A porous material of a polymer blend with radiative cooling performance and a preparation method thereof

Abstract

An embodiment of the present invention discloses a polymer blend porous material with radiative cooling performance and a preparation method thereof, relating to the technical field of functional materials. Specifically, by combining the different absorption peak positions of polycarbonate and polydimethylsiloxane in the atmospheric window (8 - 13 μm) range, the synergistic effect generated by the two improves the infrared emission ability of the porous material. In addition, through the method of phase separation after solution blending in the present invention, an internally interconnected micro-nano multi-level pore structure is induced, endowing the porous foam with strong sunlight reflection ability. The polymer blend porous material obtained in the present invention has excellent radiative cooling performance, low production cost, simple processing technology, good controllability and certain self-cleaning performance, and can be applied to the outside of houses to play a role in cooling and energy saving without energy input.

Description

Technical Field

[0001] The present invention belongs to the technical field of functional materials, and particularly relates to a polymer blend porous material applied to the field of radiative cooling and a preparation method thereof. Background Art

[0002] Since the Industrial Revolution, a large amount of greenhouse gases have been emitted into the atmosphere during the rapid development of mankind, resulting in a gradual increase in the global temperature, causing many adverse effects such as glacier melting, ecological environment damage, and increased energy consumption. According to the IPCC report, to achieve the climate goal of limiting the global temperature change to 1.5°C set by the Paris Agreement, global carbon emissions must peak in 2025 and be reduced by 43% by 2030. Therefore, energy conservation and emission reduction are an inevitable requirement for the harmonious development of mankind and the world. In real life, due to people's pursuit of a comfortable living environment, the energy consumption required for summer cooling also accounts for an increasing proportion of the total energy consumption year by year; however, traditional cooling systems such as air conditioners not only consume a large amount of energy, but the greenhouse gas warming effect generated by refrigerants such as hydrofluorocarbons used in them is much higher than that of carbon dioxide. In other words, cooling actually makes our world hotter. Therefore, it is essential to find an efficient and pollution-free cooling method.

[0003] A new type of non-electric cooling technology, passive daytime radiative cooling (PDRC), can achieve selective regulation of the spectrum through structural design. On the one hand, it isolates the energy input brought by solar short-wave radiation (0.3 - 2.5 μm), and on the other hand, it uses the atmospheric long-wave infrared transparent window (8 - 13 μm) to transfer the excess heat to the cold outer space in the form of thermal radiation, thereby achieving a self-cooling behavior without energy consumption. In building cooling, strong solar radiation brings a great thermal load to air-conditioning cooling. Therefore, combining daytime radiative cooling materials can effectively reduce the energy consumption required for cooling.

[0004] Polycarbonate (PC) is a high-molecular compound rich in carbonate groups inside. Its processing technology is mature and its performance is excellent. It is one of the five major general engineering plastics in the world. Its good stability and transparency have made it widely used in optical devices, such as the face window of spacesuits and the optical lenses of precision instruments. In addition, the low absorption of polycarbonate in the solar spectrum and the rich C-O-C functional groups inside make it have good application potential in the field of radiative cooling, but there are few relevant reports nowadays. Polydimethylsiloxane (PDMS) is a green and pollution-free organic compound, which is commonly used in fields such as superhydrophobicity, cosmetics, and radiative cooling. Nowadays, most radiative cooling materials, such as photonic crystals and metamaterials, have a relatively complex preparation process and a high cost of required equipment. Therefore, finding a preparation method for radiative cooling materials with a simple process and low cost is still a difficult problem. Summary of the Invention

[0005] One of the purposes of the present invention is to provide a polymer blend porous material with daytime radiation cooling performance and a preparation method thereof. The obtained polymer blend porous foam has strong solar reflection ability and strong mid-infrared emission ability, and can be used on the outside of a house to achieve the function of passive cooling, and is easy to install and disassemble, avoiding adverse heat output caused by cold winter, and has low production cost, simple operation, and good controllability.

[0006] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is:

[0007] A polycarbonate / polydimethylsiloxane polymer blend porous material is obtained by the following preparation method, comprising the following steps:

[0008] (1) dissolving polydimethylsiloxane, a curing agent, polycarbonate particles, and a poor solvent in an organic solvent to obtain a homogeneous transparent solution;

[0009] (2) pouring the solution obtained in step (1) into a mold and freezing it in a refrigerator to form a porous structure interconnected with each other;

[0010] (3) The multiphase mixture obtained in step (2) is freeze-dried to remove the solvent and the poor solvent, thereby obtaining a polymer blend foam material rich in micro-nano multi-level pore structure.

[0011] In step (1), during dispersion, polydimethylsiloxane and curing agent are first dissolved in an organic solvent for 10 minutes to uniformly disperse the polydimethylsiloxane in the organic solvent, and then polycarbonate particles are added and stirred for 1.5 to 3 hours until they are dissolved into a homogeneous transparent solution. During this period, the stirring temperature is 50 to 70° C. and the stirring rate is 150 to 300 r / min.

[0012] In the step (1), the organic solvent is 1,4-dioxane or tetrahydrofuran, and the poor solvent is deionized water or ethanol.

[0013] Preferably, the organic solvent is 1,4-dioxane, the poor solvent is deionized water, the stirring time is 1.5 h, the stirring temperature is 60° C., and the stirring rate is 200 r / min.

[0014] In step (1), the dropping speed of the poor solvent does not exceed 0.01 ml / s.

[0015] In step (1), the mass fraction of polycarbonate in the dispersion is preferably 5.3-5.6wt%; the mass fraction of polydimethylsiloxane is 1.8-5.3wt%; the mass of the curing agent is 10%-20% of the mass of the polydimethylsiloxane, and the volume of the poor solvent is 2.63% of the volume of the solvent.

[0016] In step (2), after stirring until a homogeneous transparent liquid is obtained, the solution can be poured into a glass mold. Taking the example of pouring it into a petri dish with a diameter of 7.5 cm, the height of the solution can be controlled to be 5 mm, and it is frozen and shaped in a refrigerator at -15 to -20 °C.

[0017] Preferably, the freezing temperature is -18 °C.

[0018] In step (3), a freeze dryer is used to remove the solvent and the poor solvent, the temperature is set at -75 to -80 °C, the vacuum degree is maintained below 20 Pa, and the drying time is 48 - 96 h.

[0019] Preferably, the freezing temperature is -78 °C, the vacuum degree is maintained at 18 Pa, and the drying time is 72 h.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] 1. The polymer blend porous material prepared by the present invention combines the different absorption peaks of polycarbonate and polydimethylsiloxane in the atmospheric window, improving the spectral selectivity of the material. And by using the traditional solution blending method, within a relatively wide range of process parameters, the material still maintains good solar reflectivity and infrared thermal emissivity;

[0022] 2. The polymer blend porous foam prepared by the present invention is bright white. It can be calculated that its average reflectivity in the solar spectrum is 95% - 97%, and its average emissivity in the atmospheric window is 87% - 91%.

[0023] 3. The polymer blend porous foam prepared by the present invention spontaneously reduces its own temperature under direct sunlight, reducing by 7.4 °C compared to the environment, and reducing by 9.1 °C compared to the environmental temperature when there is no solar energy input at night, which can play a role in cooling and energy saving in a hot environment.

[0024] 4. The radiative cooling material needs to be placed outdoors, so it is affected by dust, rain erosion, etc. The addition of polydimethylsiloxane reduces the surface energy of the material, making it have certain hydrophobic properties. Therefore, the material has certain self-cleaning ability, solving the problem that traditional radiative cooling materials are easily contaminated and thus fail.

[0025] 5. The method of the present invention is simple to operate, low in cost, short in cycle, and suitable for industrialized popularization and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is the scanning electron microscope image and pore size distribution diagram of the polymer blend porous foam prepared in Example 1 of the present invention;

[0027] Figure 2Solar reflectance spectra and mid-infrared emission spectra measured for the porous materials prepared in Example 1, Example 2 and Comparative Example 1 of the present invention;

[0028] Figure 3 Solar reflectance spectra of the porous foams of the polymer blends prepared in Example 1 and Comparative Example 2 of the present invention;

[0029] Figure 4 a is a photo of the house models with the roofs made of Example 1 and Comparative Example 3 of the present invention;

[0030] Figure 4 b is a comparison chart of the real-time temperatures inside the rooms of the houses with the roofs made of Example 1 and Comparative Example 3 of the present invention respectively under a light intensity of 100 mW / cm 2 ;

[0031] Figure 4 c and d are comparison charts of the infrared thermal images of the houses with the roofs made of Example 1 and Comparative Example 3 of the present invention with and without light;

[0032] Figure 5 a is a schematic diagram of the device for outdoor testing of Example 1 and Comparative Example 1 of the present invention as a radiative cooler;

[0033] Figure 5 b is the light intensity and relative humidity curves during the outdoor testing process;

[0034] Figure 5 c is the real-time temperature curve of Example 1 and Comparative Example 1 of the present invention as a radiative cooler;

[0035] Figure 5 d is the average temperature difference between Example 1 and Comparative Example 1 of the present invention and the ambient temperature during the day and at night respectively;

[0036] Figure 6 a is the anti-fouling test chart of the porous foam of the polymer blend provided in Example 1 of the present invention;

[0037] Figure 6 b is the water contact angle test chart of the porous foam prepared in Example 1 of the present invention. Detailed Description of the Invention

[0038] To further elaborate on the advantages of the present invention, the technical solutions of the present invention will be described in detail below through specific examples.

[0039] The type of polycarbonate used in the following examples is PC-110.

[0040] Example 1

[0041] The preparation method of the polycarbonate / polydimethylsiloxane polymer blend porous material in this embodiment is as follows:

[0042] 1) Prepare a homogeneous solution of the polymer blend: Add polydimethylsiloxane and a curing agent into a 1,4-dioxane solvent. After stirring and dispersing for 10 min, add polycarbonate particles and dissolve them under strong magnetic stirring for 1.5 h. After the solution becomes a homogeneous transparent solution, slowly drop 0.5 ml of deionized water using a syringe at a dropping rate of 0.01 ml / s. Among them, the mass fraction of polydimethylsiloxane and polycarbonate is 5.3 wt%, and the mass of the curing agent is one-tenth of that of polydimethylsiloxane. The whole process is maintained in a constant temperature oil bath at 60 °C.

[0043] 2) Pour the obtained dispersion into a glass petri dish with a diameter of 7.5 cm, control the solution height to be 5 mm, and place it in a refrigerator at -18 °C for freeze molding.

[0044] 3) Prepare the polycarbonate / polydimethylsiloxane polymer blend porous material: Put the blend into a freeze dryer, set the temperature to -78 °C, keep the vacuum degree at 18 Pa, and the drying time is 72 h. Finally, obtain a bright white polycarbonate / polydimethylsiloxane polymer blend porous material.

[0045] Performance detection of this embodiment:

[0046] 1. Observe the internal morphology of the polycarbonate / polydimethylsiloxane polymer blend porous material prepared in this embodiment using a scanning electron microscope. As Figure 1 shown, the polycarbonate / polydimethylsiloxane polymer blend has abundant interconnected micro-nano pores inside. Use image pro plus software to statistically analyze the particle size distribution and find that its pore diameter is mainly concentrated in the range of 1 - 9 μm. This result has a good promoting effect on improving the solar reflectivity.

[0047] 2. Measure the solar reflectivity and infrared thermal emissivity of the polycarbonate / polydimethylsiloxane polymer blend porous material using a UV-Vis-NIR spectrophotometer and a Fourier transform infrared spectrometer (as Figure 2 shown). It can be calculated that the average solar reflectivity reaches 97%, and the average emissivity in the atmospheric window is 91%.

[0048] 3. Test the solar reflectivity of the polycarbonate / polydimethylsiloxane polymer blend porous material using an infrared camera. When the light power density is 100 mW / cm 2 , the internal temperature of the house model with the polycarbonate / polydimethylsiloxane polymer blend porous material as the roof only rises by 3.1 °C, while the internal temperature of the house with a commercial foam (comparative example 1) as the roof rises by 5.9 °C, and the temperature difference between the two is 2.8 °C (as Figure 4 b shown).

[0049] 4. Radiation Cooling Performance Test: The radiation cooling performance of the porous material of the polymer blend prepared in Example 1 was measured in comparison with the porous material prepared in Comparative Example 1. When the solar radiation reached 600 W / m 2 , and the relative humidity was in the range of 15% - 34% ( Figure 5 b), the temperature of Example 1 was always lower than that of Comparative Example 1 (such as Figure 5 c). Compared with the ambient temperature, the average temperature difference of Example 1 during the day was 7.4 °C, and the average temperature difference at night was 9.1 °C. The average temperature difference of Comparative Example 1 during the day was 6.3 °C, and the average temperature difference at night was 8.3 °C (such as Figure 5 d);

[0050] 5. Self-Cleaning Performance Test: Potassium permanganate powder was placed on the top of the porous foam of the polymer blend obtained in Example 1, and deionized water was added dropwise to detect its decontamination ability. As can be seen from Figure 6 a, the potassium permanganate powder was completely removed, and its water contact angle measured by a contact angle tester was 128° (such as Figure 6 b).

[0051] Example 2

[0052] 1) The preparation method of the porous material of the polycarbonate / polydimethylsiloxane polymer blend in this example is as follows:

[0053] 2) Preparation of the polymer blend homogeneous solution: Polydimethylsiloxane and a curing agent were added to a 1,4-dioxane solvent. After stirring and dispersing for 10 min, polycarbonate particles were added and dissolved under strong magnetic stirring for 1.5 h. After the solution became a homogeneous transparent solution, 0.5 ml of deionized water was slowly added dropwise using a syringe at a dropping rate of 0.01 ml / s. Among them, the mass fraction of polycarbonate was 5.5 wt%, the mass fraction of polydimethylsiloxane was 1.8 wt%, and the mass of the curing agent was one-tenth of that of polydimethylsiloxane. The whole process was maintained at a constant temperature of 60 °C in an oil bath.

[0054] 3) The obtained dispersion was poured into a glass petri dish with a diameter of 7.5 cm, and the solution height was controlled to be 5 mm. It was placed in a refrigerator at -18 °C for freeze molding.

[0055] 4) Preparation of the porous material of the polymer blend: The blend was placed in a freeze dryer, the temperature was set at -78 °C, the vacuum was maintained at 18 Pa, and the drying time was 72 h. Finally, a bright white porous material of the polymer blend was obtained.

[0056] Performance Detection of this Example: The solar reflectance and infrared thermal emissivity of the porous material of the polymer blend were measured using a UV-Vis-NIR spectrophotometer and a Fourier transform infrared spectrometer (such as Figure 2As shown, the calculated average solar reflectance remains at about 96%, and the average emissivity in the atmospheric window is 87%.

[0057] Comparative Example 1

[0058] The difference between the polymer porous material prepared in this comparative example and that in Example 1 is that when preparing the dispersion liquid, polydimethylsiloxane is not added, and the mass fraction of polycarbonate is 5.6 wt%, and the others are the same as in Example 1.

[0059] Performance detection of this comparative example:

[0060] 1. After measuring with a UV-Vis-NIR spectrophotometer and a Fourier transform infrared spectrometer, the calculated average solar reflectance reaches 96%, and the average mid-infrared emissivity is 85%.

[0061] 2. Use the prepared cooling device to record the temperature curves during the day and at night. It is found that its cooling effect is lower than that of Example 1.

[0062] Comparative Example 2

[0063] The difference between the polymer porous material prepared in this comparative example and that in Example 1 is that the mass fractions of polydimethylsiloxane and polycarbonate are 4.5 wt%, and the others are the same as in Example 1.

[0064] Performance detection of this comparative example:

[0065] After measuring with a UV-Vis-NIR spectrophotometer, the calculated average solar reflectance is 95%, which is lower than that of Examples 1 and 2.

[0066] Comparative Example 3

[0067] In this comparative example, commercial polystyrene foam is used for comparison, and the foam thickness is controlled at 5 mm.

[0068] Performance detection of this comparative example:

[0069] Use an infrared camera to test the solar reflection ability of the polymer blend porous material. When irradiated with light at a power density of 100 mW / cm 2 , the internal temperature of the house model with Comparative Example 3 as the roof increased by 5.9 °C (as Figure 4 shown in b, c);

[0070] It should be noted that the above is only used to illustrate the preferred solutions of the present invention and is not intended to limit the present invention. Although the foregoing embodiments have introduced the present invention in detail, those skilled in the relevant art should know that any modifications, substitutions, etc. made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A preparation method of a polymer blend porous material with radiative cooling performance, characterized in that, It includes the following steps: (1) Dissolve polydimethylsiloxane, a curing agent, polycarbonate particles, and a poor solvent in an organic solvent to obtain a homogeneous transparent solution; (2) Pour the solution obtained in step (1) into a mold, and form a porous structure with interconnected interiors after low-temperature freezing. Among them, there are no obvious insoluble particles in the solution. Control the height of the solution to be 5 mm, and freeze and shape it in a low-temperature environment of -18°C for 24 to 48 hours; (3) Remove the solvent and the poor solvent from the multiphase mixture obtained in step (2) through freeze-drying to obtain a polymer blend foam material with a micro-nano multi-level porous structure inside. Among them, the freeze-drying is carried out using a freeze-dryer, the freeze-drying temperature is -75 to -80°C, the vacuum degree is maintained below 20 Pa, and the drying time is not less than 72 hours.

2. The preparation method of the polymer blend porous material according to claim 1, characterized in that, In step (1), first dissolve polydimethylsiloxane and the curing agent in an organic solution and stir for 10 minutes until evenly dispersed, then pour the polycarbonate particles into the solution and stir for 1.5 to 3 hours. The stirring temperature is maintained at 60°C, and the stirring rate is 150 to 300 r / min; then slowly drop in the poor solvent, and the dropping rate is lower than 0.01 ml / s.

3. The preparation method of the polymer blend porous material according to claim 1, characterized in that: In the said step (1), the organic solvent is 1,4-dioxane or tetrahydrofuran, and the poor solvent is deionized water or absolute ethanol.

4. The preparation method of the polymer blend porous material according to claim 1, characterized in that, In step (1), the mass fraction of polycarbonate in the homogeneous solution is 5.3 to 5.6 wt%; the mass fraction of polydimethylsiloxane is 1.8 to 5.3 wt%; the mass of the curing agent is 1 / 10 of the mass of polydimethylsiloxane, and the volume of the poor solvent is 2.63% of the volume of the solvent.

5. A polymer blend porous material, characterized in that, The polymer blend porous material is obtained by any of the preparation methods of claims 1-4. The average solar reflectance of the polymer blend porous material within the solar spectrum of 0.3 to 2.5 μm is 95% to 97%, and the average infrared emissivity within the atmospheric window band of 8 to 13 μm is 87% to 91%.

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