Spontaneous Emulsification of Citronella Oil: Effect of Processing Conditions and Production Scale

Abstract

Nanoemulsions are gaining considerable interest for use in delivery of essential oil-based pesticides. Evaluation in the laboratory have shown promising efficacy of nanobiopesticides, and further development in nanoemulsion production at larger scale is needed for a wider application in the field. This study aimed to evaluate the changes in droplet size characteristics of citronella oil nanoemulsions produced using spontaneous emulsification at increased scales. The preparation of nanoemulsion was carried out in two stages of scale-up, namely the laboratory scale (200-1000 mL) and the larger scale (10-50 L). The process variables included stirring speed and time. Characterization was done on the oil droplet size, polydispersity index (PDI), zeta potential and microscopic structure. The oil droplet size, PDi and zeta potential varied with the emulsification process conditions and the production scale. In general, increasing mixing speed and time tended to decrease droplet size and PDI, and increase zeta potential. The changes in characteristics of nanoemulsion were minor at the higher production scales. Relatively small droplet sizes were found in the whole experiment (90-160 nm) with PDI of 0.2 - 0.4 and zeta potential of -28 to -8.8 mV. These results are useful for the design of nanoemulsion production at practical application scale.