PLA / PTFE radiation refrigeration composite film based on electrostatic spinning method as well as preparation method and application of PLA / PTFE radiation refrigeration composite film

Abstract

The invention discloses a preparation method and application of a PLA (polylactic acid) / PTFE (polytetrafluoroethylene) radiation refrigeration composite film based on an electrostatic spinning method, and belongs to the field of radiation refrigeration materials. And preparing the polymer radiation composite fiber membrane by adopting an electrostatic spinning technology. The obtained micro-nano size fiber film has a porous structure, can realize a strong Mie scattering effect on solar wavelength, improves the solar reflectivity of the radiation film, and realizes the reflectivity of 85% or above within the wavelength of 400-1400 nm and the relatively high infrared emissivity of 90% within the wavelength of 8-13 [mu] m. The radiation cooling composite film has great application potential value in the field of low-temperature grain storage.

Description

Technical Field

[0001] The present invention relates to the technical field of radiation cooling polymer film materials, in particular to a PLA / PTFE radiation cooling composite film based on an electrospinning method, and a preparation method and application thereof. Background Art

[0002] With the development of industry and the growth of the global population, energy demand and consumption are increasing rapidly. Traditional fossil fuels (oil, coal, natural gas, etc.) are non-renewable resources, and their annual consumption is enormous, leading to increased emissions of pollutants and greenhouse gases, exacerbating environmental degradation and global warming. Space heating and cooling systems, such as air conditioning, account for nearly 60% of total annual energy consumption in buildings. If this growth rate continues, energy consumption for building cooling will increase tenfold by 2050. Therefore, reducing energy consumption for indoor temperature regulation is of great significance and has been a key area of ​​research focus in recent years.

[0003] Passive radiative cooling (PRC) is a green and environmentally friendly technology that achieves spontaneous cooling without external energy input. It radiates heat from an object to a cold source in the form of electromagnetic waves, lowering the temperature of the object or room. For objects on the surface, outer space is an ideal cold source at near-zero temperatures. Radiative cooling materials exploit the spectral properties of their materials to achieve spontaneous cooling. This is achieved primarily through two approaches: first, through radiative heat exchange with outer space through the 8-13 μm atmospheric window; second, through the optical properties of the material, reflecting solar radiation, reducing the energy within the object and achieving a cooling effect.

[0004] With the continuous development of micro- and nanotechnology, electrospinning has been increasingly used to prepare porous fiber-based radiative cooling membranes, attracting considerable research interest in recent years. Electrospinning is a processing technique for producing micro- and nanofibers. Polymer droplets are ejected from a needle in a strong electric field, forming a jet. The droplets are then stretched into filaments by the electric field, forming a stacked micro- and nanofiber membrane at the receiving end. Because the structural dimensions of these fibers are close to the wavelength of visible light, they produce a strong scattering effect, achieving excellent sunlight reflection. Therefore, electrospinning, as a commonly used processing technique for preparing polymer-based radiative cooling membranes, holds great market potential and application value.

[0005] Polylactic acid (PL) is a new biodegradable material made from starch extracted from renewable plant resources such as corn. Lactic acid has excellent biocompatibility and naturally degrades in the wild, making it an environmentally friendly material. PLA holds great potential in the field of radiative cooling, but its traditional preparation process is complex and costly, hindering large-scale industrial deployment. Electrospinning technology, however, enables highly stable and efficient production of micro- and nano-PLA fibers. The micro- and nano-pores within these fibers generate a strong Mie scattering effect, effectively enhancing solar reflectivity. Polytetrafluoroethylene (PTFE), primarily composed of C-H bonds, exhibits high solar reflectivity and infrared emissivity across the entire solar radiation range (200-2500 nm). It also possesses excellent properties such as hydrophobicity, UV resistance, and chemical inertness. Therefore, combining these two properties can effectively enhance the radiative cooling performance of electrospun membranes. The application of radiant cooling film in low-temperature grain storage has great prospects. It can effectively reduce the natural heating phenomenon during rice storage, prevent and slow down the invasion of pests and quality deterioration, and is of great significance to the development of grain storage technology. Summary of the Invention

[0006] The first objective of the present invention is to provide a PLA / PTFE radiative cooling composite membrane based on electrospinning. This radiative cooling composite membrane, primarily composed of PLA and PTFE, is produced by electrospinning a micro-nanofiber membrane. This micro-nanofiber membrane possesses a porous structure, enabling a strong Mie scattering effect at solar wavelengths. This effectively increases the solar reflectivity of the radiative film and enhances its radiative cooling performance.

[0007] A second objective of the present invention is to provide a method for preparing a POM / PVDF radiative cooling composite membrane based on electrospinning. PLA is used as a matrix, and polytetrafluoroethylene (PTFE) particles are added. A uniform spinning solution is stirred in a DCM / DMF mixed solvent, and then electrospinning is used to prepare the radiative cooling composite fiber membrane.

[0008] The third object of the present invention is to provide the application of the PLA / PTFE radiation refrigeration composite membrane based on electrospinning in the field of low-temperature grain storage.

[0009] The purpose of the present invention is achieved through the following technical solutions: This invention describes a PLA / PTFE composite membrane for radiative cooling based on electrospinning. The membrane is prepared using electrospinning from raw materials consisting of poly(lactic acid) (PLA) and polytetrafluoroethylene (PTFE), along with a mixed solvent of dichloromethane (DCM) and N,N-dimethylformamide (DMF). The PLA serves as the matrix, providing the primary component of the electrospun fiber membrane. The PTFE, with its high solar reflectivity and infrared emissivity across the entire solar radiation range (200-2500 nm), acts as an additive to enhance the film's radiative cooling performance.

[0010] The solvent is selected by mixing dichloromethane (DCM) and N,N-dimethylformamide (DMF) in a certain proportion, which can effectively dissolve a variety of insoluble polymers. Dichloromethane has good volatility, which can ensure good volatilization of the solvent during the spinning process, which is conducive to the stable formation of fiber filaments. By adding N,N-dimethylformamide, the solubility and viscosity of the spinning solution are guaranteed, forming a uniform nanofiber structure.

[0011] This technical approach is based on three main research contents, as described below: 1. Add polylactic acid (PLA) to a mixed solvent of dichloromethane (DCM) and N,N-dimethylformamide (DMF) and stir to dissolve it continuously.

[0012] 2. After dissolving PLA in the solvent, add polytetrafluoroethylene (PTFE) powder and use stirring and ultrasonic technology to evenly distribute it in the spinning solution and fully and evenly combine it with the PLA component.

[0013] 3. The preliminary obtained spinning solution is subjected to electrospinning, wherein the electrospinning parameters (including spinning distance, positive and negative high voltage, needle diameter, etc.) are adjusted to obtain a radiative cooling electrospun membrane with optimal radiative cooling performance.

[0014] A method for preparing a PLA / PTFE radiative cooling composite membrane based on an electrospinning method comprises the following steps: Step 1. Before the experiment begins, calculate the amount of experimental raw materials required for each ratio, and use an electronic balance to weigh the experimental raw materials according to the calculated values: solvent dichloromethane (DCM) and N,N-dimethylformamide (DMF), polylactic acid PLA, and polytetrafluoroethylene PTFE.

[0015] Step 2: Add polylactic acid (PLA) powder to a DCM / DMF mixed solvent, stir and mix until the polylactic acid powder is fully dissolved in the solution, gradually add PTFE particle powder to the obtained PLA solution, and then use a magnetic stirrer to completely mix the two. After fully stirring for a period of time, ultrasonically treat the spinning solution.

[0016] Step 3: electrospin the obtained spinning solution, and adjust the appropriate spinning parameters so that the droplets at the needle tip can stably form a Taylor cone under the action of the electric field, and stack at the receiving end to form a fiber membrane.

[0017] Step 4: After spinning is completed, the aluminum foil at the receiving end is removed, placed at room temperature for more than 24 hours, and then subjected to low-temperature drying treatment. Finally, the performance of the film material is characterized and analyzed.

[0018] The polylactic acid (PLA) described in step 1 (purity > 99%), polytetrafluoroethylene (PTFE) (purity > 99%), solvents dichloromethane (DCM) (analytical grade), and N,N-dimethylformamide (DMF) (analytical grade), wherein the total polymer concentration is 10%, and the ratio of the DCM / DMF mixed solvent is 9:1.

[0019] The concentration of the polylactic acid PLA described in step 2 is 5%, and the mass ratio of PTFE particles to polylactic acid PLA in the solution is 1:1.

[0020] The magnetic stirrer described in step 2 was stirred at a speed of 500 r / min, a stirring temperature of room temperature (25° C.), and a stirring time of more than 12 h.

[0021] The parameters for electrospinning in step 3 are: spinning needles of size 18 to 22, spinning distance (the distance between the needle and the collecting device) of 80 to 200 mm, ambient temperature of 25 °C, voltage of 8 to 25 kV, spinning speed of 0.1 to 0.4 mm / min, and relative air humidity of 30% to 40%.

[0022] The spinning needle is preferably No. 19.

[0023] The electrospinning distance is preferably 160 mm.

[0024] The spinning voltage is preferably 20 kV.

[0025] The spinning speed is preferably 0.2 mm / min.

[0026] The relative humidity of the air is preferably 35%.

[0027] The application of the PLA / PTFE radiation refrigeration composite membrane based on the electrospinning method in the field of low-temperature grain storage.

[0028] The low-temperature grain storage field includes granary top and exterior wall covering, and grain pile packaging materials.

[0029] Compared with the prior art, the present invention has the following benefits: The present invention is a method for preparing a PLA / PTFE radiative cooling composite membrane based on electrospinning. Two polymers with good properties are blended by physical stirring, and a micro-nano fiber membrane is prepared using electrospinning technology. The obtained radiative cooling membrane has good radiative cooling performance. Compared with other fiber preparation technologies, electrospinning has the advantages of easy operation, continuousness, and large-area preparation. It is suitable for polymer film materials and can be well compatible with various different application scenarios.

[0030] The present invention provides a PLA / PTFE radiation cooling composite membrane based on electrospinning. The radiation cooling composite membrane can maintain a reflectivity of 85% in the wavelength range of 400-1400nm, can effectively reflect thermal radiation from the sun and the environment, achieve an infrared emissivity of 90% in the atmospheric window of 8-13μm, and has good radiation cooling performance.

[0031] The present invention provides a PLA / PTFE radiation refrigeration composite membrane based on electrospinning, which has important practical value in the application of low-temperature storage technology, helps to reduce energy consumption in the refrigeration system, and meets the green development requirements of environmental protection and sustainable development. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 These are SEM images of four composite membranes with different proportions obtained in Examples 1-4; among them, (a) is the SEM image of the composite membrane prepared in Example 1; (b) is the SEM image of the composite membrane prepared in Example 2; (c) is the SEM image of the composite membrane prepared in Example 3; and (d) is the SEM image of the composite membrane prepared in Example 4.

[0033] Figure 2 These are Fourier transform infrared (FT-IR) spectra of four composite films with different proportions obtained in Examples 1-4; among them, PLA is the Fourier transform infrared spectrum of the composite film prepared in Example 1; PP1 is the Fourier transform infrared spectrum of the composite film prepared in Example 2; PP3 is the Fourier transform infrared spectrum of the composite film prepared in Example 3; PP5 is the Fourier transform infrared spectrum of the composite film prepared in Example 4.

[0034] Figure 3 The reflectivity graphs of four composite films with different ratios obtained in Examples 1-4; among them, PLA is the reflectivity curve of the composite film prepared in Example 1; PP1 is the reflectivity curve of the composite film prepared in Example 2; PP3 is the reflectivity curve of the composite film prepared in Example 3; PP5 is the reflectivity curve of the composite film prepared in Example 4 Figure 4These are infrared emissivity graphs of four radiative cooling composite films with different proportions obtained in Examples 1-4; among them, PLA is the infrared emissivity curve of the composite film prepared in Example 1; PP1 is the infrared emissivity curve of the composite film prepared in Example 2; PP3 is the infrared emissivity curve of the composite film prepared in Example 3; and PP5 is the infrared emissivity curve of the composite film prepared in Example 4. DETAILED DESCRIPTION

[0035] The present invention will be described in further detail below in conjunction with the examples, but embodiments of the present invention are not limited thereto. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art. The test methods in the following examples where specific experimental conditions are not specified are generally based on conventional experimental conditions. Unless otherwise specified, the reagents and raw materials used in the present invention can be obtained commercially.

[0036] The experimental steps described in the present invention include: first, weighing a certain amount of dichloromethane (DCM) and N,N-dimethylformamide (DMF) solvents, adding them to a beaker and mixing them, then adding polylactic acid (PL) and stirring on a magnetic stirrer until the PLA is completely dissolved. Then, polytetrafluoroethylene (PTFE) micropowder is added and stirred until completely dispersed. Ultrasonic technology is used to evenly distribute the PTFE powder in the spinning solution, allowing it to combine uniformly with the PLA component. The resulting spinning solution is electrospun, where electrospinning parameters (including spinning distance, positive and negative high voltages, and needle diameter) are adjusted to obtain a radiative cooling electrospun membrane with optimal radiative cooling performance. After spinning, the aluminum foil at the receiving end is removed and the membrane is left at room temperature for at least 24 hours. The membrane is then vacuum-dried and sealed for storage. Example

[0037] This embodiment provides a method for preparing a PLA / PTFE radiative cooling composite membrane based on an electrospinning method, comprising the following steps: S1. Before the experiment begins, calculate the amount of experimental raw materials required for each ratio. Use an electronic balance to weigh the experimental raw materials according to the calculated values ​​and mix them in the specified proportions. Prepare a 9:1 mixture of dichloromethane (DCM) and N,N-dimethylformamide (DMF) with 10g of solvent, 1g of polylactic acid (PL), and 0g of polytetrafluoroethylene (PTFE) to achieve a solute content of 10%. Add the polylactic acid and polytetrafluoroethylene powders to the solvent in sequence. Stir on a magnetic stirrer at 25°C for 12 hours to thoroughly mix the solution. Set the stirring speed to 500 r / min.

[0038] S2. After stirring until the PTFE powder is initially evenly distributed, ultrasonic treatment is performed for 5 minutes to further evenly disperse the PTFE powder in the solution.

[0039] S3. The obtained spinning solution is subjected to electrospinning, and appropriate spinning parameters are adjusted so that the droplets at the needle tip can stably form a Taylor cone under the action of the electric field, and stacked at the receiving end to form a fiber membrane.

[0040] S4. After spinning is completed, remove the aluminum foil at the receiving end, place it at room temperature for more than 24 hours, and then vacuum dry it at 60°C for 6 hours. Finally, test and characterize the film material. Example

[0041] This embodiment provides a method for preparing a PLA / PTFE radiative cooling composite membrane based on an electrospinning method. The conditions of this embodiment are basically the same as those of Example 1, except that in step S1, the mass of polylactic acid PLA is 0.9 g, the mass of polytetrafluoroethylene PTFE is 0.1 g, and the mass ratio of the two is 9:1. Example

[0042] This embodiment provides a method for preparing a PLA / PTFE radiative cooling composite membrane based on an electrospinning method. The conditions of this embodiment are basically the same as those of Example 1, except that in step S1, the mass of polylactic acid PLA is 0.7 g, the mass of polytetrafluoroethylene PTFE is 0.3 g, and the mass ratio of the two is maintained at 7:3. Example

[0043] This embodiment provides a method for preparing a PLA / PTFE radiative cooling composite membrane based on an electrospinning method. The conditions of this embodiment are basically the same as those of Example 1, except that in step S1, the mass of polylactic acid PLA is 0.5 g, the mass of polytetrafluoroethylene PTFE is 0.5 g, and the mass ratio of the two is maintained at 1:1.

[0044] Characterization analysis The four radiative cooling composite films prepared in Examples 1-4 were subjected to SEM micromorphology analysis. The results are as follows: Figure 1 shown. Figure 1 Figure 2 shows SEM images of four proportional samples: (a) pure PLA fiber membrane, (b), (c), and (d) PP1, PP3, and PP5, respectively. Figure (a) shows the stacked structure of the PLA porous fiber membrane. The interlaced fibers provide a large number of pores, which are crucial for reflecting sunlight. The surfaces of the PP1, PP3, and PP5 fibers also exhibit a significant amount of pores. The addition of PTFE creates a disordered, beaded-like structure composed of nanoscale PLA fibers and micron-sized PTFE particles, providing a richer porosity. In comparison, the PP1 sample exhibits a more uniform distribution of fibers and particles, demonstrating a superior microstructural morphology.

[0045] Fourier transform infrared spectroscopy was performed on the four radiation cooling composite films prepared in Examples 1-4. The results are as follows: Figure 2 Infrared spectroscopy analysis of pure PLA and three different ratios of PLA / PTFE composite materials, namely PLA, PP1, PP3, and PP5, was performed in the test band of 400-4000cm -1 .from Figure 2 The infrared spectrum shows that the main absorption peak of PLA material is at 2850cm -1 , 1600cm -1 , 1400cm -1 The PP9, PP7, and PP3 curves show double peaks at approximately 1200 cm⁻¹ and 1150 cm⁻¹, representing C₂₁₃ stretching vibrations. These peaks increase with increasing PTFE content, consistent with the expected properties of radiative cooling materials. This is the key reason why PLA / PTFE radiative cooling films exhibit high emissivity, making them a promising candidate for radiative cooling materials.

[0046] The reflectivity test of the four radiative cooling composite films prepared in Examples 1-4 was carried out. Figure 3 shown. Figure 3 The reflectivity of four radiative cooling composite films within the wavelength range of 200-1400nm was analyzed. The four reflectivity curves, designated PLA, PP1, PP3, and PP5, reflect the reflectivity of the radiative cooling materials in the solar wavelength range. All four sample materials generally achieved reflectivity exceeding 80%, with the PP1 radiative cooling composite film exhibiting the highest reflectivity, reaching an average reflectivity of over 85% within the wavelength range of 400-1400nm. Therefore, the PP1 composite fiber film possesses superior radiative cooling performance.

[0047] The reflectivity test of the four radiative cooling composite films prepared in Examples 1-4 was conducted, and the results were as follows: Figure 4 shown. Figure 4 The infrared emissivity diagram of the samples is recorded as PLA, PP1, PP3, and PP5 respectively. The emissivity of the four radiative cooling composite films in the range of 2.5-15μm is mainly analyzed. Among them, PLA and PP1 have better emissivity performance, and the maximum emissivity reaches 90% in the range of 8-13μm.

[0048] According to characterization tests, PTFE was added to the PLA solution to form a mixed spinning solution, and the PLA / PTFE composite fiber membrane was prepared by electrospinning technology. Its radiative cooling performance was effectively enhanced. Among them, when the mass ratio of PLA to PTFE was 9:1, the average reflectivity reached more than 85% within the wavelength of 400-1400nm, and the emissivity reached a maximum of 90% at 8-13μm, and its radiative cooling comprehensive performance was good. Therefore, the PLA / PTFE radiative cooling composite membrane based on the electrospinning method of the present invention has great potential application value in the field of low-temperature grain storage. It can effectively realize radiative cooling and achieve passive cooling of granaries, thereby extending the storage time of grain and reducing grain losses caused by high temperatures. The application prospects in the field of grain storage are particularly broad.

[0049] The above description of the specific exemplary embodiments of the present invention is for illustration and purpose. The present invention is not limited to the above-described embodiments. Any obvious improvements, substitutions, or modifications that can be made by those skilled in the art without departing from the essence of the present invention are within the scope of protection of the present invention. The scope of the present invention is intended to be defined by the claims and their equivalents.

Claims

1. A method for preparing a PLA / PTFE radiative cooling composite membrane based on electrospinning, characterized in that: The following steps are involved: Step 1: Before the experiment begins, calculate the amount of experimental raw materials required for each ratio, and use an electronic balance to weigh the experimental raw materials according to the calculated values, including PLA powder, PTFE powder, DCM, and DMF reagent; Step 2: PLA powder is added to a mixed solvent and stirred to fully dissolve in the solution. PTFE particle powder is gradually added to the obtained PLA solution, and then the two are completely mixed on a magnetic stirrer. After fully stirring for 12 to 24 hours, the spinning solution is ultrasonically treated. Step 3: electrospinning the obtained spinning solution, adjusting the appropriate spinning parameters so that the droplets at the needle tip can stably form a Taylor cone under the action of the electric field, and stacking to form a fiber membrane at the receiving end; Step 4: After spinning is completed, the aluminum foil at the receiving end is removed, placed at room temperature for more than 24 hours, and then subjected to low-temperature drying treatment. Finally, the performance of the film material is characterized and analyzed.

2. The method for preparing a PLA / PTFE radiative cooling composite membrane based on electrospinning according to claim 1, characterized in that: The solvent in step 2 is a mixed solvent of DCM / DMF, with a mass ratio of DCM to DMF of 9:

1.

3. The method for preparing a PLA / PTFE radiative cooling composite membrane based on electrospinning according to claim 1, characterized in that: The total mass percentage of PLA and PTFE in step 2 is 5-15%.

4. The method for preparing a PLA / PTFE radiative cooling composite membrane based on electrospinning according to claim 5, characterized in that: The total mass content of PLA and PTFE is maintained at 10%, wherein the mass percentage of PLA is 5-10%.

5. The method for preparing a PLA / PTFE radiative cooling composite membrane based on electrospinning according to claim 1, characterized in that: During the stirring in step 2, the speed of the magnetic stirrer is set to 500 r / min, the stirring temperature is room temperature 25° C., and the stirring time is 12 h.

6. The method for preparing a PLA / PTFE radiative cooling composite membrane based on electrospinning according to claim 1, characterized in that: The parameters for electrospinning in step 3 are as follows: the spinning needle is No. 18 to No. 22, the spinning distance is 80 to 200 mm, the ambient temperature is 25 ° C, the voltage is 8 to 25 kV, the spinning speed is 0.1 to 0.4 mm / min, and the relative humidity of the air is 30%-40%.

7. The method for preparing a PLA / PTFE radiative cooling composite membrane based on electrospinning according to claim 8, characterized in that: The spinning needle was No. 19, the spinning distance was 160 mm, the ambient temperature was 25 °C, the voltage was 20 kV, the spinning speed was 0.2 mm / min, and the relative humidity of the air was 35%.

8. The method for preparing a PLA / PTFE radiative cooling composite membrane based on electrospinning according to claim 1, characterized in that: The low-temperature drying treatment in step 4 is carried out in a vacuum drying oven at 60° C. for 6 to 12 hours or more to remove the residual solvent components.

9. A PLA / PTFE radiative cooling composite membrane based on electrospinning, characterized in that: Prepared according to any one of claims 1 to 10.

10. Use of the PLA / PTFE radiation refrigeration composite membrane based on electrospinning as claimed in claim 9 in the field of low-temperature grain storage.

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