Radiation refrigeration fiber membrane as well as preparation method and application thereof

Abstract

The invention discloses a radiation refrigeration fiber membrane as well as a preparation method and application thereof. The fiber membrane comprises the following components: a polylactic acid-perfluoropolyether block copolymer, fluoroalkylated silicon dioxide and aluminum oxide in a mass ratio of 1.0: (0.05-0.50): (0.05-0.10). Fluorinated components are introduced to the surfaces of a polymer matrix and inorganic filler particles through chemical bonding, so that the radiation refrigeration performance of the composite material is improved and strengthened, the composite material is endowed with a super-hydrophobic function, the anti-pollution capacity of the material is improved, and the material can effectively bear long-term exposure in the sun and resist ultraviolet radiation damage; the scheme that the matrix and the inorganic filler are subjected to fluorination modification at the same time also overcomes the defect that the mechanical property of the composite material is insufficient due to poor compatibility of the two components; the fiber membrane is prepared through an electrostatic spinning method, the problem that a coating in a traditional coating material is prone to failure and damage is solved, and the service life of the composite material is prolonged.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of functional materials, and more particularly relates to a radiative cooling fiber membrane, a preparation method and application thereof. BACKGROUND

[0002] When an object contacts the external environment, it is often easy to adhere to dust, rainwater, fog and the like. The above substances have strong absorption of thermal infrared light, which reduces the infrared transmittance of infrared window lenses and the like to some extent. At the same time, because the refractive index of water (~1.33) is different from that of air (~1), if the surface is wet, the reflectivity of incident sunlight may be reduced, such as mirror reflection to diffuse reflection, increasing light and heat absorption. Therefore, the influence of the surface cleanliness of the radiative cooler on the radiative cooling performance cannot be ignored.

[0003] To enhance the outdoor application characteristics of the radiative cooling material, the super-hydrophobic function with self-cleaning effect is combined with the radiative cooling material, which can effectively prevent particles from depositing on the surface. The hydrophobic surface can wash away dust, particle pollutants and the like by rainwater, avoiding shielding the radiation channel or increasing heat absorption. Giving the material super-hydrophobic function can prevent pollutants from adhering to cause attenuation of spectral characteristics, which can effectively prolong the service life. In terms of preparation method, the following two strategies are generally adopted: (1) constructing a material surface with micro-nano physical structure by sol-gel method, spraying, spin coating, electrospinning, template method or chemical etching; (2) using fluoralkylation as a chemical composition to reduce the surface energy of the material and enhance the hydrophobicity.

[0004] However, the reported radiative cooling composite materials still have deficiencies, which limits the industrialized preparation and wide application of such materials. For example: (1) spraying a fluorine-containing nanoparticle or polymer dispersion liquid to the surface of a substrate can form a physical adsorption or mechanical interlocking coating, which is simple in process, but the coating is prone to uneven thickness or particle agglomeration due to the influence of the spraying process, and the weak interaction between the materials in the coating makes the materials prone to failure due to friction or solvent erosion during service. (2) Although the use of resin adhesives in traditional coating processes can enhance the interfacial bonding force, the densification tendency not only inhibits the formation of porous structures, but also hinders the functional distribution of inorganic nanomaterials introduced by the strong interfacial interaction of the composite material, greatly reducing the reflectivity in the solar spectrum band. In addition, the volume shrinkage during the curing process of the resin may cause micro-cracks, further damaging the structural integrity of the coating. (3) The mechanical properties and durability of the composite radiative cooling material are key indicators, and external humidity, temperature fluctuations and ultraviolet radiation may accelerate the degradation of the coating, affecting the service life of the composite material. SUMMARY

[0005] The purpose of the present application is to provide a radiation refrigeration fiber film, its preparation method and application, which introduces fluorinated components on the surface of inorganic filler particles and polymer matrix PLA through chemical bonding, enhances and strengthens the radiation refrigeration performance of the composite material, gives the composite material super-hydrophobic function, improves the anti-pollution ability of the material, and enables the modified material to effectively withstand long-term exposure to sunlight and resist ultraviolet radiation damage.

[0006] To achieve the above purpose, the present application is realized by the following technical scheme: In a first aspect, the present application provides a radiation refrigeration fiber film, the components of the fiber film including polylactic acid-perfluoropolyether block copolymer (PLA-PFPE), fluorinated silica and aluminum oxide; the mass ratio of the polylactic acid-perfluoropolyether block copolymer, fluorinated silica and aluminum oxide is 1.0:(0.05~0.50):(0.05~0.10). b

[0007] In a second aspect, the present application further provides a preparation method of the radiation refrigeration fiber film of the first aspect, characterized in that it comprises: Synthesizing polylactic acid-perfluoropolyether block copolymer from perfluoropolyether carboxylic acid, carboxyl activator and polylactic acid; Preparation of fluorinated silica by modifying silica particles with perfluoroalkyl silane coupling agent; Blending the polylactic acid-perfluoropolyether block copolymer, fluorinated silica and aluminum oxide in an organic solvent to obtain a precursor solution; Electrospinning the precursor solution to obtain the radiation refrigeration fiber film.

[0008] Further, the carboxyl activator is N,N-carbonyldiimidazole; the synthesis of polylactic acid-perfluoropolyether block copolymer from perfluoropolyether carboxylic acid, carboxyl activator and polylactic acid comprises: Mixing perfluoropolyether carboxylic acid, 1,3-bistrifluoromethylbenzene and N,N-carbonyldiimidazole, reacting at room temperature, then adding polylactic acid solution, heating to 40℃~100℃, and then incubating to synthesize polylactic acid-perfluoropolyether block copolymer. Further preferably, the temperature after heating is 50℃~70℃.

[0009] Further, the perfluoropolyether carboxylic acid, 1,3-bistrifluoromethylbenzene and N,N-carbonyldiimidazole are reacted at room temperature for 1h~12h; the incubation time is 1h~12h; further preferably, the room temperature reaction time is 2h~5h, and the incubation time is 5h~8h.

[0010] ​Further, the method for collecting the product after the heat preservation reaction ends comprises: removing the reaction byproducts by filtration, and then performing precipitation, washing, and vacuum drying to obtain the reaction product, polylactic acid-perfluoropolyether block copolymer.

[0011] Specifically, after the reaction ends, the byproduct imidazole is removed by filtration while hot, the filtrate is added into methanol, the white powder product is precipitated, isopropyl alcohol is added for washing to remove unreacted substances, and the white solid product, polylactic acid-perfluoropolyether block copolymer, is obtained by vacuum drying at 50℃.

[0012] Further, the perfluoroalkyl silane coupling agent is any one of heptadecafluorodecyltrimethoxysilane, heptadecafluorodecyltriethoxysilane, tridecafluorooctyltrimethoxysilane, tridecafluorooctyltriethoxysilane, nonafluorohexyltrimethoxysilane, and nonafluorohexyltriethoxysilane.

[0013] The perfluoroalkyl silane coupling agent with different carbon chain lengths is used to treat the silica in the application, and the alkoxyl group contained in the silane coupling agent is easy to react with the hydroxyl group on the surface of the silica particles during the treatment, so that chemical bonding is achieved, thereby obtaining stable fluoralkyl-modified silica. The perfluoroalkyl functional group carbon chain length of the perfluoroalkyl silane coupling agent used in the application is 8, 6, or 4, and the perfluoroalkyl group is bonded to the silicon atom through an ethylene group (-CH2CH2). When the perfluoroalkyl carbon chain length is 8, the fluorine content is high, and the mid-infrared absorption effect is excellent. Although the performance of the perfluoroalkyl with carbon chain lengths of 6 and 4 is not as good as that of the perfluoroalkyl group, they are easy to degrade and have low biological toxicity, and therefore are widely used in the field of fluorine-containing materials at present.

[0014] Further, the silica particles are prepared by a sol-gel method.

[0015] Further, the sol-gel method (Stöber method) refers to preparing monodisperse, size-controllable spherical silica particles by ammonia catalysis of tetraethyl orthosilicate hydrolysis and condensation in an alcohol-water mixed solvent. The preferred specific preparation method of the application is: ammonia water is added into isopropyl alcohol, the pH is adjusted to 9-11, and then stirred uniformly, and then tetraethyl orthosilicate is added dropwise, and the reaction is performed at 40-50℃ for 5-8h.

[0016] Further, the mass ratio of the perfluoroalkyl silane coupling agent to the silica particles is 1: (3-100); and preferably, the mass ratio is 1: (10-30).

[0017] Further, the preparation of fluoralkylated silica by modifying the silica particles with the perfluoroalkyl silane coupling agent comprises: The perfluoroalkyl silane coupling agent is dissolved and added into a reaction system for preparing the silica particles, and the reaction is carried out at a temperature of 50-100 DEG C, and the fluorinated silica is prepared after the reaction is completed. Further preferably, the reaction temperature is 70-90 DEG C. After the reaction is completed, the product is collected by filtering the solid powder product, washing with ethanol and deionized water, and drying to obtain the fluorinated silica microspheres.

[0018] Further, the organic solvent for preparing the precursor solution is hexafluoroisopropanol; and after the blending to obtain a uniformly dispersed suspension, ultrasonic is used to remove air bubbles.

[0019] Further, the electrospinning parameters can be set as follows: a voltage of 6-20 kV, a flow rate of 0.1-3.0 mL / h, a receiving distance of 10-25 cm, and an ambient humidity of 50-60%; preferably, the voltage is 8 kV, the flow rate is 0.3 mL / h, and the receiving distance is 18 cm.

[0020] In a third aspect, the application further provides a use of the radiation refrigeration fiber film in a heat management material; the heat management material includes a tent, a car cover, an outdoor tarpaulin, or an outdoor packaging material, etc.

[0021] Compared with the prior art, the application has the following beneficial effects: The radiation refrigeration fiber film is modified by chemically bonding fluorinated components on the surfaces of the polymer matrix PLA and the inorganic filler particles, and the C-F introduced by the fluorinated modification of the composite material has strong stretching vibration at 7.35-10 µm, which gives the nanofiber film high emissivity in this wavelength range; while improving and strengthening the radiation refrigeration performance of the composite material, the composite material is also given super-hydrophobic function to improve the anti-pollution ability of the material, so that the material can effectively withstand long-term exposure to sunlight and resist ultraviolet radiation damage; the scheme of simultaneously fluorinating the matrix PLA and the inorganic filler silica also overcomes the defect of poor mechanical properties of the composite material caused by poor compatibility of the two components; the fiber film is prepared by electrospinning, which avoids the problem of easy failure and damage of the coating in traditional coating materials, and prolongs the service life of the composite material. The preparation method uses perfluoropolyether carboxylic acid (PFPE-COOH) as a modifier, and after activation by N,N-carbonyl diimidazole (CDI), the PFPE-COOH reacts with PLA to introduce a perfluoropolyether block into the macromolecular chain end of polylactic acid, to prepare a hydrophobic block copolymer PLA- b The Stöber method is used to prepare a series of silica particles with controllable particle sizes, and the silica is modified by a perfluoroalkyl silane coupling agent; the fluorine alkyl-modified silica, alumina, and the block copolymer PLA- bPFPE blending, using one-step electrospinning method, prepared uniform PLA- b PFPE / F-SiO2 / Al2O3 nanofiber membrane; realize structure-function integration preparation, simple and controllable process; Using fluorination modification technical scheme, the PLA- b The PFPE / F-SiO2 / Al2O3 fiber membrane has high selective emissivity of 96.73% in the 3-25 mu m wave band, and the weighted average reflectivity of 95.89% in the 0.3-2.5 mu m wave band; the simulated calculation night theoretical refrigeration power reaches 111.97 W / m 2 , and the daytime theoretical refrigeration power reaches 101.35 W / m 2 ; in the indoor simulated sunlight temperature measurement performance test, when the light power density is 1 Sun, the temperature difference between the sample and the bare blank group reaches 3.4 DEG C; Using fluorination modification technical scheme, the composite fiber membrane prepared by the application has a high static contact angle to water, which is more than 150 DEG; through dynamic water repellency and water droplet rolling test, it is found that even if the liquid droplet is squeezed or stretched to deformation on the surface of the fiber membrane, it will not remain on the surface of the fiber membrane; at a very low inclination angle, the liquid droplet can easily slide off the surface of the fiber membrane, and the material has self-cleaning and anti-staining properties; various aqueous solutions can maintain spherical droplets on the surface of the fiber membrane, and the material is suitable for a wide range of application scenarios. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The poly lactic acid-perfluoropolyether block copolymer PLA- b The synthesis route of PFPE; Figure 2 The chemical structure and element characterization of the poly lactic acid-perfluoropolyether block copolymer prepared in the embodiment one of the application, wherein: (a) is FT-IR; (b) is 19F NMR; (c) is high-resolution C 1s; (d) is high-resolution O 1s; (e) is high-resolution F 1s; (f) is total spectrum; Figure 3 The raw materials and product characterization of the fluorinated alkylated silica prepared in the embodiment one of the application, wherein: (a) is the SEM and TEM of the unmodified inorganic filler SiO2; (b) is the SEM and TEM of the fluorinated alkylated silica F-SiO2; (c) is the particle size distribution of the fluorinated alkylated silica F-SiO2; (d) is the FT-IR of the unmodified SiO2 and the fluorinated alkylated silica F-SiO2; Figure 4 The fluorinated modified composite nanofiber membrane PLA- b XPS spectrum of PFPE / F-SiO2 / Al2O3; Figure 5 EDS spectrum of the fluorinated modified composite nanofiber membrane PLA- b -PFPE / F-SiO2 / Al2O3 prepared in Example One of the present application; Figure 6 Comparison of liquid repellency of the fluorinated modified composite nanofiber membrane prepared in Example One of the present application and the fluorinated polylactic acid fiber membrane prepared in Comparative Example Three, wherein: (a) is the different liquids contacted in the liquid repellency test of the fluorinated modified composite nanofiber membrane prepared in Example One; (b) is the repellent performance of the fluorinated modified composite nanofiber membrane prepared in Example One to different liquids; (c) is the comparison of the water contact angle of the fluorinated polylactic acid fiber membrane prepared in Comparative Example Three and the fluorinated modified composite nanofiber membrane prepared in Example One; Figure 7 Self-cleaning process of solid pollutants methylene blue powder and chalk powder on the surface of the fluorinated modified composite nanofiber membrane prepared in Example One of the present application; Figure 8 Solar spectrum comparison chart of the fluorinated modified composite nanofiber membrane prepared in Example One of the present application and the composite fiber membranes prepared in Comparative Example One and Comparative Example Two; Figure 9 Cooling power of the fluorinated modified composite nanofiber membrane prepared in Example One of the present application, wherein: (a) the solar irradiance is 0 W / m 2 , (b) the solar irradiance is 600 W / m 2 ; Figure 10 Outdoor radiation refrigeration performance test comparison of the fluorinated modified composite nanofiber membrane prepared in Example One of the present application, the composite fiber membrane prepared in Comparative Example Two and the fluorinated polylactic acid fiber membrane prepared in Comparative Example Three, wherein: (a) is the real-time temperature; (b) is the real-time humidity and heat index inside the model; (c) is the infrared imaging chart. DETAILED DESCRIPTION

[0023] The present application provides a radiation refrigeration fiber membrane, and the preparation method comprises the following steps: taking perfluoropolyether carboxylic acid (PFPE-COOH) as a modifier, activating with N,N-carbonyl diimidazole (CDI), and then performing esterification reaction with PLA to introduce perfluoropolyether blocks into the end of the polylactic acid macromolecular chain to prepare a hydrophobic block copolymer PLA- b -PFPE; a series of silica with controllable particle size is prepared by Stöber method, and the silica is modified by perfluoroalkyl silane coupling agent; the modified silica is blended with alumina and the block copolymer PLA- b -PFPE to prepare a uniform PLA- bPFPE / F-SiO2 / Al2O3 electrospun membrane.

[0024] The test method used in the present application is as follows: Fiber membrane reflectivity test: The reflectivity of the fiber membrane was tested by UV-VIS-NIR spectrophotometer with an integrating sphere. First, a standard white PTFE board was used to calibrate 100% reflectivity. A reflectivity higher than 100% indicates a reflectivity higher than the standard white board. The test wavelength range was 0.2-2.5 μm, and the test interval was 2 nm.

[0025] Fiber membrane emissivity characterization: The emissivity of the sample film was tested by FTIR with an integrating sphere. According to Kirchhoff's law, the absorptivity of an object in thermal equilibrium is equal to the emissivity. Since the white sample has a certain thickness, the transmittance can be ignored, so the formula ε(λ)=1- ρ(λ)- τ(λ) can be used. Where ε(λ) is the emissivity, ρ(λ) is the reflectivity, and τ(λ) is the zero transmittance. The test wavelength range was 2.5-25 μm, and the test interval was 5 nm.

[0026] The present application provides a radiation cooling fiber membrane, which is a fluorinated modified composite nanofiber membrane, specifically a fluorinated polylactic acid (polylactic acid-perfluoropolyether block copolymer)-fluoroalkylated silica-alumina composite nanofiber membrane, whose synthesis route is as shown in Figure 1 wherein m=900~1300, preferably m is 1000~1100; n=10~200, preferably n is 20~50.

[0027] The preferred embodiments of the present application will be described in more detail below with reference to the accompanying drawings and specific examples.

[0028] Example 1: The present embodiment provides a fluorinated polylactic acid-fluoroalkylated silica-alumina composite nanofiber membrane, and its preparation method comprises the following steps: (1) Synthesis of polylactic acid-perfluoropolyether block copolymer 80.0 g of PLA was fully dissolved in 60 mL of a mixed solvent prepared from 1,3-bistrifluoromethylbenzene and 120 mL of hexafluoroisopropanol, and stirred to fully dissolve. Under nitrogen protection, 37.5 g of perfluoropolyether carboxylic acid and 50 mL of 1,3-bistrifluoromethylbenzene were placed in a three-necked flask, and 1.5 g of tetrabutylammonium bromide was added under stirring. The mixture was heated to 80°C and stirred for 24 hours. The reaction solution was cooled to room temperature and filtered to obtain a white solid. The white solid was dissolved in 60 mL of 1,3-bistrifluoromethylbenzene, and 120 mL of hexafluoroisopropanol was added. The mixture was heated to 80°C and stirred for 24 hours. The reaction solution was cooled to room temperature and filtered to obtain a white solid. N,N-Carbonyl diimidazole (CDI) was reacted at room temperature for 3 h, followed by the addition of pre-dissolved PLA to the reaction system. The temperature was raised to 60 °C and maintained for 6 h. After the reaction was completed, the byproduct imidazole was removed by hot filtration. The filtrate was added to 550 mL of methanol, precipitating a white powdery product. Unreacted matter was removed by washing with 120 mL of isopropanol, and the product was dried under vacuum at 50 °C to obtain a white solid product, polylactic acid-perfluoropolyether block copolymer PLA- b -PFPE, the number-average molecular weight of the product was 72406 as determined by gel permeation chromatography (GPC).

[0029] The polylactic acid-perfluoropolyether block copolymer PLA- prepared in this step b Structural characterization of PFPE is as follows: Figure 2 As shown. Figure 2 In the image, (a) shows the results of characterizing the product using Fourier transform infrared spectroscopy (FTIR), PLA- b -PFPE at 1049 cm -1 1137 cm -1 A characteristic absorption peak belonging to CF appeared at 1750 cm⁻¹. -1 The characteristic peaks belong to PLA- b (a) The C=O double bond in the ester group of -PFPE indicates successful esterification; (b) The curve in the fluorine NMR spectrum shows two characteristic peaks, where the peak at -81.87 ppm represents the chemical shift of the fluorine atom on the -CF3- at the end of the molecular chain, while the low peak at -81.16 ppm represents the chemical shift of the fluorine atom on -CF2-; (c) In the C 1s narrow spectrum scan results, the C1s peak near 284.78 eV belongs to CC / CH, the characteristic peak near 287.08 eV belongs to CO, the characteristic peak near 289.08 eV belongs to C=O, and the characteristic peak at 293.08 eV is the CF of the perfluorinated segment; (d) The high-resolution O 1s region fitting results show two peaks: C=O (535.98 eV) and CO (532.98 eV); (e) The F 1s region shows FC (688.98 eV). (eV) is present; (f) shows the presence of signal peaks C1s, O 1s and F 1s in the full XPS spectrum.

[0030] (2) Preparation of fluoroalkyl modified silica particles 12.0 g of ammonia was added to 80 mL of isopropanol, and the pH was adjusted to 9-11. The mixture was then stirred vigorously for 30 min. Next, 18.1 g of tetraethyl orthosilicate (TEOS) was slowly added dropwise, and the mixture was reacted at 40 °C for 6 h. Then, a solution of 0.5 g of heptadecafluorodecyltrimethoxysilane dissolved in 5 mL of isopropanol was added dropwise, and the mixture was heated to 80 °C and reacted for 2 h. After the reaction was complete, the solid powder product was collected by filtration, washed once each with 25 mL of ethanol and deionized water, and dried to obtain fluoroalkylated silica microspheres, labeled F-SiO2.

[0031] Fluoroalkylated silica was characterized by FT-IR, SEM, and TEM, and the results are as follows: Figure 3 As shown in the figures. From (a) and (b), it can be seen from the high-resolution SEM and TEM images of SiO2 nanoparticles before and after fluoroalkylation modification that the boundaries of the SiO2 nanoparticles change from clear before modification to blurred after modification; from (d), it can be seen that Si-O-Si (1129 cm⁻¹) -1 The characteristic absorption band shared by both is 2710 cm⁻¹ in the infrared curve of F-SiO₂. -1 and 2810 cm -1 The characteristic peak at 1350 cm⁻¹ can be attributed to -CH₂. -1 and 1390 cm -1 The characteristic peak at that point is attributed to the stretching vibration of the CF bond.

[0032] (3) Electrospinning to prepare fiber membranes 1.2g PLA- b -PFPE, 3.0g F-SiO2 and 0.5g Al2O3 were added to 5.3g hexafluoroisopropanol and stirred thoroughly at room temperature to prepare a uniformly dispersed suspension. The suspension was then sonicated for 30 min to remove bubbles, thus obtaining the precursor solution.

[0033] Nanofiber membranes were prepared by electrospinning a precursor solution using an electrospinning apparatus. The electrospinning parameters were set as follows: voltage 8 kV, flow rate 0.3 mL / h, receiving distance 18 cm, and ambient humidity 50%-60%. Fluorinated modified composite nanofiber membranes (PLA-) were successfully prepared. b -PFPE / F-SiO2 / Al2O3. EDS energy dispersive spectroscopy results indicate that the surface of this fiber membrane contains three elements: C, O, and F, with percentage contents of 71.20%, 25.46%, and 3.32%, respectively.

[0034] The high-resolution elemental spectrum of the fluorinated modified composite nanofiber membrane prepared in this embodiment is shown below. Figure 4As shown in the figure, the C 1s region can be decomposed into CF (291.30 eV), C=O (289.03 eV), CO (286.46 eV), and CC (284.78 eV). The O 1s region mainly consists of three peaks: Si-O-Si (532.50 eV), C=O (533.50 eV), and CO (531.82 eV). The high-resolution Si 2p spectrum consists of two peaks at 103.70 eV and 101.52 eV, corresponding to Si-O-Si and Si-C, respectively. The peak at 75.12 eV in the high-resolution Al 2p spectrum corresponds to Al-O. Notably, FC (688.68 eV) can be observed in the F 1s region.

[0035] This embodiment also performed EDS energy dispersive spectroscopy and elemental analysis on the prepared fluorinated modified composite nanofiber membrane, and the results are as follows: Figure 5 As shown, the composite fiber membrane contains four elements: C, O, Si, and F, which is consistent with the XPS results.

[0036] This embodiment also conducted liquid-based tests on the prepared fluorinated modified composite nanofiber membrane and measured the water contact angle, such as... Figure 6 As shown in Figure (a), liquids such as coffee, acidic water, alkaline water, tea, milk, and water were dropped onto the surface of the composite fiber membrane. As shown in Figure (b), these liquids all remained as spherical droplets on the surface of the fluorinated modified composite nanofiber membrane and could maintain this state for a relatively long time, exhibiting good liquid repellency. As shown in Figure (c), the fluorinated modified fiber membrane PLA- prepared in this embodiment was measured to be... b The contact angle between -PFPE / F-SiO2 / Al2O3 and water is 154.9°±1.2°.

[0037] like Figure 7 As shown, using methylene blue powder and chalk dust as reference samples of contaminants, the sample membrane of the fluorinated modified composite nanofiber membrane was fixed on the surface of a glass slide with double-sided adhesive and placed at an 8° angle. As water droplets fell, the contaminants distributed on the sample were carried away from the sample surface by the rolling water droplets without leaving stains, proving that the fluorinated modified composite nanofiber membrane prepared in this embodiment has excellent self-cleaning properties.

[0038] Figure 8 The fluorinated modified composite nanofiber membrane PLA prepared in this embodiment was measured. bThe weighted average reflectance of -PFPE / F-SiO2 / Al2O3 in the solar band is 98.23%, the weighted emissivity across the entire band is 95.89%, and the weighted emissivity in the 8-13 μm range is 96.73%, which meets the requirements for radiation cooling materials. In addition, the emissivity of the fluorinated modified composite nanofiber membrane prepared in this embodiment at 7-10 μm is higher than that of the unfluorinated modified composite fiber membrane PLA / SiO2 / Al2O3, and the emissivity also reaches more than 95%, which proves that the fluorinated sample has excellent radiation cooling performance.

[0039] The radiative cooling power curve of the fluorinated modified composite nanofiber membrane prepared in this embodiment is shown in the figure below. Figure 9 As shown in the figure, the net radiative cooling power of the fluorinated modified composite nanofiber membrane is approximately 111.97 W / m. 2 (0 W / m) 2 ), 101.335 W / m 2 (600 W / m) 2 ).

[0040] Example 2:

[0041] This embodiment provides a fluorinated polylactic acid-fluoroalkylated silica-alumina composite nanofiber membrane, the preparation method of which includes the following steps: (1) Synthesis of polylactic acid-perfluoropolyether block copolymer Dissolve 80.0 g of PLA completely in a mixed solvent prepared with 60 mL of 1,3-bis(trifluoromethylbenzene) and 120 mL of hexafluoroisopropanol, stirring until fully dissolved. Under nitrogen protection, place 37.5 g of perfluoropolyether carboxylic acid and 50 mL of 1,3-bis(trifluoromethylbenzene) in a three-necked flask, and add 1.5 g of [amount missing] while stirring. N,N - Carbonyl diimidazole (CDI) was reacted at room temperature for 3 h, followed by the addition of pre-dissolved PLA to the reaction system. The temperature was raised to 50 °C and maintained for 6 h. After the reaction was completed, the byproduct imidazole was removed by hot filtration. The filtrate was added to 550 mL of methanol, precipitating a white powdery product. Unreacted matter was removed by washing with 120 mL of isopropanol, and the product was dried under vacuum at 50 °C to obtain a white solid product, polylactic acid-perfluoropolyether block copolymer PLA- b -PFPE.

[0042] (2) Preparation of fluoroalkyl modified silica particles 12.0 g of ammonia was added to 80 mL of isopropanol, and the pH was adjusted to 9-11. The mixture was then stirred vigorously for 30 min. Next, 18.1 g of tetraethyl orthosilicate (TEOS) was slowly added dropwise, and the mixture was reacted at 40 °C for 6 h. Then, a solution of 0.5 g of tridecafluorooctyltriethoxysilane dissolved in 5 mL of isopropanol was added dropwise, and the mixture was heated to 80 °C and reacted for 2 h. After the reaction was complete, the solid powder product was collected by filtration, washed once each with 25 mL of ethanol and deionized water, and dried to obtain fluoroalkylated silica microspheres.

[0043] (3) Electrospinning to prepare fiber membranes Same as Example 1.

[0044] The EDS energy dispersive spectroscopy test results indicate that the fluorinated modified composite nanofiber membrane prepared in this embodiment contains three elements: C, O and F, with the percentage contents of each element being 70.58%, 25.57% and 3.83%, respectively.

[0045] The water contact angle of the fiber membrane prepared in this embodiment was measured to be 160.1° ± 1.1°, indicating that the fiber membrane is superhydrophobic and possesses excellent self-cleaning properties. The weighted average reflectance of the fiber membrane prepared in this embodiment was measured to be 97.62% across the entire solar spectrum, the weighted emissivity across the entire spectrum was 95.78%, and the weighted emissivity in the 8-13 μm range was 96.23%. The product exhibits excellent radiative cooling performance, with a net radiative cooling power of approximately 111.45 W / m². 2 (0 W / m) 2 ), 101.09 W / m 2 (600 W / m) 2 ).

[0046] Example 3: This embodiment provides a fluorinated polylactic acid-fluoroalkylated silica-alumina composite nanofiber membrane, the preparation method of which includes the following steps: (1) Synthesis of polylactic acid-perfluoropolyether block copolymer Dissolve 80.0 g of PLA completely in a mixed solvent prepared with 60 mL of 1,3-bis(trifluoromethylbenzene) and 120 mL of hexafluoroisopropanol, stirring until fully dissolved. Under nitrogen protection, place 37.5 g of perfluoropolyether carboxylic acid and 50 mL of 1,3-bis(trifluoromethylbenzene) in a three-necked flask, and add 1.5 g of [amount missing] while stirring. N,N-Carbonyl diimidazole (CDI) was reacted at room temperature for 3 h, followed by the addition of pre-dissolved PLA to the reaction system. The temperature was raised to 60 °C and maintained for 6 h. After the reaction was completed, the byproduct imidazole was removed by hot filtration. The filtrate was added to 550 mL of methanol, precipitating a white powdery product. Unreacted matter was removed by washing with 120 mL of isopropanol, and the product was dried under vacuum at 50 °C to obtain a white solid product, polylactic acid-perfluoropolyether block copolymer PLA- b -PFPE.

[0047] (2) Preparation of fluoroalkyl modified silica particles 12.0 g of ammonia was added to 80 mL of isopropanol, and the pH was adjusted to 9-11. The mixture was then stirred vigorously for 30 min. Next, 18.1 g of tetraethyl orthosilicate (TEOS) was slowly added dropwise, and the mixture was reacted at 40 °C for 6 h. Then, a solution of 0.5 g of nonafluorohexyltriethoxysilane dissolved in 5 mL of isopropanol was added dropwise, and the mixture was heated to 80 °C and reacted for 2 h. After the reaction was complete, the solid powder product was collected by filtration, washed once each with 25 mL of ethanol and deionized water, and dried to obtain fluoroalkylated silica microspheres.

[0048] (3) Electrospinning to prepare fiber membranes Same as Example 1.

[0049] The EDS energy dispersive spectroscopy test results indicate that the fluorinated modified composite nanofiber membrane prepared in this embodiment contains three elements: C, O and F, with the percentage contents of each element being 70.70%, 25.43% and 3.85%, respectively.

[0050] The water contact angle of the fiber membrane prepared in this embodiment was measured to be 158.1° ± 1.6°, indicating that the fiber membrane is superhydrophobic and possesses excellent self-cleaning properties. The weighted average reflectance of the fiber membrane in the solar radiation band is 95.46%, the weighted emissivity across the entire wavelength band is 95.98%, and the weighted emissivity in the 8-13 μm range is 96.10%. The product exhibits excellent radiative cooling performance, with a net radiative cooling power of approximately 110.21 W / m². 2 (0 W / m) 2 ), 100.88 W / m 2 (600 W / m) 2 ).

[0051] Comparative Example 1: Polylactic acid-silica-alumina composite fiber membrane This comparative example provides a composite fiber membrane whose main components are polylactic acid, silica, and alumina. Its preparation method includes the following steps: (1) Preparation of silica particles 12.0 g of ammonia was added to 80 mL of isopropanol, and the pH was adjusted to 9-11. The mixture was then stirred vigorously for 30 min. Next, 18.1 g of tetraethyl orthosilicate (TEOS) was slowly added dropwise. The mixture was reacted at 40 °C for 8 h, followed by ripening at 80 °C for 2 h. After the reaction was complete, the solid powder product was collected by filtration, washed once each with 25 mL of ethanol and deionized water, and dried to obtain silica microspheres.

[0052] (2) Preparation of fiber membranes by electrospinning 1.2 g of polylactic acid, 3.0 g of silica microspheres, and 0.5 g of Al₂O₃ were added to 5.3 g of hexafluoroisopropanol and stirred thoroughly at room temperature to prepare a uniformly dispersed suspension. The suspension was then sonicated for 30 min to remove air bubbles, yielding a precursor solution. Nanofiber membranes were prepared by electrospinning the precursor solution using an electrospinning apparatus. The electrospinning parameters were set as follows: voltage 8 kV, flow rate 0.3 mL / h, receiving distance 18 cm, and ambient humidity 50%-60%. This resulted in the fabrication of a composite fiber membrane.

[0053] The fiber membrane prepared in this comparative example was found to be hydrophilic, with water droplets quickly wetting it upon contact. The weighted average reflectance of the fiber membrane across the entire solar spectrum was 71.62%, the weighted emissivity across the entire spectrum was 80.19%, and the weighted emissivity in the 8-13 μm range was 69.15%. Figure 8 As shown, the product's radiative cooling performance is poor, with a net radiative cooling power of approximately 81.09 W / m². 2 (0 W / m) 2 ), 70.76W / m 2 (600 W / m) 2 ).

[0054] Comparative Example 2: Fluorinated polylactic acid-silica-alumina composite fiber membrane This comparative example provides a composite fiber membrane whose main components are fluorinated polylactic acid, silica, and alumina. Its preparation method includes the following steps: (1) Synthesis of polylactic acid-perfluoropolyether block copolymer Same as Example 1.

[0055] (2) Preparation of silica particles Same as Comparative Example 1.

[0056] (3) Electrospinning to prepare fiber membranes 1.2g of polylactic acid-perfluoropolyether block copolymer PLA- bPFPE, 3.0 g of silica microspheres, and 0.5 g of Al2O3 were added to 5.3 g of hexafluoroisopropanol and stirred thoroughly at room temperature to prepare a uniformly dispersed suspension. The suspension was then sonicated for 30 min to remove air bubbles, yielding a precursor solution. Nanofiber membranes were prepared by electrospinning the precursor solution using an electrospinning apparatus. The electrospinning parameters were set as follows: voltage 8 kV, flow rate 0.3 mL / h, receiving distance 18 cm, and ambient humidity 50%-60%. This resulted in the fabrication of a composite fiber membrane.

[0057] The contact angle of the composite fiber membrane prepared in this comparative example with water was measured to be 142.9°±1.0°, indicating that the fiber membrane is hydrophobic. The weighted average reflectance of the fiber membrane in the solar light band was 83.28%, the weighted emissivity across the entire wavelength range was 85.11%, and the weighted emissivity in the 8-13 μm range was 76.03%. Figure 8 As shown; the product's radiative cooling performance is poor, with a net radiative cooling power of approximately 89.18 W / m². 2 (0 W / m) 2 ), 75.32W / m 2 (600 W / m) 2 ).

[0058] Comparative Example 3: Pure fluorinated polylactic acid fiber membrane This comparative example provides a fiber membrane whose main component is fluorinated polylactic acid, and its preparation method includes the following steps: (1) Synthesis of polylactic acid-perfluoropolyether block copolymer Same as Example 1.

[0059] (2) Preparation of fiber membranes by electrospinning 1.2 g of polylactic acid-perfluoropolyether block copolymer PLA-b-PFPE was dissolved in 4.0 g of hexafluoroisopropanol and stirred thoroughly at room temperature to prepare a uniformly dispersed suspension. The suspension was then sonicated for 30 min to remove air bubbles, yielding a precursor solution. Nanofiber membranes were prepared by electrospinning the precursor solution using an electrospinning apparatus. The electrospinning parameters were set as follows: voltage 8 kV, flow rate 0.3 mL / h, receiving distance 18 cm, and ambient humidity 50%-60%. Fluorinated polylactic acid nanofiber membranes were thus obtained.

[0060] The contact angle of the sample prepared in this comparative example with water was measured to be 135.2° ± 1.3°. Figure 6 As shown, the fiber membrane is hydrophobic, but not superhydrophobic. The weighted average reflectance of the fiber membrane in the solar light band is 55.51%, the weighted emissivity across the entire wavelength range is 52.92%, and the weighted emissivity in the 8-13 μm range is 51.70%. The product's radiative cooling performance is poor, with a net radiative cooling power of approximately 63.32 W / m². 2 (0 W / m)2 ), 61.29W / m 2 (600 W / m) 2 ).

[0061] This invention tested the outdoor radiative cooling performance of the fluorinated polylactic acid-fluoroalkylated silica-alumina composite nanofiber membrane prepared in Example 1, the fluorinated polylactic acid-silica-alumina composite fiber membrane prepared in Comparative Example 2, and the fluorinated polylactic acid fiber membrane prepared in Comparative Example 3. The comparative results are as follows: Figure 10 As shown in the figure, the environmental data collection results indicate that the average solar power is 787 W / m². 2 The average humidity was 17%; compared with the undoped fluorinated polylactic acid fiber membrane PLA of Comparative Example 3. b Compared to PFPE, the fluorinated polylactic acid-silica-alumina composite fiber membrane PLA prepared in Comparative Example 2... b -PFPE / SiO2 / Al2O3 and the fluorinated modified composite nanofiber membrane PLA prepared in Example 1- b The average temperature drop of -PFPE / F-SiO2 / Al2O3 reached 3.0℃ and 5.7℃, respectively, with the highest phase temperature difference reaching 6.5℃ and 8.6℃. During the test, infrared thermal images of different samples were taken using an infrared thermal imager. At the same time, the temperature distribution of PLA was 51.3℃, while that of the fluorinated polylactic acid-silica-alumina composite fiber membrane prepared in Comparative Example 2 was... b -PFPE / SiO2 / Al2O3 and the fluorinated modified composite nanofiber membrane PLA prepared in Example 1- b The fluorinated electrospun films prepared from fluorinated polylactic acid combined with fluorinated alkylated silica exhibit superior radiative cooling performance. The temperatures for fluorinated PFPE / F-SiO2 / Al2O3 were 45.3 ℃ and 42.9 ℃, respectively.

[0062] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and principles of the described embodiments, and these modifications and variations should also be considered within the scope of protection of the present invention.

Claims

1. A radiation-cooled fiber membrane, characterized in that, The fiber membrane comprises polylactic acid-perfluoropolyether block copolymer, fluoroalkylated silica and alumina; the mass ratio of polylactic acid-perfluoropolyether block copolymer, fluoroalkylated silica and alumina is 1.0:(0.05~0.50):(0.05~0.10).

2. A method for preparing the radiation-cooled fiber membrane according to claim 1, characterized in that, include: Polylactic acid-perfluoropolyether block copolymers were synthesized using perfluoropolyether carboxylic acid, carboxyl activator and polylactic acid as raw materials; Fluoroalkylated silica was prepared by modifying silica particles with a perfluoroalkylsilane coupling agent. The polylactic acid-perfluoropolyether block copolymer, the fluoroalkylated silica and alumina are added to an organic solvent and blended to obtain a precursor solution; The radiation-cooling fiber membrane was prepared by electrospinning the precursor solution.

3. The method for preparing the radiation-cooled fiber membrane according to claim 2, characterized in that, The carboxyl activator is N,N-carbonyldiimidazole; The synthesis of polylactic acid-perfluoropolyether block copolymers using perfluoropolyether carboxylic acid, carboxyl activator, and polylactic acid as raw materials includes: Perfluoropolyether carboxylic acid, 1,3-bis(trifluoromethylbenzene) and N,N-carbonyldiimidazole were mixed and reacted at room temperature. Then, polylactic acid solution was added, and the temperature was raised to 40℃~100℃ and kept at that temperature to synthesize polylactic acid-perfluoropolyether block copolymer.

4. The method for preparing the radiation-cooled fiber membrane according to claim 3, characterized in that, The perfluoropolyether carboxylic acid, 1,3-bis(trifluoromethylbenzene) and N,N-carbonyldiimidazole are reacted at room temperature for 1 h to 12 h; the heat treatment time is 1 h to 12 h.

5. The method for preparing a radiation-cooled fiber membrane according to claim 2, characterized in that, The perfluoroalkyl silane coupling agent is any one of heptadecafluorodecyltrimethoxysilane, heptadecafluorodecyltriethoxysilane, tridecafluorooctyltrimethoxysilane, tridecafluorooctyltriethoxysilane, nonafluorohexyltrimethoxysilane, and nonafluorohexyltriethoxysilane.

6. The method for preparing a radiation-cooled fiber membrane according to claim 2, characterized in that, The silica particles were prepared by the sol-gel method.

7. The method for preparing a radiation-cooled fiber membrane according to claim 2, characterized in that, The mass ratio of the perfluoroalkylsilane coupling agent to the silica particles is 1:(3~100).

8. The method for preparing a radiation-cooled fiber membrane according to claim 2, characterized in that, The preparation of fluoroalkylated silica by modifying silica particles with a perfluoroalkylsilane coupling agent includes: The perfluoroalkylsilane coupling agent was dissolved and added to the reaction system for preparing silica particles. The temperature was raised to 50℃~100℃ for reaction. After the reaction was completed, fluoroalkylated silica was obtained.

9. The method for preparing a radiation-cooled fiber membrane according to claim 2, characterized in that, The electrospinning parameters are: voltage 6 kV~20 kV, flow rate 0.1 mL / h~3.0 mL / h, receiving distance 10 cm~25 cm, and ambient humidity 50%-60%.

10. The application of the radiation-cooling fiber membrane according to claim 1 in the preparation of thermal management materials.

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