Bio-based radiant cooling fabric and preparation method thereof

Abstract

The present invention discloses a bio-based radiation cooling fabric and a preparation method thereof, wherein the bio-based radiation cooling fabric comprises a flexible substrate and a silk fibroin microsphere layer arranged on the surface of the flexible substrate, wherein the particle size of the silk fibroin microspheres in the silk fibroin microsphere layer is 0.2-2 μm. The above-mentioned silk fibroin microsphere layer is prepared by a simple impregnation method, and the silk fibroin microspheres are bonded to the surface of the flexible substrate through hydrogen bonds and van der Waals forces. After drying and curing, a silk fibroin microsphere layer is formed on the surface of the flexible substrate. The present invention uses silk fibroin microspheres with a specific particle size to prepare a radiation cooling layer on the surface of a flexible substrate. The coating makes the fabric reflectivity of sunlight as high as 0.71 or more, which can effectively isolate the input of solar radiation energy, thereby achieving a good cooling effect; in addition, the bio-based radiation cooling fabric has high air permeability, moisture permeability and tensile strength at break, and has good application prospects in outdoor clothing.

Description

Technical Field

[0001] The present invention relates to the technical field of functional fabric processing and preparation, and in particular to a bio-based radiation cooling fabric and a preparation method thereof. Background Art

[0002] Daytime radiation cooling technology is a passive cooling method that uses radiation heat exchange within the atmospheric window (8-13μm) with high emissivity and strong sunlight reflection (0.3-2.5μm) to achieve cooling below air temperature without any energy input.

[0003] Silk is a natural material with radiative cooling properties. Its fiber cross-section is randomly distributed with a high density of pores. The cross-sectional dimensions of these pores are comparable to those of visible and near-infrared wavelengths, strongly reflecting sunlight. Furthermore, due to the diversity of silk fibroin chemical bonds, silk fibers achieve a high emissivity of 88% in the mid-infrared range, enabling effective radiative cooling (Choi SH, Kim SW, Ku Z, et al. Anderson light localization in biological nanostructures of native silk. Nature Communications, 2018, 9(1):452). Shi et al. used the optical properties of silk fibers to degummed silk and prepared nanostructured regenerated silk fibers by wet spinning a fibroin solution. The fibers had a solar reflectivity of 73% and an emissivity of 90%, showing excellent radiative cooling performance (Shi NN, Tsai CC, Carter MJ, et al. Nanostructured fibers as aversatile photonic platform: radiative cooling and waveguiding through transverse Anderson localization. Light: Science & Applications, 2018, 7(1): 37.). Xiang et al. obtained a nanosized fibroin fiber membrane by electrospinning a fibroin solution. The membrane had a solar reflectivity of 96% and an infrared emissivity of 97% (Xiang B, Xu P, Chang Y, et al. Biodegradable radiative cooling membrane based on electrospun silk fibroin fiber. Polymers for Advanced Technologies, 2023.). However, the above-mentioned regenerated silk fibers and nanofiber membranes with radiative cooling properties have poor mechanical properties and are extremely easy to break, thus limiting the application of such silk fibroin-based radiative cooling materials in real life. Summary of the Invention

[0004] In order to solve the problems of complex preparation methods, high production costs and poor mechanical properties of silk fibroin-based daytime radiation cooling fabric materials in the prior art, the present invention provides a new type of bio-based radiation cooling fabric and its preparation method. By coating a silk fibroin microsphere layer on the surface of the fabric, the high infrared emissivity of silk fibroin and the high reflectivity of silk fibroin microspheres with a specific particle size to sunlight are utilized to make the fabric have a good radiation cooling effect, while also having high air permeability, moisture permeability and good mechanical properties.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0006] The present invention provides a bio-based radiation cooling fabric, which comprises a flexible substrate and a silk fibroin microsphere layer arranged on the surface of the flexible substrate, wherein the particle size of the silk fibroin microspheres in the silk fibroin microsphere layer is 0.2-2 μm.

[0007] The present invention prepares a silk fibroin microsphere layer on the surface of a fabric, utilizing the diversity of silk fibroin chemical bonds to increase the fabric's high emissivity within the atmospheric window (8-13 μm). The silk fibroin is then formed into microspheres, used as a reflective layer, and the particle size of the silk fibroin microspheres is controlled to reflect ultraviolet, visible, and near-infrared light, thereby effectively increasing the fabric's reflection of sunlight and providing the fabric with a good radiant cooling effect. Furthermore, the silk fibroin microsphere layer prepared by the present invention can be directly adsorbed on the fabric surface through forces such as hydrogen bonds and van der Waals forces. Furthermore, because silk fibroin is rich in hydrophilic groups, the fabric modified with the silk fibroin microspheres still has good moisture and air permeability.

[0008] Furthermore, the flexible substrate is preferably a hydrophilic fabric, such as cotton fabric, wool fabric, linen fabric or silk fabric. Selecting a hydrophilic fabric as the flexible substrate is more conducive to improving the interfacial bonding force between the flexible substrate and the silk fibroin microsphere layer.

[0009] Furthermore, the thickness of the flexible substrate is preferably 0.1-1 mm, for example, 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm, etc., including but not limited to the values ​​listed above.

[0010] Furthermore, the thickness of the silk fibroin microsphere layer is 10-50 μm, for example, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, etc.

[0011] Furthermore, the silk fibroin microsphere layer contains silk fibroin microspheres with a particle size of 0.4-0.8 μm. The silk fibroin microspheres with a particle size within this range have the highest reflectivity to sunlight.

[0012] In some preferred embodiments of the present invention, the thickness of the flexible substrate is 0.217 mm, and the thickness of the silk fibroin microsphere layer is about 20 μm.

[0013] A second aspect of the present invention provides a method for preparing the bio-based radiant cooling fabric according to the first aspect, comprising the following steps:

[0014] (1) pre-treating the flexible substrate to remove impurities on the surface of the flexible substrate;

[0015] (2) mixing the silk fibroin solution with ethanol and subjecting the mixture to freeze-thaw treatment to obtain a silk fibroin microsphere solution;

[0016] (3) The flexible substrate pretreated in step (1) is immersed in the silk fibroin microsphere solution prepared in step (2), and after immersion, it is taken out and dried, and the number of immersions is adjusted to form a silk fibroin microsphere layer of target thickness on the surface of the flexible substrate to obtain the bio-based radiation cooling fabric.

[0017] The present invention utilizes the self-assembly property of silk fibroin to prepare silk fibroin microspheres through a simple freeze-thaw method, and controls the particle size of the prepared silk fibroin microspheres by adjusting the ethanol content. Then, a silk fibroin microsphere layer is prepared on the surface of a flexible substrate by a simple impregnation method. In order to increase the loading amount of silk fibroin microspheres on the fabric surface, a silk fibroin microsphere layer of a target thickness can be prepared on the fabric surface by multiple impregnation methods.

[0018] Furthermore, in step (1), the pretreatment specifically comprises: placing the flexible substrate in a non-ionic detergent solution, washing it at 40-60° C. for 15-60 minutes, then removing the flexible substrate and drying it to obtain a pretreated flexible substrate; the concentration of the non-ionic detergent in the non-ionic detergent solution is 1-4 g / L, and the bath ratio of the flexible substrate to the non-ionic detergent solution is 1:30-60. Before preparing the silk fibroin microsphere layer on the surface of the flexible substrate, the surface of the flexible substrate is first subjected to a decontamination treatment to prevent dust adhering to the surface of the flexible substrate from affecting the bonding strength between the silk fibroin microsphere layer and the surface of the flexible substrate.

[0019] Furthermore, in step (2), the preparation method of the silk fibroin solution is: placing the silk in a sodium carbonate aqueous solution for soaking, taking out the silk after soaking and washing and drying, then dissolving the dried silk in a lithium bromide solution for heat treatment, and dialyzing the mixed solution obtained after the heat treatment to obtain a silk fibroin solution.

[0020] Furthermore, the concentration of the sodium carbonate aqueous solution is preferably 0.2-1 wt%.

[0021] Furthermore, the soaking time is preferably 0.5-2h.

[0022] Furthermore, the silk obtained after soaking and boiling is washed with water at 50-70°C and dried at 40-50°C.

[0023] Furthermore, the concentration of the lithium bromide solution is 5-10 mol / L; and the bath ratio of the silk to the lithium bromide solution is 1:4-6.

[0024] Furthermore, in the preparation of the silk fibroin solution, the temperature of the heating treatment is 50-70° C., and the time of the heating treatment is 0.5-2 h.

[0025] Furthermore, in step (2), the concentration of the silk fibroin solution is 2-5 wt %; and the mass ratio of the silk fibroin solution to ethanol is 1:0.1-0.4.

[0026] Furthermore, in step (2), the freeze-thaw treatment is specifically as follows: the silk fibroin solution is mixed with ethanol and the mixed solution is transferred to -15 to -30°C and frozen for more than 12 hours, and then taken out and thawed at 20-30°C to obtain the silk fibroin microsphere solution.

[0027] Furthermore, in step (3), the bath ratio of the flexible substrate to the silk fibroin microsphere solution is 1:40-60.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. The present invention provides a bio-based radiative cooling fabric. This fabric is obtained by disposing a layer of silk fibroin microspheres on the fabric surface to achieve a radiative cooling effect. The fabric utilizes the diversity of silk fibroin chemical bonds to increase its high emissivity within the atmospheric window (8-13 μm). Furthermore, the fabric utilizes the differences in the reflection of ultraviolet, visible, and near-infrared light by silk fibroin microspheres of varying particle sizes. By regulating the size of the silk fibroin microspheres in the layer, the reflectivity of the silk fibroin microsphere layer to sunlight is increased. Compared to unmodified fabrics, this bio-based radiative cooling fabric can effectively reflect sunlight, achieving a cooling effect with a temperature difference of up to 6°C. It also exhibits high air and moisture permeability and excellent mechanical properties, and has promising application prospects in outdoor clothing such as sun hats and sun-protective clothing.

[0030] 2. The present invention also provides a method for preparing the above-mentioned bio-based radiation cooling fabric. Silk fibroin microspheres are arranged on the surface of the fabric by a simple impregnation method, and the density and thickness of the silk fibroin microsphere layer on the fabric surface can be controlled by regulating the concentration of the silk fibroin microsphere solution and the number of impregnation times. The above-mentioned preparation method is simple to operate, the process is easy to control, and the preparation process is green and pollution-free. It is suitable for industrial mass production and can effectively reduce the preparation cost of radiation cooling fabrics. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The SEM images of the silk fibroin microspheres prepared in the examples, wherein: a is the SEM image of SF-1, b is the SEM image of SF-2, and c is the SEM image of SF-3;

[0032] Figure 2 This is a particle size distribution diagram of the silk fibroin microsphere solution prepared in Example;

[0033] Figure 3 : a is the emissivity of silk fibroin microspheres with different particle sizes prepared in the embodiment, b is the solar reflectivity of silk fibroin microspheres with different particle sizes;

[0034] Figure 4 These are SEM images of the bio-based radiant cooling fabrics prepared in the examples, where a and d are SEM images of SF-cotton-1, b and e are SEM images of SF-cotton-2, and c and f are SEM images of SF-cotton-3.

[0035] Figure 5 FTIR images of cotton fabric, SF-cotton-1 and silk fibroin solution before modification;

[0036] Figure 6 is the air permeability of SF-cotton-1 to SF-cotton-3 and unmodified cotton fabric;

[0037] Figure 7 The hydrophilicity test diagram of SF-cotton-1 to SF-cotton-3;

[0038] Figure 8 : a is the emissivity graph of SF-cotton-1 to SF-cotton-3, SF-cotton and unmodified cotton fabrics, b is the reflectivity graph of SF-cotton-1 to SF-cotton-3, SF-cotton and unmodified cotton fabrics;

[0039] Figure 9 This is a simulation diagram of an outdoor test, where 1 is a foam box, 2 is a polyolefin film, 3 is a test sample, and 4 is a probe;

[0040] Figure 10 This is a temperature change chart for outdoor tests of SF-cotton-1 to SF-cotton-3, SF-cotton and unmodified cotton fabrics. DETAILED DESCRIPTION

[0041] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terms used in this specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0042] The present invention will be further described below with reference to the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it. However, the embodiments are not intended to limit the present invention.

[0043] Example

[0044] This embodiment relates to the preparation of a bio-based radiant cooling fabric, and the specific preparation process is as follows:

[0045] (1) Place the cotton fabric in a solution containing 2 g / L nonionic detergent (bath ratio of 1:50) and wash it at 50°C for 30 min to remove surface impurities. Place the fabric in an oven for drying to obtain the pretreated cotton fabric, and cut it into 5 × 5 cm cotton fabric samples.

[0046] (2) 7 g of silk was placed in a 0.5% sodium carbonate aqueous solution, boiled for 30 minutes, taken out, washed with 60°C deionized water, repeated three times, and dried at 45°C. It was then dissolved in a 9.3 mol / L lithium bromide solution (bath ratio of 1:5), heated in a 60°C water bath for 30 minutes, placed in a dialysis bag, and dialyzed with deionized water for three days to obtain a 3 wt% silk fibroin solution; the prepared silk fibroin solution was mixed with anhydrous ethanol at a mass ratio of 1:0.2, and then freeze-thawed to obtain a silk fibroin microsphere solution SF-1;

[0047] (3) The cotton fabric sample prepared in step (1) is placed in the silk fibroin microsphere solution prepared in step (2), immersed for 10 minutes, taken out and dried, and then immersed once again. After drying, the bio-based radiation cooling fabric SF-cotton-1 is obtained.

[0048] Preparation of SF-cotton-2: The mass ratio of the silk fibroin solution to anhydrous ethanol in the above step (2) was adjusted to 1:0.25, and the silk fibroin microsphere solution SF-2 was obtained after freeze-thaw treatment. The remaining steps were the same to prepare the bio-based radiation cooling fabric SF-cotton-2.

[0049] Preparation of SF-cotton-3: The mass ratio of the silk fibroin solution to anhydrous ethanol in the above step (2) was adjusted to 1:0.4, and the silk fibroin microsphere solution SF-3 was obtained after freeze-thaw treatment. The remaining steps were the same to prepare the bio-based radiation cooling fabric SF-cotton-3.

[0050] The SEM images and particle size distribution of the silk fibroin microspheres in the silk fibroin microsphere solutions SF-1 to SF-3 prepared in this example are shown in FIG. Figure 1 、 2 As shown in the figure, it can be seen that the particle size of the silk fibroin microspheres obtained by freeze-thaw treatment decreases with the increase of the mass of anhydrous ethanol. Among them, the particle size of the silk fibroin microspheres in SF-1 is greater than 1 μm, the particle size of the silk fibroin microspheres in SF-2 is mainly distributed around 1 μm, and the particle size of the silk fibroin microspheres in SF-1 is less than 1 μm.

[0051] The emissivity of the silk fibroin microspheres in the silk fibroin microsphere solutions SF-1 to SF-3 prepared in this example to the 3-25 μm band and the reflectivity to the 0.2-2.5 μm band are as follows: Figure 3 As shown in Figures 3a and 3b, the emissivity of silk fibroin microspheres with different particle sizes in the 3-25μm band is similar, but there are large differences in the reflectivity in the 0.2-2.5μm band. Among them, SF-2 has the highest reflectivity in the 0.5-1.25μm band, which can be as high as about 90%, while the reflectivity of SF-1 and SF-3 in the 0.5-1.25μm band is significantly lower than that of SF-2, at around 80%.

[0052] The SEM images of SF-cotton-1 to SF-cotton-3 prepared in this example are as follows: Figure 4 As shown (4a, 4d are SEM images of SF-cotton-1, 4b, 4e are SEM images of SF-cotton-2, 4c, 4f are SEM images of SF-cotton-3), a coating with a granular morphology can be observed on the surface of the cotton fabric fiber. The silk fibroin microspheres are adsorbed on the cotton fiber surface by physical effects such as hydrogen bonds and van der Waals forces. It can also be clearly observed that the particle size of the microspheres in the silk fibroin microsphere layer on the surface of SF-cotton-1 to SF-cotton-3 gradually decreases. Taking SF-cotton-1 as an example, the infrared of SF-cotton-1, untreated cotton fabric and silk fibroin solution was tested, as shown in FIG. Figure 5 As shown, characteristic peaks completely attributable to the surface groups of silk fibroin can be observed on the infrared image of SF-cotton-1 (impregnated cotton in the figure). It can be seen that a completely coated silk fibroin microsphere layer can be formed on the surface of the cotton fabric through the above-mentioned impregnation method.

[0053] Comparative Example

[0054] This comparative example relates to the preparation of a silk fibroin modified fabric. The fabric is directly immersed in a silk fibroin solution. The specific operation is as follows:

[0055] (1) Place the cotton fabric in a solution containing 2 g / L nonionic detergent (bath ratio of 1:50) and wash it at 50°C for 30 min to remove surface impurities. Place the fabric in an oven for drying to obtain the pretreated cotton fabric, and cut it into 5 × 5 cm cotton fabric samples.

[0056] (2) 7g of silk was placed in a 0.5% sodium carbonate aqueous solution, boiled for 30 minutes, taken out, washed with 60℃ deionized water, repeated three times, and dried at 45℃. It was then dissolved in a 9.3mol / L lithium bromide solution (bath ratio of 1:5), heated in a 60℃ water bath for 30 minutes, placed in a dialysis bag, and dialyzed with deionized water for three days to obtain a 3wt% silk fibroin solution;

[0057] (3) The cotton fabric sample prepared in step (1) is placed in the silk fibroin solution prepared in step (2), immersed for 10 minutes, taken out and dried, and then immersed once again. After drying, the bio-based radiation cooling fabric SF-cotton is obtained.

[0058] Performance Research

[0059] 1. Air permeability

[0060] The air permeability of SF-cotton-1 to SF-cotton-3 prepared in the above examples was tested under the conditions of a test pressure of 100 Pa and a nozzle diameter of 4.0 mm. The test results are as follows: Figure 6 As shown in the figure, the air permeability of the cotton fabric modified with silk fibroin microspheres did not decrease significantly, and the high air permeability performance was still maintained, and the air permeability was higher than 300 mm / s.

[0061] 2. Hydrophilicity

[0062] Hydrophilicity test: The hydrophilicity of the fabric is characterized by testing the diffusion time of water droplets on the fabric surface. The hydrophilicity test results of SF-cotton-1 to SF-cotton-3 prepared in the above examples are as follows: Figure 7 As shown, the diffusion time of water droplets on the surface of SF-cotton-1 to SF-cotton-3 is less than 16s, which also shows that the bio-based radiant cooling fabric prepared by the above-mentioned modification treatment of the present invention has high hydrophilicity.

[0063] 3. Hygroscopicity

[0064] The moisture regain of the above fabrics is tested to reflect the hygroscopicity of each fabric. The specific operation is as follows:

[0065] Moisture regain test: Refer to the oven method of GB / T 6102.1-2006 and conduct the experiment. Specifically, the fabric is first placed in a 105°C oven to dry for 4 hours. The mass of the dry fabric is recorded as G0 (g). Then the fabric is placed in a constant temperature and humidity chamber (humidity 65±5%, temperature 25±5°C). The mass of the fabric after treatment for 1 hour is recorded as G (g). The moisture regain of the fabric W can be obtained by the following formula:

[0066]

[0067] Where: W is the moisture regain of the fabric; G0 is the dry weight of the fabric; G is the actual weight of the fabric.

[0068] Three copies of each sample were prepared and the average value was taken to obtain the rewetting rate of each sample. The test results are shown in Table 1 below:

[0069] Table 1

[0070] sample cotton fabric SF-cotton-1 SF-cotton-2 SF-cotton-3 Moisture regain (%) 7.9 6.0 6.5 6.6

[0071] As can be seen from Table 1, compared with the untreated cotton fabrics, the moisture regains of SF-cotton-1 to SF-cotton-3 prepared in the present invention are reduced, but the reduction is small. It is speculated that this is because the good hydrophilicity of silk fibroin and the gaps between silk fibroin microspheres are conducive to the adsorption of water vapor.

[0072] 4. Mechanical properties

[0073] The tensile strength at break of the SF-cotton-1 to SF-cotton-3 prepared in the above examples and the untreated cotton fabrics was tested as follows:

[0074] The mechanical properties of the samples were tested using a 5967 universal material testing machine. The samples were cut into rectangles with a length of 300 mm and a width of 60 mm, and the burrs on both sides were removed. The tensile rate of the universal material testing machine was set to 100 mm min. -1 The distance between the upper and lower chucks is 200 mm. Each sample is tested 5 times and the average value of the 5 tests is taken.

[0075] The test results are shown in Table 2 below:

[0076] Table 2

[0077]

[0078] It can be seen from the above table that the present invention can effectively improve the tensile strength at break of cotton fabric by preparing a silk fibroin microsphere layer on the surface of cotton fabric.

[0079] 4. Emissivity and reflectivity of different fabrics

[0080] The emissivity of the modified cotton fabrics (SF-cotton-1 to SF-cotton-3, SF-cotton) and the unmodified cotton fabrics prepared in the above examples and comparative examples in the 3-25 μm band and the reflectivity in the 0-2.5 μm band were tested. The test results are as follows: Figure 8 shown.

[0081] Figure 8 a is the emissivity diagram of modified cotton fabric and unmodified cotton fabric in the 3-25 μm band. It can be seen from the figure that the emissivity is not significantly affected by the morphology of silk fibroin before and after modification and on the surface of cotton fabric. Figure 8 b is the reflectivity diagram of modified cotton fabric and unmodified cotton fabric in the 0-2.5μm band. It can be seen from the figure that for illumination in the 0.5-1.25μm band, the unmodified cotton fabric and SF-cotton have relatively low light reflectivity within this band, and the light reflectivity of SF-cotton before the 0.75μm band is slightly lower than that of the unmodified cotton fabric. The light reflectivity of SF-cotton-1 to SF-cotton-3 prepared by the present invention in the 0.5-1.25μm band is higher than that of the unmodified cotton fabric, among which SF-cotton-2 shows a higher light reflectivity, which is also consistent with the higher light reflectivity of the above-mentioned SF-2 silk fibroin microspheres.

[0082] 5. Radiation cooling performance test

[0083] The radiant cooling performance of the modified cotton fabrics (SF-cotton-1 to SF-cotton-3, SF-cotton) and unmodified cotton fabrics prepared in the above examples and comparative examples was tested. The specific operation is as follows:

[0084] The outdoor cooling performance test of the samples was carried out using a self-built device, such as Figure 9 As shown, the apparatus primarily consists of an insulated polystyrene foam box 1 measuring 40 cm × 40 cm × 32 cm (length × width × height), with a wall thickness of 2 cm. The top is open and covered with a 10-micron-thick transparent low-density polyethylene film 2 to prevent air convection. The other three sides are sealed, and the surface is covered with highly reflective aluminum foil. Eight small polystyrene foam boxes measuring 4 cm × 4 cm × 4 cm, with a wall thickness of 1 cm, are placed inside. Test samples 3 are placed in the top openings of the small polystyrene foam boxes. A thermocouple probe 4 is inserted into the middle of the small foam box. The thermocouple is connected to a temperature recorder to record temperature changes within the foam box.

[0085] The test results are as follows Figure 10 As shown in the figure, the temperature changes of SF-cotton and unmodified cotton during the outdoor test are almost the same, while the temperature below SF-cotton-1 to SF-cotton-3 with silk fibroin microparticle layer is significantly lower than that below the unmodified cotton, and SF-cotton-2 has the best cooling effect, with the temperature difference between it and the unmodified cotton fabric reaching 6°C, showing a good radiation cooling effect.

[0086] The above-described embodiments are merely preferred examples for the purpose of fully illustrating the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are within the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

Claims

1. A bio-based radiant cooling fabric, characterized in that: The bio-based radiant cooling fabric comprises a flexible substrate and a silk fibroin microsphere layer disposed on the surface of the flexible substrate, wherein the particle size of the silk fibroin microspheres in the silk fibroin microsphere layer is 0.4-0.8 μm; The silk fibroin microsphere layer is prepared by the following method: The mixed solution obtained by mixing the silk fibroin solution and ethanol was transferred to a freezer at -30 to -15°C for more than 12 hours, and then taken out and thawed at 20 to 30°C to obtain a silk fibroin microsphere solution; The pretreated flexible substrate is immersed in the silk fibroin microsphere solution, taken out and dried after dipping, and the number of dippings is adjusted to form a silk fibroin microsphere layer of target thickness on the surface of the flexible substrate.

2. The bio-based radiant cooling fabric according to claim 1, characterized in that: The flexible substrate is cotton fabric, wool fabric, linen fabric or silk fabric.

3. The bio-based radiant cooling fabric according to claim 1, characterized in that: The thickness of the flexible substrate is 0.1-1 mm; the thickness of the silk fibroin microsphere layer is 10-30 μm.

4. A method for preparing the bio-based radiant cooling fabric according to any one of claims 1 to 3, characterized in that: The following steps are involved: (1) Pre-treating the flexible substrate to remove impurities on the surface of the flexible substrate; (2) Transfer the mixed solution obtained by mixing the silk fibroin solution and ethanol to -30~-15℃ and freeze it for more than 12 hours, then take it out and thaw it at 20-30℃ to obtain a silk fibroin microsphere solution; (3) The flexible substrate pretreated in step (1) is immersed in the silk fibroin microsphere solution prepared in step (2), taken out and dried after dipping, and the number of dipping times is adjusted to form a silk fibroin microsphere layer of target thickness on the surface of the flexible substrate to obtain the bio-based radiation cooling fabric.

5. The preparation method according to claim 4, characterized in that In step (1), the pretreatment is specifically as follows: placing the flexible substrate in a non-ionic detergent solution, washing at 40-60° C. for 15 min-60 min, then taking out the flexible substrate and drying it to obtain a pretreated flexible substrate; The concentration of the nonionic detergent in the nonionic detergent solution is 1-4 g / L, and the bath ratio of the flexible substrate to the nonionic detergent solution is 1:30-60.

6. The preparation method according to claim 4, characterized in that In step (2), the preparation method of the silk fibroin solution is as follows: placing silk in a sodium carbonate aqueous solution for soaking, taking out the silk after soaking and washing, and drying, then dissolving the dried silk in a lithium bromide solution for heating treatment, and dialyzing the mixed solution obtained after the heating treatment to obtain a silk fibroin solution.

7. The preparation method according to claim 4, characterized in that In step (2), the concentration of the silk fibroin solution is 2-5 wt %; and the mass ratio of the silk fibroin solution to ethanol is 1:0.1-0.

4.

8. The preparation method according to claim 4, characterized in that In step (3), the bath ratio of the flexible substrate to the silk fibroin microsphere solution is 1:40-60.

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