Radiation refrigeration material based on PTFE fiberization dry process, radiation refrigeration film and preparation method and application thereof

Abstract

This invention belongs to the field of radiative cooling materials technology, specifically relating to a radiative cooling material, a radiative cooling film, and their preparation method and application based on a PTFE fiberization dry process. A radiative cooling material is prepared by the following steps: S1. High-speed stirring of polytetrafluoroethylene (PTFE) particles to obtain pre-fiberized PTFE; S2. Mixing the pre-fiberized PTFE from step S1 with organic and / or inorganic particles and then high-speed stirring to obtain the radiative cooling material. This invention utilizes high-speed stirring of organic and / or inorganic particles with pre-fiberized PTFE to obtain an in-situ fiberized radiative cooling material. The preparation method of this invention employs a solvent-free dry process, avoiding solvent evaporation pollution. Furthermore, the prepared material can be bonded to a substrate and can be recyclable and reused without damage.

Description

Technical Field

[0001] This invention relates to the field of radiation cooling materials technology, and more specifically, to a radiation cooling material, a radiation cooling film, and their preparation methods and applications based on a PTFE fiber dry process. Background Technology

[0002] Traditional refrigeration methods, due to their energy dependence, exacerbate energy consumption and carbon emissions. Therefore, finding a green, clean, and energy-free refrigeration material or method is urgently needed.

[0003] Radiation cooling materials, as a novel material with a new cooling method, convert heat into infrared radiation and send it into outer space through atmospheric transmission windows as blackbody radiation. This can reduce cooling energy consumption and greenhouse gas emissions, and therefore has attracted much attention in recent years.

[0004] Currently, research on radiation-cooling materials mainly focuses on organic coatings prepared in the liquid phase. For example, existing commercially available radiation-cooling liquid coatings can produce radiation-cooling films after drying. However, these coatings are water-based, and to force the dispersion of ceramic particles such as alumina and silica in the water-based coating, a large amount of wetting agents and dispersants must be added. These wetting agents and dispersants remain in the coating substrate after film formation, reducing the purity of the coating and potentially absorbing energy in the mid-infrared band, weakening the cooling effect. Moreover, during the coating evaporation process, solvent evaporation can easily pollute the air. In addition, since the coating is directly applied to the substrate surface to form a film, the radiation-cooling film cannot be recycled and reused, increasing costs.

[0005] A Chinese patent application discloses a reflective radiative cooling material, a thin film, a preparation method, and its application, comprising the following steps: surface modification of ceramic particles such as alumina and silica using surface modifiers such as silane coupling agents to improve their miscibility with a polymer substrate; mixing these particles with a polytetrafluoroethylene (PTFE) polymer substrate in solvents such as butyl acetate and cyclohexane; and then preparing a thin film on the substrate using dip coating, spray coating, or casting processes. However, this method for preparing radiative cooling films still suffers from the drawbacks of solvent evaporation pollution and difficulty in recycling. Moreover, due to the poor compatibility between ceramic particles and the polymer substrate in solvents, modification treatment of the ceramic particles is usually required to improve their compatibility, which also increases costs. Summary of the Invention

[0006] The purpose of this invention is to overcome the defects and shortcomings of the above-mentioned solvent-based methods for preparing radiation-cooling films, which have high pollution from solvent evaporation and poor recyclability of the coating. This invention provides a radiation-cooling material that is obtained by high-speed stirring of organic particles and / or inorganic particles with pre-fiberized polytetrafluoroethylene to obtain an in-situ fiberized radiation-cooling material. The method for preparing the radiation-cooling material of this invention adopts a solvent-free dry process, which avoids solvent evaporation pollution. Moreover, the prepared material can be bonded to a substrate and can be recycled and reused without damage.

[0007] Another object of the present invention is to provide a radiation-cooling thin film.

[0008] The above-mentioned objective of the present invention is achieved through the following technical solution: A radiation cooling material, the preparation method of which includes the following steps: S1. Stir the polytetrafluoroethylene particles at high speed to obtain pre-fiberized polytetrafluoroethylene; S2. The pre-fiberized polytetrafluoroethylene from step S1 is mixed with organic particles and / or inorganic particles and then stirred at high speed to obtain a radiation cooling material; In step S1, the weight-average molecular weight of the polytetrafluoroethylene particles is at least 4.5 million; the stirring speed is 8000~15000 r / min, and the stirring time is 5~25 min; In step S2, the mass ratio of organic particles and / or inorganic particles to pre-fiberized polytetrafluoroethylene is (0.1~1.1):1; the stirring speed is 8000~12000 r / min, and the stirring time is 5~25 min.

[0009] The radiation cooling material of the present invention is based on a dry solvent-free process of in-situ fiberization of organic / inorganic PTFE particles, which can produce recyclable radiation cooling materials.

[0010] This invention involves solvent-free mixing of fibrous polytetrafluoroethylene (PTFE) particles with organic and / or inorganic particles, followed by high-speed stirring to induce in-situ fiberization of the PTFE particles. This yields a radiative cooling material with a particle-PTFE nanofiber composite structure. The radiative cooling material possesses a stable fibrous network hybrid micro / nano structure. The fibers and organic and / or inorganic particles synergistically construct a multi-scale scattering surface. This hybrid micro / nano structure can simultaneously achieve subwavelength Mie scattering, broadband reflection with enhanced dielectric constant contrast, and phonon-mediated radiation channels, overcoming the inherent optical limitations of single-phase systems. It enables ultra-wideband solar reflection and mid-infrared emission, and the prepared material exhibits excellent radiative cooling performance. This radiative cooling material is prepared using a dry fiberization method, allowing for non-destructive dry recycling and reuse, and exhibits excellent thermal stability and mechanical properties.

[0011] This invention employs in-situ fiberization of polytetrafluoroethylene (PTFE) particles with a weight-average molecular weight of at least 4.5 million using a high-speed stirring dry process. The fiberization capability of PTFE is closely related to its weight-average molecular weight and the degree of molecular chain entanglement. Essentially, PTFE in-situ fiberization is a shear-induced cold stretching process: under external force, PTFE particles are stretched to form long-chain oriented micro / nano fibers. This process requires a sufficiently high weight-average molecular weight to ensure strong entanglement and high melt strength between molecular chains. As the weight-average molecular weight increases, the molecular chains become longer and the entanglement density higher. Under shear, PTFE particles are more prone to plastic stretching rather than breakage, thus forming a stable fiber network. Conversely, when the weight-average molecular weight of PTFE particles is below 4.5 million, the entanglement between molecular chains is insufficient. PTFE particles are more prone to brittle breakage or flow deformation during shearing, making it difficult to form a continuous fiber structure. Therefore, the fiberization capability is significantly reduced, and subsequent dry processes cannot be used to prepare films.

[0012] In steps S1 and S2 of this invention, during the in-situ fiberization of PTFE, the stirring time directly determines the degree of fiberization and the integrity of the three-dimensional network structure: when the stirring time is too short, the PTFE particles only undergo partial deformation, the number of fibers is small and the network is not connected, the porosity is low, and the multiple light scattering is insufficient, resulting in a decrease in solar reflectivity and weak mechanical properties; as the stirring time increases, the particles are fully stretched under high shear to form a continuous micro-nano fiber network, constructing a multi-scale porous structure (nanofibers + micron pores), increasing the air / polymer interface, which can significantly improve the solar light scattering ability and mid-infrared emissivity, while also improving the material strength, thereby obtaining the best radiative cooling performance; however, if the stirring time is too long, excessive shearing will cause fiber breakage and network collapse, the structure tends to be denser, the porosity decreases, the effective refractive index increases, the multiple scattering paths decrease, ultimately leading to a decrease in solar reflectivity and an increase in thermal conductivity, and the radiative cooling performance weakens. Therefore, only within a moderate fiberization time window can a high reflectivity, high emissivity, porous and stable radiative cooling material be obtained.

[0013] The present invention discloses a method for preparing radiative cooling materials using a solvent-free process. This eliminates the need for adding large amounts of wetting agents and dispersants, preventing these agents from weakening the cooling effect. Furthermore, the absence of solvents during preparation avoids pollution caused by solvent evaporation. Additionally, no modification treatment of organic and / or inorganic particles is required, simplifying the process and reducing costs.

[0014] Preferably, in step S1, the polytetrafluoroethylene particles are polytetrafluoroethylene particles obtained by suspension polymerization.

[0015] Preferably, the polytetrafluoroethylene particles have a weight-average molecular weight of 6 million to 8 million.

[0016] Preferably, the organic particles are one or more of polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, or trifluorochloroethylene-ethylene copolymer.

[0017] Preferably, the inorganic particles are one or more of titanium dioxide, aluminum oxide, silicon dioxide, zirconium oxide, barium titanate, barium sulfate, sodium aluminum silicate, magnesium oxide, zinc oxide, aluminum phosphate, silicon nitride, and silicon carbide; the average diameter of the inorganic particles is 0.1~5μm.

[0018] Inorganic particles of different sizes and types achieve different scattering efficiencies through the combination of light scattering and refraction within the material.

[0019] More preferably, the inorganic particles are silicon dioxide and other inorganic particles, the silicon dioxide is hollow silicon dioxide, and the average diameter of the hollow silicon dioxide is 1~5μm.

[0020] More preferably, the average diameter of the other inorganic particles is 0.1~0.3μm.

[0021] Preferably, the mass ratio of organic particles and / or inorganic particles to pre-fiberized polytetrafluoroethylene is (0.11~1):1.

[0022] The present invention also protects a radiation-cooling thin film prepared from any of the radiation-cooling materials described above.

[0023] This invention is based on a dry solvent-free process for in-situ fiberization of organic / inorganic PTFE particles, which can prepare recyclable radiation-cooling films.

[0024] The present invention also protects a method for preparing the radiation-cooling thin film, comprising the following steps: placing the radiation-cooling material prepared by any of the above-described methods in a mold and pressing it into a block material; then rolling it into a radiation-cooling thin film.

[0025] This invention involves solvent-free mixing of fibrous polytetrafluoroethylene (PTFE) particles with organic and / or inorganic particles in a specific ratio, followed by high-speed stirring to induce in-situ fiberization of the PTFE particles, resulting in a radiation-cooling material. This material is then subjected to roll pressing to obtain a radiation-cooling film with a particle-PTFE nanofiber composite structure. The film possesses a stable fibrous network structure, with fibers and micro / nano particles synergistically constructing a multi-scale scattering surface, enabling ultra-wideband solar reflection and mid-infrared emission. The prepared film exhibits excellent radiation cooling performance.

[0026] The radiation cooling film of the present invention is prepared by dry fiberization. This film can be recycled and reused without damage, and has excellent thermal stability and mechanical properties.

[0027] The radiation cooling film of the present invention is easy to prepare on a large scale, has low cost, and is recyclable.

[0028] Preferably, the rolling process includes at least one of calendering, hot melt direct pressing, roll-to-roll hot rolling, and extrusion calendering composite process.

[0029] In practical applications, the radiation cooling film can be laminated to a substrate using an adhesive. The substrate includes at least one of various metallic or inorganic materials such as aluminum plate, iron plate, copper plate, wood plate, plastic plate, glass, ceramic, and cement.

[0030] This invention also protects the application of the aforementioned radiative cooling film in building exterior walls, building facades, power energy facilities, transportation vehicles, agricultural photothermal control facilities, or outdoor equipment. The radiative cooling film of this invention combines passive radiative cooling, thermal insulation, and UV resistance, making it suitable for use in building exterior walls, building facades, power energy facilities, transportation vehicles, agricultural photothermal control facilities, or outdoor equipment.

[0031] Compared with the prior art, the beneficial effects of the present invention are: This invention provides a radiative cooling material. By solvent-free mixing of fibrous polytetrafluoroethylene (PTFE) particles with organic and / or inorganic particles in a specific ratio followed by high-speed stirring, the PTFE particles are in-situ fiberized, resulting in a radiative cooling material with a particle-PTFE nanofiber composite structure. This material possesses a stable fibrous network hybrid micro / nano structure. The fibers and organic / / or inorganic particles synergistically construct a multi-scale scattering surface. This hybrid micro / nano structure can simultaneously achieve subwavelength Mie scattering, broadband reflection with enhanced dielectric constant contrast, and phonon-mediated radiation channels, overcoming the inherent optical limitations of single-phase systems. It can achieve ultra-wideband solar reflection and mid-infrared emission, and the prepared material exhibits excellent radiative cooling performance. This invention's radiative cooling material is prepared using a dry fiberization method, avoiding solvent evaporation pollution and preventing wetting agents and dispersants in the solvent from weakening the cooling effect. Furthermore, the prepared material can be bonded to a substrate, enabling non-destructive dry recycling and reuse, and exhibits excellent thermal stability and mechanical properties. Attached Figure Description

[0032] Figure 1 This is a photograph of the radiation-cooling thin film of Example 1.

[0033] Figure 2 The solar reflectance and mid-infrared emission spectra of Example 1 and Comparative Examples 1-2 are shown.

[0034] Figure 3 The daytime temperature tracking curves for Example 1 and Comparative Examples 1-2 from 10:00 to 14:00 are shown.

[0035] Figure 4This is an electron microscope image of the interior of the radiation-cooling thin film in Example 1.

[0036] Figure 5 This is an electron microscope image of the radiation-cooled thin film in Comparative Example 3.

[0037] Figure 6 This is an electron microscope image of the radiation-cooled thin film in Comparative Example 4.

[0038] Figure 7 The graph shows the reflectivity and emissivity data of the radiation-cooling thin film in Example 1 in its initial state, after 2 and 5 recycling cycles.

[0039] Figure 8 The radiation cooling temperature of the radiation cooling film in Example 1 was tested in its initial state, after 2 and 5 recycling cycles. Detailed Implementation

[0040] To more clearly and completely describe the technical solution of the present invention, the present invention will be further described in detail below through specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention. Various changes can be made within the scope of the claims of the present invention.

[0041] The raw materials used in each embodiment and comparative example are as follows. Unless otherwise specified, all reagents used are commercially available products.

[0042] Polytetrafluoroethylene granules 1, purchased from KELOD, with a weight-average molecular weight of 7.7 million.

[0043] Polytetrafluoroethylene granules 2, purchased from KELOD, with a weight-average molecular weight of 5 million.

[0044] Polyvinylidene fluoride, purchased from KELU, has an average diameter of 200 nm and a weight-average molecular weight of 1.1 million.

[0045] The barium titanate nanoparticles were purchased from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd., with an average diameter distribution of 100nm-300nm.

[0046] Hollow silica 1, purchased from Zhejiang Manli Nanotechnology Co., Ltd., has an average diameter of 1 μm.

[0047] Hollow silica 2, purchased from Zhejiang Manli Nanotechnology Co., Ltd., has an average diameter of 3μm.

[0048] Hollow silica 3, purchased from Zhejiang Manli Nanotechnology Co., Ltd., has an average diameter of 5μm.

[0049] Titanium dioxide, purchased from Shanghai Maclean Biochemical Technology Co., Ltd., with an average diameter of 100 nm.

[0050] Alumina, purchased from Dongguan Dongchao New Material Technology Co., Ltd., with an average diameter of 1μm.

[0051] Barium sulfate, purchased from Shenzhen Haiyang Powder Technology Co., Ltd., has an average diameter of 100 nm.

[0052] Example 1 A radiation cooling material, the preparation method of which includes the following steps: S1. Place polytetrafluoroethylene particles 1 into a high-speed stirrer and stir at 15000 r / min for 20 min to obtain pre-fiberized polytetrafluoroethylene.

[0053] S2. After mixing the pre-fiberized polytetrafluoroethylene, hollow silica 1 and barium titanate from step S1, stir at 10000 r / min for 20 min using a high-speed stirrer to obtain the radiation cooling material. In step S2, the mass ratio of the raw materials is: polytetrafluoroethylene 1: hollow silica 1: barium titanate = 50: 25: 25, and the mass ratio of inorganic particles (hollow silica 1 and barium titanate) to pre-fiberized polytetrafluoroethylene is 1:1.

[0054] A radiation-cooling thin film, the preparation method of which includes the following steps: The aforementioned radiation-cooling material was placed in a metal mold and pressed into a block material; then, the block material was rolled into a 400μm radiation-cooling film using a hot roll press. (See image below.) Figure 1 As shown; The rolling temperature is 80℃, the rolling pressure is 4t, and the rolling speed is 0.3m / min.

[0055] Example 2 The preparation method of a radiation cooling material differs from that of Example 1 in that: In step S2, the mass ratio of the raw materials is: polytetrafluoroethylene particles 1: alumina: polyvinylidene fluoride = 90:5:5. The mass ratio of the sum of the mass of alumina and polyvinylidene fluoride to the mass of pre-fiberized polytetrafluoroethylene is 0.11:1. In step S2, the speed of the high-speed stirrer is 10000 r / min, and the high-speed stirring is carried out for 10 min.

[0056] A radiation-cooling thin film, which differs from Example 1 in that it uses the above-mentioned radiation-cooling material, but the preparation method is the same as that of Example 1.

[0057] Example 3 The preparation method of a radiation cooling material differs from that of Example 1 in that: In step S1, the stirring time is 10 minutes.

[0058] In step S2, the mass ratio of the raw materials is: polytetrafluoroethylene resin 2: hollow silica 3: barium titanate = 80:15:5. The mass ratio of inorganic particles (hollow silica 3 and barium titanate) to pre-fiberized polytetrafluoroethylene is 0.25:1. In step S2, the speed of the high-speed stirrer is 8000 r / min, and the stirring time is 10 min.

[0059] A radiation-cooling thin film, which differs from Example 1 in that it uses the above-mentioned radiation-cooling material, but the preparation method is the same as that of Example 1.

[0060] Example 4 The preparation method of a radiation cooling material differs from that of Example 1 in that: In step S2, the mass ratio of the raw materials is: polytetrafluoroethylene particles 1: alumina: barium sulfate = 70:15:15. The mass ratio of inorganic particles (alumina and barium sulfate) to pre-fiberized polytetrafluoroethylene is 0.43:1. In step S2, the speed of the high-speed stirrer is 8000 r / min.

[0061] A radiation-cooling thin film, which differs from Example 1 in that it uses the above-mentioned radiation-cooling material, but the preparation method is the same as that of Example 1.

[0062] Example 5 The preparation method of a radiation cooling material differs from that of Example 1 in that: In step S2, the mass ratio of the raw materials is: polytetrafluoroethylene particles 1: hollow silica 2: titanium dioxide = 75:10:15. The mass ratio of inorganic particles (hollow silica 2 and titanium dioxide) to pre-fiberized polytetrafluoroethylene is 0.33:1. In step S2, the speed of the high-speed stirrer is 8000 r / min.

[0063] A radiation-cooling thin film, which differs from Example 1 in that it uses the above-mentioned radiation-cooling material, but the preparation method is the same as that of Example 1.

[0064] Example 6 The preparation method of a radiation cooling material differs from that of Example 1 in that: The mass ratio of the raw materials is: polytetrafluoroethylene particles 1: hollow silica 1: polyvinylidene fluoride = 90:8:2. The mass ratio of hollow silica 1 to polyvinylidene fluoride and the mass ratio of pre-fiberized polytetrafluoroethylene is 0.11:1. In step S2, the high-speed stirrer is used to stir at 10,000 r / min for 10 min.

[0065] A radiation-cooling thin film, which differs from Example 1 in that it uses the above-mentioned radiation-cooling material, but the preparation method is the same as that of Example 1.

[0066] Comparative Example 1 A radiation cooling material, the preparation method of which includes the following steps: Polytetrafluoroethylene particles 1 were placed in a stirrer and stirred for 20 minutes at a speed of 15000 r / min to obtain a radiation cooling material.

[0067] A radiation-cooling thin film, the preparation method of which includes the following steps: The radiative cooling material is placed in a metal mold and pressed into a block material; then, the block material is pressed into a 400μm radiative cooling film using a hot roller press. The rolling temperature is 80℃, the rolling pressure is 4t, and the rolling speed is 0.3m / min.

[0068] The difference from Example 1 is that the raw materials of the radiation cooling material do not include organic or inorganic particles.

[0069] Comparative Example 2 A radiation-cooling thin film, the raw material of which is a commercially available radiation-cooling liquid coating. The manufacturer is Wuhan Duoge Technology Co., Ltd., and the brand name is duogetech-50 water-based reflective coating.

[0070] The above-mentioned commercial radiation cooling liquid coating was poured into a square mold (400 μm deep), and the mold was transferred to a constant temperature and humidity chamber at 40 °C and 50% RH for drying for 1 h. Finally, a cooling film with a thickness of 400 μm was obtained by peeling it off from the mold.

[0071] Comparative Example 3 A radiation cooling material, the preparation method of which includes the following steps: Polytetrafluoroethylene particles 1 were placed in a stirrer and stirred for 1 minute at a speed of 10,000 r / min to obtain a radiative cooling material. The difference from Comparative Example 1 lies in the speed and stirring time.

[0072] A radiation-cooling thin film, prepared using the same method as in Example 1.

[0073] Comparative Example 4 A radiation cooling material, the preparation method of which includes the following steps: Polytetrafluoroethylene particles 1 were placed in a stirrer and stirred at 10,000 r / min for 60 min to obtain a radiative cooling material. The difference between this and Comparative Example 1 lies in the rotation speed and stirring time.

[0074] A radiation-cooling thin film, prepared using the same method as in Example 1.

[0075] Performance testing The performance of the radiation-cooling films of each embodiment and Comparative Example 1, and the coating of Comparative Example 2, was measured as follows. During the measurement, the radiation-cooling films of each embodiment and comparative example were bonded to a heat-spreading copper substrate using a thermally conductive adhesive, and then a thermocouple was connected to the heat-spreading plate to measure the temperature.

[0076] (1) Reflectivity and Emissivity: Infrared emissivity was measured using a Nicolet Apex FTIR spectrometer with an integrating sphere. Ultraviolet-visible reflectance was measured using a UV-3600 Plus ultraviolet-visible-near-infrared spectrometer. The test results for Example 1, Comparative Example 1, and Comparative Example 2 are as follows: Figure 2 The results are shown in Table 1. Test results for other embodiments and comparative examples are also shown in Table 1.

[0077] The calculation formula is as follows: Solar reflectivity R solar The calculation formula is as follows:

[0078] Emission rate epsilon IR The calculation formula is as follows:

[0079] lambda For wavelength, R ( lambda ) for wavelength under Reflectivity I solar ( lambda () represents the intensity of the solar spectrum.

[0080] Table 1

[0081] from Figure 3 As can be seen, within the solar spectrum and atmospheric transparency window, compared with Comparative Examples 1, 3 and 4, the embodiment has higher reflectivity and emissivity, with reflectivity reaching 87.2~96.4% and emissivity reaching 88.6~91.2%, achieving efficient reflection in the visible light region and efficient emission in the near-infrared region.

[0082] As can be seen from the above data, the in-situ fibrous membrane constructed in this invention can reflect most of the energy of solar radiation, reduce heat absorption, and thus significantly reduce the temperature of the membrane.

[0083] (2) Radiative Cooling Performance: The test method was as follows: Under clear outdoor natural light conditions, a self-made multi-parameter radiative cooling performance tester (RDLBM-RCE1000) was used to test the radiative cooling performance of the film. The device consists of a cylindrical outer shell made of aluminum alloy. The outer surface is chrome-plated to provide a specular reflective interface, reflecting most of the incident solar radiation. This design ensures that the outer shell maintains a low solar absorptivity and prevents unnecessary heat accumulation inside the shell. A 10×10 cm aperture is located at the top of the chamber and is sealed with a polyethylene (PE) film. This film effectively eliminates convective heat exchange between sunlight and the transmissive material while allowing sunlight to pass through. During the test, the specific time period of the test was recorded, and the temperature change of the film was continuously monitored. After the test, the collected temperature data was processed and analyzed to evaluate the radiative cooling performance of the film. The larger the maximum temperature difference and the average temperature difference, the better the radiative cooling performance.

[0084] Figure 3 The daytime temperature tracking curves for Example 1 and Comparative Examples 1-2 from 10:00 to 14:00 are shown in the figure. As can be seen from the figure, the maximum temperature difference between Comparative Example 1 and the environment is 6.1 ℃, and the average temperature difference is 4.2 ℃. The maximum temperature difference between Comparative Example 2 and the environment is 13.2 ℃, and the average temperature difference is 7.2 ℃. The maximum temperature difference in Example 1 can reach 18 ℃, and the average temperature difference is 11.9 ℃. The test results for the remaining examples and comparative examples are shown in Table 2 below.

[0085] Table 2

[0086] As can be seen from Table 2 above, compared with Comparative Examples 1, 3 and 4, the maximum temperature difference and average temperature difference of the embodiments of the present invention are larger, indicating that the radiation cooling film of the present invention has excellent radiation cooling effect.

[0087] As can be seen from the embodiments of the present invention and Comparative Example 2, the radiation cooling film prepared by the solvent-free dry process of the present invention has a radiation cooling effect that is similar to or even better than that of the radiation cooling film prepared by the solvent method.

[0088] (3) Electron microscope image: Figure 4 The image shown is an electron microscope image of the interior of the radiation-cooling film in Example 1. It can be seen that the inorganic particles inside are wrapped by polytetrafluoroethylene fibers, forming a dense inorganic particle-fiber hybrid network structure with a network spacing of nanometer to submicrometer.

[0089] Figure 5 The electron microscope image of the radiation-cooled thin film in Comparative Example 3 shows that the material is still mainly composed of spherical particles with less fibrous structure. Figure 6The electron microscope image of the radiation-cooling film in Comparative Example 4 shows a significantly increased fibrous structure. The results indicate that extending the stirring time facilitates the stretching of PTFE particles under shear stress and the gradual formation of a fibrous structure. During the in-situ fiberization of PTFE, the stirring time significantly affects the degree of fiberization and the network structure: With shorter stirring times, the particles undergo only limited deformation, resulting in fewer fibers that are difficult to form a continuous network, lower porosity, and insufficient light scattering ability, leading to poor solar reflectivity and mechanical properties, and ultimately, failure to form a film. As the stirring time increases, PTFE gradually forms micro / nano fibers that interweave into a three-dimensional network, simultaneously generating a hierarchical porous structure and increasing the air / polymer interface, which enhances solar light scattering and mid-infrared emission, thereby improving radiation-cooling performance. However, when the stirring time is too long, excessive shearing may lead to fiber breakage or localized network collapse, causing the structure to become denser, reducing porosity, weakening multiple scattering, and ultimately decreasing the material's radiation-cooling performance.

[0090] (4) Recyclability test: The film from Example 1 is separated from the substrate, and then a radiation-cooling material is prepared according to step S2 of the preparation method of the radiation-cooling material in Example 1. A radiation-cooling film is then prepared according to the preparation method of the radiation-cooling film in Example 1. This completes one film recycling cycle.

[0091] Figure 7 The data show the reflectivity and emissivity of the radiation-cooling thin film in Example 1 in its initial state, after 2 and 5 recycling cycles. It can be seen that the performance of the thin film does not change significantly before and after recycling.

[0092] Figure 8 The radiation cooling temperature tests of the radiation cooling film in Example 1 were conducted in its initial state, after 2 and 5 recycling cycles. It can be seen that the radiation cooling performance of the film does not change significantly before and after recycling.

[0093] (5) Thermal decomposition temperature test: The thermal decomposition temperature of the radiation cooling film in Example 1 is greater than 500℃. This indicates that the radiation cooling film has excellent thermal stability.

[0094] (6) Mechanical property test: The test standard is GB / T 1040.1-2025. The test specimen is a strip with a width of 15 mm, a length of 150 mm, a gauge length of 50 mm, and a speed of 50 mm / min. The tensile strength of the radiation cooling film in Example 1 is 24.7 MPa. This shows that the radiation cooling film has excellent mechanical properties.

[0095] In summary, the radiation cooling material of this invention is prepared using a solvent-free dry process, avoiding solvent evaporation pollution. Furthermore, the prepared material can be bonded to a substrate and can be recyclable and reused without damage. The radiation cooling film of this invention exhibits excellent radiation cooling effect, as well as superior thermal stability and mechanical properties.

[0096] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A radiation cooling material, characterized in that, The preparation method includes the following steps: S1. Stir the polytetrafluoroethylene particles at high speed to obtain pre-fiberized polytetrafluoroethylene; S2. The pre-fiberized polytetrafluoroethylene from step S1 is mixed with organic particles and / or inorganic particles and then stirred at high speed to obtain a radiation cooling material; In step S1, the weight-average molecular weight of the polytetrafluoroethylene particles is at least 4.5 million; the stirring speed is 8000~15000 r / min, and the stirring time is 5~25 min; In step S2, the mass ratio of organic particles and / or inorganic particles to pre-fiberized polytetrafluoroethylene is (0.1~1.1):1; the stirring speed is 8000~12000 r / min, and the stirring time is 5~25 min.

2. The radiative cooling material according to claim 1, characterized in that, The polytetrafluoroethylene particles have a weight-average molecular weight of 6 million to 8 million.

3. The radiative cooling material according to claim 1, characterized in that, The organic particles are one or more of polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, or trifluorochloroethylene-ethylene copolymer.

4. The radiative cooling material according to claim 1, characterized in that, The inorganic particles are one or more of titanium dioxide, aluminum oxide, silicon dioxide, zirconium oxide, barium titanate, barium sulfate, sodium aluminum silicate, magnesium oxide, zinc oxide, aluminum phosphate, silicon nitride, and silicon carbide; the average diameter of the inorganic particles is 0.1~5μm.

5. The radiative cooling material according to claim 4, characterized in that, The inorganic particles are silicon dioxide and other inorganic particles, and the silicon dioxide is hollow silicon dioxide with an average diameter of 1~5μm.

6. The radiative cooling material according to claim 5, characterized in that, The average diameter of the other inorganic particles is 0.1~0.3μm.

7. A radiation-cooling thin film, characterized in that, It is prepared from the radiation cooling material described in any one of claims 1 to 6.

8. The method for preparing the radiation-cooled thin film according to claim 7, characterized in that, The process includes the following steps: placing the radiation cooling material according to any one of claims 1 to 6 in a mold and pressing it into a block material; then rolling it into a radiation cooling film.

9. The method for preparing a radiation-cooled thin film according to claim 8, characterized in that, The rolling process includes at least one of the following: calendering, hot melt direct pressing, roll-to-roll hot rolling, and extrusion calendering composite process.

10. The application of the radiation cooling film of claim 7 in building exterior walls, building facades, power energy facilities, transportation vehicles, agricultural photothermal control facilities, or outdoor equipment.

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