A rapidly degradable starch-based fully biodegradable mulch film and its preparation method

Abstract

The invention discloses a kind of rapidly degradable starch-based fully biodegradable mulch film and its preparation method, belong to the technical field of degradable materials, the preparation method includes: preparing tea polyphenol calcium salt, preparing filler, thermoplasticization, film making;The described preparation filler, silicon dioxide is added to polyacrylic acid aqueous solution, stirred at room temperature, centrifuged, precipitated, the precipitate is added to polyvinyl pyrrolidone aqueous solution, pH is adjusted to 3 3.5, stirred at room temperature, centrifuged, precipitated, the precipitate is added to polyacrylic acid aqueous solution, pH is adjusted to 3 3.5, stirred at room temperature, centrifuged, precipitated, freeze-dried, and filler is obtained. The starch-based fully biodegradable mulch film prepared by the present invention has good processability, waterproofness and heat resistance, high mechanical strength, no phase separation problem occurs in preparation, plasticizer precipitation problem is not easily occurred in long-term use, and rapid degradation can be achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of degradable materials, and in particular to a rapidly degradable starch-based fully biodegradable mulch film and a preparation method thereof. Background Art

[0002] Agricultural mulch films have the functions of heat preservation and moisture retention, indirectly affecting the growing environment of crops and thus increasing crop yields. Therefore, mulch films are one of the important means of production used in agricultural production. The materials of traditional mulch films currently produced and used are mainly non-degradable materials, such as polyethylene (PE) and polyvinyl chloride (PVC). Therefore, traditional mulch films are non-degradable. For a long time, the unscientific use of non-degradable mulch films and the lack of recycling processes have led to the increasingly serious problem of mulch film residue pollution, which has greatly hindered the sustainable development of agriculture. When addressing the problem of mulch film residue pollution, the traditional method is to promptly collect and harmlessly dispose of mulch film remaining in the soil before planting and after harvesting crops. However, this traditional method is difficult and costly. Therefore, the promotion and application of rapidly degradable and fully biodegradable mulch films has become an important path to solving the problem of mulch film residue pollution.

[0003] Fully biodegradable mulch films degrade quickly into small inorganic molecules such as carbon dioxide and water in the natural environment. Therefore, while retaining the heat and moisture retention properties of traditional mulch films, they also offer environmental benefits. Currently, the most researched fully biodegradable mulch film materials are polybutylene adipate / terephthalate (PBAT) and polylactic acid (PLA). PBAT, made from adipic acid, terephthalic acid, and butylene glycol via an esterification process, offers the advantages of easy processing and 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, and He Jing. Environmental Science, Vol. 46, No. 1. In January 2005, a mulch film made from PBAT was reported. When used to cover crops, the film showed noticeable surface cracking after 60 days and significant surface area loss after 110 days. However, the weight loss rate after 110 days was only 19.04%, indicating slow degradation. For crops with short growth cycles, such as peanuts, lettuce, and rapeseed, a rapidly degradable fully biodegradable mulch film is required. PLA is produced using a polymerization process using lactic acid, offering the advantage of a pollution-free 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, Volume 33, Issue 2. Published in March 2016, a 15μm-thick PLA film used for crop covering developed small cracks on the surface after 17 days, entered the rupture stage after 56 days, and entered the disintegration stage after 129 days, breaking into small fragments. An 18μm-thick PLA film used for crop covering developed small cracks on the surface after 22 days, entered the rupture stage after 64 days, and entered the disintegration stage after 153 days, breaking 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. Chinese Vegetables. Published in September 2021, a PLA film decomposes earlier than a PBAT film. However, PLA has poor heat resistance and high brittleness, which affects the application effect of PLA film.

[0004] Starch is a polysaccharide compound widely found in the seeds, roots, and stems of crops such as cereals and tubers. It is renewable, biodegradable, and easy to preserve. Currently, there are many reports on the use of starch in biodegradable plastics, but fewer on its use in fully biodegradable mulch films. When starch is used in the preparation of biodegradable plastics, the resulting biodegradable plastics can be divided into three types based on the amount of starch used: starch-filled plastics, starch-plastic blends, 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 be degraded, the plastic will disintegrate into fragments and remain in the natural environment, resulting in an inability to fundamentally solve the problem of environmental pollution. The mass fraction of starch in starch-plastic blended materials is generally 30-70%. This is technically mature and has good comprehensive performance in terms of mechanical strength, processability, and biodegradability. However, due to compatibility issues between starch and plastic, it is difficult for starch and plastic to be evenly dispersed, further affecting the dimensional stability of the starch-plastic blended materials. The mass fraction of starch in starch-based fully biodegradable materials is generally 70-90%. Starch-based fully biodegradable materials are made by blending starch as the main component with an appropriate amount of degradable additives. They are a type of material that can be fully integrated into the natural material cycle system and does not cause any harm to the ecological environment. In research reports on the application of starch in fully biodegradable mulch, the material used is starch-based fully biodegradable material.

[0005] However, when starch-based fully biodegradable materials are used to prepare fully biodegradable mulch films, the following deficiencies exist: First, due to the presence of hydrogen bonds in the molecular chains of starch, the interaction between the molecular chains of starch is strong, the solubility is strong, and it is easy to decompose at high temperatures without melting. When used in 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 chains of starch, the hydrophilicity of starch is also strong, and the fully biodegradable mulch films prepared from starch have poor waterproof properties and are difficult to maintain their original mechanical strength in rainy weather; Third, due to the influence of molecular structure, crystallinity, and intermolecular forces, the mechanical strength of starch-based fully biodegradable materials is poor.

[0006] In view of the above-mentioned deficiencies, the prior art has respectively carried out blending modification and chemical modification on starch-based fully biodegradable materials.

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

[0008] Chemical modification is the introduction of some new functional groups into starch molecules through chemical reactions. The chemical reactions are generally esterification, oxidation, grafting and cross-linking. Among them, the esterification reaction is the esterification reaction between the carboxyl group in the acid and the hydroxyl group in the starch molecule, which destroys the hydrogen bonds between the starch molecules and lowers the glass transition temperature of the starch; the oxidation reaction is the introduction of oxidants into the starch molecules under the control of temperature and pH, thereby improving the mechanical properties of starch and reducing the hydrophilicity of starch; grafting modification is the introduction of other monomers or polymers into the starch main chain through covalent bonds, thereby obtaining a polymer with the comprehensive functional properties of starch and the polymer used; the cross-linking reaction is the use of a cross-linking agent to react with the hydroxyl groups between starch to cross-link multiple starch molecules, thereby improving the mechanical properties of starch and reducing the hydrophilicity of starch. However, the esterification reaction, oxidation reaction and grafting reaction may cause the starch molecular chain to decompose and the molecular weight to decrease during the reaction, resulting in a decrease in the heat resistance of the starch-based fully biodegradable material. Decomposition is prone to occur during the preparation of fully biodegradable mulch, which further leads to poor mechanical strength of the prepared fully biodegradable mulch. In addition, other groups will be introduced during the esterification reaction and grafting reaction, which will also affect the degradation rate of the starch-based fully biodegradable material; the cross-linking reaction will affect the plasticization of starch, resulting in a decrease in the melt flow rate of the starch-based fully biodegradable material, which further leads to poor processability of the prepared fully biodegradable mulch.

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

[0010] In response to the shortcomings of the existing technology, the present invention provides a rapidly degradable starch-based fully biodegradable mulch film and a preparation method thereof. The prepared starch-based fully biodegradable mulch film has good processability, waterproofness and heat resistance, high mechanical strength, no phase separation problem occurs during preparation, and is not prone to plasticizer precipitation problems during long-term use, and can achieve rapid degradation.

[0011] In order to solve the above technical problems, the technical solutions adopted by the present invention are as follows:

[0012] A method for preparing a rapidly degradable starch-based fully biodegradable ground film, comprising: preparing tea polyphenol calcium salt, preparing filler, thermoplasticizing, and film making;

[0013] The preparation of tea polyphenol calcium salt comprises adding tea polyphenol to an ethanol aqueous solution, stirring at room temperature at a stirring speed of 100-400 rpm for 30-40 minutes, adding calcium chloride, adding ammonia water to adjust the pH to 7.4-7.7, continuing stirring for 1-1.5 hours, standing at room temperature for 40-60 minutes, centrifuging at a centrifugal speed of 11000-12000 rpm for 20-30 minutes, collecting a precipitate, and freeze-drying to obtain tea polyphenol calcium salt;

[0014] In the preparation of tea polyphenol calcium salt, the mass ratio of tea polyphenol to ethanol aqueous solution is 10:1400-1600;

[0015] The mass ratio of tea polyphenols to calcium chloride is 10:100-110;

[0016] The freeze-drying temperature is -45°C to -40°C, and the time is 48-52h;

[0017] The volume fraction of the ethanol aqueous solution is 80%;

[0018] The mass fraction of the ammonia water is 5%;

[0019] The filler is prepared by adding silica to a first portion of a polyacrylic acid aqueous solution, stirring at a stirring speed of 100-400 rpm for 3-4 hours at room temperature, centrifuging at a centrifugal speed of 11000-12000 rpm for 30-40 minutes, taking a precipitate, adding the precipitate to a polyvinylpyrrolidone aqueous solution, adding a hydrochloric acid aqueous solution to adjust the pH to 3-3.5, stirring at a stirring speed of 100-400 rpm for 2-3 hours at room temperature, centrifuging at a centrifugal speed of 11000-12000 rpm for 30-40 minutes, taking a precipitate, adding the precipitate to a second portion of a polyacrylic acid aqueous solution, adding a hydrochloric acid aqueous solution to adjust the pH to 3-3.5, stirring at a stirring speed of 100-400 rpm for 2-3 hours at room temperature, centrifuging at a centrifugal speed of 11000-12000 rpm for 30-40 minutes, taking a precipitate, and freeze-drying to obtain a filler;

[0020] In the preparation of the filler, the mass ratio of silicon dioxide to the first portion of the polyacrylic acid aqueous solution is 100:1000-1200;

[0021] The mass ratio of silicon dioxide and polyvinyl pyrrolidone aqueous solution is 100:1500-1700;

[0022] The mass ratio of silicon dioxide to the second polyacrylic acid aqueous solution is 100:1000-1200;

[0023] The freeze-drying temperature is -45°C to -40°C, and the time is 48-52h;

[0024] The D90 particle size of the silicon dioxide is 40 nm;

[0025] The first polyacrylic acid aqueous solution and the second polyacrylic acid aqueous solution are both prepared by mixing polyacrylic acid and deionized water in a mass ratio of 10:1000-1100, stirring at room temperature at a stirring speed of 100-400 rpm for 30-40 minutes, and then adjusting the pH to 8-8.5 using sodium hydroxide;

[0026] The number average molecular weight of the polyacrylic acid in the first polyacrylic acid aqueous solution and the second polyacrylic acid aqueous solution is 450,000;

[0027] The preparation method of the polyvinyl pyrrolidone aqueous solution is as follows: polyvinyl pyrrolidone and deionized water are mixed in a mass ratio of 10:1000-1100, stirred at room temperature at a stirring speed of 100-400 rpm for 30-40 minutes, and then adjusted to a pH of 8-8.5 using sodium hydroxide;

[0028] The number average molecular weight of polyvinyl pyrrolidone in the polyvinyl pyrrolidone aqueous solution is 50,000;

[0029] The molar concentration of the hydrochloric acid aqueous solution is 1 mol / L;

[0030] The heat plasticization comprises pre-plasticizing the mixture of corn starch, glycerol, gelatin and tea polyphenol calcium salt after uniform mixing, and then adding the mixture into a twin-screw extruder for extrusion granulation to obtain heat plasticized starch;

[0031] In the thermal plasticization, the mass ratio of corn starch, glycerol, gelatin and tea polyphenol calcium salt is 100:27-30:16-18:1.8-2;

[0032] The pre-plasticization temperature is 90-95°C and the time is 4-5h;

[0033] 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 150-200rpm;

[0034] The film making comprises mixing thermoplasticized starch, PBAT, maleic anhydride, a chain extender, and a filler uniformly, adding the mixture into a twin-screw extruder for extrusion granulation to obtain a mixed masterbatch, and then adding the mixed masterbatch into a film blowing machine for film blowing to obtain a rapidly degradable starch-based fully biodegradable mulch film;

[0035] In the film preparation, 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;

[0036] In the extrusion granulation, the temperature of zone 1 of the twin-screw extruder is 130-135°C, the temperature of zone 2 is 135-140°C, the temperature of zone 3 is 140-145°C, the temperature of zone 4 is 145-150°C, the temperature of zone 5 is 150-155°C, the temperature of zone 6 is 155-160°C, the temperature of zone 7 is 160-165°C, the temperature of zone 8 is 165-170°C, the temperature of zone 9 is 160-165°C, and the screw speed is 50-60rpm;

[0037] The temperature of the film blowing is 130-135°C;

[0038] The model of the chain extender is ADR-4368C.

[0039] A rapidly degradable starch-based fully biodegradable mulch film prepared by the above-mentioned preparation method.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] (1) Since starch molecules contain a large number of hydroxyl groups, a large number of hydrogen bonds are formed between the hydroxyl groups, which makes the starch molecules have strong intermolecular forces, further causing the glass transition temperature and melting temperature of starch to be higher than the decomposition temperature. It does not have thermoplasticity and cannot be directly melt-processed. The existing plasticizing theories of plasticizers mainly include lubricant theory, gel theory, and free volume theory. The lubricant theory states that the plasticizer acts as a lubricant and can promote the movement between starch macromolecules; the gel theory states that the addition of plasticizers destroys the hydrogen bonds between starch, destroys the crystalline structure of starch, and improves the mobility of starch molecular chains; the free volume theory states that the plasticizer increases the free volume between starch and lowers its glass transition temperature. In the present invention, gelatin and tea polyphenol calcium salt are added during the thermoplasticization of starch. During the extrusion granulation process, the high temperature destroys the interaction between some tea polyphenols and calcium in the tea polyphenol calcium salt. There is interaction between gelatin, starch, and tea polyphenols, thereby destroying the interaction between starch molecular chains and increasing the free volume between starches. Calcium ions can fix glycerol and prevent glycerol from causing phase separation and precipitation.

[0042] (2) Considering the problem of easy agglomeration of silica, the present invention treats silica, specifically using polyacrylic acid aqueous solution, polyvinyl pyrrolidone aqueous solution, and polyacrylic acid aqueous solution for treatment, respectively. It utilizes the ability of polyacrylic acid to generate hydrogen bonds with polyvinyl pyrrolidone, and by adjusting the pH, the interaction force between polyacrylic acid and polyvinyl pyrrolidone is adjusted, so that polyacrylic acid, polyvinyl pyrrolidone, and polyacrylic acid are coated on the surface of silica in sequence, thereby preventing silica from agglomerating. The hydrophobic groups in polyvinyl pyrrolidone can improve the hydrophobicity of silica and further improve the hydrophobicity of the ground film. The outermost layer of polyacrylic acid can also combine with glycerol to fix glycerol, thereby preventing glycerol from causing phase separation and precipitation.

[0043] (3) The starch-based fully biodegradable mulch prepared by the present invention has good processability, waterproofness and heat resistance, high mechanical strength, no phase separation problem occurs during preparation, and is not prone to plasticizer precipitation problems during long-term use, and can achieve rapid degradation. The melt flow rate of the mixed 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 is 95.3-97.4°, the tensile strength is 18.75-19.80 MPa, and the elongation at break is 365.7-375.2%. A degradation rate test shows that the mass loss rate after 60 days is 32.8-34.5%, the mass loss rate after 90 days is 57.7-59.3%, and the mass loss rate after 110 days is 70.2-73.6%; there is no phase separation problem in the preparation of the mulch, and when the prepared mulch is placed at 60°C and left to stand for 10 days, there is no plasticizer precipitation problem on the surface. DETAILED DESCRIPTION

[0044] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, the specific embodiments of the present invention are now described.

[0045] Example 1

[0046] A method for preparing a rapidly degradable starch-based fully biodegradable mulch film, specifically comprising:

[0047] Step 1. Preparing tea polyphenol calcium salt: adding tea polyphenol to an ethanol aqueous solution, controlling the mass ratio of tea polyphenol to the ethanol aqueous solution to be 10:1400, stirring at room temperature at a stirring speed of 100 rpm for 30 minutes, adding calcium chloride, controlling the mass ratio of tea polyphenol to calcium chloride to be 10:100, adding ammonia water to adjust the pH to 7.4, continuing stirring for 1 hour, standing at room temperature for 40 minutes, centrifuging at a centrifugal speed of 11000 rpm for 20 minutes, taking the precipitate, and freeze-drying, controlling the freeze-drying temperature to -45°C and the time to be 48 hours, to obtain tea polyphenol calcium salt;

[0048] The volume fraction of the ethanol aqueous solution is 80%;

[0049] The mass fraction of the ammonia water is 5%;

[0050] Step 2. Prepare the filler: add silica to 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 room temperature at a stirring speed of 100 rpm for 3 hours, centrifuge at a centrifugal speed of 11000 rpm for 30 minutes, take the precipitate, add the precipitate to a polyvinyl pyrrolidone aqueous solution, control the mass ratio of silica to polyvinyl pyrrolidone aqueous solution to be 100:1500, add hydrochloric acid aqueous solution to adjust the pH to 3, stir at room temperature at a stirring speed of 100 rpm for 2 hours, centrifuge at a centrifugal speed of 11000 rpm for 30 minutes, take the precipitate, add the precipitate to 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 room temperature at a stirring speed of 100 rpm for 2 hours, centrifuge at a centrifugal speed of 11000 rpm for 30 minutes, take the precipitate, freeze-dry, control the freeze-drying temperature to be -45°C and the time to be 48 hours to obtain the filler;

[0051] The D90 particle size of the silicon dioxide is 40 nm;

[0052] The first polyacrylic acid aqueous solution and the second polyacrylic acid aqueous solution were both prepared by mixing polyacrylic acid and deionized water in a mass ratio of 10:1000, stirring at room temperature at a stirring speed of 100 rpm for 30 minutes, and then adjusting the pH to 8 using sodium hydroxide;

[0053] The number average molecular weight of the polyacrylic acid in the first polyacrylic acid aqueous solution and the second polyacrylic acid aqueous solution is 450,000;

[0054] The polyvinyl pyrrolidone aqueous solution is prepared by mixing polyvinyl pyrrolidone and deionized water in a mass ratio of 10:1000, stirring at room temperature at a stirring speed of 100 rpm for 30 minutes, and then adjusting the pH to 8 using sodium hydroxide;

[0055] The number average molecular weight of polyvinyl pyrrolidone in the polyvinyl pyrrolidone aqueous solution is 50,000;

[0056] The molar concentration of the hydrochloric acid aqueous solution is 1 mol / L;

[0057] Step 3. Thermoplasticization: corn starch, glycerol, gelatin, and tea polyphenol calcium salt are mixed uniformly in a mass ratio of 100:27:16:1.8 and pre-plasticized. The pre-plasticization temperature is controlled at 90° C. for 4 hours, and then added to a twin-screw extruder for extrusion granulation. During the extrusion granulation, the temperature of the first zone of the twin-screw extruder is controlled at 90° C., the temperature of the second zone is controlled at 110° C., the temperature of the third zone is controlled at 120° C., the temperature of the fourth zone is controlled at 130° C., the temperature of the fifth zone is controlled at 130° C., the temperature of the sixth zone is controlled at 135° C., the temperature of the seventh zone is controlled at 135° C., and the screw speed is controlled at 150 rpm to obtain thermoplasticized starch;

[0058] Step 4. Film preparation: The thermoplasticized starch, PBAT, maleic anhydride, chain extender, and filler are mixed in a mass ratio of 85:13:3:0.4:9 and then added to a twin-screw extruder for extrusion granulation. The temperature of zone 1 of the twin-screw extruder is controlled to be 130°C, the temperature of zone 2 is 135°C, the temperature of zone 3 is 140°C, the temperature of zone 4 is 145°C, the temperature of zone 5 is 150°C, the temperature of zone 6 is 155°C, the temperature of zone 7 is 160°C, the temperature of zone 8 is 165°C, the temperature of zone 9 is 160°C, and the screw speed is 50 rpm to obtain a mixed masterbatch, which is then added to a film blowing machine for film blowing. The film blowing temperature is controlled to be 130°C to obtain a rapidly degradable starch-based fully biodegradable mulch film with a thickness of 18 μm.

[0059] The model of the chain extender is ADR-4368C.

[0060] This embodiment also provides a rapidly degradable starch-based fully biodegradable mulch film prepared by the aforementioned preparation method.

[0061] Example 2

[0062] A method for preparing a rapidly degradable starch-based fully biodegradable mulch film, specifically comprising:

[0063] Step 1. Preparing tea polyphenol calcium salt: adding tea polyphenol to an ethanol aqueous solution, controlling the mass ratio of tea polyphenol to the ethanol aqueous solution to be 10:1500, stirring at room temperature at a stirring speed of 200 rpm for 35 minutes, adding calcium chloride, controlling the mass ratio of tea polyphenol to calcium chloride to be 10:105, adding ammonia water to adjust the pH to 7.5, continuing stirring for 1.5 hours, standing at room temperature for 50 minutes, centrifuging at a centrifugal speed of 12000 rpm for 25 minutes, taking the precipitate, and freeze-drying, controlling the freeze-drying temperature to -40°C and the time to be 50 hours, to obtain tea polyphenol calcium salt;

[0064] The volume fraction of the ethanol aqueous solution is 80%;

[0065] The mass fraction of the ammonia water is 5%;

[0066] Step 2. Prepare filler: add silica to the first polyacrylic acid aqueous solution, control the mass ratio of silica to the first polyacrylic acid aqueous solution to be 100:1100, stir at room temperature at a stirring speed of 200 rpm for 3.5 hours, centrifuge at a centrifugal speed of 12000 rpm for 35 minutes, take the precipitate, add the precipitate to polyvinyl pyrrolidone aqueous solution, control the mass ratio of silica to polyvinyl pyrrolidone aqueous solution to be 100:1600, add hydrochloric acid aqueous solution to adjust the pH to 3.5, and centrifuge at room temperature at 200 rpm. The mixture was stirred at a stirring speed of 200 rpm for 2.5 hours, centrifuged at a centrifugal speed of 12000 rpm for 35 minutes, and a precipitate was taken. The precipitate was added to the second portion of the polyacrylic acid aqueous solution, and the mass ratio of the silica and the second portion of the polyacrylic acid aqueous solution was controlled to be 100:1100. A hydrochloric acid aqueous solution was added to adjust the pH to 3.5. The mixture was stirred at a stirring speed of 200 rpm for 2.5 hours at room temperature, and centrifuged at a centrifugal speed of 12000 rpm for 35 minutes. The precipitate was taken and freeze-dried. The freeze-drying temperature was controlled to be -40°C and the time was controlled to be 50 hours to obtain a filler.

[0067] The D90 particle size of the silicon dioxide is 40 nm;

[0068] The first polyacrylic acid aqueous solution and the second polyacrylic acid aqueous solution were both prepared by mixing polyacrylic acid and deionized water in a mass ratio of 10:1050, stirring at room temperature at a stirring speed of 200 rpm for 35 minutes, and then adjusting the pH to 8.5 using sodium hydroxide;

[0069] The number average molecular weight of the polyacrylic acid in the first polyacrylic acid aqueous solution and the second polyacrylic acid aqueous solution is 450,000;

[0070] The polyvinyl pyrrolidone aqueous solution is prepared by mixing polyvinyl pyrrolidone and deionized water in a mass ratio of 10:1050, stirring at room temperature at a stirring speed of 200 rpm for 35 minutes, and then adjusting the pH to 8.5 using sodium hydroxide;

[0071] The number average molecular weight of polyvinyl pyrrolidone in the polyvinyl pyrrolidone aqueous solution is 50,000;

[0072] The molar concentration of the hydrochloric acid aqueous solution is 1 mol / L;

[0073] Step 3. Thermoplasticization: corn starch, glycerol, gelatin, and tea polyphenol calcium salt are uniformly mixed in a mass ratio of 100:28:17:1.9 and pre-plasticized. The pre-plasticization temperature is controlled at 90° C. for 4.5 hours, and then added to a twin-screw extruder for extrusion granulation. During the extrusion granulation, the temperature of zone 1 of the twin-screw extruder is controlled at 90° C., the temperature of zone 2 is controlled at 110° C., the temperature of zone 3 is controlled at 120° C., the temperature of zone 4 is controlled at 130° C., the temperature of zone 5 is controlled at 130° C., the temperature of zone 6 is controlled at 135° C., the temperature of zone 7 is controlled at 135° C., and the screw speed is controlled at 150 rpm to obtain thermoplasticized starch;

[0074] Step 4. Film preparation: The thermoplasticized starch, PBAT, maleic anhydride, chain extender, and filler are mixed in a mass ratio of 85:14:3.4:0.5:10 and then added to a twin-screw extruder for extrusion granulation. The temperature of zone 1 of the twin-screw extruder is controlled to be 130°C, the temperature of zone 2 is 135°C, the temperature of zone 3 is 140°C, the temperature of zone 4 is 145°C, the temperature of zone 5 is 150°C, the temperature of zone 6 is 155°C, the temperature of zone 7 is 160°C, the temperature of zone 8 is 165°C, the temperature of zone 9 is 160°C, and the screw speed is 50 rpm to obtain a mixed masterbatch, which is then added to a film blowing machine for film blowing. The film blowing temperature is controlled to be 130°C to obtain a rapidly degradable starch-based fully biodegradable mulch film with a thickness of 18 μm.

[0075] The model of the chain extender is ADR-4368C.

[0076] This embodiment also provides a rapidly degradable starch-based fully biodegradable mulch film prepared by the aforementioned preparation method.

[0077] Example 3

[0078] A method for preparing a rapidly degradable starch-based fully biodegradable mulch film, specifically comprising:

[0079] Step 1. Preparing tea polyphenol calcium salt: adding tea polyphenol to an ethanol aqueous solution, controlling the mass ratio of tea polyphenol to the ethanol aqueous solution to be 10:1600, stirring at room temperature at a stirring speed of 400 rpm for 40 minutes, adding calcium chloride, controlling the mass ratio of tea polyphenol to calcium chloride to be 10:110, adding ammonia water to adjust the pH to 7.7, continuing stirring for 1.5 hours, standing at room temperature for 60 minutes, centrifuging at a centrifugal speed of 12000 rpm for 30 minutes, taking the precipitate, and freeze-drying, controlling the freeze-drying temperature to -40°C and the time to be 52 hours, to obtain tea polyphenol calcium salt;

[0080] The volume fraction of the ethanol aqueous solution is 80%;

[0081] The mass fraction of the ammonia water is 5%;

[0082] Step 2. Prepare the filler: add silica to the first polyacrylic acid aqueous solution, control the mass ratio of silica to the first polyacrylic acid aqueous solution to be 100:1200, stir at room temperature at a stirring speed of 400 rpm for 4 hours, centrifuge at a centrifugal speed of 12000 rpm for 40 minutes, take the precipitate, add the precipitate to a polyvinyl pyrrolidone aqueous solution, control the mass ratio of silica to polyvinyl pyrrolidone aqueous solution to be 100:1700, add hydrochloric acid aqueous solution to adjust the pH to 3.5, stir at room temperature at a stirring speed of 400 rpm for 3 hours, centrifuge at a centrifugal speed of 12000 rpm for 40 minutes, take the precipitate, add the precipitate to the second polyacrylic acid aqueous solution, control the mass ratio of silica to the second polyacrylic acid aqueous solution to be 100:1200, add hydrochloric acid aqueous solution to adjust the pH to 3.5, stir at room temperature at a stirring speed of 400 rpm for 3 hours, centrifuge at a centrifugal speed of 12000 rpm for 40 minutes, take the precipitate, freeze-dry, control the freeze-drying temperature to be -40°C and the time to be 52 hours to obtain the filler;

[0083] The D90 particle size of the silicon dioxide is 40 nm;

[0084] The first polyacrylic acid aqueous solution and the second polyacrylic acid aqueous solution were both prepared by mixing polyacrylic acid and deionized water in a mass ratio of 10:1100, stirring at room temperature at a stirring speed of 400 rpm for 40 minutes, and then adjusting the pH to 8.5 using sodium hydroxide;

[0085] The number average molecular weight of the polyacrylic acid in the first polyacrylic acid aqueous solution and the second polyacrylic acid aqueous solution is 450,000;

[0086] The polyvinyl pyrrolidone aqueous solution is prepared by mixing polyvinyl pyrrolidone and deionized water in a mass ratio of 10:1100, stirring at a stirring speed of 400 rpm at room temperature for 40 minutes, and then adjusting the pH to 8.5 using sodium hydroxide;

[0087] The number average molecular weight of polyvinyl pyrrolidone in the polyvinyl pyrrolidone aqueous solution is 50,000;

[0088] The molar concentration of the hydrochloric acid aqueous solution is 1 mol / L;

[0089] Step 3. Thermoplasticization: corn starch, glycerol, gelatin, and tea polyphenol calcium salt are mixed uniformly in a mass ratio of 100:30:18:2 and pre-plasticized. The pre-plasticization temperature is controlled at 95°C for 5 hours, and then added to a twin-screw extruder for extrusion granulation. During the extrusion granulation, the temperature of zone 1 of the twin-screw extruder is controlled at 95°C, the temperature of zone 2 is 115°C, the temperature of zone 3 is 125°C, the temperature of zone 4 is 135°C, the temperature of zone 5 is 135°C, the temperature of zone 6 is 140°C, the temperature of zone 7 is 140°C, and the screw speed is 200 rpm to obtain thermoplasticized starch;

[0090] Step 4. Film preparation: The thermoplasticized starch, PBAT, maleic anhydride, chain extender, and filler are mixed in a mass ratio of 85:15:3.5:0.6:11 and then added to a twin-screw extruder for extrusion granulation. The temperature of zone 1 of the twin-screw extruder is controlled to be 135°C, the temperature of zone 2 is 140°C, the temperature of zone 3 is 145°C, the temperature of zone 4 is 150°C, the temperature of zone 5 is 155°C, the temperature of zone 6 is 160°C, the temperature of zone 7 is 165°C, the temperature of zone 8 is 170°C, the temperature of zone 9 is 165°C, and the screw speed is 60 rpm to obtain a mixed masterbatch, which is then added to a film blowing machine for film blowing. The film blowing temperature is controlled to be 135°C to obtain a rapidly degradable starch-based fully biodegradable mulch film with a thickness of 18 μm.

[0091] The model of the chain extender is ADR-4368C.

[0092] This embodiment also provides a rapidly degradable starch-based fully biodegradable mulch film prepared by the aforementioned preparation method.

[0093] Comparative Example 1

[0094] Based on the method for preparing the rapidly degradable starch-based fully biodegradable mulch film described in Example 2, step 1. preparing tea polyphenol calcium salt is omitted, and in step 3. thermoplasticization, tea polyphenols of equal mass are used instead of adding tea polyphenol calcium salt.

[0095] The remaining operations remain the same as in Example 2.

[0096] The thickness of the rapidly degradable starch-based fully biodegradable mulch film prepared in this comparative example is 18 μm.

[0097] Comparative Example 2

[0098] Based on the method for preparing the rapidly degradable starch-based fully biodegradable mulch film described in Example 2, step 1. preparing tea polyphenol calcium salt is omitted, and in step 3. thermoplasticization, the addition of tea polyphenol calcium salt is omitted.

[0099] The remaining operations remain the same as in Example 2.

[0100] The thickness of the rapidly degradable starch-based fully biodegradable mulch film prepared in this comparative example is 18 μm.

[0101] Comparative Example 3

[0102] Based on the preparation method of the rapidly degradable starch-based fully biodegradable mulch film described in Example 2, in step 3. thermal plasticization, the addition of gelatin is omitted.

[0103] The remaining operations remain the same as in Example 2.

[0104] The thickness of the rapidly degradable starch-based fully biodegradable mulch film prepared in this comparative example is 18 μm.

[0105] Comparative Example 4

[0106] Based on the method for preparing the rapidly degradable starch-based fully biodegradable mulch film described in Example 2, step 2. preparing the filler is omitted, and in step 4. film making, silicon dioxide with a D90 particle size of 40 nm is used instead of the filler.

[0107] The remaining operations remain the same as in Example 2.

[0108] The thickness of the rapidly degradable starch-based fully biodegradable mulch film prepared in this comparative example is 18 μm.

[0109] Performance Test Example 1

[0110] In Examples 1-3 and Comparative Examples 1-4, the melt flow rate of the mixed masterbatch was tested in the film-making step. During the test, referring to GB / T3682.1-2018 standard, the test temperature was 190° C., and the load was 2.16 kg. The test results are shown in Table 1:

[0111] Table 1

[0112]

[0113] It can be seen from the above results that the melt flow rates of the mixed masterbatches of Comparative Examples 2-4 are lower than those of Example 2, indicating that tea polyphenol calcium salt, gelatin and filler can all increase the melt flow rate of the mixed masterbatch.

[0114] Performance Test Example 2

[0115] The water contact angles of the rapidly degradable starch-based fully biodegradable mulch films prepared in Examples 1-3 and Comparative Examples 1-4 were tested. The test results are shown in Table 2:

[0116] Table 2

[0117]

[0118] The above results show that the water contact angles of the rapidly degradable starch-based fully biodegradable mulch films of Comparative Examples 1-4 are lower than those of Example 2, indicating that tea polyphenol calcium salt, gelatin, and fillers can all improve the water resistance of the rapidly degradable starch-based fully biodegradable mulch films.

[0119] Performance Test 3

[0120] In Examples 1-3 and Comparative Examples 1-4, the Vicat softening point of the mixed masterbatch was tested in the film-making step. The test was conducted with reference to the GB / T1633-2000 standard. The test results are shown in Table 3:

[0121] Table 3

[0122]

[0123] It can be seen from the above results that the Vicat softening points of the mixed masterbatches of Comparative Examples 2-4 are lower than those of Example 2, indicating that tea polyphenol calcium salt, gelatin and fillers can all increase the Vicat softening point of the mixed masterbatch.

[0124] Performance Test 4

[0125] 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. The GB / T1040-2006 standard was used as a reference during the test. The test results are shown in Table 4:

[0126] Table 4

[0127]

[0128] The above results show that the tensile strength and elongation at break of the rapidly degradable starch-based fully biodegradable mulch films of Comparative Examples 1-4 are lower than those of Example 2. This indicates that tea polyphenol calcium salt, gelatin, and fillers can all improve the tensile strength and elongation at break of the rapidly degradable starch-based fully biodegradable mulch films.

[0129] Performance Test 5

[0130] The rapidly degradable starch-based fully biodegradable mulch films prepared in Examples 1-3 and Comparative Examples 1-4 were observed to see if they had phase separation problems. The rapidly degradable starch-based fully biodegradable mulch films prepared in Examples 1-3 and Comparative Examples 1-4 were placed at 60° C. for 10 days to see if there was plasticizer precipitation on the surface. The results are shown in Table 5:

[0131] Table 5

[0132]

[0133] The above results show that compared with Example 2, the rapidly degradable starch-based fully biodegradable mulch films of Comparative Examples 1-2 and 4 all had phase separation problems or plasticizer precipitation problems after standing. This indicates that tea polyphenol calcium salt and fillers can avoid phase separation and plasticizer precipitation problems.

[0134] Performance Test 6

[0135] 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 40 cm × 30 cm test samples. Three test samples of each mulch film were taken, weighed and marked, respectively, and placed in 100-mesh bags. The bags were buried in a 10 cm deep soil layer. After 60 days, 90 days, and 110 days of burial, one of the test samples was taken out and weighed, and the mass loss rate was calculated. The test was repeated 5 times according to the above method, and the average value was taken. The results are shown in Table 6:

[0136] Table 6

[0137]

[0138] The above results show that the degradation rates of the rapidly degradable starch-based fully biodegradable mulch films of Comparative Examples 2 and 4 are lower than those of Example 2, indicating that both tea polyphenol calcium salt and filler improve the degradation rate of the rapidly degradable starch-based fully biodegradable mulch films.

Claims

1. A method for preparing a rapidly degradable starch-based fully biodegradable mulch film, characterized in that: include: Preparation of tea polyphenol calcium salt, preparation of filler, thermal plasticization, and film making; The preparation of tea polyphenol calcium salt comprises adding tea polyphenol to an ethanol aqueous solution, stirring at room temperature, adding calcium chloride, adjusting the pH to 7.4-7.7, continuing stirring, standing at room temperature, centrifuging, collecting a precipitate, and freeze-drying to obtain tea polyphenol calcium salt; The filler is prepared by adding silica to a first portion of a polyacrylic acid aqueous solution, stirring at room temperature, centrifuging, collecting a precipitate, adding the precipitate to a polyvinyl pyrrolidone aqueous solution, adjusting the pH to 3-3.5, stirring at room temperature, centrifuging, collecting a precipitate, adding the precipitate to a second portion of a polyacrylic acid aqueous solution, adjusting the pH to 3-3.5, stirring at room temperature, centrifuging, collecting a precipitate, and freeze-drying to obtain the filler; The heat plasticization comprises pre-plasticizing the mixture of corn starch, glycerol, gelatin and tea polyphenol calcium salt after uniform mixing, and then adding the mixture into a twin-screw extruder for extrusion granulation to obtain heat plasticized starch; The film making comprises mixing thermoplasticized starch, PBAT, maleic anhydride, a chain extender, and a filler uniformly, adding the mixture into a twin-screw extruder for extrusion granulation to obtain a mixed masterbatch, and then adding the mixed masterbatch into a film blowing machine for film blowing to obtain a rapidly degradable starch-based fully biodegradable mulch film; In the film preparation, 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.

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

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

4. The method for preparing a rapidly degradable starch-based fully biodegradable mulch film according to claim 1, characterized in that: In the preparation of the filler, the first polyacrylic acid aqueous solution and the second polyacrylic acid aqueous solution are both prepared by mixing polyacrylic acid and deionized water in a mass ratio of 10:1000-1100, stirring at room temperature, and then adjusting the pH to 8-8.5; The number average molecular weight of the polyacrylic acid in the first polyacrylic acid aqueous solution and the second polyacrylic acid aqueous solution are both 450,000.

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

6. The method for preparing a rapidly degradable starch-based fully biodegradable mulch film according to claim 1, characterized in that: In the thermal plasticization, the mass ratio of corn starch, glycerol, gelatin and tea polyphenol calcium salt is 100:27-30:16-18:1.8-2; The pre-plasticization temperature is 90-95° C. and the time is 4-5 hours.

7. The method for preparing a rapidly degradable starch-based fully biodegradable mulch film according to claim 1, characterized in that: During the thermal plasticization, the temperature of zone 1 of the twin-screw extruder in the extrusion granulation is 90-95°C, the temperature of zone 2 is 110-115°C, the temperature of zone 3 is 120-125°C, the temperature of zone 4 is 130-135°C, the temperature of zone 5 is 130-135°C, the temperature of zone 6 is 135-140°C, the temperature of zone 7 is 135-140°C, and the screw speed is 150-200rpm.

8. The method for preparing a rapidly degradable starch-based fully biodegradable mulch film according to claim 1, characterized in that: In the film preparation, the model of the chain extender is ADR-4368C.

9. The method for preparing a rapidly degradable starch-based fully biodegradable mulch 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 50-60rpm; The temperature of the film blowing 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 to 9.

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