Preparation method of biodegradable flexible radiative cooling film

Abstract

The application relates to a preparation method of a biodegradable flexible radiation refrigeration film, and relates to a preparation method of a radiation refrigeration film. The application aims to solve the problem that the existing polymer radiation cooling material cannot simultaneously have excellent ultraviolet resistance, cooling performance and biodegradation. The method comprises the following steps: one, preparation of a spinning solution; two, synthesis of nanometer and micrometer EC fibers by using electrostatic spinning. The application is used for the preparation of the biodegradable flexible radiation refrigeration film.

Description

Technical Field

[0001] This invention relates to a method for preparing a radiation-cooled thin film. Background Technology

[0002] The continued consumption of fossil fuels leads to a steady increase in greenhouse gas emissions, causing global warming. Cooling technologies have become an urgent necessity in our daily lives and industrial production. However, traditional cooling technologies typically consume fossil fuels, exacerbating global warming. Therefore, the search for new green, fuel-free cooling technologies is particularly pressing. Passive daytime radiative cooling (PDRC) radiates excess heat from the Earth's surface into ultra-cool outer space (approximately 3K) through the 8-13 micrometer spectral range of the atmosphere, passively cooling objects without consuming any energy. In recent years, this cooling method has received increasing attention as an environmentally friendly alternative to electric cooling, helping to mitigate global warming. This cooling technology has been applied intentionally or unintentionally in various scenarios, including energy-efficient buildings, dew harvesting, personal thermal management, photovoltaic cooling, refrigeration and storage, and power generation.

[0003] Currently, PDRC materials typically employ complex multilayered, porous structures composed of photonic crystals, polymers, and dielectric polymers to enhance solar reflectivity and mid-infrared emissivity. However, photonic crystal-based PDRC materials are difficult to mass-produce due to their complex and expensive manufacturing processes. On the other hand, polymer-based PDRC materials are favored due to their low cost and simple manufacturing methods. However, many polymer-based radiation cooling materials exhibit poor ultraviolet (UV) resistance, and prolonged exposure to UV radiation leads to oxidation and yellowing. Furthermore, increased UV absorption reduces cooling performance, limiting the widespread application of polymer-based radiation cooling materials. By combining UV-resistant photonic crystals with polymers, the UV resistance of polymer-based radiation cooling materials can be improved. However, UV-resistant polymer-based radiation cooling materials are generally non-biodegradable, exacerbating environmental pollution problems. Summary of the Invention

[0004] This invention aims to address the problem that existing polymer radiation cooling materials cannot simultaneously possess excellent UV resistance, cooling performance, and biodegradability, and thus provides a method for preparing a biodegradable flexible radiation cooling film.

[0005] A method for preparing a biodegradable flexible radiation-cooling thin film, comprising the following steps:

[0006] I. Preparation of spinning solution:

[0007] Ethyl cellulose is dissolved in a solvent to obtain a spinning solution;

[0008] II. Electrospinning is used to synthesize nano and micron-sized EC fibers;

[0009] Electrospinning was performed under the following conditions: voltage of 13kV to 15kV, injection speed of 0.03mm / min to 0.08mm / min, temperature of 20℃ to 30℃, humidity of 20% to 30%, syringe needle inner diameter of 0.06mm to 0.25mm, distance between syringe needle and receiving spinneret of 20cm to 25cm, translational speed of syringe needle of 400mm / min to 600mm / min, and rotational speed of receiving spinneret of 1r / min to 3r / min. Finally, the solvent was removed by drying to obtain a biodegradable flexible radiation cooling film.

[0010] The beneficial effects of this invention are:

[0011] This invention prepares a fiber membrane with high reflectivity in the solar radiation band by controlling the concentration of the spinning solution and process parameters. It achieves performance comparable to, or even better than, that of a cooling membrane with added fillers. This fiber membrane, prepared through structural design, maximizes performance while reducing unnecessary filler additions, which is significant for cost savings and maintaining the intrinsic properties of the material.

[0012] The biodegradable flexible radiation-cooling film prepared by this invention features UV resistance, excellent radiation-cooling effect, and biodegradability. It achieves 98.1% solar reflectance and 88.4% emissivity within the atmospheric window, enabling effective passive radiation-cooling during the day. After 600 hours of strong UV irradiation, the EC film showed almost no change in solar reflectance. Comparison of optical images and CIE 1931 chromaticity diagrams before and after UV irradiation revealed that the EC film did not yellow under UV irradiation. When the biodegradable flexible radiation-cooling film was placed in soil, the EC film partially degraded. Attached Figure Description

[0013] Figure 1 The images show the physical image, SEM image, and comparison of solar reflectance and mid-infrared emissivity of the EC fiber membrane prepared in Example 1. a is the physical image, b is the SEM image, and c is the solar reflectance and mid-infrared emissivity.

[0014] Figure 2 The solar reflectance of the EC fiber membrane prepared in Example 1 under different ultraviolet irradiation times;

[0015] Figure 3 The images show the CIE 1931 chromaticity diagram and optical image of the EC fiber membrane prepared in Example 1 after 600 hours of UV irradiation and without UV irradiation. a) CIE 1931 chromaticity diagram without UV irradiation, b) CIE 1931 chromaticity diagram after UV irradiation, c) optical image without UV irradiation, and d) optical image after UV irradiation.

[0016] Figure 4 The images show the natural degradation test diagrams of the EC fiber membrane and PE membrane prepared in Example 1, and the scanning electron microscope image of the EC fiber membrane after natural degradation. a is the natural degradation test diagram, and b is the scanning electron microscope image of the EC membrane after natural degradation.

[0017] Figure 5 The following graphs show the cooling performance test results of the EC fiber membrane prepared in Example 1: a) is a photograph of the outdoor daytime radiative cooling test; b) is a schematic diagram of the equipment structure for real-time monitoring of daytime radiative cooling performance; c) shows the relationship between temperature (T) and time during the test; and d) shows the temperature difference (ΔT = T) during the test. amb -T cooler The relationship between time and time. Detailed Implementation

[0018] Specific Implementation Method 1: This implementation method provides a method for preparing a biodegradable flexible radiation-cooling thin film, which is carried out according to the following steps:

[0019] I. Preparation of spinning solution:

[0020] Ethyl cellulose is dissolved in a solvent to obtain a spinning solution;

[0021] II. Electrospinning is used to synthesize nano and micron-sized EC fibers;

[0022] Electrospinning was performed under the following conditions: voltage of 13kV to 15kV, injection speed of 0.03mm / min to 0.08mm / min, temperature of 20℃ to 30℃, humidity of 20% to 30%, syringe needle inner diameter of 0.06mm to 0.25mm, distance between syringe needle and receiving spinneret of 20cm to 25cm, translational speed of syringe needle of 400mm / min to 600mm / min, and rotational speed of receiving spinneret of 1r / min to 3r / min. Finally, the solvent was removed by drying to obtain a biodegradable flexible radiation cooling film.

[0023] The beneficial effects of this embodiment are:

[0024] This embodiment prepares a fiber membrane with high reflectivity in the solar radiation band by controlling the concentration of the spinning solution and process parameters. It achieves performance comparable to, or even better than, that of a cooling membrane with added fillers. This fiber membrane, prepared through structural design, maximizes performance while reducing unnecessary filler additions, which is significant for cost savings and maintaining the intrinsic properties of the material.

[0025] The biodegradable flexible radiation-cooling film prepared in this embodiment features UV resistance, excellent radiation-cooling effect, and biodegradability. It achieves 98.1% solar reflectance and 88.4% emissivity within the atmospheric window, enabling effective passive radiation-cooling during the day. After 600 hours of strong UV irradiation, the EC film showed almost no change in solar reflectance. Comparison of optical images and CIE 1931 chromaticity diagrams before and after UV irradiation revealed that the EC film did not yellow under UV irradiation. When the biodegradable flexible radiation-cooling film was placed in soil, the EC film partially degraded.

[0026] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the solvent used in step one is a mixed solvent of glacial acetic acid, anhydrous ethanol, and pure water. Everything else is the same as in Specific Implementation Method One.

[0027] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that: the volume ratio of glacial acetic acid to anhydrous ethanol in the mixed solvent of glacial acetic acid / anhydrous ethanol / pure water is 7:(2-3); and the volume ratio of glacial acetic acid to pure water in the mixed solvent of glacial acetic acid / anhydrous ethanol / pure water is 7:(1-2). Everything else is the same as in Specific Implementation Method One or Two.

[0028] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the mass percentage of ethyl cellulose in the spinning solution described in step one is 20% to 28%. Everything else is the same as in Specific Implementation Method Three.

[0029] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that the solvent removal drying in step two is specifically carried out at room temperature for 12 to 24 hours. Everything else is the same as in Specific Implementation Methods One to Four.

[0030] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the receiving spinner in step two is a rotating roller wrapped with aluminum foil. Everything else is the same as in Specific Implementation Methods One to Five.

[0031] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that the fiber diameter of the biodegradable flexible radiation cooling film prepared in step two is 0.10 μm to 1.3 μm, and the pore size is 0.20 μm to 2.5 μm. Everything else is the same as in Specific Implementation Methods One to Six.

[0032] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that: the solvent mentioned in step one is a mixed solvent of glacial acetic acid / anhydrous ethanol / pure water; the volume ratio of glacial acetic acid to anhydrous ethanol in the mixed solvent of glacial acetic acid / anhydrous ethanol / pure water is 7:2; and the volume ratio of glacial acetic acid to pure water in the mixed solvent of glacial acetic acid / anhydrous ethanol / pure water is 7:1. Everything else is the same as in Specific Implementation Methods One to Seven.

[0033] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that the mass percentage of ethyl cellulose in the spinning solution described in step one is 28%. Everything else is the same as in Specific Implementation Methods One to Eight.

[0034] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods One to Nine in that: in step two, electrospinning is performed under the following conditions: voltage of 15kV, injection speed of 0.06mm / min, temperature of 25℃, humidity of 25%, syringe needle inner diameter of 0.23mm, distance between syringe needle and receiving spinneret of 25cm, translational speed of syringe needle of 500mm / min, and rotational speed of receiving spinneret of 2r / min. All other conditions are the same as in Specific Implementation Methods One to Nine.

[0035] The beneficial effects of the present invention are verified using the following embodiments:

[0036] Example 1:

[0037] A method for preparing a biodegradable flexible radiation-cooling thin film, comprising the following steps:

[0038] I. Preparation of spinning solution:

[0039] Ethyl cellulose is dissolved in a solvent to obtain a spinning solution;

[0040] II. Electrospinning is used to synthesize nano and micron-sized EC fibers;

[0041] Electrospinning was performed under the following conditions: voltage of 15kV, injection speed of 0.06mm / min, temperature of 25℃, humidity of 25%, syringe needle inner diameter of 0.23mm, distance between syringe needle and receiving spinneret of 25cm, translational speed of syringe needle of 500mm / min, and rotational speed of receiving spinneret of 2r / min. Finally, the solvent was removed by drying to obtain a biodegradable flexible radiation cooling film, namely EC fiber membrane.

[0042] The solvent mentioned in step one is a mixed solvent of glacial acetic acid, anhydrous ethanol, and pure water; the volume ratio of glacial acetic acid to anhydrous ethanol in the mixed solvent of glacial acetic acid, anhydrous ethanol, and pure water is 7:2; the volume ratio of glacial acetic acid to pure water in the mixed solvent of glacial acetic acid, anhydrous ethanol, and pure water is 7:1.

[0043] The mass percentage of ethyl cellulose in the spinning solution described in step one is 28%.

[0044] The solvent removal process described in step two specifically involves drying at room temperature for 12 hours.

[0045] The receiving spinner mentioned in step two is a rotating roller wrapped with aluminum foil.

[0046] The biodegradable flexible radiation-cooling film prepared in step two has a fiber diameter of 0.10 μm to 1.3 μm and a pore size of 0.20 μm to 2.5 μm.

[0047] Figure 1 The figures show the physical image, SEM image, and comparison of solar reflectance and mid-infrared emissivity of the EC fiber membrane prepared in Example 1. a is the physical image, b is the SEM image, and c is the solar reflectance and mid-infrared emissivity. As can be seen from the figures, the membrane formed by fiber stacking contains nano- and micro-sized fibers and pores, which can strongly scatter sunlight, thereby achieving passive radiative cooling during the day. The EC membrane achieves 98.1% solar reflectance and 88.4% emissivity within the atmospheric window, effectively enabling passive radiative cooling during the day.

[0048] The EC fiber membrane prepared in Example 1 was subjected to a 600-hour strong ultraviolet (UV) irradiation test (0.7 kW·h). - 1) This is equivalent to approximately 400 days of continuous outdoor exposure in the Harbin area. The test results are as follows: Figure 2 and Figure 3 As shown;

[0049] Figure 2 The figure shows the solar reflectance of the EC fiber membrane prepared in Example 1 under different UV irradiation times. As can be seen from the figure, the solar reflectance of the EC membrane hardly changed after 600 hours of strong UV irradiation, as shown in Table 1.

[0050] Table 1

[0051] UV irradiation time Solar reflectance (%) 0h 98.05609 100h 98.08368 200h 98.21156 300h 98.53732 400h 98.19011 500h 98.12102 600h 98.05698

[0052] Figure 3 The images show the CIE 1931 chromaticity diagram and optical image of the EC fiber membrane prepared in Example 1 after 600 hours of UV irradiation and without UV irradiation. a) CIE 1931 chromaticity diagram without UV irradiation; b) CIE 1931 chromaticity diagram after UV irradiation; c) optical image without UV irradiation; d) optical image after UV irradiation. The scale bar in the optical image is 1 cm. As can be seen from the figures, by comparing the optical images and CIE 1931 chromaticity diagram before and after UV irradiation, it was found that the EC membrane did not yellow under UV irradiation.

[0053] The EC fiber membrane and polyethylene nanomembrane (PE membrane) prepared in Example 1 were placed in soil to test their natural degradation properties from April 2, 2024 to November 25, 2024. Figure 4 Figure 1 shows the natural degradation test results of the EC fiber membrane and PE membrane prepared in Example 1, and the scanning electron microscope (SEM) image of the EC fiber membrane after natural degradation. Figure 2a shows the natural degradation test result, and Figure 3b shows the SEM image of the EC membrane after natural degradation. As shown in Figure 2a, after approximately 8 months, the EC fiber membrane partially degraded in the soil, while the control PE membrane maintained its intact morphology and structure. Figure 3b shows that the fibrous structure at the membrane's edge had disappeared and transformed into fine particles. As a natural cellulose derivative, ethyl cellulose still exhibits good biodegradability in nature. The edges of the EC membrane are more easily exposed to environmental factors such as moisture and oxygen, thus degrading faster, while the surface structure of the membrane is relatively stable, resulting in slower degradation.

[0054] Real-time monitoring of daytime radiative cooling performance: The equipment mainly consists of a top-covering PE film for shielding heat convection, surrounding insulating foam, an aluminum foil covering layer (for isolating ambient heat), thermocouples, and a temperature signal conversion module, and is equipped with thermocouples for real-time monitoring of sample temperature. Figure 5 (a and 5b). Six identical rectangular recesses (4cm × 4cm × 2cm) were prepared on the top of the device for placing test samples (EC film, black carbon fiber, black carbon fiber covered with EC film, and white paper) (4cm × 4cm) and thermocouples. During outdoor testing, solar radiation power was measured using a solar radiometer (TES1333R, TES Electrical & Electronic Co., Ltd., China). Ambient humidity and wind speed were read using a hygrometer and anemometer. Real-time temperature data were collected using a data logging thermometer with thermocouples (EX4000, Eion (Shenzhen) Technology Co., Ltd., China). The device was placed on a rack on a rooftop to reduce heat convection from the ground; the test location was Harbin Institute of Technology (May 23, 2024, UTC+8, sunny to cloudy), to study the environmental cooling performance of EC film under direct sunlight in Harbin, China (45°43′49″N, 126°38′11″E, altitude 128 meters). Figure 5 The following graphs show the cooling performance test results of the EC fiber membrane prepared in Example 1: a) is a photograph of the outdoor daytime radiative cooling test; b) is a schematic diagram of the equipment structure for real-time monitoring of daytime radiative cooling performance; c) shows the relationship between temperature (T) and time during the test; and d) shows the temperature difference (ΔT = T) during the test. amb -T cooler The relationship between ) and time; field tests show that in a dry and sunny environment (relative humidity of approximately 20%, solar radiation greater than 600 W / m²), 2 The peak value is approximately 961 W / m 2From 12:00 to 13:00, when solar radiation was strong, the ambient temperature was 35.6℃, the temperature of the black carbon fiber reached 65.3℃, while the temperature of the carbon fiber covered by the EC film remained at 25.2℃, representing an actual temperature drop of 40.1℃. This demonstrates its cooling performance in real-world conditions. Figure 5 c). Compared to the ambient temperature (35.6℃), the EC membrane (25.2℃) achieved a temperature reduction of approximately 10.4℃ (ΔT = T). amb -T cooler T amb For ambient temperature, T cooler (Refrigeration temperature of the cooling film) Figure 5 d), while the actual temperature drop of the white paper was about 5.2℃, which is far lower than the cooling effect of the EC film, further proving the excellent cooling performance of the EC film.

[0055] According to the GB / T 16491-2022 testing standard, the mechanical properties of the EC fiber membrane prepared in Example 1 were tested, and the Young's modulus of the EC fiber membrane was measured to be 10.1 MPa.

Claims

1. A method for preparing a biodegradable flexible radiation-cooling thin film, characterized in that... It is done in the following steps: I. Preparation of spinning solution: Ethyl cellulose is dissolved in a solvent to obtain a spinning solution; II. Electrospinning is used to synthesize nano and micron-sized EC fibers; Electrospinning was performed under the following conditions: voltage 15kV, injection speed 0.06mm / min, temperature 25℃, humidity 25%, syringe needle inner diameter 0.23mm, distance between syringe needle and receiving spinneret 25cm, translational speed of syringe needle 500mm / min, and rotational speed of receiving spinneret 2r / min. Finally, the solvent was removed by drying to obtain a biodegradable flexible radiation cooling film. The solvent mentioned in step one is a mixed solvent of glacial acetic acid, anhydrous ethanol, and pure water; the volume ratio of glacial acetic acid to anhydrous ethanol in the mixed solvent of glacial acetic acid, anhydrous ethanol, and pure water is 7:2; the volume ratio of glacial acetic acid to pure water in the mixed solvent of glacial acetic acid, anhydrous ethanol, and pure water is 7:

1. The mass percentage of ethyl cellulose in the spinning solution described in step one is 28%; The solvent removal process described in step two specifically involves drying at room temperature for 12 hours. The receiving spinner mentioned in step two is a rotating roller wrapped with aluminum foil; The biodegradable flexible radiation cooling film prepared in step two has a fiber diameter of 0.10 μm to 1.3 μm and a pore size of 0.20 μm to 2.5 μm. The prepared biodegradable flexible radiation-cooling thin film has a solar reflectance of 98.1% and an emissivity of 88.4% in the atmospheric window. The prepared biodegradable flexible radiation cooling film was subjected to 0.7 kW·h - ¹ After 600 hours of intense ultraviolet radiation, the solar reflectance is 98.05698%; The prepared biodegradable flexible radiation-cooling film has a Young's modulus of 10.1 MPa.

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