Method for preparing double-layer coated urea slow-release fertilizer from sulfamic acid modified cellulose and application of double-layer coated urea slow-release fertilizer

Abstract

The invention provides a method for preparing a double-layer coated urea slow-release fertilizer by using sulfamic acid modified cellulose and application of the double-layer coated urea slow-release fertilizer, and relates to a preparation method of an environment-friendly coated slow-release fertilizer. The invention aims to solve the problems that the utilization rate of urea in the existing fertilizer is low, secondary pollution is easily caused by non-degradability of most slow-release fertilizer coated matrix materials, and straw cellulose is poor in dissolvability and is not beneficial to being used as a slow-release fertilizer coated matrix. Comprising the following steps: 1, preparing sulfamic acid modified cellulose; and 2, preparing the sulfamic acid modified cellulose double-layer coated urea slow-release fertilizer. According to the method, the biomass straw is used as a raw material for cellulose extraction, the defects of poor solubility and poor thermoplasticity of the cellulose are overcome through chemical modification, and resource utilization of the straw can be achieved. In addition, the prepared slow-release fertilizer has the advantages of being simple in process, low in cost, environmentally friendly, degradable in matrix and the like, and is suitable for large-scale preparation and agricultural production.

Description

Technical Field

[0001] The invention relates to a method for preparing a double-layer coated slow-release urea fertilizer by using aminosulfonic acid modified cellulose. Background Art

[0002] Fertilizers play an important role in meeting the growing demand for food. Due to their high solubility, some nutrients in traditional fertilizers are lost during use through surface runoff, ammonia sublimation, and microbial denitrification. In fact, less than 60% of the nutrients can be absorbed by crops. Therefore, the utilization efficiency of traditional fertilizers is low, resulting in waste of resources, increased labor input, and the lost fertilizers will also pollute the environment.

[0003] Slow-release fertilizer is a new type of fertilizer that can effectively prolong the bioavailability of fertilizer. Fertilizer coating is the most commonly used technology for the preparation of slow-release fertilizer. It is to coat the surface of soluble fertilizer with one or more layers of hydrophobic inorganic or organic materials. Common coating materials include inorganic coating materials (sulfur or minerals) and synthetic polymers (polyvinyl alcohol, polyurethane). However, inorganic coating materials (such as sulfur) are brittle and not conducive to transportation, and have poor slow-release performance. In addition, they will affect the activity of soil microorganisms. Synthetic polymers are expensive and non-degradable, which will pollute the soil. Therefore, natural polymer compounds such as starch, cellulose, lignin, sodium alginate, etc. have the advantages of low cost, rich sources, and green degradability. They are considered to be very potential slow-release fertilizer coating materials and have received widespread attention, especially cellulose, which is a very abundant renewable natural polymer material. However, cellulose is not easy to dissolve in solvents and has poor film-forming properties, which is not conducive to the preparation of slow-release fertilizers. Therefore, modifying cellulose to improve its film-forming properties and developing a process technology suitable for preparing cellulose-coated fertilizers are urgent issues to be solved in the current preparation of biomass-coated slow-release fertilizers. Summary of the invention

[0004] The purpose of the present invention is to solve the problem of low utilization rate of existing chemical fertilizers, the non-degradability of most slow-release fertilizer coating matrix materials themselves, and the poor solubility and thermoplasticity of pure cellulose itself, which is not conducive to being used as a fertilizer coating matrix. A preparation method of aminosulfonic acid modified cellulose double-layer coated urea slow-release fertilizer is provided.

[0005] A method for preparing a double-layer coated urea slow-release fertilizer using aminosulfonic acid modified cellulose is completed by the following steps:

[0006] 1. Preparation of aminosulfonic acid modified cellulose: ① Stirring the cellulose extracted from hemp stalks with distilled water at room temperature to obtain a dispersed cellulose aqueous dispersion; ② Adding aminosulfonic acid reagent to the cellulose aqueous dispersion system obtained in step 1①, stirring at room temperature to obtain a mixed dispersion system of aminosulfonic acid and cellulose; ③ Loading the mixed dispersion system of aminosulfonic acid and cellulose into a polytetrafluoroethylene-lined reactor for microwave reaction; ④ The obtained crude product is washed with deionized water and ethanol, and then vacuum dried and ground to obtain aminosulfonic acid modified cellulose;

[0007] 2. Preparation of aminosulfonic acid modified cellulose double-layer coated urea slow-release fertilizer: ① Add polymethyl methacrylate into acetone solution and stir to dissolve at room temperature; ② Slowly add urea to the solution stirred in step 2① and stir to form a uniform coating on the urea surface; ③ Place the uniformly coated urea obtained in step 2② in a vacuum drying oven and dry for a period of time. Cool to room temperature; ④ Add the aminosulfonic acid-modified cellulose and sodium alginate obtained in step 1 into a certain volume of water to prepare a mixed solution, and stir at room temperature; ⑤Dissolve calcium chloride in water to form a mixed solution; ⑥ Add the coated urea obtained in step 2③ to the mixed solution obtained in step 2④, then add the calcium chloride solution obtained in step 2⑤ and pour into the mold for cross-linking. After the cross-linking is completed, put it into an oven for drying to obtain aminosulfonic acid modified cellulose double-layer coated urea slow-release fertilizer;

[0008] Principles and advantages of the present invention

[0009] 1. The cellulose used in the present invention is derived from agricultural biomass materials such as hemp straw, which has the advantages of being environmentally friendly, cheap and abundant in source, and has important value for the high-value utilization of straw produced in agriculture;

[0010] Second, the present invention adopts a microwave-assisted heating method to prepare aminosulfonic acid modified cellulose, which has a simple process and operation flow and is suitable for large-scale production. At the same time, the modified cellulose has more significant water solubility, thereby effectively improving the swelling performance of sodium alginate hydrogel, and finally improving the slow-release performance of the double-layer coated slow-release fertilizer;

[0011] 3. The aminosulfonic acid modified cellulose double-layer coated urea slow-release fertilizer of the present invention, the urea fertilizer is coated with a polymethyl methacrylate film and a modified cellulose and sodium alginate composite film in sequence, which greatly reduces the fertilizer release rate, prolongs the urea release time, improves the fertilizer utilization efficiency, and reduces the pollution of urea to the environment. In addition, the modified cellulose and sodium alginate are natural polymers with good biodegradability and environmental compatibility, and will not cause secondary pollution to the environment.

[0012] The invention can obtain a sulfamic acid modified cellulose double-layer coated urea slow-release fertilizer. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 The figure is a flow chart for preparing aminosulfonic acid modified cellulose double-layer coated urea slow-release fertilizer;

[0014] Figure 2 are infrared spectra, wherein (a) is the infrared spectrum of unmodified hemp straw cellulose, and (b) is the infrared spectrum of aminosulfonic acid modified cellulose obtained in step 1 of Example 1;

[0015] Figure 3 are swelling diagrams, wherein (1) is the swelling of sodium alginate hydrogel, (2) is the swelling of unmodified hemp straw cellulose hydrogel, and (3) is the swelling of aminosulfonic acid modified cellulose hydrogel obtained in Example 1;

[0016] Figure 4 The release curves of urea and the prepared slow-release fertilizer in water, (a) is the release curve of ordinary double-layer coated slow-release fertilizer in water, (b) is the release curve of unmodified hemp straw cellulose double-layer coated slow-release fertilizer in water, and (c) is the release curve of aminosulfonic acid modified cellulose double-layer coated urea slow-release fertilizer prepared in Example 1 in water;

[0017] Figure 5 The release curves of urea and the prepared slow-release fertilizer in soil, (a) is the release curve of common urea in soil, (b) is the release curve of common double-layer coated slow-release fertilizer in soil, (c) is the release curve of unmodified hemp straw cellulose double-layer coated slow-release fertilizer in soil, and (d) is the release curve of aminosulfonic acid modified cellulose double-layer coated urea slow-release fertilizer prepared in Example 1 in soil;

[0018] Figure 6 The stem diameter of corn plants at different stages after and without slow-release fertilizer application. (a) is the stem diameter of the blank control group, and (b) is the stem diameter of the plant after slow-release fertilizer application. DETAILED DESCRIPTION

[0019] Specific implementation method 1: This implementation method is a method for preparing a sulfamic acid modified cellulose double-layer coated urea slow-release fertilizer, which is completed by the following steps:

[0020] 1. Preparation of aminosulfonic acid modified cellulose: ① Stirring the cellulose extracted from hemp stalks with distilled water at room temperature to obtain a dispersed cellulose aqueous dispersion; ② Adding aminosulfonic acid reagent to the cellulose aqueous dispersion system obtained in step 1①, stirring at room temperature to obtain a mixed dispersion system of aminosulfonic acid and cellulose; ③ Loading the mixed dispersion system of aminosulfonic acid and cellulose into a polytetrafluoroethylene-lined reactor for microwave reaction; ④ The obtained crude product is washed with deionized water and ethanol, and then vacuum dried and ground to obtain aminosulfonic acid modified cellulose;

[0021] 2. Preparation of aminosulfonic acid modified cellulose double-layer coated urea slow-release fertilizer: ① Add polymethyl methacrylate into acetone solution and stir to dissolve at room temperature; ② Slowly add urea to the solution stirred in step 2① and stir to form a uniform coating on the urea surface; ③ Place the uniformly coated urea obtained in step 2② in a vacuum drying oven and dry for a period of time. Cool to room temperature; ④ Add the aminosulfonic acid-modified cellulose and sodium alginate obtained in step 1 into a certain volume of water to prepare a mixed solution, and stir at room temperature; ⑤Dissolve calcium chloride in water to form a mixed solution; ⑥ Add the coated urea obtained in step 2③ to the mixed solution obtained in step 2④, then add the calcium chloride solution obtained in step 2⑤ and pour into the mold for cross-linking. After the cross-linking is completed, put it into an oven for drying to obtain aminosulfonic acid modified cellulose double-layer coated urea slow-release fertilizer;

[0022] Principles and advantages of the present invention

[0023] 1. The cellulose used in the present invention is derived from agricultural biomass materials such as hemp straw, which has the advantages of being environmentally friendly, cheap and abundant in source, and has important value for the high-value utilization of straw produced in agriculture;

[0024] Second, the present invention adopts a microwave-assisted heating method to prepare aminosulfonic acid modified cellulose, which has a simple process and operation flow and is suitable for large-scale production. At the same time, the modified cellulose has more significant water solubility, thereby effectively improving the swelling performance of sodium alginate hydrogel, and finally improving the sustained-release performance of double-layer coated sustained-release hypertrophy;

[0025] 3. The aminosulfonic acid modified cellulose double-layer coated urea slow-release fertilizer of the present invention, the urea fertilizer is coated with a polymethyl methacrylate film and a modified cellulose and sodium alginate composite film in sequence, which greatly reduces the fertilizer release rate, prolongs the urea release time, improves the fertilizer utilization efficiency, and reduces the pollution of urea to the environment. In addition, the modified cellulose and sodium alginate are natural polymers with good biodegradability and environmental compatibility, and will not cause secondary pollution to the environment.

[0026] The invention can obtain a sulfamic acid modified cellulose double-layer coated urea slow-release fertilizer.

[0027] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that: in step 1①, the water bath temperature is 50° C. The other steps are the same as those in specific embodiment 1.

[0028] Specific implementation method 3: This implementation method is different from the specific implementation method 1 in that the stirring speed in step 1② is 300r / min~800r / min and the stirring time is 30min. The other steps are the same as the specific implementation method 1.

[0029] Specific embodiment 4: This embodiment differs from specific embodiment 1 in that the microwave temperature in step 1③ is 80°C and the time is 30 minutes. The other steps are the same as those in specific embodiment 1.

[0030] Specific embodiment 5: This embodiment differs from specific embodiment 1 in that: the number of ethanol washing in step 1④ is 4 to 6 times, and the vacuum drying temperature is 60° C. The other steps are the same as those in specific embodiment 1.

[0031] Specific embodiment 6: This embodiment differs from the specific embodiment 1 in that the vacuum drying temperature in step 2③ is 60° C. The other steps are the same as those in the specific embodiment 1.

[0032] Specific embodiment 7: The difference between this embodiment and specific embodiment 1 is that the cross-linking time in step 2⑤ is 3h~5h, the drying temperature is 60℃, and the drying time is 24h~48h

[0033] The following examples are used to verify the beneficial effects of the present invention:

[0034] Embodiment 1: A method for preparing a sulfamic acid modified cellulose double-layer coated urea slow-release fertilizer is completed by the following steps:

[0035] 1. Preparation of aminosulfonic acid modified cellulose: ① 2.002 g of cellulose extracted from hemp straw was stirred with 20.0 mL of distilled water at 50°C for 30 min to obtain a dispersed cellulose aqueous dispersion; ② Add 6.003 g of aminosulfonic acid solid to the cellulose aqueous dispersion obtained in step 1①, and stir at room temperature for 30 min to obtain a mixed dispersion of aminosulfonic acid and cellulose; ③ The mixed dispersion system of aminosulfonic acid and cellulose was loaded into a polytetrafluoroethylene-lined reactor and subjected to microwave reaction at 80°C for 30 minutes; ④ The obtained crude product was washed with deionized water and ethanol for 6 times, and then vacuum dried at 60° C. for 24 h, and ground to obtain aminosulfonic acid-modified cellulose;

[0036] 2. Preparation of aminosulfonic acid modified cellulose double-layer coated urea slow-release fertilizer: ① Add 50.0 ml of acetone solution to 5.004 g of polymethyl methacrylate and stir at room temperature for 3 h; ② Slowly add 2.014g of urea granules with a particle size of 2mm into the stirred solution and stir for 2 minutes to form a uniform coating on the urea surface; ③ Place the evenly coated urea in a vacuum drying oven and dry at 60°C for 5 hours. Cool to room temperature; ④ Add 2.009 g of aminosulfonic acid-modified cellulose obtained in step 1 and 6.024 g of sodium alginate into 300 ml of water to prepare a mixed solution, and stir at room temperature for 5 min; ⑤ Dissolve 3.047g calcium chloride in 51.0ml water to form a mixed solution; ⑥ Add the coated urea to the sodium alginate solution, then add the calcium chloride solution, pour the prepared mixed solution into the mold for cross-linking for 3 hours, and after the cross-linking is completed, put it in an oven at 60°C for drying for 48 hours to obtain aminosulfonic acid modified cellulose double-layer coated urea slow-release fertilizer;

[0037] Embodiment 2: A method for preparing a sulfamic acid modified cellulose double-layer coated urea slow-release fertilizer is completed by the following steps:

[0038] 1. Preparation of aminosulfonic acid modified cellulose: ① 2.021 g of cellulose extracted from hemp straw was stirred with 20.0 mL of distilled water at 50°C for 30 min to obtain a dispersed cellulose aqueous dispersion; ② Add 7.023 g of aminosulfonic acid solid to the cellulose aqueous dispersion obtained in step 1①, and stir at room temperature for 30 min to obtain a mixed dispersion of aminosulfonic acid and cellulose; ③ The mixed dispersion system of aminosulfonic acid and cellulose was loaded into a polytetrafluoroethylene-lined reactor and subjected to microwave reaction at 80°C for 30 minutes; ④ The obtained crude product was washed with deionized water and ethanol for 6 times, and then vacuum dried at 60° C. for 24 h, and ground to obtain aminosulfonic acid-modified cellulose;

[0039] 2. Preparation of aminosulfonic acid modified cellulose double-layer coated urea slow-release fertilizer: ① Add 50.4 ml of acetone solution to 5.006 g of polymethyl methacrylate and stir at room temperature for 3 h; ② Slowly add 2.038g of urea granules with a particle size of 3mm into the stirred solution and stir for 2 minutes to form a uniform coating on the urea surface; ③ Place the evenly coated urea in a vacuum drying oven and dry at 60°C for 5 hours. Cool to room temperature; ④ Add 2.026 g of aminosulfonic acid-modified cellulose obtained in step 1 and 6.039 g of sodium alginate into 300 ml of water to prepare a mixed solution, and stir at room temperature for 5 min; ⑤ Dissolve 3.019g calcium chloride in 51.0ml water to form a mixed solution; ⑥ Add the coated urea to the sodium alginate solution, then add the calcium chloride solution, pour the prepared mixed solution into the mold for cross-linking for 3 hours, and after the cross-linking is completed, put it in an oven at 60°C for drying for 48 hours to obtain aminosulfonic acid modified cellulose double-layer coated urea slow-release fertilizer;

[0040] Embodiment 3: A method for preparing a sulfamic acid modified cellulose double-layer coated urea slow-release fertilizer is completed by the following steps:

[0041] 1. Preparation of aminosulfonic acid modified cellulose: ① 1.985 g of cellulose extracted from hemp straw was stirred with 20.0 mL of distilled water at 50 ° C for 30 min to obtain a dispersed cellulose aqueous dispersion; ② Add 5.975 g of aminosulfonic acid solid to the cellulose aqueous dispersion obtained in step 1①, and stir at room temperature for 30 min to obtain a mixed dispersion of aminosulfonic acid and cellulose; ③ The mixed dispersion system of aminosulfonic acid and cellulose was loaded into a polytetrafluoroethylene-lined reactor and subjected to microwave reaction at 80°C for 30 minutes; ④ The obtained crude product was washed with deionized water and ethanol for 6 times, and then vacuum dried at 60° C. for 24 h, and ground to obtain aminosulfonic acid-modified cellulose;

[0042] 2. Preparation of aminosulfonic acid modified cellulose double-layer coated urea slow-release fertilizer: ① Add 52.0 ml of acetone solution to 5.042 g of polymethyl methacrylate and stir at room temperature for 3 h; ② Slowly add 2.067g of urea granules with a particle size of 2mm into the stirred solution and stir for 2 minutes to form a uniform coating on the urea surface; ③ Place the evenly coated urea in a vacuum drying oven and dry at 60°C for 5 hours. Cool to room temperature; ④ Add 2.041 g of aminosulfonic acid-modified cellulose obtained in step 1 and 6.032 g of sodium alginate into 300 ml of water to prepare a mixed solution, and stir at room temperature for 5 min; ⑤ Dissolve 3.047g calcium chloride in 51.0ml water to form a mixed solution; ⑥ Add the coated urea to the sodium alginate solution, then add the calcium chloride solution, pour the prepared mixed solution into the mold for cross-linking for 3 hours, and after the cross-linking is completed, put it in an oven at 60°C for drying for 48 hours to obtain aminosulfonic acid modified cellulose double-layer coated urea slow-release fertilizer;

[0043] Embodiment 4: A method for preparing a sulfamic acid modified cellulose double-layer coated urea slow-release fertilizer is completed by the following steps:

[0044] 1. Preparation of aminosulfonic acid modified cellulose: ① 2.021 g of cellulose extracted from hemp straw was stirred with 20.0 mL of distilled water at 50°C for 30 min to obtain a dispersed cellulose aqueous dispersion; ② Add 6.031 g of aminosulfonic acid solid to the cellulose aqueous dispersion obtained in step 1①, and stir at room temperature for 30 min to obtain a mixed dispersion of aminosulfonic acid and cellulose; ③ The mixed dispersion system of aminosulfonic acid and cellulose was loaded into a polytetrafluoroethylene-lined reactor and subjected to microwave reaction at 80°C for 30 minutes; ④ The obtained crude product was washed with deionized water and ethanol for 6 times, and then vacuum dried at 60° C. for 24 h, and ground to obtain aminosulfonic acid-modified cellulose;

[0045] 2. Preparation of aminosulfonic acid modified cellulose double-layer coated urea slow-release fertilizer: ① Add 51.0 ml of acetone solution to 5.013 g of polymethyl methacrylate and stir at room temperature for 3 h; ② Slowly add 2.035g of urea granules with a particle size of 3mm into the stirred solution and stir for 2 minutes to form a uniform coating on the urea surface; ③ Place the evenly coated urea in a vacuum drying oven and dry at 60°C for 5 hours. Cool to room temperature; ④ Add 2.014 g of aminosulfonic acid-modified cellulose obtained in step 1 and 6.031 g of sodium alginate into 300 ml of water to prepare a mixed solution, and stir at room temperature for 5 min; ⑤ Dissolve 2.987g calcium chloride in 50.0ml water to form a mixed solution; ⑥ Add the coated urea to the sodium alginate solution, then add the calcium chloride solution, pour the prepared mixed solution into the mold for cross-linking for 3 hours, and after the cross-linking is completed, put it in an oven at 60°C for drying for 48 hours to obtain aminosulfonic acid modified cellulose double-layer coated urea slow-release fertilizer;

[0046] Embodiment 5: A method for preparing a sulfamic acid modified cellulose double-layer coated urea slow-release fertilizer is completed according to the following steps:.

[0047] 1. Preparation of aminosulfonic acid modified cellulose: ① 2.018 g of cellulose extracted from hemp straw was stirred with 22.0 mL of distilled water at 50 ° C for 30 min to obtain a dispersed cellulose aqueous dispersion; ② Add 6.034 g of aminosulfonic acid solid to the cellulose aqueous dispersion obtained in step 1①, and stir at room temperature for 30 min to obtain a mixed dispersion of aminosulfonic acid and cellulose; ③ The mixed dispersion system of aminosulfonic acid and cellulose was loaded into a polytetrafluoroethylene-lined reactor and subjected to microwave reaction at 80°C for 30 minutes; ④ The obtained crude product was washed with deionized water and ethanol for 6 times, and then vacuum dried at 60° C. for 24 h, and ground to obtain aminosulfonic acid-modified cellulose;

[0048] 2. Preparation of aminosulfonic acid modified cellulose double-layer coated urea slow-release fertilizer: ① Add 50.0 ml of acetone solution to 4.969 g of polymethyl methacrylate and stir at room temperature for 3 h; ② Slowly add 2.045g of urea granules with a particle size of 3mm into the stirred solution and stir for 2 minutes to form a uniform coating on the urea surface; ③ Place the evenly coated urea in a vacuum drying oven and dry at 60°C for 5 hours. Cool to room temperature; ④ Add 2.009 g of aminosulfonic acid-modified cellulose obtained in step 1 and 6.042 g of sodium alginate into 300 ml of water to prepare a mixed solution, and stir at room temperature for 5 min; ⑤ Dissolve 3.027g calcium chloride in 50.0ml water to form a mixed solution; ⑥ Add the coated urea to the sodium alginate solution, then add the calcium chloride solution, pour the prepared mixed solution into the mold for cross-linking for 3 hours, and after the cross-linking is completed, put it in an oven at 60°C for drying for 48 hours to obtain aminosulfonic acid modified cellulose double-layer coated urea slow-release fertilizer;

[0049] Detection of urea in the aminosulfonic acid modified cellulose double-layer coated urea slow-release fertilizer prepared in Examples 1 to 5: Urea reacts with p-dimethylaminobenzaldehyde under acidic conditions to generate a lemon-colored substance, and the urea content can be determined by ultraviolet spectrophotometry. According to the European Committee for Standardization, the slow-release fertilizer should have several standards: that is, at 25°C (1) the release rate of nutrients in the fertilizer within 24 hours (that is, the chemical form of the fertilizer is converted into an effective form that can be used by plants) does not exceed 15%; (2) the nutrient release rate within 28 days does not exceed 75%; (3) within the specified time, the nutrient release rate is not less than 75%; (4) the nutrient release curve of the special slow-release fertilizer is consistent with the nutrient absorption curve of the corresponding crop.

[0050] The 10-day release rate of the aminosulfonic acid modified cellulose double-layer coated urea slow-release fertilizer in the soil prepared in Example 1 was 17.3%;

[0051] The 10-day release rate of the aminosulfonic acid modified cellulose double-layer coated urea slow-release fertilizer in the soil prepared in Example 2 was 17.8%;

[0052] The 10-day release rate of the aminosulfonic acid modified cellulose double-layer coated urea slow-release fertilizer in the soil prepared in Example 3 was 18.3%;

[0053] The 10-day release rate of the aminosulfonic acid modified cellulose double-layer coated urea slow-release fertilizer in the soil prepared in Example 4 was 17.9%;

[0054] The 10-day release rate of the aminosulfonic acid modified cellulose double-layer coated urea slow-release fertilizer prepared in Example 5 in the soil was 19.7%;

[0055] Figure 1 The figure is a flow chart for preparing aminosulfonic acid modified cellulose double-layer coated urea slow-release fertilizer;

[0056] Figure 2 are infrared spectra, wherein (a) is the infrared spectrum of unmodified hemp straw cellulose, and (b) is the infrared spectrum of aminosulfonic acid modified cellulose obtained in step 1 of Example 1;

[0057] from Figure 2 It can be seen that 3450 cm -1 The peaks correspond to the asymmetric stretching vibration of -OH at 1450, 1270, and 818 cm -1 New characteristic peaks appeared, corresponding to the appearance of O=S and COS bonds, indicating that cellulose was successfully modified by aminosulfonic acid;

[0058] Figure 3are swelling diagrams, wherein (1) is the swelling of sodium alginate hydrogel, (2) is the swelling of unmodified hemp straw cellulose hydrogel, and (3) is the swelling of aminosulfonic acid modified cellulose hydrogel obtained in Example 1;

[0059] from Figure 3 It can be seen that (1) the maximum swelling of sodium alginate hydrogel is 16.12 g / g, (2) the maximum swelling of hemp straw cellulose hydrogel is 27.38 g / g, and (3) the maximum swelling of aminosulfonic acid modified cellulose hydrogel is 47.71 g / g, indicating that the modified cellulose hydrogel has better water absorption and can be better used in water-retaining slow-release fertilizers.

[0060] Figure 4 The release curves of urea and the prepared slow-release fertilizer in water, (a) is the release curve of ordinary double-layer coated slow-release fertilizer in water, (b) is the release curve of unmodified hemp straw cellulose double-layer coated slow-release fertilizer in water, and (c) is the release curve of aminosulfonic acid modified cellulose double-layer coated urea slow-release fertilizer prepared in Example 1 in water;

[0061] from Figure 4 It can be seen that ordinary double-layer coated slow-release fertilizers have the fastest release rate in water, while the aminosulfonic acid modified cellulose double-layer coated urea slow-release fertilizer prepared in Comparative Example 1 forms a double-layer coating system. The structure of the combination of the membrane and the hydrogel not only ensures that the fertilizer can be filled therein, but also prevents the diffusion of water to a certain extent, thereby slowing down the release of the fertilizer.

[0062] Figure 5 The release curves of urea and the prepared slow-release fertilizer in soil, (a) is the release curve of common urea in soil, (b) is the release curve of common double-layer coated slow-release fertilizer in soil, (c) is the release curve of unmodified hemp straw cellulose double-layer coated slow-release fertilizer in soil, and (d) is the release curve of aminosulfonic acid modified cellulose double-layer coated urea slow-release fertilizer prepared in Example 1 in soil;

[0063] from Figure 5 It can be seen that the initial release rate of urea in the soil is very fast, while the slow-release urea is released slowly 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.

[0064] Figure 6 The diagrams show the stem diameter of corn plants at different stages without and after the application of slow-release fertilizer. (a) shows the stem diameter of the blank control group, and (b) shows the stem diameter of the slow-release fertilizer-applied plants.

[0065] from Figure 6It can be seen that the stem diameter of the blank group was 0.56 cm after 4 weeks, and the stem diameter of the plants using the fertilizer was 0.80 cm, indicating that the fertilizer has a significant promoting effect on the growth of crops.

Claims

1. A method for preparing double-layer coated urea slow-release fertilizer by modifying cellulose with aminosulfonic acid and its application, characterized in that The method for preparing double-layer coated urea slow-release fertilizer by using aminosulfonic acid modified cellulose is completed according to the following steps:

1. Preparation of aminosulfonic acid modified cellulose: The cellulose extracted from the hemp stalks was stirred with distilled water at room temperature to obtain a dispersed cellulose aqueous dispersion; In step 1 ① the cellulose aqueous dispersion system obtained by adding sulfamic acid reagent, stirring at room temperature to obtain a mixed dispersion of sulfamic acid and cellulose; The mixed dispersion system of aminosulfonic acid and cellulose was loaded into a polytetrafluoroethylene-lined reactor for microwave reaction; The obtained crude product is washed with deionized water and ethanol, then vacuum dried and ground to obtain aminosulfonic acid modified cellulose and prepare aminosulfonic acid modified cellulose double-layer coated urea slow-release fertilizer; Add polymethyl methacrylate into acetone solution and stir to dissolve at room temperature; In step 2①, slowly add urea to the stirred solution and stir to form a uniform coating on the urea surface; The uniformly coated urea obtained in step 2② was placed in a vacuum drying oven, dried for a period of time, and cooled to room temperature; The aminosulfonic acid-modified cellulose and sodium alginate obtained in step 1 were added to a certain volume of water to prepare a mixed solution, and stirred at room temperature; Dissolve calcium chloride in water to form a mixed solution, add the coated urea obtained in step 2③ to the mixed solution obtained in step 2④, then add the calcium chloride solution obtained in step 2⑤ and pour into a mold for cross-linking. After the cross-linking is completed, put it into an oven for drying to obtain aminosulfonic acid modified cellulose double-layer coated urea slow-release fertilizer.

2. The method for preparing a sulfamic acid modified cellulose double-layer coated urea slow-release fertilizer according to claim 1, characterized in that In step 1①, the stirring speed is 300r / min~800r / min, the stirring time is 20min~40min, and the ratio of cellulose to distilled water is (1g~5g):(10mL~50mL).

3. The method for preparing a sulfamic acid modified cellulose double-layer coated urea slow-release fertilizer according to claim 1, characterized in that In step 1②, the stirring speed is 400r / min~1000r / min, the stirring time is 0.5h~3h, and the ratio of cellulose to aminosulfonic acid is (1g~5g):(3g~15g).

4. The method for preparing a sulfamic acid modified cellulose double-layer coated urea slow-release fertilizer according to claim 1, characterized in that In step 1③, the microwave temperature is 80°C~120°C, and the time is 20min~40min.

5. The method for preparing a sulfamic acid modified cellulose double-layer coated urea slow-release fertilizer according to claim 1, characterized in that In step 1④, the number of ethanol washings is 4 to 6 times, and the vacuum drying temperature is 40°C to 60°C.

6. The method for preparing a sulfamic acid modified cellulose double-layer coated urea slow-release fertilizer according to claim 1, characterized in that In step 2①, the stirring speed is 300r / min~800r / min, the stirring time is 1h~1.5h, and the ratio of polymethyl methacrylate to acetone is (5g~10g):(50ml~100ml).

7. The method for preparing a sulfamic acid modified cellulose double-layer coated urea slow-release fertilizer according to claim 1, characterized in that The urea particles added in step 2② have a particle size of 1 mm to 3 mm and a gram weight of 1 g to 3 g.

8. The method for preparing a sulfamic acid modified cellulose double-layer coated urea slow-release fertilizer according to claim 1, characterized in that In step 2③, the vacuum drying temperature is 40°C to 60°C.

9. The method for preparing a sulfamic acid modified cellulose double-layer coated urea slow-release fertilizer according to claim 1, characterized in that In step 2④, the ratio of aminosulfonic acid modified cellulose to sodium alginate to water is (1g~3g):(3g~9g):(150ml~450ml), and the stirring time is 3min~5min.

10. The method for preparing a sulfamic acid modified cellulose double-layer coated urea slow-release fertilizer according to claim 1, characterized in that In step 2⑤, the cross-linking time is 3h~5h, the drying temperature is 60℃~80℃, the drying time is 24h~48h, and the ratio of calcium chloride to water is (3g~6g):(50ml~100ml).

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