Analytical Method for the Determination of Oil Absorption Number of Cosmetic Powders, Pigments and Pearlescent Pigments

The objective of this study is to correlate the oil absorption of cosmetic powders, pigments and pearlescent pigments with a number applying an instrumental analytical method. Two different analytical instruments have been evaluated for the determination of oil absorption number as alternative of the current manual method. Technical parameters of each instrument, data provided and reproducibility of trials have been evaluated. Absorptometer “C”, data acquisition system provided by Brabender, results to be the right instrument to determine the oil absorption number.

Oil absorption number (OAN) is the measurement of the ability of powders to absorb liquids and in particular OAN of carbon black is already detected for use in the rubber industry according to ISO method 4656:2012 (en)(1). OAN data and oil absorbing analysis are crucial in the characterization of cosmetic pearlescent pigments, inorganic and organic colorants in order to design makeup products and guarantee the proper texture performances within an entire shades lineup.
Actually, a rigorous study of oil absorption with strictly accurate and reproducible results has not been widely applied in the cosmetic field.
In fact, the most commonly used method is manual and mainly based on the experience of the technician who visually evaluates the quantity of oil necessary to get a “saturated” powder. Texture gaps due to shade extensions of the same product and quality issues related to incoming raw materials batches rises the necessity of an analytical method to determine in an accurate and reproducible way oil absorption value of powders.

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