Preparation method of ethyl cellulose and isocyanate cross-linked coated urea slow-release fertilizer

Abstract

The invention discloses a preparation method of an ethyl cellulose and isocyanate cross-linked coated urea slow-release fertilizer, and relates to a preparation method of a urea slow-release fertilizer. The invention aims to solve the problems that the existing nitrogen fertilizer is low in utilization rate and easy to absorb moisture and cake, a polyurethane coating material is non-degradable, and pure ethyl cellulose is insufficient in mechanical strength and limited in water resistance and is not beneficial to being used as a coating matrix of the fertilizer. The method comprises the following steps: 1, preparing an ethyl cellulose cross-linked isocyanate enveloping solution; and 2, preparing the ethyl cellulose and isocyanate cross-linked coated urea slow-release fertilizer. According to the preparation method, etherified derivative ethyl cellulose of cellulose is taken as a raw material, and the defects that a pure ethyl cellulose membrane is insufficient in mechanical strength, limited in water resistance and low in nutrient separation control precision are overcome by utilizing isocyanate crosslinking modification. The prepared slow-release fertilizer has the advantages of being simple in process, low in cost, environmentally friendly, degradable in matrix, capable of effectively preventing urea from absorbing moisture and caking and the like, and is suitable for large-scale preparation and used in agricultural production.

Description

Technical Field

[0001] This invention relates to a method for preparing urea slow-release fertilizer. Background Technology

[0002] Under immense pressure to ensure global food security, improving fertilizer efficiency and environmentally friendly utilization has become a core issue for sustainable agricultural development. However, traditional fertilizers, especially nitrogen fertilizers, suffer losses exceeding 40% after application due to leaching, volatilization, and denitrification. This not only represents significant economic waste and repetitive labor input but also triggers a series of serious environmental problems such as water eutrophication, soil acidification, and greenhouse gas emissions. Furthermore, the inherent hygroscopicity of fertilizers like urea makes them highly susceptible to moisture absorption and clumping during storage and transportation, causing inconvenience in application, inaccurate dosage, and further affecting the uniformity and efficiency of fertilization. Developing efficient and environmentally friendly new fertilizers is an inevitable choice to overcome resource and environmental constraints and practice green agriculture. Slow-release fertilizers, by regulating the nutrient release rate to synchronize with crop needs, represent a key technological direction for improving fertilizer utilization. Among these, coating technology has become the mainstream of research and application due to its strong controllability and relatively mature process. An ideal coating can not only precisely control nutrient release and reduce losses but also effectively isolate moisture through its physical barrier function, fundamentally solving the problem of fertilizer caking. An ideal coating material needs to possess good film-forming properties, moderate permeability, environmental friendliness, and economic efficiency. Currently widely used inorganic coating materials (such as sulfur) suffer from high brittleness and uneven release; while petroleum-based polymer coating materials (such as polyolefins), although stable, lead to the accumulation of "white pollution" in soil due to their non-degradable nature, contradicting the concept of sustainable development. Therefore, naturally derived, biodegradable polymers, such as cellulose, starch, lignin, and their derivatives, are considered highly promising environmentally friendly coating materials due to their abundant resources, low cost, and green renewable characteristics.

[0003] Ethyl cellulose, as an important etherified derivative of cellulose, inherits the renewability and biodegradability of cellulose, and its solubility in organic solvents and film-forming processing properties are significantly improved through ethyl substitution, making it an ideal matrix material for preparing coated slow-release fertilizers. However, pure ethyl cellulose membranes often suffer from insufficient mechanical strength, limited water resistance, and low precision in nutrient separation, which restricts their application in high-performance slow-release fertilizers.

[0004] In summary, using green and renewable ethyl cellulose as a base material and cross-linking it with isocyanate to develop coated urea with excellent mechanical properties, precise slow-release characteristics, moisture-proof and anti-caking ability, and complete biodegradability potential is an effective strategy to solve the problems of pollution, inconvenience of application, and synthetic polymer residues of traditional fertilizers. Summary of the Invention

[0005] The purpose of this invention is to address the problems of low nitrogen fertilizer utilization, easy moisture absorption and clumping, non-degradable polyurethane coating materials, and insufficient mechanical strength and limited water resistance of pure ethyl cellulose, which are unsuitable for use as a coating matrix for fertilizers.

[0006] A method for preparing urea slow-release fertilizer cross-coated with ethyl cellulose and isocyanate is provided.

[0007] A method for preparing a urea slow-release fertilizer cross-coated with ethyl cellulose and isocyanate is specifically carried out according to the following steps:

[0008] I. Preparation of ethyl cellulose crosslinked isocyanate coating solution:

[0009] ① Disperse the isocyanate monomer in ethyl acetate and stir to obtain an isocyanate solution;

[0010] ② Add ethyl cellulose to the isocyanate solution and stir to react, to obtain an ethyl cellulose cross-linked isocyanate coating solution;

[0011] II. Preparation of Ethyl Cellulose and Isocyanate Cross-coated Urea Slow-Release Fertilizer:

[0012] ① Place the urea granules in an oven and preheat;

[0013] ② Pour the ethyl cellulose crosslinked isocyanate coating solution into the atomizing spray gun;

[0014] ③ Place the preheated urea granules in a disc granulator, spray them with a coating solution for coating, and then put them in an oven for drying to obtain ethyl cellulose and isocyanate cross-coated urea slow-release fertilizer.

[0015] The principle of this invention:

[0016] Isocyanate crosslinking agents contain highly active -NCO groups, which can react with hydroxyl groups and other groups on the ethyl cellulose molecular chain to form stable urethane bonds. This invention constructs a three-dimensional crosslinking network by chemically reacting isocyanate monomers with hydroxyl groups on the ethyl cellulose molecular chain. Through chemical crosslinking modification, the network structure of the membrane can be effectively enhanced, thereby precisely controlling its swelling properties, mechanical properties, and nutrient permeation rate; thus, a green coating material with excellent mechanical properties, water resistance, and controllable degradation characteristics is prepared.

[0017] Compared with the prior art, the present invention has the following significant advantages:

[0018] I. Green and environmentally friendly, sustainable from the source: The main raw material ethyl cellulose in this invention comes from waste corn stalks, which is a renewable resource; after isocyanate participates in the reaction, it forms a polymer with high stability; the final cross-linked polymer has the potential to be biodegradable, which fundamentally avoids the "white pollution" problem caused by the long-term residue of traditional synthetic polymer coatings such as polyurethane in the soil, and meets the requirements of green agricultural development.

[0019] Second, this invention overcomes the shortcomings of low strength and high brittleness of pure ethyl cellulose membranes through chemical cross-linking, forming a tough and dense coating that is not easily damaged during storage, transportation and application.

[0020] Third, the cross-linked network in this invention improves the hydrophobicity and anti-swelling ability of the membrane, effectively slows down the rate of water penetration and nutrient dissolution, thereby significantly improving fertilizer utilization and reducing nutrient loss.

[0021] IV. By changing process parameters such as the amount of crosslinking agent and the number of coating layers (the weight gain rate of urea particles after coating is 1%~5%), the release period of nutrients can be flexibly adjusted to meet the nutritional needs of different crops and different growth stages.

[0022] V. The preparation process of this invention is carried out at room temperature, without the need for complex equipment or harsh conditions, and has low energy consumption; the solution spraying-disc granulation process used is a mature industrial technology, which is easy to achieve large-scale production, with good coating uniformity and controllable production costs.

[0023] VI. This invention can effectively prevent fertilizer from caking. The dense hydrophobic film formed by cross-linking can effectively block the direct contact between environmental moisture and the urea core, preventing urea from absorbing moisture and deliquescing from the source. This completely solves the problem of traditional urea easily clumping during storage, ensuring good fluidity and ease of application of the fertilizer.

[0024] This invention provides a urea slow-release fertilizer that is cross-linked with ethyl cellulose and isocyanate. Attached Figure Description

[0025] Figure 1 Figure 1 shows scanning electron microscope (SEM) images. Figure 2(a) is a scanning electron microscope image of an ethyl cellulose membrane, and Figure 3(b) is a scanning electron microscope image of an ethyl cellulose cross-linked isocyanate membrane.

[0026] Figure 2 The figures show infrared spectra. Figure (a) shows the infrared spectrum of isocyanate, Figure (b) shows the infrared spectrum of ethyl cellulose, and Figure (c) shows the infrared spectrum of ethyl cellulose cross-linked isocyanate membrane.

[0027] Figure 3Figure 1 shows the release curves of urea and the prepared slow-release fertilizer in water. Figure 2(a) shows the release curve of ordinary urea in water, Figure 2(b) shows the release curve of ethyl cellulose coated urea fertilizer in water, and Figure 2(c) shows the release curve of ethyl cellulose and isocyanate cross-linked coated urea slow-release fertilizer prepared in Example 1 in water.

[0028] Figure 4 The figures show the release curves of urea and the prepared slow-release fertilizer in the soil. Figure (a) shows the release curve of ordinary urea in the soil, Figure (b) shows the release curve of ethyl cellulose coated urea fertilizer in the soil, and Figure (c) shows the release curve of ethyl cellulose and isocyanate cross-linked coated urea slow-release fertilizer prepared in Example 1 in the soil.

[0029] Figure 5 The figures show the dry and fresh weights of cherry radish fruits before and after fertilization. In the figures, the left side shows the dry and fresh weights of urea slow-release fertilizer with cross-linked ethyl cellulose and isocyanate prepared in Example 1, the middle side shows the dry and fresh weights of ordinary urea, and the right side shows the dry and fresh weights of the blank control group without fertilizer.

[0030] Figure 6 The figure shows the hygroscopicity of the ethyl cellulose and isocyanate cross-coated urea slow-release fertilizer prepared in Example 1 in a constant temperature and humidity incubator with a relative humidity of 50%. In the figure, (a) shows the change in compressive strength of the ethyl cellulose and isocyanate cross-coated urea slow-release fertilizer prepared in Example 1 after 21 days of moisture absorption, and (b) shows the change in mass of the ethyl cellulose and isocyanate cross-coated urea slow-release fertilizer prepared in Example 1 after 21 days of moisture absorption. Detailed Implementation

[0031] Specific Implementation Method 1: This implementation method is a preparation method of urea slow-release fertilizer cross-coated with ethyl cellulose and isocyanate, specifically completed according to the following steps:

[0032] I. Preparation of ethyl cellulose crosslinked isocyanate coating solution:

[0033] ① Disperse the isocyanate monomer in ethyl acetate and stir to obtain an isocyanate solution;

[0034] ② Add ethyl cellulose to the isocyanate solution and stir to react, to obtain an ethyl cellulose cross-linked isocyanate coating solution;

[0035] II. Preparation of Ethyl Cellulose and Isocyanate Cross-coated Urea Slow-Release Fertilizer:

[0036] ① Place the urea granules in an oven and preheat;

[0037] ② Pour the ethyl cellulose crosslinked isocyanate coating solution into the atomizing spray gun;

[0038] ③ Place the preheated urea granules in a disc granulator, spray them with a coating solution for coating, and then put them in an oven for drying to obtain ethyl cellulose and isocyanate cross-coated urea slow-release fertilizer.

[0039] This embodiment uses ethyl cellulose, an etherified derivative of cellulose, as raw material. Isocyanate crosslinking modification addresses the shortcomings of pure ethyl cellulose membranes, such as insufficient mechanical strength, limited water resistance, and low precision in nutrient separation. Furthermore, the slow-release fertilizer prepared by this invention has advantages such as simple processing, low cost, environmental friendliness, biodegradable substrate, and effective prevention of urea hygroscopic agglomeration, making it suitable for large-scale production and application in agricultural production.

[0040] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the stirring speed in step one ① is 300 r / min to 1500 r / min, and the stirring time is 1 h to 8 h. The other steps are the same as in Specific Implementation Method One.

[0041] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 1 or 2 in that: the isocyanate monomer mentioned in step 1① is 2,6-toluene diisocyanate (TDI); the mass ratio of the isocyanate monomer to the volume of ethyl acetate in step 1① is (0.25g~25g):(10mL~1000mL). Other steps are the same as in Specific Implementation Method 1 or 2.

[0042] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that: the stirring reaction temperature in step one ② is 20℃~50℃, the rotation speed is 300r / min~1500r / min, and the stirring time is 1h~8h. Other steps are the same as in Specific Implementation Methods One to Three.

[0043] Specific Implementation Method Five: The difference between this implementation method and Specific Implementation Methods One to Four is that the mass ratio of ethyl cellulose and isocyanate monomer in step one ② is (0.75g~75g):(0.25g~25g). The other steps are the same as in Specific Implementation Methods One to Four.

[0044] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the preheating temperature in step two① is 60℃~80℃, and the preheating time is 0.5h~2h. The other steps are the same as in Specific Implementation Methods One to Five.

[0045] Specific Implementation Method Seven: The difference between this implementation method and Specific Implementation Methods One to Six is ​​that the weight gain rate of the urea particles after coating in step two ③ is 1% to 5%. The other steps are the same as those in Specific Implementation Methods One to Six.

[0046] Specific Implementation Method Eight: The difference between this implementation method and Specific Implementation Methods One to Seven is that the disc tilt angle of the disc granulator described in step two ③ is 30°~60°, and the disc rotation speed is 20r / min~40r / min. Other steps are the same as in Specific Implementation Methods One to Seven.

[0047] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that the drying temperature in step two ③ is 60℃~80℃, and the drying time is 2h~4h. The other steps are the same as in Specific Implementation Methods One to Eight.

[0048] Specific implementation method ten: This implementation method is a urea slow-release fertilizer cross-coated with ethyl cellulose and isocyanate.

[0049] The beneficial effects of the present invention are verified using the following embodiments:

[0050] Example 1: A method for preparing a urea slow-release fertilizer cross-coated with ethyl cellulose and isocyanate, specifically completed according to the following steps:

[0051] I. Preparation of ethyl cellulose crosslinked isocyanate coating solution:

[0052] ① Disperse 0.2540g of isocyanate monomer in 10mL of ethyl acetate and stir at 300r / min for 1h to obtain an isocyanate solution;

[0053] The isocyanate monomer mentioned in step 1① is 2,6-toluene diisocyanate (TDI).

[0054] ② Add 0.7502g of dried ethyl cellulose to the isocyanate solution and stir for 4h at 20℃ and a stirring speed of 300r / min to obtain the coating solution;

[0055] II. Preparation of Ethyl Cellulose and Isocyanate Cross-coated Urea Slow-Release Fertilizer:

[0056] ① Place 5g of uniformly sized and shaped urea granules into a 60℃ oven and preheat for 1 hour;

[0057] ② Pour the coating solution into the atomizing spray gun;

[0058] ③ Place 5g of preheated urea granules in a disc granulator, spray with a coating solution for coating, and then place in a 60℃ oven for drying for 2 hours to obtain ethyl cellulose and isocyanate cross-coated urea slow-release fertilizer.

[0059] In step 2③, the weight gain rate of the urea particles after coating was 3%.

[0060] The disc tilt angle of the disc granulator described in step 2③ is 50°, and the disc rotation speed is 30 r / min.

[0061] Example 2: A method for preparing a urea slow-release fertilizer cross-coated with ethyl cellulose and isocyanate, specifically completed according to the following steps:

[0062] I. Preparation of ethyl cellulose crosslinked isocyanate coating solution:

[0063] ① Disperse 1.031g of isocyanate monomer in 40mL of ethyl acetate and stir at 500r / min for 1h to obtain an isocyanate solution;

[0064] The isocyanate monomer mentioned in step 1① is 2,6-toluene diisocyanate (TDI).

[0065] ② Add 3.013g of dried ethyl cellulose to the isocyanate solution and stir for 4h at 20℃ and a stirring speed of 500r / min to obtain the coating solution;

[0066] II. Preparation of Ethyl Cellulose and Isocyanate Cross-coated Urea Slow-Release Fertilizer:

[0067] ① Place 20g of uniformly sized and shaped urea granules into an 80℃ oven and preheat for 1 hour;

[0068] ② Pour the coating solution into the atomizing spray gun;

[0069] ③ Place 20g of preheated urea granules in a disc granulator, spray with a coating solution for coating, and then place in an 80℃ oven for drying for 2 hours to obtain ethyl cellulose and isocyanate cross-coated urea slow-release fertilizer.

[0070] In step 2③, the weight gain rate of the urea particles after coating was 3%.

[0071] The disc tilt angle of the disc granulator described in step 2③ is 50°, and the disc rotation speed is 30 r / min.

[0072] Example 3: A method for preparing a urea slow-release fertilizer cross-coated with ethyl cellulose and isocyanate, specifically completed according to the following steps:

[0073] I. Preparation of ethyl cellulose crosslinked isocyanate coating solution:

[0074] ① Disperse 1.004 g of isocyanate monomer in 30 mL of ethyl acetate and stir at 800 r / min for 1 h to obtain an isocyanate solution;

[0075] The isocyanate monomer mentioned in step 1① is 2,6-toluene diisocyanate (TDI).

[0076] ② Add 3.006 g of dried ethyl cellulose to the isocyanate solution and stir for 4 h at 40 °C and a stirring speed of 800 r / min to obtain the coating solution;

[0077] II. Preparation of Ethyl Cellulose and Isocyanate Cross-coated Urea Slow-Release Fertilizer:

[0078] ① Place 10g of uniformly sized and shaped urea granules into a 60℃ oven and preheat for 1 hour;

[0079] ② Pour the coating solution into the atomizing spray gun;

[0080] ③ Place 10g of preheated urea granules in a disc granulator, spray with a coating solution for coating, and then place in a 60℃ oven for drying for 2 hours to obtain ethyl cellulose and isocyanate cross-coated urea slow-release fertilizer.

[0081] In step 2③, the weight gain rate of the urea particles after coating was 3%.

[0082] The disc tilt angle of the disc granulator described in step 2③ is 50°, and the disc rotation speed is 30 r / min.

[0083] Example 4: A method for preparing a urea slow-release fertilizer cross-coated with ethyl cellulose and isocyanate, specifically completed according to the following steps:

[0084] I. Preparation of ethyl cellulose crosslinked isocyanate coating solution:

[0085] ① Disperse 1.013g of isocyanate monomer in 50mL of ethyl acetate and stir at 800r / min for 1h to obtain an isocyanate solution;

[0086] The isocyanate monomer mentioned in step 1① is 2,6-toluene diisocyanate (TDI).

[0087] ② Add 4.014 g of dried ethyl cellulose to the isocyanate solution and stir for 2 h at 40 °C and a stirring speed of 800 r / min to obtain the coating solution.

[0088] II. Preparation of Ethyl Cellulose and Isocyanate Cross-coated Urea Slow-Release Fertilizer:

[0089] ① Place 10g of uniformly sized and shaped urea granules into a 60℃ oven and preheat for 1 hour;

[0090] ② Pour the coating solution into the atomizing spray gun;

[0091] ③ Place 10g of preheated urea granules in a disc granulator, spray with a coating solution for coating, and then place in a 60℃ oven for drying for 2 hours to obtain ethyl cellulose and isocyanate cross-coated urea slow-release fertilizer.

[0092] In step 2③, the weight gain rate of the urea particles after coating was 4%.

[0093] The disc tilt angle of the disc granulator described in step 2③ is 50°, and the disc rotation speed is 30 r / min.

[0094] Example 5: A method for preparing a urea slow-release fertilizer cross-coated with ethyl cellulose and isocyanate, specifically completed according to the following steps:

[0095] I. Preparation of ethyl cellulose crosslinked isocyanate coating solution:

[0096] ① Disperse 0.2501g of isocyanate monomer in 10mL of ethyl acetate and stir at 800r / min for 1h to obtain an isocyanate solution;

[0097] The isocyanate monomer mentioned in step 1① is 2,6-toluene diisocyanate (TDI).

[0098] ② Add 0.7511g of dried ethyl cellulose to the isocyanate solution and stir for 2 hours at 20℃ and a stirring speed of 800r / min to obtain the coating solution.

[0099] II. Preparation of Ethyl Cellulose and Isocyanate Cross-coated Urea Slow-Release Fertilizer:

[0100] ① Place 5g of uniformly sized and shaped urea granules into an 80℃ oven and preheat for 1 hour;

[0101] ② Pour the coating solution into the atomizing spray gun;

[0102] ③ Place 5g of preheated urea granules in a disc granulator, spray with a coating solution for coating, and then place in an 80℃ oven for drying for 1 hour to obtain ethyl cellulose and isocyanate cross-coated urea slow-release fertilizer.

[0103] In step 2③, the weight gain rate of the urea granules after coating was 5%;

[0104] The disc tilt angle of the disc granulator described in step 2③ is 50°, and the disc rotation speed is 30 r / min.

[0105] Comparative Example: The preparation method of ethyl cellulose coated urea fertilizer is specifically carried out according to the following steps:

[0106] I. Preparation of ethyl cellulose coating solution:

[0107] ① Disperse 1.0201g of ethyl cellulose in 10mL of ethyl acetate and stir for 2h to obtain an ethyl cellulose coating solution;

[0108] II. Preparation of Ethyl Cellulose-Coated Urea Slow-Release Fertilizer:

[0109] ① Place 5g of urea granules in an oven and preheat;

[0110] ② Pour 10 mL of ethyl cellulose coating solution into the atomizing spray gun;

[0111] ③ Place 5g of preheated urea granules in a disc granulator and spray with 10mL of ethyl cellulose coating solution for coating. Then place in an oven to dry to obtain ethyl cellulose coated urea fertilizer.

[0112] Detection of urea in the ethyl cellulose and isocyanate cross-coated urea slow-release fertilizer prepared in Examples 1 to 5: Urea reacts with p-dimethylaminobenzaldehyde under acidic conditions to form a lemon-colored substance, and the urea content can be determined by ultraviolet spectrophotometry. According to the European Committee for Standardization, slow-release fertilizers should meet several standards: (1) at 25°C, the nutrient release rate (i.e., the chemical form of the fertilizer is converted into an effective form that can be utilized by plants) does not exceed 15% within 24 hours; (2) the nutrient release rate does not exceed 75% within 28 days; (3) the nutrient release rate is not less than 75% within a specified time; (4) the nutrient release curve of the special slow-release fertilizer matches the nutrient absorption curve of the corresponding crop.

[0113] The ethyl cellulose and isocyanate cross-coated urea slow-release fertilizer prepared in Example 1 had a 10-day release rate of 38.2% in the soil.

[0114] The ethyl cellulose and isocyanate cross-coated urea slow-release fertilizer prepared in Example 2 had a 10-day release rate of 38.6% in the soil.

[0115] The ethyl cellulose and isocyanate cross-coated urea slow-release fertilizer prepared in Example 3 had a 10-day release rate of 39.3% in the soil.

[0116] The ethyl cellulose and isocyanate cross-linked urea slow-release fertilizer prepared in Example 4 had a 10-day release rate of 37.2% in the soil.

[0117] The ethyl cellulose and isocyanate cross-coated urea slow-release fertilizer prepared in Example 5 had a 10-day release rate of 35.6% in the soil.

[0118] The release rate of uncoated raw urea particles in soil was 93.4% after 10 days.

[0119] The ethyl cellulose-coated urea fertilizer prepared in the comparative example had a 10-day release rate of 61.5% in the soil.

[0120] 0.7511 g of dried ethyl cellulose was added to 10 mL of ethyl acetate and stirred at 800 r / min for 1 h to obtain an ethyl cellulose solution. The ethyl cellulose solution was then poured onto a glass slide and dried to obtain an ethyl cellulose membrane.

[0121] 0.2501 g of isocyanate monomer was dispersed in 10 mL of ethyl acetate and stirred at 800 r / min for 1 h to obtain an isocyanate solution; 0.7511 g of dried ethyl cellulose was added to the isocyanate solution and stirred at 20 °C and a stirring speed of 800 r / min for 2 h to obtain a coating solution; the coating solution was cast onto a glass slide and dried to obtain an ethyl cellulose crosslinked isocyanate membrane.

[0122] Figure 1 Figure 1 shows scanning electron microscope (SEM) images. Figure 2(a) is a scanning electron microscope image of an ethyl cellulose membrane, and Figure 3(b) is a scanning electron microscope image of an ethyl cellulose cross-linked isocyanate membrane.

[0123] from Figure 1 It is evident that the surface of the pure ethyl cellulose membrane exhibits a distinctly porous and loose structure. Numerous circular pores and depressions of varying sizes are visible, resulting in a rough and uneven surface. In contrast, the surface of the ethyl cellulose cross-linked isocyanate membrane demonstrates a highly dense, smooth, and continuous structure. The original numerous pores have largely disappeared, and the membrane surface is smooth and structurally uniform, with only nanoscale undulations. This indicates that the cross-linking of ethyl cellulose and isocyanate was successful, resulting in a denser membrane structure.

[0124] Figure 2 The figures show infrared spectra. Figure (a) shows the infrared spectrum of isocyanate, Figure (b) shows the infrared spectrum of ethyl cellulose, and Figure (c) shows the infrared spectrum of ethyl cellulose cross-linked isocyanate membrane.

[0125] from Figure 2 As can be seen from the curve (a), pure isocyanate is at ~2270 cm⁻¹ -1 There is a very sharp and strong absorption peak at ~1050 cm⁻¹, which is a characteristic peak of its -N=C=O functional group. Curve (b) shows that pure ethyl cellulose has an absorption peak at ~1050 cm⁻¹. -1 The strong peaks nearby represent the stretching vibrations of the COC ether bond. Curve (c) is at ~1700 cm⁻¹. -1 A strong and sharp new peak appeared nearby, which is due to the stretching vibration of C=O caused by the formation of urethane bonds, and the characteristic peak of -N=C=O completely disappeared, indicating that the isocyanate reacted completely, proving the success of the cross-linking reaction between ethyl cellulose and isocyanate.

[0126] Figure 3 Figure 1 shows the release curves of urea and the prepared slow-release fertilizer in water. Figure 2(a) shows the release curve of ordinary urea in water, Figure 2(b) shows the release curve of ethyl cellulose coated urea fertilizer in water, and Figure 2(c) shows the release curve of ethyl cellulose and isocyanate cross-linked coated urea slow-release fertilizer prepared in Example 1 in water.

[0127] from Figure 3 It is known that ordinary urea releases fastest in water, followed by pure ethyl cellulose-coated urea fertilizer. However, the ethyl cellulose and isocyanate cross-linked urea slow-release fertilizer prepared in Example 1 significantly reduces water permeability and urea diffusion rate due to the tighter cross-linked network structure formed by the composite membrane, thereby slowing down fertilizer release.

[0128] Figure 4 The figures show the release curves of urea and the prepared slow-release fertilizer in the soil. Figure (a) shows the release curve of ordinary urea in the soil, Figure (b) shows the release curve of ethyl cellulose coated urea fertilizer in the soil, and Figure (c) shows the release curve of ethyl cellulose and isocyanate cross-linked coated urea slow-release fertilizer prepared in Example 1 in the soil.

[0129] from Figure 4 As can be seen, the initial release rate of ordinary urea in the soil is very fast, followed by pure ethyl cellulose coated urea fertilizer, while the ethyl cellulose and isocyanate cross-linked coated urea slow-release fertilizer prepared in Example 1 releases the slowest in the soil; the initial release rate is slower than that in water because there is less free water in the soil, and the exchange rate between free water and fertilizer in the soil is reduced, thereby reducing the release of urea.

[0130] Figure 5 The figures show the dry and fresh weights of cherry radish fruits before and after fertilization. In the figures, the left side shows the dry and fresh weights of urea slow-release fertilizer with cross-linked ethyl cellulose and isocyanate prepared in Example 1, the middle side shows the dry and fresh weights of ordinary urea, and the right side shows the dry and fresh weights of the blank control group without fertilizer.

[0131] from Figure 5 As can be seen, the average fresh weight and dry weight of cherry radishes treated with the ethyl cellulose and isocyanate cross-coated urea slow-release fertilizer prepared in Example 1 were 24.39 g and 2.01 g, respectively, which were significantly higher than the weights of cherry radishes treated with pure ethyl cellulose-coated urea fertilizer and those without fertilizer. This indicates that the fertilizer had a significant promoting effect on crop growth.

[0132] Figure 6The figure shows the hygroscopicity of the ethyl cellulose and isocyanate cross-coated urea slow-release fertilizer prepared in Example 1 in a constant temperature and humidity incubator with a relative humidity of 50%. In the figure, (a) shows the change in compressive strength of the ethyl cellulose and isocyanate cross-coated urea slow-release fertilizer prepared in Example 1 after 21 days of moisture absorption, and (b) shows the change in mass of the ethyl cellulose and isocyanate cross-coated urea slow-release fertilizer prepared in Example 1 after 21 days of moisture absorption.

[0133] from Figure 6 As can be seen, the compressive strength and weight of the coated urea did not change significantly in a constant temperature and humidity incubator with a relative humidity of 50%. The slight fluctuations were due to the differences in the size of the urea particles. This indicates that the ethyl cellulose and isocyanate cross-coated urea slow-release fertilizer has good moisture-proof and anti-caking properties.

Claims

1. A method for preparing a urea slow-release fertilizer cross-coated with ethyl cellulose and isocyanate, characterized in that... The preparation method is specifically completed according to the following steps: I. Preparation of ethyl cellulose cross-linked isocyanate coating solution:

1. Disperse isocyanate monomer in ethyl acetate, and stir to obtain an isocyanate solution; 2. Add ethyl cellulose into the isocyanate solution, and stir to react to obtain an ethyl cellulose cross-linked isocyanate coating solution; II. Preparation of ethyl cellulose and isocyanate cross-linked coating urea slow-release fertilizer:

1. Preheat urea particles in an oven; 2. Pour the ethyl cellulose cross-linked isocyanate coating solution into an atomizing spray gun; 3. Spray the coating solution on the preheated urea particles in a disc granulator to coat, and then dry in an oven to obtain ethyl cellulose and isocyanate cross-linked coating urea slow-release fertilizer.

2. The preparation method of the ethyl cellulose and isocyanate cross-linked coated urea slow-release fertilizer according to claim 1, characterized in that The stirring speed in step 1 1 is 300 r / min to 1500 r / min, and the stirring time is 1 h to 8 h.

3. The preparation method of the ethyl cellulose and isocyanate cross-linked coated urea slow-release fertilizer according to claim 1, characterized in that The isocyanate monomer in step 1 1 is 2,6-toluene diisocyanate; and the mass of the isocyanate monomer to the volume of ethyl acetate is (0.25 g to 25 g):(10 mL to 1000 mL).

4. The preparation method of the ethyl cellulose and isocyanate cross-linked coated urea slow-release fertilizer according to claim 1, characterized in that The stirring reaction temperature in step 1 2 is 20°C to 50°C, the stirring speed is 300 r / min to 1500 r / min, and the stirring time is 1 h to 8 h.

5. The preparation method of the ethyl cellulose and isocyanate cross-linked coated urea slow-release fertilizer according to claim 1, characterized in that The mass ratio of ethyl cellulose to isocyanate monomer in step 1 2 is (0.75 g to 75 g):(0.25 g to 25 g).

6. The preparation method of the ethyl cellulose and isocyanate cross-linked coated urea slow-release fertilizer according to claim 1, characterized in that The preheating temperature in step 2 1 is 60°C to 80°C, and the preheating time is 0.5 h to 2 h.

7. The preparation method of the ethyl cellulose and isocyanate cross-linked coated urea slow-release fertilizer according to claim 1, characterized in that The weight gain rate of the coated urea particles in step 2 3 is 1% to 5%.

8. The preparation method of the ethyl cellulose and isocyanate cross-linked coated urea slow-release fertilizer according to claim 1, characterized in that The disc granulator in step 2 3 has a disc inclination angle of 30° to 60°, and a disc rotation rate of 20 r / min to 40 r / min.

9. The preparation method of the ethyl cellulose and isocyanate cross-linked coated urea slow-release fertilizer according to claim 1, characterized in that The drying temperature in step 2 3 is 60°C to 80°C, and the drying time is 2 h to 4 h.

10. Ethyl cellulose and isocyanate cross-linked coating urea slow-release fertilizer prepared by the preparation method of any one of claims 1 to 9.

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