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

Abstract

The invention provides an organosilicon-based polyurethane coated controlled-release fertilizer and a preparation method thereof, and belongs to the technical field of coated fertilizers. The organic silicon-based polyurethane coated controlled-release fertilizer is prepared from the following raw materials in percentage by mass: 2wt%-3wt% of organic silicon polyol, 1wt%-2wt% of isocyanate and 94wt%-97wt% of fertilizer particles, wherein the organic silicon polyol and the isocyanate form an organic silicon-based polyurethane coating which is coated on the surfaces of fertilizer particles.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of coated fertilizers, and particularly relates to an organic silicon-based polyurethane coated controlled-release fertilizer and a preparation method thereof. BACKGROUND

[0002] Under the general trend of sustainable agricultural development, coated controlled-release fertilizers have become an environmentally friendly agricultural technology with great development potential because they can simultaneously achieve crop yield increase and resource waste reduction. The research and development of coated controlled-release fertilizers have always occupied a hot spot position in the industry. At present, the fertilizer utilization rate of the three major food crops has increased to 42.6%, but there is still a gap of about 30% compared with the existing advanced level, and the total application amount of chemical fertilizers has been at a high level for a long time. This situation not only causes serious resource waste, but also causes a series of environmental problems such as soil degradation and water eutrophication. Therefore, further improving the fertilizer utilization rate has important practical significance for promoting high-quality agricultural development and reducing pollution emissions.

[0003] At present, the mainstream synthetic high molecular polyurethane coated fertilizers on the market mostly use polyether polyol and polycarbonate polyol as coating raw materials. Although this kind of synthetic high molecular polyurethane coating has promoted the industrialization process of coated controlled-release fertilizers to a certain extent, it has significant performance short boards. On the one hand, its performance is single and can only play a basic coating role; on the other hand, the coating itself is insufficiently hydrophobic and is prone to swelling and damage in a humid soil environment, thereby causing nutrient burst release and failing to guarantee stable controlled-release effect; on the other hand, due to the high regularity of the molecular chain of this kind of synthetic high molecular polyurethane, its degradation performance is poor, and long-term residues can break down to form microplastic particles. These particles are small in size and strong in hydrophobicity, are difficult to be adsorbed by soil colloids, and are easy to diffuse in the environment, and long-term accumulation can destroy the structure of soil microbial communities and bring potential ecological risks, which seriously restricts its large-scale popularization and application in the agricultural field.

[0004] In order to improve the environmental friendliness of synthetic high molecular polyurethane coating, bio-based polyurethane coating has been developed in the industry. However, due to the problem of excessive hydrophilicity of the structure of this kind of bio-based polyurethane coating, if it is not modified, its nutrient release period cannot meet the basic 30-day controlled-release standard required by agricultural production. Existing modification processes often have the disadvantages of complicated process and high cost, and some modification methods also sacrifice the mechanical properties or degradation efficiency of the material, making it difficult to achieve a balance between performance and economy.

[0005] In summary, the existing coated controlled-release fertilizers cannot meet the needs of agricultural production for high efficiency, stability, environmental friendliness and economy, and therefore, it is urgent to develop a coated controlled-release fertilizer with excellent hydrophobicity, stable controlled-release performance, high-efficiency degradation and suitable production cost. SUMMARY

[0006] In order to solve the above technical problems, the present application provides a kind of organic silicon-based polyurethane coated controlled-release fertilizer and its preparation method, to at least partially solve the above technical problems, thus the specific technical scheme provided by the present application is as follows.

[0007] As a first aspect of the present application, an organic silicon-based polyurethane coated controlled-release fertilizer is provided, and the composition of the organic silicon-based polyurethane coated controlled-release fertilizer includes 2wt%-3wt% organic silicon polyol, 1wt%-2wt% isocyanate, and 94wt%-97wt% fertilizer particles.

[0008] As a second aspect of the present application, a preparation method of an organic silicon-based polyurethane coated controlled-release fertilizer is provided, which includes: pouring the fertilizer particles into the fluidized bed and preheating, with the preheating temperature being 80-90℃; coating the organic silicon polyol and isocyanate on the surface of the fertilizer particles to form an organic silicon-based polyurethane coating, thereby obtaining the organic silicon-based polyurethane coated controlled-release fertilizer.

[0009] In the embodiments of the present application, the organic silicon-based polyurethane coated controlled-release fertilizer (hereinafter referred to as coated controlled-release fertilizer) has the following beneficial effects by optimizing the composition of raw materials and the preparation process: first, the organic silicon-based polyurethane coating formed by the reaction of organic silicon polyol and isocyanate in a specific mass ratio has excellent hydrophobicity and structural stability due to the higher bond energy and lower surface energy characteristics of the organic silicon segment, effectively avoiding the swelling, damage and nutrient burst problems of traditional polyurethane coating caused by insufficient hydrophobicity, significantly prolonging the nutrient controlled-release period, improving the fertilizer utilization rate to a higher level, reducing the amount of chemical fertilizer and resource waste; second, the organic silicon polyol has good biodegradability, which makes the organic silicon-based polyurethane coating gradually degrade into non-toxic and harmless oligomers in the soil environment, and the released silicon elements can be absorbed and utilized by crops, which can enhance the mechanical strength of crops to improve the resistance to lodging, disease and pests, promote photosynthesis and nutrient absorption efficiency, and also enhance the drought resistance, salt tolerance and other stress resistance of crops, while silicon elements help to improve soil structure and promote soil microbial activity, avoiding the environmental risks caused by the long-term accumulation of traditional polyurethane coating, which meets the development needs of environmentally friendly agriculture; third, the fluidized bed preheating coating process is simple to operate and can realize uniform coating of the organic silicon-based polyurethane coating, which is suitable for continuous and large-scale industrial production, solving the defects of complicated process and narrow application range of some related slow-release technologies, and balancing the technical practicability and economic feasibility. BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1 X-ray photoelectron spectrogram of the organic silicon-based polyurethane coating in Example 1 of the present application;

[0011] Figure 2 A scanning electron microscope image of the silicone-based polyurethane coating in Example 3 of the present application;

[0012] Figure 3 A scanning electron microscope image of the silicone-based polyurethane coating in Example 5 of the present application;

[0013] Figure 4 A graph of the water contact angle test results of the coated controlled-release fertilizers in Comparative Example 1, Comparative Example 2, Example 3, and Example 5 of the present application;

[0014] Figure 5 A graph of the water contact angle test results of the coated controlled-release fertilizers in Example 4, Example 6-Example 9 of the present application. DETAILED DESCRIPTION

[0015] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application is further described in detail below with reference to specific examples and the accompanying drawings.

[0016] In the process of implementing the concept of the present application, it is found that the silicone polyol material has excellent hydrophobicity and other properties, can be rapidly degraded into oligomers in a soil environment, and is non-toxic and harmless, and is not easy to cause environmental pollution. When it is applied in the field of polyurethane waterproof and antifouling coatings, the water contact angle of the prepared polyurethane film material can reach 107.9°, the water absorption rate is as low as 8.7%, and the tensile strength can reach 35.9 MPa. However, the silicone polyol material is usually used as a modifier in the application of polyurethane coated controlled-release fertilizers. Under the condition of a coating rate of 7-10%, the controlled-release period of the bio-based polyurethane coated controlled-release fertilizer modified by the silicone polyol material can reach 60-90 days, and the water contact angle can reach 107°. Related technologies also use the silicone polyol material to prepare polyurethane carrier embedded fertilizers for slow release, but only apply to potting and have a complicated process, and cannot be mass-produced industrially. The silicone polyol material with a main silicon chain structure has higher bond energy, is not easy to break, and has lower surface energy, and has better performance than the carbon chain structure. However, related research has not used the silicone polyol material as the main raw material to prepare polyurethane coated controlled-release fertilizers.

[0017] Based on this, the present application provides a silicone-based polyurethane coated controlled-release fertilizer and a preparation method thereof. The silicone polyol material is used to prepare a silicone-based polyurethane coating, and the stability, hydrophobicity and other properties of the silicone polyol material are given to the silicone-based polyurethane coating, so as to improve the performance of the silicone-based polyurethane coating and the controlled-release effect of the coated controlled-release fertilizer, and finally prepare a silicone-based polyurethane coated controlled-release fertilizer with good hydrophobicity and controlled-release performance.

[0018] As a first aspect of the present application, a silicone-based polyurethane coated controlled-release fertilizer is provided. The silicone-based polyurethane coated controlled-release fertilizer comprises, in mass percentage: 2wt%-3wt% silicone polyol, 1wt%-2wt% isocyanate, and 94wt%-97wt% fertilizer particles; wherein the silicone polyol and the isocyanate form a silicone-based polyurethane coating wrapped around the surface of the fertilizer particles.

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

[0020] In the embodiments of the present application, the silicone-based polyurethane coating formed by the reaction of the silicone polyol and the isocyanate has excellent hydrophobicity and structural stability due to the high bond energy and low surface energy of the silicone segment, effectively solving the problems of easy swelling and damage of traditional polyurethane coatings and nutrient burst, and greatly improving the fertilizer utilization rate. At the same time, the silicone polyol can be degraded into non-toxic oligomers in the soil, avoiding environmental accumulation risks.

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

[0022] In the embodiments of the present application, specific other organic polyols are added in the silicone-based polyurethane coating. The selected other organic polyols have good compatibility with the silicone polyol and isocyanate, and the hydroxyl value is adjusted to meet the requirements of the reaction system. It can synergize with the silicone segment to optimize the mechanical properties of the silicone-based polyurethane coating, avoid brittle fracture or excessive softening of the silicone-based polyurethane coating, improve the structural integrity and compactness of the silicone-based polyurethane coating, and further enhance the nutrient controlled release stability. The preferred castor oil polyol can also improve the biodegradability of the silicone-based polyurethane coating, balance performance and environmental protection properties, and effectively balance production costs, providing support for the large-scale agricultural application of silicone-based polyurethane coating controlled release fertilizers.

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

[0024] In the embodiments of the present application, the selected silicone polyol of the present application has excellent compatibility with raw materials such as isocyanate, and can efficiently react to form a stable silicone-based polyurethane coating. The preferred hydroxybutyl silicone oil can further fully utilize the hydrophobicity and structural stability advantages of silicone materials, further optimizing the performance of the silicone-based polyurethane coating. By precisely controlling the hydroxyl value and molecular weight of the silicone polyol, the reaction system requirements can be adapted, the reaction rate can be adjusted, the uniformity and compactness of the silicone-based polyurethane coating can be ensured, the nutrient controlled release effect can be significantly improved, and the degradation performance of the silicone-based polyurethane coating can be considered.

[0025] Further, in the selection of silicone polyol, in addition to hydroxybutyl silicone oil, hydroxypropyl silicone oil and other silicone oil substances containing hydroxyl groups, other carbon skeleton high molecular compounds with both silicon structure and polyhydroxyl structure can also be used as silicone polyol components to react with isocyanate, and then the corresponding silicone-based polyurethane coating and coating controlled release fertilizer can be prepared. It should be noted that the silicone polyol mentioned in the present application can be obtained by commercial purchase or self-preparation.

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

[0027] In embodiments of the present application, the selected isocyanate of the present application has good compatibility with the components such as silicone polyol, and the reactivity is adapted, which can efficiently crosslink to form a stable silicone-based polyurethane coating. The preferred liquefied MDI not only has excellent processing suitability, but also can significantly improve the mechanical strength and structural stability of the silicone-based polyurethane coating when used as a reactant to form the hard segment of the silicone-based polyurethane coating. The adapted NCO group content can ensure that the reaction proceeds fully, which is conducive to the formation of a dense and uniform silicone-based polyurethane coating structure, effectively enhances the nutrient controlled release effect, and at the same time, takes into account the process feasibility and the demand for large-scale production.

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

[0029] In embodiments of the present application, the molar ratio of isocyanate group to hydroxyl group defined in the present application can not only ensure that the isocyanate and the silicone polyol and other organic polyols are fully crosslinked, but also can prevent the problems of pore defects in the silicone-based polyurethane coating due to incomplete reaction and brittle fracture and easy damage of the silicone-based polyurethane coating caused by excessive crosslinking. The ratio can effectively regulate the reaction process and product structure, form a dense and uniform silicone-based polyurethane coating with stable mechanical properties, significantly improve the nutrient controlled release stability and the durability of the silicone-based polyurethane coating; at the same time, the reaction rate is more easily controlled, and the process feasibility and the demand for large-scale production are taken into account.

[0030] In some embodiments, the fertilizer particles are selected from at least one of water-soluble nitrogen fertilizer, water-soluble phosphorus fertilizer, and water-soluble potassium fertilizer. Further preferably, the fertilizer particles are selected from urea particles. The particle size of the fertilizer particles is 2-5 mm, which can be 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, for example.

[0031] In the embodiments of the present application, the selected water-soluble fertilizer particles have good adaptability with the silicone-based polyurethane coating system. The water-soluble characteristics can form synergy with the controlled-release function of the silicone-based polyurethane coating to ensure that the nutrients are released on demand to match the growth needs of crops. The preferred urea particles are stable in performance, more easily combined with the silicone-based polyurethane coating, and have a suitable particle size to ensure uniform flow of the fertilizer particles during preparation, making the silicone-based polyurethane coating dense and uniform in thickness, and avoiding defects in the silicone-based polyurethane coating caused by differences in the morphology or properties of the fertilizer particles. This selection not only improves the application versatility of the coated controlled-release fertilizer, but also ensures the stability of the nutrient controlled-release effect, while being compatible with large-scale production processes.

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

[0033] In the embodiments of the present application, 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 can further exhibit excellent sealing effects. The sealing agent can effectively fill the small pores 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 the pores, strengthening the hydrophobicity and controlled-release stability of the silicone-based polyurethane coating, and avoiding nutrient burst problems. At the same time, the sealing agent does not affect the biodegradability of the silicone-based polyurethane coating and the bonding force with the fertilizer particles, and is compatible with existing preparation processes, ensuring the stability of large-scale production.

[0034] Further, the structural formula of the silicone polyol (formula (1)), isocyanate (formula (2)), and silicone-based polyurethane (formula (3)) formed by the silicone polyol and isocyanate are as follows (using hydroxybutyl silicone oil and MDI as an example):

[0035] Formula (1);

[0036] Formula (2);

[0037] Formula (3);

[0038] Ph represents a benzene ring.

[0039] The organic silicon-based polyurethane coated controlled-release fertilizer provided by the present application has better hydrophobicity and release control performance compared with the polyurethane coating prepared from polyether, polyester polyol and bio-based polyol, and the organic silicon-based polyurethane coated controlled-release fertilizer has better weather resistance and is better prepared for subsequent modification.

[0040] As a second aspect of the present application, a preparation method of the organic silicon-based polyurethane coated controlled-release fertilizer is provided, which comprises: flowing and preheating the fertilizer particles in a fluidized bed, and the preheating temperature is 80-90 DEG C; coating the organic silicon polyol and isocyanate on the surface of the fertilizer particles to form an organic silicon-based polyurethane coating, thereby obtaining the organic silicon-based polyurethane coated controlled-release fertilizer.

[0041] In order to further improve the hydrophobicity of the organic silicon-based polyurethane coating and optimize the release control performance, a process of batch coating combined with the use of sealing agent can be used in the process of coating the organic silicon polyol and isocyanate on the surface of the fertilizer particles: first, a layer of sealing agent is coated on the surface of the fertilizer particles, then the organic silicon polyol and isocyanate are batch coated on the surface of the fertilizer particles, and after all the raw materials of the organic silicon-based polyurethane coating are coated, a layer of sealing agent is coated on the outer layer of the organic silicon-based polyurethane coating.

[0042] For example, the present application provides a preparation method of an organic silicon-based polyurethane coated controlled-release fertilizer, and the specific operation steps include steps S1-S3.

[0043] Step S1: start the air blower and heater, and flow the fertilizer particles in the fluidized bed to preheat the fertilizer particles, and the temperature is set between 80-90 DEG C, preferably 80 DEG C; after preheating, add part of the sealing agent to modify the surface of the fertilizer.

[0044] Step S2: enable peristaltic pump, silicone polyol, other organic polyols, isocyanate and other coating materials are sprayed into the fluidized bed through the nozzle at the same time to coat on the surface of the fertilizer particles and react to form a film, which is divided into 3-6 times, preferably 4 times, and each time is added after 2-5 min, preferably 3 min.

[0045] Step S3: after all the coating materials are added, wait for 10 min, add the remaining hole sealing agent to modify the surface of the fertilizer particles again, wait for 3 min and take out, to obtain the silicone-based polyurethane coated controlled-release fertilizer.

[0046] The present application will be further described by examples and related test experiments. In the following detailed description, many specific details are set forth in order to provide a thorough understanding of the embodiments of the present application. It will be apparent, however, that one or more embodiments can be practiced without these specific details. In other instances, well-known methods, procedures and components have not been described in detail so as not to unnecessarily obscure aspects of the embodiments. The details in each of the following embodiments can be arbitrarily combined in other possible embodiments.

[0047] Example 1

[0048] This example 1 provides a silicone-based polyurethane coated controlled-release fertilizer, and the specific implementation is as follows.

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

[0050] The preparation method is as follows: the fluidized bed is preheated to about 80℃, the urea particles are added and uniformly rolled in the fluidized bed; after the urea particles are completely heated for 5min, continue to maintain for 5min, then uniformly spray 0.2wt% liquid wax on the surface of the urea particles. The hydroxypropyl silicone oil and the liquefied MDI are synchronously delivered to the fluidized bed by the peristaltic pump, and are uniformly sprayed on the surface of the urea particles after being atomized by the nozzle; after all the coating materials are sprayed, the reaction is maintained for 10min. Finally, 0.2wt% liquid wax is added, and the silicone-based polyurethane coated controlled-release fertilizer is prepared by continuing to maintain for 5min.

[0051] Figure 1 The X-ray photoelectron spectrogram of the silicone-based polyurethane coating in example 1 of the present application.

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

[0053] Example 2

[0054] The present example 2 provides an organic silicon-based polyurethane coated controlled-release fertilizer, and the specific implementation is as follows.

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

[0056] The preparation method is as follows: the fluidized bed is preheated to about 80℃, the urea particles are added and uniformly rolled in the fluidized bed; after the urea particles are completely heated for 5min, the temperature is maintained for another 5min, and then 0.2wt% liquid wax is uniformly sprayed on the surface of the urea particles. The hydroxybutyl silicone oil and TDI are synchronously delivered into the fluidized bed by a peristaltic pump, and are uniformly sprayed on the surface of the urea particles after being atomized by a nozzle; after the coating raw materials are completely sprayed, the temperature is maintained for 10min for reaction. Finally, 0.2wt% liquid wax is added, and the temperature is maintained for another 5min, thereby obtaining the organic silicon-based polyurethane coated controlled-release fertilizer.

[0057] Example 3

[0058] The present example 3 provides an organic silicon-based polyurethane coated controlled-release fertilizer, and the specific implementation is as follows.

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

[0060] The preparation method is as follows: the fluidized bed is preheated to about 80℃, the urea particles are added and uniformly rolled in the fluidized bed; after the urea particles are completely heated for 5min, the temperature is maintained for another 5min. The hydroxybutyl silicone oil and liquid MDI are synchronously delivered into the fluidized bed by a peristaltic pump, and are uniformly sprayed on the surface of the urea particles after being atomized by a nozzle; after the coating raw materials are completely sprayed, the temperature is maintained for 10min for reaction, thereby obtaining the organic silicon-based polyurethane coated controlled-release fertilizer.

[0061] Figure 2 Scanning electron microscope image of the silicone-based polyurethane coating in Example 3 of the present application.

[0062] As can be seen from Figure 2 It can be seen that the silicone-based polyurethane coating forms a continuous and relatively uniform film layer on the surface of the fertilizer particles, with a coating rate of 4%, and the film layer thickness has certain fluctuations (7.22 μm-14 μm) but is overall controllable, because the dynamic flow of the fertilizer particles and the stepwise reaction of the silicone polyol and isocyanate will cause the film layer to have thickness fluctuations due to slight differences in reaction progress and material distribution. The silicone-based polyurethane coating structure is dense, with no obvious pores or defects, indicating that the silicone-based polyurethane coating has achieved effective coating on the surface of the fertilizer particles, and reflects that the silicone-based polyurethane coating prepared by the preparation process of the present application has good film-forming property and coating uniformity, laying a structural foundation for the performance of its controlled release.

[0063] Example 4

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

[0065] Example 5

[0066] Example 5 provides a silicone-based polyurethane coated controlled release fertilizer, and the specific implementation is as follows.

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

[0068] The preparation method is as follows: the fluidized bed is preheated to about 80°C, and the urea particles are added and uniformly rolled in the fluidized bed; after the urea particles are completely heated for 5 min, the temperature is maintained for another 5 min, and then 0.2 wt% liquid wax is uniformly sprayed on the surface of the urea particles. The hydroxybutyl silicone oil and the liquefied MDI are added into the fluidized bed by a peristaltic pump, and are added in 4 batches, with an interval of 3 min between each batch. After atomization by a nozzle, they are uniformly sprayed on the surface of the urea particles. After all the coating raw materials are sprayed, the temperature is maintained for 10 min for reaction. Finally, 0.2 wt% liquid wax is added, and the temperature is maintained for another 5 min, to obtain the silicone-based polyurethane coated controlled release fertilizer.

[0069] Figure 3The scanning electron microscope image of the organic silicon-based polyurethane coating in Example 5 of the present application.

[0070] It can be seen from Figure 3 The organic silicon-based polyurethane coating forms a film layer with a thickness of about 8.02 μm on the surface of the fertilizer particles, and the coating rate is 4%; the organic silicon-based polyurethane coating has a certain continuity, which reflects the good film-forming coating ability of the organic silicon-based polyurethane material, lays a structural foundation for the release performance to play, and also reflects the structural controllability of the organic silicon-based polyurethane coating in different examples.

[0071] Example 6

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

[0073] The preparation method is as follows: compared with Example 5, the difference lies in the pretreatment method of the polyol component, specifically, the organic silicon polyol and the polyether polyol are uniformly mixed and placed on a 80℃ micro-heating platform for preheating for 20min for standby. The remaining preparation steps are consistent with Example 5.

[0074] Example 7

[0075] Example 7 provides an organic silicon-based polyurethane coating controlled-release fertilizer, which comprises the following components by mass fraction: 2.1wt% hydroxybutyl silicone oil, 0.6wt% polycarbonate polyol, 1.9wt% liquefied MDI, 0.4wt% liquid wax, and 95wt% urea particles. The hydroxybutyl silicone oil has a hydroxyl value of 175mg KOH / g and a molecular weight of 3000, and the polycarbonate polyol has a hydroxyl value of 250mg KOH / g. The urea particles have a particle size of 3mm.

[0076] The preparation method is as follows: compared with Example 5, the difference lies in the pretreatment method of the polyol component, specifically, the organic silicon polyol and the polycarbonate polyol are uniformly mixed and placed on a 80℃ micro-heating platform for preheating for 20min for standby. The remaining preparation steps are consistent with Example 5.

[0077] Example 8

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

[0079] The preparation method is as follows: compared with the embodiment 5, the difference lies in that the pretreatment method of the polyol component is that the silicone polyol and the castor oil polyol are uniformly mixed and placed on a 80℃ micro-heating platform for preheating for 20min for standby. The remaining preparation steps are consistent with the embodiment 5.

[0080] Embodiment 9

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

[0082] The preparation method is as follows: compared with the embodiment 5, the difference lies in that the pretreatment method of the polyol component is that the silicone polyol and the castor oil polyol are uniformly mixed and placed on a 80℃ micro-heating platform for preheating for 20min for standby. The remaining preparation steps are consistent with the embodiment 5.

[0083] Comparative example 1

[0084] The comparative example 1 provides a polyurethane coated controlled release fertilizer, and the specific implementation is as follows.

[0085] The comparative example 1 provides a polyurethane coated controlled release fertilizer, and the specific implementation is as follows.

[0086] The preparation method is as follows: the fluidized bed is preheated to about 75°C, urea particles are added and uniformly rolled in the fluidized bed; after the urea particles are completely heated for 5 min, 0.2 parts of liquid wax are uniformly sprayed on the surface of the urea particles. Polypropylene glycol and liquefied MDI are synchronously delivered into the fluidized bed by a peristaltic pump, and are uniformly sprayed on the surface of the urea particles after atomization by a nozzle; after the coating raw materials are completely sprayed, the temperature is maintained for 10 min. Finally, 0.2 parts of liquid wax are added, and the temperature is maintained for 5 min, to obtain the polyurethane coated controlled release fertilizer.

[0087] Comparative Example 2

[0088] The comparative example 2 provides a silicone-based polyurethane coated controlled release fertilizer, and the specific implementation is as follows.

[0089] The following components are included 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, and the urea particles have a particle size of 3 mm.

[0090] The preparation method is as follows: the fluidized bed is preheated to about 80°C, urea particles are added and uniformly rolled in the fluidized bed; after the urea particles are completely heated for 5 min, 0.2 wt% of liquid wax is uniformly sprayed on the surface of the urea particles. Hydroxybutyl silicone oil and liquefied MDI are synchronously delivered into the fluidized bed by a peristaltic pump, and are uniformly sprayed on the surface of the urea particles after atomization by a nozzle; after the coating raw materials are completely sprayed, the temperature is maintained for 10 min. Finally, 0.2 wt% of liquid wax is added, and the temperature is maintained for 5 min, to obtain the silicone-based polyurethane coated controlled release fertilizer.

[0091] Comparative Example 3

[0092] The comparative example 3 provides a silicone-based polyurethane coated controlled release fertilizer, and the specific implementation is as follows.

[0093] The following components are included 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, and the urea particles have a particle size of 3 mm.

[0094] The preparation method is as follows: the fluidized bed is preheated to about 80°C, urea particles are added and uniformly rolled in the fluidized bed; after the urea particles are completely heated for 5 min, 0.2wt% liquid wax is uniformly sprayed on the surface of the urea particles. Hydroxybutyl silicone oil and liquefied MDI are synchronously delivered into the fluidized bed by a peristaltic pump, and are uniformly sprayed on the surface of the urea particles after atomization by a nozzle; after all the coating raw materials are sprayed, the temperature is maintained for 10 min. Finally, 0.2wt% liquid wax is added, and the temperature is maintained for 5 min, to obtain the silicone-based polyurethane coated controlled-release fertilizer.

[0095] Comparative Example 4

[0096] The comparative example 4 provides a silicone-based polyurethane coated controlled-release fertilizer, and the specific implementation is as follows.

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

[0098] The preparation method is as follows: the fluidized bed is preheated to about 80°C, urea particles are added and uniformly rolled in the fluidized bed; after the urea particles are completely heated for 5 min, 0.2wt% liquid wax is uniformly sprayed on the surface of the urea particles. Hydroxybutyl silicone oil and liquefied MDI are synchronously delivered into the fluidized bed by a peristaltic pump, and are uniformly sprayed on the surface of the urea particles after atomization by a nozzle; after all the coating raw materials are sprayed, the temperature is maintained for 10 min. Finally, 0.2wt% liquid wax is added, and the temperature is maintained for 5 min, to obtain the silicone-based polyurethane coated controlled-release fertilizer.

[0099] Comparative Example 5

[0100] The comparative example 5 provides a silicone-based polyurethane coated controlled-release fertilizer, and the difference from the comparative example 4 is that the addition method of the coating raw materials is adjusted, the hydroxybutyl silicone oil and the liquefied MDI are uniformly mixed in advance, and then are delivered by a peristaltic pump, and are uniformly sprayed on the surface of the urea particles in the fluidized bed after atomization by a nozzle. After all the coating raw materials are sprayed, the temperature is maintained for 10 min. The remaining preparation steps and the types and amounts of raw materials are consistent with those of the example 2.

[0101] Further, the nutrient release performance and water contact angle of the coated controlled-release fertilizers obtained in the above examples and comparative examples are tested, and the nutrient release performance test method is as follows, and the test results are shown in Table 1.

[0102] Figure 4Figure of water contact angle test results of the coated controlled-release fertilizer in the present application comparative example 1, comparative example 2, example 3, example 5; Figure 5 Figure of water contact angle test results of the coated controlled-release fertilizer in the present application example 4, example 6 to example 9.

[0103] Nutrient release test method: 10 g of the coated controlled-release fertilizer in example 1 to example 9 and comparative example 1 was put into a 150 pm (100 mesh) nylon gauze bag, sealed and put into a 250 mL plastic bottle, 200 mL of deionized water was added and sealed and put into a 25℃ biochemical incubator, the nutrient release data was measured every 7 days (ultraviolet spectrophotometer-colorimetric method), and finally the overall nutrient release was obtained, and the specific release rate calculation formula was shown as formula (4):

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

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

[0106] Table 1 Nutrient release performance test results of the coated controlled-release fertilizer in each example and comparative example

[0107]

[0108] From Figure 4 , Figure 5 and Table 1, it can be seen that in the pure organic silicon-based polyurethane coated controlled-release fertilizer system (comparative example 2 to comparative example 5, example 1 to example 5), the controlled-release performance of example 5 (hydroxyl value 175 mg KOH / g) was the best, and the release period reached 43 days, which was similar to that of comparative example 1 and met the international standard (ISO 18644:2016); from the hydrophobicity (water contact angle), the water contact angle of example 5 was significantly higher than that of comparative example 1 and other examples (such as Figure 4 ​The water contact angle of Example 5 is 119.4°, which is much higher than 78.6° of Comparative Example 1, which reflects excellent hydrophobic controlled release foundation, and the effect of hydroxybutyl silicone oil in the system is obviously better than that of hydroxypropyl silicone oil and hydroxyl silicone oil. In the addition process (Comparative Example 3, Comparative Example 5, Example 5), if the coating raw materials are added too fast, the fertilizer will be bonded and the controlled release performance will be poor due to slow curing of polyurethane, and the process of adding in batches and interval reaction in Example 5 effectively solves this problem, and the controlled release period can reach 43 days. When the silicone polyol is modified by mixing with other polyols (Example 6-Example 9), the controlled release performance of the fertilizer of each example is significantly improved, among which the controlled release period of Example 8 (20% proportion, hydroxyl value 179 mg KOH / g castor oil polyol) is improved to 90 days, which is the most outstanding; from Figure 5 It can be seen that its water contact angle and other hydrophobic properties also meet the needs of controlled release. Overall, under the condition of 4% coating rate, the film shell thickness of the coated controlled release fertilizer is concentrated in the interval of 8-15 μm (Table 1), which provides structural support for the controlled release performance.

[0109] The above specific examples further illustrate the purpose, technical solutions and advantages of the present application. It should be understood that the above description is only a specific embodiment of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application should be included in the protection scope of the present application.

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 polyol, 1wt%-2wt% isocyanate, 94wt%-97wt% fertilizer granules; The organosilicon polyol and isocyanate form an organosilicon-based polyurethane coating that covers the surface of the fertilizer particles.

2. The organosilicon-based polyurethane-coated controlled-release fertilizer according to claim 1, characterized in that, The silicone-based polyurethane coating also includes: 0.1wt%-0.6wt% other organic polyols; The other organic polyols are selected from at least one of polyether polyols, castor oil polyols, and polycarbonate polyols.

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

4. The organosilicon-based polyurethane-coated controlled-release fertilizer according to claim 1, characterized in that, The organosilicon polyol is selected from at least one of hydroxybutyl silicone oil, hydroxypropyl silicone oil, and hydroxyl silicone oil.

5. The organosilicon-based polyurethane-coated controlled-release fertilizer according to claim 4, characterized in that, The hydroxyl value of the organosilicon polyol is 70-315 mg KOH / g; The molecular weight of the organosilicon polyol is 1000-4000.

6. The organosilicon-based polyurethane-coated controlled-release fertilizer according to claim 1, characterized in that, The isocyanate is selected from at least one of diphenylmethane diisocyanate, toluene diisocyanate, and isophorone diisocyanate.

7. The organosilicon-based polyurethane-coated controlled-release fertilizer according to claim 2, characterized in that, 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.

8. 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.

9. 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.

10. A method for preparing an organosilicon-based polyurethane-coated controlled-release fertilizer as described in any one of claims 1-9, characterized in that, include: Fertilizer granules are poured into a fluidized bed and preheated to a temperature of 80-90℃. Organosilicon polyols and isocyanates are coated onto the surface of the fertilizer granules to form an organosilicon-based polyurethane coating, thereby obtaining an organosilicon-based polyurethane-coated controlled-release fertilizer.

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