Preparation method of ultraviolet radiation-resistant polyurethane-based radiative refrigeration film

Abstract

A method for preparing a polyurethane-based radiative cooling film resistant to ultraviolet radiation belongs to the field of radiative cooling technology. The present invention is a radiative cooling material based on TPU, which aims to enhance ultraviolet durability while maintaining its excellent cooling performance and structural integrity. Method: 1. Prepare shell spinning solution; 2. Prepare core spinning solution; 3. Prepare BST‑PVP@TPU fiber membrane. The BST‑PVP@TPU prepared by the present invention exhibits a reflectivity of up to 97.2% (0.25‑2.5μm), and the infrared emissivity in the atmospheric transparent window reaches 93.2% (8‑13μm). These properties enable the film to cool effectively, providing 125.21Wm ‑2 The cooling power can reduce the temperature by a maximum of 12.4°C, providing important support for efficient thermal management. The present invention can obtain a polyurethane-based radiative cooling film that is resistant to ultraviolet radiation.

Description

Technical Field

[0001] The invention belongs to the technical field of radiation refrigeration, and in particular relates to a method for preparing a polyurethane-based radiation refrigeration film resistant to ultraviolet radiation. Background Art

[0002] Refrigeration is the most effective and direct method for providing thermal comfort, long-term food preservation, and preventing heat shock. Radiative cooling, as an energy-free, sustainable cooling mechanism, has garnered widespread attention. Among daytime radiative cooling materials, polymer-based radiative cooling materials, with their high intrinsic infrared emissivity and wide-band high sunlight reflectivity, have dominated the development of radiative cooling technology.

[0003] Polyurethane itself has highly absorbing functional groups (such as CO, CH, COC) within the "atmospheric window" range. Its strong polarity facilitates the construction of nanoscale structures through electrospinning to induce significant refractive index differences at the air / solid interface, resulting in significant solar radiation scattering. Although the fiber membrane provides a larger specific surface area to increase scattering, it also exposes a larger area susceptible to UV damage. Intervention in the film composition is required to achieve a significant improvement in its UV weather resistance while maintaining the radiative cooling capacity of the TPU fiber membrane.

[0004] Current research on improving the UV aging performance of polymers tends to incorporate suitable inorganic particles into the polymer matrix. This approach effectively optimizes the optical properties of the material, including modulated reflection enhancement and optimized optical absorption. Al2O3 and BaSO4, for example, are commonly used as UV reflectors. TiO2 particles have high UV absorption and are dispersed in the polymer matrix to offset the effects of UV. However, when inorganic particles are directly added to the polymer solution via uniaxial spinning, the fibers often exhibit an uneven particle distribution or even a beaded morphology, which is mainly attributed to compatibility issues, resulting in a decrease in overall optical reflectivity compared to the ideal structure expected by Mie theory. Summary of the Invention

[0005] The purpose of the present invention is to solve the following technical problems:

[0006] 1) The phase separation method has difficulty controlling pore size and effectively scattering UV light, thus limiting high reflectivity; electrospun fiber membranes have a larger specific surface area and are more susceptible to UV damage;

[0007] 2) Radiative cooling materials are often doped with reflective (Al2O3 and BaSO4) / absorbent (TiO2) inorganic particles to improve UV weathering resistance. However, the particles in the prepared fibers are unevenly distributed and even exhibit a bead-like morphology, which does not conform to Mie theory.

[0008] 3) TPU is mostly used as a particle carrier in electrospinning radiation refrigeration materials. There is little research on its own optical properties, and even less research on improving its UV aging performance.

[0009] A method for preparing a polyurethane-based radiative refrigeration film resistant to ultraviolet radiation is provided.

[0010] A method for preparing a polyurethane-based radiative cooling film resistant to ultraviolet radiation is specifically completed by the following steps:

[0011] 1. Preparation of shell spinning solution:

[0012] dissolving TPU in N,N-dimethylformamide to obtain a shell spinning solution;

[0013] The mass fraction of TPU in the shell spinning solution described in step 1 is 12% to 20%.

[0014] 2. Preparation of core layer spinning solution:

[0015] Will Ba 0·6 Sr 0·4 TiO3 nanorods and polyvinyl pyrrolidone were dissolved in a mixed solution of anhydrous ethanol and DMF to obtain a core spinning solution;

[0016] Ba in the core spinning solution described in step 2 0·6 Sr 0·4 The mass ratio of TiO3 to polyvinyl pyrrolidone is (5-8):10;

[0017] Ba described in step 2 0·6 Sr 0·4 The total mass of TiO3 and polyvinyl pyrrolidone is 10% to 20% of the mass of the core spinning solution;

[0018] 3. Preparation of BST-PVP@TPU fiber membrane:

[0019] The core layer spinning solution and the shell layer spinning solution are added to a disposable syringe, a coaxial spinning metal needle is fixed, the positive electrode is connected to the metal needle and a high voltage of 10kV to 15kV is applied, the receiving distance is 18cm to 25cm, the cabin temperature is 30℃ to 50℃, the humidity is 20% to 25%, the shell layer speed is fixed at 0.1mm / min to 0.2mm / min, and the injection speed of the core layer is controlled for electrospinning to obtain a BST-PVP@TPU fiber membrane with a core-shell structure; the BST-PVP@TPU fiber membrane with a core-shell structure is placed in a blast oven and dried to obtain a polyurethane-based radiation refrigeration film resistant to ultraviolet radiation.

[0020] Principle of the present invention:

[0021] The most important factor affecting TPU is ultraviolet radiation with a wavelength of 330 to 410 nm. Compared with TiO2 (3.2 eV), Ba has a band gap of about 3.04 eV. 0·6 Sr 0·4 TiO3(BST) allows for more efficient absorption of UV radiation with wavelengths below 408nm. In addition, through the design of the preparation process, Ba 0·6 Sr 0·4 TiO3 can carry a negative charge, which can electrostatically adsorb free radicals generated during the aging process of TPU. It can even further match the crystal lattice for physical adsorption to prevent the occurrence of aging reactions. In addition, Ba 0·6 Sr 0·4 TiO3 has a higher refractive index and can scatter visible light more effectively, maintaining the optical properties of the composite fiber membrane. Inorganic nanorods with a high aspect ratio are more easily oriented in an electric field. By utilizing coaxial electrospinning technology, these nanorods can be evenly arranged in the TPU matrix (BST-PVP@TPU).

[0022] The present invention is a TPU-based radiative cooling material designed to enhance UV durability while maintaining its superior cooling performance and structural integrity, with the following benefits:

[0023] (1) The present invention uses coaxial electrospinning technology to successfully prepare a core-shell structured ultraviolet radiation-resistant polyurethane-based radiative cooling film (BST-PVP@TPU), which exhibits excellent durability and good mechanical properties under ultraviolet irradiation, providing a wide range of potential for different applications;

[0024] (2) The combination of BST nanorods in the UV spectrum is characterized by a high extinction coefficient and a relatively large refractive index, allowing effective UV absorption without significantly affecting the overall reflectivity of the TPU film; BST-PVP@TPU exhibits a reflectivity of up to 97.2% (0.25-2.5μm) and an infrared emissivity of 93.2% (8-13μm) in the atmospheric transparent window. These properties enable the film to be cooled effectively, providing a cooling power of 125.21Wm-2, capable of reducing the temperature by a maximum of 12.4°C, providing important support for efficient thermal management;

[0025] (3) The -NH· free radicals generated by TPU under ultraviolet irradiation are adsorbed by BST nanorods, thereby further delaying the aging reaction of TPU; at 0.7kWm -2Under continuous UV irradiation for 216 hours, the reflectivity of the BST-PVP@TPU film stabilized at 92.1%, maintaining a stable cooling power of 85.78 Wm⁻². The TPU film essentially lost its radiative cooling capacity (-0.42 Wm⁻²) after the same aging treatment. The BST-PVP@TPU maintained its cooling potential during continuous outdoor use for up to 144 days, while the TPU film maintained the same performance for 48 days. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 These are the reflectance and emissivity spectra of the BST-PVP@TPU fiber film prepared in Example 2 at different UV aging times;

[0027] Figure 2 Transmission electron microscopy and scanning electron microscopy images of the BST-PVP@TPU fiber film prepared in Example 2;

[0028] Figure 3 The BST-PVP@TPU fiber film prepared in Example 2 and the TPU fiber film prepared in Example 1 were heated at 0.7 kWm -2 Comparison of radiative cooling power after 216 hours of continuous ultraviolet irradiation. DETAILED DESCRIPTION

[0029] Specific embodiment 1: This embodiment provides a method for preparing a polyurethane-based radiative cooling film resistant to ultraviolet radiation, which is specifically completed by the following steps:

[0030] 1. Preparation of shell spinning solution:

[0031] dissolving TPU in N,N-dimethylformamide to obtain a shell spinning solution;

[0032] The mass fraction of TPU in the shell spinning solution described in step 1 is 12% to 20%.

[0033] 2. Preparation of core layer spinning solution:

[0034] Will Ba 0·6 Sr 0·4 TiO3 nanorods and polyvinyl pyrrolidone were dissolved in a mixed solution of anhydrous ethanol and DMF to obtain a core spinning solution;

[0035] Ba in the core spinning solution described in step 2 0·6 Sr 0·4 The mass ratio of TiO3 to polyvinyl pyrrolidone is (5-8):10;

[0036] Ba described in step 2 0·6 Sr 0·4The total mass of TiO3 and polyvinyl pyrrolidone is 10% to 20% of the mass of the core spinning solution;

[0037] 3. Preparation of BST-PVP@TPU fiber membrane:

[0038] The core layer spinning solution and the shell layer spinning solution are added to a disposable syringe, a coaxial spinning metal needle is fixed, the positive electrode is connected to the metal needle and a high voltage of 10kV to 15kV is applied, the receiving distance is 18cm to 25cm, the cabin temperature is 30℃ to 50℃, the humidity is 20% to 25%, the shell layer speed is fixed at 0.1mm / min to 0.2mm / min, and the injection speed of the core layer is controlled for electrospinning to obtain a BST-PVP@TPU fiber membrane with a core-shell structure; the BST-PVP@TPU fiber membrane with a core-shell structure is placed in a blast oven and dried to obtain a polyurethane-based radiation refrigeration film resistant to ultraviolet radiation.

[0039] Specific implementation method 2: This implementation method is different from the specific implementation method 1 in that: the Ba 0· 6Sr 0·4 TiO3 nanorods are prepared by sol-gel method and electrospinning method. The specific preparation method is as follows:

[0040] ①, preparing barium strontium titanate sol spinning solution;

[0041] First, 0.02 mol of tetrabutyl titanate was dissolved in 0.04 mol of acetylacetone and stirred at 40°C for 30 minutes to obtain solution A; then, 0.012 mol of barium acetate and 0.008 mol of strontium acetate were dissolved in 15 mL of acetic acid and stirred continuously at 60°C for 30 minutes, and then cooled to 40°C to obtain solution B; solution B was dropwise added to solution A and aged at room temperature for 48 hours to obtain a mixed solution; then, 10 mL of DMF was added to the mixed solution, and PVP accounting for 8 wt% of the total mass of the mixed solution was added while stirring to obtain a light yellow spinning solution, i.e., barium strontium titanate sol spinning solution;

[0042] ②Preparation of barium strontium titanate gel fiber:

[0043] The barium strontium titanate sol spinning solution was added to a disposable syringe, a coaxial spinning metal needle was fixed, the positive electrode was connected to the metal needle, and a high voltage of 10 kV was applied. Electrospinning was performed at a receiving distance of 20 cm, a cabin temperature of 40°C, a humidity of 20%, and a push injection speed of 0.2 mm / min to obtain barium strontium titanate gel fibers.

[0044] ③ Calcination:

[0045] The barium strontium titanate gel fiber is calcined at high temperature to obtain Ba 0·6Sr 0·4 TiO3 nanorods. Other steps are the same as those in the first embodiment.

[0046] Specific embodiment 3: This embodiment differs from specific embodiment 1 or 2 in that the high-temperature calcination temperature in step ③ is 750°C to 900°C and the calcination time is 2h to 4h. The other steps are the same as specific embodiment 1 or 2.

[0047] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that the volume ratio of anhydrous ethanol to DMF in the mixed solution of anhydrous ethanol and DMF in step 2 is 1:1. The other steps are the same as specific embodiments 1 to 3.

[0048] Specific embodiment 5: This embodiment differs from specific embodiments 1 to 4 in that: the Ba 0·6 Sr 0·4 The total mass of TiO3 and polyvinyl pyrrolidone is 15% of the mass of the core layer spinning solution. The other steps are the same as those in the first to fourth embodiments.

[0049] Specific embodiment 6: This embodiment differs from specific embodiments 1 to 5 in that the injection speed ratio of the core layer to the shell layer in step 3 is (1 to 5): 10. The other steps are the same as specific embodiments 1 to 5.

[0050] Specific embodiment 7: This embodiment differs from specific embodiments 1 to 6 in that the injection speed ratio of the core layer to the shell layer in step 3 is 4:10. The other steps are the same as specific embodiments 1 to 6.

[0051] Specific Embodiment 8: This embodiment differs from Specific Embodiments 1 to 7 in that, in step 3, the core layer spinning solution and the shell layer spinning solution are added to a disposable syringe. A coaxial spinning metal needle is fixed, the positive electrode is connected to the metal needle, and a high voltage of 10 kV is applied. The receiving distance is 20 cm, the chamber temperature is 40°C, and the humidity is 20%. The shell layer speed is fixed at 0.2 mm / min, and the core layer injection speed is controlled for electrospinning to obtain a BST-PVP@TPU fiber membrane with a core-shell structure. The other steps are the same as Specific Embodiments 1 to 7.

[0052] Specific embodiment 9: This embodiment differs from specific embodiments 1 to 8 in that the metal needle described in step 3 is a No. 22 single-axis needle. The other steps are the same as specific embodiments 1 to 8.

[0053] Specific embodiment 10: This embodiment differs from specific embodiments 1 to 9 in that in step 3, the core-shell BST-PVP@TPU fiber membrane is placed in a forced air oven at 80°C to 90°C and dried for 20 to 28 hours. The other steps are the same as specific embodiments 1 to 9.

[0054] The following examples are used to verify the beneficial effects of the present invention:

[0055] Example 1: The preparation method of TPU fiber membrane is completed according to the following steps:

[0056] 1. Preparation of spinning solution:

[0057] dissolving thermoplastic polyurethane (TPU) in N,N-dimethylformamide (DMF) to obtain a TPU spinning solution;

[0058] The mass fraction of TPU in the TPU spinning solution described in step 1 is 18%;

[0059] 2. Preparation of TPU fiber membrane:

[0060] The TPU spinning solution was added to a 5mL disposable syringe, the spinning metal needle was fixed, the positive electrode was connected to the metal needle and a high voltage of 10kV was applied. The receiving distance was 20cm, the cabin temperature was 40°C, and the humidity was 20%. The injection speed of the TPU spinning solution was fixed at 0.2mm / min for electrospinning, and then placed in a blast oven at 85°C for drying for 24 hours to obtain a TPU fiber membrane.

[0061] Example 2: A method for preparing a polyurethane-based radiative cooling film resistant to ultraviolet radiation is specifically completed by the following steps:

[0062] 1. Preparation of shell spinning solution:

[0063] dissolving thermoplastic polyurethane (TPU) in N,N-dimethylformamide (DMF) to obtain a shell spinning solution;

[0064] The mass fraction of TPU in the shell spinning solution described in step 1 is 18%;

[0065] 2. Preparation of core layer spinning solution:

[0066] Will Ba 0·6 Sr 0·4 TiO3 nanorods (BST) and polyvinyl pyrrolidone were dissolved in a mixed solution of anhydrous ethanol and DMF to obtain a core spinning solution;

[0067] The volume ratio of anhydrous ethanol to DMF in the mixed solution of anhydrous ethanol and DMF described in step 2 is 1:1;

[0068] Ba in the core spinning solution described in step 2 0·6 Sr 0·4 The mass ratio of TiO3 to polyvinyl pyrrolidone is 8:10;

[0069] Ba described in step 2 0·6 Sr 0·4 The total mass of TiO3 and polyvinyl pyrrolidone is 15% of the mass of the core spinning solution;

[0070] 3. Preparation of BST-PVP@TPU fiber membrane:

[0071] The core layer spinning solution and the shell layer spinning solution were added to a 5mL disposable syringe, a coaxial spinning metal needle was fixed, the positive electrode was connected to the metal needle and a high voltage of 10kV was applied, the receiving distance was 20cm, the cabin temperature was 40℃, and the humidity was 20%. The injection speed of the shell layer was fixed at 0.2mm / min, and the injection speed of the core layer was fixed at 0.08mm / min for electrospinning to obtain a BST-PVP@TPU fiber membrane with a core-shell structure; the BST-PVP@TPU fiber membrane with a core-shell structure was placed in a blast oven at a temperature of 85℃ and dried for 24h to obtain a polyurethane-based radiation refrigeration film (BST-PVP@TPU fiber membrane) resistant to ultraviolet radiation.

[0072] Ba described in Example 2 0·6 Sr 0·4 TiO3 nanorods are prepared by sol-gel method and electrospinning method. The specific preparation method is as follows:

[0073] ①, preparing barium strontium titanate sol spinning solution;

[0074] First, 0.02 mol of tetrabutyl titanate was dissolved in 0.04 mol of acetylacetone and stirred at 40°C for 30 minutes to obtain solution A; then, 0.012 mol of barium acetate and 0.008 mol of strontium acetate were dissolved in 15 mL of acetic acid and stirred continuously at 60°C for 30 minutes, and then cooled to 40°C to obtain solution B; solution B was dropwise added to solution A and aged at room temperature for 48 hours to obtain a mixed solution; then, 10 mL of DMF was added to the mixed solution, and PVP accounting for 8 wt% of the total mass of the mixed solution was added while stirring to obtain a light yellow spinning solution, i.e., barium strontium titanate sol spinning solution;

[0075] ②Preparation of barium strontium titanate gel fiber:

[0076] The barium strontium titanate sol spinning solution was added to a disposable syringe, a coaxial spinning metal needle was fixed, the positive electrode was connected to the metal needle, and a high voltage of 10 kV was applied. Electrospinning was performed at a receiving distance of 20 cm, a cabin temperature of 40°C, a humidity of 20%, and a push injection speed of 0.2 mm / min to obtain barium strontium titanate gel fibers.

[0077] ③ Calcination:

[0078] The barium strontium titanate gel fiber was calcined at 850℃ for 3h to obtain Ba 0·6 Sr 0·4 TiO3 nanorods.

[0079] Figure 1 These are the reflectance and emissivity spectra of the BST-PVP@TPU fiber film prepared in Example 2 at different UV aging times;

[0080] from Figure 1 It can be seen that: BST-PVP@TPU fiber membrane has a strength of 0.7kW h -1 After 144 hours of ultraviolet irradiation, the reflectivity of the film changed little. When the ultraviolet irradiation time was continued to 216 hours, the reflectivity of the BST-PVP@TPU film remained at 92.1%.

[0081] Figure 2 Transmission electron microscopy and scanning electron microscopy images of the BST-PVP@TPU fiber film prepared in Example 2;

[0082] from Figure 2 It can be seen that BST is uniformly distributed in the TPU matrix, presenting a clear interface between them. Coaxial electrospinning leads to a uniform distribution of TPU and BST, as well as a more ordered interfacial contact, which is beneficial to ensuring the optical and mechanical properties of the film.

[0083] Figure 3 The BST-PVP@TPU fiber film prepared in Example 2 and the TPU fiber film prepared in Example 1 were heated at 0.7 kWm -2 Comparison of radiative cooling power after 216 hours of continuous ultraviolet irradiation;

[0084] from Figure 3 It can be seen that after 216 hours of UV aging cycle, TPU showed -0.42Wm -2 The maximum theoretical cooling power of the BST-PVP@TPU film was 85.78 W m-1 under the same aging conditions. -2 The theoretical cooling power of BST is shown in Figure 2. It is proved that the addition of BST improves the UV durability of TPU.

[0085] The effects of Examples 1 and 2 are listed in Table 1.

[0086] Table 1

[0087]

[0088] From the results shown in Table 1, it can be seen that although BST has certain ultraviolet absorption in Example 2, the reflectivity of the BST-PVP@TPU fiber membrane prepared by coaxial spinning is higher than that of the TPU fiber membrane, which is mainly due to the strong scattering caused by BST evenly distributed in the TPU. Infrared light is mainly transmitted in the form of material absorption without obvious reflection. Since the absorption characteristics of TPU are relatively stable, the surface morphology and internal structure of the fiber have little effect on the infrared emissivity. Reasonable optimization of the morphology of the film and the scattering ability of visible light can avoid the weakening of the material's cooling capacity due to the strong ultraviolet absorption of BST. After constructing a coaxial structure fiber film with uniform morphology, the BST-PVP@TPU fiber film has the best cooling power, which can reach up to 125.21W / m 2 .

Claims

1. A method for preparing a polyurethane-based radiative cooling film resistant to ultraviolet radiation, characterized in that The preparation method is specifically completed according to the following steps:

1. Preparation of shell spinning solution: dissolving TPU in N,N-dimethylformamide to obtain a shell spinning solution; The mass fraction of TPU in the shell spinning solution described in step 1 is 12% to 20%; 2. Preparation of core layer spinning solution: Will Ba 0·6 Sr 0·4 TiO3 nanorods and polyvinyl pyrrolidone were dissolved in a mixed solution of anhydrous ethanol and DMF to obtain a core layer spinning solution; Ba in the core spinning solution described in step 2 0·6 Sr 0·4 The mass ratio of TiO3 to polyvinyl pyrrolidone is (5-8):10; Ba described in step 2 0·6 Sr 0·4 The total mass of TiO3 and polyvinyl pyrrolidone is 10% to 20% of the mass of the core spinning solution; Ba described in step 2 0·6 Sr 0·4 TiO3 nanorods are prepared by sol-gel method and electrospinning method. The specific preparation method is as follows: ①, preparing barium strontium titanate sol spinning solution; First, 0.02 mol of tetrabutyl titanate was dissolved in 0.04 mol of acetylacetone and stirred at 40°C for 30 minutes to obtain solution A; then, 0.012 mol of barium acetate and 0.008 mol of strontium acetate were dissolved in 15 mL of acetic acid and stirred continuously at 60°C for 30 minutes, and then cooled to 40°C to obtain solution B; solution B was dropwise added to solution A and aged at room temperature for 48 hours to obtain a mixed solution; then, 10 mL of DMF was added to the mixed solution, and PVP accounting for 8 wt% of the total mass of the mixed solution was added while stirring to obtain a light yellow spinning solution, i.e., barium strontium titanate sol spinning solution; ②Preparation of barium strontium titanate gel fiber: The barium strontium titanate sol spinning solution was added to a disposable syringe, a coaxial spinning metal needle was fixed, the positive electrode was connected to the metal needle, and a high voltage of 10 kV was applied. Electrospinning was performed at a receiving distance of 20 cm, a cabin temperature of 40°C, a humidity of 20%, and a push injection speed of 0.2 mm / min to obtain barium strontium titanate gel fibers. ③ Calcination: The barium strontium titanate gel fiber is calcined at high temperature to obtain Ba 0·6 Sr 0·4 TiO3 nanorods; 3. Preparation of BST-PVP@TPU fiber membrane: The core layer spinning solution and the shell layer spinning solution are added to a disposable syringe, a coaxial spinning metal needle is fixed, the positive electrode is connected to the metal needle and a high voltage of 10kV to 15kV is applied, the receiving distance is 18cm to 25cm, the cabin temperature is 30℃ to 50℃, the humidity is 20% to 25%, the shell layer speed is fixed at 0.1mm / min to 0.2mm / min, and the injection speed of the core layer is controlled for electrospinning to obtain a BST-PVP@TPU fiber membrane with a core-shell structure; the BST-PVP@TPU fiber membrane with a core-shell structure is placed in a blast oven and dried to obtain a polyurethane-based radiation refrigeration film resistant to ultraviolet radiation.

2. The method for preparing a polyurethane-based radiative cooling film resistant to ultraviolet radiation according to claim 1, characterized in that The high-temperature calcination temperature in step ③ is 750° C. to 900° C., and the calcination time is 2 h to 4 h.

3. The method for preparing a polyurethane-based radiative cooling film resistant to ultraviolet radiation according to claim 1, characterized in that The volume ratio of anhydrous ethanol to DMF in the mixed solution of anhydrous ethanol and DMF described in step 2 is 1:

1.

4. The method for preparing a polyurethane-based radiative cooling film resistant to ultraviolet radiation according to claim 3, characterized in that Ba described in step 2 0·6 Sr 0·4 The total mass of TiO3 and polyvinyl pyrrolidone is 15% of the mass of the core layer spinning solution.

5. The method for preparing a polyurethane-based radiative cooling film resistant to ultraviolet radiation according to claim 1, characterized in that In step 3, the injection speed ratio of the core layer to the shell layer is (1-5):

10.

6. The method for preparing a polyurethane-based radiative cooling film resistant to ultraviolet radiation according to claim 5, characterized in that In step 3, the injection speed ratio of the core layer to the shell layer is 4:

10.

7. The method for preparing a polyurethane-based radiative cooling film resistant to ultraviolet radiation according to claim 1, characterized in that In step three, the core layer spinning solution and the shell layer spinning solution are added to a disposable syringe, the coaxial spinning metal needle is fixed, the positive electrode is connected to the metal needle and a high voltage of 10kV is applied. The receiving distance is 20cm, the cabin temperature is 40°C, the humidity is 20%, the shell layer speed is fixed at 0.2mm / min, and the injection speed of the core layer is controlled for electrospinning to obtain a BST-PVP@TPU fiber membrane with a core-shell structure.

8. The method for preparing a polyurethane-based radiative cooling film resistant to ultraviolet radiation according to claim 1, characterized in that The metal needle described in step 3 is a NO.22 single-axis needle.

9. The method for preparing a polyurethane-based radiative cooling film resistant to ultraviolet radiation according to claim 1, characterized in that In step three, the BST-PVP@TPU fiber membrane with a core-shell structure is placed in a forced air oven at a temperature of 80° C. to 90° C. and dried for 20 h to 28 h.

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