CN114369309B - Preparation method of polyetherimide coated magnesium oxide/polypropylene nano composite film - Google Patents

Abstract

The invention discloses a preparation method of a polyetherimide-coated magnesium oxide/polypropylene nanocomposite film. First, a layer of organic matter is coated on the surface of the inorganic nanoparticle to form a transition layer, which weakens the gap between the nanofiller and the polymer matrix. The decrease in breakdown strength of nanocomposite dielectrics caused by the difference in dielectric properties of the nanocomposite provides a new idea for synergistically improving the dielectric constant and breakdown field strength, thereby maximizing the energy density of polymer films.

Description

Preparation method of polyetherimide-coated magnesium oxide/polypropylene nanocomposite film

technical field

The invention belongs to the field of polymer nanocomposite dielectric preparation, and particularly relates to a preparation method of a polyetherimide-coated magnesium oxide/polypropylene nanocomposite film with high breakdown strength.

Background technique

Energy is a key element for human survival and development. Fossil energy and other non-renewable energy sources cannot be used for a long time due to their non-renewability and harm to the environment. Today's global energy landscape has undergone profound changes, and the utilization of clean energy has gradually become a focus of attention. However, the utilization of wind energy and solar energy is difficult and inefficient. At present, photovoltaic and wind power can convert two clean energy sources into electric energy, but they are subject to the instability and discontinuity of solar energy and wind energy. In order to ensure the stability of the power grid, and Clean energy cannot be directly connected to the grid. In addition, due to the disadvantage of uneven distribution of clean energy, the consumption of clean energy has become a problem that cannot be ignored. In order to solve the above problems, energy storage has become an important node for the centralized access of clean energy to the power grid.

Capacitors have become key devices in energy storage technology due to their simple fabrication process, high power density, and excellent charge-discharge capability. Polymer nanocomposite dielectrics, as third-generation insulating materials, are key materials for the development of next-generation thin-film capacitors. Polymer nanocomposite dielectrics combine the excellent dielectric properties of inorganic fillers with the high breakdown field strength and ease of processing of polymer matrices and are widely used in film capacitors. However, due to the large difference in dielectric properties between the nanofiller and the polymer matrix, the breakdown strength of the nanocomposite dielectric decreases. For example, Fridin et al. The dielectric constant is increased to 15.4, but at the expense of the breakdown field strength. This severely limits the improvement of the energy storage performance of polypropylene nanocomposite dielectrics.

SUMMARY OF THE INVENTION

In order to synergistically improve the dielectric and breakdown properties of the polymer nanocomposite dielectric, thereby enhancing its energy storage performance, the present invention proposes a high breakdown strength polyetherimide-coated magnesium oxide/polypropylene nanocomposite dielectric film preparation method.

In order to achieve the above purpose, the preparation method of the polyetherimide-coated magnesium oxide/polypropylene nanocomposite film of the present invention comprises the following steps:

Step 1. Surface treatment of magnesium oxide nanoparticles with hydrogen peroxide to obtain hydroxylated magnesium oxide nanoparticles;

Step 2, performing surface amination treatment on the hydroxylated magnesium oxide nanoparticles to form amino groups on the surface of the hydroxylated magnesium oxide nanoparticles to obtain aminated magnesium oxide nanoparticles;

Step 3. With the help of the amino group on the surface of the magnesium oxide nanoparticle, connect the bisphenol A diether dianhydride monomer (BPADA) on the surface of the aminated magnesium oxide nanoparticle, add m-phenylenediamine (mPDA), and use in-situ polymerization A polyetherimide coating layer is formed on the surface of the magnesium oxide nanoparticles by the method to obtain the magnesium oxide nanoparticles coated with the polyetherimide;

Step 4. Incorporating polyetherimide-coated magnesium oxide nanoparticles into polypropylene by a solution blending method, wherein the mass ratio of polypropylene and polyetherimide-coated nanoparticles is: 1 : (0.005-0.05), and evaporate the solvent to prepare polypropylene nanocomposite dielectric;

Step 5, hot pressing the polypropylene nanocomposite dielectric by a flat plate hot pressing method to obtain a polypropylene nanocomposite dielectric film.

Further, step 1 includes the following steps:

Step 1.1, drying the magnesium oxide nanoparticles;

Step 1.2, adding hydrogen peroxide to the dried magnesium oxide nanoparticles, and ultrasonically dispersing into a suspension;

Step 1.3, heating the suspension to above 80°C, then condensing and refluxing with a condenser tube, and waiting for the magnesium oxide nanoparticles to react with hydrogen peroxide for more than 6 hours to obtain suspension A;

In step 1.4, the suspension A is centrifuged, washed repeatedly with hydrogen peroxide, and dried in vacuum to obtain hydroxylated magnesium oxide nanoparticles.

Further, step 2 includes the following steps:

Step 2.1, adding toluene to the hydroxylated magnesium oxide nanoparticles, and ultrasonically dispersing into suspension B;

Step 2.2, drop the silane coupling agent into suspension B, and ultrasonically disperse again;

Step 2.3, heating the dispersed suspension to 110°C, then condensing and refluxing with a condenser tube, and reacting for more than 6 hours;

In step 2.4, the reacted suspension B is centrifugally precipitated, washed repeatedly, and dried in vacuum to obtain aminated magnesium oxide nanoparticles.

Further, in step 2.2, the silane coupling agent is KH550.

Further, step 3 includes the following steps:

Step 3.1, adding absolute ethanol to the aminated magnesium oxide nanoparticles, and ultrasonically dispersing into suspension C;

Step 3.2, dissolving bisphenol A type diether dianhydride and m-phenylenediamine in dimethylacetamide solution respectively to obtain BPADA solution and mPDA solution;

Step 3.3, adding the BPADA solution to suspension C for ultrasonic dispersion to obtain substance D;

Step 3.4, adding mPDA solution to substance D, feeding nitrogen at the same time, adding a drying tube, and reacting;

Step 3.5. After the reaction, the suspension is centrifuged and precipitated, washed with absolute ethanol, and placed in an oven to complete thermal imidization to obtain magnesium oxide nanoparticles coated with polyetherimide.

Further, in step 3.4, mPDA solution was added to substance D in three times.

Further, in step 3.5, the thermal imidization process is as follows: firstly, the temperature is raised to 70 °C for 1 h to remove residual dimethylacetamide, and then the temperature is stepped up at a heating rate of 1 °C/min, and the temperature is increased at 100 °C and 150 °C. ℃, 200 ℃, 250 ℃ each for 1 hour, and after the oven is naturally cooled to room temperature, the magnesium oxide nanoparticles coated with polyetherimide are obtained.

Further, step 4 includes the following steps:

4.1. Clean and dry polypropylene particles;

4.2. Place the dried polypropylene particles in container A, add xylene, introduce nitrogen at the same time, install a serpentine condenser tube and a drying tube, and stir to dissolve;

4.3. Add the polyetherimide-coated magnesium oxide nanoparticles into container B, add xylene, and ultrasonically disperse to obtain a nanoparticle dispersion;

4.4. Add the nanoparticle dispersion into the container A, and after the reaction is complete, a mixed solution is obtained;

4.5. Remove xylene in the mixed solution to obtain a polypropylene nanocomposite dielectric.

Further, step 5 includes the following steps:

5.1. Put the polypropylene nanocomposite dielectric into the middle of the polyimide mold, then put the mold between two thermally conductive plates, and then place the two in a hot-pressing device;

5.2. Pre-press for 10 minutes under no pressure to melt the polypropylene nanocomposite dielectric; then press for 5 minutes at 10 MPa, 15 MPa and 20 MPa, respectively, open the mold to exhaust before each pressurization; then cool down to room temperature and open the mold, A polypropylene nanocomposite dielectric film was obtained.

Further, in the step 4, the doping mass fraction of the nanoparticles is 3wt%.

Compared with the prior art, the present invention has at least the following beneficial technical effects:

The present invention proposes a method for preparing a high breakdown strength polyetherimide-coated magnesium oxide/polypropylene nanocomposite dielectric. The decrease of the breakdown strength of the nanocomposite dielectric due to the large difference in dielectric properties with the polymer matrix provides a new idea for synergistically improving the dielectric constant and breakdown field strength, thereby maximizing the energy density of polymer films .

The preparation method of the nanocomposite dielectric provided by the present invention is simple to operate and easy to realize. Hydroxylation treatment of the surface of magnesium oxide nanoparticles can connect more hydroxyl groups to the surface of magnesium oxide, making it easier for the coupling agent to connect to the surface of the particles. Nanoparticles are doped into polypropylene by solution blending method, and the uniform dispersion of nanoparticles in the matrix can be achieved by continuous heating and stirring.

Further, using KH550 to treat the nanoparticles to introduce more amino groups can form a more uniform and tight coating layer on the surface of the nanoparticles.

Further, the sandwich structure hot pressing film makes the film thickness controllable and uniform, and reduces the thickness error.

Further, the present invention greatly improves the DC breakdown strength of the polypropylene polymer. In the present invention, in the process of coating magnesium oxide nanoparticles with polyetherimide, the ratio and addition sequence of bisphenol A diether dianhydride (BPADA) and m-phenylenediamine (mPDA) have strict requirements, and bisphenol A is added first. Type diether dianhydride and its excess, then add m-phenylenediamine three times, the molar ratio of bisphenol A type diether dianhydride and m-phenylenediamine is (1.02-1.03): 1, to ensure that bisphenol A type diether The dianhydride fully reacts with the amino group on the surface of the magnesium oxide nanoparticle, and the m-phenylenediamine added later can fully react with the bisphenol A type diether dianhydride connected to the surface of the magnesium oxide nanoparticle. This process can maximize the coating probability of the polyetherimide and avoid the polyetherimide being in a free state.

Description of drawings

Fig. 1 is a flow chart of nanoparticle surface treatment;

Fig. 2 is a schematic diagram of nanoparticle amination;

Figure 3 is a schematic diagram of the reaction principle of polyetherimide-coated nanoparticles;

Fig. 4 is the infrared spectrogram of magnesium oxide nanoparticles;

Fig. 5 is the Weibull distribution diagram of DC breakdown field strength of polyetherimide-coated magnesium oxide/polypropylene nanocomposite electric thin film;

FIG. 6 is a characteristic breakdown field strength diagram of DC breakdown field strength of polyetherimide-coated magnesium oxide/polypropylene nanocomposite electric film.

Detailed ways

In order to make the purpose and technical solutions of the present invention clearer and easier to understand. The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. The specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

The preparation method of polyetherimide-coated magnesium oxide/polypropylene nanocomposite film comprises the following steps:

Step 1. The magnesium oxide nanoparticles are surface-treated with 30% hydrogen peroxide to introduce more hydroxyl groups to obtain hydroxylated magnesium oxide nanoparticles.

Step 2: Select a silane coupling agent to aminate the surface of the hydroxylated magnesium oxide nanoparticles, and form amino groups on the surface of the hydroxylated magnesium oxide nanoparticles to obtain aminated magnesium oxide nanoparticles.

Step 3. With the help of the amino group on the surface of the magnesium oxide nanoparticles, connect the bisphenol A diether dianhydride (BPADA) monomer on the surface of the aminated magnesium oxide nanoparticles, add m-phenylenediamine (mPDA), The mass ratio of the particles, BPADA, and mPDA is 1g: 1.6942g: 0.3402g, and the polyetherimide coating layer on the surface of the magnesium oxide nanoparticles is formed by in-situ polymerization to obtain the polyetherimide-coated magnesium oxide. Nanoparticles.

Step 4. Incorporating the polyetherimide-coated nanoparticle filler into the polypropylene matrix by the solution blending method, wherein the mass ratio of the polypropylene and the polyetherimide-coated nanoparticles is: 1: (0.005-0.05), and the solvent was evaporated with a rotary evaporator to prepare a polypropylene nanocomposite dielectric.

Step 5, using a flat plate hot pressing method to obtain a polypropylene nanocomposite dielectric film by hot pressing with a sandwich structure. The sandwich structure is a complete polyimide film mold at the bottom and top, and a polyimide film mold with a circular hole structure in the middle to ensure the uniformity of the sample thickness. The thickness of the polyimide film mold with a circular hole structure Determines the thickness of the dielectric film.

As a further improvement of the present invention, the concrete steps of step 1 are:

1.1) drying the magnesium oxide nanoparticles;

1.2) place the dried magnesium oxide nanoparticles in the single-necked flask A, add 30% hydrogen peroxide, and ultrasonically disperse it into a suspension; the magnesium oxide nanoparticles and 30% hydrogen peroxide solid-liquid ratio are 1g:16ml;

1.3) heating the single-necked flask A to 80°C, adding a serpentine condenser to condense and refluxing, and reacting the magnesium oxide nanoparticles with hydrogen peroxide for more than 6 hours to obtain a suspension;

1.4) After the reaction, the suspension was centrifuged for precipitation, washed repeatedly with hydrogen peroxide, and dried in a vacuum oven for 12 hours to obtain hydroxylated nanoparticles.

As a further improvement of the present invention, the concrete steps of step 2 are:

2.1) place in the single-necked flask B after grinding the magnesium oxide nanoparticles after the hydroxylation, and add toluene, and ultrasonically disperse into a suspension; the magnesium oxide nanoparticles and the toluene solid-to-liquid ratio are 1g:60ml;

2.2) Slowly add KH550 coupling agent dropwise into the suspension, and ultrasonically disperse again; the solid-liquid ratio of magnesium oxide nanoparticles to coupling agent is 1g:1ml;

2.3) Heat the dispersed suspension to 110°C, install a serpentine condenser to condense and reflux, and react for more than 6 hours;

2.4) After the reaction, the suspension was centrifuged and precipitated, washed repeatedly with toluene, and dried in a vacuum oven for more than 12 hours to obtain aminated magnesium oxide nanoparticles.

As a further improvement of the present invention, the concrete steps of step 3 are:

3.1) the aminated nanoparticles are ground and placed in the there-necked flask A, and add dehydrated alcohol, and ultrasonically disperse into a suspension; the nanoparticle and dehydrated alcohol solid-to-liquid ratio is 1g:125ml;

3.2) Dissolve bisphenol A diether dianhydride (BPADA) and m-phenylenediamine (mPDA) in dimethylacetamide (DMAc) solution respectively to obtain BPADA solution and mPDA solution, in the same volume of DMAc solution, The mass ratio of BPADA to mPDA is 1.6942g: 0.3402g;

3.3) Add the BPADA solution to the suspension in step 3.1, and ultrasonicate for 30min;

3.4) Place the three-necked flask A on a magnetic stirrer, keep the temperature below 10°C, slowly add the mPDA solution into the three-necked flask A in three times, introduce nitrogen at the same time, install a drying tube, and react for 24h;

3.5) After the reaction is completed, the suspension is centrifuged for precipitation, washed repeatedly with absolute ethanol, and then placed in a blast oven to complete the thermal imidization process. The specific steps are: firstly raise the temperature to 70°C for 1h to remove residual DMAc, then step up the temperature at a heating rate of 1°C/min, stay at 100°C, 150°C, 200°C, and 250°C for 1h each, and let the oven cool down to room temperature naturally Then, magnesium oxide nanoparticles coated with polyetherimide are obtained.

As a further improvement of the present invention, the concrete steps of step 4 are:

4.1) Use deionized water and absolute ethanol to ultrasonically clean the polypropylene particles respectively, and then place them in a vacuum oven to dry for more than 12 hours;

4.2) Place the dried polypropylene particles in the three-necked flask B, add xylene, raise the temperature to 140°C, feed nitrogen at the same time, add a serpentine condenser and a drying tube, stir and dissolve for 90min; The solid-liquid ratio of particles and xylene is 1g:20ml;

4.3) adding the magnesium oxide nanoparticles coated with polyetherimide into a beaker, adding xylene, and ultrasonically dispersing for 30 min to obtain a nanoparticle dispersion;

4.4) Slowly add the nanoparticle dispersion into the three-necked flask B, and react for 12h to obtain a mixed solution;

4.5) After the reaction was completed, the mixed solution was transferred to a single-necked flask C, the xylene was removed by rotary evaporation, dried in a vacuum oven at 80° C. for 12 h, and the xylene was evaporated to obtain a polyetherimide-coated magnesium oxide/ Polypropylene nanocomposites.

As a further improvement of the present invention, the concrete steps of step 5 are:

5.1) Weigh a certain quality of polyetherimide-coated magnesium oxide/polypropylene nanocomposite material and put it in the middle of the polyimide mold, then put the mold between two thermally conductive plates, and then place the two in the middle of the polyimide mold. in hot pressing equipment;

5.2) Pre-press for 10min under no pressure and temperature of 180℃ to melt the material; then pressurize for 5min at 10MPa, 15MPa and 20MPa respectively, open the mold for 2-3s before each pressurization; then water-cool for 10min to The mold was opened after room temperature to obtain a polypropylene nanocomposite dielectric film of 23-27 microns.

Example 1

A preparation method of a high breakdown strength polyetherimide-coated magnesium oxide/polypropylene nanocomposite dielectric film, the specific steps are as follows:

Step 1. Nanoparticle Hydroxylation

1.1) Dry the magnesium oxide nanoparticles in a vacuum oven at 80°C for 12h;

1.2) 2.5g of dried nanoparticles are placed in a 150ml single-necked flask A, add 40ml of 30% hydrogen peroxide, and ultrasonically disperse for 30min to form a suspension;

1.3) The suspension was heated from 40°C to 10°C every 10min, and the temperature was raised to 80°C in steps, and a 300ml serpentine condenser was added to condense and reflux, and the reaction was performed for more than 6h;

1.4) After the reaction, the suspension was centrifuged for 10 min at a speed of 6000 r/min, washed with hydrogen peroxide 3 times, 5 min each time, and the precipitate was dried in a vacuum oven at 80 ° C for 12 h to obtain hydroxylated magnesium oxide. Nanoparticles.

Step 2. Nanoparticle amination

2.1) place in the single-necked flask B of 250ml after grinding the magnesium oxide nanoparticles after 2g hydroxylation, and add 120ml toluene, ultrasonically disperse 30min into a suspension;

2.2) 2ml of KH550 coupling agent was slowly added dropwise to the suspension using a pipette, and ultrasonically dispersed again for 15min to fully hydrolyze;

2.3) The suspension after dispersion was heated from 70°C to 110°C in steps, and the temperature was increased by 20°C every 10 minutes, and a 200ml serpentine condenser was added to condense and reflux, and the reaction was performed for more than 6 hours;

2.4) After the reaction, the suspension was centrifuged for 10 min at a speed of 6000 r/min, washed with toluene for 3 times, 5 min each time, and the precipitate was dried in a vacuum oven at 80 ° C for 12 h to obtain the aminated oxidation Magnesium nanoparticles.

Step 3. Polyetherimide Coating Magnesium Oxide Nanoparticles

3.1) place in the three-necked flask A of 500ml after grinding the magnesium oxide nanoparticles after 1g amination, and add 125ml absolute ethanol, ultrasonically disperse 30min into a suspension;

3.2) The BPADA of 1.6942g and the mPDA of 0.3402g are respectively dissolved in the 50ml beaker containing the DMAc solution of 20ml;

3.3) Add the BPADA solution to the suspension, ultrasonically for 30min;

3.4) Place the three-necked flask A on a magnetic stirrer, keep the temperature below 10°C, slowly add the mPDA solution into the three-necked flask A in three times, introduce nitrogen at the same time, install a drying tube, and react for 24h;

3.5) After the reaction is completed, the suspension is centrifuged for 10 minutes at a rotational speed of 6000 r/min, washed with absolute ethanol for 3 times, 5 minutes each time, and the precipitate is placed in a blast oven to complete the thermal imidization process. The specific steps are as follows: : First heat up to 70°C and hold for 1h to remove residual DMAc, then ramp up the temperature at a heating rate of 1°C/min, stay at 100°C, 150°C, 200°C, and 250°C for 1h each, and wait for the oven to naturally cool to room temperature to obtain Magnesium oxide nanoparticles coated with polyetherimide.

Step 4, polypropylene-doped magnesium oxide nanoparticles: the mass fraction of nanoparticles is 0.5 wt%.

4.1) The polypropylene particles were ultrasonically cleaned with deionized water and absolute ethanol for 15 minutes, and then dried in a vacuum oven at 80°C for 12 hours;

4.2) Place 3g of polypropylene particles in a 250ml three-necked flask B, add 60ml of xylene, step up the temperature from 70°C to 140°C, introduce nitrogen at the same time, add a 200ml serpentine condenser and a drying tube, stir and dissolve for 90min ;

4.3) adding 0.015g of polyetherimide-coated magnesium oxide nanoparticles into a 50ml beaker, and adding 25ml of xylene, and ultrasonically dispersing for 30min to obtain a polyetherimide-coated magnesium oxide nanoparticle dispersion;

4.4) Slowly add the magnesium oxide nanoparticle dispersion solution coated with polyetherimide into the three-necked flask B, and react for 12h to obtain a mixed solution;

4.5) After the reaction, the mixed solution in the three-necked flask B was transferred to a 250ml single-necked flask C, the xylene was removed by rotary evaporation, dried in a vacuum oven at 80°C for 12 h, and the xylene was evaporated to obtain polyetherimide. Coated magnesium oxide/polypropylene nanocomposites.

Step 5. Preparation of polypropylene nanocomposite dielectric film by hot pressing

5.1) Lay down the bottom layer and the 25-micron circular hole structure polyimide mold in the middle, and weigh four 44.6 mg polyetherimide-coated magnesium oxide/polypropylene nanocomposites into the circular holes respectively. In the four holes of the structural polyimide mold, cover the upper polyimide mold, put it between two heat-conducting plates, and place it in a hot-pressing equipment;

5.2) Pre-press for 10min under no pressure and temperature of 180℃ to melt the material; then pressurize for 5min at 10MPa, 15MPa and 20MPa respectively, open the mold for 2-3s before each pressurization; then water-cool for 10min to After room temperature, the mold was opened to obtain a polyetherimide-coated magnesium oxide/polypropylene nanocomposite dielectric film.

Example 2

A preparation method of a high breakdown strength polyetherimide-coated magnesium oxide/polypropylene nanocomposite dielectric film, the steps are as follows:

Step 1. Use 30% hydrogen peroxide to conduct surface hydroxylation treatment on the magnesium oxide nanoparticles.

Step 2. Select KH550 silane coupling agent to perform surface amination treatment on the hydroxylated magnesium oxide nanoparticles.

Step 3. With the help of the amino group on the surface of the magnesium oxide nanoparticle, connect the BPADA monomer on the surface of the magnesium oxide nanoparticle, add mPDA, and use the in-situ polymerization method to form a polyetherimide coating on the surface of the magnesium oxide nanoparticle to obtain a polyetherimide coating. Magnesium oxide nanoparticles coated with etherimide.

Step 4. Add 0.030 g of polyetherimide-coated magnesium oxide nanoparticles into 3 g of polypropylene matrix by solution blending method, and use a rotary evaporator to evaporate the solvent to prepare a nano-doped polymer with a mass fraction of 1.0 wt %. Etherimide-coated magnesium oxide/polypropylene nanocomposites.

Step 5, using a flat plate hot pressing method to obtain a polyetherimide-coated magnesium oxide/polypropylene nanocomposite dielectric film by hot pressing with a sandwich structure.

The remaining specific steps are the same as those in Example 1.

Example 3

A preparation method of a high breakdown strength polyetherimide-coated magnesium oxide/polypropylene nanocomposite dielectric film, the steps are as follows:

Step 1. Use 30% hydrogen peroxide to conduct surface hydroxylation treatment on the magnesium oxide nanoparticles.

Step 2. Select KH550 silane coupling agent to perform surface amination treatment on the hydroxylated magnesium oxide nanoparticles.

Step 3: Connect the BPADA monomer on the surface of the magnesium oxide nanoparticle with the help of the amino group on the surface of the magnesium oxide nanoparticle, add mPDA, and use the in-situ polymerization method to form a polyetherimide coating layer on the surface of the magnesium oxide nanoparticle.

Step 4. Add 0.061 g of polyetherimide-coated magnesium oxide nanoparticles into 3 g of polypropylene matrix by solution blending method, and use a rotary evaporator to evaporate the solvent to prepare a nano-doped polymer with a mass fraction of 2.0 wt %. Etherimide-coated magnesium oxide/polypropylene nanocomposites.

Step 5, using a flat plate hot pressing method to obtain a polyetherimide-coated magnesium oxide/polypropylene nanocomposite dielectric film by hot pressing with a sandwich structure.

The remaining specific steps are the same as those in Example 1.

Example 4

A preparation method of a high breakdown strength polyetherimide-coated magnesium oxide/polypropylene nanocomposite dielectric film, the steps are as follows:

Step 1. Use 30% hydrogen peroxide to conduct surface hydroxylation treatment on the magnesium oxide nanoparticles.

Step 2. Select KH550 silane coupling agent to perform surface amination treatment on the hydroxylated magnesium oxide nanoparticles.

Step 3: Connect the BPADA monomer on the surface of the magnesium oxide nanoparticle with the help of the amino group on the surface of the magnesium oxide nanoparticle, add mPDA, and use the in-situ polymerization method to form a polyetherimide coating layer on the surface of the magnesium oxide nanoparticle.

Step 4. Add 0.093 g of polyetherimide-coated magnesium oxide nanoparticles into 3 g of polypropylene matrix by solution blending method, and use a rotary evaporator to evaporate the solvent to prepare a nano-doped polymer with a mass fraction of 3.0 wt %. Etherimide-coated magnesium oxide/polypropylene nanocomposites.

Step 5, using a flat plate hot pressing method to obtain a polyetherimide-coated magnesium oxide/polypropylene nanocomposite dielectric film by hot pressing with a sandwich structure.

The remaining specific steps are the same as those in Example 1.

Example 5

A preparation method of a high breakdown strength polyetherimide-coated magnesium oxide/polypropylene nanocomposite dielectric film, the steps are as follows:

Step 1. Use 30% hydrogen peroxide to conduct surface hydroxylation treatment on the magnesium oxide nanoparticles.

Step 2. Select KH550 silane coupling agent to perform surface amination treatment on the hydroxylated magnesium oxide nanoparticles.

Step 3: Connect the BPADA monomer on the surface of the magnesium oxide nanoparticle with the help of the amino group on the surface of the magnesium oxide nanoparticle, add mPDA, and use the in-situ polymerization method to form a polyetherimide coating layer on the surface of the magnesium oxide nanoparticle.

Step 4. Add 0.158g of polyetherimide-coated magnesium oxide nanoparticles into 3g of polypropylene matrix by solution blending method, and use a rotary evaporator to evaporate the solvent to prepare a nano-doped polymer with a mass fraction of 5.0wt%. Etherimide-coated magnesium oxide/polypropylene nanocomposites.

Step 5, using a flat plate hot pressing method to obtain a polyetherimide-coated magnesium oxide/polypropylene nanocomposite dielectric film by hot pressing with a sandwich structure.

The remaining specific steps are the same as those in Example 1.

The magnesium oxide nanoparticles are treated with hydrogen peroxide to connect more hydroxyl groups on the surface. When the coupling agent encounters hydroxyl groups, it will connect to the surface of magnesium oxide in the form of Si-O bonds to form amino groups. BPADA will be connected to the amino group on the surface of magnesium oxide, and then mPDA and BPADA will be added to polymerize in situ to form polyetherimide, so as to realize the coating of magnesium oxide nanoparticles by polyetherimide. The reaction principle is shown in Figures 1 to 3.

Using the infrared transmission mode, the infrared spectra of untreated magnesium oxide, hydroxylated magnesium oxide, aminated magnesium oxide, and coated magnesium oxide can be observed, as shown in FIG. 4 . 1775cm ^-1 and 1721cm ^-1 are vibrations of C=O bond, 1620cm ^-1 and 1503cm ^-1 are characteristic peaks of benzene ring, 1081cm ^-1 and 1238cm ^-1 are characteristic peaks of RO-R' ether bond . This proves that the polyetherimide coating is successful.

DC breakdown field strength test: place the polypropylene nanocomposite dielectric film in the middle of the spherical copper electrode, apply a linear DC voltage at a rate of 1kV/s until the sample breaks down, record the breakdown voltage of the sample, and calculate Its DC breakdown field strength, the whole experimental process is carried out in the transformer oil at room temperature. DC breakdown tests were performed on pure polypropylene and polypropylene nanocomposite dielectric films with doping concentrations of 0.5wt%, 1.0wt%, 2.0wt%, 3.0wt%, and 5.0wt%, respectively. The test results are shown in Figure 5 and Figure 6. shown.

From the DC breakdown field strength results, the doping of nanoparticles helps to improve the breakdown performance of polypropylene dielectrics. With the increase of doping concentration, the breakdown performance of polypropylene nanocomposite dielectric increased first and then decreased. When the doping mass fraction of nanoparticles was 3wt%, the breakdown performance of polypropylene nanocomposite dielectric increased by 19%, and the breakdown Best performance increase.

The above content is only to illustrate the technical idea of the present invention, and cannot limit the protection scope of the present invention. Any changes made on the basis of the technical solution according to the technical idea proposed by the present invention all fall within the scope of the claims of the present invention. within the scope of protection.

Claims (10)

1. The preparation method of the polyetherimide coated magnesium oxide/polypropylene nano composite film is characterized by comprising the following steps:

step 1, performing surface treatment on magnesium oxide nanoparticles by using hydrogen peroxide to obtain hydroxylated magnesium oxide nanoparticles;

step 2, performing surface amination treatment on the hydroxylated magnesium oxide nanoparticles to form amino groups on the surfaces of the hydroxylated magnesium oxide nanoparticles to obtain aminated magnesium oxide nanoparticles;

step 3, with the help of amino groups on the surfaces of the aminated magnesium oxide nanoparticles, connecting a bisphenol A type diether dianhydride monomer (BPADA) to the surfaces of the aminated magnesium oxide nanoparticles, adding m-phenylenediamine (mPMDA), and forming a polyetherimide coating layer on the surfaces of the magnesium oxide nanoparticles by using an in-situ polymerization method to obtain polyetherimide coated magnesium oxide nanoparticles; adding bisphenol A type diether dianhydride in an excessive amount, adding m-phenylenediamine in three times, wherein the molar ratio of the bisphenol A type diether dianhydride to the m-phenylenediamine is (1.02-1.03): 1,

and 4, doping polyetherimide-coated magnesium oxide nanoparticles into polypropylene by adopting a solution blending method, wherein the mass ratio of the polypropylene to the polyetherimide-coated nanoparticles is as follows: 1 (0.005-0.03), and evaporating the solvent to prepare the polypropylene nano composite dielectric medium;

and 5, hot-pressing the polypropylene nano composite dielectric by using a flat hot-pressing method to prepare the polypropylene nano composite dielectric film.

2. The method for preparing the polyetherimide-coated magnesium oxide/polypropylene nanocomposite film according to claim 1, wherein the step 1 comprises the following steps:

step 1.1, drying the magnesium oxide nano particles;

step 1.2, adding hydrogen peroxide into the dried magnesium oxide nanoparticles, and performing ultrasonic dispersion to obtain a suspension;

step 1.3, heating the suspension to above 80 ℃, then condensing and refluxing by using a condensing tube, and obtaining a suspension A after the magnesium oxide nano particles and hydrogen peroxide react for more than 6 hours;

and step 1.4, centrifugally precipitating the suspension A, repeatedly washing with hydrogen peroxide, and drying in vacuum to obtain the hydroxylated magnesium oxide nanoparticles.

3. The method for preparing the polyetherimide coated magnesium oxide/polypropylene nanocomposite film according to claim 1, wherein the step 2 comprises the following steps:

step 2.1, adding toluene into the hydroxylated magnesium oxide nanoparticles, and performing ultrasonic dispersion to obtain a suspension B;

2.2, dripping the silane coupling agent into the suspension B, and performing ultrasonic dispersion again;

step 2.3, heating the dispersed suspension to 110 ℃, and then carrying out condensation reflux by using a condensing tube to react for more than 6 hours;

and 2.4, centrifugally precipitating the suspension B after reaction, repeatedly washing, and drying in vacuum to obtain the aminated magnesium oxide nanoparticles.

4. The method for preparing the polyetherimide coated magnesium oxide/polypropylene nano composite film according to claim 3, wherein in the step 2.2, the silane coupling agent is KH550.

5. The method for preparing the polyetherimide coated magnesium oxide/polypropylene nanocomposite film according to claim 1, wherein the step 3 comprises the following steps:

step 3.1, adding absolute ethyl alcohol into the aminated magnesium oxide nanoparticles, and performing ultrasonic dispersion to obtain a suspension C;

step 3.2, respectively dissolving bisphenol A type diether dianhydride and m-phenylenediamine in a dimethylacetamide solution to obtain a BPADA solution and an mPDA solution;

step 3.3, adding the BPADA solution into the suspension C for ultrasonic dispersion to obtain a substance D;

step 3.4, adding the mPDA solution into the substance D, introducing nitrogen, adding a drying tube, and reacting;

and 3.5, after the reaction is finished, centrifugally precipitating the suspension, washing the suspension by using absolute ethyl alcohol, and putting the washed suspension in an oven to complete thermal imidization to obtain the polyetherimide-coated magnesium oxide nanoparticles.

6. The method for preparing the polyetherimide coated magnesium oxide/polypropylene nano composite film according to the claim 5, wherein in the step 3.4, the mPDA solution is added to the substance D in three times.

7. The method for preparing the polyetherimide coated magnesium oxide/polypropylene nano composite film according to claim 5, wherein in the step 3.5, the thermal imidization process comprises: heating to 70 ℃ for 1h to remove residual dimethylacetamide, then heating in a stepped manner at a heating rate of 1 ℃ per min, standing at 100 ℃, 150 ℃, 200 ℃ and 250 ℃ for 1h, and cooling to normal temperature in an oven to obtain polyetherimide-coated magnesium oxide nanoparticles.

8. The method for preparing the polyetherimide-coated magnesium oxide/polypropylene nanocomposite film according to claim 1, wherein the step 4 comprises the following steps:

4.1, cleaning and drying the polypropylene particles;

4.2, placing the dried polypropylene particles in a container A, adding dimethylbenzene, introducing nitrogen, adding a serpentine condenser pipe and a drying pipe, and stirring for dissolving;

4.3, adding the polyetherimide-coated magnesium oxide nanoparticles into a container B, adding xylene, and performing ultrasonic dispersion to obtain a nanoparticle dispersion liquid;

4.4, adding the nanoparticle dispersion liquid into the container A, and obtaining a mixed liquid after complete reaction;

and 4.5, removing dimethylbenzene in the mixed solution to obtain the polypropylene nano composite dielectric.

9. The method for preparing the polyetherimide coated magnesium oxide/polypropylene nanocomposite film according to claim 1, wherein the step 5 comprises the following steps:

5.1, placing the polypropylene nano composite dielectric medium in the middle of a polyimide mould, placing the mould between two heat conduction plates, and then placing the two in hot-pressing equipment;

5.2, prepressing under a non-pressure state to melt the polypropylene nano composite dielectric medium; pressurizing at 10MPa, 15MPa and 20MPa for 5min, and opening the mold before pressurizing each time for exhausting; and then cooling to room temperature, and opening the mold to obtain the polypropylene nano composite dielectric film.

10. The method for preparing the polyetherimide coated magnesium oxide/polypropylene nano composite film according to claim 1, wherein in the step 4, the doping amount fraction of the nano particles is 3wt%.

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