Radiation refrigeration film, preparation method and application in logistics preservation of fruits and vegetables

Abstract

The invention belongs to the technical field of food fresh-keeping and new materials, and discloses a radiation refrigeration film which comprises the following components in parts by weight: 2 parts of polyvinyl alcohol; 1.4 parts of glycerol; 10 parts of nano titanium dioxide or nano barium sulfate or nano silicon dioxide particles; and 20 parts of deionized water. The polyvinyl alcohol has good flexibility and processability, is easy to manufacture large-area films or complex shapes, is suitable for different application scenes, particularly has good fitness and practicability in the fields of fruit postharvest preservation and the like so as to degrade potential hazards of materials to the environment, and meets the requirements of sustainable development. The film has excellent spectral characteristics, and can achieve the purposes of improving the quality of fruits and vegetables and prolonging the shelf life of the fruits and vegetables when applied to logistics preservation of the fruits and vegetables.

Description

Technical Field

[0001] The invention belongs to the technical field of food preservation and new materials, and in particular to a radiation refrigeration film, a preparation method and application in the logistics preservation of fruits and vegetables. Background Art

[0002] Refrigeration is an important means of food preservation. By lowering the temperature, food spoilage can be delayed. There are many common low-temperature control methods, such as cold storage and freezers, which use refrigeration systems to achieve cooling. Traditional refrigeration methods usually rely on large equipment and consume energy. Radiative cooling is an emerging technology that radiates heat into outer space through specific materials or structures to achieve passive cooling without energy consumption. This technology has brought new possibilities to the field of food preservation and may become one of the important refrigeration methods in the future. Radiative cooling is a process that uses thermal radiation to transfer heat from an object to the external environment. Thermodynamics shows that when a hot object and a cold object participate in radiation exchange, heat will spontaneously flow from the hot body to the cold body. Therefore, the huge temperature difference between the earth (about 300K) and the cold universe (3K) drives the earth's objects to emit heat energy into the vast universe, resulting in radiative cooling. Based on this principle, researchers have developed a variety of high-efficiency radiative cooling materials, such as multilayer nanofilms and polymer-based composites with high solar reflectivity and high mid-infrared emissivity.

[0003] The intrinsic properties and structural composition of radiative cooling materials are key factors in improving cooling efficiency. The rapid development of nanophotonics and metamaterials has provided new ideas for realizing spectral control devices. By introducing periodic nanostructures to control spectral characteristics, researchers can simultaneously improve the solar reflectivity and infrared emissivity of the film. In addition, film materials adapted to different scenarios are also being developed, such as colored films, transparent films, and flexible coatings to meet the needs of architectural exterior design, agricultural coverage, and portable electronic devices. Although radiative cooling technology has significant potential, it still faces many challenges, such as high production costs, limited service life, and limited performance in hot and humid or cloudy environments. To achieve widespread application, future research will focus on developing more economical and durable materials, optimizing manufacturing processes, and integrating energy storage technologies to improve adaptability. With continuous technological breakthroughs, radiative cooling is expected to have a revolutionary impact in areas such as building energy conservation, agricultural preservation, and industrial heat dissipation.

[0004] At present, the relevant technical solutions and defects in the prior art are specifically as follows:

[0005] 1. Technical solution of prior art 1

[0006] The preparation of super-hydrophobic self-cleaning temperature-adaptive radiation cooling film includes multiple steps to be completed in coordination. First, a tungsten-doped vanadium dioxide suspension is prepared, and uniform particles are obtained by grinding and ultrasonic dispersion; a PU-PDMS sol is prepared, and a transparent bubble-free sol is formed by mixing, cross-linking and degassing; a fluorine-modified nano-titanium oxide colloid is prepared, and after surface modification, it is cleaned, dried and dispersed in a solvent. Subsequently, the PE film is activated and heated to soften, and an embedded microstructure array is formed by template imprinting, and the tungsten-doped vanadium dioxide suspension is sprayed and cured. In the encapsulation stage, the PE film is encapsulated with an Ag / PET polymer composite film and the stacking order is adjusted to facilitate subsequent operations. Finally, PU-PDMS sol and fluorine-modified nano-titanium oxide colloid are sprayed on the surface of the film in turn, and a super-hydrophobic self-cleaning coating is formed by microwave heating and curing to complete the preparation of the film.

[0007] Defects of prior art 1:

[0008] Multi-step process: This technology involves multiple processes, such as grinding and dispersion of tungsten-doped vanadium dioxide, imprinting of microstructure arrays, and spraying and curing of multi-layer materials. The process is complicated and the process requirements are high, resulting in long production cycles and low efficiency.

[0009] Dependence on high-precision equipment: Precision equipment such as high-pressure spray guns, microwave devices, cylindrical rolling machines, etc. are required. These devices have high procurement and maintenance costs and are not suitable for low-cost large-scale production.

[0010] Lack of environmental friendliness: The radiation refrigeration raw material polydimethylsiloxane (PDMS) has poor biodegradability, is unstable when heated and easily decomposes, producing toxic and harmful volatile substances. This raw material is difficult to expand its application in the agricultural field.

[0011] 2. Technical solution of prior art 1

[0012] The preheated film substrate is subjected to hot embossing treatment by a embossing roller to form a raised structure on its surface, and the embossing temperature is dynamically adjusted to match the substrate moving speed. The nanoparticles are filled between the raised structures using an electrostatic spray gun, and the excess particles are removed by extrusion and a scraper to complete the filling; a protective film is covered on the surface of the raised structure and hot embossing treatment is performed by a hot embossing roller to form an overall film structure.

[0013] Defects of the second prior art:

[0014] Nanoparticle filling non-uniformity: Electrostatic spraying and filling of nanoparticles may be affected by the equipment status and operating conditions, resulting in non-uniform filling, which in turn affects the radiation performance of the film.

[0015] Expensive equipment: High-precision equipment such as printing rollers, electrostatic spraying devices, hot pressing roller assemblies, etc. are required, the initial investment cost is high, and the equipment maintenance is complicated.

[0016] By comparison, the patent application of the present invention is essentially different from the above-mentioned patent publications. Summary of the invention

[0017] The purpose of the present invention is to overcome the deficiencies in the prior art and to provide a radiation refrigeration film, a preparation method and an application in the logistics and preservation of fruits and vegetables.

[0018] The technical solution adopted by the present invention to solve its technical problem is:

[0019] A radiation cooling film, the components and weight proportions of which are as follows:

[0020] 2 parts of polyvinyl alcohol;

[0021] 1.4 parts of glycerol;

[0022] 10 parts of nano titanium dioxide or nano barium sulfate or nano silicon dioxide particles;

[0023] 20 parts of deionized water.

[0024] Furthermore, the titanium dioxide is TiO2 nanoparticles with a diameter of 550nm.

[0025] The method for preparing the radiation cooling film as described above comprises the following steps:

[0026] First, polyvinyl alcohol is dissolved in deionized water, heated to 90°C and stirred for 1 hour to form a uniform solution; then, glycerol is added as a plasticizer and stirring is continued to reduce the viscosity; then, nano-titanium dioxide or nano-barium sulfate or nano-silicon dioxide particles are added, and a constant temperature in the range of 50°C-90°C is maintained and stirred to ensure uniform mixing; finally, a radiative cooling film is obtained.

[0027] Furthermore, the uniform mixing specifically comprises: uniformly compounding the inorganic micro-nano particles and polyvinyl alcohol through a chemical dissolution mixing or physical blending step.

[0028] Furthermore, the radiant cooling film is obtained by a Roll-to-Roll (R2R) process, which specifically includes uniformly coating the TiO2-PVA mixed solution on a substrate. Common substrates include glass, plastic, silicone, polystyrene, aluminum, etc. The coating speed and the amount of raw material added are controlled by gravure coating, and the film thickness is accurately controlled with high uniformity, which is suitable for large-scale production.

[0029] The method for preparing the radiation cooling film as described above comprises the following steps:

[0030] First, polyvinyl alcohol is dissolved in deionized water, heated to 90°C and stirred for 1 hour to form a uniform solution; then, glycerol is added as a plasticizer and stirring is continued to reduce the viscosity; then, nano-titanium dioxide or nano-barium sulfate or nano-silicon dioxide particles are added, and a constant temperature in the range of 50°C-90°C is maintained and stirred to ensure uniform mixing; finally, the mixture is placed at -20°C for freeze-thaw to form a uniform gel film, and finally a radiant refrigeration film with excellent performance is obtained.

[0031] The method for preparing the radiation cooling film as described above comprises the following steps:

[0032] First, polyvinyl alcohol is dissolved in deionized water to form a uniform solution; then, glycerol is added as a plasticizer and stirring is continued to reduce the viscosity; then, nano-titanium dioxide or nano-barium sulfate or nano-silicon dioxide particles are added, and a constant temperature in the range of 50°C-90°C is maintained and stirred to ensure uniform mixing; finally, a radiative cooling film is obtained.

[0033] Furthermore, the uniform mixing specifically comprises: uniformly compounding the inorganic micro-nano particles and polyvinyl alcohol through a chemical dissolution mixing or physical blending step.

[0034] Furthermore, the radiant cooling film is obtained by a Roll-to-Roll (R2R) process, which specifically includes uniformly coating the TiO2-PVA mixed solution on a substrate. Common substrates include glass, plastic, silicone, polystyrene, aluminum, etc. The coating speed and the amount of raw material added are controlled by gravure coating, and the film thickness is accurately controlled with high uniformity, which is suitable for large-scale production.

[0035] The application of the radiation refrigeration film as described above in the logistics and preservation of fruits and vegetables.

[0036] The advantages and positive effects achieved by the present invention are:

[0037] 1. The method of the present invention simplifies the process flow and reduces costs. The composite process of the polyvinyl alcohol substrate and titanium dioxide nanoparticles is simple, avoiding complex multi-layer structures and cumbersome equipment dependence, while improving production efficiency and significantly reducing manufacturing costs.

[0038] 2. The mixture of polyvinyl alcohol and titanium dioxide used as the radiation refrigeration material in the present invention has excellent environmental protection and biocompatibility. The three raw materials used have good biocompatibility, are non-toxic and harmless, and can be degraded or recycled, avoiding the use of solvents or difficulties in traditional methods.

[0039] 3. The polyvinyl alcohol in the present invention has good flexibility and processability, and is easy to manufacture into large-area films or complex shapes, which are suitable for different application scenarios, especially in the fields of post-harvest fruit preservation, etc., and has good fit and practicality, which can degrade the potential harm of materials to the environment and meet the requirements of sustainable development. The film has excellent spectral characteristics, and can be used in the logistics preservation of fruits and vegetables to achieve the goal of improving the quality of fruits and vegetables and extending the shelf life of fruits and vegetables.

[0040] 4. The present invention adopts polyvinyl alcohol (PVA) as a substrate, and adds titanium dioxide (TiO2) nanoparticles and glycerol. The present invention not only solves the problems of traditional radiation refrigeration films in production cost, environmental friendliness, spectral performance and applicability through material selection and design optimization (using virtual simulation technology to analyze the difference between the refractive index of nanoparticles and the refractive index of the substrate, and taking the scattering efficiency factor as the measurement indicator), but also successfully expands its application to the field of post-harvest fruit preservation, delays the softening of fruits and vegetables under the same environment, prolongs the shelf life of fruits, and reduces the economic value of post-harvest waste of fruits and vegetables, providing new direction and potential for the actual promotion and commercialization of this technology.

[0041] 5. The spectral regulation in the present invention improves the cooling effect. By selecting raw materials with large differences in refractive index through simulation, titanium dioxide nanoparticles have excellent spectral regulation ability. Combined with the polyvinyl alcohol substrate, it can effectively reflect sunlight and enhance infrared radiation heat dissipation, which significantly improves the radiation cooling performance of the film and ensures excellent cooling effect in high temperature environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 The figure is a multi-particle scattering efficiency factor diagram of the TiO2-PVA film prepared in Example 1 of the present invention; wherein the left figure is a dimensionless scattering coefficient diagram (Mie scattering effect of a single particle), and the right figure is a scattering coefficient diagram (simulating the Mie scattering effect of multiple particles);

[0043] Figure 2 The nanoparticle size (left), polymer dispersion coefficient (middle) and potential diagram (right) of the TiO2-PVA solution system prepared in Example 1 of the present invention;

[0044] Figure 3 The transmission electron microscope images of the thin film prepared in Example 1 of the present invention are shown in FIG. 1 ; the left image is a diagram showing the internal structure of the TiO2-PVA thin film, and the right image is a diagram showing the internal structure of the TiO2-PVA solution; the scale bars are both 100 nm;

[0045] Figure 4 Spectral characteristics of the radiative cooling film prepared in Example 1 of the present invention in the solar radiation band (left) and the mid-infrared thermal radiation band (right);

[0046] Figure 5is a Fourier transform infrared spectrum (FTIR) of the radiation cooling film prepared in Example 1 of the present invention;

[0047] Figure 6 This is a diagram of an indoor simulated temperature reduction experiment of the radiative cooling film prepared in Example 1 of the present invention;

[0048] Figure 7 The radiative cooling film physical picture (left) and application form picture (right) of the radiative cooling film prepared in Example 1 of the present invention;

[0049] Figure 8 This is a picture showing the effect of applying the radiation cooling film prepared in Example 1 of the present invention to post-harvest winter peaches;

[0050] Fig. 9 This is a photo of a polyvinyl alcohol (PVA) film prepared in Comparative Example 2 of the present invention; wherein the polyvinyl alcohol agglomerates when stirred at room temperature

[0051] Fig.10 This is a photo of a large composite film based on polyvinyl alcohol (PVA) and titanium dioxide (TiO2) nanoparticles (a film with a mass ratio of TiO2:PVA of 1:1) prepared in Comparative Example 3 of the present invention. DETAILED DESCRIPTION

[0052] The present invention will be further described below in conjunction with the embodiments. The following embodiments are descriptive rather than restrictive, and the protection scope of the present invention cannot be limited by the following embodiments.

[0053] The various experimental operations involved in the specific embodiments are all routine techniques in the art. For parts not specially annotated in this document, ordinary technicians in the art can implement them by referring to various commonly used reference books, scientific and technological literature or related instructions, manuals, etc. before the filing date of this invention.

[0054] A radiation cooling film, the components and weight proportions of which are as follows:

[0055] 2 parts of polyvinyl alcohol;

[0056] 1.4 parts of glycerol;

[0057] 10 parts of nano titanium dioxide or nano barium sulfate or nano silicon dioxide particles;

[0058] 20 parts of deionized water.

[0059] Preferably, the titanium dioxide is TiO2 nanoparticles with a diameter of 550 nm.

[0060] The method for preparing the radiation cooling film as described above comprises the following steps:

[0061] First, polyvinyl alcohol is dissolved in deionized water, heated to 90°C and stirred for 1 hour to form a uniform solution; then, glycerol is added as a plasticizer and stirring is continued to reduce the viscosity; then, nano-titanium dioxide or nano-barium sulfate or nano-silicon dioxide particles are added, and a constant temperature in the range of 50°C-90°C is maintained and stirred to ensure uniform mixing; finally, a radiative cooling film is obtained.

[0062] Preferably, the uniform mixing is specifically: the inorganic micro-nano particles and polyvinyl alcohol are uniformly compounded by chemical dissolution mixing or physical blending steps.

[0063] Preferably, the radiant cooling film is obtained by a Roll-to-Roll (R2R) process, which specifically includes uniformly coating the TiO2-PVA mixed solution on a substrate, and commonly used substrates include glass, plastic, silicone, polystyrene, aluminum, etc., by controlling the coating speed and the amount of raw material added and adopting gravure coating to accurately control the film thickness, achieve high uniformity, and be suitable for large-scale production.

[0064] The method for preparing the radiation cooling film as described above comprises the following steps:

[0065] First, polyvinyl alcohol is dissolved in deionized water, heated to 90°C and stirred for 1 hour to form a uniform solution; then, glycerol is added as a plasticizer and stirring is continued to reduce the viscosity; then, nano-titanium dioxide or nano-barium sulfate or nano-silicon dioxide particles are added, and a constant temperature in the range of 50°C-90°C is maintained and stirred to ensure uniform mixing; finally, the mixture is placed at -20°C for freeze-thaw to form a uniform gel film, and finally a radiant refrigeration film with excellent performance is obtained.

[0066] The method for preparing the radiation cooling film as described above comprises the following steps:

[0067] First, polyvinyl alcohol is dissolved in deionized water to form a uniform solution; then, glycerol is added as a plasticizer and stirring is continued to reduce the viscosity; then, nano-titanium dioxide or nano-barium sulfate or nano-silicon dioxide particles are added, and a constant temperature in the range of 50°C-90°C is maintained and stirred to ensure uniform mixing; finally, a radiative cooling film is obtained.

[0068] Preferably, the uniform mixing is specifically: the inorganic micro-nano particles and polyvinyl alcohol are uniformly compounded by chemical dissolution mixing or physical blending steps.

[0069] Preferably, the radiant cooling film is obtained by a Roll-to-Roll (R2R) process, which specifically includes uniformly coating the TiO2-PVA mixed solution on a substrate, and commonly used substrates include glass, plastic, silicone, polystyrene, aluminum, etc., by controlling the coating speed and the amount of raw material added and adopting gravure coating to accurately control the film thickness, achieve high uniformity, and be suitable for large-scale production.

[0070] The application of the radiation refrigeration film as described above in the logistics and preservation of fruits and vegetables.

[0071] Specifically, the relevant tests and preparations are as follows:

[0072] Example 1

[0073] This experiment aims to improve the cooling and preservation effects of PVA film, and selects the appropriate combination of polymer and nanoparticles through finite time-domain difference method (FDTD) simulation. Figure 1 As shown in the figure, TiO2 nanoparticles have high scattering efficiency and scattering coefficient, especially in the ultraviolet and visible light bands (0.2-0.8μm), making them efficient light shielding materials, which can significantly enhance the film's reflectivity to sunlight and ultraviolet shielding ability, thereby improving the cooling effect and fruit preservation performance. In contrast, SiO2 nanoparticles and CaCO3 nanoparticles have lower dimensionless scattering coefficients, indicating that their scattering effect on light is lower than that of TiO2 nanoparticles.

[0074] A method for preparing a composite large film based on polyvinyl alcohol (PVA) and titanium dioxide (TiO2) nanoparticles, specifically comprising the following steps:

[0075] Weigh 2 g of newly purchased polyvinyl alcohol (PVA) and add it to 20 g of deionized water. Heat the mixture to 90 ° C and stir at a stirring speed of 500 rpm for 1 hour until the polyvinyl alcohol is completely dissolved to form a uniform polymer solution. Add 1.4 grams of glycerol as a plasticizer to the mother liquor and continue to stir at a speed of 500 rpm for 1 hour to ensure that the plasticizer is evenly dispersed. It is observed that the viscosity of the solution is reduced, which enhances the flexibility of the subsequent film. Add 10 g of titanium dioxide (TiO2) nanoparticles with a diameter of 550 nm to the mother liquor, maintain the temperature at 90 ° C, and continue to stir at a speed of 500 rpm for 1 hour to ensure that the titanium dioxide nanoparticles are fully mixed with the polymer matrix to form a uniform composite solution (hereinafter referred to as TiO2-PVA solution). Take 5 g of the mixed composite solution, pour it into a glass culture dish with a diameter of 15 cm, and shake it to ensure that the film is evenly spread on the surface of the culture dish to achieve the desired thickness and smoothness. Through the above steps, a large film with excellent performance, namely a radiation cooling film (hereinafter referred to as TiO2-PVA film), can be obtained, which is suitable for various subsequent applications. The actual photo of the prepared sample is shown in the figure Figure 7 shown.

[0076] The relevant tests and results are as follows:

[0077] TiO2-PVA solution (i.e., in the above preparation method: weigh 2g of newly purchased polyvinyl alcohol (PVA) and add it to 20g of deionized water. Heat the mixture to 90°C and stir at a stirring speed of 500rpm for 1h until the polyvinyl alcohol is completely dissolved to form a uniform polymer solution. Add 1.4g of glycerol to the mother liquor as a plasticizer, and continue stirring at a speed of 500rpm for 1h to ensure that the plasticizer is evenly dispersed. It was observed that the viscosity of the solution decreased, which enhanced the flexibility of the subsequent film. Add 10g of titanium dioxide (TiO2) nanoparticles with a diameter of 550nm to the mother liquor, maintain the temperature at 90°C, and continue stirring at a speed of 500rpm for 1h to ensure that the titanium dioxide nanoparticles and the polymer matrix are fully mixed to form a uniform composite solution, which is the TiO2-PVA solution.) There is electrostatic repulsion, and the overall uniformity and stability. In the TiO2-PVA solution system, the TiO2 nanoparticles are small in size and evenly distributed. Affected by the electrostatic repulsion, the solution is stable as a whole, which is suitable for the preparation of high-performance films ( Figure 2 ). The transmission electron microscopy image of the film shows that it has a layer-wrapped structure inside. This structure not only improves the mechanical strength of the film, but also enhances the light scattering ability, which is beneficial to improving the light reflectivity in the solar band ( Figure 3 ). In the solar radiation band (0.3-2.5μm), the average reflectivity of the film reaches 0.92, which can effectively shield solar thermal radiation; in the mid-infrared atmospheric window band (8-13μm), the emissivity is as high as 0.95, showing significant thermal radiation ability and achieving excellent radiation cooling effect ( Figure 4 ). Fourier infrared spectroscopy showed that PVA provided CO stretching vibration, and there was a stretching vibration peak in the atmospheric window band (769-1250cm-1), showing a clear absorption peak, which further verified the high-efficiency thermal radiation performance of the film ( Figure 5 In an indoor simulated cooling experiment, the radiant cooling film covered a beaker and was irradiated by an ordinary xenon lamp. The temperature under the film was 20°C lower than the ambient temperature. The temperature difference was as high as 20°C when irradiated by an ordinary xenon lamp, proving its excellent cooling ability ( Figure 6 ). The actual picture shows that the diameter of the radiation cooling film is 15cm, the thickness is 0.02cm, and it has good flexibility. It is suitable for use in food preservation and packaging materials, showing high practicality ( Figure 7 ).

[0078] TiO2-PVA film and PVA film (PVA film preparation steps are: weigh 2g of newly purchased polyvinyl alcohol (PVA) and add it to 20g of deionized water. Heat the mixture to 90°C and stir at a stirring speed of 500rpm for 1h until the polyvinyl alcohol is completely dissolved to form a uniform polymer solution. Add 1.4g of glycerol to the mother liquor as a plasticizer, and continue to stir at a speed of 500rpm for 1h to ensure that the plasticizer is evenly dispersed. Take 5g of the mixed composite solution, pour it into a glass culture dish with a diameter of 15cm, and shake it to ensure that the film is evenly spread on the surface of the culture dish to achieve the required thickness and smoothness, that is, to obtain a PVA film.) Compared with winter peaches, it has many advantages in preservation, such as Figure 8 As shown, the effect of application on post-harvest winter peaches. Polyvinyl alcohol-nano titanium dioxide film can effectively slow down the weight loss rate and hardness loss of fruits and vegetables, slow down the ripening of fruits and vegetables, and extend the shelf life. Among them, △E=[(△L)+(△a)+(△b)]1 / 2, and the brightness difference △L, red-green difference △A and yellow-blue difference △B are used to adjust the color. The ΔE value represents the total color difference value, which is an important indicator for evaluating the degree of difference between two colors. The smaller the ΔE value, the closer the two colors are; the larger the ΔE value, the more obvious the color difference. From Figure 8 It can be seen that TiO2 nanoparticles have excellent light scattering and reflection capabilities in the ultraviolet and visible light bands, which can effectively reduce light penetration, reduce ultraviolet damage to winter peach pigments, reduce the surface temperature of fruits and vegetables, help maintain the bright color of winter peaches, slow down the respiratory metabolic rate of winter peaches, and slow down softening. After the sixth day of placement, the softening trend of winter peaches showed that the hardness of the winter peaches wrapped with TiO2-PVA film was 7.87±0.59N, which was significantly higher than the weight loss rate of winter peaches in the control group of 5.46±0.34N (p<0.05). From the perspective of the color change of winter peaches, the a* value (redness) of the winter peaches wrapped with TiO2-PVA film was 1.73, while the a* value of the winter peaches in the control group was 10.20. At the same time, the addition of TiO2 enhanced the shielding effect of the film on solar radiation and reduced the driving force of water evaporation. The addition of nanoparticles may change the microstructure of the film, reduce the water vapor permeability, and thus effectively inhibit water loss. After the winter peaches were placed for 6 days, the weight loss rate of the winter peaches wrapped with TiO2-PVA film was 15.75±1.04%, which was significantly lower than the weight loss rate of the winter peaches in the control group (25.79±1.72%) (p<0.05).

[0079] Comparative Example 1

[0080] A preparation method based on polyvinyl alcohol (PVA) film, the method prepares an atmospheric window high emissivity film by a solution casting method, specifically comprising the following steps:

[0081] Weigh 2g of newly purchased polyvinyl alcohol (PVA) and add it to 20g of deionized water. Heat the mixture to 90°C and stir at a stirring speed of 500rpm for 1h until the polyvinyl alcohol is completely dissolved to form a uniform polymer solution. Add 1.4 grams of glycerol to the mother liquor as a plasticizer and continue stirring at 500rpm for 1h to ensure that the plasticizer is evenly dispersed. It was observed that the viscosity of the solution decreased, which enhanced the flexibility of the subsequent film. Take 5g of the evenly mixed composite solution, pour it into a glass culture dish with a diameter of 15cm, and shake it to ensure that the film is evenly spread on the surface of the culture dish to achieve the desired thickness and smoothness. Through the above steps, a film with moisturizing properties, that is, a film with a high emissivity spectral characteristic, can be obtained, which is suitable for various subsequent applications.

[0082] The relevant tests and results are as follows:

[0083] FT-IR( Figure 5 ) Tests show that PVA and TiO2-PVA films have obvious stretching vibration peaks at 1090cm-1 and 1045cm-1, which are usually related to the stretching vibration of CO or CC. This characteristic peak is determined by the presence of hydroxyl (-OH) and carbon oxygen bonds (CO) in the PVA molecule. The vibrations of these functional groups have strong absorption characteristics in the infrared region. These groups tend to form wider absorption bands, especially in the ultraviolet and visible light bands (part of the solar band). The enhancement of molecular absorption will reduce the film's reflection of incident light. At the same time, its low refractive index and surface smoothness inhibit the reflection behavior, so the reflectivity of the PVA film is low. The logistics preservation effect of PVA film on winter peaches is much lower than that of TiO2-PVA film ( Figure 8 ), additional nanoparticles need to be added to improve its reflectivity in the solar band. After the second day of storage, the weight loss rate of winter peach wrapped with PVA film was 14.38±1.81%, and its water loss rate was significantly higher than that of TiO2-PVA film (p<0.05).

[0084] Comparative Example 2

[0085] A preparation method based on polyvinyl alcohol (PVA) film specifically comprises the following steps:

[0086] Weigh 2 g of newly purchased polyvinyl alcohol (PVA) and add it to 20 g of deionized water. Heat the mixture to 90°C and stir at 1000 rpm for 1 h. It is found that the solution system agglomerates. Fig. 9 As shown, from Fig. 9It was found in the analysis that high-speed stirring significantly increased the shear force in the solution, causing the polymer chains of PVA to be overstretched and re-entangled under intense stirring. Due to the strong hydrogen bonding between PVA molecules, this entanglement further leads to aggregation between local molecular chains. The process parameter of Example 1 - the stirring rate is lower, the unfolding and dissolution process of the PVA molecular chain is more complete, the molecular chain is not easy to entangle, and the solution system is more uniform, which is conducive to film formation by solution casting.

[0087] Comparative Example 3

[0088] A method for preparing a composite large film based on polyvinyl alcohol (PVA) and titanium dioxide (TiO2) nanoparticles, specifically comprising the following steps:

[0089] Weigh 2g of newly purchased polyvinyl alcohol (PVA) and add it to 20g of deionized water. Heat the mixture to 90°C and stir at 500rpm for 1h until the polyvinyl alcohol is completely dissolved to form a uniform polymer solution. Add 1.4g of glycerol as a plasticizer to the mother liquor and continue stirring at 500rpm for 1h to ensure that the plasticizer is evenly dispersed. It was observed that the viscosity of the solution decreased, which enhanced the flexibility of the subsequent film. Add 20g of titanium dioxide (TiO2) nanoparticles with a diameter of 550nm to the mother liquor, maintain the temperature at 90°C, and continue stirring at 500rpm for 1h to ensure that the titanium dioxide nanoparticles are fully mixed with the polymer matrix to form a uniform composite solution. Take 5g of the evenly mixed composite solution and pour it into a glass culture dish to form a film. Radiative cooling film such as Fig.10 shown.

[0090] As the amount of TiO2 added increases, the ductility of the film decreases significantly, resulting in poor flexibility and brittle cracking. This degradation of mechanical properties limits the processability and practical application of the film, which may cause the film to be unable to withstand stresses such as stretching or bending in actual operation, affecting the continuity of the production line and the quality of the finished product. Therefore, it is necessary to balance the effects of the TiO2 content on mechanical and optical properties while optimizing the TiO2 content to ensure that the film has sufficient toughness to meet the requirements of industrial production. As the amount of TiO2 added increases, the ductility of the film decreases significantly, resulting in poor flexibility and brittle cracking. This degradation of mechanical properties limits the processability and practical application of the film, which may cause the film to be unable to withstand stresses such as stretching or bending in actual operation, affecting the continuity of the production line and the quality of the finished product. Therefore, it is necessary to balance the effects of the TiO2 content on mechanical and optical properties while optimizing the TiO2 content to ensure that the film has sufficient toughness to meet actual needs.

[0091] At the same time, by comparing Example 1, Comparative Example 1 and Comparative Example 2, it can be seen that the polyvinyl alcohol and titanium dioxide in the present invention have a synergistic effect, and can synergistically improve the relevant properties of the prepared radiation cooling film. In particular, when the mass ratio of polyvinyl alcohol to titanium dioxide is 1:5, the relevant properties of the prepared radiation cooling film can be significantly synergistically improved.

[0092] At the same time, by comparing Example 1 and Comparative Examples 1 to 3, it can be seen that the addition amount of titanium dioxide and titanium dioxide in the present invention has a synergistic effect, which can synergistically improve the relevant properties of the prepared radiation cooling film. In particular, when the mass ratio of polyvinyl alcohol to titanium dioxide is 1:5, the relevant properties of the prepared radiation cooling film can be significantly synergistically improved.

[0093] Although the embodiments of the present invention are disclosed for illustrative purposes, those skilled in the art will appreciate that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments.

Claims

1. A radiation cooling film, characterized in that: Its components and weight parts are as follows: 2 parts of polyvinyl alcohol; 1.4 parts of glycerol; 10 parts of nano titanium dioxide or nano barium sulfate or nano silicon dioxide particles; 20 parts of deionized water.

2. The radiative cooling film according to claim 1, characterized in that: The titanium dioxide is TiO2 nanoparticles with a diameter of 550 nm.

3. The method for preparing a radiative cooling film according to claim 1 or 2, characterized in that: The steps include: First, polyvinyl alcohol is dissolved in deionized water, heated to 90°C and stirred for 1 hour to form a uniform solution; then, glycerol is added as a plasticizer and stirring is continued to reduce the viscosity; then, nano-titanium dioxide or nano-barium sulfate or nano-silicon dioxide particles are added, and a constant temperature in the range of 50°C-90°C is maintained and stirred to ensure uniform mixing; finally, a radiative cooling film is obtained.

4. The preparation method according to claim 3, characterized in that: The uniform mixing specifically comprises: uniformly compounding the inorganic micro-nano particles and polyvinyl alcohol through a chemical dissolution mixing or physical blending step.

5. The preparation method according to claim 3 or 4, characterized in that: The radiant cooling film is obtained by adopting a Roll-to-Roll process, which specifically includes uniformly coating the TiO2-PVA mixed solution on the substrate, and obtaining it by gravure coating by controlling the coating speed and the amount of raw material added.

6. The method for preparing a radiative cooling film according to claim 1 or 2, characterized in that: The steps include: First, polyvinyl alcohol is dissolved in deionized water, heated to 90°C and stirred for 1 hour to form a uniform solution; then, glycerol is added as a plasticizer and stirring is continued to reduce the viscosity; then, nano-titanium dioxide or nano-barium sulfate or nano-silicon dioxide particles are added, and a constant temperature in the range of 50°C-90°C is maintained and stirred to ensure uniform mixing; finally, the mixture is placed at -20°C for freeze-thaw to form a uniform gel film, and finally a radiant refrigeration film with excellent performance is obtained.

7. The method for preparing a radiative cooling film according to claim 1 or 2, characterized in that: The steps include: First, polyvinyl alcohol is dissolved in deionized water to form a uniform solution; then, glycerol is added as a plasticizer and stirring is continued to reduce the viscosity; then, nano-titanium dioxide or nano-barium sulfate or nano-silicon dioxide particles are added, and a constant temperature in the range of 50°C-90°C is maintained and stirred to ensure uniform mixing; finally, a radiative cooling film is obtained.

8. The preparation method according to claim 7, characterized in that: The uniform mixing specifically comprises: uniformly compounding the inorganic micro-nano particles and polyvinyl alcohol through a chemical dissolution mixing or physical blending step.

9. The preparation method according to claim 7 or 8, characterized in that: The radiant cooling film is obtained by adopting a Roll-to-Roll process, which specifically includes uniformly coating the TiO2-PVA mixed solution on the substrate, and obtaining it by gravure coating by controlling the coating speed and the amount of raw material added.

10. Use of the radiation refrigeration film according to claim 1 or 2 in the logistics and preservation of fruits and vegetables.

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