Difference between PEG-7 Glyceryl Cocoate and PEG-40 Hydrogenated Castor Oil Emulsifiers in Cream Formulation (HLB)

Subject: Re: Question about Surfactants (PEG-7 Glyceryl Cocoate and PEG-40 Hydrogenated Castor Oil)

Dear Myskin Team,

Thank you for your question regarding PEG-7 Glyceryl Cocoate and PEG-40 Hydrogenated Castor Oil. You are correct that both are non-ionic surfactants commonly used as emulsifiers in cosmetic formulations like creams.

The key difference when using them as primary vs. secondary emulsifiers lies in their HLB values and how they contribute to the overall emulsifier system's HLB.

1. What is HLB? HLB stands for Hydrophilic-Lipophilic Balance. It's a scale (typically 1-20) that indicates how much a surfactant "likes" water (hydrophilic) versus oil (lipophilic).

   • Lower HLB values (e.g., 1-8) indicate more oil-loving surfactants, often used for W/O (water-in-oil) emulsions.
   • Higher HLB values (e.g., 9-18) indicate more water-loving surfactants, often used for O/W (oil-in-water) emulsions.
   • PEG-7 Glyceryl Cocoate has an HLB of 11.
   • PEG-40 Hydrogenated Castor Oil has an HLB of 16.

2. Why use a blend? Different oil phases (the specific mix of oils, esters, etc., in a cream) require a specific "required HLB" to be effectively emulsified and remain stable. It's often difficult to find a single emulsifier with the exact required HLB. Therefore, formulators typically use a blend of two or more emulsifiers with different HLB values (one lower, one higher) to create an emulsifier system whose average HLB matches the required HLB of the oil phase.

3. Primary vs. Secondary: When you use PEG-40 (HLB=16) as the primary emulsifier and PEG-7 (HLB=11) as the secondary, it means you are using a larger proportion of PEG-40 than PEG-7. This results in an emulsifier blend with an average HLB closer to 16. Conversely, using PEG-7 as primary and PEG-40 as secondary means using a larger proportion of PEG-7, resulting in an average HLB closer to 11.

4. The Difference in Effect: The difference in outcome you observe in creams is due to this change in the effective HLB of the emulsifier system.

   • A blend with a higher average HLB (more PEG-40) is better suited for emulsifying oil phases that have a higher required HLB.
   • A blend with a lower average HLB (more PEG-7) is better suited for emulsifying oil phases that have a lower required HLB.

Using the correct emulsifier blend HLB that matches the oil phase's required HLB is crucial for creating a stable emulsion with the desired texture, appearance, and feel. If the HLB match is not optimal, the emulsion may be unstable (separate over time).

While PEG-40 is noted to be thicker, this physical property is generally a secondary consideration compared to the primary function of achieving the correct HLB balance for emulsification stability. The ratio of the two emulsifiers is primarily adjusted to fine-tune the HLB of the blend to match the specific oil phase.

In summary, the difference arises because changing the ratio of PEG-7 and PEG-40 changes the overall HLB of the emulsifier system, which in turn affects its ability to effectively emulsify the specific oil phase used in the cream formulation.

We hope this explanation is helpful!

Best regards,
Myskin Team