Organosilicon-based polyurethane-coated controlled-release fertilizer and its preparation method

Abstract

This invention provides a silicone-based polyurethane-coated controlled-release fertilizer and its preparation method, belonging to the field of coated fertilizer technology. By mass percentage, the raw materials comprising the silicone-based polyurethane-coated controlled-release fertilizer include: 2wt%-3wt% silicone polyol, 1wt%-2wt% isocyanate, and 94wt%-97wt% fertilizer granules; wherein the silicone polyol and isocyanate form a silicone-based polyurethane coating on the surface of the fertilizer granules.

Description

Technical Field

[0001] This invention belongs to the field of coated fertilizer technology, specifically relating to an organosilicon-based polyurethane coated controlled-release fertilizer and its preparation method. Background Technology

[0002] Under the general trend of sustainable agricultural development, coated controlled-release fertilizers have become an environmentally friendly agricultural technology with great development potential due to their ability to simultaneously increase crop yields and reduce resource waste. Their research and development has consistently been a hot topic in the industry. Currently, the fertilizer utilization rate of the three major grain crops has increased to 42.6%, but this still lags behind advanced levels by about 30%, and the total amount of chemical fertilizers applied remains high. This situation not only causes serious resource depletion but also triggers a series of environmental problems such as soil degradation and eutrophication of water bodies. Therefore, further improving fertilizer utilization is of crucial practical significance for promoting high-quality agricultural development and reducing pollution emissions.

[0003] Currently, most mainstream synthetic polymer polyurethane-coated fertilizers on the market use polyether polyols and polycarbonate polyols as coating materials. While this type of synthetic polymer polyurethane coating has promoted the industrialization of coated controlled-release fertilizers to some extent, it has significant performance shortcomings. On the one hand, its performance is limited, only providing basic coating functions; on the other hand, the coating itself lacks sufficient hydrophobicity, making it prone to swelling and breakage in moist soil environments, leading to nutrient burst release and failing to guarantee a stable controlled-release effect; furthermore, due to the high molecular chain regularity of this type of synthetic polymer polyurethane, its degradation performance is poor. Long-term residues will break down into microplastic particles. These particles are small in size and highly hydrophobic, making them difficult to be adsorbed by soil colloids and easily diffuse in the environment. Long-term accumulation can damage the soil microbial community structure, posing potential ecological risks. This problem seriously restricts its large-scale promotion and application in the agricultural field.

[0004] To improve the environmental friendliness of synthetic polymer polyurethane coatings, the industry has developed bio-based polyurethane coatings. However, these bio-based polyurethane coatings suffer from excessive hydrophilicity due to their structural characteristics. Without modification, their nutrient release cycle falls far short of the 30-day controlled-release standard required for agricultural production. Existing modification processes are often cumbersome and costly, and some modification methods even sacrifice the material's mechanical properties or degradation efficiency, making it difficult to achieve a balance between performance and economy.

[0005] In summary, existing coated controlled-release fertilizers cannot meet the agricultural production's demand for high efficiency, stability, environmental protection, and economy. Therefore, there is an urgent need to develop a coated controlled-release fertilizer that combines excellent hydrophobicity, stable controlled-release performance, high degradability, and suitable production costs. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides an organosilicon-based polyurethane-coated controlled-release fertilizer and its preparation method, aiming to at least partially solve the above-mentioned technical problems. The specific technical solution provided by this invention is as follows.

[0007] As a first aspect of the present invention, an organosilicon-based polyurethane-coated controlled-release fertilizer is provided, wherein the raw materials comprising the organosilicon-based polyurethane-coated controlled-release fertilizer by weight percentage are: 2wt%-3wt% organosilicon polyol, 1wt%-2wt% isocyanate, and 94wt%-97wt% fertilizer granules; wherein the organosilicon polyol and isocyanate form an organosilicon-based polyurethane coating on the surface of the fertilizer granules.

[0008] As a second aspect of the present invention, a method for preparing an organosilicon-based polyurethane-coated controlled-release fertilizer is provided, comprising: pouring fertilizer granules into a fluidized bed for flow and preheating at a preheating temperature of 80-90°C; coating the surface of the fertilizer granules with organosilicon polyol and isocyanate to form an organosilicon-based polyurethane coating, thereby obtaining an organosilicon-based polyurethane-coated controlled-release fertilizer.

[0009] In this embodiment of the invention, the organosilicon-based polyurethane-coated controlled-release fertilizer (hereinafter referred to as coated controlled-release fertilizer) of the present invention has the following beneficial effects through optimization of raw material composition and preparation process: First, the organosilicon-based polyurethane coating formed by the reaction of organosilicon polyol and isocyanate in a specific mass ratio, with the high bond energy and low surface energy characteristics of organosilicon segments, endows the organosilicon-based polyurethane coating with excellent hydrophobicity and structural stability, effectively avoiding the swelling, damage and nutrient burst release problems caused by insufficient hydrophobicity of traditional polyurethane coatings, significantly extending the nutrient controlled-release cycle, improving fertilizer utilization to a higher level, and reducing fertilizer application and resource waste; Second, the organosilicon polyol has good biodegradability, making the organosilicon-based polyurethane coating... In the soil environment, it can gradually degrade into non-toxic and harmless oligomers, and the released silicon can be absorbed and utilized by crops. Silicon can enhance the mechanical strength of crops to improve their resistance to lodging and pests, promote photosynthesis and nutrient absorption efficiency, and enhance their resistance to drought, salt and alkali and other stresses. At the same time, silicon helps to improve soil structure and promote soil microbial activity, avoiding the environmental risks caused by the long-term accumulation of traditional polyurethane coatings, which meets the needs of environmentally friendly agriculture development. Thirdly, the fluidized bed preheating coating process is simple to operate and can achieve uniform coating of organosilicon-based polyurethane film, which is suitable for continuous and large-scale industrial production. It solves the defects of some related slow-release technologies, such as complicated processes and narrow application range, and takes into account the practicality and economic feasibility of the technology. Attached Figure Description

[0010] Figure 1 The image shows the X-ray photoelectron spectrum of the organosilicon-based polyurethane coating in Example 1 of this invention.

[0011] Figure 2 This is a scanning electron microscope image of the silicone-based polyurethane coating in Example 3 of the present invention;

[0012] Figure 3 This is a scanning electron microscope image of the silicone-based polyurethane coating in Example 5 of the present invention;

[0013] Figure 4 The figures show the water contact angle test results of the coated controlled-release fertilizers in Comparative Examples 1, 2, 3, and 5 of this invention.

[0014] Figure 5 The figures show the water contact angle test results of the coated controlled-release fertilizer in Examples 4, 6-9 of this invention. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0016] In realizing the concept of this invention, it was discovered that organosilicon polyol materials possess excellent hydrophobic properties, can rapidly degrade into oligomers in soil environments, and are non-toxic and harmless, unlikely to cause environmental pollution. When applied in the field of polyurethane waterproof and antifouling coatings, the prepared polyurethane membrane material can achieve a water contact angle of 107.9°, a water absorption rate as low as 8.7%, and a tensile strength of 35.9 MPa. However, in the application of polyurethane-coated controlled-release fertilizers, this organosilicon polyol material is usually only used as a modifier. Under a coating rate of 7-10%, the controlled-release period of the modified bio-based polyurethane-coated controlled-release fertilizer can reach 60-90 days, and the water contact angle can reach 107°. Other related technologies use it to prepare polyurethane carrier-embedded fertilizers for slow release, but this is only suitable for potted plants and the process is cumbersome, making industrial mass production impossible. Organosilicon polyols with a silicon segment structure have higher bond energy, are less prone to breakage, and have lower surface energy compared to carbon chain structures, resulting in superior performance. However, related research has not used it as a main raw material for preparing polyurethane-coated controlled-release fertilizers.

[0017] Based on this, the present invention provides an organosilicon-based polyurethane-coated controlled-release fertilizer and its preparation method. The organosilicon-based polyurethane coating is prepared by organosilicon polyol, and the stability, hydrophobicity and other properties of organosilicon polyol material are imparted to the organosilicon-based polyurethane coating, thereby improving the performance of the organosilicon-based polyurethane coating and the controlled-release effect of the coated controlled-release fertilizer, and finally preparing an organosilicon-based polyurethane-coated controlled-release fertilizer with good hydrophobic and controlled-release properties.

[0018] As a first aspect of the present invention, an organosilicon-based polyurethane-coated controlled-release fertilizer is provided, wherein the raw materials comprising the organosilicon-based polyurethane-coated controlled-release fertilizer by weight percentage are: 2wt%-3wt% organosilicon polyol, 1wt%-2wt% isocyanate, and 94wt%-97wt% fertilizer granules; wherein the organosilicon polyol and isocyanate form an organosilicon-based polyurethane coating on the surface of the fertilizer granules.

[0019] For example, the content of organosilicon polyol can be 2wt%, 2.25wt%, 2.5wt%, 2.75wt%, or 3wt%; the content of isocyanate can be 1wt%, 1.25wt%, 1.5wt%, 1.75wt%, or 2wt%; and the content of fertilizer granules can be 94wt%, 94.5wt%, 95wt%, 95.5wt%, 96wt%, 96.5wt%, or 97wt%.

[0020] In this embodiment of the invention, the organosilicon-based polyurethane coating formed by the reaction of organosilicon polyol and isocyanate possesses excellent hydrophobicity and structural stability due to the high bond energy and low surface energy of the organosilicon segments. This effectively solves the problems of easy swelling and damage, and sudden nutrient release of traditional polyurethane coatings, significantly improving fertilizer utilization. Simultaneously, the organosilicon polyol can degrade into non-toxic oligomers in the soil, avoiding environmental accumulation risks.

[0021] In some embodiments, the silicone-based polyurethane coating further includes 0.1 wt% to 0.6 wt% of other organic polyols. Exemplarily, the content of other organic polyols may be 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, or 0.6 wt%. These other organic polyols are selected from at least one of polyether polyols, castor oil polyols, and polycarbonate polyols. More preferably, castor oil polyols are selected as the other organic polyols. The hydroxyl value of the other organic polyols is 123-450 mg KOH / g, for example, 123 mg KOH / g, 200 mg KOH / g, 300 mg KOH / g, 400 mg KOH / g, or 450 mg KOH / g, preferably 179 mg KOH / g.

[0022] In this embodiment of the invention, specific other organic polyols are added to the silicone-based polyurethane coating. These selected organic polyols exhibit good compatibility with silicone polyols and isocyanates, and their hydroxyl values ​​are adjusted to suit the reaction system requirements. They synergistically interact with silicone segments to optimize the mechanical properties of the silicone-based polyurethane coating, preventing brittleness or excessive softening, improving the structural integrity and density of the coating, and further enhancing the stability of nutrient controlled-release. Preferred castor oil polyols can also improve the biodegradability of the silicone-based polyurethane coating, balancing performance and environmental attributes while effectively balancing production costs, thus supporting the large-scale agricultural application of silicone-based polyurethane-coated controlled-release fertilizers.

[0023] In some embodiments, the organosilicon polyol is selected from at least one of hydroxybutyl silicone oil, hydroxypropyl silicone oil, and hydroxyl silicone oil. More preferably, the organosilicon polyol is hydroxybutyl silicone oil. The hydroxyl value of the organosilicon polyol is 70-315 mg KOH / g, for example, 70 mg KOH / g, 100 mg KOH / g, 175 mg KOH / g, 200 mg KOH / g, 300 mg KOH / g, or 315 mg KOH / g, preferably 175 mg KOH / g; the molecular weight of the organosilicon polyol is 1000-4000, for example, 1000, 2000, 2300, 2800, 3000, or 4000, more preferably 2300-2800.

[0024] In this embodiment of the invention, the selected organosilicon polyols and isocyanates exhibit excellent compatibility, enabling efficient reaction to form a stable organosilicon-based polyurethane coating. The preferred hydroxybutyl silicone oil further leverages the hydrophobicity and structural stability advantages of organosilicon materials, further optimizing the performance of the organosilicon-based polyurethane coating. By precisely controlling the hydroxyl value and molecular weight of the organosilicon polyol, the reaction system requirements can be adapted, the reaction rate adjusted, ensuring a uniform and dense organosilicon-based polyurethane coating, significantly improving the controlled nutrient release effect, while also considering the degradation performance of the organosilicon-based polyurethane coating.

[0025] Furthermore, in the selection of organosilicon polyols, besides hydroxyl-containing silicone oils such as hydroxybutyl silicone oil and hydroxypropyl silicone oil, other carbon skeleton polymers possessing both silicon and polyhydroxy structures can also be used as organosilicon polyol components to react with isocyanates, thereby preparing corresponding organosilicon-based polyurethane coatings and coated controlled-release fertilizers. It should be noted that the organosilicon polyols mentioned in this invention can be obtained commercially or prepared in-house.

[0026] In some embodiments, the isocyanate is selected from at least one of diphenylmethane diisocyanate (MDI), toluene diisocyanate (TDI), and isophorone diisocyanate (IPDI). More preferably, the isocyanate is liquefied MDI, wherein the content of isocyanate groups (-NCO) is 36%.

[0027] In this embodiment of the invention, the selected isocyanate and organosilicon polyols exhibit good compatibility and suitable reactivity, enabling efficient cross-linking to form a stable organosilicon-based polyurethane coating. The preferred liquefied MDI not only boasts excellent processing suitability, but using it as a reactant to form the hard segments of the organosilicon-based polyurethane coating significantly enhances its mechanical strength and structural stability. Its suitable NCO group content ensures a complete reaction, facilitating the formation of a dense and uniform organosilicon-based polyurethane coating structure, effectively enhancing nutrient controlled release, while also considering process feasibility and adapting to the needs of large-scale production.

[0028] In some embodiments, the molar ratio (-NCO:-OH, R value) of the isocyanate group in the isocyanate to the hydroxyl group in the organosilicon polyol and other organic polyols is 1-1.25:1, for example, it can be 1:1, 1.05:1, 1.1:1, 1.15:1, 1.2:1, or 1.25:1.

[0029] In this embodiment of the invention, the molar ratio of isocyanate groups to hydroxyl groups specified in this invention ensures sufficient cross-linking reaction between isocyanate and organosilicon polyols and other organic polyols, avoiding porosity defects in the organosilicon-based polyurethane coating due to incomplete reaction. It also prevents the organosilicon-based polyurethane coating from becoming brittle and easily damaged due to excessive cross-linking. This ratio effectively controls the reaction process and product structure, forming a dense, uniform, and mechanically stable organosilicon-based polyurethane coating, significantly improving the stability of nutrient controlled release and the durability of the organosilicon-based polyurethane coating. Simultaneously, it makes the reaction rate easier to control, balancing process feasibility and the needs of large-scale production.

[0030] In some embodiments, the fertilizer granules are selected from at least one of water-soluble nitrogen fertilizer, water-soluble phosphate fertilizer, and water-soluble potassium fertilizer. More preferably, the fertilizer granules are urea granules. The particle size of the fertilizer granules is 2-5 mm, for example, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, or 5 mm.

[0031] In this embodiment of the invention, the water-soluble fertilizer granules selected in this invention have good compatibility with the organosilicon-based polyurethane coating system. Their water-soluble properties synergize with the controlled-release function of the organosilicon-based polyurethane coating, ensuring that nutrients are released on demand to match crop growth needs. The preferred urea granules are stable and more easily bonded to the organosilicon-based polyurethane coating. Furthermore, the suitable particle size ensures uniform flow of the fertilizer granules during preparation, resulting in a dense and uniformly thick organosilicon-based polyurethane coating, avoiding defects in the coating caused by differences in fertilizer granule morphology or properties. This selection enhances the versatility of the coated controlled-release fertilizer, ensures the stability of the nutrient control effect, and is compatible with large-scale production processes.

[0032] In some embodiments, the silicone-based polyurethane coating further includes 0.1 wt% to 0.4 wt% of a sealing agent. Exemplarily, the content of the sealing agent can be 0.1 wt%, 0.2 wt%, 0.25 wt%, 0.3 wt%, or 0.4 wt%. The sealing agent is selected from at least one of liquid wax, solid wax, and petrolatum oil. More preferably, liquid wax is selected as the sealing agent.

[0033] In this embodiment of the invention, a specific sealing agent is added to the silicone-based polyurethane coating. The sealing agent has good compatibility with the silicone-based polyurethane coating system, and the preferred liquid wax exhibits superior sealing effect. The sealing agent can effectively fill the micropores that may be generated during the formation of the silicone-based polyurethane coating, further improving the density and overall integrity of the silicone-based polyurethane coating, reducing the risk of nutrient leakage through pores, enhancing the hydrophobicity and controlled-release stability of the silicone-based polyurethane coating, and avoiding nutrient burst release problems. At the same time, the sealing agent does not affect the biodegradability of the silicone-based polyurethane coating or its binding force with fertilizer particles, and is compatible with existing preparation processes, ensuring the stability of large-scale production.

[0034] Furthermore, the structural formulas of the organosilicon polyol (Formula (1)), isocyanate (Formula (2)), and organosilicon-based polyurethane (Formula (3)) coating formed by organosilicon polyol and isocyanate are shown below (taking hydroxybutyl silicone oil and MDI as examples):

[0035] Equation (1);

[0036] Equation (2);

[0037] Equation (3);

[0038] Ph represents the benzene ring.

[0039] The organosilicon-based polyurethane-coated controlled-release fertilizer provided by this invention, compared with polyurethane coatings made from polyether, polyester polyols, and bio-based polyols, exhibits superior hydrophobic properties due to the presence of organosilicon segments in the organosilicon polyols. This is equivalent to endowing the organosilicon-based polyurethane coating with corresponding hydrophobic capabilities, making it more suitable for improving the controlled-release performance of organosilicon-based polyurethane-coated controlled-release fertilizers in water. Furthermore, at the same dosage, the resulting organosilicon-based polyurethane-coated controlled-release fertilizer also possesses better weather resistance, better preparing it for subsequent modification. This invention, through a detailed comparison of the organosilicon polyol properties of organosilicon-based polyurethane-coated controlled-release fertilizers, ultimately determined suitable polyol properties and the appropriate ratio with isocyanates. The resulting organosilicon-based polyurethane-coated controlled-release fertilizer not only has excellent controlled-release performance but also superior hydrophobicity. After modification with other organic polyols, the controlled-release performance of this organosilicon-based polyurethane-coated controlled-release fertilizer can be further improved. The organosilicon-based polyurethane-coated controlled-release fertilizer film layer of the present invention contains relatively stable organosilicon segments, and exhibits outstanding hydrophobic properties compared with common carbon chain polyurethane-coated controlled-release fertilizer film layers. It mainly improves the controlled-release performance of organosilicon-based polyurethane-coated controlled-release fertilizer by enhancing the hydrophobic properties of the organosilicon-based polyurethane-coated controlled-release fertilizer, providing a new approach for the research and development of coated controlled-release fertilizers.

[0040] As a second aspect of the present invention, a method for preparing an organosilicon-based polyurethane-coated controlled-release fertilizer is provided, comprising: pouring fertilizer granules into a fluidized bed for flow and preheating at a preheating temperature of 80-90°C; coating the surface of the fertilizer granules with organosilicon polyol and isocyanate to form an organosilicon-based polyurethane coating, thereby obtaining an organosilicon-based polyurethane-coated controlled-release fertilizer.

[0041] To further enhance the hydrophobicity and optimize the controlled-release performance of the silicone-based polyurethane coating, a process combining batch coating with a sealing agent can be adopted during the coating of silicone polyol and isocyanate on the surface of fertilizer granules: first, a layer of sealing agent is coated on the surface of the fertilizer granules, then silicone polyol and isocyanate are coated on the surface of the fertilizer granules in batches, and after all the silicone-based polyurethane coating materials are coated, a layer of sealing agent is coated on the outer layer of the silicone-based polyurethane coating.

[0042] For example, the present invention provides a method for preparing organosilicon-based polyurethane-coated controlled-release fertilizer, the specific operation steps of which include steps S1-S3.

[0043] Step S1: Start the blower and heater, and pour the fertilizer granules into the fluidized bed to preheat the fertilizer granules. Set the temperature between 80-90℃, preferably 80℃. After preheating, add some sealing agent to modify the surface of the fertilizer.

[0044] Step S2: Activate the peristaltic pump to simultaneously atomize the coating materials such as organosilicon polyol, other organic polyols, and isocyanate into the fluidized bed through the nozzle and coat them onto the surface of the fertilizer granules to form a film. The materials are added in 3-6 batches, preferably in 4 batches, with an interval of 2-5 minutes between each addition, preferably 3 minutes.

[0045] Step S3: After all the coating materials are added, wait 10 minutes, add the remaining sealing agent to modify the surface of the fertilizer particles again, wait 3 minutes and then take them out to obtain organosilicon-based polyurethane-coated controlled-release fertilizer.

[0046] The present invention will be further illustrated below through embodiments and related test experiments. In the following detailed description, numerous specific details are set forth for ease of explanation to provide a comprehensive understanding of the embodiments of the present invention. However, it will be apparent that one or more embodiments may be practiced without these specific details. Moreover, the details in the following embodiments can be arbitrarily combined to form other feasible embodiments without conflict. All instruments, consumables, and reagents used in the following embodiments are commercially available unless otherwise specified.

[0047] Example 1

[0048] This embodiment 1 provides an organosilicon-based polyurethane-coated controlled-release fertilizer, the specific implementation of which is as follows.

[0049] The product comprises the following components by mass fraction: 2.6 wt% hydroxypropyl silicone oil, 1 wt% liquefied MDI, 0.4 wt% liquid wax, and 96 wt% urea particles. The hydroxypropyl silicone oil has a hydroxyl value of 175 mg KOH / g and a molecular weight of 2000. The urea particles have a particle size of 3 mm.

[0050] The preparation method is as follows: Preheat the fluidized bed to approximately 80°C, add urea granules and allow them to roll evenly within the fluidized bed; maintain this temperature for 5 minutes until the urea granules are fully heated, then continue for another 5 minutes. Next, uniformly spray 0.2 wt% liquid wax onto the surface of the urea granules. Hydroxypropyl silicone oil and liquefied MDI are simultaneously delivered to the fluidized bed via a peristaltic pump, atomized through nozzles, and uniformly sprayed onto the surface of the urea granules; after all coating materials have been sprayed, maintain the temperature for 10 minutes. Finally, add 0.2 wt% liquid wax and continue maintaining the temperature for 5 minutes to obtain the organosilicon-based polyurethane-coated controlled-release fertilizer.

[0051] Figure 1 This is the X-ray photoelectron spectrum of the organosilicon-based polyurethane coating in Example 1 of the present invention.

[0052] from Figure 1It can be seen that the organosilicon-based polyurethane coating contains characteristic peaks of C 1s, O 1s, N 1s, Si 2s, and Si 2p, indicating that the sample contains carbon, oxygen, nitrogen, and silicon elements. This is consistent with the composition of organosilicon-based polyurethane (the types of elements contained in raw materials such as organosilicon polyols and isocyanates), which directly proves the successful synthesis of the organosilicon-based polyurethane coating. Moreover, the characteristic peaks of each element are clearly present, providing a characterization basis for the chemical composition and structure of the organosilicon-based polyurethane coating, and further supporting the rationality of its molecular structure design.

[0053] Example 2

[0054] This embodiment 2 provides an organosilicon-based polyurethane-coated controlled-release fertilizer, the specific implementation of which is as follows.

[0055] The product comprises the following components by mass fraction: 2.6 wt% hydroxybutyl silicone oil, 1 wt% TDI, 0.4 wt% liquid wax, and 96 wt% urea particles. The hydroxybutyl silicone oil has a hydroxyl value of 175 mg KOH / g and a molecular weight of 3000. The urea particles have a particle size of 3 mm.

[0056] The preparation method is as follows: Preheat the fluidized bed to approximately 80°C, add urea granules and allow them to roll evenly within the fluidized bed; maintain this temperature for 5 minutes until the urea granules are fully heated, then continue maintaining this temperature for another 5 minutes. Subsequently, uniformly spray 0.2 wt% liquid wax onto the surface of the urea granules. Hydroxybutyl silicone oil and TDI are simultaneously delivered to the fluidized bed via a peristaltic pump, atomized through nozzles, and uniformly sprayed onto the surface of the urea granules; after all coating materials have been sprayed, maintain the temperature for 10 minutes. Finally, add 0.2 wt% liquid wax and continue maintaining the temperature for 5 minutes to obtain the organosilicon-based polyurethane-coated controlled-release fertilizer.

[0057] Example 3

[0058] This embodiment 3 provides an organosilicon-based polyurethane-coated controlled-release fertilizer, the specific implementation of which is as follows.

[0059] The product comprises the following components by mass fraction: 2.9 wt% hydroxybutyl silicone oil, 1.1 wt% liquefied MDI, and 96 wt% urea granules. The hydroxybutyl silicone oil has a hydroxyl value of 175 mg KOH / g and a molecular weight of 2500, while the urea granules have a particle size of 3 mm.

[0060] The preparation method is as follows: Preheat the fluidized bed to about 80℃, add urea granules and make them roll evenly in the fluidized bed; keep warm for 5 minutes until the urea granules are fully heated, and continue to maintain this temperature for another 5 minutes. Hydroxybutyl silicone oil and liquefied MDI are simultaneously delivered to the fluidized bed through a peristaltic pump, and then atomized through a nozzle and sprayed evenly onto the surface of the urea granules; after all the coating materials have been sprayed, keep warm for 10 minutes to obtain the organosilicon-based polyurethane-coated controlled-release fertilizer.

[0061] Figure 2 This is a scanning electron microscope image of the silicone-based polyurethane coating in Example 3 of the present invention.

[0062] from Figure 2 As can be seen, the organosilicon-based polyurethane coating forms a continuous and relatively uniform film layer on the surface of fertilizer particles, with a coating rate of 4%. The film thickness fluctuates to some extent (7.22μm-14μm), but is generally controllable. This is because the dynamic flow of fertilizer particles and the stepwise reaction between organosilicon polyol and isocyanate cause local thickness fluctuations due to slight differences in reaction progress and material distribution. The organosilicon-based polyurethane coating has a dense structure without obvious pores or defects, indicating that the organosilicon-based polyurethane coating effectively coats the surface of fertilizer particles. This demonstrates that the organosilicon-based polyurethane coating prepared by the present invention has good film-forming properties and coating uniformity, laying a structural foundation for its controlled-release performance.

[0063] Example 4

[0064] Example 4 provides an organosilicon-based polyurethane-coated controlled-release fertilizer. Compared with Example 1, the difference is that the organosilicon polyol used is adjusted to hydroxyl silicone oil with a hydroxyl value of 175 mg KOH / g and a molecular weight of 2000. The remaining preparation steps and the types and amounts of raw materials are consistent with those in Example 2.

[0065] Example 5

[0066] This embodiment 5 provides an organosilicon-based polyurethane-coated controlled-release fertilizer, the specific implementation of which is as follows.

[0067] The product comprises the following components by mass fraction: 2.6 wt% hydroxybutyl silicone oil, 1 wt% liquefied MDI, 0.4 wt% liquid wax, and 96 wt% urea particles. The hydroxybutyl silicone oil has a hydroxyl value of 175 mg KOH / g and a molecular weight of 3000. The urea particles have a particle size of 3 mm.

[0068] The preparation method is as follows: Preheat the fluidized bed to approximately 80°C, add urea granules and allow them to roll evenly within the fluidized bed; maintain this temperature for 5 minutes until the urea granules are fully heated, then continue for another 5 minutes. Next, uniformly spray 0.2 wt% liquid wax onto the surface of the urea granules. Hydroxybutyl silicone oil and liquefied MDI are simultaneously added to the fluidized bed in batches using a peristaltic pump, specifically in four equal batches, with a 3-minute interval between each batch. The mixture is atomized through a nozzle and sprayed uniformly onto the surface of the urea granules. After all the coating material has been sprayed, maintain the temperature for 10 minutes. Finally, add 0.2 wt% liquid wax and continue maintaining the temperature for 5 minutes to obtain the organosilicon-based polyurethane-coated controlled-release fertilizer.

[0069] Figure 3This is a scanning electron microscope image of the silicone-based polyurethane coating in Example 5 of the present invention.

[0070] from Figure 3 As can be seen, the organosilicon-based polyurethane coating forms a film layer with a thickness of about 8.02 μm on the surface of fertilizer particles, with a coating rate of 4%. The organosilicon-based polyurethane coating has a certain degree of continuity, which reflects the good film-forming and coating ability of organosilicon-based polyurethane materials, laying a structural foundation for its controlled-release performance. It also reflects the structural controllability of the organosilicon-based polyurethane coating of the present invention under different embodiments.

[0071] Example 6

[0072] Example 6 provides an organosilicon-based polyurethane-coated controlled-release fertilizer, comprising the following components by mass fraction: 2.3 wt% hydroxybutyl silicone oil, 0.6 wt% polyether polyol, 1.7 wt% liquefied MDI, 0.4 wt% liquid wax, and 95 wt% urea granules. The hydroxybutyl silicone oil has a hydroxyl value of 175 mg KOH / g and a molecular weight of 3000; the polyether polyol has a hydroxyl value of 450 mg KOH / g; and the urea granules have a particle size of 3 mm.

[0073] The preparation method is as follows: Compared with Example 5, the difference lies in the pretreatment method of the polyol component. Specifically, the organosilicon polyol and the polyether polyol are mixed evenly and preheated on an 80°C micro-heating platform for 20 minutes. The remaining preparation steps are consistent with those of Example 5.

[0074] Example 7

[0075] This embodiment 7 provides an organosilicon-based polyurethane-coated controlled-release fertilizer, comprising the following components by mass fraction: 2.1 wt% hydroxybutyl silicone oil, 0.6 wt% polycarbonate polyol, 1.9 wt% liquefied MDI, 0.4 wt% liquid wax, and 95 wt% urea granules. The hydroxyl value of the hydroxybutyl silicone oil is 175 mg KOH / g, and its molecular weight is 3000; the hydroxyl value of the polycarbonate polyol is 250 mg KOH / g; and the particle size of the urea granules is 3 mm.

[0076] The preparation method is as follows: Compared with Example 5, the difference lies in the pretreatment method of the polyol component. Specifically, the organosilicon polyol and polycarbonate polyol are mixed evenly and preheated on an 80°C micro-heating platform for 20 minutes. The remaining preparation steps are consistent with those of Example 5.

[0077] Example 8

[0078] This embodiment 8 provides an organosilicon-based polyurethane-coated controlled-release fertilizer, comprising the following components by mass fraction: 2.5 wt% hydroxybutyl silicone oil, 0.5 wt% castor oil polyol, 1.6 wt% liquefied MDI, 0.4 wt% liquid wax, and 95 wt% urea granules. The hydroxybutyl silicone oil has a hydroxyl value of 175 mg KOH / g and a molecular weight of 3000; the castor oil polyol has a hydroxyl value of 179 mg KOH / g; and the urea granules have a particle size of 3 mm.

[0079] The preparation method is as follows: Compared with Example 5, the difference lies in the pretreatment method of the polyol component. Specifically, the organosilicon polyol and castor oil polyol are mixed evenly and preheated on an 80°C micro-heating platform for 20 minutes. The remaining preparation steps are consistent with those of Example 5.

[0080] Example 9

[0081] This embodiment 9 provides an organosilicon-based polyurethane-coated controlled-release fertilizer, comprising the following components by mass fraction: 2.6 wt% hydroxybutyl silicone oil, 0.58 wt% castor oil polyol, 1.42 wt% liquefied MDI, 0.4 wt% liquid wax, and 95 wt% urea granules. The hydroxybutyl silicone oil has a hydroxyl value of 175 mg KOH / g and a molecular weight of 3000; the castor oil polyol has a hydroxyl value of 123 mg KOH / g; and the urea granules have a particle size of 3 mm.

[0082] The preparation method is as follows: Compared with Example 5, the difference lies in the pretreatment method of the polyol component. Specifically, the organosilicon polyol and castor oil polyol are mixed evenly and preheated on an 80°C micro-heating platform for 20 minutes. The remaining preparation steps are consistent with those of Example 5.

[0083] Comparative Example 1

[0084] Comparative Example 1 provides a polyether polyurethane coated controlled-release fertilizer, the specific implementation of which is as follows.

[0085] The product comprises the following components by mass fraction: 2.1 wt% polypropylene glycol, 2.5 wt% liquefied MDI, 0.4 wt% liquid wax, and 95 wt% urea particles. The polyether polyol has a hydroxyl value of 450 mg KOH / g, and the urea particles have a particle size of 3 mm.

[0086] The preparation method is as follows: Preheat the fluidized bed to approximately 75°C, add urea granules and allow them to roll evenly within the fluidized bed; maintain this temperature for 5 minutes until the urea granules are fully heated, then continue maintaining this temperature for another 5 minutes. Next, uniformly spray 0.2 parts of liquid wax onto the surface of the urea granules. Simultaneously deliver polypropylene glycol and liquefied MDI to the fluidized bed using a peristaltic pump, atomize them through nozzles, and spray them uniformly onto the surface of the urea granules; after all the coating materials have been sprayed, maintain the temperature for 10 minutes. Finally, add 0.2 parts of liquid wax and continue maintaining the temperature for 5 minutes to obtain the polyurethane-coated controlled-release fertilizer.

[0087] Comparative Example 2

[0088] Comparative Example 2 provides an organosilicon-based polyurethane-coated controlled-release fertilizer, the specific implementation of which is as follows.

[0089] The product comprises the following components by mass fraction: 3.1 wt% hydroxybutyl silicone oil, 0.5 wt% liquefied MDI, 0.4 wt% liquid wax, and 96 wt% urea particles. The hydroxybutyl silicone oil has a hydroxyl value of 70 mg KOH / g and a molecular weight of 1000, while the urea particles have a particle size of 3 mm.

[0090] The preparation method is as follows: Preheat the fluidized bed to approximately 80°C, add urea granules and allow them to roll evenly within the fluidized bed; maintain this temperature for 5 minutes until the urea granules are fully heated, then continue maintaining this temperature for another 5 minutes. Subsequently, uniformly spray 0.2 wt% liquid wax onto the surface of the urea granules. Hydroxybutyl silicone oil and liquefied MDI are simultaneously delivered to the fluidized bed via a peristaltic pump, atomized through nozzles, and uniformly sprayed onto the surface of the urea granules; after all coating materials have been sprayed, maintain the temperature for 10 minutes. Finally, add 0.2 wt% liquid wax and continue maintaining the temperature for 5 minutes to obtain the organosilicon-based polyurethane-coated controlled-release fertilizer.

[0091] Comparative Example 3

[0092] Comparative Example 3 provides an organosilicon-based polyurethane-coated controlled-release fertilizer, the specific implementation of which is as follows.

[0093] The product comprises the following components by mass fraction: 2.7 wt% hydroxybutyl silicone oil, 0.9 wt% liquefied MDI, 0.4 wt% liquid wax, and 96 wt% urea particles. The hydroxybutyl silicone oil has a hydroxyl value of 175 mg KOH / g and a molecular weight of 3000. The urea particles have a particle size of 3 mm.

[0094] The preparation method is as follows: Preheat the fluidized bed to approximately 80°C, add urea granules and allow them to roll evenly within the fluidized bed; maintain this temperature for 5 minutes until the urea granules are fully heated, then continue maintaining this temperature for another 5 minutes. Subsequently, uniformly spray 0.2 wt% liquid wax onto the surface of the urea granules. Hydroxybutyl silicone oil and liquefied MDI are simultaneously delivered to the fluidized bed via a peristaltic pump, atomized through nozzles, and uniformly sprayed onto the surface of the urea granules; after all coating materials have been sprayed, maintain the temperature for 10 minutes. Finally, add 0.2 wt% liquid wax and continue maintaining the temperature for 5 minutes to obtain the organosilicon-based polyurethane-coated controlled-release fertilizer.

[0095] Comparative Example 4

[0096] Comparative Example 4 provides an organosilicon-based polyurethane-coated controlled-release fertilizer, the specific implementation of which is as follows.

[0097] The product comprises the following components by mass fraction: 2.5 wt% hydroxybutyl silicone oil, 2.1 wt% liquefied MDI, 0.4 wt% liquid wax, and 95 wt% urea particles. The hydroxybutyl silicone oil has a hydroxyl value of 315 mg KOH / g and a molecular weight of 2500. The urea particles have a particle size of 3 mm.

[0098] The preparation method is as follows: Preheat the fluidized bed to approximately 80°C, add urea granules and allow them to roll evenly within the fluidized bed; maintain this temperature for 5 minutes until the urea granules are fully heated, then continue maintaining this temperature for another 5 minutes. Subsequently, uniformly spray 0.2 wt% liquid wax onto the surface of the urea granules. Hydroxybutyl silicone oil and liquefied MDI are simultaneously delivered to the fluidized bed via a peristaltic pump, atomized through nozzles, and uniformly sprayed onto the surface of the urea granules; after all coating materials have been sprayed, maintain the temperature for 10 minutes. Finally, add 0.2 wt% liquid wax and continue maintaining the temperature for 5 minutes to obtain the organosilicon-based polyurethane-coated controlled-release fertilizer.

[0099] Comparative Example 5

[0100] Comparative Example 5 provides an organosilicon-based polyurethane-coated controlled-release fertilizer. The difference from Comparative Example 4 is that the method of adding the coating material is adjusted. Hydroxybutyl silicone oil and liquefied MDI are first mixed evenly beforehand, then transported via a peristaltic pump and atomized through a nozzle before being uniformly sprayed onto the surface of urea particles in a fluidized bed. After all the coating material has been sprayed, it is kept at a constant temperature for 10 minutes. The remaining preparation steps and the types and amounts of raw materials are consistent with those in Example 2.

[0101] Furthermore, the nutrient release performance and water contact angle of the coated controlled-release fertilizers obtained in the above embodiments and comparative examples were tested. The nutrient release performance test method is described below, and the test results are shown in Table 1.

[0102] Figure 4The figures show the water contact angle test results of the coated controlled-release fertilizers in Comparative Examples 1, 2, 3, and 5 of this invention. Figure 5 The figures show the water contact angle test results of the coated controlled-release fertilizer in Examples 4, 6-9 of this invention.

[0103] Nutrient release test method: Take 10g of the coated controlled-release fertilizer from Examples 1-9 and Comparative Example 1, put it into a 150pm (100 mesh) nylon mesh bag, seal it and put it into a 250mL plastic bottle, add 200mL of deionized water, seal it and put it into a 25℃ biochemical constant temperature incubator, and measure its nutrient release data (ultraviolet spectrophotometer-colorimetric method) every 7 days. Finally, the overall nutrient release situation is obtained. The specific release rate calculation formula is shown in formula (4):

[0104] Release rate = ρ 25 V 0.001 / m / n / 0.46 Equation (4);

[0105] Wherein, ρ is the concentration of the leachate measured by spectrophotometer, in mg / L; 25 is the dilution factor, 1 mL of the test solution is diluted to 25 mL; V is the volume of the fertilizer soaking solution, generally 0.2, in L; m is the mass of the soaked coated controlled-release fertilizer, generally 10, in g; n is the mass percentage of nutrient fertilizer in the coated controlled-release fertilizer; 0.46 is the nitrogen nutrient content in the urea, which is 46%.

[0106] Table 1. Nutrient release performance test results of coated controlled-release fertilizers in each embodiment and comparative example.

[0107]

[0108] from Figure 4 , Figure 5 As shown in Table 1, among the pure organosilicon-based polyurethane-coated controlled-release fertilizer systems (Comparative Examples 2-5, Examples 1-5), Example 5 (hydroxyl value 175 mg KOH / g) exhibited the best controlled-release performance, with a release period of 43 days, similar to Comparative Example 1 and conforming to international standards (ISO 18644:2016). In terms of hydrophobicity (water contact angle), the water contact angle of Example 5 was significantly higher than that of Comparative Example 1 and other examples (e.g., ...). Figure 4In Example 5, the water contact angle reached 119.4°, significantly higher than the 78.6° of Comparative Example 1, demonstrating excellent hydrophobic controlled-release properties. Furthermore, hydroxybutyl silicone oil performed significantly better than hydroxypropyl silicone oil and hydroxyl silicone oil in this system. Regarding the addition process (Comparative Examples 3, 5, and Example 5), if the coating material is added too quickly, the slow curing of polyurethane can lead to fertilizer adhesion and poor controlled-release performance. Example 5, employing a process of adding the material in stages with intermittent reactions, effectively solved this problem, achieving a controlled-release period of up to 43 days. When organosilicon polyols were compounded and modified with other polyols (Examples 6-9), the controlled-release performance of the fertilizers in each example was significantly improved. Example 8 (20% content, hydroxyl value 179 mg KOH / g castor oil polyol) showed the most outstanding performance, with a controlled-release period of 90 days. Figure 5 It is evident that its hydrophobic properties, such as water contact angle, are also suitable for controlled release requirements. Overall, under the condition of a coating rate of 4%, the film thickness of the coated controlled-release fertilizer is concentrated in the range of 8-15 μm (Table 1), providing structural support for the controlled-release performance.

[0109] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A silicone-based polyurethane-coated controlled-release fertilizer, characterized in that, The raw materials comprising the organosilicon-based polyurethane-coated controlled-release fertilizer, by weight percentage, include: 2wt%-3wt% organosilicon polyols, 0.1wt%-0.6wt% other organic polyols, 1wt%-2wt% isocyanates, 94wt%-97wt% fertilizer granules; The organosilicon polyol, other organic polyols, and isocyanate form an organosilicon-based polyurethane coating that covers the surface of the fertilizer particles. The other organic polyols are selected from at least one of polyether polyols, castor oil polyols, and polycarbonate polyols; The organosilicon polyol is selected from at least one of hydroxybutyl silicone oil, hydroxypropyl silicone oil, and hydroxyl silicone oil; The hydroxyl value of the organosilicon polyol is 70-315 mg KOH / g; The molecular weight of the organosilicon polyol is 1000-4000; The isocyanate is selected from at least one of diphenylmethane diisocyanate, toluene diisocyanate, and isophorone diisocyanate; The molar ratio of the isocyanate group in the isocyanate to the hydroxyl group in the organosilicon polyol and the other organic polyols is 1-1.25:1; The organosilicon-based polyurethane-coated controlled-release fertilizer is prepared by the following method: Fertilizer granules are poured into a fluidized bed and preheated to a temperature of 80-90℃. Organosilicon polyols, other organic polyols, and isocyanates are coated in batches onto the surface of the fertilizer granules to form an organosilicon-based polyurethane coating, thereby obtaining an organosilicon-based polyurethane-coated controlled-release fertilizer.

2. The organosilicon-based polyurethane-coated controlled-release fertilizer according to claim 1, characterized in that, The hydroxyl values ​​of the other organic polyols are 123-450 mg KOH / g.

3. The organosilicon-based polyurethane-coated controlled-release fertilizer according to claim 1, characterized in that, The fertilizer granules are selected from at least one of water-soluble nitrogen fertilizer, water-soluble phosphate fertilizer, and water-soluble potassium fertilizer. The fertilizer granules have a particle size of 2-5 mm.

4. The organosilicon-based polyurethane-coated controlled-release fertilizer according to claim 1, characterized in that, The silicone-based polyurethane coating also includes: 0.1wt%-0.4wt% sealing agent; The sealing agent is selected from at least one of liquid wax, solid wax, and petrolatum oil.

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