A thin radiation cooling film and its preparation method and application

Abstract

The present invention discloses a thin and light radiative cooling film, its preparation method, and application. The preparation method comprises: mixing a fluorocarbon resin-based polymer, a two-component solvent, and water to form a spinning solution, using the spinning solution as a raw material for electrostatic spinning, and depositing a fiber film on the surface of a collecting plate to produce a thin and light radiative cooling film. Compared with existing conventional radiative cooling materials, the thin and light radiative cooling film produced by the present invention can achieve high reflection and high radiation of sunlight while being thin, has lighter weight, and has better flexibility. It combines the advantages of "thin thickness, light weight, good radiative cooling effect, and high tensile strength" and can be processed into a high-strength radiative cooling thin fabric with excellent cooling function and wearability. At the same time, the preparation method of the present invention can achieve low-cost, large-scale preparation, and also has the advantages of simple process, convenient operation, and mild production conditions, which facilitates the industrial application of thin and light radiative cooling films.

Description

Technical Field

[0001] The invention belongs to the technical field of radiation ester cooling, and relates to a light and thin radiation cooling film and a preparation method and application thereof. Background Art

[0002] With the rapid development of society, people's demand for cooling is increasing. Therefore, it is imperative to develop efficient and environmentally friendly cooling methods, such as passive daytime radiative cooling technology. This technology effectively blocks the input of solar energy in the wavelength range of approximately 250-2500nm, while selectively radiating its own heat through an atmospheric transparent window with a wavelength of 8-13μm to the cold outer space with a temperature close to 0K. This technology achieves efficient cooling and even refrigeration without energy consumption, and has become an emerging research hotspot.

[0003] In order to enable daytime radiative cooling devices to have the above-mentioned spectral selectivity, researchers have developed a series of radiative cooling devices based on photonic crystals and metamaterials, and have achieved certain cooling effects in outdoor cooling performance tests. However, due to the complex manufacturing process, radiative cooling materials based on ordered photonic crystals are difficult to prepare on a large scale. With the rapid development of nanoscience and technology, disordered media are playing an increasingly important role in the production of functional devices. Combining disordered media with polymer photonics to achieve multi-band spectral regulation has become an effective way to achieve large-scale preparation of daytime radiative cooling materials. In particular, polymer membranes based on disordered porous structures are easier to achieve low cost and lightweight because they do not involve the use of fillers. In recent years, they have received widespread attention and extensive research in domestic and foreign academic circles.

[0004] Currently, one of the key issues limiting the widespread application of radiative cooling materials is the conflict between their cooling performance and wearability. High porosity and sufficient thickness are crucial for achieving high solar reflectivity, but high porosity inevitably weakens the material's mechanical properties, while increased thickness compromises its flexibility. Therefore, achieving a balance of "thin, light, cool, and strong" is essential for radiative cooling materials to reach market success, but existing materials struggle to meet these requirements simultaneously. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a thin radiation cooling film with high tensile strength, excellent flexibility, and excellent thermal insulation and cooling performance, as well as a preparation method and application thereof, in response to the deficiencies in the prior art.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A method for preparing a thin radiation cooling film comprises the following steps:

[0008] (1) mixing a fluorocarbon resin-based polymer and a two-component solvent, and stirring until completely dissolved to obtain a fluorocarbon resin-based polymer solution; the two-component solvent is a mixed solvent of acetone and a non-volatile organic solvent; the mass ratio of the acetone to the non-volatile organic solvent is 0.25 to 4:1;

[0009] (2) mixing the fluorocarbon resin-based polymer solution obtained in step (1) with water and stirring to obtain a spinning solution;

[0010] (3) Using the spinning solution obtained in step (2) as a raw material, electrospinning is performed to deposit the fiber membrane on the surface of a collecting plate, and drying is performed to obtain a thin radiation cooling membrane.

[0011] The above preparation method is further improved, in step (1), the mass ratio of the fluorocarbon resin-based polymer to the two-component solvent is 1 to 2:10; the fluorocarbon resin-based polymer is at least one of polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride, and polytetrafluoroethylene; and the non-volatile organic solvent is at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide.

[0012] The above preparation method is further improved in that, in step (2), the mass ratio of water to the two-component solvent is ≤1:10.

[0013] The above preparation method is further improved in that in step (2), the mass ratio of water to the two-component solvent is 0.1 to 1:10.

[0014] The above preparation method is further improved in that in step (1), the stirring is carried out at a temperature of 25°C to 80°C.

[0015] The above preparation method is further improved in that, in step (2), the stirring is carried out at a temperature of 25°C to 80°C; and the stirring time is ≥10 min.

[0016] The above preparation method is further improved, in which, in step (3), an electrospinning machine is used for electrospinning; the process conditions of the electrospinning are: a spinning temperature of 15°C to 35°C, a spinning humidity of 20% to 60%, a propulsion speed of the spinning solution of 0.6mL / h to 2mL / h, a distance between the spinneret and the collecting plate of 12cm to 30cm, a spinning voltage of 8kV to 12kV, and a drum collector speed of 50rpm to 500rpm.

[0017] As a general technical concept, the present invention also provides a thin and light radiation cooling film, which is prepared by the above-mentioned preparation method.

[0018] The above-mentioned thin and light radiation cooling film is further improved, wherein the thin and light radiation cooling film is a porous film formed by fiber stacking; the diameter of the fiber is 50nm~1.8μm; the pore size of the thin and light radiation cooling film is 0.1μm~7μm; the porosity of the thin and light radiation cooling film is 55%~85%; the thickness of the thin and light radiation cooling film is 80μm~400μm.

[0019] As a general technical concept, the present invention also provides an application of the above-mentioned thin radiation cooling film, wherein the thin radiation cooling film is used as a raw material for processing into thin fabrics.

[0020] The above application is further improved, wherein the thin fabric includes one of a car parasol, a car cover, a sun-proof clothing, a sun-proof tarpaulin, and a handheld parasol.

[0021] Compared with the prior art, the advantages of the present invention are:

[0022] (1) In view of the defects of existing radiation cooling materials that cannot be "thin, light, cold and strong", the present invention creatively proposes a method for preparing a thin radiation cooling film, which is prepared by electrospinning. By optimizing the components of the spinning solution, a fiber material with a diameter comparable to the wavelength of the reflected light, a smooth surface and high toughness can be prepared. These fibers can then be used to composite into a thin film with a rich porous structure. In this way, while ensuring that the film is thin, light and has high tensile strength, the film's reflective performance to sunlight and its own infrared radiation performance can be significantly improved, and finally a radiation cooling film with the characteristics of "thin, light, cold and strong" can be formed. The cooling film is specifically made of fluorocarbon resin-based polymer as raw material. It is a semi-crystalline polymer that is easy to crystallize when precipitated from the solvent, so it is easier to achieve the "thin, light, cold and strong" film material by regulating the morphology and crystal form of the polymer fiber; on this basis, the morphology and crystal form of the polymer fiber are effectively regulated by optimizing the formula of the spinning solution, wherein the fluorocarbon resin-based polymer is dissolved in a two-component solvent composed of acetone and an organic solvent that is not easy to be used, and acetone can be used to dilute the concentration of the spinning solution and reduce the viscosity of the spinning solution. At the same time, the rapid volatilization of acetone can promote the low viscosity spinning solution to be exposed to the air. The polymer concentration increases sharply, thereby forming a high-concentration jet during the jet injection process, which is conducive to obtaining thicker (larger diameter) fibers. The fiber diameter becomes thicker, the defects become fewer, and its strength can be improved. However, the rapid volatilization of acetone will also increase the viscosity of the spinning solution and the spinning cost, which is not conducive to the stability of the spinning flow, and the surface of the obtained fiber is not smooth enough. Based on this, in the present invention, water is also added to the fluorocarbon resin-based polymer solution. Under the synergistic effect of water and acetone, thick fibers with equivalent diameter and smooth surface can be obtained without excessively increasing the concentration and dosage of the polymer, while also saving the polymer. More importantly, the addition of water can destroy the thermodynamically metastable state of the spinning solution when acetone evaporates, causing the spinning solution to become unstable and undergo phase separation, thereby accelerating the coagulation of the polymer in the jet. This not only helps to obtain dense fibers, but also prevents the polymers from having time to arrange themselves regularly, which is beneficial to reducing the crystallinity of the fibers and further improving the deformability of the molecular chains. Macroscopically, this is manifested as improved toughness. Therefore, the introduction of water effectively solves the problem of difficulty in obtaining smooth and flat coarse fibers from high-concentration spinning solutions. Furthermore, the present invention also optimizes the mass ratio of acetone to the non-volatile organic solvent in the two-component solvent to 0.25~4:1, by optimizing the content of acetone in the two-component solvent, not only the spinnability of the spinning solution can be improved, which is beneficial to converting high-concentration spinning solution into smooth and thick fibers, but also the coagulation rate of the spinning solution can be effectively regulated, which is beneficial to the formation of semi-dry fibers, and the semi-dry fibers are disorderly stacked on the surface of the collecting plate to form a loose structure with high porosity, thereby forming a porous film with rich pores between fibers. Therefore, not only the toughness of the fiber membrane can be improved by increasing the porosity of the material, but also high reflection and high radiation of the film can be achieved under the premise of thin thickness, and then the film has excellent thermal insulation and cooling properties while ensuring that the film is thin, and finally a radiation cooling film with the characteristics of "thin, light, cold and strong" is obtained. In particular, when the ratio of acetone in the two-component solvent is too low (e.g., less than 1:4), the acetone volatilization has little effect on improving the viscosity of the spinning solution. At this time, the low viscosity of the spinning solution makes it difficult to form a normal jet, and droplets are still present when it reaches the collector, resulting in problems such as poor spinnability, excessively fine fibers, and droplet accumulation. When the ratio is too high (greater than 4:1), the resulting fibers become significantly thicker, and the spinning solution can also rapidly solidify at the outlet, blocking the pipeline. Compared with existing conventional radiative cooling materials, the radiative cooling film prepared in the present invention can achieve high reflectivity and high radiation of sunlight while being thin, resulting in lighter weight and more excellent flexibility. It combines the advantages of "thin thickness, light weight, good radiative cooling effect, and high tensile strength" and can be used to process into high-intensity radiative cooling thin fabrics that combine excellent cooling function and wearability. In addition, compared with other preparation technologies, the present invention's method for preparing thin and light radiative cooling membranes based on electrospinning technology can achieve low-cost, large-scale preparation. It also has the advantages of simple process, convenient operation, and mild production conditions, facilitating the industrial application of thin and light radiative cooling membranes.

[0023] (2) The viscosity of the spinning solution plays a decisive role in the uniformity of electrospinning. In addition to the "solvent and polymer type", factors affecting the viscosity of the spinning solution also include the concentration of the polymer in the spinning solution and the amount of water added. Based on this, the preparation method of the present invention optimizes the mass ratio of the fluorocarbon resin-based polymer to the two-component solvent to 1 to 2:10. By optimizing the concentration of the fluorocarbon resin-based polymer in the spinning solution, the spinning stability can be improved and smooth and coarse fibers can be obtained. If the polymer concentration is too low, it is easy to cause the viscosity of the spinning solution to be low, making it difficult to form a normal jet. When it reaches the collector, there are still droplets, resulting in poor spinnability, too thin fibers, droplet accumulation and other problems. If the polymer concentration is too high, it will seriously affect the uniformity and surface smoothness of the fiber, and will cause the spinning solution to flow poorly, thereby blocking the pipeline. At the same time, the present invention also optimizes the mass ratio of water to the two-component solvent to ≤ 1:10, specifically, the mass ratio of water to the two-component solvent is 0.1 to 1:10, thereby improving the smoothness of the fiber surface and controlling the crystallinity of the fiber. If the water content is too low, the improvement effect is not obvious, while when the ratio of water to the two-component solvent is too high (greater than 1:10), it will cause thermodynamic instability in the spinning solution, induce phase separation prematurely, and form a polymer-rich phase, which manifests as a sharp increase in viscosity and difficulty in spinning.

[0024] (3) In the preparation method of the present invention, the process conditions of electrospinning are also optimized, which can assist in regulating the morphology and porosity of the fiber to meet the reflection requirements of the incident light, and can also help improve the mechanical properties of the fiber.

[0025] (4) The present invention provides a thin radiation cooling film, which is a porous film formed by fiber stacking, wherein the diameter of the fiber is 50nm~1.8μm, the pore size of the thin radiation cooling film is 0.1μm~7μm, the porosity of the thin radiation cooling film is 55%~85%, and the thickness of the thin radiation cooling film is 80μm~400μm. It has the advantages of high tensile strength, excellent flexibility, and excellent heat insulation and cooling performance. It is a filler-free porous film that is "thin, light, cold, and strong". It can effectively overcome the contradiction between the cooling function of the radiation cooling material and the wearability. It has high use value and good application prospects. In addition, the porosity of the graded porous radiation cooling film prepared by conventional phase separation method, template method and other methods is limited, so it mainly relies on increasing the thickness of the porous film to achieve its high reflectivity of sunlight. Only with sufficient thickness can multiple backscattering of incident sunlight be achieved to obtain a sufficiently high reflectivity. However, this will cause the graded porous radiation cooling film to have defects such as heavy weight and poor flexibility, which is not suitable for processing into light and thin fabrics. In contrast, the light and thin radiation cooling film of the present invention mainly relies on the rich pore structure between fibers to achieve the reflection of sunlight, and the fibers with smooth surface and diameter comparable to the reflected light to further improve the film's reflection of full-band sunlight and effective reflection of mid-wave infrared. The existence of this double reflection structure determines that the porous membrane composed of fiber composites of the present invention can be used in extremely At a thin thickness, it exhibits solar reflection performance comparable to or even better than other porous materials. Specifically, the thin radiation cooling film of the present invention can efficiently reflect solar ultraviolet rays, visible light, and near-infrared rays in the range of 350 to 2500 nm, preventing the sun's heat from accumulating on the surface of the shielded object and causing temperature rise. It can also efficiently reflect medium-wave infrared heat in the 2.5 to 8 μm band radiated from the environment to the surface of the fabric to prevent the infrared heat radiated from the surrounding environment from entering the shielded object. It can also radiate the internal accumulated heat out through the atmospheric window of 8 to 13 μm. In addition, the low thermal conductivity of the polymer itself and the porous structure between the fibers can further isolate the conduction of heat from the outside to the inside. These four major effects ensure the radiation cooling performance of the material, and it can exhibit a considerable cooling effect even in a hot and humid environment.

[0026] (5) The present invention also provides an application of a thin radiation cooling film, specifically, the thin radiation cooling film is used as a raw material to be processed into thin fabrics, such as car parasols, car covers, sun-proof clothing, sun-proof tarpaulins or handheld parasols, so that these thin fabrics can demonstrate efficient heat insulation and cooling effects, greatly save refrigeration energy consumption, have high use value and good application prospects. At the same time, due to the excellent flexibility of the thin radiation cooling film, it can be bent and curled at will, thereby significantly improving the processability and comfort of these thin fabrics, and is conducive to increasing their service life, and has a very high market promotion prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0028] Figure 1 This is an SEM image of the thin radiation cooling film prepared in Example 1 of the present invention.

[0029] Figure 2 This is a spectrum curve diagram of the thin radiation cooling film prepared in Example 1 of the present invention.

[0030] Figure 3 This is a stress-strain curve of the thin radiation cooling film prepared in Example 1 of the present invention.

[0031] Figure 4 This is a diagram showing the outdoor cooling effect of the thin radiation cooling film prepared in Example 1 of the present invention.

[0032] Figure 5 This is an SEM image of the radiation cooling film prepared in Comparative Example 1 of the present invention.

[0033] Figure 6 This is an SEM image of the radiation cooling film prepared in Comparative Example 3 of the present invention.

[0034] Figure 7 This is a diagram showing the outdoor cooling effect of the radiative cooling film prepared in Comparative Example 3 of the present invention. DETAILED DESCRIPTION

[0035] The present invention will be further described below in conjunction with the accompanying drawings and specific preferred embodiments, but the scope of protection of the present invention is not limited thereby.

[0036] In the following examples, unless otherwise specified, all materials and instruments used are commercially available.

[0037] The present invention first dissolves the polymer in a two-component solvent to obtain a uniform mixed solution, then adds water and stirs until uniformly dispersed to form a spinning solution, and then deposits the spinning solution onto the surface of silicone oil paper through an electrospinning machine to obtain a wet film. The wet film evaporates and dries in the air to obtain a thin radiative cooling film.

[0038] Example 1

[0039] A method for preparing a thin radiation cooling film comprises the following steps:

[0040] (1) 15 g of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) was added to a two-component solvent of 70 g of acetone and 30 g of N,N-dimethylformamide (DMF), and stirred at 50°C until fully dissolved to obtain a polyvinylidene fluoride-hexafluoropropylene solution.

[0041] (2) 5 g of water was added to the solution obtained in step (1), and the mixture was stirred at 50° C. and 250 rpm for 20 min until fully dispersed to obtain a spinning solution.

[0042] (3) The spinning solution prepared in step (2) is sucked into a syringe, which is fixed to the transmitting end. The electrospinning machine is turned on for electrospinning. After observing that the spinning is stable, the receiver is opened. After the spinning is completed, the fiber membrane is removed from the receiver and dried naturally at room temperature to obtain a thin radiative cooling film. After testing, the thickness of the thin radiative cooling film is 100 μm.

[0043] In step (3), the electrospinning experimental parameters are: relative humidity of 40%, temperature of 25° C., voltage of 10 kV, distance of 15 cm, injection speed of 10 μL / min, and drum collector speed of 100 rpm.

[0044] Figure 1 This is a SEM image of the thin radiation cooling film prepared in Example 1 of the present invention. Figure 1 It can be seen that the thin and light radiative cooling membrane produced in Example 1 is composed of stacked fibers and is a porous membrane. The fiber surface is dense, flat, and smooth, with fiber diameters ranging from 100 nm to 1.5 μm. The pore size of the thin and light radiative cooling membrane is also between 0.3 μm and 5 μm. Because the fiber surface is dense, flat, and smooth, and its diameter is comparable to the wavelength of the reflected light, the thin and light radiative cooling membrane can effectively scatter incident sunlight, thereby increasing reflectivity. Furthermore, because the pore size ranges from 0.3 μm to 5 μm and the porosity is 75%, the thin and light radiative cooling membrane ensures the air and moisture permeability of the fabric. Figure 2 This is a spectrum curve of the thin radiation cooling film prepared in Example 1 of the present invention. Figure 2 It can be seen that the thin and light radiative cooling film exhibits a high reflectivity for both sunlight and infrared heat from ambient radiation, especially in the sunlight band. The average reflectivity in the 0.3-2.5 μm band is 94.31%, the average reflectivity in the 2.5-8 μm band is 54.1%, and the average emissivity in the 8-13 μm band is 96.5%.

[0045] Figure 3 The stress-strain curve of the thin radiation cooling film prepared in Example 1 of the present invention is shown in FIG. Figure 3It can be seen that the tensile strength of the thin radiation cooling film is 6.43 MPa.

[0046] Figure 4 This is a diagram showing the outdoor cooling effect of the thin radiative cooling film produced in Example 1 of the present invention. As can be seen, under direct sunlight, at an ambient temperature of 36°C, the material can achieve a maximum temperature reduction of 15°C compared to the blank control (i.e., an uncovered glass plate).

[0047] An application of the thin radiation cooling film prepared in the above-mentioned embodiment is specifically to use the thin radiation cooling film as raw material and process it into thin fabrics, which can achieve a temperature reduction of more than 10°C. These thin fabrics include but are not limited to car parasols, car covers, sun-proof clothing, sun-proof tarpaulins, and handheld parasols.

[0048] Example 2

[0049] A method for preparing a thin radiation cooling film is basically the same as the method for preparing a thin radiation cooling film in Example 1, with the only difference being that the amount of polyvinylidene fluoride-hexafluoropropylene used in step (1) is 18 g.

[0050] The thin and light radiation cooling membrane prepared in Example 2 is composed of stacked fibers and is a porous membrane. The fiber surface is dense, flat and smooth, the average fiber diameter becomes larger, and the diameter distribution is between 200nm and 1.5μm. At the same time, the pore size distribution of the thin and light radiation cooling membrane is between 0.3μm and 3μm, and the porosity is 65%.

[0051] The thickness of the thin radiation cooling film prepared in Example 2 is 108 μm. The spectral test results show that the average reflectivity in the 0.3-2.5 μm band is 92.38%, the average reflectivity in the 2.5-8 μm band is 53.6%, and the average emissivity in the 8-13 μm band is 96.1%.

[0052] The stress-strain test results show that the tensile strength of the thin radiation cooling film prepared in Example 2 is 6.30 MPa.

[0053] The thermal insulation test results show that the thin radiative cooling film prepared in Example 2 can achieve a temperature reduction of 14.0°C compared to the uncovered control group.

[0054] Example 3

[0055] A method for preparing a thin radiation cooling film is basically the same as the method for preparing a thin radiation cooling film in Example 1, with the only difference being that the amount of water used in step (2) is 7.5 g.

[0056] The thin, lightweight radiative cooling membrane produced in Example 3 is composed of stacked fibers and is a porous membrane. The fiber surface is dense, but its smoothness is slightly reduced. The average fiber diameter increases, ranging from 400 nm to 1.5 μm. The pore size of this thin, lightweight radiative cooling membrane ranges from 0.4 μm to 3.5 μm, with a porosity of 65%. This indicates that increasing the amount of water helps accelerate the phase separation rate in the jet. However, at this polymer concentration, excessive water levels can increase the viscosity of the jet, hindering the achievement of a smooth surface.

[0057] The thickness of the thin radiation cooling film prepared in Example 3 is 110 μm. The spectral test results show that the average reflectivity in the 0.3-2.5 μm band is 93.41%, the average reflectivity in the 2.5-8 μm band is 52.9%, and the average emissivity in the 8-13 μm band is 94.7%.

[0058] The stress-strain test results show that the tensile strength of the thin radiation cooling film prepared in Example 3 is 6.12 MPa.

[0059] The thermal insulation test results show that the thin radiative cooling film prepared in Example 3 can achieve a temperature reduction of 14.6°C compared to the uncovered control group.

[0060] Example 4

[0061] A method for preparing a thin radiation cooling film is basically the same as the method for preparing a thin radiation cooling film in Example 1, with the only difference being that the amount of water used in step (2) is 2.5 g.

[0062] The thin and light radiation cooling membrane prepared in Example 4 is composed of stacked fibers and is a porous membrane. The fiber surface is dense, flat and smooth, the average fiber diameter becomes smaller, and the diameter distribution is between 100nm and 1μm. At the same time, the pore size of the thin and light radiation cooling membrane is between 0.8μm and 7μm, and the porosity is 80%.

[0063] The thickness of the thin radiation cooling film prepared in Example 4 is 106 μm. The spectral test results show that the average reflectivity in the 0.3-2.5 μm band is 93.21%, the average reflectivity in the 2.5-8 μm band is 51.3%, and the average emissivity in the 8-13 μm band is 96.0%.

[0064] The stress-strain test results show that the tensile strength of the thin radiation cooling film prepared in Example 4 is 5.64 MPa.

[0065] The thermal insulation test results show that the thin radiative cooling film prepared in Example 4 can achieve a temperature reduction of 14.4°C compared to the uncovered control group.

[0066] Example 5

[0067] A method for preparing a thin radiative cooling film is basically the same as the method for preparing a thin radiative cooling film in Example 1, with the only difference being that the two-component solvent composition in step (1) is 30 g acetone and 70 g DMF.

[0068] The thin, lightweight radiative cooling membrane produced in Example 5 is composed of stacked fibers and is a porous membrane. The fiber surface is dense, smooth, and the average fiber diameter is small, ranging from 60 nm to 500 nm. The pore size of the thin, lightweight radiative cooling membrane ranges from 0.2 μm to 2 μm, with a porosity of 70%. This indicates that reducing the proportion of acetone in the two components results in a lower polymer concentration in the jet, lowering the viscosity, and making it easier to produce fibers with finer diameters.

[0069] The thickness of the thin radiation cooling film prepared in Example 5 is 105 μm. The spectral test results show that the average reflectivity in the 0.3-2.5 μm band is 90.7%, the average reflectivity in the 2.5-8 μm band is 50.3%, and the average emissivity in the 8-13 μm band is 88.1%.

[0070] The stress-strain test results show that the tensile strength of the thin radiation cooling film prepared in Example 5 is 3.68 MPa.

[0071] The thermal insulation test results show that the thin radiative cooling film prepared in Example 5 can achieve a temperature reduction of 13.0°C compared to the uncovered control group.

[0072] Example 6

[0073] A method for preparing a thin radiative cooling film is basically the same as the method for preparing a thin radiative cooling film in Example 1, except that the two-component solvent composition in step (1) is 30g acetone and 70g DMF; and the amount of water used in step (2) is 7.5g.

[0074] The thin and light radiation cooling membrane prepared in Example 6 is made of stacked fibers and is a porous membrane. The fiber surface is dense, flat and smooth, and the fiber diameter is distributed between 50nm and 500nm. At the same time, the pore size of the thin and light radiation cooling membrane is between 0.1μm and 1μm, and the porosity is 70%.

[0075] The thickness of the thin radiation cooling film prepared in Example 6 is 93 μm. The spectral test results show that the average reflectivity in the 0.3-2.5 μm band is 88.4%, the average reflectivity in the 2.5-8 μm band is 48.1%, and the average emissivity in the 8-13 μm band is 86.5%.

[0076] Stress-strain test results show that the thin radiative cooling membrane produced in Example 6 has a tensile strength of 4.26 MPa. Reducing the acetone ratio in the two-component system results in a lower polymer concentration in the jet, lower viscosity, and a tendency to produce fibers with finer diameters. However, adding water increases the phase separation rate in the jet, inhibits crystallization, and thus improves mechanical properties.

[0077] The thermal insulation test results show that the thin radiative cooling film prepared in Example 6 can achieve a temperature reduction of 12.5°C compared to the uncovered control group.

[0078] Example 7

[0079] A method for preparing a thin radiation cooling film is basically the same as the method for preparing a thin radiation cooling film in Example 1, with the only difference being that in step (3), the electrospinning experimental parameters are: a distance of 30 cm and a drum collector speed of 400 rpm.

[0080] The thin and light radiation cooling membrane prepared in Example 7 is composed of stacked fibers and is a porous membrane. The fiber surface is dense, flat and smooth, the average fiber diameter becomes smaller, and the diameter distribution is between 50nm and 400nm. At the same time, the pore size of the thin and light radiation cooling membrane is between 0.1μm and 2μm, and the porosity is 82%.

[0081] The thickness of the thin radiation cooling film prepared in Example 7 is 110 μm. The spectral test results show that the average reflectivity in the 0.3-2.5 μm band is 93.07%, the average reflectivity in the 2.5-8 μm band is 49.1%, and the average emissivity in the 8-13 μm band is 96.7%.

[0082] The stress-strain test results show that the tensile strength of the thin radiation cooling film prepared in Example 7 is 4.10 MPa.

[0083] The thermal insulation test results show that the thin radiative cooling film prepared in Example 7 can achieve a temperature reduction of 14.2°C compared to the uncovered control group.

[0084] Example 8

[0085] A method for preparing a thin radiation cooling film is basically the same as the method for preparing the thin radiation cooling film in Example 1, with the only difference being that the spinning time is extended to obtain a fiber film with a thickness greater than 200 μm.

[0086] The thin and light radiation cooling membrane prepared in Example 8 is made of stacked fibers and is a porous membrane. The fiber surface is dense, flat and smooth, and the fiber diameter is distributed between 100nm and 1.5μm. At the same time, the pore size of the thin and light radiation cooling membrane is between 0.3μm and 5μm, and the porosity is 75%.

[0087] The thickness of the thin radiation cooling film prepared in Example 8 is 212 μm. The spectral test results show that the average reflectivity in the 0.3-2.5 μm band is 97.11%, the average reflectivity in the 2.5-8 μm band is 58.7%, and the average emissivity in the 8-13 μm band is 96.6%.

[0088] The stress-strain test results show that the tensile strength of the thin radiation cooling film prepared in Example 8 is 6.82 MPa.

[0089] The thermal insulation test results show that the thin radiative cooling film prepared in Example 8 can achieve a temperature reduction of 16.5°C compared to the uncovered control group.

[0090] Example 9

[0091] A method for preparing a thin radiative cooling film is basically the same as the method for preparing a thin radiative cooling film in Example 1, except that polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) is replaced with polyvinylidene fluoride (PVDF) in step (1).

[0092] The thin and light radiation cooling membrane prepared in Example 9 is made of stacked fibers and is a porous membrane. The fiber surface is dense, flat and smooth, and the fiber diameter is distributed between 100nm and 1μm. At the same time, the pore size of the thin and light radiation cooling membrane is between 0.3μm and 5μm, and the porosity is 72%.

[0093] The thickness of the thin radiation cooling film prepared in Example 9 is 60 μm. The spectral test results show that the average reflectivity in the 0.3-2.5 μm band is 92.86%, the average reflectivity in the 2.5-8 μm band is 51.2%, and the average emissivity in the 8-13 μm band is 93.4%.

[0094] The stress-strain test results show that the tensile strength of the thin radiation cooling film prepared in Example 9 is 4.85 MPa.

[0095] The thermal insulation test results show that the thin radiative cooling film prepared in Example 9 can achieve a temperature reduction of 14.2°C compared to the uncovered control group.

[0096] Comparative Example 1

[0097] A method for preparing a radiative cooling film is basically the same as the method for preparing a thin radiative cooling film in Example 1, with the only difference being that the two-component solvent in step (1) is changed to a single-component DMF in an amount of 100 g.

[0098] like Figure 5 As shown, the thickness of the radiation cooling film prepared in Comparative Example 1 is 100 μm, and the spectral test results show that the average reflectivity in the 0.3-2.5 μm band is 68.65%, the average reflectivity in the 2.5-8 μm band is 25.4%, and the average emissivity in the 8-13 μm band is 90.4%.

[0099] The stress-strain test results show that the tensile strength of the radiation cooling film prepared in Comparative Example 1 is only 0.76 MPa.

[0100] The thermal insulation test results show that the radiative cooling film prepared in Comparative Example 1 can achieve a temperature reduction of 5.4°C compared to the uncovered control group.

[0101] Comparative Example 2

[0102] A method for preparing a radiative cooling film is substantially the same as the method for preparing a thin radiative cooling film in Example 1, with the only difference being that the two-component solvent composition in step (1) is 90 g acetone and 10 g DMF.

[0103] As a result, the spinning solution easily clogs the pipes and needles and is not spinnable.

[0104] Comparative Example 3

[0105] A method for preparing a radiative cooling film is substantially the same as the method for preparing a thin radiative cooling film in Example 1, with the only difference being that no water is added in step (2).

[0106] The radiative cooling film prepared in Comparative Example 3 had a thickness of 112 μm. Spectral measurements showed an average reflectivity of 93.27% in the 0.3-2.5 μm band, 53.5% in the 2.5-8 μm band, and 95.9% in the 8-13 μm band. While the reflectivity values ​​were higher than those in Examples 5 and 6, this was primarily due to the greater thickness of the film in Comparative Example 3.

[0107] The morphology of the radiation cooling film obtained in Comparative Example 3 is as follows: Figure 6 As shown. Figure 6It can be seen that in the radiation cooling film, the average fiber diameter is thinner than that in Example 1, and there are many beads. The polymer molecular chains form entanglements in the solution and have a certain viscosity, which is a necessary condition for preparing polymer fibers by electrospinning technology. After the polymer solution jet is formed on the surface of the Taylor cone, the jet is stretched by the electric field force in the high-voltage electrostatic field to form fibers. However, if the viscosity of the jet is not enough, it will not be able to balance the stretching of the electric field force during axial orientation, and it will be difficult to maintain the continuity of the jet, so it will break and form beaded structure fibers. The addition of water is conducive to promoting the separation of the polymer-rich phase from the jet, thereby quickly increasing the viscosity of the jet, thereby avoiding the formation of beads and obtaining fibers with uniform thickness and smooth surface. The beaded structure is very unfavorable to the mechanical properties of the fiber.

[0108] The insulation test results show that Figure 7 As shown, although the radiative cooling film prepared in Comparative Example 3 can also achieve a temperature reduction of 14°C compared with the uncovered control group, which is slightly lower than Example 1, the tensile strength of the radiative cooling film prepared in Comparative Example 3 is about 1.8 MPa, which is significantly lower than Example 1, and cannot withstand external pulling during outdoor use, that is, it cannot simultaneously meet the performance requirements of "thin, light, cool, and strong".

[0109] Comparative Example 4

[0110] A method for preparing a radiative cooling film is basically the same as the method for preparing a thin radiative cooling film in Example 1, except that the amount of polyvinylidene fluoride-hexafluoropropylene used in step (1) is 21 g; and the amount of water used in step (2) is 1.0 g.

[0111] As a result, the viscosity of the spinning solution was too high, which caused the jet to be unstable and made spinning difficult to complete.

[0112] Comparative Example 5

[0113] A method for preparing a radiative cooling film is basically the same as the method for preparing a thin radiative cooling film in Example 1, with the only difference being that the amount of water used in step (2) is 12 g.

[0114] As a result, the spinning solution easily clogs the pipe and needle and is not spinnable. This is because the large amount of water added easily causes phase separation in the spinning solution prematurely.

[0115] Comparative Example 6

[0116] A method for preparing a radiative cooling film is substantially the same as the method for preparing a thin radiative cooling film in Example 1, except that: in step (1), the amount of polyvinylidene fluoride-hexafluoropropylene used is 8 g; the two-component solvent composition is 50 g acetone and 50 g DMF; and no water is added in step (2).

[0117] The thickness of the radiation cooling film prepared in Comparative Example 6 is 103 μm. The spectral test results show that the average reflectivity in the 0.3-2.5 μm band is 78.93%, the average reflectivity in the 2.5-8 μm band is 50.1%, and the average emissivity in the 8-13 μm band is 88.3%.

[0118] The stress-strain test results show that the tensile strength of the radiation cooling film prepared in Comparative Example 6 is 0.84 MPa.

[0119] The thermal insulation test results show that the radiative cooling film prepared in Comparative Example 6 can achieve a temperature reduction of 6.8°C compared to the uncovered control group.

[0120] Comparative Example 7

[0121] A method for preparing a radiative cooling film is basically the same as the method for preparing a thin radiative cooling film in Example 1, except that: the amount of polyvinylidene fluoride-hexafluoropropylene used in step (1) is 8g; and the two-component solvent composition is 50g acetone and 50g DMF.

[0122] The thickness of the radiation cooling film prepared in Comparative Example 7 is 108 μm. The spectral test results show that the average reflectivity in the 0.3-2.5 μm band is 79.64%, the average reflectivity in the 2.5-8 μm band is 50.8%, and the average emissivity in the 8-13 μm band is 87.5%.

[0123] The stress-strain test results show that the tensile strength of the radiative cooling film prepared in Comparative Example 7 is 1.12 MPa.

[0124] The thermal insulation test results show that the radiative cooling film prepared in Comparative Example 7 can achieve a temperature reduction of 7.0°C compared to the uncovered control group.

[0125] It can be seen that in Comparative Examples 6 and 7, the radiative cooling films prepared still cannot simultaneously meet the requirements of "thin, light, cold, and strong" because the polymer concentration is relatively low, resulting in insufficient viscosity. On the one hand, it is difficult to obtain continuous fibers with uniform thickness, and a beaded structure is easily obtained, which is not conducive to improving the mechanical properties; on the other hand, the obtained fibers are very thin, concentrated below 70nm, and cannot meet the requirements of effective reflection of full-band sunlight.

[0126] Comparative Example 8

[0127] A method for preparing a radiative cooling film is basically the same as the method for preparing a thin radiative cooling film in Example 1, with the only difference being that the thickness of the fiber film is 27 μm.

[0128] The thickness of the radiation cooling film prepared in Comparative Example 8 is 27 μm. The spectral test results show that the average reflectivity in the 0.3-2.5 μm band is 56.72%, the average reflectivity in the 2.5-8 μm band is 40.2%, and the average emissivity in the 8-13 μm band is 92.5%.

[0129] The stress-strain test results show that the tensile strength of the radiation cooling film prepared in Comparative Example 8 is 1.55 MPa.

[0130] The thermal insulation test results show that the radiative cooling film prepared in Comparative Example 8 can achieve a temperature reduction of 3.9°C compared to the uncovered control group.

[0131] The above results demonstrate that, compared to existing conventional radiative cooling materials, the radiative cooling film produced in the present invention achieves high sunlight reflection and radiation while maintaining a relatively thin thickness, resulting in lighter weight and superior flexibility. Combining the advantages of thinness, light weight, excellent radiative cooling effects, and high tensile strength, it can be processed into high-strength radiative cooling, lightweight fabrics that combine excellent cooling performance with wearability. Furthermore, compared to other preparation technologies, the present method for preparing thin radiative cooling films based on electrospinning technology allows for low-cost, large-scale production. It also offers advantages such as simple processing, convenient operation, and mild production conditions, facilitating the industrial application of thin radiative cooling films.

[0132] The foregoing description is merely a preferred embodiment of the present invention, and the scope of protection of the present invention is not limited to the foregoing embodiment. Any technical solution that falls within the scope of protection of the present invention is within the scope of protection of the present invention. It should be noted that improvements and modifications that can be made by a person skilled in the art without departing from the principles of the present invention are also considered to be within the scope of protection of the present invention.

Claims

1. A method for preparing a thin radiation cooling film, characterized in that: The following steps are involved: (1) mixing a fluorocarbon resin-based polymer and a two-component solvent, and stirring until the two-component solvent is completely dissolved to obtain a fluorocarbon resin-based polymer solution; the two-component solvent is a mixed solvent of acetone and a non-volatile organic solvent; the mass ratio of the acetone to the non-volatile organic solvent is 0.25 to 4:1; (2) mixing the fluorocarbon resin-based polymer solution obtained in step (1) with water and stirring to obtain a spinning solution; the mass ratio of the water to the two-component solvent is ≤1:10; (3) Using the spinning solution obtained in step (2) as a raw material, electrospinning is performed to deposit the fiber membrane on the surface of a collecting plate, and drying is performed to obtain a thin radiation cooling membrane.

2. The preparation method according to claim 1, characterized in that In step (1), the mass ratio of the fluorocarbon resin-based polymer to the two-component solvent is 1 to 2:10; the fluorocarbon resin-based polymer is at least one of polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride, and polytetrafluoroethylene; and the non-volatile organic solvent is at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide.

3. The preparation method according to claim 2, characterized in that In step (2), the mass ratio of water to the two-component solvent is 0.1 to 1:

10.

4. The preparation method according to any one of claims 1 to 3, characterized in that In step (1), the stirring is carried out at a temperature of 25°C to 80°C; In step (2), the stirring is carried out at a temperature of 25°C to 80°C; and the stirring time is ≥10 min.

5. The preparation method according to any one of claims 1 to 3, characterized in that In step (3), an electrospinning machine is used for electrospinning; the process conditions of the electrospinning are as follows: a spinning temperature of 15°C to 35°C, a spinning humidity of 20% to 60%, a propulsion speed of the spinning solution of 0.6 mL / h to 2 mL / h, a distance between the spinneret and the collecting plate of 12 cm to 30 cm, a spinning voltage of 8 kV to 12 kV, and a drum collector speed of 50 rpm to 500 rpm.

6. A thin radiation cooling film, characterized in that: The thin radiation cooling film is prepared by the preparation method according to any one of claims 1 to 5.

7. The thin and light radiation cooling film according to claim 6, characterized in that: The thin and light radiation cooling film is a porous film formed by fiber stacking; the diameter of the fiber is 50 nm to 1.8 μm; the pore size of the thin and light radiation cooling film is 0.1 μm to 7 μm; the porosity of the thin and light radiation cooling film is 55% to 85%; the thickness of the thin and light radiation cooling film is 80 μm to 400 μm.

8. An application of the thin radiation cooling film according to claim 6 or 7, characterized in that: The application is to use a light and thin radiation cooling film as a raw material to process it into a light and thin fabric.

9. The use according to claim 8, characterized in that The thin fabric includes one of a car sunshade, a car cover, a sun-proof clothing, a sun-proof tarpaulin, and a handheld sunshade.

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