CN112159580A - Preparation method of completely degradable agricultural plastic film - Google Patents
Preparation method of completely degradable agricultural plastic film Download PDFInfo
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Abstract
The invention relates to a preparation method of a completely degradable agricultural plastic film, belonging to the technical field of plastic films. The invention takes polylactic acid and polyvinyl alcohol as raw materials, and adds corn stalk, tea stalk, polyethylene glycol, high amylose starch, nano titanium dioxide and kaolin to prepare the completely degradable agricultural plastic film, the polylactic acid can be biodegraded, the corn stalk and the tea stalk both contain plant fiber, the plant fiber has biodegradability and can become organic matter components after degradation, the polyvinyl alcohol and the polyethylene glycol can be mutually crosslinked with hydrogen bonds on plant fiber molecules, the mechanical property of the film is improved, the high amylose starch has better water resistance, shearing resistance and film forming property, and can be completely degraded, the titanium dioxide can absorb ultraviolet rays, generate active free radicals, initiate the molecular chain of the polymer to be broken and decomposed, and then the polymer is converted into carbon dioxide and water, the kaolin can improve the decomposition force of the polymer by microorganisms, and complete decomposition is realized.
Description
Technical Field
The invention relates to a preparation method of a completely degradable agricultural plastic film, belonging to the technical field of plastic films.
Background
The plastic film plays an important role in crop cultivation, the transparent plastic film has little influence on the light quality of visible light, and the transmittance can meet the growth requirement of a seedbed; meanwhile, the plastic film has high transmittance to ultraviolet rays, so that the plant does not grow excessively even under the high-temperature and high-humidity condition covered by the film. Secondly, the heat preservation performance is realized, the heat penetration rate of the plastic film covering is higher than that of the well-known glass, so that the heat absorption and the heat dissipation are faster, and the temperature difference between day and night is larger than that of the glass; when the plastic film is used for covering in a tunnel mode, the temperature can be increased by 5-10 ℃ compared with the temperature in the open field. The plastic film and the colored plastic film made of some novel materials can play an important role in preventing and controlling plant diseases and insect pests, so that the using amount of pesticides on crops is reduced, the plastic film is widely used in the production of the crops, the using amount is large, and the most important reason is great economic benefit brought by the yield increase of the crops after the plastic film is used. Different crop varieties research shows that the yield can be improved by 20-70% after the plastic film is used.
The agricultural plastic film prepared by adopting polyethylene and polyvinyl chloride materials of high molecular polymers is difficult to degrade. Besides directly influencing the growth environment of crops, the increase of plastic film residue can also increase the difficulty of field cultivation, and cause the conditions of uneven fertilization and the like due to the winding of agricultural machinery. In addition, air pollution can be caused by burning the plastic film residual film, and the phthalic dicarboxaldehyde ester compounds in the plastic film can poison plant root systems after permeating soil and can influence the health of human beings after being absorbed by crops. At present, two ways for solving the white pollution of the plastic film are provided, namely recycling the agricultural plastic film and developing the degradable agricultural plastic film. However, the amount and the coverage area of the mulching film are large, and the thickness of the film is too thin (6-24 micrometers), so that the film is extremely difficult to recover and is irrevocable economically, and therefore, the development and the application of the degradable agricultural plastic film are more important to be enhanced, which is a development trend of the agricultural plastic film.
Disclosure of Invention
The technical problems to be solved by the invention are as follows: aiming at the problems of difficult degradation and difficult recovery of the existing agricultural plastic film, the preparation method of the completely degradable agricultural plastic film is provided.
In order to solve the technical problems, the invention adopts the technical scheme that:
(1) placing nano titanium dioxide, kaolin, polyvinyl alcohol, high amylose starch, polymer-coated plant fiber powder and polylactic acid in a high-speed stirrer, and stirring and mixing at the normal temperature at the rotating speed of 1200-1600 r/min for 30-40 min to obtain a mixture;
(2) placing the mixture in a double-screw extruder, and extruding and granulating at the screw rotating speed of 120-160 r/min at the temperature of 160-180 ℃ to obtain mixed granules
(3) And (3) placing the mixed granules into a film blow molding machine, and carrying out blow molding at the temperature of 100-120 ℃ and under the pressure of 4-6 MPa to obtain the completely degradable agricultural plastic film.
The nanometer titanium dioxide, the kaolin, the polyvinyl alcohol, the high amylose starch, the polymer coated plant fiber powder and the polylactic acid are respectively in parts by weight: 10-20 parts of nano titanium dioxide, 10-20 parts of kaolin, 40-60 parts of polyvinyl alcohol, 20-40 parts of high amylose starch, 60-80 parts of polymer-coated plant fiber powder and 120-160 parts of polylactic acid.
The average thickness of the completely degradable agricultural plastic film is 18-24 mu m.
The specific preparation steps of the high amylose starch are as follows:
(1) adding potato starch into absolute ethyl alcohol, and stirring at the rotating speed of 300-400 r/min for 20-30 min at normal temperature to obtain a potato starch ethanol solution;
(2) adding a sodium carbonate solution into the potato starch mixed solution, and stirring for 20-30 min at a rotating speed of 300-400 r/min under a water bath condition of 80-90 ℃ to obtain a starch dispersion liquid;
(3) standing the starch dispersion liquid at normal temperature for 2-4 h, placing the starch dispersion liquid in a centrifuge, centrifuging the starch dispersion liquid at the normal temperature at the rotating speed of 3000-3500 r/min for 15-20 min, taking supernatant liquid, and adjusting the pH value to be neutral to obtain a starch mixed liquid;
(4) adding n-butyl alcohol and glycerol into the starch mixed solution, stirring for 10-15 min at the rotating speed of 300-400 r/min under the water bath condition of 80-90 ℃, standing for 1-2 h at normal temperature, and standing for 20-24 h in a refrigerator at the temperature of 2-4 ℃ to obtain a refrigerating solution;
(5) and (3) placing the cold storage liquid in a centrifuge, centrifuging for 15-20 min at the normal temperature at 3000-3500 r/min, taking the lower-layer precipitate, and placing the precipitate in a drying oven to dry for 1-2 h at the temperature of 55-60 ℃ to obtain the high amylose starch.
The potato starch, the absolute ethyl alcohol, the sodium carbonate solution, the n-butyl alcohol and the glycerol are respectively in parts by weight: 20-30 parts of potato starch, 40-60 parts of absolute ethyl alcohol, 60-80 parts of a 10% sodium carbonate solution, 40-50 parts of n-butyl alcohol and 40-50 parts of glycerol.
The pH adjustment adopts a citric acid solution with the mass concentration of 1%.
The preparation method of the polymer-coated plant fiber powder comprises the following specific steps:
(1) placing corn straws and tea stems in a crusher, and crushing for 20-30 min at normal temperature to obtain mixed plant fiber powder;
(2) adding the mixed plant fiber powder into absolute ethyl alcohol, stirring at the normal temperature at the rotating speed of 200-300 r/min for 20-30 min, standing for 2-4 h, performing suction filtration, taking a filter cake, placing the filter cake in a drying box, and drying at the temperature of 40-60 ℃ for 1-2 h to obtain treated mixed plant fiber powder;
(3) adding polyethylene glycol into deionized water, and stirring at a rotating speed of 300-400 r/min for 30-40 min under a water bath condition of 40-60 ℃ to obtain a polyethylene glycol solution;
(4) and adding the treated mixed plant fiber powder into a polyethylene glycol solution, cooking for 2-4 h under the water bath condition of 60-80 ℃, filtering, putting a filter cake into a drying oven of 60-80 ℃ and drying for 1-2 h to obtain the polymer-coated plant fiber powder.
The corn straw, the tea stem, the polyethylene glycol, the absolute ethyl alcohol and the deionized water are respectively in parts by weight: 40-60 parts of corn straw, 40-60 parts of tea stem, 10-20 parts of polyethylene glycol, 120-160 parts of absolute ethyl alcohol and 60-80 parts of deionized water.
Compared with other methods, the method has the beneficial technical effects that:
(1) the invention takes polylactic acid and polyvinyl alcohol as raw materials, and adds corn stalk, tea stalk and polyethylene glycol to prepare the fully degradable agricultural plastic film, the polylactic acid is a polymer obtained by polymerizing lactic acid as main raw material, the raw material source is sufficient and can be regenerated, the production process of the polylactic acid has no pollution, and the product can be biodegraded, thereby realizing the circulation in the nature, the corn stalk and the tea stalk belong to plant fiber, the plant fiber has the advantages of wide source and strong regeneration, the molecular structure of the plant fiber is D-glucopyranose anhydride, linear homogeneous polymers formed by connecting with each other by beta-1, 4 glycosidic bonds, each glucose ring in cellulose macromolecule has three hydroxyl groups, the three hydroxyl groups have different activity characteristics in heterogeneous chemical reaction, the structure ensures that the plant fiber has excellent biodegradability, the film with good biodegradability can be prepared through proper treatment, the degraded film can become organic matter components of soil, soil fertility is increased, polyethylene glycol is a polymer capable of being completely degraded, the polyvinyl alcohol and the polyethylene glycol can be mutually crosslinked with hydrogen bonds on plant fiber molecules to form a net structure, mechanical properties of the film can be improved, and the durability and the biodegradability of the plastic film can be effectively improved by adding the polyethylene glycol;
(2) the completely degradable agricultural plastic film is prepared by adding high amylose starch, the starch is the most widely used completely biodegradable natural high polymer material at present, the starch has the advantages of wide source, low price, reproducibility, biodegradability, no harm to the environment of degradation products and the like, the amylose starch is a linear high polymer, and is connected by alpha-D-glucose through alpha (1, 4) -D-glycosidic bond, so that the amylose starch has the performance similar to fiber;
(3) the invention prepares the completely degradable agricultural plastic film by adding nanometer titanium dioxide and kaolin, the titanium dioxide is a semiconductor, has good photocatalytic activity, can absorb ultraviolet rays in sunlight, generates very active free radicals through the action with oxygen and water in the air, thereby initiating the molecular chain of a polymer to be broken and decomposed, and finally converting plastics into substances such as carbon dioxide, water and the like, the titanium dioxide also has the advantages of strong stability, no toxicity and the like, the titanium dioxide is a safe and effective photodegradation catalyst, the kaolin is one of clays, as having good plasticity, electrical insulation, high caking property and good acid resistance and fire resistance, the kaolin is a mineral, is a natural microbial culture medium, is beneficial to the growth of microorganisms, the kaolin is added into the polymer film, can improve the performance of the film, especially the biodegradability, and in addition, the kaolin is used as a bioactive substance, can effectively improve the decomposition force of microorganisms on polymers, thereby realizing complete decomposition.
Detailed Description
Weighing 40-60 parts of corn straw, 40-60 parts of tea stem, 10-20 parts of polyethylene glycol, 120-160 parts of absolute ethyl alcohol and 60-80 parts of deionized water respectively, placing the corn straw and the tea stem in a crusher, crushing for 20-30 min at normal temperature to obtain mixed plant fiber powder, adding the mixed plant fiber powder into the absolute ethyl alcohol, stirring for 20-30 min at 200-300 r/min at normal temperature, standing for 2-4 h, performing suction filtration, placing a filter cake in a drying box, drying for 1-2 h at 40-60 ℃ to obtain treated mixed plant fiber powder, adding the polyethylene glycol into the deionized water, stirring for 30-40 min at 300-400 r/min at 40-60 ℃ to obtain a polyethylene glycol solution, adding the treated mixed plant fiber powder into the polyethylene glycol solution, cooking for 2-4 h at 60-80 ℃ in a water bath, filtering, and drying the filter cake in a drying oven at 60-80 ℃ for 1-2 h to obtain polymer-coated plant fiber powder;
respectively weighing 20-30 parts by weight of potato starch, 40-60 parts by weight of absolute ethyl alcohol, 60-80 parts by weight of a 10% sodium carbonate solution, 40-50 parts by weight of n-butanol and 40-50 parts by weight of glycerol, adding the potato starch into the absolute ethyl alcohol, stirring at 300-400 r/min for 20-30 min at normal temperature to obtain a potato starch ethanol solution, adding the sodium carbonate solution into the potato starch mixed solution, stirring at 300-400 r/min for 20-30 min under the water bath condition of 80-90 ℃ to obtain a starch dispersion, standing the starch dispersion at normal temperature for 2-4 h, placing the starch dispersion in a centrifuge, centrifuging at 3000-3500 r/min for 15-20 min at normal temperature, taking the supernatant, dropwise adding 1% by weight of citric acid to adjust the pH to be neutral to obtain a starch mixed solution, adding the n-butanol and the glycerol into the starch mixed solution, stirring at 300-400 r/min for 10-15 min under the water bath condition of 80-90 ℃, standing for 1-2 h at normal temperature, then standing for 20-24 h in a refrigerator at 2-4 ℃ to obtain a refrigerating liquid, placing the refrigerating liquid in a centrifuge, centrifuging for 15-20 min at 3000-3500 r/min at normal temperature, taking a lower layer precipitate, and placing in a drying oven to dry for 1-2 h at 55-60 ℃ to obtain high amylose;
respectively weighing 10-20 parts of nano titanium dioxide, 10-20 parts of kaolin, 40-60 parts of polyvinyl alcohol, 20-40 parts of high amylose starch, 60-80 parts of polymer-coated plant fiber powder and 120-160 parts of polylactic acid according to parts by weight, placing the nano titanium dioxide, the kaolin, the polyvinyl alcohol, the high amylose starch, the polymer-coated plant fiber powder and the polylactic acid in a high-speed stirrer, stirring and mixing at the normal temperature at the rotating speed of 1200-1600 r/min for 30-40 min to obtain a mixture, placing the mixture in a double-screw extruder, extruding and granulating at the screw rotating speed of 120-160 r/min under the condition of 160-180 ℃ to obtain mixed granules, placing the mixed granules into a film blow molding machine, blow molding at 100-120 ℃ and 4-6 MPa to obtain the completely degradable agricultural plastic film with the average thickness of 18-24 mu m.
Example 1
Weighing 40 parts of corn straw, 40 parts of tea stem, 10 parts of polyethylene glycol, 120 parts of absolute ethyl alcohol and 60 parts of deionized water respectively, placing the corn straw and the tea stem in a pulverizer, pulverizing for 20min at normal temperature to obtain mixed plant fiber powder, adding the mixed plant fiber powder into the absolute ethyl alcohol, stirring for 20min at 200r/min at normal temperature, standing for 2h, performing suction filtration, placing a filter cake in a drying box, drying for 1h at 40 ℃ to obtain treated mixed plant fiber powder, adding the polyethylene glycol into the deionized water, stirring for 30min at 300r/min at 40 ℃ water bath to obtain polyethylene glycol solution, adding the treated mixed plant fiber powder into the polyethylene glycol solution, cooking for 2h at 60 ℃ water bath, filtering, placing the filter cake in a 60 ℃ oven for drying for 1-2 h, to obtain the plant fiber powder coated by the polymer,
respectively weighing 20 parts of potato starch, 40 parts of absolute ethyl alcohol, 60 parts of sodium carbonate solution with the mass concentration of 10%, 40 parts of n-butyl alcohol and 40 parts of glycerol, adding the potato starch into the absolute ethyl alcohol, stirring for 20min at the normal temperature at the rotating speed of 300r/min to obtain potato starch ethanol solution, adding the sodium carbonate solution into the potato starch mixed solution, stirring for 20min at the rotating speed of 300r/min under the water bath condition of 80 ℃ to obtain starch dispersion, standing the starch dispersion at the normal temperature for 2h, placing the starch dispersion in a centrifuge, centrifuging for 15min at the normal temperature at the rotating speed of 3000r/min, taking supernatant, dropwise adding 1% by mass of citric acid to adjust the pH to 7.0 to obtain starch mixed solution, adding the n-butyl alcohol and the glycerol into the starch mixed solution, stirring for 10min at the rotating speed of 300r/min under the water bath condition of 80 ℃, standing for 1h at the normal temperature, standing in a refrigerator at 2 deg.C for 20 hr to obtain refrigerated solution, centrifuging in a centrifuge at room temperature at 3000r/min for 15min, taking the precipitate, drying in a drying oven at 55 deg.C for 1 hr to obtain high amylose starch,
respectively weighing 10 parts of nano titanium dioxide, 10 parts of kaolin, 40 parts of polyvinyl alcohol, 20 parts of high amylose starch, 60 parts of polymer-coated plant fiber powder and 120 parts of polylactic acid according to parts by weight, placing the nano titanium dioxide, the kaolin, the polyvinyl alcohol, the high amylose starch, the polymer-coated plant fiber powder and the polylactic acid in a high-speed stirrer, stirring and mixing at the rotating speed of 1200r/min for 30min at normal temperature to obtain a mixture, placing the mixture in a double-screw extruder, extruding and granulating at the rotating speed of 120r/min at 160 ℃ to obtain mixed granules, placing the mixed granules in a film blowing machine, and performing blow molding at the temperature of 100 ℃ and the pressure of 4MPa to obtain the completely degradable agricultural plastic film with the thickness of 18 mu m.
Example 2
Respectively weighing 50 parts of corn straw, 50 parts of tea stalk, 15 parts of polyethylene glycol, 140 parts of absolute ethyl alcohol and 70 parts of deionized water according to parts by weight, placing the corn straw and the tea stalk in a pulverizer, pulverizing at room temperature for 25min to obtain mixed plant fiber powder, adding into anhydrous ethanol, stirring at 250r/min for 25min at normal temperature, standing for 3h, vacuum filtering, placing the filter cake in a drying oven, drying at 50 deg.C for 3 hr to obtain treated mixed plant fiber powder, adding polyethylene glycol into deionized water, stirring at 350r/min for 35min in 50 deg.C water bath to obtain polyethylene glycol solution, adding the treated mixed plant fiber powder into the polyethylene glycol solution, steaming and boiling for 3h under the condition of water bath at 70 ℃, filtering, and drying a filter cake in a drying oven at 70 ℃ for 1.5h to obtain polymer-coated plant fiber powder;
respectively weighing 25 parts of potato starch, 50 parts of absolute ethyl alcohol, 70 parts of sodium carbonate solution with the mass concentration of 10%, 45 parts of n-butyl alcohol and 45 parts of glycerol, adding the potato starch into the absolute ethyl alcohol, stirring for 25min at the normal temperature at the rotating speed of 350r/min to obtain potato starch ethanol solution, adding the sodium carbonate solution into the potato starch mixed solution, stirring for 25min at the rotating speed of 350r/min under the water bath condition of 85 ℃ to obtain starch dispersion, standing the starch dispersion for 3h at the normal temperature, placing the starch dispersion in a centrifugal machine, centrifuging for 17min at the normal temperature at the rotating speed of 3250r/min, taking supernatant, dropwise adding citric acid with the mass concentration of 1% to adjust the pH to 7.2 to obtain starch mixed solution, adding the n-butyl alcohol and the glycerol into the starch mixed solution, stirring for 13min at the rotating speed of 350r/min under the water bath condition of 85 ℃, standing for 1.5h at the normal temperature, standing in a refrigerator at 3 deg.C for 22h to obtain refrigerated solution, centrifuging in a centrifuge at room temperature at 3250r/min for 17min, collecting the lower layer precipitate, and drying in a drying oven at 57 deg.C for 1.5h to obtain high amylose starch;
respectively weighing 15 parts of nano titanium dioxide, 15 parts of kaolin, 50 parts of polyvinyl alcohol, 30 parts of high amylose starch, 70 parts of polymer-coated plant fiber powder and 140 parts of polylactic acid according to parts by weight, placing the nano titanium dioxide, the kaolin, the polyvinyl alcohol, the high amylose starch, the polymer-coated plant fiber powder and the polylactic acid in a high-speed stirrer, stirring and mixing at the rotating speed of 1400r/min for 35min at normal temperature to obtain a mixture, placing the mixture in a double-screw extruder, extruding and granulating at the rotating speed of 140r/min at the temperature of 170 ℃ to obtain mixed granules, placing the mixed granules in a film blowing machine, and performing blow molding at the temperature of 110 ℃ and the pressure of 5MPa to obtain the completely degradable agricultural plastic film with the thickness of 21 mu m.
Example 3
Respectively weighing 60 parts of corn straws, 60 parts of tea stems, 20 parts of polyethylene glycol, 160 parts of absolute ethyl alcohol and 80 parts of deionized water according to parts by weight, placing the corn straws and the tea stems in a pulverizer, pulverizing at room temperature for 30min to obtain mixed plant fiber powder, adding into anhydrous ethanol, stirring at normal temperature at the rotating speed of 300r/min for 30min, standing for 4h, suction filtering, placing the filter cake in a drying oven, drying at 60 deg.C for 2 hr to obtain treated mixed plant fiber powder, adding polyethylene glycol into deionized water, stirring at 400r/min for 40min in water bath at 60 deg.C to obtain polyethylene glycol solution, adding the treated mixed plant fiber powder into the polyethylene glycol solution, steaming and boiling for 4h under the condition of water bath at 80 ℃, filtering, and drying a filter cake in a drying oven at 80 ℃ for 2h to obtain polymer-coated plant fiber powder;
respectively weighing 0 part of potato starch, 60 parts of absolute ethyl alcohol, 80 parts of sodium carbonate solution with the mass concentration of 10%, 50 parts of n-butyl alcohol and 50 parts of glycerol, adding the potato starch into the absolute ethyl alcohol, stirring at the normal temperature at the rotating speed of 400r/min for 30min to obtain a potato starch ethanol solution, adding the sodium carbonate solution into a potato starch mixed solution, stirring at the rotating speed of 400r/min for 30min under the water bath condition of 90 ℃ to obtain a starch dispersion, standing the starch dispersion at the normal temperature for 4h, placing the starch dispersion in a centrifuge, centrifuging at the normal temperature at the rotating speed of 3500r/min for 20min, taking the supernatant, dropwise adding 1% by mass of citric acid to adjust the pH to 7.4 to obtain a starch mixed solution, adding the n-butyl alcohol and the glycerol into the starch mixed solution, stirring at the rotating speed of 400r/min for 10-15 min under the water bath condition of 90 ℃, standing at the normal temperature for 2h, standing in a refrigerator at 4 deg.C for 24 hr to obtain refrigerated solution, centrifuging in a centrifuge at room temperature at 3500r/min for 20min, collecting the lower layer precipitate, drying in a drying oven at 60 deg.C for 2 hr to obtain high amylose starch,
respectively weighing 20 parts of nano titanium dioxide, 20 parts of kaolin, 60 parts of polyvinyl alcohol, 40 parts of high amylose starch, 80 parts of polymer-coated plant fiber powder and 120-160 parts of polylactic acid according to parts by weight, placing the nano titanium dioxide, the kaolin, the polyvinyl alcohol, the high amylose starch, the polymer-coated plant fiber powder and the polylactic acid in a high-speed stirrer, stirring and mixing at the rotating speed of 1600r/min for 40min at normal temperature to obtain a mixture, placing the mixture in a double-screw extruder, extruding and granulating at the rotating speed of 160r/min under the condition of 160-180 ℃ to obtain mixed granules, placing the mixed granules in a film blowing machine, and performing blow molding under the conditions of 120 ℃ and 6MPa to obtain the fully degradable agricultural plastic film with the thickness of 24 mu m.
Comparative example: agricultural plastic film produced by Nantong company
The completely degradable agricultural plastic film prepared by the invention and the agricultural plastic film produced by a certain company of Nantong are detected, and the detection method comprises the following steps: the measurements were carried out according to the standard GB/T19276.2-2003/ISO14852:1999 determination of the ultimate aerobic biological decomposition capacity of materials in aqueous culture broth by the method for determining the evolution of carbon dioxide, the results of which are given in Table 1 below:
TABLE 1
| Performance characterization | Example 1 | Example 2 | Example 3 | Comparative example |
| Weight loss rate by photodegradation (%) | 22.4 | 24.1 | 23.4 | 4.2 |
| Weight loss rate of biodegradation (%) | 70.3 | 69.7 | 70.9 | 8.37 |
As can be seen from Table 1, the completely degradable agricultural plastic film prepared by the invention has good photodegradability and biodegradability, is an excellent agricultural plastic film, and has excellent market prospect and application prospect.
Claims (8)
1. A preparation method of a completely degradable agricultural plastic film is characterized by comprising the following specific preparation steps:
(1) placing nano titanium dioxide, kaolin, polyvinyl alcohol, high amylose starch, polymer-coated plant fiber powder and polylactic acid in a high-speed stirrer, and stirring and mixing at the normal temperature at the rotating speed of 1200-1600 r/min for 30-40 min to obtain a mixture;
(2) placing the mixture in a double-screw extruder, and extruding and granulating at the screw rotating speed of 120-160 r/min at the temperature of 160-180 ℃ to obtain mixed granules;
(3) and (3) placing the mixed granules into a film blow molding machine, and carrying out blow molding at the temperature of 100-120 ℃ and under the pressure of 4-6 MPa to obtain the completely degradable agricultural plastic film.
2. The preparation method of the fully degradable agricultural plastic film as claimed in claim 1, wherein the weight parts of the nano titanium dioxide, the kaolin, the polyvinyl alcohol, the high amylose starch, the polymer coated plant fiber powder and the polylactic acid are respectively 10-20 parts of the nano titanium dioxide, 10-20 parts of the kaolin, 40-60 parts of the polyvinyl alcohol, 20-40 parts of the high amylose starch, 60-80 parts of the polymer coated plant fiber powder and 120-160 parts of the polylactic acid.
3. The method for preparing a fully degradable agricultural plastic film as claimed in claim 1, wherein the average thickness of the fully degradable agricultural plastic film in the step (2) is 18-24 μm.
4. The method for preparing a fully degradable agricultural plastic film as claimed in claim 1, wherein the specific preparation steps of the high amylose starch in step (1) are as follows:
(1) adding potato starch into absolute ethyl alcohol, and stirring at the rotating speed of 300-400 r/min for 20-30 min at normal temperature to obtain a potato starch ethanol solution;
(2) adding a sodium carbonate solution into the potato starch mixed solution, and stirring for 20-30 min at a rotating speed of 300-400 r/min under a water bath condition of 80-90 ℃ to obtain a starch dispersion liquid;
(3) standing the starch dispersion liquid at normal temperature for 2-4 h, placing the starch dispersion liquid in a centrifuge, centrifuging the starch dispersion liquid at the normal temperature at the rotating speed of 3000-3500 r/min for 15-20 min, taking supernatant liquid, and adjusting the pH value to be neutral to obtain a starch mixed liquid;
(4) adding n-butyl alcohol and glycerol into the starch mixed solution, stirring for 10-15 min at the rotating speed of 300-400 r/min under the water bath condition of 80-90 ℃, standing for 1-2 h at normal temperature, and standing for 20-24 h in a refrigerator at the temperature of 2-4 ℃ to obtain a refrigerating solution;
(5) and (3) placing the cold storage liquid in a centrifuge, centrifuging for 15-20 min at the normal temperature at 3000-3500 r/min, taking the lower-layer precipitate, and placing the precipitate in a drying oven to dry for 1-2 h at the temperature of 55-60 ℃ to obtain the high amylose starch.
5. The preparation method of the completely degradable agricultural plastic film as claimed in claim 4, wherein the weight parts of the potato starch, the absolute ethyl alcohol, the sodium carbonate solution, the n-butanol and the glycerol are respectively as follows: 20-30 parts of potato starch, 40-60 parts of absolute ethyl alcohol, 60-80 parts of a 10% sodium carbonate solution, 40-50 parts of n-butyl alcohol and 40-50 parts of glycerol.
6. The method for preparing a fully degradable agricultural plastic film as claimed in claim 4, wherein the pH adjustment in step (3) is performed using a citric acid solution with a mass concentration of 1%.
7. The method for preparing a fully degradable agricultural plastic film as claimed in claim 1, wherein the polymer-coated plant fiber powder of step (1) is prepared by the following steps:
(1) placing corn straws and tea stems in a crusher, and crushing for 20-30 min at normal temperature to obtain mixed plant fiber powder;
(2) adding the mixed plant fiber powder into absolute ethyl alcohol, stirring at the normal temperature at the rotating speed of 200-300 r/min for 20-30 min, standing for 2-4 h, performing suction filtration, taking a filter cake, placing the filter cake in a drying box, and drying at the temperature of 40-60 ℃ for 1-2 h to obtain treated mixed plant fiber powder;
(3) adding polyethylene glycol into deionized water, and stirring at a rotating speed of 300-400 r/min for 30-40 min under a water bath condition of 40-60 ℃ to obtain a polyethylene glycol solution;
(4) and adding the treated mixed plant fiber powder into a polyethylene glycol solution, cooking for 2-4 h under the water bath condition of 60-80 ℃, filtering, putting a filter cake into a drying oven of 60-80 ℃ and drying for 1-2 h to obtain the polymer-coated plant fiber powder.
8. The preparation method of the completely degradable agricultural plastic film as claimed in claim 1, wherein the weight parts of the corn straw, the tea stem, the polyethylene glycol, the absolute ethyl alcohol and the deionized water are respectively as follows: 40-60 parts of corn straw, 40-60 parts of tea stem, 10-20 parts of polyethylene glycol, 120-160 parts of absolute ethyl alcohol and 60-80 parts of deionized water.
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