Janus polylactic acid fiber membrane for cooling and its preparation method

Abstract

The application provides a Janus polylactic acid fiber membrane for cooling and a preparation method thereof, and the method comprises the following steps: S1, synthesizing silica nanoparticles; S2, dissolving the silica nanoparticles, a surfactant and polylactic acid in an organic solvent to obtain an electrospinning solution A; S3, uniformly dissolving polylactic acid to obtain an electrospinning solution B; S4, preparing an inner layer of the Janus fiber membrane; and S5, preparing the Janus polylactic acid fiber membrane. In the method, the introduction of the silica nanoparticles and the spectral selective regulation of the fiber diameter enable the polylactic acid fiber membrane to have high infrared emissivity and high sunlight reflection capacity, and the wetting gradient of the fiber membrane can rapidly transport moisture from the inner layer to the outer layer. The fiber membrane not only has excellent radiation cooling effect and rapid moisture absorption and perspiration capacity, but also has good biocompatibility and degradability, and the preparation process is simple, so that the fiber membrane is an individual cooling material with wide application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of fully degradable individual cooling fibers, in particular to a Janus polylactic acid fiber film for cooling and a preparation method thereof. BACKGROUND

[0002] With the intensification of global warming, outdoor workers are more likely to be exposed to high-temperature environments and suffer from heat-related diseases, resulting in decreased labor productivity and economic losses. Although adjusting the temperature of the space through ventilation and air conditioning systems can effectively maintain the thermal comfort of the human body, this cooling method comes at the cost of energy consumption, and outdoor workers cannot use it. Textiles with radiative cooling properties can spontaneously reflect sunlight to reduce energy absorption and transfer heat to outer space through the atmospheric window, providing an innovative method for cooling outdoor individuals.

[0003] Nanofiber structures have high porosity and can exhibit enhanced light scattering, and have received widespread attention and extensive research in the field of radiative cooling. Polylactic acid (PLA) fibers are a sustainable and eco-friendly fiber with biocompatibility and biodegradability, and have been explored for radiative cooling. However, the inherent low infrared emissivity of polylactic acid limits its heat radiation ability. In addition, the radiative cooling fiber film faces the negative impact of sweating on thermal comfort and cooling efficiency in practical applications. Unexcreted sweat has a large specific heat capacity, which will store heat on the skin, reducing the cooling efficiency. Therefore, taking into account the high-efficiency radiative cooling performance and excellent sweat-wicking performance is the key to the development of polylactic acid individual cooling fiber films, but the existing technology is difficult to meet at the same time. SUMMARY

[0004] The present application is to meet the demand for high-efficiency individual cooling materials in high-temperature outdoor work scenarios. The present application prepares a Janus polylactic acid cooling fiber film composed of a silica-modified polylactic acid hydrophilic inner layer and a polylactic acid hydrophobic outer layer by electrospinning. The fiber film not only has excellent radiative cooling effect and rapid moisture absorption and sweat-wicking ability, but also has good biocompatibility and degradability, and the preparation process is simple. It is an individual cooling material with broad application prospects.

[0005] The present application specifically provides a preparation method of a Janus polylactic acid fiber film for cooling, comprising the following steps:

[0006] Step S1, preparing silica nanoparticles: dissolving an organic acid in a polar solvent until the mixture is uniform to obtain a solution, adding a silicon-containing compound to the solution, stirring uniformly, and then adding an alkaline adjusting agent, placing the mixed solution in a microwave reaction kettle, centrifuging, washing, and drying after the reaction is completed to obtain silica nanoparticles;

[0007] Step S2, preparing electrospinning solution A: dissolving silica nanoparticles, surfactant and polylactic acid in organic solvent in turn, stirring to obtain electrospinning solution A;

[0008] Step S3, preparing electrospinning solution B: dissolving polylactic acid in organic solvent, stirring to obtain electrospinning solution B;

[0009] Step S4, preparing inner layer of Janus fiber membrane: electrospinning with electrospinning solution A as raw material to prepare inner layer of Janus fiber membrane;

[0010] Step S5, preparing Janus polylactic acid fiber membrane: electrospinning with electrospinning solution B as raw material, depositing fibers on the surface of Janus inner layer fiber membrane to prepare outer layer of Janus fiber membrane, drying the composite fiber membrane in an oven to obtain target Janus polylactic acid fiber membrane.

[0011] In step S1, the polar solvent is at least one of ethylene glycol, polyvinyl alcohol, dimethyl sulfoxide, acetone, ethanolamine and water;

[0012] After stirring, a basic adjusting agent is added to adjust the pH value to 9-11.

[0013] In step S1, the organic acid is at least one of succinic acid, maleic acid, oxalic acid and citric acid, and the concentration of the organic acid is 0.04-4 mol / L.

[0014] In step S1, the silicon-containing compound is at least one of tetraethyl orthosilicate, silicic acid, silicon tetrachloride, sodium silicate, methyl orthosilicate, propyl orthosilicate, silane and siloxane.

[0015] In step S1, the volume ratio of the silicon-containing compound to the solution is 1:2-1:5.

[0016] In step S1, the basic adjusting agent is at least one of ammonia, sodium hydroxide, potassium hydroxide, triethanolamine and sodium carbamate.

[0017] In step S1, the output power of the microwave reaction kettle is 500-6000 W, the reaction temperature is 80-300℃, and the reaction time is 30 seconds-15 minutes.

[0018] In step S2, the organic solvent is at least one of chloroform, acetone, ethyl acetate, dimethylformamide, ethanol, dichloromethane and trichloromethane, and the concentration of polylactic acid in the organic solvent is 0.5-20 wt%;

[0019] The mass ratio of the silica nanoparticles to polylactic acid is 1:1-1:100.

[0020] The surface active agent is at least one of cetyltrimethylammonium bromide, sodium cetylbenzenesulfonate, polyvinyl alcohol, and sodium dodecyl sulfate, and the mass ratio of the surface active agent to polylactic acid is 1:2 to 1:100.

[0021] In step S3, the organic solvent is at least one of chloroform, acetone, ethyl acetate, dimethylformamide, ethanol, dichloromethane, and trichloromethane, and the concentration of polylactic acid in the organic solvent is 0.5 to 40 wt%;

[0022] In step S4, the electrospinning voltage is 20 to 40 kV, the consumption rate of the spinning solution is 0.5 to 3 mL / h, the receiving distance is 10 to 24 cm, the temperature is 0 to 40 DEG C, the relative humidity is 30 to 90%, the average diameter of the obtained polylactic acid inner layer fiber is 100 to 800 nm, and the fiber membrane thickness is 100 to 500 mu m.

[0023] In step S5, the electrospinning voltage is 15 to 30 kV, the consumption rate of the spinning solution is 5 to 10 mL / h, the receiving distance is 10 to 24 cm, the temperature is 0 to 40 DEG C, the relative humidity is 30 to 90%, the average diameter of the obtained polylactic acid outer layer fiber is 1.2 to 4 mu m, and the fiber membrane thickness is 50 to 200 mu m.

[0024] The application also provides a Janus polylactic acid fiber membrane for cooling, which is prepared by the method and can be used in sports clothes, outdoor equipment or air-conditioned clothes, effectively reduces the body surface temperature of the wearer through high infrared emissivity and high sunlight reflection capacity, ensures safety and comfort during long-time contact with the skin due to good biocompatibility and degradability, and promotes the concept of sustainable development. In addition, the moisture absorption and sweat releasing characteristics of the fiber membrane can improve the comfort during exercise, adapt to various exercise scenes such as running, cycling and outdoor exploration, and greatly enhance the activity freedom and comfort of the user.

[0025] Beneficial effects: the application provides a Janus polylactic acid cooling fiber membrane and a preparation method thereof, the Janus polylactic acid fiber membrane is composed of a silica-modified polylactic acid inner layer and a polylactic acid outer layer, the introduction of silica nanoparticles and the spectral selective regulation of the fiber diameter enable the polylactic acid fiber membrane to have high infrared emissivity and high sunlight reflection capacity, the wetting gradient of the fiber membrane can rapidly transport moisture from the inner layer to the outer layer, the fiber membrane not only has excellent radiation cooling effect and rapid moisture absorption and sweat releasing capacity, but also has good biocompatibility and degradability, the preparation process is simple, and is an individual cooling material with wide application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0026] The above and / or other aspects of the present application will become apparent and more readily appreciated from the following description, taken in conjunction with the accompanying drawings in which:

[0027] Figure 1 is a flow chart of the method of the present application.

[0028] Figure 2 is a scanning electron microscope image of the outer layer of the Janus polylactic acid fiber membrane in Example 1.

[0029] Figure 3 is a scanning electron microscope image of the inner layer of the Janus polylactic acid fiber membrane in Example 1. DETAILED DESCRIPTION

[0030] Example 1

[0031] As shown in the following, Figure 1 the present embodiment provides a preparation method of a Janus polylactic acid cooling fiber membrane, comprising the following steps:

[0032] S11. Preparation of silica nanoparticles: dissolve succinic acid (succinic acid concentration is 0.04 mol / L) in ethylene glycol until mixed uniformly, then add tetraethyl orthosilicate (volume ratio of tetraethyl orthosilicate to ethylene glycol is 1:2), stir uniformly, then add ammonia water to the solution to adjust the pH value to 9, and then place the mixed solution into a microwave reaction kettle (microwave reaction kettle output power is 700 W, reaction temperature is 80℃, and reaction time is 15 minutes), after the reaction is completed, centrifuge, wash, and dry to obtain silica nanoparticles;

[0033] S12. Preparation of electrospinning solution A: dissolve silica nanoparticles (mass ratio of silica nanoparticles to polylactic acid is 1:10), cetyltrimethylammonium bromide (mass ratio of cetyltrimethylammonium bromide to polylactic acid is 1:20), and polylactic acid (polylactic acid concentration in the solution is 10wt%) in dichloromethane / dimethylformamide (mass ratio 7:3) in sequence, stir uniformly to obtain electrospinning solution A;

[0034] S13. Preparation of electrospinning solution B: dissolve polylactic acid in dichloromethane / dimethylformamide (mass ratio 7:3) (polylactic acid concentration in the solution is 15wt%), stir uniformly to obtain electrospinning solution B;

[0035] S14. Preparation of the inner layer of the Janus fiber membrane: electrospinning is performed with electrospinning solution A as raw material (voltage 20kV, solution consumption rate 1mL / h, receiving distance 20cm, temperature 25℃, relative humidity 40%), to prepare the inner layer of the Janus fiber membrane, the average diameter of the obtained fibers is 600nm, and the thickness of the fiber membrane is 200μm;

[0036] S15. Preparation of Janus polylactic acid fiber membrane: electrospinning solution B raw material is electrospun at a voltage of 20 kV, a solution consumption rate of 5 mL / h, a receiving distance of 15 cm, a temperature of 25℃, and a relative humidity of 40%, so that the fibers are deposited on the surface of the Janus inner layer fiber membrane, and an outer layer of Janus fiber membrane with an average fiber diameter of 2.3 μm and a fiber membrane thickness of 150 μm is obtained. The composite fiber membrane is dried in an oven to obtain the target Janus polylactic acid fiber membrane.

[0037] Example 2

[0038] The present embodiment provides a preparation method of a Janus polylactic acid cooling fiber membrane, comprising the following steps:

[0039] S21. Preparation of silica nanoparticles: citric acid (concentration of citric acid is 0.8 mol / L) is dissolved in acetone / dimethyl sulfoxide (mass ratio 5:5) until the mixture is uniform, then silicon tetrachloride (volume ratio of silicon tetrachloride to polyvinyl alcohol is 1:4) is added, and after stirring uniformly, sodium hydroxide is added to the solution to adjust the pH value to 11. The mixed solution is placed in a microwave reaction kettle (microwave reaction kettle output power is 6000W, reaction temperature is 150℃, reaction time is 2 minutes), after the reaction is completed, centrifugation, washing and drying are carried out to obtain silica nanoparticles;

[0040] S22. Preparation of electrospinning solution A: silica nanoparticles (mass ratio of silica nanoparticles to polylactic acid is 1:100), sodium dodecyl sulfate (mass ratio of sodium dodecyl sulfate to polylactic acid is 1:80) and polylactic acid (concentration of polylactic acid in the solution is 0.5wt%) are sequentially dissolved in dichloromethane / acetone (mass ratio 6:4) to obtain electrospinning solution A after stirring uniformly;

[0041] S23. Preparation of electrospinning solution B: polylactic acid is dissolved in dichloromethane / acetone (mass ratio 6:4) (concentration of polylactic acid in the solution is 15wt%), and stirring uniformly to obtain electrospinning solution B;

[0042] S24. Preparation of Janus fiber membrane inner layer: electrospinning is carried out with electrospinning solution A raw material (voltage 30 kV, solution consumption rate 0.5 mL / h, receiving distance 18 cm, temperature 30℃, relative humidity 40%), to prepare the Janus fiber membrane inner layer, and the average fiber diameter of the obtained fiber is 300 nm and the fiber membrane thickness is 300 μm;

[0043] S25. Preparation of Janus polylactic acid fiber membrane: electrospinning solution B raw material is electrospun at a voltage of 15 kV, a solution consumption rate of 2 mL / h, a receiving distance of 15 cm, a temperature of 30 °C, and a relative humidity of 40%, so that the fibers are deposited on the surface of the Janus inner layer fiber membrane, and an outer layer of Janus fiber membrane with an average fiber diameter of 1.8 μm and a fiber membrane thickness of 50 μm is obtained. The composite fiber membrane is dried in an oven to obtain the target Janus polylactic acid fiber membrane.

[0044] Example 3

[0045] The present embodiment provides a preparation method of a Janus polylactic acid cooling fiber membrane, comprising the following steps:

[0046] S31. Preparation of silica nanoparticles: oxalic acid (oxalic acid concentration of 4 moles / liter) is dissolved in water until mixed uniformly, then sodium silicate (volume ratio of sodium silicate to polyvinyl alcohol is 1:5) is added, stirred uniformly, then sodium hydroxide is added to the solution to adjust the pH value to 10, and the mixed solution is placed in a microwave reaction kettle (microwave reaction kettle output power is 600 W, reaction temperature is 300 °C, reaction time is 1 minute), after reaction, centrifugation, washing and drying, silica nanoparticles are obtained;

[0047] S32. Preparation of electrospinning solution A: silica nanoparticles (mass ratio of silica nanoparticles to polylactic acid is 1:1), cetyltrimethylammonium bromide (mass ratio of cetyltrimethylammonium bromide to polylactic acid is 1:2) and polylactic acid are successively dissolved in dichloromethane (concentration of polylactic acid in the solution is 15 wt%), and stirred uniformly to obtain electrospinning solution A;

[0048] S33. Preparation of electrospinning solution B: polylactic acid is dissolved in dichloromethane (concentration of polylactic acid in the solution is 40 wt%), and stirred uniformly to obtain electrospinning solution B;

[0049] S34. Preparation of Janus fiber membrane inner layer: electrospinning solution A raw material is electrospun (voltage 20 kV, solution consumption rate 2.5 mL / h, receiving distance 18 cm, temperature 24 °C, relative humidity 45%), to prepare the Janus fiber membrane inner layer, the average fiber diameter is 750 nm, and the fiber membrane thickness is 150 μm;

[0050] S35. Preparation of Janus polylactic acid fiber membrane: electrospinning is carried out with the raw material of electrospinning solution B (voltage 18 kV, solution consumption rate 8 mL / h, receiving distance 20 cm, temperature 24°C, relative humidity 45%), so that the fibers are deposited on the surface of the Janus inner layer fiber membrane, and the Janus fiber membrane outer layer with an average fiber diameter of 3.5 μm and a fiber membrane thickness of 200 μm is obtained. The composite fiber membrane is placed in an oven for drying to obtain the target Janus polylactic acid fiber membrane.

[0051] Comparative Example 1 (polylactic acid fiber membrane without modification of silica nanoparticles)

[0052] The polylactic acid cooling temperature fiber membrane is prepared basically by the method of Example 1. The difference is that in this example, no silica nanoparticles are added when preparing the electrospinning solution A. Specifically, cetyltrimethylammonium bromide (mass ratio of cetyltrimethylammonium bromide to polylactic acid is 1:20) and polylactic acid (concentration of polylactic acid in the solution is 10 wt%) are sequentially dissolved in dichloromethane / dimethylformamide (mass ratio 7:3) to obtain electrospinning solution A; polylactic acid is dissolved in dichloromethane / dimethylformamide (mass ratio 7:3) (concentration of polylactic acid in the solution is 15 wt%) to obtain electrospinning solution B; electrospinning is carried out with the raw material of electrospinning solution A (voltage 20 kV, solution consumption rate 1 mL / h, receiving distance 20 cm, temperature 25°C, relative humidity 40%) to prepare the Janus fiber membrane inner layer, and the obtained fiber has an average diameter of 480 nm and a fiber membrane thickness of 200 μm; electrospinning is carried out with the raw material of electrospinning solution B (voltage 20 kV, solution consumption rate 5 mL / h, receiving distance 15 cm, temperature 25°C, relative humidity 40%) to make the fibers deposited on the surface of the Janus inner layer fiber membrane, and the Janus fiber membrane outer layer with an average fiber diameter of 2.3 μm and a fiber membrane thickness of 150 μm is obtained. The composite fiber membrane is placed in an oven for drying to obtain the polylactic acid fiber membrane without modification of silica nanoparticles.

[0053] Comparative Example 2 (single diameter distribution polylactic acid fiber membrane)

[0054] The polylactic acid cooling temperature fiber membrane was prepared by substantially using the method of Example 3. The difference is that the diameter of the outer fiber membrane is kept consistent with the diameter of the inner layer fiber by controlling the spinning parameters. Specifically, oxalic acid (oxalic acid concentration of 4 moles / liter) was dissolved in water until the mixture was uniform, then silicon tetrachloride (volume ratio of silicon tetrachloride to polyvinyl alcohol was 1:5) was added, after stirring uniformly, sodium hydroxide was added to the solution to adjust the pH value to 10, the mixed solution was placed in a microwave reaction kettle (microwave reaction kettle output power was 600W, reaction temperature was 300℃, reaction time was 1 minute), after the reaction was completed, centrifugation, washing, drying, silica nanoparticles were obtained; silica nanoparticles (mass ratio of silica nanoparticles to polylactic acid was 1:1), cetyltrimethylammonium bromide (mass ratio of cetyltrimethylammonium bromide to polylactic acid was 1:2) and polylactic acid were successively dissolved in dichloromethane (concentration of polylactic acid in the solution was 15wt%), to obtain an electrospinning solution A; polylactic acid was dissolved in dichloromethane (concentration of polylactic acid in the solution was 15wt%) to obtain an electrospinning solution B; electrospinning was performed with electrospinning solution A raw material (voltage 20kV, solution consumption rate 2.5mL / h, receiving distance 18cm, temperature 24℃, relative humidity 45%), to prepare the inner layer of the Janus fiber membrane, the average diameter of the obtained fiber was 750nm, and the thickness of the fiber membrane was 150μm; electrospinning was performed with electrospinning solution B raw material (voltage 20kV, solution consumption rate 2.5mL / h, receiving distance 18cm, temperature 24℃, relative humidity 45%), to make the fiber deposited on the surface of the Janus inner layer fiber membrane, to obtain a fiber membrane outer layer with an average fiber diameter of 750nm and a fiber membrane thickness of 200μm, the composite fiber membrane was placed in an oven for drying, to obtain a single diameter distribution polylactic acid fiber membrane.

[0055] Comparative Example 3 (polylactic acid fiber membrane without adding surfactant)

[0056] A polylactic acid cooling and temperature-lowering fiber membrane was prepared using the method of Example 2. The difference is that no surfactant was added when preparing the electrospinning solution A. Specifically, citric acid (citric acid concentration of 0.8 mol / L) was dissolved in acetone / dimethyl sulfoxide (mass ratio of 5:5) until the mixture was uniform, then sodium silicate (volume ratio of sodium silicate to polyvinyl alcohol of 1:4) was added, and after stirring uniformly, sodium hydroxide was added to the solution to adjust the pH value to 11. The mixed solution was placed in a microwave reaction kettle (microwave reaction kettle output power of 6000 W, reaction temperature of 150°C, reaction time of 2 minutes), after the reaction was completed, centrifugation, washing, and drying were performed to obtain silica nanoparticles; the silica nanoparticles (mass ratio of silica nanoparticles to polylactic acid of 1:100) and polylactic acid (polylactic acid concentration in the solution of 0.5 wt%) were sequentially dissolved in dichloromethane / acetone (mass ratio of 6:4) to obtain the electrospinning solution A; polylactic acid was dissolved in dichloromethane / acetone (mass ratio of 6:4) (polylactic acid concentration in the solution of 15 wt%) to obtain the electrospinning solution B; electrospinning was performed using the electrospinning solution A as the raw material (voltage of 30 kV, solution consumption rate of 0.5 mL / h, receiving distance of 18 cm, temperature of 30°C, and relative humidity of 40%) to prepare the inner layer of the fiber membrane, and the average diameter of the obtained fibers was 310 nm, and the thickness of the fiber membrane was 300 pm; electrospinning was performed using the electrospinning solution B as the raw material (voltage of 15 kV, solution consumption rate of 2 mL / h, receiving distance of 15 cm, temperature of 30°C, and relative humidity of 40%) to make the fibers deposit on the surface of the inner layer of the fiber membrane, and the average diameter of the fibers was 1.8 pm, and the thickness of the fiber membrane was 50 pm, thereby obtaining the outer layer of the fiber membrane; the composite fiber membrane was dried in an oven to obtain the polylactic acid fiber membrane without adding a surfactant.

[0057] Structural characterization and performance testing:

[0058] Scanning electron microscope observation: The microstructure of the Janus polylactic acid cooling and temperature-lowering fiber membrane was observed by a field emission scanning electron microscope (model SU8220, HITACHI) (as shown in FIG. 1). Figure 2 , Figure 3

[0059] Solar reflectance test: An ultraviolet-visible-near infrared spectrophotometer (model UV-3600, Shimadzu) was used to measure the reflectance of the fiber membrane at 300-2500 nm.

[0060] Infrared reflectance test: An FTIR spectrometer (model NEXUS-670, Thermo Fisher) equipped with a diffuse gold integrating sphere (PIKE Technologies) was used to measure the infrared reflectance and transmittance of the fiber membrane at 8-13 pm.

[0061] ​One-way water transport test: 15 μL of deionized water was dropped onto the outside of the Janus fiber membrane, and the transfer time of the water droplet from the outside to the inside was recorded. At least 5 different locations were tested for each group of fiber membranes, and the average value of the results was taken.

[0062] Outdoor cooling performance test: The cooling performance of the fiber membrane was measured outdoors (11:00-13:00, August 25, 2024, Xuzhou). A silicone rubber heating plate was used to heat the simulated skin (insulating foam wrapped in aluminum foil) and the temperature was maintained at 37°C. A K-type thermocouple (model YET-640X, Dickwell) was used to record the temperature difference between the fiber membrane and the exposed simulated skin.

[0063] Experimental results:

[0064] like Figure 2 As shown, the average diameter of the outer layer of Janus polylactic acid (PLA) fiber is 600 nm. The "protrusions" on the fiber surface and the "bulges" inside indicate that silica nanoparticles have been introduced into the PLA fiber. Figure 3 As shown, the average diameter of the inner layer of Janus polylactic acid fiber is 2.3 μm, and the fiber surface is smooth. In Example 1, the inner and outer layers of the fiber membrane exhibit a pore size gradient, which provides favorable conditions for the directional water transport characteristics of Janus polylactic acid fiber.

[0065] Table 1 compares the specific surface area, dielectric properties, and filtration performance test results of the Janus polylactic acid fiber membranes obtained in the examples and comparative examples. Examples 1-3 and Comparative Example 2 have high average infrared emissivity (90.51%-95.32%), which is because the stretching vibrations of the -Si-O-Si- and -Si-O- bonds in the silica nanoparticles introduced into the polylactic acid fibers greatly enhance the emission of infrared light by the fiber membrane.

[0066] Table 1

[0067]

[0068] Examples 1-3 and Comparative Example 3 all exhibit high solar reflectance (92.31%-93.76%) because the diameter distribution of the polylactic acid (PLA) fiber membrane (including the inner and outer fiber layers) ranges from 0.3 to 3.2 μm, covering the entire solar wavelength range (0.3-2.5 μm), thus generating broadband solar scattering. Furthermore, the silica particles with a particle size distribution of 0.1 to 1.1 μm effectively scatter sunlight. The PLA fiber membrane of Comparative Example 1, which does not incorporate silica particles, has a lower solar reflectance of 85.01%. The PLA fiber membrane of Comparative Example 2 has relatively uniform inner and outer layer diameters, but a narrower fiber diameter distribution, resulting in a solar reflectance of only 83.31%.

[0069] Examples 1-3 and Comparative Example 1 all have excellent moisture absorption and perspiration ability, with one-way water transmission time distributed between 15-25s, which is driven by the wettability gradient and pore size gradient between the inner and outer layers of the fiber membrane. Comparative Example 2 has comparable pore sizes in the inner and outer layers, and water transport is only driven by the wettability gradient, so it exhibits slower one-way water transmission time. The outer layer of the fiber membrane in Comparative Example 3 is not modified with a hydrophilic surfactant, and the fiber membrane does not have a wettability gradient, so it does not exhibit one-way water transmission performance.

[0070] Examples 1-3 and Comparative Example 3 exhibit better radiative cooling performance (cooling temperature: 10.5-11.9℃), which benefits from their high infrared emission and high solar emissivity. Comparative Examples 1 and 2 have poorer radiative cooling performance, with cooling temperatures of 6.7℃ and 7.2℃, respectively.

[0071] Therefore, the technical scheme proposed in the present embodiment enables the Janus polylactic acid cooling fiber membrane to have excellent radiative refrigeration effect and rapid moisture absorption and perspiration ability, which is likely to benefit from: (1) the silica nanoparticles obtained by the microwave-assisted method have uniform size and regular structure, and can be well dispersed in the fiber; (2) the introduction of silica nanoparticles enhances the emission of infrared light and the scattering of visible light by the fiber membrane; (3) the diameter of the fiber membrane is widely distributed in the broadband solar spectrum, enabling the polylactic acid fiber membrane to produce broadband solar scattering; (4) the wettability gradient and pore size gradient between the inner and outer fibers promote the rapid directional transport of water.

[0072] The present application provides a Janus polylactic acid fiber membrane for cooling and its preparation method. There are many methods and ways to realize this technical scheme, and the above description is only the preferred embodiment of the present application. It should be noted that for ordinary skilled persons in the technical field, several improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements should also be considered within the scope of protection of the present application. The components not explicitly described in the present embodiment can be realized by existing technology.

Claims

1. A method for preparing a Janus polylactic acid fiber film for cooling, characterized by, The method comprises the following steps: Step S1, preparing silica nanoparticles: dissolving an organic acid in a polar solvent to obtain a solution, adding a silicon-containing compound to the solution, stirring uniformly, then adding a basic regulator, placing the mixed solution in a microwave reaction kettle, centrifuging, washing and drying after the reaction to obtain silica nanoparticles; Step S2, preparing electrospinning solution A: dissolving silica nanoparticles, a surfactant and polylactic acid in an organic solvent in sequence, stirring uniformly to obtain electrospinning solution A; Step S3, preparing electrospinning solution B: dissolving polylactic acid in an organic solvent, stirring uniformly to obtain electrospinning solution B; Step S4, preparing the inner layer of a Janus fiber membrane: electrospinning the raw material of electrospinning solution A to prepare the inner layer of a Janus fiber membrane; Step S5, preparing a Janus polylactic acid fiber membrane: electrospinning the raw material of electrospinning solution B to make the fiber deposit on the surface of the Janus inner layer fiber membrane to prepare the outer layer of a Janus fiber membrane, and drying the composite fiber membrane in an oven to obtain the target Janus polylactic acid fiber membrane; In step S1, the output power of the microwave reaction kettle is 500-6000 W, the reaction temperature is 80-300℃, and the reaction time is 30 seconds-15 minutes; In step S2, the organic solvent is at least one of chloroform, acetone, ethyl acetate, dimethylformamide, ethanol, dichloromethane and trichloromethane, and the concentration of polylactic acid in the organic solvent is 0.5-20 wt %; The mass ratio of the silica nanoparticles to polylactic acid is 1:1-1:100; The surfactant is at least one of cetyltrimethylammonium bromide, sodium cetylbenzenesulfonate, polyvinyl alcohol and sodium dodecyl sulfate, and the mass ratio of the surfactant to polylactic acid is 1:2-1:100; In step S3, the organic solvent is at least one of chloroform, acetone, ethyl acetate, dimethylformamide, ethanol, dichloromethane and trichloromethane, and the concentration of polylactic acid in the organic solvent is 0.5-40 wt %; In step S4, the electrospinning voltage is 20-40 kV, the consumption rate of the spinning solution is 0.5-3 mL / h, the receiving distance is 10-24 cm, the temperature is 0-40℃, the relative humidity is 30-90%, the average diameter of the polylactic acid inner layer fiber is 100-800 nm, and the thickness of the fiber membrane is 100-500 μm; In step S5, the electrospinning voltage is 15-30 kV, the consumption rate of the spinning solution is 5-10 mL / h, the receiving distance is 10-24 cm, the temperature is 0-40℃, the relative humidity is 30-90%, the average diameter of the polylactic acid outer layer fiber is 1.2 μm-4 μm, and the thickness of the fiber membrane is 50-200 μm.

2. The method of claim 1, wherein, In step S1, the polar solvent is at least one of ethylene glycol, polyvinyl alcohol, dimethyl sulfoxide, acetone, ethanolamine and water; The pH value is adjusted to 9-11 after stirring uniformly and adding the basic regulator.

3. The method of claim 1, wherein, In step S1, the organic acid is at least one of butanedioic acid, maleic acid, oxalic acid and citric acid, and the concentration of the organic acid is 0.04-4 mol / L.

4. The method of claim 1, wherein, In step S1, the silicon-containing compound is at least one of tetraethyl orthosilicate, silicic acid, silicon tetrachloride, sodium silicate, methyl orthosilicate, propyl orthosilicate, silane, siloxane.

5. The method of claim 1, wherein, In step S1, the volume ratio of the silicon-containing compound to the solution is 1:2 to 1:

5.

6. The method of claim 1, wherein, In step S1, the alkaline adjusting agent is at least one of ammonia, sodium hydroxide, potassium hydroxide, triethanolamine, sodium carbamate.

7. A Janus polylactic acid fiber film for cooling, characterized by, Prepared by a method as claimed in any one of claims 1 to 6.

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