Ultraviolet-shielding self-cleaning polylactic acid fiber cooling film and preparation method thereof

Abstract

The invention discloses an ultraviolet-shielding self-cleaning polylactic acid fiber cooling film and a preparation method thereof.The preparation method comprises the following steps that S1, UiO-66 porous crystals are prepared, specifically, a zirconium source, an organic acid ligand, a template agent and a solvent A are mixed, and the UiO-66 porous crystals are prepared through a template induction method; s2, preparing a polylactic acid spinning solution: dissolving polylactic acid in a solvent B to obtain the polylactic acid spinning solution; s3, a UiO-66 dispersion liquid is prepared, wherein UiO-66 is dissolved in a solvent C, and the UiO-66 dispersion liquid is obtained; s4, preparing a fiber cooling film: preparing the fiber cooling film by adopting an electric centrifugal spinning method, forming a surface light reflection hole through phase change induction, and anchoring UiO-66 on the fiber surface through a gas spraying technology to obtain the ultraviolet shielding self-cleaning polylactic acid fiber cooling film. The polylactic acid fiber cooling film has the advantages of high infrared emissivity, high sunlight reflectivity, excellent radiation refrigeration effect, prominent ultraviolet shielding effect and self-cleaning capability, and wide application prospect and market potential in the fields of heat management and building cooling.

Description

Technical Field

[0001] The invention relates to the field of building cooling and personal thermal management materials, and in particular to an ultraviolet shielding self-cleaning polylactic acid fiber cooling film and a preparation method thereof. Background Art

[0002] Human thermal balance is crucial to health and safety. Mild symptoms may cause dizziness, nausea, and even organ failure, which can be life-threatening. Especially for those who often work outdoors, strong solar radiation not only affects their work efficiency, but also poses a serious threat to their health. Traditional cooling equipment usually uses active cooling to achieve a comfortable temperature for the human body by lowering the indoor ambient temperature, but it has disadvantages such as high energy consumption, high installation and maintenance costs, and environmental pollution. Therefore, a method that can reduce consumption and emissions while being economical is needed. Radiative cooling is a method that achieves cooling by emitting thermal radiation to the sky through the material itself, and does not require the consumption of external energy. It is a method with very broad application prospects.

[0003] Although radiation cooling fiber textiles have been widely studied, the influence of ultraviolet light is an issue that cannot be ignored in practical applications. Ultraviolet light can cause yellowing of the material, reduce the reflectivity and cooling effect of the fiber membrane, and thus affect the long-term performance of the material. Therefore, the preparation of radiation cooling fiber textiles with ultraviolet shielding function has become a top priority. UiO-66, as a typical MOFs material, has high solar reflectivity and high infrared emissivity. Good optical properties and chemical stability give it excellent ultraviolet shielding effect. However, how to effectively combine UiO-66 with fiber materials and maintain its optical properties and chemical stability is still an important challenge in current research.

[0004] In order to solve the problem of fiber aging and cooling performance degradation caused by ultraviolet irradiation, the present invention uses polylactic acid (PLA) and homemade UiO-66 porous crystals as raw materials to prepare a high-performance radiation cooling fiber membrane. The fiber membrane not only has high infrared emissivity, high solar reflectivity and good outdoor cooling effect, but also has good UV shielding and degradability. Due to the simple preparation process, it has broad application prospects in the fields of personal thermal management and building cooling. Summary of the invention

[0005] The purpose of the present invention is to invent high-performance radiant cooling fabrics with UV shielding and self-cleaning functions to meet the needs of personal thermal management and building cooling.

[0006] In order to achieve the above-mentioned purpose, the present invention uses polylactic acid (PLA) and homemade UiO-66 porous crystals as raw materials, prepares a fiber cooling film by electrocentrifugal spinning, utilizes phase change induction to obtain fibers with rich light reflection holes on the surface, and uses gas spray technology to anchor UiO-66 on the fiber surface to obtain a UV-shielding self-cleaning polylactic acid fiber cooling film.

[0007] According to the first aspect of the present invention, a method for preparing a UV-shielding self-cleaning polylactic acid fiber cooling film is provided, comprising the following steps: step S1, preparing UiO-66 porous crystals: uniformly mixing a zirconium source, an organic acid ligand, a template agent, and a solvent A to obtain a mixed solution, transferring the mixed solution to a high-temperature reactor, reacting by a template induction method, and removing the template agent after the reaction to obtain UiO-66 porous crystals; step S2, preparing a polylactic acid spinning solution: dissolving polylactic acid in a solvent B to obtain a polylactic acid spinning solution; step S3, preparing a polylactic acid spinning solution: dissolving polylactic acid in a solvent B to obtain a polylactic acid spinning solution; step S4, preparing a polylactic acid spinning solution: dissolving polylactic acid in a solvent B to obtain a polylactic acid spinning solution; step S5, preparing a polylactic acid spinning solution: dissolving polylactic acid in a solvent B to obtain a polylactic acid spinning solution; step S6, preparing a polylactic acid spinning solution: dissolving polylactic acid in a solvent B to obtain a polylactic acid spinning solution; step S7, preparing a polylactic acid spinning solution: dissolving polylactic acid in a solvent B to obtain a polylactic acid spinning solution; step S8, preparing a polylactic acid spinning solution: dissolving polylactic acid in a solvent B to obtain a polylactic acid spinning solution; step S9, preparing a polylactic acid spinning solution: dissolving polylactic acid in a solvent B to obtain a polylactic acid spinning solution; step S10, preparing a polylactic acid spinning solution: dissolving polylactic acid in a solvent B to obtain a polylactic acid spinning solution; step S11, preparing a polylactic acid spinning solution: dissolving polylactic acid in a solvent B to obtain a polylactic acid spinning solution; step S12, preparing a polylactic acid spinning solution: dissolving polylactic acid in a solvent B to obtain a polylactic acid spinning solution; step S13, preparing a polylactic acid spinning solution: dissolving polylactic S3, prepare UiO-66 dispersion: disperse UiO-66 porous crystals in solvent C to obtain UiO-66 dispersion; step S4, prepare fiber cooling film: prepare fiber cooling film by electrocentrifugal spinning method using the polylactic acid spinning solution obtained in step S2, make the fiber surface of the fiber cooling film rich in light reflection holes through phase change induction, and then use gas spray technology to anchor UiO-66 in the UiO-66 dispersion obtained in step S3 on the fiber surface of the fiber cooling film to obtain UV shielding self-cleaning polylactic acid fiber cooling film.

[0008] A further solution is that the zirconium source in step S1 is one or more of zirconium tetrachloride, zirconium nitrate, zirconium dichloride octahydrate, zirconium sulfate, and tetraethoxy zirconium, and the purity of the zirconium source is ≥98%; and the solvent A in step S1 is one or more of water, methanol, ethanol, acetone, chloroform, N,N-dimethylformamide, and ethylacetamide.

[0009] In a further embodiment, the organic acid ligand in step S1 is one or more of terephthalic acid, glacial acetic acid, formic acid, hydrochloric acid, and acetic acid.

[0010] A further solution is that the template agent in step S1 is one or more of polyethylene glycol, hexadecyltrimethylammonium bromide, octadecyltrimethylammonium chloride, sodium dodecyl sulfate, triethylamine, ethylenediamine, and polyvinylpyrrolidone; and the pH value of the mixed solution in step S1 is 2-5.

[0011] A further solution is that the reaction conditions of the template induction method in step S1 are: reaction temperature is 100-300° C., and reaction time is 5-60 min; the average diameter of the obtained UiO-66 porous crystals is 0.3-2 μm.

[0012] In a further embodiment, in step S2, solvent B is one or more of chloroform, acetone, ethyl acetate, N,N-dimethylformamide, ethanol, dichloromethane, and chloroform, and the concentration of polylactic acid in solvent B is 5 to 20 wt %.

[0013] A further solution is that in step S3, solvent C is one or more of chloroform, ethylacetamide, ethylene glycol, N,N-dimethylformamide, ethanol, dichloromethane, and chloroform, and the concentration of UiO-66 in the UiO-66 dispersion is 5 to 30 wt %.

[0014] A further solution is that the conditions of the electrocentrifugal spinning method in step S4 are: voltage of 10 to 30 kV, spinning solution consumption rate of 0.5 to 10 mL / h, receiver speed of 300 to 2000 rpm, receiving distance of 10 to 25 cm, rotation radius of 5 to 20 cm, spinning temperature of 10 to 30 °C, and humidity of 40% to 80%.

[0015] A further solution is that the gas spray dispersion liquid consumption rate of the gas spray technology in step S4 is 0.5-10 mL / h, the nozzle diameter is 0.2-3 mm, and the gas pressure is 0.1-1 MPa.

[0016] In order to achieve the above object, according to the second aspect of the present invention, the present invention also provides a polylactic acid fiber cooling film prepared by the aforementioned preparation method.

[0017] Preferably, the obtained fiber membrane has an average fiber diameter of 0.3 to 3 μm, a porosity of 70% to 90%, and a thickness of 300 to 600 μm.

[0018] The polylactic acid fiber cooling film prepared by the above method can be used in the field of personal protective clothing, such as sun protection clothing, masks, etc. The high infrared emissivity and solar reflectivity make it have a good cooling effect, ensuring the thermal comfort of the wearer. At the same time, it has a series of functions such as ultraviolet shielding to prevent the fiber membrane from yellowing, and the self-cleaning function reduces the frequency of cleaning. It has broad application prospects in personal thermal management and building cooling.

[0019] The beneficial effects of the present invention are: (1) providing a UV-shielding self-cleaning polylactic acid fiber cooling film and a preparation method thereof. The fiber membrane not only has an excellent radiation cooling effect, but also has an average infrared emissivity of 95.7% to 97.3%, an average solar reflectivity of 95.4% to 98.1%, an average outdoor cooling temperature of 9.5 to 13.6°C, no yellowing reaction under the irradiation of ultraviolet light, and has the characteristics of self-cleaning; (2) The UiO-66 porous crystal synthesized by template induction not only has a perfect morphology and highly regular crystallization, but also exhibits excellent reflectivity, The good emissivity and rich chemical vibration bonds of UiO-66 give the fiber membrane a high infrared emissivity; (3) The surface pore structure makes the water contact angle of the fiber membrane larger and the hydrophobic effect better, which makes the fiber membrane have a good self-cleaning effect; (4) The good chemical stability of UiO-66 and the surface light reflection pore structure cause ultraviolet light to scatter, making the fiber membrane have efficient ultraviolet shielding performance; (5) The fiber membrane not only has the characteristics of high infrared emissivity, high solar reflectivity, and good outdoor cooling effect, but also has ultraviolet shielding and self-cleaning functions. Due to its simple preparation process, it is a cooling material with broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 It is a schematic flow chart of the method of the present invention.

[0022] Figure 2 is a scanning electron microscope image of the UiO-66 porous crystal synthesized by template induced in Example 1.

[0023] Figure 3 This is a scanning electron microscope image of the polylactic acid fiber without UiO-66 anchoring in Comparative Example 2.

[0024] Figure 4 is a scanning electron microscope image of the polylactic acid fiber anchored by UiO-66 in Example 1. DETAILED DESCRIPTION

[0025] To make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in the field without creative work belong to the scope of protection of the present invention. The present invention will be described in detail below in conjunction with the embodiments.

[0026] like Figure 1 As shown, Example 1 of the present invention provides a method for preparing a UV-shielding self-cleaning polylactic acid fiber cooling film, comprising the following steps.

[0027] S11. Preparation of UiO-66 porous crystals: dissolve zirconium tetrachloride in N,N-dimethylformamide (the concentration of N,N-dimethylformamide is 0.2 mol / L), add polyethylene glycol as a template, terephthalic acid (the concentration of terephthalic acid is 0.1 mol / L) and formic acid (the concentration of formic acid is 3 mol / L) as the main and secondary organic acid ligands, stir until the pH value reaches 3, mix well and place in a high-temperature reactor, and perform template-induced reaction (reaction temperature is 130°C, reaction time is 10 minutes). After the reaction is completed, centrifuge, wash and dry to remove excess template to obtain UiO-66 porous crystals with an average diameter of 700 nm.

[0028] S12. Prepare polylactic acid spinning solution: dissolve polylactic acid in dichloromethane / N,N-dimethylformamide (mass ratio 9:1) (the concentration of polylactic acid in the solution is 12 wt %), and stir evenly to obtain a spinning solution.

[0029] S13. Preparation of UiO-66 dispersion: Dispersing UiO-66 porous crystals (concentration of 15 wt %) in ethylene glycol to obtain a UiO-66 dispersion.

[0030] S14. Preparation of fiber cooling film: The polylactic acid spinning solution prepared in S12 was used to prepare a fiber cooling film by electrocentrifugal spinning. The phase change was used to induce the formation of fibers with rich light reflection holes on the surface, and UiO-66 was anchored on the fiber surface by gas spray technology. The electrocentrifugal spinning solution consumption rate was 1.5 mL / h, the voltage was 20 kV, the receiver speed was 300 rpm, the receiving distance was 12 cm, the rotation radius was 10 cm, the gas spray diameter was 0.3 mm, the gas spray rate was 2 mL / h, the gas pressure was 0.2 MPa, the temperature was 25±2℃, and the relative humidity was 45±3%. Finally, the fiber membrane was dried for 24 h to remove the residual solvent. A cooling fiber membrane anchored by UiO-66 and rich in light reflection holes on the fiber surface was obtained. The average fiber diameter was 800nm, the porosity was 80%, and the membrane thickness was 500μm.

[0031] Embodiment 2 of the present invention provides a method for preparing a UV-shielding self-cleaning polylactic acid fiber cooling film, comprising the following steps.

[0032] S21. Preparation of UiO-66 porous crystals: dissolve zirconium oxychloride octahydrate in methanol (methanol concentration is 0.2 mol / L), add polypyrrolidone as a template, terephthalic acid (terephthalic acid concentration is 0.3 mol / L) and hydrochloric acid (hydrochloric acid concentration is 2 mol / L) as the main and secondary organic ligands, stir until the pH value reaches 4, mix well and place in a high-temperature reactor (the reaction temperature of the high-temperature reactor is 130°C, and the reaction time is 20 minutes). After the reaction is completed, centrifuge, wash and dry to remove the excess template to obtain UiO-66 porous crystals with an average diameter of 600 nm.

[0033] S22. Prepare polylactic acid spinning solution: dissolve polylactic acid in dichloromethane / N,N-dimethylformamide (mass ratio 8:2) (the concentration of polylactic acid in the solution is 15wt%), and stir evenly to obtain a spinning solution.

[0034] S23 Preparation of UiO-66 dispersion: Dissolve UiO-66 porous crystals (concentration of 20 wt%) in ethylene glycol and stir evenly to obtain UiO-66 dispersion.

[0035] S24. Preparation of fiber cooling membrane: The polylactic acid spinning solution prepared in S22 was used to prepare a fiber cooling membrane by electrocentrifugal spinning. Phase change was used to induce the formation of fibers with rich light reflection holes on the surface, and UiO-66 was anchored on the fiber surface by gas spray technology. The voltage was 20 kV, the electrocentrifugal spinning solution consumption rate was 1 mL / h, the receiver speed was 800 rpm, the rotation radius was 12 cm, the receiving distance was 15 cm, the temperature was 25±2℃, the relative humidity was 45±3%, the gas spray diameter was 0.5 mm, the gas spray rate was 1.5 mL / h, and the gas pressure was 0.4mpa. Finally, the fiber membrane was dried for 24h to remove the residual solvent. A cooling fiber membrane anchored by UiO-66 and rich in light reflection holes on the fiber surface was obtained, and the average fiber diameter was 600 nm. The porosity was 85% and the membrane thickness was 450μm.

[0036] Embodiment 3 of the present invention provides a method for preparing a UV-shielding self-cleaning polylactic acid fiber cooling film, comprising the following steps.

[0037] S31. Preparation of UiO-66 porous crystals: dissolve zirconium nitrate in ethylacetamide (the concentration of ethylacetamide is 0.2 mol / L), add triethylamine as a template, terephthalic acid (the concentration of terephthalic acid is 0.2 mol / L) and glacial acetic acid (the concentration of glacial acetic acid is 2 mol / L)) as the main and secondary organic ligands, until the pH value reaches 3, stir evenly and place the mixed solution in a high-temperature reactor (the reaction temperature of the high-temperature reactor is 130°C and the reaction time is 30 min). After the reaction is completed, centrifuge, wash and dry to remove the excess template to obtain UiO-66 porous crystals with an average diameter of 550 nm.

[0038] S32. Prepare polylactic acid spinning solution: dissolve polylactic acid in dichloromethane / N,N-dimethylformamide (mass ratio 7:3) (the concentration of polylactic acid in the solution is 10wt%), and stir evenly to obtain a spinning solution.

[0039] S33. Prepare UiO-66 dispersion: dissolve UiO-66 porous crystals (concentration of 10 wt%) in ethylene glycol and stir evenly to obtain UiO-66 dispersion.

[0040] S34. Preparation of fiber cooling membrane: The polylactic acid spinning solution prepared in S32 was used to prepare fiber membrane by electrocentrifugal spinning, and the fiber with rich light reflection holes on the surface was formed by phase change induction, and UiO-66 was anchored on the fiber surface by gas spray technology. The electrocentrifugal spinning solution consumption rate was 1.2 mL / h, the rotation radius was 5 cm, the voltage was 20 kV, the receiver speed was 500 rpm, the receiving distance was 15 cm, the temperature was 25±2℃, the relative humidity was 45±3%, the gas spray diameter was 0.7 mm, the gas spray rate was 2.4 mL / h, and the gas spray pressure was 0.6 MPa. Finally, the fiber membrane was dried for 24 hours to remove the residual solvent, and a cooling fiber membrane anchored by UiO-66 and rich in light reflection holes on the fiber surface was obtained. The average fiber diameter was 500 nm, the porosity was 78%, and the membrane thickness was 450μm.

[0041] Embodiment 4 of the present invention provides a method for preparing a UV-shielding self-cleaning polylactic acid fiber cooling film, comprising the following steps.

[0042] S41. Preparation of UiO-66 porous crystals: dissolve tetraethoxy zirconium in deionized water, add ethylenediamine as a template, terephthalic acid (terephthalic acid concentration is 0.2 mol / L) and hydrochloric acid (hydrochloric acid concentration is 2 mol / L) as the main and secondary organic ligands, until the pH value reaches 4, stir evenly and place the mixed solution in a high-temperature reactor (the reaction temperature of the high-temperature reactor is 130°C, and the reaction time is 40 minutes). After the reaction is completed, centrifuge, wash and dry to remove excess template to obtain UiO-66 porous crystals with an average diameter of 500 nm.

[0043] S42. Prepare a polylactic acid spinning solution: dissolve polylactic acid in dichloromethane / N,N-dimethylformamide (mass ratio 10:0) (the concentration of polylactic acid in the solution is 18 wt %), and stir evenly to obtain a spinning solution.

[0044] S43. Prepare UiO-66 dispersion: dissolve UiO-66 porous crystals (concentration of 5 wt%) in ethylene glycol and stir evenly to obtain UiO-66 dispersion.

[0045] S44. Preparation of fiber cooling film: The polylactic acid spinning solution prepared in S42 was used to prepare a fiber cooling film by electrocentrifugal spinning. The phase change was used to induce the formation of fibers with rich light reflection holes on the surface, and UiO-66 was anchored on the fiber surface by gas spray technology. The voltage was 20 kV, the electrocentrifugal spinning solution consumption rate was 0.5 mL / h, the rotation radius was 8 cm, the receiver speed was 1000 rpm, the receiving distance was 12 cm, the temperature was 25±2℃, the relative humidity was 45±3%, the gas spray diameter was 1mm, and the gas spray rate was 1.5mL / h. Finally, the fiber membrane was dried for 24h to remove the residual solvent. A cooling fiber membrane anchored by UiO-66 and rich in light reflection holes on the fiber surface was obtained. The average fiber diameter was 400nm, the porosity was 82%, and the membrane thickness was 400μm.

[0046] Comparative Example 1 (polylactic acid fiber membrane without UiO-66 modification and light reflection holes) is basically prepared by the method of Example 3. The difference is that in this example, UiO-66 is not anchored on the fiber surface, and the phase change induction is prevented so that no light reflection holes are generated on the fiber surface. Specifically, polylactic acid is dissolved in dichloromethane / N,N-dimethylformamide (mass ratio 7:3) (the concentration of polylactic acid in the solution is 10wt%), and stirred evenly to obtain an electrocentrifugal spinning solution; a polylactic acid fiber membrane is prepared by electrocentrifugal spinning, the voltage is 20 kV, the electrocentrifugal spinning solution consumption rate is 1.2mL / h, the rotation radius is 10cm, the receiver speed is 500 rpm, the receiving distance is 15 cm, the temperature is 25±2℃, and the relative humidity is 45±3%. Finally, the fiber membrane is dried for 24h to remove the residual solvent to obtain a cooling fiber membrane without UiO-66 anchoring and without pores on the fiber surface. The average fiber diameter is 500 nm, the fiber membrane thickness is 400 μm, and the porosity is 78%.

[0047] Comparative Example 2 (polylactic acid fiber membrane rich in light reflection holes without UiO-66 modification) is basically prepared by the method of Example 1. The difference is that in this example, UiO-66 is not anchored on the fiber surface, but a phase change is induced to make the fiber surface rich in light reflection holes. Specifically, polylactic acid is dissolved in dichloromethane / N,N-dimethylformamide (mass ratio 9:1) (polylactic acid concentration in the solution is 12wt%), and stirred evenly to obtain a spinning solution; a polylactic acid fiber membrane is prepared by electrocentrifugal spinning, the voltage is 20 kV, the electrocentrifugal spinning solution consumption rate is 1.5 mL / h, the receiver speed is 300 rpm, the receiving distance is 12 cm, the rotation radius is 10 cm, the temperature is 25±2°C, and the relative humidity is 45±3%. Finally, the fiber membrane is dried for 24 hours to remove the residual solvent to obtain a cooling fiber membrane with rich light reflection holes on the fiber surface without UiO-66 anchoring. The average fiber diameter is 800nm, the fiber membrane thickness is 500μm, and the porosity is 80%.

[0048] The structural characterization and performance test results are as follows.

[0049] Scanning electron microscope observation: The morphology of UiO-66 and the microstructure of the polylactic acid cooling fiber membrane rich in light reflection holes were observed by field emission scanning electron microscope (model SU8220, HITACHI) ( Figure 2 , Figure 3 , Figure 4 ).

[0050] Solar reflectivity test: The reflectivity of the fiber membrane at the atmospheric window wavelength of 0.3-2.5 μm was measured using an ultraviolet-visible-near infrared spectrophotometer (model UV-3600, Shimadzu).

[0051] Infrared emissivity test: The infrared reflectivity and transmittance of the fiber membrane at a wavelength of 8-13 μm were measured using an FTIR spectrometer (model NEXUS-670, Thermo Fisher) equipped with a diffuse gold integrating sphere (PIKE Technologies). Infrared emissivity = 1-reflectivity-transmittance.

[0052] Outdoor cooling performance test: The cooling performance of the fiber membrane was measured outdoors (10:00-16:00, August 17, 2024, Xuzhou). The simulated skin (insulating foam wrapped in aluminum foil) was heated using a silicone rubber heating plate and the temperature was maintained at 37 °C. A K-type thermocouple (model YET-640X, Dickway) was used to record the temperature difference between the underside of the fiber membrane and the exposed simulated skin.

[0053] UV shielding performance test: It was carried out in a self-made UV aging chamber. The radiation source was composed of two UVA-340 ultraviolet lamps to simulate the wavelength and intensity of ultraviolet rays in nature. The temperature of the aging chamber was maintained at 25±2℃. The irradiation time was 72h to observe whether the color of the fiber membrane changed.

[0054] Contact angle test: Use a contact angle meter to drop a certain volume of water or other test liquid on the fiber membrane surface to measure the contact angle between the liquid and the fiber membrane surface. To ensure data accuracy, multiple measurements are required at different locations on the fiber membrane and the average value is taken.

[0055] Self-cleaning effect test: Place the fiber membrane on a 45° tilted glass slide and drip the sediment contamination liquid on the fiber membrane, with a total drip volume of 4 ml. Then drip clean water at a rate of 2 ml / s to observe whether the sediment contamination is cleaned.

[0056] The experimental results are as follows: Figure 2 As shown, the UiO-66 porous crystal synthesized by template in Example 1 has a complete morphology and regular crystallization, and its average diameter is 700 nm. Figure 3 As shown, the fiber surface in Comparative Example 2 is rich in light-reflecting holes, with an average pore size of 150 nm and a porosity of 80%. Figure 4 For the fiber membrane prepared by electrocentrifugal spinning combined with gas spraying, UiO-66 was anchored on the fiber surface.

[0057] Table 1 compares the test results of the average infrared emissivity, average solar reflectivity, radiation cooling temperature, ultraviolet shielding effect, and water contact angle of the polylactic acid fiber membrane obtained in the examples and comparative examples. Examples 1-4 have a higher average infrared emissivity (95.7%-97.5%) because UiO-66 has abundant chemical bonds in the infrared band, and these chemical bonds have strong vibration absorption, thereby enhancing the infrared emissivity of the fiber membrane; compared with Examples 1-4, Comparative Examples 1 and Comparative Example 2 show lower average infrared emissivity, which are 71.6% and 85.1%, respectively.

[0058] Table 1 Project Category Average infrared emissivity (%) Average solar reflectivity (%) Average outdoor cooling temperature (℃) UV shielding test Water contact angle test (°) Example 1 97.5 97.3 11.8 No change 124° Example 2 96.1 95.7 10.6 No change 126° Example 3 95.7 96.8 11.2 No change 129° Example 4 96.9 96.2 10.5 No change 127° Comparative Example 1 71.6 79.3 2.2 Yellowing 98° Comparative Example 2 85.1 87.3 5.3 Yellowing 103° Examples 1 to 4 all have high solar reflectivity (95.7%-97.5%). This is because the fiber surface is rich in light reflection holes and complex fiber networks, which prolongs the propagation path of light in the material and increases the number of reflections of light in the propagation path. At the same time, thanks to the porous crystals of UiO-66, light scattering is enhanced. The average solar reflectivity of Comparative Example 2 is 87.3%, which is lower than that of Examples 1-4, proving that the fiber membrane anchored by UiO-66 enhances the light scattering efficiency. This may be due to the high reflectivity of UiO-66, which effectively reflects visible light and scatters incident light. The polylactic acid fiber membrane without UiO-66 anchoring and light reflection holes in Comparative Example 1 exhibits the lowest solar emittance, which is 79.3%.

[0059] Examples 1 to 4 exhibited good radiative cooling performance (cooling temperature: 10.5-11.8°C), which was due to their high infrared emission and high solar reflectivity. Comparative Examples 1 and 2 had poor radiative cooling performance, with cooling temperatures of 2.2°C and 5.3°C, respectively.

[0060] In the water contact angle test, the contact angles of Examples 1 to 4 were all greater than 120°, and the fiber membrane surface was more hydrophobic than that of Comparative Examples 1 and 2. This is mainly due to the presence of a large number of pores in the porous structure of the surface, which makes it difficult for droplets to penetrate into the pores under the action of gravity, and the interaction between the droplets and the air in the pores will also hinder the spread of the droplets, resulting in an increase in the contact angle.

[0061] In the UV shielding test, the fiber membranes of Comparative Examples 1 and 2 had yellowing reaction on the surface of the fiber membranes. In the UV shielding test, the fiber membranes of Examples 1-4 did not have yellowing reaction, indicating that the fiber membranes anchored by UiO-66 can effectively shield ultraviolet rays. This may be mainly due to the good chemical stability of UiO-66, and the porous crystal structure increases the transmission path of ultraviolet rays, increases the reflection and scattering of ultraviolet light, and reduces the absorption of ultraviolet rays, thus having a good ultraviolet shielding effect.

[0062] This shows that the technical solution proposed in the present invention enables the cooling fiber membrane to have excellent radiation cooling effect, excellent UV shielding and self-cleaning properties, which are likely due to: (1) the porous crystal structure of UiO-66 synthesized by template induction is regular, and the fiber surface is rich in light reflection holes, which makes the fiber membrane have high solar reflectivity; (2) UiO-66 has good emissivity and abundant chemical vibration bonds, which makes the fiber membrane have high infrared emissivity; (3) The surface pore structure makes the water contact angle of the fiber membrane larger and the hydrophobic effect better, which makes the fiber membrane have good self-cleaning effect; (4) The good chemical stability of UiO-66 and the surface light reflection hole structure cause ultraviolet light to scatter, which makes the fiber membrane have high ultraviolet shielding performance.

[0063] The present invention relates to a UV shielding self-cleaning polylactic acid fiber cooling film and a preparation method thereof. The technical solution adopted by the present invention has a variety of implementation methods and approaches, and the above is only a preferred implementation method of the present invention. It should be pointed out that ordinary technicians in this field can make various improvements and optimizations to the present invention without departing from the basic principles of the present invention, and these improvements and optimizations should be included in the protection scope of the present invention. In addition, each component not described in detail in this embodiment can be implemented with the help of existing technology.

Claims

1. A method for preparing a UV-shielding self-cleaning polylactic acid fiber cooling film, characterized in that: The following steps are involved: Step S1, preparing UiO-66 porous crystals: mixing a zirconium source, an organic acid ligand, a template agent, and a solvent A to obtain a mixed solution, transferring the mixed solution to a high-temperature reactor, reacting by a template induction method, and removing the template agent after the reaction to obtain UiO-66 porous crystals; Step S2, preparing a polylactic acid spinning solution: dissolving polylactic acid in solvent B to obtain a polylactic acid spinning solution; Step S3, preparing a UiO-66 dispersion: dispersing the UiO-66 porous crystals obtained in step S1 in solvent C to obtain a UiO-66 dispersion; Step S4, preparing a fiber cooling film: preparing a fiber cooling film by electrocentrifugal spinning of the polylactic acid spinning solution obtained in step S2, forming light reflection holes on the fiber surface of the fiber cooling film by phase change induction, and then anchoring the UiO-66 in the UiO-66 dispersion obtained in step S3 on the fiber surface of the fiber cooling film by gas spray technology to obtain a UV shielding self-cleaning polylactic acid fiber cooling film.

2. The method for preparing the ultraviolet shielding self-cleaning polylactic acid fiber cooling film according to claim 1, characterized in that: The zirconium source in step S1 is one or more of zirconium tetrachloride, zirconium nitrate, zirconium oxychloride octahydrate, zirconium sulfate, zirconium nitrate, and tetraethoxy zirconium; the solvent A in step S1 is one or more of water, methanol, ethanol, acetone, chloroform, dichloromethane, N,N-dimethylformamide, and ethylacetamide.

3. The method for preparing the ultraviolet shielding self-cleaning polylactic acid fiber cooling film according to claim 1, characterized in that: The organic acid ligand in step S1 is one or more of terephthalic acid, glacial acetic acid, formic acid, hydrochloric acid, and acetic acid.

4. The method for preparing the ultraviolet shielding self-cleaning polylactic acid fiber cooling film according to claim 1, characterized in that: The template agent in step S1 is one or more of polyethylene glycol, hexadecyltrimethylammonium bromide, octadecyltrimethylammonium chloride, sodium dodecyl sulfate, triethylamine, ethylenediamine, and polyvinylpyrrolidone; the pH value of the mixed solution in step S1 is 2-5.

5. The method for preparing the ultraviolet shielding self-cleaning polylactic acid fiber cooling film according to claim 1, characterized in that: The reaction conditions of the template induction method in step S1 are: reaction temperature of 100-300° C., and reaction time of 5-60 min.

6. The method for preparing the ultraviolet shielding self-cleaning polylactic acid fiber cooling film according to claim 1, characterized in that: The solvent B in step S2 is one or more of chloroform, acetone, ethyl acetate, N,N-dimethylformamide, ethanol, dichloromethane, and chloroform, and the concentration of the polylactic acid in the solvent B is 5-20 wt %.

7. The method for preparing the ultraviolet shielding self-cleaning polylactic acid fiber cooling film according to claim 1, characterized in that: The solvent C in step S3 is one or more of chloroform, ethylacetamide, ethylene glycol, N,N-dimethylformamide, ethanol, dichloromethane, and chloroform. The concentration of UiO-66 in the UiO-66 dispersion is 5 to 30 wt %.

8. The method for preparing the ultraviolet shielding self-cleaning polylactic acid fiber cooling film according to claim 1, characterized in that: The conditions of the electrocentrifugal spinning method in step S4 are: voltage of 10-30 kV, spinning solution consumption rate of 0.5-10 mL / h, receiver speed of 300-2000 rpm, receiving distance of 10-25 cm, rotation radius of 5-20 cm, spinning temperature of 10-30 ° C, and humidity of 40%-80%.

9. The method for preparing the ultraviolet shielding self-cleaning polylactic acid fiber cooling film according to claim 1, characterized in that: The conditions of the gas spraying technology in step S4 are that the consumption rate of the gas spraying dispersion is 0.5-10 mL / h, the nozzle diameter is 0.2-3 mm, and the gas pressure is 0.1-1 MPa.

10. A polylactic acid fiber cooling film prepared by the method for preparing a UV-shielding self-cleaning polylactic acid fiber cooling film according to any one of claims 1 to 9.

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