Dual-selective radiative emissivity material and method of making

Abstract

The application provides a radiation refrigeration material and a manufacturing method thereof. The radiation refrigeration material comprises polyformaldehyde and polytetrafluoroethylene, and is characterized in that infrared rays can be selectively emitted in a first atmospheric window wave band (8-13 mu m) and a second atmospheric window wave band (16-25 mu m), that is, the radiation refrigeration material is a double selective thermal emitter with high selective thermal emissivity in the two atmospheric window wave bands. The thermal emitter can radiate heat to outer space through the two atmospheric windows while excluding atmospheric parasitic heat, thereby realizing excellent refrigeration performance under zero energy consumption. The radiation refrigeration material can be prepared by a spinning method, a solution method and a hot-pressing method, and has the advantages of high tensile strength, high ultraviolet resistance and high environmental stability. The application field of the radiation refrigeration material is relatively wide, and the radiation refrigeration material can be used as a building outer layer material, a sun-proof car cover, a sunshade umbrella, a sun-proof garment, a special work garment and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of new energy nanomaterials, in particular to a dual-selective radiative cooling material and a manufacturing method thereof. BACKGROUND

[0002] Daytime radiative cooling is an energy-saving cooling technology that can achieve sub-environmental cooling (lowering the temperature of an object below the ambient temperature) under sunlight, without consuming any energy and emitting any greenhouse gases, and is an ideal alternative to traditional power-consuming cooling systems, which is expected to help achieve the "double carbon" goal. The sub-environmental cooling capability of daytime radiative cooling materials is derived from their ability to emit heat to the cold outer space (about 3K) through the atmospheric window while excluding solar heat (high solar reflectivity), so they are a kind of heat emitter.

[0003] At present, various efficient heat emitters have been developed as daytime radiative cooling materials. According to their spectral characteristics in the mid-infrared (MIR) band, they can be mainly divided into non-selective heat emitters and selective heat emitters. Among them, non-selective heat emitters have high thermal absorption / emissivity in the entire MIR band (mainly 4 μm to 25 μm); while selective heat emitters have high absorption / emissivity only in the atmospheric window of 8 μm to 13 μm, and have low thermal emissivity in the MIR band outside the window, which is named "single-selective" radiative cooling material. Compared with non-selective heat emitters, a single-selective heat emitter can exclude atmospheric parasitic heat (heating effect from the atmospheric environment), so it theoretically has better cooling performance than the former. However, in the actual environment, single-selective heat emitters do not have significantly better cooling performance than non-selective materials, and most of the current research on radiative cooling materials is still on non-selective heat emitters without special spectral design. The reason is that in addition to atmospheric radiation, there is also significant non-radiative heat (including thermal convection and thermal conduction) in the actual environment, which greatly reduces the cooling performance of single-selective heat emitters and cannot fully exert their ultra-high theoretical cooling performance. So far, selective heat emitters only have high emissivity in the first atmospheric window band (8 μm to 13 μm), and lack the use of the second atmospheric window band (16 μm to 25 μm), resulting in insufficient cooling capacity. SUMMARY

[0004] The present application aims to develop a dual-selective radiative cooling material that has high selective emissivity in the 8 μm to 13 μm band and the 16 μm to 25 μm band, and low emissivity in the non-window infrared band.

[0005] In one aspect of the present application, the present application provides a radiation cooling material. According to an embodiment of the present application, the radiation cooling material comprises polyoxymethylene and polytetrafluoroethylene, and the radiation cooling material can selectively emit infrared rays in both a first atmospheric window of 8-13 μm and a second atmospheric window of 16-25 μm. Thus, the radiation cooling material of the present application has high selective thermal emissivity in both atmospheric windows of two wave bands, can serve as a dual-selective thermal emitter, and can dissipate heat to outer space through both atmospheric windows while excluding atmospheric parasitic heat, thereby having higher cooling potential than existing radiation cooling emitters. Moreover, since the atmospheric transparency of the second atmospheric window is much higher in a dry climate than in a high-humidity environment, the radiation cooling material will exhibit significantly better cooling performance than single-selective radiation cooling materials in dry and hot regions. In addition, the radiation cooling material is composed of two common polymers, polyoxymethylene and polytetrafluoroethylene, both of which have good physical and chemical properties (high thermal stability and high mechanical strength, etc.) and have been commercialized, laying a foundation for the practical application and mass production of dual-selective radiation cooling materials. Furthermore, the radiation cooling material of the present application has a wide range of application fields, and can be used as a building outer layer (roof or wall) material, a sun-proof car cover, a sunshade, a sun-proof garment, a special workwear (such as medical protective clothing, construction worker's workwear, and military uniform, etc.), and many other fields.

[0006] According to an embodiment of the present application, the emissivity of the radiation cooling material in the first atmospheric window is greater than or equal to 70%, the emissivity in the second atmospheric window is greater than or equal to 60%, and the solar reflectivity of the radiation cooling material is greater than or equal to 90%.

[0007] According to an embodiment of the present application, based on the total mass of the radiation cooling material, the radiation cooling material comprises, in terms of mass percentage: 1wt%-80wt% of polytetrafluoroethylene; and 20wt%-99wt% of polyoxymethylene.

[0008] According to an embodiment of the present application, the radiation cooling material satisfies at least one of the following conditions: the molecular weight of the polytetrafluoroethylene is 100000-1000000; the melting point of the polytetrafluoroethylene is 327-342℃; the molecular weight of the polyoxymethylene is 2000-200000; and the melting point of the polyoxymethylene is 140-190℃.

[0009] According to an embodiment of the present application, in the radiation cooling material, the polyoxymethylene is in a fibrous form, and the polytetrafluoroethylene is in a granular form, with polytetrafluoroethylene particles embedded in the polyoxymethylene fibers.

[0010] According to an embodiment of the present application, the radiation refrigeration material satisfies at least one of the following conditions: the diameter of the polyformal fiber is 200-3000 nm; the particle size of the polytetrafluoroethylene particle is 200-3000 nm.

[0011] In another aspect of the present application, the present application provides a method for preparing the radiation refrigeration material described above. According to an embodiment of the present application, the method for preparing the radiation refrigeration material comprises: configuring a polyformal solution and a polytetrafluoroethylene liquid; mixing the polyformal solution and the polytetrafluoroethylene liquid uniformly to obtain a mixed liquid; and preparing the radiation refrigeration material from the mixed liquid by using a spinning method, a solution method or a hot-pressing method. Thus, the radiation refrigeration material prepared by the above method can have thermal emissivity in both the first atmospheric window and the second atmospheric window, can be used as a double-selective thermal emitter, and can radiate heat to the outer space through the two atmospheric windows while excluding atmospheric parasitic heat, thereby having higher refrigeration potential than existing radiation refrigeration emitters. Moreover, since the atmospheric transparency of the second atmospheric window in a dry climate is much higher than that in a high-humidity environment, the radiation refrigeration material will have a refrigeration performance significantly better than that of a single-selective radiation refrigeration material in a dry and hot area. In addition, the radiation refrigeration material is composed of two common polymers, polyformal and polytetrafluoroethylene, both of which have good physical and chemical properties (high thermal stability and high mechanical strength, etc.) and have been commercialized, which lays a foundation for the practical application and mass production of the double-selective radiation refrigeration material. Furthermore, the application field of the radiation refrigeration material of the present application is relatively wide, and it can be used as a building outer layer (roof or wall) material, a sun-proof car cover, a sunshade umbrella, a sun-proof clothing, special work clothing (such as medical protective clothing, construction worker's clothing, and military uniform, etc.), and many other fields.

[0012] According to an embodiment of the present application, the mass percentage of polyformal in the polyformal solution is 0.1wt% to 50wt%, and the mass percentage of polytetrafluoroethylene in the polytetrafluoroethylene liquid is 1wt% to 50wt%.

[0013] According to an embodiment of the present application, the radiation refrigeration material is prepared by electrospinning, and the process conditions of the electrospinning satisfy at least one of the following process conditions: the voltage of the electrospinning is 1kV to 50kV; the spinning speed is 0.1mL / h to 20mL / h; the humidity is 10% to 70%; the temperature is 10℃ to 50℃; the distance between the positive electrode and the negative electrode is 5cm to 25cm; and the rotation speed of the negative electrode roller is 10rpm to 300rpm.

[0014] According to an embodiment of the present application, the polyoxymethylene solution and the solvent of the polytetrafluoroethylene liquid are both polar solvents selected from at least one of dimethylformamide, N-methyl-2-pyrrolidone and 1,1,1,3,3,3-hexafluoro-2-propanol. BRIEF DESCRIPTION OF DRAWINGS

[0015] The above and / or additional aspects and advantages of the present application will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings in which:

[0016] Figure 1 is the Fourier transform infrared spectroscopy attenuated total reflectance spectrum of the polyoxymethylene (POM) and polytetrafluoroethylene (PTFE) raw materials used in the present application;

[0017] Figure 2 is a scanning electron microscope photo of the POM-PTFE fiber membrane prepared in Example 1 of the present application;

[0018] Figure 3 is a flowchart of the preparation of a radiative cooling material in one embodiment of the present application;

[0019] Figure 4 is a macroscopic photo of the POM-PTFE fiber membrane prepared in Example 1 of the present application;

[0020] Figure 5 is the spectral response of the POM-PTFE fiber membrane prepared in Example 1 of the present application, including solar reflectance and mid-infrared emissivity;

[0021] Figure 6 is a test chart of the outdoor cooling performance test of the POM-PTFE fiber membrane prepared in Example 1 of the present application;

[0022] Figure 7 is a macroscopic photo of the POM-PTFE fiber membrane prepared in Example 1 of the present application, and white color steel plate, black asphalt plate, pure aluminum foil, white paint coated aluminum foil, white pigment coated black asphalt plate;

[0023] Figure 8 is a macroscopic photo of the POM-PTFE fiber membrane prepared in Example 1 of the present application, and white color steel plate, black asphalt plate, pure aluminum foil, white paint coated aluminum foil, white pigment coated black asphalt plate; Figure 7 is an infrared photo of the six materials (POM-PTFE fiber membrane, white color steel plate, black asphalt plate, pure aluminum foil, white paint coated aluminum foil, white pigment coated black asphalt plate). DETAILED DESCRIPTION

[0024] The schemes of the present application will be explained below with reference to examples. Those skilled in the art will understand that the examples below are only for illustration of the present application and should not be regarded as limiting the scope of the present application. If no specific technique or condition is specified in the examples, the technique or condition described in the literature in the art or according to the product manual is used. If no manufacturer of the reagent or instrument is specified, it is a conventional product that can be obtained commercially.

[0025] The present application will be described below with reference to specific examples. It should be noted that these examples are only descriptive and do not limit the present application in any way.

[0026] In one aspect of the present application, the present application provides a radiation refrigeration material. According to an embodiment of the present application, the radiation refrigeration material comprises polyoxymethylene (POM) and polytetrafluoroethylene (PTFE), and the radiation refrigeration material can selectively emit infrared rays in both a first atmospheric window and a second atmospheric window, the first atmospheric window being 8 μm to 13 μm, and the second atmospheric window being 16 μm to 25 μm. Thus, the radiation refrigeration material can have a high selective thermal emissivity in both wavebands of the atmospheric window, can be used as a dual-selective thermal emitter, and has a low emissivity in the non-window infrared waveband, and can dissipate heat to the outer space through the two atmospheric windows while excluding atmospheric parasitic heat, thereby having a higher refrigeration potential than existing radiation refrigeration emitters. Moreover, since the atmospheric transparency of the second atmospheric window is much greater in a dry climate than in a high-humidity environment, the radiation refrigeration material will exhibit a refrigeration performance significantly superior to that of a single-selective radiation refrigeration material in a dry and hot region. In addition, the radiation refrigeration material is composed of two common polymers, POM and PTFE, both of which have good physical and chemical properties (high thermal stability and high mechanical strength, etc.) and have been commercialized, which lays a foundation for the practical application and mass production of dual-selective radiation refrigeration materials. Furthermore, the application field of the radiation refrigeration material of the present application is relatively wide, and it can be used as a building outer layer (roof or wall) material, a sun-proof car cover, a sunshade umbrella, a sun-proof clothing, a special workwear (such as a medical protective clothing, a construction worker's workwear, and a military uniform, etc.), and many other fields.

[0027] Since the absorption / emission characteristics of a polymer material in a specific waveband are derived from the absorption vibration of the molecular bond / function group contained therein in the corresponding waveband. In order to realize a dual-selective characteristic radiation refrigeration material, it is necessary to select a molecular bond / function group that has strong absorption / vibration only in the two atmospheric window wavebands, and has no strong absorption vibration in the MIR waveband outside the atmospheric window. The inventors found that among the molecular bonds / functions of polymers and the corresponding absorption vibration wavebands, referring to Table 1, the molecular bond / function group of POM and PTFE has strong absorption / vibration only in the two atmospheric window wavebands, and has no strong absorption vibration in the MIR waveband outside the atmospheric window. Figure 1It can be seen from the Fourier transform infrared spectrum (FTIR-ATR) spectrum in the figure that the polyoxymethylene (POM) containing only C-O-C bonds in the main chain has strong absorption vibration mainly in the first atmospheric window (8 μm to 13 μm); and the polytetrafluoroethylene (PTFE) containing mainly C-F bonds has strong absorption vibration mainly in the second atmospheric window (16 μm to 25 μm).

[0028] According to an embodiment of the present application, the emissivity of the radiation refrigeration material in the first atmospheric window is greater than or equal to 70% (such as 70%, 75%, 77%, 79%, 80%, 82%, 85%, 88%, 90%, 95%, 98%, etc. in the first atmospheric window), and the emissivity in the second atmospheric window is greater than or equal to 60% (such as 60%, 61%, 62%, 65%, 68%, 70%, 72%, 75%, 78%, 80%, etc. in the second atmospheric window). As can be seen, the radiation refrigeration material of the present application has high thermal emissivity in the atmospheric window of two wave bands, thereby helping to improve the refrigeration efficiency of the radiation refrigeration material. In some embodiments, the emissivity of the radiation refrigeration material in the first atmospheric window is greater than or equal to 80%, and the emissivity in the second atmospheric window is greater than or equal to 65%. Thus, the thermal emissivity of the radiation refrigeration material can be further improved, and the refrigeration efficiency can be further improved.

[0029] According to an embodiment of the present application, the solar reflectivity (solar wave band is 300-2500 nm) of the radiation refrigeration material is greater than or equal to 90%, such as 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, etc. Thus, the refrigeration radiation material has high solar reflectivity, can reflect the daytime sunlight heat, and ensures good refrigeration efficiency.

[0030] According to an embodiment of the present application, the radiation cooling material comprises, in terms of mass percentage based on the total mass of the radiation cooling material, 1wt%-80wt% (such as 1wt%, 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, 80wt%) of polytetrafluoroethylene and 20wt%-99wt% (such as 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, 75wt%, 80wt%, 85wt%, 90wt%, 95wt%, 99wt%) of polyoxymethylene. The radiation cooling material formed by the above ratio has good infrared emission effect in the two atmospheric windows, i.e., has better emissivity in the two atmospheric windows. Those skilled in the art can flexibly select the specific ratio of the two polymers according to the actual situation of the specific application environment (such as dry environment or humid environment) of the radiation cooling material, for example, in a dry and hot environment, the second atmospheric window is particularly obvious, at this time, the atmospheric transmittance of the second atmospheric window is higher, at this time, the amount of polytetrafluoroethylene can be appropriately increased; if in a relatively humid environment, because the water molecules in the atmosphere have strong absorption to the thermal radiation of the second atmospheric window, at this time, the amount of polyoxymethylene can be appropriately increased.

[0031] According to an embodiment of the present application, the molecular weight of the polytetrafluoroethylene is 100000-1000000, such as 100000, 200000, 300000, 400000, 500000, 600000, 700000, 800000, 900000, 1000000; the melting point of the polytetrafluoroethylene is 327°C-342°C, such as 327°C, 330°C, 332°C, 334°C, 336°C, 338°C, 340°C, 342°C. The polytetrafluoroethylene under the above conditions has better emissivity to the second atmospheric window band.

[0032] According to an embodiment of the present application, the polyformaldehyde has a molecular weight of 2000 to 200000, such as 2000, 5000, 8000, 10000, 15000, 20000, 30000, 40000, 50000, 60000, 70000, 80000, 90000, 100000, 110000, 130000, 150000, 170000, 190000, 200000; the polyformaldehyde has a melting point of 140°C to 190°C, such as 140°C, 145°C, 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, 180°C, 185°C, 190°C, etc. The polyformaldehyde under the above conditions has better emissivity in the first atmospheric window band.

[0033] According to an embodiment of the present application, referring to Figure 2 In the radiation refrigeration material, the polyformaldehyde is in a fibrous form, and the polytetrafluoroethylene is in a granular form, and the polytetrafluoroethylene particles 10 are embedded into the polyformaldehyde fibers 20. In the radiation refrigeration material with the above microstructure, the polytetrafluoroethylene particles can be uniformly dispersed in the polyformaldehyde fibers, thereby ensuring the uniformity and stability of the reflectivity of the radiation refrigeration material; and the polyformaldehyde and the polytetrafluoroethylene with the above morphology have relatively stable structures.

[0034] According to an embodiment of the present application, the polyformaldehyde fibers have a diameter of 200 to 3000 nm, such as 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, 1200 nm, 1400 nm, 1600 nm, 1800 nm, 2000 nm, 2200 nm, 2400 nm, 2500 nm, 2700 nm, 2900 nm, 3000 nm; the polytetrafluoroethylene particles have a particle size of 200 to 3000 nm, such as 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, 1200 nm, 1400 nm, 1600 nm, 1800 nm, 2000 nm, 2200 nm, 2400 nm, 2500 nm, 2700 nm, 2900 nm, 3000 nm. In this way, when at least one of the diameter of the polyformaldehyde fibers and the particle size of the polytetrafluoroethylene particles is close to the solar band (300 to 2500 nm), the radiation refrigeration material has a relatively strong scattering efficiency, and can achieve a high solar reflectivity. In some embodiments, the diameter of the polyformaldehyde fibers and the particle size of the polytetrafluoroethylene particles are both in the range of 200 to 3000 nm, which is close to the solar band (300 to 2500 nm), and the radiation refrigeration material has the strongest scattering efficiency, which is more conducive to achieving a high solar reflectivity.

[0035] In another aspect of the present application, the present application provides a method for preparing the above-mentioned radiative cooling material. According to an embodiment of the present application, the method for preparing the radiative cooling material comprises Figure 3

[0036] S100: configuring a polyformaldehyde solution and a polytetrafluoroethylene liquid.

[0037] In some embodiments, the polytetrafluoroethylene liquid is a polytetrafluoroethylene suspension.

[0038] In this step, the mass percentage of polyformaldehyde in the polyformaldehyde solution is 0.1wt% to 50wt% (such as 0.1wt%, 1wt%, 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%), and the mass percentage of polytetrafluoroethylene in the polytetrafluoroethylene liquid is 1wt% to 50wt% (such as 1wt%, 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%). The polyformaldehyde in the polyformaldehyde solution with the above-mentioned concentration can be uniformly dispersed or dissolved in the solvent of the polyformaldehyde solution; and the polytetrafluoroethylene in the polytetrafluoroethylene liquid with the above-mentioned concentration can be uniformly dispersed or dissolved in the solvent of the polytetrafluoroethylene.

[0039] Further, the solvents of the polyformaldehyde solution and the polytetrafluoroethylene liquid are both polar solvents, and the polar solvents are selected from at least one of dimethylformamide, N-methyl-2-pyrrolidone and 1,1,1,3,3,3-hexafluoro-2-propanol. The above-mentioned solvents can be well mixed with polyformaldehyde or polytetrafluoroethylene to obtain a liquid with uniform mixing. Further, the solvents of the polyformaldehyde solution and the polytetrafluoroethylene liquid are the same. Thus, when the polyformaldehyde solution and the polytetrafluoroethylene liquid are mixed, there is no repulsion between the two liquids, and they can be well mixed, which helps to obtain a mixed liquid with uniform mixing of polyformaldehyde and polytetrafluoroethylene.

[0040] In some specific embodiments, the step of configuring the polyformaldehyde solution comprises dissolving a polyformaldehyde homopolymer in a solvent and stirring at a constant temperature of 30°C to 80°C until a uniform solution is formed, i.e. the polyformaldehyde solution is obtained; and the step of configuring the polytetrafluoroethylene liquid comprises adding polytetrafluoroethylene particles to the same solvent as the polyformaldehyde solution, and forming a uniform suspension after ultrasonic and stirring treatment, i.e. the polytetrafluoroethylene suspension is obtained.

[0041] In the above-mentioned method, the requirements for the molecular weight and melting point of polyformaldehyde and polytetrafluoroethylene are consistent with the above-mentioned requirements, and will not be repeated here.

[0042] ​S200: uniformly mixing the polyformaldehyde solution and the polytetrafluoroethylene liquid to obtain a mixed liquid.

[0043] In the mixed liquid, the mass of the polytetrafluoroethylene accounts for 1wt% to 80wt% of the total mass of the polyformaldehyde and the polytetrafluoroethylene. Thus, in the finally prepared radiation refrigeration material, based on the total mass of the radiation refrigeration material, the radiation refrigeration material includes, by mass percentage: 1wt% to 80wt% of the polytetrafluoroethylene; 20wt% to 99wt% of the polyformaldehyde. The radiation refrigeration material formed by the above ratio has good infrared emission effect in the above two atmospheric windows, i.e., has better emissivity in the above two atmospheric windows. Those skilled in the art can flexibly select the specific ratio of the two polymers according to the actual situation of the specific application environment of the radiation refrigeration material (such as dry environment or humid environment) and the like. For example, in a dry and hot environment, the second atmospheric window is particularly obvious, at this time the atmospheric transmittance of the second atmospheric window is higher, at this time the amount of polytetrafluoroethylene can be appropriately increased; if in a relatively humid environment, since the water molecules in the atmosphere have strong absorption to the thermal radiation of the second atmospheric window, at this time the amount of polyformaldehyde can be appropriately increased.

[0044] S300: using a spinning method, a solution method or a hot pressing method to prepare the mixed liquid to obtain the radiation refrigeration material.

[0045] According to an embodiment of the present application, the radiation cooling material is prepared by electrospinning, and the process conditions of electrospinning satisfy at least one of the following process conditions: the voltage of electrospinning is 1 kV to 50 kV (such as 1 kV, 5 kV, 10 kV, 15 kV, 20 kV, 25 kV, 30 kV, 35 kV, 40 kV, 45 kV, 50 kV); the spinning speed is 0.1 mL / h to 20 mL / h (such as 0.1 mL / h, 1 mL / h, 3 mL / h, 5 mL / h, 8 mL / h, 10 mL / h, 12 mL / h, 15 mL / h, 17 mL / h, 20 mL / h); the humidity is 10% to 70% (such as 10%, 20%, 30%, 40%, 50%, 60%, 70%); the temperature is 10°C to 50°C (such as 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C); the distance between the positive electrode and the negative electrode is 5 cm to 25 cm (such as 5 cm, 10 cm, 15 cm, 20 cm, 25 cm); and the rotation speed of the negative electrode roller is 10 rpm to 300 rpm (such as 10 rpm, 50 rpm, 100 rpm, 150 rpm, 200 rpm, 250 rpm, 300 rpm). The radiation cooling film obtained by electrospinning under the above conditions has the advantages of high cooling performance, high tensile strength, high ultraviolet resistance, and high environmental stability, and the preparation process has the advantages of simple operation, fine control of composition and microstructure, and large-area preparation.

[0046] According to an embodiment of the present application, the radiation cooling material prepared by the above method can have thermal emissivity in both of the two atmospheric window bands (the first atmospheric window and the second atmospheric window), can be used as a double-selective thermal emitter, and can radiate heat to outer space through the two atmospheric windows while excluding atmospheric parasitic heat, thereby having higher cooling potential than existing radiation cooling emitters. Moreover, since the atmospheric transparency of the second atmospheric window is much higher in a dry climate than in a high-humidity environment, the radiation cooling material will exhibit significantly better cooling performance than single-selective radiation cooling materials in dry and hot regions. In addition, the radiation cooling material is composed of two common polymers, polyoxymethylene and polytetrafluoroethylene, both of which have good physical and chemical properties (high thermal stability and high mechanical strength, etc.) and have been commercialized, thereby laying a foundation for the practical application and mass production of double-selective radiation cooling materials. Furthermore, the application field of the radiation cooling material of the present application is relatively wide, and it can be used as a building outer layer (roof or wall) material, a sun-proof car cover, a sunshade umbrella, a sun-proof garment, a special workwear (such as a medical protective garment, a construction worker's workwear, and a military uniform, etc.), and many other fields.

[0047] Embodiment

[0048] Embodiment 1

[0049] (1) Preparation of POM-PTFE suspension: First, prepare POM solution and PTFE suspension respectively. POM solution is prepared by dissolving POM particles (1 g) in 1,1,1,3,3,3-hexafluoro-2-propanol (25 g) solvent, then constant temperature (50℃) stirring to form a uniform solution, that is, POM solution; PTFE suspension is prepared by adding PTFE particles (0.1 g) to 1,1,1,3,3,3-hexafluoro-2-propanol (10 g) solvent, ultrasonic (1 hour) and stirring (1 hour) treatment to form a uniform suspension, that is, PTFE suspension; then mix the PTFE suspension with the POM solution, further stir for 8 hours to form a uniform POM-PTFE suspension. Among them, the polytetrafluoroethylene particle molecular weight is 100000 to 1000000, the melting point is 327℃ to 342℃; polyoxymethylene is a homopolymer, the molecular weight is 10000 to 200000, the melting point is 140℃ to 190℃.

[0050] (2) Preparation of POM-PTFE fiber film (radiation refrigeration material): The POM-PTFE suspension obtained in step (1) is electrospun, and the POM-PTFE fiber is collected using aluminum foil. The voltage of the spinning process is 12kV, the spinning speed is 4mL / h, the humidity is 50%, the temperature is 20℃, the distance between the positive and negative electrodes is 18cm, and the rotation speed of the negative electrode roller is 150rpm. The double-selective POM-PTFE fiber film obtained by spinning is a disordered stack of string-like fibers composed of POM fibers and PTFE particles. The macroscopic photograph can be referred to Figure 4 , and the microscopic photograph is shown in Figure 2 . Among them, the diameter of the polytetrafluoroethylene particles in the POM-PTFE fiber film is 1000nm to 3000nm, and the diameter of the polyoxymethylene fibers is 200nm to 1500nm.

[0051] The spectral response of the POM-PTFE fiber film is shown in Figure 5 , and it can be seen from Figure 5 that the POM-PTFE fiber film in this embodiment 1 has a high solar reflectivity in the solar wave band (300-2500nm), and has a high emissivity in the first atmospheric window band and the second atmospheric window band. The emissivity in the first atmospheric window band can reach more than 90%, and the emissivity in the second atmospheric window band can basically reach more than 60%.

[0052] The outdoor refrigeration performance of the POM-PTFE fiber film obtained in this embodiment 1 was tested, and the test content included environmental humidity, temperature of POM-PTFE fiber film, environmental humidity, and solar radiation (tested on September 6, 2022 in Alashan League, Inner Mongolia). The test results can be seen in Figure 6 .

[0053] (3) Refrigeration performance test of POM-PTFE fiber membrane: The POM-PTFE fiber membrane (4#) obtained in step (2) was compared with common building materials (including white color steel plate (1#), black asphalt board (2#), pure aluminum foil (3#), aluminum foil coated with white paint (5#), and black asphalt board coated with white pigment (6#), such as Figure 7 For comparison, their cooling performance was tested using infrared photographs (as shown). The infrared photographs can be found in [reference needed]. Figure 8 ,Depend on Figure 8 It is evident that the radiation cooling material (POM-PTFE fiber membrane) of this invention exhibits significantly superior cooling performance compared to other building materials. Specifically, the white color steel plate (type 825) was purchased from Foshan Gangzuo Steel Trade Co., Ltd., the black asphalt board from Jiangsu Huangzhai Construction Engineering Co., Ltd., the white spray paint pigment from Beijing Xingjia Trade Co., Ltd., and the aluminum foil from Beijing Hongjie Technology Co., Ltd., with a thickness of 15μm.

[0054] Example 2

[0055] (1) Preparation of POM-PTFE suspension: First, prepare POM solution and PTFE suspension separately. POM solution is prepared by dissolving POM particles (0.5g) in 1,1,1,3,3,3-hexafluoro-2-propanol (10g) solvent, and then stirring at a constant temperature (50℃) until a homogeneous solution is formed. PTFE suspension is prepared by adding PTFE particles (0.3g) to 1,1,1,3,3,3-hexafluoro-2-propanol (5g) solvent, and then treating with sonication (1 hour) and stirring (1 hour) to form a homogeneous suspension. Then, mix the PTFE suspension with the POM solution and stir for another 8 hours to form a homogeneous POM-PTFE suspension. The polytetrafluoroethylene particles have a molecular weight of 100,000 to 1,000,000 and a melting point of 327°C to 342°C; the polyoxymethylene is a homopolymer with a molecular weight of 10,000 to 200,000 and a melting point of 140°C to 190°C.

[0056] (2) Preparation of POM-PTFE fiber membrane (radiative cooling material): The POM-PTFE suspension obtained in step (1) was electrospun, and the POM-PTFE fibers were collected using aluminum foil. The spinning process was carried out at a voltage of 18 kV, a spinning speed of 2 mL / h, a humidity of 45%, a temperature of 20 °C, a distance of 18 cm between the positive and negative electrodes, and a rotation speed of 150 rpm for the negative electrode roller. The biselective POM-PTFE fiber membrane obtained by spinning was composed of disordered stacking of beaded fibers consisting of POM fibers and PTFE particles. Its macroscopic photograph can be found in [reference needed]. Figure 4The POM-PTFE fiber film has a high solar reflectivity in a solar wave band (300-2500 nm), and the reflectivity is greater than 90%. The POM-PTFE fiber film has a high emissivity in a first atmospheric window wave band and a second atmospheric window wave band, and the emissivity in the first atmospheric window wave band is greater than 75%, and the emissivity in the second atmospheric window wave band is greater than 60%.

[0057] The POM-PTFE fiber film prepared in Example 2 has a high solar reflectivity in a solar wave band (300-2500 nm), and the reflectivity is greater than 90%. The POM-PTFE fiber film has a high emissivity in a first atmospheric window wave band and a second atmospheric window wave band, and the emissivity in the first atmospheric window wave band is greater than 75%, and the emissivity in the second atmospheric window wave band is greater than 60%.

[0058] Example 3

[0059] (1) Preparation of POM-PTFE suspension: POM solution and PTFE suspension were prepared respectively. The POM solution was prepared by dissolving POM particles (0.8 g) in 1,1,1,3,3,3-hexafluoro-2-propanol (10 g) solvent, and then stirring at a constant temperature (50 °C) to form a uniform solution, thereby obtaining the POM solution. The PTFE suspension was prepared by adding PTFE particles (0.4 g) to 1,1,1,3,3,3-hexafluoro-2-propanol (5 g) solvent, and then ultrasonic treatment (1 hour) and stirring treatment (1 hour) to form a uniform suspension, thereby obtaining the PTFE suspension. Then, the PTFE suspension and the POM solution were mixed, and further stirred for 8 hours to form a uniform POM-PTFE suspension. In the POM-PTFE fiber film, the polytetrafluoroethylene particles have a diameter of 1000 nm to 3000 nm, and the polyoxymethylene fibers have a diameter of 200 nm to 1500 nm.

[0060] (2) Preparation of POM-PTFE fiber film (radiation cooling material): The POM-PTFE suspension obtained in step (1) was subjected to electrospinning, and POM-PTFE fibers were collected using an aluminum foil. The voltage in the spinning process was 15 kV, the spinning speed was 4 mL / h, the humidity was 40%, the temperature was 25 °C, the distance between the positive and negative electrodes was 18 cm, and the rotation speed of the negative electrode roller was 200 rpm. The double-selective POM-PTFE fiber film obtained by spinning is a disordered stack of string-like fibers composed of POM fibers and PTFE particles, and the macroscopic photograph thereof can be referred to Figure 4 The POM-PTFE fiber film has a high solar reflectivity in a solar wave band (300-2500 nm), and the reflectivity is greater than 90%. The POM-PTFE fiber film has a high emissivity in a first atmospheric window wave band and a second atmospheric window wave band, and the emissivity in the first atmospheric window wave band is greater than 75%, and the emissivity in the second atmospheric window wave band is greater than 60%.

[0061] The POM-PTFE fiber film prepared in this embodiment 3 has a high solar reflectivity in the solar wave band (300-2500 nm), and the reflectivity is greater than 95%. It has a high emissivity in the first atmospheric window band and the second atmospheric window band. The emissivity in the first atmospheric window band can reach more than 80%, and the emissivity in the second atmospheric window band can reach more than 65%.

[0062] Embodiment 4

[0063] (1) Preparation of POM-PTFE suspension: First, prepare POM solution and PTFE suspension respectively. The POM solution is prepared by dissolving POM particles (0.75 g) in 1,1,1,3,3,3-hexafluoro-2-propanol (10 g) solvent, and then stirring at a constant temperature (50°C) until a uniform solution is formed to obtain the POM solution. The PTFE suspension is prepared by adding PTFE particles (0.35 g) to 1,1,1,3,3,3-hexafluoro-2-propanol (5 g) solvent, and then ultrasonic treatment (1 hour) and stirring (1 hour) to form a uniform suspension, which is the PTFE suspension. Then, the PTFE suspension and the POM solution are mixed, and further stirred for 8 hours to form a uniform POM-PTFE suspension. The polytetrafluoroethylene particles have a molecular weight of 100000 to 1000000 and a melting point of 327°C to 342°C. The polyoxymethylene is a homopolymer with a molecular weight of 10000 to 200000 and a melting point of 140°C to 190°C.

[0064] (2) Preparation of POM-PTFE fiber film (radiation cooling material): The POM-PTFE suspension obtained in step (1) is subjected to electrospinning, and the POM-PTFE fiber is collected using an aluminum foil. The voltage during the spinning process is 15 kV, the spinning speed is 1 mL / h, the humidity is 40%, the temperature is 25°C, the distance between the positive and negative electrodes is 10 cm, and the rotation speed of the negative electrode roller is 100 rpm. The double-selective POM-PTFE fiber film obtained by spinning is a disordered stack of string-like fibers composed of POM fibers and PTFE particles. The macroscopic photograph can be referred to Figure 4 . In the POM-PTFE fiber film, the polytetrafluoroethylene particles have a diameter of 1000 nm to 3000 nm, and the polyoxymethylene fibers have a diameter of 200 nm to 1500 nm.

[0065] The POM-PTFE fiber film prepared in this embodiment 4 has a high solar reflectivity in the solar wave band (300-2500 nm), and the reflectivity is greater than 95%. It has a high emissivity in the first atmospheric window band and the second atmospheric window band. The emissivity in the first atmospheric window band can reach more than 80%, and the emissivity in the second atmospheric window band can reach more than 65%.

[0066] The terms "first", "second", etc. are used only for the purpose of description and are not to be interpreted in a relative manner or to imply relative importance or to imply a number of the technical features indicated. Thus, the features defined with "first", "second" can include one or more of the features explicitly or implicitly. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise specifically limited.

[0067] In the description of the present application, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present application, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any suitable manner in any one or more embodiments or examples. Furthermore, the person skilled in the art can combine and combine the different embodiments or examples described in the present application and the features of the different embodiments or examples, without contradiction.

[0068] Although the embodiments of the present application have been shown and described above, it is understood that the above-described embodiments are exemplary and are not to be construed as limiting the present application, and the person skilled in the art can make changes, modifications, replacements and variations to the above-described embodiments within the scope of the present application.

Claims

1. A radiative cooling material, characterized in that, The radiation refrigeration material comprises polyformaldehyde and polytetrafluoroethylene, and the radiation refrigeration material can selectively emit infrared rays in a first atmospheric window and a second atmospheric window, the first atmospheric window is 8-13 μm, and the second atmospheric window is 16-25 μm. The method for preparing the radiation refrigeration material comprises the following steps: configuring a polyformaldehyde solution and a polytetrafluoroethylene liquid; mixing the polyformaldehyde solution and the polytetrafluoroethylene liquid uniformly to obtain a mixed liquid; preparing the radiation refrigeration material from the mixed liquid by using a spinning method; in the radiation refrigeration material, the polyformaldehyde is in a fibrous form, the polytetrafluoroethylene is in a particulate form, and the polytetrafluoroethylene particles are embedded in the polyformaldehyde fibers.

2. The radiative cooling material of claim 1, wherein, The emissivity of the radiation refrigeration material in the first atmospheric window is greater than or equal to 70%, the emissivity of the radiation refrigeration material in the second atmospheric window is greater than or equal to 60%, and the solar reflectivity of the radiation refrigeration material is greater than or equal to 90%.

3. The radiative cooling material of claim 1 or 2, wherein, Based on the total mass of the radiation refrigeration material, the radiation refrigeration material comprises, in terms of mass percentage: 1 wt%-80 wt% of polytetrafluoroethylene; 20 wt%-99 wt% of polyformaldehyde.

4. The radiative cooling material of claim 1 or 2, wherein, At least one of the following conditions is met: the molecular weight of the polytetrafluoroethylene is 100000-1000000; the melting point of the polytetrafluoroethylene is 327-342 ℃; the molecular weight of the polyformaldehyde is 2000-200000; the melting point of the polyformaldehyde is 140-190 ℃.

5. The radiative cooling material of claim 1, wherein, At least one of the following conditions is met: the diameter of the polyformaldehyde fibers is 200-3000 nm; the particle size of the polytetrafluoroethylene particles is 200-3000 nm.

6. A method of making the radiative cooling material of any one of claims 1-5, wherein, The method comprises the following steps: configuring a polyformaldehyde solution and a polytetrafluoroethylene liquid; mixing the polyformaldehyde solution and the polytetrafluoroethylene liquid uniformly to obtain a mixed liquid; preparing the radiation refrigeration material from the mixed liquid by using a spinning method.

7. The method of claim 6, wherein, The mass percentage of polyformaldehyde in the polyformaldehyde solution is 0.1 wt%-50 wt%, and the mass percentage of polytetrafluoroethylene in the polytetrafluoroethylene liquid is 1 wt%-50 wt%.

8. The method of claim 6, wherein, The radiation refrigeration material is prepared by using electrospinning, and the process conditions of the electrospinning meet at least one of the following process conditions: the voltage of the electrospinning is 1 kV-50 kV; the spinning speed is 0.1 mL / h-20 mL / h; the humidity is 10%-70%; the temperature is 10-50 ℃; the distance between the positive electrode and the negative electrode is 5-25 cm; the rotation speed of the negative electrode roller is 10 rpm-300 rpm.

9. The method of claim 6, wherein, The solvents of the polyformaldehyde solution and the polytetrafluoroethylene liquid are both polar solvents, and the polar solvents are selected from at least one of dimethylformamide, N-methyl-2-pyrrolidone, and 1,1,1,3,3,3-hexafluoro-2-propanol.

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