A bio-based thermoplastic polyurethane coating material and controlled-release fertilizer that is easily and rapidly degradable

Abstract

This invention discloses a bio-based thermoplastic polyurethane coating material and a controlled-release fertilizer that are easily and rapidly degradable. The coating material comprises 0.8-2.0 parts of a bio-chain matrix and 0.5-1.5 parts of a chain reinforcing agent; the bio-chain matrix is ​​a mixture of pre-oxidized vegetable oil diol and bio-based polyester diol; the chain reinforcing agent is a mixture of a curing agent, a hardening agent, and a toughening agent. The bio-based thermoplastic polyurethane-coated controlled-release fertilizer comprises fertilizer granules and a bio-based thermoplastic polyurethane coating material sprayed onto the surface of the fertilizer granules; the amount of the bio-based thermoplastic polyurethane coating material sprayed is 0.8-10% of the mass of the fertilizer granules. This invention, through precise control of the coating material formulation, can achieve a combined improvement in the tensile strength and toughness of the bio-based thermoplastic coating material, thereby achieving a superior controlled-release effect and resolving the contradiction between the degradability and controlled-release performance of current bio-based polyurethane coating materials.

Description

Technical Field

[0001] This invention relates to the field of controlled-release fertilizer technology, specifically to a bio-based thermoplastic polyurethane coating material that is easily and rapidly degradable and a controlled-release fertilizer. Background Technology

[0002] After decades of large-scale verification worldwide, coated controlled-release fertilizers have been proven to significantly improve nutrient utilization. Therefore, developing coated controlled-release fertilizers is a strategic priority for my country to address the problems of fertilizer resource waste and environmental pollution. Since petrochemical membrane materials are difficult to degrade and are non-renewable, the preparation of coated controlled-release fertilizers using bio-based polyurethane is currently a hot research topic. Patent CN118580455A prepared a biodegradable polyurethane-based controlled-release fertilizer coating material, but its membrane material raw material is not bio-based. Patents CN102320883B, CN112159269B, and CN113788711B respectively use densification modification, surface superhydrophobic modification, and self-healing modification technologies to solve the problems of easy water absorption and damage of bio-based membrane materials, but their degradation effects or degradation performance are generally poor. In summary, current research on bio-based polyurethane-coated controlled-release fertilizers faces a core challenge: achieving both excellent controlled-release performance and rapid degradation of the membrane material. This is primarily due to the contradiction between the cross-linking structure and degradation performance of the bio-based polyurethane membrane. Increasing the degree of chemical cross-linking to enhance density can improve the mechanical properties of the membrane material, maintain pore integrity, and significantly prolong the controlled-release performance.

[0003] Thermosetting polyurethane coating materials have been widely used in the preparation of controlled-release fertilizers. They achieve controlled release through a dense structure, but their reliance on irreversible chemical covalent crosslinking makes degradation difficult. Furthermore, the lack of toughness in the coating material makes it prone to breakage in the later stages of nutrient release due to increased osmotic pressure. Thermoplastic polyurethane, on the other hand, possesses a unique linear molecular chain structure with extremely low crosslinking. Therefore, compared to thermosetting polyurethane, it has better ductility and toughness, making it a promising candidate for high-performance coating materials. More importantly, it has been proven to have significant degradation advantages, thus possessing enormous application potential. To achieve the sustainable development of controlled-release fertilizers, ideal thermoplastic polyurethane coating materials should possess excellent degradation performance while also exhibiting high mechanical strength and high crack resistance / toughness. This is crucial to prevent potential membrane damage during production and transportation and to resist nutrient loss due to crack propagation under osmotic pressure differences. These performance indicators are particularly important to ensure a long controlled-release lifespan. However, the degradability and controlled-release performance of bio-based thermoplastic polyurethane present a significant contradiction and challenge. Specifically, controlled-release membranes with high mechanical strength and toughness typically require more complex chemical bonds and cross-linking structures for support, which is difficult to achieve with non-crosslinked or weakly crosslinked thermoplastic polyurethane membranes. Furthermore, the excessively dense cross-linked structure of the membrane introduces a large number of difficult-to-degrade covalent bonds, increasing the complexity of the chain and thus making the membrane difficult to degrade. Therefore, there is an urgent need to develop bio-based thermoplastic coated controlled-release fertilizers with excellent performance and rapid degradation. Currently, there are no research reports, either domestically or internationally, on the preparation of coated controlled-release fertilizers using bio-based thermoplastic polyurethane. Summary of the Invention

[0004] To address the aforementioned limitations of existing technologies, the present invention aims to provide a readily biodegradable bio-based thermoplastic polyurethane coating material and a controlled-release fertilizer. This invention modifies the chemical cross-linking structure of traditional polyurethane-coated controlled-release fertilizers. While maintaining its original linear cross-linking characteristics, it introduces a large number of non-covalent physical cross-linking domains. These domains can provide sacrificial bonds to dissipate external force energy through non-covalent interactions without affecting the original chemical cross-linking structure. By precisely controlling the coating material formulation, the tensile strength and toughness of the bio-based thermoplastic controlled-release membrane material can be simultaneously improved, resulting in a superior controlled-release effect and resolving the contradiction between the degradability and controlled-release performance of current bio-based polyurethane coating materials.

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

[0006] In a first aspect, the present invention provides a readily biodegradable, bio-based thermoplastic polyurethane coating material, comprising the following raw materials in parts by weight:

[0007] 0.8-2.0 parts of bio-chain matrix and 0.5-1.5 parts of chain enhancer;

[0008] The biochain matrix is ​​a mixture of pre-oxidized vegetable oil diol and bio-based polyester diol;

[0009] The pre-oxidized vegetable oil diol is prepared by the following method:

[0010] (1) Mix vegetable oil, small molecule short-chain alcohol with solid base catalyst, heat to react, and separate the glycerol product;

[0011] (2) Add hydrogen peroxide, formic acid and phosphotungstic acid to the reaction system obtained in step (1), and stir under heating;

[0012] (3) Add dilute sulfuric acid and small molecule diol to the reaction system obtained in step (2), heat and stir to react and obtain vegetable oil diol;

[0013] (4) The vegetable oil diol is oxidized by passing air through it under heating to obtain a pale yellow transparent liquid, which is the pre-oxidized vegetable oil diol;

[0014] The bio-based polyester diol is prepared by the following method:

[0015] Pre-oxidized vegetable oil diol was mixed with bio-based dicarboxylic acid and heated under negative pressure in a protective atmosphere. The temperature was then increased to continue the reaction. Calcium carbonate was added and stirred. After filtration to remove calcium carbonate, the product was obtained by vacuum filtration, which is bio-based polyester diol.

[0016] The chain reinforcing agent is a mixture of curing agent, hardening agent, and toughening agent.

[0017] 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; and the toughening agent is aliphatic flexible diamine or diol.

[0018] 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'-biphenylhydrazine; 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)glyoxamide, or 1,4-cyclohexanediethanol.

[0019] More preferably, the diisocyanate is diphenylmethane diisocyanate, dicyclohexane 4,4'-diisocyanate, etc.

[0020] At least one of hexamethylene diisocyanate or pentamethylene diisocyanate.

[0021] Preferably, in step (1), the mass ratio of the vegetable oil, the small molecule short-chain alcohol and the solid base catalyst is 20:4:1; the heating reaction temperature is 70°C and the time is 2.5h.

[0022] More preferably, the vegetable oil is selected from at least one of palm oil, camellia oil, rice bran oil, and tallow tree oil; the small molecule short-chain alcohol is methanol; and the solid base catalyst is NaAlO2.

[0023] 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 hours.

[0024] More preferably, the hydrogen peroxide has a mass concentration of 35%.

[0025] 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 1h.

[0026] More preferably, the small molecule diol is ethylene glycol.

[0027] Preferably, in step (4), the heating temperature is 65-75℃; the oxidation time is 12-18h; and the air flow rate is 0.8-1.2 L·min. -1 ·kg -1 .

[0028] Preferably, the mass ratio of the pre-oxidized vegetable oil diol to the bio-dicarboxylic acid is 1.05:1; the negative pressure is -0.05 MPa; the heating reaction temperature is 120°C and the time is 2 hours; the further heating reaction is carried out by raising the temperature to 160°C and continuing the reaction for 3 hours; and the amount of calcium carbonate added accounts for 0.1% of the total mass of the pre-oxidized vegetable oil diol and the bio-dicarboxylic acid.

[0029] More preferably, the biogenic dicarboxylic acid is at least one of succinic acid, sebacic acid, azelaic acid, malic acid, or 2,5-furandicarboxylic acid.

[0030] Preferably, the bio-based thermoplastic polyurethane coating material is prepared by the following method:

[0031] (1) Under vacuum conditions, pre-oxidized vegetable oil diol and bio-based polyester diol were heated and mixed to obtain a bio-chain matrix;

[0032] (2) The curing agent, hardener, and toughening agent are mixed under stirring and heating to obtain a chain reinforcing agent;

[0033] (3) Mix the bio-chain matrix and chain reinforcing agent and stir evenly, then ultrasonically vibrate at room temperature to obtain a bio-based thermoplastic polyurethane coating material.

[0034] A second aspect of the present invention provides the application of bio-based thermoplastic polyurethane coating materials in the preparation of easily and rapidly degradable controlled-release fertilizers.

[0035] In a third aspect, the present invention provides a bio-based thermoplastic polyurethane-coated controlled-release fertilizer that is readily and rapidly degradable, the bio-based thermoplastic polyurethane-coated controlled-release fertilizer comprising fertilizer granules and a bio-based thermoplastic polyurethane coating material sprayed onto the surface of the fertilizer granules; the amount of the bio-based thermoplastic polyurethane coating material sprayed is 0.8 to 10% of the mass of the fertilizer granules.

[0036] Preferably, the fertilizer is prepared by the following method: preheating the fertilizer granules, then spraying or dripping a bio-based thermoplastic polyurethane coating material onto the surface of the fertilizer granules, stirring the fertilizer while keeping it warm, forming a coating material, cooling down, spraying or dripping the bio-based thermoplastic polyurethane coating material again, then heating up to cure, repeating the above operation 1 to 10 times, and after the last layer has cured, waiting for the temperature to drop to room temperature to obtain the bio-based thermoplastic polyurethane coated controlled-release fertilizer.

[0037] 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.

[0038] More preferably, the preheating temperature is 85-95℃; the cooling temperature is reduced to 60℃; and the heating and curing temperature is 80-90℃.

[0039] The beneficial effects of this invention are:

[0040] (1) This invention is the first to utilize bio-based thermoplastic polyurethane to prepare a fully linearly cross-linked coated controlled-release fertilizer membrane, replacing the commonly used three-dimensional chemically cross-linked bio-based thermosetting polyurethane coating material, significantly reducing the time required for membrane degradation. Its 180-day degradation rate is at least 67.8% higher than that of thermosetting polyurethane controlled-release membranes. Furthermore, the plant oil diol in the bio-chain matrix is ​​subjected to controlled pre-oxidation treatment (acid value 60-100 mg KOH / g), which causes it to generate C8-C12 short-chain carboxylic acids in situ. The carboxylic acid groups form a hydrogen bond network with the urethane of the polyurethane main chain, replacing the chemical cross-linking function. The dynamic hydrogen bonds maintain the membrane density during the controlled-release period. When the nutrient release reaches 80%, the membrane absorbs water and swells, leading to pore expansion. The hydrogen bond cross-linking domains dissociate, and the carboxylic acid seeps out through the pore channels, accelerating the exposure of the main chain to the hydrolysis environment and achieving rapid degradation.

[0041] (2) This invention utilizes a chain reinforcing agent to enhance and modify bio-based thermoplastic polyurethane membrane materials. The introduction of the chain reinforcing agent allows the original membrane material to form supramolecular aggregated segments through the π-π stacking of planar aromatic structures, the intermolecular interactions of multiple hydrogen bonds, and the van der Waals forces between bio-based long-chain alkanes. This adds non-covalent dynamic physical weak crosslinking domains to the original linear polyurethane membrane material chain, thereby enhancing the film-forming effect and physical properties of the membrane material. This enhances its physical properties and film-forming performance without affecting its chemical crosslinking degree. Since the chain reinforcing agent is prepared through a rational design of alternating rigid and flexible small molecule segments, the membrane material exhibits both strong rigidity and toughness, meeting the requirements for mechanical strength during the production and transportation of coated controlled-release fertilizers and the requirements for membrane material flexibility in the later stages of use.

[0042] (3) This invention develops a dynamic temperature gradient coating process adapted to bio-based thermoplastic polyurethane coating materials, achieving synergistic optimization of film structure and performance through segmented temperature control. In the primary curing stage, rapid gelation and pre-curing are achieved, eliminating internal stress accumulation during the material's phase transition process; subsequently, cooling induces the directional alignment of physical cross-linking domains; in the secondary curing stage, temperature is dynamically controlled to enhance the interfacial bonding force between the film layer and the base fertilizer particles or between the film layers through the molecular chain relaxation effect; at the end of the final coating layer, the temperature is lowered to room temperature, achieving complete curing of the thermoplastic components while retaining the dynamic hydrogen bond dissociation characteristics.

[0043] (4) This invention achieves easy degradation of membrane material (degradation rate ≥50% in 180 days, ≥80% in 1 year, avoiding environmental residue) and long-term controlled release performance (nutrient controlled release period exceeds 110 days) through the time-series synergistic design between controlled release and degradation performance. Attached Figure Description

[0044] Figure 1 Scanning electron microscope (SEM) image (a) of the coated controlled-release fertilizer prepared in Example 1 of this invention and atomic force microscope (AFM) image (b) of its membrane shell;

[0045] Figure 2 The soil degradation rate of the membrane shell of the coated controlled-release fertilizer prepared by this invention;

[0046] Figure 3 Nutrient release characteristics of the coated controlled-release fertilizer prepared by this invention under constant temperature conditions (25℃). Detailed Implementation

[0047] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0048] As described in the background section, existing bio-based polyurethane-coated controlled-release fertilizers primarily use thermosetting polyurethane as the coating material. Its cross-linked structure is a three-dimensional network. Because these structures are based on highly stable and difficult-to-break chemical covalent bonds, and have a high degree of cross-linking, it is difficult to achieve bond-breaking degradation of the membrane structure in the soil environment. Although thermoplastic polyurethane is degradable, its direct application in coated controlled-release fertilizers fails to meet the required controlled-release period, with nutrients being completely released within two days. This is mainly due to the weak cross-linking characteristics of thermoplastic polyurethane, resulting in poor film-forming performance and the inability of the membrane material's physical properties to meet the requirements of controlled-release fertilizers.

[0049] Based on this, the purpose of this 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 this invention includes a bio-chain matrix and a chain reinforcing agent. The bio-chain matrix, composed of pre-oxidized vegetable oil diol and bio-based polyester diol, is the main component of the membrane material and the primary source of the bio-based content. The selected vegetable oil has a high saturation content and can maintain structural stability under continuous alcoholization and esterification reaction conditions, making it suitable as the matrix for the coating material. The chain reinforcing agent consists of a curing agent, a hardening agent, and a toughening agent. The curing agent can react with the bio-chain matrix to form the linear main chain structure of the bio-based thermoplastic polyurethane membrane material, while the hardening agent and toughening agent can be grafted into the linear structure through the reaction of urethane and urea esters, introducing supramolecular aggregated segments with multiple hydrogen bonds, interchain van der Waals forces, and planar π-π stacking interactions, thereby forming non-covalent physical cross-linking domains, providing a large number of external force sacrificial bonds, and significantly improving the film-forming effect and physical properties of the bio-based thermoplastic polyurethane membrane material. The bio-based thermoplastic polyurethane is composed of pre-oxidized vegetable oil diol and bio-based polyester diol linearly linked by urethane bonds, avoiding three-dimensional network chemical cross-linking. Through controlled pre-oxidation treatment, the vegetable oil diol is converted into C8-C12 short-chain carboxylic acids. In the controlled-release stage, the carboxylic acids stabilize the physically cross-linked network through hydrogen bonding. In the later stage of controlled release, the membrane absorbs water and swells, leading to the dissociation of the physically cross-linked domains. The carboxylic acids then seep out through the pore channels, accelerating the exposure of the main chain to the hydrolytic environment. This dual-functional mechanism enables the material to achieve a precise dynamic balance between controlled release and degradation without exogenous additives.

[0050] This invention further develops a bio-based thermoplastic polyurethane-coated controlled-release fertilizer that is easily and rapidly degradable, and constructs a dedicated coating and curing process system for bio-based thermoplastic polyurethane. Complete curing of the membrane is achieved through segmented temperature control: in the initial curing stage, a constant temperature (85-95℃ range, with periodic fluctuations of ±5℃) rapidly achieves gelation and pre-curing, eliminating internal stress accumulation during the material's phase transition; subsequently, the temperature is lowered to 60℃ to induce the directional alignment of physical cross-linking domains; in the secondary curing stage, dynamic temperature control is applied (raising the temperature to 80-90℃), enhancing the interfacial bonding between the membrane layer and the base fertilizer particles or between the membrane layers through the molecular chain relaxation effect; at the end of the final coating layer, the temperature is lowered to room temperature (cooling rate ≤5℃ / min), achieving complete curing of the thermoplastic components while retaining the dynamic hydrogen bond dissociation characteristics. This process overcomes the limitations of traditional coating and controlled-release fertilizer membrane curing methods, achieving a synergistic improvement in film formation speed and structural stability.

[0051] This invention innovatively solves the technical contradictions inherent in traditional bio-based polyurethane coating materials. Specifically, it addresses the dual technical shortcomings of existing bio-based thermosetting polyurethane films—difficult degradation and insufficient film-forming performance of thermoplastic polyurethane—by, for the first time, using bio-based thermoplastic polyurethane as the primary coating material to construct a novel bio-based polyurethane-coated controlled-release fertilizer system. This technological breakthrough achieves the following synergistic effects: 1) By designing a linear cross-linked structure, the film material is endowed with controllable biodegradability, achieving rapid degradation after release while ensuring the stability of the controlled-release period; 2) By using chain reinforcing agents to introduce non-covalent physical cross-linking domains to enhance the intermolecular forces of the linear molecular chains of thermoplastic polyurethane, significantly improving film-forming performance and overcoming the industrial bottleneck of the difficulty in simultaneously achieving degradation performance and controlled-release efficiency in existing technologies; 3) By optimizing the coating curing method specifically for thermoplastic polyurethane and maintaining the uniformity and integrity of the film structure through gradient temperature control.

[0052] To enable those skilled in the art to better understand the technical solution of this application, the technical solution of this application will be described in detail below with reference to specific embodiments.

[0053] 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 Maclean Biochemical Technology Co., Ltd.; the jojoba oil (CAS No. 61789-91-1) and coconut oil (CAS No. 8001-31-8) were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0054] The test materials used in the embodiments of this invention are all conventional test materials in the art and can be purchased through commercial channels.

[0055] Example 1: Preparation of easily degradable bio-based thermoplastic polyurethane coated controlled-release fertilizer

[0056] (1) Preparation of biological chain matrix:

[0057] Palm oil, camellia oil, and rice bran oil were mixed in a mass ratio of 6:1:1 to obtain vegetable oil. The vegetable oil was then mixed with methanol and NaAlO2 in a mass ratio of 20:4:1 and reacted at 70°C for 2.5 h under NaAlO2 catalysis. Glycerol was separated from the product. Hydrogen peroxide (35%), formic acid, and phosphotungstic acid were 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 were then added to the above system in a mass ratio of 5:2:1 and stirred at 60°C for 1 h. The mixture was then oxidized at 70°C with air at a flow rate of 0.9 L·min⁻¹·kg⁻¹ for 12 h to obtain pre-oxidized vegetable oil diol (acid value of 80 mg KOH / g, peroxide value of 10 meq / kg).

[0058] Pre-oxidized vegetable oil diol and succinic acid were mixed at a mass ratio of 1.05:1 and added to a reaction vessel. Nitrogen gas was used to replace the air. The reaction was carried out at 120℃ and -0.05 MPa for 2 hours. After the reaction was completed, the temperature was raised to 160℃ and the reaction was continued for 3 hours. Then, 0.1 g of calcium carbonate was added, stirred, filtered to remove calcium carbonate, and then vacuum filtered for 1 hour to obtain the product, which is bio-based polyester diol.

[0059] Pre-oxidized vegetable oil diol and bio-based polyester diol were uniformly mixed at a mass ratio of 10:4 to obtain a bio-chain matrix.

[0060] (2) Preparation of chain reinforcing agents:

[0061] Diphenylmethane diisocyanate and dicyclohexane 4,4'-diisocyanate were mixed at a mass ratio of 3:1 and heated at 80°C for 1.5 h in a vacuum environment to obtain a curing agent.

[0062] The curing agent, 4,4'-diaminodiphenylmethane, and 1,6-hexanediamine were mixed at 45°C in a mass ratio of 80:20:20 and stirred until homogeneous to obtain the chain reinforcing agent.

[0063] (3) Preparation of coating material:

[0064] The bio-chain matrix prepared in step (1) and the chain reinforcing agent component prepared in step (2) are mixed at a mass ratio of 1:1 and stirred evenly. The mixture is then ultrasonically vibrated at room temperature for 30 minutes to obtain a uniform coating material.

[0065] (4) Preparation of coated controlled-release fertilizer:

[0066] 2 kg of urea granules were added as fertilizer granules to a drum preheated to 85°C. The coating material prepared in step (3) was then sprayed onto the surface of the fertilizer granules. The drum temperature was maintained during the rotation of the drum, and the fertilizer was stirred with a glass rod. The coating material formed a coating layer. After about 15 minutes, the temperature was lowered to 60°C. The next batch of coating material was added, and the temperature was raised to 80°C. The mass of the coating material sprayed onto the surface of the fertilizer granules each time accounted for 0.8% of the mass of the fertilizer granules. The above operation was repeated 8 times, and a total of 128 g of coating material was sprayed. After the last layer was cured, the drum was kept running. After the temperature dropped to room temperature, the fertilizer was removed to obtain easily degradable bio-based thermoplastic polyurethane coated controlled-release fertilizer. The surface of the controlled-release fertilizer was examined by scanning electron microscopy and atomic force microscopy. Figure 1 Observations using a and b in Example 1 demonstrate that a uniform and complete coated controlled-release fertilizer was successfully prepared.

[0067] Example 2: Preparation of easily degradable bio-based thermoplastic polyurethane coated controlled-release fertilizer:

[0068] (1) Preparation of biological chain matrix:

[0069] The difference from step (1) of Example 1 is that:

[0070] Palm oil, camellia oil, and tallow tree oil were mixed in a mass ratio of 7:1:1 to prepare vegetable oil. The vegetable oil was then mixed with methanol and NaAlO2 in a mass ratio of 20:4:1 and reacted at 70°C for 2.5 h under NaAlO2 catalysis. Glycerol was separated from the product. Hydrogen peroxide (35%), formic acid, and phosphotungstic acid were 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 were added to the above system in a mass ratio of 5:2:1 and stirred at 60°C for 1 h. The mixture was then oxidized at 70°C with air at a flow rate of 0.9 L·min⁻¹·kg⁻¹ for 12 h to obtain pre-oxidized vegetable oil diol (acid value of 80 mg KOH / g, peroxide value of 10 meq / kg).

[0071] Pre-oxidized vegetable oil diol and sebacic acid were mixed at a mass ratio of 1.05:1 and added to a reaction vessel. Nitrogen gas was used to replace the air. The reaction was carried out at 120℃ and -0.05 MPa for 2 hours. After the reaction was completed, the temperature was raised to 160℃ and the reaction was continued for 3 hours. Then 0.1 g of calcium carbonate was added, stirred, filtered to remove calcium carbonate, and then vacuum filtered for 1 hour to obtain the product, which is bio-based polyester diol.

[0072] Pre-oxidized vegetable oil diol and bio-based polyester diol were uniformly mixed at a mass ratio of 10:4 to obtain a bio-chain matrix.

[0073] (2) Preparation of chain reinforcing agents:

[0074] The difference from step (2) of Example 1 is that the curing agent, 4,4'-diaminodiphenyl ether and 1,6-hexanediamine are mixed and stirred evenly at 45°C in a mass ratio of 60:15:15 to obtain the chain reinforcing agent.

[0075] (3) Preparation of coating material:

[0076] Same as step (3) in Example 1.

[0077] (4) Preparation of coated controlled-release fertilizer:

[0078] The difference from step (4) of Example 1 is that the total amount of coating material sprayed is 7.2% of the fertilizer particle mass, and finally a biodegradable bio-based thermoplastic polyurethane coated controlled-release fertilizer is obtained.

[0079] Example 3: Preparation of easily degradable bio-based thermoplastic polyurethane coated controlled-release fertilizer:

[0080] (1) Preparation of biological chain matrix:

[0081] The difference from step (1) of Example 1 is as follows: Camellia oil, rice bran oil, and 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 2.5h under NaAlO2 catalysis. 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. The mixture is stirred continuously at 60°C for 5h, and dilute sulfuric acid and ethylene glycol are added to the above system in a mass ratio of 5:2:1. The mixture is stirred at 60°C for 1h, and then oxidized with air at 70°C at an air flow rate of 0.9L·min⁻¹·kg⁻¹ for 12h to obtain pre-oxidized vegetable oil diol (acid value of 80 mg KOH / g, peroxide value of 10 meq / kg).

[0082] Pre-oxidized vegetable oil diol and 2,5-furandicarboxylic acid were mixed at a mass ratio of 1.05:1 and added to a reaction vessel. Nitrogen gas was used to replace the air. The reaction was carried out at 120℃ and -0.05 MPa for 2 hours. After the reaction was completed, the temperature was raised to 160℃ and the reaction was continued for 3 hours. Then 0.1 g of calcium carbonate was added, stirred, filtered to remove calcium carbonate, and then vacuum filtered for 1 hour to obtain the product, which is bio-based polyester diol.

[0083] Pre-oxidized vegetable oil diol and bio-based polyester diol were uniformly mixed at a mass ratio of 10:4 to obtain a bio-chain matrix. (2) Preparation of chain reinforcing agent:

[0084] The difference from step (2) of Example 1 is that the curing agent, 4,4'-biphenyl and 1,6-hexanediamine are mixed at 45°C in a mass ratio of 60:15:15 and stirred evenly to obtain the chain reinforcing agent.

[0085] (3) Preparation of coating material:

[0086] The bio-chain matrix and chain enhancer components were mixed at a mass ratio of 1.2:1 and stirred evenly. The mixture was then ultrasonically vibrated at room temperature for 20-40 minutes to obtain a uniform coating material.

[0087] (4) Preparation of coated controlled-release fertilizer:

[0088] The difference from step (4) of Example 1 is that the total amount of coating material sprayed is 8% of the fertilizer particle mass, and finally a biodegradable bio-based thermoplastic polyurethane coated controlled-release fertilizer is obtained.

[0089] Comparative Example 1:

[0090] The difference between this comparative example and Example 1 is that the preparation of the bio-chain matrix involves the preparation of plant oil polyols and bio-based polyester polyols, and the specific preparation method is as follows:

[0091] Flaxseed oil, camellia oil, and rice bran oil were mixed in a mass ratio of 7:2:1 to prepare vegetable oil raw materials. The raw materials were then reacted with methanol at 70°C for 2.5 h under the catalysis of NaAlO2 (mass ratio of the three components being 20:4:1). After separating the glycerol product, hydrogen peroxide (35%), formic acid, and phosphotungstic acid were added (mass ratio of the four components being 30:10:3:0.1). The mixture was stirred continuously at 70°C for 8 h. Then, dilute sulfuric acid and ethylene glycol were added (mass ratio of the three components being 5:2:1). The mixture was stirred at 60°C for 1 h. NaOH was then added to adjust the pH to 10, and the reaction was continued at 80°C for 2 h to obtain vegetable oil polyol. The obtained vegetable oil polyol was mixed with citric acid (a tricarboxylic acid) (mass ratio of 800:1) and added to a reaction vessel. Then, 1% of the total mass fraction of pentaerythritol was added for chain extension, and nitrogen was used to replace the air. The reaction was carried out at 150℃ and -0.09MPa for 2 hours, then the temperature was raised to 160℃ and the reaction was continued for 3 hours. 0.1g of calcium carbonate was added, and the mixture was stirred and filtered to remove the calcium carbonate. The product was obtained by vacuum filtration for 1 hour, which was a bio-based polyester polyol. The vegetable oil polyol and the bio-based polyester polyol were mixed uniformly at a mass ratio of 2.5:1 to obtain the bio-chain matrix.

[0092] The remaining preparation steps are the same as in Example 1, resulting in a coated controlled-release fertilizer.

[0093] Comparative Example 2:

[0094] The difference between this comparative example and Example 1 is that the pre-oxidation step of vegetable oil diol is omitted, and the biological chain matrix is ​​prepared directly using vegetable oil diol. The specific preparation method is as follows:

[0095] Palm oil, camellia oil, and rice bran oil were mixed in a mass ratio of 6:1:1 to prepare vegetable oil raw materials. The raw materials were reacted with methanol at 70°C for 2.5 h under the catalysis of NaAlO2 (mass ratio of the three:20:4:1). After separating the glycerol product, hydrogen peroxide (35%), formic acid, and phosphotungstic acid were added (mass ratio of the four:20:10:3:0.1). The mixture was stirred continuously at 60°C for 5 h. Then, dilute sulfuric acid and ethylene glycol were added (mass ratio of the three:5:2:1). The mixture was stirred at 60°C for 1 h to obtain vegetable oil diol. The obtained vegetable oil diol was mixed with succinic acid (mass ratio of 1000:1) and added to a reaction vessel. Nitrogen gas was used to replace the air. The reaction was carried out at 120℃ and -0.05 MPa for 2 hours, then the temperature was raised to 160℃ and the reaction was continued for 3 hours. 0.1 g of calcium carbonate was added, and the mixture was stirred and filtered to remove the calcium carbonate. The product was obtained by vacuum filtration for 1 hour, which was bio-based polyester diol. Vegetable oil diol and bio-based polyester diol were mixed uniformly at a mass ratio of 10:4 to obtain the bio-chain matrix.

[0096] The remaining preparation steps are the same as in Example 1, resulting in a coated controlled-release fertilizer.

[0097] Comparative Example 3:

[0098] The difference between this comparative example and Example 1 is that no hardener or toughening agent was used in the preparation process of the chain reinforcing agent. The specific preparation method is as follows:

[0099] Diphenylmethane diisocyanate and dicyclohexane 4,4'-diisocyanate were heated in a vacuum at 80°C for 1-2 hours at a mass ratio of 3:1 as a chain reinforcing agent.

[0100] The remaining preparation steps are the same as in Example 1, resulting in a coated controlled-release fertilizer.

[0101] Comparative Example 4:

[0102] The preparation steps of the coating material in this comparative example are the same as in Example 1. The difference is that the coating method described in the specific implementation method is not used in the preparation of the coated controlled-release fertilizer. The specific preparation method is as follows: 2 kg of fertilizer granules are added to a rotating drum and preheated to 85°C. After 10 minutes, the coating material is sprayed or coated onto the surface of the fertilizer granules. The temperature is maintained continuously during the rotation of the drum, and the coating material solidifies to form a coating layer, thus preparing the coated controlled-release fertilizer. The mass of the coating material sprayed or dripped onto the surface of the fertilizer granules each time accounts for 0.8% of the mass of the fertilizer granules. The above operation is repeated 8 times to obtain a coated controlled-release fertilizer with a coating thickness of 6.4%.

[0103] Experimental Example 1: Soil Simulation Degradation Rate Test of Coated Controlled-Release Fertilizer

[0104] The coated controlled-release fertilizers prepared in Examples 1-3 and Comparative Examples 1-4 were ground in a grinder for 5 seconds, then removed and placed in deionized water. 10g of the residual membrane material floating to the water surface was collected from each group, placed in a 10cm×10cm nylon mesh bag, and buried in 1kg of test soil (collected from a suburb of Taishan District, Tai'an City, Shandong Province; ordinary brown soil (simple-grown moist leached soil); naturally air-dried and passed through a 5mm sieve; treated at 25℃ and 60% humidity; then placed in a constant temperature incubator for membrane shell degradation simulation experiments). Samples were removed, washed, and dried every 30 days, and the mass loss rate (%) was calculated as the degradation rate. After the test, the membrane shell was returned to the mesh bag and reburied in the soil.

[0105] Degradation rate (%) = (W0-W1) / W0×100%. Where W0 is the initial weight and W1 is the weight at the time of sampling.

[0106] like Figure 2 As shown, the membrane materials in the embodiments all exhibited degradation rates exceeding 50% after 180 days and ≥80% after 1 year. The degradation mechanism stemmed from the enzymatic hydrolysis of the linear polyurethane backbone by microorganisms and the dynamic dissociation of physical cross-linking domains. Comparative Example 1, using a thermosetting polyurethane with a three-dimensional chemical cross-linking network, had a risk of membrane residue due to the difficulty in breaking high-density chemical covalent bonds (365-day degradation rate ≤50%). Comparative Example 2, lacking a pre-oxidation step, suffered from a significant decrease in degradation performance due to the absence of a carboxylic acid system. Comparative Example 3, lacking a chain reinforcing agent, resulted in the membrane's basic structure easily disintegrating, leading to premature degradation. Comparative Example 4, employing a one-step curing process, had a loose coating structure with poor uniformity and integrity, resulting in a significantly faster degradation rate than the embodiments, and also leading to rapid nutrient release. Figure 3 The fact that 80% of nutrients are released within 50 days demonstrates the sharp contradiction between degradation rate and controlled-release performance in traditional processes. This invention, however, achieves the synergistic goal of long-term controlled nutrient release and rapid degradation of the membrane shell after release through precise and rational design of linear molecular chains and a stepwise solidification process.

[0107] Experimental Example 2: Determination of Nutrient Release Rate

[0108] The test method refers to the People's Republic of China National Standard GB / T 23348-2009 Slow-Release Fertilizers, and the specific test method is as follows:

[0109] 10g of the coated controlled-release fertilizers prepared in Examples 1-3 and Comparative Examples 1-4 were placed in glass bottles containing 200mL of deionized water and stored statically in a 25℃ constant temperature incubator. Water samples of each fertilizer were taken on days 1, 3, 5, 7, 14, 21, and 28 of the incubation period, with subsequent sampling intervals of 7 days, until the cumulative nutrient release rate reached 80%. After each sampling, the remaining water in the bottle was poured out, and 200mL of deionized water was added back into the bottle. The nitrogen concentration of the water samples was determined using the Kjeldahl method.

[0110] according to Figure 3 As shown, Example 1 uses a pre-oxidized vegetable oil diol and bio-based polyester diol at a mass ratio of 2.5:1 to construct a bio-chain matrix, and introduces a chain reinforcing agent. Non-covalent physical cross-linking domains are formed through dynamic π-π stacking, hydrogen bonding, and van der Waals forces. Combined with a dynamic temperature gradient coating process, a controlled-release period of ≥110 days and a degradation rate of ≥50% at 180 days are achieved. Comparative Example 1 uses highly chemically cross-linked thermosetting polyurethane, whose three-dimensional cross-linking network results in an excessively long controlled-release period (release rate of only 48.5% at 119 days). Comparative Example 3 does not add a chain reinforcing agent; the membrane layer exhibits brittle fracture due to the lack of physical cross-linking domains, and the release rate surges to 58.4% at 21 days. Comparative Example 4 uses a simplified coating process, failing to form a complete gradient-cured membrane structure; the membrane shell is loose and uneven, and the release rate reaches 58.8% at 35 days. The faster the controlled-release fertilizer membrane shell degrades, the faster the nutrients are released, resulting in poor controlled-release effects. The above comparison verifies the necessity of non-covalent physical cross-linking domain design and dynamic temperature gradient coating process for controlled-release long-term effects and degradation synergy. The embodiments of this invention achieve optimized controlled-release performance through the synergistic effect of the biological chain matrix and chain enhancer.

[0111] Experimental Example 3: Tensile Properties of Coated Controlled-Release Fertilizer Film

[0112] The experiments were conducted in accordance with the People's Republic of China National Standard GB / T 1040. The tensile properties of the coated controlled-release fertilizers prepared according to Examples 1, 2, 3, Comparative Examples 1, 2, 3, and 4 of this invention were tested. The specific test methods are as follows:

[0113] The coating material was made into dumbbell-shaped specimens (1 mm thick, 25 mm gauge length). Using an Instron 5969 universal testing machine, the specimens were stretched to fracture at a speed of 50 mm / min. The maximum tensile force and elongation at break were recorded, and the tensile strength (MPa) and elongation at break (%) were calculated.

[0114] Tensile strength (MPa) = Maximum tensile force (N) / Cross-sectional area (mm²) 2 ).

[0115] Elongation at break (%) = (gauge length at break - initial gauge length) / initial gauge length × 100%. The results are shown in Table 1.

[0116] Table 1. Tensile strength (MPa) and elongation at break (%) of controlled-release fertilizer film materials

[0117]

[0118] Note: Significance analysis was performed using a two-sample t-test (comparing the example and control examples, α=0.05). Where: p<0.001 (highly significant); p<0.01 (highly significant); p<0.05 (significant).

[0119] As shown in Table 1, this design enables the membrane material to maintain the low chemical crosslinking characteristics of linear polymers while possessing both high tensile strength (18.7 ± 1.3 MPa in Example 1) and high elongation at break (318.5 ± 14.2% in Example 1). Compared to Comparative Example 3 (without chain reinforcement, tensile strength was only 6.8 ± 1.1 MPa, and elongation at break was 38.6 ± 5.7%), the improved mechanical properties of the examples stem from the synergistic enhancement effect of rigid and flexible segments on the linear polyurethane structure: the rigid segments enhance the intermolecular forces through the aromatic structure, while the flexible segments enhance ductility through the aliphatic structure, effectively inhibiting the propagation of microcracks. Furthermore, Comparative Example 1, using highly chemically cross-linked thermosetting polyurethane, showed a significant difference in toughness compared to Example 1 (elongation at break 58.3 ± 7.9%). Comparative Example 2, lacking carboxylic acid-mediated multi-level intermolecular forces, experienced reduced rigid segment stacking efficiency and limited energy dissipation capacity of flexible segments, resulting in significantly deteriorated mechanical properties. This demonstrates that the synergistic non-covalent physical cross-linking formed by the pre-oxidation process and chain reinforcing agent in this invention offers greater mechanical coordination advantages compared to traditional chemical cross-linking. This invention, through the innovative design of the chain reinforcing agent, significantly improves the mechanical properties of bio-based thermoplastic polyurethane films.

[0120] Experiment Example 4: Field Maize Planting Experiment

[0121] The tested maize variety was Zhengdan 958, the experimental area was Qihe County, Dezhou City, Shandong Province, the climate type was warm temperate continental monsoon climate, the soil type was alluvial soil, and the annual planting method was maize-wheat rotation. The basic physicochemical properties of the 0-20cm soil layer were as follows: organic matter content was 5.48 g / kg, nitrate nitrogen content was 31.54 mg / kg, ammonium nitrogen content was 9.64 mg / kg, available phosphorus content was 23.4 mg / kg, and pH value was 7.04.

[0122] The area of ​​a single test cell is 16.7m². 2(Length 6.67m × Width 2.5m) The experiment was divided into 7 groups: a blank control group with no fertilizer, a positive control group with urea, and control-release fertilizers applied according to Example 1 and Comparative Examples 1-4, respectively. Each plot was planted with 5 rows of corn, with a row spacing of 50cm and a plant spacing of 33.4cm. Corn seeds were buried at a depth of 5cm, and fertilizer was buried at a depth of 10-15cm, 10cm from the seed row. The ratio of corn seed rows to fertilizer rows was 1:1, and the nitrogen application rate was 285kg / ha (pure). Sowing was carried out in mid-June, and yield was measured and harvested at the end of September. Urea in the ordinary urea treatment was provided by Shandong Agricultural Fertilizer Technology Co., Ltd. In each treatment, the phosphorus fertilizer used was superphosphate, with an application rate of 125kg / ha (pure); the potassium fertilizer used was potassium sulfate, with an application rate of 165kg / ha (pure). After sowing, field management, including irrigation, pesticide application, and weeding, was carried out according to farmers' habits. Yield measurement and harvesting were conducted by statistically analyzing biomass, number of grains per ear, 100-grain weight, and actual yield. SPAS Statistics 26 software was used for statistical analysis. Three months after harvest, three fertilization sites were randomly selected from each plot. Soil samples were dug to a depth of 15 cm, and incompletely dissolved coated fertilizer granules were collected. The surface soil and residual urea inside the granules were washed with deionized water, the residual film was peeled off, and the granules were dried in a 60℃ oven to constant weight. The weight loss rate was calculated (using the same method as in Experiment 1). The results are shown in Table 2.

[0123] Table 2. Maize yield composition and natural degradation rate of membrane-covered soil under different fertilization treatments.

[0124]

[0125] As shown in Table 2, Example 1, without fertilization, increased yield by 44.02%, with a degradation rate of 58.2%. This indicates that the introduction of a non-covalent physical cross-linked network and thermoplastic linear polyurethane coated with a gradient temperature layer ensures controlled nutrient release (110 days) while achieving orderly membrane disintegration. In comparison, Comparative Example 1, although having a higher yield (9405.22 kg / hm²), had a degradation rate of only 18.1%, posing a significant risk of long-term residue. Comparative Example 4, due to its incomplete membrane structure, had a yield of only 7912.33 kg / hm², confirming the necessity of temperature gradient coating technology for controlling membrane performance. The remaining comparative examples (without pre-oxidation, without reinforcing agents, etc.) showed yield increases of less than 20%. In summary, this application's multi-component formulation has a synergistic effect on increasing maize yield, achieving a balance between yield improvement and environmental friendliness through "controlled release-degradation" synergistic optimization.

[0126] This invention optimizes the selection of bio-based materials, introduces chain reinforcing agents and dynamic temperature gradient coating processes, so that the degradation rate, release curve and mechanical properties of each embodiment form a dynamic synergy, which meets the needs of different agricultural fertilization scenarios.

[0127] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A bio-based thermoplastic polyurethane coating material that is readily and rapidly degradable, characterized in that, The raw materials include the following parts by weight: 0.8-2.0 parts of bio-chain matrix and 0.5-1.5 parts of chain enhancer; The biochain matrix is ​​a mixture 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 with solid base catalyst, heat to react, and separate the glycerol product; (2) Add hydrogen peroxide, formic acid and phosphotungstic acid to the reaction system obtained in step (1), and stir under heating; (3) Add dilute sulfuric acid and small molecule diol to the reaction system obtained in step (2), heat and stir to react and obtain vegetable oil diol; (4) The vegetable oil diol is oxidized by passing air through it under heating to obtain a pale yellow transparent liquid, which is the pre-oxidized vegetable oil diol; the heating temperature is 65-75℃; the oxidation time is 12-18h; and the air flow rate is 0.8-1.2L·min. -1 ·kg -1 ; The bio-based polyester diol is prepared by the following method: Pre-oxidized vegetable oil diol was mixed with bio-dicarboxylic acid and heated under negative pressure in a protective atmosphere. The temperature was then increased to continue the reaction. Calcium carbonate was added and stirred. After filtration to remove calcium carbonate, the product was obtained by vacuum filtration, which is bio-based polyester diol. The chain reinforcing agent is a mixture of a curing agent, a hardening agent, and a toughening agent; the curing agent is a diisocyanate; and the hardening agent is an aromatic rigid diamine or a diol.

2. The bio-based thermoplastic polyurethane coating material according to claim 1, characterized in that, 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 toughening agent is an aliphatic flexible diamine or diol.

3. The bio-based thermoplastic polyurethane coating material according to claim 2, characterized in that, 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'-biphenylhydrazine; 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)glyoxamide, or 1,4-cyclohexanediethanol.

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, the small molecule short-chain alcohol, and the solid base catalyst is 20:4:1; the heating reaction temperature is 70℃ and the time is 2.5h; 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℃; and the stirring reaction time is 5h.

5. The bio-based thermoplastic polyurethane coating material according to claim 1, characterized in that, 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℃ and the time is 1h.

6. The bio-based thermoplastic polyurethane coating material according to claim 1, characterized in that, The mass ratio of the pre-oxidized vegetable oil diol to the bio-dicarboxylic acid is 1.05:1; the negative pressure is -0.05 MPa; the heating reaction temperature is 120℃ and the time is 2h; the further heating reaction is carried out by raising the temperature to 160℃ and continuing the reaction for 3h; the amount of calcium carbonate added accounts for 0.1% of the total mass of the pre-oxidized vegetable oil diol and the bio-dicarboxylic acid; the bio-dicarboxylic 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, characterized in that, The bio-based thermoplastic polyurethane coating material is prepared by the following method: (1) Under vacuum conditions, pre-oxidized vegetable oil diol and bio-based polyester diol were heated and mixed to obtain a bio-chain matrix; (2) The curing agent, hardener, and toughening agent are mixed under stirring and heating to obtain a chain reinforcing agent; (3) Mix the bio-chain matrix and chain reinforcing agent and stir evenly, then ultrasonically vibrate at room temperature to obtain a bio-based thermoplastic polyurethane coating material.

8. The application of the bio-based thermoplastic polyurethane coating material according to any one of claims 1 to 7 in the preparation of easily and rapidly degradable controlled-release fertilizer.

9. A bio-based thermoplastic polyurethane-coated controlled-release fertilizer that is readily and rapidly degradable, characterized in that, The bio-based thermoplastic polyurethane-coated controlled-release fertilizer includes fertilizer granules and a bio-based thermoplastic polyurethane coating material as described in any one of claims 1 to 7, sprayed onto the surface of the fertilizer granules; the amount of the bio-based thermoplastic polyurethane coating material sprayed is 0.8 to 10% of the mass of the fertilizer granules.

10. The bio-based thermoplastic polyurethane-coated controlled-release fertilizer according to claim 9, characterized in that, The fertilizer is prepared by the following method: preheating the fertilizer granules, then spraying the bio-based thermoplastic polyurethane coating material according to any one of claims 1 to 7 onto the surface of the fertilizer granules, stirring the fertilizer while keeping it warm, forming a coating material, cooling down, spraying the bio-based thermoplastic polyurethane coating material again, then heating up to cure, repeating the above operation 1 to 10 times, and after the last layer has cured, waiting for the temperature to drop to room temperature to obtain the bio-based thermoplastic polyurethane coated controlled-release fertilizer.

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