Polyvinyl alcohol composite silicon oxide microcapsule temperature control material and preparation method thereof

Abstract

The application discloses a polyvinyl alcohol composite silicon oxide microcapsule temperature control material and a preparation method thereof, and relates to the technical field of temperature control materials.The emulsion prepared by Pickering emulsification and covered by nanometer silicon oxide and decanoic acid-stearic acid eutectic crystals is mixed with a polyvinyl alcohol solution, and electrostatic spinning treatment is performed, so that a spinning film is obtained, namely the polyvinyl alcohol composite silicon oxide microcapsule temperature control material.The polyvinyl alcohol composite silicon oxide microcapsule temperature control material prepared by the application can provide all-weather radiation refrigeration and phase change energy storage, has excellent recycling performance, and has the characteristics of simple process, stable performance, safe and efficient, low cost, and can be widely applied to the fields of food, medicine and textiles.

Description

Technical Field

[0001] This invention relates to the field of temperature control materials technology, and in particular to a polyvinyl alcohol composite silica microcapsule temperature control material and its preparation method. Background Technology

[0002] Temperature is a crucial indicator for social production and daily life, and temperature management is a concern in many fields. For example, the storage and transportation of temperature-sensitive foods and medicines require temperature control through the cold chain; and the temperature of fabrics and buildings is controlled to ensure human comfort. However, temperature control methods such as cold chain transportation and air conditioning consume significant amounts of energy, contradicting the current demand for energy conservation. Therefore, passive temperature control technologies and materials are being extensively researched and developed.

[0003] Latent heat storage and radiative cooling have attracted attention due to their energy-independent nature and excellent temperature control. Latent heat storage can achieve peak and valley energy utilization, enabling not only the effective use of renewable energy sources but also the utilization of waste heat in the system. Radiative cooling radiates heat into the near-absolute-zero ultra-cold outer space through a long-wave infrared transparent window in the atmosphere (λ in the range of 8–13 micrometers), causing the material surface to cool spontaneously. To minimize energy input from the sun, radiative cooling materials must possess good diffuse reflectance.

[0004] Current temperature control methods do not integrate radiative cooling and phase change energy storage into a unified system, as different materials each have their own disadvantages. If radiative cooling and phase change energy storage materials could be flexibly combined to form a cohesive system, achieving temperature reduction through radiative cooling and buffering of temperature shocks through phase change energy storage, the material's temperature adaptability would be significantly improved. Therefore, the production of a temperature control material that is easy to manufacture, scalable, low-cost, widely applicable, and environmentally friendly, combining radiative cooling and phase change energy storage synergistically, will have a very broad market prospect. Summary of the Invention

[0005] The purpose of this invention is to provide a polyvinyl alcohol composite silica microcapsule temperature control material and its preparation method, so as to solve the problems existing in the prior art. In this way, a temperature control system that reduces temperature by radiation cooling and buffers temperature shock by phase change energy storage is formed through a simple preparation process, which greatly reduces the energy consumption of temperature control.

[0006] To achieve the above objectives, the present invention provides the following solution:

[0007] This invention provides a method for preparing a polyvinyl alcohol composite silica microcapsule temperature-controlling material, comprising the following steps:

[0008] An emulsion consisting of nano-silica coated with decanoic acid-stearic acid eutectic was prepared by the Pickering emulsification method;

[0009] The emulsion is mixed with a polyvinyl alcohol solution to obtain an electrospinning solution;

[0010] The electrospinning solution is subjected to electrospinning treatment to obtain a spun film, which is the polyvinyl alcohol composite silica microcapsule temperature control material.

[0011] As a further preferred embodiment of the present invention, in the process of preparing the emulsion using the Pickering emulsification method, the mass ratio of water to decanoic acid-stearic acid eutectic is (50:50)-(95:5), and the mass ratio of water to silicon oxide is (100:1)-(100:10).

[0012] More specifically, the physically mixed water, silica, and decanoic acid-stearic acid eutectic are directly emulsified into an emulsion at a rotation speed of 10,000 r / min-20,000 r / min using the Pickering emulsification method, with the high-speed shear emulsification time being greater than 2 min.

[0013] Under the raw material ratios of this invention, the emulsion prepared by the Pickering emulsification method can remain stable for 3-10 days without demulsification, and it does not demulsify even after centrifugation at speeds of 3000-8000 rpm for 3-10 minutes. After mixing with a polyvinyl alcohol solution, its stability is further enhanced, remaining stable for over 30 days, and it does not demulsify even after centrifugation at speeds of 3000-15000 rpm for 3-10 minutes. Figure 1 The images show actual emulsions from Examples 1, 2, and 3 of this invention, as well as visual and microscopic changes in the emulsion of Example 1 before and after thickening with polyvinyl alcohol.

[0014] As a further preferred embodiment of the present invention, the concentration of polyvinyl alcohol in the electrospinning solution is 4%-12%.

[0015] As a further preferred embodiment of the present invention, the concentration of the polyvinyl alcohol solution is 6%-15%. The polyvinyl alcohol is any type of water-soluble polyvinyl alcohol.

[0016] The preferred steps for preparing a polyvinyl alcohol solution are as follows: Polyvinyl alcohol is stirred in cold water at a speed of 100-500 rpm for 1 hour to swell; then, it is heated and stirred at a speed of 100-500 rpm at a temperature of 20℃-100℃ for ≥2 hours until the polyvinyl alcohol is completely dissolved. Finally, the prepared solution is allowed to stand for 6-24 hours to defoam, yielding the polyvinyl alcohol solution.

[0017] As a further preferred embodiment of the present invention, the decanoic acid-stearic acid eutectic is a eutectic obtained by mixing decanoic acid and stearic acid at 80-90°C.

[0018] As a further preferred embodiment of the present invention, the mass ratio of the decanoic acid to the stearic acid is (4:6)-(9:1).

[0019] As a further preferred embodiment of the present invention, the electrospinning process uses a needle with an inner diameter of 0.25mm-0.84mm, a voltage of 20kV-50kV, a spinning solution injection speed of 1.0ml / h-2.0ml / h, a spinning distance of 10cm-25cm, and a final deposited film thickness of 300μm-1000μm.

[0020] The present invention also provides a polyvinyl alcohol composite silica microcapsule temperature control material prepared by the above preparation method.

[0021] The polyvinyl alcohol composite silica microcapsule temperature control material prepared by this invention has a fiber diameter of 100nm-3μm and a microcapsule diameter of 300nm-10μm; its dual-fixed structure helps to improve the thermal reliability of decanoic acid-stearic acid eutectic.

[0022] Polyvinyl alcohol (PVA) is widely used as a common industrial raw material, possessing excellent solubility, thermal stability, chemical resistance, storage stability, processability, biodegradability, and mechanical properties. It is non-toxic, harmless, and environmentally friendly. Due to the large number of C-OH structures in its chemical structure, PVA exhibits extremely high atmospheric window emissivity, making it a promising candidate for applications related to radiative cooling. Inorganic particles such as silica are low-cost, stable, non-toxic, harmless, and pollution-free. Their chemical structure contains numerous Si-O-Si structures, resulting in excellent atmospheric window emissivity. Furthermore, silica has good reflectivity of solar radiation, further enhancing its potential for applications related to radiative cooling. Fatty acids are the main components of neutral fats, phospholipids, and glycolipids. Fatty acids and their eutectic crystals are non-toxic, harmless, and pollution-free, with adjustable melting points and large latent heat storage capacity.

[0023] The polyvinyl alcohol composite silica microcapsule temperature-regulating material film prepared by this invention has a "beaded" structure with polyvinyl alcohol fibers of micro-nano diameter as "chains" and silica microcapsules of micro-nano diameter as "beads". The decanoic acid-stearic acid eutectic is doubly bound by the polyvinyl alcohol fibers and silica shell, playing a phase change energy storage role in the material; polyvinyl alcohol and silica possess high atmospheric window emissivity, and their properties and microstructure achieve high solar radiation reflectivity, thus providing radiative cooling in the material.

[0024] In this invention, the Pickering emulsification method uses a high-speed shear dispersion device to shear and disperse a mixed liquid, causing solid particles to spontaneously adsorb at the oil-water interface to form a stable emulsion. The electrospinning method uses an electrospinning device to overcome the surface tension of droplets under a sufficiently large electric field, forming jets of fine streams, and in the process, evaporating the solvent to form solid fibers. The material preparation process of this invention does not involve chemical reactions, uses water as the sole solvent, and is environmentally friendly. The materials used are low-cost and non-toxic, with a simple process, stable performance, and high safety and efficiency. This material can be widely used in food packaging, pharmaceutical packaging, and thermal management fabrics.

[0025] The present invention discloses the following technical effects:

[0026] This invention utilizes the properties of polyvinyl alcohol, nano-silica, and decanoic acid-stearic acid eutectic to combine the three materials into a whole, thus preparing a temperature-controlled thin film with synergistic phase change energy storage and radiative cooling. This material is characterized by scalability, low cost, ease of preparation, and environmental friendliness.

[0027] The polyvinyl alcohol composite silica microcapsule material prepared by this invention can provide all-weather radiative cooling and phase change energy storage, with a solar radiation reflectance of 85%-93% and an atmospheric window reflectance of 93%-98%. It can achieve a temperature reduction of 0-8°C below ambient temperature, with an average cooling power of 20W / m². 2 -80W / m 2 It has a latent heat storage of 20J / g-70J / g and still maintains good thermal reliability after 500-1000 temperature cycles.

[0028] The present invention has a simple process, stable performance, safety and efficiency, and low cost, and can be widely used in food, pharmaceutical, textile and other fields. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 The images show actual images of the emulsions in Examples 1, 2, and 3 of this invention, as well as the visual and microscopic changes of the emulsion in Example 1 before and after thickening with polyvinyl alcohol.

[0031] Wherein, a is a physical image of the emulsion in Example 1, b is a physical image of the emulsion in Example 2, c is a physical image of the emulsion in Example 3; d is bright field and fluorescence field images of the emulsion in Example 1 before and after thickening with polyvinyl alcohol on day 0 and day 30 (gray is bright field, red is fluorescence field); e is the visual changes of the emulsion in Example 1 before and after thickening with polyvinyl alcohol after standing for 0 days, standing for 10 days, standing for 30 days, and after centrifugation at 5000 r / min for 3 min.

[0032] Figure 2 The images show (a) of the electrospun film of Embodiment 1 of the present invention and (b) its microstructure under a scanning electron microscope.

[0033] Figure 3 The temperature difference between the electrospun film of Example 1 of this invention and the plastic cling film under direct sunlight in a blueberry temperature protection simulation experiment is shown in the figure; (a) is a FLIR image, and (b) is a picture of the actual object; in (a) and (b), the left side is the plastic cling film and the right side is the electrospun film of Example 1 of this invention.

[0034] Figure 4 The images show (a) of the electrospun film of Embodiment 2 of the present invention and (b) its microstructure under a scanning electron microscope.

[0035] Figure 5 The temperature difference between the electrospun film of Example 2 of this invention and the plastic cling film under direct sunlight in a blueberry temperature protection simulation experiment is shown in the figure; (a) is a FLIR image, and (b) is a picture of the actual object; in (a) and (b), the left side is the plastic cling film and the right side is the electrospun film of Example 2 of this invention.

[0036] Figure 6 The images show (a) of the electrospun film of Embodiment 3 of the present invention and (b) its microstructure under a scanning electron microscope.

[0037] Figure 7 The temperature difference between the electrospun film of Example 3 of the present invention and the plastic cling film under direct sunlight in a blueberry temperature protection simulation experiment is shown in the figure; (a) is a FLIR image, and (b) is a picture of the actual object; in (a) and (b), the left side is the plastic cling film and the right side is the electrospun film of Example 3 of the present invention. Detailed Implementation

[0038] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0039] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0040] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0041] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0042] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0043] Example 1

[0044] A method for preparing a polyvinyl alcohol composite silica microcapsule temperature-controlling material:

[0045] (1) Mix solid polyvinyl alcohol of type 1799 with deionized water at a mass ratio of 6:45 at room temperature and at a speed of 200 r / min for 1 h. Then, dissolve the polyvinyl alcohol in an oil bath at a temperature of 100℃ and a speed of 300 r / min for 2 h to obtain a polyvinyl alcohol solution.

[0046] (2) Dissolve and stir decanoic acid and stearic acid in an oil bath at a mass ratio of 8:2 at 80°C and 300r / min for 2 hours to obtain fatty acid cocrystals.

[0047] (3) Deionized water, 15nm silica powder and fatty acid cocrystal prepared in step (2) are mixed at a mass ratio of 6:0.36:4 and emulsified for 3 minutes at a speed of 12000r / min using a digital display disperser to obtain an emulsion.

[0048] (4) The emulsion prepared in step (3) and the polyvinyl alcohol solution prepared in step (1) are mixed at a mass ratio of 15.54:51 and stirred at a speed of 300 r / min for 2 h to obtain a spinning solution. At this time, the polyvinyl alcohol concentration in the spinning solution is 10%.

[0049] (5) Electrospinning the spinning solution prepared in step (4) using an electrospinning apparatus to prepare a spun film. Aluminum foil is attached to the surface of the roller receiver. The spinning voltage is 32kV, the receiving distance is 15cm, the injection speed is 1.4mL / h, and the needle type is 22G. After spinning, the film is peeled off from the aluminum foil to obtain a "beaded" electrospun film with a thickness of 800μm.

[0050] The electrospun thin film prepared in Example 1 of this invention has a solar radiation reflectance of 86.8% and an atmospheric window reflectance of 95.5%, and can achieve a temperature reduction of 3.7°C below ambient temperature with an average cooling power of 37.4 W / m. 2 This indicates that the thin film has good radiative cooling capacity. The latent heat storage of the thin film is 54.9 J / g. After 500 temperature cycles, the latent heat storage value of the thin film is less than 10% compared with the thin film that has not been temperature cycled, indicating that the thin film has good thermal reliability.

[0051] The testing method is as follows:

[0052] Diffuse reflectance was measured using a UV / Vis / NIR spectrophotometer in integrating sphere mode, with a BaSO4 white panel as a reference. The solar composite reflectance R was measured. m The calculation formula is:

[0053]

[0054] Where R(λ) is the spectral reflectance of the material, I s (λ) represents the solar spectral intensity, λ1 = 0.28 μm, λ2 = 2.50 μm. The data are taken from ASTM G173-03 (2020) and represent the standard solar spectral irradiance distribution at an atmospheric mass of AM1.5.

[0055] Emissivity measurements were performed using a Fourier transform infrared spectrometer, employing an indirect method in spherical integration mode, i.e., emissivity = 1 - transmittance (spherical integral) - reflectance. The overall emissivity ε... m The calculation formula is:

[0056]

[0057] Where ε(λ,T) is the spectral emissivity of the material at temperature T, I b(λ,T) is the spectral emissivity of the blackbody at temperature T, where λ1 = 8 μm and λ2 = 13 μm.

[0058] Temperature reduction and average cooling power were tested using a self-made platform. A piece of polystyrene was used as the experimental platform, and a cavity measuring 25cm × 25cm × 5cm (length × width × height) was cut in its center. The sample and thermocouples were placed inside the cavity. Temperature compensation was performed on the sample using thermocouples, and the resulting heating power was taken as the measured net radiative cooling power of the sample. By reading the surface temperatures of several groups of samples, the temperature difference generated by the cooling of the experimental groups was obtained. The temperature reduction and average cooling power were calculated as the average values ​​over 24 hours.

[0059] Specifically: Two identical spunbond membranes (50mm × 50mm × 0.5mm) were placed side-by-side at the bottom of the chamber, and these two membranes were named Sample 1 and Sample 2, respectively. Sample 1 was tightly attached to an aluminum film (50mm × 50mm × 1mm) above a silicone rubber heater (50mm × 50mm × 2mm, 24V, 6W). The heater was supported by four wooden pillars, using air as the heat transfer medium between the silicone rubber heater and the PS foam to prevent downward heat loss from the heater. Each pillar was 5mm high and 2mm in diameter. Thermocouple 1 (±0.1℃) was fixed below Sample 1, and its temperature (T1) over time was measured. The silicone rubber heater was controlled by a thermal feedback control program to keep T1 approximately equal to the ambient temperature T2. The power of the silicone rubber heater varied over time, and the value was automatically recorded by the program. The ambient temperature T2, which changes over time, is measured by a second thermocouple 2 (±0.1℃), fixed next to sample 1 in a location not exposed to direct sunlight, with no aluminum foil or sample on its surface. The air temperature is read as the ambient temperature. Due to the energy supply from the silicone rubber heater, T1 fluctuates continuously with T2. That is, the heater compensates for the energy lost through radiative cooling; therefore, the power of the silicone rubber heater represents the net radiative cooling power of the sample. A third thermocouple 3 (±0.1℃) is fixed below sample 2, and its temperature (T3) changes over time. Sample 2 is identical to sample 1 except that the silicone rubber heater is turned off. Under sunlight, T3 represents the sample temperature below ambient temperature, and T1-T3 represents the temperature difference between the film and the environment caused by radiative cooling.

[0060] The thermal properties (latent heat storage test) of "beaded" electrospun films and PVA / emulsion cast films were tested using differential scanning calorimetry (DSC). The temperature range was -50℃ to 50℃. Melting temperature, crystallization temperature, enthalpy of melting, and enthalpy of crystallization were measured. Three parallel samples were used in the experiment, with the mean as the result and the standard deviation as the error bar. The encapsulation efficiency R is expressed as:

[0061]

[0062] Where, ΔH m，Flim The enthalpy of melting of the thin film, ΔH m，PCM The enthalpy of fusion represents the CS eutectic phase change material, and k is the mass ratio of the phase change material to the dry weight of the thin film, k = 6 / 12.54 = 0.478.

[0063] The beaded electrospun film and PVA / emulsion cast film were placed in a temperature cycling chamber for thermal reliability testing. The program was set as follows: the chamber temperature was adjusted to -20°C. The chamber temperature was then raised to 50°C and held for 5 minutes. The chamber temperature was then lowered to -20°C and held for 5 minutes. Steps 2 and 3 were counted as one temperature cycle. The specified number of temperature cycles was used, with a heating rate of approximately 3-5°C / min and a cooling rate of approximately 2-3°C / min. Each temperature cycle lasted approximately 70 minutes, and the upper and lower temperature limits were ensured to pass through the melting and crystallization points of the material. Sufficient heating and cooling time allowed the material to undergo a complete phase transition cycle. At 100, 300, and 500 cycles, a portion of the beaded electrospun film and PVA / emulsion cast film were subjected to differential scanning calorimetry (DSC) testing using the same method as above.

[0064] Figure 2 The images shown are (a) a physical image of the electrospun thin film of Embodiment 1 of the present invention and (b) a microscopic morphology image under a scanning electron microscope.

[0065] The electrospun film prepared in Example 1 of this invention has a fiber diameter range of 100 nm to 3 μm and a microcapsule diameter range of 300 nm to 10 μm.

[0066] Blueberry Preservation Simulation Experiment: The experiment used Chungao blueberries from Yunnan Province, harvested from the farm on the same day and transported immediately to the laboratory. Plastic boxes were used as storage containers, cleaned, and dried under UV sterilization lamps in a sterile operating table. To simulate the real-world conditions of retail commercial temperatures and home refrigeration, the artificial climate chamber was set at 10℃ and 66% RH. Blueberries without obvious mechanical damage and similar shape and size were randomly divided into two groups for the preservation experiment: an experimental group and a control group. The experimental group blueberries were wrapped in a beaded electrospun film, placed in plastic boxes, and stored in the artificial climate chamber with the lid closed. The chamber was opened at 11:00 AM daily and placed in sunlight for 1 hour to simulate natural sunlight conditions and verify the heat protection effect of the electrospun film on blueberries. The control group blueberries were wrapped in PE plastic film, placed in plastic boxes, and stored in the artificial climate chamber with the lid closed. The chamber was opened at 11:00 AM daily and placed in sunlight for 1 hour to simulate the preservation effect of blueberries under possible real-world storage conditions. The experimental and control groups were preserved and tested simultaneously, with identical experimental conditions except for the use of different films for wrapping. The surface temperatures of the experimental and control groups under direct sunlight were read daily at 12:00 PM using an infrared camera to study the temperature difference after one hour of irradiation.

[0067] Figure 3 The temperature difference between the electrospun film of Example 1 of this invention and the plastic cling film under direct sunlight in a blueberry temperature protection simulation experiment is shown in the figure; (a) is a FLIR image, and (b) is a picture of the actual object; in (a) and (b), the left side is the plastic cling film and the right side is the electrospun film of Example 1 of this invention.

[0068] Example 2

[0069] A method for preparing a polyvinyl alcohol composite silica microcapsule temperature-controlling material:

[0070] (1) Mix solid polyvinyl alcohol of type 1788 with deionized water at a mass ratio of 6:51 at room temperature and at a speed of 200 r / min for 1 h. Then dissolve and stir in an oil bath at a temperature of 80°C and a speed of 300 r / min for 2 h to obtain a polyvinyl alcohol solution.

[0071] (2) Dissolve and stir decanoic acid and stearic acid in an oil bath at a mass ratio of 8:2 at 80°C and 300r / min for 2 hours to obtain fatty acid cocrystals.

[0072] (3) Mix deionized water, 30nm silica powder and fatty acid cocrystal obtained in step (2) at a mass ratio of 9:0.5:1, and emulsify for 3 minutes at a speed of 18000r / min using a digital display disperser to obtain an emulsion.

[0073] (4) The emulsion obtained in step (3) and the polyvinyl alcohol solution obtained in step (1) are mixed at a mass ratio of 21:57 and stirred at a speed of 300 r / min for 2 h to obtain a spinning solution. At this time, the polyvinyl alcohol concentration in the spinning solution is 8%.

[0074] (5) Electrospinning the spinning solution prepared in step (4) using an electrospinning apparatus to prepare a spun film. Aluminum foil is attached to the surface of the roller receiver. The spinning voltage is 30kV, the receiving distance is 20cm, the injection speed is 1.8mL / h, and the needle type is 25G. After spinning, the film is peeled off from the aluminum foil to obtain a "beaded" electrospun film with a thickness of approximately 500μm.

[0075] The electrospun film prepared in Example 2 of this invention has a solar radiation reflectance of 88.4%, an atmospheric window reflectance of 97.3%, can achieve a temperature reduction of 7.1°C below ambient temperature, and an average cooling power of 68.7 W / m. 2 This indicates that the thin film has good radiative cooling capacity. The latent heat storage of the thin film is 28.8 J / g. After 1000 temperature cycles, the latent heat storage value of the thin film after the temperature cycle is less than 10% compared with the thin film without temperature cycle, indicating that the thin film has good thermal reliability.

[0076] Figure 4 The images show (a) of the electrospun film of Embodiment 2 of the present invention and (b) its microstructure under a scanning electron microscope.

[0077] The electrospun film prepared in Example 2 of this invention has a fiber diameter of 100nm-3μm and a microcapsule diameter of 300nm-10μm.

[0078] Figure 5 FLIR image (a) and physical image (b) show the temperature difference effect of the electrospun film prepared in Example 2 of this invention under direct sunlight.

[0079] Example 3

[0080] A method for preparing a polyvinyl alcohol composite silica microcapsule temperature-controlling material:

[0081] (1) Dissolve and stir 1750 type polyvinyl alcohol solid and deionized water at a mass ratio of 6:78 at room temperature at a speed of 300 r / min for 2 h to obtain polyvinyl alcohol solution.

[0082] (2) Dissolve and stir decanoic acid and stearic acid in an oil bath at a mass ratio of 8:2 at 80°C and 300r / min for 2 hours to obtain fatty acid cocrystals.

[0083] (3) Mix deionized water, 30nm silica powder and fatty acid eutectic obtained in step (2) at a mass ratio of 8:0.5:2, and emulsify for 3 minutes at a speed of 15000r / min using a digital display disperser to obtain an emulsion.

[0084] (4) The emulsion obtained in step (3) and the polyvinyl alcohol solution obtained in step (1) are mixed at a mass ratio of 21:84 and stirred at a speed of 300 r / min for 2 h to obtain a spinning solution. At this time, the polyvinyl alcohol concentration in the spinning solution is 6%.

[0085] (5) Electrospinning film was prepared using an electrospinning apparatus. Aluminum foil was attached to the surface of the roller receiver. The spinning voltage was 25kV, the receiving distance was 15cm, the injection speed was 2.0mL / h, and the needle type was 20G. After spinning, the film was peeled off from the aluminum foil to obtain a "beaded" electrospinned film with a thickness of approximately 300μm.

[0086] The electrospun film prepared in Example 3 of this invention has a solar radiation reflectance of 87.4%, an atmospheric window reflectance of 96.1%, can achieve a temperature reduction of 5.7°C below ambient temperature, and an average cooling power of 62.7 W / m. 2 This indicates that the thin film has good radiative cooling capacity. The latent heat storage of the thin film is 46.2 J / g. The latent heat storage value of the thin film after 1000 temperature cycles is less than 10% compared with the thin film without temperature cycling, indicating that the thin film has good thermal reliability.

[0087] Figure 6 The images show (a) of the electrospun film of Embodiment 3 of the present invention and (b) its microstructure under a scanning electron microscope.

[0088] The electrospun film prepared in Example 2 of this invention has a fiber diameter of 100nm-3μm and a microcapsule diameter of 300nm-10μm.

[0089] Figure 7 FLIR image (a) and physical image (b) show the temperature difference effect of the electrospun film prepared in Example 3 of this invention under direct sunlight.

[0090] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a polyvinyl alcohol composite silicon oxide microcapsule temperature control material, characterized by, The method comprises the following steps: Preparation of an emulsion of nano-silicon oxide coated decanoic acid-stearic acid eutectic by Pickering emulsification method; Mixing of the emulsion with a polyvinyl alcohol solution to obtain an electrospinning solution; Electrospinning treatment of the electrospinning solution to obtain a spinning film, i.e. the polyvinyl alcohol composite silicon oxide microcapsule temperature control material; In the process of preparing the emulsion by Pickering emulsification method, the mass ratio of water to decanoic acid-stearic acid eutectic is (50:50)-(95:5), and the mass ratio of water to silicon oxide is (100:1)-(100:10); The concentration of polyvinyl alcohol in the electrospinning solution is 4%-12%; The decanoic acid-stearic acid eutectic is a eutectic obtained by mixing n-decanoic acid and stearic acid at 80-90℃; The mass ratio of n-decanoic acid to stearic acid is (4:6)-(9:1); The voltage of the electrospinning treatment is 20kV-50kV.

2. The production method according to claim 1, characterized by, The concentration of the polyvinyl alcohol solution is 6%-15%.

3. The method of claim 1, wherein, The thickness of the polyvinyl alcohol composite silicon oxide microcapsule temperature control material is 300μm-1000μm.

4. The polyvinyl alcohol composite silicon oxide microcapsule temperature control material prepared by the preparation method according to any one of claims 1-3.

Images