Radiation refrigeration composite film, preparation method thereof and application of radiation refrigeration composite film in food preservation

Abstract

The invention belongs to the technical field of food packaging materials, and particularly relates to a radiation refrigeration composite film as well as a preparation method and application thereof in food preservation. Chitosan and micro / nano-sized spherical silicon dioxide are uniformly mixed at room temperature through a one-pot method to form a composite solution, and the composite solution is evaporated to prepare the multifunctional radiation refrigeration composite film with high reflectivity, high emissivity, good hydrophobicity, cooling performance, antibacterial property, antioxidant property and biocompatibility. The preservative is used for food preservation, such as fruits, seafood, meat and the like. The composite film can prolong the shelf life of food under direct solar radiation or at 25 / 4 DEG C. The radiation refrigeration composite film is simple in preparation method, easily available in raw materials and low in cost.

Description

Technical Field

[0001] This invention belongs to the field of food packaging materials technology, specifically relating to a radiation-cooling composite film, its preparation method, and its application. Background Technology

[0002] Food quality and safety have always been a key focus of food packaging research. However, due to global warming, the rate of microbial growth on food surfaces is accelerating, leading to increasingly serious spoilage and significant food waste. To effectively preserve food ingredients, maintain food quality, and extend shelf life, a novel food preservation technology is needed. Currently used traditional preservation technologies such as modified atmosphere packaging, edible coatings, and active packaging largely rely on refrigeration equipment like refrigerators to regulate the internal temperature of food for long-term preservation. However, refrigeration equipment not only consumes a lot of energy, but the large amounts of carbon dioxide emitted during operation also exacerbate the greenhouse effect, negatively impacting the ecological environment. Furthermore, traditional preservation technologies struggle to extend food shelf life under high temperatures. Therefore, developing a new, energy-efficient, high-temperature-adaptable, and environmentally friendly green preservation technology is urgently needed.

[0003] Radiative cooling is an emerging, non-electric cooling technology widely used in building and personal thermal management. This technology primarily dissipates heat from the Earth's surface into the cold outer space through thermal radiation, and lowers the surface temperature of objects by highly reflecting sunlight. Materials possessing this capability are called radiative cooling materials. They exhibit unique spectral selectivity, displaying high reflectivity (>0.9) in the solar radiation band (0.3-2.5 µm) and high emissivity (>0.9) in the mid-infrared atmospheric window band (8-13 µm). Based on these optical properties, radiative cooling materials can effectively modulate the optical properties of object surfaces, enabling them to reflect solar heat and continuously radiate energy into outer space through atmospheric windows. This significantly reduces the surface temperature of food, inhibits microbial growth, extends shelf life, and reduces food waste. Summary of the Invention

[0004] The purpose of this invention is to provide a radiation-cooling composite film with good optical properties and excellent food preservation effect, as well as its preparation method and application.

[0005] The method for preparing the radiation-cooling composite film provided by this invention includes the following specific steps:

[0006] (1) Dissolve chitosan powder in glacial acetic acid aqueous solution and stir until homogeneous to obtain a uniform and transparent mixed solution, denoted as A;

[0007] (2) Dissolve micro / nano-sized spherical silica in ethanol, stir evenly, and disperse by ultrasonication to obtain a milky white mixed solution, denoted as B;

[0008] (3) Slowly add the mixed solution B described in step (2) to the mixed solution A described in step (1), stir evenly, and degas by ultrasonication to obtain mixed solution C; slowly pour mixed solution C into the organic glass substrate, and obtain the radiation cooling composite film after the solvent has completely evaporated.

[0009] Furthermore:

[0010] In step (1), the chitosan has a molecular weight of 100-1200 kDa, and the chitosan can be replaced by one or more combinations of any biomass materials such as sodium alginate, cellulose, starch and carrageenan.

[0011] In step (1), the mass-volume ratio of chitosan to glacial acetic acid aqueous solution is 0.002-0.04.

[0012] In step (1), the volume fraction of glacial acetic acid in the glacial acetic acid aqueous solution is 0.01-1.5%.

[0013] In step (1), the stirring temperature is 20-60 ℃, the speed is 250-1500 rpm / min, and the time is 0.5-5h.

[0014] In step (2), the diameters of the micro / nano-sized spherical silica are 50-1000 nm (nanometer level) and 1-50 µm (micrometer level), respectively. The ratio of micrometer / nano-sized spherical silica is 10:1 to 1:5.

[0015] In step (2), the spherical silica with micro / nano dimensions can be replaced with materials such as aluminum oxide, zinc oxide, titanium dioxide, magnesium oxide, barium sulfate, and calcium carbonate. These materials all have high reflectivity and are white. The film prepared according to the method of this invention also has high reflectivity and emissivity, as well as a cooling effect, which can extend the shelf life of food at high temperatures.

[0016] In step (2), the amount of spherical silica used is 1-20 g.

[0017] In step (2), the volume of ethanol is 5-30 mL, and ethanol can be replaced with and / or water.

[0018] In step (2), the stirring temperature is 20-40 ℃, the stirring speed is 250-1500 rpm / min, and the stirring time is 0.5-2 h.

[0019] In step (2), the power of the ultrasound is 80-150 W and the duration is 0.5-6 h.

[0020] In step (3), the stirring temperature is 20-40 ℃, the speed is 250-1500 rpm / min, and the time is 2-12 h.

[0021] In step (3), the power of the ultrasound is 80-150 W and the duration is 2-8 h.

[0022] In step (3), the evaporation process is carried out at a temperature of 20-40 °C for 24-96 h.

[0023] In the composite film of this invention, two different sizes of silicon dioxide are specifically used. The goal is to improve the scattering efficiency of the material for visible and near-infrared light, thereby enhancing the reflectivity of the material in visible and near-infrared light to maximize the reflection of solar energy.

[0024] In the composite film of this invention, spherical silicon dioxide is specifically used. The principle is that the sphere is isotropic, and its reflection of light does not change with the angle, thus giving the material high reflectivity in all directions.

[0025] In the composite membrane of this invention, chitosan is used, which has a low extinction coefficient and a large number of chemical bonds in the infrared band (atmospheric window band: 8-13 μm), giving it high absorption efficiency and thus endowing the composite membrane with high emissivity. Chitosan itself is an antibacterial and antioxidant material, with high antibacterial activity against bacteria and fungi, and also has a high scavenging rate against free radicals.

[0026] Compared with the prior art, the present invention has the following significant advantages:

[0027] 1. This invention utilizes chitosan as a matrix and spherical silica as a filler to successfully prepare a radiation-cooling composite membrane with high reflectivity (>0.92) and high emissivity (>0.94). Compared with existing radiation-cooling materials, this composite membrane not only has higher cooling performance (~18 ℃), but also possesses antibacterial, antioxidant, biodegradable, gas-barrier, and biocompatible properties, thus expanding the application range of radiation-cooling composite membranes.

[0028] 2. This radiation-cooling composite film was applied to the field of food preservation, and its performance was demonstrated at a solar irradiance of 1000 W / m². 2 Under these conditions, the internal temperature of food can be reduced by approximately 15°C, significantly slowing down the rate of spoilage and extending its shelf life. Furthermore, it can also extend the shelf life of food at 25 / 4°C, thus preventing food waste. This invention not only provides new ideas for the application of radiative cooling materials but also offers new insights into the field of food preservation.

[0029] 3. It has simple composition, simple preparation process, is easy to operate, green and environmentally friendly, and highly reproducible. It can be used for large-scale production and has broad application prospects in the fields of radiation refrigeration and food preservation. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a schematic flowchart illustrating the method for preparing a composite film for radiation cooling materials provided in an embodiment of this application.

[0032] Figure 2 This is an appearance diagram of the radiation-cooling composite membrane provided in an embodiment of this application.

[0033] Figure 3 This is a microstructure diagram of the radiation-cooling composite membrane provided in an embodiment of this application.

[0034] Figure 4 This is a schematic diagram of the spectrum of the radiation-cooling composite membrane provided in the embodiments of this application.

[0035] Figure 5 The cooling performance diagram of the radiation cooling composite membrane provided in the embodiments of this application is shown.

[0036] Figure 6 The diagram shows the preservation performance of the radiation cooling composite film provided in this application embodiment on chicken breast under high temperature conditions.

[0037] Figure 7 The diagram shows the internal temperature change of chicken breast when the radiation cooling composite membrane provided in this application is used for chicken breast preservation in a high-temperature environment.

[0038] Figure 8 The diagram shows the banana preservation performance of the radiation cooling composite film provided in this application embodiment under high temperature conditions.

[0039] Figure 9 The diagram shows the internal temperature change of a banana when the radiation cooling composite film provided in this application is used for banana preservation in a high-temperature environment.

[0040] Figure 10 The diagram shows the preservation performance of the radiation cooling composite film provided in this application at 25 °C for chicken breast.

[0041] Figure 11 The diagram shows the banana preservation performance of the radiation cooling composite film provided in this application embodiment at 25 °C.

[0042] Figure 12 The diagram shows the banana preservation performance of the radiation cooling composite film provided in this application embodiment at 4 °C.

[0043] Figure 13 The diagram shows the banana preservation performance of the radiation cooling composite film provided in this application embodiment at 4 °C. Detailed Implementation

[0044] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0045] Example 1: Preparation of radiation-cooled composite film; the preparation process is described in [link to example]. Figure 1 The specific steps are as follows:

[0046] (1) Dissolve 1.0 g of chitosan powder in 60 mL of glacial acetic acid aqueous solution (volume fraction of 0.05%), and then place the solution in a magnetic stirrer at 40 °C and 600 rpm / min for 2 h to obtain a uniform and transparent mixed solution A.

[0047] (2) Dissolve 1.0 g of spherical silica with a diameter of 500 nm and 0.3 g of spherical silica with a diameter of 5 μm in 10 mL of ethanol, place it in a magnetic stirrer at 25 °C and 800 rpm / min for 2 h, and then place it in a 120 W ultrasonic instrument for 4 h to obtain a milky white mixed solution B.

[0048] (3) Slowly add mixed solution B to mixed solution A, place it in a magnetic stirrer at 25 ℃ and 1200 rpm / min, stir for 12 h, and then place it in a 120 W ultrasonic instrument for ultrasonic degassing for 6 h. Mixed solution C is obtained. Slowly pour mixed solution C onto the surface of an organic glass substrate, place it at 25 ℃ and let it dry naturally for 72 h to obtain a radiation cooling composite film.

[0049] Example 2, the preparation of a radiation-cooling composite membrane and its application in food preservation, includes the following steps:

[0050] (1) Dissolve 1.5 g of chitosan powder in 60 mL of glacial acetic acid aqueous solution (volume fraction of 0.1%), and then place the solution in a magnetic stirrer at 30 °C and 500 rpm / min for 2 h to obtain a uniform and transparent mixed solution A.

[0051] (2) Dissolve 1.5 g of spherical silica with a diameter of 500 nm and 0.3 g of spherical silica with a diameter of 5 μm in 10 mL of ethanol, place it in a magnetic stirrer at 25 °C and 800 rpm / min for 2 h, and then place it in a 120 W ultrasonic instrument for 4 h to obtain a milky white mixed solution B.

[0052] (3) Slowly add mixed solution B to mixed solution A, place it in a magnetic stirrer at 25 ℃ and 1200 rpm / min, stir for 12 h, and then place it in a 120 W ultrasonic instrument for ultrasonic degassing for 6 h. Mixed solution C is obtained. Slowly pour mixed solution C onto the surface of an organic glass substrate, place it at 25 ℃ and let it dry naturally for 72 h to obtain a radiation cooling composite film.

[0053] Example 3, the preparation of a radiation-cooling composite membrane and its application in food preservation, includes the following steps:

[0054] (1) Dissolve 1.0 g of chitosan powder in 60 mL of glacial acetic acid aqueous solution (volume fraction of 0.15%), and then place the solution in a magnetic stirrer at 50 °C and 800 rpm / min for 2 h to obtain a uniform and transparent mixed solution A.

[0055] (2) Dissolve 0.8 g of spherical silica with a diameter of 500 nm and 0.5 g of spherical silica with a diameter of 5 μm in 10 mL of ethanol, place it in a magnetic stirrer at 25 °C and 600 rpm / min for 1 h, and then place it in a 120 W ultrasonic instrument for 2 h to obtain a milky white mixed solution B.

[0056] (3) Slowly add mixed solution B to mixed solution A, place it in a magnetic stirrer at 25 ℃ and 1200 rpm / min, stir for 8 h, and then place it in a 120 W ultrasonic instrument for ultrasonic degassing for 4 h. Mixed solution C is obtained. Slowly pour mixed solution C onto the surface of an organic glass substrate, place it at 25 ℃ and let it dry naturally for 72 h to obtain a radiation cooling composite film.

[0057] Example 4: Preparation of a radiation-cooling composite film and its application in food preservation, including the following steps:

[0058] (1) Dissolve 1.5 g of chitosan powder in 60 mL of glacial acetic acid aqueous solution (volume fraction of 0.1%), and then place the solution in a magnetic stirrer at 50 °C and 600 rpm / min for 1 h to obtain a uniform and transparent mixed solution A.

[0059] (2) Dissolve 1.5 g of spherical silica with a diameter of 500 nm and 0.5 g of spherical silica with a diameter of 5 μm in 10 mL of ethanol, place it in a magnetic stirrer at 25 °C and 1000 rpm / min for 3 h, and then place it in a 120 W ultrasonic instrument for 6 h to obtain a milky white mixed solution B.

[0060] (3) Slowly add mixed solution B to mixed solution A, place it in a magnetic stirrer at 25 ℃ and 1200 rpm / min and stir for 6 h, then place it in a 120 W ultrasonic instrument for ultrasonic degassing for 4 h. Mixed solution C is obtained. Slowly pour mixed solution C onto the surface of an organic glass substrate and place it at 25 ℃ for natural drying for 72 h to obtain a radiation cooling composite film.

[0061] Comparative Example 1: Preparation of a radiation-cooling composite membrane in which chitosan is replaced with sodium alginate, including the following steps:

[0062] (1) Dissolve 1.0 g sodium alginate powder in 60 mL of aqueous solution, and then place the solution in a magnetic stirrer at 40 °C and 600 rpm / min for 2 h to obtain a uniform and transparent mixed solution A.

[0063] (2) Dissolve 1.0 g of spherical silica with a diameter of 500 nm and 0.3 g of spherical silica with a diameter of 5 μm in 10 mL of ethanol, place it in a magnetic stirrer at 25 °C and 800 rpm / min for 2 h, and then place it in a 120 W ultrasonic instrument for 4 h to obtain a milky white mixed solution B.

[0064] (3) Slowly add mixed solution B to mixed solution A, place it in a magnetic stirrer at 25 ℃ and 1200 rpm / min, stir for 12 h, and then place it in a 120 W ultrasonic instrument for ultrasonic degassing for 6 h. Mixed solution C is obtained. Slowly pour mixed solution C onto the surface of an organic glass substrate, place it at 25 ℃ and let it dry naturally for 72 h to obtain a radiation cooling composite film.

[0065] Comparative Example 2, the preparation of chitosan membrane includes the following steps:

[0066] (1) Dissolve 1.0 g of chitosan powder in 60 mL of glacial acetic acid aqueous solution (volume fraction of 0.05%), then place the solution in a magnetic stirrer at 40 °C and 600 rpm / min for 2 h, and then place it in a 120 W ultrasonic instrument for ultrasonic degassing for 6 h. A uniform and transparent mixed solution is obtained.

[0067] Then, the mixed solution is slowly poured onto the surface of the plexiglass substrate and placed at 25 °C for natural drying for 72 h to obtain the composite film.

[0068] Comparative Example 3 uses commercially available ordinary food-grade polyethylene plastic wrap as Comparative Example 3.

[0069] Characterization and performance testing

[0070] 1. Microstructure testing of radiation-cooled composite membranes

[0071] A small sample was weighed and placed on the surface of a silicon wafer. Before testing, a layer of gold was sprayed onto the sample surface, and the microstructure of the radiation-cooled composite film was observed at 1000x magnification.

[0072] 2. Hydrophobicity test of radiation-cooled composite membrane

[0073] The hydrophobicity of the radiation-cooled composite membrane (20 mm × 20 mm) was measured using an OCA20 video optical contact angle meter. Deionized water (3 μL) was dropped onto the surface of the radiation-cooled composite membrane using a syringe, and the contact angle was measured and recorded after 30 seconds of stabilization.

[0074] 3. Optical performance testing of radiation-cooled composite films

[0075] (1) Ultraviolet-visible-near-infrared spectroscopy determination: The reflectance of the radiation-cooled composite film was tested using an ultraviolet-visible-near-infrared spectrophotometer with an integrating sphere. The test wavelength range was 0.3-2.5 μm.

[0076] (2) Mid-infrared spectroscopy determination: The reflectance and transmittance of the radiation-cooled composite film were tested using a Fourier transform infrared spectrometer with an integrating sphere. The test wavelength range was 2.5-15μm.

[0077] 4. Cooling performance test of radiation-cooled composite membrane

[0078] A self-built temperature and outdoor environment testing device was used to test the outdoor cooling performance of the radiative cooling composite membrane. The testing device consisted of 20 cm × 20 cm × 20 cm high-density polystyrene foam, with a recess of 5 cm in length and width and 2 cm in depth at the top. The outer surface of the foam was covered with high solar reflectivity aluminum foil tape. Temperature probes for measuring the sample and the environment were placed at the same position in the 2 cm deep recess, with the other end of the probe connected to a four-channel thermometer to monitor the real-time temperature of the sample and the environment.

[0079] 5. Gas barrier properties test of radiation-cooled composite membrane

[0080] (1) The water vapor permeability of the radiation-cooling composite membrane was evaluated according to the ASTM standard, with some modifications. Simply wrap the radiation-cooling composite membrane (4cm × 4cm) around the mouth of a glass bottle containing 8g of silica gel and seal it tightly. Place all the glass bottles in a constant temperature and humidity incubator (25℃, 50% RH), weighing them every 12 hours until 72 hours. Finally, calculate the water vapor permeability of each composite membrane using the formula shown below:

[0081]

[0082] (2) Place 40 mL of corn oil into a test cup with a diameter of 5 cm and a height of 8 cm, and seal it with a 12 cm diameter radiation-cooling composite membrane. Place the test cup in a constant temperature and humidity chamber (25 ℃, 75% RH) for 7 days. The lipid peroxidation value (mmol / kg) is calculated according to the Chinese national standard (GB / T 5538-2005) and is used to evaluate oxygen permeability.

[0083] (3) Testing the carbon dioxide transmittance of the radiation-cooled composite membrane. Simply put, place a saturated potassium solution (20 mL) into a test cup with a diameter of 5 cm and a height of 8 cm, and seal it with a radiation-cooled composite membrane with a diameter of 12 cm. Place the test cup in a constant temperature and humidity chamber (25 °C, 75% RH) for 48 h and weigh it. The formula for calculating the carbon dioxide transmittance is as follows:

[0084]

[0085] 6. Antibacterial and antioxidant tests of radiation-cooled composite membranes

[0086] (1) Antibacterial test: Escherichia coli and Staphylococcus aureus were cultured in cerebral heart perfusion fluid to the logarithmic phase, forming approximately 10-1... 9 Colony forming units (CFU) / mL. Add 1 mL of 0.1% radiation-cooled composite membrane to 10 mL of bacterial suspension. After culturing in a shaker for 24 h, transfer 0.1 mL of the bacterial suspension to a 9.9 mL 0.85% sodium chloride test tube. Calculate the total number of viable bacteria remaining for *Escherichia coli* and *Staphylococcus aureus* using a 10-fold serial dilution method. Simultaneously, spread 10 μL of the bacterial suspension onto Luria-Bertani agar medium and incubate for 24 h, then observe the growth of *Escherichia coli* and *Staphylococcus aureus*.

[0087] (2) Antioxidant activity test: The radiation-cooling composite membrane was cut into circular slices (6 mm in diameter). The slices were placed in 0.5 mL of 2,2-diazo-bis(3-ethyl-benzothiazole-6-sulfonic acid) diammonium salt solution and reacted in the dark for 30 min to determine the antioxidant activity of the radiation-cooling composite membrane. The absorbance was measured at 734 nm using a UV-Vis spectrophotometer. Ascorbic acid solution (70 μg / mL) and ultrapure water were used as positive and negative controls, respectively. The 2,2-diazo-bis(3-ethyl-benzothiazole-6-sulfonic acid) diammonium salt (ATBS) of the radiation-cooling composite membrane was calculated using the following formula. + Scavenging activity:

[0088]

[0089] (3) Antioxidant test: The radiation-cooled composite membrane was cut into circular slices (6 mm in diameter) and immersed in 30 mL of 50% ethanol solution for 30 min. Then, 1 mL of the extract was mixed with 5 mL of 0.1 mmol / L 1,1-diphenyl-2-picrylhydrazyl solution and reacted at room temperature in the dark for 30 min. The absorbance of the solution was then measured at 517 nm using a UV-Vis spectrophotometer. The 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging activity of the radiation-cooled composite membrane was calculated using the following formula:

[0090]

[0091] 7. Biocompatibility test of radiation-cooled composite membrane

[0092] The biocompatibility of the radiation-cooling composite membrane was evaluated using L-929 cells. 100 μL of cell culture was placed in a 96-well plate, and 2 mg of the radiation-cooling composite membrane was added. The plates were then incubated in a 5% CO2 incubator at 37 °C for 3–5 h. The OD values ​​were read at 490 nm using a microplate reader, and the viability of the L-929 cells was calculated.

[0093] .

[0094] 8. Food preservation test using radiation-cooled composite film

[0095] (1) Food weight test: Bananas were weighed at a fixed time each day using an electronic scale with a resolution of 1 / 10000. The weight loss rate of the food was calculated using the following formula:

[0096]

[0097] (2) The pH value and acidity of the food were measured using a pH-3C precision pH meter. Simply put, 20 g of food stored for different times was chopped, added to 50 mL of deionized water, and homogenized.

[0098] (3) Total phenol content test of food: The total phenol content of food was determined using the Folin-Ciocalteu method with gallic acid as the standard. In short, the food was crushed, dissolved in deionized water, and filtered. The filtrate (1 mL) was mixed with Folin-Ciocalteu solution (0.5 mL) and sodium carbonate solution (10%, 1 mL), and incubated at 35 ℃ with shaking for 30 min. The absorbance of the mixed solution at 750 nm was measured.

[0099] (4) Determination of total bacterial count in food

[0100] Weigh 5 g of food powder and place it in a sterile bag containing 45 mL of physiological saline. Perform serial dilutions of the solution, and plate the supernatants at different concentrations. Incubate at 37°C for 24 hours to count the total bacterial count. Calculate the total bacterial count using the formula:

[0101]

[0102] (5) Determination of total volatile basic nitrogen in food

[0103] Weigh 5 g of food powder, mix it in 25 mL of deionized water, and determine the total volatile basic nitrogen in the solution according to the national standard GB 5009.228-2016.

[0104] .

[0105] Results Analysis

[0106] The appearance and microstructure of the radiation-cooling composite membrane are shown in the figure. Figure 2 and 3 As shown, the radiation-cooling composite membrane is white in appearance, with multi-scale silica microspheres distributed on its surface and cross-section, and a porous structure with a wide range of internal sizes. The composite membrane exhibits good hydrophobicity, giving it self-cleaning properties. Simultaneously, the composite membrane possesses high reflectivity (92.28%) and emissivity (94.55%). Figure 4 At a solar irradiance of 1000 W / m 2 Under certain conditions, the radiation-cooled composite membrane can reduce the temperature by approximately 18 °C. Figure 5Furthermore, the composite membrane also possesses excellent gas barrier properties, antibacterial and antioxidant properties, and biocompatibility, which expands its application in the field of food preservation. (Under a solar irradiance of 1000 W / m²) 2 Under certain conditions, the radiation-cooling composite film can significantly extend the shelf life of food by 4-8 hours and reduce the internal temperature of food by approximately 15°C. Figure 6-9 Furthermore, the composite film can significantly extend the shelf life of food under conditions of 25 ℃ and 4 ℃. Figure 10-13 ).

[0107] It should be understood that the various processes shown above can be used, with steps rearranged, added, or deleted. For example, the various steps described in this invention disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution of this disclosure can be achieved, and this document does not impose any limitations.

[0108] The above description is merely a specific embodiment of this disclosure, but the scope of protection of this disclosure is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this disclosure should be included within the scope of protection of this disclosure. Therefore, the scope of protection of this disclosure should be determined by the scope of the claims.

Claims

1. A method for preparing a radiation-cooled composite film, characterized in that, The specific steps are as follows: (1) Dissolve chitosan powder in glacial acetic acid aqueous solution and stir until homogeneous to obtain a uniform and transparent mixed solution, denoted as A; (2) Dissolve micro / nano-sized spherical high reflectivity materials in ethanol, stir evenly, and ultrasonically disperse to obtain a milky white mixed solution, denoted as B; the high reflectivity materials are selected from silicon dioxide, aluminum oxide, zinc oxide, titanium dioxide, magnesium oxide, barium sulfate, and calcium carbonate; (3) Slowly add the mixed solution B described in step (2) to the mixed solution A described in step (1), stir evenly, and degas by ultrasonication to obtain a mixed solution, which is denoted as C; slowly pour the mixed solution C into the organic glass substrate, and wait for the solvent to completely evaporate to obtain the radiation cooling composite film. The high reflectivity material is selected from silicon dioxide, aluminum oxide, zinc oxide, titanium dioxide, magnesium oxide, barium sulfate, and calcium carbonate.

2. The method for preparing the radiation-cooling composite film according to claim 1, characterized in that, The chitosan in step (1) has a molecular weight of 100-1200 kDa.

3. The method for preparing the radiation-cooling composite film according to claim 1, characterized in that, In step (1): The mass-to-volume ratio of chitosan to glacial acetic acid aqueous solution is 0.002-0.04; The volume percentage of glacial acetic acid in the glacial acetic acid aqueous solution is 0.01-1.5%.

4. The method for preparing the radiation-cooling composite film according to claim 1, characterized in that, In step (1), the stirring temperature is 20-60 ℃, the speed is 250-1500 rpm / min, and the time is 0.5-5 h.

5. The method for preparing the radiation-cooling composite film according to claim 1, characterized in that, In step (2), the diameters of the spherical high reflectivity materials with micro / nano dimensions are 50-1000 nm and 1-50 µm, respectively; the mass ratio of the two is 10:1-1:

5.

6. The method for preparing the radiation-cooled composite film according to claim 5, characterized in that, In step (2), the amount of the spherical high reflectivity material used is 1-20 g; the volume of the ethanol is 5-30 mL.

7. The method for preparing the radiation-cooling composite film according to claim 5, characterized in that, In step (2): The stirring temperature is 20-40 ℃, the stirring speed is 250-1500 rpm / min, and the stirring time is 0.5-2 h; The ultrasonic power is 80-150 W, and the ultrasonic time is 0.5-6 h.

8. The method for preparing the radiation-cooling composite film according to claim 1, characterized in that, In step (3): The stirring temperature is 20-40 ℃, the stirring speed is 250-1500 rpm / min, and the stirring time is 2-12 h; The ultrasonic power is 80-150 W, and the ultrasonic time is 2-8 h; The evaporation process takes place at a temperature of 20-40 °C for 24-96 h.

9. A radiation-cooling composite membrane obtained by the preparation method according to any one of claims 1-8.

10. The application of the radiation cooling composite film as described in claim 9 in food preservation.

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