Starch-based full-biodegradable mulching film capable of being quickly degraded and preparation method of starch-based full-biodegradable mulching film

Abstract

The invention discloses a starch-based full-biodegradable mulching film capable of being rapidly degraded and a preparation method of the starch-based full-biodegradable mulching film, and belongs to the technical field of degradable materials.The preparation method comprises the steps of tea polyphenol calcium salt preparation, filler preparation, thermal plasticization and film preparation. The preparation of the filler comprises the following steps: adding silicon dioxide into a polyacrylic acid aqueous solution, stirring and centrifuging at room temperature, taking a precipitate, adding the precipitate into a polyvinylpyrrolidone aqueous solution, adjusting the pH value to 3-3.5, stirring and centrifuging at room temperature, taking the precipitate, adding the precipitate into the polyacrylic acid aqueous solution, adjusting the pH value to 3-3.5, stirring and centrifuging at room temperature, taking the precipitate, and freeze-drying to obtain the filler. The starch-based full-biodegradable mulching film prepared by the preparation method disclosed by the invention is good in processability, waterproofness and heat resistance and high in mechanical strength, the problem of phase separation does not occur in preparation, the problem of plasticizer precipitation does not easily occur in long-term use, and rapid degradation can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of degradable materials, and particularly relates to a starch-based fully biodegradable mulching film capable of rapid degradation and a preparation method thereof. Background Art

[0002] Agricultural mulching films have the functions of heat preservation and moisture preservation, can indirectly affect the growth environment of crops, and thus improve the yield of crops. Therefore, mulching films are one of the important production materials used in agricultural production. At present, the materials of traditional mulching films produced and used are mainly non-degradable materials, such as polyethylene (PE) and polyvinyl chloride (PVC). Therefore, traditional mulching films are non-degradable mulching films. For a long time, the unscientific use and lack of recycling links of non-degradable mulching films have led to an increasingly serious problem of mulching film residue pollution, which has greatly hindered the sustainable development of agriculture. When solving the problem of mulching film residue pollution, the traditional method is to timely pick up the mulching films remaining in the soil before and after crop planting and carry out harmless treatment. However, the above traditional method has the problems of high difficulty and high cost. Therefore, promoting the application of rapidly degradable fully biodegradable mulching films has become an important path to solve the problem of mulching film residue pollution.

[0003] The fully biodegradable mulch film can be degraded into small molecule inorganic substances such as carbon dioxide and water in a short time in the natural environment. Therefore, while having the functions of heat preservation and moisture retention of traditional mulch films, it also has the advantages of environmental friendliness. At present, the most studied fully biodegradable mulch film materials are polybutylene adipate terephthalate (PBAT) and polylactic acid (PLA). Among them, PBAT is prepared by an esterification method using adipic acid, terephthalic acid and butylene glycol as raw materials, and has the advantages of easy processing, excellent heat resistance, elongation at break and impact resistance. Degradation characteristics of PBAT fully biodegradable mulch film. Jin Anni, Yu Fenxia, Wang Yulin, Du Te, He Jing. Environmental Science, Vol. 46, No. 1. January 2005 disclosed the preparation of a mulch film using PBAT as the material and using this mulch film to cover crops. After 60 days, obvious cracks appeared on the surface. After 110 days, there was an obvious area loss on the surface, but the weight loss rate after 110 days was only 19.04%, and the degradation speed was slow. For short growth cycle crops such as peanuts, lettuce, and rapeseed, a fully biodegradable mulch film that can be quickly degraded is required. PLA is prepared by a polymerization method using lactic acid as the raw material and has the advantage of no pollution in the production process. Effects of polylactic acid biodegradable mulch film on soil temperature and cotton yield. Zhang Ni, Li Qi, Hou Zhen'an, Ye Jun. Journal of Agricultural Resources and Environment, Vol. 33, No. 2. March 2016 disclosed the use of a 15-μm-thick PLA film to cover crops. Small cracks appeared on the surface after 17 days, entered the rupture stage after 56 days, and entered the disintegration stage after 129 days, and the film surface was broken into small fragments; the 18-μm-thick PLA film was used to cover crops. Small cracks appeared on the surface after 22 days, entered the rupture stage after 64 days, and entered the disintegration stage after 153 days, and the film surface was broken into small fragments. Effects of different types of fully biodegradable mulch films on taro yield and soil environment. Zeng Xiaoping, Wang Li, Ma Jinjun, Yin Jianmei, Guo Wenqi, Han Xiaoyong, Li Chunhong, Jiang Lu, Zhang Peitong. China Vegetables. September 2021 disclosed that the PLA film cracked earlier than the PBAT film. However, the poor heat resistance and high brittleness of PLA affected the application effect of the PLA film.

[0004] Starch is a polysaccharide compound widely present in the seeds, roots, and stem tissues of crops such as cereals and tubers. It has the advantages of being renewable, biodegradable, and easy to store. Currently, there are many research reports on the application of starch in biodegradable plastics, but there are few research reports on the application of starch in fully biodegradable mulch films. When applying starch to the preparation of biodegradable plastics, according to the amount of starch used, the prepared biodegradable plastics can be divided into three types, namely starch-filled plastic materials, starch-plastic blend materials, and starch-based fully biodegradable materials. The mass fraction of starch in starch-filled plastic materials is generally 10-30%. During degradation, since only starch can degrade, the plastic will disintegrate into fragments and remain in the natural environment, resulting in the inability to fundamentally solve the environmental pollution problem. The mass fraction of starch in starch-plastic blend materials is generally 30-70%. Technically, it is relatively mature, and the comprehensive performance of mechanical strength, processability, and biodegradability is good. However, due to the compatibility problem between starch and plastic, it is difficult to disperse them evenly, further affecting the dimensional stability of starch-plastic blend materials. The mass fraction of starch in starch-based fully biodegradable materials is generally 70-90%. Starch-based fully biodegradable materials are prepared by blending starch as the main body with appropriate biodegradable additives. They are a type of material that can be fully incorporated into the natural material cycle system and cause no harm to the ecological environment. In the research reports on the application of starch in fully biodegradable mulch films, the materials used are starch-based fully biodegradable materials.

[0005] However, when using starch-based fully biodegradable materials to prepare fully biodegradable mulch films, there are the following deficiencies: First, due to the presence of hydrogen bonds in the molecular chain of starch, the intermolecular force between the molecular chains of starch is strong, with strong solubility, and it is prone to decomposition rather than melting at high temperatures. When applied to the preparation of fully biodegradable mulch films, there is a problem of poor processability. Second, due to the presence of hydrogen bonds in the molecular chain of starch, it also leads to strong hydrophilicity of starch, and the waterproof property of the fully biodegradable mulch film prepared from starch is poor, and it is difficult to maintain its original mechanical strength in rainy weather. Third, affected by the molecular structure, crystallinity, and intermolecular force, the mechanical strength of starch-based fully biodegradable materials is poor.

[0006] In response to the above deficiencies, the existing technology has carried out blending modification and chemical modification on starch-based fully biodegradable materials respectively.

[0007] Blending modification involves blending starch with materials such as plasticizers, hydrophobic agents, and nanomaterials. The plasticizers used include small molecule plasticizers and macromolecule plasticizers. Small molecule plasticizers are mainly small molecule polyols such as ethylene glycol, glycerol, and sorbitol. The small molecule polyols have strong mobility and can enter the interior of starch, forming new hydrogen bond groups with the hydroxyl groups in starch, thereby reducing the intermolecular forces of starch molecules and improving the processability and mechanical strength of starch-based fully biodegradable materials. However, hydrogen bonds belong to intermolecular forces, which are weaker than chemical bonds and are greatly affected by temperature. Phase separation is likely to occur when using starch-based fully biodegradable materials to prepare fully biodegradable mulch films, or plasticizer exudation is likely to occur during long-term use. Moreover, plasticizers will also increase the hydrophilicity of starch-based fully biodegradable materials, further reducing the waterproofness of the prepared fully biodegradable mulch films. Macromolecule plasticizers are mainly polyethylene glycol, polyvinyl alcohol, and polyester. The plasticization mechanism of macromolecule plasticizers is the separation process of macromolecule plasticizers. According to the lattice law, when small molecule plasticizers are plasticizing, it is a process of filling the lattice with single molecules, while macromolecule plasticizers act through chain segments, shielding the interaction centers of some starch molecular chains, weakening the intermolecular forces between adjacent starch molecular chains, and causing the starch molecular chains to separate. However, the macromolecule plasticizers have weak mobility and poor plasticization effect. The hydrophobic agents used are mainly hydrophobic polymers, such as nanocellulose and other biodegradable plastics. Nanocellulose can form new hydrogen bond groups with the hydroxyl groups in starch, thereby reducing the intermolecular forces of starch molecules. However, cellulose has a unique chair-like molecular structure and is extremely easy to aggregate and form tight and complex aggregates through hydrogen bond interaction, resulting in poor thermoplasticity and solubility of nanocellulose. For other biodegradable plastics, they are generally PBAT and PLA. However, there is a large polarity gap between starch and PBAT and PLA. Therefore, the compatibility between starch and other biodegradable plastics is poor. Moreover, for starch-based fully biodegradable materials, the addition amount of other biodegradable plastics is small, resulting in little improvement in the mechanical strength of starch-based fully biodegradable materials. For nanomaterials, although a small amount of nanomaterials can improve the mechanical strength of starch-based fully biodegradable materials and reduce the hydrophilicity of starch-based fully biodegradable materials, nanomaterials are extremely easy to aggregate. When the addition amount of nanomaterials exceeds a certain value, it will also reduce the mechanical strength of starch-based fully biodegradable materials.

[0008] Chemical modification involves introducing some new functional groups into starch molecules through chemical reactions, which generally include esterification, oxidation, grafting, and crosslinking reactions. Among them, esterification is the esterification reaction between the carboxyl group in the acid and the hydroxyl group in the starch molecule, which breaks the hydrogen bonds between starch molecules and lowers the glass transition temperature of starch; oxidation is to introduce an oxidant into the starch molecule under the control of temperature and pH, thereby improving the mechanical properties of starch and reducing its hydrophilicity; graft modification is to introduce other monomers or polymers onto the starch backbone through covalent bonds to obtain a polymer with the comprehensive functional characteristics of starch and the polymer used; crosslinking reaction is to use a crosslinking agent to react with the hydroxyl groups in starch to crosslink multiple starch molecules, thereby improving the mechanical properties of starch and reducing its hydrophilicity. However, for esterification, oxidation, and grafting reactions, the starch molecular chain may decompose during the reaction, resulting in a decrease in molecular weight, which reduces the heat resistance of starch-based fully biodegradable materials and is prone to decomposition during the preparation of fully biodegradable mulch films, further leading to poor mechanical strength of the prepared fully biodegradable mulch films. Moreover, other groups are introduced in esterification and grafting reactions, which also affects the degradation rate of starch-based fully biodegradable materials; the crosslinking reaction affects the plasticization of starch, resulting in a decrease in the melt flow rate of starch-based fully biodegradable materials, further leading to poor processability of the prepared fully biodegradable mulch films.

[0009] In summary, it is difficult to obtain a fully biodegradable mulch film with good processability, waterproofness, heat resistance, high mechanical strength, no phase separation problem during preparation, no plasticizer precipitation problem during long-term use, and rapid degradation using existing modification methods. Summary of the Invention

[0010] Aiming at the deficiencies of the existing technology, the present invention provides a method for preparing a rapidly degradable starch-based fully biodegradable mulch film. The prepared starch-based fully biodegradable mulch film has good processability, waterproofness, and heat resistance, high mechanical strength, no phase separation problem during preparation, no plasticizer precipitation problem during long-term use, and can achieve rapid degradation.

[0011] To solve the above technical problems, the technical solutions adopted by the present invention are as follows: A method for preparing a rapidly degradable starch-based fully biodegradable mulch film, comprising: preparing calcium tea polyphenolate, preparing a filler, thermoplasticizing, and film forming; To prepare calcium tea polyphenolate, add tea polyphenol into an ethanol aqueous solution, stir at a stirring speed of 100 - 400 rpm at room temperature for 30 - 40 min, add calcium chloride, add ammonia water to adjust the pH to 7.4 - 7.7, continue to stir for 1 - 1.5 h, stand at room temperature for 40 - 60 min, centrifuge at a centrifugal speed of 11000 - 12000 rpm for 20 - 30 min, take the precipitate, and freeze-dry to obtain calcium tea polyphenolate; In the preparation of calcium tea polyphenolate, the mass ratio of tea polyphenol to the ethanol aqueous solution is 10:1400 - 1600; The mass ratio of tea polyphenol to calcium chloride is 10:100 - 110; The temperature of the freeze-drying is -45°C to -40°C, and the time is 48 - 52 h; The volume fraction of the ethanol aqueous solution is 80%; The mass fraction of the ammonia water is 5%; To prepare the filler, add silica to the first polyacrylic acid aqueous solution, stir at a stirring speed of 100 - 400 rpm at room temperature for 3 - 4 h, centrifuge at a centrifugal speed of 11000 - 12000 rpm for 30 - 40 min, take the precipitate, add the precipitate to the polyvinylpyrrolidone aqueous solution, add hydrochloric acid aqueous solution to adjust the pH to 3 - 3.5, stir at a stirring speed of 100 - 400 rpm at room temperature for 2 - 3 h, centrifuge at a centrifugal speed of 11000 - 12000 rpm for 30 - 40 min, take the precipitate, add the precipitate to the second polyacrylic acid aqueous solution, add hydrochloric acid aqueous solution to adjust the pH to 3 - 3.5, stir at a stirring speed of 100 - 400 rpm at room temperature for 2 - 3 h, centrifuge at a centrifugal speed of 11000 - 12000 rpm for 30 - 40 min, take the precipitate, and freeze-dry to obtain the filler; In the preparation of the filler, the mass ratio of silica to the first polyacrylic acid aqueous solution is 100:1000 - 1200; The mass ratio of silica to the polyvinylpyrrolidone aqueous solution is 100:1500 - 1700; The mass ratio of silica to the second polyacrylic acid aqueous solution is 100:1000 - 1200; The temperature of the freeze-drying is -45°C to -40°C, and the time is 48 - 52 h; The D90 particle size of the silica is 40 nm; The preparation methods of both the first polyacrylic acid aqueous solution and the second polyacrylic acid aqueous solution are as follows: mix polyacrylic acid and deionized water according to a mass ratio of 10:1000 - 1100, stir at a stirring speed of 100 - 400 rpm at room temperature for 30 - 40 min, and then use sodium hydroxide to adjust the pH to 8 - 8.5; The number-average molecular weight of polyacrylic acid in the first and second aqueous polyacrylic acid solutions is 450,000; The preparation method of the aqueous polyvinylpyrrolidone solution is as follows: Mix polyvinylpyrrolidone and deionized water in a mass ratio of 10:1000 - 1100, stir at a stirring speed of 100 - 400 rpm for 30 - 40 min at room temperature, and then adjust the pH to 8 - 8.5 using sodium hydroxide; The number-average molecular weight of polyvinylpyrrolidone in the aqueous polyvinylpyrrolidone solution is 50,000; The molar concentration of the hydrochloric acid aqueous solution is 1 mol / L; For the thermoplasticization, corn starch, glycerol, gelatin, and calcium tea polyphenolate are mixed evenly and then pre-thermoplasticized, and then added to a twin-screw extruder for extrusion granulation to obtain thermoplasticized starch; In the thermoplasticization, the mass ratio of corn starch, glycerol, gelatin, and calcium tea polyphenolate is 100:27 - 30:16 - 18:1.8 - 2; The temperature of the pre-thermoplasticization is 90 - 95 °C, and the time is 4 - 5 h; In the extrusion granulation, the temperature of the first zone of the twin-screw extruder is 90 - 95 °C, the temperature of the second zone is 110 - 115 °C, the temperature of the third zone is 120 - 125 °C, the temperature of the fourth zone is 130 - 135 °C, the temperature of the fifth zone is 130 - 135 °C, the temperature of the sixth zone is 135 - 140 °C, the temperature of the seventh zone is 135 - 140 °C, and the screw speed is 150 - 200 rpm; For the film making, thermoplasticized starch, PBAT, maleic anhydride, chain extender, and filler are mixed evenly and then added to a twin-screw extruder for extrusion granulation to obtain a masterbatch, and then the masterbatch is added to a blown film machine for blown film to obtain a rapidly degradable starch-based fully biodegradable ground film; In the film making, the mass ratio of thermoplasticized starch, PBAT, maleic anhydride, chain extender, and filler is 85:13 - 15:3 - 3.5:0.4 - 0.6:9 - 11; In the extrusion granulation, the temperature of the first zone of the twin-screw extruder is 130 - 135 °C, the temperature of the second zone is 135 - 140 °C, the temperature of the third zone is 140 - 145 °C, the temperature of the fourth zone is 145 - 150 °C, the temperature of the fifth zone is 150 - 155 °C, the temperature of the sixth zone is 155 - 160 °C, the temperature of the seventh zone is 160 - 165 °C, the temperature of the eighth zone is 165 - 170 °C, the temperature of the ninth zone is 160 - 165 °C, and the screw speed is 50 - 60 rpm; The temperature of the blown film is 130 - 135 °C; The model of the chain extender is ADR-4368C.

[0012] A rapidly degradable starch-based fully biodegradable mulch film prepared by the aforementioned preparation method.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Since a large number of hydroxyl groups are contained on the starch molecule, a large number of hydrogen bonds are formed between the hydroxyl groups, making the starch molecule have a strong intermolecular force, which further leads to the glass transition temperature and melting temperature of starch being higher than the decomposition temperature, and it does not have thermoplasticity and cannot be directly melt-processed. The existing plasticizer plasticization theories mainly include the lubricant theory, the gel theory, and the free volume theory. The lubricant theory is that the plasticizer plays the role of a lubricant and can promote the movement of starch macromolecules with each other; the gel theory is that the addition of the plasticizer destroys the hydrogen bonds between starches, destroys the crystalline structure of starch, and improves the movement ability of starch molecular chains; the free volume theory is that the plasticizer increases the free volume between starches and reduces its glass transition temperature. In the present invention, during the thermoplasticization of starch, gelatin and calcium tea polyphenolate are added. During the extrusion granulation process, the high temperature destroys the interaction between part of the tea polyphenol and calcium in the calcium tea polyphenolate. There is an interaction between gelatin, starch, and tea polyphenol, thereby destroying the interaction between starch molecular chains, increasing the free volume between starches, and calcium ions can play a role in fixing glycerol, avoiding phase separation and precipitation caused by glycerol; (2) Considering the problem that silica is prone to agglomeration, the present invention treats silica, specifically by treating it with aqueous polyacrylic acid solution, polyvinylpyrrolidone aqueous solution, and polyacrylic acid aqueous solution in sequence. Polyacrylic acid can form hydrogen bonds with polyvinylpyrrolidone, and by adjusting the pH, the interaction between polyacrylic acid and polyvinylpyrrolidone is adjusted, so that polyacrylic acid, polyvinylpyrrolidone, and polyacrylic acid are sequentially coated on the surface of silica, thereby avoiding the agglomeration of silica. The hydrophobic groups in polyvinylpyrrolidone can improve the hydrophobicity of silica, further improving the hydrophobicity of the mulch film. The outermost polyacrylic acid can also combine with glycerol to fix glycerol, avoiding phase separation and precipitation caused by glycerol; (3) The starch-based fully biodegradable mulch film prepared by the present invention has good processability, water resistance and heat resistance, high mechanical strength, no phase separation problem during preparation, no plasticizer exudation problem during long-term use, and can achieve rapid degradation. The melt flow rate of the masterbatch used in the preparation is 15.3 - 15.8 g / 10 min at a test temperature of 190 °C and a load of 2.16 kg, and the Vicat softening point is 87.1 - 88.9 °C; the water contact angle of the prepared mulch film is 95.3 - 97.4°, the tensile strength is 18.75 - 19.80 MPa, the elongation at break is 365.7 - 375.2%, the degradation rate is tested, the mass loss rate after 60 d is 32.8 - 34.5%, the mass loss rate after 90 d is 57.7 - 59.3%, and the mass loss rate after 110 d is 70.2 - 73.6%; during the preparation of the mulch film, there is no phase separation problem, and the prepared mulch film is placed at 60 °C for 10 d, and there is no plasticizer exudation problem on the surface. Detailed implementation manners

[0014] In order to have a clearer understanding of the technical features, objectives and effects of the present invention, the specific implementation manners of the present invention are described below.

[0015] Example 1 A preparation method of a starch-based fully biodegradable mulch film that can be rapidly degraded, specifically: Step 1. Prepare calcium tea polyphenolate: Add tea polyphenols to an ethanol aqueous solution, control the mass ratio of tea polyphenols to the ethanol aqueous solution to be 10:1400, stir at a stirring speed of 100 rpm at room temperature for 30 min, add calcium chloride, control the mass ratio of tea polyphenols to calcium chloride to be 10:100, add ammonia water to adjust the pH to 7.4, continue stirring for 1 h, stand at room temperature for 40 min, centrifuge at a centrifugal speed of 11000 rpm for 20 min, take the precipitate, and freeze-dry, control the freeze-drying temperature to be -45 °C and the time to be 48 h to obtain calcium tea polyphenolate; The volume fraction of the ethanol aqueous solution is 80%; The mass fraction of the ammonia water is 5%; Step 2. Preparation of filler: Add silica into the first polyacrylic acid aqueous solution, control the mass ratio of silica to the first polyacrylic acid aqueous solution to be 100:1000, stir at a stirring speed of 100 rpm at room temperature for 3 h, centrifuge at a centrifugal speed of 11000 rpm for 30 min, take the precipitate, add the precipitate into the polyvinylpyrrolidone aqueous solution, control the mass ratio of silica to the polyvinylpyrrolidone aqueous solution to be 100:1500, add hydrochloric acid aqueous solution to adjust the pH to 3, stir at a stirring speed of 100 rpm at room temperature for 2 h, centrifuge at a centrifugal speed of 11000 rpm for 30 min, take the precipitate, add the precipitate into the second polyacrylic acid aqueous solution, control the mass ratio of silica to the second polyacrylic acid aqueous solution to be 100:1000, add hydrochloric acid aqueous solution to adjust the pH to 3, stir at a stirring speed of 100 rpm at room temperature for 2 h, centrifuge at a centrifugal speed of 11000 rpm for 30 min, take the precipitate, and freeze-dry, control the temperature of freeze-drying to be -45 °C and the time to be 48 h to obtain the filler; The D90 particle size of the silica is 40 nm; The preparation methods of both the first polyacrylic acid aqueous solution and the second polyacrylic acid aqueous solution are: Mix polyacrylic acid and deionized water according to a mass ratio of 10:1000, stir at a stirring speed of 100 rpm at room temperature for 30 min, and then use sodium hydroxide to adjust the pH to 8; The number-average molecular weight of polyacrylic acid in both the first polyacrylic acid aqueous solution and the second polyacrylic acid aqueous solution is 450,000; The preparation method of the polyvinylpyrrolidone aqueous solution is: Mix polyvinylpyrrolidone and deionized water according to a mass ratio of 10:1000, stir at a stirring speed of 100 rpm at room temperature for 30 min, and then use sodium hydroxide to adjust the pH to 8; The number-average molecular weight of polyvinylpyrrolidone in the polyvinylpyrrolidone aqueous solution is 50,000; The molar concentration of the hydrochloric acid aqueous solution is 1 mol / L; Step 3. Thermoplastification: Mix corn starch, glycerol, gelatin, and calcium tea polyphenolate evenly according to a mass ratio of 100:27:16:1.8 and carry out pre-plastification, control the temperature of pre-plastification to be 90 °C and the time to be 4 h, then add them into a twin-screw extruder for extrusion granulation, control the temperature of the first zone of the twin-screw extruder in extrusion granulation to be 90 °C, the temperature of the second zone to be 110 °C, the temperature of the third zone to be 120 °C, the temperature of the fourth zone to be 130 °C, the temperature of the fifth zone to be 130 °C, the temperature of the sixth zone to be 135 °C, the temperature of the seventh zone to be 135 °C, and the screw speed to be 150 rpm to obtain thermoplastic starch; Step 4. Film formation: Thermoplastic starch, PBAT, maleic anhydride, chain extender, and filler are mixed evenly according to a mass ratio of 85:13:3:0.4:9 and then added into a twin-screw extruder for extrusion granulation. Control the temperature of the first zone of the twin-screw extruder in the extrusion granulation to be 130 °C, the second zone to be 135 °C, the third zone to be 140 °C, the fourth zone to be 145 °C, the fifth zone to be 150 °C, the sixth zone to be 155 °C, the seventh zone to be 160 °C, the eighth zone to be 165 °C, the ninth zone to be 160 °C, and the screw speed to be 50 rpm to obtain a mixed masterbatch. Then, add the mixed masterbatch into a blown film machine for blown film, and control the temperature of the blown film to be 130 °C to obtain a rapidly degradable starch-based fully biodegradable mulch film with a thickness of 18 μm; The model of the chain extender is ADR-4368C.

[0016] This example also provides a rapidly degradable starch-based fully biodegradable mulch film prepared by the foregoing preparation method.

[0017] Example 2 A preparation method of a rapidly degradable starch-based fully biodegradable mulch film, specifically: Step 1. Preparation of calcium tea polyphenolate: Add tea polyphenols into an ethanol aqueous solution, control the mass ratio of tea polyphenols to the ethanol aqueous solution to be 10:1500, stir at a stirring speed of 200 rpm at room temperature for 35 min, add calcium chloride, control the mass ratio of tea polyphenols to calcium chloride to be 10:105, add ammonia water to adjust the pH to 7.5, continue stirring for 1.5 h, stand at room temperature for 50 min, centrifuge at a centrifugal speed of 12000 rpm for 25 min, take the precipitate, and freeze-dry. Control the temperature of the freeze-drying to be -40 °C and the time to be 50 h to obtain calcium tea polyphenolate; The volume fraction of the ethanol aqueous solution is 80%; The mass fraction of the ammonia water is 5%; Step 2. Preparation of filler: Add silicon dioxide into the first aqueous polyacrylic acid solution, control the mass ratio of silicon dioxide to the first aqueous polyacrylic acid solution to be 100:1100, stir at a stirring speed of 200 rpm at room temperature for 3.5 h, centrifuge at a centrifugal speed of 12000 rpm for 35 min, take the precipitate, add the precipitate into the aqueous polyvinylpyrrolidone solution, control the mass ratio of silicon dioxide to the aqueous polyvinylpyrrolidone solution to be 100:1600, add hydrochloric acid aqueous solution to adjust the pH to 3.5, stir at a stirring speed of 200 rpm at room temperature for 2.5 h, centrifuge at a centrifugal speed of 12000 rpm for 35 min, take the precipitate, add the precipitate into the second aqueous polyacrylic acid solution, control the mass ratio of silicon dioxide to the second aqueous polyacrylic acid solution to be 100:1100, add hydrochloric acid aqueous solution to adjust the pH to 3.5, stir at a stirring speed of 200 rpm at room temperature for 2.5 h, centrifuge at a centrifugal speed of 12000 rpm for 35 min, take the precipitate, and freeze-dry, control the temperature of freeze-drying to be -40 °C and the time to be 50 h to obtain the filler; The D90 particle size of the silicon dioxide is 40 nm; The preparation methods of the first aqueous polyacrylic acid solution and the second aqueous polyacrylic acid solution are both: Mix polyacrylic acid and deionized water according to a mass ratio of 10:1050, stir at a stirring speed of 200 rpm at room temperature for 35 min, and then use sodium hydroxide to adjust the pH to 8.5; The number-average molecular weight of polyacrylic acid in the first aqueous polyacrylic acid solution and the second aqueous polyacrylic acid solution is both 450,000; The preparation method of the aqueous polyvinylpyrrolidone solution is: Mix polyvinylpyrrolidone and deionized water according to a mass ratio of 10:1050, stir at a stirring speed of 200 rpm at room temperature for 35 min, and then use sodium hydroxide to adjust the pH to 8.5; The number-average molecular weight of polyvinylpyrrolidone in the aqueous polyvinylpyrrolidone solution is 50,000; The molar concentration of the hydrochloric acid aqueous solution is 1 mol / L; Step 3. Thermoplasticization: Mix corn starch, glycerol, gelatin, and calcium tea polyphenolate evenly according to a mass ratio of 100:28:17:1.9, and perform pre-plasticization, control the temperature of pre-plasticization to be 90 °C and the time to be 4.5 h, then add it into a twin-screw extruder for extrusion granulation, control the temperature of the first zone of the twin-screw extruder in extrusion granulation to be 90 °C, the temperature of the second zone to be 110 °C, the temperature of the third zone to be 120 °C, the temperature of the fourth zone to be 130 °C, the temperature of the fifth zone to be 130 °C, the temperature of the sixth zone to be 135 °C, the temperature of the seventh zone to be 135 °C, and the screw speed to be 150 rpm to obtain thermoplastic starch; Step 4. Film formation: Thermoplastic starch, PBAT, maleic anhydride, chain extender, and filler are mixed evenly according to a mass ratio of 85:14:3.4:0.5:10 and then added into a twin-screw extruder for extrusion granulation. Control the temperature of the first zone of the twin-screw extruder in the extrusion granulation to be 130°C, the second zone to be 135°C, the third zone to be 140°C, the fourth zone to be 145°C, the fifth zone to be 150°C, the sixth zone to be 155°C, the seventh zone to be 160°C, the eighth zone to be 165°C, the ninth zone to be 160°C, and the screw speed to be 50 rpm to obtain a mixed masterbatch. Then, the mixed masterbatch is added into a blown film machine for blown film, and control the temperature of the blown film to be 130°C to obtain a rapidly degradable starch-based fully biodegradable mulch film with a thickness of 18 μm; The model of the chain extender is ADR-4368C.

[0018] This embodiment also provides a rapidly degradable starch-based fully biodegradable mulch film prepared by the foregoing preparation method.

[0019] Example 3 A preparation method of a rapidly degradable starch-based fully biodegradable mulch film, specifically: Step 1. Preparation of calcium tea polyphenolate: Add tea polyphenols into an ethanol aqueous solution, control the mass ratio of tea polyphenols to the ethanol aqueous solution to be 10:1600, stir at a stirring speed of 400 rpm at room temperature for 40 min, add calcium chloride, control the mass ratio of tea polyphenols to calcium chloride to be 10:110, add ammonia water to adjust the pH to 7.7, continue stirring for 1.5 h, stand at room temperature for 60 min, centrifuge at a centrifugal speed of 12000 rpm for 30 min, take the precipitate, and freeze-dry. Control the temperature of the freeze-drying to be -40°C and the time to be 52 h to obtain calcium tea polyphenolate; The volume fraction of the ethanol aqueous solution is 80%; The mass fraction of the ammonia water is 5%; Step 2. Preparation of filler: Add silica into the first aqueous polyacrylic acid solution, control the mass ratio of silica to the first aqueous polyacrylic acid solution to be 100:1200, stir at a stirring speed of 400 rpm for 4 h at room temperature, centrifuge at a centrifugal speed of 12000 rpm for 40 min, take the precipitate, add the precipitate into the aqueous polyvinylpyrrolidone solution, control the mass ratio of silica to the aqueous polyvinylpyrrolidone solution to be 100:1700, add hydrochloric acid aqueous solution to adjust the pH to 3.5, stir at a stirring speed of 400 rpm for 3 h at room temperature, centrifuge at a centrifugal speed of 12000 rpm for 40 min, take the precipitate, add the precipitate into the second aqueous polyacrylic acid solution, control the mass ratio of silica to the second aqueous polyacrylic acid solution to be 100:1200, add hydrochloric acid aqueous solution to adjust the pH to 3.5, stir at a stirring speed of 400 rpm for 3 h at room temperature, centrifuge at a centrifugal speed of 12000 rpm for 40 min, take the precipitate, and freeze-dry, control the temperature of freeze-drying to be -40 °C and the time to be 52 h to obtain the filler; The D90 particle size of the silica is 40 nm; The preparation methods of both the first aqueous polyacrylic acid solution and the second aqueous polyacrylic acid solution are as follows: Mix polyacrylic acid and deionized water according to a mass ratio of 10:1100, stir at a stirring speed of 400 rpm for 40 min at room temperature, and then use sodium hydroxide to adjust the pH to 8.5; The number-average molecular weight of polyacrylic acid in both the first aqueous polyacrylic acid solution and the second aqueous polyacrylic acid solution is 450,000; The preparation method of the aqueous polyvinylpyrrolidone solution is as follows: Mix polyvinylpyrrolidone and deionized water according to a mass ratio of 10:1100, stir at a stirring speed of 400 rpm for 40 min at room temperature, and then use sodium hydroxide to adjust the pH to 8.5; The number-average molecular weight of polyvinylpyrrolidone in the aqueous polyvinylpyrrolidone solution is 50,000; The molar concentration of the hydrochloric acid aqueous solution is 1 mol / L; Step 3. Thermoplastication: Mix corn starch, glycerol, gelatin, and calcium tea polyphenolate evenly according to a mass ratio of 100:30:18:2 and carry out pre-thermoplastication, control the temperature of pre-thermoplastication to be 95 °C and the time to be 5 h, then add it into a twin-screw extruder for extrusion granulation, control the temperature of the first zone of the twin-screw extruder in extrusion granulation to be 95 °C, the temperature of the second zone to be 115 °C, the temperature of the third zone to be 125 °C, the temperature of the fourth zone to be 135 °C, the temperature of the fifth zone to be 135 °C, the temperature of the sixth zone to be 140 °C, the temperature of the seventh zone to be 140 °C, and the screw speed to be 200 rpm to obtain thermoplastic starch; Step 4. Film formation: Thermoplastic starch, PBAT, maleic anhydride, chain extender, and filler are mixed evenly according to a mass ratio of 85:15:3.5:0.6:11, and then added into a twin-screw extruder for extrusion granulation. Control the temperature of the first zone of the twin-screw extruder in the extrusion granulation to be 135°C, the second zone to be 140°C, the third zone to be 145°C, the fourth zone to be 150°C, the fifth zone to be 155°C, the sixth zone to be 160°C, the seventh zone to be 165°C, the eighth zone to be 170°C, the ninth zone to be 165°C, and the screw speed to be 60 rpm to obtain a mixed masterbatch. Then, the mixed masterbatch is added into a blown film machine for blown film, and control the temperature of the blown film to be 135°C to obtain a rapidly degradable starch-based fully biodegradable mulch film with a thickness of 18 μm. The model of the chain extender is ADR-4368C.

[0020] This embodiment also provides a rapidly degradable starch-based fully biodegradable mulch film prepared by the foregoing preparation method.

[0021] Comparative Example 1 On the basis of the preparation method of the rapidly degradable starch-based fully biodegradable mulch film described in Example 2, omit Step 1. Preparation of calcium tea polyphenolate, and in Step 3. Thermoplasticization, use an equal mass of tea polyphenols to replace the addition of calcium tea polyphenolate.

[0022] The remaining operations are the same as those in Example 2.

[0023] The thickness of the rapidly degradable starch-based fully biodegradable mulch film prepared in this comparative example is 18 μm.

[0024] Comparative Example 2 On the basis of the preparation method of the rapidly degradable starch-based fully biodegradable mulch film described in Example 2, omit Step 1. Preparation of calcium tea polyphenolate, and in Step 3. Thermoplasticization, omit the addition of calcium tea polyphenolate.

[0025] The remaining operations are the same as those in Example 2.

[0026] The thickness of the rapidly degradable starch-based fully biodegradable mulch film prepared in this comparative example is 18 μm.

[0027] Comparative Example 3 On the basis of the preparation method of the rapidly degradable starch-based fully biodegradable mulch film described in Example 2, in Step 3. Thermoplasticization, omit the addition of gelatin.

[0028] The remaining operations are the same as those in Example 2.

[0029] The thickness of the rapidly degradable starch-based fully biodegradable mulch film prepared in this comparative example is 18 μm.

[0030] Comparative Example 4 On the basis of the preparation method of the rapidly degradable starch-based fully biodegradable mulch film described in Example 2, step 2 of preparing the filler was omitted, and in step 4 of film making, silica with a D90 particle size of 40 nm was used to replace the addition of the filler in equal mass.

[0031] The remaining operations were the same as those in Example 2.

[0032] The thickness of the rapidly degradable starch-based fully biodegradable mulch film prepared in this comparative example was 18 μm.

[0033] Performance Test Example 1 In Examples 1-3 and Comparative Examples 1-4, during the film making step, the melt flow rate of the masterbatch was tested. When testing, referring to the GB / T3682.1-2018 standard, the test temperature was 190 °C, the load was 2.16 kg, and the test results are shown in Table 1: Table 1

[0034] It can be seen from the above results that compared with Example 2, the melt flow rate of the masterbatch in Comparative Examples 2-4 was lower. This shows that calcium tea polyphenolate, gelatin, and the filler can all improve the melt flow rate of the masterbatch.

[0035] Performance Test Example 2 The water contact angle of the rapidly degradable starch-based fully biodegradable mulch films prepared in Examples 1-3 and Comparative Examples 1-4 was tested, and the test results are shown in Table 2: Table 2

[0036] It can be seen from the above results that compared with Example 2, the water contact angle of the rapidly degradable starch-based fully biodegradable mulch films in Comparative Examples 1-4 was lower. This shows that calcium tea polyphenolate, gelatin, and the filler can all improve the waterproof property of the rapidly degradable starch-based fully biodegradable mulch film.

[0037] Performance Test 3 In Examples 1-3 and Comparative Examples 1-4, during the film making step, the Vicat softening point of the masterbatch was tested. When testing, referring to the GB / T1633-2000 standard, the test results are shown in Table 3: Table 3

[0038] It can be seen from the above results that compared with Example 2, the Vicat softening point of the masterbatch in Comparative Examples 2-4 was lower. This shows that calcium tea polyphenolate, gelatin, and the filler can all improve the Vicat softening point of the masterbatch.

[0039] Performance Test 4 The tensile strength and elongation at break of the rapidly degradable starch-based fully biodegradable mulch films prepared in Examples 1-3 and Comparative Examples 1-4 were tested. During the test, referring to the GB / T 1040-2006 standard, the test results are shown in Table 4: Table 4

[0040] It can be seen from the above results that compared with Example 2, the tensile strength and elongation at break of the rapidly degradable starch-based fully biodegradable mulch films in Comparative Examples 1-4 are lower. It shows that calcium tea polyphenolate, gelatin and filler can all improve the tensile strength and elongation at break of the rapidly degradable starch-based fully biodegradable mulch film.

[0041] Performance Test 5 Observe whether there is a phase separation problem in the rapidly degradable starch-based fully biodegradable mulch films prepared in Examples 1-3 and Comparative Examples 1-4, and place the rapidly degradable starch-based fully biodegradable mulch films prepared in Examples 1-3 and Comparative Examples 1-4 at 60 °C for 10 d, and observe whether there is a problem of plasticizer precipitation on the surface. The results are shown in Table 5: Table 5

[0042] It can be seen from the above results that compared with Example 2, the rapidly degradable starch-based fully biodegradable mulch films in Comparative Examples 1-2 and 4 all have a phase separation problem or a problem of plasticizer precipitation after standing. It shows that calcium tea polyphenolate and filler can both avoid the phase separation problem or the problem of plasticizer precipitation.

[0043] Performance Test 6 The rapidly degradable starch-based fully biodegradable mulch films prepared in Examples 1-3 and Comparative Examples 1-4 were subjected to an embedding experiment. Specifically, the mulch films were cut into test specimens of 40 cm × 30 cm. Three test specimens were taken for each type of mulch film. After weighing and marking respectively, they were put into 100-mesh bags and buried in a 10-cm deep soil layer. One test specimen was taken out after 60 d, 90 d, and 110 d of burial respectively, weighed, and the mass loss rate was calculated; the above method was repeated for 5 tests, and the average value was taken; the results are shown in Table 6: Table 6

[0044] It can be seen from the above results that compared with Example 2, the degradation rates of the rapidly degradable starch-based fully biodegradable mulch films in Comparative Examples 2 and 4 are lower. It shows that calcium tea polyphenolate and filler both improve the degradation rate of the rapidly degradable starch-based fully biodegradable mulch film.

Claims

1. A preparation method of a starch-based fully biodegradable mulch film capable of rapid degradation, characterized in that, Including: Preparing calcium tea polyphenolate, preparing filler, thermoplastifying, and film-making; For the preparation of calcium tea polyphenolate, add tea polyphenols to an ethanol aqueous solution, stir at room temperature, add calcium chloride, adjust the pH to 7.4 - 7.7, continue stirring, let stand at room temperature, centrifuge, take the precipitate, and freeze-dry to obtain calcium tea polyphenolate; For the preparation of filler, add silica to the first polyacrylic acid aqueous solution, stir at room temperature, centrifuge, take the precipitate, add the precipitate to a polyvinylpyrrolidone aqueous solution, adjust the pH to 3 - 3.5, stir at room temperature, centrifuge, take the precipitate, add the precipitate to the second polyacrylic acid aqueous solution, adjust the pH to 3 - 3.5, stir at room temperature, centrifuge, take the precipitate, and freeze-dry to obtain filler; For the thermoplastifying, mix corn starch, glycerol, gelatin, and calcium tea polyphenolate evenly and then perform pre-plasticization, and then add them to a twin-screw extruder for extrusion granulation to obtain thermoplastic starch; For the film-making, mix thermoplastic starch, PBAT, maleic anhydride, chain extender, and filler evenly and then add them to a twin-screw extruder for extrusion granulation to obtain a masterbatch, and then add the masterbatch to a blown film machine for blown film to obtain a rapidly degradable starch-based fully biodegradable mulch film.

2. The preparation method of the rapidly degradable starch-based fully biodegradable mulch film according to claim 1, characterized in that, In the preparation of calcium tea polyphenolate, the mass ratio of tea polyphenols to the ethanol aqueous solution is 10:1400 - 1600; The mass ratio of tea polyphenols to calcium chloride is 10:100 - 110; The temperature of the freeze-drying is -45°C to -40°C, and the time is 48 - 52h; The volume fraction of the ethanol aqueous solution is 80%.

3. The preparation method of the rapidly degradable starch-based fully biodegradable ground film according to claim 1, characterized in that, In the preparation of filler, the mass ratio of silica to the first polyacrylic acid aqueous solution is 100:1000 - 1200; The mass ratio of silica to the polyvinylpyrrolidone aqueous solution is 100:1500 - 1700; The mass ratio of silica to the second polyacrylic acid aqueous solution is 100:1000 - 1200; The temperature of the freeze-drying is -45°C to -40°C, and the time is 48 - 52h; The D90 particle size of the silica is 40nm.

4. The preparation method of the starch-based fully biodegradable mulch film capable of being rapidly degraded according to claim 1, wherein, In the preparation of filler, the preparation methods of the first polyacrylic acid aqueous solution and the second polyacrylic acid aqueous solution are both to mix polyacrylic acid and deionized water according to a mass ratio of 10:1000 - 1100, stir at room temperature, and then adjust the pH to 8 - 8.5; The number-average molecular weight of polyacrylic acid in both the first polyacrylic acid aqueous solution and the second polyacrylic acid aqueous solution is 450,000.

5. The preparation method of the rapidly degradable starch-based fully biodegradable mulch film according to claim 1, characterized in that, In the preparation of filler, the preparation method of the polyvinylpyrrolidone aqueous solution is: mix polyvinylpyrrolidone and deionized water according to a mass ratio of 10:1000 - 1100, stir at room temperature, and then adjust the pH to 8 - 8.5; The number-average molecular weight of polyvinylpyrrolidone in the polyvinylpyrrolidone aqueous solution is 50,000.

6. The preparation method of the rapidly degradable starch-based fully biodegradable mulch film according to claim 1, wherein, In the thermoplastifying, the mass ratio of corn starch, glycerol, gelatin, and calcium tea polyphenolate is 100:27 - 30:16 - 18:1.8 - 2; The temperature of the pre-plasticization is 90 - 95°C, and the time is 4 - 5h.

7. The preparation method of the rapidly degradable starch-based fully biodegradable mulch film according to claim 1, characterized in that, In the thermoplastification, the temperature of the first zone of the twin-screw extruder in the extrusion granulation is 90 - 95 °C, the temperature of the second zone is 110 - 115 °C, the temperature of the third zone is 120 - 125 °C, the temperature of the fourth zone is 130 - 135 °C, the temperature of the fifth zone is 130 - 135 °C, the temperature of the sixth zone is 135 - 140 °C, the temperature of the seventh zone is 135 - 140 °C, and the screw speed is 150 - 200 rpm.

8. The preparation method of the rapidly degradable starch-based fully biodegradable ground film according to claim 1, characterized in that, In the film making, the mass ratio of thermoplastic starch, PBAT, maleic anhydride, chain extender, and filler is 85:13 - 15:3 - 3.5:0.4 - 0.6:9 - 11; The model of the chain extender is ADR-4368C.

9. The preparation method of the rapidly degradable starch-based fully biodegradable mulching film according to claim 1, characterized in that, In the film making, the temperature of the first zone of the twin-screw extruder in the extrusion granulation is 130 - 135 °C, the temperature of the second zone is 135 - 140 °C, the temperature of the third zone is 140 - 145 °C, the temperature of the fourth zone is 145 - 150 °C, the temperature of the fifth zone is 150 - 155 °C, the temperature of the sixth zone is 155 - 160 °C, the temperature of the seventh zone is 160 - 165 °C, the temperature of the eighth zone is 165 - 170 °C, the temperature of the ninth zone is 160 - 165 °C, and the screw speed is 50 - 60 rpm; The temperature of the blown film is 130 - 135 °C.

10. A rapidly degradable starch-based fully biodegradable mulch film prepared by the preparation method according to any one of claims 1 - 9.

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