VISCOELASTICITY OF PERSONAL CARE PRODUCTS

As well as foaming, detergency and mildness, the theology of personal care products such as shampoos, shower gels, etc. is a key property. With regard to their application, the consumer desires shear thinning behaviour of the liquid, i.e. slow flow from the bottle neck, largely free of long threads, and easy distribution on the skin or hair. Up to now, this pattern has been followed by measuring the flow curves, although it is well known that surfactant solutions forming transient networks often display viscoelasticity. Employing a fatty alcohol ether sulphate (FAES) as the basic model surfactant, loss and storage moduli were measured with use of an oscillation viscometer, and the formation of the liquid thread was investigated with a special apparatus. The effects of surfactant and salt (NaCl) concentration, the addition of fatty alcohol ethoxylates and alkyl polyglucosides as non-ionic surfactants and cocoamidopropyl betain as a zwitterionic surfactant, and also the influence of thickener on the network are studied. Further, FAES is substituted by another anionic, very mild surfactant, a carboxymethylated fatty alcohol ethoxylate (FAECM). FAES and also FAECM solutions in the presence of salt and non-ionic surfactants behave as Maxwell fluids; this changes when conventional polymers are added. The thread properties, in many eases, can be explained by the balance of viscosity and elasticity.