Studies On The Physical Stability And Mechanism Of Diflubenzuron SC

With the increasing requirement of pesticide chemicals to environmental compatibility, pesticide water suspension concertration with many advantages such as safety and high effectiveness has been one of the important represents in pesticide formulation that green chemistry initiated. This thesis had chosen Diflubenzuron as the research object, on the basic of the selection of the wet dispersant, we did more research systemicly about the effects of different facts on the dispersed stability mechanism and rheology of pesticide suspension concentrate system, and probed into the related mechanism. We also prepared Mg-Al MMH and applied it to pesticide suspension concentrate as thixotropy. The influences of mass fractions of Mg-Al MMH(ω) , electrolytes concentration and temperature on the rheology of the system and Mg-Al MMH on the thixotropy mechanism of Diflubenzuron SC were studied in this paper.The main researches were following:1. The selection of the wet dispersant was the core during the selection of SC prescription process. The result after compositely comparing of such three methods (drop-point, average size and Zeta potential.) in dispersant selecting showed that :(1) The three methods had thire own characters respectively and certain correlate at the same time. a. The drop-point method which was fit to selection among any dispersants was a quick selecting progress. However, it was a premilinary selection method because of its poor accurate. b. The suitable dispersant could be determined exactly after particle size determination, and this method could be applied to the selection of any species dispersants. c. The method of Zeta potential which was aggrement with the selection result of particle size determination was fit to the selection of ionic dispersant.(2) The methods of average size, Zeta potential and viscosity curve determined the content of dispersant. They had better correspondence.(3) The selection result for 20% Diflubenzuron SC was MOTAS:700# = 4:1 with the total conent of 2%.(4) Non-ionic wet dispersant combined with ionic wet dispersant playing better dispersion was further verified by thermogravimetric analysis(TG).2. The adsorption behaviour of dispersant MOTAS on the interface of Diflubenzuron particles was studied by the measurement of IR spectrogram and adsorption isotherm. The dispersion stability of Diflubenzuron SC was studied by average size and Zeta potential. The result showed that:(1) The IR spectrogram showed that MOTAS adsorded on the interface of Diflubenzuron particles by hydrogen bonding, and the dispersed stability of SC was keeped by electrostatic repulsion and steric hindrance effect. The result of adsorption isotherm showed that the adsorption capacity increased with the polymer concentration increasing until it reached saturation, and the adsorption isotherm was correspond with Langmuir equilibrium. The more dispersant molecular weight, the bigger saturated adsorption capacity of the interface of the technical material particles, and the saturated adsorption capacity decreased with the pH value increased which the pH value effect the ionization of polymer dispesant, and the saturated adsorption capacity decreased with the temperature increased under the same conditions.(2) The dispersion stability decreased with excessive or shortage dispersant which the optimal content is 2%, and the dispersion stability increased with bigger molecular weight of dispersant and bigger electrostatic repulsion and steric hindrance of original particles, and the pH value effect the ionization of polymer dispesant. At the pH value of 9 the dispersion stability of suspension concentrate was best. The addition of electrolytes could destroy dispersion stability, and the ability of compressing double-layer of monovalent Na⁺ was more distinct than bivalent Ca²⁺ when they were at the same concentration, and it decreased the dispersion stability more distinct.3. The prepared Diflubenzuron SC with adding MOTAS and MT as auxiliary agent was studied by flow curve experiment and Steady Shear Method, and its thixotropic behavior was studied by stable shear experiment. The result showed that:(1) Diflubenzuron SC was non-newtonina fluid of"shear-thinning", which correspond with Herschel-Buckley rheological model. SC had certain thixotropic behavior after the adding of MT, and the rheological parameters and thixotropic degree increased with the content of MT increasing.(2) The rheological parameters of SC decreased after increasing with the dispersant mass fraction increasing, while the thixotropic behavior of dispersion system decreased with the dispersant mass fraction increasing. The system had good fluidity and thixotropic behavior when the dispersant mass fraction was 2%.(3) The pH value didn't have effect on the fluid pattern and positive thixotropy, while it had a great impact on the surface charge of Diflubenzuron particles and forces between particles of MT, the rheological parameters and thixotropic degree of the system had a trend of decreasing and then increasing with the increased pH value under the composite effects. When the pH value was between 8 and 9, the system had certain thixotropic and its fluidity was best. The property of rheogram"shear-thinning"of the pseudo-plasticity and positive thixotropy of the SC added with electrolytes were not changed.(4) The effects of electrolytes with various concentration on the Diflubenzuron SC system were dependented on the composite effects of two different surface potentials electrolytes exerted between technical material particles and MT particles. The rheological parameters and thixotropic behavior of SC had a trend of increasing and then decreasing and then increasing with the dispersant mass fraction increasing. The influences of CaCl₂ were more significant than NaCl at the same concentration.(5) Temperature had a big influence on the dispersant adsorption capacity of technical material particles. Therefore, Temperature effected the rheology of SC. As the temperature increased, the property of rheogram"shear-thinning"of the pseudo-plasticity and positive thixotropy of the SC were not changed . However, the rheological parameters of Diflubenzuron SC increased with increase of temperature. The thixotropic degree of SC decreased when the temperature reached 55℃.4. Mg-Al MMH colloidal was prepared by liquid co-precipitation method, the analysis of rheological curve and thixotropic behavior showed that:(1) The XRD spectrogram showed that the particles had a structure of hydrotalcite crystal.(2) Mg-Al MMH acted as thixotropic agent which was applied to Diflubenzuron SC had better positive thixotropy, and the prepared SC system corresponded the property of rheogram"shear-thinning"of the pseudo-plasticity. The rheological parameters and thixotropic behavior of SC increased with the increase of the mass fractions of Mg-Al MMH..The space network structure was formed by electrostatic attraction between Mg-Al MMH and technical material particles with negative charged which adsorbed dispersant. (3) The rheological parameters of Diflubenzuron SC increased with increase of temperature at a certain temperature range, but the property of rheogram"shear-thinning"of the pseudo-plasticity and positive thixotropy of the SC were not changed.(4) The property of rheogram"shear-thinning"of the pseudo-plasticity and positive thixotropy of the SC added with electrolytes were not changed, too. The rheological parameters and thixotropic behavior of SC had a trend of increasing and then decreasing and then increasing with the dispersant mass fraction increasing. The influences of CaCl₂ were more significant than NaCl at the same concentration.