“Ionic, or non-ionic Emulsifying Waxes… that is the question”
Many cream and ointment formulations include emulsifying wax as a fundamental component. The ability of the product to allow mixtures of oils, waxes and water to be blended into a coherent, stable product makes emulsifying waxes very versatile raw materials.
Emulsifying waxes are predominantly long chain fatty alcohols (16 and 18 Carbons long) with a surfactant to provide the ‘bridge’ between the waxy fatty alcohol and water. Emulsifying Wax BP and Cetostearyl Alcohol Emulsifying (Type B) EP both use Sodium Lauryl Sulfate as the surfactant. This is a highly effective surfactant and therefore not much is needed (minimum 8.7% and 7% respectively) to provide the necessary emulsifying effect, however there are possible downsides to the use of such an efficient ionic type of surfactant. Some formulators believe that Sodium Lauryl Sulfate can result in skin sensitisation and potential irritation, especially when finished products made using this type of emulsifying wax are applied to damaged skin areas such as burns.
There are alternative surfactants which are suitable for use in emulsifying waxes and these are generally much less ‘potent’ than Sodium Lauryl Sulfate. Surfactants work by combining a highly charged end of a molecule which is attracted to water, with a very low charge ‘backbone’, which has an affinity to oils and waxes. The combination of these properties allows oils or waxes to be dispersed in water. Anionic, Sodium based surfactants use the Sodium metal ion to provide a very concentrated area of charge, whereas non-ionic surfactants use the charge developed by hydrogen bonds in the molecule to give the necessary hydrophilic quality. Hydrogen bonds do not result in any free ions, and are therefore ‘non-ionic’. This type of surfactant is less effective, but more gentle in character, the result is that greater quantities of the surfactant are required to give the necessary stability to the finished cream or ointment. Non-ionic surfactant levels are often around 20% of the formulation of the emulsifying wax.
Non-ionic surfactants used include ethoxylated alcohols (Cetomacrogol), polyethylene glycol (PEG) esters and polysorbate (60) esters. Kerax Ltd offers a whole range of emulsifying waxes which include the ionic, SLS based EP and BP grades with the recent addition to our portfolio of Cetomacrogol EP and Polysorbate 60 USNF.
For further information on the portfolio of Emulsifying waxes available from Kerax contact Clare Tighe or Adrian Fisk on +44 (0) 1257 237 350.