Preparation method of aramid fiber-based ultrathin electrothermal film and obtained electrothermal film

Abstract

The invention provides a preparation method of an aramid fiber-based ultrathin electrothermal film and the obtained electrothermal film. The preparation method comprises the following steps: S1, adding aramid fibers into a mixed solution of potassium hydroxide and dimethyl sulfoxide, adding isopropanol, unbundling to obtain aramid nanofibers, and carrying out reinforced dispersion to obtain an aramid nanofiber suspension; s2, adding pyrrole into the aramid nanofiber suspension, magnetically stirring, adding a ferric trichloride aqueous solution, and performing in-situ polymerization to obtain an aramid nanofiber coated polypyrrole suspension; and S3, adding the aramid nanofiber suspension into the aramid nanofiber coated polypyrrole suspension, forming a film, soaking the film in a polyvinylidene fluoride organic solvent solution, and polymerizing to obtain the electrothermal film. The contact resistance is low, the number of conductive paths is large, and the conductivity is good, durable and stable; the heating uniformity is good, the thermal response speed is high, and the electro-thermal conversion efficiency is high; the material consumption is small, the weight is light, the thickness is small, the cost is low, the flexibility is good, and the method is easy to process and widely applied to large-scale commercialization.

Description

A method for preparing an aramid fiber-based ultrathin electrothermal film and the resulting electrothermal film. Technical Field

[0001] This invention relates to the technical field of electrothermal films, and in particular to a method for preparing an aramid fiber-based ultrathin electrothermal film and the resulting electrothermal film. Background Technology

[0002] Electrothermal film, also known as conductive heating film, is a highly efficient and energy-saving electrothermal conversion material that has shown broad application prospects in multiple fields. In the civilian sector, this type of material is widely used in building heating, household appliances (such as heating blankets and defogging mirrors), and healthcare (such as far-infrared therapy equipment), with its core value lying in its ability to achieve uniform surface heating and rapid thermal response. In the industrial sector, conductive heating film also plays an irreplaceable role in aerospace de-icing systems, oil pipeline insulation, and thermal management of new energy vehicle batteries. These applications place more stringent requirements on the material, including high-temperature stability (>150℃), mechanical strength, and flame retardant safety.

[0003] Traditional conductive heating films primarily utilize heating elements from metal, carbon materials, ceramics, and polymer composite conductive heating elements. Metal heating elements use metal materials (such as copper, silver, nickel-chromium alloys, and stainless steel) as the conductive heating carrier, typically fabricated through printing, etching, or sputtering processes. These elements offer excellent conductivity, high stability, precise control, and mature manufacturing processes. However, they suffer from poor flexibility, are prone to breakage with repeated bending, are thick, cannot be made into thin and lightweight products, exhibit uneven heating, and are relatively expensive. Carbon material heating elements use carbon materials (such as graphite, carbon nanotubes, graphene, and carbon fibers) as the core, forming a conductive heating layer on a substrate through printing or coating with a binder. These elements offer excellent flexibility, good heating uniformity, strong corrosion resistance, and moderate cost. However, they have slightly lower conductivity, poorer resistance stability, and require more sophisticated manufacturing processes. Ceramic heating elements use semiconductor ceramics (such as barium titanate and tin oxide) as the substrate, forming a conductive heating layer through doping. They are usually used in conjunction with an insulating ceramic substrate. These heating elements have strong high-temperature resistance, good insulation, and long lifespan; however, they are brittle, have low heating efficiency, and are expensive. Polymer composite conductive heating elements are made by combining conductive polymer materials (such as polyacetylene and polyaniline) with a substrate, achieving heating through the conductive properties of the polymer chains. These heating elements have advantages such as high flexibility and plasticity, good chemical resistance, and light weight, making them a current research hotspot; however, they also have disadvantages such as poor high-temperature resistance, poor conductivity, and insufficient stability.

[0004] Aramid fiber, also known as aromatic polyamide fiber, is a high-performance synthetic fiber. It is divided into para-aramid (such as Kevlar) and meta-aramid (such as Nomex). With its unique molecular structure (aromatic ring combined with amide bond), it has advantages such as high strength, high modulus, high temperature resistance (>500℃) and inherent flame retardancy. In recent years, it has also been applied by scientists to conductive heating films. For example, Chinese patent CN109788586A disclosed a flexible high-strength aramid nanofiber-based composite electrothermal film and its preparation method on May 21, 2019. The preparation method of this flexible high-strength aramid nanofiber-based composite electrothermal film includes the following steps: adding aramid fibers to a potassium hydroxide and dimethyl sulfoxide solution system and stirring at room temperature to obtain a dispersion; performing a first vacuum-assisted filtration using a nylon filter membrane to obtain colloidal aramid nanofiber sheets; ultrasonically dispersing silver nanowires in deionized water to obtain a silver nanowire dispersion; adding the silver nanowire dispersion to the above colloidal aramid nanofiber sheets and performing a second vacuum-assisted filtration; washing with deionized water; hot-pressing and drying at 60-120℃ for 24 hours; and curing at 60-100℃ for 20-60 minutes to obtain a flexible high-strength aramid nanofiber-based composite electrothermal film. This flexible, high-strength aramid nanofiber-based composite electrothermal film possesses excellent flexibility, a wide heating temperature range, rapid response, and superior heat resistance and mechanical properties, making it suitable for applications in wearable thermotherapy, personal thermal management, defogging and de-icing, transportation heating, military heating equipment, and artificial intelligence. However, the use of silver nanowires in this method results in low electrical conductivity, easy attenuation, relatively poor heating performance, a large film thickness, and high cost, limiting its large-scale commercial application. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing an aramid fiber-based ultrathin electrothermal film and the resulting electrothermal film, aiming to solve the problems of existing electrothermal films, which suffer from low conductivity, easy decay, relatively poor heating performance, large film thickness, and high cost due to the use of silver nanowires, thus limiting their application in large-scale commercialization.

[0006] To solve the above-mentioned technical problems, the technical solution of the present invention is implemented as follows.

[0007] In one aspect, a method for preparing an aramid fiber-based ultrathin electrothermal film according to the present invention includes the following steps: S1. Aramid fiber unbundling and dispersion 1) Take dimethyl sulfoxide, then take potassium hydroxide, grind them, add them to dimethyl sulfoxide, the molar ratio of potassium hydroxide to dimethyl sulfoxide is 1:30-1:50, stir, dissolve, and obtain a mixed solution; 2) Take aramid fibers, add them to the mixed solution obtained in step 1), the mass ratio of aramid fibers to dimethyl sulfoxide is 1:100-1:120, stir, add isopropanol, the mass ratio of isopropanol to dimethyl sulfoxide is 1:3- 1:8, continue stirring, unbundle, wash with deionized water to obtain aramid nanofibers; 3) Add deionized water to the aramid nanofibers obtained in step 2), strengthen dispersion for 30-50 min, and add more deionized water to make the solid content 1-5 mg / mL to obtain an aramid nanofiber suspension; S2 In-situ polymerization to form a conductive layer 4) Take the aramid nanofiber suspension obtained in step 3), take pyrrole, add it to the aramid nanofiber suspension, the mass ratio of pyrrole to aramid nanofibers in the aramid nanofiber suspension is 1:0.1-1:5, and magnetically stir in an ice-water bath. 5) Take an aqueous solution of ferric chloride and add it to the mixed suspension obtained in step 4). The mass ratio of ferric chloride in the aqueous solution to pyrrole in the mixed suspension is 0.6:1-6:1. Continue to stir magnetically in an ice-water bath, polymerize in situ, filter, wash, and disperse in deionized water to make the solid content 0.5-1.5 mg / mL, to obtain an aramid nanofiber@polypyrrole suspension; Preparation of S3 electrothermal film 6) Take another aramid nanofiber suspension obtained in step 3) and add it to the aramid nanofiber@polypyrrole suspension obtained in step 5). The mass ratio of aramid nanofibers in the aramid nanofiber suspension to aramid nanofibers@polypyrrole in the aramid nanofibers@polypyrrole suspension is 0.25:1-4:1. The mixture is magnetically stirred, film-forming, and dried to obtain an aramid nanofibers & (aramid nanofibers@polypyrrole) composite film; 7) The aramid nanofibers & (aramid nanofibers@polypyrrole) composite film obtained in step 6) is immersed in a polyvinylidene fluoride organic solvent solution and polymerized at 80-100℃ for 5-10h to obtain a (aramid nanofibers & (aramid nanofibers@polypyrrole))@polyvinylidene fluoride electrothermal film.

[0008] The present invention discloses a method for preparing an aramid fiber-based ultrathin electrothermal film. First, aramid fibers (AFs) are unbundled and dispersed to obtain aramid nanofibers (ANFs). Then, aramid nanofibers are in-situ coated with pyrrole (Py) to firmly attach polypyrrole (PPy) to the aramid nanofibers. Finally, the polypyrrole-coated aramid nanofibers (aramid nanofibers@polypyrrole, i.e., ANFs@PPy, abbreviated as AP) and uncoated aramid nanofibers (ANFs) are scientifically controlled to form a film, and a layer of polyvinylidene fluoride (PVDF) is cured on its surface to form a (aramid nanofibers & (aramid nanofibers@polypyrrole))@PVDF composite electrothermal film ((ANFs & (ANFs@PPy))@PVDF composite electrothermal film, i.e. AsPF composite electrothermal film). This composite electrothermal film uses uncoated aramid nanofibers as a framework, with polypyrrole-coated aramid nanofibers forming a densely interconnected three-dimensional conductive network between the framework. The two are organically combined and complement each other, with good interfacial contact, low electron transport resistance, and low contact resistance, forming a conductive layer with wide coverage and good connectivity. It has multiple conductive pathways, good conductivity, and long-lasting stability. Moreover, it has good heating uniformity, fast thermal response speed, and high electrothermal conversion efficiency. Furthermore, this composite electrothermal film uses less material, is lightweight, thin, low-cost, flexible, and easy to process. It can be widely used in curved surfaces or bending applications (such as wearable devices and curved heating elements), and can also be applied to cutting-edge fields such as biomedicine, deep space exploration, and intelligent transportation.

[0009] In a preferred embodiment, in step 6), drying is performed at 70-90°C for 10-15 hours. This invention controls the drying temperature and time of the aramid nanofiber & (aramid nanofiber@polypyrrole) composite film (i.e., ANFs&AP composite film, abbreviated as AsP composite film) to ensure uniform film formation and consistent texture, while also preserving its conductive layer and maintaining good electrical and thermal properties.

[0010] In a preferred embodiment, in step 6), the film formation method is vacuum depressurization filtration. This invention can use vacuum depressurization filtration to form an aramid nanofiber & (aramid nanofiber@polypyrrole) composite membrane (i.e., an AsPF composite electrothermal membrane). This method offers fast film formation speed, high efficiency, and a uniform membrane layer.

[0011] In a preferred embodiment, the magnetic stirring time in step 6) is 10-20 minutes. This invention uses magnetic stirring to ensure thorough and uniform mixing of the aramid nanofiber suspension and the aramid nanofiber@polypyrrole suspension, allowing the aramid nanofibers and aramid nanofiber@polypyrrole to fully interact, thereby improving the overall performance of the resulting (aramid nanofiber & (aramid nanofiber@polypyrrole))@polyvinylidene fluoride composite electrothermal film.

[0012] In a preferred embodiment, in step 7), the mass concentration of the polyvinylidene fluoride organic solvent solution is 2-10 mg / mL. This invention involves impregnating and curing a layer of polyvinylidene fluoride onto the surface of an aramid nanofiber & (aramid nanofiber@polypyrrole) composite film. Polyvinylidene fluoride possesses excellent thermal stability, chemical stability, and mechanical properties, which can further enhance the mechanical properties, thermal stability, and chemical corrosion resistance of the electrothermal film. Simultaneously, the presence of polyvinylidene fluoride can also improve the flexibility and processing performance of the electrothermal film, broadening its application range.

[0013] In a preferred embodiment, in step 7), the organic solvent is any one of dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, and dimethyl sulfoxide. The polyvinylidene fluoride (PVDF) of this invention is impregnated onto the surface of an aramid nanofiber & (aramid nanofiber@polypyrrole) composite membrane via an organic solution. Then, during polymerization, the organic solvent evaporates, and simultaneously, the PVDF solidifies onto the surface of the aramid nanofiber & (aramid nanofiber@polypyrrole) composite membrane. PVDF exhibits good solubility and uniform dispersion in organic solvents such as dimethylacetamide (DMAC), N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), and dimethyl sulfoxide (DMSO), ensuring the uniformity and consistency of the PVDF layer on the surface of the aramid nanofiber & (aramid nanofiber@polypyrrole) composite membrane.

[0014] In a preferred embodiment, the immersion time in step 7) is 10-60 min. Since the thickness of the polyvinylidene fluoride (PVDF) layer affects the flexibility and heating efficiency of the electrothermal film, this invention controls the thickness of the PVDF layer by adjusting the mass concentration of the PVDF organic solvent solution and the immersion time, keeping its thickness between 5-50 µm. Of course, precision coating equipment can be used to precisely control the immersion time, such as microgravure coating.

[0015] In a preferred embodiment, in step 5), the molar concentration of the ferric chloride aqueous solution is 1.5-2.0 mol / L. In this invention, ferric chloride is used as an oxidant and added in the form of an aqueous solution to the mixed suspension formed by pyrrole and aramid nanofibers. The ferric chloride aqueous solution, as a homogeneous solution, diffuses rapidly and disperses evenly in the mixed suspension, increasing the active sites of the in-situ polymerization reaction, accelerating the rate of the in-situ polymerization reaction, and enhancing the uniformity of the in-situ polymerization reaction.

[0016] In a preferred embodiment, the magnetic stirring time in step 5) is 1-3 hours. This invention further improves the rate of the in-situ polymerization reaction and enhances its uniformity through magnetic stirring. The ferric chloride aqueous solution in this invention can be obtained by dissolving ferric chloride hexahydrate and ferric chloride powder in deionized water.

[0017] In a preferred embodiment, the magnetic stirring time in step 4) is 0.5-1.5 hours. In this invention, pyrrole is first mixed uniformly with the aramid nanofiber suspension under magnetic stirring to form a mixed suspension. Then, under the action of the oxidant ferric chloride, in-situ polymerization occurs, resulting in aramid nanofibers@polypyrrole. In the aramid nanofibers@polypyrrole structure, the aramid nanofibers have a large specific surface area and good dispersibility, and the polypyrrole coating on their surface forms a conductive layer with wide coverage and good connectivity. Moreover, the polypyrrole and aramid nanofibers are tightly bonded, with good interfacial contact and low electron transport resistance. The polypyrrole conductive layer is firmly attached to the aramid nanofibers and is not easily detached or migrated during subsequent processing or use, ensuring its long-lasting and stable conductivity.

[0018] In a preferred embodiment, in step 3), a cell disruptor with a power of 125-1000W is used for enhanced dispersion. This invention mechanically disperses and strengthens the unbundled aramid nanofibers, further improving their dispersion performance. The cell disruptor has a strong dispersing effect, easily achieving completely uniform dispersion of the aramid nanofibers. These highly dispersed aramid nanofibers have a diameter of only about 10nm, possessing a large specific surface area and good dispersibility. When pyrrole is polymerized in situ on their surface, the formed polypyrrole tightly and uniformly coats the surface of the aramid nanofibers, forming a continuous conductive network.

[0019] In a preferred embodiment, in step 3), the enhanced dispersion mode is to break the cells for 2 seconds, then pause for 3 seconds, process for 10 minutes, and repeat 3-5 times. This invention controls the power of the cell disruptor and the dispersion mode, thereby controlling the dispersion time and intensity. This achieves high dispersion of the aramid nanofibers without damaging their length, fully ensuring the performance of the dispersed aramid nanofibers.

[0020] In a preferred embodiment, step 2) involves washing with deionized water by adding deionized water, stirring at 500-700 rpm for 30-50 minutes, and centrifuging at 4000-8000 rpm for 3-7 minutes. The purpose of washing with deionized water in this invention is to remove isopropanol, potassium hydroxide, and dimethyl sulfoxide from the aramid nanofibers, purify the aramid nanofibers, and prevent these substances from affecting the subsequent in-situ polymerization and film formation processes.

[0021] In a preferred embodiment, step 2) involves washing with deionized water 3-5 times. In this invention, deionized water is used for repeated washing until the washing water level is neutral, i.e., the conductivity is ≤5μS / cm, thereby obtaining unbound aramid nanofibers (ANFs).

[0022] In a preferred embodiment, in step 2), stirring is carried out at room temperature, at a rotation speed of 500-700 r / min, for 1-2 hours, followed by a further stirring time of 30-60 minutes. In this invention, hydrogen bonds and π-π conjugation exist between the molecular chains of aramid fibers, resulting in tightly intertwined molecular chains. Potassium hydroxide acts as a deprotonating agent; the hydroxide ions ionized from potassium hydroxide in solution can react with certain groups on the molecular chains of aramid fibers (also known as Kevlar fibers), weakening or eliminating the hydrogen bonds and π-π conjugation between molecular chains, thereby dispersing large-sized aramid fibers into small-sized aramid nanofibers. Isopropanol accelerates the deprotonation rate, and its addition further enhances the overall unbundling speed of the aramid fibers.

[0023] In a preferred embodiment, in step 1), stirring is carried out at room temperature, with a rotation speed of 300-500 r / min, for 0.5-1 h. This invention uses stirring to rapidly dissolve potassium hydroxide in dimethyl sulfoxide (DMSO), thereby forming a homogeneous mixed solution. DMSO is a polar solvent that can dissolve potassium hydroxide, forming a potassium hydroxide-DMSO polar solvent mixture. In this system, DMSO helps potassium hydroxide to better perform its deprotonation function, while simultaneously providing a suitable solvent environment for aramid fibers, allowing the interchain interactions of the aramid fibers to be weakened or eliminated, thereby achieving the unbundling and dispersion of the aramid fibers.

[0024] In another aspect, the present invention provides an electrothermal film, which is prepared according to the preparation method of aramid fiber-based ultrathin electrothermal film described in any one of the above claims as an (aramid nanofibers & (aramid nanofibers@polypyrrole))@polyvinylidene fluoride electrothermal film.

[0025] The electrothermal film of this invention comprises both aramid nanofibers coated with pyrrole in situ and uncoated aramid nanofibers. The aramid nanofibers are unbundled and reinforced, exhibiting a large specific surface area, high dispersibility, and excellent mechanical properties. In the aramid nanofibers coated with pyrrole in situ, polypyrrole is tightly and uniformly coated on the surface of the aramid nanofibers, forming a continuous conductive network. The polypyrrole and aramid nanofibers are firmly connected with good interfacial contact. After scientific regulation, the aramid nanofibers coated with pyrrole in situ... The nanofibers form a densely interconnected three-dimensional conductive network between the uncoated aramid nanofiber skeleton. Under the protection of the polyvinylidene fluoride (PVDF) layer, the overall performance of the electrothermal film is greatly improved, resulting in good and long-lasting conductivity. In addition, it has good heating uniformity, fast thermal response, high electrothermal conversion efficiency, low material consumption, light weight, thinness, low cost, good flexibility, and easy processing. It can be widely used in curved surfaces or bending applications (such as wearable devices and curved heating elements), and can also be applied to cutting-edge fields such as biomedicine, deep space exploration, and intelligent transportation.

[0026] In a preferred embodiment, the thickness of the electrothermal film is 50-200µm. The thickness of the electrothermal film of the present invention can be adjusted between tens and hundreds of micrometers. It is lightweight, thin, flexible, and easy to process, and can be widely used in curved surfaces or applications requiring bending (such as wearable devices, curved heating elements). It can also be applied to cutting-edge fields such as biomedicine, deep space exploration, and intelligent transportation.

[0027] Compared with existing technologies, the advantages of this invention are as follows: This invention obtains aramid nanofibers by unbundling and dispersing aramid fibers, then uses pyrrole to perform in-situ polymerization coating on the aramid nanofibers, allowing polypyrrole to firmly adhere to the aramid nanofibers. The polypyrrole-coated aramid nanofibers and uncoated aramid nanofibers are then scientifically controlled to form a film, and a layer of polyvinylidene fluoride is cured on its surface, forming a (aramid nanofiber & (aramid nanofiber @ polypyrrole)) @ polyvinylidene fluoride composite electrothermal film. This method for preparing the composite electrothermal film is simple to operate, has a short process flow, mild conditions, and is easy to industrialize. The resulting composite electrothermal film uses uncoated aramid nanofibers as a framework, with polypyrrole-coated aramid nanofibers forming a densely interconnected three-dimensional conductive network between the framework. The two are organically combined and complement each other, with good interfacial contact, low electron transport resistance, and low contact resistance, forming a conductive layer with wide coverage and good connectivity. It has multiple conductive pathways, good conductivity, and long-lasting stability. Moreover, it has good heating uniformity, fast thermal response speed, and high electrothermal conversion efficiency. It uses less material, is lightweight, thin, low-cost, flexible, and easy to process. It can be widely used in curved surfaces or bending applications (such as wearable devices and curved heating elements), and can also be applied to cutting-edge fields such as biomedicine, deep space exploration, and intelligent transportation. Attached Figure Description

[0028] Figure 1 is a photograph of the appearance of the electrothermal film obtained in Embodiment 3 of the present invention;

[0029] Figure 2 is a photograph of the appearance of the first comparative sample of the present invention;

[0030] Figure 3 is a photograph of the appearance of the second comparative sample of the present invention;

[0031] Figure 4 is a photograph of the appearance of the control sample three of the present invention;

[0032] Figure 5 is a thermal imaging image of the electrothermal film obtained in Embodiment 3 of the present invention;

[0033] Figure 6 is a thermal image of the electrothermal film obtained from the control sample of the present invention.

[0034] Figure 7 is a thermal image of the electrothermal film obtained from the control sample 2 of the present invention;

[0035] Figure 8 is a thermal image of the electrothermal film obtained from the control sample 3 of this invention. Detailed Implementation

[0036] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] The present invention discloses a method for preparing an aramid fiber-based ultrathin electrothermal film, comprising the following steps:

[0038] S1 aramid fiber unbundling and dispersion

[0039] 1) Take dimethyl sulfoxide and potassium hydroxide, grind them, add them to dimethyl sulfoxide, the molar ratio of potassium hydroxide to dimethyl sulfoxide is 1:30-1:50, stir, dissolve, and obtain a mixed solution;

[0040] 2) Take aramid fibers and add them to the mixed solution obtained in step 1). The mass ratio of aramid fibers to dimethyl sulfoxide is 1:100-1:120. Stir, add isopropanol, and the mass ratio of isopropanol to dimethyl sulfoxide is 1:3-1:8. Continue stirring, unbundle, wash with deionized water, and obtain aramid nanofibers.

[0041] 3) Add deionized water to the aramid nanofibers obtained in step 2) to enhance dispersion for 30-50 min, and add to deionized water to make the solid content 1-5 mg / mL to obtain an aramid nanofiber suspension.

[0042] S2 in-situ polymerization forms a conductive layer.

[0043] 4) Take the aramid nanofiber suspension obtained in step 3), take pyrrole, add it to the aramid nanofiber suspension, the mass ratio of pyrrole to aramid nanofiber in the aramid nanofiber suspension is 1:0.1-1:5, stir magnetically in an ice-water bath to obtain a mixed suspension.

[0044] 5) Take an aqueous solution of ferric chloride and add it to the mixed suspension obtained in step 4). The mass ratio of ferric chloride in the aqueous solution to pyrrole in the mixed suspension is 0.6:1-6:1. Continue to stir magnetically in an ice-water bath, polymerize in situ, filter, wash, and disperse in deionized water to make the solid content 0.5-1.5 mg / mL, to obtain an aramid nanofiber@polypyrrole suspension.

[0045] Preparation of S3 electrothermal film

[0046] 6) Take another aramid nanofiber suspension obtained in step 3) and add it to the aramid nanofiber@polypyrrole suspension obtained in step 5). The mass ratio of aramid nanofiber in the aramid nanofiber suspension to aramid nanofiber@polypyrrole in the aramid nanofiber@polypyrrole suspension is 0.25:1-4:1. Stir magnetically, form a film, and dry to obtain an aramid nanofiber & (aramid nanofiber@polypyrrole) composite film.

[0047] 7) The aramid nanofibers & (aramid nanofibers@polypyrrole) composite film obtained in step 6) are immersed in a polyvinylidene fluoride organic solvent solution and polymerized at 80-100℃ for 5-10 hours to obtain (aramid nanofibers & (aramid nanofibers@polypyrrole))@polyvinylidene fluoride electrothermal film.

[0048] Preferably, in step 6), the drying is performed at 70-90°C for 10-15 hours.

[0049] Furthermore, in step 6), the film formation method is vacuum decompression filtration film formation.

[0050] Specifically, in step 6), the magnetic stirring time is 10-20 minutes.

[0051] Preferably, in step 7), the mass concentration of the polyvinylidene fluoride organic solvent solution is 2-10 mg / mL.

[0052] Further, in step 7), the organic solvent is any one of dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, and dimethyl sulfoxide.

[0053] Specifically, in step 7), the soaking time is 10-60 minutes.

[0054] Preferably, in step 5), the molar concentration of the ferric chloride aqueous solution is 1.5-2.0 mol / L.

[0055] Furthermore, in step 5), the magnetic stirring time is 1-3 hours.

[0056] Preferably, in step 4), the magnetic stirring time is 0.5-1.5h.

[0057] Preferably, in step 3), a cell disruptor is used for enhanced dispersion, and the power of the cell disruptor is 125-1000W.

[0058] Furthermore, in step 3), the enhanced dispersion mode is to break the material for 2 seconds, then pause for 3 seconds, process for 10 minutes, and repeat 3-5 times.

[0059] Preferably, in step 2), the deionized water washing is performed by adding deionized water, stirring at 500-700 r / min for 30-50 min, and centrifuging at 4000-8000 r / min for 3-7 min.

[0060] Furthermore, in step 2), the washing with deionized water is repeated 3-5 times.

[0061] Specifically, in step 2), stirring is carried out at room temperature, at a speed of 500-700 r / min, for 1-2 hours, and then stirring is continued for 30-60 minutes.

[0062] Preferably, in step 1), stirring is carried out at room temperature, at a speed of 300-500 r / min, for a time of 0.5-1 h.

[0063] The present invention provides an electrothermal film, wherein the electrothermal film is prepared according to the preparation method of aramid fiber-based ultrathin electrothermal film described in any one of the above claims, which is a (aramid nanofiber & (aramid nanofiber @ polypyrrole)) @ polyvinylidene fluoride electrothermal film.

[0064] Preferably, the thickness of the electrothermal film is 50-200µm.

[0065] Example 1

[0066] The present invention discloses a method for preparing an aramid fiber-based ultrathin electrothermal film, comprising the following steps:

[0067] S1 aramid fiber unbundling and dispersion

[0068] 1) Take 110g of dimethyl sulfoxide (DMSO) and 1.9g of potassium hydroxide (KOH), grind them, add them to the dimethyl sulfoxide, stir at room temperature at a speed of 300r / min for 1h, so that the potassium hydroxide is completely dispersed and dissolved in the dimethyl sulfoxide to obtain a mixed solution;

[0069] 2) Take 1g of aramid fibers (AFs) and add them to the mixed solution obtained in step 1). Stir at room temperature at a speed of 600r / min for 1h to fully disperse the aramid fibers. Under continuous stirring, add 15g of isopropanol and continue stirring for 30min to unbundle the fibers. Add 100mL of deionized water and stir at 600r / min for 30min. Then centrifuge at 8000r / min for 5min. Repeat the deionized water washing process 3 times until the conductivity of the washing water does not exceed 5μS / cm to obtain aramid nanofibers (ANFs).

[0070] 3) Transfer the aramid nanofibers obtained in step 2) to a 250 mL beaker, add 100 mL of deionized water, and use a cell disruptor at 175 W to enhance dispersion for 10 min at a 2 s break interval of 3 s. Repeat the enhanced dispersion 3 times. Then, add the product to deionized water and adjust the solid content to 1 mg / mL to obtain a suspension of aramid nanofibers that is completely unbundled and uniformly dispersed.

[0071] S2 in-situ polymerization forms a conductive layer.

[0072] 4) Take 50 mL of the aramid nanofiber suspension obtained in step 3), add 100 mg of pyrrole to the aramid nanofiber suspension, and stir magnetically in an ice-water bath for 1 h to fully disperse the pyrrole monomer in the aramid nanofiber suspension to obtain a mixed suspension.

[0073] 5) Take hexahydrate and ferric chloride (FeCl3) · 5g of ferric chloride hexahydrate and 10mL of deionized water were dissolved in the deionized water to prepare a ferric chloride aqueous solution with a concentration of 1.8mol / L. 1mL of the ferric chloride aqueous solution was added to the mixed suspension obtained in step 4), and the mixture was magnetically stirred in an ice-water bath for 2h. Under the action of ferric chloride, pyrrole monomers underwent in-situ polymerization. The reaction product was filtered and repeatedly washed in deionized water until the pH of the washing water was about 7, thereby removing excess ferric chloride and unreacted pyrrole monomers and giving the product good purity. Finally, the product was dispersed in deionized water and the solid content was adjusted to 1mg / mL to obtain an aramid nanofiber@polypyrrole suspension.

[0074] Preparation of S3 electrothermal film

[0075] 6) Take another 20 mL of the aramid nanofiber suspension obtained in step 3) and place it in a 100 mL beaker. Take another 20 mL of the aramid nanofiber@polypyrrole suspension obtained in step 5) and add the aramid nanofiber suspension to the aramid nanofiber@polypyrrole suspension. Mix and stir magnetically for 15 min. Form a film by vacuum filtration at room temperature and dry it in an oven at 80℃ for 12 h to obtain an aramid nanofiber & (aramid nanofiber@polypyrrole) composite membrane (i.e., ANFs & AP composite membrane, abbreviated as AsP composite membrane).

[0076] 7) The aramid nanofiber & (aramid nanofiber@polypyrrole) composite film obtained in step 6) is immersed in a polyvinylidene fluoride N,N-dimethylformamide solution with a concentration of 5 mg / mL. After 10 min, it is taken out and polymerized in an oven at 80℃ for 6 h to obtain (aramid nanofiber & (aramid nanofiber@polypyrrole))@polyvinylidene fluoride electrothermal film (i.e. (ANFs & (ANFs@PPy))@PDVF electrothermal film, abbreviated as AsPF electrothermal film).

[0077] Example 2

[0078] The present invention discloses a method for preparing an aramid fiber-based ultrathin electrothermal film, comprising the following steps:

[0079] S1 aramid fiber unbundling and dispersion

[0080] 1) Take 117g of dimethyl sulfoxide (DMSO) and 2.8g of potassium hydroxide (KOH), grind them, add them to the dimethyl sulfoxide, stir at room temperature at a speed of 500r / min for 0.5h, so that the potassium hydroxide is completely dispersed and dissolved in the dimethyl sulfoxide to obtain a mixed solution;

[0081] 2) Take 1.17g of aramid fibers (AFs) and add them to the mixed solution obtained in step 1). Stir at room temperature at a speed of 700r / min for 1.5h to fully disperse the aramid fibers. Under continuous stirring, add 39g of isopropanol and continue stirring for 60min to unbundle the fibers. Add 100mL of deionized water and stir at 500r / min for 50min. Then centrifuge at 6000r / min for 3min. Repeat the deionized water washing process 5 times until the conductivity of the washing water does not exceed 5μS / cm to obtain aramid nanofibers (ANFs).

[0082] 3) Transfer the aramid nanofibers obtained in step 2) to a 250 mL beaker, add 100 mL of deionized water, and use a cell disruptor at 1000 W to enhance dispersion for 10 min at a 2 s break interval of 3 s. Repeat the enhanced dispersion 4 times. Then, add the product to deionized water and adjust the solid content to 2 mg / mL to obtain a suspension of aramid nanofibers that is completely unbundled and uniformly dispersed.

[0083] S2 in-situ polymerization forms a conductive layer.

[0084] 4) Take 15 mL of the aramid nanofiber suspension obtained in step 3), add 300 mg of pyrrole to the aramid nanofiber suspension, and stir magnetically in an ice-water bath for 1.5 h to fully disperse the pyrrole monomer in the aramid nanofiber suspension to obtain a mixed suspension.

[0085] 5) Take hexahydrate and ferric chloride (FeCl3) · 5.41 g of ferric chloride hexahydrate and 10 mL of deionized water were dissolved in the deionized water to prepare a 2 mol / L ferric chloride aqueous solution. 5.5 mL of the ferric chloride aqueous solution was added to the mixed suspension obtained in step 4), and the mixture was magnetically stirred in an ice-water bath for 3 h. Under the action of ferric chloride, pyrrole monomers underwent in-situ polymerization. The reaction product was filtered and repeatedly washed in deionized water until the pH of the washing water was approximately 7, thereby removing excess ferric chloride and unreacted pyrrole monomers and giving the product good purity. Finally, the product was dispersed in deionized water and the solid content was adjusted to 1.5 mg / mL to obtain an aramid nanofiber@polypyrrole suspension.

[0086] Preparation of S3 electrothermal film

[0087] 6) Take another 10 mL of the aramid nanofiber suspension obtained in step 3) and place it in a 100 mL beaker. Take 5 mL of the aramid nanofiber@polypyrrole suspension obtained in step 5) and add the aramid nanofiber suspension to the aramid nanofiber@polypyrrole suspension. Mix and stir magnetically for 10 min. Form a film by vacuum filtration at room temperature and dry it in an oven at 70 °C for 10 h to obtain an aramid nanofiber & (aramid nanofiber@polypyrrole) composite membrane (i.e., ANFs & AP composite membrane, abbreviated as AsP composite membrane).

[0088] 7) The aramid nanofiber & (aramid nanofiber@polypyrrole) composite film obtained in step 6) is immersed in a polyvinylidene fluoride dimethyl sulfoxide solution with a concentration of 2 mg / mL. After 60 min, it is taken out and polymerized in an oven at 90℃ for 10 h to obtain (aramid nanofiber & (aramid nanofiber@polypyrrole))@polyvinylidene fluoride electrothermal film (i.e. (ANFs & (ANFs@PPy))@PDVF electrothermal film, abbreviated as AsPF electrothermal film).

[0089] Example 3

[0090] The present invention discloses a method for preparing an aramid fiber-based ultrathin electrothermal film, comprising the following steps:

[0091] S1 aramid fiber unbundling and dispersion

[0092] 1) Take 78g of dimethyl sulfoxide (DMSO) and 1.12g of potassium hydroxide (KOH), grind them, add them to the dimethyl sulfoxide, stir at room temperature at a speed of 400r / min for 0.8h, so that the potassium hydroxide is completely dispersed and dissolved in the dimethyl sulfoxide to obtain a mixed solution;

[0093] 2) Take 0.65g of aramid fibers (AFs) and add them to the mixed solution obtained in step 1). Stir at room temperature at a speed of 500r / min for 2h to fully disperse the aramid fibers. Under continuous stirring, add 9.75g of isopropanol and continue stirring for 40min to unbundle the fibers. Add 100mL of deionized water and stir at 700r / min for 40min. Then centrifuge at 4000r / min for 7min. Repeat the deionized water washing process 4 times until the conductivity of the washing water does not exceed 5μS / cm to obtain aramid nanofibers (ANFs).

[0094] 3) Transfer the aramid nanofibers obtained in step 2) to a 250 mL beaker, add 100 mL of deionized water, and use a cell disruptor at 125 W to enhance dispersion for 10 min at a 2 s break interval of 3 s. Repeat the enhanced dispersion 5 times. Then, add the product to deionized water and adjust the solid content to 5 mg / mL to obtain a suspension of aramid nanofibers that is completely unbundled and uniformly dispersed.

[0095] S2 in-situ polymerization forms a conductive layer.

[0096] 4) Take 40 mL of the aramid nanofiber suspension obtained in step 3), add 40 mg of pyrrole to the aramid nanofiber suspension, and stir magnetically in an ice-water bath for 1 h to fully disperse the pyrrole monomer in the aramid nanofiber suspension to obtain a mixed suspension.

[0097] 5) Take hexahydrate and ferric chloride (FeCl3) ·4.2 g of ferric chloride hexahydrate and 10 mL of deionized water were dissolved in the deionized water to prepare a ferric chloride aqueous solution with a concentration of 1.5 mol / L. 49 mL of the ferric chloride aqueous solution was added to the mixed suspension obtained in step 4), and the mixture was magnetically stirred in an ice-water bath for 2 h. Under the action of ferric chloride, pyrrole monomers underwent in-situ polymerization. The reaction product was filtered and repeatedly washed in deionized water until the pH of the washing water was about 7, thereby removing excess ferric chloride and unreacted pyrrole monomers and giving the product good purity. Finally, the product was dispersed in deionized water and the solid content was adjusted to 0.5 mg / mL to obtain an aramid nanofiber@polypyrrole suspension.

[0098] Preparation of S3 electrothermal film

[0099] 6) Take 1 mL of the aramid nanofiber suspension obtained in step 3) and place it in a 100 mL beaker. Take 40 mL of the aramid nanofiber@polypyrrole suspension obtained in step 5) and add the aramid nanofiber suspension to the aramid nanofiber@polypyrrole suspension. Mix and stir magnetically for 10 min. Form a film by vacuum filtration at room temperature and dry it in an oven at 90 °C for 15 h to obtain an aramid nanofiber & (aramid nanofiber@polypyrrole) composite membrane (i.e., ANFs & AP composite membrane, abbreviated as AsP composite membrane).

[0100] 7) The aramid nanofiber & (aramid nanofiber@polypyrrole) composite film obtained in step 6) is immersed in a polyvinylidene fluoride N-methylpyrrolidone solution with a concentration of 10 mg / mL. After 30 min, it is taken out and polymerized in an oven at 100℃ for 5 h to obtain (aramid nanofiber & (aramid nanofiber@polypyrrole))@polyvinylidene fluoride electrothermal film (i.e. (ANFs & (ANFs@PPy))@PDVF electrothermal film, abbreviated as AsPF electrothermal film).

[0101] Comparative Example 1

[0102] A method for preparing an aramid fiber-based electrothermal film includes the following steps:

[0103] S1 aramid fiber unbundling and dispersion

[0104] 1) Take 110g of dimethyl sulfoxide (DMSO) and 1.9g of potassium hydroxide (KOH), grind them, add them to the dimethyl sulfoxide, stir at room temperature at a speed of 300r / min for 1h, so that the potassium hydroxide is completely dispersed and dissolved in the dimethyl sulfoxide to obtain a mixed solution;

[0105] 2) Take 1g of aramid fibers (AFs) and add them to the mixed solution obtained in step 1). Stir at room temperature at a speed of 600r / min for 1h to fully disperse the aramid fibers. Under continuous stirring, add 15g of isopropanol and continue stirring for 30min to unbundle the fibers. Add 100mL of deionized water and stir at 600r / min for 30min. Then centrifuge at 8000r / min for 5min. Repeat the deionized water washing process 3 times until the conductivity of the washing water does not exceed 5μS / cm to obtain aramid nanofibers (ANFs).

[0106] 3) Transfer the aramid nanofibers obtained in step 2) to a 250 mL beaker, add 100 mL of deionized water, and use a cell disruptor at 175 W to enhance dispersion for 10 min at a 2 s break interval of 3 s. Repeat the enhanced dispersion 3 times. Then, add the product to deionized water and adjust the solid content to 1 mg / mL to obtain a suspension of aramid nanofibers that is completely unbundled and uniformly dispersed.

[0107] S2 in-situ polymerization forms a conductive layer.

[0108] 4) Take 50 mL of the aramid nanofiber suspension obtained in step 3), add 100 mg of pyrrole to the aramid nanofiber suspension, and stir magnetically in an ice-water bath for 1 h to fully disperse the pyrrole monomer in the aramid nanofiber suspension to obtain a mixed suspension.

[0109] 5) Take hexahydrate and ferric chloride (FeCl3) · 5g of ferric chloride hexahydrate and 10mL of deionized water were dissolved in the deionized water to prepare a ferric chloride aqueous solution with a concentration of 1.8mol / L. 1mL of the ferric chloride aqueous solution was added to the mixed suspension obtained in step 4), and the mixture was magnetically stirred in an ice-water bath for 2h. Under the action of ferric chloride, pyrrole monomers underwent in-situ polymerization. The reaction product was filtered and repeatedly washed in deionized water until the pH of the washing water was about 7, thereby removing excess ferric chloride and unreacted pyrrole monomers and giving the product good purity. Finally, the product was dispersed in deionized water and the solid content was adjusted to 1mg / mL to obtain an aramid nanofiber@polypyrrole suspension.

[0110] Preparation of S3 electrothermal film

[0111] 6) Take another 20 mL of the aramid nanofiber suspension obtained in step 3) and place it in a 100 mL beaker. Take 2 mL of the aramid nanofiber@polypyrrole suspension obtained in step 5) and add the aramid nanofiber suspension to the aramid nanofiber@polypyrrole suspension. Mix and stir magnetically for 15 min. Form a film by vacuum filtration at room temperature and dry in an oven at 80 °C for 12 h to obtain an aramid nanofiber & (aramid nanofiber@polypyrrole) composite membrane.

[0112] 7) The aramid nanofiber & (aramid nanofiber@polypyrrole) composite film obtained in step 6) was immersed in a polyvinylidene fluoride N,N-dimethylformamide solution with a concentration of 5 mg / mL. After 10 min, it was taken out and polymerized in an oven at 80℃ for 6 h to obtain (aramid nanofiber & (aramid nanofiber@polypyrrole))@polyvinylidene fluoride electrothermal film, i.e., control sample 1.

[0113] Comparative Example 2

[0114] A method for preparing an aramid fiber-based electrothermal film includes the following steps:

[0115] S1 aramid fiber unbundling and dispersion

[0116] 1) Take 110g of dimethyl sulfoxide (DMSO) and 1.9g of potassium hydroxide (KOH), grind them, add them to the dimethyl sulfoxide, stir at room temperature at a speed of 300r / min for 1h, so that the potassium hydroxide is completely dispersed and dissolved in the dimethyl sulfoxide to obtain a mixed solution;

[0117] 2) Take 1g of aramid fibers (AFs) and add them to the mixed solution obtained in step 1). Stir at room temperature at a speed of 600r / min for 1h to fully disperse the aramid fibers. Under continuous stirring, add 15g of isopropanol and continue stirring for 30min to unbundle the fibers. Add 100mL of deionized water and stir at 600r / min for 30min. Then centrifuge at 8000r / min for 5min. Repeat the deionized water washing process 3 times until the conductivity of the washing water does not exceed 5μS / cm to obtain aramid nanofibers (ANFs).

[0118] 3) Transfer the aramid nanofibers obtained in step 2) to a 250 mL beaker, add 100 mL of deionized water, and use a cell disruptor at 175 W to enhance dispersion for 10 min at a 2 s break interval of 3 s. Repeat the enhanced dispersion 3 times. Then, add the product to deionized water and adjust the solid content to 1 mg / mL to obtain a suspension of aramid nanofibers that is completely unbundled and uniformly dispersed.

[0119] S2 in-situ polymerization forms a conductive layer.

[0120] 4) Take 50 mL of the aramid nanofiber suspension obtained in step 3), add 2 mg of pyrrole to the aramid nanofiber suspension, and stir magnetically in an ice-water bath for 1 h to fully disperse the pyrrole monomer in the aramid nanofiber suspension to obtain a mixed suspension.

[0121] 5) Take hexahydrate and ferric chloride (FeCl3) · 5g of ferric chloride hexahydrate and 10mL of deionized water were dissolved in the deionized water to prepare a ferric chloride aqueous solution with a concentration of 1.8mol / L. 20μL of the ferric chloride aqueous solution was added to the mixed suspension obtained in step 4), and the mixture was magnetically stirred in an ice-water bath for 2h. Under the action of ferric chloride, pyrrole monomers underwent in-situ polymerization. The reaction product was filtered and repeatedly washed in deionized water until the pH of the washing water was about 7, thereby removing excess ferric chloride and unreacted pyrrole monomers and giving the product good purity. Finally, the product was dispersed in deionized water and the solid content was adjusted to 1mg / mL to obtain an aramid nanofiber@polypyrrole suspension.

[0122] Preparation of S3 electrothermal film

[0123] 6) Take another 20 mL of the aramid nanofiber suspension obtained in step 3) and place it in a 100 mL beaker. Take another 20 mL of the aramid nanofiber@polypyrrole suspension obtained in step 5) and add the aramid nanofiber suspension to the aramid nanofiber@polypyrrole suspension. Mix and stir magnetically for 15 min. Form a film by vacuum filtration at room temperature and dry in an oven at 80 °C for 12 h to obtain an aramid nanofiber & (aramid nanofiber@polypyrrole) composite membrane.

[0124] 7) The aramid nanofiber & (aramid nanofiber@polypyrrole) composite film obtained in step 6) was immersed in a polyvinylidene fluoride N,N-dimethylformamide solution with a concentration of 5 mg / mL. After 10 min, it was taken out and polymerized in an oven at 80℃ for 6 h to obtain (aramid nanofiber & (aramid nanofiber@polypyrrole))@polyvinylidene fluoride electrothermal film, i.e., control sample 2.

[0125] Comparative Example 3

[0126] A method for preparing an aramid fiber-based electrothermal film includes the following steps:

[0127] S1 aramid fiber unbundling and dispersion

[0128] 1) Take 110g of dimethyl sulfoxide (DMSO) and 1.9g of potassium hydroxide (KOH), grind them, add them to the dimethyl sulfoxide, stir at room temperature at a speed of 300r / min for 1h, so that the potassium hydroxide is completely dispersed and dissolved in the dimethyl sulfoxide to obtain a mixed solution;

[0129] 2) Take 1g of aramid fibers (AFs) and add them to the mixed solution obtained in step 1). Stir at room temperature at a speed of 600r / min for 1h to fully disperse the aramid fibers. Under continuous stirring, add 15g of isopropanol and continue stirring for 30min to unbundle the fibers. Add 100mL of deionized water and stir at 600r / min for 30min. Then centrifuge at 8000r / min for 5min. Repeat the deionized water washing process 3 times until the conductivity of the washing water does not exceed 5μS / cm to obtain aramid nanofibers (ANFs).

[0130] 3) Transfer the aramid nanofibers obtained in step 2) to a 250 mL beaker, add 100 mL of deionized water, and use a cell disruptor at 175 W to enhance dispersion for 10 min at a 2 s break interval of 3 s. Repeat the enhanced dispersion 3 times. Then, add the product to deionized water and adjust the solid content to 1 mg / mL to obtain a suspension of aramid nanofibers that is completely unbundled and uniformly dispersed.

[0131] Preparation of S2 electrothermal film

[0132] 4) Take another 20 mL of the aramid nanofiber suspension obtained in step 3), form a film by vacuum filtration at room temperature, and dry it in an oven at 80°C for 12 h to obtain an aramid nanofiber membrane (i.e., ANFs membrane, abbreviated as As membrane).

[0133] 5) The aramid nanofiber membrane obtained in step 4) was immersed in a polyvinylidene fluoride N,N-dimethylformamide solution with a concentration of 5 mg / mL. After 10 min, it was taken out and polymerized in an oven at 80℃ for 6 h to obtain (aramid nanofiber@polyvinylidene fluoride electrothermal film, i.e., control sample three).

[0134] Performance Test 1

[0135] The aramid nanofibers (aramid nanofibers@polypyrrole)@polyvinylidene fluoride electrothermal films obtained in Examples 1 to 3 of this invention, as well as control sample 1 obtained in Comparative Example 1, control sample 2 obtained in Comparative Example 2, and control sample 3 obtained in Comparative Example 3, were subjected to performance tests, including the resistance of the electrothermal film, heating temperature under different voltages, thickness, tensile properties, and stability. The electrothermal film was cut to a diameter of 35 mm, and the thickness was measured using SEM film profile measurement and high-precision vernier calipers. The resistance of the film was measured using a multimeter, and the heating temperature of the electrothermal film was measured under different DC voltages using a DC power supply. The electrothermal film was cut into strips with dimensions of 10 mm × 30 mm, and the tensile mechanical properties of the samples were tested using a universal testing machine. Stability was determined by cyclic stability after 100 cycles of switching on and off at 12V. Each group of samples was measured at least 3 times, and the average value was taken. The experimental results are listed in Table 1.

[0136] Table 1 Performance test results of different electrothermal films

[0137]

[0138] As shown in Table 1, the resistance of the (aramid nanofibers & (aramid nanofibers@polypyrrole))@polyvinylidene fluoride electrothermal film obtained in this invention is 35-133 Ω / sq, while the resistance of the control sample is 1.025×10⁻⁶. 6 Ω / sq, however, control samples two and three are not conductive. Therefore, the (aramid nanofibers & (aramid nanofibers@polypyrrole))@polyvinylidene fluoride electrothermal film obtained in this invention has low contact resistance. Therefore, the (aramid nanofibers & (aramid nanofibers@polypyrrole))@polyvinylidene fluoride electrothermal film obtained in this invention has good electrical conductivity.

[0139] As shown in Table 1, the (aramid nanofibers & (aramid nanofibers@polypyrrole))@polyvinylidene fluoride electrothermal film obtained in this invention exhibits different heating temperatures under different applied voltages. Furthermore, the heating temperature increases with increasing applied voltage. The heating temperature of Example 2 shows the largest variation, reaching a maximum of 150.2℃. The heating temperature of Control Sample 1 remains essentially unchanged under different applied voltages. However, Control Samples 2 and 3 are both non-conductive. Therefore, the (aramid nanofibers & (aramid nanofibers@polypyrrole))@polyvinylidene fluoride electrothermal film obtained in this invention has good heating performance.

[0140] As shown in Table 1, the film thickness of the (aramid nanofibers & (aramid nanofibers@polypyrrole))@polyvinylidene fluoride electrothermal film obtained in this invention is 50-70 μm, while the film thickness of control sample 1 is 45 μm, control sample 2 is 60 μm, and control sample 3 is 35 μm. The (aramid nanofibers & (aramid nanofibers@polypyrrole))@polyvinylidene fluoride electrothermal film obtained in this invention has a thinner thickness than control samples 1, 2, and 3. Therefore, the (aramid nanofibers & (aramid nanofibers@polypyrrole))@polyvinylidene fluoride electrothermal film obtained in this invention has a thinner thickness.

[0141] As shown in Table 1, the tensile strength of the (aramid nanofibers & (aramid nanofibers@polypyrrole))@polyvinylidene fluoride electrothermal film obtained in this invention is 162-218 MPa, while the tensile strength of control sample 1 is 107 MPa, control sample 2 is 211 MPa, and control sample 3 is 149 MPa. The tensile strength of the (aramid nanofibers & (aramid nanofibers@polypyrrole))@polyvinylidene fluoride electrothermal film obtained in this invention is comparable to that of control sample 2, and is significantly greater than that of control samples 1 and 3. Therefore, the (aramid nanofibers & (aramid nanofibers@polypyrrole))@polyvinylidene fluoride electrothermal film obtained in this invention has excellent tensile properties.

[0142] As shown in Table 1, the (aramid nanofibers & (aramid nanofibers@polypyrrole))@polyvinylidene fluoride electrothermal film obtained in this invention exhibits normal cycle stability after 100 cycles of power-on and power-off at 12V. Control sample one also shows normal cycle stability after 100 cycles of power-on and power-off at 12V. However, control samples two and three, being non-conductive, do not meet the requirements for 100 cycles of power-on and power-off stability testing at 12V. Therefore, the (aramid nanofibers & (aramid nanofibers@polypyrrole))@polyvinylidene fluoride electrothermal film obtained in this invention demonstrates durable and stable performance.

[0143] Performance Test 2

[0144] The aramid nanofibers (aramid nanofibers@polypyrrole)@polyvinylidene fluoride electrothermal film obtained in Example 3 of this invention, as well as control sample 1 obtained in Comparative Example 1, control sample 2 obtained in Comparative Example 2, and control sample 3 obtained in Comparative Example 3, were subjected to appearance and heating uniformity tests. The appearance of the electrothermal films was observed visually and compared with each other. The electrothermal films were cut to a diameter of 35 mm, and the electrothermal temperature of the electrothermal films was observed and recorded using an infrared camera. Each group of samples was measured at least 3 times, and the average value was taken.

[0145] As can be seen from Figures 1, 2, 3, and 4, the (aramid nanofibers & (aramid nanofibers@polypyrrole))@polyvinylidene fluoride electrothermal film obtained in this invention has a dark black appearance. However, the appearance of control sample one is light black, control sample two is brown, and control sample three is pale yellow, which is the natural color of the aramid nanofibers. Generally, the darker the color, the better the conductivity. Therefore, the (aramid nanofibers & (aramid nanofibers@polypyrrole))@polyvinylidene fluoride electrothermal film obtained in this invention has the best conductivity.

[0146] As can be seen from Figures 5, 6, 7, and 8, the (aramid nanofibers & (aramid nanofibers@polypyrrole))@polyvinylidene fluoride electrothermal film obtained in Example 3 of the present invention exhibits uniform temperature distribution and good electrical conductivity and heating performance in the thermal imaging at 12V, with a maximum temperature reaching 69.3℃ and a temperature difference in the central region not exceeding 18℃. While control sample 1 is conductive at 12V, its surface temperature only reaches 25.7℃ due to its high resistance. Furthermore, control samples 2 and 3, being non-conductive, only reached room temperature on their film surfaces during testing at 12V. Therefore, the (aramid nanofibers & (aramid nanofibers@polypyrrole))@polyvinylidene fluoride electrothermal film obtained in this invention demonstrates good electrical conductivity and heating uniformity.

[0147] Therefore, compared with the prior art, the beneficial effects of this invention are as follows: This invention obtains aramid nanofibers by unbundling and dispersing aramid fibers, and uses pyrrole to perform in-situ polymerization coating on the aramid nanofibers, so that polypyrrole is firmly attached to the aramid nanofibers. The polypyrrole-coated aramid nanofibers and uncoated aramid nanofibers are then scientifically controlled to form a film, and a layer of polyvinylidene fluoride is cured on its surface to form a (aramid nanofibers & (aramid nanofibers @ polypyrrole)) @ polyvinylidene fluoride composite electrothermal film. This method for preparing the composite electrothermal film is simple to operate, has a short process flow, mild conditions, and is easy to industrialize. The resulting composite electrothermal film uses uncoated aramid nanofibers as a framework, with polypyrrole-coated aramid nanofibers forming a densely interconnected three-dimensional conductive network between the framework. The two are organically combined and complement each other, with good interfacial contact, low electron transport resistance, and low contact resistance, forming a conductive layer with wide coverage and good connectivity. It has multiple conductive pathways, good conductivity, and long-lasting stability. Moreover, it has good heating uniformity, fast thermal response speed, and high electrothermal conversion efficiency. It uses less material, is lightweight, thin, low-cost, flexible, and easy to process. It can be widely used in curved surfaces or bending applications (such as wearable devices and curved heating elements), and can also be applied to cutting-edge fields such as biomedicine, deep space exploration, and intelligent transportation.

[0148] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing an aramid fiber-based ultrathin electrothermal film, characterized in that, Includes the following steps: S1 Aramid Fiber Unbundling and Dispersion: 1) Take dimethyl sulfoxide and potassium hydroxide, grind them, and add them to dimethyl sulfoxide. The molar ratio of potassium hydroxide to dimethyl sulfoxide is 1:30-1:

50. Stir and dissolve to obtain a mixed solution; 2) Take aramid fibers and add them to the mixed solution obtained in step 1). The mass ratio of aramid fibers to dimethyl sulfoxide is 1:100-1:

120. Stir and add isopropanol. The mass ratio of isopropanol to dimethyl sulfoxide is 1:3-1:

8. Continue stirring, unbundle the fibers, and wash with deionized water to obtain aramid fibers. Nanofibers; 3) Add deionized water to the aramid nanofibers obtained in step 2) to enhance dispersion for 30-50 min, and add to deionized water to make the solid content 1-5 mg / mL to obtain an aramid nanofiber suspension; S2 In-situ polymerization to form a conductive layer 4) Take the aramid nanofiber suspension obtained in step 3), take pyrrole, add to the aramid nanofiber suspension, the mass ratio of pyrrole to aramid nanofibers in the aramid nanofiber suspension is 1:0.1-1:5, and magnetically stir in an ice-water bath to obtain a mixed suspension; 5) Take an aqueous solution of ferric chloride and add it to the mixed suspension obtained in step 4). The mass ratio of ferric chloride in the aqueous solution to pyrrole in the mixed suspension is 0.6:1-6:

1. Continue magnetic stirring in an ice-water bath for in-situ polymerization, filtration, washing, and dispersion in deionized water to achieve a solid content of 0.5-1.5 mg / mL, obtaining an aramid nanofiber@polypyrrole suspension; Preparation of S3 electrothermal film 6) Take another aramid nanofiber suspension obtained in step 3) and add it to the aramid nanofiber@polypyrrole suspension obtained in step 5). The mass ratio of aramid nanofibers in the rice fiber suspension to aramid nanofibers@polypyrrole in the polypyrrole suspension is 0.25:1-4:

1. The mixture is magnetically stirred, film-forming, and dried to obtain an aramid nanofiber & (aramid nanofiber@polypyrrole) composite film; 7) The aramid nanofiber & (aramid nanofiber@polypyrrole) composite film obtained in step 6) is immersed in a polyvinylidene fluoride organic solvent solution and polymerized at 80-100℃ for 5-10h to obtain a (aramid nanofiber & (aramid nanofiber@polypyrrole))@polyvinylidene fluoride electrothermal film.

2. The method for preparing the aramid fiber-based ultrathin electrothermal film according to claim 1, characterized in that: In step 6), the drying is carried out at 70-90℃ for 10-15 hours; preferably, in step 6), the film formation method is vacuum decompression filtration film formation; preferably, in step 6), the magnetic stirring time is 10-20 minutes.

3. The method for preparing the aramid fiber-based ultrathin electrothermal film according to claim 1, characterized in that: In step 7), the mass concentration of the polyvinylidene fluoride organic solvent solution is 2-10 mg / mL; preferably, in step 7), the organic solvent is any one of dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, and dimethyl sulfoxide; preferably, in step 7), the soaking time is 10-60 min.

4. The method for preparing the aramid fiber-based ultrathin electrothermal film according to claim 1, characterized in that: In step 5), the molar concentration of the ferric chloride aqueous solution is 1.5-2.0 mol / L; preferably, in step 5), the magnetic stirring time is 1-3 h.

5. The method for preparing the aramid fiber-based ultrathin electrothermal film according to claim 1, characterized in that: In step 4), the magnetic stirring time is 0.5-1.5 hours.

6. The method for preparing the aramid fiber-based ultrathin electrothermal film according to any one of claims 1-5, characterized in that: In step 3), a cell disruptor is used for enhanced dispersion, and the power of the cell disruptor is 125-1000W. Preferably, in step 3), the enhanced dispersion mode is to disrupt for 2 seconds, then pause for 3 seconds, process for 10 minutes, and repeat 3-5 times.

7. The method for preparing the aramid fiber-based ultrathin electrothermal film according to claim 1, characterized in that: In step 2), the deionized water washing is performed by adding deionized water, stirring at 500-700 r / min for 30-50 min, and centrifuging at 4000-8000 r / min for 3-7 min; preferably, in step 2), the deionized water washing is repeated 3-5 times; preferably, in step 2), the stirring is performed at room temperature at 500-700 r / min for 1-2 h, and the stirring is continued for 30-60 min.

8. The method for preparing the aramid fiber-based ultrathin electrothermal film according to claim 1, characterized in that: In step 1), stirring is carried out at room temperature, at a speed of 300-500 r / min, for a time of 0.5-1 h.

9. An electrothermal film, characterized in that: The electrothermal film is prepared by the method for preparing an aramid fiber-based ultrathin electrothermal film according to any one of claims 1-8, which is a (aramid nanofiber & (aramid nanofiber @ polypyrrole)) @ polyvinylidene fluoride electrothermal film.

10. The method for preparing the aramid fiber-based ultrathin electrothermal film according to claim 9, characterized in that: The thickness of the electrothermal film is 50-200µm.

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