Synthesis Of Comb Anionic Dispersant For Pendimethalin Suspension

At present,pesticide formulations are developing in the direction of environmental protection such as water-based,granulation,functionalization and refinement.Suspending agent is one of the fastest growing dosage forms.35% pendimethalin suspension is a high-content and low-melting type suspension agent,which mainly has the problem of poor physical stability after heat storage.It is found that the application of suitable dispersant is the key to solve this problem.Therefore,according to the characteristics of 35% pendimethalin suspension,two dispersants were designed and synthesized,then the formula was screened and optimized,and the factors affecting the stability of the system were systematically studied.It provides a valuable theoretical basis for the preparation of high-level water suspensions for low-melting pesticides.(1)In this paper,dispersants were designed according to the nature and dispersion mechanism of pendimethalin.A ternary polysulfonate having a comb structure was synthesized by a free radical polymerization method using methacrylic acid polyoxyethylene ether,sodium p-benzenesulfonate,hydroxyethyl methacrylate as a monomer and ammonium persulfate as an initiator.The dispersion properties were investigated by measuring the suspension rate,flow point,surface tension,average particle diameter.The molar ratio of hydroxyethyl methacrylate:sodium p-benzenesulfonate is equal to 9.5,the temperature is 60~70 ° C,the initiator accounts for 8% of the total mass of the monomer,and the molar ratio of polyoxyethylene ether:sodium p-benzenesulfonate is equal to 0.6.Under the reaction conditions,the polysulfonate dispersant with the best pour value is obtained.The surface tension of the dispersant can reach 54.41 mN/m,the suspension rate is over 90%.The average particle size of the prepared pendimethalin suspension before and after heat storage is 1.1520 um and 1.7496 um,respectively.The dynamic contact angle attenuation coefficients on the lipophilic and hydrophilic leaves were 0.26 and 0.47,respectively.(2)The comb-like ternary polycarboxylic acid type dispersant was synthesized by RAFT method using methacrylic acid,sodium p-benzenesulfonate and polyethylene glycol monomethyl ether methacrylate as monomers.The surface tension of the dispersant can reach 53.1 mN/m,the suspension rate is 90.21%,and the flow point is 1.8392.The average particle size of the suspension agent before and after heat storage is 1.6186 um and 4.3324 um,respectively.The dynamic contact angle attenuation coefficients on the lipophilic and hydrophilic leaves were 0.19 and 0.40,respectively.Therefore,the two dispersants can effectively adsorb on the surface of the particles and provide electrostatic and steric hindrance,and also inhibit the growth of crystals after heat storage,which are beneficial to improve the stability of the 35% pendimethalin suspension system.(3)The auxiliaries were screened by measuring the water synersis rate,rheological properties,particle size change before and after storage,and then preparing and optimizing 35% pendimethalin suspension: Dispersing agent 12%,wetting agent 2%,antifreeze 5%,thickener agent 1.2%.The performance of the optimized formulation was tested.The results showed that the suspension had a cloud-like dispersing ability with a suspension rate of 97.91%,a ZETA potential of 49.13 mv before heat storage,and 40.65 mv and 48.22 mv after heat storage and cold storage,respectively.The suspension system achieves moderate stability and provide theoretical data for practical applications.