The Research Of Formulation Selection And Formation Mechanism On Azoxystrobin And Thiamethoxam Suspension Concentrate

This paper provides meticulous and comprehensive research on the 25% azoxystrobin suspension concentrate and 21% thiamethoxam suspension concentrate by utilizing X-ray photoelectron energy spectrum analyzer, Fourier infrared spectrum analyzer, scanning electron microscope, Zeta-potential instrument, differential thermal analyzer, rheometer and other technical means, which provide a basis for the preparation of high performance of suspension concentrate. Its conclusions are as follows.The adsorption mechanism of the dispersing agent on the surface of azoxystrobin and thiamethoxam were researched. During the experimental temperature of the 298K,308K and 318K, the adsorption isotherm model of the dispersing agent on the surface of azoxystrobin and thiamethoxam particles were fit for Lamgmuir model, and the adsorption dynamics model can be better described by the pseudo-second-order model. The result of the thermodynamic parameters of the dispersant agent on the surface of the azoxystrobin and thiamethoxam particles showed that the adsorption are spontaneous processes, which belong to the physical adsorption, and the adsorption process is the process of entropy increasing. The concentration of sodium ion and pH could affect the adsorption of the dispersant on the surface of azoxystrobin and thiamethoxam. The analysis results of the FTIR showed that the Van der Waals force were the main force between dispersant D-425,2700 and 2210 with the azoxystrobin and the dispersants 2700,2210 with the thiamethoxam. Zeta potential results showed that the optimal dosage of the dispersant D-425,2700 and 2210 in azoxystrobin suspension concentrate were 2.5%,2.0% and 3.0%, respectively; the optimal dosage of the dispersant 2700 and 2210 in thiamethoxam suspension concentrate were both for 3.0%. The XPS results demonstrated that the C 1s and O 1s content of the azoxystrobin and thiamethoxam were increased significantly after adsorption dispersant. The adsorption layer thickness of the dispersants on the surface of azoxystrobin and thiamethoxam particles changed with the temperature, and consistent with the results of adsorption isotherm. The adsorption layer thickness was maximum when the dispersant content is the optimal dosge by preparing the suspension concentrate.The thermogravimetric data results showed that the system of dispersant/azoxystrobin was decomposed simply with one steps at 600℃, and the system of dispersant/thiamethoxam was decomposed simply with two steps at 400℃. The thermal degradation kinetics research on the system of the dispersant/azoxystrobin and dispersant/thiamethoxam was calculated by FWO method. The fitted dosge of dispersant of the two systems were consistent with the consequence of Zeta and XPS. Within the scope of the recommended content of dispersant (2～3%), the parallelism of the fitting formula of different conversion a was good under the same dosge of dispersant, which suggested that FWO method could be better guided the dosge application of dispersant in prepareing suspension concentrate.The rheological curve of the system of dispersant/azoxystrobin and dispersant/thiamethoxam were fit for the Hershel-Bulkley model. Under the best dosage of the dispersants, the yield value τH and viscosity of the system were minimum. The consistency index κ increased gradually and the predominate flow characteristic index n decreases with the increase of the dispersant dosage. The viscosity of the system of the dispersant/azoxystrobin and dispersant/thiamethoxam have periodic oscillation behavior with the time changed. At the best dosage of the dispersant D-425,2700 and 2210, the oscillation amplitude of the system is small, more concentrated, and better stability The rheological oscillation curve of the system of the 2700/thiamethoxam had amplitud between 0-1.5% in 3 min and 10 min. When the dispersants content is more than 2%, the oscillation amplitude decreased, and oscillation was almost nothing at high concentration. The oscillation amplitude of the system of 2210/thiamethoxam was smaller. Under the 298K,308K and 318K, the viscosity of the suspension system of the dispersant/azoxystrobin and dispersant/thiamethoxam were reduced gradually with the increase of temperature. The three represents parameters:yield value τH, consistency index κ and predominate flow characteristic index n of the Herschel-Bulkley model were all varied along with the change of temperature and pH. The oscillation frequency and the amplitude of oscillation curves of the system of the dispersant/azoxystrobin and dispersant/thiamethoxam were all changed with the increase of experimental temperature. The amplitude of oscillation was bigger when the temperature gets higher, and the oscillation curve get mixed and disorderly.Screening formula of suspension concentrate with the microcosmic, precise and quantificated results and conventional methods. Determined that the best dosage of the dispersant D-425,2700 and 2210 were 2.5%,2.0% and 3.0% respectively in 25% azoxystrobin suspension concentrate. During the research process of 21% thiamethoxam suspension concentrate, only the dispersant 2210 could prepare the qualified suspension concentrate, whose optimum dosage was 3.0%. In this paper, the 25% of azoxystrobin and 21% thiamethoxam suspension concentrate have excellent physical and chemical properties, and meet the industry standard requirements.