A pH-responsive biodegradable coated controlled-release fertilizer and preparation method thereof

Abstract

The present invention discloses a bio-based degradable coated controlled-release fertilizer that can respond to pH and a preparation method thereof, and belongs to the technical field of controlled-release fertilizer production. The bio-based degradable coating that can respond to pH of the present invention comprises: an inner coating material and an outer coating material; the inner coating material is formed by mixing a dendritic mesh polyester polyol and an isocyanate in a mass ratio of (1-2):1; the outer coating material is formed by mixing an auxiliary agent, a hydroxyalkyl di-terminated polydimethylsiloxane and an isocyanate; the mass ratio of the auxiliary agent to the hydroxyalkyl di-terminated polydimethylsiloxane is (3-5):1. The controlled-release fertilizer of the present invention can accurately release fertilizer nutrients under specific environmental stimulation, breaking the traditional concept that traditional controlled-release fertilizers can only regulate nutrient release by changing the coating thickness. When the rhizosphere acidity increases, the film material of the controlled-release fertilizer made of the material provided by the present invention begins to decompose and release nutrients, which can further achieve accurate controlled release of nutrients.

Description

Technical Field

[0001] The invention relates to the technical field of controlled-release fertilizer production, and in particular to a pH-responsive bio-based degradable coated controlled-release fertilizer and a preparation method thereof. Background Art

[0002] Traditional chemical fertilizers have low utilization efficiency (about 30% to 50%), which not only causes serious economic losses, but also brings agricultural non-point source pollution. Polymer-coated controlled-release fertilizers (PCU) supply nutrients at a slower rate and in a sustainable manner throughout the season and reduce the risks associated with fertilizers. It is one of the most effective alternative methods to improve the utilization rate of fertilizer nutrients and promote the development of agricultural production.

[0003] Although bio-based film materials represented by vegetable oils, animal oils, polysaccharides (starch, cellulose) and their derivatives have promoted the large-scale production and application of bio-based film materials in PCU to a certain extent, bio-based coating materials represented by polyurethane have a loose structure, poor polymerization degree and cross-linking degree, and moisture will prematurely infiltrate the film shell, resulting in accelerated nutrient release in the early stage. Therefore, the controlled release life of these fertilizers often fails to meet the expected requirements (<30 days). This limits the further development and application of bio-based PCU. Therefore, improving the polymerization degree and cross-linking density of bio-based polyurethane is a hot issue for future industry development.

[0004] Polyester polyols have abundant ester groups, polar groups and high hydroxyl values ​​in their molecules. In the prior art, more and more reports have been reported that polyester polyols are used to synthesize polyurethanes with excellent wear resistance, flexibility, mechanical strength and high polymerization degree. However, current related studies have shown that although the polymerization degree of commercial polyester polyols with isocyanates is high, most of them are linear or slightly branched linear polyols. Although the degree of polymerization of polyurethanes synthesized based on commercial polyester polyols has been improved to a certain extent, their cross-linking degree often does not reach the best. Therefore, how to further improve the molecular weight of polyester polyols, broaden its network branching structure, obtain a polyester polyol-type polyurethane with ultra-high cross-linking degree and apply it to controlled-release fertilizers is an effective way to improve the nutrient release cycle of coated controlled-release fertilizers.

[0005] Existing patent CN 105622904 A discloses a method for preparing hyperbranched polyester polyols, wherein polyacid, polyol, and catalyst are sequentially added to a reactor; then the temperature is slowly increased several times, the solvent is extracted under negative pressure, and finally dimethylol propionic acid and p-toluenesulfonic acid are added to react to generate hyperbranched polyester polyols; however, the method needs to be carried out under a high temperature environment of 210°C to 250°C, and the requirements for equipment safety are relatively high in actual production. In addition, the method needs to be heated several times and the solvent is extracted under negative pressure before hyperbranching, which is labor-intensive and time-consuming. Patent CN 111187393 A melt-polycondenses castor oil and 2,2-bishydroxymethyl propionic acid to obtain hyperbranched polyester polyols. However, the method reacts under a temperature condition of 140 to 170°C, and the melting point of 2,2-bishydroxymethyl propionic acid is 185 to 190°C. It is easy to have a low temperature resulting in incomplete reaction of 2,2-bishydroxymethyl propionic acid and castor oil, resulting in a low yield.

[0006] Although compared with traditional chemical fertilizers, existing controlled-release fertilizers have significantly improved the utilization efficiency of fertilizer nutrients. However, the regulation method of nutrient release of existing controlled-release fertilizers has no direct correlation with the nutritional needs of plants, and its nutrient release life is only directly regulated by the thickness of the coating. Therefore, in order to further improve the nutrient utilization efficiency of controlled-release fertilizers in the soil, it is urgent to explore intelligent fertilizer coatings that release nutrients according to the nutritional needs of plants under specific stimuli. Many biochemical reactions will occur in plants when they need nutrients. At this time, the plant roots will release some organic acids (citric acid, malic acid), amino acids and other organic acidic compounds into the surrounding soil environment. In addition, when the plant roots absorb cationic nutrients such as ammonium nitrogen, they will release H into the soil environment. + To balance the charge; plant roots consume a lot of oxygen during respiration, causing the redox potential near the rhizosphere to drop. The above-mentioned plant root behavior will cause soil acidification near the plant roots. Changes in soil pH can become a stimulus signal to trigger the release of nutrients from controlled-release fertilizers, providing impetus for the development of controlled-release fertilizers that can be precisely released according to the nutrient needs of plants under specific stimuli. Therefore, the research on pH-responsive coated controlled-release fertilizers has important practical significance. Summary of the invention

[0007] In view of the problems existing in the above-mentioned prior art, the object of the present invention is to provide a pH-responsive bio-based degradable coated controlled-release fertilizer and a preparation method thereof.

[0008] To achieve the above object, the present invention adopts the following technical solutions:

[0009] The first aspect of the present invention provides a pH-responsive biodegradable coating material, comprising: an inner coating material and an outer coating material;

[0010] The inner film material is prepared by mixing dendritic polyester polyol and isocyanate in a mass ratio of (1-2):1;

[0011] The outer coating material is prepared by mixing an auxiliary agent, hydroxyl-di-terminated polydimethylsiloxane and isocyanate; the mass ratio of the auxiliary agent to the hydroxyl-di-terminated polydimethylsiloxane is (3-5):1.

[0012] Preferably, the dendritic polyester polyol is prepared by the following method:

[0013] The 2,2-dihydroxymethylbutyric acid is melted at 120°C to 150°C, and then a catalyst and monoglyceride are added, and the mixture is reacted at 170°C to 200°C for 4h to 8h under a nitrogen atmosphere; after the reaction, the by-products are removed by rotary evaporation to prepare a dendritic polyester polyol.

[0014] More preferably, the molar ratio of monoglyceride to 2,2-dihydroxymethylbutyric acid is (0.5-1.5):2; and the amount of the catalyst added is 0.01-0.4 wt % of the monoglyceride.

[0015] More preferably, the monoglyceride is selected from one or more of palmitic acid monoglyceride, monostearic acid glyceride, monocaprylic acid glyceride, lauric acid glyceride, monooleic acid glyceride, monocapric acid glyceride, monomyristic acid glyceride, glyceryl monooleate, and glyceryl monoacetate.

[0016] More preferably, the catalyst is an organic compound containing a sulfonic acid group, selected from one or more of toluenesulfonic acid, aminosulfonic acid, methanesulfonic acid, ethanesulfonic acid, and benzenesulfonic acid.

[0017] Preferably, the auxiliary agent is a compound containing a tertiary amine group and a hydroxyl group, such as one or more of N-methyldiethanolamine, N-propyldiethanolamine, N-tert-butyldiethanolamine, and N-butyldiethanolamine.

[0018] Preferably, in the outer film material, NCO - Groups and OH in additives and hydroxyl-terminated polydimethylsiloxane - The molar ratio of the groups (R value) is 1-3.

[0019] The second aspect of the present invention provides the use of the above-mentioned pH-responsive bio-based degradable coating material in the preparation of controlled-release fertilizers.

[0020] The third aspect of the present invention provides a pH-responsive bio-based degradable coated controlled-release fertilizer, comprising a fertilizer core, and an inner coating material and an outer coating material sprayed on the surface of the fertilizer core;

[0021] The spraying amount of the inner coating material is 2%-10% of the weight of the fertilizer core; the spraying amount of the outer coating material is 1%-3% of the weight of the fertilizer core.

[0022] The fourth aspect of the present invention provides a method for preparing the above-mentioned bio-based degradable coated controlled-release fertilizer capable of pH response, comprising the following steps:

[0023] (1) preheating the fertilizer core to 70° C. to 80° C., then spraying the inner coating material on the surface of the fertilizer core and curing it to form an inner coating layer;

[0024] (2) Under the temperature condition of 70°C to 80°C, the outer coating material is continuously sprayed on the surface of the inner coating layer to form an outer coating layer, thereby preparing a pH-responsive biodegradable coated controlled-release fertilizer.

[0025] Beneficial effects of the present invention:

[0026] (1) Improved the problem of low degree of polymerization and cross-linking of the existing traditional controlled-release fertilizer polyurethane membrane shell. The present invention uses a dendritic network polyester polyol A as the basic soft segment of polyurethane. Compared with traditional bio-based polyols, it not only introduces abundant ester groups, but also gives traditional linear polyols a huge dendritic network structure, greatly improving its degree of polymerization and cross-linking with isocyanate. It prevents moisture from infiltrating the membrane shell too early, thereby improving the nutrient release characteristics of the controlled-release fertilizer. In addition, the dendritic network polyester polyol A and isocyanate can be quickly cured at a lower temperature, reducing energy loss and saving production costs.

[0027] (2) Compared with traditional controlled-release fertilizers, the controlled-release fertilizers of the present invention can accurately release fertilizer nutrients under specific environmental stimulation, breaking the traditional concept that traditional controlled-release fertilizers can only rely on changing the film thickness to regulate nutrient release. When the rhizosphere acidity increases, the film material of the controlled-release fertilizer made of the material provided by the present invention begins to decompose and release nutrients, which can further achieve accurate controlled release of nutrients. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 : Schematic diagram of the synthesis route of the dendritic polyol of the present invention.

[0029] Figure 2 : Schematic diagram of the synthesis route of the inner envelope material of the present invention.

[0030] Figure 3 : Schematic diagram of the synthesis route of the outer membrane material of the present invention.

[0031] Figure 4 : Fourier transform infrared spectrum of the dendritic polyol prepared in Example 1 of the present invention.

[0032] Figure 5: Cumulative nutrient release rate of the coated controlled-release fertilizers prepared in Examples 1 to 3 of the present invention and Comparative Example 1.

[0033] Figure 6 : Cumulative nutrient release rate of the coated controlled-release fertilizer prepared in Example 1 of the present invention under different pH buffer solutions.

[0034] Figure 7 : Cumulative nutrient release rate of the coated controlled-release fertilizer prepared in Comparative Example 2 of the present invention under different pH buffer solutions.

[0035] Figure 8 : The biodegradation of the inner and outer coating materials of the present invention. DETAILED DESCRIPTION

[0036] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0037] As mentioned above, the existing bio-based polyurethane as a membrane material for controlled-release fertilizers has poor polymerization and cross-linking degrees, so water will prematurely infiltrate the membrane shell, resulting in accelerated nutrient release in the early stage, so that the controlled-release life of the fertilizer often cannot meet the expected requirements. In addition, the nutrient release of existing controlled-release fertilizers is mainly regulated by the thickness of the coating. The change of soil pH can become a stimulus signal to trigger the release of nutrients from controlled-release fertilizers. pH-responsive coated fertilizers are an emerging type of controlled-release fertilizers. Existing pH-responsive materials can be divided into two categories according to their responsiveness mechanism: one is with a large number of amino, carboxyl or amide groups, such as polyacrylic acid, polyvinyl pyridine, polymethacrylic acid, chitosan, etc. These groups are easy to combine with protons in the solution or ionize protons. At low pH values, -COOH is protonated, and the hydrophobic effect plays a dominant role, resulting in the curling of the polymer chain containing the carboxyl group, which enlarges the micropore size on the membrane surface, thereby facilitating the passage of the permeable medium. At high pH values, -COOH is ionized into -COO-, which stretches the polymer chain, reduces the pore size, and makes it difficult for the permeable medium to pass through. The other type contains imine bonds, ester bonds, etc., and is accompanied by the breaking and recombination of chemical bonds, such as polyallylamine hydrochloride and polymethacrylate-2-(diethylamino)ethyl ester, which are easily hydrolyzed under acidic conditions and can disintegrate in a low pH environment, thereby achieving the release of the medium.

[0038] In view of this, the present invention designs a pH-responsive biodegradable coating material, comprising: an inner coating material and an outer coating material; wherein:

[0039] The inner film material is prepared by using a dendritic network polyol as the basic soft segment of polyurethane, which is then mixed with isocyanate in a mass ratio of (1-2):1.

[0040] The synthetic route of dendritic polyols is as follows Figure 1 Compared with traditional bio-based polyols, the dendritic network polyol used in the present invention not only introduces abundant ester groups, but also gives the traditional linear polyol a huge dendritic network structure, greatly improving its polymerization degree and cross-linking degree with isocyanate, preventing moisture from infiltrating the membrane shell too early, and improving the nutrient release characteristics of the controlled-release fertilizer.

[0041] The synthetic route of inner envelope material is as follows Figure 2 As shown, the dendritic polyol and isocyanate can be cured quickly at a lower temperature, reducing energy loss and saving production costs.

[0042] The outer coating material is prepared by the reaction of an auxiliary agent, a hydroxyl-dicapped polydimethylsiloxane and an isocyanate. The synthetic route is as follows: Figure 3 The outer coating material has pH response characteristics and can begin to decompose when the acidity of the plant rhizosphere increases. The mechanism of pH response is:

[0043] Tertiary amine groups are introduced into the polyurethane main chain of the outer film layer material. Under neutral and alkaline conditions, the tertiary amine groups and the urethane bonds from the polyurethane can form dense hydrogen bonds. However, under acidic conditions, the tertiary amine groups are positively charged, and the tertiary amine groups and H + The strong electrostatic repulsion between them destroys the dense hydrogen bonds formed under neutral and alkaline conditions, causing the outermost coating membrane shell of the controlled-release fertilizer to depolymerize and degrade, and the cross-linking degree to deteriorate, allowing moisture to enter the inner coating and then into the core of the fertilizer, accelerating the release of nutrients.

[0044] Based on the bio-based degradable coating material designed by the present invention, the present invention further develops a pH-responsive bio-based degradable coating controlled-release fertilizer, including a fertilizer core, and an inner coating material and an outer coating material sprayed on the surface of the fertilizer core; the spraying amount of the inner coating material is 2%-10% of the weight of the fertilizer core; the spraying amount of the outer coating material is 1%-3% of the weight of the fertilizer core.

[0045] The coating layer of the controlled-release fertilizer of the present invention is a double-layer structure, which is composed of an ultra-high cross-linked inner coating layer and an outer coating layer with pH response characteristics. The inner coating layer has ultra-high polymerization degree and cross-linking degree, which further delays the nutrient release of the fertilizer. At the same time, the outer coating layer gives the controlled-release fertilizer excellent pH response characteristics: the outer coating layer of the controlled-release fertilizer can sensitively respond to the organic acids released by the plant roots when they are "hungry", and then depolymerize and degrade, so that the fertilizer can accurately control the release of nutrients according to the nutrient needs of the plant under specific environmental stimulation. The controlled-release fertilizer improves the problem of low polymerization degree and cross-linking degree of the polyurethane membrane shell of traditional controlled-release fertilizers, and breaks the traditional concept that traditional controlled-release fertilizers can only rely on changing the thickness of the coating to regulate the release of nutrients, so that the fertilizer can truly respond quickly to changes in environmental conditions in the soil, and independently and accurately regulate the intensity of nutrient release, which has great practical production significance.

[0046] In order to enable those skilled in the art to more clearly understand the technical solution of the present application, the technical solution of the present application will be described in detail below in conjunction with specific embodiments.

[0047] The test materials used in the examples and comparative examples of the present invention are all conventional test materials in the art and can be purchased through commercial channels. The experimental methods without detailed conditions are carried out in accordance with conventional test methods or the operating instructions recommended by the supplier. Among them:

[0048] The acid value is determined according to the steps in the national standard (GB / T 12008.5-2010). The specific method is to add 100ml of isopropanol and 1ml of phenolphthalein indicator to a 250ml conical flask, use 0.02mol / L potassium hydroxide-methanol standard titration solution to drop until light pink, and keep it for 30s. Weigh 50-60g of polyol in the above conical flask and record the mass of the polyol. Stir or shake the solution in the conical flask until the polyol is completely dissolved. Titrate with 0.02mol / L potassium hydroxide-methanol standard titration solution.

[0049] The calculation formula is: acid value = (A × N × 56.1) / W

[0050] A—volume of potassium hydroxide-methanol standard titration solution consumed by titrating the sample, mol;

[0051] N—concentration of potassium hydroxide-methanol standard titration solution, mol / L;

[0052] 56.1—Numerical value of the molar mass of potassium hydroxide, g / mol;

[0053] W—mass of liquefied product, g.

[0054] The hydroxyl value is determined according to the steps in the national standard (GB / T12008.3-2009). The specific method is to take 3g of the liquefied product in a conical flask, add 25ml of phthalic anhydride acylating agent (500mL of pyridine, 74g of anhydrous phthalic anhydride and 12g of imidazole are placed in a brown reagent bottle, and the prepared acylating agent is placed in a dark place for 24h for standby use.). Shake the bottle until the liquefied product dissolves, connect each conical flask to a condenser, and esterify in an oil bath at 115±2℃ for 30min. Take the device out of the oil bath and cool to room temperature. Rinse the condenser with 30ml of pyridine and remove the condenser. Transfer the solution quantitatively to a 250ml beaker and rinse the conical flask with 20ml of pyridine. Titrate to the equilibrium point with 0.5mol / L of sodium hydroxide.

[0055] Calculation formula: Hydroxyl value = ((V1-V2) × c × 56.1) / w

[0056] V1—volume of sodium hydroxide standard solution consumed by titrating the sample, ml;

[0057] V2—the volume of sodium hydroxide standard titration solution consumed in the titration blank, ml;

[0058] c—concentration of sodium hydroxide standard solution, mol / L;

[0059] w—mass of liquefied product, g.

[0060] The isocyanate can be any existing isocyanate. The isocyanate used in the examples and comparative examples of the present invention is 4,4'-methylenebis(phenyl isocyanate).

[0061] The isocyanate used in the inner coating material and the outer coating material of the pH-responsive bio-based degradable coated controlled-release fertilizer of the present invention is the same isocyanate, which is 4,4'-methylenebis(phenyl isocyanate).

[0062] The CAS number of hydroxyalkyl di-terminated polydimethylsiloxane is 156327-07-0.

[0063] The commercial polyester polyol was purchased from Ruicong Biotechnology (Shandong) Co., Ltd., and the product name is: bio-based polyester polyol.

[0064] Example 1: Preparation of pH-responsive biodegradable coated controlled-release fertilizer

[0065] 1. Preparation of inner membrane material:

[0066] (1) Preparation of dendritic polyester polyol:

[0067] 0.5 mol of 2,2-dihydroxymethylbutyric acid was placed in a three-necked round-bottom flask at 120°C to completely melt it, and then a catalyst (the catalyst is p-toluenesulfonic acid) accounting for 0.01 wt% of monoglyceride was added, and then 0.25 mol of monoglyceride (the monoglyceride is palmitic acid monoglyceride) was slowly poured in. After the addition was completed, the reaction mixture was maintained at a temperature of 170°C and under a nitrogen atmosphere, and the reaction was regularly monitored (after every 1 hour) by checking the acid value until it reached up to 8-15 mg KOH per gram of sample. The reaction was completed after 4 hours.

[0068] The system after the reaction was rotary evaporated at 65° C. for 2 h on a rotary evaporator to remove excess by-product water, thereby obtaining a dendritic polyester polyol.

[0069] The prepared dendritic polyester polyol was tested by Fourier transform infrared spectrometer. The results are as follows: Figure 4 As shown, the results show that at 2850cm -1 and 2923cm -1 There is a methylene and methyl vibration band at 3434cm -1 There is a broad OH stretching vibration band at 1719 cm. This indicates that BPP contains -OH for polyurethane synthesis. -1 The peak at 1118 cm is the stretching vibration of the ester group C=O in polyester polyol. -1 The absorption peak at corresponds to CO in polyester polyol.

[0070] The crosslinking degree of the dendritic polyester polyol prepared in this example was measured by a nuclear magnetic resonance crosslinking density analyzer, and the result was 15.40×10 -4 mol ml -1 .

[0071] (2) Preparation of inner envelope material:

[0072] 10 g of the dendritic polyester polyol prepared above and 7.14 g of isocyanate were mixed evenly in a glass cup using a glass rod to obtain a prepolymer of polyester polyol type polyurethane, which was used as the inner coating material of the controlled-release fertilizer.

[0073] 2. Preparation of outer membrane materials:

[0074] 9 g of an auxiliary agent (the auxiliary agent is N-methyldiethanolamine), 3 g of hydroxyalkyl di-terminated polydimethylsiloxane and 19.28 g of isocyanate are put into a glass cup and mixed evenly with a glass rod to obtain a pH-responsive polyurethane prepolymer as an outer coating material for controlled-release fertilizer.

[0075] 3. Preparation of bio-based degradable coated controlled-release fertilizer:

[0076] Weigh 500 g of urea (nitrogen content 46%; diameter 2-4 mm) and put it into a drum for preheating at 70° C. and 22 rpm for 10 minutes.

[0077] The inner coating material is sprayed on the surface of the urea particles at 70° C. to form an inner coating layer with a super high cross-linking degree; the spraying amount of the inner coating material is 2% of the weight of the urea particles.

[0078] Keeping the temperature at 70°C unchanged, continue to spray the outer coating material on the surface of the inner coating layer to form a pH-responsive outer coating layer; the spraying amount of the outer coating material is 1% of the weight of the fertilizer particles, thus preparing a pH-responsive bio-based degradable coated controlled-release fertilizer.

[0079] Example 2: Preparation of pH-responsive biodegradable coated controlled-release fertilizer

[0080] 1. Preparation of inner membrane material:

[0081] (1) Preparation of dendritic polyester polyol:

[0082] 0.5 mol of 2,2-dihydroxymethylbutyric acid was placed in a three-necked round-bottom flask at 130°C to completely melt it, and then a catalyst (the catalyst was aminosulfonic acid) accounting for 0.03 wt% of monoglyceride was added, and then 0.25 mol of monoglyceride (the monoglyceride was monotransoleic acid glyceride) was slowly poured in. After the addition was completed, the reaction mixture was maintained at a temperature of 180°C and under a nitrogen atmosphere, and the reaction was regularly monitored (after every 1 hour) by checking the acid value until it reached up to 8-15 mg KOH per gram of sample. The reaction was completed after 5 hours.

[0083] The system after the reaction was rotary evaporated at 65° C. for 3 h on a rotary evaporator to remove excess by-product water, thereby obtaining a dendritic polyester polyol.

[0084] (2) Preparation of inner envelope material:

[0085] 10 g of the dendritic polyester polyol and 7.14 g of isocyanate were mixed evenly in a glass cup using a glass rod to obtain a prepolymer of polyester polyol type polyurethane as an inner coating material for controlled-release fertilizer.

[0086] 2. Preparation of outer membrane materials:

[0087] 10g of an auxiliary agent (the auxiliary agent is N-propyldiethanolamine), 2g of hydroxyalkyl di-terminated polydimethylsiloxane and 25.88g of isocyanate are put into a glass cup and mixed evenly with a glass rod to obtain a pH-responsive polyurethane prepolymer as an outer coating material for controlled-release fertilizer.

[0088] 3. Preparation of bio-based degradable coated controlled-release fertilizer:

[0089] Weigh 500 g of urea (nitrogen content 46%; diameter 2-4 mm) and put it into a drum for preheating at 75° C. and 22 rpm for 10 minutes.

[0090] The inner coating material is sprayed on the surface of the urea particles at 75° C. to form an inner coating layer with a super high cross-linking degree; the spraying amount of the inner coating material is 3% of the weight of the urea particles.

[0091] Keeping the temperature at 75°C unchanged, continue to spray the outer coating material on the surface of the inner coating layer to form a pH-responsive outer coating layer; the spraying amount of the outer coating material is 1% of the weight of the fertilizer particles, thus preparing a pH-responsive bio-based degradable coated controlled-release fertilizer.

[0092] Example 3: Preparation of pH-responsive biodegradable coated controlled-release fertilizer

[0093] 1. Preparation of inner membrane material:

[0094] (1) Preparation of dendritic polyester polyol:

[0095] 0.5 mol of 2,2-dihydroxymethylbutyric acid was placed in a three-necked round-bottom flask at 150°C to completely melt it, and then a catalyst (the catalyst is methanesulfonic acid) accounting for 0.08 wt% of monoglyceride was added, and then 0.25 mol of monoglyceride (the monoglyceride is lauric acid glyceride) was slowly poured in. After the addition was completed, the reaction mixture was maintained at a temperature of 200°C and under a nitrogen atmosphere, and the reaction was regularly monitored (after every 1 hour) by checking the acid value until it reached up to 8-15 mg KOH per gram of sample. The reaction was completed after 8 hours.

[0096] The system after the reaction was rotary evaporated on a rotary evaporator at 65° C. for 4 h to remove excess by-product water, thereby obtaining a dendritic polyester polyol.

[0097] (2) Preparation of inner envelope material:

[0098] 10 g of the dendritic polyester polyol and 7.14 g of isocyanate were mixed evenly in a glass cup using a glass rod to obtain a prepolymer of polyester polyol type polyurethane as an inner coating material for controlled-release fertilizer.

[0099] 2. Preparation of outer membrane materials:

[0100] 8g of an auxiliary agent (the auxiliary agent is N-butyldiethanolamine), 2g of hydroxyalkyl di-terminated polydimethylsiloxane and 25.34g of isocyanate are put into a glass cup and mixed evenly with a glass rod to obtain a pH-responsive polyurethane prepolymer as an outer coating material for controlled-release fertilizer.

[0101] 3. Preparation of bio-based degradable coated controlled-release fertilizer:

[0102] Weigh 500 g of urea (nitrogen content 46%; diameter 2-4 mm) and put it into a drum for preheating at 80° C. and 22 rpm for 10 minutes.

[0103] The inner coating material is sprayed on the surface of the urea particles at 80° C. to form an inner coating layer with a super high cross-linking degree; the spraying amount of the inner coating material is 4% of the weight of the urea particles.

[0104] Keeping the temperature at 80°C unchanged, continue to spray the outer coating material on the surface of the inner coating layer to form a pH-responsive outer coating layer; the spraying amount of the outer coating material is 1% of the weight of the fertilizer particles, thus preparing a pH-responsive bio-based degradable coated controlled-release fertilizer.

[0105] Comparative Example 1:

[0106] The difference from Example 1 is that the "dendritic polyester polyol" used to prepare the inner membrane material is replaced by commercial polyester polyol; the other preparation conditions are the same as Example 1.

[0107] The crosslinking degree of commercial polyester polyol was measured by nuclear magnetic resonance crosslinking density analyzer. The result was 6.52×10 -4 mol ml -1 .

[0108] Comparative Example 2:

[0109] The preparation method of the inner envelope material is the same as that of Example 1.

[0110] Weigh 500 g of urea (nitrogen content 46%; diameter 2-4 mm) and put it into a drum for preheating at 70° C. and 22 rpm for 10 minutes.

[0111] The inner coating layer material is sprayed on the surface of the fertilizer particles at 70° C. to obtain a bio-based polyurethane controlled-release fertilizer with an ultra-high cross-linking degree. The spraying amount of the inner coating layer material is 3% of the weight of the fertilizer particles.

[0112] Comparative Example 3:

[0113] The preparation method of the outer coating material is the same as that of Example 1.

[0114] Weigh 500 g of urea (nitrogen content 46%; diameter 2-4 mm) and put it into a drum for preheating at 70° C. and 22 rpm for 10 minutes.

[0115] The outer coating material is sprayed on the surface of the urea particles at 70° C. The spraying amount of the outer coating material is 3% of the weight of the urea particles to prepare a controlled release fertilizer.

[0116] Test Example 1: Nutrient release determination:

[0117] According to the National Standard of the People's Republic of China for Slow-Release Fertilizers GB / T 23348-2009, the N nutrient release rates of the coated controlled-release fertilizers prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were measured.

[0118] The results are as follows Figure 5 As shown, the release period of the coated fertilizer prepared in Example 1 is 38 days; the release period of the coated fertilizer prepared in Example 2 is 42 days, and the release period of the coated fertilizer prepared in Example 3 is 55 days; the release period of the coated fertilizer prepared in Comparative Example 1 is 20 days, the release period of the coated fertilizer prepared in Comparative Example 2 is 35 days, and the release period of the coated fertilizer prepared in Comparative Example 3 is 30 days.

[0119] Experimental Example 2: Nutrient release determination under different pH buffers

[0120] The nutrient release rates of the coated controlled-release fertilizers prepared in Example 1 and Comparative Example 2 were measured under different pH buffers. The specific measurement method was as follows:

[0121] Prepare buffer solutions of pH=5, pH=7 and pH=9. At 25°C, 10 g of the coated controlled-release fertilizer prepared in Example 1 and Comparative Example 2 were placed in glass bottles containing 200 mL of buffer solutions of different pH values, and repeated 3 times at 25±5°C. Water samples were taken every 1, 3, 5, 7, 14, 21, 28, 35, 42, 49, 56, 63, 70, 77, 84, 91 and 98 days. The nitrogen concentration in each sample was determined by the Kjeldahl method until the nitrogen release rate reached 80%. After each sampling, the residual water in the bottle was poured out, and another 200 mL of pH buffer solution was added to the bottle for subsequent testing.

[0122] The results are as follows Figure 6-7 As shown, from Figure 6 It can be seen that the nutrient cumulative release rate of the controlled-release fertilizer prepared in Example 1 in different gradient pH buffer solutions is different, indicating that the controlled-release fertilizer prepared in Example 1 has certain pH response characteristics. The controlled-release fertilizer prepared in Example 1 releases nutrients faster under acidic conditions and slower under alkaline conditions. This indicates that the amine groups on the outer coating layer material of the controlled-release fertilizer prepared in Example 1 react with H under acidic conditions. + The strong electrostatic repulsion between them destroyed the dense hydrogen bonds formed under neutral and alkaline conditions, causing the outermost coating membrane shell of the controlled-release fertilizer to depolymerize and degrade, and the cross-linking degree to deteriorate, thereby allowing water to enter the inner coating and then the fertilizer core, accelerating the release of nutrients. Comparative Example 2 did not show obvious pH response characteristics in different gradient pH buffer solutions because the outer coating material with pH response characteristics was not sprayed.

[0123] Test Example 3: Degradability test of coating material

[0124] The degradation performance of the inner and outer coating materials prepared in Example 1 was calculated using the weight method. The weight of the inner and outer coating materials prepared in the mold after wiping off the surface moisture was recorded as the initial value S. a Then the inner and outer coating materials were buried in soil with a pH of 7.15 and placed in a constant temperature incubator at 25°C. At each set point, they were weighed again on an analytical balance and recorded as S b .

[0125] Degradation rate (%) = (S a -S b ) / S a ×100.

[0126] The results are as follows Figure 8 As shown, the results show that both the inner coating material and the outer coating material prepared by the present invention have degradable properties.

[0127] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A pH-responsive biodegradable coating material, characterized in that: include: Inner and outer coating materials; The inner film material is prepared by mixing dendritic polyester polyol and isocyanate in a mass ratio of (1-2):1; The outer coating material is mixed with an auxiliary agent, hydroxyl-di-terminated polydimethylsiloxane and isocyanate; the mass ratio of the auxiliary agent to the hydroxyl-di-terminated polydimethylsiloxane is (3-5):1; The dendritic polyester polyol is prepared by the following method: 2,2-dihydroxymethylbutyric acid is melted at 120-150°C, and then a catalyst and monoglyceride are added, and the reaction is carried out at 170-200°C under a nitrogen atmosphere for 4-8 hours; after the reaction, the by-products are removed by rotary evaporation to prepare a dendritic polyester polyol; the molar ratio of monoglyceride to 2,2-dihydroxymethylbutyric acid is (0.5-1.5):2; the amount of the catalyst added is 0.01-0.4wt% of the monoglyceride; the catalyst is selected from one or more of toluenesulfonic acid, aminosulfonic acid, methanesulfonic acid, ethanesulfonic acid, and benzenesulfonic acid; The auxiliary agent is selected from one or more of N-methyldiethanolamine, N-propyldiethanolamine, N-tert-butyldiethanolamine, and N-butyldiethanolamine; In the outer film material, NCO - Groups and additives and OH in hydroxyl-terminated polydimethylsiloxane - The molar ratio of the groups is 1-3.

2. The pH-responsive biodegradable coating material according to claim 1, characterized in that: The monoglyceride is selected from one or more of palmitic acid monoglyceride, monostearic acid glyceride, monocaprylic acid glyceride, lauric acid glyceride, monooleic acid glyceride, monocapric acid glyceride, monomyristic acid glyceride, glyceryl monooleate, and glyceryl monoacetate.

3. Use of the pH-responsive biodegradable coating material according to claim 1 or 2 in the preparation of controlled-release fertilizers.

4. A pH-responsive biodegradable coated controlled-release fertilizer, characterized in that: It comprises a fertilizer core, and the inner coating material and the outer coating material of claim 1 or 2 sprayed on the surface of the fertilizer core; The spraying amount of the inner coating material is 2%-10% of the weight of the fertilizer core; the spraying amount of the outer coating material is 1%-3% of the weight of the fertilizer core.

5. The method for preparing the pH-responsive biodegradable coated controlled-release fertilizer according to claim 4, characterized in that: The following steps are involved: (1) preheating the fertilizer core to 70° C. to 80° C., then spraying the inner coating material on the surface of the fertilizer core and curing it to form an inner coating layer; (2) Under the temperature condition of 70°C to 80°C, the outer coating material is continuously sprayed on the surface of the inner coating layer to form an outer coating layer, thereby preparing a pH-responsive biodegradable coated controlled-release fertilizer.

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