Persistent radiation refrigeration film material and preparation method thereof

Abstract

The invention discloses a preparation method of a persistent radiation refrigeration film material, which comprises the following steps: preparing a composite polymer of PVDF-HFP and ZnO coated SiO2 nanoparticles, uniformly spraying the composite polymer on a film, and finally preparing the persistent radiation refrigeration film material. According to the PVDF-HFP porous structure prepared by the method, the reflectivity of the film is effectively improved, and an excellent cooling effect is realized. The introduced ZnO coated SiO2 nanoparticles can absorb high-energy ultraviolet photons and convert the high-energy ultraviolet photons into heat with small harm, so that the stability of ultraviolet rays is improved, and the film still keeps excellent cooling performance under long-term ultraviolet irradiation. Therefore, the problem that the radiation cooling performance of a radiation cooling material in the prior art is reduced due to the fact that the radiation cooling material is easily influenced by environmental aging, high temperature and ultraviolet irradiation is effectively solved, and the radiation cooling film has a more durable radiation cooling effect and a longer service life in an outdoor environment.

Description

Technical Field

[0001] The invention relates to the technical field of film preparation, and in particular to a durable radiation refrigeration film material and a preparation method thereof. Background Art

[0002] In the context of no external energy input, daytime radiative cooling technology has been increasingly valued due to its characteristic of heat dissipation through thermal radiation. The core of this technology is that the material can reflect most of the solar radiation (wavelength 0.3 to 2.5μm) and emit strong long-wave infrared radiation through the atmospheric transparent window (wavelength 8 to 13μm). Radiative cooling film materials have shown great potential in the field of radiative cooling due to their sustainability and high infrared emissivity. In order to enhance the solar heat dissipation efficiency of radiative cooling materials, porous structures are usually constructed to enhance the scattering efficiency of sunlight, but the mechanical stability of radiative cooling materials is easily damaged due to the increase in pores, that is, the solar heat dissipation efficiency is enhanced but the mechanical stability is reduced. In addition, the high solar reflectivity of radiative cooling materials is easily affected by environmental aging, high temperature and ultraviolet radiation, which greatly reduces the cooling performance of radiative cooling materials and makes it impossible to maintain good radiative cooling performance for a long time, limiting its industrial application.

[0003] In response to these problems, the present invention proposes a long-lasting radiative cooling film material and a preparation method, which not only maintains high solar reflectivity and infrared emissivity, but also significantly improves the mechanical stability and UV resistance of the material, so that it has a longer service life and a more stable cooling effect in outdoor environments. Summary of the invention

[0004] The embodiments of the present application provide a long-lasting radiative cooling film material and a preparation method, thereby effectively solving the problem in the prior art that the radiative cooling materials in the prior art are easily affected by environmental aging, high temperature and ultraviolet radiation, which reduces the radiative cooling performance, thereby achieving a more lasting radiative cooling effect and a longer service life of the radiative cooling film in an outdoor environment.

[0005] The present application embodiment provides a method for preparing a durable radiation cooling film material, and the specific steps are as follows: S01 Preparation of PVDF-HFP / ZnO@SiO2 mixed solution, PVDF-HFP and ZnO@SiO2 are added to an organic solvent in a certain proportion and mixed to prepare a PVDF-HFP / ZnO@SiO2 mixed solution, wherein the ZnO@SiO2 is prepared by chemical coprecipitation technology with monodispersed silica nanospheres as the core; S02 The PVDF-HFP / ZnO@SiO2 mixed solution in step S01 is uniformly sprayed on the base film by a spraying process, and finally a film with UV resistance is obtained.

[0006] Preferably, the mass ratio of the PVDF-HFP to the ZnO@SiO2 is 25-100:1, preferably 33.33:1.

[0007] Preferably, the preparation steps of the PVDF-HFP / ZnO@SiO2 mixed solution are: S011 dissolving an appropriate amount of PVDF-HFP powder in an organic solvent by heating in a water bath to prepare a PVDF-HFP solution; S012 Preparation of ZnO@SiO2 powder, using monodispersed SiO2 nanospheres as cores, dissolving SiO2NPs and Zn(NO3)2·6H2O in anhydrous ethanol, stirring with hexamethylenetetramine solution and calcining to prepare ZnO@SiO2 powder; S013 Dissolve the ZnO@SiO2 powder in step S012 in a certain proportion in the PVDF-HFP solution, and stir evenly to obtain a PVDF-HFP / ZnO@SiO2 mixed solution.

[0008] Preferably, the organic solvent in step S011 is a mixed solution of acetone solution and N,N-dimethylformamide, and the mass ratio thereof is 16:1 to 13:1.

[0009] Preferably, the solid content of the PVDF-HFP solution used in step S011 is 10-15 wt %.

[0010] Preferably, in step S012, the mass ratio of SiO2 to Zn(NO3)2·6H2O is 1:2 to 1:3.

[0011] The present invention also provides another preparation step of PVDF-HFP / ZnO@SiO2 mixed solution: S011 Preparation of ZnO@SiO2 powder, using monodispersed SiO2 nanospheres as cores, dissolving SiO2NPs and Zn(NO3)2·6H2O in anhydrous ethanol, stirring with hexamethylenetetramine solution and calcining to prepare ZnO@SiO2 powder; S012 A certain proportion of PVDF-HFP powder and ZnO@SiO2 powder are mixed, and then added into an organic solvent together, and the PVDF-HFP / ZnO@SiO2 solution is prepared by heating in a water bath and stirring evenly.

[0012] The present invention also provides a durable radiation refrigeration film material, which is prepared by any of the above preparation methods.

[0013] One or more technical solutions provided in the embodiments of the present application have at least the following technical effects or advantages: 1. By preparing a composite polymer of PVDF-HFP and ZnO@SiO2 nanoparticles, the composite polymer is evenly sprayed on the film, and finally a long-lasting radiation cooling film material is made. The PVDF-HFP porous structure prepared by this method effectively improves the reflectivity of the film and achieves an excellent cooling effect. The introduced ZnO@SiO2 nanoparticles can absorb high-energy ultraviolet photons and convert them into less harmful heat, thereby improving the stability of ultraviolet rays and allowing the film to maintain excellent cooling performance under long-term ultraviolet irradiation. Therefore, the problem that the radiation cooling material in the prior art is easily affected by environmental aging, high temperature and ultraviolet irradiation, thereby reducing the radiation cooling performance, is effectively solved, thereby achieving a more lasting radiation cooling effect and a longer service life of the radiation cooling film in an outdoor environment.

[0014] 2. The scanning electron microscope image of the durable radiative cooling film provided by the present invention shows that the PVDF-HFP in the material prepared by the preparation method provided by the present invention has spherical particles uniformly dispersed, and these particles are ZnO@SiO2. This structure not only maintains the original porosity characteristics of PVDF-HFP, that is, it does not affect the solar reflectivity, but also improves the mechanical stability of the overall structure of the material through the addition of ZnO@SiO2.

[0015] 3. The durable radiation refrigeration film provided by the present invention also has a self-cleaning function, and its surface is super hydrophobic with a water contact angle of 129.3°, which can effectively reduce dirt accumulation.

[0016] 4. The long-lasting radiant cooling film provided by the present invention has excellent anti-ultraviolet performance. In the accelerated aging test, after 15 days of natural sunlight exposure, the solar reflectivity in the optimal embodiment only decreased by 2.3%, showing excellent long-term stability.

[0017] 5. The method for preparing the durable radiative cooling film provided by the present invention is simple to operate and has extremely low cost. Moreover, the prepared durable radiative cooling film can still show excellent solar reflectivity after long-term ultraviolet irradiation, and can be fully industrialized. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a SEM image of the durable radiative cooling film of Example 2 of the present application; Figure 2 This is a spectrum diagram of the persistent radiation cooling film in the range of 0.3-2.5 μm according to Example 2 of the present application; Figure 3 The difference in reflectivity of the long-term radiation cooling film of Example 2 of the present application after 15 days of ultraviolet irradiation compared with the film without adding nanoparticles; Figure 4 This is a diagram showing the cooling effect of the long-term radiation cooling film measured outdoors in Example 2 of the present application; Figure 5 This is an experimental diagram of the self-cleaning performance of the surface of the long-term radiation cooling film in Example 2 of the present application. DETAILED DESCRIPTION

[0019] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods. Embodiment 1

[0020] Step 1: Preparation of ZnO@SiO2 composite nanoparticles The ZnO@SiO2 composite nanoparticles were prepared by chemical coprecipitation technique with monodispersed silica nanospheres as the core.

[0021] First, 1 g of silica nanospheres and 2 g of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) were mixed in 60 ml of anhydrous ethanol and treated by ultrasound for 15 min to obtain a uniformly dispersed solution A.

[0022] Subsequently, hexamethylenetetramine (HMT) was used to prepare a 40 ml deionized water solution and quickly mixed with solution A. The mixture was stirred at 75 ° C at a speed of 100 rpm for 2 hours, and then the mixture was divided into centrifuge tubes. Deionized water and anhydrous ethanol were used for centrifugal washing at a speed of 8000 rpm for 3 times. The washed precipitate was dried at 80 ° C for 6 hours, then transferred to a ceramic crucible, and calcined in a high-temperature furnace at 500 ° C for 2 hours to finally obtain ZnO@SiO2 nanoparticle powder for subsequent use.

[0023] Step 2: Preparation of PVDF-HFP solution 15 g of PVDF-HFP powder was weighed and placed in a mixed solution consisting of 80 g of acetone solution and 5 g of N,N-dimethylformamide (DMF), and stirred in a water bath at 35° C. for 2 h to prepare a PVDF-HFP solution.

[0024] Step 3: Preparation of PVDF-HFP / ZnO@SiO2 mixed solution Weigh 0.45 g of the ZnO@SiO2 nanoparticle powder prepared in step 1 and put it into the PVDF-HFP solution prepared in step 2, and stir evenly. To ensure the uniform fraction of thermal nanoparticles, put the PVDF-HFP / ZnO@SiO2 mixed solution in a beaker and put it into an ultrasonic cleaner for 30 minutes of ultrasonic dispersion to obtain a PVDF-HFP / ZnO@SiO2 mixed solution.

[0025] Step 4: Preparation of durable radiative cooling film Then immediately pour the mixed solution in step 3 into the air pressure spray gun and spray the base film evenly. The spraying tools are K-3 high atomization 0.5mm pot-type spray gun and a small industrial-grade 220v oil-free silent air compressor. The spraying pressure is about 6Kpa, the spraying distance is about 3cm, the spray width is about 170mm, and after about 5 minutes of continuous spraying, it is left to dry for about 60 minutes to remove the solvent, and a high-lasting radiation refrigeration film-1 is obtained. Embodiment 2

[0026] Step 1 is the same as that of embodiment 1.

[0027] Step 2 Preparation of PVDF-HFP / ZnO@SiO2 mixed solution Weigh 15g of PVDF-HFP powder and mix it with 0.45g of ZnO@SiO2 composite nanoparticles. Then add the mixed powders into a mixed solvent consisting of 5g of N,N-dimethylformamide DMF and 80g of acetone, and stir in a water bath at 35°C for 2h to obtain a PVDF-HFP / ZnO@SiO2 mixed solution. Then, to ensure the uniform dispersion of the thermal nanoparticles, the PVDF-HFP / ZnO@SiO2 mixed solution was placed in a beaker and placed in an ultrasonic cleaner for 30min of ultrasonic dispersion.

[0028] Step three is the same as that of embodiment one.

[0029] A high-durability radiation cooling film-2 was produced. Embodiment 3

[0030] The mass of ZnO@SiO2 is 0.15 g, and other conditions are the same as those in Example 1, and finally a high-lasting radiative refrigeration film-3 is obtained. Embodiment 4

[0031] The mass of ZnO@SiO2 is 0.3 g, and other conditions are the same as those in Example 1, and finally a high-lasting radiative refrigeration film-4 is obtained. Embodiment 5

[0032] The mass of ZnO@SiO2 is 0.6 g, and other conditions are the same as those in Example 1, and finally a high-lasting radiative refrigeration film-5 is obtained.

[0033] Please refer to Figure 1 , Figure 1 This is the SEM image of the high-durability radiative cooling film-1. It can be seen from the figure that the film contains macroscopic pores and nanometer-sized micropores. In addition, spherical particles are evenly dispersed in this material, and these particles are ZnO@SiO2. This structure not only maintains the original pore characteristics of PVDF-HFP, but also enhances the stability of the overall structure through the addition of nanoparticles.

[0034] Please refer to Figure 2 , Figure 3 and Figure 4 , five different high-durability radiative cooling films were tested for solar reflectivity, reflectivity change difference of the films before and after ultraviolet irradiation for 15 days, and outdoor measured cooling effect. The final data obtained are shown in Table 1.

[0035] Table 1 Test data results Solar reflectivity Reflectivity change difference after 15 days of ultraviolet irradiation Cooling temperature compared to ambient temperature High durability radiation cooling film-1 96.6% 2.3% 7.5ºC High durability radiation cooling film-2 96.55% 2.3% 7.4ºC High durability radiation cooling film-3 96.13% 3.6% 6.4ºC High durability radiation cooling film-4 95.14% 3.2% 6.9ºC High durability radiation cooling film-5 95.26% 3.9% 6.1ºC PVDF-HFP film without added nanoparticles 94.8% 8.1% 5.8ºC As can be seen from the data in Table 1, the solar emissivity of the high-durable radiative cooling films prepared in the embodiments of the present invention is above 95%, and the reflectivity of the high-durable radiative cooling films prepared in Embodiments 1 to 3 can reach above 96%. The difference in reflectivity change of the film after 15 days of ultraviolet irradiation can be controlled within 4%, and the difference in change of the best embodiment is only 2.3%. All embodiments can reduce the temperature to above 6°C.

[0036] In addition, although the preparation methods of PVDF-HFP / ZnO@SiO2 in Example 1 and Example 2 are different, the performance and structure of the obtained high-durability radiative cooling films are basically the same.

[0037] Please refer to Figure 5 , it can be seen that the pollutants falling on the film are not easy to adhere, showing its excellent self-cleaning properties.

[0038] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0039] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for preparing a durable radiation cooling film material, comprising the following specific steps: S01 Preparation of PVDF-HFP / ZnO@SiO2 mixed solution, PVDF-HFP and ZnO@SiO2 are added to an organic solvent in a certain proportion and mixed to prepare a PVDF-HFP / ZnO@SiO2 mixed solution, wherein the ZnO@SiO2 is prepared by chemical coprecipitation technology with monodispersed silica nanospheres as the core; S02 The PVDF-HFP / ZnO@SiO2 mixed solution in step S01 is uniformly sprayed on the base film by a spraying process, and finally a film with UV resistance is obtained.

2. The method according to claim 1, characterized in that The mass ratio of the PVDF-HFP to the ZnO@SiO2 is 25-100:1, preferably 33.33:

1.

3. The method according to claim 2, characterized in that The preparation steps of the PVDF-HFP / ZnO@SiO2 mixed solution are as follows: S011 dissolving an appropriate amount of PVDF-HFP powder in an organic solvent by heating in a water bath to prepare a PVDF-HFP solution; S012 Preparation of ZnO@SiO2 powder, using monodispersed SiO2 nanospheres as cores, dissolving SiO2NPs and Zn(NO3)2·6H2O in anhydrous ethanol, stirring with hexamethylenetetramine solution and calcining to prepare ZnO@SiO2 powder; S013 Dissolve the ZnO@SiO2 powder in step S012 in a certain proportion in the PVDF-HFP solution, and stir evenly to obtain a PVDF-HFP / ZnO@SiO2 mixed solution.

4. The method according to claim 3, characterized in that The organic solvent in step S011 is a mixed solution of acetone solution and N,N-dimethylformamide, and the mass ratio thereof is 16:1 to 13:

1.

5. The method according to claim 4, characterized in that The solid content of the PVDF-HFP solution used in step S011 is 10-15 wt %.

6. The method according to claim 3, characterized in that In the step S012, the mass ratio of SiO2 to Zn(NO3)2·6H2O is 1:2~1:

3.

7. The method according to claim 2, characterized in that The preparation steps of the PVDF-HFP / ZnO@SiO2 mixed solution are as follows: S011 Preparation of ZnO@SiO2 powder, using monodispersed SiO2 nanospheres as cores, dissolving SiO2NPs and Zn(NO3)2·6H2O in anhydrous ethanol, stirring with hexamethylenetetramine solution and calcining to prepare ZnO@SiO2 powder; S012 A certain proportion of PVDF-HFP powder and ZnO@SiO2 powder are mixed, and then added into an organic solvent together, and the PVDF-HFP / ZnO@SiO2 solution is prepared by heating in a water bath and stirring evenly.

8. A durable radiation cooling film material, characterized in that: Prepared according to the method according to any one of claims 1 to 7.

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