Progressive coating method for microbial fertilizer particles
By using a progressive coating method, employing a hydrophobic microbial fertilizer core layer, a hydrophobic PPC progressive layer, and a hydrophilic membrane layer, the problems of inactivation and poor wettability of microbial fertilizer particles during storage and use were solved, thereby improving the coating effect and extending the fertilizer efficacy.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- QINGDAO UNIV OF SCI & TECH
- Filing Date
- 2026-02-02
- Publication Date
- 2026-04-14
AI Technical Summary
Microbial fertilizer granules are prone to inactivation during storage and use and are difficult to wet with water. Existing hydrophilic biodegradable materials have poor affinity with hydrophobic microbial fertilizer granules, resulting in poor coating effect.
A progressive coating method was adopted, using a hydrophobic microbial fertilizer core layer, a relatively hydrophobic PPC progressive layer, and a hydrophilic membrane layer. The coating membrane was constructed by using a mixture of low molecular weight PPC and PVA/glycogen, and the surface properties of the microbial fertilizer particles were regulated to improve affinity.
It extends the shelf life of microbial fertilizer granules, improves their germination and survival rate and fertilizer efficiency in the soil, and solves the problems of microbial inactivation and poor wettability during storage.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of microbial fertilizer preparation technology, and provides a method for coating progressive microbial fertilizer particles. Background Technology
[0002] Microbial fertilizer granules are agricultural fertilizers with active microorganisms as their main functional component. Through the action of beneficial bacteria, they promote crop growth, improve the soil environment, and enhance plant disease resistance. These environmentally friendly fertilizers are characterized by low input costs and significant ecological benefits. They not only effectively increase soil organic matter content and nutrient utilization but also inhibit soil-borne diseases. Functional microbial technology has demonstrated significant application value in soil improvement. Accelerating the development of the microbial fertilizer industry is of great strategic importance in implementing the national "double reduction" policy (reducing the use of chemical fertilizers and pesticides) and achieving the goal of green agricultural transformation.
[0003] However, microbial fertilizer granules generally suffer from problems such as short shelf life and difficulty in being wetted by water. Constructing a hydrophilic coating film on microbial fertilizer granules is an effective solution to these problems. Hydrophilic biodegradable materials, such as cellulose, starch, chitosan, sodium alginate, lignin, pectin, and polyvinyl alcohol (PVA), are promising candidates for coating films on microbial fertilizer granules. However, the affinity between hydrophobic microbial fertilizer granules and hydrophilic biodegradable materials differs greatly, making it difficult for hydrophilic biodegradable materials to be adsorbed by microbial fertilizer granules and form a uniform film. Therefore, a coating method for microbial fertilizer granules is urgently needed to solve the above-mentioned technical problems. Summary of the Invention
[0004] The purpose of this invention is to overcome the shortcomings of the existing technology and propose a progressive microbial fertilizer granule coating method.
[0005] To achieve the above objectives, the present invention adopts the following technical solution: A progressive microbial fertilizer granule coating method is provided, wherein the coated microbial fertilizer granules prepared by the method include a hydrophobic microbial fertilizer granule core layer, a relatively hydrophobic PPC layer, and a hydrophilic membrane layer covering the fertilizer core, and the mass ratio of the fertilizer core layer, the progressive layer and the membrane layer is 100:(0.5-10):(0.5-10).
[0006] The microbial fertilizer granules are microbial fertilizer granules such as Trichoderma harzianum, Penicillium barometz, or Aspergillus niger.
[0007] The microbial fertilizer granules can also be microbial fertilizer granules obtained by mixing microbial agents such as Trichoderma harzianum, Penicillium barometz or Aspergillus niger with one or more carriers such as bentonite and diatomaceous earth. The number of live bacteria can be controlled by the weight ratio of the agent to the carrier, ranging from about 100 million / g to 50 billion / g.
[0008] The progressive layer of the microbial fertilizer is a relatively hydrophobic liquid PPC with a molecular weight of less than 2000 g / mol. The relatively hydrophobic property can be adjusted by changing the molecular weight.
[0009] The membrane layer of the microbial fertilizer granules is a mixture of PVA and hydrophilic materials that can provide glycogen, such as starch, glucose, maltose, and dextrin, with a mass ratio ranging from 9:1 to 1:9, preferably from 7:3 to 3:7.
[0010] When the external ambient temperature exceeds 40 °C, microbial fertilizers deactivate rapidly. Therefore, a relatively hydrophobic material that retains low viscosity and easy flowability at low temperatures (<40 °C) should be selected as the transitional inner shell membrane for the microbial fertilizer. In this invention, the asymptotic layer of the microbial fertilizer particles is low molecular weight PPC, a typical aliphatic polycarbonate. During production, it consumes a large amount of CO2 and is completely biodegradable, making it a high-value-added, environmentally friendly material. As an amorphous polymer, its viscosity and hydrophobicity are closely related to its molecular weight. Therefore, by controlling its molecular weight, it is possible to utilize the relatively hydrophobic PPC to coat the microbial fertilizer particles at low temperatures (<40 °C) as a transitional inner shell membrane, thereby regulating the surface properties of the microbial fertilizer, reducing its surface hydrophobicity, and enhancing its affinity with hydrophilic coating materials.
[0011] The membrane layer of the microbial fertilizer granules is a mixture of PVA and hydrophilic materials that can provide glycogen, such as starch, glucose, maltose, and dextrin. The selection criteria are as follows: materials such as starch, glucose, maltose, and dextrin have advantages such as low cost and renewability, and can provide nutrients for the germination and growth of microbial agents when used as coating membranes. However, their low viscosity and poor film-forming properties make them difficult to use alone. PVA has excellent film-forming ability and can be used to modify sugar raw materials. It has been reported that the PVA / glycogen composite system has excellent water absorption, mechanical properties, and biodegradability; therefore, the PVA / glycogen system can serve as the outer shell membrane of microbial fertilizers.
[0012] The coating process of the microbial fertilizer granules includes the following steps, taking PVA / starch-PPC coated microbial fertilizer granules as an example: Step 1—Preparing an aqueous solution of PVA: Add PVA to deionized water and stir continuously at 300 r / min for 2 hours at 105℃ until it is completely dissolved to form a transparent and homogeneous PVA solution. Step 2—Preparing a soluble starch solution: Mix soluble starch with deionized water and stir at 300 r / min for 10 minutes at a constant temperature of 75℃ to fully gelatinize the starch and form a transparent solution; Step 3—Preparing the PVA / starch mixed solution: Mix the two solutions in a predetermined ratio, place them in a 75°C water bath, and stir at 600 r / min for 30 minutes to ensure thorough mixing. Transfer the mixed solution to an ultrasonic cleaner and sonicate for 15 minutes to completely remove air bubbles from the solution, obtaining a clear coating solution for later use. Step 4—Preparation of coated microbial fertilizer granule intermediate: Using a coating machine, low molecular weight PPC (molecular weight approximately 1000 g / mol) is uniformly sprayed onto the surface of the microbial fertilizer granules. The spraying rate is controlled to ensure complete coverage of the coating layer. By constructing a progressive PPC layer, the hydrophilicity of the microbial fertilizer granule surface is enhanced, thereby increasing its affinity with the hydrophilic coating material. Step 5—Preparation of Coated Microbial Fertilizer Granules: Using a coating machine, the prepared mixed solution is evenly sprayed onto the surface of the intermediate microbial fertilizer granules, controlling the spraying rate to ensure complete coverage. The coated granules are dried at a temperature ≤90℃ (preferably ≤40℃) to obtain the final coated microbial fertilizer product.
[0013] Advantages of the product of this invention: 1. The coating membrane in the coated microbial fertilizer granules prepared by the present invention can improve the shelf life of the microbial fertilizer granules and enhance their wettability, which can solve the problems of easy inactivation and difficulty in wetting of traditional microbial fertilizer granules, and has good promotion and application value. Specifically: (1) The coating membrane can effectively isolate the microbial fertilizer granules from the external environment. In particular, its excellent oxygen barrier performance can significantly reduce the germination probability of microorganisms during storage, reduce the number of dead live bacteria, and thus extend the shelf life of the product. At the same time, when the fertilizer is applied to the soil, the coating membrane can be naturally degraded by microorganisms and water in the soil. During the degradation process, the sugars produced by the decomposition of the coating membrane material can also provide nutrients for microorganisms, promote their germination and growth. This characteristic not only ensures storage stability, but also does not affect the efficacy of the fertilizer in the soil, and may even enhance its fertilizer effect. (2) The hydrophilic outer coating membrane overcomes the problem that hydrophobic microbial fertilizers are difficult to wet quickly in water. The coated microbial fertilizer is more easily wetted by water, which is very helpful in improving its germination and survival rate in the soil.
[0014] 2. The coated microbial fertilizer granules prepared by the present invention use relatively hydrophobic low molecular weight PPC as a progressive layer. At low temperature (<40 ℃), microbial fertilizer can be uniformly coated as a transitional inner shell membrane, which regulates the surface properties of microbial fertilizer, reduces its surface hydrophobicity, improves its affinity with hydrophilic coating materials, and improves the coating rate of microbial fertilizer granules. Attached Figure Description
[0015] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the following figures are provided for illustration: Figure 1 This is an optical photograph (undried) of the coated microbial fertilizer prepared in Example 1. Figure 2 This is an optical photograph (undried) of the coated microbial fertilizer prepared in Comparative Example 1. Detailed Implementation
[0016] The technical effects of the coated microbial fertilizer granules and their preparation method of the present invention will be further explained below with reference to specific embodiments. However, the specific implementation methods mentioned in these embodiments are only examples of the technical solutions of the present invention and are not intended to limit the scope of implementation of the present invention. Any improvements or substitutions based on the above principles and on the basis of the present invention should be within the protection scope of the present invention. Example 1
[0017] Prepare a 10% PVA solution by adding PVA to deionized water and stirring continuously at 300 rpm for 2 hours at 105°C until completely dissolved to form a transparent and homogeneous PVA solution. Prepare a 10% soluble starch solution by mixing soluble starch with deionized water and stirring at 300 rpm for 10 minutes at a constant temperature of 75°C to fully gelatinize the starch and form a transparent solution. Prepare a PVA / starch mixed solution by mixing the above two solutions in a 1:1 ratio and placing the mixture in a 75°C water bath at 600 rpm. The mixture is stirred at high speed for 30 minutes to ensure thorough mixing. The solution is then transferred to an ultrasonic cleaner and sonicated for 15 minutes to completely remove air bubbles, yielding a clear coating solution. Using a coating machine, low molecular weight PPC (approximately 1000 g / mol) is uniformly sprayed onto the surface of the microbial fertilizer granules, controlling the spraying rate to ensure complete coverage and increase its affinity with the hydrophilic coating material. The prepared mixture is then uniformly sprayed onto the surface of the Harz raspberry microbial fertilizer granules (with bentonite as a carrier), again controlling the spraying rate to ensure complete coverage. The coated granules are dried at a temperature ≤40℃ to obtain the final coated microbial fertilizer product. Example 2
[0018] Prepare a 10% PVA solution by adding PVA to deionized water and stirring continuously at 300 rpm for 2 hours at 105°C until completely dissolved to form a transparent and homogeneous PVA solution. Prepare a 10% soluble starch solution by mixing soluble starch with deionized water and stirring at 300 rpm for 10 minutes at a constant temperature of 75°C to fully gelatinize the starch and form a transparent solution. Prepare a PVA / starch mixed solution by mixing the above two solutions in a 1:1 ratio and placing the mixture in a 75°C water bath at 600 rpm. The mixture is stirred at high speed for 30 minutes to ensure thorough mixing. The solution is then transferred to an ultrasonic cleaner and sonicated for 15 minutes to completely remove air bubbles, yielding a clear coating solution. Using a coating machine, low molecular weight PPC (approximately 1000 g / mol) is first uniformly sprayed onto the surface of the microbial fertilizer granules. The spraying rate is controlled to ensure complete coverage, increasing its affinity with the hydrophilic coating material. Then, the prepared mixture is uniformly sprayed onto the surface of the Penicillium baicaleum microbial fertilizer granules (with bentonite as a carrier), again controlling the spraying rate to ensure complete coverage. The coated granules are dried at a temperature ≤40℃ to obtain the final coated microbial fertilizer product. Example 3
[0019] Prepare a 10% PVA solution by adding PVA to deionized water and stirring continuously at 300 rpm for 2 hours at 105°C until completely dissolved to form a transparent and homogeneous PVA solution. Prepare a 10% soluble starch solution by mixing soluble starch with deionized water and stirring at 300 rpm for 10 minutes at a constant temperature of 75°C to fully gelatinize the starch and form a transparent solution. Prepare a PVA / starch mixed solution by mixing the above two solutions in a 1:1 ratio and placing the mixture in a 75°C water bath at 600 rpm. The mixture is stirred at high speed for 30 minutes to ensure thorough mixing. The solution is then transferred to an ultrasonic cleaner and sonicated for 15 minutes to completely remove air bubbles, yielding a clear coating solution. Using a coating machine, low molecular weight PPC (approximately 1000 g / mol) is uniformly sprayed onto the surface of the microbial fertilizer granules, controlling the spraying rate to ensure complete coverage and increase its affinity with the hydrophilic coating material. The prepared mixture is then uniformly sprayed onto the surface of the Aspergillus niger microbial fertilizer granules (with bentonite as a carrier), again controlling the spraying rate to ensure complete coverage. The coated granules are dried at a temperature ≤40℃ to obtain the final coated microbial fertilizer product. Comparative Example 1
[0020] Prepare a 10% PVA solution by adding PVA to deionized water and stirring continuously at 300 rpm for 2 hours at 105°C until completely dissolved to form a transparent and homogeneous PVA solution. Prepare a 10% soluble starch solution by mixing soluble starch with deionized water and stirring at 300 rpm for 10 minutes at a constant temperature of 75°C to fully gelatinize the starch and form a transparent solution. Prepare a PVA / starch mixed solution by mixing the two solutions in a 1:1 ratio and placing them in a 75°C water bath. Stir at 600 rpm for 30 minutes to ensure thorough mixing. Transfer the mixed solution to an ultrasonic cleaner and sonicate for 15 minutes to completely remove air bubbles, obtaining a clear coating solution for later use. Using a coating machine, uniformly spray the prepared mixed solution onto the surface of Harz raspberry microbial fertilizer granules with bentonite as the "carrier," controlling the spraying rate to ensure complete coverage of the coating layer. The coated granules are dried at a temperature ≤40℃ to obtain the final coated microbial fertilizer product. Comparative Example 2
[0021] Prepare a 10% PVA solution by adding PVA to deionized water and stirring continuously at 300 rpm for 2 hours at 105°C until completely dissolved to form a transparent and homogeneous PVA solution. Prepare a 10% soluble starch solution by mixing soluble starch with deionized water and stirring at 300 rpm for 10 minutes at a constant temperature of 75°C to fully gelatinize the starch and form a transparent solution. Prepare a PVA / starch mixed solution by mixing the two solutions in a 1:1 ratio and placing them in a 75°C water bath. Stir at 600 rpm for 30 minutes to ensure thorough mixing. Transfer the mixed solution to an ultrasonic cleaner and sonicate for 15 minutes to completely remove air bubbles, obtaining a clear coating solution for later use. Using a coating machine, uniformly spray the prepared mixed solution onto the surface of Penicillium baicale microbial fertilizer granules with bentonite as the "carrier," controlling the spraying rate to ensure complete coverage of the coating layer. The coated granules are dried at a temperature ≤40℃ to obtain the final coated microbial fertilizer product. Comparative Example 3
[0022] Prepare a 10% PVA solution by adding PVA to deionized water and stirring continuously at 300 rpm for 2 hours at 105°C until completely dissolved to form a transparent and homogeneous PVA solution. Prepare a 10% soluble starch solution by mixing soluble starch with deionized water and stirring at 300 rpm for 10 minutes at a constant temperature of 75°C to fully gelatinize the starch and form a transparent solution. Prepare a PVA / starch mixed solution by mixing the two solutions in a 1:1 ratio and placing them in a 75°C water bath. Stir at 600 rpm for 30 minutes to ensure thorough mixing. Transfer the mixed solution to an ultrasonic cleaner and sonicate for 15 minutes to completely remove air bubbles, obtaining a clear coating solution for later use. Using a coating machine, uniformly spray the prepared mixed solution onto the surface of Aspergillus niger microbial fertilizer granules with bentonite as the "carrier," controlling the spraying rate to ensure complete coverage of the coating layer. The coated granules are dried at a temperature ≤40℃ to obtain the final coated microbial fertilizer product. Comparative Example 4
[0023] Harz raspberry microbial fertilizer granules using bentonite as a "carrier". Comparative Example 5
[0024] Penicillium baicale microbial fertilizer granules using bentonite as a "carrier". Comparative Example 6
[0025] Aspergillus niger microbial fertilizer granules using bentonite as a "carrier".
[0026] like Figure 1 and Figure 2 As shown, after introducing the progressive PPC layer (as... Figure 1 The coating effect of PVA / starch on microbial fertilizer granules was significantly improved; however, directly coating microbial fertilizer granules with PVA / starch solution (such as...) Figure 2 Many particles will exhibit incomplete coating. Table 1 compares the coating rates of the coated microbial fertilizer particles prepared in Examples 1-3 with those prepared in Comparative Examples 1-3.
[0027] Table 1
[0028] As shown in Table 1, the coating rates of the coated microbial fertilizer granules prepared by the progressive coating method in Examples 1-3 of the present invention are all better than those of the microbial fertilizer granules prepared directly using hydrophilic materials in the corresponding comparative examples 1-3.
[0029] The storage time and other indicators of the coated microbial fertilizer granules prepared in Examples 1-3 were tested. The number of viable bacteria in the microbial fertilizer granules at different storage times was determined according to NY / T2321: the product was stored in a cool, dry, and ventilated warehouse, and its shelf life was then determined. A commonly available compound microbial fertilizer granule was selected as a control group, and the trend of its viable bacteria count after 120 days of storage was tested. The test results are shown in Table 2.
[0030] Table 2
[0031] As shown in Table 2, the effective viable count retention rate of the coated microbial fertilizer granules prepared by Examples 1-3 of the present invention is better than that of the microbial fertilizer granules in Comparative Examples 4-6, and the viable count retention rate is basically equivalent to that of the microbial fertilizer granules coated only with hydrophilic materials in Comparative Examples 1-3.
[0032] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.
Claims
1. A method for coating progressive microbial fertilizer particles, wherein the prepared coated microbial fertilizer particles have the following characteristics, comprising a hydrophobic microbial particle core layer, a relatively hydrophobic progressive layer, and a hydrophilic membrane layer coating the outer layer of the fertilizer. The coating process of the microbial fertilizer granules includes the following steps: Polyvinyl alcohol (PVA) and an aqueous solution that can provide sugar raw materials are prepared separately, and then the two are mixed and the air bubbles are removed before use. First, polypropylene carbonate (PPC) is uniformly sprayed onto the surface of the microbial fertilizer granules using a coating machine to prepare a PPC intermediate progressive layer. Then, the mixed solution is uniformly sprayed onto the surface of the microbial fertilizer granules coated with the uniform progressive layer using a coating machine. After drying, the coated microbial fertilizer granules are obtained.
2. The coating method for progressive microbial fertilizer granules according to claim 1, characterized in that, The core layer of the microbial particles is composed of microbial fertilizer particles such as Trichoderma harzianum, Penicillium barometz, or Aspergillus niger.
3. The microbial particle core layer according to claim 1, characterized in that, The microbial fertilizer granules containing Trichoderma harzianum, Penicillium baicalensis, or Aspergillus niger can be microbial fertilizer granules obtained by mixing Trichoderma harzianum, Penicillium baicalensis, or Aspergillus niger with one or more carriers such as bentonite or diatomaceous earth.
4. The coating method for progressive microbial fertilizer granules according to claim 1, characterized in that, The progressive layer is a relatively hydrophobic liquid PPC with a molecular weight of less than 2000 g / mol. The relatively hydrophobic property can be adjusted by changing the molecular weight.
5. The aqueous solution of PVA and the material that can provide glycogen according to claim 1, characterized in that, The aqueous solution that can provide sugar raw materials can be a mixed aqueous solution of starch, glucose, maltose and dextrin, etc., with a mass fraction of 1%-50%.
6. The aqueous solution of PVA and the material that can provide glycogen according to claim 1, characterized in that, The mass fraction of the PVA solution is 1%-50%.
7. The PVA according to claim 1 and the aqueous solution that can provide sugar raw materials, characterized in that, The mass ratio of PVA to the hydrophilic material that can provide glycogen is 1:9-9:
1.
8. The coating method for progressive microbial fertilizer granules according to claim 1, characterized in that, The mass ratio of the microbial fertilizer granule core layer, progressive layer, and membrane layer is 100:(0.5-10):(0.5-10).