Problems with thickening oil-in-water emulsions are generally caused by the presence of electrolytes in your formulation. Most oil-in-water emulsions use acrylate-based polymers as thickeners that are very sensitive to electrolytes. Acrylate-based polymers are swellable polymers that thicken through binding water by charge repulsion. Electrolytes dissipate the charge and reduce the thickening efficiency of the polymer.
- The easiest solution if you have <.5% electrolyte is to increase the concentration of thickener. If you need to use over 1-1.5% thickener to achieve your desired viscosity, you probably should consider a more salt tolerant thickener.
- Add a salt tolerant water-soluble thickener like Xanthan gum 1 to your current formulation (.1-.5%). Often you also get viscosity synergy when you combine a swellable and soluble polymer together.
- Ultrez 30 by Lubrizol (Carbomer) has significantly better electrolyte tolerance than other grades of Carbomer.
- Hydrophobically modified acrylate polymers generally have much better salt tolerance due to hydrophobe/hydrophobe interaction. SepiMax Zen by Seppic (Polyacrylate Crosspolymer-6) and Ultrez 21 by Lubrizol (Acrylates/C10-30 Alkyl Acrylate Crosspolymer) are good options to try.
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4 Responses to “Ask the Expert: What is your advice for thickening an oil-in-water emulsion?”
May I ask a question?
How can I have a fast absorbing moisturizing cream with long lasting feel?
I am just wondering that how can I thicken my soap based face wash
When are “hydrophobically modified acrylate polymers” added: post emulsion formation and cooldown? It seems like even gentle incorporation/stirring-in of the thickener after emulsification would reduce particle size too much. Should Xanthan be added before or after the acrylate polymers?
I would add the Xanthan first to make sure its hydrated before adding the acrylate polymer.
Thanks for reading!