Protective masks with synergistic cooling functions of radiation and evaporation and their preparation method

Abstract

This invention discloses a protective mask with synergistic cooling functions of radiation and evaporation, and its preparation method. The mask consists of inner and outer functional support layers and a core filter layer. The inner and outer functional support layers are made of polylactic acid (PLA) spunbond nonwoven material and spunlace nonwoven material, respectively. The core filter layer is an electrospun Janus PLA micro / nanofiber membrane with unidirectional moisture-wicking function. The core filter layer is composed of a hydrophobic PLA fiber layer and a hydrophilic modified PLA@PEO fiber layer, forming an inner and outer hydrophobic gradient to achieve rapid unidirectional moisture transfer from the inside to the outside and moisture evaporation cooling. In addition, the protective mask utilizes the high infrared emissivity of PLA material and the strong solar reflection characteristics of the electrospun micro / nanofiber structure to achieve radiative cooling. This invention can achieve synergistic cooling effects of radiation and evaporation while ensuring high filtration efficiency and particulate matter protection, improving thermal and humidity comfort when wearing the protective mask for extended periods.

Description

Technical Field

[0001] This invention relates to the field of nonwoven filtration protection, specifically to a protective mask with synergistic cooling functions of radiation and evaporation and its preparation method. Background Technology

[0002] With the development of industrialization and the frequent occurrence of respiratory infectious diseases, filtering protective masks have become essential daily protective equipment. Compared with traditional meltblown and spunbond materials, electrospun micro-nano fibers have become an emerging core filter layer material due to their high porosity and high filtration efficiency. However, most masks using this material as the core layer cannot achieve radiative cooling when used outdoors, under direct sunlight, or in high-temperature environments; and as wearing time increases, the condensation inside the mask cannot escape, exacerbating the wearer's stuffiness and discomfort. In addition, sweat retention can easily cause skin irritation or bacterial growth, further affecting the wearing experience.

[0003] While current masks on the market have improved in filtration efficiency, they still fall short in terms of thermal and moisture comfort. For example, ordinary meltblown nonwoven materials have poor moisture wicking properties; and while some masks that achieve cooling by adding cooling materials can produce a temporary cooling sensation, they lack the ability to coordinate and regulate long-term radiative cooling and moisture management.

[0004] Therefore, to overcome the aforementioned shortcomings and meet the diverse needs of the public for thermal and humidity comfort in masks, it is essential to develop a filter material that integrates radiative cooling and unidirectional moisture conduction. The filter-protective mask proposed in this invention achieves passive cooling through a composite functional layer design, combining materials with high solar reflectivity and high-to-medium infrared emissivity. Simultaneously, it utilizes the hydrophilicity-hydrophobicity gradient of the Janus structure to form moisture transport channels, allowing internal moisture to be rapidly and unidirectionally expelled. Thus, while ensuring highly efficient filtration, it significantly improves thermal and humidity comfort, which is of great significance for enhancing the wearing experience of masks and expanding their applicable scenarios. Summary of the Invention

[0005] The purpose of this invention is to provide a filtering protective mask with synergistic cooling functions of radiation and evaporation. This mask achieves a synergistic effect of passive radiative heat dissipation and unidirectional liquid water transport by constructing a Janus PLA micro / nanofiber filter layer with a wettability gradient in situ on a nonwoven substrate, aiming to significantly improve thermal and humidity comfort under high filtration protection levels.

[0006] This invention provides a protective mask with synergistic cooling functions of radiation and evaporation, comprising a supporting inner layer, a filter layer, and a supporting outer layer connected sequentially from the inside out; the filter layer is an electrospun Janus PLA micro / nanofiber membrane with unidirectional moisture-wicking properties, the electrospun Janus PLA micro / nanofiber membrane comprising a hydrophobic inner layer and a hydrophilic outer layer connected sequentially from the inside out; the thickness ratio of the hydrophilic outer layer to the hydrophobic outer layer ranges from 1:1 to 3:1.

[0007] Preferably, the thickness ratio of the hydrophilic outer layer to the hydrophobic outer layer is 2:1.

[0008] Furthermore, the hydrophobic inner layer is a hydrophobic PLA layer, and the hydrophilic outer layer is a hydrophilic modified PLA@PEO layer.

[0009] Furthermore, the inner support layer comprises a spunbond nonwoven material, and the outer support layer comprises a spunlace nonwoven material; the fiber material of the inner support layer is PLA with a basis weight of 20-40 g / m2; the fiber material of the outer support layer is cotton or silk with a basis weight of 30-60 g / m2.

[0010] Another aspect of the present invention provides a method for preparing a protective mask, comprising the following steps: S1. Preparation of hydrophobic PLA spinning solution: PLA polymer is dissolved in a composite organic solvent and mixed evenly by stirring to obtain hydrophobic PLA spinning solutions with two set concentrations; S2. Preparation of hydrophilic modified PLA@PEO spinning solution: PLA polymer is dissolved in a composite organic solvent, hydrophilic modified polymer is added sequentially, and the mixture is stirred and mixed evenly to obtain hydrophilic modified PLA@PEO spinning solutions with two set concentrations; S3. Preparation of Janus PLA micro / nanofiber membrane by electrospinning: The hydrophobic PLA spinning solution of two concentrations obtained in S1 was electrospun through a double needle device to form a hydrophobic fiber layer; then, the hydrophilic modified PLA@PEO spinning solution of two concentrations obtained in S2 was switched to continue spinning through the double needle device to form a hydrophilic fiber layer, resulting in a structurally integrated bilayer electrospun Janus PLA micro / nanofiber membrane; finally, it was placed in a vacuum oven for drying to remove residual solvent; the total spinning time was 42 min, and the ratio of spinning time of the hydrophilic fiber layer to the hydrophobic fiber layer ranged from 1:1 to 3:1.

[0011] S4. Mask assembly: The double-layer electrospun Janus PLA micro-nano fiber membrane in S3 is used as the filter layer and is composited with the inner support layer and the outer support layer to obtain the finished mask. Preferably, in S2, the spinning time ratio of the hydrophilic fiber layer to the hydrophobic fiber layer is 2:1.

[0012] Further, in S1, the mass percentage of PLA in the two concentrations of hydrophobic PLA spinning solution is 4% and 8%; the composite organic solvent is a mixed solvent of dichloromethane and N,N-dimethylformamide, with a volume ratio of 6:4.

[0013] Further, in S2, the mass percentage of PLA in the two concentrations of hydrophilic modified PLA@PEO spinning solution is 4% and 8%; the hydrophilic modified polymer is polyetheramine and polyethylene glycol diglycidyl ether, and the mass ratio of polyetheramine to polyethylene glycol diglycidyl ether is 1:2; the total amount of hydrophilic modified polymer added is 10% of the mass of PLA in the hydrophilic modified PLA@PEO spinning solution.

[0014] Furthermore, in S3, the electrospinning process parameters are: voltage 20±5 kV, ambient temperature 25±5℃, ambient humidity 50±5% RH, spinning solution propulsion speed 1.5±0.5 ml / h, receiving distance 15 cm, and rotation speed 100 rpm.

[0015] The present invention has the following beneficial effects: 1. Significant synergistic cooling effect, achieving efficient moisture management and radiative heat dissipation. This invention utilizes a hydrophilic-hydrophobic gradient design of the Janus structure, combined with the strong moisture-wicking capacity of the hydrophilic modified PLA@PEO layer, to enable rapid unidirectional transmission of exhaled moisture from the inside out. Furthermore, the high emissivity of PLA material in the atmospheric window band (8-13 μm) and the high reflectivity of the micro-nano structure to sunlight achieve efficient evaporative cooling and radiative cooling while maintaining filtration efficiency, significantly improving wearing comfort in high-temperature and high-humidity environments.

[0016] 2. The hybrid spinning process balances high-efficiency filtration with low breathing resistance. This invention employs a dual-needle cross-spinning process to construct a non-uniform micro-nano network with a mixture of coarse and fine fibers using spinning solutions of varying concentrations. This interwoven structure of coarse and fine fibers increases the capture path for dust particles and improves filtration efficiency while effectively maintaining the material's high porosity, thereby significantly reducing breathing resistance and solving the technical pain point of traditional high-efficiency filter materials being prone to stuffiness.

[0017] 3. Integrated structural design, providing excellent moisture-wicking durability and stability. Janus PLA micro / nanofiber membranes, constructed through in-situ deposition via electrospinning, achieve physical cross-linking and structural integration of their hydrophilic and hydrophobic layers at the interface. Compared to chemical finishing or coating methods, this invention does not involve easily detachable chemical reagents, making the production process environmentally friendly and pollution-free. Furthermore, its unidirectional moisture-wicking properties are more durable and stable, making it suitable for use as protective equipment worn for extended periods.

[0018] 4. The materials used are green and environmentally friendly, possessing good biodegradability and biocompatibility. The core filter layer of this invention uses PLA as the main raw material, the inner support layer uses PLA spunbond nonwoven material, and the outer support layer uses natural fibers such as cotton or silk. All components have good biodegradability, conform to the concept of green environmental protection, and are skin-friendly, avoiding skin irritation caused by sweat retention.

[0019] 5. Possesses excellent flexibility and processing adaptability, with a wide range of applications. The composite material prepared by this invention not only meets the protection requirements of the core layer of masks, but also, due to its excellent thermal management and moisture-wicking functions, can be further extended to the fields of high-performance medical protective clothing, sports protective equipment, and personal thermal management systems in special environments. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the layered structure of the protective mask of this application.

[0021] Figure 2 This is a comparison chart of unidirectional moisture-wicking data of the JanusPLA micro / nanofiber membranes in the protective masks prepared in Examples 1, 2, 3, Comparative Examples 1 and 2.

[0022] Figure 3 The image shows the test results of the solar reflectance and infrared emission performance of the protective mask prepared in Example 1.

[0023] Figure 4 This is a comparison of the radiation cooling effect of Janus PLA micro-nano fiber membrane and traditional materials in the protective mask of Example 1.

[0024] Figure 5 This is a comparison chart of the filtration performance of the protective mask in Example 1 and a traditional mask. Detailed Implementation

[0025] The present invention will now be described in further detail with reference to the accompanying drawings and data. It should be understood that the embodiments are merely illustrative of the invention and are not intended to limit the scope of the invention in any way.

[0026] The following are the test methods for the relevant performance indicators in each embodiment and comparative example, as well as the specific procedures of the related experiments: Fabric Liquid Moisture Management Capacity Test: Referring to the method for testing the transfer characteristics of sweat in fabrics in GB / T 21655.2—2009, an MMT (moisture management tester) was used to test the fabric at 20℃ and 65% humidity. 80mm × 80mm test samples were cut from the fabric parallel to the warp and weft threads. After 24 hours, five tests were performed on different parts of each sample. The data were summarized, outliers were removed, and the average value was calculated. The inner layer of the fabric was the top layer during testing, and the outer layer was the bottom layer. The liquid moisture management tester can effectively measure the dynamic moisture transfer performance of fabrics, obtaining relevant indicators such as the one-way transfer index (R) and the dynamic liquid water transfer composite index (OMMC). The One-Way Transfer Index (R) measures the cumulative one-way transfer capacity of liquid water from the wetted surface of the fabric (inner layer / skin surface) to the penetrating surface (outer layer). OMMC is a comprehensive index that refers to the comprehensive index of liquid dynamic transfer, which is calculated by combining the liquid absorption rate, the liquid one-way transfer index, and the wetting and drying speed of the penetrating surface.

[0027] Solar spectral reflectance (0.3-2.5μm): Measured using a UV-Vis-NIR spectrometer with a diffuse integrating sphere (UV3600, Shimadzu Instruments Ltd., Japan, calibrated with a standard barium sulfate white plate).

[0028] Mid-infrared spectral (8-13 μm) emissivity: measured using a Fourier transform infrared spectrometer (Nicolet 8700, Thermo Fisher Scientific, USA) equipped with a diffusion integrating sphere.

[0029] This invention provides a protective mask with synergistic cooling functions of radiation and evaporation, comprising a supporting inner layer, a filter layer, and a supporting outer layer connected sequentially from the inside out. The filter layer is an electrospun Janus PLA micro / nanofiber membrane with unidirectional moisture-wicking properties. The electrospun Janus PLA micro / nanofiber membrane includes a hydrophobic inner layer and a hydrophilic outer layer connected sequentially from the inside out, with a wettability gradient between their inner and outer surfaces. The thickness ratio of the hydrophobic inner layer to the hydrophilic outer layer ranges from 1:1 to 1:3. The hydrophobic inner layer is a hydrophobic PLA layer, and the hydrophilic outer layer is a hydrophilic modified PLA@PEO layer. The supporting inner layer comprises a spunbond nonwoven material, and the supporting outer layer comprises a spunlace nonwoven material. The fiber material of the supporting inner layer is PLA with a basis weight of 20-40 g / m², and the fiber material of the supporting outer layer is cotton or silk with a basis weight of 30-60 g / m².

[0030] The directional moisture-wicking properties of the Janus PLA micro / nanofiber membrane described in this invention are achieved by adjusting the spinning time ratio (i.e., thickness ratio) of the hydrophilic layer and the hydrophobic layer. In the following embodiments, the total electrospinning time is fixed at 42 min.

[0031] Example 1 like Figure 1 As shown, the protective mask with synergistic cooling function of radiation and evaporation in this embodiment includes inner and outer functional support layers and a core filter layer. The inner and outer functional support layers include an inner spunbond nonwoven material and an outer spunlace nonwoven material, wherein the inner spunbond nonwoven material includes PLA spunbond nonwoven material, and the outer spunlace nonwoven material includes cotton or silk spunlace nonwoven material. The core filter layer is an electrospun Janus PLA micro / nanofiber membrane with unidirectional moisture-wicking function. The core filter layer is composed of an inner hydrophobic PLA layer and an outer hydrophilic modified PLA@PEO layer, with a wettability gradient difference between the inner and outer surfaces. In this embodiment, the spinning time ratio of the hydrophilic layer to the hydrophobic layer is controlled at 2:1.

[0032] The preparation method of the above-mentioned filter protective mask with synergistic cooling function of radiation and evaporation is as follows: Step 1: Preparation of hydrophobic PLA spinning solution: Dissolve polylactic acid (PLA) polymer in a composite organic solvent of dichloromethane (DCM) and NN-dimethylformamide (DMF) (volume ratio of 6:4) to prepare a hydrophobic PLA spinning solution with PLA mass percentages of 4% and 8%, respectively, and stir evenly for later use.

[0033] Step 2: Preparation of hydrophilic modified PLA@PEO spinning solution: Dissolve polylactic acid (PLA) polymer in the above-mentioned composite organic solvent to prepare solutions with PLA mass percentages of 4% and 8% respectively; then add hydrophilic modified polymers polyetheramine (PEA) and polyethylene glycol diglycidyl ether (PEGDGE) in sequence, setting the mass ratio of PEA to PEGDGE to be 1:2, and the total addition ratio to be 10% (relative to the mass of PLA in the hydrophilic modified PLA@PEO spinning solution); stir evenly to obtain 4% and 8% hydrophilic PLA@PEO spinning solutions.

[0034] Step 3: Preparation of Janus PLA micro / nano fiber membrane by electrospinning: The electrospinning process parameters were set as follows: voltage 20±5 kV, temperature and humidity 25±5℃ and 50±5% RH, feed speed 1.5±0.5 ml / h, receiving distance 15cm, and rotation speed 100 rpm. First, the two concentrations of hydrophobic PLA spinning solutions obtained in the first step were placed in a double-needle device (4% and 8% hydrophobic PLA spinning solutions were placed in one needle respectively). Double-needle spinning was performed using PLA spunbond nonwoven material as the receiving substrate for 14 minutes, forming a thin hydrophobic PLA fiber layer. Keeping the process parameters unchanged, the spinning solution was replaced with the two concentrations of hydrophilic modified PLA@PEO spinning solutions obtained in the second step (4% and 8% hydrophilic modified PLA@PEO spinning solutions were placed in one needle respectively), and spinning was continued for 28 minutes, covering the hydrophobic layer with a thicker hydrophilic fiber layer (total time 42 minutes). The resulting composite micro / nano fiber membrane was then placed in a vacuum oven and dried at 70°C for 3 hours to remove residual solvent.

[0035] Step 4: Mask Assembly: The Janus PLA micro / nanofiber membrane prepared above is used as the core filter layer, combined with the inner PLA spunbond nonwoven material (20-40 g / m²). 2 ) and outer layer of all-cotton spunlace nonwoven material (30-60 g / m 2 The components are combined and fitted with a nose bridge strip and mask straps to obtain the finished mask.

[0036] The Janus PLA micro / nanofiber membrane prepared in the third step was tested for its ability to manage liquid moisture in fabrics. The results are as follows: Figure 2 As shown, when the hydrophilic-hydrophobic spinning time ratio is 2 / 1, due to the optimization of the thickness gradient, its unidirectional moisture conduction rate (R value) reaches 853%, and the comprehensive unidirectional moisture conduction index (OMMC) reaches the highest, demonstrating excellent unidirectional liquid water transport capability.

[0037] The solar reflectance spectrum and infrared emissivity spectrum of the protective mask in this embodiment are as follows: Figure 3 As shown, the high infrared emissivity (8-13 μm band) of PLA material and the high reflectivity (92.7%) of electrospun micro-nano structures to sunlight are utilized to achieve a significant radiative cooling effect while ensuring high filtration efficiency.

[0038] like Figure 4As shown, with a human skin surface temperature of 35.7°C as a baseline, a FOTRIC 310 infrared thermal imaging camera (manufactured by Shanghai Thermal Imaging Technology Co., Ltd.) was used to monitor the skin and fiber membrane in real time. The surface temperature of the Janus PLA micro-nanofiber membrane with unidirectional moisture-wicking function in this embodiment was measured to be 34.4°C, which is significantly higher than the 33.1°C of the pure PLA micro-nanofiber membrane and the 27.9°C of the traditional N95 mask. This higher surface temperature reflects that the Janus PLA micro-nanofiber membrane can more effectively conduct human body heat to the outer layer for dissipation, thereby avoiding heat accumulation inside the mask and significantly improving wearing comfort.

[0039] like Figure 5 As shown, the protective mask prepared in this embodiment (denoted as Janus PLA micro-nanofiber mask) was compared with the filtration performance of PLA micro-nanofiber mask and commercially available KN95 mask. The Janus PLA micro-nanofiber mask of this invention achieved a filtration efficiency of 99.59%, which is higher than the 99.1% of PLA micro-nanofiber mask and the 97.44% of traditional KN95 mask. In terms of breathing resistance, although the filtration resistance of Janus PLA micro-nanofiber mask (65.1 Pa) is slightly higher than that of PLA micro-nanofiber mask (62.6 Pa) and KN95 mask (50.9 Pa), it is still at a low level. This excellent performance balance is mainly attributed to the non-uniform fiber network of mixed coarse and fine fibers constructed by the dual-needle cross-spinning process. While increasing the particle capture path and improving the filtration efficiency, it effectively maintains the high porosity of the material, thus avoiding obvious stuffiness while ensuring a high level of protection.

[0040] Example 2 A method for preparing a protective mask differs from Example 1 in that, in the third step of the preparation method, the spinning time of the hydrophobic layer is 21 min, and the spinning time of the hydrophilic layer is 21 min.

[0041] The Janus PLA micro / nanofiber membrane prepared in the third step was tested for its ability to manage liquid moisture in fabrics. The results are as follows: Figure 2 As shown, when the hydrophilic-hydrophobic spinning time ratio is 1 / 1, due to the excessively thick hydrophobic layer, its unidirectional moisture conductivity (R value) is 374%, and its unidirectional moisture conductivity index (OMMC) is relatively low, indicating a certain unidirectional liquid water transport capability.

[0042] Example 3 The method for preparing a protective mask differs from Example 1 in that, in the third step of the preparation method, the spinning time of the hydrophobic layer is 10.5 min and the spinning time of the hydrophilic layer is 30.5 min.

[0043] The Janus PLA micro / nanofiber membrane prepared in the third step was tested for its ability to manage liquid moisture in fabrics. The results are as follows: Figure 2 As shown, when the hydrophilic-hydrophobic spinning time ratio is 3 / 1, due to the excessively thick hydrophilic layer, its unidirectional moisture conductivity (R value) is 320%, and its unidirectional moisture conductivity index (OMMC) is relatively low, indicating a certain unidirectional liquid water transport capability.

[0044] Comparative Example 1 The method for preparing a protective mask differs from Example 1 in that, in the third step of the preparation method, the spinning time of the hydrophobic layer is 31.5 min and the spinning time of the hydrophilic layer is 10.5 min.

[0045] The Janus PLA micro / nanofiber membrane prepared in the third step was tested for its ability to manage liquid moisture in fabrics. The results are as follows: Figure 2 As shown, when the hydrophilic-hydrophobic spinning time ratio is 1 / 3, due to the excessively thick hydrophobic layer, its unidirectional moisture conductivity (R value) is only -744%, and its unidirectional moisture conductivity index (OMMC) is extremely low, exhibiting extremely poor unidirectional liquid water transport capability.

[0046] Comparative Example 2 A method for preparing a protective mask differs from Example 1 in that, in the third step of the preparation method, the spinning time of the hydrophobic layer is 28 minutes and the spinning time of the hydrophilic layer is 14 minutes.

[0047] The Janus PLA micro / nanofiber membrane prepared in the third step was tested for its ability to manage liquid moisture in fabrics. The results are as follows: Figure 2 As shown, when the hydrophilic / hydrophobic spinning time ratio is 1 / 2, due to the excessively thick hydrophobic layer, its unidirectional moisture conductivity (R value) is only -695%, and its unidirectional moisture conductivity index (OMMC) is extremely low, exhibiting extremely poor unidirectional liquid water transport capability.

[0048] Combination Figure 2 A comparison of the unidirectional moisture-wicking data of Janus PLA micro / nanofiber membranes in protective masks prepared in Examples 1, 2, 3, Comparative Examples 1 and 2 shows that when the hydrophobic layer is thicker than the hydrophobic layer, the Janus PLA micro / nanofiber membrane exhibits extremely poor unidirectional liquid water transport capability. As the thickness ratio of the hydrophilic layer to the hydrophobic layer increases, the unidirectional liquid water transport capability of the Janus PLA micro / nanofiber membrane first increases and then decreases. The Janus PLA micro / nanofiber membrane has the greatest unidirectional liquid water transport capability when the thickness ratio of the hydrophilic layer to the hydrophobic layer is 2:1.

[0049] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A protective mask with synergistic cooling function of radiation and evaporation, characterized in that, The membrane consists of a supporting inner layer, a filter layer, and a supporting outer layer connected sequentially from the inside out. The filter layer is an electrospun Janus PLA micro / nanofiber membrane with unidirectional moisture-wicking properties. The electrospun Janus PLA micro / nanofiber membrane includes a hydrophobic inner layer and a hydrophilic outer layer connected sequentially from the inside out. The thickness ratio of the hydrophilic outer layer to the hydrophobic outer layer ranges from 1:1 to 3:

1.

2. The protective mask as described in claim 1, characterized in that, The thickness ratio of the hydrophilic outer layer to the hydrophobic outer layer is 2:

1.

3. The protective mask as described in claim 1, characterized in that, The hydrophobic inner layer is a hydrophobic PLA layer, and the hydrophilic outer layer is a hydrophilic modified PLA@PEO layer.

4. The protective mask as described in claim 1, characterized in that, The inner support layer comprises a spunbond nonwoven material, and the outer support layer comprises a spunlace nonwoven material; the fiber material of the inner support layer is PLA, with a basis weight of 20-40 g / m². 2 The outer supporting layer is made of pure cotton or silk, with a weight of 30-60 g / m². 2 .

5. The method for preparing a protective mask as described in claim 1, characterized in that, Includes the following steps: S1. Preparation of hydrophobic PLA spinning solution: PLA polymer is dissolved in a composite organic solvent and mixed evenly by stirring to obtain two concentrations of hydrophobic PLA spinning solution; S2. Preparation of hydrophilic modified PLA@PEO spinning solution: PLA polymer is dissolved in a composite organic solvent, and hydrophilic modified polymer is added sequentially. The mixture is stirred and mixed evenly to obtain two concentrations of hydrophilic modified PLA@PEO spinning solution. S3. Preparation of Janus PLA micro / nanofiber membrane by electrospinning: The hydrophobic PLA spinning solution of two concentrations obtained in S1 was electrospun through a double-needle device to form a hydrophobic fiber layer; then, the hydrophilic modified PLA@PEO spinning solution of two concentrations obtained in S2 was switched to continue spinning through a double-needle device to form a hydrophilic fiber layer, resulting in a structurally integrated bilayer electrospun JanusPLA micro / nanofiber membrane; finally, it was placed in a vacuum oven to dry to remove residual solvent; the total spinning time was 42 min, and the ratio of spinning time of the hydrophilic fiber layer to the hydrophobic fiber layer ranged from 1:1 to 3:1; S4. Mask assembly: The double-layer electrospun Janus PLA micro-nano fiber membrane in S3 is used as the filter layer and is composited with the inner support layer and the outer support layer to obtain the finished mask.

6. The method for preparing a protective mask as described in claim 5, characterized in that, In S2, the spinning time ratio of the hydrophilic fiber layer to the hydrophobic fiber layer is 2:

1.

7. The method for preparing a protective mask as described in claim 5, characterized in that, In S1, the mass percentage of PLA in the two concentrations of hydrophobic PLA spinning solution is 4% and 8% respectively; the composite organic solvent is a mixture of dichloromethane and N,N-dimethylformamide in a volume ratio of 6:

4.

8. The method for preparing a protective mask as described in claim 5, characterized in that, In S2, the mass percentage of PLA in the two concentrations of hydrophilic modified PLA@PEO spinning solution is 4% and 8% respectively; the hydrophilic modified polymer is polyetheramine and polyethylene glycol diglycidyl ether, and the mass ratio of polyetheramine to polyethylene glycol diglycidyl ether is 1:2; the total amount of hydrophilic modified polymer added is 10% of the mass of PLA in the hydrophilic modified PLA@PEO spinning solution.

9. The method for preparing a protective mask as described in claim 5, characterized in that, In S3, the electrospinning process parameters are: voltage 20±5kV, ambient temperature 25±5℃, ambient humidity 50±5%RH, spinning solution feed speed 1.5±0.5ml / h, receiving distance 15cm, and speed 100rpm.

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