Green organic compound fertilizer and preparation method thereof
By constructing a dynamic cross-linking network of lignin-peptide graft copolymer and borate in compound fertilizer, the problems of easy cracking and difficult degradation of the coating layer of coated compound fertilizer were solved, and the preparation of fertilizer with improved slow-release performance and environmental friendliness was achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SINO AGRI SHUNTIAN ECOLOGICAL FERTILIZER CO LTD
- Filing Date
- 2026-04-16
- Publication Date
- 2026-06-05
AI Technical Summary
Existing coated compound fertilizers have poor coating toughness, which makes them prone to cracking in hot and humid environments, leading to rapid nutrient loss. Furthermore, traditional coating materials are difficult to degrade, which may cause soil pollution.
A dynamic crosslinking network was constructed by using a biodegradable lignin-peptide graft copolymer to form borate ester bonds with borate and introducing a metal crosslinking agent to form metal coordination bonds. The coating layer was then prepared by a two-fluid spraying in-situ crosslinking process.
It improves the dimensional stability and slow-release performance of fertilizer coating, realizes the slow and controlled release of nutrients, avoids soil pollution from traditional materials, and combines the resource utilization of agricultural waste with a complete nutrient system.
Smart Images
Figure CN122145236A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of controlled-release compound fertilizer preparation, specifically to green organic compound fertilizer and its preparation method. Background Technology
[0002] Compound fertilizers, as agricultural inputs that combine organic matrix and readily available inorganic nutrients, are widely used in supplementing soil nutrition. Coated compound fertilizers, with their slow-release properties, can effectively control the nutrient release rate. However, conventional fertilizers often use petrochemical resins as coating materials, which are difficult to degrade in soil. At the same time, conventional single-layer coatings lack dynamic cross-linking support, resulting in insufficient mechanical strength and poor water resistance, making them prone to cracking under water immersion and nutrient loss. Furthermore, traditional premixing processes are prone to premature gelation of the solution, causing particle agglomeration and uneven film thickness. To address the aforementioned problems with coated fertilizers, a technical solution is provided that uses biodegradable bio-based materials for network reconstruction. The material modification is achieved by constructing a dual crosslinking network, namely, in the lignin and polypeptide graft copolymer system, borates are used to form dynamic and reversible borates, and metal crosslinking agents are introduced to form metal coordination bonds. The preparation is carried out using a two-fluid spraying in-situ crosslinking process, which avoids premature solidification of the precursor and results in a uniform and dense film. Summary of the Invention
[0003] The purpose of this invention is to provide a green organic compound fertilizer and its preparation method, which solves the defects of existing coated compound fertilizers, such as poor coating toughness and easy cracking under humid and hot environments, leading to rapid nutrient loss. Furthermore, it can significantly improve the dimensional stability and slow-release performance of the fertilizer coating by constructing an interface with a dynamic stress dissipation mechanism. Specifically, the technical solution of this invention includes the following steps: The inner core is a fertilizer base granule containing organic matter and inorganic nitrogen, phosphorus and potassium; A coating layer, the coating layer covering the surface of the inner core, the coating layer being formed by cross-linking and curing a coating liquid and a curing liquid on the surface of the inner core; The coating solution comprises an aqueous solution of lignin-peptide graft copolymer and borate, wherein the lignin-peptide graft copolymer is formed by linking carboxymethylated alkaline lignin with amino-rich peptides or polyaspartic acid derivatives via amide bonds. The curing solution is an aqueous solution containing a metal ion crosslinking agent; In the coating layer, the lignin-peptide graft copolymer forms a borate bond with the borate, and the lignin-peptide graft copolymer forms a metal coordination bond with the metal ion crosslinking agent.
[0004] Furthermore, the fertilizer base granules are made by mixing and granulating fermented and decomposed livestock and poultry manure, straw powder and inorganic nitrogen, phosphorus and potassium salts.
[0005] Furthermore, the amino-rich polypeptide is a soybean polypeptide; the borate is borax; and the metal ion crosslinking agent includes zinc salt and calcium salt.
[0006] A method for preparing green organic compound fertilizer, comprising the following steps: Fermented and decomposed livestock and poultry manure, straw powder and inorganic nitrogen, phosphorus and potassium salts are mixed and granulated to obtain fertilizer base granules as the inner core. The inner core is placed in a coating machine, and the bed temperature is maintained at 60-80℃; A coating solution is prepared, and the coating solution and curing solution are sprayed onto the inner core surface in a coating machine for in-situ crosslinking coating treatment. The coating solution includes lignin-peptide graft copolymer and borate, and the curing solution includes metal ion crosslinking agent. After the in-situ cross-linking coating treatment is completed, hot air drying is performed to allow the coating liquid and curing liquid to cross-link and solidify on the inner core surface, thereby obtaining the green organic compound fertilizer.
[0007] Furthermore, the coating solution is prepared through the following steps: (1) Disperse alkali lignin in an aqueous sodium hydroxide solution, heat to dissolve, and then add chloroacetic acid aqueous solution dropwise to carry out carboxymethylation reaction; after the reaction is completed, add hydrochloric acid solution to adjust the pH value of the reaction solution to neutral, and then dialyze and freeze dry to obtain carboxymethylated alkali lignin; (2) The carboxymethylated alkaline lignin is dissolved together with amino-rich polypeptide or polyaspartic acid derivative in deionized water to form a mixture. The pH of the mixture is adjusted to 5.5-6.0. 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide are added as activators. The mass ratio of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride to N-hydroxysuccinimide is 1:1-2:1. An amidation reaction is carried out to generate a lignin-polypeptide graft copolymer solution. (3) Add borate to the lignin-peptide graft copolymer solution, wherein the amount of borate added is 5-15% of the mass of the lignin-peptide graft copolymer, and adjust the pH of the system to 7.5-8.5 to obtain the coating solution.
[0008] Further, in step (1), the mass fraction of the sodium hydroxide aqueous solution is 15-25%; the heating and dissolving temperature is 65-75℃; the carboxymethylation reaction temperature is 65-75℃, and the reaction time is 3-5 hours.
[0009] Further, the feature is that, in step (2), the mass ratio of the carboxymethylated alkali lignin to the amino-rich polypeptide or polyaspartic acid derivative is 2:1-3:1; the amidation reaction is carried out at room temperature and the stirring reaction time is 10-14 hours.
[0010] Furthermore, the curing solution is a mixed aqueous solution containing zinc sulfate and calcium chloride; in the mixed aqueous solution, the mass fraction of zinc sulfate is 3-8% and the mass fraction of calcium chloride is 3-8%.
[0011] Furthermore, the in-situ crosslinking coating treatment employs a two-fluid spray granulation process, simultaneously or alternately spraying the coating liquid and the curing liquid onto the inner core surface.
[0012] Furthermore, the hot air drying process takes 15-25 minutes.
[0013] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention adopts a core-shell structure, with fertilizer base particles containing organic matter and inorganic nitrogen, phosphorus and potassium as the inner core, realizing the resource recycling of agricultural waste, combining the fast-acting properties of inorganic fertilizers with the long-term improvement advantages of organic fertilizers; at the same time, the coating layer uses lignin-peptide graft copolymer, the material is naturally sourced and belongs to green organic matter, avoiding the secondary pollution problem to the soil caused by the degradation of traditional polymer chemical resin coating materials; 2. During the curing process of the coating layer of the present invention, the lignin-peptide graft copolymer not only reacts with borate to form borate ester bonds, but also reacts with the curing liquid containing metal ion crosslinking agent to form metal coordination bonds. The introduction of this multiple chemical bond forms a dense and stable three-dimensional crosslinked network structure in situ on the surface of the fertilizer core, giving the coating layer mechanical strength and water resistance, and achieving a good slow-release effect on the fertilizer nutrients in the core. 3. In the preparation of the coating layer, the borax, zinc sulfate and calcium chloride introduced by the present invention act as cross-linking agents to participate in the solidification and molding of the network structure. After the coating layer is gradually degraded, it is absorbed by the plant as a micronutrient required for crop growth. In addition, the degradation of amino-rich polypeptides or polyaspartic acid derivatives provides crops with amino acids and other nutrients, which together with the inorganic nitrogen, phosphorus and potassium in the core form a complete nutrient system. 4. The preparation method employs a two-fluid spray granulation process for in-situ cross-linking coating treatment, enabling the coating liquid and curing liquid to undergo rapid cross-linking reactions simultaneously or alternately on the inner core surface. This process avoids the agglomeration of the coating material, ensuring a tight bond between the coating layer and the fertilizer core, and a uniform coating. Combined with hot air drying, the coating layer is rapidly cured, improving production efficiency and making it suitable for industrial applications. Attached Figure Description
[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Figure 1 This is a graph showing the test results of various performance improvements and degradation rates provided in an embodiment of the present invention. Detailed Implementation
[0015] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.
[0016] Example 1: The compound fertilizer has a core-shell structure, comprising: an inner core, which is a fertilizer base granule containing organic matter and inorganic nitrogen, phosphorus, and potassium; a coating layer, which covers the surface of the inner core and is formed by cross-linking and curing a coating liquid and a curing liquid on the surface of the inner core; the coating liquid includes an aqueous solution of lignin-peptide graft copolymer and borate, wherein the lignin-peptide graft copolymer is formed by linking carboxymethylated alkali lignin with amino-rich peptides or polyaspartic acid derivatives through amide bonds; The curing solution is an aqueous solution containing a metal ion crosslinking agent; in the coating layer, the lignin-peptide graft copolymer forms borate ester bonds with the borate, and the lignin-peptide graft copolymer forms metal coordination bonds with the metal ion crosslinking agent; In Example 1, the green organic compound fertilizer is prepared using a core-shell structure; the inner core is made of fertilizer base particles containing organic matter and inorganic nitrogen, phosphorus and potassium, and the coating layer is formed by in-situ crosslinking of coating liquid and curing liquid on the surface of the inner core; the coating layer is not a single barrier layer, but a double crosslinking network composed of lignin-peptide graft copolymer, borates and metal ion crosslinking agents. The lignin portion provides hydrophobicity, water erosion resistance, and skeletal strength, while the polypeptide or polyaspartic acid derivative portion provides hydrophilic regulation, post-degradation nutrient replenishment, and chelation sites. Boron ester bonds provide dynamic reversible cross-linking, and metal coordination bonds provide rapid curing capabilities. Thus, a functional layer with film-forming, adhesion, and slow-release properties is formed on the surface of fertilizer particles. This structure differs from conventional petrochemical resin coatings. Its coating layer can be gradually degraded in the soil, releasing lignin derivatives and polypeptide components during the degradation process, which improves soil aggregate formation and the rhizosphere microenvironment.
[0017] Example 2: The base granules of green organic compound fertilizer are made by mixing and granulating fermented and decomposed livestock and poultry manure, straw powder and inorganic nitrogen, phosphorus and potassium salts. In this embodiment, the fertilizer base granules are prepared by granulation after mixing 6.0 kg of fermented and decomposed livestock and poultry manure, 1.5 kg of straw powder and 2.5 kg of inorganic nitrogen, phosphorus and potassium salts. The livestock and poultry manure is a mixture of fermented and decomposed chicken manure and cow manure with a moisture content of 24%. The straw powder is passed through a 40-mesh sieve. The inorganic nitrogen, phosphorus and potassium salts are composed of urea, monoammonium phosphate and potassium sulfate. The above materials were put into a horizontal mixer and mixed for 18 minutes. After being mixed evenly, they were fed into a disc granulator with a disc inclination angle of 48° and a rotation speed of 19 r / min to obtain fertilizer base granules with a particle size of 3.0 mm to 4.5 mm. The fertilizer base granules prepared using the constant values in this embodiment have both organic matrix and fast-acting inorganic nutrients. When used as the inner core of the coating, the pelleting rate is as high as 95% or more. They can form a good interfacial bond with the carboxyl and phenolic hydroxyl groups in the outer coating, which significantly improves the adhesion stability of the coating layer.
[0018] Example 3: Green organic compound fertilizer, rich in amino peptides (soybean peptides); borates (borax); metal ion cross-linking agents (zinc salts and calcium salts); In Example 1, the amino-rich polypeptide was selected from soybean polypeptide with an average molecular weight of 1200 Da and a free amino content of 6.8 mmol / g; the borate was selected from borax decahydrate; the metal ion crosslinking agent was a combination of zinc sulfate and calcium chloride; the amino groups in the soybean polypeptide were used to condense with the carboxyl groups introduced by carboxylation modification in carboxymethylated alkali lignin to form amide bonds for grafting, thus clarifying the crosslinking target and avoiding ambiguity and uncertainty in the spatial structure; Borax provides borate ions under alkaline conditions, which form borate ester bonds with the residual ortho-phenolic hydroxyl groups in the lignin structure. Zinc sulfate and calcium chloride provide Zn²⁺ and Ca²⁺, which are used to form coordination crosslinks with the carboxyl groups in the lignin-peptide graft copolymer. When zinc salts and calcium salts are used together, zinc ions help to improve the crosslinking strength, while calcium ions help to improve the toughness and agricultural safety of the film. The combination of the two can enable the sprayed liquid film to cure in a short time and maintain good mechanical integrity. In Example 3, only the ratio of peptides and cross-linking agents was changed, while the remaining steps were the same as in Example 1; the amino-rich peptides were still soybean peptides, the borates were still borax, and the metal ion cross-linking agents still included zinc salts and calcium salts. The amount of soybean peptides was increased to 25g, the mass ratio of carboxymethylated alkali lignin to soybean peptides was 2:1, the amount of borax added was 15% of the mass of the graft copolymer, and the pH of the system was adjusted to 8.5. The higher peptide content gives the coating layer higher hydrophilicity and biodegradation rate in the soil, and the higher amount of borax gives the coating layer stronger dynamic cross-linking characteristics. This combination is suitable for crop cultivation conditions that require rapid nutrient release but still require significant slow-release effects.
[0019] Example 4: The preparation method of green organic compound fertilizer includes the following steps: mixing fermented and decomposed livestock and poultry manure, straw powder and inorganic nitrogen, phosphorus and potassium salts and then granulating them to obtain fertilizer base granules as the inner core; placing the inner core in a coating machine and maintaining the bed temperature at 60-80℃; preparing a coating liquid and spraying the coating liquid and curing liquid onto the surface of the inner core in the coating machine for in-situ cross-linking coating treatment; The coating solution includes lignin-peptide graft copolymer and borates, and the curing solution includes metal ion crosslinking agent. After the in-situ crosslinking coating treatment is completed, hot air drying is performed to allow the coating solution and curing solution to crosslink and solidify on the inner core surface, thus obtaining a green organic compound fertilizer. In Example 1, 10.0 kg of the prepared fertilizer base granules were placed in a rotary drum coating machine, and the bed temperature was maintained at 60°C. The coating liquid was delivered to the dual-fluid spray gun via a metering pump at a flow rate of 20 mL / min. The curing liquid was delivered via another metering pump at a flow rate of 10 mL / min. The atomization pressure of the spray gun was 0.25 MPa, and the spraying time was 55 min. The coating liquid and curing liquid come into contact with the particle surface and undergo in-situ cross-linking while the particles are rolling, forming a continuous liquid film; the hot air drying temperature is 70℃; this process adopts a spray-and-curing method, which allows the liquid precursor to be instantly shaped on the particle surface, reducing particle adhesion and clumping; the key technical point of this preparation method is that the coating liquid and curing liquid are not pre-mixed, but react on the particle surface, avoiding premature gelation of the solution system and facilitating continuous production; In Example 3, the fertilizer base granules were maintained at 10.0 kg, and the bed temperature was 80°C; the coating liquid was sprayed at a rate of 18 mL / min, and the curing liquid was sprayed at a rate of 12 mL / min; the in-situ cross-linking coating was carried out by alternating spraying, that is, the coating liquid was sprayed for 15 seconds and the curing liquid was sprayed for 10 seconds, and the process was repeated. This method creates a layered, progressively cured structure on the particle surface, resulting in a more uniform coating thickness. After spraying, the particles are dried with hot air at 75°C for 25 minutes. The finished particles have a moisture content of 5.8%, and the cumulative release rates of nitrogen, phosphorus, and potassium within 30 days are 26.1%, 23.5%, and 25.0%, respectively. Compared with Example 1, the film layer in this embodiment has higher toughness and a lower powder shedding rate during transportation.
[0020] Example 5: The preparation method of green organic compound fertilizer involves preparing the coating solution through the following steps: (1) Disperse alkali lignin in an aqueous sodium hydroxide solution, heat to dissolve, and then add chloroacetic acid aqueous solution dropwise to carry out carboxymethylation reaction; after the reaction is completed, add hydrochloric acid solution to adjust the pH value of the reaction solution to neutral, and then dialyze and freeze dry to obtain carboxymethylated alkali lignin; (2) Carboxymethylated alkaline lignin and amino-rich polypeptides or polyaspartic acid derivatives are dissolved together in deionized water to form a mixture. The pH of the mixture is adjusted to 5.5-6.0. 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide are added as activators. The mass ratio of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride to N-hydroxysuccinimide is 1:1-2:1. An amidation reaction is carried out to generate a lignin-polypeptide graft copolymer solution. (3) Add borate to the lignin-peptide graft copolymer solution. The amount of borate added is 5-15% of the mass of the lignin-peptide graft copolymer. Adjust the pH of the system to 7.5-8.5 to obtain the coating solution. In Example 1, the coating solution was prepared according to the following steps: 100g of alkali lignin was added to 500mL of a 15% sodium hydroxide aqueous solution, stirred and dissolved at 65°C for 40min, and 80g of an aqueous solution prepared with chloroacetic acid was added dropwise. The reaction was carried out at 65°C for 3h. After the reaction was completed, the pH of the reaction solution was adjusted to 7.0 with 1mol / L hydrochloric acid, dialyzed through a dialysis bag with a molecular weight cutoff of 3500Da for 48h, and freeze-dried for 36h to obtain carboxymethylated alkali lignin. Take 50g of carboxymethylated alkaline lignin and 20g of soybean polypeptide and dissolve them in 800mL of deionized water. Adjust the pH to 5.5, add 5g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 5g of N-hydroxysuccinimide, and stir the reaction at room temperature for 10h to obtain a lignin-polypeptide graft copolymer solution. Add 5.6g of borax to the solution, the amount of borax added is 8% of the mass of the lignin-polypeptide graft copolymer, and adjust the pH of the system to 7.5 to obtain a coating solution. This preparation method makes carboxymethylated alkali lignin both soluble and reactive. After the grafting reaction, it forms a composite polymer containing both aromatic backbone and polypeptide segments, providing suitable viscosity and reaction sites for subsequent spray coating film formation. The preparation method of green organic compound fertilizer involves preparing the coating solution through the following steps: (1) Disperse alkali lignin in an aqueous sodium hydroxide solution, heat to dissolve, and then add chloroacetic acid aqueous solution dropwise to carry out carboxymethylation reaction; after the reaction is completed, add hydrochloric acid solution to adjust the pH value of the reaction solution to neutral, and then dialyze and freeze dry to obtain carboxymethylated alkali lignin; (2) Carboxymethylated alkaline lignin and amino-rich polypeptides or polyaspartic acid derivatives are dissolved together in deionized water to form a mixture. The pH of the mixture is adjusted to 5.5-6.0. 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide are added as activators. The mass ratio of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride to N-hydroxysuccinimide is 1:1-2:1. An amidation reaction is carried out to generate a lignin-polypeptide graft copolymer solution. (3) Add borate to the lignin-peptide graft copolymer solution. The amount of borate added is 5-15% of the mass of the lignin-peptide graft copolymer. Adjust the pH of the system to 7.5-8.5 to obtain the coating solution. In Example 2, only the preparation parameters of the coating solution were changed, while the rest of the structure and process were the same as in Example 1. 100g of alkali lignin was added to 500mL of 20% sodium hydroxide aqueous solution, heated to dissolve at 70°C, 80g of chloroacetic acid aqueous solution was added dropwise, and the reaction was carried out at 70°C for 4h. The pH was adjusted to 7.0 with hydrochloric acid, dialyzed and freeze-dried to obtain carboxymethylated alkali lignin. 50g of carboxymethylated alkali lignin and 18g of aminated polyaspartic acid were dissolved in 800mL of deionized water, and the pH was adjusted to 5.8. 12g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 6g of N-hydroxysuccinimide were added, and the mixture was stirred at room temperature for 12h to generate a lignin-polyaspartic acid graft copolymer solution. 7.7g of borax was added to this solution, with the amount of borax added being 11% of the mass of the graft copolymer. The pH was adjusted to 8.0 to obtain the coating solution. In this embodiment, the polyaspartic acid derivative introduces more carboxyl sites, and the resulting coating layer has a significant ion exchange capacity after absorbing water, which has a regulatory effect on the release of nutrients in the middle and late stages. In the above preparation process of the coating liquid, both Example 1 and Example 2 adopted specific point value ratios. Compared with the comparative preparation scheme using non-preferred constants, the coating liquid using the specific point value ratios of this example showed better spreadability and cross-linking curing speed during spraying, and the immersion resistance of the final coating layer was improved by about 20-30%.
[0021] Example 6: The preparation method of green organic compound fertilizer, in step (1), the mass fraction of sodium hydroxide aqueous solution is 15-25%; the heating and dissolving temperature is 65-75℃; the carboxymethylation reaction temperature is 65-75℃, and the reaction time is 3-5 hours; In Example 1, step (1) uses a 15% sodium hydroxide aqueous solution, and alkali lignin is heated and dissolved at 65°C. The carboxymethylation reaction temperature is 65°C and the reaction time is 3h. These parameters enable lignin to achieve carboxymethylation at a lower reaction intensity. The resulting carboxymethylated alkali lignin has good dispersibility in water and can retain more aromatic structures and phenolic hydroxyl groups, providing sites for the subsequent formation of borate ester bonds. These parameters are beneficial for balancing reaction efficiency and film structure integrity.
[0022] Example 7: In the preparation method of green organic compound fertilizer, in step (2), the mass ratio of carboxymethylated alkali lignin to amino-rich polypeptide or polyaspartic acid derivative is 2:1-3:1; the amidation reaction is carried out at room temperature and the stirring reaction time is 10-14 hours. In Example 1, the mass ratio of carboxymethylated alkali lignin to soybean polypeptide was 2.5:1. The amidation reaction was carried out at 25°C for 10 hours. This mass ratio resulted in a higher lignin backbone content in the graft copolymer, which is beneficial to the water resistance and mechanical support of the coating layer. At the same time, it retained an appropriate amount of polypeptide segments, which improved the spreadability of the coating liquid during spraying and its bioactivity after degradation. When the amidation time was 10 hours, the grafting reaction was relatively complete, and the viscosity of the system was moderate, which was suitable for subsequent pumping and atomization.
[0023] Example 8: The preparation method of green organic compound fertilizer involves a solidification solution that is a mixed aqueous solution containing zinc sulfate and calcium chloride; in the mixed aqueous solution, the mass fraction of zinc sulfate is 3-8%, and the mass fraction of calcium chloride is 3-8%. In Example 1, the curing solution was a mixed aqueous solution of zinc sulfate (3% by mass) and calcium chloride (3% by mass), with a total volume of 550 mL. Zinc sulfate and calcium chloride were added to deionized water in sequence, stirred until completely dissolved, and then filtered for later use. After the coating liquid is sprayed, the Zn²⁺ and Ca²⁺ in the curing solution can coordinate and crosslink with the carboxyl groups in the graft copolymer to form an ionic network with high initial strength, which works together with the dynamic network of borate ester. The construction of this dual network helps to control the swelling rate of the coating layer when water enters, so that the nutrient release changes from rapid dissolution to gradual diffusion. In Example 2, the curing solution was a mixed aqueous solution of 5% zinc sulfate and 5% calcium chloride, and the temperature of the coating machine bed was maintained at 70°C. At this concentration, the crosslinking rate of metal ions was increased compared with Example 1, and a curing film was formed on the surface of the particles more quickly after spraying, with a coating weight gain of 6.5%. This embodiment is suitable for products requiring high early immersion resistance. The cumulative release rates of nitrogen, phosphorus, and potassium within 30 days were 24.9%, 22.7%, and 23.8%, respectively.
[0024] Example 9: In-situ cross-linking coating treatment employs a two-fluid spray granulation process, simultaneously or alternately spraying coating liquid and curing liquid onto the inner core surface; In Example 1, the in-situ cross-linking coating treatment adopts a two-fluid spray granulation process, in which coating liquid and curing liquid are sprayed onto the inner core surface at the same time; the angle between the coating liquid nozzle and the curing liquid nozzle is set to 35°, and the spray point is located in the particle tumbling and falling area; When using a simultaneous spraying method, the droplets make short-range contact with the particle surface and solidify rapidly, forming a uniform coating layer. This process differs from dip coating or single-liquid spraying, as it shortens the droplet residence time, reduces the accumulation of the spray liquid on the equipment wall and between particles, and improves the uniformity of the coating. In Example 1, the coating weight gain was 6.2%, the particle roundness was good, and the pass rate after sieving was 93.4%. The preparation method of green organic compound fertilizer adopts a two-fluid spray granulation process for in-situ cross-linking coating treatment, and simultaneously or alternately sprays coating liquid and curing liquid onto the inner core surface. In Example 3, the in-situ crosslinking coating treatment adopted the alternating spraying method in the two-fluid spraying granulation process. Compared with the simultaneous spraying in Example 1, the residence state of droplets on the particle surface is easier to control with alternating spraying, which is especially suitable for continuous production under higher bed temperature conditions. The particle agglomeration rate under this process is 4.1%, which is lower than that of the comparative example. This shows that alternating spraying can improve the stability of film formation under high temperature conditions.
[0025] Example 10: The preparation method of green organic compound fertilizer involves hot air drying for 15-25 minutes. In Example 1, after the in-situ cross-linking coating treatment was completed, the product was dried with hot air at 70°C for 20 minutes to obtain the green organic compound fertilizer. This drying time allowed the free water in the coating layer to be basically removed, while avoiding excessive denaturation of the polypeptide components due to continuous high temperature. The dried granules had a moisture content of 6.1%, and the coating layer was continuous without obvious cracks. The product was tested for water solubility, and the cumulative release rates of nitrogen, phosphorus, and potassium within 30 days were 27.6%, 24.8%, and 26.3%, respectively, indicating that the coating layer can provide a stable slow-release effect while maintaining biodegradability. The hot air drying time was 15-25 minutes. In Example 3, the hot air drying time was 25 minutes. The longer drying time allowed the coating layer formed by the higher amount of borax and the higher proportion of peptides to obtain a more stable moisture content, reducing the reabsorption of particles during storage. After 30 days of storage, the clumping rate of Example 3 was 3.6%, which is suitable for bagged transportation and room temperature storage.
[0026] Comparative Example 1: The same fertilizer base granules, bed temperature, spraying speed and drying time as in Example 2 were used, but borax was not added to the coating solution, only lignin-polyaspartic acid graft copolymer solution was used, and the curing solution was still a mixed aqueous solution of 5% zinc sulfate and 5% calcium chloride. In this comparative example, the coating layer only had metal coordination crosslinking and lacked dynamic crosslinking of borate esters; the resulting particle coating weight gain rate was 6.1%, but the coating layer cracked locally after immersion in water for 48 hours, and the cumulative release rates of nitrogen, phosphorus and potassium increased to 36.8%, 33.9% and 35.2% within 30 days, respectively.
[0027] Comparative Example 2: The same coating liquid and curing liquid composition as in Example 1 were used, but the coating liquid and curing liquid were premixed for 30 seconds before being sprayed onto the inner core surface through a single spray gun. The bed temperature remained at 60°C, and the drying time remained at 20 minutes. Due to partial gelation before spraying, the atomization effect decreased, the film layer formed on the particle surface was uneven in thickness, the particle agglomeration rate increased to 11.7%, and the qualified rate after sieving decreased to 81.2%. The cumulative release rates of nitrogen, phosphorus, and potassium within 30 days were 31.5%, 29.6%, and 30.8%, respectively. In this comparative example, the coating liquid and curing liquid were mixed before spraying, which reduced the uniformity of the coating and decreased the slow-release effect.
[0028] Verification experiment: The green organic compound fertilizers obtained in Examples 1, 2, 3, Comparative Example 1 and Comparative Example 2 were subjected to structural characterization, slow-release performance testing, degradation performance testing and agronomic related index testing; FT-IR was used to verify amide bond formation, XPS was used to verify metal coordination crosslinking, and rheology was used to verify the rapid gelation behavior after the coating liquid and curing liquid came into contact. The slow-release performance was tested for water dissolution rate according to GB / T23348-2009; the soil degradation test adopted the natural soil burial method, with a burial depth of 10cm and a temperature of 25℃, and the mass loss of the coating layer was tested within 120 days; the pot experiment used maize seedlings, the test soil was moist soil, each pot contained 5kg of soil, the fertilizer application was calculated based on pure nitrogen of 0.20g / kg soil, and the root activity and zinc absorption and utilization rate were measured after 45 days of cultivation.
[0029] Specific testing process: In the water dissolution rate test, 50g of each sample was placed in 500mL of deionized water and allowed to stand at 25℃. Samples were taken at predetermined intervals to determine the nitrogen, phosphorus, and potassium content in the solution, and the same volume of deionized water was added. In the soil degradation test, the separated coated samples were placed in 100-mesh nylon mesh bags and buried in the soil. They were periodically removed, washed, dried, and weighed. Root activity was determined using the TTC reduction method, and zinc uptake and utilization rate was determined using atomic absorption spectrometry to determine the zinc content in the aboveground parts of the plant. Table 1 Performance test data of Examples 1-3 and Comparative Examples 1-2:
[0030] As shown in Table 1, Examples 1 to 3 all showed low 30-day cumulative release rates, indicating that the coating layer formed by the lignin-peptide graft copolymer, borate and metal ion crosslinking agent can control nutrient release; Example 2 had a higher metal ion concentration, better early immersion resistance, and the lowest cumulative release rate; Example 3 used a higher peptide ratio and an alternating spraying method to maintain the sustained release effect while taking into account the toughness of the coating layer. Comparative Example 1 lacked borate ester bonds, resulting in decreased film integrity and a significantly increased release rate, indicating that the dual crosslinking network contributes to the sustained-release stability. Comparative Example 2 did not employ in-situ crosslinking spraying, leading to decreased film uniformity and increased agglomeration rate, demonstrating that two-fluid spraying and crosslinking curing on the particle surface are necessary process conditions for achieving a stable coating structure. Comprehensive test results show that Example 1 has relatively balanced overall performance, Example 2 has a stronger sustained-release effect, and Example 3 has good storage and transportation stability. In addition, the microstructure characterization results show the construction of a cross-linked network. In the FT-IR spectra of Examples 1-3, obvious characteristic absorption peaks of amide I and amide II bands appear near 1650 cm⁻¹ and 1540 cm⁻¹, respectively. At the same time, a vibration peak of BOC bond appears near 1340 cm⁻¹, indicating the formation of amide bonds in the graft copolymer and the formation of borate bonds between lignin and borate. XPS spectral analysis showed that the binding energies of Zn2p and Ca2p on the surface of the coating layer in Examples 1-3 were significantly shifted compared to those of free metal ions, and signal peaks corresponding to metal-oxygen coordination bonds appeared in the O1s spectrum, indicating that metal coordination bonds were formed between the lignin-peptide / polyaspartic acid graft copolymer and the metal ion crosslinking agent; this provides strong microscopic data support for the dual crosslinking network of the coating layer of the present invention and its macroscopic sustained-release performance.
[0031] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments that can be applied to other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.
Claims
1. A green organic compound fertilizer, characterized in that, The compound fertilizer has a core-shell structure, including: The inner core is a fertilizer base granule containing organic matter and inorganic nitrogen, phosphorus and potassium; A coating layer, the coating layer covering the surface of the inner core, the coating layer being formed by cross-linking and curing a coating liquid and a curing liquid on the surface of the inner core; The coating solution comprises an aqueous solution of lignin-peptide graft copolymer and borate, wherein the lignin-peptide graft copolymer is formed by linking carboxymethylated alkaline lignin with amino-rich peptides or polyaspartic acid derivatives via amide bonds. The curing solution is an aqueous solution containing a metal ion crosslinking agent; In the coating layer, the lignin-peptide graft copolymer forms a borate bond with the borate, and the lignin-peptide graft copolymer forms a metal coordination bond with the metal ion crosslinking agent.
2. The green organic compound fertilizer according to claim 1, characterized in that, The fertilizer base granules are made by mixing and granulating fermented and decomposed livestock and poultry manure, straw powder and inorganic nitrogen, phosphorus and potassium salts.
3. The green organic compound fertilizer according to claim 1, characterized in that, The amino-rich polypeptide is a soybean polypeptide; the borate is borax; and the metal ion crosslinking agent includes zinc salt and calcium salt.
4. A method for preparing a green organic compound fertilizer as described in any one of claims 1-3, characterized in that, The method includes the following steps: Fermented and decomposed livestock and poultry manure, straw powder and inorganic nitrogen, phosphorus and potassium salts are mixed and granulated to obtain fertilizer base granules as the inner core. The inner core is placed in a coating machine, and the bed temperature is maintained at 60-80℃. A coating solution is prepared, and the coating solution and curing solution are sprayed onto the inner core surface in a coating machine for in-situ crosslinking coating treatment. The coating solution includes lignin-peptide graft copolymer and borate, and the curing solution includes metal ion crosslinking agent. After the in-situ cross-linking coating treatment is completed, hot air drying is performed to allow the coating liquid and curing liquid to cross-link and solidify on the inner core surface, thereby obtaining the green organic compound fertilizer.
5. The method for preparing the green organic compound fertilizer according to claim 4, characterized in that, The coating solution is prepared through the following steps: (1) Disperse alkali lignin in an aqueous sodium hydroxide solution, heat to dissolve, and then add chloroacetic acid aqueous solution dropwise to carry out carboxymethylation reaction; after the reaction is completed, add hydrochloric acid solution to adjust the pH value of the reaction solution to neutral, and then dialyze and freeze dry to obtain carboxymethylated alkali lignin; (2) The carboxymethylated alkaline lignin is dissolved together with amino-rich polypeptide or polyaspartic acid derivative in deionized water to form a mixture. The pH of the mixture is adjusted to 5.5-6.
0. 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide are added as activators. The mass ratio of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride to N-hydroxysuccinimide is 1:1-2:
1. An amidation reaction is carried out to generate a lignin-polypeptide graft copolymer solution. (3) Add borate to the lignin-peptide graft copolymer solution, wherein the amount of borate added is 5-15% of the mass of the lignin-peptide graft copolymer, and adjust the pH of the system to 7.5-8.5 to obtain the coating solution.
6. The method for preparing the green organic compound fertilizer according to claim 5, characterized in that, In step (1), the mass fraction of the sodium hydroxide aqueous solution is 15-25%; the heating and dissolution temperature is 65-75℃; the carboxymethylation reaction temperature is 65-75℃, and the reaction time is 3-5 hours.
7. The method for preparing the green organic compound fertilizer according to claim 5, characterized in that, In step (2), the mass ratio of the carboxymethylated alkali lignin to the amino-rich polypeptide or polyaspartic acid derivative is 2:1-3:1; the amidation reaction is carried out at room temperature and the stirring reaction time is 10-14 hours.
8. The method for preparing the green organic compound fertilizer according to claim 4, characterized in that, The curing solution is a mixed aqueous solution containing zinc sulfate and calcium chloride; in the mixed aqueous solution, the mass fraction of zinc sulfate is 3-8% and the mass fraction of calcium chloride is 3-8%.
9. The method for preparing the green organic compound fertilizer according to claim 4, characterized in that, The in-situ crosslinking coating process employs a two-fluid spray granulation process, in which the coating liquid and the curing liquid are sprayed onto the inner core surface simultaneously or alternately.
10. The method for preparing the green organic compound fertilizer according to claim 4, characterized in that, The hot air drying process takes 15-25 minutes.