Peer-reviewed Cosmetics & Toiletries article by Tagra R&D on encapsulated iron oxide pigments that release color only when rubbed: stability, color strength and dust safety.
Under Pressure: Color Release Microcapsules for Dynamic Product Dimensions
By Shaher Dochi, Ph.D. and Danny Goldstein, Ph.D., Tagra Biotechnologies. Peer-reviewed article published in Cosmetics & Toiletries, Vol. 137, No. 3, March 2022. Reprinted with permission.
The Challenge
Inorganic pigments such as iron oxides and titanium dioxide don't dissolve in formulations, so they are hard to disperse evenly. Poor dispersion weakens color strength and gloss, changes rheology and destabilizes the product. Today's fixes, mostly surface coatings and treatments, can bring their own problems: color shift, incompatibility with the base formula, poor adhesion to skin, and safety or environmental concerns from silicones, solvents and reactive coatings.
Tagra's Approach
Tagra encapsulates a blend of brown iron oxides inside a shell of bio-based, biodegradable cellulose acetate and titanium dioxide, using its solvent-extraction microencapsulation process (done twice for a double encapsulation). The result is Cameleon CelluBrown: a light gray, free-flowing powder that hides the pigment until the consumer rubs the product onto skin, when the color is released.
Key Findings
Capsules: spherical, about 150µm on average, fully coated, and surviving the mixing, filling and pumping of production.
Flow: an angle of repose of 25.5°, rated excellent, while the free pigment showed no flow at all.
Color strength: after rubbing, color strength equaled or beat free pigment at the same concentration (10,110% vs 9,642% WSUM).
Stability: after three months at 40°C in O/W and W/O creams, capsules stayed intact, with no color leakage, no phase separation and no change in color (ΔE* < 1).
Safety: the respirable dust fraction was 0.19%, a safe value, giving a better safety profile than non-encapsulated iron oxide and titanium dioxide.
How to Formulate
No special production line is needed. Add the microcapsules gradually in the last stage of formulation with a paddle mixer, up to 40°C. There is no need to grind or pre-disperse pigments. The capsules work in O/W and W/O creams, lotions, silicone-based formulas, water gels, lipsticks and pressed powders, for color-change effects in makeup and skin care alike.
Download the Full Article
The complete article, with methods, figures and references, is available as a PDF below. See the full range in the CameleonCaps™ brochure.
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