Timed release pesticide and preparation method and application thereof

Abstract

The invention relates to the technical field of plant protection, in particular to a timed release pesticide and a preparation method and application thereof. The timed release pesticide comprises a core material and a coating coated on the surface of the core material, the core material is a pyrazosulfuron-pretilachlor effervescent tablet; the coating is prepared from eudragit, ethyl cellulose and triethyl citrate. Compared with pyrazosulfuron-pretilachlor effervescent tablets, the timed release pesticide disclosed by the invention has the advantages that the proportion of a coating material can be adjusted according to needs, the release time can be controlled, rice transplanting or mechanical transplanting and pesticide application can be synchronously carried out, labor saving is realized, and the timed release pesticide has a good control effect on gramineous weeds and broadleaf weeds; moreover, phytotoxicity to rice caused by application of pyrazosulfuron-pretilachlor effervescent tablets during transplanting is avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of plant protection, in particular to a timed-release pesticide and a preparation method and application thereof. BACKGROUND

[0002] Rice is an important food crop, and is often invaded by weeds such as barnyard grass, alligator grass and heterotypic sedge, resulting in a yield loss of 10-20%, and even more than 50% in severe cases. There is an increasing demand for simplified weed control technology in agricultural production. At present, chemical weed control is still the most economical and effective means of weed control.

[0003] As a labor-saving dosage form for rice fields, effervescent tablets have the limitation of application timing - they usually need to be used 5-7 days after transplanting, which increases the operation steps; if they are directly applied at the time of transplanting, the rapid release of the herbicide can easily cause phytotoxicity to rice. Therefore, the realization of the timed release of pesticides has become a key problem to be solved.

[0004] Although attempts have been made at home and abroad to break through this dilemma through pesticide microcapsules and granule coating technologies, there are obvious shortcomings: (1) the microcapsule process is complex and costly, and because of the small particle size, it usually needs to be processed into a microcapsule suspension concentrate, which still needs to be sprayed for application, and the operation cannot be truly simplified; (2) the core particles of the reported granule coating technology rely on the physical expansion of the core material (containing water-swellable materials such as bentonite) after water penetration to gradually expand and eventually break the film, and the herbicide is released as the core particles disintegrate, which is a physical process that can only achieve slow release, lacks the necessary burst effect, and is difficult to meet the dynamic needs of weed control.

[0005] Therefore, it is an urgent need to develop a timed / controlled-release pyrazogyl-propaquizafop effervescent tablet with "nearly zero release in the early stage → concentrated release in the middle stage → stable supplementation in the later stage", which takes into account the safe production of rice, the persistent control of weeds and the friendly ecological environment. SUMMARY

[0006] Based on the above, the present application provides a timed-release pesticide and a preparation method and application thereof.

[0007] To achieve the above-mentioned purpose, the present application provides the following solutions:

[0008] One of the technical solutions of the present application is a timed-release pesticide, comprising a core material and a coating material coated on the surface of the core material.

[0009] The core material is a pyrazogyl-propaquizafop effervescent tablet.

[0010] The coating material comprises Eudragit (RS), ethyl cellulose (EC) and triethyl citrate (TEC).

[0011] In a preferred embodiment of the present application, the mass of the coating material is 1.5% to 8.0% of the mass of the core material.

[0012] In a preferred embodiment of the present application, the mass ratio of the Eudragit, ethyl cellulose and triethyl citrate is (0.5 to 1.0):(1.5 to 2.0):(0.1 to 1.0).

[0013] The second technical solution of the present application is a preparation method of the above-mentioned time-released pesticide, which sprays the coating material on the surface of the core material by fluidized bed coating method, solidifies and dries to obtain the time-released pesticide.

[0014] In a preferred embodiment of the present application, the conditions of the fluidized bed coating method are set as follows: air inlet temperature: 55 to 60℃; material temperature: 35 to 40℃; fan: 3000 rpm; air volume: 100 m 3 / h; atomization pressure: 0.20 MPa; peristaltic pump: 5.0 to 6.0 L / h.

[0015] In a preferred embodiment of the present application, the coating liquid is prepared by spraying the coating material on the surface of the core material, and the preparation method of the coating liquid comprises the following steps:

[0016] The Eudragit and ethyl cellulose are dissolved in anhydrous ethanol, and then the triethyl citrate is added. After complete dissolution, filtration is performed to obtain the coating liquid.

[0017] In some embodiments of the present application, before the triethyl citrate is added to the mixed solution of the Eudragit and ethyl cellulose, the step of dissolving the triethyl citrate in anhydrous ethanol and purifying (such as physical purification: filtration) is further included.

[0018] The third technical solution of the present application is the application of the above-mentioned time-released pesticide in rice planting.

[0019] The present application discloses the following technical effects:

[0020] Compared with the pyrazolam·propaquizafop effervescent tablet, the time-released pesticide of the present application has better control effect on gramineous weeds and broadleaf weeds, and avoids the phytotoxicity (leaf yellowing, which is mild 1-level phytotoxicity) of the pyrazolam·propaquizafop effervescent tablet on rice; the time-released pesticide of the present application has no phytotoxicity (0 level) on rice. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0022] Figure 1 Contour and 3D response surface of the interrelationship of each factor and the complete release time in Example 1 of the present application.

[0023] Figure 2 Contour and 3D response surface of the interrelationship of each factor and the coating weight gain in Example 1 of the present application.

[0024] Figure 3 Contour and 3D response surface of the interrelationship of each factor and the coating efficiency in Example 1 of the present application.

[0025] Figure 4 SEM images of the time-release pesticide prepared in Example 1 of the present application under the optimal coating liquid formulation condition at different magnifications.

[0026] Figure 5 FTIR spectra of EC, RS, and TEC.

[0027] Figure 6 FTIR spectra of the coating surface of the time-release pesticide prepared in Example 1 of the present application under the optimal coating liquid formulation condition.

[0028] Figure 7 Standard curve of pretilachlor.

[0029] Figure 8 Coating release curves of the time-release pesticide prepared in Example 1 of the present application under three different coating liquid formulation conditions. DETAILED DESCRIPTION

[0030] Various illustrative embodiments of the present application are now described in detail. Such description, however, should not be taken to limit the scope of the present application, but rather, it should be taken as merely illustrative of the present application. The description is made defining specific embodiments, with the understanding that the same elements within the context of different embodiments are to be identified similarly.

[0031] It should be understood that the terms used herein are merely descriptive, but that the application should not be construed as being limited thereto. In addition, with respect to numerical ranges in the present application, it should be understood that each intermediate value between the upper and lower limits of that range and any other stated or intervening unit is encompassed within the scope of the application. Each smaller range between any two of the stated values or intervening units in the stated ranges and each value between any stated value or intervening unit is also encompassed within the scope of the application. The upper and lower limits of these smaller ranges can independently be included or excluded in the ranges.

[0032] All technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains unless clearly indicated otherwise. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application, the preferred methods and materials are described. All publications mentioned in this specification are herein incorporated by reference to disclose and describe the methods and / or materials in connection with which the publications are cited. The citation of any reference is not an admission that it is prior art with respect to the present application. All literature and similar materials cited in this application, including but not limited to, patents, genetic code, scientific and / or technical articles, and / or treatises, are expressly incorporated by reference.

[0033] Many modifications and variations of this application described in the specific embodiments of the application can be made by those skilled in the art without departing from the spirit or scope of the application. Other implementations of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. The specification and examples given are exemplary only.

[0034] As used herein, the terms "comprises", "comprising", "includes", "including", "has", "having", "contains", "containing", or variations thereof, are intended to be open-ended terms that mean inclusion, but not limited to, the listed material or step.

[0035] The first aspect of the present application provides a time-release pesticide, comprising a core material and a coating material coated on the surface of the core material.

[0036] The core material is a pyrazosulfuron-ethyl · propaquizafop effervescent tablet.

[0037] The coating material comprises Eudragit (RS), ethyl cellulose (EC) and triethyl citrate (TEC).

[0038] In a preferred embodiment of the present application, the mass of the coating material is 1.5% to 8.0% of the mass of the core material.

[0039] In a preferred embodiment of the present application, the mass ratio of Eudragit, ethyl cellulose and triethyl citrate is (0.5 to 1.0) : (1.5 to 2.0) : (0.1 to 1.0).

[0040] In a further preferred embodiment of the present application, the mass ratio of Eudragit, ethyl cellulose and triethyl citrate is (0.9 to 1.0) : (1.9 to 2.0) : (0.1 to 0.2); more preferably 0.92: 1.96: 0.18.

[0041] The present application also experiments the RS + talc (anti-adhesion agent) + TEC, EC + TEC + PVP (polyvinylpyrrolidone, pore-forming agent) as the coating material, and the results show that in the fluidized bed coating process, the introduction of talc can improve the physical properties of the coating film (such as reducing the stickiness, enhancing the hydrophobicity), but it has potential damage to the equipment. The particle size and dispersity of talc directly affect the risk of spray gun blockage: talc is prone to sedimentation or agglomeration in the coating liquid due to its coarse particles, leading to the blockage of silica gel tube or nozzle. In addition, long-term use of talc accelerates the wear of the equipment, especially for low-purity products containing quartz impurities, although its Mohs hardness is relatively low, but long-term high-concentration use may still cause mechanical damage to the inner wall of the spray gun or the atomizing disc. The control effects of the time-release pesticides prepared by the above two coating materials are all not as good as that of the time-release pesticide prepared by RS + EC + TEC.

[0042] The second aspect of the present application provides a preparation method of the above-mentioned time-release pesticide, which sprays the coating material on the surface of the core material by the fluidized bed coating method, solidifies and dries to obtain the time-release pesticide.

[0043] In the preferred embodiments of the present application, the conditions of the fluidized bed coating method are set as follows: air inlet temperature: 55-60℃; material temperature: 35-40℃; fan: 3000rpm; air volume: 100m 3 / h; atomization pressure: 0.20MPa; peristaltic pump: 5.0-6.0L / h.

[0044] In the preferred embodiments of the present application, the coating liquid is prepared by spraying the coating material on the surface of the core material, and the preparation method of the coating liquid comprises the following steps:

[0045] The Eudragit and ethyl cellulose are dissolved in anhydrous ethanol, then triethyl citrate is added, and after complete dissolution, filtration is performed to obtain the coating liquid.

[0046] In some embodiments of the present application, before adding the triethyl citrate to the mixed solution of Eudragit and ethyl cellulose, the step of purifying (such as physical purification: filtration) the triethyl citrate dissolved in anhydrous ethanol is further included.

[0047] The present application also experiments the preparation of time-release pesticide by coating pan coating method, and the results show that mechanical friction during the coating process easily leads to edge damage of effervescent tablets, the coating layer has low density, the release time stability and process uniformity are not as good as the fluidized bed process.

[0048] The third aspect of the present application provides the application of the above-mentioned time-release pesticide in rice planting.

[0049] The present application innovatively combines the rapidly-released effervescent tablets with the hydrophobic and hydrophilic material film coating, uses the characteristics of the effervescent tablets that a large amount of gas (such as carbon dioxide) is rapidly generated through acid-base reaction after the effervescent tablets meet water to induce the violent chemical disintegration, and develops a timing / sustained-release type pyrazogly·propaquizafop effervescent tablet with the characteristics of "nearly zero release in early stage → concentrated release in middle stage → stable supplement in late stage". The dosage form can be applied synchronously with the rice transplanting (mechanical transplanted seedlings), can guarantee the safe production of rice, can realize the persistent control of weeds, and effectively meets the labor-saving and work-saving requirements of agricultural production.

[0050] The technical solutions described in the present application are conventional solutions in the field if not specifically described, and the reagents or raw materials used are purchased from commercial channels or are disclosed if not specifically described.

[0051] The raw materials used in the embodiments of the present application are shown in Table 1:

[0052] Table 1

[0053]

[0054] The technical solutions provided by the present application will be described in detail below in combination with the embodiments, but they cannot be understood as limitations on the protection scope of the present application.

[0055] Example 1

[0056] Step 1, at room temperature, slowly pour RS and EC into anhydrous ethanol, pay attention to avoid agglomeration or sedimentation, put into a magnetic stirrer and stir for 2.5 h to form a clear solution. Purify TEC in ethanol in advance, then add to the above clear solution, and filter with a 40-mesh sieve to obtain a coating solution.

[0057] Step 2, place the pyrazogly·propaquizafop effervescent tablets into a fluidized bed (fluidized granulation coating machine, Mini-XYT, manufacturer: Shenzhen Xinyite Technology Co., Ltd.) to make the granular material present in a flowing state by heating and air supply, and preheat until the material temperature rises to 35℃.

[0058] Turn on the atomization, and uniformly spray the coating solution on the surface of the pyrazogly·propaquizafop effervescent tablets through a spray gun to form a coating layer.

[0059] After the coating is completed, solidification and drying are carried out to ensure that the coating layer can be firmly attached to the surface of the pyrazogly·propaquizafop effervescent tablets. By heating the inlet air at 55℃, the coating layer is quickly solidified and dried.

[0060] The fluidized bed coating parameters are set as follows:

[0061] Inlet air temperature: 55℃

[0062] Material temperature: 35℃

[0063] Fan: 3000rpm

[0064] Air volume: 100m³ 3 / h

[0065] Atomization pressure: 0.20MPa

[0066] Peristaltic pump: 5.0L / h.

[0067] 1. Single-factor analysis of coating solution formulation

[0068] With other conditions remaining constant in the fixed coating formulation (100 ml of anhydrous ethanol and 50 g of pyrimisulfuron-methyl effervescent tablets), single-factor studies were conducted on EC, RS, and TEC. The effect of each factor on the coating release time was investigated by measuring the coating release time.

[0069] (1) Screening of EC content in coating solution

[0070] Table 2 shows that EC content significantly regulates drug release time in the coating solution: when the EC content increases from 1g to 2g (with RS=1 and TEC=0.75 fixed), the release time increases from 15h to 86h, indicating that the hydrophobicity and film-forming properties of EC effectively delay drug diffusion. However, when the EC content increases to 2.5g, the drug cannot be released at all, possibly because excessive EC leads to an overly thick or dense coating layer with extremely low porosity, hindering water penetration and drug dissolution. Therefore, this invention uses 1.5g of EC for subsequent experiments.

[0071] Table 2 Screening of EC content in coating solutions

[0072]

[0073]

[0074] (2) Screening of RS content in coating solution

[0075] Table 3 shows that the RS content has a significant impact on the drug release time and film-forming properties of the coating solution: when the RS content increases from 0.5g to 1.5g (with EC = 2g and TEC = 0.75g fixed), the release time gradually increases from 55h to 97h, indicating that RS effectively delays drug diffusion by enhancing the hydrophobicity and density of the coating layer. At RS = 2.0g, the coating solution cannot form a film due to excessive viscosity, possibly because excessive RS leads to a sharp increase in viscosity, making it difficult for droplets to disperse evenly during spraying, resulting in localized agglomeration or uneven drying. Therefore, 0.5g of RS was selected for subsequent experiments in this study.

[0076] Table 3 Screening of RS content in coating solutions

[0077]

[0078] (3) Screening of TEC content in coating liquid

[0079] Table 4 shows that the TEC (triethyl citrate) content has a nonlinear regulating effect on the drug release time of the coating liquid. When the TEC content increases from 0.50 g to 1.00 g (fixed EC = 2 g, RS = 1 g), the release time is prolonged from 42 h to 59 h, indicating that TEC effectively delays drug diffusion by enhancing the flexibility and compactness of the coating film. When the TEC content increases to 1.50 g, the release time suddenly decreases to 17 h, which may be due to excessive TEC causing the molecular chains of the coating film to be excessively relaxed, increasing the porosity and forming a rapid release channel. Considering the above, 1.00 g of TEC is selected for subsequent studies.

[0080] Table 4 Screening of TEC content in coating liquid

[0081]

[0082] 2. Optimization of coating liquid formulation by response surface method

[0083] With the other conditions in the coating liquid formulation unchanged (100 ml of absolute ethanol, 50 g of pyrazosulfuron-ethyl + propaquizafop effervescent tablets), the factors EC (A), RS (B), and TEC (C) that have a greater impact on the release time of the coating are selected, and process optimization is performed according to the single-factor experiment results. A 3-factor 3-level experimental design is used, and the Box-behnken experimental design is shown in Table 5. A total of 17 experiments are performed (as shown in Table 5), and the Design-Expert 13 software is used for processing. The results obtained are verified and compared accordingly to determine the optimal coating liquid formulation.

[0084] Table 5 Box-behnken experimental design

[0085]

[0086] Table 6 Box-behnken experimental results

[0087]

[0088]

[0089] The model fitting takes the complete release time (Y1), coating weight gain (Y2), and coating efficiency (Y3) as the response values, and the Design Expert 13 software is used for multiple linear regression and binomial fitting of A (EC), B (RS), and C (TEC), respectively, to obtain the regression equation:

[0090] Y1=16.4+12.31A+9.88B-9.06C+5.25AB+1.38AC-1.75BC+10.74A 2 +0.1125B 2 -3.01C 2 ,

[0091] R 2 =0.9236, P<0.05, F=1.44>0.05.

[0092] Y2=2.96+0.9075A+0.5475B-0.76C-0.095AB-0.75AC-0.59BC+0.4145A 2 +0.1945B 2 -0.6705C 2 R 2 =0.9645, P<0.01, F=1.45>0.05 for the lack of fit.

[0093] Y3=73.9+3.48A-4.28B-14.92C-2.17AB-15.67AC-8.19BC+8.31A 2 +7.13B 2 -15.67C 2 ,

[0094] R 2 =0.9452, P<0.05, F=0.34>0.05.

[0095] The analysis of variance for the regression models of each response value is shown in Tables 7, 8, and 9. From the fitted equations and the results of the analysis of variance, it can be seen that for Y1, A, B, C, and A... 2 All were significant or highly significant (P < 0.05 or P < 0.01), others were not significant; for Y2, A, B, C, AC, BC, A 2 C 2 All were significant or highly significant (P < 0.05 or P < 0.01), others were not significant; for Y3, C, AB, BC, A in the model 2 C 2 All were significant (P < 0.05 or P < 0.01), others were not significant. From the goodness of fit R... 2 The model significance (P) and model lack of fit (F) indicate that the established prediction model is relatively reliable. This model can be used to study the coating formulation process of pyrimethanil effervescent tablets.

[0096] Table 7. Analysis of Variance for the Regression Model of Complete Coating Release Time

[0097]

[0098]

[0099] Table 8 Analysis of variance of coating weight gain regression model

[0100]

[0101] Table 9 Analysis of variance of coating efficiency regression model

[0102]

[0103]

[0104] Table 10 Analysis of variance of coating efficiency regression model

[0105]

[0106] The response surface method was used for optimization and prediction, Design-Expert 13 software was used, based on a binomial fitting model, one of the three variables was fixed, and three-dimensional response surfaces of the effects of the other two variables on release time, coating weight gain and coating efficiency were drawn, and the results are shown in Figures 1-3 The steeper the response surface, the more significant the effect of the factor on the response value. The contour plot can also reflect the effect of each factor on the response value. The more dense and closer to the ellipse the contour is, the more significant the effect. According to the three-dimensional response surface, the interaction of EC content (A) and TEC content (C) has a significant effect on coating weight gain; the interaction of EC content (A) and RS content (B) has a significant effect on coating efficiency. Figure 1 It can be seen that the response surface in the A and B directions is steeper than in the C direction, indicating that the effects of EC and RS on release time are more significant than that of TEC. Figure 2 It can be seen that the effects of the factors on coating weight gain are in the order of EC > RS > TEC.

[0107] The experimental data were optimized and predicted by Design Expert 13, and the optimization conditions were set as release time of 48-72 h and maximum coating efficiency. The best coating liquid formula for pyrazosulfuron-ethyl + clomazone effervescent tablets is EC 1.96 g, RS 0.92 g and TEC 0.18 g.

[0108] 3. Coating film morphology observation

[0109] Figure 4 SEM images of the time-release pesticide prepared according to the best coating liquid formula of Example 1 at different magnifications; from Figure 4It can be seen that EC and RS can form a dense, continuous, smooth and uniform coating film on the surface of the effervescent tablet. The coating layer is completely covered with no exposed areas and no pores on the surface. The effervescent tablet is completely wrapped by the film formed by EC and RS.

[0110] 4. FTIR analysis of the coating film

[0111] The FTIR spectra of RS, EC, and TEC show ( Figure 5 The characteristic peak of RS is 1732.11 cm⁻¹. -1 The C=O stretching vibration at this point corresponds to the acrylate group. 1244.33 cm⁻¹ -1 The asymmetric stretching vibration of COC at this point. 2994.62 cm -1 The aromatic ring CH stretching vibration at this point. The characteristic peak of EC is at 1114.94 cm⁻¹. -1 The COC ether bond vibration at 2979.12 cm⁻¹. -1 and 2878.58cm -1 CH stretching vibration at 3470.60 cm -1 The OH stretching vibration at that point. The characteristic peak of TEC is 1730.88 cm⁻¹. -1 The C=O stretching vibration at point 1178.72 cm. -1 and 1375.59cm -1 The CO ester bond vibration at that location.

[0112] FTIR spectrum of the coating film ( Figure 6 1729.77cm was observed in the study. -1 The absorption peak at 1241.95 cm⁻¹ is consistent with the C=O peak of RS. -1 The peak at 2921.17 cm⁻¹ perfectly matches the COC peak of RS, with no shift. -1 This corresponds to the CH peak of RS. 1114.94cm -1 The absorption peak at 2855.50 cm⁻¹ is completely consistent with the COC ether bond peak of EC; -1 and 2921.17cm -1 The corresponding EC stretching vibration at point CH has a displacement of <35cm. -1 This may be due to differences in the arrangement of ethyl chains in the coating film. Typical peaks (such as CO3) in effervescent tablet bases (e.g., sodium bicarbonate, citric acid) are also present. 2- 1450-1410cm -1 The fact that it did not appear clearly in the coating film spectrum indicates that the coating layer effectively covers the matrix.

[0113] The C=O (1729.77 cm⁻¹) value of RS was clearly detected in the FTIR spectrum of the coated film. -1) and C-O-C (1241.95 cm -1 ) characteristic peaks, which were consistent with the pure RS spectrum. The C-O-C ether bond peak (1114.94 cm -1 ) and C-H vibration peak (2855.50 cm -1 and 2921.17 cm -1 ) of EC were detected, which matched the pure EC spectrum. The coexistence of multiple characteristic peaks and the absence of significant interference peaks indicated that RS and EC were uniformly coated onto the effervescent tablet surface through the coating process, forming a functional coating layer.

[0114] The present application reveals the internal relationship between the composition of the coating material and the drug release behavior, membrane structure characteristics by systematically screening the coating formula and multi-dimensionally characterizing its performance, providing a scientific basis for optimizing the controlled release performance of pyrazolate · propaquizafop effervescent tablets. The experimental results show that the compounding of EC and RS significantly prolongs the drug release time (the release time is 58 h when EC = 2 g and RS = 1 g), which is due to the complementary characteristics of the two: EC as a hydrophobic film-forming material provides a sustained-release basis by reducing the membrane permeability, and the pH-independent and high mechanical strength of RS can enhance the stability of the membrane. The plasticizing effect of TEC shows duality: an appropriate amount of TEC can improve the flexibility of the membrane (SEM shows that the membrane surface is smooth without cracks), but an excessive amount (TEC = 2 g) leads to an increase in membrane porosity, and the release time drops to 0.5 h. This phenomenon may be consistent with the mechanism that TEC reduces the intermolecular force of the polymer chain, promoting molecular migration, indicating that the amount of plasticizer needs to be strictly controlled below the critical value.

[0115] The regression model established by Box-Behnken design (release time model R 2 = 0.9236, weight gain model R 2 = 0.9645, and coating efficiency model R 2 = 0.9452) can effectively predict the coating performance, and the best coating formula fitted by the model is EC 1.96 g, RS 0.92 g, and TEC 0.18 g. The SEM image shows that the EC / RS compounded membrane surface is smooth and has no cracks, confirming the effectiveness of the formula optimization; and the characteristic peak shift of EC (C-O-C stretching vibration, 1100 cm -1 ) and RS (quaternary ammonium group, 1480 cm -1 ) does not appear in the FTIR spectrum, indicating that the two do not interact chemically, but mainly coexist in a physical mixture. This result supports the "physical controlled release" mechanism of the coating membrane, that is, the drug release is dominated by the membrane porosity rather than the chemical bond rupture.

[0116] The application successfully constructs the EC / RS / TEC composite coating system of pyrazolam·propaquizafop effervescent tablets through multi-factor interaction analysis and response surface optimization, and illustrates the quantitative relationship between material ratio and film performance, thereby providing a generalizable methodological framework for the functional coating development of agricultural preparations.

[0117] 6. Coating release dynamic experiment

[0118] (1) Preparation of propaquizafop standard stock solution

[0119] Solution preparation: A high-concentration propaquizafop technical material (0.1042 g) was weighed into a 50 mL volumetric flask, and methanol was added to the flask to dissolve the propaquizafop. The volumetric flask was placed in an ultrasonic bath for 10 minutes to degas, and then taken out to cool to room temperature. Methanol was added to the flask to the calibration mark, and the solution was shaken and filtered to obtain a 2 g / L propaquizafop standard stock solution. The propaquizafop solution required for the experiment was prepared by diluting the above standard solution by a certain multiple.

[0120] Preparation of standard curve: A 2 g / L propaquizafop solution was diluted in a 10 mL volumetric flask to obtain 2, 4, 8, 16, and 32 mg / L propaquizafop solutions, which were detected by a high-performance liquid chromatograph to draw a standard curve (as shown in Figure 7 ).

[0121] (2) Three time-release pesticides prepared in Example 1 were placed in 8 L HDPE plastic bottles filled with water, and samples were taken at certain time intervals (0.5, 1, 2, 4 h, 8, 16, 24, 48, 54, 60, 72, 78, 84, 90, and 96 h) after sufficient stirring in a constant-temperature heating magnetic stirrer. The samples were filtered through a 0.22 μm filter membrane and subjected to liquid-phase detection. Three time-release pesticides were prepared using three different coating liquid formulations, and release dynamic experiments were performed. The three different coating liquid formulations were as follows:

[0122] ①: 1.96 g EC, 0.92 g RS, and 0.18 g TEC

[0123] ②: 2.00 g EC, 1.00 g RS, and 1.00 g TEC

[0124] ③: 1.50 g EC, 0.50 g RS, and 1.00 g TEC

[0125] The calculation formula of the release rate is as follows:

[0126]

[0127] The commonly used mathematical models for evaluating the release mechanism include zero-order, first-order, Higuchi, and Ritger-Peppas models, and the formulas are as follows:

[0128] Zero-order release equation: Q t= at + b

[0129] First order release equation: Q t = a(l - e -bt )

[0130] Higuchi equation: Q t = at 1 / 2 + b

[0131] Ritger-Peppas equation: Q t = at n

[0132] where Qt is the cumulative release rate at time t, a and b are release rate constants. The diffusion mechanism of the pesticide can be judged according to the value of n, when n < 0.45, the diffusion of the pesticide mainly follows Fick diffusion.

[0133] (3) HPLC detection conditions of propaquizafop

[0134] The main component in the pyrazolam-propaquizafop effervescent tablet is propaquizafop (15%), so the release of the coating is determined by detecting the content of propaquizafop in water, and the liquid phase detection conditions of propaquizafop are as follows:

[0135] Chromatographic column: ZORBAX SB-C18 column (5-μm particle size, 150 x 4.6 mm i.d.)

[0136] Mobile phase: acetonitrile: water = 65:35

[0137] Detection wavelength: 220 nm

[0138] Column temperature: 30°C

[0139] Flow rate: 1 ml / min

[0140] Injection volume: 20 μl

[0141] Retention time: 11 min.

[0142] The coating release curve ( Figure 8 ) shows that the pyrazolam-propaquizafop effervescent tablet coating presents a phased release characteristic within 0-100 hours: the coating does not release in the early stage, indicating that the coating integrity is good, which isolates the contact between the effervescent tablet and water and inhibits the release of the effervescent tablet; the coating releases rapidly in the middle stage, and the release rate increases to 60%; the release tends to be stable in the later stage, and the final release rate reaches more than 80%, which may be related to the coating residue or insufficient observation time.

[0143] According to the coating release curve diagram, the coating liquid formula fitted by response surface (1.96 g EC, 0.92 g RS, 0.18 g TEC) is more ideal and more in line with expectations. According to the release kinetics fitting equation, Ritger-Peppas equation (Q t =at n ) presents the optimal fitting degree (R 2 =0.9939), the index n=2.3860, and the n values of the other two treatments are 2.5369 and 1.5311 respectively, all greater than 0.45, indicating that the coating release is non-Fick diffusion, indicating that the coating release is not only related to the concentration, but also affected by the temperature, medium properties (such as porosity, permeability coefficient) and the interaction between solute and medium. Non-Fick diffusion shows more complex diffusion behavior than Fick diffusion, and the molecular motion is affected by many factors, such as the non-homogeneity of the medium, the interaction between molecules and chemical reactions. In non-Fick diffusion, the interaction between molecules can significantly affect the diffusion rate and direction. Non-Fick diffusion involves complex nonlinear diffusion mechanisms, such as non-equilibrium thermodynamic effects and intermolecular interactions. This diffusion mechanism is not only related to the concentration gradient of molecules, but also involves intermolecular forces and the microstructure characteristics of materials.

[0144] 7. Field test (field test of timed-release pesticide prepared under the condition of optimal coating liquid formula of Example 1) (1) The test site is located in the plant protection base of Hunan Agricultural University. The recommended dose of pyrazolam + propaquizafop effervescent tablets is 129-259 g / acre, and the control method is to control annual weeds by spreading. One effervescent tablet is 1.3 g, and each effervescent tablet has an effect of 3.5 m 2 of soil.

[0145] Treatment 1: blank control, no treatment

[0146] Treatment 2: 17% pyrazolam + propaquizafop effervescent tablets

[0147] Treatment 3: 17% pyrazolam + propaquizafop effervescent tablets coated

[0148] This test is divided into 3 treatments, each with 3 repetitions, a total of 9 plots, with an area of 20 m 2 . The rice is transplanted in a clean field without weeds, and treatment 2 and treatment 3 are evenly spread with 5 effervescent tablets and effervescent tablet coating agents in each plot on the day of transplanting. The application time is August 4, 2024 in the morning. The weather during the test was good, with an average temperature of 28°C, and there was no disastrous weather during the test that affected the test results.

[0149] After the application, the number of weeds in each plot was investigated by using the method of 5-point diagonal random sampling on the 15th and 30th day. The area of each point was 0.25 m 2 (0.5m×0.5m). The control effect of fresh weight on the ground was investigated after 30 days of application. The control effect of fresh weight and the control effect of fresh weight on weeds were calculated in units of fresh weight of the ground. The fresh weight was weighed after removing the roots during the measurement of fresh weight. No other pesticides were used one month before the start of the test, and no other pesticides were used during the application period. According to the investigation data, the fresh weight control effect and the fresh weight control effect were calculated according to the following formula:

[0150]

[0151] The results were analyzed and compared by using DPS statistical software to determine whether there were significant differences between the test results of each treatment.

[0152] (2) Pesticide injury investigation

[0153] The effects of the test pesticide on rice production were observed by visual observation 5, 10, 15, and 30 days after application, and the occurrence and degree of pesticide injury were recorded. Herbicide injury was divided into six levels:

[0154] 0: No effect on crops;

[0155] 1-2: Light injury, generally no effect on yield;

[0156] 3: Moderate injury, damage to crops, affect yield, and can recover;

[0157] 4: Serious injury, seriously affecting yield;

[0158] 5: Extremely serious injury, crop death and absolute yield

[0159] (3) The test selected rice transplanted fields. The selected rice transplanted fields were irrigated conveniently, with flat terrain and soil that was ideal loam, well-ventilated and water-permeable. The test site had convenient drainage conditions, and the irrigation system was a single row and single irrigation to avoid string irrigation. A small amount of barnyard grass seeds was uniformly scattered during rice transplanting to ensure the density of weeds. Artificial weeding was performed before application to remove all weeds in the plots.

[0160] Table 11 Effect of coated and uncoated treatments on grass weeds

[0161]

[0162] Note: The lower case letters in the same column in the table indicate that the difference is significant at the 0.05 level.

[0163] Table 12 Effect of coated and uncoated treatments on broadleaf weeds

[0164]

[0165]

[0166] Note: The lower case letters after the same column data in the table indicate that they are significantly different at the 0.05 level.

[0167] As can be seen from the data in Table 11, the coating treatment has a significant effect on the control of grass weeds. The uncoated treatment (treatment 2) and the coated treatment (treatment 3) completely inhibited the growth of weeds (0 plants / ㎡, 100% plant control) 15 days after application, and still maintained a high control effect (1 plant / ㎡, 0 plants / ㎡, 97.85% and 98.92% plant control) 30 days after application, and the fresh weight control effect reached 97.54% and 97.70%, respectively. The data in Table 12 show that the coated treatment has a significant effect on the control of broadleaf weeds, with a 15-day plant control effect of 94.44%, and a 30-day plant control effect and fresh weight control effect of 94.92% and 98.10%, respectively, which is better than the uncoated treatment (91.53% plant control and 97.93% fresh weight control), further verifying the high efficiency of the coated treatment. Overall, the coated treatment has a rapid and persistent control effect on grass weeds and broadleaf weeds.

[0168] The test shows that, after 10 days, 20 days and 30 days of application, the growth of rice in each treatment area is observed, and 30 days after application, the rice in each treatment is investigated. No phytotoxicity phenomena such as yellowing, wilting, and malformation of rice seedlings are found in the blank treatment (treatment 1) and the coated treatment (treatment 3) (0 level of phytotoxicity). The effervescent tablets treatment (treatment 2) finds a slight yellowing of the rice seedlings, which is judged to be a mild 1 level of phytotoxicity. It is possible that the coating of the effervescent tablets delays the release of the pesticide, thereby reducing the degree of phytotoxicity.

[0169] The field test data further confirm the effectiveness and safety of the coating technology. Compared with the uncoated treatment, the coated effervescent tablets can achieve 100% control of weeds within 15 days, and the plant control effect still remains at 98.92% 30 days after application, and the fresh weight control effect reaches 97.70%, significantly inhibiting the biomass accumulation of weeds. It is worth noting that the coated treatment is slightly better than the uncoated treatment in fresh weight control, indicating that it not only can quickly reduce the number of weeds, but also can continuously reduce the competition of weeds for nutrients. At the same time, no phytotoxicity symptoms are observed in the rice treated with the effervescent tablet coating agent during the entire test period, while the rice treated with the effervescent tablets shows yellowing, indicating that the coating technology not only ensures the efficacy, but also reduces the negative impact on crops.

[0170] The above-described embodiments are only to describe the preferred modes of the present application, and do not limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements to the technical solutions of the present application made by those skilled in the art shall fall within the protection scope determined by the claims of the present application.

Claims

1. A timed release pesticide, characterized in that, The core material and a coating material coated on the surface of the core material; The core material is pyrazosulfuron-ethyl and propaquizafop effervescent tablets; The coating material comprises eudragit, ethyl cellulose and triethyl citrate.

2. The timed release pesticide according to claim 1, wherein The mass of the coating material is 1.5% to 8.0% of the mass of the core material.

3. The timed release pesticide of claim 1, wherein, The mass ratio of the eudragit, ethyl cellulose and triethyl citrate is (0.5 to 1.0) : (1.5 to 2.0) : (0.1 to 1.0).

4. A process for the preparation of the timed release pesticide according to any one of claims 1 to 3, characterized in that, The coating material is sprayed on the surface of the core material by a fluidized bed coating method, and is solidified and dried to obtain the timed-release pesticide.

5. The preparation method according to claim 4, characterized in that, The fluidized bed coating method is set as follows: air inlet temperature: 55-60°C; material temperature: 35-40°C; fan: 3000 rpm; air volume: 100 m 3 / h; atomization pressure: 0.20 MPa; peristaltic pump: 5.0-6.0 L / h.

6. The preparation method according to claim 4, characterized in that, The coating material is prepared into a coating liquid which is sprayed on the surface of the core material, and the preparation method of the coating liquid comprises the following steps: The eudragit and ethyl cellulose are dissolved in anhydrous ethanol, and then the triethyl citrate is added. After complete dissolution, the coating liquid is obtained by filtration.

7. The use of the timed-release pesticide according to any one of claims 1 to 3 in rice planting.

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