Aramid insulation paper and preparation method and application thereof

Abstract

The application relates to the technical field of materials, in particular to aramid insulation paper and a preparation method and application thereof. The aramid insulation paper provided by the application takes graphene-modified aramid nanofiber and silicon dioxide-coated carbon nanotube as composite fillers, fills the fillers in aramid fiber paper base material through a vacuum filtration method, parallel arrangement of the nanofillers can provide more heat conduction channels, and the heat conduction path is enhanced; the aramid composite paper is endowed with high heat conduction; through vacuum annealing treatment, the residual stress in the composite paper is reduced, the grain structure of the material is homogenized, the strength, toughness and plasticity of the composite paper are improved, and the aramid insulation paper can be used as a heat-resistant insulation material to guarantee reliable operation of a transformer or a motor in power equipment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of materials, and particularly relates to aramid insulation paper and a preparation method and application thereof. BACKGROUND

[0002] Power transformer is an essential core electrical equipment in power system, and plays a vital role in the stable operation of power system. Oil-filled transformer is the most widely used transformer at present, and the internal insulation of the oil-filled transformer is an oil-paper combined insulation system composed of insulation paper and insulation oil. According to a large number of actual operation experiences, the performance of the insulation paper is the main factor determining the long-term operation reliability of the oil-filled transformer. Therefore, higher requirements are put forward for the performance of the heat-conducting material. The heat-conducting material not only needs to have high thermal conductivity, but also needs to have low density, high strength, high flexibility, high thermal stability, high electrical insulation and excellent comprehensive properties such as flame retardancy, so as to meet the reliable operation of the power equipment under harsh environments such as high temperature, high frequency and high voltage. Traditional heat-conducting materials such as metals, ceramics and polymers often cannot meet these performance requirements at the same time, and therefore new heat-conducting materials need to be developed.

[0003] In recent years, nanomaterials have attracted extensive attention and research due to their unique structure and properties. For example, aramid nanofiber (ANF), graphene (GN) and carbon nanotube (CNT) are three kinds of nanomaterials with high heat-conducting potential. Among them, aramid nanofiber (ANF) is a one-dimensional rigid nanofiber which is tightly packed by poly-p-phenylene terephthalamide (PPTA) molecular chains, and has high crystallinity and orientation degree, and also has excellent mechanical properties and thermal stability. Although there are many researches on aramid nanofiber film materials, there are few reports on the introduction of aramid nanofiber into polymers.

[0004] Graphene (GN) is a two-dimensional carbon atom monolayer sheet, and due to its atomic level thickness and huge specific surface area, it has extremely low density and extremely high flexibility. Graphene also has extremely high thermal conductivity (about 1000 W / mK), excellent electrical properties and flame retardancy. However, it is difficult to introduce and disperse graphene in a polymer medium, which still limits the performance improvement.

[0005] Carbon nanotubes (CNTs) have good heat transfer performance and high thermal conductivity. CNTs have a very large aspect ratio, so their heat exchange performance along the length direction is high, and their heat exchange performance in the vertical direction is relatively low. Through appropriate orientation, carbon nanotubes can be synthesized into high anisotropic heat-conducting materials. However, the poor dispersibility and low interfacial strength of carbon nanotubes in polymers limit their application. Since carbon nanotubes usually agglomerate due to strong van der Waals forces, it is difficult to disperse carbon nanotubes in a polymer matrix.

[0006] In addition, poly-p-phenyleneterephthalamide (PPTA) fibers, commonly known as Kevlar, are well known for their attractive properties such as high strength and modulus, excellent thermal stability, low density, etc., and thus, they have been widely used in both civilian and military fields. PPTA paper-based materials are made from PPTA flocculated fibers and PPTA pulp through a papermaking process, and PPTA paper has the advantages of overall weight reduction, excellent mechanical properties, strong heat resistance, good flexibility in design and post-processing, etc. However, PPTA fibers have poor interfacial adhesion due to their rigid molecular chains and high crystallinity and orientation. The prior art discloses a large number of chemical and physical modification methods, which can improve the interfacial adhesion between PPTA fibers and polymer matrix by introducing active groups on the surface and / or increasing the surface roughness of the fibers, but the actual improvement effect is still very limited, and it is difficult to adsorb more nanomaterials with excellent thermal conductivity. SUMMARY

[0007] Therefore, the technical problem to be solved by the present application is to provide an aramid insulation paper and a preparation method and application thereof. The aramid insulation paper provided by the present application has high thermal conductivity and strength performance.

[0008] The present application provides an aramid insulation paper, comprising: an aramid fiber paper-based material and a composite filler filled in the aramid fiber paper-based material; the composite filler is made of raw materials including silicon dioxide coated carbon nanotubes and composite fibers; the composite fibers are made of raw materials including graphene and aramid nanofibers.

[0009] The present application discloses that the aramid nanofiber modified by graphene and the silicon dioxide coated carbon nanotube are used as the composite filler, which is filled in the aramid fiber paper-based material to realize good interfacial interaction and realize the synergistic improvement of thermal conductivity and mechanical properties.

[0010] The aramid insulation paper provided by the present application has a thickness of 80-120 μm. In the aramid insulation paper provided by the present application, the aramid fiber paper-based material is made of aramid fibers. In some embodiments of the present application, the aramid fibers in the aramid fiber paper-based material are p-aramid fibers.

[0011] The aramid insulation paper provided by the application contains 5 wt%-15 wt% of the composite filler in the aramid fiber paper base material. The composite filler is made of raw materials including silica-coated carbon nanotubes and composite fibers made of raw materials including graphene and aramid nanofibers. The composite fibers also have silver doping, and the doping amount of silver is 2 wt%-6 wt%. In some embodiments of the application, the silica-coated carbon nanotubes are mesoporous silica-coated carbon nanotubes, and the aramid nanofibers in the raw materials for making the composite fibers are para-aramid nanofibers. In some embodiments of the application, the aramid nanofibers in the raw materials for making the composite fibers are esterified aramid nanofibers. The application changes the surface properties of aramid nanofibers by introducing ester groups, so that they have better polarity and dispersibility, and can better compatible and combine with polar materials such as graphene to form a uniform, tight and stable composite structure. In other embodiments of the application, the aramid nanofibers in the raw materials for making the composite fibers are graphene composite aramid nanofibers.

[0012] The application also provides a preparation method of the aramid insulation paper according to any of the above technical solutions, which comprises the following steps:

[0013] The aramid fiber paper base material slurry and the composite filler are mixed, vacuum filtration is performed, and hot pressing is performed to obtain the aramid insulation paper.

[0014] The vacuum filtration can make the parallel arrangement of the nanofiller provide more heat conduction channels, enhance the heat conduction path, and endow the finally obtained aramid insulation paper with high heat conduction performance. The hot pressing is specifically hot pressing the material obtained by vacuum filtration at a hot pressing pressure of 10 MPa-15 MPa and a hot pressing temperature of 100°C-150°C for 5 min-10 min. Too low hot pressing temperature is not conducive to the evaporation of the solvent in the composite insulation paper, which is mainly deionized water, thereby affecting the entanglement between the fibers in the composite paper and the interface bonding between the fibers and the two-dimensional graphene filler; too high hot pressing temperature will cause the ester groups grafted on the aramid nanofibers to decompose, which will cause the thermal degradation, oxidation, discoloration, shrinkage and cracking of the composite paper, thereby affecting the mechanical properties of the composite paper. Too high hot pressing pressure will cause the heat sealing edge to be brittle and easy to crack, and will also cause the heat sealing strength to decrease; too low hot pressing pressure is not conducive to eliminating the defects or large pores in the composite paper, and the internal stress is not released.

[0015] The application further comprises vacuum annealing after hot pressing of the material obtained by vacuum filtration, and the vacuum annealing temperature is 200°C-350°C, the vacuum annealing time is 10 min-60 min, and the vacuum degree of the vacuum annealing is 10 -3 ~10-7 The heating mode of the vacuum annealing in the present application can be resistance heating, electron beam heating, laser heating, etc. After vacuum annealing, the composite paper is cooled to room temperature or other temperature according to the required cooling mode, such as furnace cooling, gas cooling, etc., the vacuum is broken, and the aramid insulation paper is obtained. The method of heating and cooling the composite paper in a vacuum environment can enhance the crystallinity and orientation of the composite paper, improve the interfacial bonding force between aramid and graphene, further improve the thermal conductivity of aramid composite insulation paper, avoid oxidation, decarburization, carburization and other phenomena, and achieve the effect of surface light purification; it can also reduce the residual stress in the composite paper, homogenize the grain structure of the material, and improve the strength, toughness and plasticity of the composite paper.

[0016] The aramid fiber paper base material slurry is prepared by the following method: mixing aramid flocculated fibers, aramid fiber slurry and dispersant, beating to obtain aramid fiber paper base material slurry; the dispersant is selected from at least one of polyethylene oxide (PEO), polyvinyl alcohol (PVA) and polyacrylamide (PMA). The mass ratio of the aramid flocculated fibers and the aramid fiber slurry is (1.5~2.5) : (7.5~8.5), preferably 2:8; the amount of the dispersant is 0.4 wt%~0.6 wt%. In some embodiments of the present application, the aramid fiber paper base material slurry is made of p-aramid flocculated fibers and p-aramid fiber slurry, and the specific preparation method is the same as above, which will not be repeated here.

[0017] The composite filler colloid is prepared by the following method: uniformly dispersing the silica-coated carbon nanotubes and the composite fibers to form a mixed solution, and filtering under a vacuum pressure of 0.1 MPa~0.3 MPa to obtain the composite filler colloid. The mass ratio of the silica-coated carbon nanotubes and the composite fibers is 1: (8~12).

[0018] The silica-coated carbon nanotubes are prepared by the following method: ultrasonicating the carbon nanotubes in a surfactant and an alkaline solution at a power of 400 W~500 W for 30 min~60 min to obtain a carbon nanotube dispersion liquid, stirring the carbon nanotube dispersion liquid and a silicon source at a stirring speed of 600 rpm~1000 rpm while heating at 40℃~60℃ for 12 h~16 h, then centrifuging at a speed of 6000 rpm~10000 rpm for 10 min~15 min, and finally drying at 45℃~60℃ for 36 h~48 h to obtain the silica-coated carbon nanotubes; the surfactant is selected from cetyltrimethylammonium bromide (CTAB); the silicon source is selected from tetraethoxysilane (TEOS).

[0019] The composite fiber of the present application is prepared by mixing graphene dispersion liquid and aramid nanofiber solution, electrospinning, and obtaining the composite fiber. The applied voltage of the electrospinning is 10 kV-20 kV; the distance between the syringe collector of the electrospinning is 10 cm-20 cm, and the receiving speed is 30 rpm / min-50 rpm / min; the ambient temperature of the electrospinning is 20℃-35℃; and the ambient relative humidity of the electrospinning is 20%-30%. The mass ratio of graphene in the graphene dispersion liquid to aramid nanofiber in the aramid nanofiber solution is (10-15):(10-15). In some embodiments of the present application, the concentration of the graphene dispersion liquid is 10 mg / mL-15 mg / mL, and the concentration of the aramid nanofiber solution is 10 mg / mL-15 mg / mL. The graphene and aramid nanofiber are the same as described above, and will not be repeated here. The composite fiber is prepared by electrospinning technology in the present application, which retains the high strength and modulus of ANF and the high thermal conductivity of graphene. Compared with simple physical blending, the electrospinning technology makes the dispersion of nanofillers more uniform.

[0020] The graphene dispersion liquid of the present application is prepared by mixing 1 wt%-5 wt% of graphene, 0.5 wt%-2 wt% of surfactant, and 0.5 wt%-2 wt% of dispersant in a solvent, stirring at 45℃-60℃ for 1 h-2 h, and ultrasonic treatment for 6 h-8 h to obtain the graphene dispersion liquid. The surfactant of the present application is selected from at least one of polyethylene glycol and polyvinylpyrrolidone, and the dispersant is selected from at least one of sodium dodecyl benzene sulfonate and polyvinyl alcohol.

[0021] The aramid nanofiber solution is prepared by the following method: stirring aramid fibers in an alkaline solution and an organic solvent for 14-28 days to obtain the aramid nanofiber solution; the alkaline solution is at least one selected from potassium hydroxide (KOH), sodium hydroxide (NaOH), and the organic solvent is selected from dimethyl sulfoxide (DMSO). In some embodiments of the present application, the aramid nanofiber solution is a graphene composite aramid nanofiber solution, which is prepared by the following method: stirring aramid fibers in an alkaline solution and an organic solvent for 14-28 days, then mixing the obtained material and a graphene dispersion solution, ultrasonicating for 3-4 hours, and stirring for 2-3 hours to obtain the aramid nanofiber solution. The present application uses a chemical splitting method to prepare aramid nanofibers, which can effectively decompose aramid fibers into nanofibers with a diameter of tens of nanometers at a lower temperature and pressure, maintaining the high strength, high modulus and high thermal conductivity of aramid fibers, while increasing the specific surface area and porosity of aramid nanofibers and increasing the interaction force with other materials.

[0022] In some embodiments of the present application, the aramid nanofiber solution is an esterified aramid nanofiber solution, which is prepared by the following method: mixing the aramid nanofiber solution and an esterifying agent, and treating with microwave radiation at a microwave power of 200-400 W for 5-20 min, preferably 200-350 W for 10-15 min to obtain an esterified aramid nanofiber solution; the esterifying agent is selected from ethyl acetate; the mass fraction of the esterifying agent is 0.5-0.8%. The present application introduces ester groups by microwave radiation technology to change the surface charge density of aramid nanofibers, improve their dispersibility and stability in water, and facilitate their filtration, self-assembly and other treatments.

[0023] In some embodiments of the present application, the aramid nanofibers in the aramid nanofiber solution are silver-doped, specifically by mixing the aramid nanofibers with a trisodium citrate and silver salt solution, removing the trisodium citrate, and growing silver nanoparticles in situ on the surface of the aramid nanofibers in the aramid nanofiber solution; the silver salt solution is selected from silver nitrate. The surface-grown AgNPs act as a bridge to effectively increase the thermal channel density, thereby replacing part of the interfacial thermal resistance with low contact thermal resistance and suppressing phonon scattering.

[0024] The present application also provides the use of the aramid insulation paper in any of the technical solutions described above as a heat-resistant insulating material in transformers or motors in power equipment. The aramid insulation paper provided by the present application has high thermal conductivity and strength performance, and can be used as a heat-resistant insulating material to ensure the reliable operation of transformers or motors in power equipment.

[0025] The application provides aramid composite insulation paper and a preparation method and application thereof. The aramid insulation paper provided by the application uses graphene-modified aramid nanofiber and silicon dioxide-coated carbon nanotube as composite fillers, fills the nanofillers in the aramid fiber paper base material through vacuum filtration, so that the parallel arrangement of the nanofillers can provide more heat conduction channels and enhance the heat conduction path, the aramid composite paper is endowed with high heat conductivity, through vacuum annealing treatment, the residual stress in the composite paper is reduced, the grain structure of the material is homogenized, and the strength, toughness and plasticity of the composite paper are improved, and the aramid composite paper can be used as a heat-resistant insulation material to ensure the reliable operation of a transformer or a motor in a power equipment. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 A scanning electron microscope image of the graphene dispersion liquid described in the present embodiment;

[0027] Figure 2 A scanning electron microscope image of the para-aramid fiber described in the present embodiment;

[0028] Figure 3 A scanning electron microscope image of the aramid nanofiber described in the present embodiment;

[0029] Figure 4 A cross-sectional scanning electron microscope image of the composite paper obtained in the present embodiment;

[0030] Figure 5 A comparison chart of the thermal conductivity coefficients of the present embodiments 1-3 and the comparative examples 1-4;

[0031] Figure 6 A comparison chart of the tensile strengths of the present embodiments 1-3 and the comparative examples 1-4. DETAILED DESCRIPTION

[0032] The application discloses aramid composite insulation paper and a preparation method and application thereof.

[0033] The application is further described below in combination with embodiments:

[0034] Embodiment 1

[0035] Step one, preparation of graphene dispersion liquid. 1 wt% of graphene sheet layer is dispersed in water, 0.5 wt% of polyethylene glycol and 0.5 wt% of sodium dodecyl benzene sulfonate are added as surfactants and dispersants, constant temperature stirring at 45℃ for 1 h, and uniform graphene dispersion liquid is obtained by ultrasonic treatment for 6 h; as shown in Figure 1 , Figure 1 The scanning electron microscope image of the graphene dispersion liquid described in the present embodiment is shown in

[0036] Step two, 20 mg of NaOH is weighed and dissolved in 400 mL of deionized water to prepare a NaOH weak alkaline solution. The pH of the weak alkaline environment is 8.5. 40 mg of CNTs and 0.3 g of CTAB are weighed and added to the prepared alkaline solution, poured into a 500 mL round-bottom flask, and stirred constantly. Ultrasonic treatment is performed in a water bath at a power of 500 W for 60 min to prepare a dispersion liquid. The dispersion liquid is heated in an oil bath and assisted by magnetic stirring at a speed of 1000 rpm. TEOS is added to the round-bottom flask using a pipette, and then the oil bath is kept at 60℃ for 16 h. The product obtained in the above step is washed with deionized water and placed in a centrifuge at a speed of 10000 rpm for 15 min. The lower precipitate is removed and placed in a vacuum oven at 60℃ for 48 h to obtain mesoporous silica-coated boron nitride nanotubes, denoted as CNTs@mSiO2.

[0037] Step three, 4.0 g of para-aramid fiber and 6 g of KOH are added to 2000 mL of DMSO and magnetically stirred in a sealed environment for 14 d to form a uniform transparent dark red ANFs / DMSO solution; as shown in Figure 2 , Figure 2 The scanning electron microscope image of the para-aramid fiber described in the present embodiment is shown in Figure 3 , Figure 3 The scanning electron microscope image of the aramid nanofiber described in the present embodiment is shown in

[0038] Step four, mix the ANF@Ag solution with a concentration of 15 mg / mL and the graphene solution with a concentration of 15 mg / mL, place on the electrospinning injector, electrospinning voltage is 20 kV, injector collector distance is 20 cm, receiving speed is 50 rpm / min. The temperature is 25℃, and the relative humidity is 25%. Through this method, a composite fiber is prepared, which is recorded as ANF@Ag / graphene.

[0039] Step five, mix 100 mg of composite fiber with 10 mg of CNTs@mSiO2, disperse uniformly to prepare a mixed solution, and use a Buchner funnel to obtain a colloid by vacuum assisted filtration (VAF) method under a vacuum pressure of 0.1 MPa. The colloid is recorded as ANF@Ag / graphene / CNTs@mSiO2 colloid.

[0040] Step six, mix the PPTA flocculation fiber and the PPTA slurry in a beater at a weight ratio of 2:8, then add 0.4 wt% of PEO as a dispersant to disperse the fiber suspension slurry. Then, add 5 wt% of ANF@Ag / graphene / CNTs@mSiO2 colloid to the fiber suspension slurry, and stir in a paper pulp disintegrator for 5000 revolutions to form a uniform fiber slurry. Subsequently, the slurry is vacuum filtered to obtain a preliminary composite paper.

[0041] Step seven, the preliminary composite paper is subjected to hot pressing treatment. The hot pressing pressure is 10 MPa, the hot pressing temperature is 100℃, and the hot pressing time is 5 min.

[0042] Step eight, place the composite paper in a vacuum chamber, extract the vacuum to the required vacuum degree (10 -4 ), heat the composite paper to an annealing temperature of 200℃, keep the temperature at the annealing temperature for 20 min, turn off the heating source, cool the composite paper to room temperature, disconnect the vacuum, and take out the composite paper; as Figure 4 shown, Figure 4 is a scanning electron microscope cross-section of the composite paper obtained in this embodiment.

[0043] Example 2

[0044] Step one, prepare a graphene dispersion solution. Disperse 1 wt% of graphene layers in water, add 0. % of polyethylene glycol and 0.5 wt% of sodium dodecylbenzenesulfonate as surfactant and dispersant, stir at 50℃ for 1.5 h, and obtain a uniform graphene dispersion solution by ultrasonic treatment for 7 h;

[0045] Step two, 20 mg NaOH was weighed and dissolved in 400 mL deionized water to prepare a weak alkaline solution of NaOH, and the pH of the weak alkaline environment was 8.5. 40 mg CNTs and 0.3 g CTAB were weighed and added to the prepared alkaline solution, poured into a 500 mL round-bottom flask, and stirred constantly. The dispersion liquid was prepared by ultrasonicating in a water bath at a power of 500 W for 60 min. The dispersion liquid was heated in an oil bath and assisted by magnetic stirring at a speed of 1000 rpm. TEOS was added to the round-bottom flask using a pipette, and then the oil bath was kept at 60 ℃ for 16 h. The product obtained in the above step was washed with deionized water and centrifuged at a speed of 10000 rpm for 15 min. The precipitate was taken out and dried in a vacuum oven at 60 ℃ for 48 h to obtain mesoporous silica-coated boron nitride nanotubes, denoted as CNTs@mSiO2.

[0046] Step three, 4.0 g of para-aramid fibers and 6 g of KOH were added to 2000 mL of DMSO and magnetically stirred in a sealed environment for 14 d to form a uniform transparent dark red ANFs / DMSO solution. The ANFs / DMSO solution was added to 80 mL of deionized water, and then mixed with the treated graphene dispersion liquid, ultrasonicated for 3 h, stirred for 2 h, and repeatedly washed with deionized water to remove residual KOH and DMSO and organic solvents in the ANF to obtain an aramid nanofiber solution. Ethyl acetate with a mass fraction of 0.5 % was added as an esterification agent to the aramid nanofiber solution, and microwave irradiation was performed at a microwave power of 400 W for 10 min. Silver nitrate aqueous solution was added dropwise into the aramid nanofiber solution containing trisodium citrate. Stirring was performed at 60 ℃ and 1000 rpm for 24 h, and vacuum filtration was performed three times to remove trisodium citrate to obtain ANF with AgNPs adsorbed on the surface, denoted as ANF@Ag.

[0047] Step four, the ANF@Ag solution with a concentration of 15 mg / mL and the graphene solution with a concentration of 15 mg / mL were mixed and placed on an electrospinning injector. The electrospinning voltage was 20 kV, the injector collector distance was 20 cm, and the receiving speed was 50 rpm / min. The temperature was 25 ℃, and the relative humidity was 25 %. In this way, a composite fiber was prepared, denoted as ANF@Ag / graphene.

[0048] Step five, 100 mg of the composite fiber was mixed with 10 mg of CNTs@mSiO2 to prepare a mixed solution. The ANF@Ag / graphene / CNTs@mSiO2 gel was obtained by using a Buchner funnel to perform vacuum-assisted filtration (VAF) under a vacuum pressure of 0.1 MPa.

[0049] Step six, PPTA flocculation fibers and PPTA slurry were mixed in a beater at a weight ratio of 2:8, then 0.4 wt% PEO was added as a dispersant to disperse the fiber suspension slurry. Then, 10 wt% ANF@Ag / Graphene / CNTs@mSiO2colloid was added to the fiber suspension slurry, and the slurry was stirred in a paper pulp disintegrator for another 5000 revolutions to form a uniform fiber slurry. Subsequently, the slurry was vacuum filtered to obtain a preliminary composite paper.

[0050] Step seven, the preliminary composite paper was subjected to hot pressing treatment. The hot pressing pressure was 15 MPa, the hot pressing temperature was 100°C, and the hot pressing time was 5 min.

[0051] Step eight, the composite paper was placed in a vacuum chamber, vacuum was extracted to the required vacuum degree (10 -4 ), the composite paper was heated to an annealing temperature of 250°C, and kept at the annealing temperature for 30 min, the heating source was turned off, the composite paper was cooled to room temperature, the vacuum was turned off, and the composite paper was taken out.

[0052] Example 3

[0053] Step one, prepare a graphene dispersion. Disperse 1 wt% graphene sheets in water, add 0. % polyethylene glycol and 0.5 wt% sodium dodecylbenzenesulfonate as surfactant and dispersant, stir at 45°C for 1 h, and obtain a uniform graphene dispersion by ultrasonic treatment for 6 h;

[0054] Step two, weigh 20 mg NaOH and dissolve in 400 mL deionized water to prepare a NaOH weak alkaline solution, and the pH of the weak alkaline environment is 8.5. Weigh 40 mg CNTs and 0.3 g CTAB and add to the prepared alkaline solution, pour into a 500 mL round-bottom flask, and continuously stir under water bath ultrasonic treatment at a power of 500 W for 60 min to prepare a dispersion. Heat the dispersion in an oil bath and assist with magnetic stirring at a speed of 1000 rpm. Use a pipette to add TEOS to the round-bottom flask, then keep the oil bath heating at 60°C for 16 h; wash the product obtained in the above step with deionized water and place it in a centrifuge at a speed of 10000 rpm for 15 min; take the precipitate and place it in a vacuum oven at 60°C for 48 h to obtain mesoporous silica-coated boron nitride nanotubes, denoted as CNTs@mSiO2;

[0055] Step three, 4.0 g of para-aramid fiber and 6 g of KOH were added into 2000 mL of DMSO and magnetically stirred in a sealed environment for 14 d to form a uniform transparent dark red ANFs / DMSO solution. The ANFs / DMSO solution was added to 80 mL of deionized water, then mixed with the treated graphene dispersion, ultrasonicated for 3 h, stirred for 2 h, and repeatedly washed with deionized water to remove residual KOH and DMSO in ANF and organic solvents, etc. Aramid nanofiber solution was obtained. Ethyl acetate with a mass fraction of 0.5% was added as an esterification agent to the aramid nanofiber solution, and microwave irradiation was performed at a microwave power of 300 W for 10 min. Silver nitrate aqueous solution was added dropwise into the aramid nanofiber solution containing trisodium citrate. Stirring at 1000 rpm for 24 h at 60 °C, vacuum filtration and washing three times to remove trisodium citrate to obtain ANF with AgNPs adsorbed on the surface, denoted as ANF@Ag.

[0056] Step four, mix the ANF@Ag solution with a concentration of 15 mg / mL and the graphene solution with a concentration of 15 mg / mL, and place them on an electrospinning injector. The electrospinning voltage is 20 kV, the injector collector distance is 20 cm, and the receiving speed is 50 rpm / min. The temperature is 25 °C and the relative humidity is 25%. In this way, a composite fiber is prepared, denoted as ANF@Ag / graphene.

[0057] Step five, mix 100 mg of composite fiber with 10 mg of CNTs@mSiO2 to prepare a mixed solution. Under a vacuum pressure of 0.1 MPa, a Buchner funnel is used to obtain a colloid by vacuum-assisted filtration (VAF), denoted as ANF@Ag / graphene / CNTs@mSiO2 colloid.

[0058] Step six, mix PPTA flocculation fiber and PPTA slurry in a beater at a weight ratio of 2:8, then add 0.4 wt% PEO as a dispersant to disperse the fiber suspension slurry. Then, add 15 wt% ANF@Ag / graphene / CNTs@mSiO2 colloid to the fiber suspension slurry, and stir in a paper pulp disintegrator for 5000 revolutions to form a uniform fiber slurry. Then, the slurry is vacuum filtered to obtain a preliminary composite paper.

[0059] Step seven, the preliminary composite paper is subjected to hot pressing treatment. The hot pressing pressure is 10 MPa, the hot pressing temperature is 100 °C, and the hot pressing time is 5 min.

[0060] Step eight, the composite paper is placed in a vacuum chamber, and the vacuum is extracted to the desired vacuum degree (10 -4), heating the composite paper to an annealing temperature of 300 °C, keeping the composite paper at the annealing temperature for 40 min, turning off the heating source, cooling the composite paper to room temperature, turning off the vacuum, and removing the composite paper.

[0061] Comparative Example 1

[0062] Step one, mixing the PPTA flocculated fiber and PPTA slurry in a beater at a weight ratio of 2:8, then adding 0.4% PEO as a dispersant, dispersing the fiber suspension slurry, and stirring in a paper pulp disintegrator for 5000 revolutions to form a uniform fiber slurry. Subsequently, the slurry is vacuum filtered to obtain a preliminary composite paper.

[0063] Step two, heat pressing the preliminary composite paper. The heat pressing pressure is 15 MPa, the heat pressing temperature is 100 °C, and the heat pressing time is 5 min.

[0064] Step three, placing the composite paper in a vacuum chamber, extracting the vacuum to the desired vacuum degree, which is generally 10 -3 ~10 -6 heating the composite paper to an annealing temperature of 250 °C, keeping the composite paper at the annealing temperature for 30 min, turning off the heating source, cooling the composite paper to room temperature, turning off the vacuum, and removing the composite paper.

[0065] Comparative Example 2

[0066] The preparation method is the same as that of Example 1, except that no CNTs@SiO2 is added in this example, and the added colloid is ANF@Ag / graphene.

[0067] Comparative Example 3

[0068] The preparation method is the same as that of Example 2, except that no CNTs@SiO2 is added in this example, and the added colloid is ANF@Ag / graphene.

[0069] Comparative Example 4

[0070] The preparation method is the same as that of Example 3, except that no CNTs@SiO2 is added in this example, and the added colloid is ANF@Ag / graphene.

[0071] Comparative Example 5

[0072] Step one, preparing a graphene dispersion. Disperse 1 wt% of graphene sheets in water, add 0.5 wt% of polyethylene glycol and 0.5 wt% of sodium dodecylbenzenesulfonate as surfactant and dispersant, stir at 45 °C for 1 h, and obtain a uniform graphene dispersion by ultrasonic treatment for 6 h;

[0073] Step two, 4.0 g of para-aramid fiber and 6 g of KOH were added into 2000 mL of DMSO and magnetically stirred in a sealed environment for 14 days to form a uniform transparent dark red ANFs / DMSO solution. The ANFs / DMSO solution was added to 80 mL of deionized water, then mixed with the treated graphene dispersion, ultrasonicated for 3 h, stirred for 2 h, and repeatedly washed with deionized water to remove residual KOH and DMSO in ANF and organic solvents, etc., to obtain aramid nanofiber solution. Ethyl acetate with a mass fraction of 0.5 wt% was added as an esterification agent to the aramid nanofiber solution, and microwave irradiation was performed at a microwave power of 300 W for 10 min. Silver nitrate aqueous solution was added dropwise into the aramid nanofiber solution containing trisodium citrate. Stirring at 1000 rpm for 24 h at 60°C, vacuum filtration and washing three times to remove trisodium citrate to obtain ANF with AgNPs adsorbed on the surface, denoted as ANF@Ag.

[0074] Step three, the ANF@Ag solution with a concentration of 15 mg / mL and the graphene solution with a concentration of 15 mg / mL were mixed and placed on an electrospinning injector. The electrospinning voltage was 20 kV, the injector collector distance was 20 cm, and the receiving speed was 50 rpm / min. The temperature was 25°C and the relative humidity was 25%. In this way, a composite fiber was prepared, denoted as ANF@Ag / graphene.

[0075] Step four, 100 mg of the composite fiber was mixed with 10 mg of CNTs to prepare a mixed solution. A vacuum-assisted filtration (VAF) method was used to obtain a colloid using a Buchner funnel under a vacuum pressure of 0.1 MPa, denoted as ANF@Ag / graphene / CNTs colloid.

[0076] Step six, the PPTA flocculation fiber and the PPTA slurry were mixed in a beater at a weight ratio of 2:8, and then 0.4 wt% of PEO was added as a dispersant to disperse the fiber suspension slurry. Then, 5 wt% of the ANF@Ag / graphene / CNTs colloid was added to the fiber suspension slurry, and the slurry was stirred in a paper pulp disintegrator for 5000 revolutions to form a uniform fiber slurry. Subsequently, the slurry was vacuum filtered to obtain a preliminary composite paper

[0077] Step seven, the preliminary composite paper was subjected to hot pressing treatment. The hot pressing pressure was 10 MPa, the hot pressing temperature was 100°C, and the hot pressing time was 5 min.

[0078] Step eight, the composite paper was placed in a vacuum chamber, and the vacuum was extracted to the desired vacuum degree (10 -4Heat the composite paper to an annealing temperature of 200 ℃, hold it at the annealing temperature for 20 min, turn off the heating source, cool the composite paper to room temperature, disconnect the vacuum, and remove the composite paper.

[0079] Comparative Example 6

[0080] The preparation method is the same as in Example 7, except that 20 mg of CNTs were added in this example.

[0081] Comparative Example 7

[0082] The preparation method is the same as in Example 7, except that 30 mg of CNTs were added in this example.

[0083] The thermal conductivity and tensile strength of the composite papers from Examples 1-3 and Comparative Examples 1-7 were tested, and the results are shown in Table 1.

[0084] Table 1

[0085]

[0086] The thermal conductivity test results of Examples 1-3 and Comparative Examples 1-4 were compared, as follows: Figure 5 As shown, Figure 5 This is a comparison chart of the thermal conductivity of Embodiments 1-3 and Comparative Examples 1-4 of the present invention. Figure 5 As can be seen from the data in Table 1, the composite insulating paper prepared in Example 3 containing 15 wt% ANF@Ag / graphene / CNTs@mSiO2 colloid has a higher thermal conductivity, compared to Comparative Example 1, where the thermal conductivity is 1.51 W / m². -1 K -1 Increased to 10.21 Wm -1 K -1 This represents an increase of 477.48%. The thermal conductivity has been significantly improved.

[0087] The tensile strength test results of Examples 1-3 and Comparative Examples 1-4 were compared, as follows: Figure 6 As shown, Figure 6 This is a comparison chart of the tensile strength of Examples 1-3 and Comparative Examples 1-4 of the present invention. From... Figure 6 As shown in Table 1, the composite insulating paper containing 10 wt% ANF@Ag / graphene / CNTs@mSiO2 colloid prepared in Example 2 of this invention achieved a maximum tensile strength of 135.1 MPa, which is 34.93% higher than the tensile strength of 100.2 MPa in Comparative Example 1. When the ANF / graphene content was 15 wt%, the tensile strength decreased compared to Example 2. Within a certain range, the higher the content of ANF@Ag / graphene / CNTs@mSiO2 colloid, the greater the increase in tensile strength.

[0088] From the test results of Example 1 and Comparative Examples 5-7, it can be seen that the thermal conductivity of the composite paper of Example 1 added with 10 mg of CNTs@SiO2 is 6.89 W·m -1 ·K- 1 , while the thermal conductivity of the composite paper of Comparative Example 5 added with 10 mg of CNTs is 4.23 W·m -1 ·K -1 The thermal conductivity of the latter is less efficient than that of CNTs@SiO2, and the tensile strength decreases with the increase of the content of CNTs. Under the same content, the tensile strength of the composite paper added with CNTs@SiO2 is lower than that of the composite paper added with CNTs. This is because the CNTs coated with SiO2 can have better interface interaction with the matrix material, improve the dispersibility of the CNTs in the polymer matrix, alleviate the agglomeration phenomenon of the CNTs, and be conducive to the construction of efficient phonon transmission channels and the improvement of the thermal conductivity.

[0089] The above describes only the preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art, according to the technical solution and the inventive concept of the present application, can make equivalent replacements or changes within the technical range disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. An aramid insulation paper characterized by, Comprise: a para-aramid fiber paper-based material and a composite filler filled in the para-aramid fiber paper-based material; the composite filler is made of mesoporous silica-coated carbon nanotubes and a composite fiber; the preparation method of the composite fiber comprises the following steps: mixing a graphene dispersion liquid and an aramid nanofiber solution, electrospinning to obtain the composite fiber; the aramid nanofiber solution is an esterified aramid nanofiber solution; the aramid nanofiber in the aramid nanofiber solution is silver-doped.

2. The aramid insulation paper of claim 1, wherein, The doping amount of silver in the composite fiber is 2 wt% to 6 wt%.

3. The aramid insulation paper of claim 1, wherein, The content of the composite filler in the aramid fiber paper-based material is 5 wt% to 15 wt%.

4. The method of producing aramid insulation paper according to any one of claims 1 to 3, characterized in that, comprise the following steps: mixing a para-aramid fiber paper-based material slurry and the composite filler, vacuum suction filtration, hot pressing to obtain the aramid insulation paper.

5. The preparation method according to claim 4, characterized in that, The para-aramid fiber paper-based material slurry is made of para-aramid flocculation fibers and aramid fiber slurry with a mass ratio of (1.5-2.5):(7.5-8.5); The composite filler is made of mesoporous silica-coated carbon nanotubes and a composite fiber with a mass ratio of 1:(8-12).

6. The preparation method according to claim 4, characterized in that, The pressure of the hot pressing is 10 MPa to 15 MPa, the temperature of the hot pressing is 100℃ to 150℃, and the time of the hot pressing is 5 min to 10 min.

7. The preparation method according to claim 4, characterized in that, After hot pressing, it also includes vacuum annealing, the temperature of the vacuum annealing is 200℃ to 350℃, and the time of the vacuum annealing is 10 min to 60 min.

8. The application of the aramid insulation paper in any one of claims 1-3 as a heat-resistant insulation material in a transformer or a motor.

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