Compatibility of personal care thickening polymers in sulphate-free surfactants

Formulators today know that when traditional surfactants and polymers are replaced new problems occur. What was before a 'thickening problem' becomes a 'miscibility problem': the ingredients do not play well with each other anymore. However, the scientific rules are not different for these systems, which can also be understood and controlled. This study was therefore made, focusing on one of the important challenges, namely the phase separation and miscibility problem of polymers and surfactants in aqueous solution in ratios and concentrations of interest as shampoo chassis. There are three main reasons for these problems: (1) Impurities and variability from raw materials, (2) by-products or excess components and (3) high levels of background salt remaining from processing. In this work, the third factor has been investigated to learn when salts should be reduced or counteracted depending on the polymer type used for enabling thickening in the new formula spaces. Thus, the study is fundamental in nature but aims to facilitate communication with suppliers of both surfactants and polymers as well as with colleague formulators. It aims at an increased holistic approach where all ingredients are acknowledged constituents of the system, and even minor additions of simple salts are noted as relevant variables to control to maximize product performance.

Visual characterization of phase behaviour and viscosity assessment has been performed where three polymers have been combined with two different sulphate-free surfactants. Emphasis has been put on the effect of background salts.

The levels of background salts affect both viscosity and compatibility of the systems investigated, however, to different extents depending on the nature of the materials. It is therefore important to control the levels of salt (often included in the raw materials), and how this affects the nature of the polymer-surfactant interactions, to reach the desired formulation attributes.

While prior knowledge based on classical aqueous polymer-surfactant systems was seen to be valid also for newer sulphate-free systems (as long as the salt concentration could be controlled), fully compatible mixtures where viscosity and surfactant concentrations truly meet the levels desired for the end formulation proved difficult to find.