A time-controlled release fertilizer, a carrier thereof and a preparation method thereof

Abstract

The application provides a time sequence controlled release fertilizer. A preparation method of the time sequence controlled release fertilizer comprises the following steps: preparation of a core of the controlled release fertilizer and a coating layer; preparation of the core of the controlled release fertilizer: a sodium alginate solution is mixed with a water-soluble fertilizer solution and uniformly dispersed to obtain a composite gel solution; the composite gel solution is dropped into a crosslinking solution to obtain a hydrogel particle, and the hydrogel particle is washed and dried to obtain the core of the controlled release fertilizer; preparation of a coating layer solution: polylactic acid is dissolved in an organic solvent to obtain an organic solution; polyethylene glycol and an organic-soluble fertilizer are added into the organic solution, and the polyethylene glycol and the organic-soluble fertilizer are fully dissolved and uniformly mixed to obtain the coating layer solution; the core of the controlled release fertilizer is immersed in the coating layer solution to form a primary coating body; the primary coating body is transferred to a non-solvent coagulation bath to perform non-solvent induced phase separation, and the secondary coating body is obtained after being taken out and washed; and the secondary coating body is vacuum dried to obtain the time sequence controlled release fertilizer.

Description

Technical Field

[0001] This application relates to the field of compound fertilizer technology, and in particular to a time-controlled release fertilizer, its carrier, and its preparation method. Background Technology

[0002] Compared to traditional granular fertilizers, coated slow-release fertilizers have advantages such as longer-lasting effects and higher nutrient utilization rates. Traditional coated slow-release fertilizers generally use a nutrient element as the core and a polymer as the outer coating. The slow release of nutrients is achieved through the gradual degradation of both the outer coating and the core. For example, the Chinese invention patent application with application number 202510964573.4, entitled "Bio-based Polymer Compound Fertilizer Slow-Release Granules and Desert Water Conservation and Sand Fixation Method," employs this method.

[0003] However, plants have different requirements for the types and amounts of nutrients at different growth stages. Traditional coated slow-release fertilizers release multiple elements simultaneously, which is not synchronized with the nutrients required for plant growth and makes it difficult to release the corresponding nutrients according to the plant's growth stage. Summary of the Invention

[0004] Based on the above situation, this application provides a time-controlled release fertilizer carrier with sodium alginate hydrogel as the core and polylactic acid / polyethylene glycol as the controllable coating layer, so as to realize the continuous supply and phased release of nutrients in a single particle.

[0005] This application also provides a time-controlled release fertilizer that releases nutrients in stages and time periods.

[0006] This application also provides a method for preparing a time-controlled release fertilizer.

[0007] A time-controlled release fertilizer carrier comprises a core and a coating layer: The core is composed of sodium alginate and a cross-linking agent; The coating layer is composed of a mixture of polylactic acid and polyethylene glycol.

[0008] A time-controlled release fertilizer comprises a core and a coating layer: The core is composed of sodium alginate, cross-linking agent, and water-soluble fertilizer. The coating layer is composed of polylactic acid, polyethylene glycol, and organic soluble fertilizer.

[0009] A method for preparing a time-controlled release fertilizer includes the following steps: Step 1: Preparation of the core and coating layer of the controlled-release fertilizer; Preparation of controlled-release fertilizer core: Sodium alginate solution and water-soluble fertilizer solution are mixed and dispersed evenly to obtain a composite gel solution; the composite gel solution is dropped into a cross-linking solution to obtain hydrogel particles, which are then washed and dried to obtain the controlled-release fertilizer core; Preparation of coating solution: Polylactic acid is dissolved in an organic solvent to obtain an organic solution; polyethylene glycol and organic soluble fertilizer are added to the organic solution, and after being fully dissolved and mixed evenly, the coating solution is obtained. Step 2: Immerse the core of the controlled-release fertilizer in the coating solution to form a primary coating; Step 3: Transfer the primary coating to a non-solvent coagulation bath for non-solvent-induced phase separation, remove and wash to obtain the secondary coating; Step 4: Vacuum dry the secondary coating to obtain the time-controlled release fertilizer.

[0010] The technical advantage of this application is that the time-controlled release fertilizer carrier can carry different types and proportions of nutrients according to the growth needs of different plants at different stages, and release them in stages and at different times.

[0011] The time-controlled release fertilizer of this application can control the phased release of different nutrients through the stepwise degradation of the outer coating and the core, which is more in line with the growth needs of plants.

[0012] The method for preparing the time-controlled release fertilizer of this application can control the pore structure of the coating layer, thereby adjusting the release rate of the slow-release fertilizer in the outer coating layer.

[0013] The method for preparing the time-controlled release fertilizer of this application can control the concentration and / or molecular weight of the core sodium alginate and cross-linking agent, thereby adjusting the release rate of the core slow-release fertilizer. Attached Figure Description

[0014] Figure 1 A comparison chart showing the degradation degree of pure polylactic acid (PLA) coating material, PLA / polyethylene glycol (PEG) composite coating material, and the coating layer of this application over time; Figure 2 These are high-magnification SEM images of the surfaces of pure polylactic acid (PLA) coating materials, PLA / PEG composite coating materials, and the coating layer of this application. (a) A high-magnification (1 μm) SEM image of the surface of the pure PLA coating material, showing a relatively dense and smooth surface with a wavy / microcrack-like structure; (b) A low-magnification (5 μm) SEM image of the surface of the pure PLA, showing an overall dense continuous phase without obvious open pores; (c) A high-magnification (1 μm) SEM image of the surface of the PLA / PEG composite coating material, showing scattered micropores and roughening features; (d) A low-magnification (5 μm) SEM image of the surface of the PLA / PEG composite coating material, showing uniformly distributed micropores with increased pore density; (e) A low-magnification (5 μm) SEM image of the surface of the coating layer of this application.

[0015] Figure 3(a) is a graph showing the change in phosphorus release and accumulation in water over time for the sodium alginate core of Example 1 and the time-controlled release fertilizer of Example 3. (b) is a graph showing the change in phosphorus release rate in water over time for the sodium alginate core of Example 1 and the time-controlled release fertilizer of Example 3. Blue represents the sodium alginate core, and red represents the time-controlled release fertilizer.

[0016] Figure 4 This is a graph showing the cumulative nitrogen and phosphorus content of the time-controlled release fertilizer in water over time, as described in Example 3. Green represents nitrogen, and red represents phosphorus. Detailed Implementation

[0017] The embodiments of the technical solution of this application will be described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

[0018] A time-controlled release fertilizer carrier comprises a core and a coating layer: The core is composed of sodium alginate and a cross-linking agent; The coating layer is composed of a mixture of polylactic acid and polyethylene glycol.

[0019] Sodium alginate is a natural polysaccharide-based biomaterial extracted from brown algae. It is a linear polymer formed by β-D-mannuronic acid and α-L-guluronic acid linked by glycosidic bonds, possessing advantages such as biodegradability and biocompatibility. It reacts with divalent (e.g., Ca) compounds... 2+ ) or trivalent (Fe 3+ Metal ions such as calcium phosphate form a hydrogel, which serves as the core nutrient element carrier in this application. Water-soluble fertilizer sources such as dicalcium phosphate can be uniformly dispersed in the alginate matrix and gradually released.

[0020] Polylactic acid (PLA) is a bio-based material produced by chemical polymerization of lactic acid from renewable biomass resources. It possesses advantages such as environmental friendliness, good plasticity, and ease of processing. However, pure PLA membranes are dense and have poor hydrophilicity, making it difficult to form controllable channels to achieve the desired release kinetics under simple processes. This application modulates the nutrient release rate by controlling the pore structure and water permeation pathway through blending with polyethylene glycol.

[0021] The hydroxyl and carboxyl groups on the surface of sodium alginate gel interact with polylactic acid / polyethylene glycol molecules through hydrogen bonds. This simpler physical blending results in stronger bonding and prevents the coating layer from peeling off.

[0022] Simultaneously, the degradation rates of the core and coating layer enable sequential nutrient supply. In the early stages, sodium alginate swells rapidly upon contact with water, resulting in a fast degradation rate and rapid release of nutrients loaded with sodium alginate. In the middle stages, the degradation rates of the core and coating layer are comparable, leading to a more balanced release of loaded nutrients. In the later stages, the core is completely degraded, while the coating layer continues to degrade. Thus, the nutrient supply can be controlled by adjusting the carrier ratio.

[0023] In addition, the core has a high water absorption rate, and the hydrophobicity of the coating layer reduces water evaporation. After initial irrigation, the carrier rapidly absorbs water, and as water evaporates from the surrounding soil later, the coating layer effectively reduces water loss. The synergistic effect of both contributes to a good water retention effect.

[0024] A time-controlled release fertilizer comprises a core and a coating layer: The core is composed of sodium alginate, cross-linking agent, and water-soluble fertilizer. The coating layer is composed of polylactic acid, polyethylene glycol, and organic soluble fertilizer.

[0025] There are many options for the crosslinking agent. Inorganic crosslinking agents include calcium chloride, magnesium chloride, strontium chloride, ferric chloride, and aluminum chloride. From the perspective of supplementing trace elements, in a preferred embodiment, the crosslinking agent is calcium chloride. Organic crosslinking agents include epichlorohydrin, glutaraldehyde, and peroxidase. The above crosslinking agents can also be used in combination.

[0026] The water-soluble fertilizers available are varied, including nitrogen fertilizers such as urea, ammonium sulfate, ammonium nitrate, and ammonium chloride; phosphate fertilizers such as potassium dihydrogen phosphate, ammonium dihydrogen phosphate, and superphosphate; potassium fertilizers such as potassium chloride, potassium sulfate, and potassium nitrate; micronutrient fertilizers such as calcium chloride, calcium nitrate, magnesium sulfate, chelated iron, and chelated zinc; and functional fertilizers such as humic acid, amino acids, alginic acid, rhizobia, phosphate-solubilizing bacteria, and Bacillus subtilis.

[0027] When cross-linking agents are used with water-soluble fertilizers, chemical reactions should be avoided. For example, calcium ions and phosphates can form insoluble calcium phosphate precipitates. Furthermore, pH levels should be considered; for instance, aluminum ion cross-linking agents are suitable for acidic fertilizers, while calcium ion cross-linking agents are suitable for alkaline fertilizers. In addition, cross-linking agents that match the nutrient release characteristics should be selected; for example, fast-acting fertilizers are suitable for rapid cross-linking agents, while slow-acting fertilizers are suitable for slow-release cross-linking agents. The specific choice depends on the actual needs.

[0028] In a preferred embodiment, when fertilizing field crops, the cross-linking agent is CaCl2 and FeCl3, and the water-soluble fertilizer contains urea, ammonium dihydrogen phosphate, potassium chloride, and chelated zinc. A single application of fertilizer can produce fertilizer effect throughout the entire growth period. When fertilizing vegetable crops, the cross-linking agent is MgCl2 and glutaraldehyde, and the water-soluble fertilizer contains ammonium nitrate, potassium dihydrogen phosphate, calcium nitrate, and chelated iron. The above fertilizers provide balanced nutrient supply and can improve vegetable quality. In a preferred embodiment, when fertilizing flower crops, the cross-linking agent is peroxidase, and the water-soluble fertilizer contains potassium nitrate, potassium dihydrogen phosphate, chelated trace elements, and amino acids. The flowers fertilized after application have bright colors, extended flowering period, and enhanced stress resistance.

[0029] The organic soluble fertilizer described in this application is a fertilizer that can be dissolved in an organic solvent, which can also dissolve polylactic acid. Suitable organic soluble fertilizers include urea, chelated iron, chelated zinc, and other organic fertilizers that are soluble in organic solvents.

[0030] A method for preparing a time-controlled release fertilizer includes the following steps: Step 1: Preparation of the core and coating layer of the controlled-release fertilizer; Preparation of controlled-release fertilizer core: Sodium alginate solution and water-soluble fertilizer solution are mixed and dispersed evenly to obtain a composite gel solution; the composite gel solution is dropped into a cross-linking solution to obtain hydrogel particles, which are then washed and dried to obtain the controlled-release fertilizer core; Taking a water-soluble fertilizer solution of dicalcium phosphate as an example, in a preferred embodiment, the preparation process of the controlled-release fertilizer core is as follows: Sodium alginate is dissolved in deionized water to prepare a sodium alginate solution (mass fraction 1~5 wt%, preferably about 2 wt%); dicalcium phosphate (5~20 g / 100 mL, preferably 10 g / 100 mL) is added to the sodium alginate solution in batches and stirred and dispersed evenly to obtain an SA / CaHPO4 composite gel solution.

[0031] The SA / CaHPO4 composite gel solution was dripped into a CaCl2 solution using a peristaltic pump to crosslink and form hydrogel particles with a concentration of 0.05~0.5 M (preferably 0.2 M) and a crosslinking time of 5~20 min (preferably 20 min). The hydrogel particles were collected and washed with deionized water, and then vacuum dried at 60℃ to obtain CaAlgCRFs, i.e., the core of controlled-release fertilizer.

[0032] Preparation of coating solution: Polylactic acid is dissolved in an organic solvent to obtain an organic solution; polyethylene glycol and organic soluble fertilizer are added to the organic solution, and after being fully dissolved and mixed evenly, the coating solution is obtained. Taking urea as an example of an organic soluble fertilizer, in a preferred embodiment, the preparation process of the coating layer solution is as follows: polylactic acid (mass fraction of 5-15 wt%, preferably 10 wt%) is dissolved in dichloromethane; polyethylene glycol (molecular weight of 400-6000) is added to the polylactic acid solution as a hydrophilic phase, the mass of polyethylene glycol being 5-30 wt% (preferably 20-30 wt%) of the mass of polylactic acid; urea is added, the mass of urea being 5-30 wt% (preferably about 10 wt%) of the mass of polylactic acid, and the mixture is stirred / ultrasonicated until homogeneous.

[0033] Step 2: Immerse the core of the controlled-release fertilizer in the coating solution to form a primary coating; In a preferred embodiment, the immersion time is 5 to 20 minutes.

[0034] Step 3: Transfer the primary coating to a non-solvent coagulation bath for non-solvent-induced phase separation, remove and wash to obtain the secondary coating; In a preferred embodiment, the settling time of the non-solvent coagulation bath is 5 to 20 minutes (preferably 20 minutes).

[0035] Step 4: Vacuum dry the secondary coating to obtain the time-controlled release fertilizer.

[0036] Specifically, after removing and washing the secondary coating, the product is dried under vacuum at 40-60°C for 6-24 hours (preferably 60°C, 12 hours) to obtain nitrogen and phosphorus dual-element time-controlled release fertilizer granules.

[0037] To meet the needs of plant growth, a slow-release curve can be set to ensure that nutrients are released according to this curve. The slow-release curve can be optimized by using multiple dip-coating-coagulation cycles, adjusting the concentration of polylactic acid, the content or molecular weight of polyethylene glycol, and changing the type / concentration of crosslinking ions.

[0038] The following are specific embodiments of this application.

[0039] Example 1: Preparation of Controlled-Release Fertilizer Core Dissolve 2.0 g of sodium alginate in 100 mL of deionized water to obtain a 2 wt% sodium alginate solution; Add 1.0 g of dicalcium phosphate to sodium alginate solution and stir until homogeneous to obtain SA / CaHPO4 composite gel solution; SA / CaHPO4 composite gel solution was added dropwise to 0.2 M CaCl2 solution using a peristaltic pump, crosslinked for 20 min, the hydrogel particles were washed with deionized water, and then vacuum dried at 60 °C to obtain CaAlgCRFs.

[0040] Example 2: Preparation of the coating layer Weigh out 3.3 g (10 wt%) of polylactic acid and add it to 25 mL of DCM. Stir magnetically at room temperature (500 rpm) for 4 h until a homogeneous polylactic acid solution without visible agglomerates is obtained. Add polyethylene glycol (0.1 g, 3 w / w polylactic acid) with a molecular weight of 2000 to the polylactic acid solution and stir for 2 h to make the system homogeneous; Add urea (0.165 g, 5 wt%) and sonicate for 15 min (100 Hz). The mixed solution was transferred to a 10 cm diameter polytetrafluoroethylene petri dish, with a liquid layer thickness of approximately 3 mm. 50 mL of methanol was slowly added at a rate of 1 mL / min using a micro-injection pump, and the mixture was allowed to stand for 20 min to complete the non-solvent-induced phase separation. The film-forming sample was vacuum dried at 60°C for 12 h to obtain the coated film material.

[0041] Example 3: Preparation of Time-Controlled Release Fertilizer The controlled-release fertilizer core and coating solution were prepared according to the same process as in Examples 1 and 2. The controlled-release fertilizer core was immersed in the coating solution for 20 min to form a primary coating film. Then it was transferred to a methanol coagulation bath and left to stand for 20 min for non-solvent-induced phase separation. After washing, it was dried under vacuum at 60°C for 12 h to obtain nitrogen and phosphorus binary time-controlled release fertilizer particles.

[0042] To verify the effectiveness of time-controlled release fertilizer, this application also conducted a comparative experiment, as detailed below.

[0043] Comparative Example 1: Preparation of polylactic acid coated materials Weigh out 3.3 g (10 wt%) of polylactic acid and add it to 25 mL of DCM. Stir magnetically at room temperature (about 500 rpm) for 4 h until a homogeneous polylactic acid solution without visible agglomerates is obtained. The polylactic acid solution was transferred to a polytetrafluoroethylene petri dish with a diameter of 10 cm, and the mixed solution layer was about 3 mm thick.

[0044] 50 mL of methanol was slowly added at a rate of 1 mL / min using a micro-injection pump, and the mixture was allowed to stand for 20 min to complete the non-solvent-induced phase separation.

[0045] The film-forming sample was vacuum dried at 60°C for 12 h to obtain polylactic acid coated material.

[0046] Comparative Example 2: Preparation of polylactic acid and polyethylene glycol composite coating materials Weigh out polylactic acid (3.3 g, 10 wt%) and add it to 25 mL of DCM. Stir magnetically at room temperature (about 500 rpm) for 4 h until a homogeneous solution without visible agglomerates is obtained.

[0047] Add polyethylene glycol-2000 (0.1 g, 3 w / w polylactic acid) and continue stirring for 2 h to homogenize the system.

[0048] The mixed solution was transferred to a 10 cm diameter polytetrafluoroethylene petri dish, with the mixed solution layer thickness being approximately 3 mm.

[0049] 50 mL of methanol was slowly added at a rate of 1 mL / min using a micro-injection pump, and the mixture was allowed to stand for 20 min to complete the non-solvent-induced phase separation.

[0050] The film-forming sample was vacuum dried at 60°C for 12 h to obtain a polylactic acid and polyethylene glycol composite coating material.

[0051] The coating material (PPUC) of Example 2 was compared with the polylactic acid coating material (PLA) of Comparative Example 1 and the polylactic acid-polyethylene glycol composite coating material (PLA-PEG) of Comparative Example 2 in terms of degradation. The results are as follows: Figure 1 As shown. By Figure 1 It can be seen that the single polylactic acid (PLA) coating material only degraded by 5% after 90 days; the PLA / PEG composite coating material degraded by approximately 60% after 90 days, while the coating film material in Example 2 degraded by approximately 70%. This demonstrates that the addition of urea, in addition to providing nitrogen fertilizer for crops, can also promote the degradation of PLA, facilitating the release of core nutrients. Figure 2 As can be seen from the electron microscope images, the coating layer of this application has more micropores, with pore sizes ranging from hundreds of nanometers to several micrometers. The surface is rough and has obvious open channel features, which is conducive to water / solute transport.

[0052] The controlled-release fertilizer core prepared in Example 1 and the time-series controlled-release fertilizer prepared in Example 3 were subjected to a slow-release experiment in water. The cumulative release curve of phosphorus over time is shown in the figure below. Figure 3 As shown. By Figure 3 As shown in (a) and (b), the initial release rate of phosphorus in the core of the controlled-release fertilizer is the fastest. As the phosphorus concentration in the core gradually decreases, the release rate of phosphorus also gradually decreases. In contrast, due to the inhibitory effect of the outer coating layer, the release rate of phosphorus in the time-series controlled-release fertilizer is very slow for the first 100 hours after a brief period of high release in the initial stage. The release rate then gradually increases until it begins to gradually decrease around 150 hours. This demonstrates that the outer coating layer effectively inhibits the release of phosphorus.

[0053] Meanwhile, the cumulative release curve of nitrogen and phosphorus elements in the time-controlled fertilizer prepared in Example 3 over time is shown in the figure below. Figure 4 As shown. By Figure 4 It can be seen that nitrogen fertilizer in time-controlled release fertilizer is released in large quantities during the 0-150h period, while the release rate of phosphorus fertilizer gradually increases after 100h. Therefore, there is a significant time difference between the large release of nitrogen fertilizer and the large release of phosphorus fertilizer, and they can be released in a certain time sequence.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A time-controlled release fertilizer carrier, characterized in that... Includes kernel and wrapper layer: The core is composed of sodium alginate and a cross-linking agent; The coating layer is composed of a mixture of polylactic acid and polyethylene glycol.

2. A time-controlled release fertilizer, characterized in that... Includes kernel and wrapper layer: The core is composed of sodium alginate, cross-linking agent, and water-soluble fertilizer. The coating layer is composed of polylactic acid, polyethylene glycol, and organic soluble fertilizer.

3. The time-controlled release fertilizer as described in claim 2, characterized in that: The crosslinking agent is CaCl2.

4. The time-controlled release fertilizer as described in claim 2, characterized in that: The water-soluble fertilizer is calcium hydrogen phosphate.

5. The time-controlled release fertilizer as described in claim 2, characterized in that: The organic soluble fertilizer is urea.

6. A method for preparing a time-controlled release fertilizer as described in claim 2, characterized in that: Includes the following steps: Step 1: Preparation of the core and coating layer of the controlled-release fertilizer; Preparation of controlled-release fertilizer core: Sodium alginate solution and water-soluble fertilizer solution are mixed and dispersed evenly to obtain composite gel solution; The composite gel solution was dropped into the cross-linking solution to obtain hydrogel particles, which were then washed and dried to obtain the controlled-release fertilizer core. Preparation of coating solution: Polylactic acid is dissolved in an organic solvent to obtain an organic solution; Polyethylene glycol and organic soluble fertilizer are added to an organic solution, and after being fully dissolved and mixed evenly, a coating solution is obtained. Step 2: Immerse the core of the controlled-release fertilizer in the coating solution to form a primary coating; Step 3: Transfer the primary coating to a non-solvent coagulation bath for non-solvent-induced phase separation, remove and wash to obtain the secondary coating; Step 4: Vacuum dry the secondary coating to obtain the time-controlled release fertilizer.

7. The preparation method according to claim 6, characterized in that: The crosslinking agent is CaCl2, and the concentration of CaCl2 is 0.05~0.5 M.

8. The preparation method according to claim 6, characterized in that: The organic solvent is dichloromethane.

9. The preparation method according to claim 6, characterized in that: The non-solvent coagulation bath is methanol.

10. The preparation method according to claim 6, characterized in that: The molecular weight of the polyethylene glycol is 400-6000.

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