Coated slow-release granular fertilizer and preparation method thereof

Abstract

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

Description

Technical Field

[0001] The invention belongs to the technical field of fertilizers, and in particular relates to a coated slow-release granular fertilizer and a preparation method thereof. Background Art

[0002] Traditional chemical fertilizers are mostly quick-acting fertilizers. In order to increase yields, large amounts of frequent fertilization are usually required. The utilization rate of fertilizers is low, and it can cause problems such as large amounts of nutrients being soaked and volatilized.

[0003] Slow-release fertilizer refers to a fertilizer that can slowly release nutrients into the soil and has a controllable nutrient release rate. It can synchronize nutrient release with crop needs and has the advantages of high fertilizer utilization rate 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 film continuity, which allows nutrients to dissolve quickly. Furthermore, the film is brittle and has poor elasticity, making it prone to falling off during storage or transportation, affecting its slow-release performance. Organic-coated fertilizers, on the other hand, offer excellent slow-release effects and broad application prospects.

[0005] In the prior art, Chinese patent publication number CN 119899063 A discloses an environmentally friendly straw-shellac ethyl cellulose-based slow-release nitrogen fertilizer, a preparation method, and applications thereof. The technical solution comprises dissolving shellac and ethyl cellulose in anhydrous ethanol with stirring, adding a mixed powder of straw and urea to the shellac and ethyl cellulose solution, stirring thoroughly, and then dehumidifying. After dehumidification, a primary dehumidified mixed material is obtained. The primary dehumidified mixed material is then molded into cylindrical strips and dehumidified again to obtain a pre-pressed mixed material. The pre-pressed mixed material is then placed in a press for tableting, and dehumidified for a third time to obtain a primary slow-release nitrogen fertilizer. An appropriate amount of a sealing agent, ethyl cellulose ethanol solution, is then evenly sprayed on the surface of the primary slow-release nitrogen fertilizer, and allowed to dry naturally to obtain the environmentally friendly straw-shellac ethyl cellulose-based slow-release nitrogen fertilizer. However, the slow-release nitrogen fertilizer obtained by this technical solution has a cumulative release rate of approximately 73% over 28 days, and a cumulative release rate of approximately 79% over 28 days, indicating that the slow-release performance needs to be improved. Chinese patent publication number CN 119100877 A discloses a granular slow-release water-soluble fertilizer and a preparation method thereof. The granular slow-release water-soluble fertilizer comprises the following raw materials, by weight: 2-5 parts of a slow-release material and 60-70 parts of an elemental water-soluble fertilizer; the elemental water-soluble fertilizer comprises liquid ammonia, phosphorus pentoxide, sulfuric acid, zinc sulfate, potassium sulfate, ammonium nitrate phosphate, and monoammonium phosphate; the slow-release material comprises 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 above-mentioned prior art and at least provide a beneficial alternative. Specifically, the present invention provides a coated slow-release granular fertilizer and a preparation method thereof. The coated slow-release granular fertilizer provided by the present invention has good appearance, boiling resistance and slow-release performance.

[0007] On the one hand, the present invention provides a coated slow-release granular fertilizer, which includes, from the inside to the outside, a granular fertilizer core, a first coating layer and a second coating layer; the raw materials of the first coating layer include modified starch, isomalt 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 comprises: uniformly mixing modified starch, isomalt and water to obtain a first coating liquid; uniformly mixing polylactic acid, polyethylene glycol and a solvent to obtain a second coating liquid; spraying the first coating liquid on the surface of the granular fertilizer core, drying to obtain an intermediate, and spraying the second coating liquid on the surface of the intermediate, and drying to obtain the product.

[0011] Beneficial effects: The present invention forms a dense coating layer on the surface of the granular fertilizer core through the interaction of the first coating layer formed by modified starch and isomalt and the second coating layer formed by polylactic acid and polyethylene glycol, so that the coated slow-release granular fertilizer of the present invention has good appearance, boiling resistance and good slow-release performance (greater than 130 days). In particular, when the polylactic acid is modified with terminal amino hyperbranched polyamide, the coated slow-release granular fertilizer of the present invention can achieve a boiling resistance of 2 hours and a slow-release performance of 156 days. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

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

[0014] Figure 2This is the appearance 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 This is an appearance picture of the coated slow-release granular fertilizer prepared in Example 1 of the present invention after being boiled in water for 2 hours.

[0017] Figure 5 This is an appearance picture of the coated slow-release granular fertilizer prepared in Example 2 of the present invention after being boiled in water for 2 hours.

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

[0019] Figure 7 This is an appearance diagram of the coated slow-release granular fertilizer prepared in Comparative Example 1 of the present invention after being boiled in water for 1 hour. DETAILED DESCRIPTION

[0020] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are 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 comprise modified starch, isomalt, and water in a mass ratio of 3-4:0.5-1.5:30; the 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.

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

[0023] In order to obtain granular fertilizer with excellent slow-release performance, the coated slow-release granular fertilizer of the present invention has a two-layer film structure, wherein the first coating layer is composed of modified starch and isomalt; the second coating layer is composed of polylactic acid and polyethylene glycol; wherein the modified starch and isomalt in the first coating layer have good compatibility with the granular fertilizer core, easily forming a continuous surface film on the surface of the granular fertilizer core; the modified starch does not dissolve in cold water, thereby preventing the granular fertilizer core from dissolving rapidly; the polylactic acid and polyethylene glycol in the second coating layer form a film on the surface of the first coating layer having good hydrophobicity, further forming a water-blocking layer, and the two layers work together to enable the coated slow-release granular fertilizer of the present invention to achieve a slow-release performance of more than 130 days; and the inventors unexpectedly discovered that the introduction of the first film 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 potash 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 amino-terminated hyperbranched polyamide is 300-500 g / mol. More preferably, the molecular weight of the amino-terminated hyperbranched polyamide is 350-370 g / mol.

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

[0033] In some embodiments, the carboxyl-terminated polylactic acid solution comprises 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 2k Da to 6k Da.

[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: temperature of 20-30° C., and time of 4-8 h.

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

[0041] To improve the sustained-release performance of granular fertilizers, high-molecular-weight polylactic acid is often used to coat them in the prior art. However, high-molecular-weight polylactic acid has a high viscosity, which can easily cause the coated granular fertilizers to stick together. The present invention modifies low-molecular-weight polylactic acid with an amino-terminated hyperbranched polyamide. The resulting amino-terminated hyperbranched polyamide-modified polylactic acid not only prevents sticking of the coated granular fertilizers but also further improves their sustained-release performance. After a water boiling test, the film on the surface of the granular fertilizers remains intact.

[0042] In some embodiments, the relative molecular weight of the polyethylene glycol is 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: uniformly mixing nitrogen fertilizer, phosphate fertilizer, potassium fertilizer and chelated iron, granulating, and passing through an 8-mesh sieve to obtain a granular fertilizer core; uniformly mixing modified starch, isomalt and water to obtain a first coating liquid; uniformly mixing polylactic acid, polyethylene glycol and a solvent to obtain a second coating liquid; spraying the first coating liquid on the surface of the granular fertilizer core, drying to obtain an intermediate, spraying the second coating liquid on the surface of the intermediate, and drying to obtain the intermediate.

[0045] In some embodiments, the modified starch, isomalt 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 are further described in detail below with reference to the embodiments.

[0048] Example 1: This example provides a coated slow-release granular fertilizer, which comprises, from the inside to the outside, a granular fertilizer core, a first coating layer, and a second coating layer; The core of the granular fertilizer contains nitrogen fertilizer, phosphorus fertilizer, potash fertilizer and chelated iron in a mass ratio of 15:9:11:0.5.

[0049] The nitrogen fertilizer is urea, the phosphate fertilizer is potassium dihydrogen phosphate, the potash fertilizer is potassium chloride, and the chelated iron is EDDHA-FeNa (CAS No.: 16455-61-1).

[0050] The raw materials of the first coating layer are modified starch, isomalt and water in a mass ratio of 3.5:1:30; The modified starch is acetylated distarch adipate, and both acetylated distarch adipate and isomalt are sourced from Suzhou Minghua Sugar Alcohol Co., Ltd.

[0051] The raw materials of the second coating layer are polylactic acid, polyethylene glycol and solvent (DMF) in a mass ratio of 13:3:50.

[0052] The polylactic acid is amino-terminated hyperbranched polyamide-modified polylactic acid, and 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), the mixture is stirred at 25°C for 6 hours, amino-terminated hyperbranched polyamide is added, the mixture is reacted at 25°C for 10 hours, and after the reaction is completed, the amino-terminated hyperbranched polyamide is washed and dried to obtain the amino-terminated hyperbranched polyamide-modified polylactic acid.

[0053] The molecular weight of the carboxyl-terminated polylactic acid is 4k Da, and it is sourced from Xi'an Ruixi Biotechnology Co., Ltd.

[0054] The mass ratio of the carboxyl-terminated polylactic acid solution to the catalyst is 1:0.2.

[0055] The mass ratio of the carboxyl-terminated polylactic acid solution to the amino-terminated hyperbranched polyamide is 1:0.25.

[0056] The amino-terminated hyperbranched polyamide has a molecular weight of 350-370 g / mol and is sourced from Wuhan Hyperbranched Resin Technology Co., Ltd., model: N101.

[0057] The relative molecular weight of the polyethylene glycol is 360-440, and it is sourced from Nantong Yixun Chemical Co., Ltd., with the specification of PEG-400.

[0058] The preparation method of the coated slow-release granular fertilizer comprises the following steps: uniformly mixing nitrogen fertilizer, phosphorus fertilizer, potassium fertilizer and chelated iron, granulating, and passing through an 8-mesh sieve to obtain a granular fertilizer core; uniformly mixing modified starch, isomalt and water at 80° C. to obtain a first coating liquid; uniformly mixing polylactic acid, polyethylene glycol and a solvent to obtain a second coating liquid; spraying the first coating liquid on the surface of the granular fertilizer core, drying to obtain an intermediate, and spraying the second coating liquid on the surface of the intermediate, drying to obtain the product.

[0059] 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.

[0060] Example 2: This example provides a coated slow-release granular fertilizer, which is different from Example 1 only in that the weight-average molecular weight of the polylactic acid is 55,000-90,000, and is sourced from Jinan Daigang Bioengineering Co., Ltd., model: DG-L100; the rest are the same.

[0061] Example 3: This example provides a coated slow-release granular fertilizer, which is different from Example 1 only in that the raw materials of the first coating layer are modified starch, isomalt 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; the rest are the same.

[0062] Comparative Example 1 This comparative example provides a coated slow-release granular fertilizer, which is different from Example 1 only in that the raw materials of the first coating layer are modified starch, isomalt and water in a mass ratio of 0:4.5:30; the rest are the same.

[0063] Comparative Example 2 This comparative example provides a coated slow-release granular fertilizer, which is different from Example 1 only in that the raw materials of the first coating layer are modified starch, isomalt and water in a mass ratio of 4.5:0:30; the rest are the same.

[0064] Comparative Example 3 This comparative example provides a coated slow-release granular fertilizer, which is different from Example 1 only in that it includes, from the inside to the outside, a granular fertilizer core and a first coating layer; the rest are the same.

[0065] Comparative Example 4 This comparative example provides a coated slow-release granular fertilizer, which is different 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; the rest are the same.

[0066] Comparative Example 5 This comparative example provides a coated slow-release granular fertilizer, which comprises a granular fertilizer core and a second coating layer from the inside out; the rest are the same.

[0067] Test Example 1 The surfaces of the coated slow-release granular fertilizers of Examples 1-3 and Comparative Examples 1-5 were observed to see whether they were uniform and whether there was any adhesion. The results are shown in Tables 1 and Figure 1-Figure 3 shown.

[0068] Test Example 2 Boiling resistance: The coated slow-release granular fertilizers of Examples 1-3 and Comparative Examples 1-5 were placed 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. Figure 4-Figure 7 shown.

[0069] Test Example 3 Slow-release performance: The coated slow-release granular fertilizers of Examples 1-3 and Comparative Examples 1-5 were tested for slow-release fertilizers in accordance with the GB / T 23348-2009 standard: the fertilizer nutrient release period was tested using the water immersion method under static water conditions at 25°C. If the cumulative nutrient release after 28 days still did not reach 80%, the number of days required for the cumulative nutrient release to reach 80% was listed. The results are shown in Table 1.

[0070] Table 1 Performance test results of coated slow-release granular fertilizers of Examples 1-3 and Comparative Examples 1-5

[0071] Depend on Figure 1-5 As can be seen from Table 1, the coated slow-release granular fertilizers prepared in Example 1 and Example 3 have good appearance, boiling resistance and high slow-release performance. The coated slow-release granular fertilizer prepared in Example 2 exhibited adhesion due to the use of high molecular weight polylactic acid, and its boiling resistance and slow-release performance decreased. Comparative Examples 1, 2, and 5 show that the first coating layer formed by modified starch and isomalt can effectively improve the boiling resistance and slow-release performance while also improving the uniformity of the coated slow-release granular fertilizer; Example 2, Comparative Example 3 and Comparative Example 4 show that the self-made amino-terminated hyperbranched polyamide modified polylactic acid of the present invention can avoid the adhesion of the coated slow-release granular fertilizer while also effectively improving the boiling resistance and slow-release performance.

[0072] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate 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 to the outside, 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, isomalt 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.

2. The coated slow-release granular fertilizer according to claim 1, characterized in that: The modified starch is acetylated distarch adipate.

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

6.

4. The coated slow-release granular fertilizer according to claim 1, characterized in that: The polylactic acid is amino-terminated hyperbranched polyamide-modified polylactic acid; the amino-terminated hyperbranched polyamide-modified polylactic acid is obtained by reacting amino-terminated hyperbranched polyamide and carboxyl-terminated polylactic acid.

5. The coated slow-release granular fertilizer according to claim 4, characterized in that: The molecular weight of the amino-terminated hyperbranched polyamide is 300-500 g / mol; the molecular weight of the carboxyl-terminated polylactic acid is 2k Da-6k Da.

6. The coated slow-release granular fertilizer according to claim 5, characterized in that: The preparation method of amino-terminated hyperbranched polyamide modified polylactic acid comprises the following steps: adding a catalyst to a carboxyl-terminated polylactic acid solution under nitrogen protection, stirring, adding amino-terminated hyperbranched polyamide, reacting, and washing and drying after the reaction to obtain amino-terminated hyperbranched polyamide modified polylactic acid.

7. The coated slow-release granular fertilizer according to claim 6, 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.

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

9. The method for preparing the coated slow-release granular fertilizer according to any one of claims 1 to 8, characterized in that: It includes: Modified starch, isomalt and water are mixed evenly to obtain a first coating solution; lactic acid, polyethylene glycol and solvent are mixed evenly to obtain a second coating solution; The first coating liquid is sprayed on the surface of the granular fertilizer core and dried to obtain an intermediate, and the second coating liquid is sprayed on the surface of the intermediate and dried to obtain the intermediate.

10. The method for preparing the coated slow-release granular fertilizer according to claim 9, 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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