Stability of shea-paraffin oils blend emulsions with mixed nonionic emulsifiers for broad-range required hlb of shea oil

Abstract

This study aimed to determine the required hydrophile-lipophile balance (RHLB) value of shea oil to facilitate producing its stable emulsions using mixed nonionic surfactants as emulsifier. Oil-in-water (o/w) and water-in-oil (w/o) emulsion formulations were produced, containing shea oil/liquid paraffin blends as oil phase, and o/wemulsifiers: Tween 20/Span 20, Tween 80/Span 80, or w/o-emulsifier Span 85/Tween 80; using the hydrophilelipophile balance (HLB) number of each surfactant in the mixed-emulsifier pair to compute requisite proportions to use for specific prospective RHLB-value targets for shea oil (SHO*) in formulation. Physical stability characteristics of each formulation (creaming rate, mean globule size and viscosity) were monitored for 12 weeks. The stability qualities of the formulations made with different o/w-emulsifiers were significantly different. RHLB value of shea oil for o/w emulsion system (deduced from the most stable formulations using the different emulsifiers) differed; and the values for o/w and w/o systems (determined from least mean globule sizes) varied with sampling time over a broad range of prospective SHO* targets; attributed to limitations of HLB theory. Stable o/w or w/o emulsion formulations were thus produced by each emulsifier over a broad range of shea oil RHLB values. The RHLB parameter inadequately defines stability of shea oil emulsion formulations.

Keywords: Shea oil, Required hydrophile-lipophile balance (RHLB), Mixed nonionic surfactants, Emulsion formulation.