The Thickening Agents used in Personal Care Applications

The requirements for thickeners are continuously increasing. Very mild formulations such as baby shampoo, baby wash, and facial wash, which contain generally a low amount of Sodium Laureth Sulfate, and furthermore often contain amino acid surfactant, are very difficult to be thickened. Also PEG-free formulations, which are becoming more and more popular, are difficult to be thickened as well. However, special applications are required a special flow behavior –which can be achieved by specific thickeners such as shampoo and shower gel.

The most common way to thicken a surfactant based formula is to use Sodium Chloride. In standard surfactant systems based on Sodium Laureth Sulfate (SLES) and Cocamidopropyl Betaine this works quite well. This thickening effect depends on the presence of an anionic surfactant (mostly SLES), and it works up to a concentration maximum. Gelling agents like Xanthan Gum, Cellulose types or Carbomer types,  can be used in any formula that contains a high level of water. In some cases they may be additionally required to achieve a yield point. Typical thickening agents for surfactant system can be divided into two groups:

• • Hydrophobic types, with low molecular weight
    These types mostly is non ionic surfactant, E.g. CDE K-82, Cocamide MEA and Eversoft AMCO, Polyglyceryl-3 Caprate, Glyceryl laurate and Isostearamide MIPA
    
    
  • Hydrophilic types, with high molecular weight
    These types are based on highly ethoxylated oleochemical derivatives. E.g. PEG 120 Methyl Glucose dioleate, PEG-N-Distearate (Sinopol 8KDS), PEG-7 Glyceryl Cocoate and Oxiflow S6800.These two types of thickeners provide two important differences in performance: the flow behavior and the temperature dependence of the viscosity.

1. Flow behavior

The hydrophobic thickeners provide a shear thinning flow behavior, that means the viscosity decreases with increasing shear rate. This can easily be observed by measuring the viscosity with a rotational viscometer at different speeds. The hydrophilic thickeners provide a Newtonian flow behavior, which means the viscosity is independent of the shear rate. It stays constant at different speeds.

2. Temperature dependence of the viscosity

The hydrophobic thickeners provide a decrease of the viscosity at lower temperatures, but mostly stable viscosity at higher temperatures. The hydrophilic thickeners provide a strong temperature dependence of the viscosity, at lower temperatures the viscosity increases significantly, while at higher temperatures the viscosity decreases dramatically. For example in making Head to toe wash for baby, since the Sinopol 8 KDS was heated in 60° C , the viscosity of the product might be still in liquid, but after we finished all the process, and cooling the product in room temperature, the viscosity will be increase and more viscous. The main task of a thickener for surfactant formulations is to increase the viscosity. However, in order to have a successful formulation, one should also consider the consumer perception importantly.