Aramid fiber vermiculite nano paper and preparation method thereof

Abstract

The invention relates to the technical field of composite materials, in particular to aramid fiber vermiculite nano paper and a preparation method thereof. The aramid fiber vermiculite nanopaper comprises aramid fiber nanofibers and vermiculite nanosheets coated with a binder, the aramid fiber nanofibers form a three-dimensional grid structure, and the vermiculite nanosheets coated with the binder are embedded in the three-dimensional grid structure to form a three-dimensional interconnected layered structure. The aramid fiber vermiculite nanopaper disclosed by the invention has high toughness, excellent breakdown resistance and flame retardance, and the application range of the aramid fiber-based nanopaper in advanced electrical insulating materials is expanded.

Description

Technical Field

[0001] The invention relates to the technical field of composite materials, and in particular to aramid vermiculite nanopaper and a preparation method thereof. Background Art

[0002] Traditional nanopaper materials have limitations in mechanical properties, thermal stability or flame retardancy. As electronic and electrical devices continue to develop towards miniaturization, flexibility and high power output, there is an urgent need to develop electrical insulating materials that have both strength and toughness. Nature has created materials that are both lightweight, high-strength and tough over millions of years of evolution, and nacre (or mother-of-pearl) is a typical representative of such materials. Aramid fiber is a high-performance synthetic fiber with excellent properties such as high strength, high modulus, high temperature resistance and chemical corrosion resistance. Aramid fibers can also be entangled together through reprotonation to form a three-dimensional porous network structure, and together with polymers form an interconnected layered structure similar to the nacre of natural shells. Vermiculite is a layered silicate mineral whose nanosheets have high specific surface area, high barrier properties and good thermal stability. The composite of aramid fiber and vermiculite nanosheets can give full play to the advantages of both and prepare nanopaper materials with excellent comprehensive properties.

[0003] Inspired by the orderly interconnected layered structure of natural nacre, researchers have conducted extensive research on the next generation of lightweight, high-performance nanocomposites. Although shell-based composites have achieved certain success in mimicking natural shell structures, they still have problems such as low integration, poor toughness, and small preparation scale. In addition, electrical insulation materials with excellent penetration resistance and flame retardancy play a vital role in electrical safety and stable operation of equipment, and are an indispensable and important part of ensuring the safe and reliable operation of power systems. In response to the above problems, it is urgent to develop a nanopaper material that is flexible, has high dielectric strength, and has high toughness, and to simplify its preparation process. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing aramid vermiculite nanopaper, which is used to solve the problem in the prior art that nanopaper materials cannot have flexibility, high dielectric strength and high toughness at the same time.

[0005] In order to solve the above problems, the present invention proposes an aramid vermiculite nanopaper, and the technical solution adopted is: Aramid vermiculite nanopaper comprises aramid nanofibers and vermiculite nanosheets coated with a binder, wherein the aramid nanofibers form a three-dimensional grid structure, and the vermiculite nanosheets coated with a binder are embedded in the three-dimensional grid structure to form a three-dimensional interconnected layered structure.

[0006] The beneficial effects of the present invention are: The present invention uniformly embeds vermiculite nanosheets coated with a binder into the three-dimensional network structure formed by aramid nanofibers through hydrogen bonding to form a three-dimensional interconnected layered structure, which is similar to the interconnected layered structure of natural shell beads. The high strength of the aramid nanofibers, the high rigidity of the vermiculite nanosheets coated with a binder, and the uniformly interconnected layered structure of the two make the aramid vermiculite nanopaper have excellent mechanical properties; at the same time, the mechanical properties of the aramid nanofibers complement the electrical insulation performance and flame retardancy of the vermiculite nanosheets coated with a binder, and the uniformly interconnected layered structure can not only extend the breakdown path and enhance its electrical insulation performance, but also produce a higher interface density, showing an excellent thermal insulation effect. The tensile strength of the aramid vermiculite nanopaper obtained in this application reaches up to 192 MPa, and the toughness reaches 55 MJ m -3 ; In addition, aramid vermiculite nanopaper also exhibits excellent electrical insulation properties, with a dielectric strength of up to 198kV / mm. It is also non-flammable and thermally stable, making the aramid vermiculite nanopaper of the present application have high toughness, excellent breakdown resistance and flame retardancy, expanding the application range of aramid-based nanopaper in advanced electrical insulation materials.

[0007] In order to improve the adhesion between the binder and the vermiculite nanosheets and improve the high rigidity of the vermiculite nanosheets coated with the binder, preferably, the binder in the vermiculite nanosheets coated with the binder is one or a mixture of two or more of polyvinyl alcohol, polyacrylic acid, polyurethane, epoxy resin, polyvinyl pyrrolidone, carboxymethyl cellulose, aluminum phosphate or aluminum phosphate.

[0008] In order to improve the uniformity of the layered structure interconnected by aramid nanofibers and vermiculite nanosheets coated with a binder, and thus improve the excellent mechanical properties of aramid vermiculite nanopaper, preferably, the aramid nanofibers are para-aramid nanofibers, the diameter of the aramid nanofibers is 6-20 nm, and the length is 2-10 μm; the mass of the aramid nanofibers accounts for 30-70% of the aramid vermiculite nanopaper; the diameter of the vermiculite nanosheets in the vermiculite nanosheets coated with a binder is 6-20 nm, and the length is 1-10 μm; the mass of the vermiculite nanosheets in the vermiculite nanosheets coated with a binder accounts for 20-60% of the mass of the aramid vermiculite nanopaper.

[0009] The present invention also proposes a method for preparing aramid vermiculite nanopaper, and the technical scheme adopted is: A method for preparing aramid vermiculite nanopaper comprises the following steps: mixing a dispersion of aramid nanofibers and a dispersion of vermiculite nanosheets coated with a binder to obtain an aramid vermiculite composite sol; performing solvent exchange on the aramid vermiculite composite sol and a protic solvent to obtain an aramid vermiculite composite gel, and drying the gel to obtain the aramid vermiculite nanopaper.

[0010] The beneficial effects of the present invention are as follows: the preparation method of the aramid vermiculite nanopaper of the present invention is through the "continuous extrusion sol-gel film conversion" process, and the obtained aramid vermiculite nanopaper has a three-dimensional interconnected layered network structure, the method is simple, and the operability is strong, and the continuous preparation of high-strength and high-toughness electrical insulating nanopaper is realized, which is conducive to the realization of industrial production.

[0011] Preferably, the drying temperature is 80-300° C. and the drying time is 10-60 min.

[0012] Preferably, the protic solvent is one or a mixed solvent of two or more selected from the group consisting of water, ethanol, glycerol, tert-butyl alcohol and acetic acid.

[0013] In order to obtain a uniformly coated dispersion of vermiculite nanosheets coated with a binder, preferably, the preparation method of the dispersion of vermiculite nanosheets coated with a binder comprises: mixing the dispersion of vermiculite nanosheets and an aqueous binder solution by magnetic stirring and then precipitating to obtain a precipitate; washing the precipitate with dimethyl sulfoxide and then diluting it with dimethyl sulfoxide to obtain a dispersion of vermiculite nanosheets coated with a binder.

[0014] Further preferably, the magnetic stirring time is 12-72 h, and the rotation speed is 3000-8000 rpm.

[0015] More preferably, the washing temperature is 50-95°C.

[0016] In order to allow the binder to fully coat the vermiculite nanosheets, preferably, the mass ratio of the vermiculite nanosheets in the vermiculite nanosheet dispersion to the binder in the binder aqueous solution is 1:(1-20).

[0017] Further preferably, the mass ratio of the vermiculite nanosheets in the vermiculite nanosheet dispersion to the binder in the binder aqueous solution is 1:(1-10).

[0018] In order to obtain a dispersion liquid under the premise of ensuring the electrical insulation performance and flame retardancy of vermiculite nanosheets, preferably, the preparation method of the vermiculite nanosheet dispersion liquid comprises: subjecting raw vermiculite ore powder to high-temperature heat treatment to obtain expanded vermiculite powder; mixing the expanded vermiculite powder with an alkali metal salt and deionized water and placing the mixture in a stainless steel kettle for a first ion exchange reaction to obtain a vermiculite suspension liquid; stirring and washing the vermiculite suspension liquid and then mixing it with an alkali metal salt and deionized water for a second ion exchange reaction to obtain a vermiculite nanosheet suspension liquid, and washing the mixture to obtain a vermiculite nanosheet dispersion liquid.

[0019] In order to improve the efficiency and effect of the full reaction of expanded vermiculite powder, preferably, the pressure of the first ion exchange reaction and the second ion exchange reaction are both 0.4-2.5 Mpa, the temperature is both 100-180°C, and the time is both 6-48h; the temperature of the high temperature heat treatment is 300-600°C, and the time is 1-3h.

[0020] In order to allow the expanded vermiculite powder to react fully, preferably, the mass ratio of the expanded vermiculite powder, the alkali metal salt and the deionized water is 1: (5-40): (10-1000).

[0021] In order to fully obtain the vermiculite suspension, preferably, the alkali metal salt is one or a mixture of two or more of lithium salt, sodium salt, lanthanum salt, potassium salt, calcium salt or tin salt.

[0022] More preferably, the alkali metal salt is one or a mixture of two or more of lithium chloride, sodium chloride and calcium chloride.

[0023] More preferably, the stirring temperature is 50-95°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is an atomic force microscope image of the aramid micron fiber used in the method for preparing the aramid vermiculite nanopaper of the present invention.

[0025] Figure 2 This is a diameter distribution diagram of aramid micron fibers used in the method for preparing aramid vermiculite nanopaper of the present invention.

[0026] Figure 3 This is an atomic force microscope image of the vermiculite nanosheets used in the method for preparing the aramid vermiculite nanopaper of the present invention.

[0027] Figure 4 This is a diameter distribution diagram of the vermiculite nanosheets used in the method for preparing the aramid vermiculite nanopaper of the present invention.

[0028] Figure 5 This is a SEM image of the aramid vermiculite nanopaper prepared in Example 1 of the method for preparing aramid vermiculite nanopaper of the present invention.

[0029] Figure 6 This is a SEM image of the cross section of the aramid vermiculite nanopaper prepared in Example 1 of the method for preparing the aramid vermiculite nanopaper of the present invention.

[0030] Figure 7 This is a SEM image of the surface of the aramid vermiculite nanopaper prepared in Example 1 of the method for preparing the aramid vermiculite nanopaper of the present invention.

[0031] Figure 8This is a SEM image of the breakdown part of the aramid vermiculite nanopaper prepared in Example 1 of the method for preparing aramid vermiculite nanopaper of the present invention after a breakdown test.

[0032] Fig. 9 This is a surface SEM image of the aramid vermiculite nanopaper after combustion, prepared in Example 1 of the method for preparing aramid vermiculite nanopaper of the present invention.

[0033] Fig.10 This is a physical appearance picture of the aramid vermiculite nanopaper prepared in Example 2 of the method for preparing aramid vermiculite nanopaper of the present invention.

[0034] Fig.11 It is a schematic diagram of the structure of the continuous scraping device in the present invention, wherein 1 is a syringe, 2 is a scraper, 3 is a conveyor belt, 4 is a solvent tank, and 5 is a roller press. DETAILED DESCRIPTION

[0035] The nanopaper materials in the prior art cannot have flexibility, high dielectric strength and high toughness at the same time. The present invention provides an aramid vermiculite nanopaper, which comprises aramid nanofibers and vermiculite nanosheets coated with a binder, wherein the aramid nanofibers form a three-dimensional grid structure, and the vermiculite nanosheets coated with a binder are embedded in the three-dimensional grid structure to form a three-dimensional interconnected layered structure.

[0036] The technical concept of the present invention is that aramid nanofibers have good mechanical properties, and the three-dimensional network structure formed by them can improve the mechanical properties of aramid vermiculite nanopaper; vermiculite nanosheets have high rigidity, electrical insulation and flame retardancy, and at the same time, they are coated with a binder to obtain vermiculite nanosheets coated with a binder, so that they have higher rigidity, electrical insulation and flame retardancy, and have a high aspect ratio. The vermiculite nanosheets coated with a binder with a high aspect ratio are uniformly embedded in the three-dimensional network structure through hydrogen bonding to form a three-dimensional interconnected layered structure, which can extend the breakdown path, enhance its electrical insulation performance, and can also produce a higher interface density, showing excellent thermal insulation effect and electrical insulation characteristics.

[0037] Specifically, the preparation method of aramid vermiculite nanopaper comprises the following steps: (1) Preparation of aramid nanofiber dispersion: adding a strong base and para-aramid to an aprotic solvent and mechanically stirring for 12-72 h to obtain an aramid nanofiber dispersion, wherein the mass ratio of the strong base, para-aramid, and aprotic solvent is 1:(0.3-7):(8-250); (2) Preparation of vermiculite nanosheet dispersion: raw vermiculite powder is subjected to high temperature heat treatment to obtain expanded vermiculite powder, the expanded vermiculite powder is mixed and dissolved with an alkali metal salt and deionized water, and then placed in a stainless steel autoclave for a first ion exchange reaction at a pressure of 0.4-2.5 MPa and a temperature of 100-180°C for 6-48 hours to obtain a vermiculite suspension; the vermiculite suspension is taken out, stirred at a temperature of 50-95°C and a rotation speed of 100-1500 rpm for 12-168 hours, then washed, and then mixed with an alkali metal salt and deionized water, and heated at a pressure of 0.4-2.5 Mpa, and a temperature of 100-180°C for 6-48h to obtain a vermiculite nanosheet suspension; the vermiculite nanosheet suspension is washed 2-5 times with deionized water at a temperature of 50-95°C to obtain a vermiculite nanosheet dispersion; wherein the mass ratio of expanded vermiculite powder, alkali metal salt and deionized water is 1: (5-40): (10-1000); the temperature of high temperature heat treatment is 300-600°C, and the time is 1-3h; (3) A method for preparing a dispersion of vermiculite nanosheets coated with a binder: after mixing a dispersion of vermiculite nanosheets with an aqueous binder solution, the mixture is magnetically stirred at a speed of 3000-8000 rpm for 12-72 hours to obtain a mixture, the mixture is centrifuged at 5000 rpm for 30 min, and then the precipitate is collected; the precipitate is centrifugally washed 2-5 times with dimethyl sulfoxide at a temperature of 50-95°C, the water is removed, and then it is diluted with dimethyl sulfoxide to obtain a dispersion of vermiculite nanosheets coated with a binder; wherein the mass ratio of the vermiculite nanosheets in the dispersion of vermiculite nanosheets to the binder in the aqueous binder solution is 1: (1-20); the binder is one or a mixture of two or more of polyvinyl alcohol, polyacrylic acid, polyurethane, epoxy resin, polyvinyl pyrrolidone, carboxymethyl cellulose, aluminum phosphate or aluminum phosphate; (4) The aramid nanofiber dispersion of step (1) and the vermiculite nanosheet dispersion coated with a binder of step (3) are mixed by mechanical stirring for 10-60 min to obtain an aramid vermiculite composite sol; (5) placing the aramid fiber vermiculite composite sol in step (4) in a stainless steel circular mold with a diameter of 5 cm, and then immersing it in a protic solvent, taking it out, and repeating the immersion 3-8 times until the strong base and the non-protic solvent in the aramid fiber composite sol are fully exchanged; or the aramid vermiculite composite sol is subjected to solvent exchange with a protic solvent through a continuous scraping device to obtain an aramid vermiculite composite gel; (6) Placing the aramid vermiculite composite gel of step (5) in an oven and drying it at 80-300° C. for 10-60 min to obtain flexible, high dielectric strength and high toughness aramid vermiculite nanopaper.

[0038] Preferably, in step (1), the strong base is one or a mixture of two or more of sodium hydroxide, potassium hydroxide, sodium ethoxide, potassium ethoxide, sodium tert-butoxide, and potassium tert-butoxide.

[0039] Preferably, in step (1), the para-aramid fiber is one or a mixture of two or more of para-aramid chopped fibers, para-aramid pulp, and para-aramid fibrid.

[0040] Preferably, in step (1), the aprotic solvent is one or a mixed solvent of two or more selected from the group consisting of dimethyl sulfoxide, N,N-dimethylformamide and tetrahydrofuran.

[0041] Preferably, in step (3), the binder aqueous solution is prepared by mixing a binder and deionized water, and the mass ratio of the binder to the deionized water is (1-20): (10-1000).

[0042] Specifically, in step (5), the solvent exchange specifically includes: In the present invention, the aramid vermiculite composite sol is poured into a mold so that the aramid vermiculite composite sol covers the bottom of the mold, and the mold covered with the sol is immersed in a protic solvent for solvent exchange. There are no special requirements for the shape and specifications of the mold, which can be circular, square, rectangular, etc. In a specific embodiment of the present invention, the mold is preferably a circular bottom mold so as to obtain a film with uniform thickness.

[0043] In the present invention, the method of solvent exchange between the aramid vermiculite composite sol and the protic solvent by a continuous coating device is a continuous preparation method. Fig.11 As shown, the continuous scraping device includes an injector 1, a scraper 2, a conveyor belt 3, a solvent tank 4 and a roller press 5. The outlet of the injector 1 is connected to the inlet of the scraper 2, and the scraper 2 is fixedly arranged at the front end of the conveyor belt 3; the bottom of the scraper 2 is close to the conveyor belt, and the distance between the bottom of the scraper 2 and the conveyor belt 3 is 1-3 mm, preferably 2 mm; the conveyor belt 3 is placed in the solvent tank 4, and the roller press 5 is close to the end of the conveyor belt 3. Among them, the injector 1 is controlled to inject continuously by the injection pump; the conveyor belt 3 is continuously driven by a stepping motor; and the roller press 5 is preferably continuously rolled.

[0044] During the working process, the aramid vermiculite composite sol is continuously injected into the scraper 2 through the syringe 1, and the aramid vermiculite composite sol after scraping exchanges solvent with the proton solvent in the solvent tank 4. The formed hydrogel is transported to the roller press 5 through the conveyor belt 3, and is formed and rolled after being dried by the roller press 5. During the continuous injection process, the speed of the injection pump is set to 2-10 mL / min, the speed of the conveyor belt 3 is set to 0.1-2 cm / min, and the speed of the roller press 5 is consistent with the speed of the conveyor belt.

[0045] The implementation process of the present invention is described in detail below in conjunction with specific embodiments. However, it will be appreciated by those skilled in the art that the following embodiments are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. It should also be noted that, for ease of description, only the parts related to the invention are shown in the embodiments. It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail with reference to the embodiments below. It should be noted that the endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in this article.

[0046] In the following examples, among the raw materials used, commercial para-aramid pulp was purchased from DuPont, USA, and the remaining raw materials were common commercial products that can be directly purchased or can be prepared according to conventional techniques in the art.

[0047] 1. Specific embodiment of the method for preparing aramid vermiculite nanopaper of the present invention Example 1 The method for preparing aramid vermiculite nanopaper provided in this embodiment comprises the following steps: (1) Preparation of aramid nanofiber dispersion: 0.8 g potassium tert-butoxide was added to 48.2 ml dimethyl sulfoxide (mass concentration 99.5%), stirred for 0.5 h, and then 1 g commercial para-aramid pulp was added. The mixture was mechanically stirred for 24 h to obtain aramid nanofiber dispersion. (2) Preparation of vermiculite nanosheet dispersion: 2 g of raw vermiculite powder was subjected to high temperature heat treatment at 300 °C for 3 h to obtain expanded vermiculite powder. The expanded vermiculite powder and 10 g of sodium chloride were added to 250 ml of deionized water, placed in an autoclave, and heated to 100 °C at a pressure of 0.4 MPa for a first ion exchange reaction for 24 h, i.e., Na + Ion replacement of Mg between vermiculite layers + , and obtain a vermiculite suspension; take out the vermiculite suspension, stir it at a constant speed of 500 rpm / min at 50°C for 12 hours, and then wash it twice with deionized water at 50°C to remove excess sodium chloride; then add 10g lithium chloride to 250ml deionized water and stir it at a constant speed of 500 rpm / min, place it in an autoclave, and heat it to a temperature of 100°C at a pressure of 0.4Mpa for 24 hours to carry out Li + Ion replacement of Na in vermiculite interlayers +ions, and then washed with deionized water to remove residual lithium chloride, and then centrifuged at 8000 rpm / min for 20 min after ultrasonication for 30 min. Finally, the top slurry was washed three times with dimethyl sulfoxide by centrifugation and diluted to obtain vermiculite nanosheet dispersion; (3) A method for preparing a dispersion of vermiculite nanosheets coated with a binder: a dispersion of vermiculite nanosheets and an aqueous binder solution are mixed and magnetically stirred at a speed of 3000 rpm for 12 h to obtain a mixture, the mixture is centrifuged at 5000 rpm for 30 min, and then a precipitate is collected; the precipitate is centrifuged and washed twice with dimethyl sulfoxide to remove water, and then diluted with dimethyl sulfoxide to obtain a dispersion of vermiculite nanosheets coated with a binder; wherein the mass ratio of the vermiculite nanosheets in the dispersion of vermiculite nanosheets to the binder in the aqueous binder solution is 1:1; and the binder is polyvinyl alcohol; (4) mixing the dispersion of aramid nanofibers in step (1) and the dispersion of vermiculite nanosheets coated with a binder in step (3) at a mass ratio of 1:1, and mechanically stirring for 20 minutes to obtain an aramid vermiculite composite sol; (5) placing the aramid fiber vermiculite composite sol in step (4) in a stainless steel circular mold with a diameter of 5 cm, and then immersing it in deionized water, taking it out, and repeating the immersion three times, so that the dimethyl sulfoxide and potassium tert-butoxide in the aramid fiber composite sol diffuse into the deionized water, and the deionized water diffuses into the aramid fiber composite sol, and the aramid fiber composite sol gradually gels and transforms into an aramid vermiculite composite gel (yellow); (6) The aramid vermiculite composite gel of step (5) is placed in an oven and dried at 80° C. for 30 min to obtain flexible, high dielectric strength, and high toughness aramid vermiculite nanopaper (yellow); wherein the mass of the aramid nanofibers accounts for 50% of the aramid vermiculite nanopaper, and the mass of the vermiculite nanosheets in the vermiculite nanosheets coated with the binder accounts for 40% of the mass of the aramid vermiculite nanopaper.

[0048] Example 2 The method for preparing aramid vermiculite nanopaper provided in this embodiment comprises the following steps: (1) Preparation of aramid nanofiber dispersion: 0.8 g potassium tert-butoxide was added to 48.2 ml dimethyl sulfoxide (mass concentration 99.5%), stirred for 0.5 h, and then 1 g commercial para-aramid pulp was added. The mixture was mechanically stirred for 24 h to obtain aramid nanofiber dispersion. (2) Preparation of vermiculite nanosheet dispersion: 2 g of raw vermiculite powder was subjected to high temperature heat treatment at 600 °C for 1 h to obtain expanded vermiculite powder. The expanded vermiculite powder and 20 g of sodium chloride were added to 500 ml of deionized water, placed in an autoclave, and heated to 100 °C at a pressure of 0.4 MPa for 24 h to perform the first ion exchange reaction, i.e., Na+ Ion replacement of Mg between vermiculite layers + , and obtain a vermiculite suspension; the vermiculite suspension was stirred at 500 rpm / min at 50°C for 12 h, and then washed twice with deionized water at 50°C to remove excess sodium chloride; then 20 g of lithium chloride was added to 250 ml of deionized water and stirred at 500 rpm / min, placed in an autoclave, and heated to 100°C at a pressure of 0.4 MPa for 24 h, Li + Ion replacement of Na in vermiculite interlayers + ions, and then washed with deionized water to remove residual lithium chloride, and then centrifuged at 8000 rpm / min for 20 min after ultrasonication for 30 min. Finally, the top slurry was washed three times with dimethyl sulfoxide by centrifugation and diluted to obtain vermiculite nanosheet dispersion; (3) A method for preparing a dispersion of vermiculite nanosheets coated with a binder: a dispersion of vermiculite nanosheets and an aqueous binder solution are mixed and magnetically stirred at 3000 rpm for 12 h to obtain a mixture, the mixture is centrifuged at 5000 rpm for 30 min, and then a precipitate is collected; the precipitate is centrifuged and washed twice with dimethyl sulfoxide to remove water, and then diluted with dimethyl sulfoxide to obtain a dispersion of vermiculite nanosheets coated with a binder; wherein the mass ratio of the vermiculite nanosheets in the dispersion of vermiculite nanosheets to the binder in the aqueous binder solution is 1:20; and the binder is polyacrylic acid; (4) mixing the dispersion of aramid nanofibers in step (1) and the dispersion of vermiculite nanosheets coated with a binder in step (3) at a mass ratio of 1:1, and mechanically stirring for 20 minutes to obtain an aramid vermiculite composite sol; (5) The aramid vermiculite composite sol of step (4) is transferred to a 100 ml syringe 1, and the syringe 1 is fixed on a syringe pump, and continuously injected into the material storage tank of the scraper 2 through the syringe pump. With the transmission of the conveyor belt 3, the aramid fiber composite sol is evenly spread on the conveyor belt 3 through scraping, and then flows through a mold (solvent tank 4) filled with deionized water to gel, and obtain a gel tape. The syringe pump speed is set to 5 mL / min, and the conveyor belt speed is set to 2 cm / min; (6) The aramid vermiculite composite gel of step (5) is passed through a roller press 5, dried at 200°C in air for 10 min, and rolled up to obtain tear-resistant, high dielectric strength, and multi-scale aramid paper; wherein the mass of the aramid nanofiber accounts for 50% of the aramid vermiculite nanopaper, and the mass of the vermiculite nanosheets in the vermiculite nanosheets coated with a binder accounts for 40% of the mass of the aramid vermiculite nanopaper; wherein the speed of the roller press 5 is set to 2 cm / min. Specifically, the physical appearance of the aramid vermiculite nanopaper of this embodiment is as follows: Fig.10 shown.

[0049] In the present application, when the binder in the vermiculite nanosheets coated with a binder is one or a mixture of two or more of polyurethane, epoxy resin, polyvinyl pyrrolidone, carboxymethyl cellulose, aluminum phosphate or aluminum phosphate, the technical effect achieved is the same as the technical effect achieved in the above embodiment.

[0050] In the present application, when heated to 180° C. at a pressure of 2.5 MPa in an autoclave and maintained for 48 h, the technical effect obtained is the same as that obtained in the above embodiment.

[0051] In the present application, when the mass ratio of expanded vermiculite powder, alkali metal salt and deionized water is 1:40:1000, the technical effect obtained is the same as that obtained in the above embodiment.

[0052] In the present application, the alkali metal salt is one or a mixture of two or more of lanthanum salt, potassium salt, calcium salt or tin salt, and the technical effect achieved is the same as that achieved in the above embodiment.

[0053] 2. Experimental Examples Experimental Example 1 The aramid nanofibers in the aramid nanofiber dispersion and the vermiculite nanosheets in the vermiculite nanosheet dispersion prepared in the above Examples 1-2 were subjected to microscopic morphology detection. Specifically, 50 aramid nanofibers and vermiculite nanosheets were selected to test their diameters. The atomic force microscope images and diameter distribution of the obtained aramid nanofibers were as follows: Figure 1 and Figure 2 As shown in Figure 2, the atomic force microscope image and diameter distribution of vermiculite nanosheets are shown in Figure 2. Figure 3 and Figure 4 As shown, it can be concluded that the diameter of the aramid nanofibers in Examples 1 and 2 is mainly distributed between 6-20 nm, and the length is 2-10 μm; the diameter of the vermiculite nanosheets in Examples 1 and 2 is mainly distributed between 2-6 nm, and the length is 1-10 μm.

[0054] Experimental Example 2 The aramid vermiculite nanopaper prepared in Example 1 was subjected to morphological detection. Specifically, scanning electron microscopy was used for characterization at an accelerating voltage of 10 kV. The detection results are as follows: Figure 5 As shown, the vermiculite nanosheets coated with the binder are embedded in the aramid nanofibers along the plane of the film to form a three-dimensional grid structure, which is similar to the three-dimensional interconnected hierarchical structure of nacre.

[0055] The cross section of the aramid vermiculite nanopaper prepared in Example 1 was subjected to morphological detection. Specifically, scanning electron microscopy was used for characterization at an accelerating voltage of 10 kV. The detection results are as follows: Figure 6As shown, it can be seen that the aramid nanofibers and the vermiculite nanosheets coated with the binder are stacked in a layer-by-layer alternating manner, showing a close connection with each other.

[0056] The surface morphology of the aramid vermiculite nanopaper prepared in Example 1 was detected. Specifically, the surface morphology was detected using a scanning electron microscope with an acceleration voltage of 10 kV. The detection results are as follows: Figure 7 As shown, it can be seen that the surface of aramid vermiculite nanopaper is flat, smooth, dense and compact.

[0057] Experimental Example 3 The aramid vermiculite nanopaper prepared in Example 1 was electrically broken down and then subjected to microscopic morphology detection. Specifically, scanning electron microscopy was used for characterization. The results are as follows: Figure 8 As shown in the figure, the breakdown hole of aramid vermiculite nanopaper is semi-penetrating, about 110 μm in size, with rough edges and multiple cracks. This shows that the three-dimensional interconnected layered structure of aramid vermiculite nanopaper can evenly disperse the electric field inside the nanopaper, thereby weakening the impact of high-energy electrons generated by local electric field overload.

[0058] Experimental Example 4 The aramid vermiculite nanopaper prepared in Example 1 was burned and then subjected to microscopic morphology detection. Specifically, scanning electron microscopy was used for characterization. The results are as follows: Fig. 9 As shown in Figure 2, it can be seen that the aramid vermiculite nanopaper retains its layered structure without any damage at high temperature, which is attributed to its excellent thermal stability.

[0059] Experimental Example 5 The thickness of the aramid vermiculite nanopaper prepared in Examples 1 and 2 was tested. Specifically, a spiral micrometer was used to test. It was found that the thickness of the aramid vermiculite nanopaper prepared in Example 1 was 1 mm, and the thickness of the aramid vermiculite nanopaper prepared in Example 2 was 1.2 mm.

[0060] Experimental Example 6 The dielectric strength of the aramid vermiculite nanopaper prepared in the above Examples 1 and 2 was tested. Specifically, the dielectric strength of the aramid vermiculite nanopaper prepared in Example 1 was 193 kV / mm, and the dielectric strength of the aramid vermiculite nanopaper prepared in Example 2 was 198 kV / mm.

[0061] Experimental Example 7 The mechanical properties of the aramid vermiculite nanopaper prepared in Examples 1 and 2 were tested. Specifically, according to the GB / T16491-2022 standard test method, the aramid vermiculite nanopaper prepared in Example 1 had a tensile strength of 186 MPa and a toughness of 55.2 MJ m -3 The tensile strength of the aramid vermiculite nanopaper prepared in Example 2 is 192 MPa; the toughness is 53.6 MJ m -3 .

[0062] This shows that the aramid vermiculite nanopaper provided by the present application has high electrical insulation performance, thermal insulation performance and mechanical properties. That is, it is non-flammable and thermally stable, so that the aramid vermiculite nanopaper of the present application has high toughness, excellent breakdown resistance and flame retardancy, and expands the application range of aramid-based nanopaper in advanced electrical insulation materials.

[0063] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A kind of aramid vermiculite nanopaper, characterized in that: The aramid vermiculite nanopaper comprises aramid nanofibers and vermiculite nanosheets coated with a binder, wherein the aramid nanofibers form a three-dimensional mesh structure, and the vermiculite nanosheets coated with a binder are embedded in the three-dimensional mesh structure to form a three-dimensional interconnected layered structure.

2. The aramid vermiculite nanopaper according to claim 1, characterized in that: The binder in the vermiculite nanosheets coated with a binder is one or a mixture of two or more of polyvinyl alcohol, polyacrylic acid, polyurethane, epoxy resin, polyvinyl pyrrolidone, carboxymethyl cellulose, aluminum phosphate or aluminum phosphate.

3. The method for preparing aramid vermiculite nanopaper according to claim 1, characterized in that: The aramid nanofiber is a para-aramid nanofiber, the diameter of the aramid nanofiber is 6-20 nm, and the length is 2-10 μm; the mass of the aramid nanofiber accounts for 30-70% of the aramid vermiculite nanopaper; the vermiculite nanosheets coated with a binder have a diameter of 2-6 nm and a length of 1-10 μm; the mass of the vermiculite nanosheets coated with a binder accounts for 20-60% of the mass of the aramid vermiculite nanopaper.

4. The method for preparing the aramid vermiculite nanopaper according to any one of claims 1 to 3, characterized in that: The following steps are involved: A dispersion of aramid nanofibers and a dispersion of vermiculite nanosheets coated with a binder are mixed to obtain an aramid vermiculite composite sol; the aramid vermiculite composite sol is subjected to solvent exchange with a protic solvent to obtain an aramid vermiculite composite gel, which is then dried to obtain an aramid vermiculite nanopaper.

5. The method for preparing aramid vermiculite nanopaper according to claim 4, characterized in that: The preparation method of the dispersion of vermiculite nanosheets coated with a binder comprises: mixing the dispersion of vermiculite nanosheets and a binder aqueous solution by magnetic stirring and then precipitating to obtain a precipitate; washing the precipitate with dimethyl sulfoxide and then diluting it with dimethyl sulfoxide to obtain the dispersion of vermiculite nanosheets coated with a binder.

6. The method for preparing aramid vermiculite nanopaper according to claim 5, characterized in that: Said The mass ratio of the vermiculite nanosheets in the vermiculite nanosheet dispersion to the binder in the binder aqueous solution is 1:(1-20).

7. The method for preparing aramid vermiculite nanopaper according to claim 5, characterized in that: The preparation method of the vermiculite nanosheet dispersion comprises: subjecting raw vermiculite powder to high-temperature heat treatment to obtain expanded vermiculite powder; mixing the expanded vermiculite powder with an alkali metal salt and deionized water and placing the mixture in a stainless steel kettle for a first ion exchange reaction to obtain a vermiculite suspension; stirring and washing the vermiculite suspension and then mixing the mixture with an alkali metal salt and deionized water for a second ion exchange reaction to obtain a vermiculite nanosheet suspension, and washing the mixture to obtain a vermiculite nanosheet dispersion.

8. The method for preparing aramid vermiculite nanopaper according to claim 7, characterized in that: The pressure of the first ion exchange reaction and the second ion exchange reaction are both 0.4-2.5 MPa, the temperature is both 100-180° C., and the time is both 6-48 h; the temperature of the high-temperature heat treatment is 300-600° C., and the time is 1-3 h.

9. The method for preparing aramid vermiculite nanopaper according to claim 7, characterized in that: The mass ratio of the expanded vermiculite powder, the alkali metal salt and the deionized water is 1:(5-40):(10-1000).

10. The method for preparing aramid vermiculite nanopaper according to claim 7, characterized in that: The alkali metal salt is one or a mixture of two or more of lithium salt, sodium salt, lanthanum salt, potassium salt, calcium salt or tin salt.

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