Suitability and Solubility of K940 Preservative in pH 3.5 Water-Based Lip Serum

Yes, K940 Preservative is suitable for a water-based lip serum with a pH of 3.5.

Here are the key considerations for using it in your formulation:

1. pH Stability

K940 Preservative is highly stable across a wide pH range, from pH 2 to 12. Your target pH of 3.5 is well within this range, ensuring the preservative remains effective and stable.

2. Solubility in Water-Based Formulas

K940 has limited solubility in water (approximately 0.75%). Since the recommended usage rate for effective preservation is 1.0% – 1.5%, you may find it difficult to dissolve completely in a purely water-based serum.

• Recommendation: To ensure it dissolves properly, it is highly recommended to pre-mix the preservative with a glycol before adding it to the water phase. Suitable options include Butylene Glycol or Propanediol.

3. Usage Guidelines

• Usage Rate: 0.5% – 2.5% (1.0% – 1.5% is generally sufficient for most formulas).
• Temperature: Add it to the formula when the temperature is below 80°C.
• Application: It is safe and effective for leave-on products like lip serums.

4. Important Note

Because lip serums are applied to a sensitive area and can be partially ingested, always ensure your final formulation undergoes a challenge test to confirm the preservative's efficacy in your specific recipe.

Recommended Ingredients to assist solubility:

• Butylene Glycol
• Propanediol (1,3-Propanediol)