Efficient passive radiation refrigeration material suitable for sub-super environment and preparation method and application of efficient passive radiation refrigeration material

Abstract

The invention relates to the technical field of refrigeration material preparation, in particular to an efficient passive radiation refrigeration material suitable for a sub-super environment and a preparation method and application of the efficient passive radiation refrigeration material. The method comprises the following steps: uniformly mixing thermoplastic polyurethane, sunlight high-reflection inorganic particles and a phase change material in a solvent; after a chemical foaming agent is added, the obtained suspension liquid is heated and foamed in a confinement mold, and wet gel is formed; and finally, carrying out freeze drying treatment to obtain the composite porous aerogel. The prepared material has a micro-nano porous skeleton formed by TPU, and inorganic particles and PCM are uniformly dispersed in the skeleton wall. Through component cooperation and a special porous structure, the material has extremely high sunlight reflectivity and mid-infrared emissivity, self-adaptive temperature regulation and control are achieved through PCM phase change, the problem that refrigeration of a traditional material fails in the sub-environment such as the vertical surface is effectively solved, and efficient sub-super-environment heat management is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of refrigerant preparation, in particular to a high-efficiency passive radiation refrigerant material suitable for sub-super environment, a preparation method thereof and application. BACKGROUND

[0002] With the continuous growth of global energy consumption and the increasingly severe problem of climate warming, developing energy-saving and consumption-reducing technology has become an important issue in the field of science and technology. Among them, passive radiation refrigeration technology, as a "zero energy consumption" refrigeration method without any external energy input, has attracted widespread attention from academia and industry. The core principle of this technology is that through the special design of materials, on the one hand, a very high reflectivity (>90%) is achieved in the wavelength band of the main energy distribution of sunlight (0.3-2.5 μm), so as to minimize the absorption of solar heat; on the other hand, a very high emissivity (>90%) is achieved in the "atmospheric window" wavelength band (8-13 μm) with high transmittance in the earth's atmosphere, so as to directly dissipate the heat in the form of infrared radiation to the cold deep space of the universe (about 3K), thereby realizing the object surface temperature lower than the ambient temperature under all-weather conditions (including daytime).

[0003] Currently, the passive radiation refrigeration materials reported mainly include multilayer photonic crystals, metal / dielectric composite films, porous polymers, and porous ceramics, etc. However, these existing technical solutions generally have some insurmountable limitations. For example, although the multilayer photonic crystal has excellent performance, its preparation process is complex, the cost is high, and it is usually sensitive to the incident angle, making it difficult to be applied on a large scale. Although the porous ceramic material can achieve good optical performance, its inherent rigidity, brittleness and high density limit its application in non-planar, vibration or lightweight scenarios. And ordinary porous polymer materials often have difficulty in achieving very high solar reflectivity and infrared emissivity at the same time, and their comprehensive performance (usually the reflectivity and emissivity are both lower than 92%) needs to be further improved.

[0004] More importantly, the design and test of most traditional radiative cooling materials are based on ideal working conditions, i.e. horizontal placement and full sky view. However, in many practical application scenarios, such as the vertical outer wall of a building, the side of a vehicle, the outdoor equipment case and the human body wearing, the view angle between the surface to be cooled and the sky will be greatly reduced, and a large amount of heat radiation from the ground and surrounding high-temperature objects will be received. Under this non-ideal "sub-environment" working condition, the net cooling power of the traditional radiative cooling material will be greatly reduced or even become net heat absorption, resulting in cooling failure. In addition, the heat load under actual working conditions is often dynamically changing, and the existing materials lack self-adaptive regulation and control capability. Therefore, it is urgent to develop a new type of radiative cooling material, which not only has excellent optical performance, but also can effectively cope with the challenges of "sub-super environment" (i.e. cooling in sub-environment and efficient heat dissipation in super-environment (self-heating)), while having good mechanical properties and the potential for low-cost preparation, to promote the widespread practical application of passive radiative cooling technology. SUMMARY

[0005] In view of the deficiencies in the prior art above, the purpose of the present application is to provide a high-efficiency passive radiative cooling material suitable for sub-super environment, by compounding solar high-reflection inorganic particles, phase change temperature regulating materials and a polymer matrix, and using a special process of "limited foaming + freeze drying", a porous aerogel material with ultra-high solar reflectivity and high infrared emissivity is successfully prepared, achieving excellent passive radiative cooling basic performance.

[0006] Another purpose of the present application is to provide a preparation method of a high-efficiency passive radiative cooling material suitable for sub-super environment, which has a clear process route, uses low-cost raw materials, has strong equipment versatility, is easy to realize large-scale production, and has significant industrialization prospects.

[0007] The third purpose of the present application is to provide an application of a high-efficiency passive radiative cooling material suitable for sub-super environment, which is used in the fields of building energy saving, energy storage device thermal management, solar cell thermal management, electronic device heat dissipation or low-altitude aircraft thermal management.

[0008] The present application is implemented by using the following technical solutions: The preparation method of the high-efficiency passive radiative cooling material suitable for sub-super environment comprises the following steps: (1) Dissolve the polymer matrix in an organic solvent to form a first solution; add at least one component selected from phase change materials and solar high-reflection inorganic particles to the first solution, and disperse by stirring or ultrasonic to form a uniform mixed suspension; (2) Add a chemical foaming agent to the mixed suspension and stir uniformly to obtain a foaming precursor suspension; (3) Pour the foaming precursor suspension into a mold and heat it to decompose the chemical foaming agent and produce gas. Foaming is carried out under the physical constraints of the mold to form a wet gel with a porous structure. (4) The wet gel is freeze-dried to obtain a high-efficiency passive radiation cooling material suitable for sub-super environment.

[0009] The polymer matrix is ​​thermoplastic polyurethane (TPU).

[0010] The high-reflectivity inorganic particles are one or more combinations of barium sulfate, titanium dioxide, aluminum oxide, and boron nitride. Preferably, the inorganic particles are barium sulfate.

[0011] The phase change material is paraffin, fatty acid, or polyethylene glycol with a phase change temperature in the range of 30℃-50℃. Preferably, the phase change material is paraffin with a phase change temperature in the range of 30℃-50℃.

[0012] The weight ratio of each component is as follows: 100 parts by weight of polymer matrix; 30-200 parts by weight of solar highly reflective inorganic particles; and 10-100 parts by weight of phase change material. Preferably, the polymer matrix is ​​100 parts by weight; the solar highly reflective inorganic particles are 150 parts by weight; and the phase change material (PCM) is 50 parts by weight.

[0013] The chemical foaming agent is an azo or sulfonyl hydrazine foaming agent, and its addition amount is 10-20% of the weight of the polymer matrix.

[0014] In step (3), the heating temperature is 80℃-120℃.

[0015] The aforementioned high-efficiency passive radiation cooling material for sub-super-environment is prepared by the above-mentioned preparation method for high-efficiency passive radiation cooling materials suitable for sub-super-environment.

[0016] The aforementioned highly efficient passive radiation cooling material for sub-super-environment environments is a composite porous aerogel, comprising: a micro / nanoporous framework composed of the aforementioned polymer matrix; and highly reflective inorganic particles and / or phase change materials uniformly dispersed within the framework walls of the micro / nanoporous framework. The material possesses a micro / nanoporous structure, exhibiting a reflectivity of not less than 95% in the 0.3-2.5 μm solar spectral band and an emissivity of not less than 96% in the 8-13 μm mid-infrared atmospheric window band.

[0017] The aforementioned high-efficiency passive radiation cooling material suitable for sub- and ultra-high-altitude environments is used in building energy conservation, thermal management of energy storage equipment, thermal management of solar cells, heat dissipation of electronic devices, or thermal management of low-altitude aircraft.

[0018] Specifically, the preparation method of a highly efficient passive radiative cooling material suitable for sub-super-environment includes the following steps: (1) Solution and suspension preparation: The polymer matrix is ​​dissolved in an organic solvent to form a first solution; at least one or two of the phase change material (PCM) and solar high reflectance inorganic particles are added to the first solution and dispersed by stirring or ultrasonication to form a uniform mixed suspension; (2) Preparation of foaming precursor: Add chemical foaming agent to the mixed suspension and stir evenly to obtain foaming precursor suspension; (3) Confined foaming molding: The foaming precursor suspension is poured into a mold with a preset shape and adjustable height, heated to decompose the chemical foaming agent and generate gas, and foaming is carried out under the physical confinement of the mold to form a wet gel with a porous structure. (4) Drying and curing: The wet gel is freeze-dried to remove solvent and residual moisture, and the high-efficiency passive radiation cooling material is obtained.

[0019] This invention provides a highly efficient passive radiative cooling material suitable for sub-super-environments and its preparation method. Here, "sub-super-environment" refers to a unified thermal management concept: sub-environment refers to a situation where the initial temperature of the object to be cooled is close to the ambient temperature, and the material of this invention can significantly reduce its surface temperature to below the ambient temperature; super-environment refers to a situation where the object to be cooled generates heat, causing its temperature to exceed the ambient temperature, and the material of this invention can efficiently dissipate heat, significantly reducing its temperature.

[0020] A polymer matrix (TPU) serves as the structural framework, forming a micro / nanoporous structure through foaming. This porous structure contains numerous solid-gas interfaces, enabling multiple Mie scattering of incident sunlight, thus achieving high solar reflectivity. Highly reflective inorganic particles (barium sulfate), possessing broadband high reflectivity, are uniformly dispersed within the TPU framework, acting as the primary solar reflective unit and further enhancing the material's reflectivity in the 0.3-2.5 μm wavelength range. Phase change materials (PCMs, such as paraffin wax) serve as temperature-regulating and dynamic optical enhancement units. When the ambient temperature rises above its phase transition point, the PCM absorbs a large amount of latent heat, melting from a solid to a liquid state, acting as a temperature buffer to smooth out peaks and valleys. More importantly, this invention reveals that the solid-liquid phase transition process of PCM causes changes in its optical properties within the TPU matrix. Solid PCM has a clear refractive index interface with the TPU matrix. However, after melting into a liquid state, the interface state between the solid PCM and the TPU matrix changes. Simultaneously, the droplet shape may lead to additional light scattering paths, thereby dynamically improving the overall solar reflectivity of the material and achieving an adaptive cooling enhancement effect. The long molecular chains of TPU can effectively entangle and physically encapsulate the PCM during solvent blending, preventing leakage during multiple phase transition cycles.

[0021] By confining the foam within a highly controllable mold, the growth direction and final porosity of the material can be controlled. The height restriction of the mold forces the bubbles to extend, compress, and fuse in a two-dimensional plane, forming a unique, potentially anisotropic, porous structure. Subsequent freeze-drying completely preserves this fine micro / nanoporous structure, avoiding the pore collapse caused by conventional heat drying, ultimately yielding a lightweight, high-porosity aerogel. This structure maximizes the light-scattering interface, which is key to achieving high solar reflectivity and low thermal conductivity.

[0022] Compared with the prior art, the beneficial effects of the present invention are: (1) By combining high solar reflectance inorganic particles, phase change temperature regulating materials and polymer matrix, and using a special process of “confined foaming + freeze drying”, this invention successfully prepared a porous aerogel material with both ultra-high solar reflectance and high infrared emissivity, achieving excellent passive radiation cooling performance.

[0023] (2) By introducing phase change material (PCM) into the material, a large amount of latent heat is absorbed by its solid-liquid phase change, which realizes the "peak shaving and valley filling" buffer regulation of equipment or ambient temperature; furthermore, by utilizing the changes in optical properties before and after the phase change of PCM, the material's ability to scatter sunlight is dynamically enhanced, thereby realizing the adaptive cooling enhancement effect at high temperature, effectively solving the problem of the single performance of traditional materials under dynamic heat load.

[0024] (3) Through a unique “confined foaming” process, bubbles are forced to grow and fuse within a confined space. Combined with subsequent freeze-drying and curing, this invention constructs a stable micro-nano porous structure rich in solid-gas interfaces. This structure is not only key to achieving high solar reflectivity and low thermal conductivity, but also effectively solves the technical problem of cooling failure of traditional radiative cooling materials in “sub-environments” such as vertical surfaces due to the reduction of the field of view.

[0025] (4) By using flexible thermoplastic polyurethane (TPU) as the main skeleton, the material prepared by the present invention has the characteristics of being lightweight, highly resilient and flexible compared with traditional ceramic-based or metal-based radiation cooling materials, which greatly expands its application potential in fields with strict requirements on weight and shape, such as curved surfaces, wearable devices, and low-altitude aircraft.

[0026] (5) The preparation method of the present invention has a clear process route, low raw material cost, strong equipment versatility, and is easy to achieve large-scale production, and has significant industrialization prospects. Attached Figure Description

[0027] Figure 1 These are test graphs of solar reflectivity for Embodiments 1, 3, and Comparative Example 1 of the present invention; Figure 2 These are test graphs of infrared emissivity for Embodiments 1, 3, and Comparative Example 1 of the present invention; Figure 3 This is a SEM image of the product obtained in Example 1 of the present invention; Figure 4 This is a SEM image of the product obtained in Example 3 of the present invention; Figure 5 This is a SEM image of the product obtained in Comparative Example 1 of the present invention. Detailed Implementation

[0028] To make the objectives and technical solutions of this invention clearer, the invention will be further described in detail below.

[0029] Polymer: Thermoplastic polyurethane (TPU, ETPU40), Ningbo Green Mobil New Materials Technology Co., Ltd.

[0030] Phase change material (PCM): Paraffin wax (phase change temperature 45℃), Shanghai Maclean Biochemical Technology Co., Ltd.

[0031] Inorganic particles: Barium sulfate (BaSO4, analytical grade), Shanghai Aladdin Biochemical Technology Co., Ltd.

[0032] Foaming agent: Azodicarbonamide (trade name PU200).

[0033] Solvent: N,N-dimethylformamide (DMF, analytical grade).

[0034] Example 1 Raw material ratio: 2g thermoplastic polyurethane (TPU), 20g N,N-dimethylformamide (DMF), 1g paraffin, 3g barium sulfate, 0.4g foaming agent.

[0035] A method for preparing highly efficient passive radiative cooling materials suitable for sub-super-environment environments includes the following preparation steps: (1) In a beaker, add 2g TPU to 20g DMF and place it in a 60℃ water bath and stir magnetically for 30 minutes until the TPU is completely dissolved to form a clear and transparent solution A.

[0036] (2) Add 1g of paraffin to solution A and continue stirring at 60°C until the paraffin is completely melted and mixed evenly with the TPU solution to obtain a clear mixed solution B.

[0037] (3) Add 3g of barium sulfate to solution B and treat it for 15 minutes using an ultrasonic cell disruptor (power 400W, working for 3 seconds, intermittent for 3 seconds) to make the barium sulfate particles evenly dispersed and obtain a stable white suspension C.

[0038] (4) Cool the suspension C to room temperature, add 0.4g of foaming agent, and mix for 5 minutes at 2000rpm using a high-speed homogenizer to ensure uniform distribution of the foaming agent and obtain the final foaming precursor suspension D.

[0039] (5) Quickly pour the suspension D into a polytetrafluoroethylene mold with an inner size of 5cm×5cm and a height of 1cm, and immediately place it in an oven at 100℃ for 30 minutes to perform confined foaming.

[0040] (6) After foaming, the molded wet gel and the mold are placed in a -80℃ freezer for 12 hours and then transferred to a freeze dryer for 48 hours to obtain the final composite porous aerogel material.

[0041] Performance Testing: The obtained material is a white solid, lightweight and elastic. Tests showed that its average reflectivity for sunlight (0.3-2.5μm) is 97%, its average emissivity for mid-infrared light (8-13μm) is 96%, and its thermal conductivity is 0.45 W·m. -1 ·K -1 .

[0042] The average solar reflectance test results of the product obtained in Example 1 are shown below. Figure 1 The infrared emissivity test results are shown in [link to test results]. Figure 2 The SEM image of the product obtained in Example 1 is shown below. Figure 3 .

[0043] Example 2: Raw material ratio: 2g thermoplastic polyurethane (TPU), 20g DMF, 3g barium sulfate, 0.4g foaming agent.

[0044] A method for preparing highly efficient passive radiative cooling materials suitable for sub-super-environment environments includes the following preparation steps: (1) Dissolve 2g TPU in 20g DMF to obtain solution A.

[0045] (2) Add 3g of barium sulfate to solution A and sonicate for 15 minutes to obtain suspension B'.

[0046] (3) Add 0.4g of foaming agent to suspension B' and mix at high speed for 5 minutes to obtain foaming precursor suspension C'.

[0047] (4) The subsequent confined foaming and freeze-drying steps are the same as in Example 1.

[0048] Performance testing: The properties of the obtained material are similar to those of Example 1, but it lacks the phase change temperature regulation function. Tests showed that its average solar reflectance is 94.2%, its average mid-infrared emissivity is 95.8%, and its thermal conductivity is 0.26 W·m. -1 ·K -1 .

[0049] Example 3: Raw material ratio: 2g thermoplastic polyurethane (TPU), 20g DMF, 1g paraffin wax, 0.4g foaming agent.

[0050] A method for preparing highly efficient passive radiative cooling materials suitable for sub-super-environment environments includes the following preparation steps: (1) Dissolve 2g TPU and 1g paraffin together in 20g DMF to obtain mixed solution B.

[0051] (2) Add 0.4g of foaming agent to the mixed solution B and mix at high speed for 5 minutes to obtain foaming precursor suspension C''.

[0052] (3) The subsequent confined foaming and freeze-drying steps are the same as in Example 1.

[0053] Performance Testing: Due to the lack of highly reflective barium sulfate particles, the obtained material has a low solar reflectance. Tests showed an average solar reflectance of 93.1%, an average mid-infrared emissivity of 95.1%, and a thermal conductivity of 0.21 W·m. -1 ·K -1 .

[0054] The average solar reflectance test results of the product obtained in Example 3 are shown below. Figure 1 The infrared emissivity test results are shown in [link to test results]. Figure 2 The SEM image of the product obtained in Example 3 is shown below. Figure 4 .

[0055] Comparative Example 1: Raw material ratio: 2g thermoplastic polyurethane (TPU), 20g DMF, 0.4g foaming agent.

[0056] Preparation steps: Dissolve 2g TPU in 20g DMF, then add 0.4g foaming agent, mix at high speed, and then perform confined foaming and freeze drying as in Example 1.

[0057] Performance Testing: The obtained material relies solely on the porous structure formed by TPU itself for light scattering, resulting in limited reflectivity. Tests showed an average solar reflectance of 88.5%, an average mid-infrared emissivity of 94.2%, and a thermal conductivity of 0.20 W·m. -1 ·K -1 .

[0058] The test results of the average solar reflectance of the product obtained in Comparative Example 1 are shown below. Figure 1 The infrared emissivity test results are shown in [link to test results]. Figure 2 The SEM image of the product obtained in Comparative Example 1 is shown below. Figure 5 .

[0059] The test data above show that the introduction of barium sulfate is a key factor in achieving ultra-high solar reflectivity; the introduction of PCM also contributes positively to reflectivity and imparts heat buffering capacity to the material. Example 1, with its three components working synergistically, achieved optimal spectral performance and comprehensive thermal management capabilities.

Claims

1. A method for preparing a highly efficient passive radiative cooling material suitable for sub-super-environment environments, characterized in that, Includes the following steps: (1) Dissolve the polymer matrix in an organic solvent to form a first solution; At least one component selected from phase change materials and solar highly reflective inorganic particles is added to the first solution and dispersed by stirring or ultrasonication to form a uniform mixed suspension. (2) Add a chemical foaming agent to the mixed suspension and stir evenly to obtain a foaming precursor suspension; (3) Pour the foaming precursor suspension into a mold and heat it to decompose the chemical foaming agent and produce gas. Foaming is carried out under the physical constraints of the mold to form a wet gel with a porous structure. (4) The wet gel is freeze-dried to obtain a high-efficiency passive radiation cooling material suitable for sub-super environment.

2. The method for preparing a highly efficient passive radiative cooling material suitable for sub-super-environment as described in claim 1, characterized in that, The polymer matrix is ​​thermoplastic polyurethane.

3. The method for preparing a highly efficient passive radiative cooling material suitable for sub-super-environment as described in claim 1, characterized in that, The aforementioned high-reflectivity inorganic particles are one or more of barium sulfate, titanium dioxide, aluminum oxide, and boron nitride.

4. The method for preparing a highly efficient passive radiative cooling material suitable for sub-super-environment as described in claim 1, characterized in that, The phase change material is paraffin, fatty acid, or polyethylene glycol with a phase change temperature in the range of 30℃-50℃.

5. The method for preparing a highly efficient passive radiative cooling material suitable for sub-super-environment as described in claim 1, characterized in that, The weight ratio of each component is as follows: 100 parts by weight of polymer matrix; 30-200 parts by weight of high solar reflectance inorganic particles; and 10-100 parts by weight of phase change material.

6. The method for preparing a highly efficient passive radiative cooling material suitable for sub-super-environment according to claim 1, characterized in that, The chemical foaming agent is an azo or sulfonyl hydrazine foaming agent, and its addition amount is 10-20% of the weight of the polymer matrix.

7. The method for preparing a highly efficient passive radiative cooling material suitable for sub-super-environment as described in claim 1, characterized in that, In step (3), the heating temperature is 80℃-120℃.

8. A highly efficient passive radiative cooling material for sub-super-environment environments, characterized in that, It is prepared by the method for preparing a highly efficient passive radiation cooling material suitable for sub-super-environment as described in any one of claims 1-7.

9. The application of the high-efficiency passive radiative cooling material for sub-super-environments as described in claim 8, characterized in that, It is used in building energy conservation, thermal management of energy storage equipment, thermal management of solar cells, heat dissipation of electronic devices, or thermal management of low-altitude aircraft.

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