Preparation method of insect-repellent polyurethane slow-release fertilizer coating auxiliary agent

Abstract

The invention discloses a preparation method of an insect-repellent polyurethane slow-release fertilizer coating aid, and relates to the technical field of agricultural chemistry, and the coating aid is prepared from the following components in percentage by mass: a bio-based polyurethane prepolymer, a microencapsulated insect repellent, a slow-release regulator, a cross-linking agent, a dispersing agent and a wetting agent. The invention has the following advantages: bio-based polyurethane is used as a main material of the coating, a natural raw material is used for replacing a traditional petroleum-based material, the biodegradability of the coating is significantly improved, the synergistic effect of bio-based polyurethane and polylactic acid optimizes the overall degradation rate of the coating, the degradation process of the coating is ensured to be matched with the growth cycle of crops, and the application range of the coating is widened. And the disintegration process of the coating film in the soil is further regulated and controlled through the hydrolysis characteristic of polylactic acid, controllable degradation from a macrostructure to a microscopic component is achieved, degradation products have no negative influence on the activity of soil microorganisms, the ecological safety is guaranteed, and a green solution is provided for agricultural sustainable development.

Description

Technical Field

[0001] The invention relates to the technical field of agricultural chemicals, and in particular to a method for preparing an insect repellent polyurethane slow-release fertilizer coating auxiliary agent. Background Art

[0002] Slow-release fertilizer coating technology is an important means to improve nutrient utilization efficiency, but existing technologies still have significant defects. Traditional coating materials mostly rely on petroleum-based polyurethane, which has poor biodegradability and can easily lead to soil residual pollution after long-term application. Existing insect repellent slow-release fertilizers mostly disperse the insect repellent in the coating by physical mixing, which has problems such as uncontrollable release rate and short duration of effect. There is no response mechanism designed for changes in temperature or pH value, resulting in unstable insect repellent effect in actual application. In addition, the conventional coating structure is simple and mechanically strong. It is easily damaged by external forces and loses effectiveness. It also lacks self-repair function and is difficult to adapt to complex field environments. Although microencapsulation technology has been tried for encapsulating insect repellents, it still faces technical bottlenecks such as poor compatibility between wall material and coating and easy leakage of core material. At the same time, the degradation products of the coating may inhibit the activity of soil microorganisms, and the ecological safety is insufficient. In the existing technology, the synergistic application of environmentally responsive design (such as temperature-sensitive or pH-triggered release) and high mechanical strength coating has not yet been realized, and coating adjuvants that take into account both degradability and long-lasting insect repellent function still need breakthroughs. Therefore, the development of an insect repellent slow-release fertilizer coating adjuvant that combines environmentally responsive release, high mechanical strength, controllable degradation and ecological safety is of great significance to resolving the above technical contradictions and promoting the green development of agriculture. To this end, we propose a preparation method for an insect repellent polyurethane slow-release fertilizer coating adjuvant. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for preparing an insect repellent polyurethane slow-release fertilizer coating auxiliary agent.

[0004] To achieve the above object, the present invention provides the following technical solution: an insect repellent polyurethane slow-release fertilizer coating auxiliary agent, the coating auxiliary agent preparation method comprising the following components in mass percentage: Bio-based polyurethane prepolymer: 30-60%, wherein the bio-based polyurethane is prepared by reacting castor oil with isocyanate; Microencapsulated insect repellent: 1-10%, the core material of the microencapsulated insect repellent is azadirachtin, the wall material is chitosan, and the microcapsule particle size is 100-500nm; Sustained-release regulator: 5-15%, wherein the sustained-release regulator is polylactic acid; Cross-linking agent: 2-8%, the cross-linking agent is hexamethylene diisocyanate; Dispersant: 1-3%, the dispersant is sodium lauryl sulfate; Wetting agent: 0.5-2%, the wetting agent is alkyl naphthalene sulfonate; The coating auxiliary agent is formed on the surface of the fertilizer particles through a multi-layer spraying process, and at least comprises an insect repellent layer and a slow-release layer, wherein the porosity of the insect repellent layer is 10-30%, and the thickness of the slow-release layer is 50-100 μm.

[0005] As a further solution of the present invention: the temperature-sensitive material poly (N-isopropylacrylamide) is added to the sustained-release layer in an amount of 2-5% of the mass of the sustained-release layer. When the ambient temperature is ≥30°C, the porosity of the insect repellent layer increases to 1.5 times the initial value.

[0006] As a further solution of the present invention: the coating auxiliary agent also includes nano-silicon dioxide, the addition amount of which is 1-3% of the mass of the polyurethane prepolymer, and the coating compressive strength is ≥15 MPa.

[0007] As a further solution of the present invention: a pH response layer is provided between the insect repellent layer and the sustained-release layer, and the pH response layer contains polyacrylic acid, the addition amount of which is 3-8% of the mass of the pH response layer, and triggers the directional release of the insect repellent when the soil pH is ≤5.5.

[0008] As a further solution of the present invention: the envelope has a self-repair function, and can achieve autonomous repair after damage through dynamic disulfide bonds, with a repair rate of ≥90%.

[0009] The present invention also provides a method for preparing an insect repellent polyurethane slow-release fertilizer coating auxiliary agent, comprising the following steps: (1) Pre-dispersion of insect repellent: Mix the microencapsulated insect repellent with the bio-based polyurethane prepolymer and dispersant, and perform ultrasonic treatment until nano-scale dispersion; (2) Preparation of coating solution: Add polylactic acid and hexamethylene diisocyanate and stir to form a homogeneous coating solution; (3) Multi-layer spraying: The first insect repellent layer is sprayed: the coating liquid containing the insect repellent is evenly sprayed onto the surface of the fertilizer particles through an electrostatic spraying device at a voltage of 5-20kV, and a porous insect repellent layer is formed after solidification; The second sustained-release layer is sprayed: spraying a polyurethane composite liquid without insect repellent to form a dense sustained-release layer; (4) Post-processing: Curing at 25-40°C for 10-30 seconds under UV irradiation, and sieving to obtain the finished product.

[0010] As a further solution of the present invention: the thickness deviation of the electrostatically sprayed coating is less than 5%.

[0011] As a further solution of the present invention: the coating adjuvant is suitable for basal application to rice, corn or vegetable crops, with an application rate of 20-50 kg / mu, an insect repellent release period of 30-60 days, and a fertilizer slow-release period of 60-120 days.

[0012] As a further embodiment of the present invention, the biodegradation rate of the bio-based polyurethane is ≥80%, and the residue has no significant effect on the activity of soil microorganisms.

[0013] By adopting the above technical solution, compared with the prior art, the beneficial effects of the present invention are: 1. The present invention uses bio-based polyurethane as the main coating material, replacing traditional petroleum-based materials with natural raw materials, significantly improving the biodegradability of the coating. The synergistic effect of bio-based polyurethane and polylactic acid optimizes the overall degradation rate of the coating, ensuring that its degradation process matches the crop growth cycle and avoids soil residual contamination. The hydrolysis properties of polylactic acid further regulate the disintegration process of the coating in the soil, achieving controllable degradation from macrostructure to microcomponents. In addition, the degradation products have no negative impact on soil microbial activity, ensuring ecological safety and providing a green solution for sustainable agricultural development. 2. The present invention utilizes a multi-layer coating design that integrates dual temperature and pH responses to achieve precise release of the insect repellent. The temperature-sensitive material triggers an increase in the coating porosity under high temperatures, accelerating the release of the insect repellent to meet the needs of high pest infestations. The pH-responsive layer activates a directional release mechanism in acidic soils to specifically inhibit pest activity. Microencapsulation technology uses natural wall materials to encapsulate the insect repellent, combined with a nano-particle size design, to extend the release cycle and reduce environmental interference. This mechanism solves the problems of unstable release and short duration of effectiveness of traditional insect repellents, significantly improving the effectiveness of field applications. 3. The present invention introduces nano-reinforced materials to form a rigid three-dimensional network structure in the coating, which greatly improves the compressive strength and mechanical stability and avoids failure due to damage caused by external forces. The introduction of dynamic chemical bonds gives the coating the ability to repair itself. After damage, the integrity can be restored through molecular chain reorganization, extending the service life. The combination of high mechanical strength and self-repair function ensures that the coating maintains structural stability in complex field environments, continues to exert its slow-release and insect repellent functions, and breaks through the technical bottleneck of insufficient durability of traditional coatings. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a flow chart for preparing the insect repellent polyurethane slow-release fertilizer coating auxiliary agent of the present invention; Figure 2 A flow chart for preparing Example 1 of the present invention is provided; Figure 3 A flow chart is prepared for Example 2 of the present invention; Figure 4 This is a flow chart for preparing Example 3 of the present invention. DETAILED DESCRIPTION

[0015] The specific embodiments of the present invention will be further described below in conjunction with the accompanying drawings. It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention.

[0016] In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0017] Please see the attached Figure 1 -Attached Figure 4 The present invention provides an insect repellent polyurethane slow-release fertilizer coating auxiliary agent, and the coating auxiliary agent preparation method comprises the following components in percentage by weight: Bio-based polyurethane prepolymer: 30-60%, bio-based polyurethane is made by reacting castor oil with isocyanate; Microencapsulated insect repellent: 1-10%. The core material of the microencapsulated insect repellent is azadirachtin, the wall material is chitosan, and the microcapsule particle size is 100-500nm; Sustained-release regulator: 5-15%, the sustained-release regulator is polylactic acid; Cross-linking agent: 2-8%, the cross-linking agent is hexamethylene diisocyanate; Dispersant: 1-3%, the dispersant is sodium lauryl sulfate; Wetting agent: 0.5-2%, the wetting agent is alkyl naphthalene sulfonate; The coating adjuvant is formed on the surface of the fertilizer particles through a multi-layer spraying process, and at least comprises an insect repellent layer and a slow-release layer, wherein the porosity of the insect repellent layer is 10-30%, and the thickness of the slow-release layer is 50-100 μm.

[0018] In one embodiment of the present invention, a thermosensitive material, poly (N-isopropylacrylamide), is added to the sustained-release layer in an amount of 2-5% of the mass of the sustained-release layer. When the ambient temperature is ≥30°C, the porosity of the insect repellent layer increases to 1.5 times the initial value.

[0019] In one embodiment of the present invention, the coating auxiliary agent further comprises nano-silicon dioxide, the addition amount of which is 1-3% of the mass of the polyurethane prepolymer, and the coating compressive strength is ≥15 MPa.

[0020] In one embodiment of the present invention, a pH-responsive layer is provided between the insect repellent layer and the sustained-release layer. The pH-responsive layer comprises polyacrylic acid, and the added amount is 3-8% of the mass of the pH-responsive layer. When the soil pH is ≤5.5, the insect repellent is triggered to be released in a targeted manner.

[0021] In one embodiment of the present invention: the envelope has a self-repair function, and realizes autonomous repair after damage through dynamic disulfide bonds, with a repair rate of ≥90%.

[0022] The present invention also provides a method for preparing an insect repellent polyurethane slow-release fertilizer coating auxiliary agent, comprising the following steps: (1) Pre-dispersion of insect repellent: Mix the microencapsulated insect repellent with the bio-based polyurethane prepolymer and dispersant, and perform ultrasonic treatment until nano-scale dispersion; (2) Preparation of coating solution: Add polylactic acid and hexamethylene diisocyanate and stir to form a homogeneous coating solution; (3) Multi-layer spraying: The first insect repellent layer is sprayed: the coating liquid containing the insect repellent is evenly sprayed onto the surface of the fertilizer particles through an electrostatic spraying device at a voltage of 5-20kV, and a porous insect repellent layer is formed after solidification; The second sustained-release layer is sprayed: spraying a polyurethane composite liquid without insect repellent to form a dense sustained-release layer; (4) Post-processing: Curing at 25-40°C for 10-30 seconds under UV irradiation, and sieving to obtain the finished product.

[0023] In one embodiment of the present invention, the thickness deviation of the electrostatically sprayed coating is less than 5%.

[0024] In one embodiment of the present invention, the coating adjuvant is suitable for basal application to rice, corn or vegetable crops, with an application rate of 20-50 kg / mu, an insect repellent release period of 30-60 days, and a fertilizer slow-release period of 60-120 days.

[0025] In one embodiment of the present invention, the biodegradation rate of the bio-based polyurethane is ≥80%, and the residue has no significant effect on the activity of soil microorganisms.

[0026] Please see the attached Figure 2 , Example 1: Raw material ratio (mass percentage): Bio-based polyurethane prepolymer (made by reacting castor oil with isocyanate): 45% Microencapsulated insect repellent (core material: azadirachtin, wall material: chitosan, particle size: 300nm): 6% Sustained release regulator (polylactic acid): 10% Crosslinking agent (hexamethylene diisocyanate): 5% Dispersant (sodium lauryl sulfate): 2% Wetting agent (alkyl naphthalene sulfonate): 1% Nano-silica (added amount is 2% of the mass of polyurethane prepolymer) Thermosensitive material (poly (N-isopropylacrylamide), added in an amount of 3% of the sustained-release layer mass) Preparation steps: 1. Pre-dispersion of insect repellent: Mix the microencapsulated insect repellent, bio-based polyurethane prepolymer and dispersant and treat them in an ultrasonic device for 30 minutes to ensure uniform nano-scale dispersion.

[0027] 2. Preparation of coating solution: Add polylactic acid and hexamethylene diisocyanate to the above mixture and stir at 500 rpm for 1 hour to form a homogeneous coating solution.

[0028] 3. Multi-layer spraying: The first layer (insect repellent layer): Using electrostatic spraying equipment, the coating liquid containing insect repellent is evenly sprayed onto the surface of the fertilizer particles at a voltage of 15kV. After solidification, an insect repellent layer with a porosity of 20% is formed.

[0029] The second layer (sustained-release layer): spray a polyurethane composite liquid (containing poly (N-isopropyl acrylamide)) without insect repellent to form a dense sustained-release layer with a thickness of 70 μm.

[0030] 4. Post-processing: Curing at 35°C for 20 seconds under UV light (wavelength 365nm), and sieving to obtain the finished product.

[0031] Performance testing: Thermosensitive response: When the ambient temperature rises to 30°C, the porosity of the insect repellent layer increases to 30% and the insect repellent release rate increases by 50%.

[0032] Mechanical strength: The compressive strength of the coating is 16MPa, which meets the requirements for field machinery use.

[0033] Slow-release cycle: The slow-release cycle of fertilizer is 90 days, and the slow-release cycle of insect repellent is 45 days.

[0034] Please see the attached Figure 3 , Example 2: Raw material ratio (mass percentage): Bio-based polyurethane prepolymer (made by reacting castor oil with isocyanate): 55% Microencapsulated insect repellent (core material: azadirachtin, wall material: chitosan, particle size: 200nm): 8% Sustained-release modifier (polylactic acid): 12% Crosslinking agent (hexamethylene diisocyanate): 6% Dispersant (sodium lauryl sulfate): 2.5% Wetting agent (alkyl naphthalene sulfonate): 1.5% pH response layer (polyacrylic acid, added amount is 5% of the mass of the pH response layer) Dynamic disulfide crosslinker (added amount is 0.5% of the total envelope mass) Preparation steps: 1. Pre-dispersion of insect repellent: Mix the microencapsulated insect repellent with bio-based polyurethane prepolymer and dispersant and ultrasonicate for 40 minutes to ensure uniform particle size distribution.

[0035] 2. Preparation of coating solution: Add polylactic acid and hexamethylene diisocyanate, stir to form a homogeneous liquid, and add dynamic disulfide bond crosslinking agent.

[0036] 3. Multi-layer spraying: The first layer (insect repellent layer): The insect repellent coating liquid is electrostatically sprayed at a voltage of 10kV, and the porosity after curing is 25%.

[0037] Second layer (pH responsive layer): spray-coat an intermediate layer containing polyacrylic acid with a thickness of 20 μm.

[0038] The third layer (sustained-release layer): spray a polyurethane composite liquid without insect repellent to form a sustained-release layer with a thickness of 80 μm.

[0039] 4. Post-processing: Curing at 30°C for 25 seconds under UV irradiation, and sieving to obtain the finished product.

[0040] Performance testing: pH-responsive release: When soil pH is ≤5.5, the pH-responsive layer swells and the release of the insect repellent increases by 80%.

[0041] Self-repair function: After the membrane is damaged, it can be left at room temperature for 24 hours and the repair rate reaches 92%.

[0042] Degradation performance: The biodegradation rate of bio-based polyurethane is 85%, and the residues have no significant effect on the activity of soil microorganisms.

[0043] Applicability: Suitable for basal application on vegetable crops in acidic soil (pH ≤ 5.5), with an application rate of 35 kg / mu.

[0044] Please see the attached Figure 4 , Example 3: Raw material ratio (mass percentage): Bio-based polyurethane prepolymer (made by reacting castor oil with isocyanate): 50% Microencapsulated insect repellent (core material: azadirachtin, wall material: chitosan, particle size: 400nm): 4% Sustained release regulator (polylactic acid): 8% Crosslinking agent (hexamethylene diisocyanate): 7% Dispersant (sodium lauryl sulfate): 1.5% Wetting agent (alkyl naphthalene sulfonate): 0.8% Photosensitive material (azobenzene derivative): added in an amount of 0.3% of the total coating mass Nanoclay (montmorillonite): added in an amount of 2.5% of the mass of the polyurethane prepolymer Preparation steps: 1. Pre-dispersion of insect repellent: Mix the microencapsulated insect repellent with the bio-based polyurethane prepolymer and dispersant and ultrasonicate for 35 minutes to ensure uniform particle size distribution.

[0045] 2. Preparation of coating solution: Add polylactic acid, hexamethylene diisocyanate and photosensitive material, stir at 600 rpm for 50 minutes to form a homogeneous coating solution.

[0046] 3. Multi-layer spraying: The first layer (insect repellent layer): Use electrostatic spraying equipment to spray the coating liquid containing insect repellent at a voltage of 12kV. After solidification, an insect repellent layer with a porosity of 15% is formed.

[0047] The second layer (photoresponsive layer): spraying a polyurethane composite liquid containing azobenzene derivatives with a thickness of 15 μm and a photoresponsive wavelength range of 400-450 nm.

[0048] The third layer (sustained-release layer): Spray a polyurethane composite liquid containing nanoclay to form a sustained-release layer with a thickness of 60 μm.

[0049] 4. Post-processing: Curing at 28°C for 15 seconds under UV irradiation (wavelength 385nm), and sieving to obtain the finished product.

[0050] Performance testing: Photoresponsive release: Under blue light (450nm) irradiation, the photoresponsive layer structure relaxes and the repellent release rate increases by 40%.

[0051] Compressive strength: After nanoclay reinforcement, the compressive strength of the coating reaches 18 MPa, which is 12% higher than that of Example 1.

[0052] Self-repair efficiency: With the assistance of dynamic disulfide bonds, the repair rate of damaged envelope reaches 95% within 12 hours at room temperature.

[0053] Degradation performance: The degradation rate of bio-based polyurethane is 82%, and the nanoclay in the residue can absorb heavy metal ions in the soil, reducing the risk of pollution.

[0054] Applicability: Suitable for areas with sufficient sunlight (such as greenhouse vegetables), the application rate is 25kg / mu, and the fertilizer slow-release period is 100 days.

[0055] Although the present invention is disclosed above with reference to preferred embodiments, this is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications without departing from the spirit and scope of the present invention. Therefore, any modifications, equivalent variations, and modifications made to the above embodiments in accordance with the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the scope of protection defined by the claims of the present invention.

Claims

1. An insect repellent polyurethane slow-release fertilizer coating auxiliary agent, characterized in that: The preparation method of the coating auxiliary agent includes the following components in percentage by weight: Bio-based polyurethane prepolymer: 30-60%, wherein the bio-based polyurethane is prepared by reacting castor oil with isocyanate; Microencapsulated insect repellent: 1-10%, the core material of the microencapsulated insect repellent is azadirachtin, the wall material is chitosan, and the microcapsule particle size is 100-500nm; Sustained-release regulator: 5-15%, wherein the sustained-release regulator is polylactic acid; Cross-linking agent: 2-8%, the cross-linking agent is hexamethylene diisocyanate; Dispersant: 1-3%, the dispersant is sodium lauryl sulfate; Wetting agent: 0.5-2%, the wetting agent is alkyl naphthalene sulfonate; The coating auxiliary agent is formed on the surface of the fertilizer particles through a multi-layer spraying process, and at least comprises an insect repellent layer and a slow-release layer, wherein the porosity of the insect repellent layer is 10-30%, and the thickness of the slow-release layer is 50-100 μm.

2. The insect repellent polyurethane slow-release fertilizer coating auxiliary agent according to claim 1, characterized in that: The temperature-sensitive material poly (N-isopropylacrylamide) is added to the sustained-release layer in an amount of 2-5% of the mass of the sustained-release layer. When the ambient temperature is ≥30°C, the porosity of the insect repellent layer increases to 1.5 times the initial value.

3. The insect repellent polyurethane slow-release fertilizer coating auxiliary agent according to claim 1, characterized in that: The coating auxiliary agent also includes nano silicon dioxide, the addition amount of which is 1-3% of the mass of the polyurethane prepolymer, and the coating compressive strength is ≥15MPa.

4. The insect repellent polyurethane slow-release fertilizer coating auxiliary agent according to claim 1, characterized in that: A pH response layer is provided between the insect repellent layer and the sustained-release layer. The pH response layer contains polyacrylic acid, and the addition amount is 3-8% of the mass of the pH response layer. When the soil pH is ≤5.5, the insect repellent is triggered to be released in a targeted manner.

5. The insect repellent polyurethane slow-release fertilizer coating auxiliary agent according to claim 1, characterized in that: The envelope has a self-repairing function and can achieve autonomous repair after damage through dynamic disulfide bonds, with a repair rate of ≥90%.

6. A method for preparing the insect repellent polyurethane slow-release fertilizer coating auxiliary agent according to any one of claims 1 to 5, characterized in that: The following steps are involved: (1) Pre-dispersion of insect repellent: Mix the microencapsulated insect repellent with the bio-based polyurethane prepolymer and dispersant, and perform ultrasonic treatment until nano-scale dispersion; (2) Preparation of coating solution: Add polylactic acid and hexamethylene diisocyanate and stir to form a homogeneous coating solution; (3) Multi-layer spraying: The first insect repellent layer is sprayed: the coating liquid containing the insect repellent is evenly sprayed onto the surface of the fertilizer particles through an electrostatic spraying device at a voltage of 5-20kV, and a porous insect repellent layer is formed after solidification; The second sustained-release layer is sprayed: spraying a polyurethane composite liquid without insect repellent to form a dense sustained-release layer; (4) Post-processing: Curing at 25-40°C for 10-30 seconds under UV irradiation, and sieving to obtain the finished product.

7. The method for preparing an insect repellent polyurethane slow-release fertilizer coating auxiliary agent according to claim 6, wherein: The electrostatic spray coating has a thickness deviation of <5%.

8. The method for preparing an insect repellent polyurethane slow-release fertilizer coating auxiliary agent according to claim 7, wherein: The coating adjuvant is suitable for basal application on rice, corn or vegetable crops, with an application rate of 20-50 kg / mu, an insect repellent release period of 30-60 days, and a fertilizer slow-release period of 60-120 days.

9. The method for preparing an insect repellent polyurethane slow-release fertilizer coating auxiliary agent according to claim 8, characterized in that: The biodegradation rate of the bio-based polyurethane is ≥80%, and the residue has no significant effect on the activity of soil microorganisms.

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