Thickening Pearlescent Liquid Soap (pH 9): HEC vs. HPMC

For increasing the viscosity of a pearlescent liquid soap base with a pH of approximately 9, such as COS NNP, HPMC (Hydroxypropyl Methylcellulose) is highly recommended over HEC (Hydroxyethyl Cellulose) for several technical reasons:

Why HPMC is the Better Choice:

1. Superior pH Stability: HPMC is stable across a broad pH range (typically 3-11). Since your base is at pH 9, HPMC remains highly stable. In contrast, HEC is generally stable up to pH 9, which puts it at its functional limit in your formulation.
2. Foam Stabilization: Unlike HEC, which only provides thickness, HPMC acts as a foam booster and stabilizer. This is a significant advantage for liquid soaps, as it helps create a richer, longer-lasting lather.
3. Ease of Use (ColdMix™): Certain types of HPMC are specifically designed to dissolve at room temperature when the pH is alkaline (above 8.5). Since your base is already pH 9, these versions will thicken the formula easily without requiring heat.

Recommended Products:

• Hydroxypropyl Methylcellulose (HPMC ColdMix™, 12000cP): This is the most convenient option for your base. It can be dispersed in water at room temperature and will thicken once it encounters the alkaline environment (pH 9) of your soap base.
• Hydroxypropyl Methylcellulose (HPMC, 5000cP, 68C Gel): A standard high-quality HPMC that provides excellent viscosity and foam enhancement, though it requires a hot-water dispersion method.

Mixing Instructions:

• For ColdMix™: Disperse the powder in a portion of water at room temperature (it will look cloudy initially). Add this dispersion to your soap base. Because the base is pH 9, the HPMC will begin to hydrate and thicken the mixture into a clear, viscous gel.
• For Standard HPMC: Disperse the powder in hot water (80-90°C). Once dispersed, add this to the rest of the cool formulation. The decrease in temperature will cause the HPMC to hydrate and form a gel.

You can browse more options in the Cosmetics > Base / Emulsifier > Thickener / Gel-Maker > Water Gel > Cellulose > HPMC category.