Graphene reinforced polyimide nanofiber membrane layer, preparation method thereof and application of graphene reinforced polyimide nanofiber membrane layer in mask

Abstract

The invention discloses a graphene reinforced polyimide nanofiber membrane layer and a preparation method and application thereof in a mask, and the preparation method comprises the following steps: mixing a graphene suspension and a PAA solution, then carrying out electrostatic spinning and deposition to obtain a nanocellulose membrane, and then carrying out imidization reaction and hot pressing treatment to obtain the graphene reinforced polyimide nanofiber membrane layer. The graphene reinforced polyimide nanofiber membrane layer is obtained. The invention further discloses the graphene reinforced polyimide nanofiber membrane layer and application of the graphene reinforced polyimide nanofiber membrane layer in masks. The mask provided by the invention can provide wearing comfort while ensuring high-performance protection, and is very suitable for extreme environments such as fire fighting, emergency rescue and the like, and industrial and daily protection scenes.

Description

Technical Field

[0001] The present invention belongs to the technical field of medical product preparation, and in particular relates to a graphene-enhanced polyimide nanofiber membrane layer, a preparation method thereof, and an application of the same in a mask. Background Art

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

[0003] In the prior art, patent CN 111850777 A provides a method for preparing a polyimide fire-fighting fabric, which has good tensile strength at break, pilling resistance and flame retardant properties. However, the patent does not explicitly mention the waterproof performance of the fabric. In addition, since the fabric adopts a blended textile manufacturing method, the performance of the material may be affected by the degree of fiber mixing. The multifunctional flame-retardant polyimide aerogel provided by patent CN 113061286A has excellent mechanical properties and flame retardant properties, and has sensitive temperature sensing, piezoresistive sensing and other functions. However, the preparation method in the patent involves plasma treatment and the preparation of a two-dimensional thermoelectric nanomaterial dispersion, and the process is relatively complicated, which may increase the preparation cost of the material. In addition, the patent does not clearly explain the application scenarios of the aerogel and the service life of the material. Summary of the invention

[0004] In order to solve the above technical problems, the present invention proposes a graphene-reinforced polyimide nanofiber membrane layer, a preparation method thereof, and an application thereof in a mask.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A method for preparing a graphene-enhanced polyimide nanofiber film layer comprises the following steps:

[0007] The graphene suspension is mixed with a polyamic acid (PAA) solution, and then subjected to electrostatic spinning and deposition to obtain a nanocellulose membrane, which is then subjected to imidization reaction and hot pressing to obtain the graphene-reinforced polyimide nanofiber membrane layer.

[0008] Beneficial effects: The polyimide material in the present invention has high thermal stability, 5% thermal decomposition temperature ≥ 450°C, and is suitable for high temperature environments. The addition of graphene further improves the thermal conductivity of the material, ensures uniform heat distribution, and prevents local overheating. Moreover, the graphene in the present invention, as a free radical scavenger, can delay the thermal degradation process and improve the flame retardant effect, so that the obtained graphene-enhanced polyimide nanofiber film layer has no droplets in the high temperature combustion test, and the self-extinguishing time is less than 10 seconds. At the same time, graphene reduces static electricity accumulation and ensures the chemical stability and corrosion resistance of the composite film. Secondly, the graphene-enhanced polyimide nanofiber film layer obtained by the present invention has a dense structure, which makes it waterproof and can prevent moisture from entering, which helps to maintain the comfort of the wearer, and the particle filtration efficiency (PFE) is greater than 95%. The enhancement effect of graphene increases the tensile strength of the material by about 62.2%, the bending strength by about 21.6%, and the ductility and wear resistance are significantly improved. In addition, the present invention utilizes an electrospinning preparation method to make the nanofiber membrane structure have nanometer-scale gaps, which maintains a certain degree of air permeability while being waterproof, helping the wearer to breathe smoothly, with a breathing resistance of less than 150Pa, reducing the feeling of stuffiness.

[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: The density of the nanofiber membrane easily leads to high breathing resistance. By reasonably controlling the composite ratio of graphene and polyimide, a particle filtration efficiency (PFE) of ≥95% is achieved, while the breathing resistance is controlled between 85-120Pa, ensuring effective filtration and wearing comfort.

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

[0014] Preferably, the imidization reaction is carried out under the condition of temperature-raising heat treatment, specifically comprising the following steps: the first stage: raising the temperature from room temperature to 150° C. and keeping the temperature for 1 hour (removing residual solvent). The second stage: raising the temperature to 300° C. and keeping the temperature for 2 hours (promoting the imidization reaction). The third stage: raising the temperature to 350° C. and keeping the temperature for 1 hour (completing the imidization reaction).

[0015] Preferably, the heat pressing treatment is performed at a pressure of 0.5 MPa, a temperature of 200° C., and a time of 10 min.

[0016] A graphene-reinforced polyimide nanofiber membrane layer.

[0017] Application of a graphene-reinforced polyimide nanofiber membrane layer in a mask.

[0018] A heat-insulating and fire-proof 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 above-mentioned graphene-reinforced polyimide nanofiber membrane layer.

[0020] Preferably, the outer waterproof layer is waterproof ultra-fine polyester fiber;

[0021] The skin-friendly inner layer is a skin-friendly meltblown cloth.

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

[0023] The present invention adopts a nanostructure composite method to add graphene sheets to polyimide nanofibers to make a composite nanofiber membrane, wherein the graphene-enhanced polyimide nanofiber membrane layer integrates excellent properties such as high temperature resistance, flame retardancy, waterproofness, and breathability, thereby improving the thermal stability and flame retardancy of the composite membrane, and using it for the core protective layer of the mask, so that the mask can withstand high temperatures above 400°C, delay material degradation, and improve high temperature protection performance. In addition, the addition of graphene improves the mechanical properties of the material, so that the mask has high tensile strength (60-70MPa) and good toughness (8-12% elongation at break), improves durability and wear resistance, and meets long-term use requirements. The natural waterproof properties of polyimide combined with the surface hydrophobicity of graphene enable the mask to maintain its structure and filtering effect when it is wet or exposed to liquid environments, and is suitable for protection needs in harsh environments. The mask provided by the present invention can provide wearing comfort while ensuring high-performance protection, and is very suitable for extreme environments such as firefighting, emergency rescue, and industrial and daily protection scenes. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0025] Figure 1 Schematic diagram of the synthesis process of the graphene-enhanced polyimide nanofiber membrane of the present invention;

[0026] Figure 2 This is a SEM photo of the graphene-enhanced polyimide nanofiber membrane layer obtained in Example 1 of the present invention;

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

[0028] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0030] Unless otherwise specified, the raw materials in the examples of the present invention were purchased from commercial sources;

[0031] Among them, the waterproof ultra-fine polyester fiber was purchased from Weifang Shuntai Textile Co., Ltd., with the specification of 2.5D skin-friendly meltblown cloth, and the specification of 260mm pfe95 grade meltblown cloth was purchased from Dongguan Tuoyuan Composite Technology Co., Ltd.

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

[0033] Example 1

[0034] A heat-insulating and fire-proof ergonomic mask, comprising an outer waterproof layer, a core protective layer and a skin-friendly inner layer stacked in sequence;

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

[0036] (1) adding 5 wt.% of graphene to N,N-dimethylacetamide (DMAC), homogenizing for 10 minutes using a high-pressure homogenizer (1500-2500 MPa) to ensure that the graphene sheets are evenly dispersed, and leaving the mixture to stand for 1 hour to obtain a graphene suspension for later use;

[0037] (2) 4.02 g (0.02 mol) of 4,4'-diaminodiphenyl ether (ODA) was dissolved in 100 mL of DMAC solvent and stirred until completely dissolved. Then 4.36 g (0.02 mol) of pyromellitic dianhydride (PMDA) was 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 polyamic acid (PAA) solution.

[0038] (3) At room temperature, slowly add the graphene dispersion at a ratio of 10wt.% to the PAA solution and stir for 2 hours to fully disperse the graphene and evenly compound with PAA. Load the PAA / graphene composite solution into a syringe and control the viscosity of the spinning solution to be between 800mPa·s. Let the spinning solution stand for 2 hours to remove bubbles. The parameters of electrospinning are voltage: 15kV, injection rate: 0.2mL / h, distance between needle and collecting plate: 15cm, and ambient humidity: 30%. The spinning solution is slowly pushed out through a syringe pump to form nanofibers under the action of a high-voltage electrostatic field. The nanofibers are randomly deposited on the collecting plate to form a preliminary membrane structure to obtain a nanofiber membrane;

[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 subjected to a three-stage heating treatment: the first stage: from room temperature to 150°C, and kept warm for 1 hour (to remove the residual solvent); the second stage: raised to 300°C, and kept warm for 2 hours (to promote imidization reaction); the third stage: raised to 350°C, and kept warm for 1 hour to complete imidization and stabilize the membrane structure. The membrane was placed in a flat press, a pressure of 0.5 MPa was applied, and the membrane was kept warm 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.

[0040] The above graphene-enhanced polyimide nanofiber membrane layer is used as the core protective layer, and waterproof ultra-fine polyester fiber is added to the outer layer; the skin-friendly melt-blown cloth is added to the inner layer. The three layers are formed by hot pressing to ensure that they fit the face tightly, and the metal strip of the nose bridge and the ear hooks are embedded to obtain the mask.

[0041] Figure 2 This is a SEM photo of the graphene-enhanced polyimide nanofiber membrane layer obtained in Example 1 of the present invention, from which it can be seen that the fiber diameter is uniform and the pore size distribution is uniform;

[0042] Figure 3 This is the contact angle of the graphene-reinforced polyimide nanofiber membrane layer obtained in Example 1 of the present invention. It can be seen that the fiber membrane has good hydrophobicity.

[0043] Example 2

[0044] A heat-insulating and fire-proof ergonomic mask, comprising an outer waterproof layer, a core protective layer and a skin-friendly inner layer stacked in sequence;

[0045] The outer waterproof layer is waterproof ultrafine 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; the skin-friendly inner layer is a skin-friendly melt-blown cloth. The preparation method of the graphene / polyimide composite film layer includes the following steps:

[0046] (1) adding 5 wt.% of graphene to N,N-dimethylacetamide (DMAC), homogenizing for 10 minutes using a high-pressure homogenizer (1500-2500 MPa) to ensure that the graphene sheets are evenly dispersed, and leaving the mixture to stand for 1 hour to obtain a graphene suspension for later use;

[0047] (2) 4.02 g (0.02 mol) of 4,4'-diaminodiphenyl ether (ODA) was dissolved in 100 mL of DMAC solvent and stirred until completely dissolved. Then 4.36 g (0.02 mol) of pyromellitic dianhydride (PMDA) was 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 polyamic acid (PAA) solution.

[0048] (3) Slowly add the graphene dispersion at a ratio of 15wt.% to the PAA solution at room temperature and stir for 2 hours to fully disperse the graphene and evenly compound with PAA. Load the PAA / graphene composite solution into a syringe and control the viscosity of the spinning solution to be between 1200mPa·s. Let the spinning solution stand for 2 hours to remove bubbles. The parameters of electrospinning are voltage: 20kV, injection rate: 0.3mL / h, distance between needle and collecting plate: 18cm, and ambient humidity: 40%. The spinning solution is slowly pushed out through a syringe pump to form nanofibers under the action of a high-voltage electrostatic field. The nanofibers are randomly deposited on the collecting plate to form a preliminary membrane structure to obtain a nanofiber membrane;

[0049] (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 subjected to a three-stage heating treatment: the first stage: from room temperature to 150°C, and kept warm for 1 hour (to remove the residual solvent); the second stage: raised to 300°C, and kept warm for 2 hours (to promote imidization reaction); the third stage: raised to 350°C, and kept warm for 1 hour to complete imidization and stabilize the membrane structure. The membrane was placed in a flat press, a pressure of 0.5 MPa was applied, and the membrane was kept warm 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.

[0050] The above graphene-enhanced polyimide nanofiber membrane layer is used as the core protective layer, and waterproof ultra-fine polyester fiber is added to the outer layer; the skin-friendly melt-blown cloth is added to the inner layer. The three layers are formed by hot pressing to ensure that they fit the face tightly, and the metal strip of the nose bridge and the ear hooks are embedded to obtain the mask.

[0051] Example 3

[0052] A heat-insulating and fire-proof ergonomic mask, comprising an outer waterproof layer, a core protective layer and a skin-friendly inner layer stacked in sequence;

[0053] The outer waterproof layer is waterproof ultrafine 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; the skin-friendly inner layer is a skin-friendly melt-blown cloth. The preparation method of the graphene / polyimide composite film layer includes the following steps:

[0054] (1) adding 5 wt.% of graphene to N,N-dimethylacetamide (DMAC), homogenizing for 10 minutes using a high-pressure homogenizer (1500-2500 MPa) to ensure that the graphene sheets are evenly dispersed, and leaving the mixture to stand for 1 hour to obtain a graphene suspension for later use;

[0055] (2) 4.02 g (0.02 mol) of 4,4'-diaminodiphenyl ether (ODA) was dissolved in 100 mL of DMAC solvent and stirred until completely dissolved. Then 4.36 g (0.02 mol) of pyromellitic dianhydride (PMDA) was 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 polyamic acid (PAA) solution.

[0056] (3) At room temperature, slowly add the graphene dispersion at a ratio of 20wt.% to the PAA solution and stir for 2 hours to fully disperse the graphene and evenly compound with PAA. Load the PAA / graphene composite solution into a syringe and control the viscosity of the spinning solution to be between 1500mPa·s. Let the spinning solution stand for 2 hours to remove bubbles. The parameters of electrospinning are voltage: 25kV, injection rate: 0.5mL / h, distance between needle and collecting plate: 20cm, and ambient humidity: 50%. The spinning solution is slowly pushed out through a syringe pump to form nanofibers under the action of a high-voltage electrostatic field. The nanofibers are randomly deposited on the collecting plate to form a preliminary membrane structure to obtain a nanofiber membrane;

[0057] (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 subjected to a three-stage heating treatment: the first stage: from room temperature to 150°C, and kept warm for 1 hour (to remove the residual solvent); the second stage: raised to 300°C, and kept warm for 2 hours (to promote imidization reaction); the third stage: raised to 350°C, and kept warm for 1 hour to complete imidization and stabilize the membrane structure. The membrane was placed in a flat press, a pressure of 0.5 MPa was applied, and the membrane was kept warm 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 above graphene-enhanced polyimide nanofiber membrane layer is used as the core protective layer, and waterproof ultra-fine polyester fiber is added to the outer layer; the skin-friendly melt-blown cloth is added to the inner layer. The three layers are formed by hot pressing to ensure that they fit the face tightly, and the metal strip of the nose bridge and the ear hooks are embedded to obtain the mask.

[0059] Comparative Example 1

[0060] A mask comprises an outer waterproof layer, a core protective layer and a skin-friendly inner layer which are 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 comprises the following steps:

[0062] (1) 4.02 g (0.02 mol) of 4,4'-diaminodiphenyl ether (ODA) was dissolved in 100 mL of DMAC solvent and stirred until completely dissolved. Then 4.36 g (0.02 mol) of pyromellitic dianhydride (PMDA) was 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 and viscous polyamic acid (PAA) solution.

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

[0064] (3) 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 subjected to a three-stage heating treatment: the first stage: from room temperature to 150°C, and kept warm for 1 hour (to remove residual solvent); the second stage: raised to 300°C, and kept warm for 2 hours (to promote imidization reaction); the third stage: raised to 350°C, and kept warm for 1 hour to complete imidization and stabilize the membrane structure. The membrane was placed in a flat press, a pressure of 0.5 MPa was applied, and the membrane was kept warm at 200°C for 10 minutes to enhance the compactness and mechanical properties of the membrane, thereby obtaining a polyimide nanofiber membrane layer.

[0065] The above-mentioned polyimide nanofiber membrane layer is used as the core protective layer, and waterproof ultra-fine polyester fiber is added to the outer layer; the skin-friendly melt-blown cloth is added to the inner layer. The three layers are formed by hot pressing to ensure that they fit the face tightly, and the metal strip of the nose bridge and the ear hooks are embedded to obtain the mask.

[0066] Comparative Example 2

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

[0068] The outer waterproof layer is waterproof ultrafine 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; the skin-friendly inner layer is a skin-friendly meltblown cloth. The only difference from Example 3 is that in the preparation method of the graphene / polyimide composite film layer, electrospinning is not used to obtain the nanofiber membrane, and the steps are specifically included:

[0069] (1) adding 5 wt.% of graphene to N,N-dimethylacetamide (DMAC), homogenizing for 10 minutes using a high-pressure homogenizer (1500-2500 MPa) to ensure that the graphene sheets are evenly dispersed, and leaving the mixture to stand for 1 hour to obtain a graphene suspension for later use;

[0070] (2) 4.02 g (0.02 mol) of 4,4'-diaminodiphenyl ether (ODA) was dissolved in 100 mL of DMAC solvent and stirred until completely dissolved. Then 4.36 g (0.02 mol) of pyromellitic dianhydride (PMDA) was 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 polyamic acid (PAA) solution.

[0071] (3) slowly adding the graphene dispersion into the PAA solution at a ratio of 20 wt.%, stirring for 2 hours to fully disperse the graphene and uniformly compound with the PAA to obtain a PAA / graphene composite solution, and after coating, obtaining a nanofiber membrane;

[0072] (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 subjected to a three-stage heating treatment: the first stage: from room temperature to 150°C, and kept warm for 1 hour (to remove the residual solvent); the second stage: raised to 300°C, and kept warm for 2 hours (to promote imidization reaction); the third stage: raised to 350°C, and kept warm for 1 hour to complete imidization and stabilize the membrane structure. The membrane was placed in a flat press, a pressure of 0.5 MPa was applied, and the membrane was kept warm 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 above graphene-enhanced polyimide nanofiber membrane layer is used as the core protective layer, and waterproof ultra-fine polyester fiber is added to the outer layer; the skin-friendly melt-blown cloth is added to the inner layer. The three layers are formed by hot pressing to ensure that they fit the face tightly, and the metal strip of the nose bridge and the ear hooks are embedded to obtain the mask.

[0074] Comparative Example 3

[0075] A mask comprises an outer waterproof layer, a core protective layer and a skin-friendly inner layer which are stacked in sequence;

[0076] The outer waterproof layer is waterproof ultrafine 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; the skin-friendly inner layer is a skin-friendly meltblown cloth. The only difference from Example 3 is that in the preparation method of the graphene / polyimide composite film layer, the imidization process is different from that of Example 3, and specifically includes the following steps:

[0077] (1) adding 5 wt.% of graphene to N,N-dimethylacetamide (DMAC), homogenizing for 10 minutes using a high-pressure homogenizer (1500-2500 MPa) to ensure that the graphene sheets are evenly dispersed, and leaving the mixture to stand for 1 hour to obtain a graphene suspension for later use;

[0078] (2) 4.02 g (0.02 mol) of 4,4'-diaminodiphenyl ether (ODA) was dissolved in 100 mL of DMAC solvent and stirred until completely dissolved. Then 4.36 g (0.02 mol) of pyromellitic dianhydride (PMDA) was 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 polyamic acid (PAA) solution.

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

[0080] (4) The nanofiber membrane is placed in a vacuum drying oven and pre-dried at 80°C for 2 hours to remove the solvent. The dried membrane is then transferred to a programmable temperature-controlled oven and heated to 150°C at a rate of 2-5°C / min and kept warm for 1 hour. The temperature is then raised to 200°C and kept warm for 10 minutes to complete the imidization reaction (PAA is converted into polyimide). At the same time, the residual stress in the membrane is eliminated through thermal stress and the membrane structure is stabilized. The membrane is placed in a flat press, a pressure of 0.5MPa is applied, and the membrane is kept warm at 200°C for 10 minutes to enhance the density and mechanical properties of the membrane, thereby obtaining a graphene-reinforced polyimide nanofiber membrane layer.

[0081] The above graphene-enhanced polyimide nanofiber membrane layer is used as the core protective layer, and waterproof ultra-fine polyester fiber is added to the outer layer; the skin-friendly melt-blown cloth is added to the inner layer. The three layers are formed by hot pressing to ensure that they fit the face tightly, and the metal strip of the nose bridge and the ear hooks are embedded to obtain the mask.

[0082] Technical effects:

[0083] 1. According to GB / T 32610-2016 Technical Specifications for Daily Protective Masks, the mechanical properties of the nanofiber membrane products obtained in Examples 1-3 and Comparative Example 1 were tested, and the test results are shown in Table 1:

[0084] Table 1 Mechanical properties of samples

[0085]

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

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

[0088] Table 2 Thermal properties of samples

[0089] sample 5% thermal decomposition temperature (℃) 10% thermal decomposition temperature (℃) 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] It can be seen from Table 2 that although the 5% thermal decomposition temperature of the graphene-doped nanofiber membrane layer (Examples 1 to 3) has no obvious change, the 10% thermal decomposition temperature is significantly higher than that of the comparative example 1 without graphene doping; for comparative examples 2 and 3, the thermal decomposition temperatures of examples 1 to 3 are significantly higher.

[0091] 3. According to GB 2626-2019 "Respiratory Protective Equipment - Self-priming Filter-type Anti-particulate Respirator" standard, the filtration performance of the products obtained in Examples 1-3 and Comparative Example 1 was tested, and the test results are shown in Table 3:

[0092] Table 3 Filtration performance of samples

[0093]

[0094] It can be seen from Table 3 that the filtration efficiency of particulate matter in the nanofiber membrane layer doped with graphene (Examples 1 to 3) is improved to a certain extent, and the breathing resistance is significantly smaller than that of the nanofiber membrane layer of Comparative Examples 1 to 3 without graphene addition; this indicates that the nanofiber membrane layer prepared in Examples 1 to 3 has excellent filtration effect and high wearing comfort.

[0095] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A method for preparing a graphene-enhanced polyimide nanofiber film layer, characterized in that: The following steps are involved: The graphene suspension is mixed with the polyamic acid solution, and then electrostatic spinning and deposition are performed to obtain a nanocellulose membrane, which is then subjected to imidization reaction and hot pressing treatment to obtain the graphene-reinforced polyimide nanofiber membrane layer.

2. The method for preparing a graphene-enhanced polyimide nanofiber film layer according to claim 1, characterized in that: The mass ratio of the graphene suspension to the polyamic acid solution is (1-2):

10.

3. The method for preparing a graphene-enhanced polyimide nanofiber film layer according to claim 2, characterized in that: The concentration of the graphene suspension is 5%; and / or, The concentration of the polyamic acid solution is 0.2 mol / L.

4. The method for preparing a graphene-enhanced polyimide nanofiber film layer according to claim 1, characterized in that: The parameters of the electrospinning are: voltage 15-25 kV, injection rate 0.2-0.5 mL / h, distance between the needle and the collecting plate 15-20 cm, ambient humidity 30-50%, and temperature 20-25° C.

5. The method for preparing a graphene-enhanced polyimide nanofiber film layer according to claim 1, characterized in that: The imidization reaction is carried out under the condition of temperature-raising heat treatment, and specifically includes the following steps: the first stage: raising the temperature from room temperature to 150° C. and keeping it warm for 1 hour; the second stage: raising the temperature to 300° C. and keeping it warm for 2 hours; the third stage: raising the temperature to 350° C. and keeping it warm for 1 hour.

6. The method for preparing a graphene-enhanced polyimide nanofiber film layer according to claim 1, characterized in that: The heat pressing treatment was performed at a pressure of 0.5 MPa, a temperature of 200° C., and a time of 10 min.

7. A graphene-reinforced polyimide nanofiber membrane layer prepared by the preparation method according to any one of claims 1 to 6.

8. Use of a graphene-enhanced polyimide nanofiber membrane layer as claimed in claim 7 in a mask.

9. A heat-insulating and fire-proof ergonomic mask, characterized in that: It includes an outer waterproof layer, a core protective layer and a skin-friendly inner layer stacked in sequence; The core protective layer is the graphene-reinforced polyimide nanofiber membrane layer described in claim 7.

10. The heat-insulating and fire-proof ergonomic mask according to claim 9, characterized in that: The outer waterproof layer is waterproof ultra-fine polyester fiber; The skin-friendly inner layer is a skin-friendly meltblown cloth.

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