Effect Of Stvrene-maleic Anhydride Copolymcr On The Dispcrsibility Of Pesticide Suspension Concentrate

With people’s environmental awareness and safety knowledge growing, water-basedpesticide formulations with good environmental compatibility have attracted more attention.Suspension concentrate is a new formulation in the development and improvement withsaving organic solvent, less environmental pollution, relatively safe to humans and animals,high efficacy and low cost, which is becoming a hot research at home and abroad. However,current suspension concentrate research in domestic and international mainly focuses onformula screening. Larger particles coalescence, sedimentation, water separating andthickening caking restrict the development of suspension concentrate in the process ofresearch. It is clearly due to the shortage of the basic theory about the stability of suspensionconcentrate.Dispersants prevent the particles from aggregating effectively by reducing theinterfacial tension that maintain the stability of the dispersion system. Styrene-maleicanhydride copolymer and its derivatives are widely used in oil transportation, watertreatment, printing, adhesives and other industries at home and abroad, and the sulfonatedcopolymers show excellent dispersibility. Because of their adjustable functional groups,controlled molecular weight, and good environmental compatibility, they have beenbecoming a research focus in dispersant field. At present, although many studies onpoly-carboxylic salt surfactants have been made, most of them are applied in detergentswhile few in pesticide.This thesis chose benzoyl peroxide as initiator, a series of polystyrene-maleicanhydride styrene-maleic anhydride copolymers were prepared by solutioncopolymerization under different synthesis conditions. The copolymers were applied to thepesticide suspensions which were prepared by wet grind. The study was designed to explore its application in suspension concentrate and provide a theoretical basis. The followingaspects were studied in this thesis:1A series of polystyrene-maleic anhydride was prepared under different synthesistemperatures. Polystyrene-maleic anhydride sulfonic acid sodium （SSMA） with differentmolecular weights was obtained by sulfonateding the polystyrene-maleic anhdride. Thedispersibility of20%diflubenzuron suspension concentrate was identified by assaying andanalyzing diameter of particles, Zeta potentials and viscosities. It revealed the effects ofdispersant type, dispersant dosage, pH and salt ion on the dispersibility of diflubenzuronsuspension concentrate and analysised the causes affecting the dispersibility. It had beenfound that:（1） The maleic anhydride content, degree of sulfonation and molecular weight weredifferent with different synthesis temperatures. So the dispersion effects on20%diflubenzuron suspension concentrate were different, too. If the content of maleic anhydrideand degree of sulfonation were high, hydrophilic chain long, solvation strong, the SSMAwould fall off from the surface of diflubenzuron easily. And the hydrophilic chains pronedto tangles to flocculate that the dispersion effect was reduced. If the molecular weight wassmall and viscosity low, the binding between SSMA and diflubenzuron surface would soweak that the dispersibility was decreased by “bridge” coalescence. The optimal dispersantwas the SSMA which was made at75℃for20%diflubenzuron suspension concentrate.（2） The dispersibility of suspension concentrate was closely related to the mass fractionof SSMA. The dispersibility of20%diflubenzuron suspension concentrate was best whenmass fraction of SSMA was3%, and the dispersibility would be worse on condition thatSSMA was overmuch or lacking.（3） pH affected its dispersibility for suspension concentrate by affecting the ionizationof lonic dispersion in water. At the value of pH=9the dispersibility of suspensionconcentrate was best on account of strong steric hindrance which was provided bycompletely ionizing of the molecules.（4） Under different pH Na⁺or Ca²⁺was able to decrease Zeta potential by compressing the electronic double layer thickness of particles surface, which leaded to particlesaggregation due to the reduction of electric quantity and ultimately made the dispersiveeffect of suspension concentrate worse, then the higher the content of Na⁺or Ca²⁺was, theworse the dispersibility of diflubenzuron suspension concentrate was. If the ionsconcentration were the same, the coagulation capacity by Ca²⁺was stronger than Na⁺, andthe dispersibility of suspension was worse after adding Ca²⁺.2A series of SMA were prepared by changing monomers proportioning or initiatordosages. Then the SMA was applied to the sulfur suspension concentrate. The bestdispersant and its most suitable concentration were identified by assaying diameter ofparticles, Zeta potentials and pH. The results showed that the SMA which was synthesizedat BPO dosage0.5%and the ratio n（St）:n（MA）0.8:1had excellent performance for25%sulfur suspension concentrate, and its maleic anhydride content and molecular weightrespectively was43%and21019. The optimum concentration of the SMA was2%.