Abstract:

In order to provide a reference for octenyl succinic anhydride(OSA)-modified starch and methyl oleate used in green pesticide preparations, the formulation of the lambda-cyhalothrin oil-in-water emulsion with OSA-modified starch and methyl oleate as emulsifier and solvent was studied. Furthermore, the effects of different processing parameters, including the concentration of pretreating fluid of OSA-modified starch, rotational speed and shearing time on the stability of emulsion were studied by measuring oil droplet diameter distribution. Results demonstrated that OSA-modified starch had excellent emulsification ability to methyl oleate. High stable emulsions(2.5%) could be prepared with OSA-modified starch. The mean droplet diameters of emulsion were about 1.2 μm, and increased by only 0.1~0.3 μm after storing at 25 ℃ for 6 months or at (54±2) ℃ for 14 days, and approximately 100% of the oil remained stable in the emulsion. Higher stable emulsions could be prepared by emulsification at high viscosity with mass fraction of pretreating fluid of OSA-modified starch in the range of 15%~25%. Smaller oil droplet diameters were obtained when the rotational speed was increased, which had no significant effect on homogeneity of emulsions. On the other hand, an increase of the shearing time reduced the span of oil droplet diameter distribution, but had no significant impact on the mean oil droplet diameter. Lambda-cyhalothrin oil-in-water emulsion prepared with OSA-modified starch had a better stability than the conventional emulsions. The results of this study show that OSA-modified starch and methyl oleate can be used as an effective emulsifier and solvent for the environment-friendly lambda-cyhalothrin oil-in-water emulsion formulations.

Key words: lambda-cyhalothrin, oil-in-water emulsion, OSA-modified starch, methyl oleate, oil droplet diameter distribution