Polypropylene-based composites, methods of making and use thereof

Abstract

Disclosed are a polypropylene-based composite, a preparation method and applications thereof. The composite comprises 95-99.5 wt% of polypropylene and 0.5-5 wt% of gamma-alumina nanosheets. Specifically, the gamma-alumina nanosheets are compounded into polypropylene to obtain the composite, so that the dielectric constant and breakdown field strength of the composite are improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of polymer composites, and relates to a polypropylene-based composite, a preparation method and application thereof. BACKGROUND

[0002] With the increasing demand for energy, the requirements for composites in power systems are becoming higher and higher. In power systems, polypropylene (PP) is an important composite and is widely used in cable insulation, capacitor film and other fields. However, the breakdown field strength and energy storage density of pure polypropylene material are relatively low, which limits its application in high-voltage and high-energy storage fields.

[0003] In recent years, nanocomposites have attracted widespread attention due to their excellent physical and chemical properties. Although researchers have made some achievements in polypropylene / nanocomposites, there are still some problems: the dispersibility of nanosheets in the polypropylene matrix still needs to be improved to fully exert the performance advantages of nanosheets; the preparation process of the composite still needs to be optimized to realize large-scale production; the relationship between the performance of the composite and the content and size of nanosheets is not clear and needs further study.

[0004] In view of the existing problems, it is urgent to optimize the preparation process, study the influence of the content and size of nanosheets on the performance of the composite, and provide a theoretical basis for the research and application of high-performance polypropylene-based composites. SUMMARY

[0005] In order to overcome the above problems, the present application provides a polypropylene-based composite, a preparation method and application thereof, the composite comprising 95-99.5wt% of polypropylene and 0.5-5wt% of γ-alumina nanosheets. Specifically, the γ-alumina nanosheets are in-situ compounded into polypropylene to obtain the composite, so that the dielectric constant and breakdown field strength of the composite are improved, thereby achieving the present application.

[0006] Specifically, the present application aims to provide the following aspects:

[0007] In a first aspect, a polypropylene-based composite is provided, the composite comprising 95-99.5wt% of polypropylene and 0.5-5wt% of γ-alumina nanosheets.

[0008] The length of the γ-alumina nanosheets is 119-163 nanometers.

[0009] The thickness of the γ-alumina nanosheets is 8-10 nanometers.

[0010] The γ-alumina nanosheets are in-situ compounded into polypropylene to obtain the composite.

[0011] In a second aspect, a method for preparing the composite of the first aspect is provided, the method comprising:

[0012] Step 1: dissolving polypropylene pellets in an organic solvent to obtain a first solution;

[0013] Step 2: adding a suspension containing γ-alumina nanosheets to the first solution to obtain a second solution;

[0014] Step 3: purifying the second solution to obtain the composite.

[0015] In Step 1, the organic solvent is selected from one or more of decalin, toluene, and xylene.

[0016] In Step 1, the dissolving temperature of the polypropylene pellets in the organic solvent is 90-110°C.

[0017] In Step 3, the purifying includes: suction filtration, extraction, and drying.

[0018] In Step 3, the suction filtration is performed using acetone.

[0019] In a third aspect, the composite of the first aspect or prepared by the method of the second aspect is applied to polypropylene-based composite films.

[0020] The present application has the following beneficial effects:

[0021] (1) The polypropylene-based composite of the present application has improved dielectric constant and breakdown field strength by in-situ doping of polypropylene and γ-alumina nanosheets.

[0022] (2) The γ-alumina nanosheets contained in the polypropylene-based composite of the present application are prepared by stage drying and stage sintering to obtain complete nanosheet structure, thereby improving the performance of the composite. BRIEF DESCRIPTION OF DRAWINGS

[0023] Various other advantages and benefits of the present application will become apparent to those of ordinary skill in the art, upon reading the following detailed description of the preferred embodiment. The accompanying drawings are included to provide a better understanding of the preferred embodiment and are not to be considered as limitations of the present application. It should be readily understood that the drawings are merely illustrative of the present application and that they, therefore, do not limit the present application to the principles of the preferred embodiment described herein. It is also readily understood that the present application is well suited to providing other embodiments that fall within the scope of the present application.

[0024] In the drawings:

[0025] FIG. 1(a) shows one of the TEM characterizations of the γ-alumina nanosheets prepared in Example 1;

[0026] Figure 1(b) shows the second TEM characterization of the γ-alumina nanosheets prepared in Example 1;

[0027] Figure 1(c) shows the TEM characterization of the γ-alumina nanosheets prepared in Comparative Example 1;

[0028] Figure 2 The dielectric constant and material loss spectrum of the polypropylene-based composite films prepared in Examples 1-4 and the polypropylene film prepared in Comparative Example 2 are shown in comparison.

[0029] Figure 3 The diagram shows the Weibull distribution of DC breakdown for the polypropylene-based composite films prepared in Examples 1-4 and the polypropylene film prepared in Comparative Example 2. Detailed Implementation

[0030] The following will refer to the appendix. Figures 1(a) to 3 Specific embodiments of the invention will be described in more detail below. While specific embodiments of the invention are shown in the accompanying drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art.

[0031] It should be noted that certain terms are used in the specification and claims to refer to specific components. Those skilled in the art will understand that different terms may be used to refer to the same component. This specification and claims do not distinguish components based on differences in terminology, but rather on differences in function. The terms "comprising" or "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising but not limited to." The following descriptions are preferred embodiments for carrying out the invention; however, these descriptions are for the purpose of understanding the general principles of the specification and are not intended to limit the scope of the invention. The scope of protection of this invention is determined by the appended claims.

[0032] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," "outer," "front," and "rear," etc., indicate the orientation or positional relationship based on the orientation or positional relationship in the working state of this invention, and are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. Furthermore, the terms "first," "second," "third," and "fourth" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0033] To facilitate understanding of the embodiments of the present invention, further explanations and descriptions will be provided below with reference to the accompanying drawings and specific embodiments. The accompanying drawings do not constitute a limitation on the embodiments of the present invention.

[0034] On one hand, according to the present invention, a polypropylene-based composite comprises 95-99.5 wt% polypropylene and 0.5-5 wt% γ-alumina nanosheets.

[0035] In this composite system, polypropylene serves as the matrix material, while γ-alumina nanosheets act as a barrier against discharge, inhibit breakdown development, and prevent the growth of electrical trees. Low-concentration doping can improve the insulation performance of the polypropylene-based composite. Preferably, the composite comprises 99-99.5 wt% polypropylene and 0.5-1 wt% γ-alumina nanosheets; more preferably, the composite comprises 99.5 wt% polypropylene and 0.5 wt% γ-alumina nanosheets.

[0036] In this invention, the γ-alumina nanosheets have a thickness of 8-10 nanometers and a length of 119-163 nanometers.

[0037] Secondly, according to a method for preparing a polypropylene-based composite provided by the present invention, the method includes: in-situ composite of γ-alumina nanosheets into polypropylene to obtain the composite.

[0038] According to the preferred embodiment, the specific steps include:

[0039] Step 1: Dissolve the polypropylene granules in an organic solvent to obtain the first solution;

[0040] Step 2: Add the suspension containing γ-alumina nanosheets to the first solution to obtain the second solution;

[0041] Step 3: The second solution is purified to obtain the complex.

[0042] Specifically:

[0043] Step 1: Dissolve polypropylene in an organic solvent to obtain the first solution.

[0044] In step 1, the organic solvent is preferably selected from one or more of decahydronaphthalene, toluene, and xylene, with xylene being the most preferred.

[0045] The organic solvent is used to dissolve the polypropylene granules, which have excellent solubility in xylene.

[0046] Furthermore, the mass ratio (g:mL) of polypropylene granules to organic solvent is 1:(90~150), preferably 1:(95~110), for example 1:100.

[0047] The solubility of the polypropylene particles in the organic solvent is limited, and therefore more organic solvent is required to ensure that the polypropylene particles are fully dissolved, and too much organic solvent can reduce the reaction rate of the reaction system.

[0048] In step 1, the polypropylene particles are dissolved in the organic solvent and fully dissolved at 90-110°C, such as 100°C.

[0049] The polypropylene in the polypropylene particles is a non-polar polymer, and its solubility in the organic solvent increases with increasing temperature. In the temperature range of 90-110°C, it is sufficient to fully dissolve the polypropylene in the organic solvent.

[0050] In step 2, the suspension containing γ-alumina nanosheets is added to the first solution to obtain a second solution.

[0051] In step 2, the suspension containing γ-alumina nanosheets uses one or more of decalin, toluene, and xylene as the solvent, preferably consistent with the selection of the organic solvent in step 1, such as both being xylene, to avoid the influence of other impurities on the reaction system.

[0052] The γ-alumina nanosheets are dispersed in the solvent in advance to improve the dispersibility of the γ-alumina nanosheets in the first solution. To disperse the γ-alumina nanosheets as uniformly as possible in the solvent, ultrasonic treatment is preferably performed for 2-3h, such as 2h.

[0053] In step 2, the concentration of the γ-alumina nanosheets in the solvent is not strictly limited.

[0054] In step 2, the mass of the γ-alumina nanosheets is 0.5-5wt% of the total mass of the polypropylene and the γ-alumina nanosheets, preferably 0.5-1wt%, and more preferably 0.5wt%.

[0055] In step 2, the suspension containing γ-alumina nanosheets is added to the first solution, and stirring is performed for 2-4h to improve the dispersibility of the γ-alumina nanosheets in the first solution.

[0056] The inventors have found that the γ-alumina nanosheets obtained by the prior art have blurred edges, pores, and irregular shapes, and the inventors have prepared γ-alumina nanosheets by optimizing the hydrothermal reaction and optimizing the sintering method to improve the quality of the γ-alumina nanosheets.

[0057] In a preferred embodiment, the γ-alumina nanosheets are prepared by the following method:

[0058] In step 2-1, an aluminum salt is dissolved to obtain a liquid with a pH of 4.8-5.1.

[0059] Step 2-2, hydrothermally treating the liquid to obtain a first product;

[0060] Step 2-3, sintering the first product to obtain the γ-alumina nanosheet.

[0061] In step 2-1, the aluminum salt is selected from one of aluminum carbonate, aluminum acetate, and aluminum sulfate 18-hydrate powder, preferably aluminum sulfate 18-hydrate powder.

[0062] In the above, water is preferably used to dissolve the aluminum salt, which can form a solution in water more easily, and is conducive to the subsequent steps. The aluminum sulfate 18-hydrate powder usually has high purity and contains less impurities, which is helpful to prepare high-purity alumina nanosheets. More importantly, the crystal water in the aluminum sulfate 18-hydrate powder can be released during the heat treatment process, which is helpful to form porous alumina nanosheets.

[0063] In step 2-1, the concentration of the aluminum salt in water is 0.8-0.12 mol / L, for example 1 mol / L.

[0064] In step 2-1, the aluminum salt is stirred in water at a rate of 1000-2000 r / min for 1-5 h; preferably, it is stirred at a rate of 1400-1600 r / min for 2-4 h; for example, it is stirred at a rate of 1500 r / min for 3 h to obtain a uniform solution.

[0065] In step 2-1, since the soluble aluminum salt is usually strongly acidic, a weak base is usually used to adjust the pH, and at this time the aluminum hydroxide precursor formed by the reaction of the aluminum salt is suspended in water, that is, the liquid obtained at this time is a suspension.

[0066] In step 2-1, the pH is 4.8-5.1, for example 5.0. If the pH is greater than 7, a rod-shaped material will be obtained.

[0067] In step 2-1, the weak base is conducive to adjusting the pH, and in order to facilitate removal, ammonia is preferably used.

[0068] In step 2-2, the aluminum hydroxide precursor is converted into alumina by hydrothermal treatment.

[0069] In step 2-2, the temperature of the hydrothermal treatment is 180-200°C, preferably 185-195°C. For example, 190°C.

[0070] In step 2-2, the time of the hydrothermal treatment is 18-36 h, preferably 24-38 h, for example 24 h.

[0071] In the above, the temperature and time of the hydrothermal treatment can obtain the γ-alumina nanosheet with a sheet structure.

[0072] In step 2-2, the hydrothermal treatment is preferably carried out in a high-pressure reactor.

[0073] In step 2-2, after the hydrothermal treatment, the first product is obtained by washing and drying.

[0074] Preferably, the washing is carried out with water until neutralization to remove impurities, unreacted weak base such as ammonia and water-soluble impurities.

[0075] In step 1-2, the drying is a multi-stage drying, including:

[0076] First stage: drying at 25-40°C for 3-6h;

[0077] Second stage: drying at 50-65°C for 6-10h;

[0078] Third stage: drying at 70-100°C for 10-15h.

[0079] Further preferably, the drying includes:

[0080] First stage: drying at 30-35°C for 4-5h;

[0081] Second stage: drying at 55-60°C for 7-8h;

[0082] Third stage: drying at 80-85°C for 11-13h.

[0083] Most preferably, the drying includes:

[0084] First stage: drying at 30°C for 4h;

[0085] Second stage: drying at 60°C for 8h;

[0086] Third stage: drying at 80°C for 12h.

[0087] In step 2-3, the sintering is a multi-stage sintering, including:

[0088] First stage: heating from room temperature to 110-140°C at a rate of 6-15°C / min, and keeping the temperature for 0.3-1.5h;

[0089] Second stage: heating to 260-320°C at a rate of 8-20°C / min, and keeping the temperature for 0.3-1h;

[0090] Third stage: heating to 430-480°C at a rate of 6-15°C / min, and keeping the temperature for 0.3-2h;

[0091] Stage IV: increasing the temperature to 570-630 ℃ at a temperature increasing rate of 8-20 ℃ / min, and keeping the temperature for 0.5-2 h; and then naturally cooling to room temperature.

[0092] In the stage sintering, the reaction rate and the overflow speed of the product are controlled, so that a better product morphology is obtained.

[0093] Further preferably, the sintering comprises:

[0094] Stage I: increasing the temperature from room temperature to 115-130 ℃ at a temperature increasing rate of 8-10 ℃ / min, and keeping the temperature for 0.3-1 h;

[0095] Stage II: increasing the temperature to 280-310 ℃ at a temperature increasing rate of 9-11 ℃ / min, and keeping the temperature for 0.5-1 h;

[0096] Stage III: increasing the temperature to 440-460 ℃ at a temperature increasing rate of 8-10 ℃ / min, and keeping the temperature for 0.3-1.5 h;

[0097] Stage IV: increasing the temperature to 580-620 ℃ at a temperature increasing rate of 9-11 ℃ / min, and keeping the temperature for 0.6-1.2 h; and then naturally cooling to room temperature.

[0098] Further preferably, the sintering comprises:

[0099] Stage I: increasing the temperature from room temperature to 120 ℃ at a temperature increasing rate of 10 ℃ / min, and keeping the temperature for 0.5 h;

[0100] Stage II: increasing the temperature to 300 ℃ at a temperature increasing rate of 10 ℃ / min, and keeping the temperature for 0.5 h;

[0101] Stage III: increasing the temperature to 450 ℃ at a temperature increasing rate of 10 ℃ / min, and keeping the temperature for 0.5 h;

[0102] Stage IV: increasing the temperature to 600 ℃ at a temperature increasing rate of 10 ℃ / min, and keeping the temperature for 0.5 h; and then naturally cooling to room temperature.

[0103] In step 3, the purification comprises: suction filtration, extraction and drying.

[0104] In step 3, the purification comprises: suction filtration, extraction and drying.

[0105] In step 3, the suction filtration is preferably performed by using acetone. Acetone has relatively high volatility, which is beneficial for rapid removal; and acetone has high solubility, which can effectively remove the residual organic solvents and other organic impurities in the polypropylene.

[0106] In step 3, preferably, Soxhlet extractor is used for extraction in deionized water.

[0107] In step 3, the drying is preferably freeze-drying, and the time is not strictly limited, and generally 25-48h can be used.

[0108] In a third aspect, the application provides a polypropylene-based composite film, which is prepared by hot pressing a polypropylene-based composite as a filler and a polyimide film as a matrix.

[0109] In the application, the polyimide film should have a proper thickness and size so as to completely wrap the biaxially stretched composite material in the subsequent hot pressing process, and generally the thickness thereof is selected to be 100-150μm.

[0110] In the application, the hot pressing temperature is 190-220℃, the time is 8-10min, and the pressure is 15-20MPa; for example, the temperature is 210℃, the time is 10min, and the pressure is 15MPa.

[0111] In the application, the dielectric constant of the composite film is in the range of 2.2-2.45, and the maximum dielectric constant is 2.45; the breakdown field strength is 481-625 kV / mm, and the maximum is 625 kV / mm.

[0112] The application will be further described below by specific examples, but these examples are only exemplary and do not constitute any limitation on the protection scope of the application.

[0113] Example 1

[0114] (1) Preparation of γ-alumina nanosheet:

[0115] 0.05 mol of aluminum sulfate octadecahydrate powder was dissolved in 50 mL of deionized water at room temperature, and stirred at a speed of 1500r / min for 3h; then the pH value of the solution was adjusted to 5 by ammonia water, and stirred for 30min using a stirring rod to obtain a suspension;

[0116] The above suspension was transferred to a 100 mL stainless steel high-pressure reaction kettle with a Teflon lining, and hydrothermally treated at 190℃ for 24h; then the obtained product was separated by filtration and washed with deionized water until neutral, and then dried in a vacuum oven at 30℃ for 4h; dried in a vacuum oven at 60℃ for 8h; dried in a vacuum oven at 80℃ for 12h to obtain a first product;

[0117] The first product was placed in a muffle furnace in an air atmosphere and sintered in the following stages:

[0118] Stage I: increase the temperature from room temperature to 120 °C at a rate of 10 °C / min, and keep the temperature at 120 °C for 0.5 h;

[0119] Stage II: increase the temperature to 300 °C at a rate of 10 °C / min, and keep the temperature at 300 °C for 0.5 h;

[0120] Stage III: increase the temperature to 450 °C at a rate of 10 °C / min, and keep the temperature at 450 °C for 0.5 h;

[0121] Stage IV: increase the temperature to 600 °C at a rate of 10 °C / min, and keep the temperature at 600 °C for 0.5 h; and then naturally cool to room temperature.

[0122] After the above steps, the γ-alumina nanosheets are obtained and ready for use.

[0123] (2) 5 g of polypropylene pellets are dissolved in 500 mL of dimethylbenzene at 100 °C to obtain a first solution; 0.025 g of the γ-alumina nanosheets prepared in step (1) are dissolved in 10 mL of dimethylbenzene (at this time, the mass of the γ-alumina nanosheets is 0.5 wt% of the total mass of the polypropylene and the γ-alumina nanosheets), and ultrasonic dispersion is performed for 2 h to obtain a suspension containing the γ-alumina nanosheets; the above suspension of the γ-alumina nanosheets is added dropwise into the first solution using a pipette, and stirring is performed for 2 h to obtain a second solution; after the reaction is completed, the obtained product is poured into acetone and subjected to suction filtration, and a Soxhlet extractor is used to extract in a deionized water environment for 24 h, and then freeze-drying is performed for 48 h to obtain a polypropylene-based composite.

[0124] (3) A circular cutter with a diameter of 50 mm is used to cut a plurality of circular holes with a diameter of 5 cm in a first polyimide film with a thickness of 100 μm, a second polyimide film with a thickness of 100 μm is placed at the bottom of the first polyimide film, 0.2 g of the biaxially stretched composite material is placed in the circular holes of the first polyimide film, and a third polyimide film with a thickness of 100 μm is placed on the first polyimide film to encapsulate it, and then a flat plate vulcanizer is used for hot pressing treatment, the temperature is set to 210 °C, the pressure is set to 15 MPa, the treatment time is set to 10 min, the exhaust frequency is set to 15 times, and the exhaust time of each time is set to 10 s to obtain a polypropylene-based composite film.

[0125] Example 2

[0126] A polypropylene-based composite film is prepared in a similar manner to that of Example 1, except that the mass of the γ-alumina nanosheets is 1 wt% of the total mass of the polypropylene and the γ-alumina nanosheets, and specifically:

[0127] (1) Preparation of γ-alumina nanosheets:

[0128] Aluminum sulfate octadecahydrate powder, 0.05 mol, was dissolved in 50 mL of deionized water at room temperature, stirred at a rate of 1500 r / min for 3 h; then the pH value of the solution was adjusted to 5 by ammonia water, stirred with a stirring rod for 30 min to obtain a suspension;

[0129] The above suspension was transferred to a 100 mL stainless steel autoclave with a Teflon lining, hydrothermally treated at 190°C for 24 h; then the obtained product was separated by filtration and washed with deionized water until neutral, and then dried in a vacuum oven at 30°C for 4 h, dried in a vacuum oven at 60°C for 8 h, and dried in a vacuum oven at 80°C for 12 h to obtain a first product;

[0130] The first product was placed in a muffle furnace in an air atmosphere and sintered in the following stages:

[0131] Stage I: the temperature was raised from room temperature to 120°C at a rate of 10°C / min, and kept at this temperature for 0.5 h;

[0132] Stage II: the temperature was raised to 300°C at a rate of 10°C / min, and kept at this temperature for 0.5 h;

[0133] Stage III: the temperature was raised to 450°C at a rate of 10°C / min, and kept at this temperature for 0.5 h;

[0134] Stage IV: the temperature was raised to 600°C at a rate of 10°C / min, and kept at this temperature for 0.5 h; then naturally cooled to room temperature.

[0135] After the above steps, γ-alumina nanosheets were prepared for use.

[0136] (2) 5 g of polypropylene pellets were dissolved in 500 mL of xylene at 100°C to obtain a first solution; 0.05 g of γ-alumina nanosheets prepared in step (1) were dissolved in 10 mL of xylene (at this time, the mass of the γ-alumina nanosheets was 1 wt% of the total mass of the polypropylene and the γ-alumina nanosheets), and ultrasonically dispersed for 2 h to obtain a suspension containing γ-alumina nanosheets; the above suspension of γ-alumina nanosheets was added dropwise into the first solution using a pipette, and stirred for 2 h to obtain a second solution; after the reaction, the obtained product was poured into acetone and filtered, and then extracted in a deionized water environment using a Soxhlet extractor for 24 h, and then freeze-dried for 48 h to obtain a polypropylene-based composite.

[0137] (3) A circular cutter with a diameter of 50 mm is used to cut a plurality of circular holes with a diameter of 5 cm on a first polyimide film with a thickness of 100 μm, a second polyimide film with a thickness of 100 μm is placed at the bottom of the first polyimide film, 0.2 g of the biaxially stretched composite material is placed in the circular holes of the first polyimide film, a third polyimide film with a thickness of 100 μm is placed on the first polyimide film to encapsulate the first polyimide film, and then a flat plate vulcanizing instrument is used for hot pressing treatment, the temperature is set to 210 ℃, the pressure is set to 15 MPa, the treatment time is set to 10 min, the exhaust times are set to 15 times, and the exhaust time of each time is set to 10 s, to obtain a polypropylene-based composite film.

[0138] Example 3

[0139] A polypropylene-based composite film is prepared in a similar manner to that of Example 1, except that the mass of the γ-aluminum oxide nanosheets is 3 wt% of the total mass of the polypropylene and the γ-aluminum oxide nanosheets, specifically:

[0140] (1) Preparation of the γ-aluminum oxide nanosheets:

[0141] 0.05 mol of aluminum sulfate octadecahydrate powder is dissolved in 50 mL of deionized water at room temperature, and stirred at a speed of 1500 r / min for 3 h; then the pH value of the solution is adjusted to 5 by using ammonia water, and stirred for 30 min using a stirring rod to obtain a suspension;

[0142] The above suspension is transferred to a 100 mL stainless steel high-pressure reaction kettle with a Teflon lining, and hydrothermally treated at 190 ℃ for 24 h; then the obtained product is separated by filtration and washed with deionized water until neutral, and then dried in a vacuum oven at 30 ℃ for 4 h, dried in a vacuum oven at 60 ℃ for 8 h, and dried in a vacuum oven at 80 ℃ for 12 h to obtain a first product;

[0143] The first product is placed in a muffle furnace in an air atmosphere and sintered in the following stages:

[0144] Stage I: the temperature is raised from room temperature to 120 ℃ at a rate of 10 ℃ / min, and kept at this temperature for 0.5 h;

[0145] Stage II: the temperature is raised to 300 ℃ at a rate of 10 ℃ / min, and kept at this temperature for 0.5 h;

[0146] Stage III: the temperature is raised to 450 ℃ at a rate of 10 ℃ / min, and kept at this temperature for 0.5 h;

[0147] Stage IV: the temperature is raised to 600 ℃ at a rate of 10 ℃ / min, and kept at this temperature for 0.5 h; and then naturally cooled to room temperature.

[0148] The above steps end, and γ-alumina nanosheets are prepared for standby use.

[0149] (2) 5 g of polypropylene pellets were dissolved in 500 mL of xylene at 100 °C to obtain a first solution; 0.15 g of γ-alumina nanosheets prepared in step (1) were dissolved in 10 mL of xylene (at this time, the mass of the γ-alumina nanosheets was 3 wt% of the total mass of the polypropylene and the γ-alumina nanosheets), and ultrasonic dispersion was performed for 2 h to obtain a suspension containing the γ-alumina nanosheets; the above suspension of the γ-alumina nanosheets was added dropwise into the first solution using a pipette, and stirring was performed for 2 h to obtain a second solution; after the reaction was completed, the obtained product was poured into acetone and suction filtration was performed, and then a Soxhlet extractor was used for extraction in a deionized water environment for 24 h, followed by freeze-drying for 48 h, to obtain a polypropylene-based composite.

[0150] (3) A circular cutter with a diameter of 50 mm was used to cut a plurality of circular holes with a diameter of 5 cm in a first polyimide film with a thickness of 100 μm, a second polyimide film with a thickness of 100 μm was placed at the bottom of the first polyimide film, 0.2 g of the biaxially stretched composite material was placed in the circular holes of the first polyimide film, and a third polyimide film with a thickness of 100 μm was placed on the first polyimide film to encapsulate it, followed by hot-pressing treatment using a flat-plate vulcanizer, with the temperature set to 210 °C, the pressure set to 15 MPa, the treatment time set to 10 min, and the exhaust frequency set to 15 times, with each exhaust time set to 10 s, to obtain a polypropylene-based composite film.

[0151] Example 4

[0152] A polypropylene-based composite film was prepared in a similar manner to that of Example 1, except that the mass of the γ-alumina nanosheets was 5 wt% of the total mass of the polypropylene and the γ-alumina nanosheets, and specifically:

[0153] (1) Preparation of γ-alumina nanosheets:

[0154] 0.05 mol of aluminum sulfate octadecahydrate powder was dissolved in 50 mL of deionized water at room temperature, and stirring was performed at a speed of 1500 r / min for 3 h; then the pH value of the solution was adjusted to 5 by using ammonia water, and stirring was performed using a stirring rod for 30 min to obtain a suspension;

[0155] The above suspension was transferred to a 100 mL stainless steel high-pressure reaction kettle with a Teflon lining, and hydrothermal treatment was performed at 190 °C for 24 h; then the obtained product was separated by filtration and washed with deionized water until neutral, and then dried in a vacuum oven at 30 °C for 4 h, dried in a vacuum oven at 60 °C for 8 h, and dried in a vacuum oven at 80 °C for 12 h to obtain a first product;

[0156] The first product was placed in a muffle furnace in an air atmosphere and sintered in the following stages:

[0157] Stage I: temperature was raised from room temperature to 120 °C at a rate of 10 °C / min, and maintained at this temperature for 0.5 h;

[0158] Stage II: temperature was raised to 300 °C at a rate of 10 °C / min, and maintained at this temperature for 0.5 h;

[0159] Stage III: temperature was raised to 450 °C at a rate of 10 °C / min, and maintained at this temperature for 0.5 h;

[0160] Stage IV: temperature was raised to 600 °C at a rate of 10 °C / min, and maintained at this temperature for 0.5 h; and then naturally cooled to room temperature.

[0161] After the above steps, the γ-alumina nanosheets were obtained and ready for use.

[0162] (2) 5 g of polypropylene pellets were dissolved in 500 mL of dimethylbenzene at 100 °C to obtain a first solution; 0.25 g of the γ-alumina nanosheets prepared in step (1) were dissolved in 10 mL of dimethylbenzene (at this time, the mass of the γ-alumina nanosheets was 5 wt% of the total mass of the polypropylene and the γ-alumina nanosheets), and ultrasonic dispersion was performed for 2 h to obtain a suspension containing the γ-alumina nanosheets; the above suspension containing the γ-alumina nanosheets was added dropwise into the first solution using a pipette, and stirring was performed for 2 h to obtain a second solution; after the reaction was completed, the obtained product was poured into acetone and subjected to suction filtration, and a Soxhlet extractor was used to extract in a deionized water environment for 24 h, and then freeze-drying was performed for 48 h to obtain a polypropylene-based composite.

[0163] (3) A circular cutter with a diameter of 50 mm was used to cut a plurality of circular holes with a diameter of 5 cm in a first polyimide film with a thickness of 100 μm, a second polyimide film with a thickness of 100 μm was placed at the bottom of the first polyimide film, 0.2 g of the biaxially stretched composite material was placed in the circular holes of the first polyimide film, and a third polyimide film with a thickness of 100 μm was placed on the first polyimide film to encapsulate it, and then a flat plate vulcanizer was used for hot pressing treatment, the temperature was set to 210 °C, the pressure was set to 15 MPa, the treatment time was set to 10 min, the exhaust times were set to 15 times, and the exhaust time of each time was set to 10 s to obtain a polypropylene-based composite film.

[0164] Comparative Example 1

[0165] 0.05 mol aluminum sulfate octadecahydrate powder was dissolved in 50 mL of deionized water at room temperature, stirred at a speed of 1500 r / min for 3 h; then the pH value of the solution was adjusted to 5 by ammonia water, and the solution was stirred with a stirring rod for 30 min to obtain a suspension;

[0166] The above suspension was transferred to a 100 mL stainless steel autoclave with a Teflon liner, and hydrothermally treated at 190℃ for 24 h; then the obtained product was separated by filtration and washed with deionized water until neutral, and then dried in a vacuum oven at 30℃ for 4 h, dried in a vacuum oven at 60℃ for 8 h, and dried in a vacuum oven at 80℃ for 12 h to obtain a first product;

[0167] The obtained first product was placed in a muffle furnace under a nitrogen atmosphere, and heated from room temperature to 600℃ at a heating rate of 10℃ / min, and kept at 600℃ for 3 h; then naturally cooled to room temperature to obtain γ-alumina nanosheets.

[0168] Figure 1(a) shows one of the TEM characterizations of the γ-alumina nanosheets prepared in Example 1, in which the thickness of the prepared γ-alumina nanosheets is marked, and it can be seen that the length of the γ-alumina nanosheets is between 119 and 163 nm, and it can be clearly seen that the structure of the γ-alumina nanosheets is complete, which is due to the method of step sintering preventing the breakage of the intermediate product during rapid heating, thereby obtaining a complete nanosheet structure; Figure 1(b) shows the second TEM characterization of the γ-alumina nanosheets prepared in Example 1, in which the thickness of the prepared γ-alumina nanosheets is marked, and it can be seen that the thickness of the γ-alumina nanosheets is between 8 and 10 nm. Figure 1(c) shows the TEM characterization of the γ-alumina nanosheets prepared in Comparative Example 1, and it can be clearly seen that the γ-alumina nanosheets prepared in Example 1 have a more complete and clear structure.

[0169] Comparative Example 2

[0170] A circular cutter with a diameter of 50 mm was used to cut a plurality of circular holes with a diameter of 5 cm in a first polyimide film with a thickness of 100 μm. A second polyimide film with a thickness of 100 μm was placed at the bottom of the first polyimide film, and 0.2 g of polypropylene granules were placed in the circular holes of the first polyimide film. A third polyimide film with a thickness of 100 μm was placed on top of the first polyimide film to encapsulate it. Then a flat plate vulcanizer was used for hot pressing treatment, the temperature was set to 210℃, the pressure was set to 15 MPa, the treatment time was set to 10 min, the exhaust frequency was set to 15 times, and the exhaust time for each time was set to 10 s, to obtain a polypropylene film.

[0171] Figure 2The dielectric constant and material loss spectrum of the polypropylene-based composite films prepared in Examples 1-4 and the polypropylene film prepared in Comparative Example 2 are shown in the comparison chart. As shown in the chart, the dielectric constant of the polypropylene-based composite films prepared in Examples 1-4 is in the range of 2.2-2.45, and the dielectric constant of the polypropylene-based composite film prepared in Example 4 reaches 2.45, which is increased by 11.36% compared with the polypropylene film prepared in Comparative Example 2. The dielectric loss of the polypropylene-based composite films prepared in Examples 1-2 is in the order of 1E-3, which is close to the loss order of the polypropylene-based composite film prepared in Comparative Example 2.

[0172] Figure 3 The Weibull distribution of the DC breakdown of the polypropylene-based composite films prepared in Examples 1-4 and the polypropylene film prepared in Comparative Example 2 is shown in the chart. As shown in the chart, the breakdown field strength of the polypropylene-based composite films prepared in Examples 1 and 2 is 625 kV / mm and 603 kV / mm, respectively, which is increased by 8.89% and 5.05% compared with the breakdown field strength of the polypropylene film prepared in Comparative Example 2. The breakdown field strength of the polypropylene-based composite films prepared in Examples 3 and 4 is 576 kV / mm and 481 kV / mm, respectively, and the breakdown field strength of the polypropylene-based composite film prepared in Example 4 is decreased by 16.2% compared with the polypropylene film prepared in Comparative Example 2. In summary, the polypropylene-based composite film prepared in Example 1 has the best performance.

[0173] The above describes the present application in detail in combination with preferred embodiments and exemplary examples. However, it is declared that these specific embodiments are only illustrative explanations of the present application, and do not constitute any limitation on the protection scope of the present application. Various improvements, equivalent replacements or modifications can be made to the technical content and embodiments of the present application without departing from the spirit and protection scope of the present application, and these all fall within the protection scope of the present application. The protection scope of the present application is subject to the appended claims.

Claims

1. A polypropylene-based composite, characterized in that, The composite comprises 95-99.5wt% of polypropylene and 0.5-5wt% of γ-alumina nanosheets; The length of the γ-alumina nanosheets is 119-163 nanometers; the thickness of the γ-alumina nanosheets is 8-10 nanometers; The γ-alumina nanosheets are prepared by the following steps: Step 2-1, dissolving an aluminum salt to obtain a liquid with a pH of 4.8-5.1 after adjustment; Step 2-2, hydrothermally treating the liquid to obtain a first product; Step 2-3, sintering the first product to obtain the γ-alumina nanosheets; The temperature of the hydrothermal treatment is 180-200℃, and the time of the hydrothermal treatment is 18-36h; After the hydrothermal treatment, the first product is obtained after washing and drying; The drying is a staged drying, comprising: First stage: drying at 25-40℃ for 3-6h; Second stage: drying at 50-65℃ for 6-10h; Third stage: drying at 70-100℃ for 10-15h; The sintering is a staged sintering, comprising: Stage I: increasing the temperature from room temperature to 110-140℃ at a rate of 6-15 ℃ / min, and keeping the temperature for 0.3-1.5h; Stage II: increasing the temperature to 260-320℃ at a rate of 8-20 ℃ / min, and keeping the temperature for 0.3-1h; Stage III: increasing the temperature to 430-480℃ at a rate of 6-15 ℃ / min, and keeping the temperature for 0.3-2h; Stage IV: increasing the temperature to 570-630℃ at a rate of 8-20 ℃ / min, and keeping the temperature for 0.5-2h; and then naturally cooling to room temperature.

2. The composite of claim 1, wherein, The γ-alumina nanosheets are in-situ compounded into polypropylene to obtain the composite.

3. A method of preparing the complex of any one of claims 1-2, characterized in that, The method comprises: Step 1, dissolving polypropylene pellets in an organic solvent to obtain a first solution; Step 2, adding a suspension containing γ-alumina nanosheets to the first solution to obtain a second solution; Step 3, purifying the second solution to obtain the composite.

4. The method of claim 3, wherein, In step 1, the organic solvent is selected from one or more of decalin, toluene, and xylene.

5. The method of claim 4, wherein, In step 1, the dissolution temperature of the polypropylene pellets in the organic solvent is 90-110℃.

6. The method of claim 4, wherein, In step 3, the purification comprises: suction filtration, extraction, and drying.

7. The method of claim 6, wherein, Acetone is used for suction filtration.

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