EFFECT OF METHYLCELLULOSE ON THE STABILITY OF OIL-IN-WATER EMULSIONS

The objective of this study was to investigate how polymers used as au xiliary emulsifiers improve the stability of oil-in-water emulsions. O ne stable emulsion and three unstable emulsions were formulated with 3 0% mineral oil and an emulsifier blend of Tween 40 and Span(R) 20. The stable emulsion (SE) contained 2% emulsifier blend optimized for maxi mum stability. One unstable emulsion, UE1, was formulated to contain 0 .5% of the same emulsifier blend as the SE formulation. Two unstable e mulsions were formulated to contain an unbalanced emulsifier blend, on e with excessive hydrophilic emulsifier (UE2) and one with excessive l ipophilic emulsifier (UE3). A series of emulsions was prepared contain ing increasing amounts of methylcellulose for each base emulsion. Crea ming and change in particle size were measured to evaluate stability. The addition of the polymer to the stable emulsion caused instability leading to creaming and eventual oil separation. This effect of the po lymer was more pronounced in UE1 emulsions. However, the addition of t he polymer improved the stability of the UE2 and UE3 series of emulsio ns. The polymer also caused a reduction in the particle size of UE3 em ulsions and a proportionally larger increase in the viscosity of UE2 e mulsions. These results suggest that (i) methylcellulose could act as a hydrophilic emulsifier only in the absence of Tween(R) 40, (ii) meth ylcellulose and Tween(R) 40 associate to form a complex and (iii) the concentration of Tween(R) 40 is the determining factor for the stabili ty of emulsions. A model of the methylcellulose-Tween(R) 40 associatio n and its effect at the mineral oil-water interface is proposed.