Cellulose coated urea slow-release fertilizer and preparation method thereof

Abstract

The invention discloses a cellulose coated urea slow-release fertilizer and a preparation method thereof, and belongs to the technical field of slow-release fertilizer preparation. The preparation method comprises the following steps: mixing an adhesive, urea and water, and granulating to obtain mixed particles; uniformly mixing a cellulose base material, a cross-linking agent, an auxiliary agent and water to obtain a coating precursor solution; mixing the coating precursor solution with the mixed particles, and drying to obtain a coating body; co-dissolving the coating body and a surface modifier in a solvent, carrying out stirring reaction, and drying to obtain a modified body; and repeating the steps of coating and modifying for 1-3 times to obtain the composite material. The invention also discloses the cellulose coated urea slow-release fertilizer prepared by the method. The cellulose coated urea slow-release fertilizer can effectively solve the problems of poor film-forming property and poor urea slow-release property of the existing urea slow-release fertilizer, and has a relatively good practical value.

Description

Technical Field

[0001] This invention belongs to the field of slow-release fertilizer preparation technology, specifically relating to a cellulose-coated urea slow-release fertilizer and its preparation method. Background Technology

[0002] Urea, as the most widely used nitrogen fertilizer in agricultural production, has the significant advantage of high nitrogen content. However, its rapid dissolution rate after being applied to the soil results in the loss of over 50% of its nitrogen through ammonia volatilization, nitrate leaching, and denitrification. This not only leads to low fertilizer utilization and increased agricultural costs but also causes a series of serious ecological and environmental problems such as eutrophication and soil acidification. To solve this problem, slow-release fertilizer technology has emerged. By coating urea granules with hydrophobic materials to delay nutrient release, it allows for a single application that meets the needs of crops throughout their entire growth cycle.

[0003] However, existing coating materials are mainly divided into two categories, each with its own defects: one category is inorganic coating materials such as sulfur and minerals, which have low cost but have problems such as easy membrane rupture and uncontrollable release; the other category is synthetic polymers such as polyurethane and polyethylene, which have excellent controlled release performance but are difficult to degrade in soil, and long-term application will lead to microplastic accumulation and degradation of soil ecological function.

[0004] In recent years, natural bio-based materials, represented by cellulose, have attracted much attention due to their renewability, biodegradability and environmental friendliness. However, the inherent strong hydrophilicity of cellulose causes the coating layer to swell easily when exposed to water, and the nutrient release rate is too fast to meet the requirements of long-term sustained release. At the same time, existing preparation processes generally suffer from technical bottlenecks such as uneven membrane structure and insufficient mechanical strength.

[0005] How to modify cellulose and prepare uniformly coated slow-release fertilizer, control the release rate of urea, and achieve the requirement of long-term slow release is one of the current research hotspots in this field. Summary of the Invention

[0006] The problem this invention aims to solve is to provide a cellulose-coated urea slow-release fertilizer and its preparation method, in order to address the issues of poor film-forming properties and poor slow-release performance of existing urea slow-release fertilizers.

[0007] The technical solution adopted to solve the technical problem is to provide a method for preparing cellulose-coated urea slow-release fertilizer, including the following steps: (1) Mix the adhesive, urea and water and then granulate to obtain mixed granules; (2) Mix the cellulose matrix, crosslinking agent, auxiliary agent and water to obtain the coating precursor solution; (3) Mix the coating precursor liquid with the mixed particles and dry to obtain the coated body; (4) The coating and the surface modifier are dissolved together in a solvent, stirred and reacted, and then dried to obtain the modified body; (5) Repeat steps (3) to (4) 1 to 3 times to obtain cellulose-coated urea slow-release fertilizer.

[0008] The beneficial effects of the above-mentioned technical solution of this invention are as follows: In the preparation method of this invention, cellulose-based adhesives are used as the binder and coating material for urea. They have good water solubility and extremely high viscosity at low temperatures, and can form a physical barrier to prevent urea release after absorbing water. The outer coating material mainly uses cellulose substrates with good film-forming properties to ensure the continuity and integrity of the coating film structure. By constructing a multi-layer cellulose coating structure and introducing cross-linking and surface modification treatments, urea is coated in its original form. It dissolves and releases by absorbing moisture from the air and soil, effectively solving the problems of low utilization rate, easy loss, and difficult degradation of plastic coating materials in traditional urea fertilizers. Specifically, using natural renewable cellulose as the substrate, a dense three-dimensional network coating layer is formed under the action of a cross-linking agent, which significantly slows down the release rate of urea in the soil, thereby prolonging the fertilizer effect and reducing nitrogen loss. At the same time, by adjusting the hydrophilic-hydrophobic balance of the surface of the cellulose-based coating material through surface modifiers, the water absorption rate of the coating material in a high humidity environment is controlled, thereby achieving regulation of the urea release rate. In addition, the quality of the coating precursor liquid and surface modifier can be the same as or different from that in steps (3) to (4) 1 to 3 times. By adopting a combination of multiple coating and modification, the release cycle can be flexibly adjusted according to the crop's fertilizer requirements. Moreover, the preparation process uses water as the main medium, which is green, environmentally friendly, and cost-controllable. The final product has the advantages of efficient slow release, biodegradability, and strong process adaptability. While improving agricultural economic benefits, it effectively avoids microplastic pollution and soil ecological risks.

[0009] A preferred method for preparing cellulose-coated urea slow-release fertilizer includes the following steps: (1) Mix the adhesive, urea and water and then granulate to obtain mixed granules; (2) Mix the cellulose matrix, crosslinking agent, auxiliary agent and water to obtain the coating precursor solution; (3) The coating precursor liquid is mixed with the mixed particles and dried for the first time to obtain the first coated body; (4) The first coating body and the surface modifier are dissolved together in a solvent and stirred to react, and then dried for a second time to obtain the first modified body; (5) The coating precursor liquid is mixed with the first modified body and dried for a third time to obtain the second coated body; (6) The second coating and the surface modifier are dissolved in a solvent and stirred and then dried for the fourth time to obtain cellulose-coated urea slow-release fertilizer.

[0010] Preferably, the adhesive in step (1) is at least one of carboxymethyl cellulose, ethyl cellulose, hydroxypropyl cellulose and hydroxypropyl methyl cellulose.

[0011] More preferably, the mass ratio of urea, binder and water is 100:(0.5~5):(1~5); granulation is carried out by extrusion granulation or rotary granulation; the diameter of the mixed particles is 3~5 mm.

[0012] More preferably, the mass ratio of urea, binder and water is 100:(0.5~0.6):2.5.

[0013] Preferably, in step (2), the cellulose substrate is at least one of carboxymethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose and hydroxyethyl cellulose; the crosslinking agent is at least one of glutaraldehyde, glycerol triglycidyl ether, epichlorohydrin and formaldehyde; and the auxiliary agent is at least one of sodium hydroxide, potassium hydroxide, triethylamine, tributylamine, tetrabutylammonium bromide and polyethylene glycol 200.

[0014] More preferably, the mass ratio of cellulose matrix, crosslinking agent, additive and water is 100:(2~10):(0.5~5):(500~1000).

[0015] More preferably, the mass ratio of cellulose matrix, crosslinking agent, additives and water is 100:(4~6):(1~1.5):600.

[0016] Preferably, in step (3), the mass of the coating precursor solution is 5-10% of the mass of urea in the mixed particles.

[0017] Preferably, in step (3), the mass of the coating precursor solution is 5-8% of the mass of urea in the mixed particles.

[0018] Preferably, the drying temperature in step (3) is 50~100℃ and the time is 10~30 min.

[0019] Preferably, the drying temperature in step (3) is 60°C and the time is 20 min.

[0020] Preferably, in step (4), the surface modifier is at least one of octanoyl chloride, decanoyl chloride, lauroyl chloride, tetradecanoyl chloride and oleoyl chloride, and the solvent is petroleum ether; the mass of the surface modifier is 0.1~1% of the mass of the mixed particles.

[0021] More preferably, the surface modifier is 0.3 to 0.5% of the mass of the mixed particles.

[0022] Preferably, in step (4), the stirring reaction temperature is room temperature and the time is 30~120 min; the drying temperature is 60~90℃ and the time is 10~30 min.

[0023] More preferably, in step (4), the stirring reaction temperature is room temperature and the time is 60 min; the drying temperature is 80℃ and the time is 20 min.

[0024] The present invention also provides a cellulose-coated urea slow-release fertilizer prepared by the above preparation method.

[0025] The present invention has the following beneficial effects: (1) The cellulose-coated urea slow-release fertilizer prepared by the method of the present invention introduces a surface modifier on the surface of the coating layer to adjust the hydrophilic-hydrophobic balance relationship on the surface of the cellulose-coated urea slow-release fertilizer, thereby controlling its water absorption rate in a high humidity environment, so as to achieve urea release rate regulation and significantly prolong the duration of fertilizer effect.

[0026] (2) The cellulose-coated urea slow-release fertilizer prepared by the method of the present invention uses cellulose derivatives as the coating substrate. Cellulose, as the most abundant natural polymer material in nature, comes from renewable resources such as crop straw and wood pulp. It has the significant advantages of wide availability, low cost and sustainable regeneration, which reduces the dependence on petroleum-based polymer materials, reduces the production cost of slow-release fertilizer, and provides a new way for the resource utilization of agricultural waste, which is in line with the development concept of circular economy and green agriculture.

[0027] (3) The cellulose-coated urea slow-release fertilizer prepared by the method of the present invention has good biodegradability in natural soil environment. The coating material can be gradually decomposed under the action of microorganisms, avoiding the microplastic pollution problem caused by the long-term residue of traditional plastic coating materials in the soil. At the same time, by adjusting the number of coating layers, the degree of cellulose cross-linking and the type and amount of surface modifier, the present invention can achieve flexible control of the slow release cycle in the range of 30 to 90 days, which can meet the nutrient requirements of different crops at different growth stages and significantly improve the applicability and precision of the product.

[0028] (4) The cellulose-coated urea slow-release fertilizer prepared by the method of the present invention can increase the nitrogen fertilizer utilization rate by more than 30% compared with the traditional one-time urea fertilization. This is mainly due to the effective inhibition of urea dissolution by the multi-layer coating structure, which reduces the loss of nitrogen caused by volatilization, leaching and denitrification, and synchronizes the nutrient release with the crop absorption pattern, thus achieving both economic and ecological benefits. Attached Figure Description

[0029] Figure 1 The image shows the results of the static water release test. Figure 2 The image shows the results of the sand column leaching test. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention; that is, the described embodiments are only a part of the embodiments of this invention, and not all of them.

[0031] Therefore, the following detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0032] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0033] Example 1 A method for preparing a cellulose-coated urea slow-release fertilizer includes the following steps: (1) Hydroxypropyl methylcellulose, urea and water are mixed in a mass ratio of 0.5:100:2.5 and then extruded and granulated to obtain mixed particles with a diameter of 3~5 mm; (2) Mix carboxymethyl cellulose, glycerol triglycidyl ether, triethylamine, tetrabutylammonium bromide and water in a mass ratio of 100:4:1:0.5:600 to obtain the coating precursor solution. (3) Mix the coating precursor solution with the mixed particles. The mass of the coating precursor solution is 5% of the mass of urea in the mixed particles in step (1). After coating, perform initial drying at 60°C for 20 min to obtain the first coated body. (4) The first coating body and lauroyl chloride were mixed and dissolved in petroleum ether. The mass of lauroyl chloride was 0.3% of the mass of the mixed particles in step (1). The mixture was stirred and reacted at room temperature for 60 min, and then dried for a second time at 80°C for 20 min to obtain the first modified body. (5) Mix the coating precursor liquid with the first modified body. The mass of the coating precursor liquid is 5% of the mass of urea in the mixed particles in step (1). After the coating is completed, dry it for a third time at 60°C for 20 min to obtain the second coated body. (6) The second coating body and lauroyl chloride are mixed and dissolved in petroleum ether. The mass of lauroyl chloride is 0.4% of the mass of the mixed particles in step (1). The mixture is stirred and reacted at room temperature for 60 min, and then dried for the fourth time at 80℃ for 20 min to obtain cellulose-coated urea slow-release fertilizer.

[0034] Example 2 A method for preparing a cellulose-coated urea slow-release fertilizer includes the following steps: (1) Mix carboxymethyl cellulose, urea and water in a mass ratio of 0.6:100:2.5 and then granulate by rotary granulation to obtain mixed particles with a diameter of 3~5 mm; (2) Mix carboxymethyl cellulose, epichlorohydrin, triethylamine and water in a mass ratio of 100:6:1:600 ​​to obtain a coating precursor solution. (3) Mix the coating precursor solution with the mixed particles. The mass of the coating precursor solution is 5% of the mass of urea in the mixed particles in step (1). After coating, perform initial drying at 60°C for 20 min to obtain the first coated body. (4) The first coating body and decanoyl chloride were mixed and dissolved in petroleum ether. The mass of decanoyl chloride was 0.5% of the mass of the mixed particles in step (1). The mixture was stirred at room temperature for 60 min and then dried for 20 min at 80°C to obtain the first modified body. (5) Mix the coating precursor liquid with the first modified body. The mass of the coating precursor liquid is 5% of the mass of urea in the mixed particles in step (1). After the coating is completed, dry it for a third time at 60°C for 20 min to obtain the second coated body. (6) The second coating body and decanoyl chloride are mixed and dissolved in petroleum ether. The mass of decanoyl chloride is 0.5% of the mass of the mixed particles in step (1). The mixture is stirred and reacted at room temperature for 60 min, and then dried for the fourth time at 80℃ for 20 min to obtain cellulose-coated urea slow-release fertilizer.

[0035] Example 3 A method for preparing a cellulose-coated urea slow-release fertilizer includes the following steps: (1) Hydroxypropyl methylcellulose, urea and water are mixed in a mass ratio of 0.5:100:2.5 and then granulated by rotary granulation to obtain mixed particles with a diameter of 3~5 mm; (2) Mix carboxymethyl cellulose, glycerol triglycidyl ether, triethylamine, tetrabutylammonium bromide and water in a mass ratio of 100:4:1:0.5:600 to obtain the coating precursor solution. (3) Mix the coating precursor solution with the mixed particles. The mass of the coating precursor solution is 6% of the mass of urea in the mixed particles in step (1). After coating, perform initial drying at 60°C for 20 min to obtain the first coated body. (4) The first coating body and oleoyl chloride were mixed and dissolved in petroleum ether. The mass of oleoyl chloride was 0.4% of the mass of the mixed particles in step (1). The mixture was stirred and reacted at room temperature for 60 min, and then dried for a second time at 80°C for 20 min to obtain the first modified body. (5) Mix the coating precursor liquid with the first modified body. The mass of the coating precursor liquid is 8% of the mass of urea in the mixed particles in step (1). After the coating is completed, dry it for the third time at 60°C for 20 min to obtain the second coated body. (6) The second coating body and oleoyl chloride are mixed and dissolved in petroleum ether. The mass of oleoyl chloride is 0.5% of the mass of the mixed particles in step (1). The mixture is stirred and reacted at room temperature for 60 min, and then dried for the fourth time at 80℃ for 20 min to obtain cellulose-coated urea slow-release fertilizer.

[0036] Comparative Example 1 A method for preparing a cellulose-coated urea slow-release fertilizer includes the following steps: (1) Hydroxypropyl methylcellulose, urea and water are mixed in a mass ratio of 0.5:100:2.5 and then granulated by rotary granulation to obtain mixed particles with a diameter of 3~5 mm; (2) Mix carboxymethyl cellulose, glycerol triglycidyl ether, triethylamine, tetrabutylammonium bromide and water in a mass ratio of 100:4:1:0.5:600 to obtain the coating precursor solution. (3) Mix the coating precursor liquid with the mixed particles. The mass of the coating precursor liquid is 6% of the mass of urea in the mixed particles in step (1). After coating, perform initial drying at 60°C for 60 min to obtain cellulose-coated urea slow-release fertilizer.

[0037] Comparative Example 2 A method for preparing a cellulose-coated urea slow-release fertilizer includes the following steps: (1) Hydroxypropyl methylcellulose, urea and water are mixed in a mass ratio of 0.5:100:2.5 and then granulated by rotary granulation to obtain mixed particles with a diameter of 3~5 mm; (2) Mix carboxymethyl cellulose, glycerol triglycidyl ether, triethylamine, tetrabutylammonium bromide and water in a mass ratio of 100:4:1:0.5:600 to obtain the coating precursor solution. (3) Mix the coating precursor solution with the mixed particles. The mass of the coating precursor solution is 6% of the mass of urea in the mixed particles in step (1). After coating, perform initial drying at 60°C for 30 min to obtain the first coated body. (4) The first coating body and oleoyl chloride are mixed and dissolved in petroleum ether. The mass of oleoyl chloride is 0.4% of the mass of the mixed particles in step (1). The mixture is stirred and reacted at room temperature for 60 min, and then dried for a second time at 80℃ for 20 min to obtain cellulose-coated urea slow-release fertilizer.

[0038] Experimental Example The slow-release performance of the cellulose-coated urea slow-release fertilizers prepared in Examples 1-3 and Comparative Examples 1-2 was tested by static water dissolution test and sand column leaching test, respectively. The static water dissolution test procedure is as follows: Take 20 g of sample and place it in a 500 mL beaker, add 400 mL of distilled water, seal with plastic wrap, place in a 25℃ constant temperature incubator, take 2 mL of sample every certain period of time to test the nitrogen content and calculate the release rate.

[0039] The sand column leaching test procedure was as follows: Quartz sand was soaked in distilled water for 24 hours before use; then, 100 mm of quartz sand was placed in a 10 cm diameter leaching tube, and 5 g of sample was evenly spread on the surface of the quartz sand. Next, another 100 mm of quartz sand was placed on top of the sample. After the setup was completed, the tube was allowed to stand for 24 hours. Then, 120 mL of distilled water was added dropwise using a peristaltic pump to simulate 15 mm of rainfall. The filtrate was collected, the nitrogen content was measured, and the release rate was calculated. Thereafter, leaching was performed every two days until the sample release rate exceeded 90%. The results are as follows: Figures 1-2 As shown.

[0040] Through the Figures 1-2 Data analysis shows that the urea release rate of all samples gradually increased over time, but the release rate varied significantly due to different preparation processes. Overall, the sustained-release performance of Examples 1-3 was significantly better than that of Comparative Examples 1-2, with Example 3 showing the slowest release and exhibiting the best sustained-release effect; while Comparative Example 1 showed the fastest release, indicating that its coating structure was the least complete. Combined with the analysis of the preparation process, Examples 1-3 formed a more dense and complete coating structure due to the repeated steps (3) of coating and (4) of modification (1-3 times), thus significantly delaying the release of urea; while Comparative Example 1 only included one coating, and Comparative Example 2, although it had one modification, lacked repeated treatment, resulting in a weak coating layer and insufficient sustained-release capacity.

[0041] The present invention has been described according to the above embodiments. It should be understood that the above embodiments do not limit the present invention in any way. All technical solutions obtained by equivalent substitution or equivalent transformation fall within the scope of the present invention.

Claims

1. A method for preparing a cellulose-coated urea slow-release fertilizer, characterized in that, Includes the following steps: (1) Mix the adhesive, urea and water and then granulate to obtain mixed granules; (2) Mix the cellulose matrix, crosslinking agent, auxiliary agent and water to obtain the coating precursor solution; (3) Mix the coating precursor liquid with the mixed particles and dry to obtain the coated body; (4) The coating and the surface modifier are dissolved together in a solvent, stirred and reacted, and then dried to obtain the modified body; (5) Repeat steps (3) to (4) 1 to 3 times to obtain cellulose-coated urea slow-release fertilizer.

2. The method for preparing cellulose-coated urea slow-release fertilizer as described in claim 1, characterized in that, The adhesive used in step (1) is at least one of carboxymethyl cellulose, ethyl cellulose, hydroxypropyl cellulose and hydroxypropyl methyl cellulose.

3. The method for preparing cellulose-coated urea slow-release fertilizer as described in claim 1 or 2, characterized in that, The mass ratio of urea, binder and water is 100:(0.5~5):(1~5); the granulation is carried out by extrusion granulation or rotary granulation; the diameter of the mixed particles is 3~5 mm.

4. The method for preparing cellulose-coated urea slow-release fertilizer as described in claim 1, characterized in that, In step (2), the cellulose substrate is at least one of carboxymethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose and hydroxyethyl cellulose; the crosslinking agent is at least one of glutaraldehyde, glycerol triglycidyl ether, epichlorohydrin and formaldehyde; and the auxiliary agent is at least one of sodium hydroxide, potassium hydroxide, triethylamine, tributylamine, tetrabutylammonium bromide and polyethylene glycol 200.

5. The method for preparing cellulose-coated urea slow-release fertilizer as described in claim 1 or 4, characterized in that, The mass ratio of the cellulose matrix, crosslinking agent, additives and water is 100:(2~10):(0.5~5):(500~1000).

6. The method for preparing cellulose-coated urea slow-release fertilizer as described in claim 1, characterized in that, In step (3), the mass of the coating precursor solution is 5-10% of the urea mass in the mixed particles.

7. The method for preparing cellulose-coated urea slow-release fertilizer as described in claim 1, characterized in that, In step (3), the drying temperature is 50~100℃ and the time is 10~30 min.

8. The method for preparing cellulose-coated urea slow-release fertilizer as described in claim 1, characterized in that, In step (4), the surface modifier is at least one of octanoyl chloride, decanoyl chloride, lauroyl chloride, tetradecanoyl chloride and oleoyl chloride, and the solvent is petroleum ether; the mass of the surface modifier is 0.1~1% of the mass of the mixed particles.

9. The method for preparing cellulose-coated urea slow-release fertilizer as described in claim 1, characterized in that, In step (4), the stirring reaction temperature is room temperature and the time is 30~120 min; the drying temperature is 60~90℃ and the time is 10~30 min.

10. The cellulose-coated urea slow-release fertilizer prepared by the preparation method according to any one of claims 1 to 9.

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