Modified waterborne polyurethane coated fertilizer and preparation method thereof

Abstract

The invention relates to the field of fertilizers, in particular to a modified waterborne polyurethane coated fertilizer and a preparation method thereof.The modified waterborne polyurethane coated fertilizer is prepared from, by weight, 90-110 parts of fertilizer particles, 7.2-14.4 parts of vegetable oil, 1.8-3.6 parts of isocyanate, 1-6 parts of modified sodium alginate, 0.1-1 part of emulsifier and 0.5-1.5 parts of chain extender. Vegetable oil and isocyanate are used as main raw materials, a waterborne polyurethane coating material is prepared through a self-emulsifying method, the film-forming property, the film strength and the hydrophobicity are improved by introducing a modified sodium alginate component into a waterborne polyurethane network structure, and the prepared fertilizer is high in particle strength and good in nutrient slow release effect.

Description

Technical Field

[0001] The invention relates to the field of fertilizers, and in particular to a modified waterborne polyurethane coated fertilizer and a preparation method thereof. Background Art

[0002] Fertilizer is the "food" of food. In order to expand production, excessive fertilizer is applied to the soil. According to statistics, the fertilizer utilization rate of my country's three major staple crops is only 40%. At the same time, the fertilizer effect period of conventional fertilizers is very short, and fertilizers must be applied multiple times during the crop growth cycle, which not only increases manpower and production costs, but also causes environmental problems such as soil pollution and non-point source pollution. Slow-release fertilizers are a new type of fertilizer that can delay or control the release rate of nutrients. Due to their long release cycle, they can meet the nutrient needs of crops throughout their growth period. They can not only increase crop yields, but also reduce the number of fertilizer uses and reduce labor costs. They have become a research hotspot in the fertilizer field.

[0003] At present, the coated fertilizer products on the market are mainly polyurethane, which is mainly derived from petrochemical products. At the same time, in the process of fertilizer preparation, organic solvents are required as carriers for spray coating, which can easily cause environmental pollution. Therefore, environmentally friendly water-based polyurethane materials have received widespread attention. However, water-based polyurethane coatings have problems such as poor mechanical strength, poor water resistance, and poor nutrient controlled release effect. Summary of the invention

[0004] In view of the problems existing in the prior art, the object of the present invention is to provide a modified waterborne polyurethane coated fertilizer and a preparation method thereof.

[0005] The purpose of the present invention is achieved by adopting the following technical solutions:

[0006] In a first aspect, the present invention provides a modified waterborne polyurethane coated fertilizer, which comprises, calculated by weight:

[0007] 90-110 parts of fertilizer granules, 7.2-14.4 parts of vegetable oil, 1.8-3.6 parts of isocyanate, 1-6 parts of modified sodium alginate, 0.1-1 parts of emulsifier and 0.5-1.5 parts of chain extender.

[0008] The fertilizer particles are composed of one or more of nitrogen salts, phosphorus salts, potassium salts, and trace elements, wherein the trace elements are at least one of calcium, magnesium, sulfur, iron, zinc, and manganese.

[0009] Preferably, the fertilizer particles are one of compound fertilizer (15-15-15), compound fertilizer (17-17-17), and compound fertilizer (18-18-18); wherein compound fertilizer (15-15-15) refers to a fertilizer whose contents of the three main nutrients of nitrogen (N), phosphorus (P2O5), and potassium (K2O) are all ≥15%; compound fertilizer (17-17-17) refers to a fertilizer whose contents of the three main nutrients of nitrogen (N), phosphorus (P2O5), and potassium (K2O) are all ≥17%; and compound fertilizer (18-18-18) refers to a fertilizer whose contents of the three main nutrients of nitrogen (N), phosphorus (P2O5), and potassium (K2O) are all ≥18%.

[0010] Preferably, the vegetable oil is one or more of castor oil, soybean oil, palm oil and rapeseed oil.

[0011] Preferably, the isocyanate is one or more of toluene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate.

[0012] Preferably, the emulsifier is composed of one or more of 2,2-dihydroxymethylpropionic acid and 2,2-dihydroxymethylbutyric acid.

[0013] Preferably, the chain extender is one or more of 1,4-butanediol and 1,6-hexanediol.

[0014] Preferably, the preparation method of the modified sodium alginate comprises:

[0015] S1. Preparation of isocyanate-treated silicon dioxide:

[0016] Weigh nano-silicon dioxide and dimethyl sulfoxide, mix them, disperse them evenly by ultrasonication, add toluene diisocyanate (TDI), heat them to 65-85°C, keep them warm for 1-3 hours, and then cool them to room temperature to obtain a silicon dioxide mixed solution;

[0017] S2. Preparation of thiolated sodium alginate:

[0018] Weigh sodium alginate and MES buffer, mix them, fully dissolve them, add EDC·HCl (1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride) and NHS (N-hydroxysuccinimide) in turn under ice-water bath conditions, stir and react for 1-2 hours, after the reaction is completed, warm to room temperature, add L-cysteine, stir and react for 4-12 hours, after the reaction is completed, dialyze (molecular weight cutoff is 3-4 kDa) and dry to obtain thiolated sodium alginate;

[0019] S3. Preparation of modified sodium alginate:

[0020] The thiolated sodium alginate is added into dimethyl sulfoxide (DMSO), and then triethylamine (TEA) is added dropwise, and after stirring, a thiolated sodium alginate solution is obtained; at room temperature, the thiolated sodium alginate solution is added dropwise into the continuously stirred silica mixed solution, and the stirring is continued for 10-20 hours after the addition is completed. After the reaction is completed, the pH of the system is adjusted to 7, and after dialysis and drying, a modified sodium alginate is obtained;

[0021] Preferably, in S1, the particle size of nano-silica is 100±10 nm, and the mass volume ratio of nano-silica, toluene diisocyanate and dimethyl sulfoxide is 1 g:(1.3-2.6) g:(5-10) mL.

[0022] Preferably, in S2, the pH of the MES buffer is 5.5-6.5, and the concentration is 10-50 mmol / L. More preferably, the pH of the MES buffer is 6, and the concentration is 20 mmol / L.

[0023] Preferably, in S2, the molecular weight of sodium alginate is 30-40 kDa.

[0024] Preferably, in S2, the mass volume ratio of sodium alginate, EDC·HCl, NHS and MES buffer is (0.2-0.8) g: (2.1-2.7) g: (1.2-1.8) g: (15-25) mL.

[0025] Preferably, in S2, the mass ratio of sodium alginate to L-cysteine ​​is 0.2-0.8:6-16.

[0026] Preferably, in S2, dialysis is performed in pure water with a molecular weight cutoff of 3-4 kDa; and drying is vacuum drying.

[0027] Preferably, in S3, the mass volume ratio of thiolated sodium alginate, triethylamine and dimethyl sulfoxide is 1 g: (0.001-0.01) g: (10-20) mL.

[0028] Preferably, in S3, the mass ratio of thiolated sodium alginate to toluene diisocyanate in S1 is 5:1.3-2.6.

[0029] Preferably, in S3, the dripping speed is controlled at 60-80 drops / minute; glacial acetic acid is added dropwise to adjust the pH of the system to 7; the dialysis is performed in pure water with a molecular weight cutoff of 3-4 kDa; and the drying is vacuum drying.

[0030] In a second aspect, the present invention provides a method for preparing a modified waterborne polyurethane coated fertilizer, comprising the following steps:

[0031] Step 1, preparation of waterborne polyurethane dispersion: vegetable oil and preheated isocyanate are added to a reaction container and stirred evenly, acetone and a catalyst are added to the system, the temperature is raised for reaction, and then an emulsifier and a chain extender are added in sequence for reaction, acetic acid is added for reaction after the reaction system is cooled to room temperature, and deionized water is added for emulsification reaction to obtain a waterborne polyurethane dispersion;

[0032] Step 2, preparation of seaweed-based waterborne polyurethane coating liquid: adding modified sodium alginate into the waterborne polyurethane dispersion system, stirring evenly, to obtain seaweed-based waterborne polyurethane coating liquid;

[0033] Step 3, preparation of modified seaweed-based waterborne polyurethane coated fertilizer: preheating the fertilizer particles, then spraying the seaweed-based waterborne polyurethane coating liquid evenly on the surface of the fertilizer particles, and then curing the particles to obtain the modified seaweed-based waterborne polyurethane coated fertilizer.

[0034] Preferably, in step 1, the catalyst is dibutyltin dilaurate, and the added amount is 0.5%-3% of the mass of the vegetable oil.

[0035] Preferably, in step 1, the mass ratio of vegetable oil, isocyanate, acetone, acetic acid, chain extender, emulsifier and deionized water is 7.2-14.4:1.8-3.6:10-20:1.2-1.8:0.5-1.5:0.1-1:10-20.

[0036] The beneficial effects of the present invention are:

[0037] (1) The present invention uses vegetable oil and isocyanate as main raw materials, prepares waterborne polyurethane coating materials by a self-emulsification method, and introduces modified sodium alginate components into the waterborne polyurethane network structure to improve film-forming properties, film strength and hydrophobicity. The prepared fertilizer particles have high strength and good nutrient slow-release effect.

[0038] (2) The present invention obtains thiolated sodium alginate by activating sodium alginate, thereby improving hydrophobicity to a certain extent, and then undergoes a thiol-isocyanate nucleophilic addition reaction with isocyanate-treated silicon dioxide to obtain modified sodium alginate. The modified sodium alginate contains not only sodium alginate, but also a large amount of nano-silicon dioxide and thiourea groups, and has good compatibility with polyurethane, which not only improves the strength and water resistance of the waterborne polyurethane film layer, but also has the performance of activating soil nutrients, improving fertilizer utilization, and improving crop quality.

[0039] (3) The vegetable oil and sodium alginate in the coating material of the present invention are both environmentally friendly and inexpensive, and using water as the dispersion medium further reduces pollution to the environment.

[0040] (4) The modified sodium alginate added in the present invention forms a nanostructure on the polyurethane network structure, thereby improving the adsorption of nutrient ions and extending the release period of fertilizer nutrients. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The present invention is further described using the accompanying drawings, but the embodiments in the accompanying drawings do not constitute any limitation to the present invention. A person skilled in the art can obtain other drawings based on the following drawings without creative work.

[0042] Figure 1 Schematic diagram for comparing nitrogen nutrient release cycles of different fertilizers (wherein, T1: Example 1, T2: Comparative Example 1, T3: Comparative Example 2). DETAILED DESCRIPTION

[0043] The technical solution of the present invention is described below through specific examples. It should be understood that the one or more method steps mentioned in the present invention do not exclude the existence of other method steps before and after the combination step or the insertion of other method steps between these explicitly mentioned steps; it should also be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. Moreover, unless otherwise specified, the numbering of each method step is only a convenient tool for identifying each method step, and is not intended to limit the order of arrangement of each method step or to limit the scope of the present invention. The change or adjustment of the relative relationship thereof shall also be regarded as the scope of the present invention without substantially changing the technical content.

[0044] In order to better understand the above technical scheme, the exemplary embodiments of the present invention are described in more detail below. Although exemplary embodiments of the present invention are shown, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present invention and to enable the scope of the present invention to be fully communicated to those skilled in the art.

[0045] The present invention will be further described below in conjunction with the following examples.

[0046] Example 1

[0047] A modified seaweed-based waterborne polyurethane coated fertilizer comprises the following raw materials, calculated by weight: 100 parts of fertilizer granules, 10.8 parts of vegetable oil, 2.7 parts of isocyanate, 4 parts of modified sodium alginate, 0.5 parts of emulsifier and 1 part of chain extender.

[0048] The fertilizer particles are compound fertilizer (15-15-15); the vegetable oil is castor oil (hydroxyl value: 163 mgKOH / g); the isocyanate is diphenylmethane diisocyanate (MDI); the emulsifier is 2,2-dihydroxymethylpropionic acid; and the chain extender is 1,4-butanediol.

[0049] The preparation method of modified sodium alginate comprises:

[0050] S1. Weigh 1 g of nano-silicon dioxide with a particle size of 100±10 nm and 10 mL of dimethyl sulfoxide, mix them, disperse them evenly by ultrasonication, add 1.9 g of toluene diisocyanate (TDI), heat them to 75°C, keep them warm for 1-3 hours, and then cool them to room temperature to obtain a silica mixed solution;

[0051] S2, weigh 0.5g of sodium alginate with a molecular weight of 35kDa and mix with 20mL of 20mmol / L MES buffer, fully dissolve, add 2.5g of EDC·HCl and 1.5g of NHS in an ice-water bath, stir and react for 1.5h, after the reaction is completed, warm to room temperature, add 11g of L-cysteine, stir and react for 8h, after the reaction is completed, dialyze in pure water (molecular weight cutoff is 3.5kDa), and vacuum dry to obtain thiolated sodium alginate;

[0052] S3. Add 5 g of thiolated sodium alginate into 15 mL of dimethyl sulfoxide (DMSO), then drop 0.005 g of triethylamine (TEA), and stir to obtain a thiolated sodium alginate solution; at room temperature, drop the thiolated sodium alginate solution into the continuously stirred silica mixture, and control the drop rate at 70 drops / minute. Continue stirring for 15 hours after the drop addition is completed. After the reaction is completed, drop glacial acetic acid to adjust the pH of the system to 7, dialyze in pure water (molecular weight cutoff is 3.5 kDa), and obtain modified sodium alginate after vacuum drying.

[0053] The preparation method of the modified waterborne polyurethane coated fertilizer comprises the following steps:

[0054] Step 1, preparation of waterborne polyurethane dispersion: vegetable oil, isocyanate, acetone, acetic acid, chain extender, emulsifier and deionized water are weighed in a mass ratio of 10.8:2.7:15:1.5:1:0.5:15, vegetable oil and isocyanate preheated to 70°C are added to a reaction container and stirred evenly, acetone and catalyst dibutyltin dilaurate are added to the system, stirred and reacted at 80°C for 3h, then the emulsifier is added and stirred and reacted for 1h, then the chain extender is added and stirred and reacted for 1h, after the reaction system is cooled to room temperature, acetic acid is added and stirred and reacted for 1h, finally deionized water is added and emulsified and reacted for 1h to obtain a waterborne polyurethane dispersion;

[0055] Step 2, preparation of seaweed-based waterborne polyurethane coating liquid: adding modified sodium alginate into the waterborne polyurethane dispersion system, stirring for 4 hours, and obtaining seaweed-based waterborne polyurethane coating liquid;

[0056] Step 3, preparation of modified seaweed-based waterborne polyurethane coated fertilizer: heat the fertilizer particles to 60°C, then evenly spray the seaweed-based waterborne polyurethane coating liquid on the surface of the fertilizer particles, and then cure at 100°C for 1 hour to obtain the modified seaweed-based waterborne polyurethane coated fertilizer.

[0057] Example 2

[0058] A modified seaweed-based waterborne polyurethane coated fertilizer comprises the following raw materials, calculated by weight: 90 parts of fertilizer granules, 7.2 parts of vegetable oil, 1.8 parts of isocyanate, 1 part of modified sodium alginate, 0.1 part of emulsifier and 0.5 part of chain extender.

[0059] Among them, the fertilizer particles are compound fertilizer (17-17-17); the vegetable oil is soybean oil; the isocyanate is toluene diisocyanate; the emulsifier is 2,2-dihydroxymethylpropionic acid; and the chain extender is 1,6-hexanediol.

[0060] The preparation method of modified sodium alginate comprises:

[0061] S1. Weigh 1 g of nano-silicon dioxide with a particle size of 100±10 nm and 5 mL of dimethyl sulfoxide, mix them, disperse them evenly by ultrasonication, add 1.3 g of toluene diisocyanate (TDI), heat to 65°C, keep the temperature for 1 hour, and then cool to room temperature to obtain a silica mixed solution;

[0062] S2, weigh 0.2g of sodium alginate with a molecular weight of 30kDa and 15mL of MES buffer with a concentration of 20mmol / L, mix them, and after fully dissolving, add 2.1g of EDC·HCl and 1.2g of NHS in turn under ice water bath conditions, stir and react for 1h, after the reaction is completed, warm to room temperature, add 6g of L-cysteine, stir and react for 4h, after the reaction is completed, dialyze in pure water (molecular weight cutoff is 3kDa), and vacuum dry to obtain thiolated sodium alginate;

[0063] S3. Add 5 g of thiolated sodium alginate into 10 mL of dimethyl sulfoxide (DMSO), then drop 0.001 g of triethylamine (TEA), and stir to obtain a thiolated sodium alginate solution; at room temperature, drop the thiolated sodium alginate solution into the continuously stirred silica mixture, and control the drop rate at 60 drops / minute. Continue stirring for 10 hours after the drop addition is completed. After the reaction is completed, drop glacial acetic acid to adjust the pH of the system to 7, dialyze in pure water (molecular weight cutoff is 3 kDa), and obtain modified sodium alginate after vacuum drying.

[0064] The preparation method of the modified waterborne polyurethane coated fertilizer comprises the following steps:

[0065] Step 1, preparation of waterborne polyurethane dispersion: according to the mass ratio of 7.2:1.8:10:1.2:0.5:0.1:10, vegetable oil, isocyanate, acetone, acetic acid, chain extender, emulsifier and deionized water are weighed respectively, the vegetable oil and the isocyanate preheated to 60° C. are added to the reaction container and stirred evenly, acetone and catalyst dibutyltin dilaurate are added to the system, stirred and reacted at 70° C. for 4 hours, then the emulsifier is added and stirred and reacted for 1 hour, then the chain extender is added and stirred and reacted for 2 hours, after the reaction system is cooled to room temperature, acetic acid is added and stirred and reacted for 1.5 hours, and finally deionized water is added and emulsified and reacted for 2 hours to obtain a waterborne polyurethane dispersion;

[0066] Step 2, preparation of seaweed-based waterborne polyurethane coating liquid: adding modified sodium alginate into the waterborne polyurethane dispersion system, stirring for 3 hours, and obtaining a seaweed-based waterborne polyurethane coating liquid;

[0067] Step 3, preparation of modified seaweed-based waterborne polyurethane coated fertilizer: heat the fertilizer particles to 50°C, then evenly spray the seaweed-based waterborne polyurethane coating liquid on the surface of the fertilizer particles, and then cure at 80°C for 2 hours to obtain the modified seaweed-based waterborne polyurethane coated fertilizer.

[0068] Example 3

[0069] A modified seaweed-based waterborne polyurethane coated fertilizer comprises the following raw materials, calculated by weight: 110 parts of fertilizer granules, 14.4 parts of vegetable oil, 3.6 parts of isocyanate, 6 parts of modified sodium alginate, 1 part of emulsifier and 1.5 parts of chain extender.

[0070] Among them, the fertilizer particles are compound fertilizer (18-18-18); the vegetable oil is palm oil; the isocyanate is hexamethylene diisocyanate; the emulsifier is 2,2-dihydroxymethylbutyric acid; and the chain extender is 1,6-hexanediol.

[0071] The preparation method of modified sodium alginate comprises:

[0072] S1. Weigh 1 g of nano-silicon dioxide with a particle size of 100±10 nm and 10 mL of dimethyl sulfoxide, mix them, disperse them evenly by ultrasonication, add 2.6 g of toluene diisocyanate (TDI), heat them to 85°C, keep them warm for 3 hours, and then cool them to room temperature to obtain a silica mixed solution;

[0073] S2, weigh 0.8g of sodium alginate with a molecular weight of 30-40kDa and 25mL of MES buffer with a concentration of 20mmol / L, mix them, and after fully dissolving, add 2.7g of EDC·HCl and 1.8g of NHS in an ice-water bath, stir and react for 2h. After the reaction is completed, warm to room temperature, add 16g of L-cysteine, stir and react for 12h. After the reaction is completed, dialyze in pure water (molecular weight cutoff is 4kDa), and vacuum dry to obtain thiolated sodium alginate;

[0074] S3. Add 5 g of thiolated sodium alginate into 20 mL of dimethyl sulfoxide (DMSO), then drop 0.01 g of triethylamine (TEA), and stir to obtain a thiolated sodium alginate solution; at room temperature, drop the thiolated sodium alginate solution into the continuously stirred silica mixture, and control the drop rate at 80 drops / minute. Continue stirring for 20 hours after the drop addition is completed. After the reaction is completed, drop glacial acetic acid to adjust the pH of the system to 7, dialyze in pure water (molecular weight cutoff is 4 kDa), and obtain modified sodium alginate after vacuum drying.

[0075] The preparation method of the modified waterborne polyurethane coated fertilizer comprises the following steps:

[0076] Step 1, preparation of waterborne polyurethane dispersion: according to the mass ratio of 14.4:3.6:20:1.8:1.5:1:20, vegetable oil, isocyanate, acetone, acetic acid, chain extender, emulsifier and deionized water are weighed respectively, the vegetable oil and the isocyanate preheated to 90° C. are added to the reaction container and stirred evenly, acetone and catalyst dibutyltin dilaurate are added to the system, stirred and reacted at 70° C. for 4 hours, then the emulsifier is added and stirred and reacted for 3 hours, then the chain extender is added and stirred and reacted for 3 hours, after the reaction system is cooled to room temperature, acetic acid is added and stirred and reacted for 2 hours, and finally deionized water is added and emulsified and reacted for 1.5 hours to obtain a waterborne polyurethane dispersion;

[0077] Step 2, preparation of seaweed-based waterborne polyurethane coating liquid: adding modified sodium alginate into the waterborne polyurethane dispersion system, stirring for 4 hours, and obtaining seaweed-based waterborne polyurethane coating liquid;

[0078] Step 3, preparation of modified seaweed-based waterborne polyurethane coated fertilizer: heat the fertilizer particles to 80°C, then evenly spray the seaweed-based waterborne polyurethane coating liquid on the surface of the fertilizer particles, and then cure at 110°C for 0.5h to obtain the modified seaweed-based waterborne polyurethane coated fertilizer.

[0079] Comparative Example 1

[0080] A fertilizer, which differs from Example 1 in that modified sodium alginate is replaced by sodium alginate; the ingredients are calculated by weight and include the following raw materials: 100 parts of fertilizer granules, 10.8 parts of vegetable oil, 2.7 parts of isocyanate, 2.7 parts of nano-silicon dioxide, 1.3 parts of sodium alginate (35 kDa), 0.5 parts of emulsifier and 1 part of chain extender.

[0081] Comparative Example 2

[0082] A fertilizer, which is different from Example 1 in that it only contains fertilizer particles (compound fertilizer (15-15-15)) and is not coated.

[0083] Experimental test 1

[0084] According to the national standard "Slow-release Fertilizer" (GB / T 23348-2009), the release period of nitrogen nutrients of different fertilizers was measured. This experiment was divided into three groups, namely, the modified seaweed-based waterborne polyurethane coated fertilizer prepared in Example 1, denoted as T1; the fertilizer prepared in Comparative Example 1, denoted as T2; and the fertilizer prepared in Comparative Example 2, denoted as T3.

[0085] The results are as follows Figure 1 As shown, on the 7th day, the nitrogen nutrient release rate of the fertilizer prepared in Comparative Example 2 was nearly 80%, on the 45th day the nitrogen nutrient release rate was nearly 90%, and on the 70th day the nitrogen nutrient was completely released; in comparison, the nitrogen nutrient release rates of the modified seaweed-based waterborne polyurethane coated fertilizer prepared in Example 1 were 2.06%, 23.25%, 40.59%, 55.78%, 68.76%, 80.01%, and 90.76% on the 1st, 7th, 14th, 28th, 45th, 70th, and 100th days, respectively, which were better than Comparative Examples 1 and 2, and part of the nitrogen nutrients could still be supplied after 100 days, showing a good nitrogen nutrient release effect.

[0086] Experimental test 2

[0087] Experiment on the effect of corn field application

[0088] The experiment was conducted in a corn-growing area in Jingmen, Hubei. The effects of different fertilizers on corn morphology and yield indicators were determined through field experiments. The experiment was divided into three groups, namely, the modified seaweed-based water-based polyurethane coated fertilizer prepared in Example 1, denoted as T1; the fertilizer prepared in Comparative Example 1, denoted as T2; and the fertilizer prepared in Comparative Example 2, denoted as T3.

[0089] The test corn variety is 'Xiangyu 655', and the basic physical and chemical properties of the test soil are pH = 7.58, organic matter content 4.02%, alkaline nitrogen 106.2mg / kg, available phosphorus 35.2mg / kg, available potassium 312.2mg / kg, and soil EC value 290.2. Corn was sown on April 20, 2023 and harvested on August 21, 2023. The fertilizer application rate was 40kg / mu, and other field measures such as sowing, irrigation, and weeding were the same.

[0090] The effects on the morphological indicators of corn are shown in Table 1. It can be seen that compared with the application of polyurethane-coated compound fertilizer granules and commercially available compound fertilizer granules, the application of modified seaweed-based water-based polyurethane coated fertilizer has better corn stem diameter at 30d, 60d and 90d, corn cob length at 120d, and leaf area index during the entire growth period.

[0091] Table 1 Effects of different fertilizers on biological traits of corn

[0092]

[0093] The effects on corn yield indicators are shown in Table 2. It can be seen that compared with the application of the compound fertilizer granules of Comparative Example 1 and Comparative Example 2, the thousand-grain weight and yield of corn are significantly improved after the modified seaweed-based water-based polyurethane coated fertilizer is applied.

[0094] Table 2 Effects of different fertilizers on corn yield indicators

[0095] Number of grains per ear (grains / ear) Thousand-grain weight (g) Yield (kg / mu) T1 395.5 341.1 712.4 T2 394.2 338.2 680.3 T3 390.7 326.5 636.1

[0096] In summary, it can be shown that the modified seaweed-based waterborne polyurethane coated fertilizer provided in Example 1 of the present invention can improve the morphological indexes and yield indexes of corn.

[0097] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms should not be understood as necessarily being directed to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine different embodiments or examples described in this specification.

[0098] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A modified waterborne polyurethane coated fertilizer, characterized in that: Calculated by weight, including: 90-110 parts of fertilizer granules, 7.2-14.4 parts of vegetable oil, 1.8-3.6 parts of isocyanate, 1-6 parts of modified sodium alginate, 0.1-1 parts of emulsifier and 0.5-1.5 parts of chain extender.

2. A modified waterborne polyurethane coated fertilizer according to claim 1, characterized in that: The fertilizer particles are composed of one or more of nitrogen salts, phosphorus salts, potassium salts, and medium and trace elements, wherein the medium and trace elements are at least one of calcium, magnesium, sulfur, iron, zinc, and manganese.

3. The modified waterborne polyurethane coated fertilizer according to claim 1, characterized in that: The vegetable oil is one or more of castor oil, soybean oil, palm oil and rapeseed oil.

4. The modified waterborne polyurethane coated fertilizer according to claim 1, characterized in that: The isocyanate is one or more of toluene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate and hexamethylene diisocyanate.

5. The modified waterborne polyurethane coated fertilizer according to claim 1, characterized in that: The emulsifier is composed of one or more of 2,2-dihydroxymethylpropionic acid and 2,2-dihydroxymethylbutyric acid; the chain extender is composed of one or more of 1,4-butanediol and 1,6-hexanediol.

6. The modified waterborne polyurethane coated fertilizer according to claim 1, characterized in that: The preparation method of the modified sodium alginate comprises: S1. Preparation of isocyanate-treated silicon dioxide: Weigh nano-silicon dioxide and dimethyl sulfoxide, mix them, disperse them evenly by ultrasonication, add toluene diisocyanate (TDI), heat them to 65-85°C, keep them warm for 1-3 hours, and then cool them to room temperature to obtain a silicon dioxide mixed solution; S2. Preparation of thiolated sodium alginate: Weigh sodium alginate and MES buffer, mix them, fully dissolve them, add EDC·HCl and NHS in turn in an ice-water bath, stir and react for 1-2 hours, after the reaction is completed, heat to room temperature, add L-cysteine, stir and react for 4-12 hours, after the reaction is completed, dialyze and dry to obtain thiolated sodium alginate; S3. Add thiolated sodium alginate into dimethyl sulfoxide, then drop triethylamine, and stir to obtain thiolated sodium alginate solution. At room temperature, drop the thiolated sodium alginate solution into the continuously stirred silica mixture, and continue stirring for 10-20 hours after the dropwise addition. After the reaction is completed, adjust the system pH to 7, and obtain modified sodium alginate after dialysis and drying.

7. The modified waterborne polyurethane coated fertilizer according to claim 6, characterized in that: In the S1, the mass volume ratio of nano-silica, toluene diisocyanate and dimethyl sulfoxide is 1g:(1.3-2.6)g:(5-10)mL.

8. The modified waterborne polyurethane coated fertilizer according to claim 6, characterized in that: In S2, EDC·HCl is 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, and NHS is N-hydroxysuccinimide; wherein the mass volume ratio of sodium alginate, EDC·HCl, NHS and MES buffer is (0.2-0.8) g:(2.1-2.7) g:(1.2-1.8) g:(15-25) mL; and the mass ratio of sodium alginate and L-cysteine ​​is 0.2-0.8:6-16.

9. The modified waterborne polyurethane coated fertilizer according to claim 6, characterized in that: In S3, the mass volume ratio of thiolated sodium alginate, triethylamine and dimethyl sulfoxide is 1 g: (0.001-0.01) g: (10-20) mL; the mass ratio of thiolated sodium alginate to toluene diisocyanate in S1 is 5: 1.3-2.

6.

10. A method for preparing the modified waterborne polyurethane coated fertilizer according to claim 1, characterized in that: The following steps are involved: Step 1, preparation of waterborne polyurethane dispersion: vegetable oil and preheated isocyanate are added to a reaction container and stirred evenly, acetone and a catalyst are added to the system, the temperature is raised for reaction, and then an emulsifier and a chain extender are added in sequence for reaction, acetic acid is added for reaction after the reaction system is cooled to room temperature, and deionized water is added for emulsification reaction to obtain a waterborne polyurethane dispersion; Step 2, preparation of seaweed-based waterborne polyurethane coating liquid: adding modified sodium alginate into the waterborne polyurethane dispersion system, stirring evenly, to obtain seaweed-based waterborne polyurethane coating liquid; Step 3, preparation of modified seaweed-based waterborne polyurethane coated fertilizer: preheating the fertilizer particles, then spraying the seaweed-based waterborne polyurethane coating liquid evenly on the surface of the fertilizer particles, and then curing the particles to obtain the modified seaweed-based waterborne polyurethane coated fertilizer.

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