A double-modified all-biobased polyurethane coated fertilizer and preparation method thereof

Abstract

The present invention relates to the technical field of slow-release fertilizers, and discloses a double-modified all-bio-based polyurethane coated fertilizer and a preparation method thereof, wherein the preparation method comprises: mixing an alkali and a fatty acid for reaction for 1.25 to 2 hours, and obtaining a hydrophobic nanomaterial after drying; mixing a bio-based polyol and an isocyanate, and then adding the obtained hydrophobic nanomaterial and a surfactant to obtain a double-modified all-bio-based coating liquid; mixing fertilizer particles with the obtained double-modified all-bio-based coating liquid, and curing to obtain a double-modified all-bio-based polyurethane coated fertilizer. The double-modified all-bio-based polyurethane coated fertilizer prepared by the present invention has a significantly increased water contact angle, a better hydrophobic effect, and a reduced nitrogen cumulative nutrient release rate, greatly improving the release performance, and extending the controlled release period of the coated fertilizer.

Description

Technical Field

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

[0002] In order to improve the yield and quality, the growth of crops requires a continuous supply of nutrients. However, the nutrients contained in the soil itself are limited and cannot effectively meet the normal growth of a large number of crops. In agricultural production, chemical fertilizers have become the largest material investment, accounting for about 50% of all productive investments. Nowadays, the application of chemical fertilizers is the simplest, most effective and fastest way to ensure the nutrients required for plant growth. However, the utilization rate of traditional fertilizers is very low, and a large amount of nitrogen is lost through ammonia volatilization, denitrification, leaching and other pathways, which not only causes serious waste of resources, but also has serious adverse effects on the ecological environment, such as soil degradation, groundwater pollution and eutrophication of water bodies. Pollution problems continue to intensify. In order to solve the above problems, people usually adopt multiple small amounts of fertilization to meet the nutrient needs of crops at different times and avoid environmental pollution. However, this method not only increases the economic burden on farmers, but also easily causes mechanical damage to crop growth. Therefore, the research and development of chemical fertilizer types and fertilization application technology plays a key role in improving the level of agricultural production. Among the many measures to improve the utilization rate of nitrogen fertilizer, the application of coated slow-release urea has high practical value and broad application prospects in prolonging fertilizer effectiveness, reducing nitrogen loss, and increasing plant intake of effective nutrients.

[0003] Chinese patent CN 116023196A discloses a plant-derived polyurethane coated fertilizer and a preparation method thereof, wherein a polyurethane coating liquid is prepared using plant oil-based polyol and bio-based isocyanate as raw materials, and a hydrophobic nanomaterial is added to obtain a hydrophobically modified plant oil-based polyurethane coated fertilizer. However, the initial nutrient release rate of the coated fertilizer is too high. Summary of the invention

[0004] The invention provides a double-modified all-biobased polyurethane coated fertilizer and a preparation method thereof, which solves the problem that the initial nutrient release rate of the coated fertilizer prepared by the prior art is too high.

[0005] A method for preparing a double-modified all-biobased polyurethane coated fertilizer comprises the following steps:

[0006] Preparation of hydrophobic nanomaterials: mixing alkali and fatty acid for reaction for 1.25-2h at 100-105°C, and drying to constant weight to obtain hydrophobic nanomaterials; the alkali, fatty acid and solvent are in a ratio of 4g:0.95-1g:50mL;

[0007] Preparing a double-modified all-biobased coating liquid: mixing a bio-based polyol and an isocyanate, and then adding the obtained hydrophobic nanomaterial and a surfactant to obtain a double-modified all-biobased coating liquid; the mass ratio of the bio-based polyol, the bio-based isocyanate, the hydrophobic nanomaterial and the surfactant in the double-modified all-biobased coating liquid is 66:34:7:5;

[0008] Coating: The fertilizer particles are mixed with the prepared double-modified all-biobased coating liquid, and then solidified to obtain the double-modified all-biobased polyurethane coated fertilizer.

[0009] Preferably, the surfactant is polydimethylsiloxane. Polydimethylsiloxane is a good hydrophobic agent, a conventional reagent, non-toxic and tasteless, has stable chemical properties, is relatively common, and is easy to purchase.

[0010] Preferably, when preparing the hydrophobic nanomaterial, the base is copper hydroxide, the fatty acid is lauric acid, and the solvent is ethanol solution.

[0011] Preferably, the bio-based polyol is one or more of castor oil polyol, soybean oil polyol and palm oil polyol. The bio-based polyol is non-toxic and tasteless, and has good hydrophobicity and chemical stability.

[0012] Preferably, the isocyanate is one or both of polymethylene polyphenyl isocyanate and bio-based polyisocyanate. The isocyanate is a bio-based raw material, non-toxic and tasteless, and has good hydrophobicity and chemical stability.

[0013] Preferably, during coating, the mass ratio of the double-modified all-biobased coating liquid to the fertilizer particles is 50:2-3.

[0014] Preferably, during coating, the fertilizer particles are preheated at 80-85° C. for 8-12 minutes to ensure better contact between the fertilizer particles and the double-modified all-biobased coating liquid.

[0015] Preferably, the specific method of the coating is:

[0016] After preheating the fertilizer granules, add the fully bio-based coating liquid, and solidify into a film to obtain the first-coated urea granules;

[0017] After preheating the urea granules that have completed the primary coating, adding the full bio-based coating liquid, and curing the film to obtain the urea granules that have completed the secondary coating;

[0018] After preheating the urea granules that have completed the secondary coating, a fully bio-based coating liquid is added, and after solidification into a film, urea granules that have completed the third coating are obtained;

[0019] After preheating the urea granules that have completed the third coating, adding the full bio-based coating liquid, and curing the film to obtain the urea granules that have completed the fourth coating;

[0020] After preheating the urea particles that have completed four coatings, the double-modified all-bio-based coating liquid is added, and after solidification into a film, the double-modified all-bio-based polyurethane coated fertilizer is obtained.

[0021] During the coating process, the first four times all used fully bio-based coating liquid, and only the fifth time used double-modified fully bio-based coating liquid. While ensuring the reduction of nutrient release rate and the extension of nutrient release period, it also reduced the content of metal ions in the coated fertilizer and was not easy to pollute the soil.

[0022] Preferably, the preparation method of the all-biobased coating liquid is: castor oil polyol and bio-based polyisocyanate are fully mixed at room temperature according to a molar ratio of -NCO to -OH of 1:1 to obtain the all-biobased coating liquid.

[0023] The second purpose of the present invention is to protect the double-modified all-biobased polyurethane coated fertilizer prepared by the preparation method.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) The present invention uses natural polymer bio-based polyols and isocyanates as raw materials to prepare a fully bio-based coating liquid, and after adding hydrophobic nanomaterials and polydimethylsiloxane, a hydrophobic double-modified fully bio-based coating liquid is obtained. The prepared double-modified fully bio-based polyurethane coated fertilizer has a significantly increased water contact angle, a better hydrophobic effect, and reduces the cumulative nutrient release rate of nitrogen, greatly improves the release performance, and prolongs the controlled release period of the coated fertilizer. Using bio-based polyols and bio-based isocyanates as raw materials, it is non-toxic and tasteless, has good hydrophobicity and chemical stability, and has a wide range of applications.

[0026] (2) When coating the fertilizer particles, the present invention uses a fully bio-based coating liquid for the first four times, and only uses a double-modified fully bio-based coating liquid for the fifth time. While ensuring that the nutrient release rate is reduced and the nutrient release period is extended, the content of metal ions in the coated fertilizer is reduced, making it less likely to pollute the soil.

[0027] (3) The present invention simplifies the preparation process of the double-modified all-biobased polyurethane coated fertilizer, streamlines the production process, reduces the amount of nanomaterials used, and reduces the pollution caused by the accumulation of nanomaterials in the soil. The prepared film material is green, environmentally friendly and biodegradable. In the production process of polyurethane coated fertilizer, it is not necessary to use a large amount of organic solvents and organic additives, which is environmentally friendly and cost-saving, while also reducing the risk of environmental pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Nutrient release curves of the fully bio-based polyurethane coated fertilizer, the hydrophobically modified fully bio-based polyurethane coated fertilizer and the double-modified fully bio-based polyurethane coated fertilizer prepared by the present invention;

[0029] Figure 2 The water contact angle diagrams of the fully bio-based polyurethane coated fertilizer, the hydrophobically modified fully bio-based polyurethane coated fertilizer and the double-modified fully bio-based polyurethane coated material prepared in the present invention. DETAILED DESCRIPTION

[0030] The technical solutions in the present invention will be described clearly and completely below in conjunction with the specific implementation of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] The methods described in the embodiments of the present invention are conventional methods unless otherwise specified. The materials, reagents, etc. used can be obtained from commercial sources unless otherwise specified.

[0032] The castor oil polyol used in the examples and comparative examples of the present invention was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; the bio-based polyisocyanate was purchased from Mitsui Chemicals, Inc. of Japan.

[0033] Example 1

[0034] A method for preparing a double-modified all-biobased polyurethane coated fertilizer comprises the following steps:

[0035] (1) Weigh 4.00 g of copper hydroxide and 0.95 g of lauric acid, then add 25 mL of 95% ethanol and 25 mL of distilled water, stir and react for 1.25 h under ultrasonic vibration conditions to obtain a nanomaterial suspension, dry the suspension at 105° C. to constant weight, and then dry to obtain a hydrophobic nanomaterial.

[0036] (2) Castor oil polyol and bio-based polyisocyanate are fully mixed at room temperature in a molar ratio of -NCO to -OH of 1:1 to obtain a fully bio-based coating liquid. The fully bio-based coating liquid is divided into 5 parts, four of which are reserved, and the remaining part is added with hydrophobic nanomaterials and polydimethylsiloxane, and the mixture is stirred and mixed at room temperature to obtain a double-modified fully bio-based coating liquid; the mass ratio of castor oil polyol, isocyanate, hydrophobic nanomaterial and polydimethylsiloxane in the double-modified fully bio-based coating liquid is 66:34:7:5.

[0037] (3) Pour 1kg of urea into a drum coating machine and preheat at 80℃ for 8min. The particle size of the urea granules is 2.5mm. After preheating, weigh 10g of the all-bio-based coating liquid and add it to the urea granules. The all-bio-based coating liquid undergoes a process of sticking-adhesion-dispersion-drying on the surface of the fertilizer granules for 6min, and then the all-bio-based coating liquid solidifies into a film on the surface of the urea granules. After the film shell is completely dried, the first-coated urea granules are completed. Continue to preheat 1kg of urea granules at 80℃ in a drum coating machine for 8min. After preheating, add 10g of the all-bio-based coating liquid. The all-bio-based coating liquid undergoes a process of sticking-adhesion-dispersion-drying on the surface of the fertilizer granules for 6min, and then the all-bio-based coating liquid solidifies into a film on the surface of the urea granules. After the film shell is completely dried, the second-coated urea granules are completed. Continue to preheat 1kg of urea granules that have completed the second coating at 80℃ in the drum coating machine for 8min. After the preheating is completed, add 10g of all-bio-based coating liquid. The all-bio-based coating liquid undergoes a process of sticking-adhesion-dispersion-drying on the surface of the fertilizer granules for 6min, so that the all-bio-based coating liquid solidifies into a film on the surface of the urea granules. After the film shell is completely dried, the urea granules that have completed the third coating are obtained. Continue to preheat 1kg of urea granules that have completed the third coating at 80℃ in the drum coating machine for 8min. After the preheating is completed, add 10g of all-bio-based coating liquid. The all-bio-based coating liquid undergoes a process of sticking-adhesion-dispersion-drying on the surface of the fertilizer granules for 6min, so that the all-bio-based coating liquid solidifies into a film on the surface of the urea granules. After the film shell is completely dried, the urea granules that have completed the fourth coating are obtained. For the last time, the double-modified all-biobased coating liquid was added to the urea particles that had completed four coatings, with the mass ratio of the double-modified all-biobased coating liquid to the fertilizer particles being 25:1, until the film mass accounted for 5% of the mass of the fertilizer core particles. The double-modified all-biobased coating liquid was subjected to a process of adhesion-adhesion-dispersion-drying on the surface of the fertilizer particles for 6 minutes before solidifying into a film. After the film shell was completely dried, the double-modified all-biobased polyurethane coated fertilizer was obtained.

[0038] Example 2

[0039] A method for preparing a double-modified all-biobased polyurethane coated fertilizer comprises the following steps:

[0040] (1) Weigh 4.00 g of copper hydroxide and 0.96 g of lauric acid, then add 25 mL of 95% ethanol and 25 mL of distilled water, stir and react for 1.5 h under ultrasonic vibration conditions to obtain a nanomaterial suspension, dry the suspension at 105° C. to constant weight, and then dry to obtain a hydrophobic nanomaterial.

[0041] (2) Soybean oil polyol and bio-based polyisocyanate are fully mixed at room temperature in a molar ratio of -NCO to -OH of 1:1 to obtain a fully bio-based coating liquid. The fully bio-based coating liquid is divided into 5 parts, four of which are reserved, and the remaining part is added with hydrophobic nanomaterials and polydimethylsiloxane, and the mixture is stirred and mixed at room temperature to obtain a double-modified fully bio-based coating liquid; the mass ratio of soybean oil polyol, bio-based isocyanate, hydrophobic nanomaterial and polydimethylsiloxane in the double-modified fully bio-based coating liquid is 66:34:7:5.

[0042] (3) Pour 1kg of urea into a drum coating machine and preheat at 82℃ for 9min. The particle size of the urea granules is 2.5mm. After preheating, weigh 10g of the all-bio-based coating liquid and add it to the urea granules. The all-bio-based coating liquid undergoes a process of sticking-adhesion-dispersion-drying on the surface of the fertilizer granules for 6min, and then the all-bio-based coating liquid solidifies into a film on the surface of the urea granules. After the film shell is completely dried, the first-coated urea granules are completed. Continue to preheat 1kg of urea granules at 82℃ in a drum coating machine for 9min. After preheating, add 10g of the all-bio-based coating liquid. The all-bio-based coating liquid undergoes a process of sticking-adhesion-dispersion-drying on the surface of the fertilizer granules for 6min, and then the all-bio-based coating liquid solidifies into a film on the surface of the urea granules. After the film shell is completely dried, the second-coated urea granules are completed. Continue to preheat 1kg of urea granules that have completed the second coating at 82℃ in the drum coating machine for 9 minutes. After the preheating is completed, 10g of all-bio-based coating liquid is added. The all-bio-based polyurethane coating liquid undergoes a process of sticking-adhesion-dispersion-drying on the surface of the fertilizer granules for 6 minutes, so that the all-bio-based coating liquid solidifies into a film on the surface of the urea granules. After the film shell is completely dried, the urea granules that have completed the third coating are obtained. Continue to preheat 1kg of urea granules that have completed the third coating at 82℃ in the drum coating machine for 9 minutes. After the preheating is completed, 10g of all-bio-based coating liquid is added. The all-bio-based coating liquid undergoes a process of sticking-adhesion-dispersion-drying on the surface of the fertilizer granules for 6 minutes, so that the all-bio-based coating liquid solidifies into a film on the surface of the urea granules. After the film shell is completely dried, the urea granules that have completed the fourth coating are obtained. For the last time, the double-modified all-biobased coating liquid is added to the urea particles that have completed four coatings, and the mass ratio of the double-modified all-biobased coating liquid to the fertilizer particles is 20:1, until the film mass accounts for 5% of the mass of the fertilizer core particles. The double-modified all-biobased coating liquid undergoes a process of sticking-adhesion-dispersion-drying on the surface of the fertilizer particles, which lasts for 6 minutes before solidifying into a film. After the film shell is completely dried, the double-modified all-biobased polyurethane coated fertilizer is obtained.

[0043] Example 3

[0044] A method for preparing a double-modified all-biobased polyurethane coated fertilizer comprises the following steps:

[0045] (1) Weigh 4.00 g of copper hydroxide and 0.97 g of lauric acid, then add 25 mL of 95% ethanol and 25 mL of distilled water, stir and react for 1.75 h under ultrasonic vibration conditions to obtain a nanomaterial suspension, dry the suspension at 105° C. to constant weight, and then dry to obtain a hydrophobic nanomaterial.

[0046] (2) Palm oil polyol and bio-based polyisocyanate are fully mixed at room temperature according to the molar ratio of -NCO to -OH of 1:1 to obtain a fully bio-based coating liquid. The fully bio-based polyurethane coating liquid is divided into 5 parts, four parts are reserved, and the remaining part is added with hydrophobic nanomaterials and polydimethylsiloxane, and the mixture is stirred and mixed at room temperature to obtain a double-modified fully bio-based coating liquid; the mass ratio of palm oil, bio-based isocyanate, hydrophobic nanomaterial and polydimethylsiloxane in the double-modified fully bio-based coating liquid is 66:34:7:5.

[0047] (3) Pour 1kg of urea into a drum coating machine and preheat at 84℃ for 10min. The particle size of the urea granules is 2.5mm. After preheating, weigh 10g of the all-bio-based coating liquid and add it to the urea granules. The all-bio-based coating liquid undergoes a process of sticking-adhesion-dispersion-drying on the surface of the fertilizer granules for 6min, and then the all-bio-based coating liquid solidifies into a film on the surface of the urea granules. After the film shell is completely dried, the first-coated urea granules are obtained. Continue to preheat 1kg of urea granules at 84℃ in a drum coating machine for 10min. After preheating, add 10g of the all-bio-based coating liquid. The all-bio-based coating liquid undergoes a process of sticking-adhesion-dispersion-drying on the surface of the fertilizer granules for 6min, and then the all-bio-based coating liquid solidifies into a film on the surface of the urea granules. After the film shell is completely dried, the second-coated urea granules are obtained. Continue to preheat 1kg of urea granules that have completed the second coating at 84°C in a drum coating machine for 10 minutes. After the preheating is completed, 10g of all-biobased coating liquid is added. The all-biobased coating liquid undergoes a process of sticking-adhesion-dispersion-drying on the surface of the fertilizer granules for 6 minutes, and then the all-biobased coating liquid solidifies into a film on the surface of the urea granules. After the film shell is completely dried, urea granules that have completed the third coating are obtained. Continue to preheat 1kg of urea granules that have completed the third coating at 84°C in a drum coating machine for 10 minutes. After the preheating is completed, 10g of all-biobased coating liquid is added. The all-biobased coating liquid undergoes a process of sticking-adhesion-dispersion-drying on the surface of the fertilizer granules for 6 minutes, and then the all-biobased coating liquid solidifies into a film on the surface of the urea granules. After the film shell is completely dried, urea granules that have completed the fourth coating are obtained. For the last time, the double-modified all-biobased coating liquid was added to the urea particles that had completed four coatings, with the mass ratio of the double-modified all-biobased coating liquid to the fertilizer particles being 50:3, until the film mass accounted for 5% of the mass of the fertilizer core particles. The double-modified all-biobased coating liquid was subjected to a process of adhesion-adhesion-dispersion-drying on the surface of the fertilizer particles for 6 minutes before solidifying into a film. After the film shell was completely dried, the double-modified all-biobased polyurethane coated fertilizer was obtained.

[0048] Example 4

[0049] A method for preparing a double-modified all-biobased polyurethane coated fertilizer comprises the following steps:

[0050] (1) Weigh 4.00 g of copper hydroxide and 1 g of lauric acid, then add 25 mL of 95% ethanol and 25 mL of distilled water, stir and react for 2 h under ultrasonic vibration conditions to obtain a nanomaterial suspension, dry the suspension at 105° C. to constant weight, and then dry to obtain a hydrophobic nanomaterial.

[0051] (2) Castor oil polyol and bio-based polyisocyanate are fully mixed at room temperature in a molar ratio of -NCO to -OH of 1:1 to obtain a bio-based coating liquid. The all-bio-based coating liquid is divided into 5 parts, four parts are reserved, and the remaining part is added with hydrophobic nanomaterials and polydimethylsiloxane, and the mixture is stirred and mixed at room temperature to obtain a double-modified all-bio-based coating liquid; the mass ratio of castor oil polyol, isocyanate, hydrophobic nanomaterial and polydimethylsiloxane in the double-modified all-bio-based coating liquid is 66:34:7:5.

[0052] (3) Pour 1kg of urea into a drum coating machine and preheat at 85℃ for 12min. The particle size of the urea granules is 2.5mm. After preheating, weigh 10g of the all-bio-based coating liquid and add it to the urea granules. The all-bio-based coating liquid undergoes a process of sticking-adhesion-dispersion-drying on the surface of the fertilizer granules for 6min, and then the all-bio-based coating liquid solidifies into a film on the surface of the urea granules. After the film shell is completely dried, the first-coated urea granules are completed. Continue to preheat 1kg of urea granules at 85℃ in a drum coating machine for 12min. After preheating, add 10g of the all-bio-based coating liquid. The all-bio-based coating liquid undergoes a process of sticking-adhesion-dispersion-drying on the surface of the fertilizer granules for 6min, and then the all-bio-based coating liquid solidifies into a film on the surface of the urea granules. After the film shell is completely dried, the second-coated urea granules are completed. Continue to preheat 1kg of urea granules that have completed the second coating at 85℃ in the drum coating machine for 12 minutes. After the preheating is completed, 10g of all-bio-based coating liquid is added. The all-bio-based coating liquid undergoes a process of sticking-adhesion-dispersion-drying on the surface of the fertilizer granules for 6 minutes, so that the all-bio-based coating liquid solidifies into a film on the surface of the urea granules. After the film shell is completely dried, the urea granules that have completed the third coating are obtained. Continue to preheat 1kg of urea granules that have completed the third coating at 85℃ in the drum coating machine for 12 minutes. After the preheating is completed, 10g of all-bio-based coating liquid is added. The all-bio-based coating liquid undergoes a process of sticking-adhesion-dispersion-drying on the surface of the fertilizer granules for 6 minutes, so that the all-bio-based coating liquid solidifies into a film on the surface of the urea granules. After the film shell is completely dried, the urea granules that have completed the fourth coating are obtained. For the last time, the double-modified all-biobased coating liquid was added to the urea particles that had completed four coatings, with the mass ratio of the double-modified all-biobased coating liquid to the fertilizer particles being 50:3, until the film mass accounted for 5% of the mass of the fertilizer core particles. The double-modified all-biobased coating liquid was subjected to a process of adhesion-adhesion-dispersion-drying on the surface of the fertilizer particles for 6 minutes before solidifying into a film. After the film shell was completely dried, the double-modified all-biobased polyurethane coated fertilizer was obtained.

[0053] Comparative Example 1

[0054] A pure natural plant-derived polyurethane coated fertilizer, the preparation method is as follows:

[0055] (1) fully mixing castor oil polyol and bio-based polyisocyanate at room temperature in a molar ratio of -NCO to -OH of 1:1 to obtain a bio-based polyurethane coating solution;

[0056] (2) Pour 1 kg of urea into a drum coating machine and preheat for 10 minutes. The particle size of the urea particles is 2.5 mm. After preheating, weigh 10 g of the fully bio-based coating liquid and add it to the urea particles. The fully bio-based coating liquid undergoes a process of wetting-adhesion-dispersion-drying on the surface of the fertilizer particles for 6 minutes, and then the fully bio-based coating liquid solidifies into a film on the surface of the urea particles. After the film shell is completely dry, the above process is repeated four times until the film mass accounts for 5% of the mass of the fertilizer core particles.

[0057] Comparative Example 2

[0058] A fully bio-based polyurethane coated fertilizer with each layer being hydrophobically modified, and the preparation method is as follows:

[0059] (1) Weigh 4.00 g of copper hydroxide and 0.98 g of lauric acid, then add 25 mL of 95% ethanol and 25 mL of distilled water, stir and react for 1.5 h under ultrasonic vibration conditions to obtain a nanomaterial suspension, dry the suspension at 105° C. to constant weight, and obtain a hydrophobic nanomaterial after drying;

[0060] (2) according to the molar ratio of -NCO to -OH of 1:1, castor oil polyol and bio-based polyisocyanate were fully mixed at room temperature, 0.5 g of hydrophobic nanomaterial was added, and stirring and mixing were continued at room temperature to obtain a modified all-bio-based coating liquid;

[0061] (3) Pour 1 kg of urea into a drum coating machine and preheat for 10 minutes. The particle size of the urea particles is 2.5 mm. After preheating, weigh 10 g of the modified all-biobased coating liquid and add it to the urea particles. The modified all-biobased coating liquid undergoes a process of wetting-adhesion-dispersion-drying on the surface of the fertilizer particles for 6 minutes, and then the modified all-biobased coating liquid solidifies into a film on the surface of the urea particles. After the film shell is completely dry, the above process is repeated four times until the film mass accounts for 5% of the mass of the fertilizer core particles.

[0062] Comparative Example 3

[0063] A method for preparing an outermost hydrophobically modified all-biobased polyurethane coated fertilizer comprises the following steps:

[0064] (1) Weigh 4.00 g of copper hydroxide and 0.98 g of lauric acid, then add 25 mL of 95% ethanol and 25 mL of distilled water, stir and react for 1.5 h under ultrasonic vibration conditions to obtain a nanomaterial suspension, and dry the nanomaterial suspension at 105° C. to constant weight to obtain a dry hydrophobic nanomaterial;

[0065] (2) Castor oil polyol and bio-based polyisocyanate were mixed at room temperature in a molar ratio of -NCO to -OH of 1:1 to obtain a fully bio-based coating liquid; 2.8 g of hydrophobic nanomaterial was added, and stirring was continued at room temperature to obtain a hydrophobically modified fully bio-based coating liquid;

[0066] (3) Pour 1 kg of urea into a drum coating machine and preheat for 10 minutes. The particle size of the urea particles is 2.5 mm. After preheating, weigh 10 g of the all-biobased coating liquid and add it to the urea particles. The all-biobased coating liquid undergoes a process of wetting-adhesion-dispersion-drying on the surface of the fertilizer particles for 6 minutes, and then the all-biobased coating liquid solidifies into a film on the surface of the urea particles. After the film shell is completely dry, continue to add the all-biobased coating liquid to the urea particles. The above process is repeated three times; the hydrophobically modified all-biobased coating liquid is added to the urea particles for the last time until the film mass accounts for 5% of the mass of the fertilizer core particles.

[0067] Comparative Example 4 (Increasing the amount of hydrophobic nanomaterial)

[0068] A method for preparing an outermost hydrophobically modified all-biobased polyurethane coated fertilizer comprises the following steps:

[0069] (1) Weigh 4.00 g of copper hydroxide and 0.98 g of lauric acid, then add 25 mL of 95% ethanol and 25 mL of distilled water, stir and react for 1.5 h under ultrasonic vibration conditions to obtain a nanomaterial suspension, and dry the nanomaterial suspension at 105° C. to constant weight to obtain a dry hydrophobic nanomaterial;

[0070] (2) fully mixing castor oil polyol and bio-based polyisocyanate at room temperature in a molar ratio of -NCO to -OH of 1:1 to obtain a fully bio-based coating liquid; adding 3.5 g of hydrophobic nanomaterial, continuing to stir and mix at room temperature, and reacting to obtain a hydrophobically modified fully bio-based coating liquid;

[0071] (3) Pour 1 kg of urea into a drum coating machine and preheat for 10 minutes. The particle size of the urea particles is 2.5 mm. After preheating, weigh 10 g of the all-biobased coating liquid and add it to the urea particles. The all-biobased coating liquid undergoes a process of wetting-adhesion-dispersion-drying on the surface of the fertilizer particles for 6 minutes, and then the all-biobased polyurethane coating liquid solidifies into a film on the surface of the urea particles. After the film shell is completely dry, continue to add the all-biobased coating liquid to the urea particles. The above process is repeated three times; the hydrophobically modified all-biobased coating liquid is added to the urea particles for the last time until the film mass accounts for 5% of the mass of the fertilizer core particles.

[0072] Comparative Example 5 (Increasing the amount of hydrophobic nanomaterial)

[0073] A method for preparing an outermost hydrophobically modified all-biobased polyurethane coated fertilizer comprises the following steps:

[0074] (1) Weigh 4.00 g of copper hydroxide and 0.98 g of lauric acid, then add 25 mL of 95% ethanol and 25 mL of distilled water, stir and react for 1.5 h under ultrasonic vibration conditions to obtain a nanomaterial suspension, and dry the nanomaterial suspension at 105° C. to constant weight to obtain a dry hydrophobic nanomaterial;

[0075] (2) fully mixing castor oil polyol and bio-based polyisocyanate at room temperature in a molar ratio of -NCO to -OH of 1:1 to obtain a fully bio-based coating liquid; adding 4.2 g of hydrophobic nanomaterial, continuing to stir and mix at room temperature, and reacting to obtain a hydrophobically modified fully bio-based polyurethane coating liquid;

[0076] (3) Pour 1 kg of urea into a drum coating machine and preheat for 10 minutes. The particle size of the urea particles is 2.5 mm. After preheating, weigh 10 g of the all-biobased coating liquid and add it to the urea particles. The all-biobased coating liquid undergoes a process of wetting-adhesion-dispersion-drying on the surface of the fertilizer particles for 6 minutes, and then the all-biobased coating liquid solidifies into a film on the surface of the urea particles. After the film shell is completely dry, continue to add the all-biobased coating liquid to the urea particles. The above process is repeated three times; the hydrophobically modified all-biobased coating liquid is added to the urea particles for the last time until the film mass accounts for 5% of the mass of the fertilizer core particles.

[0077] Weigh 10 g of the coated fertilizers prepared in Examples 1-4 and Comparative Examples 1-5 respectively, with an error of ±0.01 g, put them into a 100-mesh nylon mesh bag, seal it, put it into a 250 mL plastic bottle, add 200 mL of distilled water, cover it and seal it, and place it in a biochemical constant temperature incubator at 25 ° C. The sampling time is 1d, 3d, 5d, 7d, 10d, 14d, 28d, 42d, and 56d, and the sampling time interval is 28d thereafter, until the cumulative nutrient dissolution rate reaches more than 80%, and the nitrogen content of the sample is determined by the Kjeldahl method; the cumulative nutrient release within 24h is the initial nutrient release rate, and the time when the cumulative nutrient release exceeds 80% is the cumulative nutrient release period of the coated fertilizer. The test results are shown in Table 1.

[0078] Table 1 Nutrient release test performance of coated fertilizers of Examples 1-4 and Comparative Examples 1-2

[0079]

[0080]

[0081] Table 1 shows the initial nutrient release rate and nutrient release period of the coated fertilizers prepared in the examples and comparative examples. The nutrient cumulative release curves of the double-modified all-biobased polyurethane coated fertilizers prepared in Examples 2 to 4 are basically consistent with that in Example 1. Figure 1 Only the nutrient cumulative release curve of Example 1 is taken as an example. The outermost hydrophobic modified all-biobased polyurethane coated fertilizer prepared in Comparative Examples 4 to 5 is basically the same as that in Comparative Example 3. Figure 1 Only the curve of Comparative Example 3 is taken as an example. Figure 1 The nutrient cumulative release curves of the pure natural plant-derived polyurethane coated fertilizer prepared in Comparative Example 1, each layer of hydrophobically modified all-biobased polyurethane coated fertilizer prepared in Example 2, the outermost layer of hydrophobically modified all-biobased polyurethane coated fertilizer prepared in Comparative Example 3, and the double-modified all-biobased polyurethane coated fertilizer prepared in Example 1 are shown in Tables 1 and Figure 1 As shown, the initial nutrient release rate of the all-bio-based polyurethane coated fertilizer prepared in Comparative Example 1 is greater than that of each layer of hydrophobically modified all-bio-based polyurethane coated fertilizer prepared in Comparative Example 2, and the nutrient release period is shorter than that of each layer of hydrophobically modified all-bio-based polyurethane coated fertilizer, and the cumulative nutrient release in 3d is more than 80%, indicating that the prepared coated fertilizer has poor controlled release performance. However, the controlled release performance of each layer of hydrophobically modified all-bio-based polyurethane coated fertilizer with the addition of nanomaterials is greatly improved. In order to reduce the consumption of nanomaterials in each layer of membrane liquid, when 2.8g of nanomaterial all-bio-based polyurethane coated fertilizer is added to the outermost layer, that is, the controlled release performance of Comparative Example 3 is relatively greatly improved, and the nutrient release period is extended, but it does not meet the nutrient demand of the crop during the entire growth period. As the amount of nanomaterial added in the outermost layer increases, its nutrient release period also increases. The nutrient release period of the all-bio-based polyurethane coated fertilizer with 3.5g of nanomaterial hydrophobically modified outermost layer, that is, Comparative Example 4, is extended, which meets the nutrient demand during the crop growth period. However, the nutrient release period of the fully bio-based polyurethane coated fertilizer with 4.2g of nanomaterial hydrophobically modified outer layer is only 52 days at most, which does not meet the nutritional needs of crops during the growth period. Therefore, adding more nanomaterials did not extend the controlled release period of the coated fertilizer, but instead decreased it. Reducing the amount of nanomaterials and adding surfactants effectively slowed down the entry of water into the membrane and the dissolution of nutrients out of the membrane, reducing the cumulative release rate of nitrogen and greatly improving the release performance.

[0082] Figure 2 The water contact angle diagram of the coating materials prepared in Example 1 and Comparative Examples 1, 2, 3, 4, and 5 of the present invention. Among them, A is the all-biobased polyurethane coating material prepared in Comparative Example 1, B is each layer of hydrophobically modified all-biobased polyurethane coating material prepared in Comparative Example 2, a, b, and c are the outermost hydrophobically modified all-biobased polyurethane coating materials of Comparative Examples 3, 4, and 5, respectively, and d is the outermost double-modified all-biobased polyurethane coating material of Example 1. Generally speaking, the larger the water contact angle, the better the hydrophobic effect. Figure 2As shown, the water contact angle of the surface of A is about 70.33°. With the addition of nanomaterials in each layer of membrane liquid, the water contact angle of B is about 82.54°, which is greater than A. In order to simplify the synthesis process of coated fertilizers, a is a thin film material with 2.8g of nanomaterials added to the outermost layer, and its water contact angle is about 85.62°, which is greater than B. When the amount of nanomaterials added to the outermost layer increases, the water contact angle also gradually increases. The water contact angle of b is about 86.62°, which is greater than a. The water contact angle of the surface of c is about 112.48°, and its water contact angle is significantly increased, but the controlled release performance is poor when culturing the nutrient release of coated fertilizers. When the amount of nanomaterials is reduced and non-toxic hydrophobic polydimethylsiloxane is added, the water contact angle of d increases to 105°, and the nutrient release period of the coated fertilizer is significantly extended. It shows that the double modification not only reduces the amount of nanomaterials used, but also makes it hydrophobic and water-repellent, thereby reducing the nutrient release rate of the coated fertilizer and extending the nutrient release period.

[0083] It should be noted that when the present invention involves a numerical range, it should be understood that the two endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as those in the embodiments, in order to avoid redundancy, the present invention describes a preferred embodiment. Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they know the basic creative concept. Therefore, the attached claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0084] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0085] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for preparing a double-modified all-biobased polyurethane coated fertilizer, characterized in that: The steps include: Preparation of hydrophobic nanomaterials: mixing alkali and fatty acid for reaction for 1.25 to 2 hours, and drying to obtain hydrophobic nanomaterials; Preparing a double-modified all-biobased coating liquid: mixing a bio-based polyol and an isocyanate; and then adding the obtained hydrophobic nanomaterial and a surfactant to obtain a double-modified all-biobased coating liquid; The mass ratio of bio-based polyol, isocyanate, hydrophobic nanomaterial and surfactant in the double-modified all-bio-based coating solution is 60-70:30-40:6-8:4-6; the surfactant is polydimethylsiloxane; Coating: mixing the fertilizer particles with the prepared double-modified all-biobased coating liquid, and curing them to obtain double-modified all-biobased polyurethane coated fertilizer; The specific method of the coating is: After preheating the fertilizer granules, add the fully bio-based coating liquid, and solidify into a film to obtain the first-coated urea granules; After preheating the urea granules that have completed the primary coating, adding the full bio-based coating liquid, and curing the film to obtain the urea granules that have completed the secondary coating; After preheating the urea granules that have completed the secondary coating, a fully bio-based coating liquid is added, and after solidification into a film, urea granules that have completed the third coating are obtained; After preheating the urea granules that have completed the third coating, adding the full bio-based coating liquid, and curing the film to obtain the urea granules that have completed the fourth coating; After preheating the urea particles that have completed four coatings, the double-modified all-bio-based coating liquid is added, and after solidification into a film, the double-modified all-bio-based polyurethane coated fertilizer is obtained.

2. The method for preparing the double-modified all-biobased polyurethane coated fertilizer according to claim 1, characterized in that: When preparing the hydrophobic nano material, the base is copper hydroxide, the fatty acid is lauric acid, and the solvent is ethanol solution.

3. The method for preparing the double-modified all-biobased polyurethane coated fertilizer according to claim 1, characterized in that: The bio-based polyol is one or more of castor oil polyol, soybean oil polyol and palm oil polyol.

4. The method for preparing the double-modified all-biobased polyurethane coated fertilizer according to claim 1, characterized in that: The isocyanate is one or both of polymethylene polyphenyl isocyanate and bio-based polyisocyanate.

5. The method for preparing the double-modified all-biobased polyurethane coated fertilizer according to claim 1, characterized in that: During coating, the mass ratio of the double-modified all-biobased coating liquid to the fertilizer particles is 50:2-3.

6. The method for preparing the double-modified all-biobased polyurethane coated fertilizer according to claim 1, characterized in that: During the coating process, the fertilizer particles are preheated at a temperature of 80 to 85° C. for 8 to 12 minutes.

7. The method for preparing the double-modified all-biobased polyurethane coated fertilizer according to claim 1, characterized in that: The preparation method of the all-biobased coating liquid is as follows: castor oil polyol and bio-based polyisocyanate are fully and uniformly mixed at room temperature according to a molar ratio of -NCO to -OH of 1:1 to obtain the all-biobased coating liquid.

8. A double-modified all-biobased polyurethane coated fertilizer prepared by the preparation method according to any one of claims 1 to 7.

Images