Spectral selective film for efficient agriculture

Abstract

The invention discloses a spectrum selective film for efficient agriculture, which adopts a four-layer composite structure and comprises a spectrum selective regulation and control layer, a composite fiber substrate layer and surface self-cleaning layers covering two sides. The film can reflect green light which contributes low to photosynthesis of most crops, meanwhile, the film can efficiently penetrate through photosynthetic core wave bands (red and blue light), and most near infrared rays can be reflected so as to reduce the temperature in the greenhouse. In addition, the surface of the film has a self-cleaning function, and pesticide residues and pollutants attached to the surface of the film can be subjected to photocatalytic degradation. The greenhouse light environment can be improved, and reliable greenhouse planting microclimate is provided for efficient agricultural production.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of passive energy utilization, and particularly relates to a spectrum-selective film for efficient agriculture. BACKGROUND

[0002] Traditional agricultural films have limited ability in light environment regulation and are difficult to meet the precise needs of crops for light spectrum. Photosynthesis mainly relies on 400-500 nm blue-violet light and 600-700 nm red-orange light, while the utilization rate of 500-600 nm green light is low, ultraviolet light (<400 nm) easily accelerates film aging and inhibits crop growth, and near-infrared light (>700 nm) is converted into heat energy, causing the temperature in the greenhouse to rise and heat stress to occur. Traditional active cooling methods such as forced ventilation and spraying have high energy consumption and high cost. Radiative cooling technology provides a new direction for light and temperature co-regulation of agricultural films. By integrating radiative cooling mechanism into film design, it can simultaneously ensure high transmittance in photosynthetic effective waveband, efficiently reflect near-infrared light and block ultraviolet light, thereby reducing heat input from the source and achieving passive cooling. The combination of this mechanism with spectrum selectivity promotes the innovative development of the next generation of intelligent agricultural films with both "light screening" and "heat management" functions.

[0003] At present, there are various functional films for agricultural production in the existing public technologies. Chinese patent CN109320821A discloses a preparation method of a light-adjusting conversion function film for greenhouses. The invention prepares an energy storage light-adjusting material by self-preparing up-conversion fluorescent light storage functional powder, and blends the resin and the functional material into a film by melt extrusion blow molding process. It can effectively utilize red light and has excellent energy storage performance. Chinese patent CN106364099A discloses an agricultural film for plant cultivation, which is composed of a base material layer, a functional intermediate layer and a weather-resistant outer surface layer: the outer surface layer effectively blocks and dissipates ultraviolet and heat rays, delaying aging; the core intermediate layer provides high light shielding and heat insulation, ensuring light stability and mechanical strength of the film. Although the above-mentioned technologies can cope with adverse weather conditions to a certain extent and support photosynthesis and normal growth of crops, their light spectrum regulation ability is still insufficient, and they are difficult to accurately respond to the needs of crops for specific light spectrum, thereby limiting the efficient growth and development of crops.

[0004] In view of the above problems, the present application discloses a spectrum-selective film for efficient agriculture. The film has precise light spectrum management capability: it can reflect green light which contributes less to photosynthesis of most crops, while efficiently transmitting photosynthetic core waveband (red and blue light); and it can reflect most of the near-infrared light to reduce the temperature in the greenhouse and alleviate the high-temperature heat stress of crops. In addition, the film surface also has a self-cleaning function, which can photocatalytically degrade pesticide residues and pollutants attached to the film surface, thereby ensuring the long-term stability and reliability of its light spectrum performance. SUMMARY

[0005] The application discloses a spectrum-selective film for high-efficiency agriculture, and has the following two purposes: the first purpose is to improve the photosynthesis environment of crop canopy by relieving the heat stress effect in the film and optimizing the transmission performance of the film to photosynthetically active radiation (PAR), so as to finally improve the growth efficiency and productivity of crops; and the second purpose is to make the film surface have a photocatalytic self-cleaning function, so that the organic pollutants such as pesticide residues attached to the film surface can be degraded, thereby maintaining the high light transmittance of the film while regulating the light and heat environment in the greenhouse, and realizing the durability and stability of the performance.

[0006] To achieve the purpose of the application, the embodiment of the application adopts the following technical scheme:

[0007] The application discloses a spectrum-selective film for high-efficiency agriculture, and has the following two purposes: the first purpose is to improve the photosynthesis environment of crop canopy by relieving the heat stress effect in the film and optimizing the transmission performance of the film to photosynthetically active radiation (PAR), so as to finally improve the growth efficiency and productivity of crops; and the second purpose is to make the film surface have a photocatalytic self-cleaning function, so that the organic pollutants such as pesticide residues attached to the film surface can be degraded, thereby maintaining the high light transmittance of the film while regulating the light and heat environment in the greenhouse, and realizing the durability and stability of the performance.

[0008] The application discloses a preparation method of a spectrum-selective film for high-efficiency agriculture, and has the following two purposes: the first purpose is to improve the photosynthesis environment of crop canopy by relieving the heat stress effect in the film and optimizing the transmission performance of the film to photosynthetically active radiation (PAR), so as to finally improve the growth efficiency and productivity of crops; and the second purpose is to make the film surface have a photocatalytic self-cleaning function, so that the organic pollutants such as pesticide residues attached to the film surface can be degraded, thereby maintaining the high light transmittance of the film while regulating the light and heat environment in the greenhouse, and realizing the durability and stability of the performance.

[0009] (a) raw material pretreatment: the surface of the functional filler is modified by using an amino silane coupling agent, the functional filler and the amino silane coupling agent are dissolved in 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 amino silane 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, mechanically stirred at a speed of 300-500 rpm at 20-25 DEG C for 1-2 h, to obtain a functional particle suspension; the obtained functional particle suspension is centrifuged at a speed of 500-700 rpm for 10-15 min; after removing the supernatant, 75% ethanol aqueous solution with a volume of 0.5-1 times that of the functional particle suspension before centrifugation is added, stirred for 30 s, and the unreacted silane coupling agent is dissolved; the obtained precipitate is placed in a vacuum drying oven and dried at 80 DEG C for 5 h, to obtain modified functional filler;

[0010] The surface modifier and the amino silane coupling agent are mixed at a mass ratio of 1: (0.1-0.3) and then added to 75% ethanol aqueous solution, the mass ratio of the total mass of the surface modifier and the amino silane coupling agent to the mass of the 75% ethanol aqueous solution is (0.1-0.2):1, and the dispersion is stirred at a speed of 300-600 rpm at 25-50 DEG C for 1-2 h to make the dispersion reach a uniform and stable state, to obtain a surface modifier dispersion;

[0011] (b) Preparation of the composite fiber base layer: trichloromethane and N,N-dimethylformamide were mixed in a volume ratio of 1:3 to obtain a trichloromethane mixed solvent; the trichloromethane mixed solvent was placed in a stirring container, and the base resin and the toughening agent were poured into the trichloromethane mixed solvent in a mass ratio of 7:3, the total mass of the base resin and the toughening agent to the mass of the trichloromethane mixed solvent was 1:(8-9); a magnetic stirrer was used to continuously stir at a speed of 300-600 rpm, and when the base resin and the toughening agent were completely dissolved in the trichloromethane mixed solvent, a resin-toughening agent mixed solution was obtained;

[0012] The resin-toughening agent mixed solution was continuously stirred at a speed of 300-600 rpm using a magnetic stirrer, and the modified functional filler obtained in step (a) was added, the mass ratio of the modified functional filler to the base resin in step (b) was 1:20-1:2, and when the modified functional filler was uniformly dispersed in the resin-toughening agent mixed solution, a modified resin-toughening agent mixed solution was obtained;

[0013] The modified resin-toughening agent mixed solution was stirred at a speed of 2000-3000 rpm using a high-shear disperser for 20-30 min, and the whole process was controlled by a water bath to keep the solution temperature below 40℃, after dispersion, sampling was checked, the system of the spinning solution was uniform, the flow was consistent, and after smearing on a glass plate without visible particles, a qualified spinning solution was obtained;

[0014] The spinning solution was prepared into a nanofiber membrane by an electrostatic spinning machine; the nanofiber membrane was placed in a vacuum drying oven at 60℃ and dried for 10-12h until the mass was constant, and a composite fiber base layer was obtained;

[0015] (c) Preparation of the spectrum selective regulation layer: the base resin and the toughening agent were dissolved in N,N-dimethylformamide in a mass ratio of 7:3, the total mass of the base resin and the toughening agent to the mass of N,N-dimethylformamide was (0.1-0.5):1, and a spectrum regulation agent was added, the mass ratio of the spectrum regulation agent to the base resin in step (c) was 1:100-1:50, and a spectrum regulation resin solution was obtained;

[0016] The spectrum regulation resin solution was stirred at 60-70℃ using a magnetic stirrer for 2-3h, and then ultrasonic treatment was performed for 10min to obtain a coating glue;

[0017] The coating glue was scraped on the composite fiber base layer obtained in step (b), and after standing at room temperature for 15-30s, vacuum pulse infiltration treatment was performed for 5min; the composite fiber base layer with the scraped coating glue was immersed in deionized water at room temperature for 10-20min to solidify and then taken out, and a spectrum selective regulation film-fiber preform was obtained;

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

[0044] The polylactic acid-thermoplastic polyurethane mixed solution was continuously stirred at a speed of 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 polylactic acid in step (b) was 1:20-1:2, and after the modified hollow silica nanoparticles were uniformly dispersed in the polylactic acid-thermoplastic polyurethane mixed solution, a modified polylactic acid-thermoplastic polyurethane mixed solution was obtained;

[0045] The modified polylactic acid-thermoplastic polyurethane mixed solution was stirred at a speed of 2000-3000 rpm using a high-shear disperser for 20-30 min, and the whole process was controlled by a water bath to keep the solution temperature below 40℃, after dispersion, the sample was checked, the system of the spinning solution was uniform, the flow was consistent, and after smearing on a glass plate without visible particles, a qualified spinning solution was obtained;

[0046] The spinning solution was prepared into a nanofiber membrane by an electrostatic spinning machine; the nanofiber membrane was placed in a vacuum drying oven at 60℃ and dried for 10-12h until the mass was constant, and a composite fiber base layer (2) was obtained;

[0047] (c) Preparation of the spectrum-selective regulation layer (1): polylactic acid and thermoplastic polyurethane were dissolved in N,N-dimethylformamide at a mass ratio of 7:3, the total mass of polylactic acid and thermoplastic polyurethane to the mass of N,N-dimethylformamide was (0.1-0.5):1, and 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, and a chromium oxide green nanoparticle-polylactic acid solution was obtained;

[0048] The chromium oxide green nanoparticle-polylactic acid solution was stirred at 60-70℃ using a magnetic stirrer for 2-3h, and then ultrasonic treatment was performed for 10min to obtain a coating glue;

[0049] The coating glue is scraped on the composite fiber substrate layer (2) obtained in step (b), and after standing at room temperature for 15-30 s, vacuum pulse infiltration treatment is performed for 5 min; the composite fiber substrate layer (2) with the scraped coating glue is immersed in deionized water at room temperature for coagulation for 10-20 min and then taken out, to obtain a spectrum-selective regulation film-fiber preform;

[0050] The spectrum-selective regulation film-fiber preform is placed at 20-25 °C for drying, and after no obvious flowing water droplets are observed, the spectrum-selective regulation film-fiber preform is transferred to an oven at 40-60 °C for drying for 1-2 h, and then taken out after complete drying, to obtain an integrated spectrum regulation composite film.

[0051] (d) Preparation of the surface self-cleaning layer (3): the titanium dioxide nanoparticle dispersion liquid is prepared according to step (a); the ethanol mixed liquid is obtained by mixing ethanol and deionized water at a volume ratio of 7:3; the titanium dioxide nanoparticle dispersion liquid prepared in step (a) is diluted with the ethanol mixed liquid, and the volume ratio of the ethanol mixed liquid to the titanium dioxide nanoparticle dispersion liquid is 1: (0.3-0.5), to obtain a modified dispersion diluent;

[0052] Octadecyltrichlorosilane is added to the modified dispersion diluent, and the volume ratio of the modified dispersion diluent to the octadecyltrichlorosilane is 0.5%-2.0%; after the pH is adjusted to 5.0-6.0 with acetic acid, magnetic stirring is performed at a stirring speed of 200-800 rpm for 2-4 hours, so that the octadecyltrichlorosilane is fully hydrolyzed and subjected to a condensation reaction with the modified dispersion diluent, to obtain a self-cleaning deposition liquid;

[0053] The integrated spectrum regulation composite film obtained in step (c) is immersed in the self-cleaning deposition liquid, and after soaking for 10-30 min, the integrated spectrum regulation composite film is slowly and uniformly vertically pulled out of the self-cleaning deposition liquid at a speed of 1-2 mm / s; the integrated spectrum regulation composite film after pulling out is horizontally placed in a blowing drying oven at 40-50 °C for drying for 10-15 min, so that the surface deposition layer is preliminarily shaped; then the temperature is increased to 80 °C for curing for 1 h, to form the surface self-cleaning layer (3), and thus an integrated spectrum regulation composite film with the surface self-cleaning layer (3) is obtained.

[0054] (e) Post-treatment: the integrated spectrum regulation composite film with the surface self-cleaning layer (3) obtained in step (d) is hot-pressed at a temperature of 200 °C for 5 min using a flat plate hot press; after hot pressing, the integrated spectrum regulation composite film with the 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 property, and thus a spectrum-selective film for efficient agriculture is obtained.

[0055] The functional fillers can be one or more of rare earth light conversion nanomaterials, zinc oxide nanoparticles, and carbon-based nanomaterials in addition to the hollow silica nanoparticles used in the examples:

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

[0057] (2) Rare earth light conversion nanomaterials: capable of absorbing ultraviolet light (such as 300-400 nm) or green light (500-600 nm) with low efficiency for plant photosynthesis, and converting them into red light (600-700 nm) or blue light (400-500 nm) that is 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 light in the 200-380 nm band, and protect crops from ultraviolet damage; at the same time, have certain spectral antibacterial properties;

[0059] (4) Carbon-based nanomaterials: such as carbon nanotubes and graphene, which can significantly improve the mechanical strength and toughness of the film, and selectively absorb near-infrared light through their unique energy band structure, thereby helping to reduce the temperature in the shed.

[0060] The surface modifiers can be one or more of fluorine-containing polysiloxane, conductive polymer nanofiber, and hexagonal boron nitride nanosheet in addition to the titanium dioxide nanoparticles used in the examples:

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

[0062] (2) Fluorine-containing polysiloxane: When used as a surface modifier, its low-surface-energy fluorine-containing segment tends to migrate to the film surface during film formation, forming a persistent hydrophobic and oleophobic layer. This can give the film surface a "lotus effect", achieving hydrophobic self-cleaning, i.e. water droplets on the surface are easy to roll off and take away contaminants, and it can also block the adhesion of liquid pesticides, fertilizers, etc. to some extent. Its siloxane backbone provides good compatibility with the organic resin matrix;

[0063] (3) Conductive polymer nanofiber: For example, nanofibers of polyaniline, polypyrrole, PEDOT:PSS, etc. When used as a surface modifier, a conductive or antistatic network can be formed inside or on the surface of the film. This mainly serves two purposes: one is to dissipate static electricity and prevent the reduction of light transmittance caused by static adsorption of dust, keeping the film surface clean; the other is to adjust its doping state, which may have some effect on specific wavebands of the light spectrum (such as near-infrared);

[0064] (4) Hexagonal boron nitride nanosheet: It has a two-dimensional sheet structure similar to graphene, but is itself an electrical insulator and has good thermal conductivity. As a surface modifier, its ultra-thin nanosheets can be arranged parallel to the surface direction of the film, forming an effective barrier. This not only improves the barrier properties of the film (such as water vapor barrier), but also promotes the uniformity of heat dissipation in the plane direction of the film, avoiding local overheating, while its own transparency to visible light does not affect light transmission.

[0065] The base resin mentioned above can be one or more of polymethyl methacrylate, polyethylene terephthalate, polycarbonate in addition to the polylactic acid used in the examples:

[0066] (1) Polylactic acid: It is a biobased degradable polymer derived from renewable resources such as corn and sugarcane. It has high transparency and good processing performance. By choosing PLA as the base resin, the film can be biodegraded under specific composting conditions at the end of its life cycle. Its disadvantage is that it has slightly poor toughness, and it usually needs to be used in combination with a toughening agent;

[0067] (2) Polymethyl methacrylate: Commonly known as acrylic or organic glass, it has excellent optical transparency (light transmittance can reach more than 92%) and good weather resistance. A film with PMMA as the base can provide a "window" with minimal optical distortion for functional fillers and spectral control agents, ensuring that the original spectral characteristics of incident light are maximally affected by the control agent, making it an ideal substrate for achieving high-precision spectral selectivity;

[0068] (3) Polyethylene terephthalate: PET, a crystalline engineering plastic, has excellent mechanical strength, rigidity and dimensional stability, and good barrier properties to water vapor and gas. A thinner, more durable, and stronger sand-resistant greenhouse film can be prepared using PET as the matrix, especially for large-span greenhouses or harsh weather environments that require high mechanical strength and durability of the film;

[0069] (4) Polycarbonate: PC, known for its excellent impact resistance and dimensional stability in a wide temperature range. PC-based films have excellent hail and wind tear resistance, with a long service life. At the same time, PC itself has good absorption of ultraviolet light, which can synergistically enhance the barrier to harmful ultraviolet light with functional fillers;

[0070] The toughening agent can be one or more of polybutylene adipate terephthalate, ethylene-vinyl acetate copolymer in addition to the thermoplastic polyurethane used in the examples:

[0071] (1) Polybutylene adipate terephthalate: a fatty-aromatic copolyester widely used in the field of biodegradable plastics. When blended with biobased resins such as polylactic acid, PBAT can significantly improve the brittleness of the base 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 with PBAT at a certain ratio (such as 70:30) is a common choice to obtain a composite material with certain strength and good flexibility;

[0072] (2) Thermoplastic polyurethane: a high-performance elastomer with urethane groups in the 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 base resin, producing a large number of crazes and shear bands when subjected to external force, thereby consuming a large amount of energy and significantly improving the impact resistance and fatigue resistance of the film. The ratio of hard segment and soft segment can be adjusted, and the polarity of the base resin can be selected to optimize the 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 rubbery, and has good compatibility with various polyolefins and engineering plastics. EVA can effectively improve the flexibility, environmental stress cracking resistance and low temperature impact resistance of the film, while it also has good light transmission and little effect on the optical properties of the film.

[0074] The spectral regulation agent can be one or more of chromium oxide green nanoparticles, neodymium oxide nanoparticles, cerium dioxide nanoparticles, and tungsten bronze nanoparticles in addition to the chromium oxide green nanoparticles used in the examples:

[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 500-600 nm band, while it has weak absorption of blue light in the 400-500 nm band and red light in the 600-700 nm band. When used as a spectral regulation agent, it can produce an agricultural film that "increases blue and red, and suppresses green". The transmittance spectrum is more matched to the absorption peaks of chlorophyll a and b, which theoretically can improve the efficiency of photosynthesis;

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

[0077] (3) Cerium dioxide nanoparticles: CeO2. It has excellent ultraviolet absorption capacity and reversible redox properties. As a spectral regulation agent, it mainly plays two roles: one is to efficiently absorb and block ultraviolet light in the 200-400 nm band, protecting crops from ultraviolet radiation damage; the other is to act as a light stabilizer, quenching free radicals generated by the film resin under ultraviolet light through the Ce³⁺ / Ce 4 ⁺ valence cycle, thereby delaying the photooxidative aging of the base resin and extending the service life of the film;

[0078] (4) Tungsten bronze nanoparticles: typically cesium tungsten bronze and rubidium tungsten bronze, with the general chemical formula MxWO3. This is a well-known near-infrared shielding material. It has good transmittance in the visible light region (380-780 nm), while it has strong absorption or scattering of near-infrared light in the 780-2500 nm band. By adding it to the film, it can significantly block the heat part of solar radiation while basically not affecting the light intensity in the greenhouse, thereby effectively reducing the temperature of the greenhouse in summer and reducing the energy consumption for cooling.

[0079] A spectral selective film for efficient agriculture obtained according to the steps of the above examples has a transmittance spectrum in the ultraviolet-visible-near-infrared region as shown in Figure 1: Figure 2As shown, the spectral selective film has an ultraviolet transmittance of less than 35% in the 200-380 nm wavelength band; a visible light transmittance of greater than 70% in the 400-500 nm wavelength band, a visible light transmittance of greater than 70% in the 600-700 nm wavelength band, and a visible light transmittance of less than 35% in the 500-560 nm wavelength band; and a near-infrared light transmittance of less than 15% in the 780-2500 nm wavelength band.

[0080] A spectral selective film for efficient agriculture is obtained according to the steps of the above embodiment, and the emissivity spectrum of the spectral selective film in the mid-infrared is as shown in Figure 3 As shown, the spectral selective film has an infrared emissivity of not less than 0.90 in the 8-13 μm wavelength band, and exhibits significant radiation refrigeration capacity.

[0081] A spectral selective film for efficient agriculture is obtained according to the steps of the above embodiment, and a schematic diagram of the principle of selective regulation of the entire sunlight in a greenhouse is as shown in Figure 4 As shown, when sunlight is incident on the film surface, the film has spectral selectivity, that is, most of the ultraviolet light and part of the green light are reflected, while the blue light, red light and photosynthetically active radiation band, which are critical for photosynthesis, are highly transmitted into the greenhouse for plant absorption and utilization. At the same time, the film can reflect near-infrared radiation, significantly reducing the input of solar thermal radiation, preventing the temperature in the greenhouse from being too high during the day. In addition, the film has high infrared transmittance in the 8-13 μm (atmospheric window) wavelength band, which can efficiently dissipate the heat accumulated in the room in the form of long-wave radiation, avoiding high-temperature heat stress. In short, the film has a spectral screening mechanism, which ensures the light and heat requirements of plants while maintaining a suitable greenhouse thermal environment, thereby promoting the healthy growth of plants.

[0082] The above-described specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present application, and it should be understood that the above-described specific embodiments are merely specific embodiments of the present application and are not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.

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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