Bio-based thermoplastic polyurethane coating material easy to degrade quickly and controlled-release fertilizer

Abstract

The invention discloses a bio-based thermoplastic polyurethane coating material easy to degrade quickly and a controlled-release fertilizer. The coating material comprises 0.8-2.0 parts of a biological chain matrix and 0.5-1.5 parts of a chain reinforcing agent; the biological chain matrix is formed by mixing pre-oxidized vegetable oil diol and bio-based polyester diol; the chain reinforcing agent is formed by mixing a curing agent, a hardening agent and a toughening agent. The bio-based thermoplastic polyurethane coated controlled-release fertilizer comprises fertilizer particles and a bio-based thermoplastic polyurethane coating material sprayed on the surfaces of the fertilizer particles, the spraying amount of the bio-based thermoplastic polyurethane coating material is 0.8-10% of the mass of the fertilizer particles. By accurately regulating and controlling the formula of the film material, the physical properties such as tensile strength and toughness of the bio-based thermoplastic coating material can be jointly improved, so that a more excellent controlled release effect is achieved, and the contradiction between the degradability and the controlled release property of the existing bio-based polyurethane coating material is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of controlled-release fertilizers, and particularly relates to a bio-based thermoplastic polyurethane coating material that is easily and rapidly degradable and a controlled-release fertilizer. Background Art

[0002] After decades of large-scale verification worldwide, coated controlled-release fertilizers have been proven to significantly improve nutrient utilization efficiency. Therefore, the development of coated controlled-release fertilizers is the strategic main direction for China to solve the problems of chemical fertilizer resource waste and environmental pollution. Since petrochemical-based film materials are difficult to degrade and non-renewable, the current research focus of scholars is on preparing coated controlled-release fertilizers using bio-based polyurethanes. Patent CN118580455A prepared a degradable polyurethane-based controlled-release fertilizer coating material, but the raw materials of its film material are not of bio-based origin; Patents CN102320883B, CN112159269B, and CN113788711B respectively solved the problems of easy water absorption and easy damage of bio-based film materials through dense modification, surface superhydrophobic modification, and self-healing modification technologies, but did not study the degradation effect of their film materials or the degradation performance of the film materials is general. In summary, there is a core problem that is difficult to overcome in the current research on bio-based polyurethane coated controlled-release fertilizers, that is, it is impossible to achieve rapid degradation of the film material while having excellent controlled-release performance, which is mainly due to the contradiction between the cross-linked structure and degradation performance of bio-based polyurethane film materials. By increasing the cross-linking degree of the chemical structure to improve the density, the mechanical properties of the film material can be enhanced, the pores can be maintained intact, and the controlled-release performance can be greatly extended.

[0003] Thermosetting polyurethane coating materials have been widely used in the preparation of controlled-release fertilizers. They can achieve controlled release through a dense structure. However, due to relying on irreversible chemical covalent cross-linking, it is difficult to degrade. Moreover, the film material lacks toughness, resulting in easy breakage during the later stage of nutrient controlled release due to the increase in osmotic pressure difference. Thermoplastic polyurethane has a special linear molecular chain structure with a very low degree of cross-linking. Therefore, compared with thermosetting polyurethane, it has better ductility and toughness and has great potential for preparing high-performance coating materials. More importantly, it has been proven to have significant degradation advantages and thus has great application potential. In order to achieve the sustainable development of controlled-release fertilizers, an ideal thermoplastic polyurethane coating material should have excellent degradation effects while taking into account high mechanical strength and high crack resistance / toughness to avoid potential damage to the film material during production and transportation and to resist nutrient loss caused by crack propagation under osmotic pressure difference. Especially to ensure a long controlled-release life, these performance indicators are crucial. However, there is a great contradiction and challenge between the degradability and controlled-release performance of bio-based thermoplastic polyurethane. Specifically, controlled-release film materials with high mechanical strength and toughness usually require more complex chemical bonds and chemical cross-linking structures to support, which are difficult to achieve for non-cross-linked or weakly cross-linked thermoplastic polyurethane film materials. And the overly dense cross-linked structure of the film material introduces a large number of covalent bonds that are difficult to degrade, increasing the complexity of the chain and thus making the film material difficult to degrade. Therefore, it is urgent to develop bio-based thermoplastic coating controlled-release fertilizers with excellent performance and easy and rapid degradation. At present, there is no clear research report on using bio-based thermoplastic polyurethane to prepare coating controlled-release fertilizers at home and abroad. Summary of the Invention

[0004] In view of the above-mentioned prior art, the purpose of the present invention is to provide a bio-based thermoplastic polyurethane coating material and a controlled-release fertilizer that are easy to rapidly degrade. The present invention changes the chemical cross-linking structure of traditional polyurethane coating controlled-release fertilizers. On the basis of maintaining its original linear cross-linking characteristics, a large number of non-covalent physical cross-linking domains are introduced. These cross-linking domains can provide sacrificial bonds through non-covalent interactions to dissipate external force energy without affecting the original chemical cross-linking structure. By precisely regulating the formula of the coating material, it is possible to simultaneously improve the physical properties such as the tensile strength and toughness of the bio-based thermoplastic controlled-release film material, thus achieving a more excellent controlled-release effect and solving the contradiction between the degradability and controlled-release performance of the current bio-based polyurethane coating materials.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions: In the first aspect of the present invention, there is provided a bio-based thermoplastic polyurethane coating material that is easy to rapidly degrade, comprising the following raw materials in parts by mass: 0.8 - 2.0 parts of a biological chain matrix and 0.5 - 1.5 parts of a chain enhancer; The biological chain matrix is composed of a pre-oxidized vegetable oil diol and a bio-based polyester diol; The pre-oxidized vegetable oil diol is prepared by the following method: (1) Mix vegetable oil, small molecule short-chain alcohol and solid base catalyst, heat for reaction, and separate glycerol product; (2) Add hydrogen peroxide, formic acid and phosphotungstic acid into the reaction system obtained in step (1), and stir for reaction under heating; (3) Add dilute sulfuric acid and small molecule diol into the reaction system obtained in step (2), and heat and stir for reaction to obtain vegetable oil diol; (4) Pass air through the vegetable oil diol under heating for oxidation to obtain a light yellow transparent liquid, which is the pre-oxidized vegetable oil diol; The bio-based polyester diol is prepared by the following method: Mix the pre-oxidized vegetable oil diol and bio-based dibasic acid, heat for reaction under negative pressure in a protective atmosphere, then raise the temperature to continue the reaction, add calcium carbonate, stir and filter to remove calcium carbonate, and vacuum filter to obtain the product, which is the bio-based polyester diol; The chain enhancer is composed of a curing agent, a hardening agent and a toughening agent.

[0006] Preferably, the mass ratio of the pre-oxidized vegetable oil diol to the bio-based polyester diol is 10:(1-5); the acid value of the pre-oxidized vegetable oil diol is 60-100 mg KOH / g, and the peroxide value is 5-15 meq / kg; the curing agent is diisocyanate; the hardening agent is aromatic rigid diamine or diol; the toughening agent is aliphatic flexible diamine or diol.

[0007] Preferably, the aromatic rigid diamine or diol is at least one of 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, 3,3'-dichloro-4,4'-diaminodiphenylmethane, 4,4'-dihydroxydiphenyl sulfone or 4,4'-biphenol; the aliphatic flexible diamine or diol is at least one of 1,6-hexanediamine, N-aminoethylpiperazine, 1,3-diamino-2-hydroxypropane, N,N'-bis(2-hydroxyethyl)oxamide or 1,4-cyclohexanedimethanol.

[0008] More preferably, the diisocyanate is at least one of diphenylmethane diisocyanate, dicyclohexylmethane 4,4'-diisocyanate, hexamethylene diisocyanate or pentamethylene diisocyanate.

[0009] Preferably, in step (1), the mass ratio of the vegetable oil, small molecule short-chain alcohol to the solid base catalyst is 20:4:1; the temperature of the heating reaction is 70 °C and the time is 2.5 h.

[0010] More preferably, the vegetable oil is selected from at least one of palm oil, camellia oil, rice bran oil, and Chinese tallow tree oil; the small molecule short-chain alcohol is methanol; the solid base catalyst is NaAlO2.

[0011] Preferably, in step (2), the mass ratio of the reaction system, hydrogen peroxide, formic acid, and phosphotungstic acid is 20:10:3:0.1; the heating temperature is 60 °C, and the stirring reaction time is 5 h.

[0012] More preferably, the mass concentration of the hydrogen peroxide is 35%.

[0013] Preferably, in step (3), the mass ratio of the reaction system, dilute sulfuric acid, and small molecule diol is 5:2:1; the heating and stirring reaction temperature is 60 °C and the time is 1 h.

[0014] More preferably, the small molecule diol is ethylene glycol.

[0015] Preferably, in step (4), the heating temperature is 65-75 °C; the oxidation time is 12-18 h; the air flow rate is 0.8-1.2 L·min -1 ·kg -1 。

[0016] Preferably, the mass ratio of the pre-oxidized vegetable oil diol to the bio-based diacid is 1.05:1; the negative pressure is -0.05 Mpa; the heating reaction temperature is 120 °C and the time is 2 h; the temperature is raised to 160 °C and the reaction continues for 3 h; the addition amount of calcium carbonate accounts for 0.1% of the total mass of the pre-oxidized vegetable oil diol and the bio-based diacid.

[0017] More preferably, the bio-based diacid is at least one of succinic acid, sebacic acid, azelaic acid, malic acid, or 2,5-furandicarboxylic acid.

[0018] Preferably, the bio-based thermoplastic polyurethane coating material is prepared by the following method: (1) Under vacuum conditions, the pre-oxidized vegetable oil diol and the bio-based polyester diol are heated and mixed to obtain a bio-chain matrix; (2) The curing agent, hardening agent, and toughening agent are heated and mixed under stirring to obtain a chain enhancer; (3) The bio-chain matrix and the chain enhancer are mixed and stirred evenly, and ultrasonically oscillated at room temperature to obtain the bio-based thermoplastic polyurethane coating material.

[0019] In the second aspect of the present invention, there is provided the use of the bio-based thermoplastic polyurethane coating material in the preparation of an easily fast-degrading controlled-release fertilizer.

[0020] In a third aspect of the present invention, a bio-based thermoplastic polyurethane-coated controlled-release fertilizer that is easily and rapidly degradable is provided. The bio-based thermoplastic polyurethane-coated controlled-release fertilizer includes fertilizer granules and a bio-based thermoplastic polyurethane coating material sprayed on the surface of the fertilizer granules; the spraying amount of the bio-based thermoplastic polyurethane coating material is 0.8-10% of the mass of the fertilizer granules.

[0021] Preferably, it is prepared by the following method: preheat the fertilizer granules, then spray or drip the bio-based thermoplastic polyurethane coating material onto the surface of the fertilizer granules, stir the fertilizer under heat preservation, the coating material forms a coating, after cooling, spray or drip the bio-based thermoplastic polyurethane coating material again, and then heat up and cure. Repeat the above operations 1-10 times. After the last layer is cured and the temperature is reduced to room temperature, the bio-based thermoplastic polyurethane-coated controlled-release fertilizer is obtained.

[0022] More preferably, the fertilizer granules are selected from at least one of urea granules, ammonium sulfate granules, superphosphate granules, potassium dihydrogen phosphate granules, and potassium sulfate granules.

[0023] More preferably, the preheating temperature is 85-95 °C; the cooling is to 60 °C; the temperature for heating up and curing is 80-90 °C.

[0024] Advantages of the present invention: (1) The present invention for the first time uses bio-based thermoplastic polyurethane to prepare a coating-controlled release fertilizer film material with a completely linear cross-linked structure, replacing the commonly used three-dimensional chemically cross-linked bio-based thermosetting polyurethane coating material, and greatly reducing the time required for film material degradation. The 180-day degradation rate of its film material is at least 67.8% higher than that of the thermosetting polyurethane controlled-release film material. And the vegetable oil diol in the biological chain matrix is subjected to controllable pre-oxidation treatment (acid value 60-100 mg KOH / g) to in-situ generate C8-C12 short-chain carboxylic acids. The carboxylic acid groups form hydrogen bond networks with the urethane groups in the polyurethane main chain, replacing the chemical cross-linking function; the dynamic hydrogen bonds maintain the denseness of the film layer during the controlled-release period. When 80% of the nutrients are released, the film material absorbs water and swells, resulting in pore expansion, the hydrogen bond cross-linked domain dissociates, and the carboxylic acid seeps out along the pore channels, accelerating the exposure of the main chain to the hydrolysis environment and achieving rapid degradation.

[0025] (2) The present invention utilizes a chain enhancer to enhance and modify the bio-based thermoplastic polyurethane film. The introduction of the chain enhancer enables the original film to form supramolecular aggregated chain segments through π-π stacking of planar aromatic structures, intermolecular interactions of multiple hydrogen bonds, and van der Waals forces between bio-based long-chain alkanes. On the basis of the original linear polyurethane film chain, non-covalent dynamic physical weak cross-linking domains are added to enhance the film-forming effect and physical properties of the film, thereby enhancing its physical properties and film-forming performance without affecting its chemical cross-linking degree. Since the chain enhancer is prepared by alternately and reasonably designing rigid and flexible small molecular chain segments, the film simultaneously exhibits strong rigidity and toughness, meeting the requirements for mechanical strength during the production and transportation of coated controlled-release fertilizers and the flexibility of the film in the later stage of use.

[0026] (3) The present invention has developed a dynamic temperature gradient coating process suitable for bio-based thermoplastic polyurethane coating materials, and realizes the coordinated optimization of film layer structure and performance through segmented temperature control. Gelation and pre-curing are rapidly achieved in the primary curing stage to eliminate the aggregation of internal stress during the phase change process of the material; subsequently, the temperature is lowered to induce the directional arrangement of physical cross-linking domains; in the secondary curing stage, the temperature is dynamically regulated, and the interfacial bonding force between the film layer and the basal fertilizer particles or between the film layers is enhanced through the molecular chain relaxation effect; at the end of the last layer of coating, the temperature is lowered to room temperature to achieve complete curing of the thermoplastic components while retaining the dynamic hydrogen bond dissociation characteristics.

[0027] (4) Through the sequential coordinated design between controlled release and degradation performance, the present invention realizes the easy degradability of the film (degradation rate ≥ 50% in 180 days, ≥ 80% in 1 year, avoiding environmental residues) and long-term controlled release performance (nutrient controlled release period exceeding 110 days). BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 : Scanning electron microscope photograph (a) of the coated controlled-release fertilizer prepared in Example 1 of the present invention and atomic force microscope photograph (b) of its film shell; Figure 2 : Soil degradation rate of the film shell of the coated controlled-release fertilizer prepared by the present invention; Figure 3 : Nutrient release characteristics of the coated controlled-release fertilizer prepared by the present invention under constant temperature conditions (25 °C). DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] It should be noted that the following detailed description is illustrative and is intended to provide further description 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.

[0030] As introduced in the background art section, most of the coating materials for existing bio-based polyurethane coated controlled-release fertilizers are thermosetting polyurethanes, and their cross-linked structure is a three-dimensional network structure. Due to the fact that these structures are cross-linked based on strong and difficult-to-break chemical covalent bonds and have a high degree of cross-linking, it is difficult to achieve the bond-breaking degradation of the film structure in the soil environment. Although thermoplastic polyurethane can be degraded, when it is directly used for coating controlled-release fertilizers, the controlled-release period cannot meet the requirements, and the nutrients are completely released within 2 days. This is mainly because the weak cross-linking characteristics of thermoplastic polyurethane result in poor film-forming effect, and the physical properties of the film material do not meet the requirements of controlled-release fertilizers.

[0031] Based on this, the object of the present invention is to provide a bio-based thermoplastic polyurethane coating material and a controlled-release fertilizer that are easily and rapidly degradable. The bio-based thermoplastic polyurethane coating material of the present invention includes a biological chain matrix and a chain enhancer. The biological chain matrix is composed of pre-oxidized vegetable oil diol and bio-based polyester diol, which is the main component of the film material and also the main source of the bio-based content. The selected vegetable oil has the characteristics of saturation content and can maintain a stable structure under the reaction conditions of continuous alcoholization and esterification, and is suitable as the matrix of the coating material; the chain enhancer is composed of a curing agent, a hardening agent and a toughening agent. The curing agent can react with the biological chain matrix to form the linear main chain structure of the bio-based thermoplastic polyurethane film material, while the hardening agent and the toughening agent can be grafted into the linear structure through the reaction of urethane and allophanate to introduce supramolecular aggregation segments with multiple hydrogen bonds, intermolecular van der Waals forces, and planar π-π stacking effects, thereby forming a non-covalent physical cross-linking domain and providing a large number of external force sacrificial bonds, significantly improving the film-forming effect and physical properties of the bio-based thermoplastic polyurethane film material. The bio-based thermoplastic polyurethane is linearly connected by pre-oxidized vegetable oil diol and bio-based polyester diol through urethane bonds, avoiding three-dimensional network chemical cross-linking. Through controllable pre-oxidation treatment, short-chain carboxylic acids with C8-C12 are generated from vegetable oil diol. In the controlled-release stage, the carboxylic acids stabilize the physical cross-linking network through hydrogen bond action; in the later stage of controlled release, the film layer absorbs water and swells, resulting in the dissociation of the physical cross-linking domain, and the carboxylic acids seep out through the pore channels, accelerating the exposure of the main chain to the hydrolysis environment. This dual-functional mechanism enables the material to achieve a precise dynamic balance between controlled release and degradation without external additives.

[0032] The present invention further develops a bio-based thermoplastic polyurethane coated controlled-release fertilizer that is easily and rapidly degradable, and constructs a special curing process system for the bio-based thermoplastic polyurethane coating. The complete curing of the film material is achieved through segmented temperature control: at a constant temperature in the primary curing stage (in the range of 85-95 °C, with a periodic fluctuation of ±5 °C), gelation and pre-curing are rapidly achieved to eliminate the aggregation of internal stress during the phase change process of the material; then the temperature is lowered to 60 °C to induce the directional arrangement of physical cross-linking domains; in the secondary curing stage, dynamic temperature control is applied (raised to 80-90 °C), and the interfacial bonding force between the film layer and the basal fertilizer particles or between the film layers is enhanced through the molecular chain relaxation effect; at the end of the last layer of coating, the temperature is lowered to room temperature (cooling rate ≤5 °C / min) to achieve the complete curing of the thermoplastic components while retaining the dynamic hydrogen bond dissociation characteristics. This process breaks through the limitations of the traditional film material curing method for coated controlled-release fertilizers and realizes the coordinated improvement of film formation speed and structural stability.

[0033] The present invention innovatively solves the technical contradictions existing in traditional bio-based polyurethane coating materials, specifically manifested as: aiming at the dual technical defects of the difficult degradation of bio-based thermosetting polyurethane film materials and the insufficient film formation performance of thermoplastic polyurethane in the prior art, for the first time, a bio-based thermoplastic polyurethane is used as the main coating material through material system innovation, and a new bio-based polyurethane coated controlled-release fertilizer system is constructed. This technical breakthrough realizes the following synergistic effects: 1) By designing a linear cross-linked structure, the film material is given controllable biodegradable characteristics, and rapid degradation after release is achieved on the premise of ensuring the stable controlled-release period of the film material; 2) The introduction of non-covalent physical cross-linking domains by chain enhancers enhances the intermolecular force between the linear molecular chains of thermoplastic polyurethane, significantly improving the film formation performance and breaking through the industrial bottleneck that it is difficult to have both degradation performance and controlled-release efficiency in the prior art; 3) Optimize the special coating curing method for thermoplastic polyurethane, and maintain the uniformity and integrity of the film layer structure by gradient control of the coating temperature.

[0034] In order to enable those skilled in the art to more clearly understand the technical solutions of the present application, the technical solutions of the present application will be described in detail below in conjunction with specific embodiments.

[0035] Note: The palm oil (CAS No. 8002-75-3) and rice bran oil (CAS No. 68553-81-1) used in the examples were purchased from Shanghai Macklin Biochemical Co., Ltd.; Jojoba oil (CAS No. 61789-91-1) and coconut oil (CAS No. 8001-31-8) were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0036] The test materials used in the embodiments of the present invention are all conventional test materials in the art and can be obtained through commercial channels.

[0037] Example 1: Preparation of easily degradable bio-based thermoplastic polyurethane coated controlled-release fertilizer (1) Preparation of biological chain matrix: Mix palm oil, camellia oil, and rice bran oil in a mass ratio of 6:1:1 to obtain vegetable oil. Mix the vegetable oil with methanol and NaAlO₂ in a mass ratio of 20:4:1, and react at 70 °C for 2.5 h under the catalysis of NaAlO₂. Separate glycerol from the product, and add hydrogen peroxide (35%), formic acid, and phosphotungstic acid to the remaining components in a mass ratio of 20:10:3:0.1. Stir continuously at 60 °C for 5 h. Add dilute sulfuric acid and ethylene glycol to the above system in a mass ratio of 5:2:1, and stir and react at 60 °C for 1 h. Pass air into the system at an air flow rate of 0.9 L·min⁻¹·kg⁻¹ at 70 °C for 12 hours to obtain pre-oxidized vegetable oil diol (acid value is 8 mg KOH / g, peroxide value is 10 meq / kg).

[0038] Mix the pre-oxidized vegetable oil diol and succinic acid in a mass ratio of 1.05:1, add them to a reaction kettle, and displace air with nitrogen. React at 120 °C and -0.05 MPa for 2 h. After the reaction is completed, raise the temperature to 160 °C and continue to react for 3 h. Then add 0.1 g of calcium carbonate, stir, filter to remove calcium carbonate, and then perform vacuum filtration for 1 h to obtain the product, which is the bio-based polyester diol.

[0039] Mix the pre-oxidized vegetable oil diol and the bio-based polyester diol evenly in a mass ratio of 10:4 to obtain the biological chain matrix.

[0040] (2) Preparation of chain enhancer: Mix diphenylmethane diisocyanate and dicyclohexylmethane 4,4'-diisocyanate in a mass ratio of 3:1, and heat at 80 °C for 1.5 h in a vacuum environment to obtain a curing agent.

[0041] Mix the curing agent, 4,4'-diaminodiphenylmethane, and 1,6-hexanediamine evenly at 45 °C in a mass ratio of 80:20:20 to obtain the chain enhancer.

[0042] (3) Preparation of coating material: Mix the biological chain matrix prepared in step (1) and the chain enhancer component prepared in step (2) evenly in a mass ratio of 1:1, and ultrasonically vibrate at room temperature for 30 min to obtain a uniform coating material.

[0043] (4) Preparation of coated controlled-release fertilizer: Add 2 kg of urea granules as fertilizer granules into a rotating drum preheated to 85 °C, and then spray the coating material prepared in step (3) onto the surface of the fertilizer granules. Continuously maintain the temperature of the rotating drum during the rotation of the drum and stir the fertilizer with a glass rod. The coating material forms a coating. After about 15 minutes, lower the temperature to 60 °C. After adding the next portion of the coating material, raise the temperature to 80 °C. The mass of the coating material sprayed onto the surface of the fertilizer granules each time accounts for 0.8% of the mass of the fertilizer granules. Repeat the above operation 8 times, and a total of 128 g of the coating material is sprayed. After the last layer is cured, while keeping the rotating drum running, wait for the temperature to drop to room temperature and then take out to obtain the biodegradable bio-based thermoplastic polyurethane-coated controlled-release fertilizer. Observe the surface of the controlled-release fertilizer ( Figure 1 in a and b) by scanning electron microscopy and atomic force microscopy to prove that the uniform and complete coated controlled-release fertilizer was successfully prepared in Example 1.

[0044] Example 2: Preparation of biodegradable bio-based thermoplastic polyurethane-coated controlled-release fertilizer: (1) Preparation of biochain matrix: The difference from step (1) of Example 1 is that: Mix palm oil, camellia oil, and Chinese tallow tree oil in a mass ratio of 7:1:1 to prepare vegetable oil; mix the vegetable oil with methanol and NaAlO2 in a mass ratio of 20:4:1, react at 70 °C for 2.5 h under the catalysis of NaAlO2, separate glycerol from the product, and add hydrogen peroxide (35%), formic acid, and phosphotungstic acid to the remaining components in a mass ratio of 20:10:3:0.1, continuously stir at 60 °C for 5 h, add dilute sulfuric acid and ethylene glycol to the above system in a mass ratio of 5:2:1, stir and react at 60 °C for 1 h, and introduce air at an air flow rate of 0.9 L·min⁻¹·kg⁻¹ at 70 °C for 12 hours to obtain pre-oxidized vegetable oil diol (acid value is 80 mg KOH / g, peroxide value is 10 meq / kg).

[0045] Mix the pre-oxidized vegetable oil diol and sebacic acid in a mass ratio of 1.05:1, add them to a reaction kettle, and displace the air with nitrogen. React at 120 °C and -0.05 MPa for 2 h. After the reaction is completed, raise the temperature to 160 °C and continue to react for 3 h. Then add 0.1 g of calcium carbonate, stir and filter to remove the calcium carbonate, and then vacuum filter for 1 h to obtain the product, which is the bio-based polyester diol; Uniformly mix the pre-oxidized vegetable oil diol and the bio-based polyester diol in a mass ratio of 10:4 to obtain the biochain matrix.

[0046] (2) Preparation of chain enhancer: The difference from step (2) of Example 1 is that: mix the curing agent, 4,4'-diaminodiphenyl ether, and 1,6-hexanediamine in a mass ratio of 60:15:15 and stir evenly at 45 °C to obtain the chain enhancer.

[0047] (3) Preparation of coating material: Same as step (3) of Example 1.

[0048] (4) Preparation of coated controlled-release fertilizer: The difference from step (4) of Example 1 is that the total spraying amount of the coating material is 7.2% of the mass of the fertilizer particles, and finally a biodegradable bio-based thermoplastic polyurethane coated controlled-release fertilizer is obtained.

[0049] Example 3: Preparation of biodegradable bio-based thermoplastic polyurethane coated controlled-release fertilizer: (1) Preparation of biological chain matrix: The difference from step (1) of Example 1 is that camellia oil, rice bran oil, and Chinese tallow tree oil are mixed in a mass ratio of 9:1:1 to prepare vegetable oil; the vegetable oil is mixed with methanol and NaAlO2 in a mass ratio of 20:4:1, and reacted at 70 °C for 2.5 h under the catalysis of NaAlO2. Glycerol in the product is separated out, and hydrogen peroxide (35%), formic acid, and phosphotungstic acid are added to the remaining components in a mass ratio of 20:10:3:0.1, and stirred continuously at 60 °C for 5 h. Dilute sulfuric acid and ethylene glycol are added to the above system in a mass ratio of 5:2:1, and stirred and reacted at 60 °C for 1 h. Air is introduced at a flow rate of 0.9 L·min⁻¹·kg⁻¹ at 70 °C for 12 hours to obtain pre-oxidized vegetable oil diol (acid value is 80 mg KOH / g, peroxide value is 10 meq / kg).

[0050] The pre-oxidized vegetable oil diol and 2,5-furandicarboxylic acid are mixed in a mass ratio of 1.05:1, added to a reaction kettle, and the air is replaced with nitrogen. React at 120 °C and -0.05 MPa for 2 h. After the reaction is completed, the temperature is raised to 160 °C and the reaction continues for 3 h. Then 0.1 g of calcium carbonate is added, stirred, filtered to remove calcium carbonate, and then vacuum filtered for 1 h to obtain the product, which is bio-based polyester diol; The pre-oxidized vegetable oil diol and bio-based polyester diol are uniformly mixed in a mass ratio of 10:4 to obtain a biological chain matrix. (2) Preparation of chain enhancer: The difference from step (2) of Example 1 is that the curing agent, 4,4'-biphenol, and 1,6-hexanediamine are mixed and stirred evenly at 45 °C in a mass ratio of 60:15:15 to obtain a chain enhancer.

[0051] (3) Preparation of coating material: The biological chain matrix and chain enhancer components are mixed and stirred evenly in a mass ratio of 1.2:1, and ultrasonically oscillated at room temperature for 20 - 40 min to obtain a uniform coating material.

[0052] (4) Preparation of coated controlled-release fertilizer: The difference from step (4) of Example 1 is that the total spraying amount of the coating material is 8% of the mass of the fertilizer particles, and finally a biodegradable bio-based thermoplastic polyurethane-coated controlled-release fertilizer is obtained.

[0053] Comparative Example 1: The difference between this comparative example and Example 1 is that the preparation process of the biological chain matrix involves the preparation of vegetable oil polyol and bio-based polyester polyol. The specific preparation method is as follows: Mix linseed oil, camellia oil, and rice bran oil in a mass ratio of 7:2:1 to prepare a vegetable oil raw material. React with methanol at 70 °C for 2.5 h under the catalysis of NaAlO2 (the mass ratio of the three is 20:4:1). After separating the glycerol product, add hydrogen peroxide (35%), formic acid, and phosphotungstic acid (the mass ratio of the four is 30:10:3:0.1), and continuously stir at 70 °C for 8 h. Then add dilute sulfuric acid and ethylene glycol (the mass ratio of the three is 5:2:1), stir and react at 60 °C for 1 h. Then add NaOH to adjust the pH to 10 and continue to react at 80 °C for 2 h to obtain vegetable oil polyol; mix the obtained vegetable oil polyol with citric acid (ternary acid) (mass ratio of 800:1) and add it to the reaction kettle. Subsequently, add 1% of the total mass fraction of pentaerythritol for chain extension, and displace the air with nitrogen. React at 150 °C and -0.09 MPa for 2 h, raise the temperature to 160 °C, continue to react for 3 h, then add 0.1 g of calcium carbonate, stir and filter to remove calcium carbonate, and vacuum filter for 1 h to obtain the product, which is bio-based polyester polyol; uniformly mix the vegetable oil polyol and bio-based polyester polyol according to a mass ratio of 2.5:1 to obtain the biological chain matrix.

[0054] The remaining preparation steps are the same as those in Example 1 to obtain the coated controlled-release fertilizer.

[0055] Comparative Example 2: The difference between this comparative example and Example 1 is that the pre-oxidation step of vegetable oil diol is cancelled, and vegetable oil diol is directly used to prepare the biological chain matrix. The specific preparation method is as follows: Prepare a vegetable oil raw material by mixing palm oil, camellia oil, and rice bran oil in a mass ratio of 6:1:1. React it with methanol at 70 °C for 2.5 h under the catalysis of NaAlO2 (the mass ratio of the three is 20:4:1). After separating the glycerol product, add hydrogen peroxide (35%), formic acid, and phosphotungstic acid and mix them (the mass ratio of the four is 20:10:3:0.1). Stir continuously at 60 °C for 5 h. Then add dilute sulfuric acid and ethylene glycol and mix them (the mass ratio of the three is 5:2:1). Stir and react at 60 °C for 1 h to obtain vegetable oil diol; mix the obtained vegetable oil diol with succinic acid (mass ratio of 1000:1) and add it to a reaction kettle. Replace the air with nitrogen. React at 120 °C and -0.05 MPa for 2 h, raise the temperature to 160 °C, continue to react for 3 h, then add 0.1 g of calcium carbonate, stir and filter to remove calcium carbonate, and perform vacuum filtration for 1 h to obtain the product, which is a bio-based polyester diol; uniformly mix the vegetable oil diol and the bio-based polyester diol according to a mass ratio of 10:4 to obtain a bio-chain matrix.

[0056] The remaining preparation steps are the same as those in Example 1 to obtain the coated controlled-release fertilizer.

[0057] Comparative Example 3: The difference between this comparative example and Example 1 is that hardening agent and toughening agent are not used in the preparation process of the chain enhancer. The specific preparation method is as follows: Heat diphenylmethane diisocyanate and dicyclohexylmethane 4,4'-diisocyanate in a mass ratio of 3:1 at 80 °C under vacuum for 1 - 2 h as the chain enhancer; The remaining preparation steps are the same as those in Example 1 to obtain the coated controlled-release fertilizer.

[0058] Comparative Example 4: The preparation steps of the coating material in this comparative example are the same as those in Example 1. The difference from Example 1 is that the coating method described in the specific implementation manner is not used in the preparation process of the coated controlled-release fertilizer. The specific preparation method is as follows: Add 2 kg of fertilizer particles to a rotary drum, preheat to 85 °C, and after 10 minutes, spray or coat the above coating material on the surface of the fertilizer particles, and continuously maintain the temperature during the rotation of the rotary drum. The coating material solidifies to form a coating to prepare the coated controlled-release fertilizer. The mass of the coating material sprayed or dropped on the surface of the fertilizer particles each time accounts for 0.8% of the mass of the fertilizer particles. Repeat the above operation 8 times to obtain a coated controlled-release fertilizer with a coating thickness of 6.4%.

[0059] Test Example 1: Test on the soil simulation degradation rate of the film shell of the coated controlled-release fertilizer The coated controlled-release fertilizers prepared in Examples 1-3 and Comparative Examples 1-4 were respectively put into a grinding machine and ground for 5 seconds. After taking them out, they were placed into deionized water. 10 g of the residual film materials floating on the water surface in each group were taken and put into a nylon mesh bag of 10 cm × 10 cm, and then buried in 1 kg of test soil (collected from a suburb in Taishan District, Tai'an City, Shandong Province, which is ordinary brown soil (Haplic Udic Cambisol), naturally air-dried and sieved through a 5-mm sieve pore, at 25°C and a humidity of 60%, and after treatment, placed in a constant temperature incubator for the film shell simulation degradation test). Samples were taken out every 30 days for cleaning and drying, and the mass loss rate (%) was calculated as the degradation rate. After the test was completed, the film shells were put back into the mesh bags and re-buried in the soil.

[0060] Degradation rate (%) = (W0 - W1) / W0 × 100%. Where W0 is the initial weight and W1 is the weight when sampling.

[0061] As Figure 2 shown, the film materials of the examples all had a degradation rate exceeding 50% in 180 days and a degradation rate ≥ 80% in 1 year. Their degradation mechanism originated from the enzymatic hydrolysis of the main chain of linear polyurethane by microorganisms and the dynamic dissociation of physical cross-linking domains. Comparative Example 1 used a thermosetting polyurethane with a three-dimensional chemical cross-linking network. Due to the difficulty of breaking high-density chemical covalent bonds, there was a risk of residue in the film shell (degradation rate ≤ 50% in 365 days); in Comparative Example 2, due to the lack of a pre-oxidation step, the carboxylic acid system was missing, resulting in a significant decline in degradation performance; while in Comparative Example 3, due to the lack of a chain enhancer, the basic structure of the film layer was extremely easy to disintegrate and degraded prematurely; Comparative Example 4 used a one-time curing process, and its coating structure was loose, with poor uniformity and integrity. Therefore, its degradation rate was significantly faster than that of the examples, and at the same time, it also led to a rapid release of nutrients ( Figure 3 80% was released in 50 days in it), verifying the sharp contradiction between the degradation rate and the controlled-release performance in the traditional process. And the present invention simultaneously achieved the synergistic goal of long-term nutrient controlled release and rapid degradation of the film shell after release through the precise and reasonable design of linear molecular chains and a step-by-step curing process.

[0062] Test Example 2: Determination of nutrient release rate The determination method referred to the national standard of the People's Republic of China "GB / T 23348-2009 Slow-release fertilizers". The specific test method was as follows: 10 g of the coated controlled-release fertilizers prepared in Examples 1-3 and Comparative Examples 1-4 were respectively put into glass bottles containing 200 mL of deionized water and stored statically in a constant temperature incubator at 25°C. The water samples of each fertilizer were taken on the 1st, 3rd, 5th, 7th, 14th, 21st, and 28th days of cultivation. The time interval for subsequent sampling was 7 days until the cumulative nutrient release rate reached 80%; after each sampling, the remaining water in the bottle was poured out, and 200 mL of deionized water was re-added to the bottle. The nitrogen concentration of the water sample was measured by the Kjeldahl method.

[0063] According to Figure 3As shown in the figure, in Example 1, pre-oxidized vegetable oil diol and bio-based polyester diol were used to construct a biological chain matrix at a mass ratio of 2.5:1, and a chain enhancer was introduced. Non-covalent physical cross-linking domains were formed through dynamic π-π stacking, hydrogen bonding, and van der Waals forces. Combining with the dynamic temperature gradient coating process, a controlled release period of ≥110 days and a degradation rate of ≥50% at 180 days were achieved. In Comparative Example 1, a highly chemically cross-linked thermosetting polyurethane was used, and its three-dimensional cross-linking network led to an overly long controlled release period (the release rate was only 48.5% at 119 days). In Comparative Example 3, no chain enhancer was added, and the film layer showed brittle fracture due to the lack of physical cross-linking domains, and the release rate increased suddenly to 58.4% at 21 days. In Comparative Example 4, the coating process was simplified, and a complete gradient cured film layer structure was not formed. The film shell was loose and uneven, and the release rate reached 58.8% at 35 days. If the film shell of the controlled release fertilizer degrades quickly, the nutrients will be released quickly, and the controlled release effect will be poor. The above comparison verified the necessity of the non-covalent physical cross-linking domain design and the dynamic temperature gradient coating process for the controlled release long-term effect and degradation synergy. In the examples of the present invention, the controlled release performance was optimized through the synergistic effect of the biological chain matrix and the chain enhancer.

[0064] Test Example 3: Tensile properties of the film material of the coated controlled release fertilizer Referring to the national standard of the People's Republic of China "GB / T 1040", the film material tensile property test was carried out on the coated controlled release fertilizers prepared in Example 1, Example 2, Example 3, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4 of the present invention. The specific test method is as follows: The coating material was made into dumbbell-shaped specimens (thickness 1 mm, gauge length 25 mm). Using a universal testing machine Instron5969, it was stretched to break at a speed of 50 mm / min, and the maximum tensile force and elongation at break were recorded. The tensile strength (MPa) and elongation at break (%) were calculated.

[0065] Tensile strength (MPa) = maximum tensile force (N) / cross-sectional area (mm 2 )

[0066] Elongation at break (%) = (gauge length at break - initial gauge length) / initial gauge length × 100%. The obtained results are shown in Table 1.

[0067] Table 1 Tensile strength (MPa) and elongation at break (%) of the film material of the controlled release fertilizer Note: The significance analysis was performed using a two-sample t-test (comparison between examples and comparative examples, α = 0.05). Among them: p < 0.001 (extremely significant); p < 0.01 (highly significant); p < 0.05 (significant) As shown in Table 1, this design enables the film material to have both high tensile strength (18.7 ± 1.3 MPa in Example 1) and high elongation at break (318.5 ± 14.2% in Example 1) while maintaining the low chemical cross-linking characteristics of linear polymers. Compared with Comparative Example 3 (without adding chain enhancer, tensile strength is only 6.8 ± 1.1 MPa, elongation at break is 38.6 ± 5.7%), the improvement in the mechanical properties of the examples is due to the synergistic enhancement effect of rigid segments and flexible segments on the linear polyurethane structure: the rigid segments enhance the intermolecular force through aromatic structures, and the flexible segments improve the ductility through aliphatic structures, effectively inhibiting the propagation of microcracks. In addition, Comparative Example 1 uses highly chemically cross-linked thermosetting polyurethane, and there is a significant difference in toughness compared with Example 1 (elongation at break is 58.3 ± 7.9%). In Comparative Example 2, due to the lack of carboxylic acid-mediated multi-level intermolecular forces, the packing efficiency of rigid segments decreases, and the energy dissipation ability of flexible segments is also limited, resulting in significant deterioration of mechanical properties, proving that the synergistic non-covalent physical cross-linking formed by the pre-oxidation process and chain enhancer in the present invention has more mechanical coordination advantages than traditional chemical cross-linking. Through the innovative design of chain enhancer, the mechanical properties of bio-based thermoplastic polyurethane film materials are significantly improved.

[0068] Test Example 4: Field corn planting experiment The tested corn variety is Zhengdan 958. The test area is Qihe County, Dezhou City, Shandong Province. The climate type is warm temperate continental monsoon climate. The tested soil type is fluvo-aquic soil. The perennial planting method is annual rotation of corn and wheat. The basic physical and chemical properties of the soil in the 0-20 cm soil layer: organic matter content is 5.48 g / kg, nitrate nitrogen content is 31.54 mg / kg, ammonium nitrogen content is 9.64 mg / kg, available phosphorus content is 23.4 mg / kg, and pH value is 7.04.

[0069] The area of a single test plot is 16.7 m 2(6.67 m in length × 2.5 m in width). The experiment was divided into 7 groups: no fertilization was used as the blank control group, urea was used as the positive control group, and the controlled-release fertilizers of Example 1 and Comparative Examples 1-4 were applied as the groups of Example 1 and Comparative Examples 1-4. Five rows of corn were planted in each plot, with a row spacing of 50 cm, a plant spacing of 33.4 cm, the corn seeds were buried 5 cm deep, the fertilizer was buried 10-15 cm deep, and 10 cm away from the seed row. The ratio of the number of corn seed rows to the number of fertilizer rows was 1:1, and the nitrogen application rate was 285 kg / ha (pure nitrogen). Sowing was carried out in mid-June, and yield was measured and harvested at the end of September; in the ordinary urea treatment, the urea was provided by Shandong Agricultural Fertilizer Technology Co., Ltd. In each treatment, triple superphosphate was selected as the phosphate fertilizer in the tested fertilizer, and the phosphorus application rate was 125 kg / ha (pure phosphorus); potassium sulfate was selected as the potassium fertilizer, and the potassium application rate was 165 kg / ha (pure potassium). After crop sowing, field management such as watering, spraying pesticides, and weeding was carried out according to farmers' habits. The biomass, number of grains per ear (number of ears), 100-grain weight, and actual yield were statistically analyzed during yield measurement and harvest, and SPAS Statistics 26 software was used to statistically analyze the relevant data. Three fertilization points were randomly selected from each plot 3 months after harvest, and the soil was dug 15 cm deep to collect the incompletely dissolved coated fertilizer particles. The soil on the surface of the particles and the residual urea inside were rinsed with deionized water, the residual film material was peeled off, and the particles were dried in an oven at 60 °C to constant weight, and the mass loss rate was calculated by weighing (the calculation method was the same as that in Test Example 1), and the results are shown in Table 2.

[0070] Table 2 Yield components of corn and natural degradation rate of film shell soil under different fertilization treatments It can be seen from Table 2 that the yield of Example 1 increased by 44.02% compared with no fertilization, and its degradation rate reached 58.2%, indicating that the introduction of a non-covalent physical cross-linking network and thermoplastic linear polyurethane with gradient temperature coating achieved the orderly disintegration of the film material while ensuring nutrient controlled release (110 days). The comparison shows that although the yield of Comparative Example 1 was relatively high (9405.22 kg / hm²), the degradation rate was only 18.1%, and the long-term residual risk was significant; due to the incomplete film layer structure in Comparative Example 4, the yield was only 7912.33 kg / hm², verifying the necessity of the temperature gradient coating process for regulating the performance of the film material. The yield increase rates of the remaining comparative examples (without pre-oxidation, no enhancer, etc.) were less than 20%. In summary, it shows that the multi-component formulation of the present application has a synergistic effect on increasing the corn yield, and through the coordinated optimization of "controlled release - degradation", a balance is achieved between yield improvement and environmental friendliness.

[0071] By optimizing the selection of bio-based materials, introducing chain enhancers, and the dynamic temperature gradient coating process, the present invention enables the degradation rate, release curve, and mechanical properties of each example to form a dynamic synergy, meeting the requirements of different agricultural fertilization scenarios.

[0072] The above are only the preferred embodiments of the present application and are not intended 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 within the protection scope of the present application.

Claims

1. A bio-based thermoplastic polyurethane coating material that is easily and rapidly degradable, characterized in that, It comprises raw materials in the following parts by mass: 0.8 - 2.0 parts of a biological chain matrix and 0.5 - 1.5 parts of a chain enhancer; The biological chain matrix is composed of pre-oxidized vegetable oil diol and bio-based polyester diol; The pre-oxidized vegetable oil diol is prepared by the following method: (1) Mix vegetable oil, small molecule short-chain alcohol and solid base catalyst, heat and react, and separate glycerol products; (2) Add hydrogen peroxide, formic acid and phosphotungstic acid into the reaction system obtained in step (1), and stir and react under heating; (3) Add dilute sulfuric acid and small molecule diol into the reaction system obtained in step (2), and heat and stir to react to obtain vegetable oil diol; (4) Pass air through the vegetable oil diol under heating for oxidation to obtain a light yellow transparent liquid, which is the pre-oxidized vegetable oil diol; The bio-based polyester diol is prepared by the following method: Mix the pre-oxidized vegetable oil diol with bio-based dibasic acid, heat and react under negative pressure in a protective atmosphere, then raise the temperature to continue the reaction, add calcium carbonate, stir and filter to remove calcium carbonate, and vacuum filter to obtain the product, which is the bio-based polyester diol; The chain enhancer is composed of a curing agent, a hardening agent and a toughening agent.

2. The bio-based thermoplastic polyurethane coating material according to claim 1, wherein The mass ratio of the pre-oxidized vegetable oil diol to the bio-based polyester diol is 10:(1 - 5); the acid value of the pre-oxidized vegetable oil diol is 60 - 100 mg KOH / g, and the peroxide value is 5 - 15 meq / kg; the curing agent is diisocyanate; the hardening agent is aromatic rigid diamine or diol; the toughening agent is aliphatic flexible diamine or diol.

3. The bio-based thermoplastic polyurethane coating material according to claim 2, wherein The aromatic rigid diamine or diol is at least one of 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, 3,3'-dichloro-4,4'-diaminodiphenylmethane, 4,4'-dihydroxydiphenyl sulfone or 4,4'-biphenol; the aliphatic flexible diamine or diol is at least one of 1,6-hexanediamine, N-aminoethylpiperazine, 1,3-diamino-2-hydroxypropane, N,N'-bis(2-hydroxyethyl)oxamide or 1,4-cyclohexanedimethanol.

4. The bio-based thermoplastic polyurethane coating material according to claim 1, characterized in that, In step (1), the mass ratio of the vegetable oil, small molecule short-chain alcohol to the solid base catalyst is 20:4:1; the temperature of the heating reaction is 70°C and the time is 2.5 h; the solid base catalyst is NaAlO2; In step (2), the mass ratio of the reaction system, hydrogen peroxide, formic acid and phosphotungstic acid is 20:10:3:0.1; the heating temperature is 60°C, and the stirring reaction time is 5 h.

5. The bio-based thermoplastic polyurethane coating material according to claim 1, wherein In step (3), the mass ratio of the reaction system, dilute sulfuric acid and small molecule diol is 5:2:1; the temperature of the heating and stirring reaction is 60°C and the time is 1 h; In step (4), the heating temperature is 65 - 75 °C; the oxidation time is 12 - 18 h; the air flow rate is 0.8 - 1.2 L·min -1 ·kg -1 .

6. The bio-based thermoplastic polyurethane coating material according to claim 1, wherein The mass ratio of the pre-oxidized vegetable oil diol to the bio-based dibasic acid is 1.05:1; the negative pressure is -0.05 Mpa; the temperature of the heating reaction is 120 °C and the time is 2 h; the continued reaction after heating is to raise the temperature to 160 °C and continue the reaction for 3 h; the addition amount of calcium carbonate accounts for 0.1% of the total mass of the pre-oxidized vegetable oil diol and the bio-based dibasic acid; the bio-based dibasic acid is at least one of succinic acid, sebacic acid, azelaic acid, malic acid or 2,5-furandicarboxylic acid.

7. The bio-based thermoplastic polyurethane coating material according to claim 1, wherein The bio-based thermoplastic polyurethane coating material is prepared by the following method: (1) Under vacuum conditions, the pre-oxidized vegetable oil diol and the bio-based polyester diol are heated and mixed to obtain a bio-chain matrix; (2) The curing agent, hardening agent and toughening agent are heated and mixed under stirring to obtain a chain enhancer; (3) The bio-chain matrix and the chain enhancer are mixed and stirred evenly, and ultrasonic oscillation is carried out at room temperature to obtain the bio-based thermoplastic polyurethane coating material.

8. Use of the bio-based thermoplastic polyurethane coating material according to any one of claims 1 to 7 in the preparation of an easily fast-degrading controlled-release fertilizer.

9. A bio-based thermoplastic polyurethane-coated controlled-release fertilizer that is easily and rapidly degradable, characterized in that, The bio-based thermoplastic polyurethane coated controlled-release fertilizer includes fertilizer particles and the bio-based thermoplastic polyurethane coating material according to any one of claims 1 to 7 sprayed on the surface of the fertilizer particles; the spraying amount of the bio-based thermoplastic polyurethane coating material is 0.8 to 10% of the mass of the fertilizer particles.

10. The bio-based thermoplastic polyurethane-coated controlled-release fertilizer according to claim 9, characterized in that, It is prepared by the following method: preheat the fertilizer particles, then spray or drip the bio-based thermoplastic polyurethane coating material according to any one of claims 1 to 7 onto the surface of the fertilizer particles, stir the fertilizer under heat preservation, and the coating material forms a coating. After cooling, spray or drip the bio-based thermoplastic polyurethane coating material again, and then heat and cure. Repeat the above operation 1 to 10 times. After the last layer is cured and the temperature is reduced to room temperature, the bio-based thermoplastic polyurethane coated controlled-release fertilizer is obtained.

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