Radiation refrigeration film and preparation method thereof

Abstract

The invention discloses a radiation refrigeration film and a preparation method thereof. The radiation refrigeration film is prepared from a film substrate, oyster shell powder and an adhesive, the emissivity of the radiation refrigeration film in the middle-infrared band of 8-13 microns is higher than 91%; the reflectivity of the radiation refrigeration film in a visible light near-infrared band of 0.3-2.5 microns is higher than 97%; the preparation method of the radiation refrigeration film comprises the following steps: (1) preparing the film substrate; (2) preparing an adhesive aqueous solution, then adding the ground oyster shell powder into the adhesive aqueous solution, and stirring to obtain a suspension; (3) soaking the membrane substrate prepared in the step (1) in the suspension obtained in the step (2), then transferring the membrane substrate into an initiator, taking out the membrane substrate, and carrying out heating treatment; and (4) repeating the operation in the step (3) for 2-5 times to obtain the radiation refrigeration film. According to the radiation refrigeration film, the oyster shell powder is introduced, so that the radiation refrigeration effect is remarkably improved, a new application way of the oyster shell powder is developed, and the radiation refrigeration film has great practical significance.

Description

Technical Field

[0001] The present invention belongs to the technical field of radiative cooling, and particularly relates to a radiative cooling film and a preparation method thereof. Background Art

[0002] With the acceleration of the industrialization process and the continuous increase of human activities, the concentration of greenhouse gases (such as carbon dioxide and methane) in the atmosphere has been rising continuously, leading to a continuous increase in the global temperature. Refrigeration technology can not only provide a comfortable living and working environment for humans, but also ensure the safe storage of food and medicine, and support the stable operation of industrial production. It has become a key support for modern life and production. However, traditional refrigeration systems usually require a large amount of electricity, resulting in huge energy consumption; secondly, a large amount of greenhouse gases and other pollutants are also emitted during the manufacturing and operation of traditional refrigeration equipment, exacerbating environmental problems. Facing these challenges, it is particularly urgent to develop more energy-saving and environmentally friendly refrigeration technologies. The radiative cooling film has a high reflectivity in the visible and near-infrared bands (0.3 - 2.5 μm) and a high emissivity in the band near the mid-infrared atmospheric window (8 - 13 μm), maximizing the dispersion of heat into the universe, thereby achieving cooling. The radiative cooling process does not require additional electrical input and does not use any refrigerants. Therefore, radiative cooling is a completely passive, energy-saving and pollution-free refrigeration method. Generally, the vibration of inherent functional groups makes the polymer-based radiative cooling film (including PEO, PVDF, PMMA, etc.) show a high infrared emissivity in the band within the atmospheric window; in addition, embedding inorganic particles such as TiO2, SiO2, MgO, CaCO3, and potassium titanate whiskers in the fabric can improve its solar reflectivity, thereby enhancing the radiative cooling effect.

[0003] In the prior art, for example, patent document CN112239328A provides a radiative cooling film, which sequentially includes a transparent emitter and a transparent reflector. The transparent emitter has a high emissivity in the mid-infrared light wavelength range, and has a low absorptivity and a high transmittance in the visible light wavelength range. The transparent reflector has a high reflectivity in the near-infrared sunlight wavelength range; in the visible light wavelength range, the effective refractive indices of air, the transparent emitter, and the transparent reflector gradually increase. For another example, patent document CN110972467A provides a composite radiative cooling film, which includes a top layer and a reflective layer disposed below the top layer. The material of the top layer includes one or more polymers, and the polymers have an emissivity of not less than 80% in the 7-μm to 14-μm band; the top layer includes a first emission layer close to the reflective layer and a second emission layer far from the reflective layer. The material of the first emission layer includes a first polymer, and the first emission layer further includes a plurality of first pores, and the plurality of first pores are distributed inside the first emission layer. The material of the second emission layer includes a second polymer, and the second emission layer further includes a plurality of second pores, and the plurality of second pores are distributed inside the second emission layer. The aperture of the first pores is 1 μm to 20 μm, and the aperture of the second pores is 1 nm to 200 nm. The radiative cooling film materials provided in the above documents have a high use cost or a complex structure, and are not easy to be controllably implemented.

[0004] Oysters are a kind of nutrient-rich and medicinally valuable saltwater bivalve animals. As an important marine resource, the breeding history of oysters has been more than 2,000 years, and they are highly regarded because of their high commercial value. However, about 70% of the total mass of oyster shells are mostly directly discarded and landfilled as waste, causing many environmental problems such as peculiar smells, air and soil pollution, and at the same time destroying the marine ecosystem. In fact, oyster shells are a structured biocomposite material secreted by the mantle of oysters, and the main components are 95% CaCO3 and 5% organic matrix. By means of bioconversion technology, converting oyster shells into bioenergy or new biomass materials can expand their applications in the fields of agriculture, industry, and biomedicine, so as to realize the efficient utilization of waste biomass resources. However, oyster shell-based biomass materials have not yet been applied to the field of radiative cooling.

[0005] Based on this, the present invention is specifically proposed. Summary of the Invention

[0006] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a radiative cooling film and a preparation method thereof, introducing oyster shell powder into the radiative cooling film to improve its radiative cooling performance.

[0007] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a radiative cooling film, which is made of a film matrix, oyster shell powder, and an adhesive;

[0009] The radiative cooling film has an emissivity higher than 91% in the 8-13 μm mid-infrared band;

[0010] The radiative cooling film has a reflectivity higher than 97% in the 0.3-2.5 μm visible-near infrared band.

[0011] As a preference of the technical solution of the present invention, the film matrix is selected from one of PEO, PVDF, PMMA, PP, PU, or cotton fabric; of course, the types of the above film matrices are only examples, and it can be other common film matrix materials in the art. Preferably, the film matrix material is PVDF, i.e., polyvinylidene fluoride.

[0012] As a preference of the technical solution of the present invention, the adhesive is selected from one of acrylic acid, latex, sodium alginate, and chitosan. Preferably, the adhesive is sodium alginate.

[0013] As a preference of the technical solution of the present invention, the mesh number of the oyster shell powder is 80-10,000 meshes.

[0014] In a second aspect, the present invention further provides a preparation method of the above radiative cooling film, including the following steps:

[0015] (1) Prepare the film matrix;

[0016] (2) Prepare an aqueous solution of the adhesive, and then add the ground oyster shell powder to the aqueous solution of the adhesive. After stirring, a suspension is obtained;

[0017] (3) Immerse the film matrix prepared in step (1) in the suspension obtained in step (2), and then transfer the film matrix to an initiator for immersion. After taking out the film matrix, heat treatment is carried out;

[0018] (4) Repeat the operation of step (3) 2-5 times to obtain the radiative cooling film.

[0019] As a preference of the technical solution of the present invention, in step (1), the preparation of the film matrix adopts one of electrospinning, extrusion molding, and casting molding.

[0020] As a preference of the technical solution of the present invention, in step (2), the concentration of the aqueous solution of the adhesive is 0.01-2 wt%, and the concentration of the oyster shell powder is 0.01-0.5 wt%.

[0021] As a preference of the technical solution of the present invention, in step (3), the immersion time of the film matrix in the suspension is 5-30 min.

[0022] Preferably, in step (3) of the technical solution of the present invention, the initiator is an aqueous solution with a pH value of 2 to 6, and the immersion time of the film matrix in the initiator is 5 to 30 minutes. The aqueous solution can be prepared by using hydrochloric acid or nitric acid, which is a general operation means for those skilled in the art.

[0023] Preferably, in step (3) of the technical solution of the present invention, the heat treatment temperature is 40 to 120 °C, and the treatment time is 5 to 30 minutes.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The radiation cooling film provided by the present invention creatively introduces oyster shell powder into the film preparation process, realizes the reuse of resource waste, has controllable costs and obvious economic benefits.

[0026] The radiation cooling film prepared by the present invention has a reflectivity of 97.4% in the range of 0.3 to 2.5 μm and an emissivity of 91.2% in the range of 8 to 13 μm; at the same time, under the sunlight of 1 kW·m -2 The temperature of the radiation cooling film containing oyster shell powder is 1.7 °C lower than that of the radiation cooling film without oyster shell powder. In the absence of sunlight, its temperature is 2.1 °C lower than that of the radiation cooling film without oyster shell powder, and the performance is excellent; at the same time, the preparation method is simple, feasible and easy to implement on a large scale. Description of the Drawings

[0027] Figure 1 It is the visible light near-infrared band reflection test spectrum of the radiation cooling film in Example 1 of the present invention.

[0028] Figure 2 It is the mid-infrared band emission test spectrum of the radiation cooling film in Example 1 of the present invention.

[0029] Figure 3 It is the temperature curve graph of the radiation cooling film in Example 1 of the present invention and the radiation cooling film in Comparative Example 1 under 1 kW·m -2 sunlight.

[0030] Figure 4 It is the temperature map of the radiation cooling film in Example 1 of the present invention and the radiation cooling film in Comparative Example 1 covering the skin surface. Detailed Embodiments

[0031] In order to make the objectives, technical solutions and advantages of the present invention clearer, the following further describes the present invention in detail with reference to embodiments. Of course, the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0032] Although the steps in the present invention are arranged with reference numerals, they are not used to limit the order of the steps. Unless the order of the steps is clearly stated or the execution of a certain step requires other steps as a basis, the relative order of the steps can be adjusted. It can be understood that the term "and / or" used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items.

[0033] Unless otherwise specified, the raw materials in the present invention are purchased from the market. Among them, PVDF is purchased from Arkema France, and the grade is HSV900.

[0034] Example 1

[0035] A preparation method of a radiative cooling film, comprising the following steps:

[0036] (1) Prepare a membrane matrix: Take a certain amount of PVDF and add it to DMF, heat and stir at 80 °C for 2 h to obtain a PVDF spinning solution with a concentration of 20%; place the spinning solution in a syringe, set the feeding speed to 2 mL / h, and the voltage to 20 kV, and prepare a PVDF membrane matrix by electrospinning;

[0037] (2) Prepare an aqueous sodium alginate solution with a concentration of 0.5 wt%; subsequently, add the ground oyster shell powder with a particle size of 1000 mesh to the aqueous sodium alginate solution at a concentration of 0.2 wt%, and stir to obtain a suspension;

[0038] (3) Immerse the PVDF membrane matrix prepared in step (1) in the suspension obtained in step (2) for 10 min; then transfer the PVDF membrane matrix to water with a pH of 4 (prepared with hydrochloric acid), take out the PVDF membrane matrix, and heat it at 80 °C for 30 min;

[0039] (4) Repeat the operation in step (3) 5 times to obtain the radiative cooling film.

[0040] Example 2

[0041] A preparation method of a radiative cooling film, comprising the following steps:

[0042] (1) Prepare a membrane matrix: Take a certain amount of PVDF and add it to DMF, heat and stir at 80 °C for 2 h to obtain a PVDF spinning solution with a concentration of 20%; place the spinning solution in a syringe, set the feeding speed to 2 mL / h, and the voltage to 20 kV, and prepare a PVDF membrane matrix by electrospinning;

[0043] (2) Prepare an aqueous sodium alginate solution with a concentration of 0.5 wt%; subsequently, add the ground oyster shell powder with a particle size of 1000 mesh to the aqueous sodium alginate solution at a concentration of 0.25 wt%, and stir to obtain a suspension;

[0044] (3) Immerse the PVDF membrane matrix prepared in step (1) in the suspension obtained in step (2) for 10 min; subsequently, transfer the PVDF membrane matrix to water with a pH of 4 (prepared with nitric acid), and after taking out the PVDF membrane matrix, heat it at 85 °C for 25 min;

[0045] (4) Repeat the operation in step (3) 4 times to obtain the radiative cooling film.

[0046] Example 3

[0047] A method for preparing a radiative cooling film, comprising the following steps:

[0048] (1) Prepare the membrane matrix: Take a certain amount of PVDF and add it to DMF, heat and stir at 80 °C for 2 h to obtain a PVDF spinning solution with a concentration of 20%; place the spinning solution in a syringe, set the propulsion speed to 2 mL / h, and the voltage to 20 kV, and prepare the PVDF membrane matrix by electrospinning;

[0049] (2) Prepare an aqueous sodium alginate solution with a concentration of 0.6 wt%; subsequently, add the ground oyster shell powder with a particle size of 1000 mesh to the aqueous sodium alginate solution at a concentration of 0.18 wt%, and stir to obtain a suspension;

[0050] (3) Immerse the PVDF membrane matrix prepared in step (1) in the suspension obtained in step (2) for 10 min; subsequently, transfer the PVDF membrane matrix to water with a pH of 4 (prepared with hydrochloric acid), and after taking out the PVDF membrane matrix, heat it at 80 °C for 35 min;

[0051] (4) Repeat the operation in step (3) 5 times to obtain the radiative cooling film.

[0052] Comparative Example 1

[0053] A method for preparing a radiative cooling film, comprising the following steps:

[0054] (1) Prepare the membrane matrix: Take a certain amount of PVDF and add it to DMF, heat and stir at 80 °C for 2 h to obtain a PVDF spinning solution with a concentration of 20%; place the spinning solution in a syringe, set the propulsion speed to 2 mL / h, and the voltage to 20 kV, and prepare the PVDF membrane matrix by electrospinning;

[0055] (2) Prepare an aqueous sodium alginate solution with a concentration of 0.5 wt%;

[0056] (3) Immerse the PVDF membrane matrix prepared in step (1) in the sodium alginate aqueous solution obtained in step (2) for 10 min; subsequently, transfer the PVDF membrane matrix to water with a pH of 4 (prepared with hydrochloric acid), take out the PVDF membrane matrix, and heat it at 80 °C for 30 min;

[0057] (4) Repeat the operation in step (3) 5 times to obtain the radiative cooling film.

[0058] Perform performance tests on the radiative cooling films prepared in Example 1 and Comparative Example 1 as follows:

[0059] (1) Reflectance and emissivity tests

[0060] Use Perkin Elmer Lambda 950 and Nicolet 6700 to test the reflectance and emissivity of the radiative cooling film prepared in Example 1. As Figure 1 、 Figure 2 shown, the reflectance of the radiative cooling film prepared in Example 1 is 97.4% in the range of 0.3 - 2.5 μm, and the emissivity is 91.2% in the range of 8 - 13 μm. Thus, it can be seen that the radiative cooling film containing oyster shell powder has a high reflectance in the visible and near-infrared bands and a high emissivity in the mid-infrared atmospheric window band, maximizing the dispersion of heat into the universe, thereby achieving cooling.

[0061] (2) Indoor daytime radiative cooling performance

[0062] Use a xenon lamp (CEL-S500) to generate simulated sunlight, control the light intensity at 1 kW·m -2 , the indoor temperature is 25 °C, and the humidity is 55%. Place the radiative cooling films prepared in Example 1 and Comparative Example 1 under the simulated sunlight respectively, and use an infrared thermal imager (223s-L19) to record the surface temperature of the radiative cooling film in real time. As Figure 3 shown, under the sunlight of 1 kW·m -2 , the temperature of the radiative cooling film prepared in Example 1 is 28.2 °C, while the temperature of the radiative cooling film prepared in Comparative Example 1 is 29.9 °C. Thus, it can be seen that the use of oyster shell powder significantly improves the indoor daytime radiative cooling performance of the film.

[0063] (3) Radiative cooling performance covering the skin

[0064] Cover the radiative cooling films prepared in Example 1 and Comparative Example 1 on the surface of the human arm skin respectively, and use an infrared thermal imager (223s-L19) to record the surface temperature of the radiative cooling film and the skin surface temperature of the bare arm. As Figure 4As shown, the temperature of the radiative cooling film prepared in Example 1 is 30.2 °C, while the temperature of the radiative cooling film prepared in Comparative Example 1 is 32.3 °C, and the temperature of the bare skin surface is 33.2 °C. It can be seen that the use of oyster shell powder significantly improves the radiative cooling performance of the film covering the skin.

[0065] In summary, for the radiative cooling film prepared by the present invention, by introducing oyster shell powder, the radiative cooling effect is significantly improved, opening up a new way for the application of oyster shell powder, which has great practical significance.

[0066] The present invention uses the above embodiments to illustrate the technical concept of the present invention. However, the present invention is not limited to the above embodiments, that is, it does not mean that the present invention must rely on the above embodiments to be implemented. Those skilled in the art should understand that any improvement of the present invention, the equivalent substitution of individual raw materials of the products of the present invention, the addition of auxiliary components, the selection of specific methods, etc. all fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A radiative cooling film, characterized in that, The radiation cooling film is made of a film matrix, oyster shell powder and an adhesive; The emissivity of the radiation cooling film in the 8-13μm mid-infrared band is higher than 91%; The reflectivity of the radiation cooling film in the 0.3-2.5μm visible and near-infrared band is higher than 97%.

2. The radiative cooling film according to claim 1, wherein The film matrix is selected from one of PEO, PVDF, PMMA, PP, PU or cotton fabric.

3. The radiative cooling film according to claim 1, wherein The adhesive is selected from one of acrylic acid, latex, sodium alginate, chitosan.

4. The radiative cooling film according to claim 1, wherein, The mesh number of the oyster shell powder is 80-10000 mesh.

5. A method for preparing the radiative cooling film according to any one of claims 1 to 4, characterized in that, It includes the following steps: (1) Prepare the film matrix; (2) Prepare an aqueous solution of the adhesive, and then add the ground oyster shell powder to the aqueous solution of the adhesive. After stirring, a suspension is obtained; (3) Immerse the film matrix prepared in step (1) in the suspension obtained in step (2), and then transfer the film matrix to an initiator for immersion. After taking out the film matrix, heat treatment is carried out; (4) Repeat the operation in step (3) 2-5 times to obtain the radiation cooling film.

6. The preparation method according to claim 5, characterized in that, In step (1), the preparation of the film matrix adopts one of electrospinning, extrusion molding, and casting molding.

7. The preparation method according to claim 5, characterized in that, In step (2), the concentration of the aqueous solution of the adhesive is 0.01-2wt%, and the concentration of the oyster shell powder is 0.01-0.5wt%.

8. The preparation method according to claim 5, characterized in that, In step (3), the immersion time of the film matrix in the suspension is 5-30min.

9. The preparation method according to claim 5, characterized in that, In step (3), the initiator is an aqueous solution with a pH value of 2-6; the immersion time of the film matrix in the initiator is 5-30min.

10. The preparation method according to claim 5, characterized in that, In step (3), the heat treatment temperature is 40-120°C, and the treatment time is 5-30min.

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