Application of modified calcium copper titanate nanofibers as dielectric fillers in the preparation of dielectric composite materials

Abstract

This invention discloses the application of modified calcium copper titanate nanofibers as dielectric fillers in the preparation of dielectric composite materials. The method involves reacting surface-hydroxylated calcium copper titanate nanofibers with alkoxysilanes containing terminal amino groups to generate aminated calcium copper titanate nanofibers. These nanofibers are then mixed with specific bismaleimides and specific diaminodiphenyl ethers and reacted under heating conditions to generate modified calcium copper titanate nanofibers. The modified calcium copper titanate nanofibers of this invention exhibit excellent dispersibility in polyetherimides, effectively enhancing interfacial polarization and significantly improving the breakdown strength of dielectric composite materials while reducing dielectric loss. This overcomes the problem of compromises that exist in existing technologies when adding calcium copper titanate particles, making it suitable for developing composite dielectric materials with excellent comprehensive dielectric properties.

Description

[0001] This invention is a divisional application of Chinese invention patent application filed on September 8, 2023, with application number 2023111541749 and titled "A Modified Copper Calcium Titanate Nanofiber and Its Preparation Method and Application". Technical Field

[0002] This invention relates to the field of dielectric composite materials, and more particularly to dielectric composite materials with high dielectric constant, low dielectric loss and high breakdown strength. Specifically, it relates to the application of modified calcium copper titanate nanofibers as dielectric fillers in the preparation of dielectric composite materials. Background Technology

[0003] The world today faces enormous challenges related to energy and the environment. A key to solving these problems is finding effective ways to store energy and reduce energy loss. Currently, commonly used energy storage devices include batteries, supercapacitors, and dielectric capacitors. Batteries have wide applications due to their higher charging and discharging capabilities, but they also suffer from significant pollution, low cycle efficiency, and difficulty in recycling. Compared to rechargeable ion batteries such as magnesium-ion, lithium-ion, and zinc-ion batteries, and other types of energy storage devices, dielectric capacitors offer rapid charging / discharging speeds, ultra-high power density, and long cycle life, making them one of the most promising options. However, their low energy density still severely restricts their rapid development. Therefore, achieving high energy density for dielectric capacitors remains a pressing issue.

[0004] Dielectric capacitors are mainly composed of electrodes and dielectric materials (also known as dielectrics). As one of the key materials in dielectric capacitors, the performance of the dielectric material significantly affects the energy storage performance of the capacitor. Dielectric constant, dielectric loss, and breakdown strength are important indicators for evaluating dielectric material performance. Dielectric constant, also known as permittivity, measures the degree of polarization of the dielectric material in an external field. The greater the degree of polarization, the higher the macroscopic dielectric constant; it is a coefficient representing the insulating ability of the dielectric. Dielectric loss refers to the phenomenon where the dielectric material heats up due to the consumption of some electrical energy in an alternating electric field (reason: the dielectric material contains charge carriers capable of conducting electricity; under the action of an external electric field, it generates a conductive current, consuming some electrical energy and converting it into heat energy). Breakdown strength, also known as dielectric breakdown strength, represents the highest electric field strength that the material can withstand to avoid being destroyed (breakdown) under the action of an electric field.

[0005] Polyetherimide is known to have good high-temperature resistance, high breakdown strength, and low dielectric loss, but its dielectric constant is low. (CaCu3Ti4O3) 12Copper titanate (CCTO) ceramic particles are known fillers with high dielectric constants. Copper titanate ceramic particles can be added to polyetherimide to create dielectric composites with relatively high dielectric constants. However, practice has shown that while this method can improve the dielectric constant of the dielectric composite to some extent, it also causes a significant decrease in breakdown strength and a significant increase in dielectric loss, which is not conducive to its application in dielectric capacitors. There is a trade-off between these two aspects. Summary of the Invention

[0006] The purpose of this invention is to overcome one or more shortcomings in the prior art and provide a new application of modified calcium copper titanate nanofibers as dielectric fillers in the preparation of dielectric composite materials. This new modified calcium copper titanate nanofibers can not only effectively enhance interfacial polarization and increase dielectric constant, but also significantly improve the breakdown strength of dielectric composite materials and reduce dielectric loss, thus overcoming the problem of trade-offs that exist when adding calcium copper titanate materials in the prior art.

[0007] To achieve the above objectives, the present invention employs the following technical solution: a method for preparing modified copper calcium titanate nanofibers, comprising: surface hydroxylation modification of copper calcium titanate nanofibers to form hydroxylated copper calcium titanate nanofibers; reacting the hydroxylated copper calcium titanate nanofibers with alkoxysilanes containing terminal amino groups to generate aminated copper calcium titanate nanofibers with terminal amino groups on their surface; mixing the aminated copper calcium titanate nanofibers, the compound shown in formula (I), and the compound shown in formula (II), and reacting under heating conditions to generate the modified copper calcium titanate nanofibers;

[0008] In equation (Ⅰ), R1 is selected from C 1-6 Alkylene R2, R3, R4, and R5 are independently selected from hydrogen and C. 1-6 Alkyl group, R8 is selected from C 1-6 Alkylene, oxygen, or NH;

[0009] In formula (II), R6 and R7 are independently selected from hydrogen and C. 1-6 alkyl.

[0010] In this invention, the carbon-carbon double bond on the compound represented by formula (Ⅰ) can undergo an addition reaction with the terminal amino group on the compound represented by formula (Ⅱ), and the reaction process is roughly illustrated below:

[0011]

[0012] Moreover, the terminal amino groups on the aminated copper titanate calcium nanofibers can also undergo addition reactions with the carbon-carbon double bonds on the compound shown in formula (I), so that the polymer generated by the addition reaction of the compound shown in formula (I) and the compound shown in formula (II) can be partially chemically bonded to the aminated copper titanate calcium nanofibers, thereby improving the integrity of the coating and the binding force.

[0013] According to some preferred aspects of the present invention, in the preparation of the modified calcium copper titanate nanofibers, the molar ratio of the compound represented by formula (I) to the compound represented by formula (II) is 1:0.8-1.2. According to a specific aspect of the present invention, in the preparation of the modified calcium copper titanate nanofibers, the molar ratio of the compound represented by formula (I) to the compound represented by formula (II) is 1:1.

[0014] According to some preferred aspects of the present invention, in the process of preparing the modified copper calcium titanate nanofibers, the mass of the compound represented by formula (II) added is greater than the mass of the aminated copper calcium titanate nanofibers added.

[0015] According to some preferred aspects of the present invention, in formula (Ⅰ), R1 is selected from -CH2-, -CH2-CH2-, -CH2-CH2-CH2-, -CH2-CH(CH3)-CH2-, -CH2-C(CH3)2-CH2-,

[0016] According to some preferred aspects of the invention, in formula (I), R2, R3, R4, and R5 are independently selected from hydrogen, methyl, ethyl, n-propyl, or isopropyl.

[0017] According to some preferred aspects of the invention, in formula (II), the amino group is substituted on the para carbon atom of the carbon atom in the benzene ring that is connected to oxygen, and R6 and R7 are independently selected from hydrogen, methyl or ethyl.

[0018] According to some preferred aspects of the present invention, in the process of preparing the modified copper calcium titanate nanofibers, the reaction of the aminated copper calcium titanate nanofibers, the compound shown in formula (I), and the compound shown in formula (II) is controlled to be carried out in a first solvent, and the solid content of the reaction system is controlled to be 1%-5%.

[0019] According to some preferred and specific aspects of the present invention, the first solvent may include, but is not limited to, N,N'-dimethylformamide, etc.

[0020] According to some preferred aspects of the present invention, in the process of preparing the modified copper calcium titanate nanofibers, the reactions of the aminated copper calcium titanate nanofibers, the compound shown in formula (I), and the compound shown in formula (II) are controlled to be carried out at 40-70°C under a protective atmosphere.

[0021] Furthermore, in the preparation of the modified copper calcium titanate nanofibers, the reaction of the aminated copper calcium titanate nanofibers, the compound shown in formula (I), and the compound shown in formula (II) is controlled to be carried out at 50-70°C. According to a specific aspect of the present invention, in the preparation of the modified copper calcium titanate nanofibers, the reaction of the aminated copper calcium titanate nanofibers, the compound shown in formula (I), and the compound shown in formula (II) is controlled to be carried out at 60°C. In some embodiments of the present invention, a protective atmosphere can be formed by introducing nitrogen or helium during the preparation of the modified copper calcium titanate nanofibers.

[0022] According to some preferred aspects of the present invention, embodiments for preparing the modified calcium copper titanate nanofibers include:

[0023] The aminated copper calcium titanate nanofibers were added to a reaction vessel containing a protective gas (such as nitrogen or helium), and then N,N'-dimethylformamide, the compound shown in formula (II), and the compound shown in formula (III) were added. The mixture was reacted under heating conditions for 1-4 hours. The resulting mixture was then poured into water to precipitate, acidified, washed, and dried to obtain the modified copper calcium titanate nanofibers.

[0024] In some embodiments of the present invention, during the preparation of the modified copper calcium titanate nanofibers, the acidification is carried out using hydrochloric acid, and the molar concentration of hydrochloric acid is 0.5-2 mol / L.

[0025] In some embodiments of the present invention, the washing process in preparing the modified copper titanate calcium nanofibers uses methanol washing.

[0026] In some embodiments of the present invention, during the preparation of the modified copper titanate calcium nanofibers, the drying is controlled to be carried out at 50-70°C for 5-15 hours.

[0027] In some preferred embodiments of the present invention, the method for preparing the hydroxylated copper calcium titanate nanofibers includes: mixing the copper calcium titanate nanofibers with hydrogen peroxide and reacting them at 140-160°C under reflux and stirring conditions.

[0028] In this invention, the surface of copper titanate calcium nanofibers is hydroxylated to improve their surface reactivity.

[0029] In some embodiments of the present invention, the preparation of the hydroxylated copper calcium titanate nanofibers includes: mixing the copper calcium titanate nanofibers and hydrogen peroxide, ultrasonicating, then refluxing and vigorously stirring at a temperature of 140-160°C, allowing the mixture to cool naturally after 4-12 hours of reaction, centrifuging to recover the mixture, washing (using deionized water), and drying (at a temperature of 50-70°C) to obtain the hydroxylated copper calcium titanate nanofibers.

[0030] In some preferred embodiments of the present invention, the average diameter of the copper calcium titanate nanofibers is 300-700 nm and the length is greater than or equal to 7 μm.

[0031] In some preferred embodiments of the present invention, the calcium copper titanate nanofibers are prepared by the following method:

[0032] Calcium nitrate, copper acetate, tetrabutyl titanate, dispersant, and second solvent are mixed and stirred to obtain a precursor solution.

[0033] The obtained precursor solution was used as the spinning solution, and electrospinning was performed to obtain calcium copper titanate precursor nanofibers.

[0034] The copper calcium titanate precursor nanofibers are sintered sequentially at 200-600℃ and 700-1200℃, and then cooled to obtain the copper calcium titanate nanofibers.

[0035] In some embodiments of the present invention, calcium nitrate and copper acetate typically contain water of crystallization. The present invention may use calcium nitrate tetrahydrate and copper acetate monohydrate.

[0036] In some embodiments of the present invention, the atomic ratio of Ca, Cu, and Ti in the added calcium nitrate, copper acetate, and tetrabutyl titanate is 1:3:4.

[0037] In some embodiments of the present invention, the second solvent comprises an alcohol solvent and an organic acid, wherein the alcohol solvent includes ethanol, preferably anhydrous ethanol, and the organic acid includes glacial acetic acid.

[0038] In some embodiments of the present invention, the dispersant is polyvinylpyrrolidone.

[0039] In some embodiments of the present invention, the spinning conditions of the electrospinning method are as follows: feed speed of 0.01-100 mL / h, voltage of 0.01-100 kV, receiving distance of 0.01-100 cm, inner diameter of spinneret of 0.01-1 mm, and spinning stroke of 1-500 mm.

[0040] Furthermore, the spinning conditions of the electrospinning method are as follows: feed speed of 1-30 mL / h, voltage of 1-50 kV, receiving distance of 3-40 cm, inner diameter of spinneret of 0.05-0.5 mm, and spinning stroke of 20-400 mm.

[0041] According to some preferred and specific aspects of the present invention, the sintering is carried out at 250-550°C (holding time approximately 0.5-2h) and 800-1100°C (holding time approximately 0.5-2h), respectively; further, the sintering is carried out at 300-500°C (holding time approximately 0.5-2h) and 850-1050°C (holding time approximately 0.5-2h), respectively; and even further, the sintering is carried out at 350-450°C (holding time approximately 0.5-2h) and 900-1000°C (holding time approximately 0.5-2h), respectively.

[0042] According to some preferred aspects of the present invention, the heating rate is controlled to be 0.01-30℃ / min during the sintering process; further, the heating rate is controlled to be 0.1-20℃ / min during the sintering process; and even further, the heating rate is controlled to be 0.1-10℃ / min during the sintering process.

[0043] According to some preferred aspects of the invention, the alkoxysilane containing a terminal amino group is selected from at least one of the compounds shown in formula (III);

[0044] In formula (Ⅲ), R9 is selected from C 1-6 Alkylene, R 10 R 11 R 12 Selected independently from C 1-6 alkyl.

[0045] Furthermore, R9 is selected from -CH2-, -CH2-CH2-, -CH2-CH2-CH2-, or -CH2-CH(CH3)-CH2-. 10 R 11 R 12 It is independently selected from methyl, ethyl, n-propyl, isopropyl, and butyl.

[0046] According to some preferred aspects of the present invention, in the process of preparing the aminated copper calcium titanate nanofibers, the reaction between the hydroxylated copper calcium titanate nanofibers and the alkoxysilane containing the terminal amino group is carried out under a protective atmosphere (which can be formed by introducing nitrogen or helium, etc.) at 70-90°C.

[0047] According to some preferred aspects of the present invention, in the process of preparing the aminated copper calcium titanate nanofibers, the reaction time between the hydroxylated copper calcium titanate nanofibers and the alkoxysilane containing the terminal amino group is controlled to be 15-35 h, preferably 20-30 h.

[0048] In some embodiments of the present invention, the methods for preparing aminated calcium copper titanate nanofibers include:

[0049] Hydroxylated copper calcium titanate nanofibers were mixed with a third solvent (including but not limited to toluene, xylene, N,N-dimethylformamide, anhydrous ethanol, etc.), sonicated, and then an alkoxysilane containing a terminal amino group was added. After multiple nitrogen purgings, the reaction was heated to 70-90°C under a nitrogen atmosphere for 15-35 hours. After the reaction was completed, the mixture was allowed to cool naturally, centrifuged, and washed repeatedly with ethanol and water. Finally, it was freeze-dried to obtain aminolated copper calcium titanate nanofibers.

[0050] The reaction mechanism of hydroxylated copper calcium titanate nanofibers and alkoxysilanes containing terminal amino groups is as follows: under heating conditions, alkoxysilanes containing terminal amino groups will release alkoxy groups to form silanol groups. The silanol groups will condense with the hydroxyl groups on the surface of hydroxylated copper calcium titanate nanofibers, thereby achieving chemical bonding and thus realizing the surface amylation modification of copper calcium titanate nanofibers.

[0051] Another technical solution provided by the present invention is a modified copper calcium titanate nanofiber, which is prepared by the above-described method for preparing modified copper calcium titanate nanofiber.

[0052] Another technical solution provided by the present invention is the application of the above-mentioned modified copper calcium titanate nanofibers as dielectric fillers in the preparation of dielectric composite materials.

[0053] Another technical solution provided by the present invention: a dielectric composite material, the dielectric composite material comprising a polymer matrix and a dielectric filler, wherein the polymer matrix is ​​polyetherimide and the dielectric filler is the modified copper titanate calcium nanofiber described above.

[0054] In this dielectric composite material, the modified copper titanate calcium nanofibers account for 0.5 vol%-20 vol% by volume, and the polyetherimide accounts for 80 vol%-99.5 vol%.

[0055] Furthermore, in the dielectric composite material, the modified copper titanate calcium nanofibers account for 0.5 vol%-15 vol% and the polyetherimide accounts for 85 vol%-99.5 vol% by volume percentage.

[0056] In some embodiments of the present invention, polyetherimide is added in the form of polyetherimide particles with a particle size of 50-900 μm, preferably 100-600 μm, and more preferably 100-500 μm.

[0057] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0058] This invention addresses the problem of compromises that arise when adding copper-calcium titanate ceramic particles to polyetherimide during the preparation of dielectric composite materials using existing techniques. It innovatively provides a novel method for preparing modified copper-calcium titanate nanofibers. This method uses copper-calcium titanate nanofibers as a base, first performing surface hydroxylation modification to activate the nanofibers, followed by amylation modification. The hydroxyl groups imparted during the surface modification condense with silanols containing terminal amino groups, introducing silicon-doped segments containing terminal amino groups onto the surface of the copper-calcium titanate nanofibers. On the one hand, the presence of these segments can… The organic compound generated by the addition reaction of the compound shown in formula (I) and the compound shown in formula (II) is coated on the inorganic material. The interaction between organic compounds improves the integrity of the organic polymer coating on the surface of the inorganic material calcium copper titanate nanofibers. On the other hand, many amino groups on the surface of the calcium copper titanate nanofibers can also undergo addition reactions with the carbon-carbon double bonds contained in the compound shown in formula (I), making the organic coating layer more tightly bound to the calcium copper titanate nanofibers. This can reduce the dielectric loss that may be caused by the introduction of calcium copper titanate nanofibers and also improve the breakdown strength.

[0059] Meanwhile, by introducing imide (from the compound shown in formula (I)) and diphenyl ether (from the compound shown in formula (II)) structures on the surface of modified copper calcium titanate nanofibers, the present invention has a high similarity to the structural units in polyether imide, which improves the dispersibility of modified copper calcium titanate nanofibers in polyether imide, increases the system compatibility, thereby greatly enhancing the degree of interfacial polarization, and can also significantly reduce the compatibility and polarization loss problems that may be caused by the introduction of high aspect ratio nanofibers;

[0060] Furthermore, the dielectric composite material made by adding modified copper calcium titanate nanofibers to polyetherimide in this invention has achieved unexpected dielectric stability, especially in maintaining dielectric stability over a wide temperature range, such as 30-150°C. Attached Figure Description

[0061] Figure 1 The image shows the morphology of the calcium copper titanate precursor nanofibers prepared in Example 1 of this invention.

[0062] Figure 2 The image shows the morphology of the calcium copper titanate nanofibers prepared in Example 1 of this invention.

[0063] Figure 3 The image shows the morphology of a single copper calcium titanate nanofiber prepared in Example 1 of this invention.

[0064] Figure 4 The XRD pattern of the calcium copper titanate nanofibers prepared in Example 1 of this invention;

[0065] Figure 5 The infrared spectrum of the modified calcium copper titanate nanofibers prepared in Example 1 of this invention;

[0066] Figure 6 Transmission electron microscopy image of the modified calcium copper titanate nanofibers prepared in Example 1 of this invention;

[0067] Figure 7 This is a graph showing the change of dielectric constant of the dielectric composite material and pure polyetherimide obtained in Examples 1-5 of this invention as a function of frequency;

[0068] Figure 8 The graph shows the change of dielectric constant with frequency for the dielectric composite materials obtained by comparative examples 1-5 in this invention.

[0069] Figure 9 This is a graph showing the change in dielectric loss of the dielectric composite material and pure polyetherimide obtained in Examples 1-5 of the present invention as a function of frequency;

[0070] Figure 10 The graph shows the change in dielectric loss of the dielectric composite material obtained by applying Comparative Examples 1-5 of this invention as a function of frequency.

[0071] Figure 11 The diagram shows the breakdown strength of pure polyetherimide and the dielectric composites obtained in Examples 1-5 and Comparative Examples 1-5 at their respective filler contents.

[0072] Figure 12 The graph shows the change of dielectric constant of the dielectric composite materials obtained in Examples 1-5 as a function of temperature;

[0073] Figure 13 The graph shows the change of dielectric constant as a function of temperature for pure polyetherimide and the dielectric composites obtained by applying Comparative Examples 1-5.

[0074] Figure 14 The graph shows the change of dielectric loss as a function of temperature for the dielectric composite materials obtained in Examples 1-5.

[0075] Figure 15 The graph shows the dielectric loss of pure polyetherimide and the dielectric composites obtained using Comparative Examples 1-5 as a function of temperature. Detailed Implementation

[0076] The above-mentioned solution will be further described below with reference to specific embodiments; it should be understood that these embodiments are used to illustrate the basic principles, main features and advantages of the present invention, and the present invention is not limited to the scope of the following embodiments; the implementation conditions used in the embodiments can be further adjusted according to specific requirements, and the implementation conditions not specified are usually the conditions in conventional experiments.

[0077] Unless otherwise specified in the following examples, all raw materials are commercially available or prepared by conventional methods in the art.

[0078] In the following, polyvinylpyrrolidone was purchased from Aladdin, brand name V3409; polyetherimide granules were purchased from Sabiq, brand name ULTEM PEI 9075.

[0079] Example 1

[0080] This example provides a method for preparing modified calcium copper titanate nanofibers and the prepared modified calcium copper titanate nanofibers. The method for preparing the modified calcium copper titanate nanofibers includes:

[0081] (1) Preparation of calcium copper titanate nanofibers

[0082] (1-1) Preparation of spinning solution: Weigh 0.2076 g of calcium nitrate tetrahydrate, 0.5275 g of copper acetate monohydrate, and 1.2 g of tetrabutyl titanate, dissolve them in 20 mL of anhydrous ethanol, add 0.3 mL of glacial acetic acid, and stir magnetically until completely dissolved;

[0083] (1-2) Slowly add 1.21g of polyvinylpyrrolidone, seal with plastic wrap, and stir at 30℃ for 3h to obtain a clear green precursor solution.

[0084] (1-3) Electrospinning: The obtained precursor solution was drawn into a 10mL disposable syringe. Electrospinning was performed under the following conditions: a feed rate of 1.6mL / h, a voltage of 20.12kV, a receiving distance of 15cm, a spinneret inner diameter of 0.23mm, and a spinning stroke of 200mm. The nanofibers were collected by a roller at a collection speed of 2400rpm to obtain uniformly oriented calcium copper titanate precursor nanofibers, the morphology of which is as follows: Figure 1 As shown, the morphology is uniform;

[0085] (1-4) Sintering of nanofibers: Calcium copper titanate precursor nanofibers were placed in a high-temperature resistant boat, which was then pushed into a muffle furnace. The temperature was then increased to 400℃ at a rate of 2℃ / min, held at 400℃ for 1 hour, and then increased to 950℃ at a rate of 2℃ / min, maintaining this temperature for approximately 1 hour. The mixture was then allowed to cool naturally to room temperature to obtain calcium copper titanate nanofibers, with the morphology shown below. Figure 2As shown, the morphology is relatively uniform, with a diameter of approximately 300–500 nm and a length reaching 10 μm. The morphology of a single sintered copper titanate calcium nanofiber is as follows: Figure 3 As shown, the copper titanate calcium nanofibers are slender and have a high aspect ratio. The XRD pattern of these nanofibers is shown below. Figure 4 As shown, this proves that calcium copper titanate was formed after sintering;

[0086] (2) Surface hydroxylation modification

[0087] 1g of copper calcium titanate nanofibers prepared according to step (1) were uniformly mixed with 40mL of hydrogen peroxide (hydrogen peroxide mass concentration of 30%), ultrasonically treated for 30min, refluxed and vigorously stirred at 150℃, and after the reaction continued for 8h, the mixture was naturally cooled and centrifuged for recovery. The product was washed with deionized water and placed in a vacuum oven at 60℃ for complete drying to obtain hydroxylated copper calcium titanate nanofibers.

[0088] (3) Surface amination

[0089] 0.5 g of hydroxylated copper titanate calcium nanofibers prepared according to step (2) were completely mixed with 30 mL of toluene. After ultrasonic treatment for 30 min, 0.5 g of 3-aminopropyltriethoxysilane (APS) was added. The system was heated to 80 °C under nitrogen atmosphere by three nitrogen purgings. The reaction was stirred and continued for 24 h. After the reaction was completed, the system was cooled naturally, centrifuged and recovered. The product was washed repeatedly by centrifugation with ethanol and water. The product was placed in a freeze dryer (freezing temperature -40 °C) and freeze-dried for 36 h to obtain hydroxylated copper titanate calcium nanofibers.

[0090] (4) Preparation of modified copper titanate calcium nanofibers

[0091] 0.3 g of the aminated copper titanate calcium nanofibers prepared according to step (3) was added to a four-necked flask purged with nitrogen. Then, 30 mL of N,N'-dimethylformamide (DMF), 0.7167 g (2 mmol) of N,N'-(methylenediphenyl)bismaleimide and 0.3966 g (2 mmol) of 4,4'-diaminodiphenyl ether were added. The mixture was reacted at 60 °C for two hours. After the reaction was completed, the mixture was poured into a large amount of water to precipitate the precipitate. The precipitate was acidified with 1 mol / L hydrochloric acid, washed with methanol, and dried under vacuum at 60 °C for 8 hours to obtain light yellow modified copper titanate calcium nanofibers.

[0092] The infrared spectrum of the prepared modified calcium copper titanate nanofibers is shown below. Figure 5 As shown, the surface of the calcium copper titanate nanofibers is at least coated with an organic polymer formed by the addition reaction of N,N'-(methylenediphenyl)bismaleimide and 4,4'-diaminodiphenyl ether; the transmission electron microscopy (TEM) image of the prepared modified calcium copper titanate nanofibers is shown below. Figure 6As shown in the figure, the surface of the copper titanate calcium nanofiber has a coating layer, and the whole structure is similar to a rod-shaped structure with inner and outer layers.

[0093] Example 2

[0094] The process is basically the same as in Example 1, except that the process for preparing calcium copper titanate nanofibers is different.

[0095] In this example, the method for preparing calcium copper titanate nanofibers includes:

[0096] (1-1) Preparation of spinning solution: Weigh 0.2082 g of calcium nitrate tetrahydrate, 0.5280 g of copper acetate monohydrate, and 1.2 g of tetrabutyl titanate, dissolve them in 20 mL of anhydrous ethanol, add 0.28 mL of glacial acetic acid, and stir magnetically until completely dissolved;

[0097] (1-2) Slowly add 1.19g of polyvinylpyrrolidone, seal with plastic wrap, and stir at 30℃ for 2.5h to obtain a clear green precursor solution;

[0098] (1-3) Electrospinning: The obtained precursor solution was drawn into a 10mL disposable syringe. Electrospinning was carried out under the following conditions: the push speed was 1.6mL / h, the voltage was 19.89l kV, the receiving distance was 15cm, the inner diameter of the spinneret was 0.23mm, and the spinning stroke was 200mm. The nanofibers of calcium copper titanate precursor were collected by a roller at a collection speed of 2400rpm to obtain uniformly oriented calcium copper titanate precursor nanofibers.

[0099] (1-4) Sintering of nanofibers: The copper calcium titanate precursor nanofibers are placed in a high-temperature resistant boat and then pushed into a muffle furnace. The temperature is then increased to 400°C at a rate of 5°C / min. After the temperature in the furnace is 400°C, it is held for 1 hour. Then the temperature is increased to 950°C at a rate of 5°C / min and held at 950°C for about 1 hour. Then it is naturally cooled to room temperature to obtain copper calcium titanate nanofibers with a diameter of about 400-600 nm and a length of more than 7 μm.

[0100] Example 3

[0101] The process is basically the same as in Example 1, except that the process for preparing calcium copper titanate nanofibers is different.

[0102] In this example, the method for preparing calcium copper titanate nanofibers includes:

[0103] (1-1) Preparation of spinning solution: Weigh 0.1036 g of calcium nitrate tetrahydrate, 0.2598 g of copper acetate monohydrate, and 0.6 g of tetrabutyl titanate, dissolve them in 10 mL of anhydrous ethanol, add 0.20 mL of glacial acetic acid, and stir magnetically until completely dissolved;

[0104] (1-2) Slowly add 0.8g of polyvinylpyrrolidone, seal with plastic wrap, and stir at 30℃ for 2.5h to obtain a clear green precursor solution;

[0105] (1-3) Electrospinning: The obtained precursor solution was drawn into a 10mL disposable syringe. Electrospinning was carried out under the following conditions: the push speed was 1.6mL / h, the voltage was 20.02kV, the receiving distance was 15cm, the inner diameter of the spinneret was 0.23mm, and the spinning stroke was 200mm. The nanofibers of calcium copper titanate precursor were collected by a roller at a collection speed of 2400rpm to obtain uniformly oriented calcium copper titanate precursor nanofibers.

[0106] (1-4) Sintering of nanofibers: The copper calcium titanate precursor nanofibers are placed in a high-temperature resistant boat and then pushed into a muffle furnace. The temperature is then increased to 400°C at a rate of 3°C / min. After the temperature in the furnace is 400°C, it is held for 1 hour. Then the temperature is increased to 950°C at a rate of 3°C / min and held at 950°C for about 1 hour. Then it is naturally cooled to room temperature to obtain copper calcium titanate nanofibers with a diameter of about 300-600 nm and a length of more than 8 μm.

[0107] Comparative Example 1

[0108] This example provides an unmodified copper calcium titanate nanofiber, which is prepared by the same method as step (1) in Example 1.

[0109] Application Example 1

[0110] This embodiment provides a dielectric composite material and its preparation method. The dielectric composite material includes polyetherimide and modified copper calcium titanate nanofibers (prepared in Example 1). By volume percentage, the modified copper calcium titanate nanofibers account for 2 vol% and the polyetherimide accounts for 98 vol%.

[0111] The preparation method of this dielectric composite material includes:

[0112] Weigh out 2 vol% (0.0032 g) of modified copper titanate nanofibers (prepared in Example 1) and place them in a beaker. Add 50 mg of polyetherimide (added in the form of polyetherimide particles) and 1.5 mL of N,N-dimethylacetamide (DMAc) and disperse. Sonicate for 1 h and stir at 30 °C until homogeneous. Then drop-coat the mixture onto a clean glass slide and dry it in a vacuum oven at 70 °C for 24 h. Peel off the dried film from the glass slide to obtain a film-like dielectric composite material with a thickness of about 20 μm.

[0113] Application Example 2

[0114] The application is basically the same as in Example 1, except that, by volume percentage, the modified copper titanate calcium nanofibers account for 4 vol% and polyetherimide accounts for 96 vol% in this dielectric composite material.

[0115] Application Example 3

[0116] The application is basically the same as in Example 1, except that, by volume percentage, the modified copper titanate calcium nanofibers account for 6 vol% and the polyetherimide accounts for 94 vol% in the dielectric composite material.

[0117] Application Example 4

[0118] The application is basically the same as in Example 1, except that, by volume percentage, the modified copper titanate calcium nanofibers account for 8 vol% and the polyetherimide accounts for 92 vol% in this dielectric composite material.

[0119] Application Example 5

[0120] The application is basically the same as in Example 1, except that, by volume percentage, the modified copper titanate calcium nanofibers account for 10 vol% and polyetherimide accounts for 90 vol% in this dielectric composite material.

[0121] Application Comparative Example 1

[0122] The application is basically the same as in Example 1, except that, by volume percentage, the unmodified copper calcium titanate nanofibers prepared in Comparative Example 1 account for 2 vol% and the polyetherimide accounts for 98 vol% in this dielectric composite material.

[0123] Application Comparative Example 2

[0124] The application is basically the same as in Example 1, except that, by volume percentage, the unmodified calcium copper titanate nanofibers prepared in Comparative Example 1 account for 4 vol% and polyetherimide accounts for 96 vol% in this dielectric composite material.

[0125] Application Comparative Example 3

[0126] The application is basically the same as in Example 1, except that, by volume percentage, the unmodified copper calcium titanate nanofibers prepared in Comparative Example 1 account for 6 vol% and the polyetherimide accounts for 94 vol%.

[0127] Application Comparative Example 4

[0128] The application is basically the same as in Example 1, except that, by volume percentage, the unmodified copper calcium titanate nanofibers prepared in Comparative Example 1 account for 8 vol% and the polyetherimide accounts for 92 vol%.

[0129] Application Comparative Example 5

[0130] The application is basically the same as in Example 1, except that, by volume percentage, the unmodified calcium copper titanate nanofibers prepared in Comparative Example 1 account for 10 vol% and the polyetherimide accounts for 90 vol% in this dielectric composite material.

[0131] Performance testing

[0132] 1. The dielectric constants of the dielectric composite materials and pure polyetherimide obtained from Application Examples 1-5 and Comparative Examples 1-5 were tested at different frequencies. Some results are shown in Table 1.

[0133] The method for testing the dielectric constant is as follows: the curve of dielectric properties changing with frequency was obtained by a broadband dielectric impedance spectrometer of model GmbH Concept 40 manufactured by Novocontrol GmbH, Germany. A circular gold film with a diameter of 3 mm was deposited on both sides of the film-like dielectric composite material sample as an electrode using an ion sputtering instrument. During the test, an AC voltage of 1 V was applied across the electrodes, and the test was performed by adjusting the frequency on the instrument.

[0134] Figure 7 The graph shows the change of dielectric constant of the dielectric composite material and pure polyetherimide obtained in Examples 1-5 as a function of frequency. It can be seen from the graph that as the content of modified copper titanate calcium nanofibers increases, the dielectric constant of the composite dielectric material gradually increases, and it is significantly higher than that of pure polyetherimide.

[0135] Figure 8 The graph shows the change in dielectric constant as a function of frequency for the dielectric composite materials obtained in Comparative Examples 1-5 (the amounts of unmodified calcium copper titanate nanofibers added in Comparative Examples 1-5 were 2 vol%, 4 vol%, 6 vol%, 8 vol%, and 10 vol%, respectively). It can be seen from the graph that when the amount of unmodified calcium copper titanate nanofibers added is relatively low (e.g., 2 vol%-6 vol%), the dielectric constant does not increase with the increase of the amount added. In particular, there are cases where the dielectric constant at the amount of 6 vol% is actually lower than that at the amounts of 2 vol% and 4 vol%, which makes the dielectric constant of the dielectric composite material significantly uncertain and uncontrollable, which is not conducive to industrial application.

[0136] 2. The dielectric loss of the dielectric composite materials and pure polyetherimide obtained from Application Examples 1-5 and Comparative Examples 1-5 was tested at different frequencies. Some results are shown in Table 1.

[0137] The method for testing dielectric loss is as follows: the dielectric performance variation curve with frequency was obtained by a broadband dielectric impedance spectrometer of model GmbH Concept 40 manufactured by Novocontrol GmbH, Germany. A circular gold film with a diameter of 3 mm was deposited on both sides of the film-like dielectric composite material as an electrode using an ion sputtering instrument. During the test, an AC voltage of 1V was applied across the electrodes, and the test was conducted by adjusting the frequency on the instrument.

[0138] Figure 9 The graph shows the dielectric loss of the dielectric composite materials obtained in Examples 1-5 and pure polyetherimide as a function of frequency. As can be seen from the graph, the dielectric loss of the dielectric composite material with the modified copper-calcium titanate nanofibers of this invention increases only slightly compared to pure polyetherimide, remaining approximately around 0.02 at different frequencies. Furthermore, even with increasing addition amounts, the dielectric loss remains at a very low level. Figure 9 As shown, when the addition amounts are 2 vol% (Application Example 1), 4 vol% (Application Example 2), 6 vol% (Application Example 3), 8 vol% (Application Example 4), and 10 vol% (Application Example 5), the dielectric loss is basically the same, and there is a large overlap at different frequencies. It can be seen that the dielectric loss of the dielectric composite material with the addition of the modified copper titanate calcium nanofiber of the present invention can be well suppressed and controlled.

[0139] Figure 10 To illustrate the dielectric loss versus frequency of the dielectric composite materials obtained in Comparative Examples 1-5, the following diagrams were created. Figure 10 It can be seen that the overall dielectric loss of the dielectric composite material obtained by adding unmodified copper calcium titanate nanofibers is relatively high. When the content of the addition gradually increases, the dielectric loss increases significantly. In particular, when the content of the addition increases to 10 vol%, the dielectric loss begins to approach 0.2, which is about 10 times that of the application example of this invention.

[0140] Table 1

[0141]

[0142] In summary, this invention introduces an organic polymer coating layer on the surface of calcium copper titanate nanofibers and partially chemically connects the coating layer with the aminated calcium copper titanate nanofibers, resulting in a higher integrity and tighter bonding of the coating layer. Furthermore, by introducing imide and diphenyl ether structures on the surface of the modified calcium copper titanate nanofibers, which have a high similarity to the structural units in polyetherimide, the dispersibility of the modified calcium copper titanate nanofibers in polyetherimide is improved, the system compatibility is increased, thereby greatly enhancing the degree of interfacial polarization. Moreover, it can also significantly reduce the compatibility and polarization loss problems that may be caused by the introduction of high aspect ratio nanofibers.

[0143] Specifically, by Figures 7-10 It can be seen that, compared with the dielectric composite material prepared by unmodified copper calcium titanate nanofibers, the dielectric composite material using the modified copper calcium titanate nanofibers of this invention not only significantly improves the dielectric constant compared with pure polyetherimide, but the dielectric constant is also basically unaffected by the negative impact of the introduced polymer (generally speaking, the introduction of organic polymers will significantly reduce the dielectric constant of the material); especially, by Figure 9 and Figure 10 Comparative analysis shows that the dielectric loss of the dielectric composite material with the modified copper titanate calcium nanofiber of this invention is significantly reduced, overcoming the common problem of sacrificing some aspects for others in the prior art. Moreover, even with a significant increase in filler content, the dielectric loss can be basically maintained without a significant increase, which is beneficial for applications in more scenarios. Furthermore, the dielectric loss is highly controllable and suitable for industrial applications.

[0144] 3. Test the breakdown strength of pure polyetherimide, and the dielectric composites obtained by applying Examples 1-5 and Comparative Examples 1-5. See the comparison chart. Figure 11 As shown in the figure, the specific results are shown in Table 2.

[0145] Table 2

[0146]

[0147] Analysis shows that the modified copper calcium titanate nanofibers of this invention, compared with unmodified copper calcium titanate nanofibers, achieve a significantly improved breakdown strength when applied to polyetherimide, especially at relatively low addition levels (around 2 vol%), where the breakdown strength shows an unexpectedly large increase. At relatively high addition levels (4 vol%-10 vol%), the decrease in breakdown strength in the application examples of this invention is smaller compared to the comparative examples as the amount of dielectric filler increases. It is believed that the dielectric loss of the dielectric composite material prepared using the modified copper calcium titanate nanofibers of this invention remains at a low level even when the amount of dielectric filler increases significantly. Electron movement in the material is significantly suppressed, resulting in improved insulation performance and a substantial increase in breakdown field strength. Furthermore, the dielectric loss does not decrease significantly with increasing dielectric filler content, remaining at a relatively high level.

[0148] It is evident that the modified calcium copper titanate nanofibers of this invention achieve better application results in polyetherimide compared to unmodified calcium copper titanate nanofibers, and significantly reduce compatibility issues that may be caused by the high aspect ratio nanofiber effect.

[0149] 4. At a frequency of 1000Hz, the dielectric constant and dielectric loss of pure polyetherimide, and the dielectric composite materials obtained in Examples 1-5 and Comparative Examples 1-5, were tested at different temperatures. Specific results can be found in [reference needed]. Figures 12-15 As shown;

[0150] Depend on Figure 12 and Figure 13 It can be seen that the dielectric constant of the dielectric composite material obtained by applying Examples 1-5 of the present invention remains basically unchanged with the increase of temperature, while the dielectric constant of the dielectric composite material obtained by applying Comparative Examples 1-5 shows some visible fluctuations with the increase of temperature, but is also basically stable.

[0151] However, by Figure 14 and Figure 15 It can be seen that the dielectric loss of the dielectric composite material obtained by applying Examples 1-5 of the present invention remains basically unchanged with the increase of temperature, while the dielectric loss of the dielectric composite material obtained by applying Comparative Examples 1-5 increases significantly with the increase of temperature. The significant increase in dielectric loss is obviously not conducive to the application of dielectric composite materials such as energy storage.

[0152] It is evident that the dielectric composite material made by adding the modified copper calcium titanate nanofibers of the present invention to polyetherimide achieves unexpected dielectric stability, especially in maintaining dielectric stability over a wide temperature range, such as 30-150°C.

[0153] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

[0154] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

Claims

1. Use of modified calcium copper titanate nanofibers as dielectric filler in the preparation of dielectric composites, characterized in that, The preparation method of the modified copper calcium titanate nanofiber comprises: (1) reacting the surface hydroxyl-modified copper calcium titanate nanofiber with an amino-terminated alkoxysilane to obtain an amino-modified copper calcium titanate nanofiber with an amino group connected to the surface; (2) mixing the amino-modified copper calcium titanate nanofiber, a compound represented by formula (I), and a compound represented by formula (II), and reacting under heating to obtain the modified copper calcium titanate nanofiber; In formula (I), R1is selected from C 1-6 alkylene, , R2, R3, R4, R5are independently selected from hydrogen, C 1-6 alkyl, R8is selected from C 1-6 alkylene, oxygen or NH; In formula (II), R6, R7are independently selected from hydrogen, C 1-6 alkyl; The amino-terminated alkoxysilane is selected from at least one of the compounds represented by formula (III). In formula (III), R9is selected from C 1-6 alkylene, R 10 , R 11 , R 12 are independently selected from C 1-6 alkyl.

2. Use of the modified copper calcium titanate nanofiber according to claim 1 as a dielectric filler in the preparation of a dielectric composite material, characterized in that, In step (1), the reaction is carried out at 70-90°C.

3. Use of the modified copper calcium titanate nanofiber according to claim 1 or 2 as a dielectric filler in the preparation of a dielectric composite material, characterized in that, Embodiments for preparing the amino-modified copper calcium titanate nanofiber comprise: The surface hydroxyl-modified copper calcium titanate nanofiber and a third solvent are mixed, ultrasonic treatment is performed, the amino-terminated alkoxysilane is added, the reaction is carried out under nitrogen atmosphere after nitrogen replacement for multiple times, heating is performed to 70-90°C, the reaction time is 15-35h, natural cooling is performed after the reaction, centrifugal recovery is performed, repeated centrifugal washing is performed with ethanol and water, and freeze-drying is performed to obtain the amino-modified copper calcium titanate nanofiber.

4. Use of the modified calcium copper titanate nanofiber according to claim 1 as a dielectric filler in the preparation of a dielectric composite, characterized in that, In formula (III), R9is selected from -CH2-, -CH2-CH2-, -CH2-CH2-CH2- or -CH2-CH(CH3)-CH2-, R 10 , R 11 , R 12 are independently selected from methyl, ethyl, n-propyl, i-propyl, butyl.

5. Use of the modified copper calcium titanate nanofiber according to claim 1 as a dielectric filler in the preparation of a dielectric composite material, characterized in that, Embodiments for preparing the modified copper calcium titanate nanofiber in step (2) comprise: The amino-modified copper calcium titanate nanofiber is added into a reaction container with a protective gas, then N,N'-dimethylformamide, the compound represented by formula (II), and the compound represented by formula (III) are added, and reaction is carried out under heating for 1-4h, the reaction mixture after reaction is poured into water for precipitation, acidification, washing, and drying to obtain the modified copper calcium titanate nanofiber.

6. Use of the modified copper calcium titanate nanofiber according to claim 5 as a dielectric filler in the preparation of a dielectric composite material, characterized in that, In the process of preparing the modified copper calcium titanate nanofiber: The acidification is performed with hydrochloric acid, and the molar concentration of the hydrochloric acid is 0.5-2mol / L; The washing is performed with methanol; The drying is controlled to be performed at 50-70°C, and the drying time is 5-15h.

7. Use of the modified copper calcium titanate nanofiber according to claim 1 as a dielectric filler in the preparation of a dielectric composite material, characterized in that, In the process of preparing the modified copper calcium titanate nanofiber in step (2), the reaction of the amino-modified copper calcium titanate nanofiber, the compound represented by formula (I), and the compound represented by formula (II) is controlled to be carried out at 50-70°C; and / or, in step (2), the reaction of the amino-modified copper calcium titanate nanofiber, the compound represented by formula (I), and the compound represented by formula (II) is controlled to be carried out under the protection of a protective atmosphere formed by introducing nitrogen or helium.

8. Use of the modified copper calcium titanate nanofiber according to claim 1 as a dielectric filler in the preparation of a dielectric composite material, characterized in that, In the process of preparing the modified copper calcium titanate nanofiber in step (2), the molar ratio of the compound represented by formula (I) to the compound represented by formula (II) is 1:0.8-1.2, and the addition amount of the compound represented by formula (II) is greater than that of the amino-modified copper calcium titanate nanofiber.

9. Use of the modified copper calcium titanate nanofiber according to claim 1 as a dielectric filler in the preparation of a dielectric composite material, characterized in that, In formula (I), R1is selected from -CH2-, -CH2-CH2-, -CH2-CH2-CH2-, -CH2-CH(CH3)-CH2-, -CH2-C(CH3)2-CH2-, , , R2, R3, R4, R5are independently selected from hydrogen, methyl, ethyl, n-propyl or isopropyl; In formula (II), the amino group is substituted on the para-position carbon atom of the carbon atom connected to oxygen in the benzene ring, and R6 and R7 are independently selected from hydrogen, methyl, or ethyl.

10. Use of the modified calcium copper titanate nanofiber according to claim 1 as a dielectric filler in the preparation of a dielectric composite material, characterized in that, The dielectric composite comprises a polymer matrix and the modified calcium copper titanate nanofiber, the polymer matrix being polyetherimide, and in the dielectric composite, the modified calcium copper titanate nanofiber accounts for 0.5vol%-20vol% and the polyetherimide accounts for 80vol%-99.5vol% in terms of volume percentage.

11. Use of the modified copper calcium titanate nanofiber according to claim 10 as a dielectric filler in the preparation of a dielectric composite material, characterized in that, In the dielectric composite, the modified calcium copper titanate nanofiber accounts for 0.5vol%-15vol% and the polyetherimide accounts for 85vol%-99.5vol% in terms of volume percentage.

12. Use of the modified calcium copper titanate nanofiber according to claim 10 as a dielectric filler in the preparation of a dielectric composite material, characterized in that, The polyetherimide is added in the form of polyetherimide particles with a particle size of 50-900μm.

13. Use of the modified copper calcium titanate nanofiber according to claim 12 as a dielectric filler in the preparation of a dielectric composite material, characterized in that, The polyetherimide particles have a particle size of 100-600μm.

14. Use of the modified copper calcium titanate nanofiber according to claim 13 as a dielectric filler in the preparation of a dielectric composite material, characterized in that, The polyetherimide particles have a particle size of 100-500μm.

15. Use of the modified copper calcium titanate nanofiber according to claim 10 as a dielectric filler in the preparation of a dielectric composite material, characterized in that, The average diameter of the calcium copper titanate nanofiber is 300-700nm, and the length is greater than or equal to 7μm; the calcium copper titanate nanofiber has a rod-like structure with an inner layer and an outer layer.

16. Use of the modified copper calcium titanate nanofiber according to claim 10 as a dielectric filler in the preparation of a dielectric composite material, characterized in that, The dielectric composite has a use temperature range of 30-150℃.

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