A methylal suspension agent with slow-release performance and a preparation method thereof

Abstract

The application relates to the technical field of pesticides, and particularly discloses a tetramethylpyrazine suspension agent with slow-release performance and a preparation method thereof. The tetramethylpyrazine is prepared into a suspension, so that the particle size of the tetramethylpyrazine can be controlled, and tetramethylpyrazine particles with a suitable particle size as a capsule core can be obtained without dissolving and emulsifying the tetramethylpyrazine technical material. The application overcomes the defect that the tetramethylpyrazine is difficult to adopt a traditional microcapsule coating process, and a capsule membrane formed by a melamine modified urea-formaldehyde resin prepolymer can hinder the degradation of the tetramethylpyrazine, thereby prolonging the persistence period of the tetramethylpyrazine suspension agent and improving the insecticidal effect of the tetramethylpyrazine pesticide.

Description

Technical Field

[0001] This application relates to the field of pesticide technology, and more specifically, to a tetraacetaldehyde suspension with sustained-release properties and a method for preparing the same. Background Technology

[0002] Gastropods serve as intermediate hosts for many parasites, potentially causing various parasitic diseases, including schistosomiasis. Furthermore, some gastropod species (such as snails, slugs, and Oncomelania hupensis) are also pests that require significant attention in agricultural production, severely impacting the yields of grains, fruits, and vegetables. To control gastropod populations and reduce their impact on agricultural production, a pesticide effectively killing gastropod pests is needed.

[0003] Metaldehyde is a white, needle-like crystalline substance. When gastropod pests come into contact with or inhale metaldehyde, it produces a stomach poison effect within the snail's body, causing rapid paralysis and the secretion of a special mucus that completely depletes the snail's energy reserves, leading to collapse. Under the influence of metaldehyde, the cell membranes and organelles of gastropod pests are significantly damaged, and the mucus membrane is also destroyed, ultimately resulting in death due to massive fluid loss. Therefore, it can be used to control pests such as slugs, snails, golden apple snails, and Oncomelania hupensis. The most prominent advantage of metaldehyde is its ability to inhibit Oncomelania hupensis from climbing and its low toxicity to aquatic organisms. Currently, metaldehyde-based pesticide products are mainly in traditional formulations such as granules, wettable powders, and suspension concentrates.

[0004] Regarding the aforementioned technologies, the inventors believe that traditional metaldehyde pesticide formulations suffer from a short residual effect, severely impacting their insecticidal efficacy. While slow-release pesticide formulations can achieve a longer residual effect, traditional slow-release formulations require dissolving the solid active ingredient in a large amount of organic solvent before undergoing subsequent emulsification and encapsulation processes to obtain microcapsules with a slow-release effect. However, metaldehyde has very low solubility in organic solvents, making traditional microencapsulation methods unsuitable, thus limiting the application of metaldehyde pesticides. Summary of the Invention

[0005] In related technologies, traditional formulations of metaldehyde pesticides suffer from short release times and short durations of action, and cannot be encapsulated using traditional microencapsulation methods, thus limiting their application. To overcome this deficiency, this application provides a metaldehyde suspension with sustained-release properties and its preparation method.

[0006] In a first aspect, this application provides a metaldehyde suspension with sustained-release properties, employing the following technical solution:

[0007] A metaldehyde suspension with sustained-release properties comprises the following components in parts by weight: 20-60 parts of metaldehyde suspension, 2-10 parts of emulsifier, 10-40 parts of melamine-modified urea-formaldehyde resin prepolymer, and 5-15 parts of acidic catalyst; wherein the mass fraction of metaldehyde in the metaldehyde suspension is 40-50%, and the acidic catalyst is a protic acid aqueous solution with a concentration of 0.5-1 mol / L.

[0008] By adopting the above technical solution, in the metaldehyde suspension, metaldehyde is suspended in the liquid phase in the form of particles. The emulsifier can improve the compatibility between the metaldehyde particles and the melamine-modified urea-formaldehyde resin prepolymer on the surface of the metaldehyde particles. Under the action of an acidic catalyst, the melamine-modified urea-formaldehyde resin prepolymer can polymerize on the surface of the metaldehyde particles, forming a membrane on the surface of the metaldehyde particles. This application achieves control over the particle size of metaldehyde by preparing it into a suspension. It obtains metaldehyde particles of suitable size as cores without dissolving and emulsifying the metaldehyde technical material, thus overcoming the shortcomings of traditional microencapsulation processes for metaldehyde. Furthermore, the membrane formed by the melamine-modified urea-formaldehyde resin prepolymer can hinder the degradation of metaldehyde, prolong the effective period of the metaldehyde suspension, and improve the insecticidal effect of metaldehyde pesticides.

[0009] Preferably, the melamine-modified urea-formaldehyde resin prepolymer is prepared according to the following method:

[0010] (1) Mix melamine, urea and formaldehyde solution, and stir in a constant temperature water bath at 60-80℃ until melamine and urea are completely dissolved to obtain resin precursor liquid;

[0011] (2) Add triethanolamine dropwise to the resin precursor solution until the pH of the resin precursor solution is adjusted to 9.2±0.7. Then continue to heat and stir for 40-80 min under constant temperature water bath conditions of 60-80℃ to obtain melamine modified urea-formaldehyde resin prepolymer.

[0012] By adopting the above technical solution, this application uses melamine, urea and formaldehyde as the main raw materials, and reacts the three with the participation of triethanolamine to obtain melamine-modified urea-formaldehyde resin prepolymer.

[0013] Preferably, the molar ratio of urea to formaldehyde is (1-1.2):1.

[0014] By adopting the above technical solution, the molar ratio of urea and formaldehyde was optimized, which helps to extend the effective period of metaldehyde suspension and improve the insecticidal effect of metaldehyde pesticide.

[0015] Preferably, the molar ratio of melamine to formaldehyde is (0.15-0.25):1.

[0016] By adopting the above technical solution, the molar ratio of melamine to formaldehyde was optimized, which helps to extend the effective period of metaldehyde suspension and improve the insecticidal effect of metaldehyde pesticide.

[0017] Preferably, in the method for preparing the melamine-modified urea-formaldehyde resin prepolymer, the temperature of the constant temperature water bath is 65-75℃.

[0018] By adopting the above technical solution, the temperature of the constant temperature water bath used in the preparation of melamine-modified urea-formaldehyde resin prepolymer was optimized, which helps to extend the effective period of metaldehyde suspension and improve the insecticidal effect of metaldehyde pesticide.

[0019] Secondly, this application provides a method for preparing a metaldehyde suspension with sustained-release properties, using the following technical solution:

[0020] A method for preparing a metaldehyde suspension with sustained-release properties includes the following steps:

[0021] (1) Mix metaldehyde, wetting agent, dispersant and thickener, and add water and additives to obtain a metaldehyde suspension;

[0022] (2) Add 2-10 parts by weight of emulsifier and 10-40 parts by weight of melamine-modified urea-formaldehyde resin prepolymer to 20-60 parts by weight of tetraacetaldehyde suspension, and stir for 0.5-2 hours under constant temperature water bath conditions to obtain reaction solution.

[0023] (3) Add 5-15 parts by weight of acidic catalyst to the reaction solution to obtain any of the above-mentioned suspension intermediates. Stir and heat the suspension intermediates for 3-6 hours under constant temperature water bath conditions of 40-60℃, and then add sodium hydroxide to adjust the pH to neutral to obtain tetraacetaldehyde suspension with sustained release properties.

[0024] By adopting the above technical solution, this application first prepared a metaldehyde suspension, then added an emulsifier, a melamine-modified urea-formaldehyde resin prepolymer, and an acidic catalyst in sequence. During the gradual addition of raw materials, stirring and constant temperature water bath heating were carried out. Finally, after heating, neutralization was performed, so that the melamine-modified urea-formaldehyde resin prepolymer polymerized on the surface of the suspended metaldehyde particles to form a capsule, thus obtaining a metaldehyde suspension with sustained-release properties.

[0025] Preferably, in steps (2) and (3) of preparing the tetraacetaldehyde suspension, the temperature of the constant temperature water bath is 45-55℃.

[0026] By adopting the above technical solution, this application has optimized the constant temperature water bath during the preparation of metaldehyde suspension, which helps to extend the effective period of metaldehyde suspension and improve the insecticidal effect of metaldehyde pesticide.

[0027] Preferably, the emulsifier is sodium salt of styrene-maleic anhydride copolymer.

[0028] By employing the above technical solution, the sodium salt of styrene-maleic anhydride copolymer is a product obtained by alkaline hydrolysis of styrene-maleic anhydride copolymer under the action of sodium hydroxide. The phenyl hydrophobic group and carboxyl hydrophilic group in this molecule are arranged alternately along the molecular chain axis. When the sodium salt of styrene-maleic anhydride copolymer is added to the suspension system, the sodium salt molecules are easily adsorbed at the interface between the suspended particles and the liquid phase, making the particles approximately negatively charged colloidal particles, thus preventing particle aggregation. Under acidic conditions, dimethylolurea in the urea-formaldehyde resin prepolymer absorbs protons to become a positively charged active prepolymer, which is then deposited onto the surface of the negatively charged suspended particles through electrostatic interaction. A condensation reaction then occurs, ultimately forming a membrane on the surface of the metraldehyde particles.

[0029] Preferably, the emulsifier is an ethylene-maleic anhydride copolymer, which is an alternating copolymer obtained by polymerizing ethylene and maleic anhydride in a 1:1 molar ratio.

[0030] By adopting the above technical solution, compared with sodium styrene-maleic anhydride copolymer, ethylene-maleic anhydride copolymer can not only exert similar effects to sodium styrene-maleic anhydride copolymer, but also improve the structure of the capsule, enhance the coating effect of the capsule on metaldehyde particles, help prolong the residual effect of metaldehyde suspension, and improve the insecticidal effect of metaldehyde pesticide.

[0031] Preferably, the number-average molecular weight of the ethylene-maleic anhydride copolymer is 24,000-28,000.

[0032] By adopting the above technical solution, the number-average molecular weight of the ethylene-maleic anhydride copolymer was optimized, which helps to extend the effective period of the metaldehyde suspension and improve the insecticidal effect of the metaldehyde pesticide.

[0033] In summary, this application has the following beneficial effects:

[0034] 1. This application achieves control over the particle size of metaldehyde by formulating it into a suspension. It obtains metaldehyde particles of suitable size as cores without dissolving and emulsifying the metaldehyde technical, thus overcoming the drawback of traditional microencapsulation processes for metaldehyde. The membrane formed by the melamine-modified urea-formaldehyde resin prepolymer can inhibit the degradation of metaldehyde, prolonging the residual effect of the metaldehyde suspension and improving the insecticidal efficacy of metaldehyde pesticides.

[0035] 2. In the method of this application, the preferred emulsifier is ethylene-maleic anhydride copolymer. After the ethylene-maleic anhydride copolymer is hydrolyzed, it undergoes a cross-linking reaction with the residual formaldehyde and melamine in the melamine-modified urea-formaldehyde resin prepolymer to form a ternary complex. This improves the structure of the capsule, enhances the coating effect of the capsule on the metaldehyde particles, helps to prolong the residual effect of the metaldehyde pesticide, and improves the insecticidal effect of the metaldehyde pesticide. Detailed Implementation

[0036] The present application will be further described in detail below with reference to the embodiments, preparation examples and comparative examples. The raw materials involved in the present application can all be obtained commercially.

[0037] Example of preparation of melamine-modified urea-formaldehyde resin prepolymer

[0038] The following explanation uses Preparation Example 1 as an example.

[0039] Preparation Example 1

[0040] In this preparation example, the melamine-modified urea-formaldehyde resin prepolymer was prepared according to the following method:

[0041] (1) Mix urea, melamine and formaldehyde in a molar ratio of 0.9:0.3:1 and stir in a constant temperature water bath at 60°C until melamine and urea are completely dissolved to obtain resin precursor liquid; In this step, formaldehyde is added in the form of aqueous solution and the mass fraction of water in the resin precursor liquid is 32%.

[0042] (2) Triethanolamine was added dropwise to the resin precursor solution until the pH of the resin precursor solution was adjusted to 7.8. Then, the resin precursor solution was heated and stirred for 40 min under constant temperature water bath at 60℃ to obtain melamine-modified urea-formaldehyde resin prepolymer.

[0043] As shown in Table 1, the difference between preparation examples 1-5 is that the pH of the resin precursor solution after the addition of triethanolamine is different.

[0044] Table 1. pH of the resin precursor solution after addition of triethanolamine

[0045]

[0046]

[0047] Preparation Examples 6-9

[0048] As shown in Table 2, the difference between Preparation Example 3 and Preparation Examples 6-9 is that the molar ratio of urea and formaldehyde is different.

[0049] Table 2 Molar ratio of urea and formaldehyde

[0050] sample Urea: Formaldehyde Preparation Example 3 0.9:1 Preparation Example 6 1:1 Preparation Example 7 1.1:1 Preparation Example 8 1.2:1 Preparation Example 9 1.3:1

[0051] Preparation Examples 10-13

[0052] As shown in Table 3, the difference between Preparation Example 7 and Preparation Examples 10-13 is that the molar ratio of melamine and formaldehyde is different.

[0053] Table 3. Molar ratio of melamine to formaldehyde

[0054] sample Melamine: Formaldehyde Preparation Example 7 0.3:1 Preparation Example 10 0.25:1 Preparation Example 11 0.2:1 Preparation Example 12 0.15:1 Preparation Example 13 0.1:1

[0055] Preparation Examples 14-17

[0056] As shown in Table 4, the difference between Preparation Example 11 and Preparation Examples 14-17 is that the temperature of the constant temperature water bath is different in the method for preparing melamine-modified urea-formaldehyde resin prepolymer.

[0057] Table 4 Temperature of the constant temperature water bath

[0058]

[0059]

[0060] Example

[0061] Examples 1-5

[0062] The following description uses Example 1 as an example.

[0063] Example 1

[0064] This embodiment provides a tetraacetaldehyde suspension with sustained-release properties, which is obtained by stirring and heating a suspension intermediate in a constant temperature water bath at 40°C for 3 hours, and then adjusting the pH to neutral. The suspension intermediate is obtained by mixing the following components in parts by weight in sequence: 20 kg of tetraacetaldehyde suspension, 2 kg of emulsifier, 10 kg of melamine-modified urea-formaldehyde resin prepolymer, and 5 kg of acid catalyst, which is a 0.5 mol / L aqueous solution of glacial acetic acid.

[0065] In this embodiment, the metaldehyde suspension contains 50% metaldehyde by mass, and also includes 5% wetting agent, 5% dispersant, 0.2% thickener, 0.1% antifreeze and 0.1% preservative by mass, with the balance made up to 100% by water; the commercial brand name of metaldehyde is SMA820, the wetting agent is fatty alcohol polyoxyethylene ether (AEO9), the dispersant is alkylphenol polyoxyethylene ether phosphate (CAS: 51811-79-1), the thickener is xanthan gum (CAS: 11138-66-2), the antifreeze is a mixture of ethylene glycol, propylene glycol and glycerol in a weight ratio of 1:1:2, and the preservative is sodium benzoate.

[0066] In this embodiment, the metaldehyde suspension with sustained-release properties is prepared according to the following steps:

[0067] (1) Mix the tetraacetaldehyde, wetting agent, dispersant and thickener, and add water and additives to obtain a tetraacetaldehyde suspension; (2) Add 2 kg of emulsifier and 10 kg of the melamine-modified urea-formaldehyde resin prepolymer of Preparation Example 1 to 20 kg of the tetraacetaldehyde suspension in sequence, and stir for 0.5 h (t1) under constant temperature water bath conditions of 40 °C to obtain a reaction solution; In this step, the emulsifier is sodium salt of styrene-maleic anhydride (alternating) copolymer;

[0068] (3) Add 5 kg of acidic catalyst to the reaction solution to obtain a suspension intermediate. Stir and heat the suspension intermediate for 3 h (t2) under constant temperature water bath at 40℃. Then add sodium hydroxide to adjust the pH to neutral to obtain a tetraacetaldehyde suspension with sustained release properties.

[0069] As shown in Table 5, the main differences between Examples 1-5 lie in the raw material ratio and preparation conditions of the suspension intermediate. Furthermore, in Examples 2-4, the acidic catalyst used was 1 mol / L hydrochloric acid.

[0070] Table 5. Raw material ratios and preparation conditions for suspension intermediates

[0071]

[0072]

[0073] Example 6-21

[0074] As shown in Table 6, the difference between Examples 6-21 and Example 5 is that the preparation examples of the melamine-modified urea-formaldehyde resin prepolymer are different.

[0075] Table 6 Examples of preparation of melamine-modified urea-formaldehyde resin prepolymer

[0076]

[0077]

[0078] Examples 22-25

[0079] As shown in Table 7, the difference between Examples 22-25 and Example 19 is that the temperature of the constant temperature water bath (hereinafter referred to as T) is different in steps (2) and (3) of preparing the tetraacetaldehyde suspension.

[0080] Table 7 Water bath temperature T

[0081] sample Example 19 Example 22 Example 23 Implementation 24 Example 25 T / ℃ 40 45 50 55 60

[0082] Examples 26-30

[0083] Example 26

[0084] The difference between this embodiment and Embodiment 23 is that the emulsifier is an ethylene-maleic anhydride copolymer, specifically an alternating copolymer obtained by polymerizing ethylene and maleic anhydride in a 1:1 molar ratio, and the number average molecular weight of the copolymer is 20,000.

[0085] As shown in Table 8, the difference between Examples 26-30 is that the number-average molecular weights of the ethylene-maleic anhydride copolymers are different.

[0086] Table 8 Number Average Molecular Weight of Ethylene-Maleic Anhydride Copolymer

[0087]

[0088] Comparative Example

[0089] Comparative Example 1

[0090] This comparative example provides a metaldehyde suspension prepared by diluting the metaldehyde suspension of Example 1, wherein the mass fraction of metaldehyde in the suspension is the same as that in the metaldehyde suspension of Example 1.

[0091] Comparative Example 2

[0092] This comparative example provides a metaldehyde suspension prepared by diluting the metaldehyde suspension of Example 3, wherein the mass fraction of metaldehyde in the suspension is the same as that in the metaldehyde suspension of Example 3.

[0093] Comparative Example 3

[0094] This comparative example provides a metaldehyde suspension prepared by diluting the metaldehyde suspension of Example 5, wherein the mass fraction of metaldehyde in the suspension is the same as that in the metaldehyde suspension of Example 5.

[0095] Performance testing methods

[0096] The experiment was conducted according to the People's Republic of China agricultural industry standard "NY / T-1617-2008 Test Methods and Evaluation of Efficacy of Molluscicides for Pesticide Registration", selecting snails with a density greater than 10 snails / 0.1m. 2 The three grasslands were used as test sites.

[0097] Before the start of the experiment at each test site, weeds taller than 5cm were removed, and then the site was divided into 34 100m² areas. 2 The minimum distance between adjacent plots is 2m.

[0098] In 33 plots at each test site, metaldehyde suspensions from Examples 1-30 and Comparative Examples 1-3 were used at a concentration of 1.800 g / m³ of metaldehyde. 2 The pesticide was applied at the specified dosage in one test plot; in the remaining plot, clean water (1L / m²) was used. 2 (This is used as a comparison plot.)

[0099] After the application of the pesticide, daily sampling surveys were conducted in each plot according to the provisions of NY / T-1617-2008, and the mortality rate of Oncomelania snails in each plot was recorded. When the difference between the mortality rate of Oncomelania snails in the test plot and the mortality rate of Oncomelania snails in the control plot was less than 20% for three consecutive times, the number of days between the date on which the difference first fell below 20% and the date of pesticide application was recorded as the ineffectiveness time.

[0100] After all tests were completed at the three test sites, the average failure time of the metaldehyde suspension measured at the three test sites was calculated and recorded as the average failure time. Then, the ratio of the average failure time of Examples 1-30 and Comparative Examples 1-3 to the average failure time of Comparative Example 1 was calculated, and this ratio was expressed as a percentage and recorded as the relative failure time. The results are shown in Table 9.

[0101] Table 9 Relative Failure Time

[0102]

[0103]

[0104] Based on Examples 1-5 and Comparative Examples 1-3, and in conjunction with Table 9, it can be seen that the relative failure times measured in Examples 1-5 are all greater than those in Comparative Examples 1-3. This indicates that in the technical solution of this application, the capsule formed by the melamine-modified urea-formaldehyde resin prepolymer can hinder the degradation of metaldehyde, overcome the defect that metaldehyde is difficult to encapsulate using traditional microcapsule processes, prolong the effective period of metaldehyde suspension, and improve the insecticidal effect of metaldehyde pesticides.

[0105] As can be seen from Examples 5 and 6-9 and Table 9, in the process of preparing melamine-modified urea-formaldehyde resin prepolymer, adjusting the pH of the resin precursor liquid to the range of 9.2±0.7 by triethanolamine is beneficial to prolonging the residual effect of metaldehyde suspension and improving the insecticidal effect of metaldehyde pesticide.

[0106] As can be seen from Examples 7, 10-13 and Table 9, when the molar ratio of urea to formaldehyde is (1-1.2):1 during the preparation of melamine-modified urea-formaldehyde resin prepolymer, it is beneficial to prolong the residual effect of metaldehyde suspension and improve the insecticidal effect of metaldehyde pesticide.

[0107] Based on Examples 11, 14-17 and Table 9, it can be seen that when the molar ratio of melamine to formaldehyde is selected as (0.15-0.25):1 during the preparation of melamine-modified urea-formaldehyde resin prepolymer, it is beneficial to prolong the residual effect of metaldehyde suspension and improve the insecticidal effect of metaldehyde pesticide.

[0108] As can be seen from Examples 15, 18-21 and Table 9, when the temperature of the constant temperature water bath is selected at 65-75℃ during the preparation of melamine-modified urea-formaldehyde resin prepolymer, it is beneficial to prolong the residual effect of metaldehyde suspension and improve the insecticidal effect of metaldehyde pesticide.

[0109] Based on Examples 19, 22-25 and Table 9, it can be seen that when the temperature of the constant temperature water bath is selected as 45-55℃ in steps (2) and (3) of preparing the metaldehyde suspension, it is beneficial to prolong the effective period of the metaldehyde suspension and improve the insecticidal effect of the metaldehyde pesticide.

[0110] As can be seen from Examples 23, 26-30, and Table 9, the ethylene-maleic anhydride copolymer, compared to the sodium salt of the styrene-maleic anhydride copolymer, is more effective in prolonging the residual effect of metaldehyde suspension, thereby improving the insecticidal effect of metaldehyde pesticides. When the number average molecular weight of the ethylene-maleic anhydride copolymer is 24,000-28,000, the metaldehyde suspension has a longer residual effect and better insecticidal effect.

[0111] The embodiments described herein are merely illustrative of this application and are not intended to limit it. Those skilled in the art can make modifications to these embodiments without contributing any inventive step after reading this specification, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A metaldehyde suspension with sustained-release properties, characterized in that, The product comprises the following components by weight: 20-60 parts of metaldehyde suspension, 2-10 parts of emulsifier, 10-40 parts of melamine-modified urea-formaldehyde resin prepolymer, and 5-15 parts of acidic catalyst; wherein the metaldehyde suspension contains 50% metaldehyde by mass, and also includes 5% wetting agent, 5% dispersant, 0.2% thickener, 0.1% antifreeze, and 0.1% preservative by mass, with the balance made up to 100% by water; the commercial brand name of metaldehyde is SMA820, the wetting agent is fatty alcohol polyoxyethylene ether AEO9, and the dispersant is alkylphenol polyoxyethylene ether. The product comprises: vinyl ether phosphate; xanthan gum as thickener; an antifreeze composed of ethylene glycol, propylene glycol, and glycerol in a weight ratio of 1:1:2; sodium benzoate as preservative; a 0.5-1 mol / L protic acid aqueous solution as acidic catalyst; an ethylene-maleic anhydride copolymer as emulsifier, wherein the ethylene-maleic anhydride copolymer is an alternating copolymer obtained by polymerizing ethylene and maleic anhydride in a 1:1 molar ratio, and the number average molecular weight of the ethylene-maleic anhydride copolymer is 24,000-28,000; and a melamine-modified urea-formaldehyde resin prepolymer prepared according to the following method: (1) Mix melamine, urea and formaldehyde solutions and stir in a constant temperature water bath at 60-80℃ until melamine and urea are completely dissolved to obtain resin precursor liquid; the molar ratio of urea to formaldehyde is (1-1.2):1 and the molar ratio of melamine to formaldehyde is (0.15-0.25):

1. (2) Add triethanolamine dropwise to the resin precursor solution until the pH of the resin precursor solution is adjusted to 9.2±0.

7. Then continue to heat and stir for 40-80 min under constant temperature water bath conditions of 60-80℃ to obtain melamine modified urea-formaldehyde resin prepolymer.

2. The metaldehyde suspension with sustained-release properties according to claim 1, characterized in that, In the method for preparing the melamine-modified urea-formaldehyde resin prepolymer, the temperature of the constant temperature water bath is 65-75℃.

3. The method for preparing a metaldehyde suspension with sustained-release properties according to claim 1, characterized in that, Includes the following steps: (1) Mixing acetaldehyde, wetting agent, dispersant and thickener, and adding water and other additives, yields a acetaldehyde suspension; in the acetaldehyde suspension, the mass fraction of acetaldehyde is 50%, and by mass fraction, it also includes 5% acetaldehyde, 5% dispersant, 0.2% thickener, 0.1% antifreeze and 0.1% preservative, with the remainder made up to 100% by water; the commercial brand name of acetaldehyde is SMA820, the acetaldehyde is fatty alcohol polyoxyethylene ether AEO9, the dispersant is alkylphenol polyoxyethylene ether phosphate, the thickener is xanthan gum, the antifreeze is a mixture of ethylene glycol, propylene glycol and glycerol in a weight ratio of 1:1:2; the preservative is sodium benzoate; (2) Add 2-10 parts by weight of emulsifier and 10-40 parts by weight of melamine-modified urea-formaldehyde resin prepolymer to 20-60 parts by weight of tetraacetaldehyde suspension, and stir for 0.5-2 hours under constant temperature water bath to obtain reaction solution; in this step, the temperature of constant temperature water bath is 45-55℃. (3) Add 5-15 parts by weight of acidic catalyst to the reaction solution to obtain a suspension intermediate. Stir and heat the suspension intermediate for 3-6 hours under constant temperature water bath conditions of 40-60℃, and then add sodium hydroxide to adjust the pH to neutral to obtain a tetraacetaldehyde suspension with sustained release properties. In this step, the temperature of the constant temperature water bath is 45-55℃.

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