A Novel Approach for Development and Characterization of Effective Mosquito Repellent Cream Formulation Containing Citronella Oil

Table 2

Heuristics for formulation development.

Mixing sequence; (i) Prepare aqueous phase and oil phase into separate containers before mixing.; (ii) Add oil soluble preservative to oil phase and water soluble preservative to water phase.; (iii) To make O/W emulsion, keep the amount of aqueous phase higher.; (iv) To make W/O emulsion, keep the amount of oil phase higher than or equal to that of aqueous phase.; (v) Add aqueous phase to oil phase through wall of the container to ensure little loss of two phases.; (vi) Stir emulsion at constant temperature (from 55 to 65°C) for 45–60 min for proper emulsification.; (vii) After proper emulsification, add heat-sensitive ingredients such as color, pH adjuster, fragrances, and perfumes at lower temperature (below 40°C).
Preparation of aqueous phase; (i) Aqueous phase ingredients such as glycerin and water soluble preservative should be predissolved with a sufficient quantity of distilled water.; (ii) The emulsifiers should be added as the last part of aqueous phase.
Preparation of oil phase; (i) Add liquid emollients to solids emollients and melt them using gentle heating.; (ii) Add essential oil (CEO) at 55°C into oil phase just before mixing the two phases.
Author recommendations; (i) Homogenizer/mixer with adjustable stirring speed is recommended to use for the bench scale experiment and also for the production scale.; (ii) Keep the stirring speed of mixer or high-shear homogenizer below 2,000 rpm to avoid breaking down the carbon chains, which leads to foaming of emulsion and causes instability.; (iii) To get proper emulsification during the addition of two phases, stirring speed should be kept at 200–400 rpm to avoid bubble formation and after that speed should be maintained near 800–1000 rpm.; (iv) After addition of two phases, emulsion should be stirred for 45–60 min.; (v) Ultrasonication (using bath sonicator) is recommended in the case of air entrapment.