Bio-based coated controlled-release fertilizer capable of being rapidly and fully degraded and preparation method of bio-based coated controlled-release fertilizer

Abstract

The invention discloses a bio-based coated controlled-release fertilizer capable of being rapidly and fully degraded and a preparation method of the bio-based coated controlled-release fertilizer, and belongs to the technical field of controlled-release fertilizer production. The bio-based coated controlled-release fertilizer comprises a fertilizer core and a bio-based coating material coating the surface of the fertilizer core, the bio-based coating material is composed of vegetable oil-based alkyd resin, amino resin and a dynamic cross-linked structure modifier. The coating of the controlled-release fertilizer disclosed by the invention can be rapidly and completely degraded after nutrients are completely released, so that the harm of microplastics generated by non-degradation or incomplete degradation of the coating of the fertilizer to a soil ecosystem is reduced. Amino resin is adopted as a curing agent of a fertilizer coating, so that the risk of pollution of isocyanate to an ecological environment system can be eliminated. Compared with a coated controlled-release fertilizer using isocyanate as a coating curing agent in the market, the coated controlled-release fertilizer better meets the development requirements of green and sustainable agriculture.

Description

Technical Field

[0001] The present invention relates to the technical field of controlled-release fertilizer production, and in particular to a rapidly and fully degradable bio-based coated controlled-release fertilizer and a preparation method thereof. Background Art

[0002] Controlled-release fertilizers (CRFs) can effectively improve fertilizer utilization, reduce environmental pollution, and completely change agricultural production. However, as the market demand for CRFs continues to expand, more and more CRFs will be put into farmland soil. Therefore, there is an urgent need to further investigate the potential risks of plastic pollution associated with their application. Although CRFs can effectively solve environmental problems associated with traditional fertilization methods, such as reducing the risk of eutrophication caused by nutrient leaching into water bodies and reducing greenhouse gases produced by fertilizer decomposition, there are still many knowledge gaps about the whereabouts and existence form of CRFs residual membrane shells in the soil after the fertilizer nutrients are fully released.

[0003] Existing controlled-release fertilizers mostly use thermosetting resins as coating materials. Traditional thermosetting polymers have a highly cross-linked network, and because their covalent cross-linked networks are irreversible, traditional thermosetting materials are very difficult to degrade. The introduction of dynamic covalent bonds can give the coating material some special properties. There are currently 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 the 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 all focus on exploring the effect of dynamic covalent bonds on the self-healing properties and reprocessability of thermosetting materials, but still do not explore whether dynamic covalent bonds can enhance the degradation properties of polymers. Therefore, developing a completely degradable membrane material and applying it to controlled-release fertilizers is of great significance to maintaining the balance of soil ecosystems and protecting the ecological environment. Summary of the Invention

[0004] In view of the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a bio-based coated controlled-release fertilizer that can be rapidly and fully degraded and a preparation method thereof.

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

[0006] The first aspect of the present invention provides a rapidly degradable 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 a vegetable oil-based alkyd resin, an amino resin, and a dynamic cross-linked structure modifier; the dynamic cross-linked structure modifier is selected from one or a mixture of several of 4,4'-oxybis(1,4-phenylene)diboronic acid, 2,5-difluoro-1,4-benzenediboronic acid, dibenzofuran-4,6-diboronic acid, (perfluoro-1,4-phenylene)diboronic acid, 2,2'-bipyridine-4,4'-diboronic acid, and thiophene[3,2-b]thiophene-2,5-diyl diboronic acid.

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

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

[0010] (1) Preheat the vegetable oil to 140 - 170 °C, then add glycerol, stir and heat up to 200 - 220 °C, then add sodium methoxide, and heat to 230 - 240 °C under a constant nitrogen gas flow rate and continuous stirring for 30 - 120 min to prepare a 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 polybasic acid (anhydride); then raise the temperature to 180 - 190 °C and react for 3 - 5 h; rotary evaporate the by-products to prepare an oil-based alkyd resin.

[0012] More preferably, the mass ratio of the vegetable oil to glycerol is (1.5 - 3):1, and the addition amount of sodium methoxide is 0.05 - 0.5% wt% of the reactant system. The mass ratio of the polybasic acid (anhydride) to the 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 perilla oil, rice bran oil, Chinese honey locust spine oil, canola oil, hemp oil, shea butter, acacia oil, and immortelle oil.

[0014] More preferably, the polybasic acid (anhydride) is selected from one or several of L-(-)-diacetyl tartaric acid, 1,2,4-benzenetricarboxylic anhydride, trans,trans-muconic acid, diethylenetriaminepentaacetic acid, tetrafluoroterephthalic acid, and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride.

[0015] Furthermore, the amino resin is selected from one or a mixture of several of melamine formaldehyde resin, urea formaldehyde resin, and phenylmelamine resin.

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

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

[0018] In the second aspect of the present invention, a method for preparing the above-mentioned bio-based coated controlled-release fertilizer is provided, including the following steps:

[0019] Load the fertilizer core into a rotating coating drum and preheat; spray the bio-based coating material on the surface of the preheated fertilizer core and cure it into shape to prepare a bio-based coated controlled-release fertilizer that can be rapidly and completely degraded.

[0020] Preferably, the preheating conditions are: preheat at 60 - 80°C, 15 - 30 rpm for 5 - 15 min.

[0021] Advantages of the present invention:

[0022] (1) In the present invention, vegetable oil-based alkyd resin is used as the main material for coating controlled-release fertilizers. Compared with other thermosetting resin-coated controlled-release fertilizers, the fertilizer coating of the vegetable oil-based alkyd resin-coated controlled-release fertilizer has stronger mechanical properties, good thermal stability and lower cost. In addition, different from the common bio-based coated controlled-release fertilizers on the market that use isocyanate as a curing agent, the present invention uses amino resin as the curing agent for the fertilizer coating, which can eliminate the risk of isocyanate pollution to the ecological environment system. Therefore, a vegetable oil-based alkyd resin-coated controlled-release fertilizer of the present invention has lower production cost and higher environmental protection value.

[0023] (2) Compared with traditional coated controlled-release fertilizers, a dynamic crosslinking structure modifier is introduced into the fertilizer coating of the controlled-release fertilizer of the present invention. By introducing the dynamic crosslinking structure modifier into the polymer network, not only the crosslinking density of the fertilizer coating is improved, the mechanical properties of the coating are enhanced, and the slow-release performance of the coated controlled-release fertilizer is improved; in addition, the dynamic crosslinking structure modifier also endows the fertilizer coating with excellent degradation performance, and the coating of the controlled-release fertilizer of the present invention can be rapidly and completely degraded under the excitation of specific environmental factors. It more meets the requirements of green and sustainable agriculture compared with the bio-based coated controlled-release fertilizers on the market, and reduces the harm of microplastics generated by non-degradation or incomplete degradation of the fertilizer coating to the soil ecosystem. Description of the drawings

[0024] Figure 1 : Fourier transform infrared spectrogram of vegetable oil-based alkyd resin and vegetable oil-based glycerol monoesters prepared in Example 1 of the present invention.

[0025] Figure 2 : Nutrient cumulative release rate of the coated controlled-release fertilizers prepared in Examples 1 - 5 and Comparative Example 1 of the present invention

[0026] Figure 3 : Coating gel content of the coated controlled-release fertilizers prepared in Examples 1 - 3 and Comparative Example 1 of the present invention

[0027] Figure 4 : Cross-sectional SEM images of the coatings of the coated controlled-release fertilizers prepared in Example 1 and Comparative Example 1 of the present invention.

[0028] Figure 5 : Coating stress-strain curves of the coated controlled-release fertilizers prepared in Example 1 and Comparative Example 1 of the present invention

[0029] Figure 6 : Degradation performance of the coatings of the coated controlled-release fertilizers prepared in Example 1 and Comparative Example 1 of the present invention in soil. Detailed Description of the Invention

[0030] It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present application belongs.

[0031] As mentioned above, most of the existing coated controlled-release fertilizers use thermosetting materials as film materials. The permanent cross-linked network of thermosetting materials greatly hinders the degradation and recycling processes of thermosetting materials, and is likely to cause environmental pollution.

[0032] In view of this, the present invention designs a bio-based coated controlled-release fertilizer that can be rapidly and completely degraded. The bio-based coated controlled-release fertilizer of the present invention includes: a urea core and a bio-based coating material wrapped on the surface of the urea core; wherein:

[0033] The bio-based coating material is composed of a vegetable oil-based alkyd resin, an amino resin, and a dynamic cross-linked structure modifier; compared with the existing thermosetting resin coating materials, the present invention selects a vegetable oil-based alkyd resin and an amino resin to form a film, which has stronger mechanical properties, good thermal stability, and lower cost. In addition, different from the common bio-based coated controlled-release fertilizers on the market that use isocyanate as a curing agent, the present invention uses an amino resin as the curing agent for the fertilizer coating, which can eliminate the risk of isocyanate pollution to the ecological environment system.

[0034] More importantly, the present invention introduces a dynamic cross-linked structure modifier into the polymer network formed by the vegetable oil-based alkyd resin and the amino resin. On the one hand, the dynamic cross-linked structure modifier can form more cross-linking points in the polymer network, increasing the cross-linking density, making the connection between molecular chains closer, thereby increasing the density of the coating and enhancing the original mechanical properties such as tensile strength and elongation at break of the polymer network, thus effectively improving the nutrient controlled-release performance of the bio-based coating material; on the other hand, the dynamic cross-linked structure modifier can also respond to changes in the acid-base environment within the coating. When stimulated by specific environmental factors, the dynamic cross-linked structure modifier serving as the cross-linking point in the polymer network will break, causing the entire polymer network to collapse, achieving the purpose of rapid degradation of the polymer.

[0035] The degradation mechanism of the rapidly fully 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 slowly release into the soil under the action of the osmotic pressure of the soil aqueous solution. Since urea itself is alkaline, an alkaline environment is always maintained inside the fertilizer coating before the urea is completely released. However, when all the urea is 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 linked as cross-linking points throughout the polymer network of the fertilizer coating will be triggered and then rapidly break, resulting in the rapid depolymerization of the entire polymer cross-linking network of the fertilizer coating, achieving the purpose of rapid and complete degradation of the coating after the nutrient release of the controlled-release fertilizer is complete.

[0036] In order to enable those skilled in the art to more clearly understand the technical solution of this application, the technical solution of this application will be described in detail below in conjunction with specific embodiments.

[0037] The test materials used in the examples and comparative examples of the present invention are all conventional test materials in the art and can be obtained through commercial channels. The experimental methods without detailed conditions are carried out according to conventional test methods or according to the operation manuals recommended by the suppliers. Among them:

[0038] CAS number of perilla oil: 68132-21-8; CAS number of rice bran oil: 68553-81-1; CAS number of canola oil: 120962-03-0; CAS number of hemp seed oil: 89958-21-4; CAS number of acacia oil: 8023-82-3; CAS number of everlasting oil: 8023-95-8; CAS number of shea butter: 68424-60-2; CAS number of borage oil: 84012-16-8. CAS number of melamine formaldehyde resin: 9003-08-1.

[0039] The determination of the gel content of the fertilizer coating is a method already existing in the prior art. For example, reference can be made to the literature "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 steps in the national standard (GB / T 12008.5-2010), and the hydroxyl value was determined according to the steps in the national standard (GB / T 12008.3-2009).

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

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

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

[0044] (2) Cool the vegetable oil-based glycerol monoester obtained in step (1) to 170 °C, and add 24.56 g of polybasic acid (anhydride) (the polybasic acid (anhydride) is a mixture of L-(-)-diacetyl tartaric acid, 1,2,4-benzenetricarboxylic anhydride, and trans,trans-muconic acid in a mass ratio of 1:1:1); then raise the temperature to 190 °C and react for 4 h; after the reaction, rotary evaporate for 1 h on a rotary evaporator to remove by-products, that is, a vegetable oil-based alkyd resin is prepared.

[0045] The above-prepared vegetable oil-based glycerol monoester and vegetable oil-based alkyd resin were tested with a Fourier transform infrared spectrometer, and the results are as Figure 1 shown. There is a broad O-H stretching vibration band near 3364 cm -1 , which indicates that the alkyd resin contains -OH for reacting with the amino group of melamine formaldehyde resin; there is a methyl and methylene vibration band at 2853 cm -1 and 2923 cm -1 , and the peak at 1719 cm -1 is the stretching vibration of the ester group C=O in the alkyd resin. It can be seen from Figure 1 that the intensity of the C=O peak in the spectrum of the vegetable oil-based alkyd resin is slightly increased compared with that of the vegetable oil-based glycerol monoester, which confirms the addition of ester bonds in the system. The peak at 1462 cm -1 corresponds to the C-H bending in the alkyd resin. The peaks near 1178 cm -1 and 1042 cm -1 are attributed to the C-O bonds in glycerol and polybasic acid (anhydride).

[0046] It was measured that the hydroxyl value of the vegetable oil-based alkyd resin prepared in this example was 218.4 mg KOH / g, and the acid value was 7.84 mg KOH / g.

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

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

[0049] Load 500 g of urea granules into a rotating coating drum, and preheat at 75 °C and 21 rpm for 10 minutes; spray the above-prepared bio-based coating material on the surface of the urea granules, and the spraying amount of the bio-based coating material is 2% of the weight of the urea granules, and cure and form to prepare a bio-based coated controlled-release fertilizer that can be rapidly and completely degraded.

[0050] Example 2: Preparation of bio-based coated controlled-release fertilizer that can be rapidly and completely degraded

[0051] The difference from Example 1 is that the dynamic crosslinked structure modifier in Example 1 is replaced by "thieno[3,2-b]thiophene-2,5-diyl diboronic acid", and the remaining preparation conditions are the same as those in Example 1, and a bio-based coated controlled-release fertilizer that can be rapidly and completely degraded is prepared.

[0052] Example 3: Preparation of bio-based coated controlled-release fertilizer that can be rapidly and completely degraded

[0053] The difference from Example 1 is that the dynamic crosslinked structure modifier in Example 1 is replaced by "a mixture of 4,4'-oxybis(1,4-phenylene)diboronic acid and thieno[3,2-b]thiophene-2,5-diyl diboronic acid in a mass ratio of 1:1", and the remaining preparation conditions are the same as those in Example 1, and a bio-based coated controlled-release fertilizer that can be rapidly and completely degraded is prepared.

[0054] Example 4: Preparation of bio-based coated controlled-release fertilizer that can be rapidly and completely degraded

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

[0056] (1) Load 96.86 g of vegetable oil (the vegetable oil is a mixture of canola oil, hemp seed oil, and shea butter in a mass ratio of 1:1:1) into a four-necked round-bottom flask, stir at 1000 rpm and preheat to 150 °C; then add 64.57 g of glycerol, raise the temperature to 210 °C under continuous stirring (500 rpm), add 0.32 g of sodium methoxide as a reaction catalyst, and heat to 230 °C under a constant nitrogen gas flow rate (170 ml / min) and continuous stirring (1000 rpm) for 60 min to obtain vegetable oil-based glycerol monoesters.

[0057] (2) Cool the vegetable oil-based glycerol monoesters obtained in step (1) to 170 °C, and add 16.143 g 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 h; after the reaction, rotate and evaporate on a rotary evaporator for 1 h to remove by-products, that is, prepare vegetable oil-based alkyd resins.

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

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

[0060] Load 500 g of urea granules into a rotating coating drum, preheat at 75 °C and 21 rpm for 10 minutes; spray the above-prepared bio-based coating material on the surface of the urea granules, and the spraying amount of the bio-based coating material is 3% of the weight of the urea granules, and cure and form to prepare a bio-based coated controlled-release fertilizer that can be rapidly and completely degraded.

[0061] Example 5: Preparation of a bio-based coated controlled-release fertilizer that can be rapidly and completely degraded

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

[0063] (1) Load 150.60 g of vegetable oil (the vegetable oil is a mixture of acacia oil and everlasting oil in a mass ratio of 1:1) into a four-necked round-bottom flask, stir at 1500 rpm and preheat to 150 °C; then add 50.2 g of glycerol, raise the temperature to 210 °C under continuous stirring (500 rpm), add 1 g of sodium methoxide as a reaction catalyst, and heat to 230 °C under a constant nitrogen gas flow rate (170 ml / min) and continuous stirring (1000 rpm) for 30 min to obtain vegetable oil-based glycerol monoesters.

[0064] (2) Cool the vegetable oil-based glycerol monoesters obtained in step (1) to 170 °C, and add 60.24 g of polybasic acid (anhydride) (the polybasic acid (anhydride) is a mixture of tetrafluoroterephthalic acid and 4,4'-(hexafluoroisopropylidene) diphthalic anhydride in a mass ratio of 1:1), then raise the temperature to 190 °C and react for 4 h; after the reaction, rotary evaporate for 1 h on a rotary evaporator to remove by-products, namely preparing vegetable oil-based alkyd resins.

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

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

[0067] Load 500 g of urea granules into a rotating coating drum, preheat at 75 °C and 21 rpm for 10 minutes; spray the above-prepared bio-based coating material on the surface of the urea granules, and the spraying amount of the bio-based coating material is 4% of the weight of the urea granules, and cure and form to prepare a bio-based coated controlled-release fertilizer that can be rapidly fully degraded.

[0068] Comparative Example 1:

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

[0070] Test Example 1: Nutrient release determination:

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

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

[0073] The dynamic cross-linking structure modifier added in Example 1 is 4,4'-oxybis(1,4-phenylene)diboronic acid. Compared with the dynamic cross-linking structure modifier added in Example 2 (thieno[3,2-b]thiophene-2,5-diyl diboronic acid), the two benzene rings in the structure of 4,4'-oxybis(1,4-phenylene)diboronic acid endow the cross-linked coating with stronger mechanical strength. Therefore, the coated controlled-release fertilizer prepared in Example 1 has a longer nutrient release period than that in Example 2. The dynamic cross-linking structure modifier added in Example 3 is a combination of 4,4'-oxybis(1,4-phenylene)diboronic acid and thieno[3,2-b]thiophene-2,5-diyl diboronic acid. The addition of the two dynamic cross-linking structure modifiers can form more cross-linking points in the polymer network. Compared with a single dynamic cross-linking structure modifier, the cross-linking density is increased, making the connection between molecular chains closer, thereby increasing the density of the coating. In addition, there may be a synergistic effect between the two dynamic cross-linking structure modifiers, which improves the stability of the cross-linked 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 the external conditions change, the double dynamic cross-linking structure modifier cross-linking system can quickly adjust through dynamic exchange reactions to maintain the dense structure of the material. Therefore, Example 3 has a longer nutrient release period than Examples 1 and 2.

[0074] Test Example 2: Determination of the gel content of the coating of the bio-based coated controlled-release fertilizer

[0075] The gel content of the coatings of the bio-based coated controlled-release fertilizers prepared in Examples 1-3 and Comparative Example 1 was calculated using the 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. Then the obtained material was dried at 80 °C until a constant weight was reached 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, and the solvent was changed every 24 hours. After that, the sample was dried in an oven at 80 °C for 24 hours. Then the gel content was calculated using the following formula:

[0076]

[0077] In the formula: m0 represents the initial mass of the dried coating material, and m represents the mass of the coating material after oven drying after solvent immersion treatment. The test was carried out 3 times, and the presented results are the average values of all samples.

[0078] The results are as follows Figure 3 As shown, for the bio-based coated controlled-release fertilizer prepared in Example 3, due to the addition of two dynamic cross-linking structure modifiers and the synergistic effect between the two dynamic cross-linking structure modifiers, the gel content of the fertilizer coating prepared in Example 3 is the highest, and the gel content of the fertilizer coating prepared in Comparative Example 1 without adding dynamic cross-linking structure modifiers is the lowest.

[0079] Test Example 3: Determination of the morphology and mechanical properties of the fertilizer coating

[0080] Add the bio-based coating materials prepared in Example 1 and Comparative Example 1 into small plastic cups, stir until the mixture starts to become viscous, then pour it onto a polytetrafluoroethylene plate, and then place the polytetrafluoroethylene plate in an oven at 75 °C and wait for 12 h. After complete curing, the coating of the controlled-release fertilizer is obtained.

[0081] The prepared coating was observed by scanning electron microscopy. 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 dynamic cross-linking structure modifiers is significantly less than that of the fertilizer coating cross-section prepared in Comparative Example 1 without adding dynamic cross-linking structure modifiers.

[0082] Use an electronic universal testing machine (MTS, CMT6103) to test the stress-strain curve of the controlled-release fertilizer coating 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 show that after introducing the dynamic cross-linking structure modifier, the cross-linking density of the original polymer network of the fertilizer coating is increased, and its mechanical properties are significantly improved. By increasing the cross-linking density of the coating, the infiltration of moisture into the fertilizer coating can be effectively blocked, thereby prolonging the nutrient release period of the controlled-release fertilizer.

[0084] Test Example 4: Determination of the degradation performance of the fertilizer coating

[0085] Add the bio-based coating materials prepared in Example 1 and Comparative Example 1 into small plastic cups, stir until the mixture starts to become viscous, then pour it onto a polytetrafluoroethylene plate, and then place the polytetrafluoroethylene plate in an oven at 75 °C and wait for 12 h. After complete curing, the coating of the controlled-release fertilizer is obtained.

[0086] The weight method was used to evaluate the degradation performance of the fertilizer coatings of Example 1 and Comparative Example 1. Denote the initial value of the coating weight as S a; Then, bury the coating in the soil and continue to let it stand in a constant temperature incubator at 25°C. Use soils with different pH values to simulate the changes in the acid-base environment inside the fertilizer coating before and after urea release. At each set node, weigh it again on an analytical balance and record it as S b .

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

[0088] The results are as Figure 6 shown. Under neutral conditions (pH = 7.2), the degradation rate of the fertilizer coating prepared in Comparative Example 1 without adding a dynamic cross-linking structure modifier is higher than that of the fertilizer coating prepared in Example 1 with a dynamic cross-linking structure modifier. This is because the cross-linking density of the fertilizer coating prepared in Example 1 with a dynamic cross-linking structure modifier is higher than that of the fertilizer coating prepared in Comparative Example 1. To a certain extent, the high cross-linking density will hinder its degradation process. When under slightly acidic conditions (pH = 5.2), the degradation rate of the fertilizer coating prepared in Example 1 significantly accelerates and exceeds the degradation rate of the fertilizer coating prepared in Comparative Example 1. This is because the dynamic cross-linking modifier is triggered to break under acidic conditions, resulting in the rapid depolymerization of the fertilizer coating. When the soil environment becomes alkaline again (pH = 8.5), the degradation rate of the fertilizer coating prepared in Example 1 significantly slows down and tends to be stable.

[0089] After the urea in the coated controlled-release fertilizer of the present invention is completely released, the acid-base environment inside the coating is slightly acidic. According to Figure 6 the degradation efficiency of the coating under the simulated slightly acidic environment (the degradation rate within 4 weeks is about 5%), it is estimated that the coating prepared in Example 1 will be completely degraded into some small nitrogen-containing substances in about two years after the urea is completely released.

[0090] The above are only the preferred embodiments of the present application and are not used to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A bio-based coated controlled-release fertilizer that can be rapidly and completely degraded, characterized in that, Comprising: A fertilizer core and a biobased coating material wrapped on the surface of the fertilizer core; The biobased coating material is composed of a vegetable oil-based alkyd resin, an amino resin, and a dynamic crosslinked structure modifier; the dynamic crosslinked structure modifier is selected from one or several mixtures of 4,4'-oxybis(1,4-phenylene)diboronic acid, 2,5-difluoro-1,4-benzenediboronic acid, dibenzofuran-4,6-diboronic acid, (perfluoro-1,4-phenylene)diboronic acid, 2,2'-bipyridine-4,4'-diboronic acid, and thiophene[3,2-b]thiophene-2,5-diyl diboronic acid.

2. The bio-based coated controlled-release fertilizer according to claim 1, wherein In the biobased coating material, the mass ratio of the vegetable oil-based alkyd resin to the amino resin is (0.8 - 1.6):1; the addition amount of the dynamic crosslinked structure modifier is 1 - 20% of the mass of the biobased coating material.

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

4. The bio-based coated controlled-release fertilizer according to claim 3, wherein, The mass ratio of the vegetable oil to glycerol is (1.5 - 3):1, the addition amount of sodium methoxide is 0.05 - 0.5% wt% of the reactant system; the mass ratio of the polybasic acid (anhydride) to the 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 several mixtures of perilla oil, rice bran oil, borage oil, canola oil, hemp oil, shea butter, acacia oil, and everlasting oil.

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

7. The bio-based coated controlled-release fertilizer according to claim 1, wherein The amino resin is selected from one or several of melamine formaldehyde resin, urea formaldehyde resin, and phenylmelamine resin.

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

9. The preparation method of the bio-based coated controlled-release fertilizer according to any one of claims 1-8, characterized in that, Including the following steps: Load the fertilizer core into a rotating coating drum and preheat; spray the biobased coating material on the surface of the preheated fertilizer core, and cure and form to prepare a biobased coated controlled-release fertilizer that can be rapidly fully degraded.

10. The preparation method according to claim 9, characterized in that, The preheating conditions are: preheat at 60 - 80 °C, 15 - 30 rpm for 5 - 15 min.

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