Self-repairing bio-based coating material with consideration of nutrient controlled release and film shell degradation and preparation method thereof

Abstract

The application discloses a self-repairing bio-based coating material considering nutrient controlled release and film shell degradation and a preparation method thereof, and belongs to the technical field of controlled-release fertilizer production.The self-repairing bio-based coating material comprises the following raw materials in parts by weight: easily-degradable polyester polyol 80-100 parts, crosslinking promoter 30-50 parts and functional chain extender 10-20 parts.The self-repairing bio-based coating material is synthesized by reacting the easily-degradable polyester polyol with the crosslinking promoter and the functional chain extender, and has the advantages that the self-repairing bio-based coating material can improve the toughness of the film material, promote the rapid repair of the damaged area, and improve the stability of nutrient release; and the degradation process of the film material can cause a chain reaction of structure fracture, thereby improving the degradation rate of the film shell after the complete release of nutrients.The application effectively solves the problem that the film shell degradation performance and the nutrient controlled release performance are difficult to coexist.

Description

Technical Field

[0001] This invention relates to the field of controlled-release fertilizer production technology, specifically to a self-healing bio-based coating material that combines nutrient controlled release and membrane degradation, and its preparation method. Background Technology

[0002] Bio-based coated controlled-release fertilizers feature the characteristic of slow, controlled nutrient release, which can significantly improve nutrient utilization. However, bio-based coated controlled-release fertilizers have the following problems, hindering the industry's progress and development: (1) Bio-based membrane materials have poor toughness and low strength, and are easily damaged by external factors, resulting in nutrient leakage and reduced nutrient control efficiency. In the large-scale production of controlled-release fertilizers, friction between fertilizers and between fertilizers and equipment causes damage.

[0003] (2) It is impossible to achieve both stable controlled-release performance and excellent degradation performance. After the nutrients in many controlled-release fertilizers are released, the membrane shell cannot be effectively degraded in a short period of time. During the slow degradation process, microplastics are easily generated, which remain in the soil for a long time and harm the soil ecology and human health.

[0004] To address the aforementioned problems with coated controlled-release fertilizers, patent CN119263918A discloses a yield-enhancing, fully biodegradable controlled-release fertilizer and its preparation method. This involves reacting a carrier-functional slow-release composite, a fully biodegradable resin, and a solvent to obtain a coating material with both yield-enhancing and excellent degradation functions. The principle is that cross-linking into the easily degradable resin within the reaction system promotes degradation in the environment. While this degradation effect is green and pollution-free, the bio-based membrane shell prepared from this material has strong hydrophilicity, leading to a decrease in controlled-release performance. Patent CN118271131A discloses a self-healing modified lignin-based polyester polyol coating material and its preparation method. This involves the stepwise reaction of lignin polyester polyol, an accelerator, and a self-healing adhesive to obtain a lignin-based coated fertilizer with self-healing functions. The principle is to embed dynamic covalent bonds into the polyurethane network, extending the molecular chain while improving molecular mobility. Although this technology can improve the toughness and strength of the membrane material, it cannot achieve effective degradation of the membrane shell after nutrient release. The relevant patent CN114621415A discloses a two-component polyol-degradable polyurethane-coated controlled-release fertilizer and its preparation method and application. A degradable bio-based polyurethane membrane is synthesized through the reaction of polyester polyol, biomass polyol and curing agent. The principle is to optimize the reaction structure arrangement by crosslinking modification of polyester polyol and liquefied biomass polyol, which promotes the phased degradation effect. Although degradation is achieved under the condition of ensuring controlled-release performance, the degradation efficiency is achieved in three steps, and the actual degradation effect is poor. Summary of the Invention

[0005] To address the problems existing in the prior art, the purpose of this invention is to provide a self-healing bio-based coating material that combines controlled nutrient release and membrane degradation, as well as its preparation method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a self-healing bio-based coating material that combines nutrient controlled release and membrane degradation, comprising the following raw materials in parts by weight: 80-100 parts of easily degradable polyester polyol, 30-50 parts of crosslinking accelerator, and 10-20 parts of functional chain extender; The functional chain extender is obtained by blending a first component and a second component in a molar ratio of 1:(1-3); the first component is one or more of thiamine disulfide, captopril disulfide, and ethyl 2-chloro-2-(oxime)acetate; the second component is one or more of polytetrahydrofuran, polycarbonate diol, and polycaprolactone diol.

[0007] Preferably, the biodegradable polyester polyol is obtained by reacting component A and component B in a molar ratio of (0.5-1.5):(0.5-1.5); component A is one or more of aspartic acid, glutamic acid, and lysine; and component B is one or more of soybean oil polyol and flaxseed oil polyol.

[0008] Preferably, the crosslinking agent is selected from one or more of isophthalic diisocyanate, 4-chloro-6-methyl-m-phenylene diisocyanate, and 2,4-difluorophenyl isocyanate.

[0009] In some preferred embodiments of the present invention, the reaction conditions for the readily degradable polyester polyol are as follows: After mixing components A and B, p-toluenesulfonic acid and toluene are added, and the mixture is heated to 140-160℃ under nitrogen protection and reacted for 6-8 hours; then cooled to 80℃ and reacted for 20-40 minutes.

[0010] In some preferred embodiments of the present invention, the blending conditions of the functional chain extender are as follows: Mix the first component with the vacuum-dried second component and stir continuously at 40-60℃ for 20-40 minutes.

[0011] A second aspect of the present invention provides a method for preparing the above-mentioned self-healing bio-based coating material that combines nutrient controlled release and membrane degradation, comprising the following steps: Easily degradable polyester polyols are added to organic solvents and stirred until the solution is homogeneous. Then, functional chain extenders are added, and the mixture is stirred continuously at 40-50°C for 0.5-1.5 hours under nitrogen protection to generate an intermediate. The intermediate was added to the crosslinking agent, and dibutyltin dilaurate was added dropwise. The mixture was stirred rapidly until a large number of bubbles were generated. An organic solvent was added, followed by nitrogen gas. The mixture was stirred slowly for 3-5 minutes. The mixed solution was then vacuum dried. After the bubbles disappeared, the self-healing bio-based coating material was obtained.

[0012] Preferably, the organic solvent is N,N-dimethylformamide or acetone.

[0013] A third aspect of the present invention provides the application of the above-mentioned self-healing bio-based coating material that combines nutrient controlled release and membrane degradation in the preparation of controlled-release fertilizers.

[0014] In a fourth aspect, the present invention provides a coated controlled-release fertilizer, comprising a fertilizer core and the aforementioned self-healing bio-based coating material that combines nutrient controlled release and membrane degradation, sprayed onto the surface of the fertilizer core.

[0015] Preferably, the amount of self-healing bio-based coating material that balances nutrient controlled release and membrane degradation accounts for 1-5% of the fertilizer core weight.

[0016] The beneficial effects of this invention are: (1) This invention improves the toughness and elasticity of the bio-based membrane shell, solves the problem of fertilizer damage caused by friction between fertilizer and fertilizer and between fertilizer and equipment during the production and transportation of controlled-release fertilizer, and ensures the stability of nutrient release.

[0017] (2) This invention coordinates the issues of nutrient release and membrane degradation. Covalent bonds are not soaked by water in a short time, resulting in low degradation efficiency. At this time, stable nutrient release is ensured. After the nutrients are fully released, the covalent bonds are fully soaked by water and begin to hydrolyze, and the membrane begins to degrade. The bio-based membrane of this invention can achieve a degradation rate of about 50% in 180 days, with fast degradation speed and high degradation efficiency.

[0018] In summary, this invention synthesizes a bio-based coating material that balances nutrient controlled release and membrane degradation by reacting readily degradable amino acids with plant oil polyols to form readily degradable polyester polyols, and then reacting these with crosslinking promoters, degradation chain extenders, and curing agents. This membrane structure exhibits excellent molecular mobility, and the readily degradable chemical bonds and amino acid structures are located at the reaction sites of each component. This structure not only enhances the membrane's toughness and promotes rapid repair of damaged areas, but more importantly, the degradation process triggers a chain reaction of structural breakage, improving degradation efficiency, the stability of nutrient release, and the degradation rate of the membrane shell after complete nutrient release. Attached Figure Description

[0019] Figure 1 Fourier transform infrared spectroscopy results of the self-healing bio-based coating materials prepared in Examples 1-3 of this invention.

[0020] Figure 2 The mechanical properties of the bio-based coating materials prepared in Example 1 and Comparative Example 1 of this invention were tested.

[0021] Figure 3 The results of the weight change of the bio-based coated controlled-release fertilizer prepared in Example 4 and Comparative Example 1 after complete release and absorption of water.

[0022] Figure 4 The results of volume change of the bio-based coated controlled-release fertilizer prepared in Example 4 and Comparative Example 1 after complete release and absorption of water.

[0023] Figure 5 Example 1 and conventional bio-based fertilizer film shells were degraded for 180 days, and the surface images of the polyurethane coatings were observed under a scanning electron microscope (SEM).

[0024] Figure 6 The degradation weight loss rate of the membrane shells in Comparative Examples 1-3 and Example 4 of this invention.

[0025] Figure 7 Nutrient release curves of the coated controlled-release fertilizers prepared in Examples 4-6 and Comparative Examples 1-3 of this invention.

[0026] Figure 8 Nutrient release curves before and after damage of the coated controlled-release fertilizer prepared in Example 4 and Comparative Example 1 of this invention. Detailed Implementation

[0027] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0028] As mentioned earlier, some agricultural wastes can be synthesized into bio-based raw materials through liquefaction and purification to prepare bio-based controlled-release fertilizers. These materials have advantages such as low cost and wide availability. However, the membranes made from these bio-based materials have poor toughness and low strength, which leads to unstable nutrient release and affects the matching degree between nutrient release and crop fertilizer requirements and nutrient utilization rate. Moreover, after the nutrients are fully released, the degradation rate of the membrane is slow, causing the accumulation of membranes in the soil and affecting the ecological environment.

[0029] In view of this, the present invention has developed a self-healing bio-based coating material that combines nutrient controlled release and membrane degradation. The present invention constructs a novel triblock structure, which crosslinks easily degradable molecular structures to the reaction sites of each component through reaction, thereby improving degradation efficiency and solving the problems of difficult and slow membrane degradation, thus alleviating the pressure on the soil environment. Furthermore, crosslinking functional chain extenders into the structure can improve molecular migration efficiency and exchange capacity, increase the toughness and strength of the membrane material, and has the function of repairing damaged areas, solving the problem of premature nutrient release caused by membrane damage and improving nutrient utilization.

[0030] The self-healing bio-based coating material of the present invention, which combines nutrient controlled release and membrane degradation, is prepared by reacting readily degradable polyester polyol, crosslinking agent, and functional chain extender. In one embodiment of the present invention, a method for preparing the self-healing bio-based coating material that combines nutrient controlled release and membrane degradation is provided, as follows: The biodegradable polyester polyol was added to an organic solvent and stirred until the solution was homogeneous. The solution was then added to a three-necked flask, followed by the addition of a functional chain extender. A magnetic stirrer was connected, and nitrogen gas was introduced to purge air. The mixture was stirred continuously at 45°C for 1 hour to generate an intermediate. The intermediate was added to the crosslinking agent, and dibutyltin dilaurate was added dropwise. The mixture was stirred rapidly until a large number of bubbles were generated. An organic solvent was added, followed by nitrogen gas. The mixture was stirred slowly for 3-5 minutes. The mixed solution was placed in a vacuum drying oven and dried under vacuum at 30°C for 5 minutes. After the bubbles disappeared, a self-healing bio-based coating material that combines nutrient controlled release and membrane degradation was obtained.

[0031] The coating material of this invention has high strength, high elasticity, stable nutrient release rate, and excellent degradation performance. The mechanism of action of the coating material of this invention is as follows: The first component in a functional chain extender primarily provides dynamic covalent bonds. The migration and recombination of these dynamic covalent bonds, which are broken due to membrane damage, are a crucial factor in determining the repair effect. The second component is a low molecular weight diol, which has a relatively low crosslinking density compared to high molecular weight polyester polyols. The addition of the second component is beneficial to improving the migration rate of molecular chains (the repair effect is closely related to the molecular migration rate). After the first and second components of the functional chain extender are mixed in an organic solvent, the functional small molecules (dynamic covalent bonds) are uniformly distributed in the solution. After the functional chain extender is added to the easily degradable polyester polyol, the uniformity of the functional small molecules is further improved, generating a viscous intermediate. During the reaction of the intermediate with the crosslinking promoter, due to electrostatic interaction, the easily degradable amino acid structure, ester structure, and functional small molecule structure are attracted to both sides by the crosslinking promoter, forming a triblock bridge structure. This structure not only effectively ensures that the functional small molecules are uniformly distributed in the entire network structure, but also that the easily degradable bonds are all located at the reaction sites of the network structure. The breaking of bonds during degradation will promote the decomposition of the overall structure, significantly improving the degradation efficiency.

[0032] The membrane repair process mainly occurs during production, transportation, and application. These three processes are susceptible to external influences that can damage the controlled-release membrane, and the repair function primarily operates in these three stages. In the damaged region of the membrane, the dynamic covalent bonds and hydrogen bonds in the network structure break due to structural damage. However, these dynamic covalent bonds and hydrogen bonds can spontaneously recombine, allowing the broken network structure to gradually recover and ultimately promoting the self-repair of the damaged membrane.

[0033] When fertilizer is applied to the soil, the dynamic disulfide bonds are very sensitive and easily attacked by microorganisms and some enzymes in the soil. After being attacked, the dynamic disulfide bonds will break or even decompose. After the nutrients are completely released, this process will gradually accelerate. The breaking of dynamic disulfide bonds will promote the breakage of the entire network structure, thereby promoting degradation.

[0034] In summary, addressing the problems of poor membrane toughness, low strength, slow degradation, and poor degradation efficiency in the large-scale application of existing bio-based coated controlled-release fertilizers, this invention innovatively synthesizes easily degradable polyester polyols and innovatively adds functional chain extenders to the coating material. These added functional chain extenders not only endow the membrane with the ability to repair damaged areas but also significantly enhance the fertilizer's strength. More importantly, the functional small molecules provided by the chain extenders also possess easily degradable properties. During the degradation process of the bio-based membrane, the functional chain extenders and easily degradable polyester polyols have a synergistic effect. The functional chain extenders and easily degradable polyester polyols react with crosslinking agents to construct a novel triblock bridge structure, significantly improving the damage resistance, toughness, and elasticity of the bio-based membrane while also maintaining excellent degradation capabilities.

[0035] To enable those skilled in the art to better understand the technical solution of this application, the technical solution of this application will be described in detail below with reference to specific embodiments.

[0036] The test materials used in the embodiments and comparative examples of this invention are all conventional test materials in the art and can be purchased through commercial channels. Specifically: Soybean oil polyols were purchased from Guangzhou Haierma Vegetable Oil Co., Ltd., and flaxseed oil polyols were purchased from Jiangxi Xinsen Natural Vegetable Oil Co., Ltd.

[0037] Thiamine disulfide: 67-16-3; Captopril disulfide: 64806-05-9; Ethyl 2-chloro-2-(oxime)ethyl acetate: 14337-43-0; Polytetrahydrofuran: 25190-06-1; Polycarbonate diol: 24937-06-2; Polycaprolactone diol: 36890-68-3.

[0038] Example 1: Preparation of a self-healing bio-based coating material that combines nutrient controlled release and membrane degradation (1) Preparation of easily degradable polyester polyols: Aspartic acid was used as component A; soybean oil polyols were used as component B. 6.65g of component A and 50g of component B were placed in a three-necked flask, and 0.57g of p-toluenesulfonic acid was added. A mechanical stirrer, a nitrogen protection system, and a water separator were connected, and 50ml of toluene was added for azeotroping. The mechanical stirrer was started, and the temperature was raised to 140℃. The nitrogen flow rate was 20ml / min, and the reaction was maintained under reflux for 8 hours. After heating was stopped, the mixture was cooled to 80℃, and the mixture was transferred to a rotary evaporator and reacted at 80℃ for 30 minutes to obtain a biodegradable polyester polyol, which was then sealed and stored.

[0039] (2) Preparation of functional chain extenders: Thiamine disulfide is used as the first component; polytetrahydrofuran is used as the second component; Place 5.62g of the first component in a beaker and add 10ml of N,N-dimethylformamide; place 20g of the second component in a beaker and then place it in a vacuum drying oven. After drying at 80℃ for half an hour, add it to the first component and stir continuously at 50℃ for 30 minutes until the mixture becomes homogeneous. Stop stirring to obtain the functional chain extender.

[0040] (3) Preparation of coating materials: Take 8g of the biodegradable polyester polyol synthesized in step (1) into a beaker, add 3ml of acetone, stir until the solution is uniform, transfer it into a three-necked flask, add 1g of the functional chain extender synthesized in step (2), connect a magnetic stirrer, purge with nitrogen to remove air, and stir continuously at 45℃ for 1h to generate an intermediate. Add 3g of crosslinking agent (m-phenylenedimethyl diisocyanate) to the intermediate, add 1 drop of dibutyltin dilaurate, stir rapidly until a large number of bubbles are generated, add 3ml of acetone, then purge with nitrogen gas, stir slowly for 3min, place the mixed solution in a vacuum drying oven, and vacuum dry at 30℃ for 5min. After the bubbles disappear, a self-healing bio-based coating material that combines nutrient controlled release and membrane degradation is obtained.

[0041] Example 2: Preparation of a self-healing bio-based coating material that combines nutrient controlled release and membrane degradation (1) Preparation of easily degradable polyester polyols: Glutamic acid is used as component A; soybean oil polyols are used as component B; 7.35g of component A and 50g of component B were placed in a three-necked flask, and 0.57g of p-toluenesulfonic acid was added. A mechanical stirrer, a nitrogen protection system, and a water separator were connected, and 50ml of toluene was added for azeotroping. The mechanical stirrer was started, and the temperature was raised to 150℃. The nitrogen flow rate was 20ml / min, and the reaction was maintained under reflux for 7 hours. After heating was stopped, the mixture was cooled to 80℃, and the mixture was transferred to a rotary evaporator and reacted at 80℃ for 30 minutes to obtain a biodegradable polyester polyol, which was then sealed and stored.

[0042] (2) Preparation of functional chain extenders: Captopril disulfide was used as the first component; polycarbonate diol was used as the second component. Place 8.64g of the first component in a beaker and add 10ml of N,N-dimethylformamide; place 20g of the second component in a beaker and place it in a vacuum drying oven. After drying at 80℃ for half an hour, add it to the first component and stir continuously at 50℃ for 30 minutes until the mixture becomes homogeneous. Stop stirring to obtain the functional chain extender.

[0043] (3) Preparation of coating materials: Take 9g of the biodegradable polyester polyol synthesized in step (1) into a beaker, add 3ml of acetone, stir until the solution is uniform, transfer it into a three-necked flask, add 1.5g of the functional chain extender synthesized in step (2), connect a magnetic stirrer, purge with nitrogen to remove air, and stir continuously at 45℃ for 1h to generate an intermediate. Add 4g of crosslinking agent (4-chloro-6-methyl-m-phenylene diisocyanate) to the intermediate, add 1 drop of dibutyltin dilaurate, stir rapidly until a large number of bubbles are generated, add 4ml of acetone, then purge with nitrogen gas, stir slowly for 4min, place the mixed solution in a vacuum drying oven, and vacuum dry at 30℃ for 5min. After the bubbles disappear, a self-healing bio-based coating material that combines nutrient controlled release and membrane degradation is obtained.

[0044] Example 3: Preparation of a self-healing bio-based coating material that combines nutrient controlled release and membrane degradation (1) Preparation of easily degradable polyester polyols: Lysine is used as component A; soybean oil polyols are used as component B. 7.3g of component A and 50g of component B were placed in a three-necked flask, and 0.57g of p-toluenesulfonic acid was added. A mechanical stirrer, a nitrogen protection system, and a water separator were connected, and then 50ml of toluene was added for azeotroping. The mechanical stirrer was started, and the temperature was raised to 160℃. The nitrogen flow rate was 20ml / min, and the reaction was maintained under reflux for 6 hours. After heating was stopped, the mixture was cooled to 80℃, and the mixture was transferred to a rotary evaporator and reacted at 80℃ for 30 minutes to obtain a biodegradable polyester polyol, which was then sealed and stored.

[0045] (2) Preparation of functional chain extenders: Ethyl 2-chloro-2-(oxime)ethyl acetate was used as the first component; polycaprolactone diol was used as the second component. Place 4.5g of the first component in a beaker, add 10ml of N,N-dimethylformamide, place 20g of the second component in a beaker, and then place the beaker in a vacuum drying oven. After drying at 80℃ for half an hour, add the second component to the first component and stir continuously at 50℃ for 30 minutes until the mixture becomes homogeneous. Stop stirring to obtain the functional chain extender.

[0046] (3) Preparation of coating materials: Take 10g of the biodegradable polyester polyol synthesized in step (1) into a beaker, add 3ml of acetone, stir until the solution is uniform, transfer it into a three-necked flask, add 2g of the functional chain extender synthesized in step (2), connect a magnetic stirrer, purge with nitrogen to remove air, and stir continuously at 45℃ for 1h to generate an intermediate. Add 5g of crosslinking agent (2,4-difluorophenyl isocyanate) to the intermediate, add 1 drop of dibutyltin dilaurate, stir rapidly until a large number of bubbles are generated, add 5ml of acetone, then purge with nitrogen gas, stir slowly for 5min, place the mixed solution in a vacuum drying oven, and vacuum dry at 30℃ for 5min. After the bubbles disappear, a self-healing bio-based coating material that combines nutrient controlled release and membrane degradation is obtained.

[0047] Example 4: Preparation of Coated Controlled-Release Fertilizer Take 2000g of polished urea granules and put them into a coating pan at 45℃. Keep the coating pan rotating at 10 rpm. Use a spray gun to spray the self-healing bio-based coating material prepared in Example 1, which combines nutrient control and membrane degradation, onto the surface of the rolling urea granules. Let it cure for 5 minutes. Each spraying amount is 0.5% of the fertilizer mass. Repeat the above spraying operation until the weight of the coating liquid accounts for 2.5% of the total weight of the urea granules, and the coated controlled-release fertilizer is obtained.

[0048] Example 5: Preparation of Coated Controlled-Release Fertilizer Take 2000g of polished urea granules and put them into a coating pan at 45℃. Keep the coating pan rotating at 12 rpm. Use a spray gun to spray the self-healing bio-based coating material prepared in Example 2, which combines nutrient control and membrane degradation, onto the surface of the rolling urea granules. Let it cure for 5 minutes. Each spraying amount is 0.5% of the fertilizer mass. Repeat the above spraying operation until the weight of the coating liquid accounts for 3% of the total weight of the urea granules, and the coated controlled-release fertilizer is obtained.

[0049] Example 6: Preparation of Coated Controlled-Release Fertilizer Take 2000g of polished urea granules and put them into a coating pan at 45℃. Keep the coating pan rotating at 15 rpm. Use a spray gun to spray the self-healing bio-based coating material prepared in Example 3, which combines nutrient control and membrane degradation, onto the surface of the rolling urea granules. Let it cure for 5 minutes. Each spraying amount is 0.5% of the fertilizer mass. Repeat the above spraying operation until the weight of the coating liquid accounts for 3.5% of the total weight of the urea granules, and the coated controlled-release fertilizer is obtained.

[0050] Comparative Example 1: Preparation of Conventional Bio-based Fertilizers (1) Take 8g of soybean oil polyol and 3g of m-phenylenedimethyl diisocyanate and mix them evenly at room temperature. Continue stirring until the solution turns white and then stop stirring to obtain a bio-based coating solution.

[0051] (2) Take 2000g of polished urea granules and put them into a coating pan at 65℃. Keep the coating pan speed at 20rps. After preheating, use a spray gun to spray the bio-based coating liquid prepared in step (1) onto the surface of the rolling urea granules. Let it solidify for 12min. Each spraying amount is 0.5% of the fertilizer mass. Repeat the above spraying operation until the weight of the coating liquid accounts for 2.5% of the total weight of the urea granules, and then the conventional bio-based fertilizer is obtained.

[0052] Comparative Example 2: The preparation method of the biodegradable polyester polyol is the same as that in Example 1, except that only thiamine disulfide is used as a functional chain extender; the coating material is prepared according to the method in Example 1.

[0053] Following the coating treatment conditions of Example 4, coated controlled-release fertilizer A was prepared.

[0054] Comparative Example 3: The preparation method of the biodegradable polyester polyol is the same as that in Example 1, except that only polytetrahydrofuran is used as a functional chain extender; the coating material is prepared according to the method in Example 1.

[0055] Following the coating treatment conditions of Example 4, coated controlled-release fertilizer B was prepared.

[0056] Experimental Example 1: The self-healing bio-based coating materials prepared in Examples 1-3 were cured to form a membrane shell. Fourier transform infrared spectroscopy was used to detect changes in characteristic functional groups within the membrane shell, and the results are as follows: Figure 1 As shown, the two characteristic peaks of polyurethane, NH group and C=O group, appear, while -NCO group completely disappears, indicating that the polyurethane coating has been formed.

[0057] Tensile tests were conducted on the membrane shell formed by the curing of the self-healing bio-based coating material prepared in Example 1 using a universal testing machine, with a tensile rate of 200 mm / s; the membrane shell formed by the curing of the bio-based coating solution in Comparative Example 1 was used as a control. The results are as follows: Figure 2 As shown, the tensile strength of the coating material prepared by the present invention can be above 700% without breaking, indicating that the self-healing bio-based coating material prepared by the present invention has good tensile properties and elasticity.

[0058] Experimental Example 2: 1. Flexibility Assessment: The absorbed weight and expansion volume of the coating are measured to assess its integrity and resilience. Specifically: The coated controlled-release fertilizers prepared in Example 4 and Comparative Example 1 were labeled, and the initial weight and volume of the coated controlled-release fertilizers were measured. Then, the labeled coated controlled-release fertilizers were immersed in water, and the weight and volume of the coated controlled-release fertilizers were measured again after 45 days. The weight increment and volume increment of the coated controlled-release fertilizers were calculated.

[0059] The results are as follows Figure 3 and Figure 4 As shown, the results indicated that, after 45 days of nitrogen release, the conventional bio-based fertilizer in Comparative Example 1 increased in weight by 8.9 mg and in volume by 19.24 mm. 3 During the same release period, the weight of the coated controlled-release fertilizer in Example 4 increased by 46.67 mg, and its volume increased by 41.66 mm. 3 The increase in weight and volume of Comparative Example 1 after absorbing water and swelling was greater than that of conventional bio-based coated fertilizers. This indicates that the coating material of the controlled-release fertilizer in Example 4 has better elasticity.

[0060] 2. Degradation performance evaluation The membrane shells of the coated controlled-release fertilizers prepared in Comparative Examples 1-3 and Example 4 were separated from the fertilizer granules, thoroughly washed, and air-dried. The dried membrane shells were then placed in mesh bags and buried 10 cm deep in farmland soil (Linyi, China; November 2024). Samples were taken at 30, 60, 90, 120, and 180 days after each treatment.

[0061] The membrane morphology of the conventional bio-based fertilizer in Comparative Example 1 and the coated controlled-release fertilizer in Example 4 after 180 days of degradation was captured using SEM. The results are as follows: Figure 5 As shown in the figure. The results show that the membrane shell of the controlled-release fertilizer in Example 4 has a more significant degradation effect.

[0062] The degradation rate of the membrane shell was calculated using weight loss, and the results are as follows: Figure 6 As shown in the figure. The results show that the membrane shell of Example 4 achieved a degradation rate of nearly 50% after 180 days, which is more than three times that of conventional bio-based fertilizers.

[0063] 3. Nutrient release assay: The nitrogen release rates of conventional bio-based fertilizers, as well as the coated controlled-release fertilizers prepared in Examples 4, 5, and 6 and Comparative Examples 1-3, were determined according to the National Standard for Slow-Release Fertilizers of the People's Republic of China GB / T 23348-2009.

[0064] The results are as follows Figure 7 As shown, the release period of conventional bio-based fertilizer is 37 days; the release period of bio-based coated fertilizer in Example 4 is 55 days; the release period of bio-based coated fertilizer in Example 5 is 64 days; the release period of bio-based coated fertilizer in Example 6 is 88 days; the release period of bio-based coated fertilizer in Comparative Example 2 is 42 days; and the release period of bio-based coated fertilizer in Comparative Example 3 is 44 days.

[0065] 4. Self-healing performance test: The coated controlled-release fertilizer granules prepared in Example 4 and Comparative Example 1 were completely punctured with a needle and left at room temperature for 24 hours. Then, 10g of the damaged fertilizer was placed in 200ml of water to test its nitrogen release rate. The coated controlled-release fertilizers prepared in Example 4 and Comparative Example 1 without puncture damage treatment were used as controls.

[0066] The results are as follows Figure 8 As shown in the figure. The results show that: after being punctured, the nutrient release of the coated controlled-release fertilizer in Comparative Example 1 was accelerated, indicating that it does not have self-repairing properties; while the nutrient release of the coated controlled-release fertilizer prepared in Example 4 was basically the same as that of the unpunctured fertilizer after being punctured, proving that the coated controlled-release fertilizer of the present invention has self-repairing properties.

[0067] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A self-healing bio-based coating material that combines controlled nutrient release and membrane degradation, characterized in that, Including the following parts by weight of raw materials: 80-100 parts of easily degradable polyester polyol, 30-50 parts of crosslinking accelerator, and 10-20 parts of functional chain extender; The readily biodegradable polyester polyol is obtained by reacting component A and component B in a molar ratio of (0.5-1.5):(0.5-1.5); component A is aspartic acid or glutamic acid; component B is soybean oil polyol or flaxseed oil polyol. The reaction conditions for the readily degradable polyester polyol are as follows: After mixing components A and B, p-toluenesulfonic acid and toluene are added, and the mixture is heated to 140-160℃ under nitrogen protection and reacted for 6-8 hours; then cooled to 80℃ and reacted for 20-40 minutes. The functional chain extender is prepared by the following method: Thiamine disulfide is used as the first component; polytetrahydrofuran is used as the second component; Place 5.62g of the first component in a beaker and add 10ml of N,N-dimethylformamide; place 20g of the second component in a beaker and place it in a vacuum drying oven. After drying at 80℃ for half an hour, add it to the first component and stir continuously at 50℃ for 30 minutes until the mixture becomes homogeneous. Stop stirring to obtain the functional chain extender. Alternatively, captopril disulfide can be used as the first component and polycarbonate diol as the second component. Place 8.64g of the first component in a beaker and add 10ml of N,N-dimethylformamide; place 20g of the second component in a beaker and place it in a vacuum drying oven. After drying at 80℃ for half an hour, add it to the first component and stir continuously at 50℃ for 30 minutes until the mixture becomes homogeneous. Stop stirring to obtain the functional chain extender. The crosslinking agent is selected from isophthalic diisocyanate or 4-chloro-6-methyl-m-phenylene diisocyanate.

2. The method for preparing the self-healing bio-based coating material according to claim 1, characterized in that, Includes the following steps: Easily degradable polyester polyols are added to organic solvents and stirred until the solution is homogeneous. Then, functional chain extenders are added, and the mixture is stirred continuously at 40-50°C for 0.5-1.5 hours under nitrogen protection to generate an intermediate. The intermediate was added to the crosslinking agent, and dibutyltin dilaurate was added dropwise. The mixture was stirred rapidly until a large number of bubbles were generated. An organic solvent was added, followed by nitrogen gas. The mixture was stirred slowly for 3-5 minutes. The mixed solution was then vacuum dried. After the bubbles disappeared, the self-healing bio-based coating material was obtained.

3. The preparation method according to claim 2, characterized in that, The organic solvent is N,N-dimethylformamide or acetone.

4. The application of the self-healing bio-based coating material according to claim 1 in the preparation of controlled-release fertilizer.

5. A coated controlled-release fertilizer, characterized in that, It includes a fertilizer core and a self-healing bio-based coating material as described in claim 1, which combines nutrient controlled release and membrane degradation, sprayed onto the surface of the fertilizer core.

6. The coated controlled-release fertilizer according to claim 5, characterized in that, The amount of self-healing bio-based coating material that balances nutrient control and membrane degradation accounts for 1-5% of the fertilizer core weight.

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