Coating agent based on polyhydroxyalkanoate, slow-release fertilizer and preparation method and application thereof

Abstract

The invention belongs to the technical field of chemical fertilizers, relates to a coating agent based on polyhydroxyalkanoate, a slow-release fertilizer and a preparation method and application of the coating agent and the slow-release fertilizer, and provides a slow-release fertilizer preparation method which takes PHA as a coating layer to wrap agricultural fertilizer particles and controls the nutrient release rate by adjusting the thickness of the PHA and an additive. Products obtained after degradation are carbon dioxide and water, no micro-plastic residues exist, and soil health is facilitated; pHA can promote proliferation of beneficial microorganisms in soil and is beneficial to crop growth. The slow-release fertilizer prepared by the invention is environment-friendly, efficient, stable, accurate in slow release regulation and control, relatively low in cost and controllable, and can be widely applied.

Description

Technical Field

[0001] The present invention belongs to the technical field of fertilizers and relates to a polyhydroxyalkanoate-based coating agent, a slow-release fertilizer, and a preparation method and application thereof. Specifically, it relates to a slow-release fertilizer with a biodegradable material polyhydroxyalkanoate (PHA) as a coating matrix and a preparation process thereof, which are used to improve fertilizer utilization and reduce environmental pollution. Background Art

[0002] Traditional chemical fertilizers face significant challenges due to low utilization rates, high erosion rates, and environmental pollution. Excessive application leads to soil compaction, eutrophication, and increased greenhouse gas emissions. Traditional slow-release fertilizers effectively address these issues, but they often use non-degradable polymers such as polyethylene and polypropylene as coating materials.

[0003] Polyethylene and polypropylene are difficult to degrade in soil. Long-term residues can disrupt soil aggregate structure and reduce soil permeability. Residual plastic fragments hinder the transport of water, nutrients, and air, leading to localized soil compaction or decreased porosity, which in turn affects crop root development and nutrient absorption. Polyethylene and polypropylene gradually decompose into microplastic particles (<5 mm) through photooxidation or mechanical action. These microplastics can enter the food chain through ingestion by soil organisms or absorb heavy metals and organic pollutants, further amplifying ecological risks. Some polyethylene coating materials may contain additives such as plasticizers and stabilizers. Long-term degradation or oxidation in soil can release harmful substances such as phthalates, contaminating soil and groundwater. The degradation cycle of polyethylene and polypropylene in soil can reach hundreds of years, and their accumulation can exceed the environmental capacity threshold, degrading the soil environment. Therefore, there is an urgent need to develop a plastic coating material that is completely biodegradable in the natural environment, independent of fossil resources, and environmentally friendly with a controlled release cycle. Summary of the Invention

[0004] In this context, the biodegradable material polyhydroxyalkanoate (PHA) has become a key carrier for the coordinated development of agricultural efficiency and environmental protection due to its unique properties.

[0005] In order to overcome the shortcomings of existing slow-release fertilizer coating technology, the present invention provides a method for preparing a slow-release fertilizer by using PHA as a coating layer to wrap agricultural fertilizer particles and controlling the nutrient release rate by adjusting the PHA thickness and additives.

[0006] PHA is a type of bio-based degradable polyester synthesized by microorganisms. It is a natural polymer synthesized by microorganisms and is completely biodegradable. The degradation rate can be controlled by molecular weight. It has good film-forming properties and thermoplasticity, making it suitable as a coating material or fertilizer carrier matrix.

[0007] The above-mentioned object of the present invention is achieved through the following technical solutions:

[0008] A polyhydroxyalkanoate-based coating agent comprising the following components:

[0009] Component A: polyhydroxyalkanoate PHA;

[0010] Component B: citrate, acetate, benzoate, glycerin;

[0011] Component C: cellulose, bentonite, tannic acid, starch;

[0012] Component A accounts for 65-90% of the coating agent, component B accounts for 2-15% of the coating agent, and component C accounts for 8-20% of the coating agent; component B can be selected from one or more thereof; component C can be selected from one or more thereof.

[0013] Furthermore, PHA includes but is not limited to: one or a mixture of PHB, PHBV, PHBHHx, and P34HB.

[0014] A slow-release fertilizer based on polyhydroxyalkanoate, which is coated with the above-mentioned coating agent.

[0015] Furthermore, fertilizers include nitrogen fertilizers, phosphorus fertilizers, potash fertilizers, compound fertilizers and trace element fertilizers.

[0016] A method for preparing a slow-release fertilizer based on polyhydroxyalkanoate, including but not limited to a spraying method. The preparation method is as follows:

[0017] (1) Preparation of PHA coating agent: Prepare the coating agent using the above formula;

[0018] (2) Fertilizer particle screening and drying: Select fertilizer particles with a particle size of 2-5 mm to ensure spraying uniformity; dry with hot air at 60-80°C to a moisture content of <1% to avoid blistering of the coating;

[0019] (3) Drum spray coating: Place the screened fertilizer into a drum coating machine and evenly spray the coating agent onto the fertilizer. The amount of coating agent used is 5-20% of the fertilizer.

[0020] (4) Low-temperature curing of coated fertilizers: 50-60℃ thermal cycle curing for 20-30 minutes to promote PHA crystallization.

[0021] (5) Screening of coated fertilizer: Use a vibrating screen to remove sticky particles. The sieve aperture is 7-8 mm.

[0022] (6) Slow-release performance test: The release detection method is carried out in accordance with "HG / T 4215-2011 Controlled-release fertilizers", and the nutrient release period is about 80 days.

[0023] The present invention provides another method for directly preparing a slow-release fertilizer based on polyhydroxyalkanoate, comprising the following steps:

[0024] (1) Preparation of the coating agent: Heat the coating agent component A to 150-200°C to dissolve, then add one or more of the components B, and maintain the temperature to ensure that the coating agent is in a molten state;

[0025] (2) Fertilizer particle screening: Use a multi-layer vibrating screen to screen and obtain fertilizer particles of 2-5 mm;

[0026] (3) Drum spray coating: The screened fertilizer particles are placed in a drum coating machine, and one or more of the C components are added to the drum at a rate of 1-5% of the fertilizer. The drum is heated to 60-80°C and dried to a moisture content of <1%. The drum speed is 5-15 rpm.

[0027] (4) The coating agent containing molten components A and B is sprayed uniformly onto the fertilizer particles by pressure. The spraying pressure is 0.2-0.5 MPa. The amount of components A and B is 5-13% of the weight of the fertilizer. After the drum coating is completed, the temperature is lowered to 50-60°C and maintained for 20-30 minutes to promote PHA crystallization.

[0028] (5) Then pass through a vibrating screen with a pore size of 7-8 mm to remove large adhering particles;

[0029] (6) Release detection method shall be carried out in accordance with "HG / T 4215-2011 Controlled Release Fertilizers"

[0030] Furthermore, the release detection method comprises the following steps:

[0031] 10g (accurate to 0.01g) of coated slow-release fertilizer was weighed and placed into a small bag made of nylon mesh with a pore size of 150μm (100 mesh). After sealing, the bag was placed in a 250mL plastic bottle, 200mL of water was added, the bottle was sealed with a lid, and the bottle was placed in a biochemical constant temperature incubator at 25°C. Sampling was carried out at 24h, 3d, 5d, 7d, 10d, 14d, 28d, 42d, 56d, 70d, and 84d. Subsequent sampling intervals were determined based on the release of the controlled-release nutrients (the longest interval did not exceed 28d) until the cumulative nutrient release rate reached above 80%. During sampling, the bottle was inverted three times to make the liquid concentration uniform. The entire amount was transferred to a 250mL volumetric flask, cooled to room temperature, and then the volume was adjusted to the scale for the determination of nutrient release. Then, 200mL of water was added, the bottle was sealed, and the next extraction period was continued.

[0032] The application of a slow-release fertilizer based on polyhydroxyalkanoates can be applied to various fields such as modern agricultural precision fertilization, saline-alkali land and ecological restoration, facility agriculture and soilless cultivation, organic agriculture and green certification, soil pollution control, emergency agriculture and post-disaster reconstruction.

[0033] The beneficial effects of the present invention compared with the prior art are:

[0034] 1. Environmentally friendly and biodegradable

[0035] The polyhydroxyalkanoate (PHA) coating agent used in the present invention is a bio-based degradable material that can be completely degraded into CO2 and H2O in the soil, avoiding the microplastic pollution of traditional plastic coatings and meeting the needs of green agricultural development.

[0036] The degradation products are small organic molecules that can improve the soil aggregate structure and enhance the soil's ability to retain water and fertilizer.

[0037] 2. Precise regulation of nutrient release

[0038] By adjusting the ratio of PHA types (such as PHB, PHBV, etc.) and B components (citrate, acetate, etc.), the degradation rate of the coating agent can be customized so that the nutrient release cycle covers 30-180 days, accurately matching the growth cycle requirements of different crops.

[0039] The slow-release performance test shows that according to the "HG / T 4215-2011" standard, the nutrient release period is about 80 days, and the nitrogen utilization rate is increased to more than 85%, which is twice the utilization rate of traditional fertilizers.

[0040] 3. The coating process is efficient and stable

[0041] The spraying method is combined with low-temperature curing technology to promote PHA crystallization through 50-60°C thermal cycling, avoiding coating cracking or nutrient loss caused by high temperature, and the coating uniformity reaches more than 95%.

[0042] The vibration screening process can effectively remove sticky particles, ensure the uniformity of product particle size (7-8mm), and improve the efficiency of mechanized fertilization.

[0043] 4. Stress resistance and soil improvement

[0044] Natural ingredients such as tannic acid and bentonite in component C can absorb heavy metal ions in the soil, reduce the EC value of saline-alkali land, and enhance crop resistance.

[0045] Field trials have shown that the application of this slow-release fertilizer can increase soil organic matter content by 15%-20%, reduce chemical fertilizer usage by 30% while maintaining crop yields.

[0046] 5. Flexible and compatible preparation methods

[0047] Two preparation processes are available:

[0048] Process 1: Suitable for conventional coating agent spraying, simple operation, suitable for small and medium-sized enterprises;

[0049] Process 2: Directly mix component C through molten spraying, reducing steps, improving production efficiency, and is suitable for large-scale industrial production.

[0050] Both processes meet the slow-release fertilizer standard of "HG / T 4215-2011 Controlled-Release Fertilizer", and the product qualification rate exceeds 98%. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 This is a process flow chart for preparing the slow-release fertilizer of the present invention;

[0052] Figure 2 The graph shows the cumulative nutrient release rate of slow-release fertilizers with different coating rates. DETAILED DESCRIPTION

[0053] The present invention is described in detail below by specific examples, but the scope of protection of the present invention is not limited. Unless otherwise specified, the experimental methods adopted in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can be obtained from commercial channels.

[0054] Example 1

[0055] 1) Preparation of the coating agent: Take 60.8 g of coating agent component A, heat to 175°C to dissolve, then add 1 g of citrate, 1 g of benzoate, and 0.2 g of glycerol from component B, and maintain the temperature to ensure that the coating agent is in a molten state;

[0056] 2) Fertilizer granule screening: Take 2 kg of urea granules and use a multi-layer vibrating screen to screen and obtain urea granules of 2-5 mm;

[0057] 3) Drum spray coating: 1 kg of screened urea granules with a particle size of 2-5 mm was placed in a drum coating machine. 7 g of cellulose from component C was added to the drum, which was heated to 80°C. The urea granules were dried to a moisture content of <1% and the drum speed was 10 rpm.

[0058] 4) The coating agent containing the molten components A and B is sprayed evenly onto the urea particles by pressure at a spraying pressure of 0.4 MPa. After the drum coating is completed, the temperature is lowered to 55°C and maintained for 25 minutes to promote PHA crystallization.

[0059] 5) Then pass through a vibrating sieve with a pore size of 7 mm to remove large adhering particles to obtain a slow-release urea with a coating of 7%;

[0060] 6) The release detection method shall be carried out in accordance with "HG / T 4215-2011 Controlled Release Fertilizers".

[0061] Example 2

[0062] 1) Preparation of the coating agent: Take 80 g of component A of the coating agent, heat it to 175°C to dissolve it, then add 5 g of acetate, 1 g of benzoate, and 2 g of glycerol from component B, and maintain the temperature to ensure that the coating agent is in a molten state;

[0063] 2) Fertilizer granule screening: Take 2 kg of urea granules and use a multi-layer vibrating screen to screen and obtain urea granules of 2-5 mm;

[0064] 3) Drum spray coating: 1 kg of screened urea granules with a particle size of 2-5 mm was placed in a drum coating machine. 8 g of starch, 2 g of cellulose, 1 g of bentonite, and 1 g of tannic acid from component C were added to the drum. The drum was heated to 80°C and dried to a moisture content of <1%. The drum speed was 15 rpm.

[0065] 4) The coating agent containing the molten components A and B is sprayed evenly onto the urea particles by pressure at a spraying pressure of 0.3 MPa. After the drum coating is completed, the temperature is lowered to 55°C and maintained for 25 minutes to promote PHA crystallization.

[0066] 5) Then pass through a vibrating sieve with a pore size of 7 mm to remove large adhering particles to obtain a slow-release urea with a coating of 10%;

[0067] 6) The release detection method shall be carried out in accordance with "HG / T 4215-2011 Controlled Release Fertilizers".

[0068] Example 3

[0069] 1) Preparation of the coating agent: Take 95 g of component A of the coating agent, heat it to 175°C to dissolve it, then add 7 g of citrate, 5 g of acetate, 3 g of benzoate, and 5 g of glycerol from component B, and maintain the temperature to ensure that the coating agent is in a molten state;

[0070] 2) Fertilizer granule screening: Take 2 kg of urea granules and use a multi-layer vibrating screen to screen and obtain urea granules of 2-5 mm;

[0071] 3) Drum spray coating: 1 kg of screened urea granules with a particle size of 2-5 mm was placed in a drum coating machine. 5 g of cellulose, 5 g of bentonite, 5 g of tannic acid, and 10 g of starch from component C were added to the drum. The drum was heated to 80°C and dried to a moisture content of <1%. The drum speed was 15 rpm.

[0072] 4) The coating agent containing the molten components A and B is sprayed evenly onto the urea particles by pressure at a spraying pressure of 0.3 MPa. After the drum coating is completed, the temperature is lowered to 55°C and maintained for 25 minutes to promote PHA crystallization.

[0073] 5) The solution was then passed through a vibrating sieve with a pore size of 7 mm to remove large adhering particles, thereby obtaining a slow-release urea with a coating of 14%;

[0074] 6) The release detection method shall be carried out in accordance with "HG / T 4215-2011 Controlled Release Fertilizers".

[0075] like Figure 2 As shown, the initial nutrient release rate of coated fertilizers with coating ratios of 7%, 10%, and 14% did not exceed 12%, and the cumulative nutrient release rate after 28 days did not exceed 75%, meeting the requirements of the standard. Furthermore, the controlled-release effect of the prepared coated fertilizers gradually increased with increasing coating ratio. According to the release period calculation formula specified in the standard, the release period of coated fertilizers with a coating ratio of 6% is 56 days, 89 days, and 190 days, respectively. The actual nutrient release period for the 6% coating ratio is 60 days, which is consistent with the calculated results.

[0076] The above description is only a preferred embodiment of the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention should be included in the scope of protection of the present invention.

Claims

1. A polyhydroxyalkanoate-based coating agent, characterized in that: Includes the following components: Component A: polyhydroxyalkanoate PHA; Component B: citrate, acetate, benzoate, glycerin; Component C: cellulose, bentonite, tannic acid, starch; Component A accounts for 65-90% of the coating agent, component B accounts for 2-15% of the coating agent, and component C accounts for 8-20% of the coating agent; component B can be selected from one or more thereof; component C can be selected from one or more thereof.

2. The polyhydroxyalkanoate-based coating agent according to claim 1, characterized in that: PHA includes but is not limited to: PHB, PHBV, PHBHHx, P34HB, one or a mixture of several.

3. A slow-release fertilizer based on polyhydroxyalkanoate, characterized in that: A fertilizer coated with the coating agent according to claim 1.

4. The slow-release fertilizer based on polyhydroxyalkanoate according to claim 3, characterized in that: Fertilizers include nitrogen fertilizers, phosphorus fertilizers, potassium fertilizers, compound fertilizers and trace element fertilizers.

5. A method for preparing a slow-release fertilizer based on polyhydroxyalkanoate, characterized in that: Including but not limited to spraying method.

6. The method for preparing a slow-release fertilizer based on polyhydroxyalkanoate according to claim 5, wherein: The preparation method is as follows: (1) Preparation of PHA coating agent; (2) Fertilizer granule screening and drying: Select fertilizer granules with a particle size of 2-5 mm and dry them to a moisture content of <1% to avoid blistering of the coating; (3) Drum spray coating: Place the screened fertilizer into a drum coating machine and evenly spray the coating agent onto the fertilizer. The amount of coating agent used is 10-20% of the fertilizer. (4) Low temperature curing of coated fertilizer: 50-60℃ heat cycle curing for 20-30 minutes to promote PHA crystallization; (5) Screening of coated fertilizer: sieve aperture 7-8mm; (6) Sustained-release performance test.

7. The method for preparing a slow-release fertilizer based on polyhydroxyalkanoate according to claim 6, wherein: Drying is done with hot air at 60-80°C.

8. The method for preparing a slow-release fertilizer based on polyhydroxyalkanoate according to claim 6, wherein: The slow-release performance test method is carried out in accordance with "HG / T 4215-2011 Controlled-release Fertilizers".

9. The method for preparing a slow-release fertilizer based on polyhydroxyalkanoate according to claim 5, wherein: The preparation method is as follows: (1) Preparation of the coating agent: Heat the coating agent component A to 150-200°C to dissolve, then add one or more of the components B, and maintain the temperature to ensure that the coating agent is in a molten state; (2) Fertilizer particle screening: Use a multi-layer vibrating screen to screen and obtain fertilizer particles of 2-5 mm; (3) Drum spray coating: The screened fertilizer particles are placed in a drum coating machine, and one or more of the C components are added to the drum at a rate of 1-5% of the fertilizer. The drum is heated to 60-80°C and dried to a moisture content of <1%. The drum speed is 5-15 rpm. (4) The coating agent containing molten components A and B is uniformly sprayed onto the fertilizer particles under pressure at a spraying pressure of 0.2-0.5 MPa. The amount of components A and B is 5-13% of the fertilizer weight. After the drum coating is completed, the temperature is lowered to 50-60°C and maintained for 20-30 minutes to promote PHA crystallization; (5) Then pass through a vibrating screen with a pore size of 7-8 mm to remove large particles; (6) The release detection method shall be carried out in accordance with "HG / T 4215-2011 Controlled Release Fertilizers".

10. An application of a slow-release fertilizer based on polyhydroxyalkanoate, characterized in that: It is used in precision fertilization in modern agriculture, saline-alkali land and ecological restoration, facility agriculture and soilless cultivation, organic agriculture and green certification, soil pollution control, emergency agriculture and post-disaster reconstruction.

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