A coated slow-release granular fertilizer and a preparation method thereof

Abstract

The application belongs to the technical field of chemical fertilizer, and particularly relates to a coated slow-release granular fertilizer and a preparation method thereof. The coated slow-release granular fertilizer comprises, from inside to outside, a granular fertilizer core, a first coating layer and a second coating layer. Raw materials of the first coating layer comprise modified starch, isomaltitol and water in a mass ratio of 3-4:0.5-1.5:30. Raw materials of the second coating layer comprise polylactic acid, polyethylene glycol and a solvent in a mass ratio of 10-15:2-5:50. The coated slow-release granular fertilizer has good appearance, boiling resistance and slow-release performance.

Description

Technical Field

[0001] This invention belongs to the field of fertilizer technology, specifically relating to a coated slow-release granular fertilizer and its preparation method. Background Technology

[0002] Traditional fertilizers are mostly fast-acting fertilizers. In order to increase yield, large amounts of fertilizers are usually applied frequently. The fertilizer utilization rate is low, and it will cause problems such as large amounts of nutrients being leached and volatilized.

[0003] Slow-release fertilizers are fertilizers that can slowly release nutrients into the soil at a controlled rate, allowing nutrient release to be synchronized with crop needs. They have the advantages of high fertilizer utilization and reduced fertilizer usage.

[0004] Coated slow-release granular fertilizers are a type of slow-release fertilizer. Based on the coating material, they can be divided into inorganic coated fertilizers and organic coated fertilizers. Inorganic coated fertilizers have poor coating continuity, allowing nutrients to dissolve quickly. Furthermore, their coatings are brittle and lack elasticity, making them prone to detachment during storage or transportation, thus affecting their slow-release performance. Organic coated fertilizers, on the other hand, offer excellent slow-release effects and have broad application prospects.

[0005] Chinese patent CN 119899063 A discloses an environmentally friendly straw-based shellac ethyl cellulose-based slow-release nitrogen fertilizer, its preparation method, and its application. This technical solution involves dissolving shellac and ethyl cellulose in anhydrous ethanol, adding a mixture of straw and urea powder to the shellac and ethyl cellulose solution, stirring thoroughly, and then dehumidifying to obtain a primary dehumidified mixture. This primary dehumidified mixture is then shaped into cylindrical strips and dehumidified again to obtain a pre-compressed mixture. The pre-compressed mixture is then pressed into sheets using a press and dehumidified a third time to obtain a primary slow-release nitrogen fertilizer. Finally, an appropriate amount of ethyl cellulose ethanol solution is uniformly sprayed onto the surface of the primary slow-release nitrogen fertilizer, and it is allowed to air dry naturally to obtain the environmentally friendly straw-based shellac ethyl cellulose-based slow-release nitrogen fertilizer. However, the cumulative release of the slow-release nitrogen fertilizer obtained by this technical solution reaches approximately 73% after 28 days and approximately 79% after 28 days, indicating that the slow-release performance needs improvement. Chinese patent CN 119100877 A discloses a granular slow-release water-soluble fertilizer and its preparation method. By weight, the granular slow-release water-soluble fertilizer contains the following raw materials: 2-5 parts of slow-release material and 60-70 parts of elemental water-soluble fertilizer; wherein, the elemental water-soluble fertilizer contains liquid ammonia, phosphorus pentoxide, sulfuric acid, zinc sulfate, potassium sulfate, ammonium nitrate phosphate and monoammonium phosphate; the slow-release material contains lignin and PLA. However, the slow-release performance of this technical solution needs to be improved. Summary of the Invention

[0006] The present invention aims to solve one or more technical problems existing in the prior art, and at least provide a beneficial solution. Specifically, the present invention provides a coated slow-release granular fertilizer and a method for preparing the same. The coated slow-release granular fertilizer provided by the present invention has good appearance, water resistance, and slow-release performance.

[0007] On one hand, the present invention provides a coated slow-release granular fertilizer, which comprises, from the inside out, a granular fertilizer core, a first coating layer and a second coating layer; the raw materials of the first coating layer include modified starch, isomaltitol and water in a mass ratio of 3-4:0.5-1.5:30; the raw materials of the second coating layer include polylactic acid, polyethylene glycol and solvent in a mass ratio of 10-15:2-5:50.

[0008] Preferably, the modified starch is acetylated distarch adipate.

[0009] Preferably, the polylactic acid is amino-terminated hyperbranched polyamide-modified polylactic acid.

[0010] On the other hand, the present invention also provides a method for preparing the above-mentioned coated slow-release granular fertilizer, which includes: mixing modified starch, isomaltitol and water evenly to obtain a first coating liquid; mixing polylactic acid, polyethylene glycol and solvent evenly to obtain a second coating liquid; spraying the first coating liquid onto the surface of the granular fertilizer core, drying to obtain an intermediate; spraying the second coating liquid onto the surface of the intermediate, and drying to obtain the final product.

[0011] Beneficial effects: The present invention utilizes the combined action of a first coating layer formed by modified starch and isomaltitol and a second coating layer formed by polylactic acid and polyethylene glycol to form a dense coating layer on the surface of the granular fertilizer core. This results in the coated slow-release granular fertilizer of the present invention having good appearance, water resistance, and good slow-release performance (greater than 130 days). In particular, when polylactic acid is modified with terminal amino hyperbranched polyamide, the coated slow-release granular fertilizer of the present invention can achieve 2 hours of water boiling resistance and 156 days of slow-release performance. Attached Figure Description

[0012] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 This is an appearance diagram of the coated slow-release granular fertilizer prepared in Example 1 of the present invention.

[0014] Figure 2This is an appearance diagram of the coated slow-release granular fertilizer prepared in Example 2 of the present invention.

[0015] Figure 3 This is an appearance diagram of the coated slow-release granular fertilizer prepared in Comparative Example 5 of the present invention.

[0016] Figure 4 The image shows the appearance of the coated slow-release granular fertilizer prepared in Example 1 of this invention after boiling in water for 2 hours.

[0017] Figure 5 The image shows the appearance of the coated slow-release granular fertilizer prepared in Example 2 of this invention after boiling in water for 2 hours.

[0018] Figure 6 This is an image showing the appearance of the coated slow-release granular fertilizer prepared in Comparative Example 5 of the present invention after boiling in water for 2 hours.

[0019] Figure 7 This is a picture of the appearance of the coated slow-release granular fertilizer prepared by Comparative Example 1 of the present invention after boiling in water for 1 hour. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0021] A coated slow-release granular fertilizer comprises, from the inside out, a granular fertilizer core, a first coating layer, and a second coating layer; the raw materials of the first coating layer include modified starch, isomaltitol, and water in a mass ratio of 3-4:0.5-1.5:30; the raw materials of the second coating layer include polylactic acid, polyethylene glycol, and a solvent in a mass ratio of 10-15:2-5:50.

[0022] In some embodiments, the modified starch is acetylated distarch adipate.

[0023] To obtain granular fertilizer with excellent slow-release performance, the coated slow-release granular fertilizer of this invention has a two-layer membrane structure. The first coating layer is composed of modified starch and isomaltitol; the second coating layer is composed of polylactic acid and polyethylene glycol. The modified starch and isomaltitol in the first coating layer have good compatibility with the granular fertilizer core, easily forming a continuous surface film on the core. The modified starch does not dissolve in cold water, preventing rapid dissolution of the granular fertilizer core. The film formed by the polylactic acid and polyethylene glycol in the second coating layer on the surface of the first coating layer has good hydrophobicity, further forming a water-blocking layer. The combined effect of these two layers enables the coated slow-release granular fertilizer of this invention to achieve a slow-release performance of more than 130 days. Furthermore, the inventors unexpectedly discovered that the introduction of the first membrane layer also improves the uniformity of the coated slow-release granular fertilizer after molding.

[0024] In some embodiments, the raw materials of the granular fertilizer core include nitrogen fertilizer, phosphorus fertilizer, potassium fertilizer and chelated iron in a mass ratio of 14-18:5-15:5-15:0.4-0.6. More preferably, the mass ratio of nitrogen fertilizer, phosphorus fertilizer, potassium fertilizer and chelated iron in the nitrogen-phosphorus-potassium compound fertilizer is 15:9:11:0.5.

[0025] In some embodiments, the nitrogen fertilizer is selected from at least one of urea, ammonium sulfate, and ammonium nitrate.

[0026] In some embodiments, the phosphate fertilizer is selected from at least one of monoammonium phosphate, potassium dihydrogen phosphate, and superphosphate.

[0027] In some embodiments, the potassium fertilizer is selected from at least one of potassium sulfate, potassium chloride, and potassium nitrate.

[0028] In some embodiments, the chelated iron is EDDHA-FeNa.

[0029] In some embodiments, the polylactic acid is amino-terminated hyperbranched polyamide-modified polylactic acid.

[0030] In some embodiments, the amino-terminated hyperbranched polyamide-modified polylactic acid is obtained by reacting amino-terminated hyperbranched polyamide and carboxyl-terminated polylactic acid.

[0031] In some embodiments, the molecular weight of the terminal amino hyperbranched polyamide is 300-500 g / mol, and more preferably, the molecular weight of the terminal amino hyperbranched polyamide is 350-370 g / mol.

[0032] In some embodiments, the preparation method of the amino-terminated hyperbranched polyamide modified polylactic acid includes the following steps: under nitrogen protection, adding a catalyst to a carboxyl-terminated polylactic acid solution, stirring, adding amino-terminated hyperbranched polyamide, reacting, and washing and drying after the reaction to obtain amino-terminated hyperbranched polyamide modified polylactic acid.

[0033] In some embodiments, the carboxyl-terminated polylactic acid solution is a mixture of carboxyl-terminated polylactic acid and dichloromethane in a mass ratio of 0.5-1.5:10.

[0034] In some embodiments, the molecular weight of the carboxyl-terminated polylactic acid is 2kDa-6kDa.

[0035] In some embodiments, the catalyst is 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide.

[0036] In some embodiments, the mass ratio of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride to N-hydroxysuccinimide is 1-3:0.5-1.

[0037] In some embodiments, the mass ratio of the carboxyl-terminated polylactic acid solution to the catalyst is 1:0.15-0.3.

[0038] In some embodiments, the mass ratio of the carboxyl-terminated polylactic acid solution to the amino-terminated hyperbranched polyamide is 1:0.2-0.3.

[0039] In some embodiments, the stirring conditions are: a temperature of 20-30°C and a time of 4-8 hours.

[0040] In some embodiments, the reaction conditions are: a temperature of 20-30°C and a time of 8-12 hours.

[0041] In existing technologies, high-molecular-weight polylactic acid (PLA) is often used to coat granular fertilizers to improve their slow-release performance. However, high-molecular-weight PLA has a high viscosity, which can easily lead to adhesion of the coated granular fertilizer. This invention modifies low-molecular-weight PLA with terminal-amino hyperbranched polyamide. The resulting terminal-amino hyperbranched polyamide-modified PLA not only avoids adhesion of the coated granular fertilizer but also further improves its slow-release performance. After a water boiling test, the film on the surface of the granular fertilizer remained undamaged.

[0042] In some embodiments, the polyethylene glycol has a relative molecular weight of 180-880.

[0043] In some embodiments, the solvent is selected from at least one of DMF (N,N-dimethylformamide), NMP (N-methylpyrrolidone), and DMAc (N,N-dimethylacetamide).

[0044] In some embodiments, the preparation method of the coated slow-release granular fertilizer includes: mixing nitrogen fertilizer, phosphorus fertilizer, potassium fertilizer and chelated iron evenly, granulating, and passing through an 8-mesh sieve to obtain a granular fertilizer core; mixing modified starch, isomaltitol and water evenly to obtain a first coating liquid; mixing polylactic acid, polyethylene glycol and solvent evenly to obtain a second coating liquid; spraying the first coating liquid onto the surface of the granular fertilizer core, drying to obtain an intermediate; spraying the second coating liquid onto the surface of the intermediate, and drying to obtain the final product.

[0045] In some embodiments, the modified starch, isomaltitol, and water are mixed uniformly at 70-85°C.

[0046] In some embodiments, the mass ratio of the first coating liquid to the granular fertilizer core is 1:4-8; the mass ratio of the second coating liquid to the intermediate is 1:4-8.

[0047] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0048] Example 1: This example provides a coated slow-release granular fertilizer, which includes, from the inside out, a granular fertilizer core, a first coating layer, and a second coating layer;

[0049] The core of the granular fertilizer consists of nitrogen fertilizer, phosphorus fertilizer, potassium fertilizer, and chelated iron in a mass ratio of 15:9:11:0.5.

[0050] The nitrogen fertilizer is urea, the phosphate fertilizer is potassium dihydrogen phosphate, the potassium fertilizer is potassium chloride, and the chelated iron is EDDHA-FeNa (CAS No.: 16455-61-1).

[0051] The raw materials for the first coating layer are modified starch, isomaltitol and water in a mass ratio of 3.5:1:30;

[0052] The modified starch is acetylated distarch adipate, and both acetylated distarch adipate and isomaltitol are sourced from Suzhou Minghua Sugar Alcohol Co., Ltd.

[0053] The second coating layer is made of polylactic acid, polyethylene glycol and solvent (DMF) in a mass ratio of 13:3:50.

[0054] The polylactic acid is amino-terminated hyperbranched polyamide modified polylactic acid. The preparation method is as follows: under nitrogen protection, a catalyst (1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide in a mass ratio of 2:1) is added to a carboxyl-terminated polylactic acid solution (carboxyl-terminated polylactic acid and dichloromethane in a mass ratio of 1:10), and the mixture is stirred at 25°C for 6 hours. Then, amino-terminated hyperbranched polyamide is added, and the mixture is reacted at 25°C for 10 hours. After the reaction is completed, the mixture is washed and dried to obtain amino-terminated hyperbranched polyamide modified polylactic acid.

[0055] The terminal carboxyl polylactic acid has a molecular weight of 4 kDa and is sourced from Xi'an Ruixi Biotechnology Co., Ltd.

[0056] The mass ratio of the carboxyl-terminated polylactic acid solution to the catalyst is 1:0.2.

[0057] The mass ratio of the carboxyl-terminated polylactic acid solution to the amino-terminated hyperbranched polyamide is 1:0.25.

[0058] The terminal amino hyperbranched polyamide has a molecular weight of 350-370 g / mol and is sourced from Wuhan Hyperbranched Resin Technology Co., Ltd., model number: N101.

[0059] The polyethylene glycol has a relative molecular weight of 360-440, is sourced from Nantong Yixun Chemical Co., Ltd., and its specification is PEG-400.

[0060] The preparation method of the coated slow-release granular fertilizer is as follows: nitrogen fertilizer, phosphorus fertilizer, potassium fertilizer and chelated iron are mixed and stirred evenly, granulated and passed through an 8-mesh sieve to obtain the granular fertilizer core; modified starch, isomaltitol and water are mixed evenly at 80°C to obtain the first coating liquid; polylactic acid, polyethylene glycol and solvent are mixed evenly to obtain the second coating liquid; the first coating liquid is sprayed on the surface of the granular fertilizer core and dried to obtain an intermediate; the second coating liquid is sprayed on the surface of the intermediate and dried to obtain the final product.

[0061] The mass ratio of the first coating liquid to the granular fertilizer core is 1:5; the mass ratio of the second coating liquid to the intermediate is 1:6.

[0062] Example 2: This example provides a coated slow-release granular fertilizer. The only difference from Example 1 is that the polylactic acid has a weight-average molecular weight of 55,000-90,000, is sourced from Jinan Daigang Bioengineering Co., Ltd., and is model DG-L100; all other aspects are the same.

[0063] Example 3: This example provides a coated slow-release granular fertilizer, which differs from Example 1 only in that the raw materials of the first coating layer are modified starch, isomaltitol and water in a mass ratio of 3:1.5:30; the raw materials of the second coating layer include polylactic acid, polyethylene glycol and solvent in a mass ratio of 10:5:50; all other aspects are the same.

[0064] Comparative Example 1

[0065] This comparative example provides a coated slow-release granular fertilizer, which differs from Example 1 only in that the raw materials of the first coating layer are modified starch, isomaltitol and water in a mass ratio of 0:4.5:30; all other aspects are the same.

[0066] Comparative Example 2

[0067] This comparative example provides a coated slow-release granular fertilizer, which differs from Example 1 only in that the raw materials of the first coating layer are modified starch, isomaltitol and water in a mass ratio of 4.5:0:30; all other aspects are the same.

[0068] Comparative Example 3

[0069] This comparative example provides a coated slow-release granular fertilizer, which differs from Example 1 only in that it includes a granular fertilizer core and a first coating layer from the inside out; all other aspects are the same.

[0070] Comparative Example 4

[0071] This comparative example provides a coated slow-release granular fertilizer, which differs from Example 1 only in that the raw materials of the second coating layer are polylactic acid, amino-terminated hyperbranched polyamide, polyethylene glycol and solvent (DMF) in a mass ratio of 10:3:3:50; all other aspects are the same.

[0072] Comparative Example 5

[0073] This comparative example provides a coated slow-release granular fertilizer, which, from the inside out, includes a granular fertilizer core and a second coating layer; all other aspects are the same.

[0074] Test Example 1

[0075] The surface uniformity and adhesion of the coated slow-release granular fertilizers in Examples 1-3 and Comparative Examples 1-5 were observed, and the results are shown in Table 1 and 2. Figures 1-3 As shown.

[0076] Test Example 2

[0077] Water resistance: The coated slow-release granular fertilizers of Examples 1-3 and Comparative Examples 1-5 were boiled in boiling water for 1 hour and 2 hours respectively, and their appearance was observed to see if they were damaged. The results are shown in Table 1. Figures 4-7 As shown.

[0078] Test Example 3

[0079] Slow-release performance: The coated slow-release granular fertilizers of Examples 1-3 and Comparative Examples 1-5 were tested for slow-release fertilizer according to GB / T 23348-2009 standard: Under static water conditions at 25℃, the fertilizer nutrient release period was tested by water immersion method. If the cumulative nutrient release was still less than 80% after 28 days, the number of days when the cumulative nutrient release reached 80% was listed. The results are shown in Table 1.

[0080] Table 1 Performance test results of coated slow-release granular fertilizers in Examples 1-3 and Comparative Examples 1-5

[0081]

[0082] Depend on Figure 1-5 As can be seen from Table 1, the coated slow-release granular fertilizers prepared in Examples 1 and 3 have good appearance, water resistance and high slow-release performance.

[0083] The coated slow-release granular fertilizer prepared in Example 2 exhibited adhesion due to the use of high molecular weight polylactic acid, and its water resistance and slow-release performance were reduced.

[0084] Comparative Examples 1, 2, and 5 show that the first coating layer formed by modified starch and isomaltitol can effectively improve water resistance and slow-release performance, while also improving the uniformity of coated slow-release granular fertilizers.

[0085] Examples 2, 3, and 4 show that the amino-terminated hyperbranched polyamide-modified polylactic acid of the present invention can avoid the adhesion of coated slow-release granular fertilizers while effectively improving water resistance and slow-release performance.

[0086] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A coated slow-release granular fertilizer, characterized in that, From the inside out, it includes a granular fertilizer core, a first coating layer, and a second coating layer; the raw materials of the first coating layer include modified starch, isomaltitol, and water in a mass ratio of 3-4:0.5-1.5:30; the raw materials of the second coating layer include polylactic acid, polyethylene glycol, and solvent in a mass ratio of 10-15:2-5:

50. The modified starch is acetylated distarch adipate; The polylactic acid is amino-terminated hyperbranched polyamide modified polylactic acid; The preparation method of the amino-terminated hyperbranched polyamide modified polylactic acid includes the following steps: under nitrogen protection, a catalyst is added to a carboxyl-terminated polylactic acid solution, and the mixture is stirred at 25°C for 6 hours. Then, amino-terminated hyperbranched polyamide is added, and the mixture is reacted at 25°C for 10 hours. After the reaction is completed, the mixture is washed and dried to obtain amino-terminated hyperbranched polyamide modified polylactic acid. The carboxyl-terminated polylactic acid solution is composed of carboxyl-terminated polylactic acid and dichloromethane in a mass ratio of 1:

10. The catalyst is 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide in a mass ratio of 2:

1.

2. The coated slow-release granular fertilizer according to claim 1, characterized in that, The raw materials for the granular fertilizer core include nitrogen fertilizer, phosphorus fertilizer, potassium fertilizer and chelated iron in a mass ratio of 14-18:5-15:5-15:0.4-0.

6.

3. The coated slow-release granular fertilizer according to claim 2, characterized in that, The terminal amino hyperbranched polyamide has a molecular weight of 300-500 g / mol; the terminal carboxyl polylactic acid has a molecular weight of 2 kDa-6 kDa.

4. The coated slow-release granular fertilizer according to claim 3, characterized in that, The mass ratio of the carboxyl-terminated polylactic acid solution to the amino-terminated hyperbranched polyamide is 1:0.2-0.

3.

5. The coated slow-release granular fertilizer according to claim 1, characterized in that, The relative molecular weight of the polyethylene glycol is 180-880.

6. The method for preparing the coated slow-release granular fertilizer according to any one of claims 1-5, characterized in that, It includes: Modified starch, isomaltitol, and water are mixed evenly to obtain the first coating solution; polylactic acid, polyethylene glycol, and solvent are mixed evenly to obtain the second coating solution. The first coating liquid is sprayed onto the surface of the granular fertilizer core, dried, and an intermediate is obtained. The second coating liquid is sprayed onto the surface of the intermediate and dried to obtain the final product.

7. The method for preparing coated slow-release granular fertilizer according to claim 6, characterized in that, The mass ratio of the first coating liquid to the granular fertilizer core is 1:4-8; the mass ratio of the second coating liquid to the intermediate is 1:4-8.

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