Spectrally selective film for high efficiency agriculture

Abstract

The application discloses a spectrum-selective film for efficient agriculture, which adopts a four-layer composite structure, and comprises a spectrum-selective regulation layer, a composite fiber base layer and surface self-cleaning layers covering two sides. The film can reflect green light which contributes less to photosynthesis of most crops, efficiently transmit core photosynthesis wave bands (red and blue light), and reflect most near-infrared rays to reduce the temperature in the greenhouse. In addition, the film surface has a self-cleaning function, and can photocatalytically degrade pesticide residues and pollutants attached to the film surface. The application can improve the light environment of the greenhouse, and provides a reliable greenhouse planting microclimate for efficient agricultural production.

Description

Technical Field

[0001] This invention belongs to the technical field of passive energy utilization, and specifically relates to a spectrally selective thin film for efficient agriculture. Background Technology

[0002] Traditional agricultural films have limited capabilities in controlling the light environment, making it difficult to meet the precise spectral requirements of crops. Photosynthesis mainly relies on 400–500nm blue-violet light and 600–700nm red-orange light, while the utilization rate of 500–600nm green light is low. Ultraviolet light (<400nm) easily accelerates film aging and inhibits crop growth, while near-infrared light (>700nm) is converted into heat energy, causing the temperature inside the greenhouse to rise and triggering heat stress. Traditional active cooling methods such as forced ventilation and spraying are energy-intensive and costly. Radiative cooling technology provides a new direction for the coordinated control of light and temperature in agricultural films. By integrating the radiative cooling mechanism into the film design, while ensuring high transmittance in the photosynthetic effective wavelength range, it can efficiently reflect near-infrared light and block ultraviolet light, reducing heat input at the source and achieving passive cooling. This mechanism, combined with spectral selectivity, promotes the innovative development of next-generation smart agricultural films that combine "light screening" and "thermal management" functions.

[0003] Currently, various functional films for agricultural production are publicly available. Chinese patent CN109320821A discloses a method for preparing a light-modulating conversion functional film for greenhouses. This invention uses self-made upconversion fluorescent light-storing functional powder to prepare an energy-storing light-modulating material, and then uses a melt extrusion blow molding process to blend the resin with this functional material to form a film. It can effectively utilize red light and has excellent energy storage performance. Chinese patent CN106364099A discloses an agricultural film for plant cultivation. The film consists of a substrate layer, a functional intermediate layer, and a weather-resistant outer layer: the outer layer effectively blocks and dissipates ultraviolet rays and heat rays, delaying aging; the core intermediate layer provides high light-shielding and heat insulation, ensuring light stability and the mechanical strength of the film. Although the above technologies can cope with adverse climatic conditions to a certain extent and support crop photosynthesis and normal growth, their spectral regulation capabilities are still insufficient, making it difficult to accurately respond to the crop's specific spectral requirements, thus limiting the efficient growth and development of crops.

[0004] To address the aforementioned problems, this invention discloses a spectrally selective film for efficient agriculture. This film possesses precise spectral management capabilities: it reflects green light, which contributes little to the photosynthesis of most crops, while efficiently transmitting the photosynthetic core wavelengths (red and blue light); it also reflects most near-infrared radiation to reduce greenhouse temperatures and alleviate high-temperature heat stress on crops. Furthermore, the film surface has a self-cleaning function, capable of photocatalytically degrading pesticide residues and pollutants adhering to the film surface, thereby ensuring the long-term stability and reliability of its spectral performance. Summary of the Invention

[0005] This invention discloses a spectrally selective film for high-efficiency agriculture. The first objective of this invention is to improve the photosynthetic environment of the crop canopy by alleviating the heat stress effect inside the film and optimizing the transmission performance of the film to photosynthetically active radiation (PAR), thereby ultimately improving crop growth efficiency and productivity. The second objective of this invention is to enable the film surface to simultaneously possess photocatalytic self-cleaning function, which can degrade organic pollutants such as pesticide residues attached to the film surface, thereby maintaining the high light transmittance of the film while regulating the light and heat environment inside the greenhouse, achieving long-lasting and stable performance.

[0006] To achieve the objectives of this invention, the embodiments of this invention adopt the following technical solutions:

[0007] This invention discloses a spectrally selective thin film for efficient agriculture, characterized in that the thin film comprises: a spectrally selective control layer, a composite fiber substrate layer, and a surface self-cleaning layer;

[0008] This invention discloses a method for preparing a spectrally selective thin film for efficient agriculture, the specific steps of which are as follows:

[0009] (a) Raw material pretreatment: The functional filler is surface-aminated using an aminosilane coupling agent. The functional filler and the aminosilane coupling agent are dissolved in a 75% ethanol aqueous solution at a mass ratio of 1:(0.1-0.3). The mass ratio of the total mass of the functional filler and the aminosilane coupling agent to the mass of the 75% ethanol aqueous solution is (0.1-0.2):1, to obtain a functional filler solution. The functional filler solution is ultrasonically treated for 10-20 min and mechanically stirred at 300-500 rpm at 20-25℃ for 1-2 h to obtain a functional particle suspension. The obtained functional particle suspension is centrifuged at 500-700 rpm for 10-15 min. After removing the supernatant, 0.5-1 times the volume of the functional particle suspension before centrifugation of a 75% ethanol aqueous solution is added and stirred for 30 s to dissolve the unreacted silane coupling agent. The resulting precipitate is placed in a vacuum drying oven and dried at 80℃ for 5 h to obtain the modified functional filler.

[0010] The surface modifier and aminosilane coupling agent were mixed at a mass ratio of 1:(0.1-0.3) and then added to a 75% ethanol aqueous solution. The mass ratio of the total mass of the surface modifier and aminosilane coupling agent to the mass of the 75% ethanol aqueous solution was (0.1-0.2):1. The mixture was stirred at 300-600 rpm for 1-2 hours at 25-50℃ to make the dispersion reach a uniform and stable state, thus obtaining the surface modifier dispersion.

[0011] (b) Preparation of composite fiber substrate: chloroform and N,N-dimethylformamide were mixed at a volume ratio of 1:3 to obtain a chloroform mixed solvent; the chloroform mixed solvent was placed in a stirring container, and the matrix resin and toughening agent were poured into the chloroform mixed solvent at a mass ratio of 7:3, with the total mass ratio of the matrix resin and toughening agent to the mass ratio of the chloroform mixed solvent being 1:(8-9); the mixture was continuously stirred at a speed of 300-600 rpm using a magnetic stirrer until the matrix resin and toughening agent were completely dissolved in the chloroform mixed solvent, thus obtaining a resin-toughening agent mixed solution;

[0012] The resin-toughening agent mixture was stirred at 300-600 rpm using a magnetic stirrer, and the modified functional filler obtained in step (a) was added. The mass ratio of the amount of modified functional filler added to the mass ratio of the matrix resin in step (b) was 1:20-1:2. When the modified functional filler was uniformly dispersed in the resin-toughening agent mixture, the modified resin-toughening agent mixture was obtained.

[0013] The modified resin-toughening agent mixture was stirred for 20-30 minutes using a high shear disperser at a speed of 2000-3000 rpm. The solution temperature was controlled to not exceed 40℃ throughout the process using a water bath. After dispersion, a sample was taken for inspection. The spinning solution was considered qualified if it was homogeneous, had consistent fluidity, and no visible particles were found when coated on a glass plate.

[0014] Nanofiber membranes were prepared from the spinning solution using an electrospinning machine; the nanofiber membranes were then dried in a vacuum drying oven at 60°C for 10-12 hours to ensure constant mass, thus obtaining a composite fiber substrate layer.

[0015] (c) Preparation of the spectrally selective control layer: The matrix resin and toughening agent are dissolved in N,N-dimethylformamide at a mass ratio of 7:3. The mass ratio of the total mass of the matrix resin and toughening agent to the mass of N,N-dimethylformamide is (0.1-0.5):1. A spectrally selective control agent is added. The mass ratio of the spectrally selective control agent to the matrix resin in step (c) is 1:100-1:50 to obtain a spectrally selective resin solution.

[0016] The spectral modulated resin solution was stirred with a magnetic stirrer at 60-70℃ for 2-3 hours, and then ultrasonically treated for 10 minutes to obtain the coating adhesive.

[0017] The coating adhesive is scraped onto the composite fiber substrate obtained in step (b), and after standing at room temperature for 15-30 seconds, it is subjected to vacuum pulse permeation treatment for 5 minutes; the composite fiber substrate with the coating adhesive is immersed in deionized water at room temperature for 10-20 minutes to solidify, and then taken out to obtain a spectrally selective tunable film-fiber preform.

[0018] The spectrally selective tunable film-fiber preform is dried at 20-25℃. When there are no obvious flowing water droplets, it is then transferred to an oven at 40-60℃ and dried for 1-2 hours until it is completely dry. The resulting integrated spectrally tunable composite film is then obtained.

[0019] (d) Preparation of the self-cleaning layer: Prepare the surface modifier dispersion according to step (a); mix ethanol and deionized water at a volume ratio of 7:3 to obtain an ethanol mixture; dilute the surface modifier dispersion prepared in step (a) with the ethanol mixture, the volume ratio of the ethanol mixture to the surface modifier dispersion is 1:(0.3-0.5), to obtain the modified dispersion dilution;

[0020] Octadecyltrichlorosilane was added to the modified dispersion dilution, with a volume ratio of 0.5%-2.0% between the modified dispersion dilution and octadecyltrichlorosilane. The pH was adjusted to 5.0-6.0 with acetic acid, and then the mixture was magnetically stirred at 200-800 rpm for 2-4 hours to allow the octadecyltrichlorosilane to fully hydrolyze and condense with the modified dispersion dilution, thus obtaining a self-cleaning sediment solution.

[0021] The integrated spectral modulation composite film obtained in step (c) is immersed in a self-cleaning deposition solution for 10-30 minutes. Then, the integrated spectral modulation composite film is slowly and uniformly pulled vertically out of the self-cleaning deposition solution at a speed of 1-2 mm / s. The pulled integrated spectral modulation composite film is placed horizontally in a forced-air drying oven at 40-50℃ for 10-15 minutes to allow the surface deposition layer to be initially set. Then, the temperature is raised to 80℃ for 1 hour to form a surface self-cleaning layer, thus obtaining an integrated spectral modulation composite film with a surface self-cleaning layer.

[0022] (e) Post-processing: The integrated spectral modulated composite film with a self-cleaning surface layer obtained in step (d) is hot-pressed at 200°C for 5 min using a flat plate hot press. After hot pressing, the integrated spectral modulated composite film with a self-cleaning surface layer is cooled to 50-60°C and then irradiated with ultraviolet light for 30 min to activate the surface photocatalytic performance, thus obtaining a spectral selective film for high-efficiency agriculture.

[0023] As a preferred example, the functional filler is one or more of hollow silica nanoparticles, rare earth light-converting nanomaterials, zinc oxide nanoparticles, and carbon-based nanomaterials.

[0024] As a preferred example, the surface modifier is one or more of titanium dioxide nanoparticles, fluorinated polysiloxanes, conductive polymer nanofibers, and hexagonal boron nitride nanosheets.

[0025] As a preferred example, the matrix resin is one or more of polylactic acid, polymethyl methacrylate, polyethylene terephthalate, and polycarbonate.

[0026] As a preferred example, the toughening agent is one or more of poly(terephthalic acid-adipic acid-butanediol) copolymer, thermoplastic polyurethane, and ethylene-vinyl acetate copolymer.

[0027] As a preferred example, the spectral modulator is one or more of chromium oxide green nanoparticles, neodymium oxide nanoparticles, cerium dioxide nanoparticles, and tungsten bronze nanoparticles.

[0028] As a preferred example, the spectrally selective film has a visible light transmittance of more than 70% in the 400-500nm wavelength range, a visible light transmittance of more than 70% in the 600-700nm wavelength range, and a visible light transmittance of less than 35% in the 500-560nm wavelength range.

[0029] As a preferred example, the spectrally selective film has an ultraviolet transmittance of less than 35% in the 200-380nm wavelength range and a near-infrared transmittance of less than 15% in the 780-2500nm wavelength range.

[0030] As a preferred example, the spectrally selective thin film has an infrared emissivity greater than 0.90 in the 8-13 μm band.

[0031] The present invention has the following advantages and beneficial effects:

[0032] This film integrates precise spectral management and self-cleaning functions. Its spectral management capabilities are manifested in: selectively reflecting green light, which contributes little to the photosynthesis of most crops, while efficiently transmitting red and blue light in the core photosynthetic band. Furthermore, its high reflectivity in the near-infrared band effectively reduces greenhouse heat gain, preventing excessively high daytime temperatures and thus controlling heat stress in crops. In addition, the film significantly inhibits photo-oxidative aging by reflecting ultraviolet light, extending the material's lifespan. Its surface also has a photocatalytic self-cleaning function, which can efficiently degrade pesticide residues and other organic pollutants adhering to the film surface, thereby ensuring the long-term stability and reliability of the film's optical performance. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the structure of a spectrally selective thin film for efficient agriculture according to the present invention;

[0034] Figure 2 This is a transmittance spectrum of the ultraviolet-visible-near-infrared region in an embodiment of the present invention;

[0035] Figure 3 This is the emissivity spectrum in the mid-infrared region of an embodiment of the present invention;

[0036] Figure 4This is a schematic diagram illustrating the principle of selective control of sunlight in a greenhouse according to an embodiment of the present invention.

[0037] Figure 1 In the middle: 1. Spectral selectivity control layer; 2. Composite fiber base layer; 3. Surface self-cleaning layer. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0039] like Figure 1 As shown, an embodiment of the present invention provides a spectrally selective film for efficient agriculture, characterized in that the film comprises: a spectrally selective control layer (1), a composite fiber substrate layer (2), and a surface self-cleaning layer (3).

[0040] The specific steps of the method for preparing a spectrally selective thin film for efficient agriculture are as follows:

[0041] (a) Raw material pretreatment: Hollow silica nanoparticles were surface-aminated using an aminosilane coupling agent. The hollow silica nanoparticles and the aminosilane coupling agent were dissolved in a 75% ethanol aqueous solution at a mass ratio of 1:(0.1-0.3). The mass ratio of the total mass of the hollow silica nanoparticles and the aminosilane coupling agent to the mass of the 75% ethanol aqueous solution was (0.1-0.2):1, yielding a hollow silica nanoparticle solution. The hollow silica nanoparticle solution was ultrasonically treated for 10-20 min at 20-25℃. The hollow silica nanoparticle suspension was mechanically stirred at 300-500 rpm for 1-2 hours to obtain a suspension. The suspension was then centrifuged at 500-700 rpm for 10-15 minutes. After removing the supernatant, 0.5-1 times the volume of the original hollow silica nanoparticle suspension was added to a 75% ethanol aqueous solution, and the mixture was stirred for 30 seconds to dissolve the unreacted silane coupling agent. The resulting precipitate was placed in a vacuum drying oven and dried at 80°C for 5 hours to obtain modified hollow silica nanoparticles.

[0042] Titanium dioxide nanoparticles and aminosilane coupling agent were mixed at a mass ratio of 1:(0.1-0.3) and then added to a 75% ethanol aqueous solution. The mass ratio of the total mass of titanium dioxide nanoparticles and aminosilane coupling agent to the mass ratio of 75% ethanol aqueous solution was (0.1-0.2):1. The mixture was stirred at 300-600 rpm for 1-2 hours at 25-50℃ to make the dispersion reach a uniform and stable state, thus obtaining a titanium dioxide nanoparticle dispersion.

[0043] (b) Preparation of composite fiber substrate (2): chloroform and N,N-dimethylformamide were mixed at a volume ratio of 1:3 to obtain a chloroform mixed solvent; the chloroform mixed solvent was placed in a stirring container, and polylactic acid and thermoplastic polyurethane were poured into the chloroform mixed solvent at a mass ratio of 7:3. The mass ratio of the total mass of polylactic acid and thermoplastic polyurethane to the mass of the chloroform mixed solvent was 1:(8-9); a magnetic stirrer was used to continuously stir at a speed of 300-600 rpm. When the polylactic acid and thermoplastic polyurethane were completely dissolved in the chloroform mixed solvent, a polylactic acid-thermoplastic polyurethane mixed solution was obtained.

[0044] The polylactic acid-thermoplastic polyurethane mixture was stirred at 300-600 rpm using a magnetic stirrer, and the modified hollow silica nanoparticles obtained in step (a) were added. The mass ratio of the modified hollow silica nanoparticles to the polylactic acid in step (b) was 1:20-1:2. When the modified hollow silica nanoparticles were uniformly dispersed in the polylactic acid-thermoplastic polyurethane mixture, the modified polylactic acid-thermoplastic polyurethane mixture was obtained.

[0045] The modified polylactic acid-thermoplastic polyurethane mixed solution was stirred for 20-30 minutes using a high shear disperser at a speed of 2000-3000 rpm. The solution temperature was controlled to not exceed 40℃ throughout the process using a water bath. After dispersion, a sample was taken for inspection. The spinning solution was considered qualified if it was homogeneous, had consistent fluidity, and no visible particles were found when coated on a glass plate.

[0046] Nanofiber membranes were prepared from the spinning solution using an electrospinning machine; the nanofiber membranes were dried in a vacuum drying oven at 60°C for 10-12 hours to ensure constant mass, thus obtaining a composite fiber substrate layer (2).

[0047] (c) Preparation of the spectrally selective control layer (1): Polylactic acid and thermoplastic polyurethane were dissolved in N,N-dimethylformamide at a mass ratio of 7:3. The mass ratio of the total mass of polylactic acid and thermoplastic polyurethane to that of N,N-dimethylformamide was (0.1-0.5):1. Chromium oxide green nanoparticles were added. The mass ratio of chromium oxide green nanoparticles to polylactic acid in step (c) was 1:100-1:50 to obtain a chromium oxide green nanoparticle-polylactic acid solution.

[0048] The chromium oxide green nanoparticle-polylactic acid solution was stirred with a magnetic stirrer at 60-70℃ for 2-3 hours, and then ultrasonically treated for 10 minutes to obtain the coating adhesive.

[0049] The coating adhesive is scraped onto the composite fiber substrate (2) obtained in step (b), and after standing at room temperature for 15-30 seconds, it is subjected to vacuum pulse penetration treatment for 5 minutes; the composite fiber substrate (2) with the coating adhesive is immersed in deionized water at room temperature for 10-20 minutes to solidify, and then taken out to obtain a spectrally selective regulated film-fiber preform.

[0050] The spectrally selective tunable film-fiber preform is dried at 20-25℃. When there are no obvious flowing water droplets, it is then transferred to an oven at 40-60℃ and dried for 1-2 hours until it is completely dry. The resulting integrated spectrally tunable composite film is then obtained.

[0051] (d) Preparation of the self-cleaning layer (3): Titanium dioxide nanoparticle dispersion was prepared according to step (a); ethanol and deionized water were mixed at a volume ratio of 7:3 to obtain an ethanol mixture; the titanium dioxide nanoparticle dispersion prepared in step (a) was diluted with the ethanol mixture, and the volume ratio of the ethanol mixture to the titanium dioxide nanoparticle dispersion was 1:(0.3-0.5) to obtain a modified dispersion dilution.

[0052] Octadecyltrichlorosilane was added to the modified dispersion dilution, with a volume ratio of 0.5%-2.0% between the modified dispersion dilution and octadecyltrichlorosilane. The pH was adjusted to 5.0-6.0 with acetic acid, and then the mixture was magnetically stirred at 200-800 rpm for 2-4 hours to allow the octadecyltrichlorosilane to fully hydrolyze and condense with the modified dispersion dilution, thus obtaining a self-cleaning sediment solution.

[0053] The integrated spectral modulation composite film obtained in step (c) is immersed in the self-cleaning deposition solution. After soaking for 10-30 minutes, the integrated spectral modulation composite film is slowly and uniformly pulled out of the self-cleaning deposition solution at a speed of 1-2 mm / s. The pulled-out integrated spectral modulation composite film is placed horizontally in a forced-air drying oven at 40-50℃ and dried for 10-15 minutes to preliminarily shape the surface deposition layer. Then, the temperature is raised to 80℃ and cured for 1 hour to form a surface self-cleaning layer (3), thus obtaining an integrated spectral modulation composite film with a surface self-cleaning layer (3).

[0054] (e) Post-processing: The integrated spectral modulation composite film with surface self-cleaning layer (3) obtained in step (d) is hot-pressed at 200°C for 5 min using a flat plate hot press. After hot pressing, the integrated spectral modulation composite film with surface self-cleaning layer (3) is cooled to 50-60°C and then irradiated with ultraviolet light for 30 min to activate the surface photocatalytic performance, thus obtaining a spectral selective film for high-efficiency agriculture.

[0055] In addition to the hollow silica nanoparticles used in the examples, the functional filler may also be one or more of rare earth optically convertible nanomaterials, zinc oxide nanoparticles, and carbon-based nanomaterials.

[0056] (1) Hollow silica nanoparticles: mainly used to enhance the ability of the film to scatter sunlight and improve the uniformity of light distribution in the greenhouse. At the same time, its porous hollow structure can effectively block heat conduction and play a certain role in heat preservation or insulation. Hollow silica nanoparticles are obtained by the following method: 14 mL of ethanol and 26.5 mL of ethanol-water mixed solution, 0.5 mL of tetraethoxysilane and 0.08 g of hexadecyltrimethylammonium bromide are mixed. After mixing, 0.5 mL of concentrated ammonia water is added under stirring at 25 °C and 600 rpm and the reaction is carried out for 2 h. After washing with high-purity water, the mixture is dried in a drying oven at 120 °C and calcined at 200 °C for 6 h to obtain hollow silica nanoparticles.

[0057] (2) Rare earth light-converting nanomaterials: can absorb ultraviolet light (such as 300-400nm) or green light (500-600nm) that have low photosynthetic efficiency for plants, and convert them into red light (600-700nm) or blue light (400-500nm) that are more easily utilized by crops, thereby improving the light energy utilization rate;

[0058] (3) Zinc oxide nanoparticles: have strong ultraviolet absorption capacity, can effectively block ultraviolet rays in the 200-380nm band, and protect crops from ultraviolet damage; at the same time, they have certain spectral antibacterial properties.

[0059] (4) Carbon-based nanomaterials, such as carbon nanotubes and graphene, can significantly improve the mechanical strength and toughness of films and selectively absorb near-infrared light through their unique band structure, thus helping to reduce the temperature inside the greenhouse.

[0060] In addition to the titanium dioxide nanoparticles used in the examples, the surface modifier may also be one or more of the following: fluorinated polysiloxanes, conductive polymer nanofibers, and hexagonal boron nitride nanosheets.

[0061] (1) Titanium dioxide nanoparticles: When used as a surface modifier, especially after nano-sizing, they can be enriched on or near the surface of the film. Under light (especially ultraviolet light), their surface generates highly oxidizing holes and hydroxyl radicals, thereby endowing the film with photocatalytic self-cleaning function, which can decompose organic pollutants (such as dust and algal metabolites) attached to the surface, and help maintain high light transmittance for a long time;

[0062] (2) Fluorinated polysiloxanes: When used as surface modifiers, their low surface energy fluorinated segments tend to migrate to the film surface during film formation, forming a durable hydrophobic and oleophobic layer. This enables the film surface to exhibit a "lotus effect," achieving hydrophobic self-cleaning, meaning that water droplets easily roll off the surface and carry away contaminants, while also preventing the adhesion of liquids such as pesticides and fertilizers to a certain extent. Their siloxane backbone provides good compatibility with organic resin matrices;

[0063] (3) Conductive polymer nanofibers: such as nanofibers of polyaniline, polypyrrole, PEDOT:PSS, etc. When used as surface modifiers, they can form conductive or antistatic networks inside or on the surface of the film. This mainly serves two purposes: first, to dissipate static charge and prevent the decrease in light transmittance caused by static dust adsorption, thus keeping the film surface clean; second, by adjusting its doping state, it may have a certain influence on the spectrum of specific wavelengths (such as near-infrared).

[0064] (4) Hexagonal boron nitride nanosheets: They have a two-dimensional sheet structure similar to graphene, but are electrically insulators and have good thermal conductivity. As a surface modifier, their ultrathin nanosheets can be arranged parallel to the surface of the film to form an effective barrier. This not only improves the barrier performance of the film (such as water vapor barrier), but also utilizes its high in-plane thermal conductivity to promote the uniformity of heat dissipation in the plane of the film, avoid local overheating, and at the same time, it is transparent to visible light and does not affect light transmission.

[0065] In addition to the polylactic acid used in the examples, the matrix resin may also be one or more of polymethyl methacrylate, polyethylene terephthalate, and polycarbonate.

[0066] (1) Polylactic acid: It is a biodegradable polymer derived from renewable resources such as corn and sugarcane. It has high transparency and good processing performance. Using PLA as the matrix resin can enable the film to be biodegraded under specific composting conditions after the end of its life cycle. Its disadvantage is that its toughness is slightly poor, and it usually needs to be used in conjunction with toughening agents.

[0067] (2) Polymethyl methacrylate (PMMA): commonly known as acrylic or plexiglass, it has excellent optical transparency (transmittance can reach over 92%) and good weather resistance. PMMA-based films can provide a "window" with minimal optical distortion for functional fillers and spectral modifiers, ensuring that the original spectral characteristics of the incident light are maximized by the modifier, making it one of the ideal matrices for achieving high-precision spectral selectivity;

[0068] (3) Polyethylene terephthalate: PET is a crystalline engineering plastic with excellent mechanical strength, rigidity and dimensional stability, and good barrier properties against water vapor and gas. With PET as the matrix, thinner, more durable and more wind and sand resistant greenhouse films can be prepared, which are particularly suitable for large-span greenhouses or harsh climate environments with high requirements for film mechanical strength and durability.

[0069] (4) Polycarbonate: also known as PC, is known for its excellent impact toughness and dimensional stability over a wide temperature range. Films based on PC have extremely strong resistance to hail and wind tearing, and have a long service life. At the same time, PC itself has good absorption of ultraviolet light, which can work synergistically with functional fillers to enhance the blocking of harmful ultraviolet rays;

[0070] In addition to the thermoplastic polyurethane used in the examples, the toughening agent may also be one or more of the following: poly(terephthalic acid-adipate-butanediol) copolymer and ethylene-vinyl acetate copolymer.

[0071] (1) Poly(terephthalic acid-adipic acid-butanediol) copolymer: This is an aliphatic-aromatic copolyester widely used in the field of biodegradable plastics. When blended with bio-based resins such as polylactic acid, PBAT can significantly improve the brittleness of the matrix resin, increase the elongation at break and toughness of the film, while maintaining the overall biodegradability of the system. The addition ratio can be adjusted according to the required flexibility. For example, blending PLA and PBAT in a certain ratio (such as 70:30) is a common choice to obtain composite materials with both certain strength and good flexibility.

[0072] (2) Thermoplastic polyurethane: It is a high-performance elastomer containing urethane groups in its molecular chain; TPU has excellent wear resistance, high elasticity and low temperature resistance. As a toughening agent, it can form an elastic dispersed phase in the matrix resin. When subjected to external force, it generates a large number of crazing and shear bands, thereby consuming a large amount of energy and significantly improving the impact resistance and fatigue resistance of the film. The ratio of its hard segment to soft segment can be adjusted and can be selected according to the polarity of the matrix resin to optimize compatibility.

[0073] (3) Ethylene-vinyl acetate copolymer: The content of vinyl acetate directly affects its flexibility and polarity. EVA used as a toughening agent usually has a high VA content, which makes it soft and rubber-like, and has good compatibility with a variety of polyolefins and engineering plastics. EVA can effectively improve the flexibility, environmental stress cracking resistance and low-temperature impact resistance of the film, while also having good light transmittance and having little impact on the optical properties of the film.

[0074] In addition to the chromium oxide green nanoparticles used in the examples, the spectral modulator may also be one or more of neodymium oxide nanoparticles, cerium dioxide nanoparticles, and tungsten bronze nanoparticles.

[0075] (1) Chromium oxide green nanoparticles: The main component is Cr2O3. This material has unique spectral selective absorption characteristics in the visible light region. It has strong absorption of green light in the 500-600nm band, but weak absorption of blue light in the 400-500nm band and red light in the 600-700nm band. Using it as a spectral modulator, agricultural films that "enhance blue and red and suppress green" can be prepared, so that the transmitted spectrum is more matched with the absorption peaks of chlorophyll a and b, which can theoretically improve the photosynthetic efficiency.

[0076] (2) Neodymium oxide nanoparticles: mainly Nd2O3. Neodymium ions have sharp characteristic absorption peaks at specific wavelengths (such as about 580nm, 740nm, 800nm). By utilizing this property, it can be incorporated into thin films to precisely filter out the energy of specific wavelengths in the solar spectrum, thereby creating a unique light environment that can be used to study or meet the special light quality requirements of certain high-value crops (such as certain herbs and flowers).

[0077] (3) Cerium dioxide nanoparticles: namely CeO2, which has excellent ultraviolet absorption capacity and reversible redox properties. As a spectral modulator, it mainly plays two roles: first, it efficiently absorbs and blocks ultraviolet rays of 200-400nm, protecting crops from ultraviolet radiation damage; second, it acts as a light stabilizer, through its Ce³⁺ / Ce 4 The valence state cycle of ⁺ quenches the free radicals generated by the film resin under ultraviolet light, thereby delaying the photo-oxidative aging of the matrix resin and extending the service life of the film;

[0078] (4) Tungsten bronze nanoparticles: usually referring to cesium tungsten bronze, rubidium tungsten bronze, etc., with the general chemical formula MxWO3, is a well-known near-infrared shielding material. It maintains good transmittance in the visible light region (380-780nm), while having a strong absorption or scattering effect on near-infrared light in the 780-2500nm range. Adding it to a thin film can significantly block part of the heat in solar radiation without significantly affecting the light intensity inside the greenhouse, thereby effectively reducing the temperature of the greenhouse in summer and reducing cooling energy consumption.

[0079] The spectrally selective thin film for efficient agriculture obtained according to the steps of the above embodiments has the following transmittance spectrum in the ultraviolet-visible-near-infrared region: Figure 2As shown, the spectrally selective film has an ultraviolet transmittance of less than 35% in the 200-380nm wavelength range; a visible light transmittance of greater than 70% in the 400-500nm wavelength range, a visible light transmittance of greater than 70% in the 600-700nm wavelength range, a visible light transmittance of less than 35% in the 500-560nm wavelength range; and a near-infrared light transmittance of less than 15% in the 780-2500nm wavelength range.

[0080] The spectrally selective thin film for efficient agriculture obtained according to the steps of the above embodiments has the following mid-infrared emissivity spectrum: Figure 3 As shown, the spectrally selective thin film exhibits an infrared emissivity of not less than 0.90 in the 8-13 μm band, demonstrating significant radiative cooling capability.

[0081] The schematic diagram illustrating the principle of selective regulation of sunlight in a greenhouse, based on the steps of the above embodiments, shows a spectrally selective thin film for efficient agriculture. Figure 4 As shown, when sunlight shines on the film surface, the film exhibits spectral selectivity, reflecting most ultraviolet light and some green light, while allowing high transmission of blue, red, and photosynthetically active radiation wavelengths—crucial for photosynthesis—into the greenhouse for plant absorption and utilization. Simultaneously, the film reflects near-infrared radiation, significantly reducing solar heat input and preventing excessively high temperatures inside the greenhouse during the day. Furthermore, the film has high infrared transmittance in the 8–13 μm (atmospheric window) band, enabling the efficient dissipation of accumulated heat from the greenhouse through long-wave radiation, avoiding high-temperature heat stress. In short, this film possesses a spectral selection mechanism, ensuring the light and heat needs of plants while maintaining a suitable greenhouse thermal environment, thereby promoting healthy plant growth.

[0082] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A spectrally selective thin film for efficient agriculture, characterized in that, The film comprises: a spectral selectivity control layer (1), a composite fiber substrate layer (2), and a surface self-cleaning layer (3). The specific steps of the method for preparing a spectrally selective thin film for efficient agriculture are as follows: (a) Raw material pretreatment: The functional filler is surface-aminated using an aminosilane coupling agent. The functional filler and the aminosilane coupling agent are dissolved in a 75% ethanol aqueous solution at a mass ratio of 1:(0.1-0.3). The mass ratio of the total mass of the functional filler and the aminosilane coupling agent to the mass of the 75% ethanol aqueous solution is (0.1-0.2):1, to obtain a functional filler solution. The functional filler solution is ultrasonically treated for 10-20 min and mechanically stirred at 300-500 rpm at 20-25℃ for 1-2 h to obtain a functional particle suspension. The obtained functional particle suspension is centrifuged at 500-700 rpm for 10-15 min. After removing the supernatant, 0.5-1 times the volume of the functional particle suspension before centrifugation of a 75% ethanol aqueous solution is added and stirred for 30 s to dissolve the unreacted silane coupling agent. The resulting precipitate is placed in a vacuum drying oven and dried at 80℃ for 5 h to obtain the modified functional filler. The surface modifier and aminosilane coupling agent were mixed at a mass ratio of 1:(0.1-0.3) and then added to a 75% ethanol aqueous solution. The mass ratio of the total mass of the surface modifier and aminosilane coupling agent to the mass of the 75% ethanol aqueous solution was (0.1-0.2):

1. The mixture was stirred at 300-600 rpm for 1-2 hours at 25-50℃ to make the dispersion reach a uniform and stable state, thus obtaining the surface modifier dispersion. (b) Preparation of composite fiber substrate (2): chloroform and N,N-dimethylformamide were mixed at a volume ratio of 1:3 to obtain a chloroform mixed solvent; the chloroform mixed solvent was placed in a stirring container, and the matrix resin and toughening agent were poured into the chloroform mixed solvent at a mass ratio of 7:3, with the total mass of the matrix resin and toughening agent being 1:(8-9) to the mass ratio of the chloroform mixed solvent; the magnetic stirrer was used to continuously stir at a speed of 300-600 rpm until the matrix resin and toughening agent were completely dissolved in the chloroform mixed solvent to obtain a resin-toughening agent mixed solution; The resin-toughening agent mixture was stirred at 300-600 rpm using a magnetic stirrer, and the modified functional filler obtained in step (a) was added. The mass ratio of the amount of modified functional filler added to the mass ratio of the matrix resin in step (b) was 1:20-1:

2. When the modified functional filler was uniformly dispersed in the resin-toughening agent mixture, the modified resin-toughening agent mixture was obtained. The modified resin-toughening agent mixture was stirred for 20-30 minutes using a high-shear disperser at a speed of 2000-3000 rpm to fully disperse the filler and obtain the spinning solution. Nanofiber membranes were prepared from the spinning solution using an electrospinning machine; the nanofiber membranes were dried in a vacuum drying oven at 60°C for 10-12 hours to ensure constant mass, thus obtaining a composite fiber substrate layer (2). (c) Preparation of the spectrally selective control layer (1): The matrix resin and toughening agent are dissolved in N,N-dimethylformamide at a mass ratio of 7:

3. The mass ratio of the total mass of the matrix resin and toughening agent to the mass of N,N-dimethylformamide is (0.1-0.5):

1. A spectrally selective control agent is added. The mass ratio of the spectrally selective control agent to the matrix resin in step (c) is 1:100-1:50 to obtain a spectrally selective resin solution. The spectral modulated resin solution was stirred with a magnetic stirrer at 60-70℃ for 2-3 hours, and then ultrasonically treated for 10 minutes to obtain the coating adhesive. The coating adhesive is scraped onto the composite fiber substrate (2) obtained in step (b), and after standing at room temperature for 15-30 seconds, it is subjected to vacuum pulse penetration treatment for 5 minutes; the composite fiber substrate (2) with the coating adhesive is immersed in deionized water at room temperature for 10-20 minutes to solidify, and then taken out to obtain a spectrally selective regulated film-fiber preform. The spectrally selective tunable film-fiber preform is dried at 20-25℃. When there are no obvious flowing water droplets, it is then transferred to an oven at 40-60℃ and dried for 1-2 hours until it is completely dry. The resulting integrated spectrally tunable composite film is then obtained. (d) Preparation of the self-cleaning surface layer (3): Prepare the surface modifier dispersion according to step (a); mix ethanol and deionized water at a volume ratio of 7:3 to obtain an ethanol mixture; dilute the surface modifier dispersion prepared in step (a) with the ethanol mixture, the volume ratio of the ethanol mixture to the surface modifier dispersion is 1:(0.3-0.5), to obtain the modified dispersion dilution; Octadecyltrichlorosilane was added to the modified dispersion dilution, with a volume ratio of 0.5%-2.0% between the modified dispersion dilution and octadecyltrichlorosilane. The pH was adjusted to 5.0-6.0 with acetic acid, and then the mixture was magnetically stirred at 200-800 rpm for 2-4 hours to allow the octadecyltrichlorosilane to fully hydrolyze and condense with the modified dispersion dilution, thus obtaining a self-cleaning sediment solution. The integrated spectral modulation composite film obtained in step (c) is immersed in the self-cleaning deposition solution. After soaking for 10-30 minutes, the integrated spectral modulation composite film is slowly and uniformly pulled out of the self-cleaning deposition solution at a speed of 1-2 mm / s. The pulled-out integrated spectral modulation composite film is placed horizontally in a forced-air drying oven at 40-50℃ and dried for 10-15 minutes to preliminarily shape the surface deposition layer. Then, the temperature is raised to 80℃ and cured for 1 hour to form a surface self-cleaning layer (3), thus obtaining an integrated spectral modulation composite film with a surface self-cleaning layer (3). (e) Post-processing: The integrated spectral modulation composite film with surface self-cleaning layer (3) obtained in step (d) is hot-pressed at 200°C for 5 min using a flat plate hot press. After hot pressing, the integrated spectral modulation composite film with surface self-cleaning layer (3) is cooled to 50-60°C and then irradiated with ultraviolet light for 30 min to activate the surface photocatalytic performance, thus obtaining a spectral selective film for high-efficiency agriculture.

2. The spectrally selective thin film for high-efficiency agriculture according to claim 1, characterized in that, The functional filler is one or more of hollow silica nanoparticles, rare earth optically convertible nanomaterials, zinc oxide nanoparticles, and carbon-based nanomaterials.

3. The spectrally selective thin film for high-efficiency agriculture according to claim 1, characterized in that, The surface modifier is one or more of titanium dioxide nanoparticles, fluorinated polysiloxanes, conductive polymer nanofibers, and hexagonal boron nitride nanosheets.

4. The spectrally selective thin film for high-efficiency agriculture according to claim 1, characterized in that, The matrix resin is one or more of polylactic acid, polymethyl methacrylate, polyethylene terephthalate, and polycarbonate.

5. A spectrally selective thin film for high-efficiency agriculture according to claim 1, characterized in that, The toughening agent is one or more of poly(terephthalic acid-adipic acid-butanediol) copolymer, thermoplastic polyurethane, and ethylene-vinyl acetate copolymer.

6. A spectrally selective thin film for high-efficiency agriculture according to claim 1, characterized in that, The spectral modulator is one or more of chromium oxide green nanoparticles, neodymium oxide nanoparticles, cerium dioxide nanoparticles, and tungsten bronze nanoparticles.

7. A spectrally selective thin film for high-efficiency agriculture according to claim 1, characterized in that, The film has a visible light transmittance of more than 70% in the 400-500nm wavelength range, a visible light transmittance of more than 70% in the 600-700nm wavelength range, and a visible light transmittance of less than 35% in the 500-560nm wavelength range.

8. A spectrally selective thin film for high-efficiency agriculture according to claim 1, characterized in that, The film has an ultraviolet transmittance of less than 35% in the 200-380nm wavelength range and a near-infrared transmittance of less than 15% in the 780-2500nm wavelength range.

9. A spectrally selective thin film for high-efficiency agriculture according to claim 1, characterized in that, The thin film has an infrared emissivity greater than 0.90 in the 8-13 μm band.

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