Phase Division and Mixing Order for Stearic Acid/TEA Lotion Formula

Formula Analysis and Texture Evaluation

Based on your formula, this is a classic Oil-in-Water (O/W) emulsion using a "soap-based" emulsification system (Stearic Acid neutralized by Triethanolamine).

Texture Analysis:

• Consistency: The combination of 4% Stearic Acid, 1.5% Glyceryl Stearate, and 0.5% Cetyl Alcohol will result in a medium-thick, creamy lotion.
• Skin Feel: Isopropyl Palmitate and Mineral Oil provide good spreadability and a smooth feel. Dimethicone helps reduce the "soaping effect" (white streaks when rubbing).
• Potential Issues:
  • Disodium EDTA (1.5%): This is extremely high. The standard usage rate is 0.1% - 0.2%. Excessive EDTA can cause skin irritation and may destabilize the emulsion.
  • pH Sensitivity: The Stearic Acid/TEA system is pH-dependent. It typically requires a pH of around 7.0–8.0 to remain stable. Adding Lactic Acid to lower the pH significantly (e.g., below 6.0) may cause the lotion to separate over time.

Recommended Phase Division and Addition Order

To ensure a stable and smooth lotion, follow these steps:

Phase A: Water Phase (Heat to 70-75°C)

1. Water (80%)
2. Glycerin (4%)
3. Disodium EDTA (Recommend reducing to 0.1-0.2%)
4. Niacinamide (2%)
5. Triethanolamine (0.8%) - Adding TEA to the water phase ensures immediate reaction with the Stearic Acid during mixing.

Phase B: Oil Phase (Heat to 70-75°C)

1. White Mineral Oil (4%)
2. Isopropyl Palmitate (2%)
3. Stearic Acid (4%)
4. Glyceryl Stearate (1.5%)
5. Cetyl Alcohol (0.5%)
6. Dimethicone (0.5%)

Phase C: Cool Down Phase (Add below 45°C)

1. Phenoxyethanol (0.8%)
2. Fragrance (0.05%)
3. Lactic Acid (0.05%) - Use only for minor pH adjustment. Monitor stability if the pH drops below 6.5.

Detailed Mixing Instructions

1. Prepare Phase A: Mix all ingredients in the water phase and heat to 70-75°C until everything is dissolved.
2. Prepare Phase B: Mix all ingredients in the oil phase and heat to 70-75°C until completely melted and clear.
3. Emulsification: While stirring Phase A (using a high-speed mixer or homogenizer), slowly pour Phase B into Phase A. Continue mixing for 5-10 minutes until a uniform white emulsion forms.
4. Cooling: Continue stirring gently as the mixture cools down.
5. Final Additions: Once the temperature drops below 45°C, add the ingredients in Phase C one by one, mixing well after each addition.
6. pH Check: The final pH should ideally be between 6.5 and 7.5 for this specific emulsifier system.

Suggestions for Improvement

• EDTA Adjustment: Definitely reduce Disodium EDTA to 0.1%.
• Modern Emulsifier: If you prefer a more stable lotion that works at a lower pH (pH 5.5), consider replacing the Stearic Acid/TEA system with a modern non-ionic emulsifier like Butter Cream Maker™ or Soft Cream Maker™, which are easier to use and provide a more luxurious skin feel.