Study On The Preparation And Stability Of Ametryne Suspension Concentrate

Pesticide suspension concentrate is the multiphase dispersing system with poorthermodynamic stability and kinetic stability. There are some problems such as waterseparating, thickening caking and crystal growth during the storage of suspension concentrate.The phenomenon is clearly due to the shortage of the basic theory on the formationmechanism and system stability. By using research ideas, methods, and effective researchtools about suspension liquid physical stability of Nano-materials, ceramics, coal-water slurrysuspension in pesticide suspension concentrate, the theory of the pesticide suspensionconcentrate will be understood deeply and improved further.This thesis selected ametryn as the research object. The form of crystal growth,adsorption curves, particle average size and Zeta potential were analysed on the base of thereasonable formula of44.8%ametryn SC. The effects of the factors such as temperature, pHvalue, and electrolyte on the dispersibility of ametryn SC were systematically studied. Thefollowing aspects were studied in this thesis:(1) Based on flow point method, the species, dosage of dispersant and grinding time of44.8%ametryn SC were selected by laser particle size instrument. Combined with appearance,measurement of syneresis rate and dispersion, the species and dosage of antifreeze andthickener were selected. Then the rational formula of44.8wt%ametryn SC the wasascertained as follows: Ametryn:44.8wt%; Maleic rosin-polyoxypropylene-polyoxyethyleneether sulfonate (SC-3):4.0wt%; Antifreeze(glycol):2.0wt%; Thickener(FT):2.0wt%; Fillwater to100%.(2) Oswald ripening was a main reason for the growth of pesticide particles. The typeand amount of dispersant were the key factors. By morphology characterization of thepesticide particles, SC-3was discovered that it can form double-layer absorption on thesurface of pesticide particles under the same condition. Double-layer absorption generatedtwo shielding layers around ametryn particles, which restrained particle growth effectively.When the dosage of SC-3was4.0%, tight absorption layer not only retarded dissolvedametryn precipitation on larger particles, but also prevented the particles and water fromcontacting with each other, thus decreased incidence of Oswald ripening. (3) The IR spectrogram showed that SC-3adsorbed on the interface of ametryn particlesby hydrogen bonding. The result of adsorption isotherm showed that in high concentrationrange, the adsorption isotherm represented a double-layer adsorption characteristics, and inlow concentration range, the adsorption isotherm corresponded with Langmuir equilibrium.the saturated adsorption capacity first increases, then decreases with the increase oftemperature; first increases and then decreases with increasing of the pH value; graduallyincreases with increasing electrolyte concentration.(4) Zeta potential of ametryn SC was negative. The dispersion stability decreased withexcessive or shortage dispersant which the optimal dosage of SC-3was4.0%. pH affected thedissociation of dispersant in water. With the increasing of pH, the absolute value of Zetapotential first increased and then decreased. pH=9, the absolute value of Zeta potential ismaximum. The type and concentration of electrolyte affected the Zeta potential of ametrynSC. With the increasing of the concentration of Mg2+and Na+, the absolute value of Zetapotential decreased. Because the ability of compressing double-layer of bivalent Mg2+wasmore distinct than univalent Na+, so the impact of MgCl2on the system was even moresignificant.