Colored daytime radiation cooling nanofiber membrane and preparation method thereof

Abstract

The invention relates to a colored daytime radiation cooling nanofiber membrane and a preparation method thereof, and the nanofiber membrane is prepared by using a cellulose acetate molecular structure through a stock solution dyeing electrostatic spinning technology. The nanofiber membrane selectively absorbs the needed color only in the visible spectrum to display the color, visible light and near-infrared light of other wave bands are strongly scattered through the nanofiber membrane structure, solar heating is reduced to the maximum extent, and meanwhile infrared heat radiation is strongly emitted in the atmospheric transparent window wave band; the coating is simple in preparation process, rich in color, good in flexibility and deformability and excellent in cooling performance, and can be applied to various practical applications, such as cooling covers of buildings and textiles.

Description

Technical Field

[0001] The invention belongs to the technical field of radiation cooling, and in particular relates to a colored daytime radiation cooling nanofiber membrane and a preparation method thereof. Background Art

[0002] Cooling system energy consumption accounts for about 15% of global electricity consumption. Traditional cooling methods not only consume a lot of energy, but also lead to the greenhouse effect. Passive radiation cooling technology emits infrared heat to outer space through the atmospheric transparent window (8-13μm), allowing objects to cool down without consuming any energy. However, solar radiation during the day will greatly reduce the cooling effect. Therefore, the ideal daytime passive radiation cooler must have a high solar reflectivity while having good mid-infrared emissivity to reduce the impact of solar radiation.

[0003] Recently, scholars have studied the use of spectrally selective surfaces to prepare photonic structures that can minimize solar absorption while maximizing emission at mid-infrared wavelengths. However, these specialized photonic structures are expensive and have complex preparation processes, which is not conducive to industrialization. Compared with the fabrication of complex photonic structures, molecular-level design based on polymer chemical bonding provides a more convenient and scalable route to achieve modulation of infrared spectral properties and thus achieve high cooling efficiency. However, typical polymer films prepared by droplet casting are transparent, which cannot meet the requirements of high solar reflectivity. According to Mie scattering theory, designing nanostructures with wavelengths similar to solar radiation can achieve efficient solar radiation reflection. But due to strong light scattering, most radiative coolers usually appear white, which does not meet aesthetic requirements and may cause glare effects that damage human eyes.

[0004] To overcome this challenge, a new approach is needed to achieve high solar reflectance while maintaining a visually pleasing appearance. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a colored daytime radiation cooling nanofiber membrane and a preparation method thereof in view of the problem that the traditional white appearance of the radiation cooler will cause strong stimulation to the human eye during actual use and is not aesthetically pleasing.

[0006] The present invention provides a colored daytime radiation cooling nanofiber membrane, which is prepared by solution dyeing electrospinning technology using the molecular structure of cellulose acetate. The molecular structure of cellulose acetate makes the material have an ideal infrared spectral emissivity in the overlapping band with the atmospheric transparent window (8-13μm).

[0007] The present invention also provides a method for preparing a colored daytime radiation cooling nanofiber membrane, comprising the following steps:

[0008] (1) dissolving cellulose acetate in an organic solvent and stirring the mixture to obtain a cellulose acetate solution;

[0009] (2) adding inorganic pigments or reactive dyes to a cellulose acetate solution to prepare a colored electrospinning solution;

[0010] (3) The colored electrospinning solution was loaded into a syringe, and the colored daytime radiation cooling nanofiber membrane was prepared by electrospinning technology.

[0011] Preferably, the organic solvent in step (1) is one or more of acetone, tetrahydrofuran, dimethylformamide and toluene.

[0012] Preferably, the mass fraction of the cellulose acetate solution in step (1) is 10-20%.

[0013] Preferably, the stirring temperature in step (1) is 20-40° C., and the stirring time is 1.5-4 h.

[0014] Preferably, the particle size of the inorganic pigment in step (2) is nanometer-scale, including one or more of iron oxide, Prussian blue, zinc oxide, and goethite.

[0015] Preferably, the reactive dyes in step (2) are reactive dyes of other colors such as pink, yellow, blue, etc.

[0016] Preferably, the electrospinning process parameters in step (3) are: voltage 15-30 kV, receiving distance 10-20 cm, and propulsion speed of the propulsion pump 0.020-0.050 mm / min.

[0017] Preferably, the relative humidity of the environment during the spinning process in step (3) is 30-50%, and the temperature is 20-30°C.

[0018] Preferably, the syringe used in step (3) is a common medical syringe, and the needle is a stainless steel needle.

[0019] The present invention also provides an application of the colored daytime radiation cooling nanofiber membrane in cooling covers of buildings and textiles.

[0020] Beneficial Effects

[0021] (1) The selective spectral absorption nanofiber membrane for colored daytime radiation cooling provided by the present invention is prepared by electrospinning technology and has a multi-layer disordered stacked nanofiber structure, which can strongly scatter sunlight and effectively resist external solar heating. The polymer material used has mid-infrared emission characteristics and has an ideal infrared spectral emissivity in the atmospheric transparent window band. In addition, the related chemical bonds of the dye CO stretching, CN stretching, aromatic CH bending and S=O stretching also contribute to the high emissivity in the mid-infrared band. As a result, the fiber membrane obtains ultra-high near-infrared reflectivity and high and medium infrared emissivity, thereby achieving a cooling effect in which the membrane surface temperature is lower than the ambient temperature.

[0022] (2) The selective spectral absorption nanofiber membrane for color daytime radiation cooling provided by the present invention is prepared by a simple coating dyeing electrospinning method. This solves the problem that chemical colors absorb visible light and generate heat, interfering with the cooling effect, and does not require a subsequent dyeing process. This dyeing process is very simple and therefore has the potential for industrialization.

[0023] (3) The selective spectral absorption nanofiber membrane for color daytime radiation cooling provided by the present invention has excellent flexibility and deformability. Its bending stiffness value is two orders of magnitude lower than that of printed paper and cotton fabric, and it can be repeatedly stretched and twisted, and can be applied in practical scenarios.

[0024] (4) The technical solution provided by the present invention can successfully achieve a cooling effect below the ambient temperature during the day while meeting aesthetic requirements. It can be applied to cooling systems such as buildings, vehicles, and even human bodies to achieve the goal of energy saving and consumption reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The scanning electron microscope image and diameter distribution curve of the nanofibers prepared in Example 1.

[0026] Figure 2 This is a comparison chart of the bending stiffness of the nanofiber membrane prepared in Example 2 with cotton fabric and printed paper.

[0027] Figure 3 The solar reflectivity of the nanofiber membranes prepared in Examples 1, 2, 3, and 4.

[0028] Figure 4 The mid-infrared emissivity of the nanofiber membranes prepared in Examples 1, 2, 3, and 4.

[0029] Figure 5 ai is the cooling temperature of the nanofiber membrane prepared in Examples 1, 2, 3, and 4 in February to March of a certain year, for 10 days, 20 days, and 30 days. DETAILED DESCRIPTION

[0030] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0031] Performance Test:

[0032] Fiber diameter: The morphology of the samples was observed using a scanning electron microscope (JSM-7500F, JEOL, Japan) at 5 kV and after gold sputtering for 90 s. The fiber diameter was calculated using ImageJ software (NIH, USA), and 200 nanofibers were measured to analyze the average fiber diameter.

[0033] Stiffness: Refer to GB / T 18318.1-2009 and use a fully automatic fabric stiffness tester to measure the stiffness of the sample. The sample size is (25±1)mm×(250±1)mm, according to the formula: G=m×C 3 ×10 -3 Calculate the stiffness. Where G is the bending stiffness (mN cm), m is the weight of the sample (gm -2 ), C is the bending length (cm), which is half of the overhang length.

[0034] Solar spectrum (0.3-2.5 μm) reflectance: measured using a UV-visible-near-infrared spectrometer with a diffuse integrating sphere (UV3600, Shimadzu Instruments Co., Ltd., Japan, calibrated with a standard barium sulfate white plate).

[0035] Mid-infrared spectroscopy (8-13 μm) emissivity was measured using a Fourier transform infrared spectrometer (Nicolet 8700, Thermo Fisher Scientific, USA) equipped with a diffuse gold integrating sphere.

[0036] Thermal performance: A self-designed device was used to measure the temperature under direct sunlight in real time to verify the daytime cooling performance of the sample. The self-designed test device consists of a thermocouple (WZPT, Songdao), a cooling test chamber, a solar radiometer (Solar-1, Jinzhou Tiannuo Environmental Energy Instrument Co., Ltd.), a hygrometer, and a feedback-controlled temperature recorder (TP700, Shenzhen Toprui Electronics Co., Ltd.). The cooling test chamber is used to prevent heat loss in the form of thermal conduction and convection. A solar radiometer with an accuracy of ±5% is used to record solar radiation outside the chamber, and a hygrometer with an accuracy of ±0.1%RH is used to measure relative air humidity. A thermocouple (with an accuracy of ±0.1℃) connected to the temperature recorder records the sample and ambient temperatures. In addition, the temperature recorder can also use a feedback control system to heat the sample, keep the sample at ambient temperature, and accurately evaluate the cooling power.

[0037] Example 1

[0038] The preparation method of the colored daytime radiation cooling nanofiber membrane comprises the following steps:

[0039] (1) Cellulose acetate fiber (CA) powder was dissolved in a mixed solvent of acetone / DMF (2:1, w / w) and stirred continuously for 2 hours at room temperature to prepare a uniform CA solution with a mass fraction of 15 wt%.

[0040] (2) Nano-Fe2O3 pigment was added into CA solution to prepare a colorful electrospinning solution.

[0041] (3) The colored electrospinning solution was loaded into a syringe with an 18-gauge needle, and the nanofiber membrane was prepared by electrospinning technology. During the electrospinning process, the spinning parameters were as follows: voltage 20 kV, collection distance 15 cm, and propulsion speed 0.030 mm / min. The spinning conditions were room temperature and 35% relative humidity.

[0042] After testing, the fiber diameter size distribution range is 372±101nm, and the main absorption wavelength of the fiber membrane is 401nm. The fiber membrane obtained in Example 1 shows a broadband mid-infrared emissivity of 95% in the atmospheric transparent window (8-13μm), an ultra-high reflectivity of 96% at near-infrared wavelengths, and an overall sunlight reflectivity of 90%. The characterization results of the long-term stability of the cooling capacity show that after 10 days, under a clear sky, the sunlight intensity is about 800W m -2 Under the conditions of about 30% humidity, the fiber membrane prepared in Example 1 can be cooled to 3.5°C lower than the ambient temperature. On the 20th day, the fiber membrane prepared in Example 1 can achieve a cooling effect of 2.9°C. After 30 days of outdoor exposure, the surface temperature of the fiber membrane prepared in Example 1 can still be 3.0°C lower than the ambient temperature.

[0043] Example 2

[0044] The preparation method of the colored daytime radiation cooling nanofiber membrane comprises the following steps:

[0045] (1) Cellulose acetate fiber (CA) powder was dissolved in a mixed solvent of acetone / DMF (2:1, w / w) and stirred continuously for 2 hours at room temperature to prepare a uniform CA solution with a mass fraction of 15 wt%.

[0046] (2) Add pink reactive dye into CA solution to prepare a colored electrospinning solution.

[0047] (3) The colored electrospinning solution was loaded into a syringe with an 18-gauge needle, and the nanofiber membrane was prepared by electrospinning technology. During the electrospinning process, the spinning parameters were as follows: voltage 20 kV, collection distance 15 cm, and propulsion speed 0.030 mm / min. The spinning conditions were room temperature and 35% relative humidity.

[0048] After testing: the bending stiffness value of the nanofiber membrane obtained in Example 2 is 0.02mN cm, the fiber diameter size distribution range is 372±101nm, and the main absorption wavelength of the fiber membrane is 540nm. The fiber membrane obtained in Example 2 shows a broadband mid-infrared emissivity of 95% in the atmospheric transparent window (8-13μm), an ultra-high reflectivity of 97% at near-infrared wavelengths, and an overall sunlight reflectivity of 90%. The characterization results of the long-term stability of the cooling capacity show that after 10 days, under a clear sky, the sunlight intensity is about 800W m -2 Under the conditions of about 30% humidity, the fiber membrane prepared in Example 2 can be cooled to 3.0°C lower than the ambient temperature. On the 20th day, the fiber membrane prepared in Example 2 can achieve a cooling effect of 2.1°C. After 30 days of outdoor exposure, the surface temperature of the fiber membrane prepared in Example 2 can still be 2.4°C lower than the ambient temperature.

[0049] Example 3

[0050] The preparation method of the colored daytime radiation cooling nanofiber membrane comprises the following steps:

[0051] (1) Cellulose acetate fiber (CA) powder was dissolved in a mixed solvent of acetone / DMF (2:1, w / w) and stirred continuously for 2 hours at room temperature to prepare a uniform CA solution with a mass fraction of 15 wt%.

[0052] (2) Yellow reactive dye was added to CA solution to prepare a colored electrospinning solution.

[0053] (3) The colored electrospinning solution was loaded into a syringe with an 18-gauge needle, and the nanofiber membrane was prepared by electrospinning technology. During the electrospinning process, the spinning parameters were as follows: voltage 20 kV, collection distance 15 cm, and propulsion speed 0.030 mm / min. The spinning conditions were room temperature and 35% relative humidity.

[0054] After testing, the fiber diameter size distribution range is 372±101nm, and the main absorption wavelength of the fiber membrane is 446nm. The fiber membrane obtained in Example 3 shows a broadband mid-infrared emissivity of 95% in the atmospheric transparent window (8-13μm), an ultra-high reflectivity of 97% at near-infrared wavelengths, and an overall sunlight reflectivity of 92%. The characterization results of the long-term stability of the cooling capacity show that after 10 days, under a clear sky, the sunlight intensity is about 800W m -2 Under the conditions of about 30% humidity, the fiber membrane prepared in Example 3 can be cooled to 4.3°C lower than the ambient temperature. On the 20th day, the fiber membrane prepared in Example 3 can achieve a cooling effect of 3.8°C. After 30 days of outdoor exposure, the surface temperature of the fiber membrane prepared in Example 3 can still be 3.7°C lower than the ambient temperature.

[0055] Example 4

[0056] The preparation method of the colored daytime radiation cooling nanofiber membrane comprises the following steps:

[0057] (1) Cellulose acetate fiber (CA) powder was dissolved in a mixed solvent of acetone / DMF (2:1, w / w) and stirred continuously for 2 hours at room temperature to prepare a uniform CA solution with a mass fraction of 15 wt%.

[0058] (2) Add blue reactive dye to CA solution to prepare a colorful electrospinning solution.

[0059] (3) The colored electrospinning solution was loaded into a syringe with an 18-gauge needle, and the nanofiber membrane was prepared by electrospinning technology. During the electrospinning process, the spinning parameters were as follows: voltage 20 kV, collection distance 15 cm, and propulsion speed 0.030 mm / min. The spinning conditions were room temperature and 35% relative humidity.

[0060] After testing, the fiber diameter size distribution range is 372±101nm, and the main absorption wavelength of the fiber membrane is 620nm. The fiber membrane obtained in Example 4 shows a broadband mid-infrared emissivity of 95% in the atmospheric transparent window (8-13μm), an ultra-high reflectivity of 99% at near-infrared wavelengths, and an overall sunlight reflectivity of 90%. The characterization results of the long-term stability of the cooling capacity show that after 10 days, under a clear sky, the sunlight intensity is about 800W m -2 Under the conditions of about 30% humidity, the fiber membrane prepared in Example 4 can be cooled to 2.1°C lower than the ambient temperature. On the 20th day, the fiber membrane prepared in Example 4 can achieve a cooling effect of 2.0°C. After 30 days of outdoor exposure, the surface temperature of the fiber membrane prepared in Example 4 can still be 1.6°C lower than the ambient temperature.

Claims

1. A colored daytime radiation cooling nanofiber membrane, characterized in that: It is prepared by using the molecular structure of cellulose acetate and the electrospinning technology of dope dyeing.

2. A method for preparing a colored daytime radiation cooling nanofiber membrane, comprising the following steps: (1) dissolving cellulose acetate in an organic solvent and stirring the mixture to obtain a cellulose acetate solution; (2) adding inorganic pigments or reactive dyes to a cellulose acetate solution to prepare a colored electrospinning solution; (3) The colored electrospinning solution was loaded into a syringe, and the colored daytime radiation cooling nanofiber membrane was prepared by electrospinning technology.

3. The preparation method according to claim 2, characterized in that: The organic solvent in step (1) is one or more of acetone, tetrahydrofuran, dimethylformamide and toluene.

4. The preparation method according to claim 2, characterized in that: The mass fraction of the cellulose acetate solution in step (1) is 10-20%.

5. The preparation method according to claim 2, characterized in that: The stirring temperature in step (1) is 20-40° C., and the stirring time is 1.5-4 h.

6. The preparation method according to claim 2, characterized in that: The particle size of the inorganic pigment in step (2) is nanometer-level, and includes one or more of iron oxide, Prussian blue, zinc oxide, and goethite.

7. The preparation method according to claim 2, characterized in that: The electrospinning process parameters in step (3) are: voltage 15-30 kV, receiving distance 10-20 cm, and propulsion speed of the propulsion pump 0.020-0.050 mm / min.

8. The preparation method according to claim 2, characterized in that: During the spinning process in step (3), the relative humidity of the environment is 30-50% and the temperature is 20-30°C.

9. Use of the colored daytime radiant cooling nanofiber membrane as claimed in claim 1 in cooling covers for buildings and textiles.

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