Preparation method of ultraviolet light cross-linking solidified coated urea

Abstract

The application provides a preparation method of ultraviolet light cross-linking and curing coated urea, and belongs to the technical field of slow-release fertilizers.The preparation method of the application is as follows: PBS oligomer powder is dissolved in dichloromethane, then a base catalyst is added, methyl acrylate is added dropwise under ice bath, after reaction at a certain temperature, the reaction solution is poured into ethanol to precipitate the product and dry, and MA-PBS is prepared; then MA-PBS is dissolved in dichloromethane, polythiol and a photoinitiator are added, and the mixture is uniformly shaken and stirred to prepare a coating reagent; finally, urea particles are placed in a rotary coating pan, the coating reagent is added dropwise in batches, the whole process is irradiated by a set light intensity ultraviolet lamp, and after the dropwise addition is completed, the light irradiation is continued to solidify, and the ultraviolet light solidification coated slow-release urea is obtained.The method has simple process and controllable parameters, the prepared coated slow-release urea has good stability, excellent slow-release performance, and is convenient for large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of slow-release fertilizer technology, and particularly relates to a method for preparing ultraviolet light cross-linking and curing coated urea. Background Technology

[0002] Urea is the most widely used fast-acting nitrogen fertilizer in agricultural production, boasting advantages such as high nitrogen content, low production cost, and convenient application, playing an irreplaceable role in ensuring crop growth and increasing yields. However, conventional urea application suffers from drawbacks such as rapid dissolution and a short nutrient release cycle, easily leading to nitrogen leaching and volatilization waste. This not only significantly reduces fertilizer nutrient utilization but also easily causes agricultural ecological and environmental problems such as soil compaction and eutrophication. Using coating slow-release technology to modify urea granules allows for precise control of the nitrogen nutrient release rate and cycle, achieving a precise match between nutrient release and crop growth requirements. This is a core technological approach to improve urea fertilizer utilization, reduce nutrient loss, and minimize agricultural non-point source pollution.

[0003] Currently, the coating materials for commercially available slow-release urea are mostly non-degradable polyurethane polymers. While these materials have good film-forming properties and mature coating processes, they are difficult to biodegrade in natural soil environments. Long-term application leaves persistent residues in the soil, damaging soil aggregate structure and affecting the soil's micro-ecological environment, exhibiting significant environmental disadvantages and failing to meet the needs of green agriculture and ecologically sustainable development. Therefore, developing novel biodegradable and environmentally compatible coating substrates has become a key research direction in the field of slow-release fertilizers.

[0004] Polybutylene succinate (PBS), a typical fully biodegradable aliphatic polyester, possesses excellent biodegradability, mechanical film-forming properties, and processing adaptability, making it a widely recognized ideal candidate substrate for slow-release fertilizer coating. However, existing commercially available high-molecular-weight PBS has significant limitations: its high crystallinity results in a brittle texture; its extremely low solubility in common organic solvents such as dichloromethane necessitates the consumption of large amounts of organic solvents for dispersion and coating when using traditional fluidized bed coating processes to prepare slow-release urea. This not only leads to high solvent consumption and significant VOC emissions, but also poses a high risk of environmental pollution. Furthermore, the low boiling point and rapid evaporation rate of dichloromethane easily cause uneven film formation on the urea particle surface, resulting in micropores and voids in the coating layer, significantly reducing the slow-release fertilizer control effect. In addition, the viscosity and volatility characteristics of high-molecular-weight PBS coating solutions are difficult to control, causing urea particles to easily adhere to each other during the coating process, severely reducing coating quality and production efficiency, and greatly limiting the practical application of PBS materials in the large-scale coating production of slow-release urea.

[0005] It is evident that existing non-degradable coating materials pose significant environmental hazards, commercially available high molecular weight PBS has poor solubility, traditional fluidized bed coating processes consume large amounts of organic solvents, have poor film uniformity, are prone to particle adhesion, and have low coating efficiency, among other technical challenges. Summary of the Invention

[0006] In view of this, the present invention aims to provide a modified PBS-based biodegradable coating material and a method for preparing UV-crosslinked coated urea. A low molecular weight PBS precursor with good solubility in dichloromethane is designed and synthesized. The precursor is then modified by grafting methacrylic acid groups onto the ends of its molecular chains to prepare an oligomeric PBS derivative with allyl active groups at the ends of the molecular chains. The methacrylic acid-grafted oligomeric PBS derivative is then co-dissolved with a photoinitiator and a polythiol crosslinking agent to prepare a uniform and stable coating solution. This solution is sprayed onto the surface of urea particles, and a mercapto-olefin click crosslinking reaction is initiated by UV irradiation, resulting in in-situ curing of a dense and stable biodegradable coating film on the surface of the urea particles. This technical solution fundamentally solves the industry bottlenecks such as poor solubility of commercial high molecular weight PBS, high consumption of organic solvents in traditional coating processes, insufficient uniformity of coating layers, severe particle adhesion, and low coating production efficiency. At the same time, the coating material is naturally biodegradable, leaves no soil residue, and combines fertilizer slow-release performance, green environmental protection, and industrial production adaptability, thus having significant practical application value and industrialization prospects.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing UV-curable coated sustained-release urea includes the following steps: (1) Preparation of methacrylamide oligobutyl succinate (MA-PBS): Oligobutyl succinate powder was dissolved in dichloromethane, and then an alkaline catalyst was added. The mixture was stirred and mixed under ice bath conditions to obtain an ice bath mixture. A dichloromethane solution containing methacrylic anhydride was added dropwise to the above ice bath mixture to carry out the reaction. After the reaction was completed, the mixture was poured into ethanol to precipitate the solid, and dried to obtain MA-PBS powder. (2) Preparation of coating reagent: Dissolve the MA-PBS powder in dichloromethane, then add polythiol and photoinitiator, mix well and set aside; (3) UV curing coating: Under UV light irradiation, the coating reagent is added dropwise to urea particles rotating at a constant speed; after the addition is completed, the UV light irradiation and constant speed rotation are maintained to carry out the reaction. After the reaction is completed, the mixture is naturally cooled to obtain UV curing coated slow-release urea.

[0008] Preferably, the preparation method of the oligobutylene succinate (PBS) in step (1) is as follows: Butanediol, succinic acid, and a catalyst are mixed and subjected to a gradient heating reaction under nitrogen protection; after the reaction is completed, the mixture is cooled to room temperature to obtain a solid crude product. The solid crude product is then dissolved in dichloromethane and subsequently poured into an ethanol solution, resulting in the precipitation of a large amount of white flocculent matter; the white flocculent matter is filtered, washed, and dried to obtain oligobutylene PBS powder. The concentration of the ethanol solution is 95%.

[0009] More preferably, the catalyst is at least one of isopropyl titanate and n-butyl titanate; the molar ratio of succinic acid, butanediol and catalyst is 1-1.1:1-1.2:0.001-0.03.

[0010] More preferably, the specific method for the gradient heating reaction under nitrogen protection is as follows: the nitrogen gas introduction rate is set to 40-80 mL / min; the temperature is first raised to 170-190℃ and kept at a constant temperature for 2-5 h; then the temperature is raised to 210-230℃ and stirred for 4-5 h under a vacuum of 5-20 Pa; the heating rate for both heating cycles is 3-8℃ / min; the preferred heating rate is 5℃ / min.

[0011] Preferably, the alkaline catalyst in step (1) is one or two of triethylamine, 4-dimethylaminopyridine, pyridine, and 1-methylimidazole; the mass-volume ratio of the oligomeric PBS powder, dichloromethane, alkaline catalyst, and methacrylic anhydride is 15-20g:50-100mL:0.05-0.3g:1.0-2.5g.

[0012] Preferably, in the dichloromethane solution containing methacrylic anhydride in step (1), the concentration of methacrylic anhydride is 3-4 g / mL; and the dropping rate is 1-2 drops / second.

[0013] Preferably, the polythiol in step (2) is at least one of pentylenetetroxide tetra-3-mercaptopropionate (PETMP), trimethylolpropane tris(3-mercaptopropionate) (TMPMP), 1,4-butanedithiol (BDT), 1,6-hexanedithiol (HDT), and ethylene glycol bis(3-mercaptopropionate) (EGMP). The photoinitiator is at least one of 2-hydroxy-2-methylphenylacetone (Irgacure1173), 1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propanone (Irgacure2959), benzoin dimethyl ether (Irgacure651), and 1-hydroxycyclohexylphenyl ketone (Irgacure184).

[0014] Preferably, the mass-to-volume ratio of MA-PBS powder, dichloromethane, polythiol and photoinitiator in step (2) is 2-2.5g:2-20mL:0.2-0.4g:0.05-0.3g.

[0015] Preferably, the wavelength of the ultraviolet lamp in step (3) is 320-400nm and the light intensity is 800-1100mW / cm². 2 The distance between the ultraviolet lamp and the surface of the urea particles is 5-12 cm. The urea particles have a diameter of 4-5 mm and a rotation speed of 10-40 r / min.

[0016] Preferably, the mass-to-volume ratio of urea to coating reagent in step (3) is 15-20g:15-20mL; The reaction time is 15-25 minutes.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention modifies oligobutylene succinate (PBS) by methacrylation, introducing unsaturated double bonds. When exposed to ultraviolet light in the presence of a photoinitiator, it can react with a crosslinking agent to form a film and solidify rapidly. This significantly improves the binding force with urea particles, effectively solving the problems of traditional commercial high molecular weight PBS coating requiring large amounts of organic solvents, making film formation difficult, and causing the coating layer to easily detach. This enhances the uniformity and stability of the coating layer.

[0018] (2) The ultraviolet curing process replaces the traditional thermal curing process. The curing time is short (only 10-30 min), energy consumption is low, operation is simple, the curing process is environmentally friendly, and there is no harmful gas emission, which is in line with the concept of green production.

[0019] (3) Optimize process parameters such as dripping rate, stirring speed, and light intensity to ensure that the coating agent evenly covers the surface of urea particles, making the coating layer uniform in thickness and without dead corners, effectively controlling the urea release rate, extending the fertilizer effect period, and improving fertilizer utilization.

[0020] (4) All the coating materials used are biodegradable and can be slowly degraded in the soil.

[0021] (5) The entire preparation process is simple, the parameters are controllable, and the repeatability is good, which facilitates large-scale production and has broad prospects for agricultural application. Attached Figure Description

[0022] Figure 1 The photocurable crosslinked film (f1) prepared in Example 1; Figure 2 The photocurable crosslinked film (f2) prepared for Comparative Example 1; Figure 3 The photocurable crosslinked film (f3) prepared for Comparative Example 2; Figure 4 The photocurable crosslinked film prepared for Comparative Example 3 (f4); Figure 5 The photocurable crosslinked film prepared for Comparative Example 4 (f5); Figure 6 This is a gel permeation chromatogram of the oligomeric PBS obtained in Example 1; Figure 7 The infrared spectrum of the methacrylated oligomeric PBS (MA-PBS) obtained in Example 1; Figure 8 Gel permeation chromatogram of the photocurable crosslinked membrane (f1) prepared in Example 1; Figure 9 Thermogravimetric analysis (TGA) of Example 1 (f1); Figure 10 Differential scanning calorimetry (DSC) of Example 1 (f1); Figure 11 The stress-strain curve diagram for Example 1 (f1); Figure 12 This is a scanning electron microscope image of the cross section of the UV-cured coated sustained-release urea (U@PBS-1) particles in Example 2 after photocuring. Figure 13 This is a release curve of UV-cured coated sustained-release urea (U@PBS-1) in pure water in Example 2; Figure 14 This is a release curve of UV-cured coated sustained-release urea (U@PBS-1) in pure water in Example 3; Figure 15 This is a release curve of UV-cured coated sustained-release urea (U@PBS-1) in pure water in Example 4. Detailed Implementation

[0023] This invention provides a method for preparing ultraviolet light-cured coated sustained-release urea, comprising the following steps: (1) Preparation of methacrylamide oligobutyl succinate (MA-PBS): Oligobutyl succinate powder was dissolved in dichloromethane, and then an alkaline catalyst was added. The mixture was stirred and mixed under ice bath conditions to obtain an ice bath mixture. A dichloromethane solution containing methacrylic anhydride was added dropwise to the above ice bath mixture to carry out the reaction. After the reaction was completed, the mixture was poured into ethanol to precipitate the solid, and dried to obtain MA-PBS powder. (2) Preparation of coating reagent: Dissolve the MA-PBS powder in dichloromethane, then add polythiol and photoinitiator, mix well and set aside; (3) UV curing coating: Under UV light irradiation, the coating reagent is dropped into urea particles rotating at a constant speed in the coating machine; after the drop is finished, the UV light irradiation and constant speed rotation are maintained to carry out the reaction. After the reaction is completed, the mixture is cooled naturally to obtain UV curing coated slow-release urea.

[0024] Preferably, the preparation method of the oligobutylene succinate (PBS) in step (1) is as follows: Butylene glycol, succinic acid, and a catalyst are mixed and subjected to a gradient heating reaction under nitrogen protection; after the reaction is completed, the mixture is cooled to room temperature to obtain a solid crude product. The solid crude product is then dissolved in dichloromethane and subsequently poured into a 95% ethanol solution, resulting in the precipitation of a large amount of white flocculent matter. The white flocculent matter is then filtered, washed, and dried to obtain oligobutylene PBS powder. Specifically, the drying is a constant-temperature drying process, with a drying temperature of 60-80℃ and a drying time of 4-12 hours.

[0025] More preferably, the catalyst is at least one of isopropyl titanate and n-butyl titanate; the molar ratio of succinic acid, butanediol and catalyst is 1-1.1:1-1.2:0.001-0.03.

[0026] More preferably, the specific method for the gradient heating reaction under nitrogen protection is as follows: the nitrogen inlet rate is set to 40-80 mL / min; the temperature is first increased to 170-190℃ at a rate of 3-8℃ / min and kept at a constant temperature for 2-5 hours; then the temperature is increased to 210-230℃ at a rate of 3-8℃ / min, and the reaction is stirred for 4-5 hours under a vacuum of 5-20 Pa to facilitate the removal of by-products generated during the reaction; the stirring speed is 150-250 r / min to ensure uniform dispersion of the raw materials and to ensure that the reaction proceeds fully; the nitrogen environment ensures that the reaction system is in an inert protective atmosphere to avoid product oxidation.

[0027] Preferably, the alkaline catalyst in step (1) is one or two of triethylamine, 4-dimethylaminopyridine, pyridine, and 1-methylimidazole; the mass-volume ratio of the oligomeric PBS powder, dichloromethane, alkaline catalyst, and methacrylic anhydride is 15-20g:50-100mL:0.05-0.3g:1.0-2.5g.

[0028] Preferably, in the dichloromethane solution containing methacrylic anhydride in step (1), the concentration of methacrylic anhydride is 3-4 g / mL; and the dropping rate is 1-2 drops / second.

[0029] Specifically, the reaction method in step (1) is as follows: after stirring in an ice bath for 20-30 minutes, remove the ice bath and heat to 50-80℃ for constant temperature reaction, with a reaction time of 4-12 hours.

[0030] Specifically, in step (1), the reactants are precipitated in ethanol and then dried at a temperature of 40-80°C.

[0031] Preferably, the polythiol in step (2) is at least one of pentaerythritol tetra-3-mercaptopropionate (PETMP), trimethylolpropane tris(3-mercaptopropionate) (TMPMP), 1,4-butanedithiol (BDT), 1,6-hexanedithiol (HDT), and ethylene glycol bis(3-mercaptopropionate) (EGMP). The photoinitiator is at least one selected from 2-hydroxy-2-methylphenylacetone (Irgacure1173), 1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propanone (Irgacure2959), benzoin dimethyl ether (Irgacure651), and 1-hydroxycyclohexylphenyl ketone (Irgacure184).

[0032] Preferably, the mass-to-volume ratio of MA-PBS powder, dichloromethane, polythiol and photoinitiator in step (2) is 2-2.5g:2-20mL:0.2-0.4g:0.05-0.3g.

[0033] Preferably, the wavelength of the ultraviolet lamp in step (3) is 320-400nm and the light intensity is 800-1100mW / cm². 2 The distance between the ultraviolet lamp and the surface of the urea particles is 5-12cm; to ensure uniform light intensity distribution, no local light dead angles, and to ensure that the cross-linking and curing reaction is fully carried out and the coating layer thickness is uniform. The urea particles have a diameter of 4-5 mm and a rotation speed of 10-40 r / min; this ensures that the urea particles rotate evenly, avoids agglomeration and splashing, and facilitates the uniform coverage of the particle surface by the coating agent.

[0034] Preferably, the mass-to-volume ratio of urea to coating reagent in step (3) is 15-20g:15-20mL; The reaction time is 15-25 minutes.

[0035] The technical solution of the present invention will now be described in detail through examples and comparative examples.

[0036] Example 1 A method for preparing a photocurable crosslinked film, comprising the following steps: (1) Preparation of oligomeric PBS: 110 mmol butanediol, 100 mmol succinic acid, and 0.056 g (0.197 mmol) isopropyl titanate were added together to a 250 ml three-necked round-bottom flask and mechanically stirred. Nitrogen gas was then introduced into the flask for protection (at a rate of 40 mL / min), and the temperature was increased to 170 °C at a rate of 5 °C / min and kept constant for 3 h. The temperature was then increased to 230 °C at a rate of 5 °C / min, maintaining a high vacuum environment (<10 Pa) and continuously stirred for 4 h. After the reaction was complete, the reaction system became viscous and cooled to room temperature to solidify. The resulting crude solid product was dissolved in 200 ml of dichloromethane and then poured into 500 ml of 95% ethanol solution, resulting in the precipitation of a large amount of white flocculent matter. The white flocculent matter was filtered and washed. The washed solid was transferred to an electric heating drying oven and dried at 60°C to obtain oligomeric PBS powder. (2) Preparation of MA-PBS: Weigh 20g of oligomeric PBS powder into a round-bottom flask, add 100mL of dichloromethane solvent, and stir until completely dissolved; add 0.13g of triethylamine and 0.0063g of 4-dimethylaminopyridine to the solution, stir at 150-250r / min under ice bath conditions, and maintain the system temperature at 0-5℃; slowly add 5mL of dichloromethane solution containing 1.981g of methacrylic anhydride to the above ice bath mixture at a rate of 1-2 drops / second, continue stirring in the ice bath for 30min, and then move to 50℃ constant temperature conditions and stir for 12h; after the reaction is completed, pour the reaction solution into pure ethanol to precipitate solid, place the solid in a 60℃ constant temperature electric heating drying oven and dry for 4-6h to obtain MA-PBS powder; (3) Preparation of coating reagent: Accurately weigh 2g of MA-PBS powder and dissolve it in 10mL of dichloromethane; add 0.2628g of PETMP and 0.15g of 2-hydroxy-2-methylphenylacetone photoinitiator to the solution, mix well and set aside; (4) UV curing of the plate film: The coating reagent prepared in step (3) above is spread evenly on a petri dish; UV curing is performed using a light intensity of 1091 mW / cm². 2 The sample was continuously irradiated with a UV lamp, with the distance between the UV lamp and the surface of the coating reagent being 8-12 cm; after irradiation for 20 minutes, a flat sheet membrane (f1) was obtained. Figure 1 As shown, from Figure 1 It can be seen that a film can be effectively formed under these conditions, and the film has strong toughness.

[0037] Comparative Example 1 A method for preparing a photocurable crosslinked film, comprising the following steps: Steps (1)-(2) are the same as in Example 1; (3) Preparation of coating reagent: Accurately weigh 2g of MA-PBS powder and dissolve it in 10mL of dichloromethane; add 0.1314g of PETMP and 0.15g of 2-hydroxy-2-methylphenylacetone photoinitiator to the solution, mix well and set aside.

[0038] Step (4) is the same as in Example 1. The resulting photocurable crosslinked film (f2) is as follows: Figure 2 As shown, from Figure 2 It can be seen that film cannot be formed effectively under these conditions, and the product is brittle.

[0039] Comparative Example 2 A method for preparing UV-curable coated sustained-release urea, comprising the following steps: Steps (1)-(2) are the same as in Example 1; (3) Preparation of coating reagent: Accurately weigh 2g of MA-PBS powder and dissolve it in 10mL of dichloromethane; add 0.3942g of PETMP and 0.15g of 2-hydroxy-2-methylphenylacetone photoinitiator to the solution, mix well and set aside.

[0040] Step (4) is the same as in Example 1. The obtained photocurable crosslinked film (f3) is as follows: Figure 3 As shown, from Figure 3 It can be seen that film cannot be formed effectively under these conditions.

[0041] Comparative Example 3 A method for preparing UV-curable coated sustained-release urea, comprising the following steps: Steps (1)-(2) are the same as in Example 1; (3) Preparation of coating reagent: Accurately weigh 2g of MA-PBS powder and 0.15g of photoinitiator, dissolve them in 10mL of dichloromethane, mix well, and set aside.

[0042] Step (4) is the same as in Example 1. A photocurable crosslinked film (f4) is obtained, as shown... Figure 4 As shown, from Figure 4 It can be seen that film cannot be formed effectively under these conditions.

[0043] Comparative Example 4 A method for preparing UV-curable coated sustained-release urea, comprising the following steps: Step (1) is the same as in Example 1, except that it does not include step (2); (3) Preparation of coating reagent: Accurately weigh 2g of oligo-PBS powder and dissolve it in 10mL of dichloromethane; add 0.2628g of PETMP and 0.15g of 2-hydroxy-2-methylphenylacetone photoinitiator to the solution, mix well and set aside.

[0044] Step (4) is the same as in Example 1. A photocurable crosslinked film (f5) is obtained, as shown below. Figure 5 As shown, from Figure 5 It can be seen that film cannot be formed effectively under these conditions.

[0045] Example 2 A method for preparing UV-curable coated sustained-release urea, comprising the following steps: Steps (1)-(2) are the same as in Example 1; (3) Preparation of coating reagent: Accurately weigh 3g of MA-PBS powder and dissolve it in 10mL of dichloromethane; add 0.3942g of pentaerythritol tetra-3-mercaptopropionate (PETMP) and 0.3g of 2-hydroxy-2-methylphenylacetone photoinitiator to the solution, mix well to obtain coating reagent, and set aside for later use; (4) UV curing coating: Weigh 20g of urea granules with a particle size of 4-5mm, place them in a coating machine and rotate them at a constant speed of 20r / min; use a dropper to draw up the above coating reagent, and add it evenly to the surface of the rotating urea granules in 5-8 batches at a total drop volume of 10mL, 1-2mL per batch, with an interval of 2-3min; the entire drop process is carried out with a light intensity of 1091mW / cm 2 The urea particles were continuously irradiated with a UV lamp, with the UV lamp 8-12 cm away from the surface of the urea particles. After the addition was complete, the UV lamp irradiation and coating pan rotation were maintained for 20 min. After the reaction was completed, the coated urea particles were naturally cooled to 20-25℃ and sealed in a dry, impurity-free container for storage to obtain UV-cured coated slow-release urea (U@PBS-1).

[0046] Example 3 A method for preparing UV-curable coated sustained-release urea, comprising the following steps: Steps (1)-(2) are the same as in Example 1; (3) Preparation of coating reagent: Accurately weigh 2g of the above-mentioned methacryloyl butyl succinate (MA-PBS) powder and dissolve it in 10mL of dichloromethane; add 0.2628g of pentaerythritol tetra-3-mercaptopropionate (PETMP) and 0.15g of 2-hydroxy-2-methylphenylacetone photoinitiator to the solution, mix them evenly and set aside as coating reagent.

[0047] Step (4) is the same as in Example 2, and the obtained UV-cured coated sustained-release urea (U@PBS-2) is obtained.

[0048] Example 4 A method for preparing UV-curable coated sustained-release urea, comprising the following steps: Steps (1)-(2) are the same as in Example 1; (3) Preparation of coating reagent: Accurately weigh 1g of the above-mentioned methacrylamide oligobutyl succinate (MA-PBS) powder and dissolve it in 10mL of dichloromethane; add 0.1314g of pentaerythritol tetra-3-mercaptopropionate (PETMP) and 0.15g of 2-hydroxy-2-methylphenylacetone photoinitiator to the solution, mix them evenly and set aside as coating reagent.

[0049] Step (4) is the same as in Example 2, and the obtained UV-cured coated sustained-release urea (U@PBS-3) is obtained.

[0050] Comparative Example 5 A method for preparing UV-curable coated sustained-release urea, wherein steps (1)-(3) are performed in accordance with Comparative Example 1; Step (4) is the same as in Example 2.

[0051] Comparative Example 6 A method for preparing UV-curable coated sustained-release urea, wherein steps (1)-(3) are performed in accordance with Comparative Example 2; Step (4) is the same as in Example 2.

[0052] Comparative Example 7 A method for preparing UV-curable coated sustained-release urea, wherein steps (1)-(3) are performed in accordance with Comparative Example 3; Step (4) is the same as in Example 2.

[0053] Comparative Example 8 A method for preparing UV-curable coated sustained-release urea, wherein steps (1)-(3) are performed in accordance with Comparative Example 4; Step (4) is the same as in Example 2.

[0054] Comparative Examples 5-8 failed to achieve coating on urea granules. The urea granules dissolved completely within minutes, failing to achieve the purpose of sustained release.

[0055] The different products prepared in the examples were analyzed as follows: The gel permeation chromatogram of the oligo-PBS obtained in Example 1 is shown below. Figure 6 The molecular weight distribution is shown in Table 1; Table 1

[0056] from Figure 6 As can be seen from Table 1, the molecular weight of the oligomeric PBS obtained is moderate, making it suitable for crosslinking. The infrared spectrum of the methacrylated oligomeric PBS (MA-PBS) obtained in Example 1 is as follows: Figure 7 ; Figure 7 It can be demonstrated that methacrylated oligomeric PBS (MA-PBS) was successfully obtained.

[0057] The gel permeation chromatogram of the photocurable crosslinked membrane (f1) prepared in Example 1 is shown below. Figure 8 The molecular weight distribution is shown in Table 2. Table 2

[0058] from Figure 8 As shown in Table 2, the molecular weight of the cross-linked polymer reaches the level of commercial PBS, proving that the cross-linking was successful.

[0059] The thermogravimetric diagram of Example 1 (f1) is as follows: Figure 9 ;from Figure 9 It can be seen that the cross-linked membrane has high thermal stability.

[0060] The differential scanning calorimeter of Example 1 (f1) is as follows: Figure 10 ;from Figure 10 It can be seen that the cross-linked membrane has a suitable melting point, and the resulting membrane can maintain a certain hardness under normal ambient temperature.

[0061] The stress-strain curve of Example 1 (f1) is shown in the figure below. Figure 11 ;from Figure 11 It can be seen that the cross-linked membrane has good toughness.

[0062] The scanning electron microscope (SEM) image of the cross-section of the urea particles after UV-cured coating in Example 2 (U@PBS-1) is shown below. Figure 12 It was confirmed that a uniform and dense film was formed on the surface of urea particles after photocrosslinking.

[0063] The release curve of UV-cured coated sustained-release urea (U@PBS-1) in pure water in Example 2 is shown below. Figure 13 ( Figure 13 (3-1, 3-2, and 3-3 represent different results from three parallel experiments). This demonstrates that photocrosslinking coating on the surface of urea particles effectively achieves sustained release in pure water, with a suitable release period. This confirms the effectiveness of the coating method.

[0064] The release curve of UV-cured coated sustained-release urea (U@PBS-1) in pure water in Example 3 is shown in Figure 3. Figure 14 ( Figure 14 (2-1, 2-2, and 2-3 represent different results from three parallel experiments). Compared to Example 2, the release rate of urea in pure water was faster after reducing the amount of coating.

[0065] The release curve of UV-cured coated sustained-release urea (U@PBS-1) in pure water in Example 4 is shown in Figure 4. Figure 15 ( Figure 15(1-1, 1-2, and 1-3 represent different results from three parallel experiments). Compared to Examples 2 and 3, urea was completely released in pure water in 3 days with a smaller amount of coating.

[0066] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing ultraviolet-cured coated sustained-release urea, characterized in that, Includes the following steps: (1) Preparation of methacrylamide oligobutyl succinate (MA-PBS): Oligobutyl succinate powder was dissolved in dichloromethane, and then an alkaline catalyst was added. The mixture was stirred and mixed under ice bath conditions to obtain an ice bath mixture. A dichloromethane solution containing methacrylic anhydride was added dropwise to the above ice bath mixture to carry out the reaction. After the reaction was completed, the mixture was poured into ethanol to precipitate the solid, and dried to obtain MA-PBS powder. (2) Preparation of coating reagent: Dissolve the MA-PBS powder in dichloromethane, then add polythiol and photoinitiator, mix well and set aside; (3) UV curing coating: Under UV light irradiation, the coating reagent is added dropwise to urea particles rotating at a constant speed; after the addition is completed, the UV light irradiation and constant speed rotation are maintained to carry out the reaction. After the reaction is completed, the mixture is naturally cooled to obtain UV curing coated slow-release urea.

2. The method for preparing UV-curable coated sustained-release urea according to claim 1, characterized in that, The preparation method of the oligobutylene succinate in step (1) is as follows: Butylene glycol, succinic acid and catalyst are mixed and subjected to a gradient heating reaction under nitrogen protection; after the reaction is completed, the mixture is cooled to room temperature to obtain a solid crude product, which is then dissolved in dichloromethane and subsequently poured into an ethanol solution, resulting in the precipitation of a large amount of white flocculent matter; the white flocculent matter is filtered, washed and dried to obtain oligobutylene PBS powder.

3. The method for preparing UV-curable coated sustained-release urea according to claim 2, characterized in that, The catalyst is at least one of isopropyl titanate and n-butyl titanate; the molar ratio of succinic acid, butanediol and catalyst is 1-1.1:1-1.2:0.001-0.

03.

4. The method for preparing UV-curable coated sustained-release urea according to claim 2, characterized in that, The specific method for the gradient heating reaction under nitrogen protection is as follows: set the nitrogen gas introduction rate to 40-80 mL / min; first heat to 170-190℃ and react at a constant temperature for 2-5 h; then heat to 210-230℃ and stir the reaction for 4-5 h under a vacuum of 5-20 Pa.

5. The method for preparing UV-curable coated sustained-release urea according to claim 1, characterized in that, The alkaline catalyst in step (1) is one or two of triethylamine, 4-dimethylaminopyridine, pyridine, and 1-methylimidazole; the mass-volume ratio of the oligomeric PBS powder, dichloromethane, alkaline catalyst and methacrylic anhydride is 15-20g:50-100mL:0.05-0.3g:1.0-2.5g.

6. The method for preparing UV-curable coated sustained-release urea according to claim 1, characterized in that, In step (1), the concentration of methacrylic anhydride in the dichloromethane solution is 3-4 g / mL; the dropping rate is 1-2 drops / second.

7. The method for preparing UV-curable coated sustained-release urea according to claim 1, characterized in that, The polythiol mentioned in step (2) is at least one of pentylenetetrol tetra-3-mercaptopropionate, trimethylolpropane tris(3-mercaptopropionate), 1,4-butanedithiol, 1,6-hexanedithiol, and ethylene glycol bis(3-mercaptopropionate). The photoinitiator is at least one of 2-hydroxy-2-methylphenylacetone, 1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propanone, benzoin dimethyl ether, and 1-hydroxycyclohexylphenyl ketone.

8. The method for preparing UV-curable coated sustained-release urea according to claim 1, characterized in that, The mass-to-volume ratio of MA-PBS powder, dichloromethane, polythiol and photoinitiator in step (2) is 2-2.5g:2-20mL:0.2-0.4g:0.05-0.3g.

9. The method for preparing UV-curable coated sustained-release urea according to claim 1, characterized in that, The wavelength of the ultraviolet lamp in step (3) is 320-400nm, and the light intensity is 800-1100mW / cm². 2 The distance between the ultraviolet lamp and the surface of the urea particles is 5-12 cm. The urea particles have a diameter of 4-5 mm and a rotation speed of 10-40 r / min.

10. The method for preparing UV-curable coated sustained-release urea according to claim 1, characterized in that, The mass-to-volume ratio of urea to coating reagent in step (3) is 15-20g:15-20mL; The reaction time is 15-25 minutes.

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