A Surfactant/Biopolymer Stabilizer for Emulsions

February 16, 2009 | Contact Author | By: T. Tadros, Wokingham; S. Leonard and M.-C. Taelman, Uniqema Personal Care
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Keywords: nonionic surfactant | biopolymer system | emulsion | viscosity | rheological measurements | steric stabilization | hydrocolloids

Abstract: An emulsifier/biopolymer system using a mixture of nonionic surfactants and two biopolymers was developed. The surfactants provide effective steric stabilization against coalescence, whereas the biopolymers provide a high residual viscosity and yield value, thus providing stability against creaming. The mechanism of stabilization is discussed in terms of the synergy between the two biopolymers.

Oil-in-Water (O/W) emulsions that are commonly used in many personal care formulations need to be stabilized against creaming or sedimentation, flocculation, Ostwald ripening, coalescence, and phase inversion. To achieve these objectives, hydrocolloids (i.e., Konjac mannan (K) and Xanthan (X) gums [KX]) have been proven as excellent stabililizers for O/W emulsions against any coalescence and creaming. K is a β-1,4–linked glucomannan with branches consisting of about 16 sugar units linked to C-3 of the glucose and mannose at approximately every 10 residues along the chain. Native K is acetylated and does not gel in water. On deacetylation in the presence of alkali, however, a thermally reversible gel is produced. Xanthan gum is a charged polysaccharide consisting of a β-1,4–linked glucopyranose backbone with a trisaccharide side chain–linked to every second glucose residue. The side chain consists of 2 mannose units separated by a glucoronic acid residue. Xanthan gum does not gel at any concentration but it undergoes a temperature-induced conformational transition from an ordered helical structure to a disordered structure. Mixtures of KX form reversible gels, which most workers agree is attributable to molecular association.

In this paper, we will demonstrate the synergy between the 2 hydrocolloids using rheological measurements. A robust “gel” is produced that prevents any creaming or sedimentation. In addition, the possible adsorption of the gums at the O/W interface enhances stabilization against coalescence. This was demonstrated by preparing emulsions containing the surfactant/biopolymer mixtures.