Bentonite is a rock composed of clay minerals formed by the alteration of minute glass particles that once were volcanic ash.The name is derived from Fort Benton in Wyoming where it was discovered. American pioneers moistened bentonite and used it to seal the roofs of their log cabins and silence squeaky wagon wheels. Meanwhile, American Indians found bentonite useful as a soap.
There are two types of bentonite, each with distinctly different properties. Sodium bentonite found in Wyoming and other western states absorbs large quantities of water, swells many times its original volume, and gives permanent suspensions with thixotropic characteristics. Calcium bentonites are non-swelling and break down to a granular substance that is used as an absorbent clay.The minerals of bentonite are mainly crystalline belonging to the montomorillonite group which is hydrous aluminum silicates containing iron, magnesium and other elements. It has many industrial uses such as oil well drilling fluids, sealants for canal walls, thickeners for lubricating greases and asphalt modifiers as well as in paper coatings and abrasives.
In the cosmetics industry, R.T. Vanderbilt, Norwalk, CT, sells a bentonite called Vanatural.It has the following uses and properties in cosmetic formulations:
• Stabilizes emulsions against separation (particularly at high temperatures);
• Prevents suspension particles from settling and coalescing;
• Gives thickening and absorptive properties in masks and poultices;
• Provides a silky, tackless feel in skin products;
• Is synergistic with xanthan gum and CMC;
• Reduces the slippery feel of gums and polymers; and
• Is compatible with most anionicand nonionic ingredients.
Vanatural is a white, free-flowing granule with a pH in water of 8.5-9.5. It disperses easily in water, but the rate of hydration is directly dependent on the mixing time, intensity and water temperature. An increase in all three conditions will speed the hydration rate. The recommendation is to disperse the material in hot water to become fully hydrated before other ingredients are added in order to avoid interference with the hydration process. Mixing the material at 75°C rather than 25°C will cut 10 minutes off the hydrating time.
Some examples of its use follow.
Skin Softening Cream
Glyceryl stearate SE9.0
C12-15 alkyl benzoate4.6
Procedure: While heating the water to 75°C, slowly add the Vanatural while mixing at maximum shear. When fully hydrated, add the butylene glycol. In a separate container, heat Part B to 75-80°C and add to water phase at 75°C. Cool and add preservative at 30°C or less.
The following formula is not heated.
Liquid Powder Foundation
Iron oxides (and) 0.40
Iron oxide (CI 77491) 0.10
Iron oxide (CI 77499) 0.03
Titanium dioxide (and) cellulose 3.50
Mica (and) cellulose4.00
Procedure: Slowly add the first two ingredients to the water agitated at the maximum shear. When fully hydrated, add the pentylene glycol. Blend Part B and add to A. Mix until smooth, then add last two items.