Biodegradable environment-friendly intelligent coated fertilizer applicable to rice seedling raising in saturated water environment with zero release within 25 days instead of field base tillering fertilizer for reducing nitrogen and phosphorus non-point source pollution

Abstract

The invention discloses a 25-day zero-release coated fertilizer suitable for a rice seedbed saturated water environment and a preparation method and application thereof, and belongs to the technical field of environmental protection, emission reduction and nitrogen and phosphorus non-point source pollution reduction. The coated fertilizer comprises a fertilizer core material and a degradable coating layer, wherein the coating layer is prepared from high-crystallization PHB, a PHBV blend, superfine talcum powder, nano silicon dioxide, a hydrophobic filler, an organic silane coupling agent (KH-570), a cross-linking agent and a plasticizer; through material synergistic modification and process optimization, the problems that an existing sustained and controlled release fertilizer is easy to release and burn seedlings in advance in a rice seedbed saturated water environment, urea is easy to decompose, a film material is difficult to degrade and the like are solved, the release period can be customized according to the field fertilizer requirement characteristic after rice transplanting, and the nutrient apparent utilization rate is as follows: nitrogen is greater than 60%, phosphorus is greater than 70%, and potassium is greater than 70%, which is far higher than that of traditional fertilization; nutrient leaching and runoff pollution to underground and environmental water bodies are avoided, and the method is suitable for popularization and application.

Description

Technical Field

[0001] This invention relates to the technical field of environmental protection and reducing the risk of nitrogen and phosphorus non-point source pollution. Specifically, it relates to a fully degradable bio-based coated fertilizer suitable for rice seedbeds with zero release within 25 days in saturated water environments, and with two or more release peaks that can replace base fertilizer, greening fertilizer, and tillering fertilizer. Because it is precisely applied to the rice rhizosphere, it is adsorbed by the soil, and each nutrient element is released as needed, which greatly reduces the pollution of groundwater and the environment by nitrogen and phosphorus leaching and runoff. The nutrient utilization rate is: nitrogen > 60%, phosphorus > 70%, potassium > 70%. Background Technology

[0002] In rice cultivation, traditional slow-release fertilizers are applied to seedbeds. When the seedbed is frequently watered and the soil moisture content is close to saturation, the coating easily absorbs water and penetrates, causing nutrients to be released prematurely, resulting in nutrient excess and burning of the seedlings. Conventional fertilization requires multiple applications of base fertilizer, greening fertilizer, and tillering fertilizer. Because rice roots are underdeveloped in the early stages, fertilizer utilization is low (nitrogen and phosphorus utilization is only about 25%). When the water layer in the paddy field is oversaturated or drainage is carried out, nitrogen and phosphorus elements leach or runoff, polluting groundwater and the environment, resulting in resource waste and increased labor costs.

[0003] In existing technologies, controlled-release fertilizers using PHA as the coating material have been disclosed, but they have the following drawbacks: 1) Conventional PHA (such as PHBV) has low crystallinity (≤50%), insufficient water resistance, and rapid water penetration under saturated water, making it impossible to achieve zero release for 25 days; 2) Coating additives mostly use hydrophilic materials such as montmorillonite, which easily absorb water and swell, leading to membrane cracking; 3) The process does not include hydrophobic modification steps designed for saturated water environments, and the membrane surface lacks an effective hydrophobic barrier; 4) The membrane material has a high melting temperature (above 140℃), which easily leads to the decomposition of urea core material to generate biuret, affecting the growth of rice seedlings; 5) Existing solutions have high material costs (such as PCL and pure hydrophobic fumed silica), resulting in low cost-effectiveness for large-scale production and making it difficult to promote and apply; while the degradation of the membrane material of fertilizers coated with PE or PU and modified with bio-based materials will lead to microplastic pollution.

[0004] Therefore, developing a coated fertilizer that is suitable for the near-saturated water environment of rice seedbeds, can stably achieve zero release for 25 days, can replace the base fertilizer, greening fertilizer, and tillering fertilizer, is degradable, easy to prepare, and has controllable cost has become an urgent technical problem to be solved. Summary of the Invention

[0005] (a) Technical problems to be solved To address the shortcomings of existing controlled-release fertilizers in near-saturated water conditions in rice seedbeds, such as poor water resistance, premature release, easy decomposition of urea core materials, and high costs, this invention achieves long-term underwater barrier properties through "material synergistic modification + cost-effective substitution + process optimization." It provides a coated fertilizer that can be applied directly under rice seeds, exhibits zero release for 25 days, and has a controllable release cycle after transplanting, meeting the nutritional needs of rice in its early and middle stages. This is achieved through "material synergistic modification + cost-effective substitution + process optimization," ensuring long-term underwater barrier properties while maintaining biodegradability, safety, and scalability.

[0006] (II) Technical Solution: A 25-day zero-release coated fertilizer suitable for saturated water environments in rice seedbeds, comprising a fertilizer core material and a biodegradable coating layer covering the surface of the core material; the coating layer raw materials, by weight, are: 60-70 parts of highly crystalline PHB, 20-30 parts of PHBV blend, 30-40 parts of 2000-mesh ultrafine talc powder, 0.5-0.8 parts of nano-silica, 0.8-1 parts of hydrophobic filler, 1.0-1.5 parts of organosilane coupling agent (KH-570), 0.3-0.5 parts of diisocyanate crosslinking agent, and 0.2-0.3 parts of plasticizer. 0007. Core Material Innovative Design: 1. High crystallinity PHB+PHBV blend system: High crystallinity PHB (crystallinity ≥70%) has a water resistance that is more than 30% higher than that of conventional PHBV. When blended with PHBV, it balances membrane density and flexibility, and significantly reduces the water permeation rate under saturated water. 2. Hydrophobic filler mixture system: Hydrophobic fumed silica and hydrophobic talc are mixed in a 1:1 ratio. This system utilizes the high density of fumed silica to fill the gaps in the film layer, while the hydrophobic talc reduces material costs and synergistically improves the hydrophobicity of the film layer, avoiding the defects of water absorption and swelling of traditional hydrophilic additives. 3. Cost-effective plasticizer alternative: Replace high-priced PCL with PEG-6000. PEG-6000 has excellent compatibility with PHA, which can reduce the melting temperature of the film material to 125-135℃, avoiding the temperature range (above 140℃) where urea core material decomposes in large quantities, while reducing costs by more than 50%. 4. Core material isolation layer design: The PEG-4000 isolation layer (thickness 0.009-0.011mm) can block the direct conduction of high temperature to the urea core material, further reducing the risk of biuret formation. Moreover, PEG-4000 is low in cost, easy to degrade, and does not affect the overall performance of the coating layer.

[0007] Process optimization design: 1. Lower the melt extrusion temperature to 125-140℃ and increase the screw speed (110-120rpm) to shorten the high-temperature residence time of the film material and reduce urea decomposition; 2. The isolation layer is sprayed twice and dried at low temperature to ensure uniform thickness and no sticking, thereby improving the adhesion strength with the coating layer; 3. The post-curing and low-temperature hydrophobic treatment are integrated to form a three-layer structure of "isolation layer - dense coating layer - hydrophobic surface layer", which enhances the water-saturated barrier effect.

[0008] The application of the coated fertilizer is suitable for application before sowing in rice seedbeds, sown below the seeds, and brought into the field during transplanting. It releases no nutrients within 25 days, and the field does not require additional base fertilizer or tillering fertilizer. The biuret content is <0.3%, and it is safe and non-irritating to rice seedlings.

[0009] (III) Beneficial Effects 1. Excellent water resistance: Under saturated water conditions in rice seedbeds, no nutrients are released within 25 days, and the nitrogen, phosphorus, and potassium content in the leachate is ≤ ±2 mg / kg of the blank water sample, with no swelling or damage to the membrane layer; 2. High safety: The decomposition rate of urea core material is ≤0.5%, and the biuret content is <0.3%, avoiding the risk of seedling burn and making it suitable for the sensitive environment of rice seedbeds; 3. Controllable cost: By replacing PCL with PEG-6000 and using a mixture of hydrophobic talc, the additional cost per ton for large-scale production is only 380-420 yuan, which is more than 30% lower than the existing solution; 4. Biodegradability: The coating layer is made of fully bio-based material, which can be completely degraded in the soil of the original plant after transplanting, leaving no environmental residue; 5. Process adaptability for large-scale production: It adopts automated continuous production process, with high equipment integration and a finished product qualification rate of ≥98%, which is suitable for promotion of 10,000-ton-level production capacity. Detailed Implementation

[0010] Example 1 (Original scheme: PCL + pure hydrophobic fumed silica) A 25-day zero-release coated fertilizer suitable for saturated water environments in rice seedbeds, comprising the following raw materials by weight: 65 parts of high-crystallinity PHB (70% crystallinity), 25 parts of PHBV blend, 35 parts of 2000-mesh ultrafine talc powder, 0.6 parts of nano-silica (20-50nm), 0.9 parts of hydrophobic fumed silica (specific surface area 180m² / g), 1.2 parts of organosilane coupling agent (KH-570), 0.4 parts of diisocyanate crosslinking agent (MDI), and 0.25 parts of tributyl citrate plasticizer; the fertilizer core material is urea (2-4mm particles) with a moisture content of 0.4%, and the surface is coated with a 0.01mm thick PEG-4000 isolation layer.

[0011] Preparation method: (1) Raw material pretreatment: urea core material was dried at 60℃ for 4 hours, and powder raw material was dried at 105℃ for 2 hours; 5% PEG-4000 solution was prepared and sprayed in two coats (1.1% of the amount of the coating), and dried at 45℃ for 2 hours. (2) Membrane material mixing: Add the mixture to a high-speed mixer according to the ratio and stir at 1000 rpm for 18 min; (3) Melt extrusion coating: Twin screw extruder, zone 1 140℃, zone 2 155℃, zone 3 160℃, screw speed 90rpm, die opening 4mm, film thickness 0.19mm; (4) Cooling and curing: Cool the conveyor belt at 25℃, speed 0.5m / min, and allow it to cool naturally for 24 hours; (5) Post-curing: Oven at 60℃ and 30% humidity for 5 hours; (6) Low temperature hydrophobic treatment: Spray 0.5% silicone hydrophobic emulsion at 60℃ and dry for 2 hours to obtain the finished product.

[0012] Example 2 (Alternative: PEG-6000 + 5:5 mixed hydrophobic filler) The difference from Example 1 is that: the plasticizer is PEG-6000 (0.28 parts), the hydrophobic filler is 0.45 parts hydrophobic fumed silica + 0.45 parts hydrophobic talc (2000 mesh); the twin-screw extruder temperature is adjusted to 125℃ in zone 1, 130℃ in zone 2, and 135℃ in zone 3, and the screw speed is 110 rpm; the other raw materials and process parameters are the same.

[0013] Example 3 (30-day release cycle) Raw materials by weight: 52 parts of high-crystallinity PHB (70%), 38 parts of PHBV blend, 36 parts of 2000-mesh ultrafine talc powder, 0.6 parts of nano-silica, 0.27 parts of hydrophobic fumed silica + 0.63 parts of hydrophobic talc powder, 1.2 parts of KH-570, 0.4 parts of MDI, 0.28 parts of PEG-6000, and 0.6 parts of starch-based degradation agent; film thickness 0.17 mm.

[0014] Performance testing: Test content result 25-day zero-release status Yes (leached liquid nitrogen content 1.1 mg / kg) Release rate in 26-55 days 92.3% (uniform release over 30 days) 6-month membrane status Completely disintegrated, with no residue. Example 4 (70-day release cycle) Raw materials by weight: 78 parts high crystallinity PHB (70%), 22 parts PHBV blend, 35 parts 2000 mesh ultrafine talc powder, 0.7 parts nano silica, 0.9 parts hydrophobic fumed silica, 1.3 parts KH-570, 0.65 parts MDI, 0.29 parts PEG-6000, 0.4 parts food-grade calcium carbonate; film thickness 0.21 mm.

[0015] Performance testing: Test Project result 25-day zero-release status Yes (leached liquid nitrogen content 0.8 mg / kg) Release rate in 26-95 days 91.7% (evenly released over 70 days) 6-month membrane status Completely degraded, leaving no residue III. Key Explanations 1. Both release cycle schemes are based on the original "25-day zero release" technical framework, with only minor adjustments to the "PHB / PHBV ratio, filler type, film thickness, and crosslinking agent dosage". No new complex processes are added, and large-scale production can share a single production line (only the formula is changed). 2. Guarantee of uniform release: By controlling the uniformity of membrane density (melt extrusion process), the daily average nutrient release rate is guaranteed to fluctuate by ≤±1%, meeting the nutrient requirements of rice during the tillering stage (30-day program) or the entire growth period (70-day program); 3. Cost impact: The additional cost per ton for the 30-day plan is 10-20 yuan lower than that for the basic plan (due to reduced use of fumed silica), while the additional cost per ton for the 70-day plan is 30-40 yuan higher (due to increased use of PHB and fumed silica), both of which are within a controllable range.

[0016] Comparative Example 1 (No isolation layer + conventional PHBV) The difference from Example 2 is that: there is no PEG-4000 isolation layer, conventional PHBV (45% crystallinity) is used instead of high crystallinity PHB, and no organosilane coupling agent is added; the other raw materials and process parameters are the same.

[0017] Comparative Example 2 (No alternative materials used + high-temperature process) The difference from Example 2 is that the plasticizer is PCL, the hydrophobic filler is pure hydrophobic fumed silica, and the twin-screw extruder temperatures are 140°C in zone 1, 150°C in zone 2, and 155°C in zone 3; the other raw materials and process parameters are the same.

[0018] Performance testing The finished products of Examples 1-2 and Comparative Examples 1-2 were tested, and the results are as follows: Test Project Example 1 (Original Scheme) Example 2 (Alternative) Comparative Example 1 Comparative Example 2 Leaching nitrogen content (mg / kg) after 25 days of saturated water immersion 1.2 1.0 32.6 1.5 Membrane state after 25 days of saturated water immersion Complete and without swelling Complete and without swelling Swelling and cracking Complete and without swelling Biuret content (%) 0.28 0.25 0.85 0.32 Film bonding strength (N) 12.8 13.1 8.5 12.6 Additional cost per ton (RMB) 540 405 0 530 25-day zero-release status yes yes no yes Test method: 1. Saturated water immersion test: The solution was continuously immersed in deionized water at 25℃ for 25 days, and the nutrient content of the leachate was determined by ultraviolet spectrophotometry. 2. Biuret content determination: determined by colorimetric method according to GB / T 2441.2-2010; 3. Membrane bonding strength: The crushing force is tested using a particle compressive strength testing machine; 4. Safety test: Rice seedling pot experiment, observe the growth status of seedlings for 15 days.

[0019] Description of Detailed Implementation The core innovation of this invention lies in the synergistic design of "highly crystalline PHB + hydrophobic mixed filler + cost-effective plasticizer replacement," combined with a core material isolation layer and a low-temperature melting process. This not only solves the technical problems of insufficient water resistance and easy decomposition of urea in existing solutions, but also reduces the cost of large-scale production through material substitution. Test results of Example 2 (alternative solution) show that its overall performance is better than the original solution, and the cost is reduced by more than 25%. Compared with Example 1, which did not use the materials and processes of this invention, it could not meet the requirements of zero release and safety. Compared with Example 2, which did not use alternative materials, the cost remained high.

[0020] Description of Detailed Implementation The core innovation of this invention lies in the synergistic design of "highly crystalline PHB + hydrophobic mixed filler + cost-effective plasticizer replacement," combined with a core material isolation layer and a low-temperature melting process. This not only solves the technical problems of insufficient water resistance and easy decomposition of urea in existing solutions, but also reduces the cost of large-scale production through material substitution. Test results of Example 2 (alternative solution) show that its overall performance is better than the original solution, and the cost is reduced by more than 25%. Compared with Example 1, which did not use the materials and processes of this invention, it could not meet the requirements of zero release and safety. Compared with Example 2, which did not use alternative materials, the cost remained high.

Claims

1. A fully biodegradable coated fertilizer with zero release for 25 days suitable for use in rice seedbeds under saturated water conditions, characterized in that, The product includes a fertilizer core material and a fully biodegradable coating layer covering the surface of the core material. The coating layer is composed of the following raw materials in parts by weight: 60-70 parts of highly crystalline PHB, 20-30 parts of PHBV blend, 30-40 parts of 2000-mesh ultrafine talc powder, 0.5-0.8 parts of nano-silica, 0.8-1 parts of hydrophobic filler, 1.0-1.5 parts of organosilane coupling agent (KH-570), 0.3-0.5 parts of diisocyanate crosslinking agent, and 0.2-0.3 parts of plasticizer. - The crystallinity of the highly crystalline PHB is ≥70%; - The hydrophobic filler is hydrophobic fumed silica, or a mixture of hydrophobic fumed silica and hydrophobic talc (mixing mass ratio 1:1). - The plasticizer is tributyl citrate or PEG-6000; - The thickness of the coating layer is 0.18-0.2 mm, and the coating layer is subjected to low-temperature hydrophobic treatment: spraying a 0.5% concentration of organosilicon hydrophobic emulsion at 60°C and then drying for 2 hours.

2. The coated fertilizer according to claim 1, characterized in that, The fertilizer core material is urea or compound fertilizer with a particle size of 2-4 mm and a moisture content of ≤0.5%. The core material surface is covered with a PEG-4000 isolation layer with a thickness of 0.009-0.011 mm.

3. The coated fertilizer according to claim 1, characterized in that, The hydrophobic fumed silica has a specific surface area of ​​150-200 m² / g and a hydrophobicity of ≥95%; the hydrophobic talc has a particle size of ≥2000 mesh and a hydrophobicity of ≥90%.

4. The coated fertilizer according to claim 1, characterized in that, When the plasticizer is PEG-6000, its dosage is 3.5%-4.0% of the total weight of the coating layer raw material, and the barrel temperature of the twin-screw extruder is adjusted to 125-135℃.

5. The coated fertilizer according to claim 1, characterized in that, The weight ratio of the organosilane coupling agent (KH-570) to the highly crystalline PHB is 1:50-1:

60.

6. A method for preparing a coated fertilizer as described in any one of claims 1-5, characterized in that, Includes the following steps: (1) Raw material pretreatment: The fertilizer core material is dried at 60℃ for 4 hours and the powder raw material is dried at 105℃ for 2 hours; after the core material is cooled, it is sprayed with PEG-4000 solution to form an isolation layer and dried at 40-50℃ for 2 hours. (2) Membrane material mixing: According to the formula, add high crystallinity PHB, PHBV blend, ultrafine talc powder, nano silica, hydrophobic filler, organosilane coupling agent, diisocyanate crosslinking agent and plasticizer into a high-speed mixer and stir at 1000 rpm for 15-20 min. (3) Melt extrusion coating: The barrel temperature of the twin-screw extruder is 125-130℃ in zone 1, 130-135℃ in zone 2, and 135-140℃ in zone 3. The screw speed is 110-120rpm. The fertilizer core material passes through the die (3-5mm) at a uniform speed and is coated with molten film. (4) Cooling and curing: Cool the conveyor belt to 25℃, conveying speed 0.5-1m / min, and allow it to cool naturally for 24 hours; (5) Post-curing treatment: Keep warm in an oven at 60℃ and 30% humidity for 4-6 hours; (6) Low temperature hydrophobic treatment: Spray 0.5% concentration of organosilicon hydrophobic emulsion at 60℃, dry for 2 hours to obtain the finished product.

7. The preparation method according to claim 6, characterized in that, In step (1), the concentration of the PEG-4000 solution is 5%-8%, the amount of spraying is 1.0%-1.2% of the core material weight, and it is sprayed in two coats.

8. The preparation method according to claim 6, characterized in that, In step (3), the film thickness adjustment accuracy of the coating head is ±0.01mm, and the core material temperature after coating is ≤130℃.

9. An application of a coated fertilizer as described in any one of claims 1-5, characterized in that, It is applied before sowing in rice seedbeds, sown below the seeds, and brought into the main field during transplanting. This eliminates the need for base fertilizer and tillering fertilizer in the main field, and there is no nutrient release within 25 days in a saturated water environment in the rice seedbed. The biuret content is <0.28%.

10. The coated fertilizer according to claim 1, characterized in that, The coated fertilizer is released after 25 days, and the nutrient release cycle is 30 days. At this time, the coating layer raw materials contain: 50-55 parts of highly crystalline PHB, 35-40 parts of PHBV blend, and the hydrophobic filler is a 3:7 mixture of hydrophobic fumed silica and hydrophobic talc. The film thickness is 0.16-0.18 mm, and 0.5-0.8 parts of starch-based degradation agent are added.

11. The coated fertilizer according to claim 1, characterized in that, The coated fertilizer is released after 25 days, and the nutrient release cycle is 70 days. At this time, the coating layer raw materials contain: 75-80 parts of highly crystalline PHB, pure hydrophobic fumed silica as the hydrophobic filler, a film thickness of 0.2-0.22 mm, 0.6-0.7 parts of crosslinking agent, and 0.3-0.5 parts of food-grade calcium carbonate.

12. The coated fertilizer according to claim 10 or 11, characterized in that, Nutrient release rate meets the following requirements: release rate ≤ 5% within 25 days, cumulative release rate ≥ 90% within the release period, and uniform release process (daily average release rate fluctuation ≤ ± 1%).