Graphene-reinforced polyimide nanofiber membrane layer, preparation method thereof and application thereof in masks

Abstract

The application discloses a graphene reinforced polyimide nanofiber membrane layer and a preparation method and application thereof in a mask, and comprises the following steps: mixing a graphene suspension and a PAA solution, and then electrospinning and depositing to obtain a nanocellulose membrane, and then performing imidization reaction and hot pressing treatment to obtain the graphene reinforced polyimide nanofiber membrane layer. The application further discloses the graphene reinforced polyimide nanofiber membrane layer and the application thereof in the mask. The mask provided by the application can ensure high-performance protection and provide wearing comfort, and is very suitable for being used in extreme environments such as firefighting and emergency rescue, and industrial and daily protection scenes.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of medical product preparation, and particularly relates to a graphene-reinforced polyimide nanofiber membrane layer and a preparation method thereof and application thereof in a mask. BACKGROUND

[0002] As an important protective material, masks play a crucial role in the current public health environment. However, while the mask industry is rapidly developing, some technical problems have also been exposed. Most masks on the market currently use melt-blown cloth as the main filter material. Although the filter performance is good, under the pressure of rising raw material costs and supply chain tension, the quality compliance of some masks needs to be improved. In addition, there are still unqualified situations in terms of filter performance, microbial indicators, and respiratory resistance of masks, which are mainly related to unreasonable melt-blown cloth parameters, inadequate post-processing measures, and unreasonable mask structure design.

[0003] In the prior art, patent CN 111850777 A provides a preparation method of a polyimide fire-fighting fabric, which has good tensile breaking strength, anti-pilling performance, and flame retardant performance. However, the patent does not explicitly mention the waterproof performance of the fabric. In addition, since the fabric is woven by blending, the performance of the material may be affected by the degree of fiber mixing. Patent CN 113061286A provides a multifunctional flame-retardant polyimide aerogel with excellent mechanical properties and flame retardant properties, and has functions such as sensitive temperature sensing and piezoresistive sensing. However, the preparation method in this patent involves plasma treatment and the preparation of a two-dimensional thermoelectric nanomaterial dispersion liquid, which is relatively complex and may increase the cost of material preparation. In addition, the patent does not explicitly mention the application scenarios and service life of the material. SUMMARY

[0004] To solve the above technical problems, the application provides a graphene-reinforced polyimide nanofiber membrane layer and a preparation method thereof and application thereof in a mask.

[0005] To achieve the above-mentioned purposes, the application provides the following technical solutions.

[0006] A preparation method of a graphene-reinforced polyimide nanofiber membrane layer, comprising the following steps:

[0007] Mixing a graphene suspension and a polyamide acid (PAA) solution, electrospinning and depositing to obtain a nanocellulose membrane, and then performing imidization reaction and hot pressing treatment to obtain the graphene-reinforced polyimide nanofiber membrane layer.

[0008] Beneficial effects: The polyimide material in the application has high thermal stability, and the 5% thermal decomposition temperature is greater than or equal to 450 DEG C, which is suitable for high temperature environment, and the addition of graphene further improves the thermal conductivity of the material, ensures uniform heat distribution, prevents local overheating, and the graphene in the application can delay the thermal degradation process and improve the flame retardant effect, so that the obtained graphene reinforced polyimide nanofiber film layer has no melt drop in the high temperature combustion test, and the self-extinguishing time is less than 10 seconds, and the graphene reduces the static electricity accumulation, while ensuring the chemical stability and corrosion resistance of the composite film. Secondly, the graphene reinforced polyimide nanofiber film layer obtained by the application has a dense structure, which has waterproof performance and can prevent moisture from entering, and helps to maintain the comfort of the wearer, and the particulate matter filtration efficiency (PFE) is greater than 95%. The reinforcing effect of graphene increases the tensile strength of the material by about 62.2%, and the bending strength is increased by about 21.6%, and the ductility and wear resistance are significantly improved. In addition, the preparation method of electrospinning in the application makes the nanofiber film structure have nanoscale voids, which is waterproof while maintaining certain air permeability, which helps the wearer to breathe smoothly, and the respiratory resistance is less than 150 Pa, reducing the stuffy feeling.

[0009] Preferably, the mass ratio of the graphene suspension to the PAA solution is (1-2):10.

[0010] Preferably, the concentration of the graphene suspension is 5%; and / or,

[0011] The concentration of the PAA solution is 0.2 mol / L.

[0012] Beneficial effects: And the denseness of the nanofiber film easily leads to high respiratory resistance, and by reasonably controlling the composite ratio of graphene and polyimide, a particulate matter filtration efficiency (PFE) of greater than or equal to 95% is realized, and the respiratory resistance is controlled between 85-120 Pa, ensuring effective filtration and wearing comfort.

[0013] Preferably, the parameters of electrospinning are: voltage 15-25 kV, injection rate 0.2-0.5 mL / h, needle and collection plate distance 15-20 cm, environmental humidity 30-50%, temperature 20-25 DEG C.

[0014] Preferably, the imidization reaction is carried out under the condition of temperature rising heat treatment, which specifically includes the following steps: the first stage: from room temperature to 150 DEG C, and the temperature is kept for 1 hour (to remove residual solvent). The second stage: to 300 DEG C, and the temperature is kept for 2 hours (to promote the imidization reaction). The third stage: to 350 DEG C, and the temperature is kept for 1 hour (to complete the imidization reaction).

[0015] Preferably, the pressure of the hot pressing treatment is 0.5 MPa, the temperature is 200 DEG C, and the time is 10 min.

[0016] A graphene-reinforced polyimide nanofiber membrane.

[0017] Application of a graphene-reinforced polyimide nanofiber membrane in face masks.

[0018] A heat-insulating and fire-resistant ergonomic mask, comprising an outer waterproof layer, a core protective layer, and a skin-friendly inner layer stacked in sequence;

[0019] The core protective layer is the graphene-reinforced polyimide nanofiber membrane layer mentioned above.

[0020] Preferably, the outer waterproof layer is made of waterproof microfiber;

[0021] The skin-friendly inner layer is made of skin-friendly meltblown fabric.

[0022] Compared with the prior art, the present invention has the following advantages and technical effects:

[0023] This invention employs a nanostructure composite method, adding graphene sheets to polyimide nanofibers to create a composite nanofiber membrane. The graphene-reinforced polyimide nanofiber membrane integrates excellent properties such as high-temperature resistance, flame retardancy, waterproofing, and breathability, thereby improving the thermal stability and flame retardancy of the composite membrane. When used as the core protective layer of a mask, it allows the mask to withstand temperatures above 400°C, delaying material degradation and enhancing high-temperature protection performance. Furthermore, the addition of graphene improves the material's mechanical properties, giving the mask high tensile strength (60-70 MPa) and good toughness (8-12% elongation at break), improving durability and abrasion resistance, meeting long-term use requirements. The natural waterproof properties of polyimide combined with the surface hydrophobicity of graphene allow the mask to maintain its structure and filtration effect even in humid or liquid-exposed environments, making it suitable for protection needs in harsh environments. The mask provided by this invention offers both high-performance protection and wearing comfort, making it ideal for extreme environments such as firefighting and emergency rescue, as well as industrial and daily protective scenarios. Attached Figure Description

[0024] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0025] Figure 1 This is a schematic diagram of the synthesis process of the graphene-reinforced polyimide nanofiber membrane of the present invention;

[0026] Figure 2 This is a SEM image of the graphene-reinforced polyimide nanofiber membrane obtained in Example 1 of this invention;

[0027] Figure 3The contact angle of the graphene-reinforced polyimide nanofiber membrane layer obtained in Example 1 of the present application. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative labor fall within the protection scope of the present application.

[0029] In order to make the above objectives, characteristics and advantages of the present application more apparent and easy to understand, the present application will be further described in detail below with reference to the drawings and specific embodiments.

[0030] Unless otherwise specified, the raw materials in the embodiments of the present application are obtained by commercial purchase.

[0031] Among them, the waterproof superfine polyester fiber is purchased from Weifang Shuntai Textile Co., Ltd., the specification is 2.5D skin-friendly melt-blown cloth purchased from Dongguan Tuoyuan Composite Technology Co., Ltd., and the specification is 260mm pfe95 level melt-blown cloth.

[0032] Unless otherwise specified, room temperature or normal temperature in the embodiments of the present application refers to 25±3℃.

[0033] Example 1

[0034] A heat-insulating and fireproof ergonomic mask, comprising an outer waterproof layer, a core protective layer and a skin-friendly inner layer which are sequentially stacked;

[0035] Among them, the outer waterproof layer is waterproof superfine polyester fiber (dustproof and waterproof); the core protective layer is a graphene / polyimide composite film layer, which is a core waterproof, flame-retardant and high-temperature-resistant layer; and the skin-friendly inner layer is skin-friendly melt-blown cloth. Among them, as shown in the formula (I), the preparation method of the graphene / polyimide composite film layer comprises the following steps: Figure 1

[0036] (1) 5wt.% of graphene is added into N,N-dimethylacetamide (DMAC), and a high-pressure homogenizer (1500-2500MPa) is used for homogenization for 10 minutes to ensure uniform dispersion of the graphene sheet layer. After standing for 1 hour, a graphene suspension is obtained and is ready for use;

[0037] ​(2) 4.02 g (0.02 mol) of 4,4'-diaminodiphenyl ether (ODA) was dissolved in 100 mL of DMAC solvent, stirred until completely dissolved, then 4.36 g (0.02 mol) of pyromellitic dianhydride (PMDA) was gradually added to the solution (batch addition to prevent violent reaction), and stirred at room temperature (20-25°C) for 4 hours to form a transparent viscous polyamic acid (PAA) solution.

[0038] (3) At room temperature, the graphene dispersion solution was slowly added to the PAA solution at a proportion of 10 wt.%, stirred for 2 hours to make the graphene fully dispersed and uniformly composite with the PAA, and the PAA / graphene composite solution was loaded into a syringe, and the viscosity of the spinning solution was controlled between 800 mPa·s. The spinning solution was left to stand for 2 hours to remove the bubbles. The parameters of electrospinning were voltage: 15 kV, injection rate: 0.2 mL / h, distance between needle and collection plate: 15 cm, ambient humidity: 30%. The spinning solution was slowly pushed out by the injection pump, and under the action of high-voltage electrostatic field, the nanofiber was formed, and the nanofiber was randomly deposited on the collection plate to form a preliminary membrane structure, and a nanofiber membrane was obtained;

[0039] (4) The nanofiber membrane was placed in a vacuum drying oven and pre-dried at 80°C for 2 hours to remove the solvent, and then the temperature was raised in three stages, the first stage: from room temperature to 150°C, and kept for 1 hour (to remove residual solvent), the second stage: to 300°C, and kept for 2 hours (to promote imidization reaction), and the third stage: to 350°C, and kept for 1 hour, to complete the imidization and stabilize the membrane structure. The membrane was placed in a flat press, a pressure of 0.5 MPa was applied, and the temperature was kept at 200°C for 10 minutes to enhance the compactness and mechanical properties of the membrane, and a graphene-reinforced polyimide nanofiber membrane layer was obtained.

[0040] The graphene-reinforced polyimide nanofiber membrane layer obtained above was used as the core protective layer, waterproof superfine polyester fibers were added to the outer layer, and skin-friendly melt-blown cloth was added to the inner layer. The three layers were hot-pressed to ensure that they were tightly attached to the face, and embedded with a nose bridge metal strip and ear hangers, and a mask was obtained.

[0041] Figure 2 The SEM photo of the graphene-reinforced polyimide nanofiber membrane layer obtained in Example 1 shows that the fiber diameter is uniform, and the pore size distribution is uniform.

[0042] Figure 3 The contact angle of the graphene-reinforced polyimide nanofiber membrane layer obtained in Example 1 shows that the fiber membrane has good hydrophobicity.

[0043] Example 2

[0044] A heat-insulating and fireproof ergonomic mask comprises an outer waterproof layer, a core protective layer and a skin-friendly inner layer which are sequentially stacked;

[0045] The outer waterproof layer is waterproof superfine polyester fiber (dustproof and waterproof); the core protective layer is a graphene / polyimide composite film layer, which is a core waterproof, flame-retardant and high-temperature-resistant layer; and the skin-friendly inner layer is a skin-friendly melt-blown cloth. The preparation method of the graphene / polyimide composite film layer comprises the following steps:

[0046] (1) 5 wt.% of graphene is added to N,N-dimethylacetamide (DMAC), and a high-pressure homogenizer (1500-2500 MPa) is used for homogenization for 10 minutes to ensure uniform dispersion of graphene sheets, and a graphene suspension is obtained after standing for 1 hour, which is ready for use;

[0047] (2) 4.02 g (0.02 mol) of 4,4'-diamino diphenyl ether (ODA) is dissolved in 100 mL of DMAC solvent, and stirred until completely dissolved, then 4.36 g (0.02 mol) of pyromellitic dianhydride (PMDA) is gradually added to the solution (batch addition to prevent violent reaction), and stirred at room temperature (20-25℃) for 4 hours to form a transparent viscous polyamic acid (PAA) solution.

[0048] (3) The graphene dispersion is slowly added to the PAA solution at a proportion of 15 wt.% at room temperature, and stirred for 2 hours to allow the graphene to be fully dispersed and uniformly compounded with the PAA, and the PAA / graphene composite solution is loaded into a syringe, and the viscosity of the spinning solution is controlled between 1200 mPa·s. The spinning solution is left to stand for 2 hours to remove air bubbles. The parameters for electrospinning are voltage: 20 kV, injection rate: 0.3 mL / h, distance between needle and collection plate: 18 cm, and ambient humidity: 40%. The spinning solution is slowly pushed out by the injection pump, and under the action of a high-voltage electrostatic field, nanofibers are formed, and the nanofibers are randomly deposited on the collection plate to form a preliminary membrane structure, and a nanofiber membrane is obtained;

[0049] (4) The nanofiber membrane is placed in a vacuum drying oven and pre-dried at 80℃ for 2 hours to remove the solvent, and then subjected to three-stage temperature treatment, the first stage: from room temperature to 150℃, and kept for 1 hour (to remove residual solvent), the second stage: to 300℃, and kept for 2 hours (to promote imidization reaction), and the third stage: to 350℃, and kept for 1 hour, to complete the imidization and stabilize the membrane structure. The membrane is placed in a flat press, and a pressure of 0.5 MPa is applied, and kept at 200℃ for 10 minutes to enhance the compactness and mechanical properties of the membrane, and a graphene-reinforced polyimide nanofiber membrane layer is obtained.

[0050] The graphene reinforced polyimide nanofiber membrane layer is used as a core protective layer, waterproof superfine polyester fibers are added to an outer layer, and skin-friendly melt-blown cloth is added to an inner layer. The three layers are ensured to be tightly attached to a face by hot-pressing and embedded with a nose bridge metal strip and ear hooks, so as to obtain a mask.

[0051] Example 3

[0052] A heat-insulating and fireproof ergonomic mask includes an outer waterproof layer, a core protective layer, and a skin-friendly inner layer which are sequentially stacked;

[0053] The outer waterproof layer is waterproof superfine polyester fiber (dustproof and waterproof), the core protective layer is a graphene / polyimide composite membrane layer which is a core waterproof, flame-retardant and high-temperature-resistant layer, and the skin-friendly inner layer is skin-friendly melt-blown cloth. The preparation method of the graphene / polyimide composite membrane layer includes the following steps:

[0054] (1) 5 wt.% of graphene is added to N,N-dimethylacetamide (DMAC), and a high-pressure homogenizer (1500-2500 MPa) is used for homogenization for 10 minutes to ensure uniform dispersion of graphene sheets. After standing for 1 hour, a graphene suspension is obtained and is ready for use;

[0055] (2) 4.02 g (0.02 mol) of 4,4'-diaminodiphenyl ether (ODA) is dissolved in 100 mL of DMAC solvent, and stirred until completely dissolved. Then, 4.36 g (0.02 mol) of pyromellitic dianhydride (PMDA) is gradually added to the solution (in batches to prevent violent reaction), and stirred at room temperature (20-25°C) for 4 hours to form a transparent viscous polyamide acid (PAA) solution.

[0056] (3) At room temperature, the graphene dispersion is slowly added to the PAA solution at a proportion of 20 wt.%, and stirred for 2 hours to allow the graphene to be fully dispersed and uniformly compounded with the PAA. The PAA / graphene composite solution is loaded into a syringe, and the viscosity of the spinning solution is controlled between 1500 mPa·s. The spinning solution is left to stand for 2 hours to remove air bubbles. The parameters of electrospinning are voltage: 25 kV, injection rate: 0.5 mL / h, distance between needle and collection plate: 20 cm, and ambient humidity: 50%. The spinning solution is slowly pushed out by an injection pump under the action of a high-voltage electrostatic field to form nanofibers, which are randomly deposited on the collection plate to form a preliminary membrane structure, and a nanofiber membrane is obtained.

[0057] (4) The nanofiber membrane is placed in a vacuum drying oven and pre-dried at 80°C for 2 hours to remove the solvent, and then subjected to three-stage temperature rising heat treatment. The first stage is from room temperature to 150°C, and the temperature is kept for 1 hour (to remove residual solvent). The second stage is to rise to 300°C, and the temperature is kept for 2 hours (to promote imidization reaction). The third stage is to rise to 350°C, and the temperature is kept for 1 hour to complete the imidization and stabilize the membrane structure. The membrane is placed in a flat press, a pressure of 0.5 MPa is applied, and the temperature is kept at 200°C for 10 minutes to enhance the compactness and mechanical properties of the membrane, thereby obtaining a graphene-reinforced polyimide nanofiber membrane layer.

[0058] The graphene-reinforced polyimide nanofiber membrane layer is used as the core protective layer, and waterproof superfine polyester fibers are added to the outer layer, and skin-friendly melt-blown cloth is added to the inner layer. The three layers are tightly attached to the face through hot pressing, and the nose bridge metal strip and ear hook are embedded, thereby obtaining a mask.

[0059] Comparative Example 1

[0060] A mask includes an outer waterproof layer, a core protective layer, and a skin-friendly inner layer stacked in sequence.

[0061] The difference from Example 1 is that the core protective layer is a polyimide nanofiber membrane layer. The preparation method of the polyimide nanofiber membrane layer includes the following steps:

[0062] (1) 4.02 g (0.02 mol) of 4,4'-diaminodiphenyl ether (ODA) is dissolved in 100 mL of DMAC solvent, and stirred until completely dissolved. Then, 4.36 g (0.02 mol) of pyromellitic dianhydride (PMDA) is gradually added to the solution (added in batches to prevent violent reaction), and stirred at room temperature (20-25°C) for 4 hours to form a transparent viscous polyamic acid (PAA) solution.

[0063] (2) The PAA solution is loaded into a syringe at room temperature, and the viscosity of the spinning solution is controlled between 800 mPa·s. The spinning solution is left to stand for 2 hours to remove air bubbles. The electrospinning parameters are voltage: 15 kV, injection rate: 0.2 mL / h, needle-to-collection plate distance: 15 cm, and ambient humidity: 30. The spinning solution is slowly pushed out by a syringe pump, and nanofibers are formed under the action of a high-voltage electrostatic field. The nanofibers are randomly deposited on the collection plate to form a preliminary membrane structure, thereby obtaining a nanofiber membrane.

[0064] (3) The nanofiber membrane is placed in a vacuum drying oven and pre-dried at 80°C for 2 hours to remove the solvent, and then subjected to three-stage temperature treatment, the first stage: from room temperature to 150°C, 1 hour (to remove residual solvent), the second stage: to 300°C, 2 hours (to promote imidization reaction), the third stage: to 350°C, 1 hour, to complete the imidization and stabilize the membrane structure. The membrane is placed in a flat press, a pressure of 0.5 MPa is applied, and it is kept at 200°C for 10 minutes to enhance the compactness and mechanical properties of the membrane, i.e. a polyimide nanofiber membrane layer is obtained.

[0065] The above polyimide nanofiber membrane layer is used as the core protective layer, and waterproof superfine polyester fibers are added to the outer layer; skin-friendly melt-blown cloth is added to the inner layer. The three layers are ensured to be tightly attached to the face by hot pressing, and the nose bridge metal strip and ear hook are embedded, i.e. a mask is obtained.

[0066] Comparative Example 2

[0067] A mask, comprising an outer waterproof layer, a core protective layer and a skin-friendly inner layer which are sequentially stacked;

[0068] The outer waterproof layer is waterproof superfine polyester fiber (dustproof and waterproof); the core protective layer is a graphene / polyimide composite membrane layer, which is a core waterproof, flame-retardant and high-temperature-resistant layer; the skin-friendly inner layer is skin-friendly melt-blown cloth. The difference from Example 3 is only that the graphene / polyimide composite membrane layer is not prepared by electrospinning to obtain a nanofiber membrane, and the preparation method specifically includes the following steps:

[0069] (1) 5 wt.% of graphene is added to N,N-dimethylacetamide (DMAC), and a high-pressure homogenizer (1500-2500 MPa) is used for homogenization for 10 minutes to ensure uniform dispersion of the graphene sheets. After standing for 1 hour, a graphene suspension is obtained and is ready for use;

[0070] (2) 4.02 g (0.02 mol) of 4,4'-diaminodiphenyl ether (ODA) is dissolved in 100 mL of DMAC solvent, and stirred until completely dissolved. Then 4.36 g (0.02 mol) of pyromellitic dianhydride (PMDA) is gradually added to the solution (added in batches to prevent violent reaction), and stirred at room temperature (20-25°C) for 4 hours to form a transparent viscous polyamic acid (PAA) solution.

[0071] (3) The graphene dispersion is slowly added to the PAA solution at a proportion of 20 wt.%, and stirred for 2 hours to allow the graphene to be fully dispersed and uniformly compounded with the PAA, obtaining a PAA / graphene composite solution. After coating, a nanofiber membrane is obtained;

[0072] (4) The nanofiber membrane is placed in a vacuum drying oven and pre-dried at 80°C for 2 hours to remove the solvent, and then subjected to three-stage temperature rising heat treatment. The first stage is from room temperature to 150°C, and the temperature is kept for 1 hour (to remove residual solvent). The second stage is to rise to 300°C, and the temperature is kept for 2 hours (to promote imidization reaction). The third stage is to rise to 350°C, and the temperature is kept for 1 hour to complete the imidization and stabilize the membrane structure. The membrane is placed in a flat press, a pressure of 0.5 MPa is applied, and the temperature is kept at 200°C for 10 minutes to enhance the compactness and mechanical properties of the membrane, thereby obtaining a graphene-reinforced polyimide nanofiber membrane layer.

[0073] The graphene-reinforced polyimide nanofiber membrane layer is used as the core protective layer, and waterproof superfine polyester fibers are added to the outer layer, and skin-friendly melt-blown cloth is added to the inner layer. The three layers are tightly attached to the face through hot pressing, and the nose bridge metal strip and ear hook are embedded, thereby obtaining a mask.

[0074] Comparative Example 3

[0075] A mask includes an outer waterproof layer, a core protective layer, and a skin-friendly inner layer stacked in sequence.

[0076] The outer waterproof layer is waterproof superfine polyester fiber (dustproof and waterproof), the core protective layer is a graphene / polyimide composite membrane layer, which is a core waterproof, flame-retardant, and high-temperature-resistant layer, and the skin-friendly inner layer is skin-friendly melt-blown cloth. The difference from Example 3 is only that the imidization process in the preparation method of the graphene / polyimide composite membrane layer is different from that of Example 3, which specifically includes the following steps:

[0077] (1) 5 wt.% of graphene is added to N,N-dimethylacetamide (DMAC), and a high-pressure homogenizer (1500-2500 MPa) is used for homogenization for 10 minutes to ensure uniform dispersion of the graphene layers. After standing for 1 hour, a graphene suspension is obtained and reserved.

[0078] (2) 4.02 g (0.02 mol) of 4,4'-diaminodiphenyl ether (ODA) is dissolved in 100 mL of DMAC solvent, and stirred until completely dissolved. Then, 4.36 g (0.02 mol) of pyromellitic dianhydride (PMDA) is gradually added to the solution (batch addition to prevent violent reaction), and stirred at room temperature (20-25°C) for 4 hours to form a transparent viscous polyamide acid (PAA) solution.

[0079] (3) Slowly add the graphene dispersion liquid into the PAA solution at a proportion of 20 wt.%, stir for 2 hours to make the graphene fully dispersed and uniformly compounded with PAA, load the PAA / graphene composite solution into a syringe, and control the viscosity of the spinning solution between 800-1500 mPa·s. Let the spinning solution stand for 2 hours to remove the bubbles. The electrospinning parameters are voltage: 15-25 kV, injection rate: 0.2-0.5 mL / h, distance between needle and collection plate: 15-20 cm, ambient humidity: 30-50%, temperature: 20-25°C. Slowly push the spinning solution out through the syringe pump, and form nanofibers under the action of high-voltage electrostatic field. The nanofibers are randomly deposited on the collection plate to form a preliminary membrane structure, and a nanofiber membrane is obtained;

[0080] (4) Place the nanofiber membrane in a vacuum drying oven, and pre-dry at 80°C for 2 hours to remove the solvent. Then transfer the dried membrane to a programmable temperature oven, and heat to 150°C at a rate of 2-5°C / min, and keep for 1 hour. Continue to heat to 200°C, and keep for 10 minutes to complete the complete imidization reaction (PAA is converted to polyimide), and at the same time, remove the residual stress in the membrane through thermal stress, and stabilize the membrane structure. Place the membrane in a flat press, and apply a pressure of 0.5 MPa at 200°C for 10 minutes to enhance the compactness and mechanical properties of the membrane, and a graphene-reinforced polyimide nanofiber membrane layer is obtained.

[0081] Use the above graphene-reinforced polyimide nanofiber membrane layer as the core protective layer, add waterproof superfine polyester fibers to the outer layer, and add skin-friendly melt-blown cloth to the inner layer. Three layers are ensured to be tightly attached to the face through hot pressing, and a nose bridge metal strip and ear hangers are embedded, and a mask is obtained.

[0082] Technical effects:

[0083] 1. Detect the mechanical properties of the nanofiber membrane layer products obtained in Examples 1-3 and Comparative Examples 1 according to the GB / T 32610-2016 "Technical Specifications for Daily Protective Masks" standard, and the detection results are shown in Table 1:

[0084] Table 1 Mechanical properties of samples

[0085]

[0086] As can be seen from Table 1, the tensile properties, elongation at break and bending strength of Examples 1-3 are significantly higher than those of Comparative Examples 1-3, indicating that the addition of graphene has a good effect on improving the mechanical properties of the nanofiber membrane layer. Moreover, as can be seen from the comparison of Examples 1-3, the ratio of graphene to polyamic acid has a certain influence on the elongation at break and bending strength of the nanofiber membrane layer. When the ratio of graphene suspension to polyamic acid is 1:10, the elongation at break and bending strength of the nanofiber membrane layer are both optimal.

[0087] 2. The thermal properties of the nanofiber membrane layer products obtained in Examples 1-3 and Comparative Example 1 were detected according to the GB / T 30776-2014 standard, and the detection results are shown in Table 2:

[0088] Table 2 Thermal properties of samples

[0089] Sample 5% thermal decomposition temperature (°C) 10% thermal decomposition temperature (°C) Comparative Example 1 472 470 Comparative Example 2 365 395 Comparative Example 3 353 389 Example 1 448 566 Example 2 451 574 Example 3 417 490

[0090] As can be seen from Table 2, the nanofiber membrane layer doped with graphene (Examples 1-3) has no obvious change in 5% thermal decomposition temperature, but the 10% thermal decomposition temperature is significantly higher than that of Comparative Example 1 without doped graphene; the thermal decomposition temperature of Comparative Examples 2 and 3 and Examples 1-3 is significantly higher.

[0091] 3. The filtration performance of the products obtained in Examples 1-3 and Comparative Example 1 was detected according to the GB 2626-2019 “Respiratory Protective Products - Self-suction Filter Type Particulate Matter Respirator” standard, and the detection results are shown in Table 3:

[0092] Table 3 Filtration performance of samples

[0093]

[0094] As can be seen from Table 3, the nanofiber membrane layer doped with graphene (Examples 1-3) has a certain improvement in particulate matter filtration efficiency, and the respiratory resistance is significantly smaller than that of the nanofiber membrane layer of Comparative Examples 1-3 without doped graphene; it shows that the nanofiber membrane layer prepared in Examples 1-3 has excellent filtration effect and high wearing comfort.

[0095] The above is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of changes or replacements within the technical scope disclosed in the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for preparing a graphene-reinforced polyimide nanofiber membrane layer for a face mask, characterized by, The method comprises the following steps: The graphene suspension and the polyamide acid solution are mixed and electrospun and deposited to obtain a nanocellulose film, and then the nanocellulose film is subjected to an imidization reaction and hot-pressing treatment to obtain the graphene-reinforced polyimide nanofiber film layer. The mass ratio of the graphene suspension to the polyamide acid solution is (1-2):

10. The concentration of the graphene suspension is 5%; and / or The concentration of the polyamide acid solution is 0.2 mol / L.

2. The method for preparing a graphene-reinforced polyimide nanofiber membrane for face masks according to claim 1, characterized in that, The electrospinning parameters are as follows: voltage 15-25 kV, injection rate 0.2-0.5 mL / h, distance between the needle and the collection plate 15-20 cm, ambient humidity 30-50%, and temperature 20-25℃.

3. The method for preparing a graphene-reinforced polyimide nanofiber membrane for face masks according to claim 1, characterized in that, The imidization reaction is performed under a temperature rising hot treatment condition, and specifically comprises the following steps: first stage: from room temperature to 150℃, and holding for 1 hour; second stage: rising to 300℃, and holding for 2 hours; third stage: rising to 350℃, and holding for 1 hour.

4. The method for preparing a graphene-reinforced polyimide nanofiber membrane for face masks according to claim 1, characterized in that, The hot-pressing treatment pressure is 0.5 MPa, the temperature is 200℃, and the time is 10 min.

5. A graphene-reinforced polyimide nanofiber film layer prepared by the preparation method in any one of claims 1-4.

6. Application of the graphene-reinforced polyimide nanofiber film layer in claim 5 to a mask.

7. A thermally and fire insulating ergonomic mask, characterized in that, The mask comprises an outer waterproof layer, a core protective layer, and a skin-friendly inner layer which are sequentially stacked; The core protective layer is the graphene-reinforced polyimide nanofiber film layer in claim 5.

8. A thermally and fire insulated ergonomic face mask according to claim 7, characterized in that, The outer waterproof layer is waterproof superfine polyester fiber. The skin-friendly inner layer is a skin-friendly melt-blown fabric.

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