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Organic farming and new trends toward the use of safer insecticides for crop protection have created new opportunities for botanical insecticides in the pesticide market. In this study, the botanical insecticide nicotine was formulated as a dispersion (20 vol %) stabilized by sodium caseinate, with nicotine oleate solutions used as the dispersed phase. The formulation showed a phase transition on increasing the nicotine oleate concentration, being an emulsion at 7.5-8.2 wt %, a suspo-emulsion at 8.2-9.7 wt %, and a suspension at 9.7-10.8 wt %. Biological activity, apparent viscosity, dispersion time, and protein surface coverage were dependent on nicotine oleate concentration. The emulsion with 8.2 wt % nicotine oleate and the suspo-emulsion with 8.7 wt % nicotine oleate were found to be the most appropriate formulations for insecticide purposes due to their high bioactivity, low viscosity, and low dispersion time. Nicotine oleate formulations showed good creaming and microbiological stability for at least 4 months without losing their biological activity.

The effect of fatty acid chain length on nicotine carboxylate insecticide emulsions has been studied in terms of particle size, interfacial tension, nicotine encapsulation on emulsion droplets, and bioactivity. The particle size of the nicotine emulsion and the interfacial tension at the nicotine carboxylate oil phase (0.03 M)--Tween 80 aqueous phase (0.001 M) were affected in a similar way by the change in the fatty acid chain length, which was correlated by the packing conformation of Tween 80 and nicotine carboxylate molecules as obtained by AM1 theoretical calculations. The amount of encapsulated nicotine inside the nicotine carboxylate emulsion droplets influenced the insecticide bioactivity of nicotine; this relationship was explained in terms of the acid value of the different fatty acids used to prepare the nicotine formulation.

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