Influence of the processing methods on the physical stability of metolachlor emulsion in water

The influence of different processing methods, order of oil or aqueous phase and the position of emulsifiers in addition, on the physical stability of metolachlor emulsion in water (EW)was studied. Short-term scan spectrum from the Turbiscan Lab, the mean diameter of droplets and Zeta potential were evaluated. Significant stability differences were obtained for metolachlor EW with the same formulation prepared by different processing methods. In method A, emulsion was prepared by inversed phase emulsification with the emulsifier in the oil phase. The backscattered light intensity over time of the short-term scan spectrum decreased slowly, and smallest mean diameter of droplets with the largest absolute value of Zeta potential were obtained. In acceleration test (54 ℃±2 ℃, 14 d), emulsion prepared by method A showed uniform appearance and the best stability and the emulsion prepared by inversed phase emulsification with the emulsifier in the aqueous phase (method B) was the second best. For the emulsions obtained by direction emulsification with the emulsifier in the aqueous phase (method C) and direction emulsification with the emulsifier in the oil phase (method D), the short-term scan spectrum changed significantly and the backscattered light intensity in the upper and lower-middle portion decreased significantly. The mean droplets diameters were larger and the absolute value of Zeta potential was smaller. Inhomogeneous appearance was observed in acceleration test. There were aqueous layer on the top, and less precipitation at the bottom. It was demonstated that the stability of metolachlor emulsions oil in water for the same formulation prepared by different processing methods were quite different, the emulsion prepared by inversed phase emulsification with the emulsifier in the oil phase had the best stability.