| Pesticides suspension concentrate (SC) has the advantages of biological efficacy, safety,economic and environment-friendly over many other traditional formulations. However, issueof SC stability has restricted the development of formulation for a long time. In this paper,stabile suspension system of30%(w/v) difenoconazole was constructed. The effects ofdispersants, thickeners on the adsorption, sedimentation and rheology of suspension systemwere studied. The wetting property of different difenoconazole formulation on leaves ofdifferent plants were evaluated. The main results were as follows:1. Determination of30%difenoconazole SC formulationThe formulation of difenoconazole SC was optimized with the orthogonal design method.The optimum formula of30%(weight percent) difenoconazole SC were difenoconazole30%,D10013.5%,8883.5%, tanemulps542.5%, XG0.08%+aluminum magnesium silicate1.2%or XG0.1%+SM-A870.1%, glycerol3%, and fill water to100%. The particle sizemaintained1-2μm, with a suspension rate of more than93%after heat storage, all the otherindex were in accorded with the requirements of SC.30%difenoconazle SC was prepared by wet-grinding method. The particle size andparticle size distribution of formulation were closely related to the processing time and thediameter and amount of zirconium oxide beads. The results of sand rubbing study suggestedthat good stability of the suspension concentration with narrow particle size distribution couldbe obtained at the zirconia bead diameter of1.2mm, the mass ratio of the material withzirconia beads volume of1:1.8, and a grinding time of2hours. The resulted particle size ofsuspension maintained at1-2μm.2. Study on the stability of30%difenoconazole SCOn the basis of30%difenoconazole SC formula, the influence of dispersant and factorsof temperature and pH on the stability of suspension system were investigated. Specificresults were as followed:（1）Adsorption of dispersant D1001on the surface of difenoconazole of different particlesize were determined, the results showed that the adsorption expressed as the Langmuir model,The adsorption amount reached the maximum at the particle size of less than1250mesh.During a temperature range of25-55℃, the adsorption amount had a trend of first increasing and then decreasing with the increasing temperature, and the maximum adsorption wasobtained maximum at the temperature of35℃. Similar trend was found within the maximumadsorption at pH of7. Kinetics of interaction between D1001and difenoconazole showedbetter agreement with lagergren first order kinetics, the adsorption capacity reached themaximum within120min, and with the adsorption rate K1of0.0605min-1.（2）By adding of different amount of the dispersant D1001, it is found that the particlesize, span, viscosity, sedimentation volume of the suspension system reached their minimumvalues, and while the suspension rate got the maximum value when4%dispersant D1001wasadding.3. On the basis of30%difenoconazole SC formula, effect of Xanthan gum, sodiumalginate, and SM-A87as suspension additives, on the rheological behavior of prepareddifenoconazole SC was evaluated. The suspension systems with all above additives havepseudoplastic of “shear-thinning” characteristics, among which Xanthan gum and SM-A87played more significant roles.In this paper, the rheological property of expolysaccharide secreted by a deep-seamesophilic bacterium in difenoconazole suspension was studied systematically for the firsttime. The results indicated that SM-A87formed a network structure in the suspension system,and this network structure enhanced with the increase of the SM-A87addition. Theconsistency coefficient KHand yield value τHof suspension increased correspondingly, andexhibiting “shear thinning” characteristics of pseudoplastic fluid. The effect of temperature onthe suspension with SM-A87showed significant pseudoplasticity in range of25-55℃. The“shear thinning” property weakened and the viscosity reduced with the increasingtemperature. The corresponding viscosity activation energy E is27.26kJ/mol. Resultsindicated that the suspension system of SM-A87was dependent on the temperature. Effect ofpH on the difenoconazole suspension concentrates with SM-A87was more complex,consistency coefficient of suepesnion KHdecreased and rheological index “n” increased withthe increasing pH. But both KHand “n” were less than1, suggesting that the systemmaintained pseudoplastic characteristics with a decreasing trend. The SC added with NaClmaintained the “shear thinning” property of pseudoplasticity, but not significantly changedwith the NaCl concentration.4. The synergistic characteristics of rheological properties of Xanthan gum/SM-A87andXanthan gum/aluminum magnesium silicate were studied, in order to guide the application ofthickening agent system in difenoconazole SC. (1) The complex system of xanthan gum with SM-A87was studied. A strong synergisticeffect was observed when the mass ratio of Xanthan gum and SM-A87was1:1. The systemwas obvious pseudoplastic fluid with shear-thinning property, and the viscosity wassignificantly increased. The rheological behavior of complex system of Xanthan gum withSM-A87was less affected by the temperature with apparent shear-thinning pseudoplasticcharacteristics in the range of25to55℃. The effect of pH on the mixed system was moresignificant, the consistency coefficient KHand yield value τHincreased with the increasing ofpH, but rheological index “n” decreased markedly. Effects of inorganic electrolyte NaCl onthe rheology of SM-A87and xanthan gum seemed more complicated, the coefficient KHandyield value τHincreased and rheological index “n” decreased with the increase of saltconcentration, and the pseudoplastic characteristics weakened.(2) Compounds of magnesium aluminum silicate and xanthan gum were also investigated.Synergistic effect on viscosity has been found when magnesium aluminum silicate andxanthan gum reached a ratio of13.7:1. With the increasing of pH, the consistency coefficientKHand yield value τHdecreased, while the rheological index “n” increased. As for theinfluence of temperature, pseudoplastic characteristics of the system decreased with theincrease of temperature, indicating from the decreased consistency coefficient K and yieldvalue τHdecreased, and the gradually increased rheological index “n”. in the matter ofinorganic salt NaCl influence, consistency coefficient K increased and rheological index “n”decreased with the increasing NaCl mass fraction.5. Wetting properties evaluated of difenoconazole SC on leaves of hydrophilic andhydrophobic plantsThe wetting properties of30%difenoconazole SC and with organosilicon wetting agent,10%difenoconazole ME on the hydrophobic plant cabbage and hydrophilic plant cucumberleaves were investigated. The critical micelle concentration(CMC) of three formulations arewere close or blow to its effective concentrations, and surface tension of30%difenoconazoleSC is51.6mN/m,10%difenoconazole ME38.9mN/m, and SC withorganosilicon wetting agent25.5mN/m. three formulations have good wetting properties onthe cucumber leaves, and formulation adding organosilicon wetting agent occurred drainphenomena; but30%difenoconazole SC could not wet the cabbage leaves and rolled downfrom leaves. The results showed that wetting property30%difenoconazole SC was closelyrelated to recommended dose concentration, CMC and the critical surface tension of plant.Itcan be seen from the results, for the hydrophilic plant,30%difenoconazole SC can reach thecritical surface tension, and wetting in leaf distribution, while for the hydrophobic plant, it is necessary that wetting agent added in the formulation to reduce the surface tension and achieve betterwetting effect. |
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