Manufacturing method of biodegradable polylactic acid agricultural film with pesticide slow-release function

Abstract

The invention relates to a manufacturing method of a biodegradable polylactic acid agricultural film with a pesticide slow-release function. Pesticide is packaged in situ through a porous organic framework material, a packaging body with a slow release function is formed, the packaging body and a polylactic acid raw material are blended, and then extrusion and film blowing are performed to form the pesticide-porous organic framework-polylactic acid composite film. The composite film can slowly release effective components such as pesticides into the environment, so that the effective period of the effective components is prolonged, and the pesticide application frequency is reduced. Meanwhile, the composite film prepared by taking a biodegradable material polylactic acid as a matrix can be degraded into pollution-free micromolecular substances within a certain time through direct composting or soil covering burying. Compared with the prior art, the method is wide in application range, high in pesticide utilization rate, low in toxicity risk and long in validity period, and has the characteristics of pesticide slow release and biodegradability.

Description

Technical Field

[0001] The present invention relates to the field of new materials, and relates to a biodegradable agricultural film with a function of sustained-release pesticides and a preparation method thereof, and in particular to a preparation method of encapsulating pesticides through a metal organic framework material and then loading the encapsulated pesticides into a polylactic acid agricultural film. Background Art

[0002] Agricultural films have the functions of suppressing weeds, retaining soil moisture, and preventing and controlling pests and diseases. They are widely used as covering materials such as ground films and greenhouse films in agricultural production activities. However, traditional agricultural films are generally made of plastic materials such as polyethylene. These agricultural films are extremely difficult to decompose in the soil, and their residues will destroy the soil structure, hinder the transportation of water and nutrients in the soil, and cause soil environmental deterioration, which in turn affects the growth and development of crops, resulting in reduced production and causing ecological and environmental problems such as "white pollution". Biodegradable agricultural films refer to a type of plastic film that is degraded in the natural environment by the action of microorganisms, etc., and are one of the important ways to solve the pollution caused by agricultural film residues.

[0003] Pesticides can be used to prevent, eliminate or control pests, diseases, weeds, etc., and purposefully regulate the metabolism, growth, development, and reproduction of plants or harmful organisms. In agricultural production, it can ensure and promote the growth of plants and crops. Therefore, it plays an extremely important role in increasing agricultural production. However, the vast majority of pesticides are toxic substances released into the environment to eliminate harmful organisms, and their utilization efficiency is low. Residual pesticides may pollute farmland and cause harm to beneficial organisms, and even enter surface waters, causing long-term chronic toxicity through enrichment in the food chain, threatening human health. Pesticide slow-release technology can effectively improve the utilization rate of pesticides, reduce the amount of pesticides used, reduce the risk of ecological and environmental toxicity caused by pesticides, and maintain a certain pesticide concentration for a long time. Patent CN202320160200.8 discloses a biodegradable mulch film with a three-layer sandwich structure and a pesticide slow-release function.

[0004] Polylactic acid (PLA) is a biodegradable material that can be synthesized from renewable biomass raw materials with high starch content such as potatoes and corn. It is decomposed into water and carbon dioxide under natural conditions and is absorbed by plants again, achieving recycling and green circulation. Porous organic frameworks (POFs) usually include metal-organic frameworks (MOFs), hydrogen-bond organic frameworks (HOFs), zeolite imidazole frameworks (ZIFs), covalent organic frameworks (COFs), etc. Most of them have the characteristics of high specific surface area, large porosity, excellent biocompatibility, etc., which can be used for the encapsulation of pesticides and achieve sustained release function. The preparation of pesticide-metal organic framework-PLA composite single-layer agricultural film is expected to reduce the "white pollution" of residual film and the frequency of pesticide application, and significantly improve its utilization efficiency and durability. Summary of the invention

[0005] The object of the present invention is to provide a method for preparing a pesticide-POFs-PLA composite film, so as to achieve reduced-amount and increased-efficiency use of pesticides and biodegradable agricultural films.

[0006] The purpose of the present invention can be achieved through the following technical solutions: A method for preparing a pesticide-porous organic framework-polylactic acid composite film, wherein the porous organic framework material is used to encapsulate the pesticide, and the porous organic framework material is mixed with polylactic acid, and the composite film is obtained by extrusion and film blowing. The synthetic raw materials are calculated by weight fraction, and the porous organic framework is 5 to 20 parts, the metal salt is 0 to 20 parts, the pesticide is 5 to 20 parts, the polylactic acid is 30 to 80 parts, the PBAT is 0 to 50 parts, and the chain extender is 0.1 to 0.5 parts.

[0007] A method for preparing a pesticide-porous organic framework-polylactic acid composite film, the preparation method comprising three steps of pesticide encapsulation, stirring and mixing, and film blowing, as described below.

[0008] Step 1: Pesticide encapsulation can be carried out by in-situ encapsulation or ex-situ encapsulation. If in-situ encapsulation is adopted, the porous organic framework ligand is mixed with the pesticide in a ratio of 1:5 to 5:1, and then 0 to 20 parts of metal salt are added to form a porous organic framework material by static precipitation, solvent thermal synthesis and other methods. If ex-situ encapsulation is adopted, 5 to 20 parts of porous organic framework are mixed with 5 to 20 parts of pesticide, and the pesticide is encapsulated in the organic framework by adsorption, the temperature is 10 to 50 ° C, the adsorption time is 10 to 60 minutes, and ultrasound, stirring and other operations can be performed as needed. Subsequently, a solid material is obtained by centrifugal separation and drying, and the solid is called an encapsulation body.

[0009] Step 2: Stirring and mixing, melt and stir 0.1 to 0.5 parts of chain extender and 30 to 80 parts of polylactic acid, then add 0 to 50 parts of PBAT, and finally add the encapsulation obtained in step 1. Then, continue stirring for 30 to 120 minutes.

[0010] Step 3: film blowing, the mixture obtained in step 2 is melt-mixed and extruded into granules by a twin-screw extruder to obtain a uniform masterbatch, and then subjected to single-screw extrusion plasticization and film blowing to obtain a pesticide-porous organic framework-polylactic acid composite film.

[0011] In the above steps, the porous organic framework can be one or more of a hydrogen-bonded organic framework, a metal-organic framework, and a covalent organic framework, preferably a hydrogen-bonded organic framework. The solvent thermal synthesis temperature in the step one is 100 to 250 ° C; the centrifugal separation speed in the step one is 3000 to 15000 r / min. The stirring and mixing in the step two is carried out by mechanical stirring, and the stirring rate is 300 to 800 r / min. The particle size of the encapsulation body added in the step two is 100 to 400 mesh.

[0012] Compared with the prior art, the porous organic framework material used in the present invention in situ encapsulates pesticides, and the encapsulation body is blended with polylactic acid raw materials, and the effective active ingredients of the pesticides are released into the environment at a slow rate by forming a pesticide-POFs-PLA composite film, thereby extending its validity period. At the same time, the composite agricultural film prepared with biodegradable material PLA as a carrier can be degraded into small molecular substances that are pollution-free to the environment after a certain period of time, thereby realizing the slow-release function of pesticides and avoiding the large-scale use of pesticides and the risk of environmental toxicity; the agricultural film can be self-degraded under natural conditions to avoid residual film pollution; the agricultural film raw material PLA biomass has a wide source, which improves safety while reducing costs.

[0013] Pesticides are encapsulated in situ by porous organic framework materials to form an encapsulation body with a sustained release function, and the encapsulation body is blended with a polylactic acid raw material, and then extruded and blown to form a pesticide-porous organic framework-polylactic acid composite film. The composite film can slowly release active ingredients such as pesticides into the environment, thereby extending their shelf life and reducing the frequency of pesticide application. At the same time, the composite film prepared with biodegradable material polylactic acid as the matrix can be degraded into non-polluting small molecules within a certain period of time by direct composting or covering with soil. Compared with the prior art, this method has a wide range of applications, high pesticide utilization, low toxicity risk and long shelf life, and has the characteristics of sustained release of pesticides and biodegradability. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a schematic diagram of the composition structure of the biodegradable polylactic acid agricultural film with the function of sustained release of pesticides according to the present invention; Figure 2 The release rate curve of the furan component encapsulated by the agricultural film of the present invention; Figure 3 The release rate curve of the imidacloprid component encapsulated by the agricultural film of the present invention; Figure 4 The dry weight change and degradation rate curve of the agricultural film of the present invention under natural conditions. DETAILED DESCRIPTION

[0015] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the preparation scheme of the present invention, and provides a detailed preparation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0016] Embodiment 1: Preparation of furan-ZIF8-PLA composite membrane. ZIF-8 was formed by a solvothermal synthesis method, and furan was encapsulated in situ. 5 parts of porous organic framework ligand (imidazole ion) were mixed with 20 parts of furan, and then zinc nitrate was added as a metal salt (5 parts). The solvothermal synthesis temperature was 70 °C, and furan was encapsulated in ZIF-8. Subsequently, centrifugal separation was performed at a centrifugal separation speed of 5000 r / min, and a solid was obtained after drying, which was called ZIF-8-furan encapsulation body. In another dry clean reactor, 0.5 parts of chain extender and 50 parts of PLAs were melt-stirred and mixed, and then 10 parts of PBAT were added, and finally 0.5 parts of ZIF-8-furan encapsulation body with a particle size of 100 mesh was added, and stirring was continued for 60 minutes. The obtained mixture was melt-mixed and extruded by a twin-screw to obtain a uniform masterbatch, and then single-screw extrusion plasticization and film blowing were used to obtain a furan-ZIF8-PLA composite membrane, referring to Figure 1 shown.

[0017] The prepared furan-ZIF8-PLA composite film has a sustained release effect of furan. Figure 2 As shown in the figure, furan is gradually released into the environment over time. After two days, the release rate of furan reached 63.51%. Subsequently, furan continued to be released slowly, and on the seventh day, the release rate of furan reached 90.52%. The sustained release of furan can effectively improve its utilization rate, reduce its usage, and maintain a certain furan concentration for a long time.

[0018] Embodiment 2: Preparation of Imidacloprid-ZIF-8-PLA Composite Film. ZIF-8 material was formed by solvothermal synthesis method. 10 parts of organic framework ligand (imidazolate ion) and 10 parts of metal salt (zinc sulfate) were mixed and hydrothermally synthesized in a hydrothermal reactor. The hydrothermal temperature was 100 °C and the hydrothermal time was 6 hours. 5 parts of ZIF-8 and 10 parts of imidacloprid were mixed and added to the reaction tube. Imidacloprid was encapsulated in ZIF-8 by ex situ encapsulation. The temperature was 25 °C, the stirring rate was 500 r / min, and the time was 60 minutes. Subsequently, centrifugation was performed at a speed of 10000 r / min. After drying, a solid was obtained, which was called imidacloprid-ZIF-8 encapsulation body. 0.2 parts of chain extender and 50 parts of PLA were melted and stirred under continuous stirring, followed by the addition of 15 parts of PBAT, and finally the imidacloprid-ZIF-8 encapsulation body with a particle size of 200 mesh was added, and the stirring was continued for 120 minutes. The obtained mixture is melt-mixed and extruded into granules by a twin-screw extruder to obtain a uniform masterbatch, and then plasticized and blown into a film by a single-screw extruder to obtain an imidacloprid-ZIF-8-PLA composite film.

[0019] The prepared imidacloprid-ZIF-8-PLA composite film was used as an agricultural film to achieve the slow release of imidacloprid. Figure 3 As shown in the figure, after two days, the release rate of imidacloprid reached 62.3%, and then, imidacloprid continued to be released slowly, and on the eighth day, the release rate of imidacloprid reached 88.4%. The slow release of imidacloprid can effectively improve its utilization rate, reduce its usage, and maintain a certain imidacloprid concentration for a long time.

[0020] Embodiment 3: The furan-ZIF8-PLA composite film described in Example 1 is covered with soil after use and can be gradually biodegraded under natural conditions. Figure 4 As shown in the figure, the dry weight of the agricultural film decreases over time, and after 60 days, its degradation rate can reach 98.79%. It can be seen that the agricultural film prepared by this method can be decomposed under natural conditions, which not only achieves the "reduction and efficiency" of pesticide application, but also reduces the "white pollution" of agricultural film residues in agricultural land.

[0021] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for preparing a biodegradable polylactic acid agricultural film with a slow-release pesticide function, characterized in that: The porous organic framework material is used to encapsulate the pesticide, which is blended with polylactic acid and extruded and blown to obtain a composite film.

2. The method for preparing a biodegradable polylactic acid agricultural film with a sustained-release pesticide function as claimed in claim 1, characterized in that: The synthetic raw materials are calculated by weight: 5 to 20 parts of porous organic framework ligand, 0 to 20 parts of metal salt, 5 to 20 parts of pesticide, 30 to 80 parts of polylactic acid, 0 to 50 parts of PBAT, and 0.1 to 0.5 parts of chain extender.

3. The method for preparing a biodegradable polylactic acid agricultural film with a slow-release pesticide function as claimed in claim 2, characterized in that: The preparation method includes three steps: pesticide encapsulation, stirring and mixing, and film blowing, which are as follows: Step 1: The pesticide encapsulation is carried out by in-situ encapsulation or ex-situ encapsulation. In the in-situ encapsulation, the porous organic framework ligand and the pesticide are mixed in a ratio of 1:5 to 5:1, and then 0 to 20 parts of metal salt are added to form a porous organic framework material by static precipitation or solvent thermal synthesis. In the ex-situ encapsulation, 5 to 20 parts of the porous organic framework are mixed with 5 to 20 parts of the pesticide, and the pesticide is encapsulated in the organic framework by adsorption, the temperature is 10 to 50 ° C, and the adsorption time is 10 to 60 minutes. Subsequently, a solid material is obtained by centrifugal separation and drying, and the solid is called an encapsulation body. Step 2: Stir and mix, melt and stir 0.1 to 0.5 parts of chain extender and 30 to 80 parts of polylactic acid, then add 0 to 50 parts of PBAT, and finally add the encapsulation obtained in step 1; then, continue stirring for 30 to 120 minutes; Step 3: film blowing, the mixture obtained in step 2 is melt-mixed and extruded into granules by a twin-screw extruder to obtain a uniform masterbatch, and then subjected to single-screw extrusion plasticization and film blowing to obtain a pesticide-porous organic framework-polylactic acid composite film.

4. The method for preparing a biodegradable polylactic acid agricultural film with a slow-release pesticide function as claimed in claim 3, characterized in that: The porous organic framework is one or more of a hydrogen-bonded organic framework, a metal-organic framework, and a covalent organic framework, preferably a hydrogen-bonded organic framework.

5. The method for preparing a biodegradable polylactic acid agricultural film with a sustained-release pesticide function as claimed in claim 3, characterized in that: The solvent thermal synthesis temperature in step 1 is 100-250°C; the centrifugal separation speed in step 1 is 3000-15000 r / min.

6. The method for preparing a biodegradable polylactic acid agricultural film with a slow-release pesticide function as claimed in claim 3, characterized in that: The stirring and mixing described in step 2 is carried out by mechanical stirring at a stirring rate of 300 to 800 r / min.

7. The method for preparing a biodegradable polylactic acid agricultural film with a slow-release pesticide function as claimed in claim 3, characterized in that: The particle size of the encapsulated body added in step 2 is 100-400 mesh.

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