J. Soc. Cosmet. Chem., 40, 205-214 (July/August 1989) Dyestaining and the removal of cationics from keratin: The structure and the influence of the washing anion C. ROBBINS, C. REICH, and J. CLARKE, Colgate Palmolive Co., 909 River Road, Piscataway, NJ 08854. Received February 24, 1989. Synopsis The Red-80 dye-staining procedure has been modified to help serve as a tool to study the removal of cationic surfactants from keratin surfaces. Results from this method and radiotracer studies demonstrate that monofunctional cationic surfactants are not completely removed from hair by washing with anionic detergents. Shorter chain length anionics are more efficient for removing cationics than longer chain length anionics. When washing hair with sodium lauryl sulfate, significantly more lauryl sulfate is left behind on hair previously treated with cationic detergent than on hair containing no cationic detergent. Lipid components of conditioning products (including fatty alcohols) adsorb onto hair along with cationic actives. The ratio of lipid/cationic adsorbed increases with the ratio of lipid/cationic in the formulation. Conditioner lipids, to a certain extent, facilitate removal of the cation from the substrate however, evi- dence also suggests that they participate in anionic detergent buildup on hair. Fully formulated conditioner products behave analogously to the binary systems containing cationic and lipid. Mechanisms are proposed to provide working models to help explain these results. INTRODUCTION In 1969, Scott, Barnhurst, and Robbins (1) described the use of a dye-staining proce- dure using Direct Fast Rubine W.S. dye to detect cationics on keratin substrates. In 1980, Crawford and Robbins (2) described the use of Red-80 dye to replace Rubine, because the latter dye is no longer being manufactured. This test is now widely used in the cosmetics industry as a rapid qualitative screening tool to detect cationics on keratin surfaces. Normally a cationic conditioner or solution containing a cationic ingredient is applied to either a hair or wool swatch, and after rinsing, dye solution is applied and the keratin is rinsed. If a cationic ingredient with a chain length of more than ten carbon atoms is on the swatch, it stains. If the swatch does not stain, the interpretation is that virtually no cationic is bound to the swatch. The objective of this work was to determine if the Red-80 staining procedure could be adapted to help study the removal of cationic/conditioning agents by anionic surfac- rants/shampoos. Thus, we have modified this dye-staining procedure by adding a wash step between application of the cationic and the dye. The new procedure is not intended to replace the former one, but it is intended to be used in conjunction with the former 205
206 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS procedure to complement it. This manuscript describes this new procedure and how varying the structure of the washing detergent influences staining and the interpreta- tion of the results. EXPERIMENTAL MATERIALS All sodium alkyl sulfate detergents were purchased from Eastman Kodak Co. and were greater than 96% pure. Ammonium lauryl sulfate (ALS)* and the alkyl ether sulfates were obtained as 30% aqueous solutions from Henkel Incorporated. Sodium deceth-2 sulfate (SDES) was obtained from Vista Chemical Corporation as a 30% aqueous solu- tion, and the alpha olefin sulfonate (AOS) detergents were obtained from the Witco Chemical Corporation as 30 to 60% aqueous solutions. Stearalkonium chloride (SAC) was used as Ammonyx 4002 from Onyx Chemical, and cetrimonium chloride (CTAC) was obtained as a 25% aqueous solution (Genamin CTAC) from American Hoechst. [•4C]SAC and CTAC were synthesized by Andrew Charig along with [35S]ALS and SDES. MODIFIED STAINING PROCEDURE Wet out under running tap water (approximately 100 degrees F) either two wool swatches (3) (3 X 4.5" and approximately 1 g each) or one 3-g blonde hair swatch (4) made from 8" hair. Apply 5 ml of 1 to 2% cationic or fully formulated conditioner and rub into the swatch for 60 seconds. Rinse under running tap water for 60 seconds. Wash the swatches with 5 ml of anionic detergent (5 to 20%) by working into a lather for 60 seconds. Rinse under the tap for 60 seconds. Immerse swatches into a small beaker containing 40 ml of 0.5% Red-80 (5) dye solution for 30 seconds. Rinse the swatches under the running tap for 30 seconds, and dry on a screen rack at room temperature. RADIOTRACER EXPERIMENTS The above-mentioned radiolabeled compounds were diluted with their non-radioactive counterparts to make final solutions of 1.7% CTAC in water, 5% ALS in water, and 1% SAC in 30:70 ethanol water. The final activities of the test solutions were 0.15 microcuries per ml for CTAC, 0.30 microcuries per ml for ALS, 0.30 microcuries per ml for SDES, and 0.075 microcuries per ml for SAC. Wool swatches were prepared for radiolabeling experiments by treating the swatches, which weighed roughly 1.5 g, with 3 ml of 20% triethanolammonium lauryl sulfate * Acronyms for surfactants used in this work: ALS, ammonium lauryl sulfate AOS, alpha olefin sulfonate CTAC, cetrimonium chloride SAC, stearalkonium chloride SDES, sodium deceth-2 sulfate SLS, sodium lauryl sulfate.
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