A rapidly biodegradable, fully degradable, bio-based coated controlled-release fertilizer and its preparation method

Abstract

This invention discloses a rapidly degradable bio-based coated controlled-release fertilizer and its preparation method, belonging to the field of controlled-release fertilizer production technology. The bio-based coated controlled-release fertilizer of this invention comprises: a fertilizer core and a bio-based coating material encapsulating the surface of the fertilizer core; the bio-based coating material is composed of plant oil-based alkyd resin, amino resin, and a dynamic cross-linking structure modifier. The coating of the controlled-release fertilizer of this invention can rapidly and completely degrade after the nutrients are fully released, reducing the harm to the soil ecosystem caused by microplastics generated from non-degradable or incompletely degraded fertilizer coatings. This invention uses amino resin as the curing agent for the fertilizer coating, which can eliminate the risk of isocyanate pollution to the ecological environment. Compared with commercially available coated controlled-release fertilizers that use isocyanate as the coating curing agent, this invention is more in line with the development needs of green and sustainable agriculture.

Description

Technical Field

[0001] This invention relates to the field of controlled-release fertilizer production technology, specifically to a rapidly degradable bio-based coated controlled-release fertilizer and its preparation method. Background Technology

[0002] Controlled-release fertilizers (CRFs) can effectively improve fertilizer utilization, reduce environmental pollution, and fundamentally transform agricultural production. However, with the ever-expanding market demand for CRFs, more and more CRFs will be applied to farmland soil. Therefore, further investigation into the potential associated plastic pollution risks from their application is urgently needed. While CRFs can effectively address environmental problems associated with traditional fertilization methods, such as reducing the risk of eutrophication due to nutrient leaching into water bodies and lowering greenhouse gas emissions from fertilizer decomposition, there is still a significant knowledge gap regarding the fate and form of residual CRF membranes in the soil after complete nutrient release.

[0003] Existing controlled-release fertilizers mostly use thermosetting resins as coating materials. Traditional thermosetting polymers have highly cross-linked networks, and because their covalent cross-linking networks are irreversible, traditional thermosetting materials are very difficult to degrade. The introduction of dynamic covalent bonds can endow coating materials with some special properties. There are some reports on the preparation of thermosetting materials containing dynamic covalent bonds. For example, the existing patent CN108484868B introduces dynamic covalent bonds (Se-Se bonds) into a polyurethane network system. However, this patent only focuses on exploring the effect of Se-Se bonds on the self-healing properties of polyurethane, and does not involve the effect of dynamic covalent bonds on its degradation properties. Similarly, patents CN113788711B, CN117886645B, and CN118271131A focus on exploring the effect of dynamic covalent bonds on the self-healing and reprocessability properties of thermosetting materials, but still do not explore whether dynamic covalent bonds can enhance the degradation properties of polymers. Therefore, developing a fully degradable membrane material and applying it to controlled-release fertilizers is of great significance for maintaining the balance of soil ecosystems and protecting the ecological environment. Summary of the Invention

[0004] To address the problems existing in the prior art, the purpose of this invention is to provide a rapidly degradable bio-based coated controlled-release fertilizer and its preparation method.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a rapidly biodegradable bio-based coated controlled-release fertilizer, comprising: a fertilizer core and a bio-based coating material wrapped around the surface of the fertilizer core;

[0007] The bio-based coating material is composed of plant oil-based alkyd resin, amino resin, and a dynamic crosslinking structure modifier; the dynamic crosslinking structure modifier is selected from one or a mixture of several of the following: 4,4'-oxobis(1,4-phenylene)diboronic acid, 2,5-difluoro-1,4-phenylenediobonic acid, dibenzofuran-4,6-diboronic acid, (perfluoro-1,4-phenylene)diboronic acid, 2,2'-bipyridine-4,4'-diboronic acid, and thieno[3,2-b]thieno-2,5-diyldiboronic acid.

[0008] Preferably, in the bio-based coating material, the mass ratio of plant oil-based alkyd resin to amino resin is (0.8-1.6):1; and the amount of dynamic crosslinking structure modifier added is 1-20% of the mass of the bio-based coating material.

[0009] Furthermore, the plant oil-based alkyd resin is prepared by the following method:

[0010] (1) Preheat the vegetable oil to 140-170℃, then add glycerol, stir and heat to 200-220℃, then add sodium methoxide, heat to 230-240℃ under constant nitrogen flow rate and continuous stirring, and react for 30-120 min to prepare vegetable oil-based glycerol monoester.

[0011] (2) Cool the vegetable oil-based glycerol monoester obtained in step (1) to 150-170°C and add a polyacid (anhydride); then raise the temperature to 180-190°C and react for 3-5 hours; evaporate the by-product to prepare an oil-based alkyd resin.

[0012] More preferably, the mass ratio of vegetable oil to glycerol is (1.5–3):1, and the amount of sodium methoxide added is 0.05–0.5% wt% of the reactant system. The mass ratio of polybasic acid (anhydride) to vegetable oil-based glycerol monoester is (1–4):10.

[0013] More preferably, the vegetable oil is selected from one or a mixture of several of the following: perilla oil, rice bran oil, soapberry thorn oil, rapeseed oil, hemp seed oil, shea butter, acacia oil, and immortelle oil.

[0014] More preferably, the polyacid (anhydride) is selected from one or more of L-(-)-diacetyl tartaric acid, 1,2,4-benzenetrianic anhydride, trans, trans-mucoconic acid, diethylenetriaminepentaacetic acid, tetrafluoroterephthalic acid, and 4,4'-(hexafluoroisopropenyl)phthalic anhydride.

[0015] Furthermore, the amino resin is selected from one or more of melamine-formaldehyde resin, urea-formaldehyde resin, and benzo-melamine resin.

[0016] Furthermore, the amount of bio-based coating material added is 0.5%-10% of the fertilizer core weight.

[0017] Preferably, the fertilizer core is urea granules.

[0018] A second aspect of the present invention provides a method for preparing the above-mentioned bio-based coated controlled-release fertilizer, comprising the following steps:

[0019] The fertilizer core is loaded into a rotating coating drum and preheated; the bio-based coating material is sprayed onto the surface of the preheated fertilizer core and cured to obtain a rapidly biodegradable bio-based coated controlled-release fertilizer.

[0020] Preferably, the preheating conditions are: 60-80℃, 15-30rpm for 5-15 minutes.

[0021] The beneficial effects of this invention are:

[0022] (1) This invention uses plant oil-based alkyd resin as the main material for its coated controlled-release fertilizer. Compared with other thermosetting resin-coated controlled-release fertilizers, the fertilizer coating of the plant oil-based alkyd resin-coated controlled-release fertilizer has stronger mechanical properties, better thermal stability, and lower cost. Furthermore, unlike commercially available bio-based coated controlled-release fertilizers that use isocyanate as a curing agent, this invention uses amino resin as the curing agent for the fertilizer coating, which eliminates the risk of isocyanate pollution to the ecological environment. Therefore, the plant oil-based alkyd resin-coated controlled-release fertilizer of this invention has lower production costs and higher environmental value.

[0023] (2) Compared to traditional coated controlled-release fertilizers, the fertilizer coating of this invention incorporates a dynamic cross-linking structure modifier. By introducing the dynamic cross-linking structure modifier into the polymer network, not only is the cross-linking density of the fertilizer coating increased, enhancing its mechanical properties and improving the slow-release performance of the coated controlled-release fertilizer, but the dynamic cross-linking structure modifier also endows the fertilizer coating with excellent degradation performance. The coating of this invention's controlled-release fertilizer can rapidly and completely degrade under the stimulation of specific environmental factors. Compared to commercially available bio-based coated controlled-release fertilizers, this invention better meets the needs of green and sustainable agriculture, reducing the harm to the soil ecosystem caused by microplastics generated from non-degradable or incompletely degraded fertilizer coatings. Attached Figure Description

[0024] Figure 1 Fourier transform infrared spectra of the plant oil-based alkyd resin and plant oil-based glycerol monoester prepared in Example 1 of this invention.

[0025] Figure 2 The cumulative nutrient release rate of the coated controlled-release fertilizers prepared in Examples 1-5 and Comparative Example 1 of this invention.

[0026] Figure 3 The coating gel content of the coated controlled-release fertilizers prepared in Examples 1-3 and Comparative Example 1 of this invention.

[0027] Figure 4 SEM images of the coatings of the controlled-release fertilizers prepared in Example 1 and Comparative Example 1 of this invention.

[0028] Figure 5 The coating stress-strain curves of the coated controlled-release fertilizers prepared in Example 1 and Comparative Example 1 of this invention.

[0029] Figure 6 The degradation performance of the coating of the controlled-release fertilizer prepared in Example 1 and Comparative Example 1 in soil. Detailed Implementation

[0030] 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.

[0031] As mentioned earlier, most existing coated controlled-release fertilizers use thermosetting materials as the membrane material. The permanent cross-linked network of thermosetting materials greatly hinders the degradation and recycling process of thermosetting materials, which can easily cause environmental pollution.

[0032] In view of this, the present invention designs a rapidly degradable bio-based coated controlled-release fertilizer. The bio-based coated controlled-release fertilizer of the present invention comprises: a urea core and a bio-based coating material coating the surface of the urea core; wherein:

[0033] The bio-based coating material is composed of plant oil-based alkyd resin, amino resin, and a dynamic cross-linking structure modifier. Compared with existing thermosetting resin coating materials, this invention selects plant oil-based alkyd resin and amino resin for curing into a film, resulting in stronger mechanical properties, better thermal stability, and lower cost. Furthermore, unlike commercially available bio-based coated controlled-release fertilizers that use isocyanate as a curing agent, this invention uses amino resin as the curing agent for the fertilizer coating, eliminating the risk of isocyanate pollution to the ecological environment.

[0034] More importantly, this invention introduces a dynamic crosslinking structure modifier into the polymer network formed by plant oil-based alkyd resin and amino resin. On the one hand, the dynamic crosslinking structure modifier can form more crosslinking points in the polymer network, increasing the crosslinking density and making the connection between molecular chains tighter, thereby increasing the density of the coating and improving the original tensile and elongation at break mechanical properties of the polymer network, thus effectively improving the nutrient control performance of the bio-based coating material. On the other hand, the dynamic crosslinking structure modifier can also respond to changes in the acid and alkaline environment within the coating. When stimulated by specific environmental factors, the dynamic crosslinking structure modifier, which is a crosslinking point in the polymer network, will break, causing the entire polymer network to collapse and achieving the purpose of rapid polymer degradation.

[0035] The degradation mechanism of the rapidly degradable bio-based coated controlled-release fertilizer of the present invention is as follows: When the bio-based coated controlled-release fertilizer of the present invention is applied to the soil, as the application time increases, the urea in the controlled-release fertilizer coating will be slowly released into the soil under the action of the osmotic pressure of the soil aqueous solution. Since urea itself is alkaline, the inside of the fertilizer coating always maintains an alkaline environment before the urea is completely released. However, after the urea is completely released into the soil, the inside of the fertilizer coating becomes slightly acidic compared to before. When the acidity inside the fertilizer coating reaches a certain threshold, the chemical bonds formed by the dynamic cross-linking structure modifiers that act as cross-linking points in the polymer network of the fertilizer coating are triggered and then rapidly broken, thereby causing the entire polymer cross-linking network of the fertilizer coating to rapidly depolymerize, achieving the purpose of rapid and complete degradation of the coating after the controlled-release fertilizer nutrients are completely released.

[0036] 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.

[0037] 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. Experimental methods without specified detailed conditions were performed according to conventional test methods or the supplier's recommended operating instructions. Wherein:

[0038] CAS No. for Perilla Oil: 68132-21-8; CAS No. for Rice Bran Oil: 68553-81-1; CAS No. for Canola Oil: 120962-03-0; CAS No. for Hemp Seed Oil: 89958-21-4; CAS No. for Acacia Oil: 8023-82-3; CAS No. for Helichrysum Oil: 8023-95-8; CAS No. for Shea Butter Oil: 68424-60-2; CAS No. for Borage Oil: 84012-16-8. CAS No. for Melamine-Formaldehyde Resin: 9003-08-1.

[0039] The determination of the gel content in fertilizer coatings is a method already available in the prior art, for example, see the reference "Controllable release fertilizer with low coating content enabled by superhydrophobic castor oil-based polyurethane nanocomposites prepared through a one-step synthetic strategy. Ind. Crops Prod. 2022, 189. DOI:10.1016 / j.indcrop.2022.115803."

[0040] The acid value was determined according to the procedure in the national standard (GB / T 12008.5-2010), and the hydroxyl value was determined according to the procedure in the national standard (GB / T12008.3-2009).

[0041] Example 1: Preparation of a rapidly biodegradable, bio-based coated controlled-release fertilizer

[0042] 1. Preparation of bio-based coating materials:

[0043] (1) 117.34g of vegetable oil (a mixture of perilla oil, rice bran oil and borage oil in a mass ratio of 1:1:1) was placed in a four-necked round-bottom flask, stirred at 500 rpm and preheated to 150°C; then 57.92g of glycerol was added, and the temperature was raised to 210°C under continuous stirring at 500 rpm. 0.18g of sodium methoxide was added as a reaction catalyst, and the mixture was heated to 230°C for 60 min under constant nitrogen flow rate (170ml / min) and continuous stirring (1000 rpm) to obtain vegetable oil-based glycerol monoester.

[0044] (2) Cool the vegetable oil-based glycerol monoester obtained in step (1) to 170°C and add 24.56g of polyacid (anhydride) (the polyacid (anhydride) is a mixture of L-(-)-diacetyl tartaric acid, 1,2,4-benzenetriosic anhydride, and trans-, trans-mucoconic acid in a mass ratio of 1:1:1); then raise the temperature to 190°C and react for 4 hours; after the reaction is completed, remove the byproducts by rotary evaporation for 1 hour to obtain the vegetable oil-based alkyd resin.

[0045] The prepared vegetable oil-based glycerol monoesters and vegetable oil-based alkyd resins were tested using Fourier transform infrared spectroscopy, and the results are as follows: Figure 1 As shown. At 3364cm -1 A broad OH stretching vibration band is present nearby, indicating that the alkyd resin contains -OH groups for reaction with the amino groups of melamine-formaldehyde resin; 2853 cm -1 and 2923cm -1 There is a methyl and methylene vibration band at 1719 cm. -1 The peak value at that point represents the stretching vibration of the C=O group in the alkyd resin. From... Figure 1 It can be seen that the intensity of the C=O peak in the spectrum of the vegetable oil-based alkyd resin is slightly increased compared to that of the vegetable oil-based glycerol monoester, which confirms the inclusion of ester bonds in the system. (1462 cm⁻¹) -1 The peak at 1178 cm⁻¹ corresponds to the CH bend in the alkyd resin. -1 and 1042cm -1 The nearby peaks are attributed to CO bonds in glycerol and polyacids (anhydrides).

[0046] The hydroxyl value of the plant oil-based alkyd resin prepared in this embodiment was determined to be 218.4 mg KOH / g, and the acid value was 7.84 mg KOH / g.

[0047] (3) Dissolve 1g of dynamic crosslinking structure modifier (the dynamic crosslinking structure modifier is 4,4'-oxobis(1,4-phenylene)diboronic acid) in 10ml of acetone, and then put it into a flask with 10g of amino resin (the amino resin is melamine-formaldehyde resin). Stir at 100rpm for 60min at 80℃ to form a prepolymer of dynamic crosslinking structure modifier and melamine-formaldehyde resin. Stir the obtained prepolymer with 10g of vegetable oil-based alkyd resin to prepare a bio-based coating material.

[0048] 2. Preparation of bio-based coated controlled-release fertilizer:

[0049] 500g of urea granules were loaded into a rotating coating drum and preheated at 75℃ and 21rpm for 10 minutes. The bio-based coating material prepared above was sprayed onto the surface of the urea granules, with the amount of bio-based coating material being 2% of the weight of the urea granules. The mixture was then cured and shaped to obtain a rapidly biodegradable bio-based coated controlled-release fertilizer.

[0050] Example 2: Preparation of a rapidly biodegradable, bio-based, coated, controlled-release fertilizer

[0051] The difference from Example 1 is that the dynamic cross-linking structure modifier in Example 1 is replaced with "thieno[3,2-b]thieno-2,5-dimethyldiboronic acid", and the other preparation conditions are the same as in Example 1, so as to prepare a bio-based coated controlled-release fertilizer that can be rapidly and fully degraded.

[0052] Example 3: Preparation of a rapidly biodegradable, fully degradable, bio-based coated controlled-release fertilizer

[0053] The difference from Example 1 is that the dynamic cross-linking structure modifier in Example 1 is replaced with "a mixture of 4,4'-oxobis(1,4-phenylene)diboronic acid and thieno[3,2-b]thiophene-2,5-dimethyldiboronic acid in a mass ratio of 1:1", and the other preparation conditions are the same as in Example 1, so as to prepare a rapidly degradable bio-based coated controlled-release fertilizer.

[0054] Example 4: Preparation of a rapidly biodegradable, bio-based, coated, controlled-release fertilizer

[0055] 1. Preparation of bio-based coating materials:

[0056] (1) 96.86g of vegetable oil (a mixture of rapeseed oil, hemp seed oil and shea butter in a mass ratio of 1:1:1) was placed in a four-necked round-bottom flask, stirred at 1000rpm and preheated to 150℃; then 64.57g of glycerol was added, and the temperature was raised to 210℃ under continuous stirring (500rpm). 0.32g of sodium methoxide was added as a reaction catalyst, and the mixture was heated to 230℃ for 60min under constant nitrogen flow rate (170ml / min) and continuous stirring (1000rpm) to obtain vegetable oil-based glycerol monoester.

[0057] (2) Cool the vegetable oil-based glycerol monoester obtained in step (1) to 170°C and add 16.143g of polybasic acid (anhydride) (the polybasic acid (anhydride) is a mixture of diethylenetriaminepentaacetic acid and tetrafluoroterephthalic acid in a mass ratio of 1:1); then raise the temperature to 190°C and react for 4 hours; after the reaction is completed, remove the byproducts by rotary evaporation for 1 hour to obtain the vegetable oil-based alkyd resin.

[0058] (3) Dissolve 1g of dynamic crosslinking structure modifier (the dynamic crosslinking structure modifier is dibenzofuran-4,6-diboronic acid) in 10ml of acetone, and then put it into a flask with 10g of amino resin (the amino resin is melamine-formaldehyde resin). Stir at 80℃ and 100rpm for 60min to form a prepolymer of dynamic crosslinking structure modifier and melamine-formaldehyde resin. Stir the obtained prepolymer with 10g of vegetable oil-based alkyd resin until uniform to prepare a bio-based coating material.

[0059] 2. Preparation of bio-based coated controlled-release fertilizer:

[0060] 500g of urea granules were loaded into a rotating coating drum and preheated at 75℃ and 21rpm for 10 minutes. The bio-based coating material prepared above was sprayed onto the surface of the urea granules, with the amount of bio-based coating material being 3% of the weight of the urea granules. The mixture was then cured and shaped to obtain a rapidly biodegradable bio-based coated controlled-release fertilizer.

[0061] Example 5: Preparation of a rapidly biodegradable, fully degradable, bio-based coated controlled-release fertilizer

[0062] 1. Preparation of bio-based coating materials:

[0063] (1) 150.60g of vegetable oil (a mixture of acacia oil and immortelle oil in a mass ratio of 1:1) was placed in a four-necked round-bottom flask, stirred at 1500rpm and preheated to 150℃; then 50.2g of glycerol was added, and the temperature was raised to 210℃ under continuous stirring (500rpm). 1g of sodium methoxide was added as a reaction catalyst, and the mixture was heated to 230℃ and reacted for 30min under constant nitrogen flow rate (170ml / min) and continuous stirring (1000rpm) to obtain vegetable oil-based glycerol monoester.

[0064] (2) Cool the vegetable oil-based glycerol monoester obtained in step (1) to 170°C and add 60.24g of polybasic acid (anhydride) (the polybasic acid (anhydride) is a mixture of tetrafluoroterephthalic acid and 4,4'-(hexafluoroisopropenyl)phthalic anhydride in a mass ratio of 1:1). Then raise the temperature to 190°C and react for 4 hours. After the reaction is completed, remove the byproducts by rotary evaporation for 1 hour to prepare the vegetable oil-based alkyd resin.

[0065] (3) Dissolve 1g of dynamic crosslinking structure modifier (the dynamic crosslinking structure modifier is (perfluoro-1,4-phenylene) diboronic acid) in 10ml of acetone, and then put it into a flask with 10g of melamine-formaldehyde resin. Stir at 100rpm for 60min at 80℃ to form a prepolymer of dynamic crosslinking structure modifier and melamine-formaldehyde resin. Stir the obtained prepolymer with 10g of vegetable oil-based alkyd resin evenly to prepare a bio-based coating material.

[0066] 2. Preparation of bio-based coated controlled-release fertilizer:

[0067] 500g of urea granules were loaded into a rotating coating drum and preheated at 75℃ and 21rpm for 10 minutes. The bio-based coating material prepared above was sprayed onto the surface of the urea granules, with the amount of bio-based coating material being 4% of the weight of the urea granules. The mixture was then cured and shaped to obtain a rapidly biodegradable bio-based coated controlled-release fertilizer.

[0068] Comparative Example 1:

[0069] The difference from Example 1 is that the bio-based coating material does not contain a dynamic cross-linking structure modifier and is composed only of plant oil-based alkyd resin and amino resin. The remaining preparation conditions are the same as in Example 1.

[0070] Experimental Example 1: Nutrient Release Assay:

[0071] The nitrogen nutrient release rate of the coated controlled-release fertilizers prepared in Examples 1-5 and Comparative Example 1 was determined according to the National Standard for Slow-Release Fertilizers of the People's Republic of China GB / T 23348-2009.

[0072] The results are as follows Figure 2As shown, the release period of the coated fertilizer prepared in Example 1 was 25 days, the release period of the coated fertilizer prepared in Example 2 was 22 days, the release period of the coated fertilizer prepared in Example 3 was 36 days, the release period of the coated fertilizer prepared in Example 4 was 40 days, the release period of the coated fertilizer prepared in Example 5 was 48 days, and the release period of the coated fertilizer prepared in Comparative Example 1 was 14 days.

[0073] The dynamic crosslinking modifier added in Example 1 was 4,4'-oxobis(1,4-phenylene)diboronic acid. Compared to the dynamic crosslinking modifier (thieno[3,2-b]thiophene-2,5-dimethyldiboronic acid) added in Example 2, the two benzene rings in the 4,4'-oxobis(1,4-phenylene)diboronic acid structure endowed the crosslinking coating with stronger mechanical strength. Therefore, the coated controlled-release fertilizer prepared in Example 1 has a longer nutrient release period compared to Example 2. In Example 3, the added dynamic crosslinking modifier was a combination of 4,4'-oxobis(1,4-phenylene)diboronic acid and thieno[3,2-b]thiophene-2,5-dimethyldiboronic acid. The addition of the two dynamic crosslinking modifiers can form more crosslinking points in the polymer network. Compared with a single dynamic crosslinking modifier, the crosslinking density is increased, making the connection between molecular chains tighter, thereby increasing the density of the coating. In addition, there may be a synergistic effect between the two dynamic crosslinking modifiers, which improves the stability of the crosslinking network. This synergistic effect can effectively resist the damage of external forces to the material structure and maintain the integrity and density of the structure. Even when external conditions change, the dual dynamic crosslinking modifier crosslinking system can be quickly adjusted through dynamic exchange reaction to maintain the dense structure of the material. Therefore, Example 3 has a longer nutrient release period than Examples 1 and 2.

[0074] Experimental Example 2: Determination of Gel Content in Bio-based Coated Controlled-Release Fertilizer Coatings

[0075] The gel content of the bio-based coated controlled-release fertilizer coatings prepared in Examples 1-3 and Comparative Example 1 was calculated using a gravimetric method. First, the bio-based coated controlled-release fertilizer was crushed and immersed in deionized water to completely dissolve the nutrients in the fertilizer core. The resulting material was then dried at 80°C until a constant weight was achieved to separate the pure coating. The coating was placed in a sealed container containing 4 ml of acetone or ethyl acetate and soaked for 72 hours, with the solvent replaced every 24 hours. Afterward, the sample was dried in an oven at 80°C for 24 hours. The gel content was then calculated using the following formula:

[0076]

[0077] In the formula: m0 represents the initial mass of the dried coating material, while m represents the mass of the coating material after solvent immersion and oven drying. The test was conducted three times, and the results presented are the average of all samples.

[0078] The results are as follows Figure 3 As shown, the bio-based coated controlled-release fertilizer prepared in Example 3 has the highest gel content because it contains two dynamic cross-linking structure modifiers. The two dynamic cross-linking structure modifiers have a synergistic effect. Therefore, the fertilizer coating prepared in Example 3 has the highest gel content, while the fertilizer coating prepared in Comparative Example 1, which does not contain dynamic cross-linking structure modifiers, has the lowest gel content.

[0079] Experimental Example 3: Determination of Morphology and Mechanical Properties of Fertilizer Coatings

[0080] The bio-based coating materials prepared in Example 1 and Comparative Example 1 were added to a small plastic cup and stirred until the mixture began to thicken. The mixture was then poured onto a polytetrafluoroethylene (PTFE) plate, which was subsequently placed in a 75°C oven for 12 hours. After complete curing, a coating for the controlled-release fertilizer was obtained.

[0081] The prepared coating was observed using a scanning electron microscope, and the results are as follows: Figure 4 As shown, the number of pores in the cross-section of the fertilizer coating prepared in Example 1 with the addition of the dynamic cross-linking structure modifier is significantly less than the number of pores in the cross-section of the fertilizer coating prepared in Comparative Example 1 without the addition of the dynamic cross-linking structure modifier.

[0082] The stress-strain curves of the controlled-release fertilizer coating were tested using an electronic universal testing machine (MTS, CMT6103) at a constant speed of 2 mm / min at room temperature. The results are as follows: Figure 5 As shown, the tensile strength of the fertilizer coating prepared in Example 1 is 26.05 MPa, and the tensile strength of the fertilizer coating prepared in Comparative Example 1 is 14.12 MPa.

[0083] The above results indicate that the introduction of a dynamic crosslinking modifier increased the crosslinking density of the original polymer network in the fertilizer coating and significantly improved its mechanical properties. Increasing the crosslinking density of the coating effectively prevents water from wetting the fertilizer coating, thereby prolonging the nutrient release period of the controlled-release fertilizer.

[0084] Experimental Example 4: Degradation Performance Test of Fertilizer Coating

[0085] The bio-based coating materials prepared in Example 1 and Comparative Example 1 were added to a small plastic cup and stirred until the mixture began to thicken. The mixture was then poured onto a polytetrafluoroethylene (PTFE) plate, which was subsequently placed in a 75°C oven for 12 hours. After complete curing, a coating for the controlled-release fertilizer was obtained.

[0086] The degradation performance of the fertilizer coatings in Example 1 and Comparative Example 1 was evaluated using a gravimetric method. The initial value of the coating weight was denoted as S. aThe coating was then buried in the soil and left to stand in a 25°C incubator. Soils with different pH values ​​were used to simulate the changes in the acid-base environment inside the fertilizer coating before and after urea release. At each set point, the coating was weighed again on an analytical balance and recorded as S. b .

[0087] Degradation rate (%) = (S) a -S b ) / S a ×100.

[0088] The results are as follows Figure 6 As shown, under neutral conditions (pH = 7.2), the degradation rate of the fertilizer coating prepared in Comparative Example 1 without the addition of the dynamic crosslinking structure modifier was higher than that of the fertilizer coating prepared in Example 1 with the addition of the dynamic crosslinking structure modifier. This is because the crosslinking density of the fertilizer coating prepared in Example 1 with the addition of the dynamic crosslinking structure modifier was higher than that of the fertilizer coating prepared in Comparative Example 1, and the high crosslinking density would hinder its degradation process to some extent. Under slightly acidic conditions (pH = 5.2), the degradation rate of the fertilizer coating prepared in Example 1 was significantly accelerated and exceeded that of the fertilizer coating prepared in Comparative Example 1. This is because the dynamic crosslinking modifier was triggered to break under acidic conditions, resulting in rapid depolymerization of the fertilizer coating. When the soil environment became alkaline again (pH = 8.5), the degradation rate of the fertilizer coating prepared in Example 1 slowed down significantly and tended to stabilize.

[0089] The coated controlled-release fertilizer coating of this invention maintains a slightly acidic acidic environment within the coating after complete urea release. According to... Figure 6 The degradation efficiency of the coating under simulated slightly acidic conditions (the degradation rate was approximately 5% over 4 weeks) indicates that the coating prepared in Example 1 is expected to completely degrade into some nitrogen-containing small molecules about two years after the urea is fully released.

[0090] 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 rapidly biodegradable, bio-based coated controlled-release fertilizer, characterized in that, include: Fertilizer core and bio-based coating material covering the surface of the fertilizer core; The bio-based coating material is composed of plant oil-based alkyd resin, amino resin, and a dynamic crosslinking structure modifier; the dynamic crosslinking structure modifier is selected from one or a mixture of several of 4,4'-oxobis(1,4-phenylene)diboronic acid, dibenzofuran-4,6-diboronic acid, (perfluoro-1,4-phenylene)diboronic acid, and thieno[3,2-b]thiophene-2,5-dimethyldiboronic acid.

2. The bio-based coated controlled-release fertilizer according to claim 1, characterized in that, In the bio-based coating material, the mass ratio of plant oil-based alkyd resin to amino resin is (0.8-1.6):1; the amount of dynamic cross-linking structure modifier added is 1-20% of the mass of the bio-based coating material.

3. The bio-based coated controlled-release fertilizer according to claim 1, characterized in that, The plant oil-based alkyd resin is prepared by the following method: (1) Preheat the vegetable oil to 140-170℃, then add glycerol, stir and heat to 200-220℃, then add sodium methoxide, heat to 230-240℃ under constant nitrogen flow rate and continuous stirring, and react for 30-120 min to prepare vegetable oil-based glycerol monoester. (2) Cool the vegetable oil-based glycerol monoester obtained in step (1) to 150~170℃ and add polybasic acid or polybasic acid anhydride; then raise the temperature to 180~190℃ and react for 3~5h; evaporate the by-product to prepare oil-based alkyd resin.

4. The bio-based coated controlled-release fertilizer according to claim 3, characterized in that, The mass ratio of vegetable oil to glycerol is (1.5~3):1, and the amount of sodium methoxide added is 0.05~0.5% wt% of the reactant system; the mass ratio of polybasic acid or polybasic acid anhydride to vegetable oil-based glycerol monoester is (1~4):

10.

5. The bio-based coated controlled-release fertilizer according to claim 3, characterized in that, The vegetable oil is selected from one or a mixture of several of the following: perilla oil, rice bran oil, borage oil, rapeseed oil, hemp seed oil, shea butter, acacia oil, and immortelle oil.

6. The bio-based coated controlled-release fertilizer according to claim 3, characterized in that, The polybasic acid or polybasic anhydride is selected from one or more of L-(-)-diacetyl tartaric acid, 1,2,4-benzenetrianic anhydride, trans, trans-mucoconic acid, diethylenetriaminepentaacetic acid, tetrafluoroterephthalic acid, and 4,4'-(hexafluoroisopropenyl)phthalic anhydride.

7. The bio-based coated controlled-release fertilizer according to claim 1, characterized in that, The amino resin is selected from one or more of melamine-formaldehyde resin, urea-formaldehyde resin, and benzo-melamine resin.

8. The bio-based coated controlled-release fertilizer according to claim 1, characterized in that, The amount of bio-based coating material added is 0.5%-10% of the fertilizer core weight.

9. The method for preparing the bio-based coated controlled-release fertilizer according to any one of claims 1-8, characterized in that, Includes the following steps: The fertilizer core is loaded into a rotating coating drum and preheated; the bio-based coating material is sprayed onto the surface of the preheated fertilizer core and cured to obtain a rapidly biodegradable bio-based coated controlled-release fertilizer.

10. The preparation method according to claim 9, characterized in that, The preheating conditions are: 60-80℃, 15-30rpm for 5-15 minutes.

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