Polypropylene-based composite material, preparation method, polypropylene-based composite film and application of polypropylene-based composite film

Abstract

The invention discloses a polypropylene-based composite material, a preparation method, a polypropylene-based composite film and application of the polypropylene-based composite film. The composite material comprises the following components in parts by mass: 5-30 parts of polypropylene, 5-20 parts of methyl methacrylate grafted polypropylene and 5-20 parts of maleic anhydride grafted polypropylene. According to the composite material, polypropylene is subjected to methyl methacrylate graft modification and maleic anhydride graft modification respectively, and the energy storage density of a polypropylene matrix is improved by means of full-organic composite modification.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer composite materials, and relates to a polypropylene-based composite material, a preparation method, a polypropylene-based composite film and applications thereof. Background Art

[0002] Power capacitors, as one of the core energy storage devices, are widely used in many fields such as pulse power systems, new energy generation, high voltage direct current transmission systems and electric vehicles due to their significant advantages such as high power density and high withstand voltage. However, compared with other energy storage components such as batteries and supercapacitors, the energy storage density of power capacitors is relatively low, resulting in their large size, which greatly limits their application in more fields. Therefore, the development of dielectric materials with high energy storage density for the manufacture of the next generation of smaller and larger capacity power capacitors has become an urgent problem that needs to be solved.

[0003] Polypropylene is currently the most widely used dielectric material for power capacitors. It has the advantages of low loss, high withstand voltage, easy biaxial stretching and large-scale film preparation. However, its too low dielectric constant (about 2.2) leads to its low energy storage density.

[0004] In addition to improving the intrinsic dielectric constant of polymers through molecular structure design, research has found that adding ceramic or conductive nanofillers to polymers to make nanocomposite dielectrics can also significantly improve the dielectric constant and obtain high energy storage density composite materials. However, in the process of studying nanocomposite materials, it was found that there were many problems such as serious agglomeration of nanofillers, decreased electrical strength, increased leakage current, increased dielectric loss, poor flexibility, difficulty in processing into films, and inability to achieve synergistic improvement of energy storage properties.

[0005] Therefore, how to improve the energy storage density of polypropylene film is an urgent problem to be solved. Summary of the invention

[0006] In order to overcome the above problems, the present invention provides a polypropylene-based composite material, a preparation method, a polypropylene-based composite film and applications thereof.

[0007] Specifically, the purpose of the present invention is to provide the following aspects:

[0008] In a first aspect, a polypropylene-based composite material is provided, wherein the composite material comprises the following components in parts by weight:

[0009] Polypropylene 5-30 parts;

[0010] 5-20 parts of methyl methacrylate grafted polypropylene;

[0011] 5-20 parts of maleic anhydride grafted polypropylene.

[0012] The energy storage density of the composite material is 2.4-2.5 J / cm 3 In a second aspect, a method for preparing the composite material according to the first aspect is provided, the method comprising:

[0013] Step 1, purifying polypropylene pellets to obtain polypropylene;

[0014] Step 2, modifying the polypropylene to prepare methyl methacrylate grafted polypropylene and maleic anhydride grafted polypropylene respectively;

[0015] Step 3: melt-blending the polypropylene, methyl methacrylate grafted polypropylene and maleic anhydride grafted polypropylene to obtain the composite material.

[0016] In step 1, polypropylene pellets are purified using an ash detergent.

[0017] Wherein, the ash detergent is selected from one or more of n-hexane, isopropanol, petroleum ether and dichloromethane.

[0018] In step 2, polypropylene is modified with methyl methacrylate to obtain methyl methacrylate grafted polypropylene.

[0019] In step 2, maleic anhydride monomer is used to modify polypropylene to obtain maleic anhydride grafted polypropylene.

[0020] In a third aspect, a polypropylene-based composite film is provided, wherein the composite film comprises the polypropylene-based composite material described in the first aspect.

[0021] Wherein, the composite film uses a polypropylene-based composite material as a filler.

[0022] In a fourth aspect, a power capacitor is provided, wherein the power capacitor comprises the polypropylene-based composite material described in the first aspect.

[0023] The beneficial effects of the present invention include:

[0024] (1) The energy storage density of the polypropylene-based composite material provided by the present invention reaches 2.43 J / cm 3 , and has a high dielectric constant and high breakdown field strength.

[0025] (2) The method for preparing the polypropylene-based composite material provided by the present invention realizes the full organic composite modification of polypropylene by modifying polypropylene with methyl methacrylate and maleic anhydride respectively, thereby effectively improving the energy storage characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] By reading the detailed description of the preferred specific embodiments below, various other advantages and benefits of the present invention will become clear to those of ordinary skill in the art. The drawings in the specification are only used for the purpose of illustrating the preferred embodiments and are not considered to be limitations of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without creative work.

[0027] In the attached picture:

[0028] Figure 1 A comparison chart of dielectric constant and material loss spectrum of the polypropylene-based composite material and polypropylene in Example 1 is shown;

[0029] Figure 2 The DC breakdown Weibull distribution diagram of the polypropylene-based composite material and polypropylene in Example 1 is shown;

[0030] Figure 3 A comparison chart of dielectric constant and material loss spectrum of polypropylene-based composite materials in Example 1, Example 2 and Example 3 is shown;

[0031] Figure 4 The DC breakdown Weibull distribution diagrams of the polypropylene-based composite materials in Example 1, Example 2 and Example 3 are shown. DETAILED DESCRIPTION

[0032] The following will refer to the attached Figures 1 to 4 Specific embodiments of the present invention are described in more detail. Although specific embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0033] It should be noted that certain words are used in the specification and claims to refer to specific components. Those skilled in the art should understand that technicians may use different nouns to refer to the same component. This specification and claims do not use the difference in nouns as a way to distinguish components, but use the difference in the functions of the components as the criterion for distinction. As mentioned throughout the specification and claims, "including" or "comprising" is an open term, so it should be interpreted as "including but not limited to". The subsequent description of the specification is a preferred embodiment of the present invention, but the description is based on the general principles of the specification and is not intended to limit the scope of the present invention. The scope of protection of the present invention shall be determined by the attached claims.

[0034] In the description of the present invention, it should be noted that the terms "upper", "lower", "inner", "outer", "front", "rear", etc. indicate positions or positional relationships based on the working state of the present invention, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", "third", and "fourth" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0035] To facilitate understanding of the embodiments of the present invention, further explanation will be given below by taking specific embodiments as examples in conjunction with the accompanying drawings, and each of the accompanying drawings does not constitute a limitation on the embodiments of the present invention.

[0036] In a first aspect, a polypropylene-based composite material is provided according to the present invention, wherein the composite material comprises the following components in parts by weight:

[0037] Polypropylene 5-30 parts;

[0038] 5-20 parts of methyl methacrylate grafted polypropylene;

[0039] 5-20 parts of maleic anhydride grafted polypropylene.

[0040] Among them, polypropylene is used as the main matrix, methyl methacrylate and maleic anhydride are used as strong polar and weak polar small molecular monomers of polypropylene respectively, which play a role in increasing the dielectric constant in the composite system; in addition, methyl methacrylate and maleic anhydride are compounded to weaken the destructive effect of the rigid maleic anhydride monomer grafting on polypropylene.

[0041] In a further preferred embodiment, the composite material comprises the following components in parts by weight:

[0042] Polypropylene 10-15 parts;

[0043] 8-12 parts of methyl methacrylate grafted polypropylene;

[0044] Maleic anhydride grafted polypropylene 8-12 parts.

[0045] In a further preferred embodiment, the composite material comprises the following components in parts by weight:

[0046] Polypropylene 10 parts;

[0047] 10 parts of methyl methacrylate grafted polypropylene;

[0048] 10 parts of maleic anhydride grafted polypropylene.

[0049] According to the present invention, the dielectric constant of the composite material is 2.5-2.7, the breakdown field strength is 460-462 kV / mm, and the energy storage density is 2.4-2.5 J / cm 3 In one embodiment, the composite material has a dielectric constant of 2.6, a breakdown field strength of 461 kV / mm, and an energy storage density of 2.43 J / cm 3 .

[0050] In a second aspect, a method for preparing the composite material according to the first aspect is provided, the method comprising:

[0051] Step 1, purifying polypropylene pellets to obtain polypropylene;

[0052] Step 2, modifying the polypropylene to prepare methyl methacrylate grafted polypropylene and maleic anhydride grafted polypropylene respectively;

[0053] Step 3: melt-blending the polypropylene, methyl methacrylate grafted polypropylene and maleic anhydride grafted polypropylene to obtain the composite material.

[0054] Specifically:

[0055] Step 1, purifying polypropylene pellets to obtain polypropylene.

[0056] In step 1, the polypropylene pellets are purified using an ash detergent, specifically comprising the following steps:

[0057] Step 1-1, washing polypropylene pellets with an ash detergent to obtain clean pellets;

[0058] Step 1-2, drying the cleaned food to obtain polypropylene.

[0059] In step 1-1, the ash detergent is selected from one or more of n-hexane, isopropanol, petroleum ether, and dichloromethane, such as n-hexane.

[0060] The ash detergent is used to remove oil and non-polar impurities on the surface of polypropylene. In particular, n-hexane has good compatibility with polypropylene and can effectively dissolve non-polar substances.

[0061] In step 1-1, the ratio (g:mL) of the polypropylene pellets to the ash detergent is 3:(30-40), preferably 3:(32-36), for example 3:35.

[0062] Among them, sufficient ash detergent can ensure the full removal of oil and non-polar impurities on the surface of polypropylene. Based on the density and surface area of ​​PP pellets, the above ratio can usually ensure that pollutants on the surface and inside of the pellets are effectively removed.

[0063] In step 1-1, the washing temperature is 70-90°C, preferably 75-85°C, for example 80°C.

[0064] Among them, the washing temperature of 70~90°C can reduce the viscosity of the ash detergent, thereby making it easier for the ash detergent to penetrate into the gaps and holes of the polypropylene pellets, thereby improving the washing efficiency; and at this temperature, the polypropylene will not undergo thermal deformation and / or degradation.

[0065] In step 1-1, the washing time is 3 to 7 hours, preferably 4 to 6 hours, for example 5 hours.

[0066] The washing time needs to be long enough to ensure that the pollutants on the surface of the polypropylene pellets are fully dissolved and removed. The above washing time can achieve a better washing effect.

[0067] In step 1-1, the stirring rate used during washing is 1000-2000 r / min, preferably 1500-1600 r / min, for example 1500 r / min.

[0068] Among them, a higher stirring rate can keep the polypropylene pellets suspended in the ash detergent to avoid sedimentation, ensuring that all polypropylene pellets can contact the ash detergent; and this stirring rate helps to break the agglomeration between particles and improve the washing efficiency. However, too high a stirring rate may cause pellet damage.

[0069] In step 1-1, the washing is preferably carried out in an inert gas such as nitrogen to reduce the possibility of oxidation reaction and maintain the performance and color of the polypropylene.

[0070] In step 1-1, the washing is performed 1 to 3 times, preferably 3 times, to obtain polypropylene with higher purity.

[0071] In step 1-2, the drying temperature is 70-90° C., preferably 75-85° C., for example 80° C., to ensure that thermal deformation and / or degradation does not occur while drying quickly.

[0072] Furthermore, the drying time is 12 to 36 hours, for example 24 hours, so as to fully remove impurities contained in the polypropylene.

[0073] Step 2, modifying the polypropylene to prepare methyl methacrylate grafted polypropylene and maleic anhydride grafted polypropylene respectively.

[0074] In step 2, the methyl methacrylate grafted polypropylene is obtained by the following steps:

[0075] Step 2-1, dissolving polypropylene in an organic solvent to obtain a first solution;

[0076] Step 2-2, adding methyl methacrylate to the first solvent to obtain a second solution;

[0077] Step 2-3, adding an initiator to the second solvent, and successively filtering and extracting to obtain methyl methacrylate grafted polypropylene.

[0078] In step 2-1, the organic solvent is preferably selected from one or more of decahydronaphthalene, toluene, and xylene, preferably xylene.

[0079] The organic solvent is used to dissolve polypropylene for grafting reaction. Xylene can also be used as a solvent for the initiator to help the initiator be evenly dispersed in the reaction system.

[0080] In step 2-1, the mass ratio of polypropylene to the volume ratio of the organic solvent (g:mL) is 3:(90-150), preferably 1:(95-110), for example 3:100.

[0081] Among them, the solubility of polypropylene in organic solvents is limited, so more organic solvents are needed to ensure that polypropylene can be fully dissolved. Too much organic solvent may reduce the reaction rate of the reaction system.

[0082] In step 2-1, polypropylene is dissolved in an organic solvent and fully dissolved at 90-110°C, such as 100°C.

[0083] Among them, polypropylene is a non-polar polymer, and its solubility in organic solvents increases with increasing temperature. In the temperature range of 90~110℃, the solubility of polypropylene is sufficient to make it fully soluble in organic solvents.

[0084] In step 2-2, methyl methacrylate is added to the first solvent at 70-80°C, such as 80°C.

[0085] Among them, the boiling point of methyl methacrylate is 100°C. Adding methyl methacrylate in an environment below its boiling point is to prevent the reaction system from boiling. The boiling liquid vapor will cause excessive gas pressure inside the reaction system and lead to safety accidents.

[0086] In step 2-2, the ratio of polypropylene to methyl methacrylate (g:mL) is 1:0.5-5, preferably 1:0.5-2.5, for example 1:1.

[0087] Among them, methyl methacrylate, as a small molecular monomer, will undergo self-polymerization reaction under certain temperature and initiator conditions, and then lose its function as a grafting monomer. Therefore, the dosage needs to be controlled. Within the above range, methyl methacrylate can be guaranteed to be grafted to polypropylene.

[0088] In step 2-3, the initiator is dibenzoyl peroxide or dicumyl peroxide, preferably dibenzoyl peroxide.

[0089] Among them, dibenzoyl peroxide has a moderate effective catalytic period as an initiator and performs well in the polypropylene grafting reaction. The reaction conditions are milder than those of diisopropylbenzene peroxide. Within a reaction time of 2 hours, the cleavage effect on the polypropylene molecular chain is weak.

[0090] In step 2-3, preferably, the initiator is first dissolved in an organic solvent to obtain a mixed solution with a concentration of 20-30%, and then the mixed solution is added to the second solution; for example, a mixed solution with a concentration of 25% is obtained, and then the mixed solution is added to the second solution.

[0091] Among them, in the graft polymerization reaction of polypropylene and methyl methacrylate, the initiator provides free radicals, which can start and accelerate the polymerization reaction. The decomposition products of dibenzoyl peroxide are relatively environmentally friendly and do not produce harmful by-products; and its decomposition products can continue to initiate the reaction, produce more free radicals, and form a chain reaction.

[0092] In step 2-3, when the initiator is added, the temperature is 85-115°C, for example, 95°C. The temperature in this step is not higher than the boiling point of the small molecule grafting monomer methyl methacrylate. If the reaction vessel is equipped with a condensation reflux device, the temperature is not higher than 115°C. When the temperature is higher than 115°C, the catalytic activity of the initiator such as dibenzoyl peroxide is lost quickly and the grafting reaction cannot be fully initiated; and the reaction is violent, resulting in serious cracking of polypropylene.

[0093] In step 2-3, the amount of initiator used is related to the amount of polypropylene raw material used in step 2-1, and the mass ratio of polypropylene to initiator is 1:0.05~0.5, for example, 1:0.13. Too much initiator content will cause serious cracking of polypropylene, and too low initiator content will lead to insufficient reaction and low grafting rate.

[0094] In step 2-3, an initiator is added to the second solvent and reacted for 2 to 10 hours, for example, 2 hours, to allow the reaction to proceed fully.

[0095] In step 2-3, acetone is preferably used for suction filtration. Acetone has a relatively high volatility, which is conducive to rapid removal; and acetone has a high solubility, which can effectively remove residual organic solvents and other organic impurities in polypropylene.

[0096] In step 2, the maleic anhydride grafted polypropylene is obtained by the following steps:

[0097] Step 2-1', dissolving polypropylene in an organic solvent to obtain a first solution;

[0098] Step 2-2', adding maleic anhydride monomer to the first solvent to obtain the second solution;

[0099] Step 2-3', adding an initiator to the second solvent, filtering and extracting in sequence to obtain maleic anhydride grafted polypropylene.

[0100] In step 2-1', the organic solvent is preferably the same as the organic solvent in step 2-1 when preparing methyl methacrylate grafted polypropylene, that is, preferably one or more selected from decahydronaphthalene, toluene, and xylene, for example, all are xylene.

[0101] The organic solvent is used to dissolve polypropylene for grafting reaction. Using the same organic solvent as in step 2-1 of preparing methyl methacrylate grafted polypropylene helps to avoid more complicated effects of other solvents on the reaction system.

[0102] In step 2-1', the mass ratio of polypropylene to the volume ratio of the organic solvent (g:mL) is 3:(90-150), preferably 3:(95-110), for example 3:100.

[0103] In step 2-1', polypropylene is dissolved in an organic solvent and fully dissolved at 90-110°C, such as 100°C.

[0104] In step 2-2', maleic anhydride monomer is added to the first solvent at 70-80°C, such as 80°C.

[0105] Among them, at 70~80℃, the reactivity of maleic anhydride monomer and polypropylene molecular chain is relatively high, which is conducive to the grafting reaction between them; in addition, at this time, the solubility of polypropylene in organic solvents is better, which helps the maleic anhydride monomer to better dissolve and diffuse into the polypropylene molecular chain, thereby improving the grafting efficiency.

[0106] In step 2-2', the mass ratio of polypropylene to maleic anhydride monomer is 1:0.005-0.25, preferably 1:0.0-0.2 g, for example 1:0.17.

[0107] Among them, maleic anhydride is a rigid grafting group. Too much maleic anhydride content is unfavorable to the insulation performance of the composite material and will lead to an increase in the free volume between molecular chains. Therefore, the reaction dosage needs to be controlled.

[0108] In step 2-3', the initiator is dibenzoyl peroxide or dicumyl peroxide, preferably dibenzoyl peroxide.

[0109] In step 2-3', preferably, the initiator is first dissolved in an organic solvent to obtain a mixed solution with a concentration of 20-30%, and then the mixed solution is added to the second solution; for example, a mixed solution with a concentration of 25% is obtained, and then the mixed solution is added to the second solution.

[0110] In step 2-3', when the initiator is added, the temperature is 85-115°C, for example 95°C; the amount of the initiator is related to the amount of polypropylene raw material in step 2-1', and the mass ratio of polypropylene to initiator is 1:0.05-0.5, for example 1:0.13.

[0111] In step 2-3', the reaction time is 2 to 10 hours, for example 2 hours, so that the reaction proceeds fully.

[0112] In step 2-3', acetone is preferably used for suction filtration.

[0113] Step 3: melt-blending the polypropylene, methyl methacrylate grafted polypropylene and maleic anhydride grafted polypropylene to obtain the composite material.

[0114] In step 3, the methyl methacrylate grafted polypropylene and the maleic anhydride grafted polypropylene are melted for the first time to obtain a composite grafted polypropylene; then the composite grafted polypropylene and the polypropylene are melted for the second time to obtain the composite material.

[0115] In step 3, the first melting temperature is 170° C. to 220° C., preferably 185° C. to 200° C., for example, 200° C. Within this temperature range, polypropylene is fully melted, has strong fluidity, and will not cause thermal degradation.

[0116] In step 3, the first melting time is 10 to 20 minutes, preferably 15 minutes.

[0117] The first melting only needs to ensure that the polypropylene is fully melted.

[0118] In step 3, the second melting temperature is 185° C. to 195° C., preferably 185° C. This temperature should be lower than the first melting temperature but higher than its melting point.

[0119] In step 3, the second melting time is 10 to 20 minutes, preferably 20 minutes, so that the composite material is completely mixed.

[0120] In a third aspect, a polypropylene-based composite film is provided according to the present invention. The composite film uses a polypropylene-based composite material as a filler and a polyimide film as a matrix, and is obtained by hot pressing.

[0121] Furthermore, the polyimide film should have an appropriate thickness and size so as to completely wrap the polypropylene-based composite material during the subsequent hot pressing process.

[0122] According to the present invention, appropriate hot pressing parameters can ensure that the composite film has good bonding strength, mechanical properties, and thermal stability. In order to improve the bonding strength and thermal stability between the filler and the matrix, the hot pressing temperature is 160-180°C, the time is 8-12 minutes, and the pressure is 14-16MPa; for example, the temperature is 170°C, the pressure is 15MPa, and the time is 10 minutes.

[0123] A fourth aspect is the application of the composite material in power capacitors.

[0124] The present invention is further described below through specific examples, but these examples are merely exemplary and do not constitute any limitation to the scope of protection of the present invention.

[0125] Example 1

[0126] (1) Add 45 g of polypropylene pellets and 525 mL of n-hexane into a 1000 mL three-necked flask, wash for 5 h in a nitrogen atmosphere, an 80 °C oil bath environment, and a stirring rate of 1500 r / min, and repeat 3 times to obtain 40 g of wet clean pellets; place the clean pellets in a 25 cm diameter Petri dish, cover with plastic wrap and punch holes evenly, and dry in an 80 °C forced air drying oven for 24 h to obtain 40 g of polypropylene.

[0127] (2) Prepare methyl methacrylate grafted polypropylene according to the following steps:

[0128] 30 g of polypropylene was dissolved in 1000 mL of xylene at 100°C to obtain a first solution; the temperature was lowered to 80°C, 30 mL of methyl methacrylate was added dropwise, and the mixture was stirred to obtain a second solution; dibenzoyl peroxide was added to xylene to obtain a mixed solution with a dibenzoyl peroxide concentration of 25%, the second solution was heated to 95°C, 16 mL of the mixed solution was added to the second solution, and the mixture was reacted for 2 h, with stirring and nitrogen atmosphere being maintained throughout the reaction. After the reaction, the obtained product was poured into acetone for suction filtration, and extracted in a deionized water environment for 24 h using a Soxhlet extractor to obtain 32 g of methyl methacrylate grafted polypropylene;

[0129] Maleic anhydride grafted polypropylene was prepared as follows:

[0130] 30 g of polypropylene was dissolved in 1000 mL of xylene at 100°C to obtain solution I; 5 g of maleic anhydride monomer was added when the temperature was lowered to 80°C, and the mixture was stirred evenly to obtain solution II; dibenzoyl peroxide was added to xylene to obtain a mixed solution with a dibenzoyl peroxide concentration of 25%, and solution II was heated to 95°C. At this time, 16 mL of the mixed solution was added to solution II and the mixture was reacted for 2 h. Stirring and nitrogen atmosphere were maintained throughout the reaction. After the reaction, the obtained product was poured into acetone for suction filtration, and extracted in a deionized water environment for 24 h using a Soxhlet extractor to obtain 32 g of maleic anhydride grafted polypropylene.

[0131] (3) 10 g of methyl methacrylate grafted polypropylene and 10 g of maleic anhydride grafted polypropylene were melted at 200 °C for 15 min to obtain 20 g of composite grafted polypropylene. Then, 20 g of composite grafted polypropylene and 10 g of polypropylene were melted at 185 °C for 20 min to obtain 30 g of polypropylene-based composite material.

[0132] (4) Use a circular cutter with a diameter of 50 mm to cut several circular holes with a diameter of 5 cm on the first polyimide film with a thickness of 100 μm, place a second polyimide film with a thickness of 100 μm on the bottom of the first polyimide film, place 0.2 g of polypropylene-based composite material in the circular hole of the first polyimide film, and place a third polyimide film with a thickness of 100 μm on top of the first polyimide film to encapsulate it. Then, a flat-plate vulcanizer is used for hot pressing treatment. The temperature is set to 170°C, the pressure is set to 15 MPa, the processing time is set to 10 minutes, the number of exhaust times is set to 15 times, and the exhaust time for each time is set to 10 seconds. The operation is completed to obtain a polypropylene-based composite film.

[0133] The polypropylene-based composite material prepared in step (3) and the polypropylene material purified in step (1) were subjected to broadband dielectric spectrum testing, and the dielectric constant and material loss spectrum comparison diagram obtained were as follows: Figure 1 As shown in the figure, the red arrow points to the Y-axis scale line of the dielectric loss tangent. It can be seen that the dielectric constant of the polypropylene-based composite material prepared in step (3) is 2.6, which is significantly improved compared with the polypropylene material purified in step (1); the dielectric loss tangent of the polypropylene-based composite material prepared in step (3) is maintained at the order of 1E-3, and no significant loss is generated.

[0134] The polypropylene-based composite material prepared in step (3) and the polypropylene purified in step (1) were subjected to a DC breakdown strength test, and the DC breakdown Weibull distribution diagram obtained was as follows: Figure 2 As shown, it can be seen that the breakdown voltage of the polypropylene-based composite material prepared in step (3) is 461 kV / mm, which is 120 kV / mm higher than that of pure polypropylene, and the improvement effect is significant.

[0135] The energy storage density of the polypropylene-based composite material obtained in step (3) was measured to be 2.43 J / cm 3 .

[0136] Example 2

[0137] (1) Add 45 g of polypropylene pellets and 525 mL of n-hexane into a 1000 mL three-necked flask, wash for 5 h in a nitrogen atmosphere, an 80 °C oil bath environment, and a stirring rate of 1500 r / min, and repeat 3 times to obtain 40 g of wet clean pellets; place the clean pellets in a 25 cm diameter Petri dish, cover with plastic wrap and punch holes evenly, and dry in an 80 °C forced air drying oven for 24 h to obtain 40 g of polypropylene.

[0138] (2) Prepare methyl methacrylate grafted polypropylene according to the following steps:

[0139] 30 g of polypropylene was dissolved in 1000 mL of xylene at 100°C to obtain a first solution; the temperature was lowered to 80°C, 30 mL of methyl methacrylate was added dropwise, and the mixture was stirred to obtain a second solution; dibenzoyl peroxide was added to xylene to obtain a mixed solution with a dibenzoyl peroxide concentration of 25%, the second solution was heated to 95°C, 16 mL of the mixed solution was added to the second solution, and the mixture was reacted for 2 h, with stirring and nitrogen atmosphere being maintained throughout the reaction. After the reaction, the obtained product was poured into acetone for suction filtration, and extracted in a deionized water environment for 24 h using a Soxhlet extractor to obtain 32 g of methyl methacrylate grafted polypropylene;

[0140] Maleic anhydride grafted polypropylene was prepared as follows:

[0141] 30 g of polypropylene was dissolved in 1000 mL of xylene at 100°C to obtain solution I; 5 g of maleic anhydride monomer was added when the temperature was lowered to 80°C, and the mixture was stirred evenly to obtain solution II; dibenzoyl peroxide was added to xylene to obtain a mixed solution with a dibenzoyl peroxide concentration of 25%, and solution II was heated to 95°C. At this time, 16 mL of the mixed solution was added to solution II and the mixture was reacted for 2 h. Stirring and nitrogen atmosphere were maintained throughout the reaction. After the reaction, the obtained product was poured into acetone for suction filtration, and extracted in a deionized water environment for 24 h using a Soxhlet extractor to obtain 32 g of maleic anhydride grafted polypropylene.

[0142] (3) 15 g of methyl methacrylate grafted polypropylene and 5 g of maleic anhydride grafted polypropylene were melted at 200 °C for 15 min to obtain 20 g of composite grafted polypropylene. Then, 20 g of composite grafted polypropylene and 10 g of polypropylene were melted at 185 °C for 20 min to obtain 30 g of polypropylene-based composite material.

[0143] (4) Use a circular cutter with a diameter of 50 mm to cut several circular holes with a diameter of 5 cm on the first polyimide film with a thickness of 100 μm, place a second polyimide film with a thickness of 100 μm on the bottom of the first polyimide film, place 0.2 g of polypropylene-based composite material in the circular hole of the first polyimide film, and place a third polyimide film with a thickness of 100 μm on top of the first polyimide film to encapsulate it. Then, a flat-plate vulcanizer is used for hot pressing treatment. The temperature is set to 170°C, the pressure is set to 15 MPa, the processing time is set to 10 minutes, the number of exhaust times is set to 15 times, and the exhaust time for each time is set to 10 seconds. The operation is completed to obtain a polypropylene-based composite film.

[0144] Example 3

[0145] (1) Add 45 g of polypropylene pellets and 525 mL of n-hexane into a 1000 mL three-necked flask, wash for 5 h in a nitrogen atmosphere, an 80 °C oil bath environment, and a stirring rate of 1500 r / min, and repeat 3 times to obtain 40 g of wet clean pellets; place the clean pellets in a 25 cm diameter Petri dish, cover with plastic wrap and punch holes evenly, and dry in an 80 °C forced air drying oven for 24 h to obtain 40 g of polypropylene.

[0146] (2) Prepare methyl methacrylate grafted polypropylene according to the following steps:

[0147] 30 g of polypropylene was dissolved in 1000 mL of xylene at 100°C to obtain a first solution; the temperature was lowered to 80°C, 30 mL of methyl methacrylate was added dropwise, and the mixture was stirred to obtain a second solution; dibenzoyl peroxide was added to xylene to obtain a mixed solution with a dibenzoyl peroxide concentration of 25%, the second solution was heated to 95°C, 16 mL of the mixed solution was added to the second solution, and the mixture was reacted for 2 h, with stirring and nitrogen atmosphere being maintained throughout the reaction. After the reaction, the obtained product was poured into acetone for suction filtration, and extracted in a deionized water environment for 24 h using a Soxhlet extractor to obtain 32 g of methyl methacrylate grafted polypropylene;

[0148] Maleic anhydride grafted polypropylene was prepared as follows:

[0149] 30 g of polypropylene was dissolved in 1000 mL of xylene at 100°C to obtain solution I; 5 g of maleic anhydride monomer was added when the temperature was lowered to 80°C, and the mixture was stirred evenly to obtain solution II; dibenzoyl peroxide was added to xylene to obtain a mixed solution with a dibenzoyl peroxide concentration of 25%, and solution II was heated to 95°C. At this time, 16 mL of the mixed solution was added to solution II and the mixture was reacted for 2 h. Stirring and nitrogen atmosphere were maintained throughout the reaction. After the reaction, the obtained product was poured into acetone for suction filtration, and extracted in a deionized water environment for 24 h using a Soxhlet extractor to obtain 32 g of maleic anhydride grafted polypropylene.

[0150] (3) 5 g of methyl methacrylate grafted polypropylene and 15 g of maleic anhydride grafted polypropylene were melted at 200 °C for 15 min to obtain 20 g of composite grafted polypropylene. Then, 20 g of composite grafted polypropylene and 10 g of polypropylene were melted at 185 °C for 20 min to obtain 30 g of polypropylene-based composite material.

[0151] (4) Use a circular cutter with a diameter of 50 mm to cut several circular holes with a diameter of 5 cm on the first polyimide film with a thickness of 100 μm, place a second polyimide film with a thickness of 100 μm on the bottom of the first polyimide film, place 0.2 g of polypropylene-based composite material in the circular hole of the first polyimide film, and place a third polyimide film with a thickness of 100 μm on top of the first polyimide film to encapsulate it. Then, a flat-plate vulcanizer is used for hot pressing treatment. The temperature is set to 170°C, the pressure is set to 15 MPa, the processing time is set to 10 minutes, the number of exhaust times is set to 15 times, and the exhaust time for each time is set to 10 seconds. The operation is completed to obtain a polypropylene-based composite film.

[0152] The polypropylene-based composite materials prepared in Example 1, Example 2 and Example 3 were subjected to broadband dielectric spectrum testing, and the dielectric constant and material loss spectrum comparison diagram obtained are shown in the figure below: Figure 3 The DC breakdown strength of the polypropylene-based composite material obtained in Example 1, Example 2 and Example 3 was tested, and the DC breakdown Weibull distribution diagram obtained was as shown Figure 4 As shown, it can be seen that the dielectric constant improvement of the polypropylene-based composite materials obtained in Example 2 and Example 3 is lower than that in Example 1, and the breakdown field strength is lower than that in Example 1. Although it is improved compared with the unmodified polypropylene, the optimal formula should be Example 1.

[0153] The present invention is described in detail above in combination with preferred embodiments and exemplary examples. However, it should be noted that these specific embodiments are only illustrative explanations of the present invention and do not constitute any limitation on the protection scope of the present invention. Without exceeding the spirit and protection scope of the present invention, various improvements, equivalent substitutions or modifications may be made to the technical content of the present invention and its embodiments, which all fall within the protection scope of the present invention. The protection scope of the present invention shall be subject to the attached claims.

Claims

1. A polypropylene-based composite material, characterized in that: The composite material comprises the following components in parts by weight: Polypropylene 5-30 parts; 5-20 parts of methyl methacrylate grafted polypropylene; 5-20 parts of maleic anhydride grafted polypropylene.

2. The composite material according to claim 1, characterized in that Preferably, the energy storage density of the composite material is 2.4-2.5 J / cm 3 .

3. A method for preparing the composite material according to claim 1, characterized in that: The method comprises: Step 1, purifying polypropylene pellets to obtain polypropylene; Step 2, modifying the polypropylene to prepare methyl methacrylate grafted polypropylene and maleic anhydride grafted polypropylene respectively; Step 3: melt-blending the polypropylene, methyl methacrylate grafted polypropylene and maleic anhydride grafted polypropylene to obtain the composite material.

4. The method according to claim 3, characterized in that In step 1, polypropylene pellets are purified using an ash detergent.

5. The method according to claim 4, characterized in that The ash detergent is selected from one or more of n-hexane, isopropanol, petroleum ether and dichloromethane.

6. The method according to claim 3, characterized in that In step 2, polypropylene is modified with methyl methacrylate to obtain methyl methacrylate grafted polypropylene.

7. The method according to claim 3, characterized in that In step 2, maleic anhydride monomer is used to modify polypropylene to obtain maleic anhydride grafted polypropylene.

8. A polypropylene-based composite film, characterized in that: The composite film comprises the polypropylene-based composite material according to claim 1.

9. The composite film according to claim 8, characterized in that The composite film uses a polypropylene-based composite material as a filler.

10. A power capacitor, characterized in that: The power capacitor comprises the polypropylene-based composite material according to claim 1.

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