A method for preparing aerogel film with high resilience and radiation cooling

Abstract

The present invention belongs to the field of functional membrane materials, and specifically relates to a method for preparing a highly resilient radiation refrigeration aerogel film. The method of the present invention is as follows: step A is to place cellulose fibers in an organic solvent and deionized water in turn for ultrasonic cleaning and drying; step B is to disperse the cellulose fibers obtained in step A in water, stir to form a suspended dispersion, and then add a cross-linking agent, a radiation refrigeration functional material and a dispersant to the suspended dispersion, stir to form a mixed dispersion; step C is to pour the mixed dispersion obtained in step B into a mold for pre-freezing treatment, and then vacuum freeze-drying to obtain. The present invention prepares a highly resilient film by using cellulose fibers, which is a reasonable use of the intrinsic properties of the fibers such as high flexibility and mechanical properties, effectively reduces the cost of preparing three-dimensional porous aerogel films from cellulose materials, and simplifies the process.

Description

Technical Field

[0001] The invention relates to a method for preparing a high-resilience radiation refrigeration aerogel film, and belongs to the field of functional membrane materials. Background Art

[0002] The massive consumption of energy and the emission of greenhouse gases have intensified the trend of global warming, and the extension of high temperature weather will seriously affect the living environment of human beings. Therefore, promoting the development and utilization of renewable energy is an important way to achieve the development of a low-carbon energy structure and protect the ecological environment. Based on the outer space and the sun as the most important cold and heat sources around the earth, the balance of the earth's heat is maintained by its unique sky radiation cooling technology. Radiative cooling is a passive heat dissipation method. Heat is radiated to the outer space of the cold source in the form of electromagnetic waves through the "atmospheric transparent window (8-13μm)" to achieve the purpose of lowering the temperature. The whole process does not require any energy input, achieving true zero carbon emissions. Radiative cooling technology can be widely used in building cooling, radiative cooling clothing fabrics, outdoor equipment heat dissipation, agricultural greenhouse cooling and other fields, and has a wide range of applications.

[0003] Radiative cooling needs to have a high emissivity and low absorptivity in the "atmospheric window" band, and most of the radiative cooling functional materials are concentrated on the design of photonic crystal structures, such as photonic crystal materials, multilayer structures, and micro-nano porous structural materials. However, there is a relative lack of research on radiative cooling substrates with high toughness and structural stability, especially cellulose materials that are widely distributed and abundant. They are green and renewable, have good biodegradability and compatibility, but after cellulose is dissolved, the flexibility, color, and mechanical properties of the fibers all show a decrease. Therefore, the present invention develops a radiative cooling film with high resilience and high radiation efficiency by utilizing the intrinsic properties of cellulose fibers and the structural design of radiative cooling functional materials, which is of great significance for energy conservation and consumption reduction as well as the development and utilization of renewable resources. Summary of the invention

[0004] In view of the above problems existing in the prior art, the object of the present invention is to provide a method for preparing a high resilience radiative cooling aerogel film.

[0005] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a high resilience radiation cooling aerogel film includes a cellulose fiber substrate, a cross-linking agent, a dispersant and a radiation cooling functional material.

[0006] A method for preparing a high resilience radiation cooling aerogel film comprises the following steps:

[0007] Step A: Cellulose fiber pretreatment:

[0008] The cellulose fibers are ultrasonically cleaned in an organic solvent for 15-30 minutes, then ultrasonically cleaned in deionized water for 30-60 minutes, and dried at 80-100° C. for 3-5 hours;

[0009] Step B: preparing a mixed dispersion of cellulose fibers and radiation cooling functional materials:

[0010] Take the cellulose fiber obtained in step A and press (2-8) mg·mL -1 Dispersed in deionized water at 500-600 r·min -1 The speed is set to stir to form a suspension dispersion;

[0011] Then, a crosslinking agent is added to the obtained suspension dispersion and stirring is continued for 2-3 hours;

[0012] Then, the radiation cooling functional material and the dispersant are added to the obtained suspension dispersion, and stirring is continued for 3-5 hours to obtain a mixed dispersion;

[0013] Step C: Film making:

[0014] The mixed dispersion obtained in step B is poured into a mold for pre-freezing treatment, and then vacuum freeze-dried to obtain a high resilience radiation cooling aerogel film.

[0015] Furthermore, in step A:

[0016] The cellulose fiber is one or more of viscose fiber, cotton fiber, bamboo fiber and cuprammonium fiber; preferably cotton fiber.

[0017] The organic solvent is ethanol, propanol, isopropanol or acetone.

[0018] The usage ratio of the cellulose fiber and the organic solvent is 1 g:(50-80) mL, preferably 1 g:50 mL.

[0019] The usage ratio of the cellulose fiber and deionized water is 1 g:(50-80) mL, preferably 1 g:50 mL.

[0020] Furthermore, in step B:

[0021] The crosslinking agent is polyvinyl alcohol, glyoxal, citric acid or 1,2,3,4-butanetetracarboxylic acid (BTCA); preferably 1,2,3,4-butanetetracarboxylic acid (BTCA).

[0022] The mass ratio of the crosslinking agent to the cellulose fiber is 0.3-1.0%.

[0023] The radiation cooling functional material is one or more of spherical silicon dioxide, titanium dioxide, magnesium hydroxide, magnesium nitride and magnesium titanate; preferably spherical silicon dioxide.

[0024] The particle size of the radiation refrigeration functional material is 500nm±10nm.

[0025] The mass ratio of the radiation cooling functional material to the cellulose fiber is 1.0-7.0%, preferably 7.0%.

[0026] The dispersant is polyvinyl pyrrolidone (K30), ethanol, isopropanol or n-hexane.

[0027] The mass ratio of the dispersant to the cellulose fiber is 0.3-1.0%.

[0028] Furthermore, in step C:

[0029] The pre-freezing treatment is carried out at a temperature of -80°C for 24-48 hours.

[0030] The vacuum freeze drying process: the cold trap temperature is -80°C and the time is 36-48h.

[0031] Due to the adoption of the above technical scheme, compared with the prior art, the present invention has the following advantages and beneficial effects:

[0032] (1) The present invention utilizes cellulose fiber, which is abundant in nature and has the widest source, as raw material. It has the characteristics of low cost, renewability, non-toxicity, and green environmental protection, and has good biodegradability and biocompatibility, which is of great significance to the efficient utilization of biomass resources.

[0033] (2) The present invention uses cellulose fibers to prepare high resilience films, which is a rational use of the intrinsic properties of the fibers, such as high flexibility and mechanical properties, effectively reducing the cost of preparing three-dimensional porous aerogel films from cellulose materials and simplifying the process.

[0034] (3) Compared with other radiative cooling films, the three-dimensional porous aerogel film constructed by cellulose fibers also has a thermal insulation effect, and the radiative cooling performance can be further enhanced by adjusting the porous structure of the aerogel and the ratio of the radiative cooling material.

[0035] (4) The preparation method of the present invention has simple process, convenient operation, high production efficiency, low cost and energy consumption, and has great application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is the emissivity curve of the 7.0% spherical silica / cotton fiber aerogel film prepared in Example 5 of the present invention within the atmospheric window band.

[0037] Figure 2 The solar radiation reflection performance curve of the pure cotton fiber aerogel film prepared in the comparative example of the present invention.

[0038] Figure 3 This is the compression resilience curve of the 7.0% spherical silica / cotton fiber aerogel film prepared in Example 5 of the present invention.

[0039] Figure 4 This is a test curve of 10, 30, and 50 compression cycles of the 7.0% spherical silica / cotton fiber aerogel film prepared in Example 5 of the present invention at a deformation of 60%.

[0040] Figure 5 The stress-strain curves of the 7.0% spherical silica / cotton fiber aerogel film prepared in Example 5 of the present invention and the pure cotton fiber aerogel film prepared in the comparative example.

[0041] Figure 6 These are the thermal conductivity test results of the 7.0% spherical silica / cotton fiber aerogel film prepared in Example 5 of the present invention and air. DETAILED DESCRIPTION

[0042] The present invention is further described in detail below in conjunction with specific embodiments.

[0043] In the following embodiments, the raw material viscose fiber used comes from: Tangshan Sanyou Chemical Co., Ltd.; the raw material bamboo fiber used comes from: Fujian Bamboo Fiber Material Technology Co., Ltd.; the raw material cotton fiber used comes from: Shanghai Hengxin Chemical Reagent Co., Ltd.; the raw material cuprammonia fiber used comes from: Shanghai Hengxin Chemical Reagent Co., Ltd.

[0044] In the following examples, the radiation cooling functional materials used, spherical silicon dioxide, titanium dioxide, magnesium hydroxide, and magnesium nitride, were purchased from Aladdin Company, and the average particle size used was 500±10 nm.

[0045] Example 1

[0046] The viscose fiber was ultrasonically cleaned in propanol at a ratio of 1g:50mL for 30min, then ultrasonically cleaned in deionized water at a ratio of 1g:50mL for 60min, and dried at 100℃ for 3h. Then 0.2g of the cleaned viscose fiber was dispersed in 100mL of deionized water and dried at 500r / min. -1The mixture was stirred and mixed at a speed of 10000rpm to form a suspension dispersion, and then 0.6 mg of polyvinyl alcohol (Da: 1750, 0.3% of the mass of the viscose fiber) was added to the obtained suspension dispersion, and stirring was continued for 2 hours. Then 2 mg of spherical silica (1.0% of the mass of the viscose fiber) and 0.6 mg of polyvinyl pyrrolidone (0.3% of the mass of the viscose fiber) were added to the viscose fiber suspension, and stirring was continued for 3 hours to obtain a mixed dispersion. Next, the mixed dispersion was poured into a mold with a thickness of 0.5 cm and pre-frozen at a pre-freezing temperature of -80°C for 24 hours. Subsequently, a vacuum freeze-drying treatment (cold trap temperature of -80°C) was carried out for 48 hours to obtain a high resilience viscose fiber radiation refrigeration aerogel film, recorded as "1.0% spherical silica / viscose fiber aerogel film".

[0047] The "1.0% spherical silica / viscose fiber aerogel film" prepared in Example 1 has an average emissivity of more than 83% in the 0.4-2.5 μm band and an average emissivity of more than 85% in the 8-13 μm band, and can be used as a radiation cooling film.

[0048] Example 2

[0049] The bamboo fiber was ultrasonically cleaned in ethanol at a ratio of 1g:50mL for 30min, then ultrasonically cleaned in deionized water at a ratio of 1g:50mL for 60min, and dried at 100℃ for 3h. Then 0.4g of the cleaned bamboo fiber was dispersed in 100mL of deionized water and heated at 500r / min. -1 The speed is stirred and mixed to form a suspension dispersion, and then 2 mg of glyoxal (the amount of which accounts for 0.5% of the mass of bamboo fiber) is added to the obtained suspension dispersion, and stirring is continued for 3 hours. Then 12 mg of titanium dioxide (the amount of which accounts for 3.0% of the mass of bamboo fiber) and 2 mg of ethanol (the amount of which accounts for 0.5% of the mass of bamboo fiber) are added to the bamboo fiber suspension, and stirring is continued for 4 hours to obtain a mixed dispersion. Next, the mixed dispersion is poured into a mold with a thickness of 0.5 cm and pre-frozen at a pre-freezing temperature of -80 ° C for 24 hours. Subsequently, a vacuum freeze-drying (cold trap temperature of -80 ° C) treatment is performed for 36 hours to obtain a high resilience bamboo fiber radiation refrigeration aerogel film, which is recorded as "3.0% titanium dioxide / bamboo fiber aerogel film".

[0050] The "3.0% titanium dioxide / bamboo fiber aerogel film" prepared in Example 2 has an average emissivity greater than 86% in the 0.4-2.5 μm band and an average emissivity greater than 89% in the 8-13 μm band, and can be used as a radiation cooling film.

[0051] Example 3

[0052] The cotton fiber was ultrasonically cleaned in isopropanol at a ratio of 1g:50mL for 30min, then ultrasonically cleaned in deionized water at a ratio of 1g:50mL for 60min, and dried at 100℃ for 3h. Then 0.6g of the cleaned cotton fiber was dispersed in 100mL of deionized water and heated at 500r / min. -1 The mixture was stirred and mixed at a speed of 1000 rpm to form a suspension dispersion, and then 4.2 mg of citric acid (0.7% of the mass of the cotton fiber) was added to the obtained suspension dispersion, and stirring was continued for 2 hours. Then 30 mg of magnesium hydroxide (5.0% of the mass of the cotton fiber) and 4.2 mg of isopropanol (0.7% of the mass of the cotton fiber) were added to the cotton fiber suspension, and stirring was continued for 5 hours to obtain a mixed dispersion. Next, the mixed dispersion was poured into a mold with a thickness of 0.5 cm and pre-frozen at a pre-freezing temperature of -80°C for 48 hours. Subsequently, a vacuum freeze-drying treatment (cold trap temperature of -80°C) was performed for 48 hours to obtain a high resilience cotton fiber radiation refrigeration aerogel film, recorded as "5.0% magnesium hydroxide / cotton fiber aerogel film".

[0053] The "5.0% magnesium hydroxide / cotton fiber aerogel film" prepared in Example 3 has an average emissivity of more than 88% in the 0.4-2.5 μm band and an average emissivity of more than 90% in the 8-13 μm band, and can be used as a radiation cooling film.

[0054] Example 4

[0055] The copper ammonia fiber was ultrasonically cleaned in acetone at a ratio of 1g:50mL for 30min, then ultrasonically cleaned in deionized water at a ratio of 1g:50mL for 60min, and dried at 100℃ for 3h. Then 0.8g of the cleaned copper ammonia fiber was dispersed in 100mL of deionized water and heated at 500r / min. -1 The mixture was stirred and mixed at a speed of 1000 rpm to form a suspension dispersion, and then 8 mg of 1,2,3,4-butanetetracarboxylic acid (1% of the mass of the copper ammonia fiber) was added to the obtained suspension dispersion, and stirring was continued for 2 hours. Then 56 mg of magnesium nitride (7.0% of the mass of the copper ammonia fiber) and 8 mg of n-hexane (1% of the mass of the copper ammonia fiber) were added to the copper ammonia fiber suspension, and stirring was continued for 3 hours to obtain a mixed dispersion. Next, the mixed dispersion was poured into a mold with a thickness of 0.5 cm and pre-frozen at a pre-freezing temperature of -80°C for 24 hours. Subsequently, a vacuum freeze-drying (cold trap temperature of -80°C) treatment was performed for 48 hours to obtain a high resilience copper ammonia fiber radiation refrigeration aerogel film, recorded as "7.0% magnesium nitride / copper ammonia fiber aerogel film".

[0056] The "7.0% magnesium nitride / copper ammonia fiber aerogel film" prepared in Example 4 has an average emissivity greater than 90% in the 0.4-2.5 μm band and an average emissivity greater than 92% in the 8-13 μm band, and can be used as a radiation cooling film.

[0057] Example 5

[0058] The cotton fiber was ultrasonically cleaned in acetone at a ratio of 1g:50mL for 30min, then ultrasonically cleaned in deionized water at a ratio of 1g:50mL for 60min, and dried at 100℃ for 3h. 0.6g of the cleaned cotton fiber was dispersed in 100mL of deionized water and heated at 500r / min. -1 The mixture was stirred and mixed at a speed of 1000 rpm to form a suspension dispersion, and then 4.2 mg of 1,2,3,4-butanetetracarboxylic acid (0.7% of the mass of the cotton fiber) was added to the obtained suspension dispersion, and stirring was continued for 2 hours. Then 42 mg of spherical silica (7.0% of the mass of the cotton fiber) and 6 mg of polyvinyl pyrrolidone (1.0% of the mass of the cotton fiber) were added to the cotton fiber suspension, and stirring was continued for 3 hours to obtain a mixed dispersion. Next, the mixed dispersion was poured into a mold with a thickness of 0.5 cm and pre-frozen at a pre-freezing temperature of -80°C for 24 hours. Subsequently, a vacuum freeze-drying (cold trap temperature of -80°C) treatment was performed for 48 hours to obtain a high resilience cotton fiber radiation refrigeration aerogel film, recorded as "7.0% spherical silica / cotton fiber aerogel film". The "7.0% spherical silica / cotton fiber aerogel film" prepared in Example 5 has an average emissivity of more than 95% in the 0.4-2.5 μm band and an average emissivity of more than 97% in the 8-13 μm band, and can be used as a radiation cooling film.

[0059] Comparative Example

[0060] The cotton fiber was ultrasonically cleaned in acetone at a ratio of 1g:50mL for 30min, then ultrasonically cleaned in deionized water at a ratio of 1g:50mL for 60min, and dried at 100℃ for 3h. 0.6g of the cleaned cotton fiber was dispersed in 100mL of deionized water and heated at 500r / min. -1 The suspension was stirred at a high speed for 5 hours to form a suspension dispersion. The suspension dispersion was then poured into a mold with a thickness of 0.5 cm and pre-frozen at a temperature of -80°C for 24 hours. It was then vacuum freeze-dried (the cold trap temperature was -80°C) for 48 hours to obtain a pure cotton fiber aerogel film.

[0061] Figure 1 It is demonstrated that the emissivity of the 7.0% spherical silica / cotton fiber aerogel film in Example 5 is above 97% within the atmospheric window (8-13 μm) band.

[0062] Figure 2 The solar radiation reflection performance curve of the pure cotton fiber aerogel film prepared in the comparative example is shown. Its reflectivity in the visible light band is 68%-82%, while it has a lower reflectivity in the near-infrared band, indicating that pure cotton fiber is insufficient in reducing solar radiation energy.

[0063] Figure 3 The compression resilience test of the 7.0% spherical silica / cotton fiber aerogel film in Example 5 is demonstrated. From the curve, it can be seen that the sample still has excellent recovery properties at a deformation of 60%.

[0064] Figure 4 The multi-cycle test of the 7.0% spherical silica / cotton fiber aerogel film in Example 5 at a deformation of 60% was demonstrated, showing high compression resilience.

[0065] Figure 5 The stress-strain curves of the 7.0% spherical silica / cotton fiber aerogel film in Example 5 and the pure cotton fiber aerogel film in the comparative example are shown, indicating that the 7.0% spherical silica / cotton fiber aerogel film has a better breaking strength.

[0066] Figure 6 The thermal conductivity test results of the 7.0% spherical silica / cotton fiber aerogel film and air in Example 5 are shown. The thermal conductivity of the 7.0% spherical silica / cotton fiber aerogel film prepared in Example 5 is 0.0678 W·m -1 ·K -1 , showing a thermal conductivity close to that of air, indicating that the spherical silica / cotton fiber aerogel film has the effect of thermal insulation.

[0067] Therefore, the series of high resilience radiation cooling aerogel films prepared by the present invention can be used as radiation cooling functional materials, thermal insulation materials, etc.

[0068] Related performance tests:

[0069] (1) Compression resilience test: The compression performance of the aerogel film was tested at room temperature using a universal testing machine equipped with two plates and a 500 N load cell. All samples used for compression testing were cylindrical and had dimensions of 40 mm × 20 mm (diameter × height).

[0070] (2) Fracture strength: The aerogel film was made into a sample with a length of 3 cm, a width of 1 cm, and a thickness of 0.5 mm. The sensitivity of the chuck was 500 N and the test rate was 5 mm min. -1 , the clamping distance is set to 2 cm and the pre-tension is 1N.

[0071] (3) Light reflectance test: The light reflectance of cellulose aerogel was measured using a UV-visible-near infrared spectrophotometer equipped with an integrating sphere, with a wavelength range of 280-2500 nm and a resolution of 0.1 nm.

[0072] (4) Infrared emissivity test: The infrared emissivity test standard of aerogel film is based on JJF (Textile) 086-2019.

[0073] (5) Thermal conductivity test: The thermal conductivity test standard of aerogel film is based on ISO 22007-2:2015.

[0074] The above-mentioned embodiments are only preferred technical solutions of the present invention and should not be regarded as limitations of the present invention. The embodiments and features in the embodiments of the present application can be arbitrarily combined with each other without conflict. The protection scope of the present invention shall be the technical solutions recorded in the claims, including the equivalent replacement solutions of the technical features in the technical solutions recorded in the claims. That is, equivalent replacement improvements within this scope are also within the protection scope of the present invention.

Claims

1. A method for preparing a high resilience radiation cooling aerogel film, It is characterized in that The following steps are involved: Step A Cellulose fiber pretreatment: The cellulose fibers are ultrasonically cleaned in an organic solvent for 15-30 minutes, then ultrasonically cleaned in deionized water for 30-60 minutes, and dried at 80-100° C. for 3-5 hours; the cellulose fibers are one or more of viscose fibers, cotton fibers, bamboo fibers, and cuprammonia fibers; Step B: preparing a mixed dispersion of cellulose fibers and radiation cooling functional materials: Take the cellulose fiber obtained in step A and press (2-8) mg·mL -1 Dispersed in deionized water at 500-600 r·min -1 The speed is set to stir to form a suspension dispersion; Then, a crosslinking agent is added to the obtained suspension dispersion, and stirring is continued for 2-3 hours; the crosslinking agent is citric acid or 1,2,3,4-butanetetracarboxylic acid; the mass ratio of the crosslinking agent to the cellulose fiber is 0.3-1.0%; Then, a radiation refrigeration functional material and a dispersant are added to the obtained suspension dispersion, and stirring is continued for 3-5 hours to obtain a mixed dispersion; the radiation refrigeration functional material is one or more of spherical silicon dioxide, titanium dioxide, magnesium hydroxide, magnesium nitride and magnesium titanate; the dispersant is polyvinyl pyrrolidone, ethanol, isopropanol or n-hexane; the mass ratio of the radiation refrigeration functional material to the cellulose fiber is 1.0-7.0%; the mass ratio of the dispersant to the cellulose fiber is 0.3-1.0%; Step C: Film preparation: The mixed dispersion obtained in step B is poured into a mold for pre-freezing treatment, and then vacuum freeze-dried to obtain a high resilience radiation cooling aerogel film.

2. The preparation method according to claim 1, It is characterized in that The organic solvent is ethanol, propanol, isopropanol or acetone.

3. The preparation method according to claim 1, It is characterized in that The pre-freezing treatment is carried out at a temperature of -80°C for 24-48 hours.

4. The preparation method according to claim 1, It is characterized in that The particle size of the radiation refrigeration functional material is 500nm±10nm.

Images