Biodegradable agricultural film and preparation method thereof

Abstract

The invention discloses a biodegradable agricultural film and a preparation method thereof, and belongs to the technical field of biodegradable agricultural films.The preparation method comprises the steps that a ZIF (at) SiO2 super-hydrophobic high-activity hybrid dispersed with assistance of silicon dioxide is prepared through assistance of ultrasonic microwaves, the ZIF (at) SiO2 super-hydrophobic high-activity hybrid and polydopamine are subjected to ultrasonic dispersion, a polylactic acid film is coated with the ZIF (at) SiO2 super-hydrophobic high-activity hybrid and polydopamine, and a water retention layer is prepared; the multi-layer biodegradable agricultural film with far-infrared warming and water retention properties is prepared by preparing a warming layer from a high-activity infrared absorbent and aliphatic polyester, preparing a high-barrier layer from high-activity nanosheets and PCL (polycaprolactone), and laminating and molding the water retention layer, the warming layer and the high-barrier layer, thereby obtaining the multi-layer biodegradable agricultural film with far-infrared warming and water retention properties. The prepared biodegradable agricultural film not only has the advantages of far infrared heating and water retention, has the effects of increasing the yield and improving the quality of crops, but also has good degradability, is expected to replace a common agricultural film to be popularized and used in a farmland, reduces the pollution of the agricultural film to soil, and accelerates the development of modern ecological agriculture.

Description

Technical Field

[0001] The invention relates to the technical field of biodegradable agricultural films, and in particular to a biodegradable agricultural film and a preparation method thereof. Background Art

[0002] Agricultural film is one of the important materials for agricultural production. The application of agricultural film technology has greatly promoted the improvement of agricultural output and benefits, and has led to changes in agricultural production methods and a leap in productivity. Agricultural film covering not only has the functions of warming, moisture retention, early maturity and increased production, but also prevents soil erosion, effectively controls soil salinity and reduces nitrogen leaching.

[0003] The raw material of plastic agricultural film is mainly polyethylene (PE), and its manufacturing raw materials are mainly extracted from petroleum, coal and natural gas. PE material is easy to process, has excellent chemical resistance, high durability, flexibility, no odor and toxicity. However, PE material has a large relative molecular mass, stable performance, and is difficult to degrade in the natural environment. It can remain in the soil for 200 to 400 years. The residual film accumulates in the soil year by year to form a barrier, which not only directly has an adverse impact on agricultural farming and sowing, but also hinders the movement of water, air and fertilizer in the soil tillage layer, destroys the soil structure, and greatly damages the agricultural ecological environment, causing serious "white pollution".

[0004] The development of biodegradable agricultural films has become one of the important hotspots of agricultural research. Existing biodegradable agricultural films are mainly made of biodegradable materials such as polybutylene succinate (PBS), polyglycolic acid (PGA), polylactic acid (PLA), polycaprolactone (PCL), polybutylene terephthalate-butylene adipate copolyester (PBAT) and the like as raw materials, and then add auxiliary materials such as water-retaining and moisturizing agents, light absorbers and barrier agents, and prepare biodegradable films by co-extrusion blow molding. However, the mixed co-extrusion of each component in the above-mentioned preparation method will inevitably lead to poor dispersion uniformity of the functional components, resulting in poor water retention and heat preservation effects of the obtained film, which greatly limits the practical application of biodegradable plastic agricultural films. Summary of the invention

[0005] The present invention provides a biodegradable agricultural film and a preparation method thereof, which effectively solves the technical problem that the biodegradable agricultural film obtained by the existing preparation method has low water and heat preservation capacity for the soil during use, which greatly limits the practical application of the biodegradable plastic agricultural film. At the same time, it provides a multilayer biological agricultural film with far-infrared warming and water retention properties, which has the effect of increasing the yield and quality of crops and has good degradability.

[0006] The first object of the present invention is to provide a method for preparing a biodegradable agricultural film, characterized in that it comprises the following steps:

[0007] SiO2, soluble zinc salt and 2-methylimidazole are used as raw materials, and ultrasonic microwave treatment is performed to cause zinc ions to react with 2-methylimidazole to obtain an organic-inorganic hybrid (ZIF@SiO2 hybrid) loaded with SiO2. Dopamine is added to form polydopamine through self-polymerization of dopamine, and the polydopamine adheres to the surface of the organic-inorganic hybrid loaded with SiO2 to obtain a water-retaining coating. The water-retaining coating is applied to a polylactic acid film to obtain a water-retaining layer of the loaded coating.

[0008] The infrared absorber and the bridging agent are mixed to generate electrophilic and nucleophilic reactions to obtain an active infrared absorber. The active infrared absorber and the aliphatic polyester are dispersed by melt shearing to obtain a warming layer.

[0009] The nanosheets and the bridging agent are mixed to generate electrophilic and nucleophilic reactions to obtain active nanosheets, and the active nanosheets and polycaprolactone are dispersed by melt shearing to obtain a barrier layer.

[0010] The water-retaining layer, the warming layer and the barrier layer are laminated to obtain a biodegradable agricultural film.

[0011] As a preferred embodiment, the molar ratio of 2-methylimidazole to soluble zinc salt is 1-10:1, and the molar ratio of soluble zinc salt to SiO2 is 8:1-10.

[0012] As a preferred embodiment, the mass ratio of the organic-inorganic hybrid loaded with SiO2 to polydopamine is 1 to 10:1.

[0013] As a preferred embodiment, the ultrasonic microwave treatment adopts an ultrasonic-microwave reactor with an output power of 500W to 6000W, a reaction temperature of 80°C to 200°C, and a reaction time of 5min to 40min.

[0014] As a preferred embodiment, the mass ratio of the infrared absorber to the bridging agent is 1 to 10:1, and the mass ratio of the active infrared absorber to the aliphatic polyester is 1 to 5:100.

[0015] As a preferred embodiment, the mass ratio of the nanosheets to the bridging agent is 1 to 10:1, and the mass ratio of the active nanosheets to polycaprolactone is 1 to 5:100.

[0016] As a preferred embodiment, the thickness of the polylactic acid film is 3 μm to 8 μm, the thickness of the coating is 0.01 μm to 2 μm, the thickness of the warming layer is 3 μm to 8 μm, and the thickness of the barrier layer is 5 μm to 10 μm.

[0017] As a preferred embodiment, the aliphatic polyester is butanediol adipate copolyester.

[0018] As a preferred embodiment, the infrared absorber is OMNISTAB near-infrared absorber H-3, H-6 or H-9; the bridging agent is at least one of diisopropylbenzene peroxide, benzoyl peroxide, di-tert-butyl peroxide and diisopropylbenzene hydroperoxide; the nanosheet is at least one of boron nitride nanosheet, graphene nanosheet, nanomica sheet and natural montmorillonite.

[0019] The second object of the present invention is to provide a biodegradable agricultural film prepared by the above preparation method.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The invention provides a biodegradable agricultural film and a preparation method thereof. The invention firstly mixes SiO2, a soluble zinc salt and 2-methylimidazole by ultrasound-microwave assistance, and the zinc ions react with the 2-methylimidazole to obtain an organic-inorganic hybrid loaded with SiO2 assisted by silicon dioxide dispersion, i.e., a ZIF@SiO2 super-hydrophobic high-activity hybrid, and then ultrasonically disperses and coats the hybrid with polydopamine on a polylactic acid film to prepare a water-retaining layer. The ultrasonic microwave reaction combines ultrasonic dispersion with microwave hydrothermal synthesis, and firstly utilizes the mechanical vibration and cavitation effect generated by ultrasonic waves. The thermal and chemical effects act on the SiO2, soluble zinc salt, and 2-methylimidazole particle clusters, breaking them up through shear and compression forces. At the same time, the high-pressure shock wave generated by the instantaneous collapse bubbles formed by the cavitation effect further promotes the dispersion of the particles. The thermal and chemical effects enhance the dispersion effect by changing the surface properties of the particles. The microwave field is used as a heat source. Due to the high temperature and high pressure conditions, the reaction activity of SiO2, soluble zinc salt solution and 2-methylimidazole solution is greatly improved. Under microwave heating conditions, the temperature of the entire reaction system can be instantly raised to The crystallization temperature greatly accelerates the speed of synthesis and crystallization, shortens the crystallization time, and thus efficiently prepares the silicon dioxide-coated ZIF@SiO2 hybrid with a core-shell structure. The ZIF@SiO2 hybrid with a core-shell structure effectively prevents the agglomeration effect of ZIF, and gives full play to the ability of ZIF to generate active free radicals and kill pests. In addition, ZIF@SiO2 provides super-hydrophobicity for agricultural films, which can prevent water evaporation, increase the temperature and humidity of crops, and produce polydopamine with adhesion properties through the self-polymerization of dopamine, and adhere to On the surface of ZIF@SiO2 hybrid, polydopamine can act as an adhesive to prevent the hybrid from falling off, and as a dispersant to prevent the hybrid from agglomerating. In addition, its wide light absorption and superior photothermal conversion ability can provide thermal insulation for biodegradable agricultural film. The warming layer is prepared with highly active infrared absorber and aliphatic polyester, and the high barrier layer is prepared with highly active nanosheets and polycaprolactone (PCL). The water-retaining layer, the warming layer and the high barrier layer are laminated to obtain a multilayer biodegradable agricultural film with far-infrared warming and water-retaining properties.

[0022] The biodegradable agricultural film prepared by the present invention has an inner water contact angle of 132.7° to 150.8°, an infrared absorption rate of 92.3% to 95.3%, an environmental humidity in the area covered by the agricultural film of 81% RH to 92% RH, an environmental temperature of 7.1°C to 12.8°C, a breaking strength of 29.4MPa to 35.8MPa, and a mass loss of more than 10.4% after being buried in the soil for 3 months. The biodegradable agricultural film prepared by the present invention not only has the advantages of far-infrared warming and water retention, but also has the effect of increasing the yield and quality of crops, and has good degradability, and is expected to replace ordinary agricultural films for promotion and use in farmland, reduce the pollution of soil caused by agricultural films, and accelerate the development of modern ecological agriculture. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a process flow chart for preparing the biodegradable agricultural film according to Example 1 of the present invention.

[0024] Figure 2 This is a water contact angle test graph of the biodegradable agricultural film prepared in Example 3 of the present invention.

[0025] Figure 3 This is a water contact angle test diagram of the biodegradable agricultural film prepared in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0026] In order to enable those skilled in the art to better understand the technical solution of the present invention and implement it, the present invention is further described below in conjunction with specific embodiments and drawings, but the embodiments are not intended to limit the present invention. The following test methods and detection methods, unless otherwise specified, are conventional methods; the reagents and raw materials, unless otherwise specified, are commercially available.

[0027] For existing biodegradable agricultural films such as polybutylene succinate (PBS), polyglycolic acid (PGA), polylactic acid (PLA), polycaprolactone (PCL), polybutylene terephthalate-butylene adipate copolyester (PBAT), although they can be degraded by soil microorganisms within a period of time after use, which can better solve the pollution problem caused by traditional agricultural films, the existing agricultural film products have low water retention and heat preservation capabilities for the soil during use, which greatly limits the practical application of biodegradable plastic agricultural films. Based on the above technical problems, the present invention provides a biodegradable agricultural film and a preparation method thereof, wherein a silicon dioxide-assisted dispersed ZIF@SiO2 hybrid is prepared by ultrasonic microwave assistance, and is ultrasonically dispersed and coated on a polylactic acid film to prepare a water-retaining layer, a highly active infrared absorber and an aliphatic polyester are used to prepare a warming layer, and a highly active nanosheet and polycaprolactone are used to prepare a high-barrier layer, and the water-retaining layer, the warming layer and the high-barrier layer are laminated to prepare a multilayer biodegradable agricultural film with far-infrared warming and water-retaining properties.

[0028] The technical solution of the present invention is analyzed and explained below.

[0029] The present invention first provides a method for preparing a biodegradable agricultural film, comprising the following steps:

[0030] SiO2, a soluble zinc salt solution and a 2-methylimidazole solution are mixed, subjected to ultrasonic microwave treatment, centrifuged, washed and dried to obtain a ZIF@SiO2 hybrid, the ZIF@SiO2 hybrid is ultrasonically mixed with polydopamine, and coated on a polylactic acid film to obtain a water-retaining layer of the load coating.

[0031] The infrared absorber and the bridging agent are mixed to obtain an active infrared absorber, and the active infrared absorber and the aliphatic polyester are dispersed by melt shearing to obtain a warming layer.

[0032] The nanosheets and the bridging agent are mixed to obtain active nanosheets, and the active nanosheets and polycaprolactone (PCL) are dispersed by melt shearing to obtain a barrier layer.

[0033] The water-retaining layer, the warming layer and the barrier layer are laminated to obtain a biodegradable agricultural film.

[0034] In the above technical scheme, a silicon dioxide-assisted dispersed ZIF@SiO2 hybrid is prepared by ultrasonic microwave assistance, and is ultrasonically dispersed and coated on a polylactic acid film with polydopamine to prepare a water-retaining layer, a high-activity infrared absorber and aliphatic polyester are used to prepare a warming layer, and a high-activity nanosheet and polycaprolactone are used to prepare a high-barrier layer. The water-retaining layer, the warming layer and the high-barrier layer are laminated to prepare a multilayer biodegradable agricultural film with far-infrared warming and water-retaining properties. The biodegradable agricultural film prepared by the present invention not only has the advantages of far-infrared warming and water-retaining, but also has the effect of increasing the yield and quality of crops, and also has good degradability.

[0035] The degradable material used for the water-retaining layer constructed by the present invention is polylactic acid (PLA), which has excellent mechanical properties, good biocompatibility, and is non-toxic and mild; ZIF has excellent light absorption ability, can provide heat preservation, and can generate a large number of active free radicals under light conditions, which have antibacterial and insect repellent effects; SiO2 auxiliary dispersion can prevent ZIF from agglomerating and ensure the activity of ZIF, and can effectively improve the hydrophobicity of agricultural film, block water evaporation, and increase the temperature and humidity of crops; polydopamine can act as an adhesive to prevent the hybrid from falling off, and can act as a dispersant to prevent the hybrid from agglomerating. In addition, its wide light absorption and excellent light-to-heat conversion ability can provide heat preservation.

[0036] The degradable material used in the warming layer constructed by the present invention is PBAT, which combines the excellent degradation performance of aliphatic polyester and the good mechanical properties of aromatic polyester; the added infrared absorber has good infrared absorption performance and optical properties, enhances the thermal insulation capacity of the film, and effectively increases crop yields.

[0037] The high-barrier outer layer constructed in the present invention mainly provides strength and barrier properties to the agricultural film. The addition of nanosheets can improve multiple mechanical and thermodynamic properties of PCL, including creep resistance, tensile strength, puncture resistance, aging resistance, thermal deformation temperature, etc.

[0038] As a preferred embodiment, the molar ratio of 2-methylimidazole to soluble zinc salt is 1 to 10:1, and the molar ratio of soluble zinc salt to SiO2 is 8:1 to 10. When the molar ratio of 2-methylimidazole to soluble zinc salt is too high, the growth of ZIF-8 crystal nuclei will be delayed, resulting in too small particle size of synthesized ZIF-8, which will weaken its light absorption ability and ability to generate active free radicals; when the molar ratio of 2-methylimidazole to soluble zinc salt is too low, Zn 2+ It cannot fully participate in the reaction, affecting the yield of ZIF-8 crystals. Too large a molar ratio of soluble zinc salt to SiO2 will lead to agglomeration of ZIF crystals; too small a molar ratio of soluble zinc salt to SiO2 will weaken the light absorption ability and ability to generate active free radicals of ZIF.

[0039] It should be noted that the soluble zinc salt used in the present invention is at least one of zinc nitrate, zinc chloride, zinc sulfate and zinc acetate. The centrifugal speed is 7000 rpm to 1200 rpm, and the centrifugal time is 5 min to 30 min. When the ZIF@SiO2 hybrid is ultrasonically mixed with polydopamine, the ultrasonic frequency is 20 kHz to 100 kHz, and the ultrasonic time is 3 min to 60 min.

[0040] In a more preferred solution, the particle size of the ZIF@SiO2 hybrid is 300nm to 2000nm. If the particle size of the hybrid is too large, the light absorption ability of ZIF@SiO2 will be weakened, and if the particle size of the hybrid is too small, it will make ZIF@SiO2 difficult to collect by centrifugation.

[0041] In order to promote the water retention effect of the agricultural film, the mass ratio of the ZIF@SiO2 hybrid to polydopamine is 1 to 10: 1. If the mass ratio of the ZIF@SiO2 hybrid to polydopamine is too large, the ZIF@SiO2 hybrid will agglomerate; if the mass ratio is too small, the hydrophobicity of the agricultural film will be affected.

[0042] It should be noted that the ultrasonic microwave treatment adopts an ultrasonic-microwave reactor with an output power of 500W to 6000W, a reaction temperature of 80°C to 200°C, and a reaction time of 5min to 40min. The present invention controls the output power, reaction temperature, and reaction time of the ultrasonic microwave reaction within the above range based on the following considerations: when the output power and temperature are too high and the time is too long, the ZIF@SiO2 hybrid will grow excessively, and the internal structure of the reactant will be damaged, affecting the generation of its active free radicals; when the output power and temperature are too low and the time is too short, the reaction will be insufficient, the ZIF@SiO2 hybrid will not grow completely, and its light absorption capacity and antibacterial and insect repellent capacity will be fully exerted.

[0043] In order to further improve the thermal insulation effect of the agricultural film, the mass ratio of the infrared absorber and the bridging agent is 1 to 10:1. Too large a mass ratio will lead to poor dispersibility and adhesion of the active infrared absorber, and too small a mass ratio will reduce the light absorption performance of the active infrared absorber. The mass ratio of the active infrared absorber and polybutylene adipate / terephthalate is 1 to 5:100. Too large a mass ratio will reduce the biodegradability and mechanical properties of the agricultural film, and too small a mass ratio will affect the light absorption capacity of the agricultural film, resulting in poor thermal insulation effect.

[0044] In order to improve the mechanical properties of the agricultural film, the mass ratio of the nanosheets and the bridging agent is 1 to 10:1. If the mass ratio is too large, the dispersibility and adhesion of the active nanosheets will be poor, and if the mass ratio is too small, the barrier properties, chemical stability and antioxidant properties of the active nanosheets will be reduced. The mass ratio of the active nanosheets and polycaprolactone is 1 to 5:100. If the mass ratio is too large, the cost and weight of the agricultural film will be increased, and the strength and rigidity of the agricultural film will be reduced. If the mass ratio is too small, the agricultural film cannot guarantee sufficient support and barrier properties.

[0045] In order to further improve the mechanical properties of the agricultural film, the thickness of the polylactic acid film is 3μm to 8μm, the thickness of the coating is 0.01μm to 2μm, the thickness of the warming layer is 3μm to 8μm, and the thickness of the barrier layer is 5μm to 10μm. If the thickness of the polylactic acid film is too large, the weight of the agricultural film will increase, affecting the covering effect; if it is too small, the mechanical properties of the agricultural film will be poor. If the thickness of the coating is too large, the cost and weight of the agricultural film will increase, affecting the covering effect; if the thickness is too small, it will affect the water retention and antibacterial and insect repellent properties of the agricultural film. If the thickness of the warming layer is too large, the internal environmental temperature of the agricultural film will be too high, which is not conducive to the normal growth of crops; if the thickness is too small, the warming effect of the agricultural film will be poor, affecting the yield of crops. If the thickness of the barrier layer is too large, the light absorption of the warming intermediate layer will be reduced, reducing the thermal insulation effect of the agricultural film; if the thickness is too small, the mechanical properties and barrier properties of the agricultural film will be poor.

[0046] In this case, the infrared absorber is OMNISTAB near-infrared absorber H-3, H-6 or H-9; the bridging agent is diisopropylbenzene peroxide, benzoyl peroxide, di-tert-butyl peroxide or diisopropylbenzene hydroperoxide; the nanosheets are boron nitride nanosheets, graphene nanosheets, nanomica sheets or natural montmorillonite.

[0047] The technical effects of the present invention are described below in conjunction with specific embodiments and comparative examples.

[0048] Example 1

[0049] A method for preparing a biodegradable agricultural film, such as Figure 1 As shown, the following steps are included:

[0050] S1, zinc acetate and 2-methylimidazole are dissolved in deionized water respectively, and the zinc acetate solution, 2-methylimidazole solution and silicon dioxide are mixed and placed in an ultrasonic-microwave reactor at 800 W and 140 ° C for 10 min according to the molar ratio of 2-methylimidazole to soluble zinc salt of 8:1 and the molar ratio of soluble zinc salt to SiO2 of 8:5, and the mixture is centrifuged at 10000 rpm for 10 min, washed and dried to obtain a ZIF@SiO2 hybrid.

[0051] S2, preparation of water-retaining inner layer: the ZIF@SiO2 hybrid of S1 and polydopamine were ultrasonically dispersed at 50 kHz for 10 min in a mass ratio of 4:1, and coated on a polylactic acid film with a thickness of 5 μm to obtain a water-retaining layer with a coating thickness of 1 μm.

[0052] S3, an infrared absorber (OMNISTAB near-infrared absorber H-3) and diisopropylbenzene peroxide are mixed in a mass ratio of 5:1 to obtain an active infrared absorber, and the active infrared absorber and butanediol adipate copolyester (PBAT) are fed into a screw extruder in a mass ratio of 5:100, the melt blending temperature is 200°C, the screw speed is 140r / min, and the blended melt extruded by the screw is successively water-cooled and air-cooled, solidified, and shear-dispersed to form a blended pellet with a warming layer; after the blended pellets are dried, they are fed into a film blowing machine, the temperature is 150°C, the screw speed is 110r / min, and the traction speed is set to 6m / min. The blended pellets are blown into film by the film blowing machine to prepare a warming layer with a thickness of 5μm.

[0053] S4, mixing boron nitride nanosheets and diisopropylbenzene peroxide in a mass ratio of 5:1 to obtain active nanosheets, and feeding the active nanosheets and polycaprolactone (PCL) into a screw extruder in a mass ratio of 5:100, with a melt blending temperature of 200°C and a screw speed of 140 r / min. The blended melt extruded by the screw is successively water-cooled and air-cooled, and then solidified and shear-dispersed to form blended pellets of a barrier layer; after the blended pellets are dried, they are fed into a film blowing machine at a temperature of 150°C, a screw speed of 110 r / min, and a traction speed set to 6 m / min. The blended pellets are blown into film by the film blowing machine to prepare a barrier layer with a thickness of 10 μm.

[0054] S5, laminating the water-retaining layer, the warming layer and the barrier layer at 100° C. and 10 MPa to obtain a biodegradable agricultural film.

[0055] Example 2

[0056] A method for preparing a biodegradable agricultural film comprises the following steps:

[0057] S1, zinc acetate and 2-methylimidazole are dissolved in deionized water respectively, and the zinc acetate solution, 2-methylimidazole solution and silicon dioxide are mixed and placed in an ultrasonic-microwave reactor at 800 W and 100 ° C for 20 min according to the molar ratio of 2-methylimidazole to soluble zinc salt of 5:1 and the molar ratio of soluble zinc salt to SiO2 of 8:3, and the mixture is centrifuged at 8000 rpm for 15 min, washed and dried to obtain a ZIF@SiO2 hybrid.

[0058] S2, preparing a water-retaining inner layer: the ZIF@SiO2 hybrid and polydopamine were ultrasonically dispersed at 30 kHz for 30 min in a mass ratio of 6:1, and coated on a polylactic acid film with a thickness of 8 μm to obtain a water-retaining layer with a coating thickness of 0.5 μm.

[0059] S3, an infrared absorber (OMNISTAB near-infrared absorber H-6) and benzoyl peroxide are mixed in a mass ratio of 3:1 to obtain an active infrared absorber, and the active infrared absorber and butylene adipate copolyester (PBAT) are fed into a screw extruder in a mass ratio of 3:100, the melt blending temperature is 200°C, the screw speed is 140r / min, and the blended melt extruded by the screw is successively water-cooled and air-cooled, solidified, and shear-dispersed to form a blended pellet with a warming layer; after the blended pellets are dried, they are fed into a film blowing machine, the temperature is 150°C, the screw speed is 110r / min, and the traction speed is set to 6m / min. The blended pellets are blown into film by the film blowing machine to prepare a warming layer with a thickness of 3μm.

[0060] S4, mixing graphene nanosheets and benzoyl peroxide in a mass ratio of 3:1 to obtain active nanosheets, and feeding the active nanosheets and polycaprolactone (PCL) into a screw extruder in a mass ratio of 3:100, with a melt blending temperature of 200°C and a screw speed of 140r / min. The blended melt extruded by the screw is successively water-cooled and air-cooled, and then solidified and shear-dispersed to form blended pellets of a barrier layer; after the blended pellets are dried, they are fed into a film blowing machine at a temperature of 150°C, a screw speed of 110r / min, and a traction speed set to 6m / min. The blended pellets are blown into film by the film blowing machine to prepare a barrier layer with a thickness of 8μm.

[0061] S5, laminating the water-retaining layer, the warming layer and the barrier layer at 100° C. and 10 MPa to obtain a biodegradable agricultural film.

[0062] Example 3

[0063] A method for preparing a biodegradable agricultural film comprises the following steps:

[0064] S1, zinc nitrate and 2-methylimidazole are dissolved in deionized water respectively, and the zinc nitrate solution, 2-methylimidazole solution and silicon dioxide are mixed and placed in an ultrasonic-microwave reactor at 1000 W and 150 ° C for 5 min according to the molar ratio of 2-methylimidazole to soluble zinc salt of 3:1 and the molar ratio of soluble zinc salt to SiO2 of 8:2, and the mixture is centrifuged at 7000 rpm for 20 min, washed and dried to obtain a ZIF@SiO2 hybrid.

[0065] S2, preparing a water-retaining inner layer: the ZIF@SiO2 hybrid and polydopamine were ultrasonically dispersed at 20 kHz for 50 min in a mass ratio of 2:1, and coated on a polylactic acid film with a thickness of 5 μm to obtain a water-retaining layer with a coating thickness of 0.2 μm.

[0066] S3, an infrared absorber (OMNISTAB near-infrared absorber H-9) and di-tert-butyl peroxide are mixed in a mass ratio of 5:1 to obtain an active infrared absorber, and the active infrared absorber and butanediol adipate copolyester (PBAT) are fed into a screw extruder in a mass ratio of 5:100, the melt blending temperature is 200°C, the screw speed is 140r / min, and the blended melt extruded by the screw is successively water-cooled and air-cooled, solidified, and shear-dispersed to form a blended pellet with a warming layer; after the blended pellets are dried, they are fed into a film blowing machine, the temperature is 150°C, the screw speed is 110r / min, and the traction speed is set to 6m / min. The blended pellets are blown into film by the film blowing machine to prepare a warming layer with a thickness of 5μm.

[0067] S4, mixing nano mica sheets and di-tert-butyl peroxide in a mass ratio of 2:1 to obtain active nano sheets, and feeding the active nano sheets and polycaprolactone (PCL) into a screw extruder in a mass ratio of 2:100, with a melt blending temperature of 200°C and a screw speed of 140 r / min. The blended melt extruded by the screw is successively water-cooled and air-cooled, and then solidified and shear-dispersed to form blended pellets of a barrier layer; after the blended pellets are dried, they are fed into a film blowing machine at a temperature of 150°C, a screw speed of 110 r / min, and a traction speed set to 6 m / min. The blended pellets are blown into film by the film blowing machine to prepare a barrier layer with a thickness of 8 μm.

[0068] S5, laminating the water-retaining layer, the warming layer and the barrier layer at 100° C. and 10 MPa to obtain a biodegradable agricultural film.

[0069] Example 4

[0070] A method for preparing a biodegradable agricultural film comprises the following steps:

[0071] S1, zinc nitrate and 2-methylimidazole are dissolved in deionized water respectively, and the zinc nitrate solution, 2-methylimidazole solution and silicon dioxide are mixed and placed in an ultrasonic-microwave reactor at 800 W and 180 ° C for 5 min according to the molar ratio of 2-methylimidazole to soluble zinc salt of 1:1 and the molar ratio of soluble zinc salt to SiO2 of 8:1, and the mixture is centrifuged at 12000 rpm for 5 min, washed and dried to obtain a ZIF@SiO2 hybrid.

[0072] S2, preparing a water-retaining inner layer: the ZIF@SiO2 hybrid and polydopamine were ultrasonically dispersed at 50 kHz for 5 min in a mass ratio of 1:1, and coated on a polylactic acid film with a thickness of 8 μm to obtain a water-retaining layer with a coating thickness of 0.05 μm.

[0073] S3, an infrared absorber (OMNISTAB near-infrared absorber H-3) and diisopropylbenzene hydroperoxide are mixed in a mass ratio of 1:1 to obtain an active infrared absorber, and the active infrared absorber and butanediol adipate copolyester (PBAT) are fed into a screw extruder in a mass ratio of 1:100, the melt blending temperature is 200°C, the screw speed is 140r / min, and the blended melt extruded by the screw is successively water-cooled and air-cooled, solidified, and shear-dispersed to form a blended pellet with a warming layer; after the blended pellets are dried, they are fed into a film blowing machine at a temperature of 150°C, a screw speed of 110r / min, and a traction speed set to 6m / min. The blended pellets are blown into film by the film blowing machine to prepare a warming layer with a thickness of 8μm.

[0074] S4, natural montmorillonite and diisopropylbenzene hydroperoxide are mixed in a mass ratio of 1:1 to obtain active nanosheets, and the active nanosheets and polycaprolactone (PCL) are fed into a screw extruder in a mass ratio of 1:100, the melt blending temperature is 200°C, the screw speed is 140r / min, and the blended melt extruded by the screw is successively water-cooled and air-cooled, and then solidified and shear-dispersed to form blended pellets of the barrier layer; after the blended pellets are dried, they are fed into a film blowing machine at a temperature of 150°C, a screw speed of 110r / min, and a traction speed set to 6m / min. The blended pellets are blown into film by the film blowing machine to prepare a barrier layer with a thickness of 5μm.

[0075] S5, laminating the water-retaining layer, the warming layer and the barrier layer at 100° C. and 10 MPa to obtain a biodegradable agricultural film.

[0076] In order to further illustrate the technical effect of the present invention, the present invention is also provided with a comparative example, as follows:

[0077] Comparative Example 1

[0078] Compared with Example 1, the difference is that the ZIF@SiO2 hybrid is not added to the water-retaining layer.

[0079] A method for preparing a biodegradable agricultural film comprises the following steps:

[0080] S1, coating polydopamine on a polylactic acid film with a thickness of 5 μm to obtain a water-retaining layer with a coating thickness of 1 μm.

[0081] S2, an infrared absorber (OMNISTAB near-infrared absorber H-3) and diisopropylbenzene peroxide are mixed in a mass ratio of 5:1 to obtain an active infrared absorber, and the active infrared absorber and butanediol adipate copolyester (PBAT) are fed into a screw extruder in a mass ratio of 5:100, the melt blending temperature is 200°C, the screw speed is 140r / min, and the blended melt extruded by the screw is successively water-cooled and air-cooled, solidified, and shear-dispersed to form a blended pellet with a warming layer; after the blended pellets are dried, they are fed into a film blowing machine, the temperature is 150°C, the screw speed is 110r / min, and the traction speed is set to 6m / min. The blended pellets are blown into film by the film blowing machine to prepare a warming layer with a thickness of 5μm.

[0082] S3, mixing boron nitride nanosheets and diisopropylbenzene peroxide in a mass ratio of 5:1 to obtain active nanosheets, and feeding the active nanosheets and polycaprolactone (PCL) into a screw extruder in a mass ratio of 5:100, with a melt blending temperature of 200°C and a screw speed of 140r / min. The blended melt extruded by the screw is successively water-cooled and air-cooled, and then solidified and shear-dispersed to form blended pellets of a barrier layer; after the blended pellets are dried, they are fed into a film blowing machine at a temperature of 150°C, a screw speed of 110r / min, and a traction speed set to 6m / min. The blended pellets are blown into film by the film blowing machine to prepare a barrier layer with a thickness of 10μm.

[0083] S4, laminating the water-retaining layer, the warming layer and the barrier layer at 100° C. and 10 MPa to obtain a biodegradable agricultural film.

[0084] Comparative Example 2

[0085] The difference compared with Example 2 is that polydopamine is not added to the water-retaining layer.

[0086] A method for preparing a biodegradable agricultural film comprises the following steps:

[0087] S1, zinc acetate and 2-methylimidazole are dissolved in deionized water respectively, and the zinc acetate solution, 2-methylimidazole solution and silicon dioxide are mixed and placed in an ultrasonic-microwave reactor at 800 W and 100 ° C for 20 min according to the molar ratio of 2-methylimidazole to soluble zinc salt of 5:1 and the molar ratio of soluble zinc salt to SiO2 of 8:3, and the mixture is centrifuged at 8000 rpm for 15 min, washed and dried to obtain a ZIF@SiO2 hybrid.

[0088] S2, preparing a water-retaining inner layer: coating the ZIF@SiO2 hybrid on a polylactic acid film with a thickness of 8 μm to obtain a water-retaining layer with a coating thickness of 0.5 μm.

[0089] S3, an infrared absorber (OMNISTAB near-infrared absorber H-6) and benzoyl peroxide are mixed in a mass ratio of 3:1 to obtain an active infrared absorber, and the active infrared absorber and butylene adipate copolyester (PBAT) are fed into a screw extruder in a mass ratio of 3:100, the melt blending temperature is 200°C, the screw speed is 140r / min, and the blended melt extruded by the screw is successively water-cooled and air-cooled, solidified, and shear-dispersed to form a blended pellet with a warming layer; after the blended pellets are dried, they are fed into a film blowing machine, the temperature is 150°C, the screw speed is 110r / min, and the traction speed is set to 6m / min. The blended pellets are blown into film by the film blowing machine to prepare a warming layer with a thickness of 3μm.

[0090] S4, mixing graphene nanosheets and benzoyl peroxide in a mass ratio of 3:1 to obtain active nanosheets, and feeding the active nanosheets and polycaprolactone (PCL) into a screw extruder in a mass ratio of 3:100, with a melt blending temperature of 200°C and a screw speed of 140r / min. The blended melt extruded by the screw is successively water-cooled and air-cooled, and then solidified and shear-dispersed to form blended pellets of a barrier layer; after the blended pellets are dried, they are fed into a film blowing machine at a temperature of 150°C, a screw speed of 110r / min, and a traction speed set to 6m / min. The blended pellets are blown into film by the film blowing machine to prepare a barrier layer with a thickness of 8μm.

[0091] S5, laminating the water-retaining layer, the warming layer and the barrier layer at 100° C. and 10 MPa to obtain a biodegradable agricultural film.

[0092] Comparative Example 3

[0093] Compared with Example 3, the difference is that no infrared absorber is added to the warming layer.

[0094] A method for preparing a biodegradable agricultural film comprises the following steps:

[0095] S1, zinc nitrate and 2-methylimidazole are dissolved in deionized water respectively, and the zinc nitrate solution, 2-methylimidazole solution and silicon dioxide are mixed and placed in an ultrasonic-microwave reactor at 1000 W and 150 ° C for 5 min according to the molar ratio of 2-methylimidazole to soluble zinc salt of 3:1 and the molar ratio of soluble zinc salt to SiO2 of 8:2, and the mixture is centrifuged at 7000 rpm for 20 min, washed and dried to obtain a ZIF@SiO2 hybrid.

[0096] S2, preparing a water-retaining inner layer: the ZIF@SiO2 hybrid and polydopamine were ultrasonically dispersed at 20 kHz for 50 min in a mass ratio of 2:1, and coated on a polylactic acid film with a thickness of 5 μm to obtain a water-retaining layer with a coating thickness of 0.2 μm.

[0097] S3, feeding butylene adipate copolyester (PBAT) into a screw extruder, with a melt blending temperature of 200°C and a screw speed of 140 r / min. The blended melt extruded by the screw is successively water-cooled and air-cooled, solidified, and shear-dispersed to form blended pellets with a warming layer; after drying, the blended pellets are fed into a film blowing machine at a temperature of 150°C, a screw speed of 110 r / min, and a traction speed of 6 m / min. The blended pellets are blown into film by the film blowing machine to prepare an intermediate layer with a thickness of 5 μm.

[0098] S4, mixing nano mica sheets and di-tert-butyl peroxide in a mass ratio of 2:1 to obtain active nano sheets, and feeding the active nano sheets and polycaprolactone (PCL) into a screw extruder in a mass ratio of 2:100, with a melt blending temperature of 200°C and a screw speed of 140 r / min. The blended melt extruded by the screw is successively water-cooled and air-cooled, and then solidified and shear-dispersed to form blended pellets of a barrier layer; after the blended pellets are dried, they are fed into a film blowing machine at a temperature of 150°C, a screw speed of 110 r / min, and a traction speed set to 6 m / min. The blended pellets are blown into film by the film blowing machine to prepare a barrier layer with a thickness of 8 μm.

[0099] S5, laminating the water-retaining layer, the warming layer and the barrier layer at 100° C. and 10 MPa to obtain a biodegradable agricultural film.

[0100] The performance of the biodegradable agricultural films prepared in the above-mentioned Examples 1 to 4 and Comparative Examples 1 to 3 of the present invention was tested, and the results are shown in Table 1 below:

[0101] Water contact angle test: The water contact angle of the water-retaining layer of the agricultural film was tested using a contact angle meter (WCA, DSA100, KRUSS, Germany).

[0102] Infrared absorption rate test: Fourier transform infrared spectrometer (FTIR, Nicolet IS10, Nicolet Company, USA) was used to test the infrared absorption rate of agricultural film.

[0103] Water retention and warming performance test: An integrated temperature and humidity sensor (DS1923-F5, Shanghai Wodisen Electronic Technology Co., Ltd.) was placed on the soil covered with agricultural film to record the changes in humidity and temperature inside the film.

[0104] Tensile property test: The obtained agricultural film was cut to obtain tensile specimens, and the tensile properties of the agricultural film were tested using a universal tensile machine (model 4403, sensor 100N) of Instron Company of the United States according to the plastic tensile property test standard ASTMD638-2003 of the American Society for Testing and Materials. At least 3 parallel test samples were guaranteed for each group, and the results were averaged.

[0105] Degradation performance test: The traditional soil burial degradation method was used to conduct a degradation experiment on the agricultural film. The agricultural film was weighed before the experiment and weighed again after being buried in the soil for 3 months. The mass loss rate was calculated to evaluate the degradation performance.

[0106] Table 1 Water retention, temperature increase, mechanical properties and degradation properties of the biodegradable agricultural film of the present invention

[0107]

[0108] As shown in Table 1, Examples 1 to 4 of the present invention and Comparative Examples 2 and 3 have relatively large water contact angles (132.7° to 150.8°). Figure 2 This is a water contact angle test diagram of the biodegradable agricultural film prepared in Example 3 of the present invention. Its water contact angle can reach 138.1°. This is because the ZIF@SiO2 hybrid greatly improves the hydrophobicity of the agricultural film, thereby effectively blocking water evaporation and ensuring that the crops are in a high humidity environment (81%RH~92%RH). The water contact angle of Comparative Example 1 is smaller, with a value of 65.7°. Figure 3 As shown, this is mainly due to the lack of loading of ZIF@SiO2 hybrids. PLA is hydrophilic due to the influence of polydopamine, and the water in the soil is easy to evaporate, and a high humidity environment cannot be guaranteed.

[0109] Examples 1 to 4 and Comparative Example 1 all have relatively high infrared absorption rates (92.3% to 95.3%), which greatly improve the light-to-heat conversion capacity of the agricultural film, and greatly improve the temperature environment inside the agricultural film (7.1°C to 12.8°C). This is due to the combined effect of polydopamine and infrared absorbers, which give the agricultural film a wide range of light absorption and superior light-to-heat conversion capacity, thereby providing good warming performance. Comparative Example 3 has the lowest infrared absorption rate (82.9%), which is due to the lack of the effect of the infrared absorber, the light-to-heat conversion capacity of the agricultural film is low, so that the temperature increase inside the agricultural film is not obvious (3.1°C). The infrared absorption rate of Comparative Example 2 is also relatively low (89.8%), which is due to the lack of polydopamine, the light absorption capacity of the agricultural film is weakened, so the temperature increase is also weak (5.3°C).

[0110] The embodiments and comparative examples all have high breaking strength (29.4MPa-35.8MPa), reflecting excellent mechanical properties. The biodegradable agricultural film prepared by the present invention fully meets the mechanical property requirements for application in farmland. The agricultural film was subjected to degradation experiments using the traditional soil burial degradation method. After 3 months of soil burial, the mass loss of the agricultural films of all embodiments and comparative examples was more than 10.4%, indicating that the multi-layer biodegradable agricultural film has good biodegradability and protects the agricultural ecological environment.

[0111] In summary, the biodegradable agricultural film prepared by the present invention not only has the advantages of far-infrared warming and water retention, which can increase the yield and quality of crops, but also has good degradability, reducing the pollution of agricultural films to the soil. This is due to the following: (1) The super-hydrophobic and highly active ZIF@SiO2 hybrid obtained by the ultrasound-microwave assisted method uses silica to assist in dispersing ZIF crystals, which reduces agglomeration and can better play its active antibacterial and insect repellent effects. Silica gives the agricultural film super-hydrophobic properties, so that the agricultural film can effectively block the evaporation of water in the soil and provide a high-humidity environment for crops; (2) ZIF, polydopamine and infrared absorbers all have excellent infrared absorption and photothermal conversion capabilities, which synergistically improve the warming performance of the agricultural film; (3) The nanosheets improve multiple mechanical and thermodynamic properties of the agricultural film, including creep resistance, tensile strength, puncture resistance, aging resistance, thermal deformation temperature, etc., which improves the service life of the agricultural film and has good application prospects.

[0112] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for preparing a biodegradable agricultural film, characterized in that: The following steps are involved: SiO2, soluble zinc salt and 2-methylimidazole are used as raw materials, and ultrasonic microwave treatment is performed to cause coordination reaction between zinc ions and 2-methylimidazole to obtain an organic-inorganic hybrid loaded with SiO2, dopamine is added, polydopamine is formed by self-polymerization of dopamine, and adheres to the surface of the organic-inorganic hybrid loaded with SiO2 to obtain a water-retaining coating, and the water-retaining coating is applied to a polylactic acid film to obtain a water-retaining layer of the loaded coating; The infrared absorber and the bridging agent are mixed to generate electrophilic and nucleophilic reactions to obtain an active infrared absorber, and the active infrared absorber and the aliphatic polyester are dispersed by melt shearing to obtain a warming layer; The nanosheets and the bridging agent are mixed to generate electrophilic and nucleophilic reactions to obtain active nanosheets, and the active nanosheets and polycaprolactone are dispersed by melt shearing to obtain a barrier layer; The water-retaining layer, the warming layer and the barrier layer are laminated to obtain a biodegradable agricultural film.

2. The preparation method according to claim 1, characterized in that: The molar ratio of the 2-methylimidazole to the soluble zinc salt is 1-10:1, and the molar ratio of the soluble zinc salt to SiO2 is 8:1-10.

3. The preparation method according to claim 1, characterized in that: The mass ratio of the SiO2-loaded organic-inorganic hybrid to polydopamine is 1 to 10:

1.

4. The preparation method according to claim 1, characterized in that: The ultrasonic microwave treatment adopts an ultrasonic-microwave reactor with an output power of 500W to 6000W, a reaction temperature of 80°C to 200°C, and a reaction time of 5min to 40min.

5. The preparation method according to claim 1, characterized in that: The mass ratio of the infrared absorber to the bridging agent is 1 to 10:1, and the mass ratio of the active infrared absorber to the aliphatic polyester is 1 to 5:

100.

6. The preparation method according to claim 1, characterized in that: The mass ratio of the nanosheets to the bridging agent is 1 to 10:1, and the mass ratio of the active nanosheets to the polycaprolactone is 1 to 5:

100.

7. The preparation method according to claim 1, characterized in that: The thickness of the polylactic acid film is 3 μm to 8 μm, the thickness of the coating is 0.01 μm to 2 μm, the thickness of the warming layer is 3 μm to 8 μm, and the thickness of the barrier layer is 5 μm to 10 μm.

8. The preparation method according to claim 1, characterized in that: The aliphatic polyester is butanediol adipate copolyester.

9. The preparation method according to claim 1, characterized in that: The bridging agent is diisopropylbenzene peroxide, benzoyl peroxide, di-tert-butyl peroxide or diisopropylbenzene hydroperoxide; the nanosheet is boron nitride nanosheet, graphene nanosheet, nano-mica sheet or natural montmorillonite.

10. A biodegradable agricultural film prepared by the preparation method according to any one of claims 1 to 9.

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