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

Abstract

The application discloses an ultraviolet shielding self-cleaning polylactic acid fiber cooling film and a preparation method thereof, and comprises the following steps: S1, preparing UiO-66 porous crystals: mixing a zirconium source, an organic acid ligand, a template agent and a solvent A, and preparing the UiO-66 porous crystals 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, preparing a UiO-66 dispersion liquid: dissolving the UiO-66 in a solvent C to obtain the UiO-66 dispersion liquid; S4, preparing a fiber cooling film: preparing the fiber cooling film through an ionized centrifugal spinning method, forming surface light reflection holes through phase transition induction, anchoring the UiO-66 on the surface of the fiber through a gas spraying technology, and obtaining the ultraviolet shielding self-cleaning polylactic acid fiber cooling film. The polylactic acid fiber cooling film has high infrared emissivity and high solar reflectivity, excellent radiation cooling effect, outstanding ultraviolet shielding effect and self-cleaning capacity, and wide application prospect and market potential in the fields of heat management and building cooling.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of building cooling and personal thermal management materials, and particularly relates to a kind of ultraviolet shielding self-cleaning polylactic acid fiber cooling film and preparation method thereof. BACKGROUND

[0002] Human body heat balance is crucial to health and safety. Mild human body may cause dizziness, nausea and other symptoms, and severe organ failure may even endanger life. Especially those who often work outdoors, intense solar radiation not only affects their work efficiency, but also poses a serious threat to their health. Traditional cooling equipment usually uses active refrigeration method to reduce the indoor environmental temperature to achieve human comfort temperature, but it has the disadvantages of high energy consumption, high installation and maintenance cost, and environmental pollution. Therefore, a method that is both energy-saving and cost-effective is needed. Radiative cooling is a method of achieving cooling by emitting thermal radiation from the material to the sky without consuming external energy, and it is a method with very wide application prospects.

[0003] Although radiative cooling fabrics have been widely studied, the influence of ultraviolet light cannot be ignored in practical application. Ultraviolet light can cause the material to yellow, reducing the reflectivity of the fiber film and the cooling effect, thereby affecting the long-term performance of the material. Therefore, it is crucial to prepare radiative cooling fabrics with ultraviolet shielding function. UiO-66 is a typical MOFs material with high solar reflectance and high infrared emissivity. Good optical properties and chemical stability make it have excellent ultraviolet shielding effect. However, how to effectively combine UiO-66 with fiber materials while maintaining its optical properties and chemical stability remains an important challenge in current research.

[0004] To solve the problem of cooling performance decline caused by fiber aging under ultraviolet light, the present application uses polylactic acid (PLA) and self-made UiO-66 porous crystals as raw materials to prepare a high-performance radiative cooling fiber film. The fiber film not only has high infrared emissivity, high solar reflectivity and good outdoor cooling effect, but also has good UV shielding property and biodegradability. Due to the simple preparation process, it has broad application prospects in the fields of personal thermal management and building cooling. SUMMARY

[0005] The purpose of the present application is to invent a high-performance radiative cooling fabric with ultraviolet shielding and self-cleaning functions to meet the needs of personal thermal management and building cooling.

[0006] In order to achieve the above object, the application takes polylactic acid (PLA) and self-made UiO-66 porous crystals as raw materials, prepares a fiber cooling film through electrocentesis spinning, obtains a fiber with a surface rich in light-reflecting holes through phase transition induction, and anchors the UiO-66 on the surface of the fiber through a gas spraying technology to obtain a kind of ultraviolet shielding self-cleaning polylactic acid fiber cooling film.

[0007] According to a first aspect of the application, a method for preparing an ultraviolet 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 reaction kettle, and performing a reaction through a template induction method, removing the template agent after the reaction is completed to obtain the UiO-66 porous crystals; Step S2, preparing a polylactic acid spinning solution: dissolving polylactic acid in a solvent B to obtain the polylactic acid spinning solution; Step S3, preparing a UiO-66 dispersion liquid: dispersing the UiO-66 porous crystals in a solvent C to obtain the UiO-66 dispersion liquid; Step S4, preparing a fiber cooling film: preparing the fiber cooling film through electrocentesis spinning of the polylactic acid spinning solution obtained in Step S2, making the surface of the fiber of the fiber cooling film rich in light-reflecting holes through phase transition induction, and anchoring the UiO-66 in the UiO-66 dispersion liquid obtained in Step S3 on the surface of the fiber of the fiber cooling film through a gas spraying technology to obtain the ultraviolet shielding self-cleaning polylactic acid fiber cooling film.

[0008] Further, in Step S1, the zirconium source is one or more of zirconium tetrachloride, zirconium nitrate, zirconium dichlorohydrate, zirconium sulfate and zirconium tetraethoxide, and the purity of the zirconium source is greater than or equal to 98%; and in Step S1, the solvent A is one or more of water, methanol, ethanol, acetone, chloroform, N,N-dimethylformamide and ethyl acetamide.

[0009] Further, in Step S1, the organic acid ligand is one or more of terephthalic acid, glacial acetic acid, formic acid and hydrochloric acid.

[0010] Further, in Step S1, the template agent is one or more of polyethylene glycol, cetyltrimethylammonium 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] Further, in Step S1, the reaction conditions of the template induction method are that the reaction temperature is 100-300 DEG C and the reaction time is 5-60 min; and the average diameter of the obtained UiO-66 porous crystals is 0.3-2 microns.

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

[0013] Further, in step S3, the solvent C is one or more of chloroform, ethyl acetamide, ethylene glycol, N,N-dimethylformamide, ethanol, dichloromethane, and trichloromethane, and the concentration of UiO-66 in the UiO-66 dispersion liquid is 5-30 wt%.

[0014] Further, in step S4, the conditions of the electrospinning method are as follows: the voltage is 10-30 kV, the consumption rate of the spinning solution is 0.5-10 mL / h, the rotation speed of the receiver is 300-2000 rpm, the receiving distance is 10-25 cm, the spinning radius is 5-20 cm, the spinning temperature is 10-30℃, and the humidity is 40%-80%.

[0015] Further, in step S4, the conditions of the electrospinning method are as follows: the voltage is 10-30 kV, the consumption rate of the spinning solution is 0.5-10 mL / h, the rotation speed of the receiver is 300-2000 rpm, the receiving distance is 10-25 cm, the spinning radius is 5-20 cm, the spinning temperature is 10-30℃, and the humidity is 40%-80%.

[0016] To achieve the above-mentioned purpose, according to the second aspect of the present application, the present application also provides a polylactic acid fiber cooling film prepared by the above-mentioned preparation method.

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

[0018] The polylactic acid fiber cooling film prepared by the above-mentioned 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 good cooling effect, ensuring the thermal comfort of the wearer. At the same time, it has the functions of ultraviolet shielding, preventing the fiber film from yellowing, self-cleaning, reducing the frequency of cleaning, etc. It has broad application prospects in personal thermal management and building cooling.

[0019] The present application has the following beneficial effects: (1) the present application provides a kind of ultraviolet shielding self-cleaning polylactic acid fiber cooling film and its preparation method.The fiber film not only has excellent radiation cooling effect, the average infrared emissivity of the fiber film is 95.7%~97.3%, the average sunlight reflectivity is 95.4%~98.1%, the outdoor average cooling temperature is 9.5~13.6℃, there is no yellowing reaction under the irradiation of ultraviolet lamp, with self-cleaning and other characteristics;(2) the UiO-66 porous crystal synthesized by template induction not only has perfect morphology and highly regular crystallization, but also shows excellent reflectivity, the good emissivity of UiO-66 and rich chemical vibration bond make the fiber film have high infrared emissivity;(3) the surface pore structure makes the water contact angle of the fiber film larger, and the hydrophobic effect is better, so that the fiber film has good self-cleaning effect;(4) the good chemical stability of UiO-66 and the surface light reflection pore structure make ultraviolet light scattering, so that the fiber film has high-efficiency ultraviolet shielding performance;(5) the fiber film not only has high infrared emissivity, high sunlight reflectivity, good outdoor cooling effect and other characteristics, but also has ultraviolet shielding and self-cleaning functions, and the preparation process is simple, so it is a cooling material with broad application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0021] Figure 1 is a schematic diagram of the method flow of the present application.

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

[0023] Figure 3 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 with UiO-66 anchoring in example 1. DETAILED DESCRIPTION

[0025] In order to make the objectives, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described in detail below. Obviously, the described embodiments are only some of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work belong to the scope of protection of the present application. The present application will be described in detail below in combination with embodiments.

[0026] As shown in Figure 1 Embodiment 1 of the present application provides a preparation method of an ultraviolet 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 agent, 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 primary and secondary organic acid ligands, stir until the pH value reaches 3, and then place the mixture in a high-temperature reaction kettle. The template-induced reaction is carried out (the reaction temperature is 130°C, and the reaction time is 10 minutes). After the reaction is completed, centrifugation, washing and drying are performed to remove excess template agent, and UiO-66 porous crystals with an average diameter of 700 nm are obtained.

[0028] S12. Preparation of 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 12wt %), and stir uniformly to obtain a spinning solution.

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

[0030] S14. Preparation of fiber cooling film: The polylactic acid spinning solution prepared in S12 is used to prepare a fiber cooling film by electrocentrifugal spinning. The surface of the fiber is enriched with light-reflecting pores by phase transition induction, and UiO-66 is anchored on the surface of the fiber by gas spraying technology. The consumption rate of the electrocentrifugal spinning solution is 1.5 mL / h, the voltage is 20 kV, the rotation speed of the receiver is 300 rpm, the receiving distance is 12 cm, the rotation radius is 10 cm, the gas spraying diameter is 0.3 mm, the gas spraying rate is 2 mL / h, the gas pressure is 0.2mpa, the temperature is 25±2°C, and the relative humidity is 45±3%. Finally, the fiber film is dried for 24 h to remove residual solvents. A cooling fiber film with UiO-66 anchored and the surface of the fiber enriched with light-reflecting pores is obtained. The average diameter of the fiber is 800 nm, the porosity is 80%, and the film thickness is 500μm.

[0031] Embodiment 2 of the present application provides a preparation method of an ultraviolet shielding self-cleaning polylactic acid fiber cooling film, comprising the following steps.

[0032] S21. Preparation of UiO-66 porous crystals: Dissolve zirconium dichloride octahydrate in methanol (concentration of methanol is 0.2 mol / L), add polyvinylpyrrolidone as a template agent, terephthalic acid (concentration of terephthalic acid is 0.3 mol / L) and hydrochloric acid (concentration of hydrochloric acid is 2 mol / L) as primary and secondary organic ligands, stir until the pH value reaches 4, and then place the mixture in a high-temperature reaction kettle (reaction temperature of the high-temperature reaction kettle is 130℃, and reaction time is 20 minutes). After the reaction is completed, centrifuge, wash, and dry to remove excess template agent to obtain UiO-66 porous crystals with an average diameter of 600 nm.

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

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

[0035] S24. Preparation of fiber cooling film: The polylactic acid spinning solution prepared in S22 is subjected to electrospinning to prepare a fiber cooling film. The surface of the fiber is enriched with light-reflecting pores by phase transition induction, and UiO-66 is anchored on the surface of the fiber by gas spraying technology. The voltage is 20 kV, the consumption rate of the electrospinning solution is 1 mL / h, the rotation speed of the receiver is 800 rpm, the rotation radius is 12 cm, the receiving distance is 15 cm, the temperature is 25±2℃, the relative humidity is 45±3%, the gas spraying diameter is 0.5 mm, the gas spraying rate is 1.5 mL / h, and the gas pressure is 0.4mpa. Finally, the fiber membrane is dried for 24h to remove residual solvent. A UiO-66-anchored fiber cooling film with a fiber surface enriched with light-reflecting pores is obtained, and the average diameter of the fiber is 600 nm. The porosity is 85%, and the thickness of the film is 450μm.

[0036] Embodiment 3 of the present application provides a preparation method of an ultraviolet shielding self-cleaning polylactic acid fiber cooling film, comprising the following steps.

[0037] S31. Preparation of UiO-66 porous crystals: dissolve zirconium nitrate in ethyl acetamide (concentration of ethyl acetamide is 0.2 mol / L), add triethylamine as a template, terephthalic acid (concentration of terephthalic acid is 0.2 mol / L) and glacial acetic acid (concentration of glacial acetic acid is 2 mol / L) as primary and secondary organic ligands until the pH value reaches 3, and then place the mixed solution in a high-temperature reaction kettle (reaction temperature of the high-temperature reaction kettle is 130°C, and reaction time is 30 min). After the reaction is completed, centrifugation, washing and drying are performed to remove excess template to obtain UiO-66 porous crystals with an average diameter of 550 nm.

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

[0039] S33. Preparation of UiO-66 dispersion: dissolve UiO-66 porous crystals (concentration is 10wt %) in ethylene glycol, and stir uniformly to obtain a UiO-66 dispersion.

[0040] S34. Preparation of fiber cooling film: the polylactic acid spinning solution prepared in S32 is subjected to electrospinning to prepare a fiber film, phase change induction is used to form a fiber with a surface rich in light-reflecting holes, and a gas spraying technique is used to anchor UiO-66 on the surface of the fiber. The consumption rate of the electrospinning solution is 1.2 mL / h, the radius of rotation is 5 cm, the voltage is 20 kV, the rotation speed of the receiver is 500 rpm, the receiving distance is 15 cm, the temperature is 25±2°C, the relative humidity is 45±3%, the gas spraying diameter is 0.7 mm, the gas spraying rate is 2.4 mL / h, the gas spraying pressure is 0.6 MPa, and finally the fiber film is dried for 24 h to remove residual solvents, thereby obtaining a UiO-66-anchored fiber cooling film with a surface rich in light-reflecting holes. The average diameter of the fiber is 500 nm, the porosity is 78%, and the thickness of the film is 450 μm.

[0041] Embodiment 4 of the present application provides a preparation method of an ultraviolet shielding self-cleaning polylactic acid fiber cooling film, which comprises the following steps.

[0042] S41. Preparation of UiO-66 porous crystals: dissolve tetraethoxysilane in deionized water, add ethylenediamine as a template, terephthalic acid (concentration of terephthalic acid is 0.2 mol / L) and hydrochloric acid (concentration of hydrochloric acid is 2 mol / L) as primary and secondary organic ligands until the pH value reaches 4, and then place the mixed solution in a high-temperature reaction kettle (reaction temperature of the high-temperature reaction kettle is 130°C, and reaction time is 40 min). After the reaction is completed, centrifugation, washing and drying are performed to remove excess template to obtain UiO-66 porous crystals with an average diameter of 500 nm.

[0043] S42. Preparation of polylactic acid spinning solution: polylactic acid was dissolved in dichloromethane / N,N-dimethylformamide (mass ratio 10:0) (the concentration of polylactic acid in the solution was 18wt %), and stirred uniformly to obtain a spinning solution.

[0044] S43. Preparation of UiO-66 dispersion liquid: UiO-66 porous crystals (concentration of 5wt%) were dissolved in ethylene glycol, and stirred uniformly to obtain a UiO-66 dispersion liquid.

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

[0046] Comparative Example 1 (polylactic acid fiber film without UiO-66 modification and without light-reflecting holes) was prepared by basically using the method of Example 3. The difference is that, in this example, UiO-66 is not anchored on the fiber surface, and the occurrence of phase change induction is prevented so that the fiber surface does not produce light-reflecting holes. Specifically, polylactic acid was dissolved in dichloromethane / N,N-dimethylformamide (mass ratio 7:3) (the concentration of polylactic acid in the solution was 10wt %), and stirred uniformly to obtain an electrospinning solution; a polylactic acid fiber film was prepared by electrospinning, the voltage was 20 kV, the consumption rate of the electrospinning solution was 1.2 mL / h, the rotation radius was 10 cm, the receiver rotation speed was 500 rpm, the receiving distance was 15 cm, the temperature was 25±2℃, and the relative humidity was 45±3%. Finally, the fiber film was dried for 24 h to remove residual solvents, and a UiO-66-anchored fiber surface without hole cooling fiber film was obtained. The average fiber diameter was 500 nm, the fiber film thickness was 400 μm, and the porosity was 78%.

[0047] Comparative Example 2 (PLA fiber membrane without UiO-66 modification, rich in light-reflective pores) was prepared according to the method of Example 1. The difference is that UiO-66 is not anchored on the fiber surface but phase transition induction is generated to make the fiber surface rich in light-reflective pores. Specifically, PLA was dissolved in dichloromethane / N,N-dimethylformamide (mass ratio 9:1) (PLA concentration in solution was 12 wt %), and stirred uniformly to obtain a spinning solution; PLA fiber membrane was prepared by electrospinning, the voltage was 20 kV, the consumption rate of electrospinning solution was 1.5 mL / h, the receiver rotation speed was 300 rpm, the receiving distance was 12 cm, the rotation radius was 10 cm, the temperature was 25±2℃, and the relative humidity was 45±3%. Finally, the fiber membrane was dried for 24 h to remove residual solvent, and a cooled fiber membrane with light-reflective pores on the fiber surface without UiO-66 anchoring was obtained. The average diameter of the fiber was 800 nm, the thickness of the fiber membrane was 500 μm, and the porosity was 80%.

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

[0049] Scanning electron microscope observation: The morphological structure of UiO-66 and the microstructure of the PLA cooled fiber membrane rich in light-reflective pores were observed by field emission scanning electron microscope (model SU8220, HITACHI) Figure 2 , Figure 3 , Figure 4 ).

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

[0051] Infrared emissivity test: The infrared reflectance 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), and the infrared emissivity = 1-reflectance-transmittance.

[0052] Outdoor cooling performance test: The cooling performance of the fiber membrane was measured outdoors (10:00-16:00, August 17, 2024, Xuzhou), a silicon rubber heating plate was used to heat the simulated skin (insulating foam wrapped with aluminum foil), and the temperature was maintained at 37℃, and a K-type thermocouple (model YET-640X, Dickvi) was used to record the temperature difference between the underside of the fiber membrane and the bare simulated skin.

[0053] Ultraviolet shielding performance test: In a self-made ultraviolet aging chamber, the radiation source uses two UVA-340 ultraviolet lamps to simulate the wavelength and intensity of natural ultraviolet light, and the temperature of the aging chamber is maintained at 25±2℃, the irradiation time is 72h, and the color change of the fiber membrane is observed.

[0054] Contact angle test: using a contact angle measuring instrument, a certain volume of water droplets or other test liquids are dropped on the surface of the fiber membrane, and the contact angle formed by the liquid and the surface of the fiber membrane is measured. To ensure data accuracy, multiple measurements at different locations on the fiber membrane are required and the average value is taken.

[0055] Self-cleaning effect test: Place the fiber membrane on a 45° inclined glass slide and add sand contaminated liquid on the fiber membrane, with a total drop amount of 4ml. Then add clean water at a rate of 2ml / s, and observe whether the sand contaminants are cleaned.

[0056] The experimental results are as follows, as shown in Figure 2 The template-induced synthesis of UiO-66 porous crystals in Example 1 has complete morphology and regular crystallization, with an average diameter of 700nm. Figure 3 As shown in FIG. 2B, the fiber surface in Comparative Example 2 is rich in light-reflecting pores, with an average pore size of 150nm and a porosity of 80%. Figure 4 The fiber membrane prepared by the combination of electrospinning and gas spraying has UiO-66 anchored on the fiber surface.

[0057] Table 1 compares the average infrared emissivity, average solar reflectivity, radiation cooling temperature, ultraviolet shielding effect, and water contact angle of the polylactic acid fiber membranes obtained in the examples and comparative examples. Examples 1-4 have a higher average infrared emissivity (95.7%-97.5%), because UiO-66 has rich 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 2 exhibit lower average infrared emissivity, which is 71.6% and 85.1%, respectively.

[0058] Table 1

[0059] Item Group Average Infrared Emissivity (%) Average Solar Reflectance (%) Outdoor Average Cooling Temperature (°C) Ultraviolet 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°

[0060] Examples 1-4 all have high solar reflectance (95.7%-97.5%), because the fiber surface is rich in light reflection holes and complex fiber network, which prolongs the light propagation path in the material and increases the number of light reflection in the propagation path. At the same time, thanks to the UiO-66 porous crystal, the light scattering is enhanced. The average solar reflectance of Comparative Example 2 is 87.3%, which is lower than Examples 1-4, proving that the UiO-66 anchored fiber membrane enhances the light scattering efficiency, which 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 emissivity, with a value of 79.3%.

[0061] Examples 1-4 exhibit good radiative cooling performance (cooling temperature: 10.5-11.8℃), which benefits from their high infrared emissivity and high solar reflectance. Comparative Examples 1 and 2 have poor radiative cooling performance, with cooling temperatures of 2.2℃ and 5.3℃, respectively.

[0062] During the water contact angle test, Examples 1-4 exhibit a contact angle of more than 120°, making the fiber membrane surface more hydrophobic than Comparative Examples 1 and 2. This is mainly due to the presence of a large number of pores in the surface porous structure, making it difficult for liquid droplets to penetrate into the pores under the action of gravity, and the interaction between the liquid droplets and the air in the pores also hinders the spreading of the liquid droplets, resulting in an increase in the contact angle.

[0063] Comparative Examples 1 and 2 exhibit yellowing on the surface of the fiber membrane during the ultraviolet shielding test. Examples 1-4 do not exhibit yellowing on the surface of the fiber membrane during the ultraviolet shielding test, indicating that the fiber membrane anchored by UiO-66 can effectively shield ultraviolet light. This may be mainly due to the good chemical stability of UiO-66 and the porous crystal structure, which increases the transmission path of ultraviolet light, increases the reflection and scattering of ultraviolet light, and reduces the absorption of ultraviolet light, thereby having good ultraviolet shielding effect.

[0064] Therefore, the technical scheme proposed in the present application makes the cooling fiber membrane have excellent radiative cooling effect, excellent ultraviolet shielding and self-cleaning performance, which may be due to the following reasons: (1) the regular UiO-66 porous crystal structure synthesized by template induction and the rich light reflection holes on the fiber surface make the fiber membrane have high solar reflectance; (2) the good emissivity and rich chemical vibration bonds of UiO-66 make 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, making the fiber membrane have good self-cleaning effect; (4) the good chemical stability of UiO-66 and the surface light reflection hole structure make the ultraviolet light scatter, making the fiber membrane have high-efficiency ultraviolet shielding performance.

[0065] The present application relates to a kind of ultraviolet shielding self-cleaning polylactic acid fiber cooling film and its preparation method.The technical solutions used in the present application have various implementation methods and ways, the above-mentioned is only the preferred implementation method of the present application.It should be pointed out that the ordinary skilled in the art can make various improvements and optimizations to the present application without departing from the basic principles of the present application, and these improvements and optimizations should be included in the protection scope of the present application.In addition, the components not described in detail in the present embodiment can be realized by means of prior art.

Claims

1. A method for preparing an ultraviolet-shielding self-cleaning polylactic acid fiber cooling film, characterized by, The method comprises the following steps: 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 reaction kettle, and performing a reaction by a template induction method, removing the template agent after the reaction is completed, and obtaining the UiO-66 porous crystals; Step S2, preparing a polylactic acid spinning solution: dissolving polylactic acid in a solvent B to obtain the polylactic acid spinning solution; Step S3, preparing a UiO-66 dispersion liquid: dispersing the UiO-66 porous crystals obtained in step S1 in a solvent C to obtain the UiO-66 dispersion liquid; Step S4, preparing a fiber cooling film: preparing the fiber cooling film by an electrocentesis spinning method from the polylactic acid spinning solution obtained in step S2, forming light reflection holes on the fiber surface of the fiber cooling film by phase transition induction, and anchoring the UiO-66 in the UiO-66 dispersion liquid obtained in step S3 on the fiber surface of the fiber cooling film by a gas spraying technology, to obtain the ultraviolet shielding self-cleaning polylactic acid fiber cooling film.

2. The method for preparing the UV-shielded self-cleaning polylactic acid fiber cooling film according to claim 1, characterized in that, The zirconium source in the step S1 is one or more of zirconium tetrachloride, zirconium nitrate, zirconium dichlorohydrate, zirconium sulfate, zirconium nitrate, and tetraethoxysilane; and the solvent A in the step S1 is one or more of water, methanol, ethanol, acetone, chloroform, dichloromethane, N,N-dimethylformamide, and ethyl acetamide.

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

5. The method for preparing the UV-shielded self-cleaning polylactic acid fiber cooling film according to claim 1, characterized in that, The reaction condition of the template induction method in the step S1 is that the reaction temperature is 100-300 DEG C, and the reaction time is 5-60 min.

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

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

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

9. The method for preparing the UV-shielded self-cleaning polylactic acid fiber cooling film according to claim 1, characterized in that, The condition of the gas spraying technology in the step S4 is that the gas spraying dispersion liquid consumption rate 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 poly-lactic acid fiber cooling film prepared by the method of claim 1 to 9.

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