Troubleshooting Phase Separation in Water-in-Oil Emulsions

Subject: Troubleshooting Water-in-Oil Emulsions

Thank you for providing your formulations and details about the phase separation issue. It's common to face challenges when developing stable emulsions, especially Water-in-Oil (W/O) types, which can be more sensitive than Oil-in-Water (O/W).

Let's analyze each formula and suggest potential solutions.

General Principles for W/O Emulsion Stability:

• Emulsifier Selection & Concentration: The emulsifier must be suitable for W/O and used at an adequate concentration relative to the oil and water phases.
• Phase Ratio: W/O emulsions typically have a higher oil phase percentage. High internal (water) phase can be challenging.
• Presence of Electrolytes: Ingredients like Zinc Sulfate are electrolytes, which can destabilize emulsions by affecting the charge and interaction of dispersed droplets.
• Viscosity: Sufficient viscosity in the continuous (oil) phase or the dispersed (water) phase helps prevent droplet movement and coalescence.
• Processing: Proper mixing speed, duration, and cooling procedure are crucial.

Analysis and Recommendations:

Formula 1 (using POLYGLYCERYL-2 SESQUIOLEATE)

• Analysis:
  • POLYGLYCERYL-2 SESQUIOLEATE is a suitable W/O emulsifier.
  • The oil phase contains waxes (Bee wax, Cetyl palmitate) which help build structure.
  • The water phase is very high (approx. 82%) and contains a significant amount of Zinc Sulfate heptahydrate (5%).
  • The high internal water phase combined with a high electrolyte concentration is likely the main challenge for stability. The emulsifier concentration (4%) might be insufficient to stabilize this challenging system.
• Recommendations:
  1. Increase Emulsifier: Try increasing the concentration of POLYGLYCERYL-2 SESQUIOLEATE to 5-6%.
  2. Add Co-emulsifier/Stabilizer: Consider adding a co-emulsifier or stabilizer to enhance stability. This could be:
     • Adding a small amount of a W/O polymeric stabilizer or a wax that contributes to the oil phase structure.
     • Adding a gum or polymer to the water phase to increase its viscosity and help suspend the internal phase. Ensure it is compatible with electrolytes (e.g., certain modified starches, specific grades of Xanthan Gum or Carbomer designed for electrolytes).
  3. Review Zinc Sulfate Level: If possible, evaluate if the 5% Zinc Sulfate is strictly necessary. Lowering the electrolyte concentration would significantly improve stability.

Formula 2 (using Soy Lecithin)

• Analysis:
  • Soy Lecithin is a natural emulsifier but often requires co-emulsifiers for robust and stable emulsions, especially in systems with electrolytes or high oil loads.
  • The oil phase is high (70%), which is typical for W/O.
  • The water phase contains Zinc Sulfate (0.5%), though at a lower concentration than Formula 1.
  • Using Soy Lecithin as the sole emulsifier might not provide sufficient stability against coalescence and separation, particularly during cooling and storage.
• Recommendations:
  1. Add Co-emulsifier: Combine Soy Lecithin with a co-emulsifier to improve stability. Suitable options include fatty alcohols (like Cetyl Alcohol, Stearyl Alcohol) or waxes added to the oil phase, or another synthetic W/O emulsifier compatible with Lecithin.
  2. Add Thickener/Stabilizer: Incorporate a thickener into either the oil phase (e.g., a wax, oil gellant) or the water phase (e.g., a gum compatible with electrolytes) to increase viscosity and help maintain the emulsion structure.
  3. Processing: Ensure the heating and cooling process is optimized for Lecithin, which can be sensitive to prolonged high temperatures.

General Tips for Processing:

• Mixing: Use a high-shear mixer (e.g., homogenizer, high-speed stirrer) during the emulsification step when combining the heated oil and water phases. This creates small, uniform droplets.
• Cooling: Stir the emulsion continuously and moderately during the cooling phase until it reaches room temperature (below 30°C). This is critical for W/O emulsions as viscosity increases and the structure sets. Avoid vigorous stirring during cooling that could whip in air.

By adjusting the emulsifier system, potentially adding stabilizers/thickeners, and optimizing the processing technique, you should be able to improve the stability of your W/O emulsions. It's recommended to make small test batches when trying these modifications.