Preparation method of herbicide slow-release microcapsules

Abstract

A method for preparing a slow-release microcapsule of a herbicide. The present invention relates to the field of preparing slow-release microcapsules of herbicides. The present invention aims to solve the technical problems that the urea-formaldehyde resin forming the capsule wall of the existing slow-release pesticide microcapsules has a very dense structure, resulting in difficult release of the drug in the capsule core and difficult control of the release rate. Method: First, prepare a prepolymer solution; second, add the herbicide, then add a surfactant, and react to prepare a suspension; third, spray-dry to obtain microcapsule powder; fourth, cure and crosslink under heating conditions to obtain the slow-release microcapsule of the herbicide. In the present invention, adding a high-molecular pore-forming agent can effectively adjust the drug release rate and overcome the problem that the drug cannot be released due to the overly dense wall material of the urea-formaldehyde resin. The drug is absorbed into the weeds through the roots of the weeds, resulting in difficult germination of weed seeds and rapid death of germinated weeds. The present invention is used for preparing slow-release microcapsules of herbicides.

Description

Technical Field

[0001] The present invention relates to the field of preparation of herbicide slow-release microcapsules. Background Art

[0002] Selective pre-emergence herbicides and cell division inhibitor herbicides are suitable for transplanted paddy fields and dry fields. The objects to be controlled are annual gramineous weeds and sedges, such as barnyard grass, bald barnyard grass, sprangletop, flatsedge, monochoria vaginalis, floating grass, etc. They are absorbed through the young buds and underground stems of plants, inhibit cell fission and extension, make it difficult for new leaves of weeds to emerge, stop growing, and finally wither and die. They have the best effect on germinating weeds; they have a poorer effect on grown-up weeds. After being treated with the medicine, the weeds stop growing, the leaves turn dark green, sometimes decolorize, the leaves become short and thick, are extremely easy to break, the heart leaves are not easy to emerge, and finally the whole plant withers and dies. The biggest drawback of this conventional spraying method is that it requires multiple applications, resulting in a large amount of medicine application and high labor cost for spraying.

[0003] With the continuous strengthening of people's environmental protection awareness, the safety and residual effect of pesticides are required to be more stringent. Therefore, it is necessary to synthesize a new pesticide with high efficiency, low toxicity, long residual period and small dosage to the greatest extent. Encapsulating pesticides into microcapsules can control the decomposition and loss caused by environmental factors, increase the stability of products, and reduce volatility because the active components are encapsulated in the capsule membrane. Since the amount of medicine used is reduced, the harm to humans, livestock and crops is reduced, and the pesticide residue can also be reduced.

[0004] Among the currently marketed pesticide microcapsules, most are prepared by the interfacial polymerization method. And the in-situ polymerization method is also a promising method for pesticide microencapsulation. The in-situ polymerization method is to disperse all monomers and initiators in the dispersed phase or continuous phase, that is, all monomers and initiators are dissolved inside or outside the core material. Since the monomer is soluble in one phase and the generated polymer is insoluble in the whole system, the polymer will deposit on the surface of the core material droplets. Compared with other microencapsulation methods, the in-situ polymerization method is relatively easy to form capsules, the wall thickness and the content of the internal inclusion can be controlled, the yield is high, the cost is low, and it is easy to industrialize.

[0005] In the in-situ polymerization process, it is most economical to use urea-formaldehyde resin as the capsule wall material. Its initial raw materials for forming capsules are formaldehyde and urea. The comprehensive cost is much lower than that of the interfacial polymerization technology. The microcapsule pesticides manufactured have a high encapsulation rate, stable capsules, strong water penetration resistance, good morphology, and great market potential. This method is a relatively commonly used method in many studies on slow-release pesticide microcapsules. However, this method has a most fatal problem: Since the urea-formaldehyde resin forming the capsule wall has a very dense structure, it is very difficult for the core drug to be released. Summary of the Invention

[0006] The present invention aims to solve the technical problems that the urea-formaldehyde resin forming the capsule wall of the existing slow-release pesticide microcapsules has a very dense structure, resulting in difficult release of the drug in the capsule core and difficult control of the release rate, and provides a preparation method for herbicide slow-release microcapsules.

[0007] A preparation method for herbicide slow-release microcapsules is specifically carried out according to the following steps:

[0008] I. Put urea and formaldehyde solution into a reaction kettle, stir and dissolve, add an alkaline substance to adjust to alkaline, then raise the temperature to 70 °C, and continue stirring and reacting to obtain a mixed solution. Add the mixed solution to distilled water for dilution, then add a pore-forming agent solution, and then adjust to acidic with an acidic substance, control the temperature at 40 - 60 °C, and keep warm to obtain a prepolymer solution;

[0009] II. Add the herbicide to the prepolymer solution obtained in step I, then add a surfactant, and use a high-shear emulsification mechanism to make a stable emulsion, and then react under the condition of a temperature of 40 - 60 °C to obtain a suspension;

[0010] III. Spray-dry the suspension obtained in step II to obtain microcapsule powder;

[0011] IV. Cure and crosslink the microcapsule powder obtained in step III under heating conditions to obtain the herbicide slow-release microcapsules.

[0012] The mixed solution obtained in step II is a clear, transparent and slightly viscous solution.

[0013] Further, the mass concentration of the formaldehyde solution in step I is 37 - 40%.

[0014] Further, the molar ratio of urea to formaldehyde in step I is (1.2 - 2.0)∶1.

[0015] Preferably, the molar ratio of urea to formaldehyde in step I is (1.6 - 1.85)∶1.

[0016] Further, the alkaline substance in step I is sodium hydroxide, potassium hydroxide or triethanolamine.

[0017] Further, in step I, adding an alkaline substance is adjusted to a pH of 7.5 - 11.0.

[0018] Further, in step I, the heating rate is controlled at 0.3 - 5 °C and heated to 70 °C.

[0019] Preferably, in step I, the heating rate is controlled at 0.5 - 1.5 °C and heated to 70 °C.

[0020] Further, in step I, the stirring reaction is carried out for 0.5 - 3 h.

[0021] Preferably, in step one, the stirring reaction is carried out for 0.8 to 1.2 h.

[0022] Further, in step one, the volume ratio of the mixed solution to distilled water is 1∶(0.2 - 5).

[0023] Further, in step one, the pore - forming agent is a water - soluble polymer material.

[0024] Preferably, in step one, the pore - forming agent is a starch solution or a gelatin solution.

[0025] Further, in step one, the dosage of the pore - forming agent is 0.5 - 30% of the mass of the wall material.

[0026] Preferably, in step one, the dosage of the pore - forming agent is 1 - 5% of the mass of the wall material.

[0027] Further, in step one, the acidic substance is butyric acid, caproic acid, citric acid or tartaric acid.

[0028] Further, in step one, it is adjusted to a pH of 4.5 - 2.0 with the acidic substance.

[0029] Further, in step two, the herbicide is pretilachlor, butachlor, alachlor, isopropyl pretilachlor or metolachlor.

[0030] Further, in step two, the herbicide is dissolved in an organic solvent and then added to the prepolymer solution, where the mass ratio of the organic solvent to the herbicide is (10 - 0.5)∶1, and the organic solvent is acetone, chloroform, toluene or xylene.

[0031] Further, in step two, the surfactant is a polyether surfactant.

[0032] Preferably, in step two, the surfactant is alkylphenol polyoxyethylene ether.

[0033] Further, in step two, the average particle size of the emulsion is 0.5 - 100 μm.

[0034] Further, in step two, the reaction is carried out at a temperature of 40 - 60 °C for 0.5 - 6 h.

[0035] Further, in step four, the microcapsule powder is heated to 40 - 80 °C for curing, and the curing time is 0.5 - 12 h.

[0036] Preferably, in step four, the microcapsule powder is heated to 50 - 70 °C for curing, and the curing time is 4 - 8 h.

[0037] The beneficial effects of the present invention are:

[0038] 1. The addition of a polymer pore-forming agent in the present invention can effectively adjust the drug release rate and overcome the problem that the drug cannot be released due to the overly dense urea-formaldehyde resin wall material. Through adjustment, 80% of the drug can be released within 1 day, or the release can be adjusted so that 80% of the drug is released in 2 months, achieving the purpose of controllable release rate.

[0039] 2. Since urea-formaldehyde resin is a strongly hydrophobic wall material, it is very difficult to add a general water-soluble pore-forming agent using the traditional in-situ polymerization method. Even if a small amount can be added, the process reproducibility is very poor and it is difficult to industrialize. The present invention uses spray drying to dry the wall material and the pore-forming agent that have not been fully crosslinked and cured together, which can effectively add the pore-forming agent into the urea-formaldehyde resin wall material to adjust the drug release rate. And an acid that is not easily volatile is used to adjust the pH value so that the microcapsules can still be fully crosslinked and cured after spray drying to form a complete and dense wall material.

[0040] 3. The microcapsules prepared by the present invention have a good sustained-release effect. The drug release rate can be adjusted according to actual needs by adjusting the amount of the pore-forming agent and the core-wall ratio, achieving long-term slow drug release. Only one application is needed for one season of rice, which can reduce the labor cost for farmers when applying pesticides.

[0041] 4. Since the slow drug release can effectively avoid the occurrence of pesticide damage events caused by uneven pesticide application by farmers when applying pesticides.

[0042] 5. Ordinary herbicide preparations are applied twice in one season. The sustained-release preparation prepared by the present invention is only applied once in one season, and the drug usage amount is 1 / 2 - 2 / 3 of that of ordinary preparations. Therefore, the pesticide application amount can be effectively reduced, which is environmentally friendly and has low residues.

[0043] 6. After the drug is made into microcapsules, it can quickly settle on the surface of the soil at the bottom of the water. After the drug is released, it is easily adsorbed in a large amount in the soil. Since the drug enters the inside of the weeds through the absorption of the roots of the weeds, it is difficult for the weed seeds to germinate, and the germinated weeds will also die quickly.

[0044] The present invention is used for preparing herbicide sustained-release microcapsules. Description of the Drawings

[0045] Figure 1 It is the drug release curve graph of the herbicide sustained-release microcapsules prepared in Example 1. Detailed Embodiments

[0046] The technical solution of the present invention is not limited to the following specific embodiments listed, and also includes any combination between the specific embodiments.

[0047] Detailed Embodiment 1: A preparation method of herbicide sustained-release microcapsules in this embodiment is specifically carried out according to the following steps:

[0048] 1. Put urea and formaldehyde solution into a reaction kettle, stir and dissolve, add an alkaline substance to adjust to alkaline, then heat up to 70 °C, and continue to stir and react to obtain a mixed solution. Add the mixed solution to distilled water for dilution, then add a pore-forming agent solution, and then adjust to acidic with an acidic substance, control the temperature at 40 - 60 °C, keep warm, and obtain a prepolymer solution;

[0049] 2. Add a herbicide to the prepolymer solution obtained in step 1, then add a surfactant, and use a high-shear emulsification mechanism to make a stable emulsion, and then react under the condition of a temperature of 40 - 60 °C to obtain a suspension;

[0050] 3. Spray-dry the suspension obtained in step 2 to obtain microcapsule powder;

[0051] 4. Cure and crosslink the microcapsule powder obtained in step 3 under heating conditions to obtain the herbicide slow-release microcapsules.

[0052] Specific Embodiment 2: The difference between this embodiment and Specific Embodiment 1 is that the mass concentration of the formaldehyde solution in step 1 is 37 - 40%. Others are the same as Specific Embodiment 1.

[0053] Specific Embodiment 3: The difference between this embodiment and Specific Embodiment 1 or 2 is that the molar ratio of urea to formaldehyde in step 1 is (1.2 - 2.0)∶1. Others are the same as Specific Embodiment 1 or 2.

[0054] Specific Embodiment 4: The difference between this embodiment and any one of Specific Embodiments 1 to 3 is that the molar ratio of urea to formaldehyde in step 1 is (1.6 - 1.85)∶1. Others are the same as any one of Specific Embodiments 1 to 3.

[0055] Specific Embodiment 5: The difference between this embodiment and any one of Specific Embodiments 1 to 4 is that the alkaline substance in step 1 is sodium hydroxide, potassium hydroxide or triethanolamine. Others are the same as any one of Specific Embodiments 1 to 4.

[0056] Specific Embodiment 6: The difference between this embodiment and any one of Specific Embodiments 1 to 5 is that in step 1, adding an alkaline substance adjusts the pH to 7.5 - 11.0. Others are the same as any one of Specific Embodiments 1 to 5.

[0057] Specific Embodiment 7: The difference between this embodiment and any one of Specific Embodiments 1 to 6 is that in step 1, control the heating rate at 0.3 - 5 °C and heat up to 70 °C. Others are the same as any one of Specific Embodiments 1 to 6.

[0058] Specific Embodiment 8: The difference between this embodiment and any one of Specific Embodiments 1 to 7 is that in step 1, control the heating rate at 0.5 - 1.5 °C and heat up to 70 °C. Others are the same as any one of Specific Embodiments 1 to 7.

[0059] Embodiment Nine in Detail: The difference between this embodiment and any one of Embodiments One to Eight is that in Step One, the stirring reaction is carried out for 0.5 - 3 h. Others are the same as any one of Embodiments One to Eight.

[0060] Embodiment Ten in Detail: The difference between this embodiment and any one of Embodiments One to Nine is that in Step One, the stirring reaction is carried out for 0.8 - 1.2 h. Others are the same as any one of Embodiments One to Nine.

[0061] Embodiment Eleven in Detail: The difference between this embodiment and any one of Embodiments One to Ten is that in Step One, the volume ratio of the mixed solution to distilled water is 1∶(0.2 - 5). Others are the same as any one of Embodiments One to Ten.

[0062] Embodiment Twelve in Detail: The difference between this embodiment and any one of Embodiments One to Eleven is that in Step One, the pore - forming agent is a water - soluble polymer material. Others are the same as any one of Embodiments One to Eleven.

[0063] Embodiment Thirteen in Detail: The difference between this embodiment and any one of Embodiments One to Twelve is that in Step One, the pore - forming agent is a starch solution or a gelatin solution. Others are the same as any one of Embodiments One to Twelve.

[0064] Embodiment Fourteen in Detail: The difference between this embodiment and any one of Embodiments One to Thirteen is that in Step One, the dosage of the pore - forming agent is 0.5 - 30% of the mass of the wall material. Others are the same as any one of Embodiments One to Thirteen.

[0065] Embodiment Fifteen in Detail: The difference between this embodiment and any one of Embodiments One to Fourteen is that in Step One, the dosage of the pore - forming agent is 1 - 5% of the mass of the wall material. Others are the same as any one of Embodiments One to Fourteen.

[0066] Embodiment Sixteen in Detail: The difference between this embodiment and any one of Embodiments One to Fifteen is that in Step One, the acidic substance is butyric acid, caproic acid, citric acid or tartaric acid. Others are the same as any one of Embodiments One to Fifteen.

[0067] Embodiment Seventeen in Detail: The difference between this embodiment and any one of Embodiments One to Sixteen is that in Step One, it is adjusted to a pH of 4.5 - 2.0 with the acidic substance. Others are the same as any one of Embodiments One to Sixteen.

[0068] Embodiment Eighteen in Detail: The difference between this embodiment and any one of Embodiments One to Seventeen is that in Step Two, the herbicide is pretilachlor, butachlor, alachlor, propisochlor or metolachlor. Others are the same as any one of Embodiments One to Seventeen.

[0069] The herbicide used in this embodiment is a pre-emergence herbicide.

[0070] Embodiment XIX: The difference between this embodiment and any one of Embodiments 1 to 18 is that in Step 2, the herbicide is dissolved in an organic solvent and then added to the prepolymer solution, where the mass ratio of the organic solvent to the herbicide is (10 - 0.5):1, and the organic solvent is acetone, chloroform, toluene or xylene. Others are the same as any one of Embodiments 1 to 18.

[0071] Embodiment XX: The difference between this embodiment and any one of Embodiments 1 to 19 is that in Step 2, the surfactant is a polyether surfactant. Others are the same as any one of Embodiments 1 to 19.

[0072] Embodiment XXI: The difference between this embodiment and any one of Embodiments 1 to 20 is that in Step 2, the surfactant is an alkylphenol polyoxyethylene ether. Others are the same as any one of Embodiments 1 to 20.

[0073] Embodiment XXII: The difference between this embodiment and any one of Embodiments 1 to 21 is that in Step 2, the average particle size of the emulsion is 0.5 - 100 μm. Others are the same as any one of Embodiments 1 to 21.

[0074] Embodiment XXIII: The difference between this embodiment and any one of Embodiments 1 to 22 is that in Step 2, the reaction is carried out at a temperature of 40 - 60 °C for 0.5 - 6 h. Others are the same as any one of Embodiments 1 to 22.

[0075] Embodiment XXIV: The difference between this embodiment and any one of Embodiments 1 to 23 is that in Step 4, the microcapsule powder is heated to 40 - 80 °C for curing, and the curing time is 0.5 - 12 h. Others are the same as any one of Embodiments 1 to 23.

[0076] Embodiment XXV: The difference between this embodiment and any one of Embodiments 1 to 24 is that in Step 4, the microcapsule powder is heated to 50 - 70 °C for curing, and the curing time is 4 - 8 h. Others are the same as any one of Embodiments 1 to 24.

[0077] The following examples are used to verify the beneficial effects of the present invention:

[0078] Example 1:

[0079] A method for preparing a herbicide slow-release microcapsule in this example is specifically carried out according to the following steps:

[0080] 1. Put 1 kg of urea and 2.5 L of formaldehyde solution with a mass concentration of 37% into a 5 L reactor, stir and dissolve, add triethanolamine to adjust the pH to 8.0, then control the heating rate at 1 °C / min, heat up to 70 °C, and continue to stir and react for 1 h to obtain a mixed solution. Transfer the mixed solution to a 50 L heated reactor, add 14 kg of distilled water for dilution, then add 0.5 kg of gelatin solution with a mass concentration of 20%, and then adjust the pH to 3.5 with a citric acid solution with a mass concentration of 20%. Control the temperature at 50 °C and keep it warm to obtain a prepolymer solution;

[0081] 2. Put 20 kg of pretilachlor into a 50 L reactor, stir and dissolve, and then add it together with the prepolymer solution obtained in step 1 into a 200 L reactor with high-shear function. Then add 1.25 kg of OP10 emulsifier, and use a high-shear emulsifier to make a stable emulsion. The average particle size of the emulsion is 6.8 μm, and then react at a temperature of 50 °C for 2 h to obtain a suspension;

[0082] 3. Spray-dry the suspension obtained in step 2 to obtain microcapsule powder;

[0083] 4. Cure and crosslink the microcapsule powder obtained in step 3 in an oven at 60 °C for 5 h to obtain the herbicide slow-release microcapsules.

[0084] The drug release curve of the herbicide slow-release microcapsules prepared in this example is as shown in Figure 1 As shown. It can be seen from the figure that the drug release amount of the herbicide slow-release microcapsules prepared by the preparation method of this example in 20 days is 80%. Therefore, in the present invention, due to the addition of a high-molecular pore-forming agent, the drug release rate can be effectively adjusted, overcoming the problem that the drug cannot be released due to the overly dense wall material of urea-formaldehyde resin. Through adjustment, 80% of the drug can be released within 20 days, achieving the purpose of controlling the drug release rate. And because the drug is slowly released, it can effectively avoid the occurrence of phytotoxicity events caused by uneven application of pesticides by farmers during pesticide application.

Claims

1. A preparation method of a herbicide slow-release microcapsule, characterized in that The method is specifically carried out according to the following steps:

1. Put 1 kg of urea and 2.5 L of formaldehyde solution with a mass concentration of 37% into a 5 L reactor, stir and dissolve, add triethanolamine to adjust the pH to 8.0, then control the heating rate at 1 °C / min, heat up to 70 °C, and continue to stir and react for 1 h to obtain a mixed solution. Transfer the mixed solution to a 50 L reactor with heating, add 14 kg of distilled water for dilution, then add 0.5 kg of gelatin solution with a mass concentration of 20%, and then adjust the pH to 3.5 with a citric acid solution with a mass concentration of 20%. Control the temperature at 50 °C and keep it warm to obtain a prepolymer solution; 2. Put 20 kg of pretilachlor into a 50 L reactor, stir and dissolve, and then add it together with the prepolymer solution obtained in step 1 into a 200 L reactor with high-shear function. Then add 1.25 kg of OP10 emulsifier, and use a high-shear emulsification mechanism to make a stable emulsion. The average particle size of the emulsion is 6.8 μm, and then react at a temperature of 50 °C for 2 h to obtain a suspension; 3. Spray-dry the suspension obtained in step 2 to obtain microcapsule powder; 4. Cure and crosslink the microcapsule powder obtained in step 3 in an oven at 60 °C for 5 h to obtain the herbicide slow-release microcapsules.

Images