Preparation method of biodegradable waterborne polyurethane-based slow release fertilizer

Abstract

The invention discloses a preparation method of a biodegradable waterborne polyurethane-based slow-release fertilizer, relates to the technical field of slow-release fertilizer preparation, and comprises a preparation method of a waterborne polyurethane-based slow-release fertilizer, and the preparation raw materials of the waterborne polyurethane-based slow-release fertilizer comprise a waterborne polyurethane system raw material, a functional raw material, fertilizer particles and an auxiliary raw material. The waterborne polyurethane system is prepared from the following raw materials: polybutanediol oxalate, isophorone diisocyanate, dihydracrylic acid, 1, 4-butanediol, 2-methyl-2-morpholine propanesulfonic acid, polyvinyl alcohol and potassium persulfate, and natural biodegradable polyester diol is used and is subjected to compound modification with tannic acid, so that the waterborne polyurethane is prepared. The water-based polyurethane material has good biodegradability, can be gradually decomposed by microorganisms in a soil environment, avoids long-term residue in soil, effectively solves the problem that a traditional water-based polyurethane material causes potential hazards to the soil ecological environment, and protects the ecological balance of the soil.

Description

Technical Field

[0001] The invention relates to the technical field of slow-release fertilizer preparation, in particular to a method for preparing a biodegradable waterborne polyurethane-based slow-release fertilizer. Background Art

[0002] In agricultural production, efficient fertilizer utilization is crucial to increasing crop yields and ensuring food security. Traditional fertilizers, after application, are prone to nutrient loss due to leaching and volatilization, which not only reduces fertilizer utilization but also causes environmental problems such as eutrophication of water bodies and soil compaction. Waterborne polyurethane has been gradually applied to the field of slow-release fertilizers due to its good film-forming properties, flexibility, and biocompatibility. By forming a polymer film to coat the fertilizer, nutrients are slowly released, thereby improving fertilizer utilization. However, existing water-based polyurethane-based slow-release fertilizers still have many defects. On the one hand, some water-based polyurethane materials have poor biodegradability, and their residues in the soil will cause long-term potential harm to the soil ecological environment. On the other hand, the slow-release performance of existing slow-release fertilizers is not accurately regulated, making it difficult to meet the differentiated nutrient needs of different crops at different growth stages. In addition, the preparation process is complex and the cost is high, which limits its large-scale promotion and application. To this end, we propose a method for preparing biodegradable water-based polyurethane-based slow-release fertilizer. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for preparing a biodegradable waterborne polyurethane-based slow-release fertilizer.

[0004] To achieve the above objectives, the present invention provides the following technical solutions: a method for preparing a biodegradable water-based polyurethane-based slow-release fertilizer, comprising a method for preparing a water-based polyurethane-based slow-release fertilizer, wherein the raw materials for preparing the water-based polyurethane-based slow-release fertilizer include water-based polyurethane system raw materials, functional raw materials, fertilizer particles, and auxiliary raw materials, wherein the water-based polyurethane system raw materials include polybutylene glycol oxalate diol, isophorone diisocyanate, dihydroxypropionic acid, 1,4-butanediol, 2-methyl-2-morpholinepropanesulfonic acid, polyvinyl alcohol, and potassium persulfate. The specific steps for preparing the biodegradable water-based polyurethane-based slow-release fertilizer are as follows: Step 1: Polybutylene oxalate diol and tannic acid are composite-modified to prepare modified polyester diol, and urea and nano-silica are mixed for standby treatment; Step 2: mixing the modified biodegradable polyester diol with isophorone diisocyanate to prepare a prepolymer, and adding hydroxyethyl acrylate to the prepolymer to prepare a prepolymer mixture for later use; Step 3: adding 1,4-butanediol as a chain extender to the prepolymer mixture, adding 2-methyl-2-morpholinepropanesulfonic acid and deionized water after the reaction to perform an emulsification operation, adding polyvinyl alcohol to the emulsion, and bubbling nitrogen to prepare an aqueous polyurethane emulsion, adding potassium persulfate to the emulsion to perform a polymerization reaction to prepare a polyurethane emulsion for later use; Step 4: Surface amination treatment is performed on the graphene oxide quantum dots, and after completion, the graphene oxide quantum dots and sodium alginate are added to the polyurethane emulsion at the same time, and reacted under light conditions to obtain a finished polyurethane emulsion for standby use; Step 5: The fertilizer particles are coated by ultrasonic-assisted spray granulation. After coating, the particles are added to the polyurethane emulsion product for spray granulation to obtain slow-release fertilizer particles. The particles are dried to remove moisture to obtain the slow-release fertilizer particle product.

[0005] As a further solution of the present invention: the functional raw materials include tannic acid, p-toluenesulfonic acid, hydroxyethyl acrylate, graphene oxide quantum dots, ethylenediamine and sodium alginate, the fertilizer particles include urea and nano-silicon dioxide, and the auxiliary raw materials include dimethyl sulfoxide, deionized water and nitrogen.

[0006] As a further embodiment of the present invention: in the step 1, polybutylene glycol oxalate diol and tannic acid are mixed in a dimethyl sulfoxide solvent in a mass ratio of 5:1, 0.5% of p-toluenesulfonic acid is added as a catalyst, and the mixture is stirred and reacted at a temperature of 60° C. for 8 h-10 h to obtain a modified polyester diol.

[0007] As a further solution of the present invention: in step 1, urea is mixed with nano-silicon dioxide, and the amount of nano-silicon dioxide added is 3% of the total mass of the fertilizer. After mixing, the mixture is ball-milled for 30 minutes to 45 minutes to uniformly attach the nano-silicon dioxide to the surface of the fertilizer particles.

[0008] As a further solution of the present invention: in the step 2, nitrogen is filled into the high-pressure reactor, the modified polyester diol and isophorone diisocyanate are mixed in a molar ratio of 1:2.2, and the mixture is reacted at a temperature of 95°C-100°C for 2.5 hours to obtain a prepolymer for standby use, and hydroxyethyl acrylate containing a double bond is added to the prepolymer in an amount of 8% of the total mass of the prepolymer. The reaction is continued for 1.5 hours to 3 hours to obtain a prepolymer mixture for standby use.

[0009] As a further solution of the present invention: in the step three, 1,4-butanediol is added as a chain extender to the prepolymer mixture for mixed reaction, the molar ratio of the chain extender to the prepolymer mixture is 1.1:1, and the mixture is reacted at a temperature of 75°C for 1.2 hours. After the reaction is completed, 2-methyl-2-morpholinepropanesulfonic acid is added to neutralize the carboxyl groups in the prepolymer mixture, and the degree of neutralization is controlled between 85% and 87%. After the neutralization is completed, deionized water is slowly added for emulsification, and polyvinyl alcohol with a mass fraction of 1.5% is added to the emulsion at the same time, and nitrogen is bubbled into it. An aqueous polyurethane emulsion is prepared at a stirring speed of 2000 r / min-3000 r / min. After the stirring is completed, 0.3% potassium persulfate initiator is added, and a free radical polymerization reaction is carried out at a temperature of 40°C for 2 hours to obtain a polyurethane emulsion for standby use.

[0010] As a further solution of the present invention: in the step 4, the graphene oxide quantum dots are reacted with ethylenediamine at a temperature of 60° C. for 4 hours to achieve surface amination treatment, the amination-treated graphene oxide quantum dots are added to the polyurethane emulsion at a ratio of 0.8% of the total mass of the aqueous polyurethane emulsion, and 0.5% by mass of sodium alginate is added at the same time, and the mixture is stirred and mixed at a temperature of 25° C. to prepare a finished polyurethane emulsion for standby use.

[0011] As a further solution of the present invention: in the step five, an ultrasonic-assisted spray granulation method is used for fertilizer coating, and the pretreated fertilizer particles are added to an aqueous polyurethane emulsion containing an intelligent response material. Under the conditions of an ultrasonic power of 200 W and a frequency of 40 kHz, the feed rate is controlled to be 6 mL / min, the inlet air temperature is 130°C, and the outlet air temperature is 80°C for spray granulation, and the emulsion is coated on the surface of the fertilizer particles to prepare slow-release fertilizer particles for later use.

[0012] As a further solution of the present invention: in the step five, the coated slow-release fertilizer particles are dried at a temperature of 45°C for 7-8 hours, and after removing moisture, they are placed in an environment with a humidity of 80% and a temperature of 30°C for aging for 48 hours to obtain finished slow-release fertilizer particles.

[0013] By adopting the above technical solution, compared with the prior art, the beneficial effects of the present invention are: 1. The present invention uses natural biodegradable polyester diols and performs composite modification with tannic acid to make the waterborne polyurethane material have good biodegradability. It can be gradually decomposed by microorganisms in the soil environment, avoiding long-term residue in the soil. This effectively solves the problem of traditional waterborne polyurethane materials causing potential harm to the soil ecological environment and protects the soil ecological balance. By introducing nanocellulose and modifying its surface, it is evenly dispersed in the waterborne polyurethane emulsion, forming a nanoscale pore structure inside the coating film. At the same time, ultrasound-assisted spray granulation allows the emulsion to form a gradient structure coating film on the surface of the fertilizer particles, further enhancing the ability to accurately control the nutrient release rate and meeting the differentiated nutrient requirements of different crops at different growth stages. 2. The present invention adopts natural degradable raw materials and common functional materials, avoids the use of expensive special materials, reduces raw material costs, and improves production efficiency and shortens the production cycle by using operations such as ultrasound-assisted spray granulation, thereby effectively reducing the overall preparation cost, which is conducive to the large-scale promotion and application of the slow-release fertilizer. Through the composite modification and construction of the raw materials, the coating film is given self-repairing ability and good mechanical properties. When the coating film is damaged by external force, the dynamic covalent bonds can recombine and repair the damaged parts, ensuring the integrity of the coating film during storage and transportation of the slow-release fertilizer, reducing the premature release of fertilizer, and enhancing the stability and flexibility of the coating film, so that it can better adapt to changes in the soil environment, further improving fertilizer utilization, and reducing environmental pollution problems caused by nutrient loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a flow chart for preparing a polyurethane-based slow-release fertilizer according to an embodiment of the present invention; Figure 2 A comparison chart of nutrient release characteristic data in an embodiment of the present invention; Figure 3 A comparison chart of biodegradation data in the embodiments of the present invention; Figure 4 This is a comparison chart of crop growth test data A in an embodiment of the present invention; Figure 5 This is a comparison chart of crop growth test data B in an embodiment of the present invention. DETAILED DESCRIPTION

[0015] The specific embodiments of the present invention will be further described below in conjunction with the accompanying drawings. It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention.

[0016] In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0017] Please see the attached Figure 1 -Attached Figure 2 The present invention provides a method for preparing a biodegradable water-based polyurethane-based slow-release fertilizer, including a method for preparing a water-based polyurethane-based slow-release fertilizer. The raw materials for preparing the water-based polyurethane-based slow-release fertilizer include water-based polyurethane system raw materials, functional raw materials, fertilizer particles, and auxiliary raw materials. The water-based polyurethane system raw materials include polybutylene glycol oxalate diol, isophorone diisocyanate, dihydroxypropionic acid, 1,4-butanediol, 2-methyl-2-morpholinepropanesulfonic acid, polyvinyl alcohol, and potassium persulfate. The specific steps for preparing the biodegradable water-based polyurethane-based slow-release fertilizer are as follows: Step 1: Polybutylene oxalate diol and tannic acid are composite-modified to prepare modified polyester diol, and urea and nano-silica are mixed for standby treatment; Step 2: mixing the modified biodegradable polyester diol with isophorone diisocyanate to prepare a prepolymer, and adding hydroxyethyl acrylate to the prepolymer to prepare a prepolymer mixture for later use; Step 3: adding 1,4-butanediol as a chain extender to the prepolymer mixture, adding 2-methyl-2-morpholinepropanesulfonic acid and deionized water after the reaction to perform an emulsification operation, adding polyvinyl alcohol to the emulsion, and bubbling nitrogen to prepare an aqueous polyurethane emulsion, adding potassium persulfate to the emulsion to perform a polymerization reaction to prepare a polyurethane emulsion for later use; Step 4: Surface amination treatment is performed on the graphene oxide quantum dots, and after completion, the graphene oxide quantum dots and sodium alginate are added to the polyurethane emulsion at the same time, and reacted under light conditions to obtain a finished polyurethane emulsion for standby use; Step 5: The fertilizer particles are coated by ultrasonic-assisted spray granulation. After coating, the particles are added to the polyurethane emulsion product for spray granulation to obtain slow-release fertilizer particles. The particles are dried to remove moisture to obtain the slow-release fertilizer particle product.

[0018] In one embodiment of the present invention, the functional raw materials include tannic acid, p-toluenesulfonic acid, hydroxyethyl acrylate, graphene oxide quantum dots, ethylenediamine and sodium alginate, the fertilizer particles include urea and nano-silicon dioxide, and the auxiliary raw materials include dimethyl sulfoxide, deionized water and nitrogen.

[0019] In one embodiment of the present invention: in step 1, polybutylene glycol oxalate diol and tannic acid are mixed in a dimethyl sulfoxide solvent in a mass ratio of 5:1, 0.5% of p-toluenesulfonic acid is added as a catalyst, and the reaction is stirred at a temperature of 60° C. for 8 h-10 h to obtain a modified polyester diol.

[0020] In one embodiment of the present invention: in step 1, urea is mixed with nano-silica, and the amount of nano-silica added is 3% of the total mass of the fertilizer. After mixing, the mixture is ball-milled for 30 minutes to 45 minutes to uniformly attach the nano-silica to the surface of the fertilizer particles.

[0021] In one embodiment of the present invention: in step 2, nitrogen is charged into a high-pressure reactor, the modified polyester diol and isophorone diisocyanate are mixed in a molar ratio of 1:2.2, and the mixture is reacted at a temperature of 95° C. to 100° C. for 2.5 hours to obtain a prepolymer for standby use, and hydroxyethyl acrylate containing a double bond is added to the prepolymer in an amount of 8% of the total mass of the prepolymer. The reaction is continued for 1.5 hours to 3 hours to obtain a prepolymer mixture for standby use.

[0022] In one embodiment of the present invention: in step three, 1,4-butanediol is added as a chain extender to the prepolymer mixture for mixed reaction, the molar ratio of the chain extender to the prepolymer mixture is 1.1:1, and the mixture is reacted at a temperature of 75°C for 1.2 hours. After the reaction is completed, 2-methyl-2-morpholinepropanesulfonic acid is added to neutralize the carboxyl groups in the prepolymer mixture, and the degree of neutralization is controlled between 85% and 87%. After the neutralization is completed, deionized water is slowly added for emulsification, and polyvinyl alcohol with a mass fraction of 1.5% is added to the emulsion at the same time, and nitrogen is bubbled into the emulsion to prepare an aqueous polyurethane emulsion at a stirring speed of 2000 r / min-3000 r / min. After the stirring is completed, 0.3% potassium persulfate initiator is added, and free radical polymerization is carried out at a temperature of 40°C for 2 hours to prepare a polyurethane emulsion for standby use.

[0023] In one embodiment of the present invention: in step 4, graphene oxide quantum dots are reacted with ethylenediamine at a temperature of 60°C for 4 hours to achieve surface amination treatment, and the amination-treated graphene oxide quantum dots are added to the polyurethane emulsion at a ratio of 0.8% of the total mass of the aqueous polyurethane emulsion, and sodium alginate with a mass fraction of 0.5% is added at the same time, and the mixture is stirred and mixed at a temperature of 25°C to prepare a finished polyurethane emulsion for standby use.

[0024] In one embodiment of the present invention: in step five, ultrasound-assisted spray granulation is used for fertilizer coating, and the pretreated fertilizer particles are added to an aqueous polyurethane emulsion containing an intelligent response material. Under the conditions of an ultrasonic power of 200 W and a frequency of 40 kHz, the feed rate is controlled to be 6 mL / min, the inlet air temperature is 130°C, and the outlet air temperature is 80°C for spray granulation, and the emulsion is coated on the surface of the fertilizer particles to prepare slow-release fertilizer particles for later use.

[0025] In one embodiment of the present invention: in step five, the coated slow-release fertilizer particles are dried at a temperature of 45°C for 7-8 hours, and after removing moisture, they are placed in an environment with a humidity of 80% and a temperature of 30°C for aging for 48 hours to obtain finished slow-release fertilizer particles.

[0026] In one embodiment of the present invention: in step three, polyvinyl alcohol and waterborne polyurethane form an interpenetrating network structure, which can enhance the mechanical properties and stability of the coating film.

[0027] In one embodiment of the present invention: in step five, during the aging process, the dynamic covalent bonds are rearranged, the interpenetrating network structure is further improved, and the interaction between sodium alginate and graphene oxide quantum dots is enhanced, ultimately obtaining a biodegradable waterborne polyurethane-based slow-release fertilizer product with excellent performance.

[0028] Example Raw material preparation, Waterborne polyurethane system raw materials: 200g polybutylene adipate diol, 440mol isophorone diisocyanate, 10g dihydroxypropionic acid, 220mol 1,4-butanediol, 17g 2-methyl-2-morpholinopropanesulfonic acid, 30g polyvinyl alcohol and 6g potassium persulfate; Functional raw materials: 40g tannic acid, 1.2g p-toluenesulfonic acid, 36.8g hydroxyethyl acrylate, 2.4g graphene oxide quantum dots, 3g ethylenediamine and 1.5g sodium alginate; Fertilizer granules: 160g urea and 4.8g nano-silicon dioxide; Auxiliary materials: 300 mL of dimethyl sulfoxide, 1000 mL of deionized water, and an appropriate amount of nitrogen; Polybutylene adipate diol and tannic acid were mixed in a mass ratio of 5:1 in 300 mL of dimethyl sulfoxide solvent, and 0.5% of p-toluenesulfonic acid was added as a catalyst. The mixture was reacted at a constant temperature of 60°C and a stirring speed of 200 r / min for 8 hours to obtain a modified polyester diol. 160 g of urea was mixed with 4.8 g of nano-silica, placed in a ball mill, and ball-milled at a speed of 300 r / min for 30 minutes to uniformly adhere the nano-silica to the surface of the fertilizer particles. A high-pressure reactor equipped with a thermometer, a stirrer and a reflux condenser was filled with nitrogen. After exhausting the air, the modified polyester diol and isophorone diisocyanate were added to the reactor at a molar ratio of 1:2.2, and the temperature was raised to 95°C. The reaction was carried out under nitrogen protection for 2.5 hours to obtain a prepolymer. Then, hydroxyethyl acrylate accounting for 8% of the total mass of the prepolymer was added to the prepolymer, and the reaction was continued for 1.5 hours to obtain a prepolymer mixture for standby use. 1,4-butanediol was added to the prepolymer mixture as a chain extender. The molar ratio of the chain extender to the prepolymer mixture was 1.1:1. The mixture was heated in an oil bath at 75°C. The mixture was reacted for 1.2 hours. After the reaction was completed, 2-methyl-2-morpholinepropanesulfonic acid was added to neutralize the carboxyl groups in the prepolymer mixture, and the neutralization degree was controlled to be 85%. Subsequently, 1000 mL of deionized water was slowly added for emulsification. At the same time, 1.5% of polyvinyl alcohol was added to the emulsion, and nitrogen was bubbled into it. The mixture was stirred at a stirring speed of 2500 r / min for 30 minutes to prepare an aqueous polyurethane emulsion. After the stirring was completed, 0.3% of potassium persulfate initiator was added, and a free radical polymerization reaction was carried out in a constant temperature water bath at 40°C for 2 hours to prepare a polyurethane emulsion for standby use. Graphene oxide quantum dots and ethylenediamine were reacted at a mass ratio of 1:1.25 at a temperature of 60°C for 4 hours to achieve surface amination treatment. Aminated graphene oxide quantum dots were added to the polyurethane emulsion at a ratio of 0.8% of the total mass of the aqueous polyurethane emulsion, and sodium alginate with a mass fraction of 0.5% was added at the same time. The mixture was stirred at 25°C and 150 r / min for 30 minutes to obtain a polyurethane emulsion product for standby use. Ultrasonic-assisted spray granulation was used for fertilizer coating, and the pretreated fertilizer particles were added to the emulsion. The slow-release fertilizer particles were prepared by adding the emulsion into an aqueous polyurethane emulsion containing the smart response material, and spray granulation was carried out under the conditions of ultrasonic power of 200 W and frequency of 40 kHz, while controlling the feed rate to 6 mL / min, the air inlet temperature to 130°C, and the air outlet temperature to 80°C. The emulsion was coated on the surface of the fertilizer particles to obtain slow-release fertilizer particles. The coated slow-release fertilizer particles were dried in a blast drying oven at 45°C for 7 hours. After removing the moisture, the particles were placed in a constant temperature and humidity chamber at a humidity of 80% and a temperature of 30°C for aging for 48 hours to obtain the finished slow-release fertilizer particles.

[0029] Comparative Example 1 Fertilizer granules: 160g urea, 80g potassium dihydrogen phosphate and 4.8g nano silicon dioxide, Preparation steps: Pour urea, potassium dihydrogen phosphate and nano-silicon dioxide directly into a mixer and stir at a speed of 200 r / min for 15 minutes to mix the three raw materials evenly to obtain a fertilizer product. In this comparative example, the fertilizer is not coated in any way, and the nutrients are easily lost and have no slow-release function.

[0030] Comparative Example 2 Raw material preparation, Core fertilizer: urea 200g; Coating materials: sulfur 50g, paraffin 10g, micronized talc 8g; Auxiliary materials: binder solution containing film-forming agent (made by dissolving 5 g of polyvinyl alcohol in 100 mL of water); Preparation steps, Sulfur melting: Place the sulfur in a heating container and heat it to 130-140°C to completely melt it, keeping the temperature constant; Urea preheating: Place the urea granules in a constant temperature box at 60℃-70℃ for 30 minutes to facilitate better adhesion of the coating material; Coating operation: Add the preheated urea granules to the molten sulfur and spray the binder solution at the same time. Roll and mix in a rotating drum at a speed of 80-100 rpm for 15 minutes to evenly coat the sulfur on the urea surface. Then, add paraffin wax to fill the pores of the sulfur layer using its fluidity at high temperature. Continue rolling for 5 minutes. Curing and post-treatment: After the temperature drops to room temperature and the sulfur layer solidifies, micronized talcum powder is evenly sprayed on the surface of the coated urea to prevent particles from sticking together. This produces sulfur-coated urea slow-release fertilizer. Although this comparative example has a certain slow-release effect, the sulfur coating degrades slowly in the soil, and it is difficult to precisely control nutrient release according to crop needs. At the same time, the preparation process consumes a lot of energy.

[0031] By conducting multi-dimensional tests on the finished slow-release fertilizer granules of the embodiment, the fertilizers of comparative example 1 and comparative example 2, the advantages of the finished slow-release fertilizer granules of the embodiment in terms of nutrient release, biodegradation, and promotion of crop growth were compared and analyzed; 2. Test steps (1) Nutrient release characteristics test, Preparation of simulated soil solution: Weigh 100 g of air-dried soil, add 500 mL of deionized water, stir evenly, let stand for 24 hours, and filter to obtain the simulated soil solution; Fertilizer sample preparation: Weigh 5 g each of the finished product of the slow-release fertilizer granules of Example 1, the fertilizer of Comparative Example 1, and the fertilizer of Comparative Example 2, place them in a 250 mL conical flask, add 150 mL of the simulated soil solution, and seal the flask. Testing process: Place the conical flask in a constant temperature oscillator at 25°C and an oscillation speed of 120 r / min. Take 10 mL of solution on the 1st, 7th, 14th, 28th, and 56th day, and use an ion chromatograph to measure the concentrations of urea and phosphate ions in the solution. After each sampling, add 10 mL of fresh simulated soil solution. (2) Biodegradability test, Soil burial test: Soil of the same texture was selected and placed in plastic boxes of the same specifications. 3g of the finished slow-release fertilizer granules of the embodiment and the fertilizer of comparative example 2 were buried in the soil at a depth of 5cm. Three parallel groups were set up for each sample. Comparative example 1 did not have biodegradability and was not included in this test. Degradation rate determination: Fertilizer samples were taken out on the 30th, 60th, and 90th days, carefully rinsed with deionized water, dried to constant weight, and weighed. The degradation rate was calculated according to the formula: Degradation rate (%) = (initial mass - residual mass) / initial mass × 100%; (3) Crop growth impact test, Potting setup: Tomato seedlings with consistent growth conditions were selected and planted in pots filled with the same substrate, with one plant planted in each pot. The experiment was divided into four groups: a control group (no fertilizer), a group using the slow-release fertilizer granules of the embodiment, a group using the fertilizer of comparative example 1, and a group using the fertilizer of comparative example 2. Ten replicates were set for each group. Fertilization and management: Apply 0.5g of nitrogen per pot evenly on the surface of the soil in the pot, then water it. Maintain the same lighting, temperature, watering and other conditions for daily management. Index determination: On the 30th and 60th day after planting, the plant height, stem diameter, number of leaves, and chlorophyll content of the tomato plants were measured (determined using a portable chlorophyll meter). At harvest, the single-plant yield of tomatoes and the vitamin C content of the fruit were measured (determined using the 2,6-dichloroindophenol titration method).

[0032] Nutrient release advantage: The finished product of the slow-release fertilizer granules in the embodiment exhibits a slow and continuous nutrient release characteristic. Compared with the comparative example 1, it avoids the rapid loss of nutrients. Compared with the comparative example 2, the nutrient release during the entire test period is more in line with the growth needs of the crops. Biodegradation advantage: The biodegradability of the finished slow-release fertilizer granules in Example 2 is significantly better than that of the sulfur-coated urea slow-release fertilizer in Comparative Example 2, with a degradation rate of 76.5% in 90 days, which is beneficial to reducing soil pollution. Advantages in promoting crop growth: In terms of various crop growth indicators and yield quality indicators, the finished product group of slow-release fertilizer granules in the embodiment performed best, effectively verifying its role in promoting crop growth and its application value in agricultural production.

[0033] Although the present invention is disclosed above with reference to preferred embodiments, this is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications without departing from the spirit and scope of the present invention. Therefore, any modifications, equivalent variations, and modifications made to the above embodiments in accordance with the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing a biodegradable waterborne polyurethane-based slow-release fertilizer, comprising a method for preparing a waterborne polyurethane-based slow-release fertilizer, characterized in that: The raw materials for preparing the waterborne polyurethane-based slow-release fertilizer include waterborne polyurethane system raw materials, functional raw materials, fertilizer particles, and auxiliary raw materials. The waterborne polyurethane system raw materials include polybutylene glycol oxalate diol, isophorone diisocyanate, dihydroxypropionic acid, 1,4-butanediol, 2-methyl-2-morpholinepropanesulfonic acid, polyvinyl alcohol, and potassium persulfate. The specific steps for preparing the biodegradable waterborne polyurethane-based slow-release fertilizer are as follows: Step 1: Polybutylene oxalate diol and tannic acid are composite-modified to prepare modified polyester diol, and urea and nano-silica are mixed for standby treatment; Step 2: mixing the modified biodegradable polyester diol with isophorone diisocyanate to prepare a prepolymer, and adding hydroxyethyl acrylate to the prepolymer to prepare a prepolymer mixture for later use; Step 3: adding 1,4-butanediol as a chain extender to the prepolymer mixture, adding 2-methyl-2-morpholinepropanesulfonic acid and deionized water after the reaction to perform an emulsification operation, adding polyvinyl alcohol to the emulsion, and bubbling nitrogen to prepare an aqueous polyurethane emulsion, adding potassium persulfate to the emulsion to perform a polymerization reaction to prepare a polyurethane emulsion for later use; Step 4: Surface amination treatment is performed on the graphene oxide quantum dots, and after completion, the graphene oxide quantum dots and sodium alginate are added to the polyurethane emulsion at the same time, and reacted under light conditions to obtain a finished polyurethane emulsion for standby use; Step 5: The fertilizer particles are coated by ultrasonic-assisted spray granulation. After coating, the particles are added to the polyurethane emulsion product for spray granulation to obtain slow-release fertilizer particles. The particles are dried to remove moisture to obtain the slow-release fertilizer particle product.

2. The method for preparing a biodegradable waterborne polyurethane-based slow-release fertilizer according to claim 1, characterized in that: The functional raw materials include tannic acid, p-toluenesulfonic acid, hydroxyethyl acrylate, graphene oxide quantum dots, ethylenediamine and sodium alginate; the fertilizer particles include urea and nano-silicon dioxide; and the auxiliary raw materials include dimethyl sulfoxide, deionized water and nitrogen.

3. The method for preparing a biodegradable waterborne polyurethane-based slow-release fertilizer according to claim 2, characterized in that: In the step 1, polybutylene glycol oxalate diol and tannic acid are mixed in a dimethyl sulfoxide solvent at a mass ratio of 5:1, 0.5% of p-toluenesulfonic acid is added as a catalyst, and the mixture is stirred and reacted at a temperature of 60° C. for 8 h-10 h to obtain a modified polyester diol.

4. The method for preparing a biodegradable waterborne polyurethane-based slow-release fertilizer according to claim 3, characterized in that: In the step 1, urea and nano-silicon dioxide are mixed, and the amount of nano-silicon dioxide added is 3% of the total mass of the fertilizer. After mixing, the mixture is ball-milled for 30 minutes to 45 minutes to uniformly attach the nano-silicon dioxide to the surface of the fertilizer particles.

5. The method for preparing a biodegradable waterborne polyurethane-based slow-release fertilizer according to claim 4, characterized in that: In the step 2, nitrogen is charged into the autoclave, the modified polyester diol and isophorone diisocyanate are mixed in a molar ratio of 1:2.2, and the mixture is reacted at a temperature of 95° C. to 100° C. for 2.5 hours to obtain a prepolymer for standby use, and hydroxyethyl acrylate containing a double bond is added to the prepolymer in an amount of 8% of the total mass of the prepolymer. The reaction is continued for 1.5 hours to 3 hours to obtain a prepolymer mixture for standby use.

6. The method for preparing a biodegradable waterborne polyurethane-based slow-release fertilizer according to claim 5, characterized in that: In the step three, 1,4-butanediol is added as a chain extender to the prepolymer mixture for mixed reaction, the molar ratio of the chain extender to the prepolymer mixture is 1.1:1, and the mixture is reacted at a temperature of 75°C for 1.2 hours. After the reaction is completed, 2-methyl-2-morpholinepropanesulfonic acid is added to neutralize the carboxyl groups in the prepolymer mixture, and the degree of neutralization is controlled between 85% and 87%. After the neutralization is completed, deionized water is slowly added for emulsification, and polyvinyl alcohol with a mass fraction of 1.5% is added to the emulsion at the same time, and nitrogen is bubbled into the emulsion to prepare an aqueous polyurethane emulsion at a stirring speed of 2000 r / min-3000 r / min. After the stirring is completed, 0.3% potassium persulfate initiator is added, and a free radical polymerization reaction is carried out at a temperature of 40°C for 2 hours to prepare a polyurethane emulsion for standby use.

7. The method for preparing a biodegradable waterborne polyurethane-based slow-release fertilizer according to claim 6, characterized in that: In the step 4, the graphene oxide quantum dots are reacted with ethylenediamine at a temperature of 60° C. for 4 hours to achieve surface amination treatment, the amination-treated graphene oxide quantum dots are added to the polyurethane emulsion at a ratio of 0.8% of the total mass of the aqueous polyurethane emulsion, and 0.5% by mass of sodium alginate is added at the same time. The mixture is stirred and mixed at a temperature of 25° C. to prepare a finished polyurethane emulsion for standby use.

8. The method for preparing a biodegradable waterborne polyurethane-based slow-release fertilizer according to claim 7, characterized in that: In the step five, an ultrasound-assisted spray granulation method is used to coat the fertilizer. The pretreated fertilizer particles are added to an aqueous polyurethane emulsion containing an intelligent response material. Under the conditions of an ultrasonic power of 200 W and a frequency of 40 kHz, the feed rate is controlled to be 6 mL / min, the inlet air temperature is 130° C., and the outlet air temperature is 80° C. for spray granulation. The emulsion is coated on the surface of the fertilizer particles to prepare slow-release fertilizer particles for later use.

9. The method for preparing a biodegradable waterborne polyurethane-based slow-release fertilizer according to claim 8, characterized in that: In the step 5, the coated slow-release fertilizer particles are dried at a temperature of 45° C. for 7-8 hours to remove moisture, and then placed in an environment with a humidity of 80% and a temperature of 30° C. for aging for 48 hours to obtain finished slow-release fertilizer particles.

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