Abstract
Most synthetic surfactants are harmful to humans and can cause health problems after prolonged exposure or consumption. This study explores in extensive detail the use of a natural surfactant saponin, extracted from fruit of S. mukorossi, to synthesise oil in water nanoemulsions and gas–liquid foams. The effects of saponin concentration (0.1–2 wt%), pH conditions (2–10) and salt concentration (100–500 mM) on stability and average droplet diameter of sunflower oil-in-water emulsion were investigated. Emulsions were stable at pH 4–10 and salt concentration 100–400 mM for up to 30 days. Critical micellar concentration of 0.5 wt% and the average hydrodynamic diameter of saponin micelle of 4.25 nm are observed. A gas inducing impeller-based device was used to generate foam from saponin solution having different gas hold up values (εG: 0.31, 0.45 and 0.62). Average bubble size of foam and its stability (drainage rate and half-life) are measured. 100% of saponin solution gets incorporated into foam in every trial. Foam drainage rate increased and half-life decreased with increase in gas holdup. It is shown that saponin can be an effective natural and non-toxic alternative to synthetic surfactants for various industrial applications.
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