlled at 20 kV / mm, and the feed rate is 2 ml / h.

[0034] S3: After collecting unidirectional nanofibers using a roller and hot-pressing them, a functional layer is formed; the hot-pressing temperature is 230℃ and the hot-pressing pressure is 10MPa.

[0035] S4: The functional layer and the polypropylene film are hot-pressed in the order of functional layer-polypropylene film layer-functional layer. The hot-pressing temperature is controlled at 200℃, the hot-pressing pressure is 15MPa, and the hot-pressing time is 2 minutes, so as to form a good interface between the polypropylene and the functional layer and form a composite layer. In the polypropylene composite material, the thickness of each functional layer is 10μm and the thickness of the polypropylene film layer is 10μm.

[0036] S5: The hot-pressed composite layer is directionally magnetized using a magnetizer to make the magnetic particles reach magnetic saturation, forming a magnetic field perpendicular to the electric field direction, thus obtaining a polypropylene composite material.

[0037] Example 3 In an exemplary embodiment of the present invention, the method for preparing the polypropylene composite material includes the following steps: S1: Polyetherimide (PEI) particles were vacuum dried at 80°C for 12 hours to remove moisture. 20 parts of the dried polyetherimide particles were dissolved in 80 parts of N-methylpyrrolidone and stirred for 12 hours to form a 20 wt% electrospinning solution. S2: Add 1 part of strontium ferrite nanoparticles with a particle size of 80 nm to the electrospinning solution, ultrasonically disperse for 30 min, and then perform electrospinning; the electrospinning voltage is controlled at 15 kV / mm, and the feed rate is 1 ml / h.

[0038] S3: After collecting unidirectional nanofibers using a roller and hot-pressing them, a functional layer is formed; the hot-pressing temperature is 220℃ and the hot-pressing pressure is 10MPa.

[0039] S4: The functional layer and the polypropylene film are hot-pressed in the order of functional layer-polypropylene film layer-functional layer. The hot-pressing temperature is controlled at 160℃, the hot-pressing pressure is 10MPa, and the hot-pressing time is 2 minutes, so as to form a good interface between the polypropylene and the functional layer and form a composite layer. In the polypropylene composite material, the thickness of each functional layer is 50μm and the thickness of the polypropylene film layer is 50μm.

[0040] S5: The hot-pressed composite layer is directionally magnetized using a magnetizer to make the magnetic particles reach magnetic saturation, forming a magnetic field perpendicular to the electric field direction, thus obtaining a polypropylene composite material.

[0041] Example 4 Based on Example 1, the main difference is that, in S2: 0.1 parts of barium ferrite nanoparticles with a particle size of 80 nm are added to the electrospinning solution, ultrasonically dispersed for 30 min, and then electrospinned; the electrospinning voltage is controlled at 18 kV / mm and the feed rate is 1 ml / h.

[0042] Example 5 The main difference from Example 1 is that the nano-magnetic particles are strontium ferrite with a particle size of 200 nm.

[0043] Example 6 The main difference from Example 1 is that the nano-magnetic particles are strontium ferrite with a particle size of 800 nm.

[0044] Example 7 Based on Example 1, the main difference is that in step S4, the hot pressing temperature is 250°C and the hot pressing pressure is 15MPa.

[0045] Example 8 Based on Example 1, the main difference is that in step S4, the hot pressing temperature is 180°C and the hot pressing pressure is 6MPa.

[0046] Comparative Example 1 The main difference from Example 1 is that wet spinning is used.

[0047] Comparative Example 2 Based on Example 1, the main difference is that, in S2: 0.05 parts of barium ferrite nanoparticles with a particle size of 80 nm are added to the electrospinning solution, ultrasonically dispersed for 30 min, and then electrospinned; the electrospinning voltage is controlled at 18 kV / mm and the feed rate is 1 ml / h.

[0048] Comparative Example 3 The main difference from Example 1 is that the voltage for electrospinning is 10 kV / mm.

[0049] Comparative Example 4 The main difference from Example 1 is that the voltage for electrospinning is 30 kV / mm.

[0050] Test case The polypropylene composite materials prepared in the above examples and comparative examples were subjected to performance tests, and the test results are shown in Table 1.

[0051] The hysteresis loop test involves placing the sample in the central induction coil of a magnetic pole and setting the magnetic field strength to 2T. Once the test begins, the sample generates an alternating magnetic flux, and the induced voltage can be obtained using the principle of electromagnetic induction. Data collection yields the sample's demagnetization curve, from which magnetic property parameters such as remanence (Br), coercivity (H), and magnetization (M) can be derived.

[0052] Leakage current: Before testing, dry the sample in a 60℃ oven for 2 hours. Place the dried sample in the electrode, apply a high voltage to the upper electrode, and connect a protective resistor and a 6517 ammeter to the lower electrode. During testing, place the electrode in a constant temperature oven, set the temperature to 25℃, apply pressure for 1 minute, and wait for the sample's absorbed current to disappear. The measured current is the leakage current of the sample.

[0053] Breakdown voltage: The DC breakdown strength of the composite specimens was tested using a universal breakdown tester according to IEC 60243-1:2013. First, the specimens were dried in a 60°C oven for 2 hours to remove surface moisture. To prevent surface breakdown, the specimens were immersed in silicone oil for the breakdown test. The breakdown test was conducted at 25°C, with the voltage increased at a rate of 500V / s until the specimen broke down. The voltage at breakdown was recorded. The breakdown field strength was obtained by dividing the breakdown voltage by the specimen thickness. Ten tests were performed on each specimen, and the data were processed using a Weibull distribution.

[0054] Table 1

[0055] Referring to Table 1, the polypropylene composite material prepared in this application successfully solves the technical problems of space charge accumulation, decreased insulation performance, and even breakdown failure, reducing the leakage current to 10. -8 The A-level design increases the breakdown voltage to over 320kV / mm. Preferably, it reduces the leakage current to 10 kV / mm. -9 The A-level will increase the breakdown voltage to over 340kV / mm.

[0056] In Comparative Example 1, wet spinning is not conducive to the pre-orientation of magnetic particles. Electrospinning voltage has a certain pre-orientation effect on the magnetic domain orientation of magnetic particles. If the nanofibers are not collected in the same orientation, it affects the final magnetization effect. This results in a reduction in the remanent magnetic induction of the final film at the same amount of magnetic particles.

[0057] In Comparative Example 2, when the mass fraction of magnetic particles was 0.05%, the internal magnetic field strength was too small, and the performance was not significantly different from that without the addition of magnetic particles.

[0058] In Comparative Example 3, if the voltage of electrospinning is too low, stable fibers cannot be formed.

[0059] In Comparative Example 4, if the voltage of electrospinning is too high, the fibers will split and become disordered.

[0060] The above description is merely an embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A method for preparing a polypropylene composite material, characterized in that, The preparation method includes the following steps: S1: Dissolve polyetherimide in a solvent to form an electrospinning solution; S2: Add nano-magnetic particles to the electrospinning solution and perform electrospinning; S3: Collect unidirectional nanofibers and hot-press them to form a functional layer; S4: Hot-press the functional layer and the polypropylene film in the order of functional layer-polypropylene film layer-functional layer to form a composite layer; S5: The composite layer is directionally magnetized to obtain a polypropylene composite material; By mass, the composition is 15-25 parts polyetherimide, 75-85 parts solvent, and 0.1-5 parts nano-magnetic particles.

2. The method for preparing the polypropylene composite material according to claim 1, characterized in that, In step S5, the composite layer is directionally magnetized to form a magnetic field perpendicular to the direction of the electric field.

3. The method for preparing the polypropylene composite material according to claim 1, characterized in that, Nanomagnetic particles are single-domain particles.

4. The method for preparing the polypropylene composite material according to claim 3, characterized in that, The nanomagnetic particles are strontium ferrite or barium ferrite.

5. The method for preparing the polypropylene composite material according to claim 1, characterized in that, The particle size of the nanomagnetic particles ranges from tens to hundreds of nanometers.

6. The method for preparing the polypropylene composite material according to claim 1, characterized in that, The voltage for electrospinning is 15-20 kV / mm, and the feed rate is 1-2 ml / h.

7. The method for preparing the polypropylene composite material according to claim 1, characterized in that, In step S4, the hot pressing temperature is 160-200℃ and the hot pressing pressure is 10-15MPa.

8. The method for preparing the polypropylene composite material according to claim 1, characterized in that, In step S3, the hot pressing temperature is 220-230℃ and the hot pressing pressure is 10-15MPa.

9. A polypropylene composite material prepared by the preparation method according to any one of claims 1-8, characterized in that, In the polypropylene composite material, the thickness of the functional layer is 10-50 μm, and the thickness of the polypropylene film layer is 10-50 μm.

10. A capacitor, characterized in that, The capacitor comprises the polypropylene composite material as described in claim 9.

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