Preparation method of aramid nanofiber-based composite film with high thermal conductivity and high breakdown resistance

Abstract

The application relates to a preparation method of a high-thermal-conductivity and breakdown-resistant aramid nanofiber-based composite film, which comprises the following steps: dispersing mixed transverse micron-sized boron nitride nanosheets mBNNS and transverse nanometer-sized boron nitride nanosheets nBNNS in an organic solvent to obtain a BNNS dispersion liquid; dispersing silver nanowires AgNWs in an organic solvent to obtain an AgNWs dispersion liquid; mixing aramid nanofiber sol, the BNNS dispersion liquid and the AgNWs dispersion liquid, and then heating and stirring to obtain an ANF / BNNS / AgNWs dispersion liquid; performing film coating through scraping, solvent replacement, vacuum drying, re-protonation and finally drying treatment to obtain the high-thermal-conductivity and breakdown-resistant aramid nanofiber-based composite film. Through the mixed use of the micro-nano-sized thermal-conductivity fillers BNNS, the BNNS can be closely packed and effectively contacted in the composite film, an efficient thermal-conductivity channel is constructed, the pores and defects in the composite film are reduced, and the breakdown resistance of the composite film is improved.

Description

Technical Field

[0001] This invention belongs to the field of aramid nanofiber composite material technology, and specifically relates to a method for preparing a high thermal conductivity and breakdown resistant aramid nanofiber-based composite film. Background Technology

[0002] With the rapid development of electronic devices towards miniaturization, integration, flexibility, and high power, traditional materials face greater challenges. Especially in high-frequency operating environments, the heat generated by electrical equipment accumulates rapidly. There is an urgent need to design and prepare insulating materials with high thermal conductivity so that the heat accumulated in the coils of the equipment can be quickly and timely transferred to heat dissipation equipment or insulating oil, thereby ensuring the normal operation of electrical equipment and extending its service life.

[0003] Aramid nanofibers (ANFs) are a novel nanomaterial that has attracted widespread attention in recent years. They have unique nanoscale structures, large aspect ratios and specific surface areas. Compared with smooth and inert aramid fibers, aramid nanofibers have more surface active groups, higher interfacial compatibility with the matrix and stronger bonding strength. Therefore, they are widely used as reinforcing materials for composite materials. In addition, due to the good thermal stability, excellent mechanical properties and insulation properties of macroscopic aramid fibers, they are often used to prepare films and composite materials, which are widely used in adsorption filtration, battery separators, electronic and electrical fields.

[0004] Aramid, as a liquid crystal polymer, has a thermal conductivity of only 0.04 W·m. -1 ·K -1 The difficulty in achieving rapid heat transfer limits the further application of ANF in fields such as electronics and electrical engineering. Hexagonal boron nitride (h-BN, hereinafter referred to as BN) has a high thermal conductivity (300 W·m). -1 ·K -1 Boron nitride (BNNS) exhibits good insulation and thermal stability, and is inexpensive, making it suitable for large-scale applications. The thermal conductivity of BNNS prepared by exfoliating boron nitride can reach 1000 W·m. -1 ·K -1 The above is comparable to carbon materials such as diamond and carbon nanotubes.

[0005] Combining aramid nanofibers and boron nitride nanosheets holds promise for developing film materials that combine toughness, electrical insulation, heat resistance, and good thermal conductivity. However, this still relies on the rational design and effective control of the composite material structure. The most common method is to modify the surface of the thermally conductive filler. For example, CN118909309A discloses a surface-modified hexagonal boron nitride and polyimide composite thermally conductive film and its preparation method. Hexagonal boron nitride is surface-treated sequentially with a small molecule coupling agent and a polymer modifier, introducing hydrophilic groups onto the surface of the hexagonal boron nitride, improving its compatibility with polyimide, and enhancing the thermal conductivity of the composite film. In addition, there are methods that use external fields such as magnetic fields, electric fields, and force fields to orient the thermally conductive filler. For example, CN119331381A discloses a method for preparing a vertically oriented boron nitride / epoxy resin thermally conductive composite material under a magnetic field. This method prepares boron nitride nanosheets with iron oxide attached to the surface and orients the boron nitride along the magnetic field direction, improving the thermal conductivity of the composite material in the orientation direction.

[0006] The methods described above all use single-size boron nitride (BNNS) as thermally conductive fillers, which makes it difficult to form a complete and uniform coverage within the surface of the thermally conductive material, reducing the number of thermally conductive pathways. Furthermore, all of these methods require surface modification of boron nitride, which not only involves a long and complex preparation process but also results in poor modification effects due to the high chemical stability and surface inertness of boron nitride, leading to poor thermal conductivity of the composite material. If a large amount of easily surface-modifiable materials such as graphene and carbon nanotubes are used to prepare thermally conductive composite materials with a polymer matrix, it will severely damage the insulation properties of the composite material, failing to meet the insulation performance requirements of materials used in high-frequency motors, high-voltage transformers, and other fields. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing a high thermal conductivity and breakdown resistant aramid nanofiber-based composite film, so as to overcome the technical problems in the prior art, such as the complex preparation process of boron nitride / polymer thermally conductive composite materials, poor thermal conductivity, and the difficulty in achieving both thermal conductivity and insulation properties.

[0008] This invention provides a method for preparing a highly thermally conductive and breakdown-resistant aramid nanofiber-based composite film, comprising the following steps:

[0009] (1) The transverse micron-sized boron nitride nanosheets mBNNS and transverse nano-sized boron nitride nanosheets nBNNS were mixed and dispersed in an organic solvent to obtain a BNNS dispersion.

[0010] (2) Silver nanowires (AgNWs) were dispersed in an organic solvent to obtain an AgNWs dispersion;

[0011] (3) ANF / BNNS / AgNWs dispersion is obtained by mixing aramid nanofiber sol, BNNS dispersion and AgNWs dispersion and heating and stirring.

[0012] (4) The ANF / BNNS / AgNWs dispersion was coated into a film by scraping, solvent replacement, vacuum drying, and re-protonation. Finally, it was dried to obtain a high thermal conductivity and puncture-resistant aramid nanofiber-based composite film.

[0013] Preferably, in step (1), the mBNNS has a lateral dimension of 1~10µm and a thickness of 1~500nm; the nBNNS has a lateral dimension of 10~1000nm and a thickness of 1~500nm.

[0014] Preferably, the mass ratio of mBNNS to nBNNS in step (1) is 0.1~100:100~0.1.

[0015] Preferably, the preparation method of mBNNS and nBNNS includes the following steps: lateral micron-sized boron nitride mBN and lateral nano-sized boron nitride nBN are dispersed in isopropanol at a boron nitride:isopropanol mass ratio of 1~10:100, ultrasonically treated at 100~500W power for 4~24h, centrifuged at 100rpm~1000rpm for 10~30min to remove the precipitate, centrifuged at 1000rpm~5000rpm for 10~30min to remove the supernatant, and then dried to obtain the final product.

[0016] Preferably, the mass fraction of the BNNS dispersion in step (1) is 0.1% to 10%.

[0017] Preferably, the AgNWs in step (2) have a diameter of 10~100nm and a length of 0.1~100µm.

[0018] Preferably, the mass fraction of the AgNWs dispersion in step (2) is 0.1% to 10%.

[0019] Preferably, the preparation method of the aramid nanofiber sol in step (3) includes the following steps: mixing a strong alkali, an organic solvent, a proton donor and para-aramid, and stirring to react to obtain the aramid nanofiber sol.

[0020] Furthermore, the organic solvent used in the BNNS dispersion, AgNWs dispersion, and aramid nanofiber sol is dimethyl sulfoxide (DMSO).

[0021] Further, the strong base is at least one selected from potassium hydroxide, sodium hydroxide, potassium methoxide, sodium methoxide, potassium ethoxide, sodium ethoxide, potassium tert-butoxide, and sodium tert-butoxide; the mass ratio of the strong base to the para-aramid is 0.5~1.5:1.

[0022] Furthermore, the proton donor is at least one of water, methanol, ethanol, ethylene glycol, isopropanol, and tert-butanol; the volume ratio of the proton donor to DMSO is 1:5 to 100.

[0023] Further, the para-aramid is at least one of poly(p-phenylene terephthalamide) polymer, para-aramid filament, para-aramid staple fiber, and para-aramid product; the mass fraction of para-aramid in the aramid nanofiber sol is 2wt%~15wt%.

[0024] Furthermore, the stirring reaction temperature is room temperature to 80°C, the stirring rate is 50 to 300 rpm, and the stirring reaction time is 4 to 48 hours.

[0025] Preferably, the mass ratio of ANF, BNNS and AgNWs in the ANF / BNNS / AgNWs dispersion in step (3) is 100:0.1~100:0.1~5.

[0026] Preferably, the heating and stirring temperature in step (3) is room temperature to 80°C.

[0027] Preferably, the thickness of the film formed by scraping in step (4) is 0.3~2mm.

[0028] Preferably, the solvent used for solvent replacement in step (4) is at least one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, acetone, ethyl acetate, acetonitrile, dichloromethane, and chloroform; and the solvent used for reprotonation is at least one of hydrochloric acid, sulfuric acid, formic acid, acetic acid, water, methanol, ethanol, ethylene glycol, and isopropanol.

[0029] Preferably, the vacuum drying temperature in step (4) is room temperature to 100°C, the vacuum degree is -0.1MPa, and the drying time is 10min to 5h.

[0030] Preferably, the drying temperature in step (4) is from room temperature to 100°C, and the drying time is from 10 min to 5 h.

[0031] Beneficial effects

[0032] (1) By using two different sizes of thermally conductive fillers BNNS in micro and nano dimensions, the present invention can achieve close packing and effective contact of BNNS in composite films, construct efficient thermal conductive paths, reduce phonon scattering at the filler interface, reduce interface thermal resistance, and at the same time reduce pores and defects in composite films, thereby improving their breakdown resistance.

[0033] (2) The present invention adds a small amount of AgNWs with high aspect ratio and high thermal conductivity to the composite film, which can act as a "bridge" and "high-speed path" for heat transfer between BNNS, increasing the number of thermal conductive paths and promoting the rapid transfer of heat between BNNS, thereby further improving its thermal conductivity without damaging the insulation performance of the composite film.

[0034] (3) The present invention uses highly surface-active aramid nanofibers as the matrix material. Without the need to modify the surface of the thermally conductive filler, the two can have good compatibility. Moreover, thanks to the excellent comprehensive properties of aramid, the prepared composite film has high strength, good toughness and excellent heat resistance, and can be used for heat dissipation applications of various electronic devices. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the thermal conductivity path of the aramid nanofiber-based composite film of the present invention.

[0036] Figure 2 SEM images of mBNNS used in the embodiments and comparative examples (A) and (B) of nBNNS used in the embodiments and comparative examples.

[0037] Figure 3 SEM images of AgNWs used in the examples and comparative examples.

[0038] Figure 4 This is a SEM image of the surface of the aramid nanofiber-based composite film prepared in Example 1.

[0039] Figure 5 This is a SEM image of the surface of the aramid nanofiber-based composite film prepared in Example 3.

[0040] Figure 6 SEM image of the surface of the aramid nanofiber-based composite film prepared in Comparative Example 1.

[0041] Figure 7 SEM image of the surface of the aramid nanofiber-based composite film prepared in Comparative Example 2.

[0042] Figure 8 This is a SEM image of the surface of the aramid nanofiber-based composite film prepared in Comparative Example 3. Detailed Implementation

[0043] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0044] Test methods

[0045] 1. Surface morphology

[0046] The microstructure of boron nitride nanosheets and films was characterized using a SEM (Regulus 8230, HITACHI, Japan). Diluted boron nitride was dropped onto conductive copper foil and observed after the solvent dried. For the films, they were adhered to conductive adhesive, sputtered with gold for 60 seconds, and then observed using an accelerating voltage of 5 kV.

[0047] 2. Mechanical properties

[0048] The mechanical properties of the composite film were tested using an electronic universal testing machine (INSTRON 5966, USA). The samples were cut into strips with a width of 5 mm and a tensile rate of 5 mm / min. Each set of strips was tested 5 times and the average value was taken.

[0049] 3. Thermal conductivity test

[0050] The composite film was cut into circular pieces with a diameter of 25.4 mm. After carbon spraying, the thermal diffusivity α of the composite film was tested using an in-plane template of a laser flare thermal conductivity meter (LFA467, Netzsch, Germany). The specific heat capacity C of the film was tested using a differential scanning calorimeter (Q20, TA, USA). p The density ρ of the thin film was tested using the water displacement method. The thermal conductivity λ of the thin film was calculated using the following formula:

[0051] λ=α×C p ×ρ

[0052] 4. Breakdown strength test

[0053] The breakdown strength of the thin film was tested in silicone oil using a withstand voltage tester (CS9916BX, Nanjing Changsheng, China) at a voltage ramp rate of 500V / s until the film broke down. Fifteen sets of data were collected for each sample.

[0054] Example 1

[0055] (1) Prepare mBNNS with a transverse dimension of 1.8µm and a thickness of 50nm and nBNNS with a transverse dimension of 200nm and a thickness of 10nm. Disperse 1.05g mBNNS and 0.45g nBNNS in 20mL DMSO to obtain BNNS / DMSO dispersion.

[0056] (2) Disperse 0.25g of AgNWs with a diameter of 50nm and a length of 10µm in 100mL of DMSO to prepare an AgNWs / DMSO dispersion with a concentration of 2.5mg / mL. Take 3mL of the above dispersion and combine it with the BNNS / DMSO dispersion in (1) to obtain an AgNWs / BNNS / DMSO dispersion.

[0057] (3) Mix 2.95g potassium methoxide, 100mL DMSO, 5mL tert-butanol and 5g para-aramid short fibers, and stir at 300rpm for 24h at 60℃ to obtain an aramid nanofiber sol with a concentration of 5wt%. Take 30mL of the above aramid nanofiber sol and heat it to 60℃ with the AgNWs / BNNS / DMSO dispersion in (2) to obtain an ANF / BNNS / AgNWs / DMSO dispersion. The mass ratio of ANF, BNNS and AgNWs in the dispersion is 100:100:0.5.

[0058] (4) The ANF / BNNS / AgNWs / DMSO dispersion was coated onto a clean, flat glass plate with a thickness of 0.8 mm. Then it was immersed in acetone for solvent replacement for 1 h, then vacuum dried at 80 °C for 2 h, then immersed in water for proton reduction for 30 min, and finally dried at 60 °C for 1 h to obtain an aramid nanofiber-based composite film.

[0059] The prepared aramid nanofiber-based composite film has a tensile strength of 134.4 MPa, an elastic modulus of 9.7 GPa, an elongation at break of 17.2%, and an in-plane thermal conductivity of 15.3 W·m. -1 ·K -1 The breakdown strength is 147.0 kV / mm.

[0060] Example 2

[0061] (1) Prepare mBNNS with a transverse dimension of 1.8µm and a thickness of 50nm and nBNNS with a transverse dimension of 200nm and a thickness of 10nm. Disperse 1.05g mBNNS and 0.45g nBNNS in 20mL DMSO to obtain BNNS / DMSO dispersion.

[0062] (2) Disperse 0.25g of AgNWs with a diameter of 50nm and a length of 10µm in 100mL of DMSO to prepare an AgNWs / DMSO dispersion with a concentration of 2.5mg / mL. Take 6mL of the above dispersion and combine it with the BNNS / DMSO dispersion in (1) to obtain an AgNWs / BNNS / DMSO dispersion.

[0063] (3) Mix 2.95g potassium methoxide, 100mL DMSO, 5mL tert-butanol and 5g para-aramid short fibers, and stir at 300rpm for 24h at 60℃ to obtain an aramid nanofiber sol with a concentration of 5wt%. Take 30mL of the above aramid nanofiber sol and heat it to 60℃ with the AgNWs / BNNS / DMSO dispersion in (2) to obtain an ANF / BNNS / AgNWs / DMSO dispersion. The mass ratio of ANF, BNNS and AgNWs in the dispersion is 100:100:1.

[0064] (4) The ANF / BNNS / AgNWs / DMSO dispersion was coated onto a clean, flat glass plate with a thickness of 0.8 mm. Then it was immersed in acetone for solvent replacement for 1 h, then vacuum dried at 80 °C for 2 h, then immersed in water for proton reduction for 30 min, and finally dried at 60 °C for 1 h to obtain an aramid nanofiber-based composite film.

[0065] The prepared aramid nanofiber-based composite film has a tensile strength of 125.3 MPa, an elastic modulus of 9.1 GPa, an elongation at break of 13.5%, and an in-plane thermal conductivity of 17.9 W·m. -1 ·K -1 The breakdown strength is 131.4 kV / mm.

[0066] Example 3

[0067] (1) Prepare mBNNS with a transverse dimension of 1.8µm and a thickness of 50nm and nBNNS with a transverse dimension of 200nm and a thickness of 10nm. Disperse 1.05g mBNNS and 0.45g nBNNS in 20mL DMSO to obtain BNNS / DMSO dispersion.

[0068] (2) Disperse 0.25g of AgNWs with a diameter of 50nm and a length of 10µm in 100mL of DMSO to prepare an AgNWs / DMSO dispersion with a concentration of 2.5mg / mL. Take 18mL of the above dispersion and combine it with the BNNS / DMSO dispersion in (1) to obtain an AgNWs / BNNS / DMSO dispersion.

[0069] (3) Mix 2.95g potassium methoxide, 100mL DMSO, 5mL tert-butanol and 5g para-aramid short fibers, and stir at 300rpm for 24h at 60℃ to obtain an aramid nanofiber sol with a concentration of 5wt%. Take 30mL of the above aramid nanofiber sol and heat it to 60℃ with the AgNWs / BNNS / DMSO dispersion in (2) to obtain an ANF / BNNS / AgNWs / DMSO dispersion. The mass ratio of ANF, BNNS and AgNWs in the dispersion is 100:100:3.

[0070] (4) The ANF / BNNS / AgNWs / DMSO dispersion was coated onto a clean, flat glass plate with a thickness of 0.8 mm. Then it was immersed in acetone for solvent replacement for 1 h, then vacuum dried at 80 °C for 2 h, then immersed in water for proton reduction for 30 min, and finally dried at 60 °C for 1 h to obtain an aramid nanofiber-based composite film.

[0071] The prepared aramid nanofiber-based composite film has a tensile strength of 80.0 MPa, an elastic modulus of 6.8 GPa, an elongation at break of 11.8%, and an in-plane thermal conductivity of 17.8 W·m. -1 ·K -1 The breakdown strength is 42.7 kV / mm.

[0072] Comparative Example 1

[0073] (1) 1.3g of mBNNS with a transverse dimension of 1.8µm and a thickness of 50nm was dispersed in 40mL of DMSO to obtain a BNNS / DMSO dispersion;

[0074] (2) Mix 2.95g potassium methoxide, 100mL DMSO, 5mL tert-butanol with 5g para-aramid short fibers and stir at 300rpm for 24h at 60℃ to obtain an aramid nanofiber sol with a concentration of 5wt%. Take 60mL of the above aramid nanofiber sol and heat it to 60℃ with the BNNS / DMSO dispersion in (1) to obtain an ANF / BNNS / DMSO dispersion. The mass ratio of ANF to BNNS in the dispersion is 100:43.

[0075] (3) The ANF / BNNS / DMSO dispersion was coated onto a clean, flat glass plate with a thickness of 0.8 mm. Then it was immersed in acetone for solvent replacement for 1 h, then vacuum dried at 80 °C for 2 h, then immersed in water for proton reduction for 30 min, and finally dried at 60 °C for 1 h to obtain an aramid nanofiber-based composite film.

[0076] The prepared aramid nanofiber-based composite film has a tensile strength of 135.6 MPa, an elastic modulus of 7.1 GPa, an elongation at break of 24.3%, and an in-plane thermal conductivity of 6.6 W·m. -1 ·K -1 The breakdown strength is 384.5 kV / mm.

[0077] Comparative Example 2

[0078] (1) Prepare mBNNS with a transverse dimension of 1.8µm and a thickness of 50nm and nBNNS with a transverse dimension of 200nm and a thickness of 10nm. Disperse 0.9g mBNNS and 0.4g nBNNS in 40mL DMSO to obtain BNNS / DMSO dispersion.

[0079] (2) Mix 2.95g potassium methoxide, 100mL DMSO, 5mL tert-butanol with 5g para-aramid short fibers and stir at 300rpm for 24h at 60℃ to obtain an aramid nanofiber sol with a concentration of 5wt%. Take 60mL of the above aramid nanofiber sol and heat it to 60℃ with the BNNS / DMSO dispersion in (1) to obtain an ANF / BNNS / DMSO dispersion. The mass ratio of ANF to BNNS in the dispersion is 100:43.

[0080] (3) The ANF / BNNS / DMSO dispersion was coated onto a clean, flat glass plate with a thickness of 0.8 mm. Then it was immersed in acetone for solvent replacement for 1 h, then vacuum dried at 80 °C for 2 h, then immersed in water for proton reduction for 30 min, and finally dried at 60 °C for 1 h to obtain an aramid nanofiber-based composite film.

[0081] The prepared aramid nanofiber-based composite film has a tensile strength of 157.1 MPa, an elastic modulus of 8.2 GPa, an elongation at break of 26.9%, and an in-plane thermal conductivity of 10.2 W·m. -1 ·K -1 The breakdown strength is 396.2 kV / mm.

[0082] Comparative Example 3

[0083] (1) Disperse 0.25g of AgNWs with a diameter of 50nm and a length of 10µm in 100mL of DMSO to prepare an AgNWs / DMSO dispersion with a concentration of 2.5mg / mL;

[0084] (2) Mix 2.95g potassium methoxide, 100mL DMSO, 5mL tert-butanol and 5g para-aramid short fibers, and stir at 300rpm for 24h at 60℃ to obtain an aramid nanofiber sol with a concentration of 5wt%. Take 30mL of the above aramid nanofiber sol, 20mL DMSO and 6mL of AgNWs / DMSO dispersion in (1), heat to 60℃ and stir to combine, to obtain ANF / AgNWs / DMSO dispersion. The mass ratio of ANF to AgNWs in the dispersion is 100:1.

[0085] (3) The ANF / AgNWs / DMSO dispersion was coated onto a clean, flat glass plate with a thickness of 0.8 mm. Then it was immersed in acetone for solvent replacement for 1 h, then vacuum dried at 80 °C for 2 h, then immersed in water for proton reduction for 30 min, and finally dried at 60 °C for 1 h to obtain an aramid nanofiber-based composite film.

[0086] The prepared aramid nanofiber-based composite film has a tensile strength of 220.3 MPa, an elastic modulus of 7.2 GPa, an elongation at break of 48.2%, and an in-plane thermal conductivity of 0.145 W·m. -1 ·K -1 The breakdown strength is 285.7 kV / mm.

[0087] Figure 1 The diagram shows a typical internal structure and thermal conductivity pathway of the aramid nanofiber-based composite film of the present invention. In the diagram, mBNNS forms a relatively loose arrangement in the matrix, nBNNS fills its gaps, and AgNWs are uniformly distributed in the matrix and connect multiple BNNS, which promotes the formation of continuous thermal conductivity pathways (red arrows) and is beneficial to the transfer of heat in the composite film.

[0088] Figure 2 The invention demonstrates that the BNNS used in this invention is an approximately circular sheet material with a high aspect ratio (length (lateral dimension) to diameter (thickness), which facilitates its in-plane parallel orientation arrangement in the polymer matrix, thereby improving the in-plane thermal conductivity of the composite film.

[0089] Figure 3 The invention demonstrates that the AgNWs used in this invention have a relatively uniform diameter and length, and a high aspect ratio, which allows AgNWs to connect a large number of BNNSs with a small amount of addition, thereby accelerating the heat conduction between BNNSs and improving the thermal conductivity of the composite film.

[0090] Figure 4 and Figure 5The results show that as the content of AgNWs in the composite film increases, the amount of AgNWs on the surface of the composite film gradually increases, which increases the current conduction on the surface and inside of the film. This results in a certain degree of decrease in the insulation performance of the composite film, with the breakdown strength decreasing from 147.0 kV / mm to 42.7 kV / mm. However, overall, its insulation performance is still relatively good, indicating that the addition of a small amount of AgNWs will not seriously damage the insulation performance of the composite film.

[0091] Figure 6 This indicates that when only a single-size mBNNS is used as the thermally conductive filler, there are many voids in the composite film that cannot be covered by the thermally conductive filler (the area within the yellow circle), thus failing to form a complete thermally conductive path. However, when mBNNS and nBNNS are used in a certain proportion, such as Figure 7 As shown, the thermally conductive filler is completely and uniformly distributed in the composite film, promoting the formation of thermal conductivity pathways and increasing the thermal conductivity of the composite film from 6.6 W·m. -1 ·K -1 Increased to 10.2 W·m -1 ·K -1 Meanwhile, the reduced voids and potential internal defects in the composite film also improve the mechanical and insulation properties of the film, with its tensile strength increasing from 135.6 MPa to 157.1 MPa and its breakdown strength increasing from 384.5 kV / mm to 396.2 kV / mm.

[0092] like Figure 8 As shown, when only AgNWs are used to composite with aramid nanofibers, the surface of the composite film is relatively dense, with no BNNS and obvious AgNWs. At this time, the thermal conductivity of the composite film is only 0.145 W·m. -1 ·K -1 This indicates that using AgNWs alone cannot significantly improve the thermal conductivity of composite materials. Only when BNNS and AgNWs are used in combination can AgNWs act as a "bridge" for heat transfer between BNNS and effectively improve the thermal conductivity of composite materials.

Claims

1. A method for preparing a highly thermally conductive and puncture-resistant aramid nanofiber-based composite film, characterized in that, Includes the following steps: (1) The transverse micron-sized boron nitride nanosheets mBNNS and transverse nano-sized boron nitride nanosheets nBNNS were mixed and dispersed in an organic solvent to obtain a BNNS dispersion; wherein the mass ratio of mBNNS:nBNNS was 0.1~100:100~0.1; (2) Silver nanowires (AgNWs) were dispersed in an organic solvent to obtain an AgNWs dispersion; (3) ANF / BNNS / AgNWs dispersion is obtained by mixing aramid nanofiber sol, BNNS dispersion and AgNWs dispersion and heating and stirring. (4) The ANF / BNNS / AgNWs dispersion was coated into a film by scraping, solvent replacement, vacuum drying, and re-protonation. Finally, it was dried to obtain a high thermal conductivity and puncture-resistant aramid nanofiber-based composite film.

2. The preparation method according to claim 1, characterized in that, In step (1), the mBNNS has a lateral dimension of 1~10µm and a thickness of 1~500nm; the nBNNS has a lateral dimension of 10~200nm and a thickness of 1~10nm.

3. The preparation method according to claim 1, characterized in that, The AgNWs in step (2) have a diameter of 10~100nm and a length of 0.1~100µm.

4. The preparation method according to claim 1, characterized in that, The preparation method of the aramid nanofiber sol in step (3) includes the following steps: mixing strong alkali, organic solvent, proton donor and para-aramid, and stirring to react to obtain aramid nanofiber sol.

5. The preparation method according to claim 1, characterized in that, In step (3), the mass ratio of ANF, BNNS and AgNWs in the ANF / BNNS / AgNWs dispersion is 100:0.1~100:0.1~5.

6. The preparation method according to claim 1, characterized in that, The thickness of the film formed by scraping in step (4) is 0.3~2mm.

7. The preparation method according to claim 1, characterized in that, The solvent used for solvent replacement in step (4) is at least one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, acetone, ethyl acetate, acetonitrile, dichloromethane, and chloroform; the solvent used for reprotonation is at least one of hydrochloric acid, sulfuric acid, formic acid, acetic acid, water, methanol, ethanol, ethylene glycol, and isopropanol.

8. The preparation method according to claim 1, characterized in that, The vacuum drying temperature in step (4) is from room temperature to 100°C, the vacuum degree is -0.1MPa, and the drying time is from 10min to 5h.

9. The preparation method according to claim 1, characterized in that, The drying temperature in step (4) is from room temperature to 100°C, and the drying time is from 10 min to 5 h.

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