Study On Preparation And Physical And Chemical Stability Of 25% Pyraclostrobin Aqueous Suspension Concentrate

This experiment has studied the effect of dispersant on the physical and chemical stability of 25% pyraclostrobin aqueous suspension concentrate.Two dispersants of Agrilan 700 and Morewet D-809 and 99% pyraclostrobin crystal form II are used to re-screen formulation.The adsorption behavior of two dispersants on the surface of pyraclostrobin is studied on the basis of formulation screening,the adsorption mode between drug and dispersing agent is determined.And the rheological behavior of the suspension system prepared by two dispersants and the change trend of the apparent viscosity and shear force of the suspension system are studied.Finally,the physical and chemical properties of the liquid are determined,including surface tension,dynamic surface tension,contact angle,particle growth,and indoor virulence determination.The improvement of the stability of 25% pyraclostrobin aqueous suspension concentrate is studied from formulation screening,adsorption behavior,rheology and physical and chemical properties.The specific conclusions are as follows:1.The flow point method and viscosity curve method are used to determine dispersant dosage of Agrilan 700 and Morewet D-809.The optimum dosage of the wetting agent and thickener are re-screen based on the preliminary formulation,and finally two formulations of pyraclostrobin aqueous suspension concentrates are obtained: 25% pyraclostrobin,2% Agrilan 700 / 1% Morewet D-809,wetting agent 3% SP-SC29,thickener 1% magnesium aluminum silicate and 0.1% xanthan gum,antifreeze 4% ethylene glycol,defoamer 0.5%,preservative 0.2% BIT,deionized water is added to 100%.The quality index and physical and chemical properties of prepared 25% pyraclostrobin aqueous suspension concentrate all meet the standard.2.The adsorption behavior of dispersant on the surface of pesticide is studied by infrared spectroscopy and ultraviolet absorption.The new absorption peak is not generated after adsorpting Agrilan 700 and Morewet D-809 of original drug,the force between dispersing agent and original drug is determined to be van der Waals force,and the adsorption is monolayer adsorption,adsorption isotherm is similar to Langmuir.Adsorption data are fitted according to the Langmuir adsorption isotherm,the correlation coefficients are above 0.96,the equilibrium concentration of Agrilan 700 on the surface of original drug is determined to be 15.4 g/L,which is about 1.5%.The equilibrium concentration of Morewet D-809 is 3.8 g/L,which is about 0.4%.3.Study on the effect of different concentration of dispersant and different thickener combinations on the rheological properties of suspension system,the results are as follows: the apparent viscosity of aqueous suspension prepared by two dispersing agents gradually decreased with the increase of shear rate,and the shearing force gradually increased.The suspension system shows the behavior of shear thinning,and it has non-Newtonian fluid and pseudoplastic fluid characteristics.When the dispersant is the adsorption equilibrium concentration,the rheological model is consistent with the HershelBulkley model,and the fitting coefficients are 0.9982 and 0.9952.The suspension system is positive thixotropic.The steady shear test results reveal that the apparent viscosity of the system changes periodically with the shear time.When dispersants are both the equilibrium concentration of adsorption,the viscosity and rheological model of aqueous suspension concentrate prepared by the combination of 1.1% magnesium magnesium silicate,0.1% xanthan gum,1% magnesium aluminum silicate and 0.1% xanthan gum has changed after accelerated storage,but all suspension systems have typical non-Newtonian fluid and pseudoplastic fluid characteristics,they exhibit positive thixotropy.4.The prepared liquid is diluted to different concentrations,physical and chemical properties of liquid are determined.The measurement shows that the surface tension value decreases with the increase of the dispersant concentration,which is basically between 50-40 mN/m,and the surface tension value is small when the dispersant is the adsorption equilibrium concentration.The curve can quickly enter the interstitial equilibrium zone,and the larger concentration of dispersant,the smaller the dynamic surface tension value.The contact angle of the liquid gradually decreases with time and gradually decreases with the concentration of the dispersant.After the suspension is accelerated at different temperatures,the particle size is no difference,and particle size is below 5 ?m.The virulence of the suspension prepared by two dispersants against Botrytis cinerea is comparable to the control agent pyraclostrobin aqueous suspension concentrate.