An investigation into interactions between polyacrylic polymers and a non-ionic surfactant: an emulsion preformulation study

The aim of this study was to investigate possible interactions between a po lymeric emulsifier and a non-ionic surfactant, with a view of achieving bet ter understanding of emulsion stabilisation mechanisms. The polymeric emuls ifier used was acrylates/C10-30 alkyl acrylate crosspolymer (Pemulen TR-2(R )), while Polyoxyethylene 20 sorbitan mono-oleate (Polysorbate 80) has been chosen as a model surfactant. Both materials were used within the concentr ation range relevant for their practical application. A 0.2%w/w aqueous dis persion of polymeric emulsifier, containing various amounts of surfactant ( from 0.01 to 1.0% w/w) was used throughout the study. Interfacial aspects o f the proposed polymer/surfactant interactions were analysed by means of su rface tension measurements. Changes in the network structure of the test di spersions were quantified by continuous shear rheometry, supported by the t exture analysis. To analyse the influence of hydrophobic alkyl groups prese nt on the Pemulen TR-2(R) chains, an unmodified, hydrophilic polyacrylic ac id polymer, Carbopol 934P(R), was assessed under the same conditions. The r esults obtained by both surface tension and rheological studies have reveal ed large differences in behaviour of the two polymers in the presence of th e model surfactant. Pemulen TR-2(R) was shown to desorb the surfactant from the surface, within the whole concentration range studied. Furthermore, an increase in viscosity and texture profile parameters with increasing Polys orbate 80 concentration up to 0.3% w/w was evident in the case of Pemulen T R-2(R) dispersions. This was followed by a decrease in the gel network stre ngth at higher surfactant concentrations. On the other hand, Carbopol 934P( R) has shown no signs of surfactant desorption and only small changes in th e network structure with the increasing concentration of surfactant. It is shown in this study that an interaction between a polymeric emulsifier Pemu len TR-2(R) and a non-ionic surfactant Polysorbate 80 does occur in their a queous dispersion, and that it is: (a) hydrophobic in nature; (b) concentra tion-dependent; and (c) has an impact on the rheological properties of disp ersion. (C) 1999 Elsevier Science B.V. All rights reserved.