HUMAN HAIR MOISTURIZATION WITH COSMETIC PRODUCTS 307 the sorption data in the entire humidity range, and especially in the 10–60% RH range which is most relevant to the effi cacy of cosmetic products. This is a result of small sample mass and small space where experimental conditions such as temperature and humidity can be maintained accurately. This suggests that a single S-D run on a sample may be adequate to obtain reliable data on a well-prepared sample of hair. Table I Moisture Sorption Da t a for S–D Isotherms in Figure 1 (n = 3) RH (%) Average regain % 95% Average regain % 95% sorption confi dence level desorption confi dence level 0 0 0 0.8 0.72 10 2.8 0.46 5.1 0.29 20 5.4 0.41 7.7 0.17 30 7.5 0.11 9.8 0.21 40 9.3 0.09 11.7 0.21 50 11.0 0.14 13.5 0.25 60 12.7 0.25 15.5 0.29 70 14.6 0.24 17.7 0.29 80 17.6 0.19 20.6 0.19 90 23.4 0.38 25.1 0.25 Figure 1 . Hair–water S–D isotherms for untreated hair. Expt.1: ¡ Expt. 2: o Expt. 3: x.
JOURNAL OF COSMETIC SCIENCE 308 EFFECT OF COND ITIONER ACTIVES ON HYSTERESIS Conditioner ac tives generally are cationic substances which interact strongly with nega- tively charged surface of hair. In this preliminary study, we have used three pure condi- tioning actives, i.e., Polymer JR-400 (Ucare Polymer JR-400, Dow Chemical, Piscataway, NJ), Jaguar C-17 (Rhodia, Bristol, PA), and Rhodaquat [cetyltrimethylammonium bro- mide (CETAB)]. Depending on their molecular weight, they can adsorb on the surface or penetrate into the hair (6). High molecular weight cationic actives such as polymer JR 400 and Jaguar C-17 essentially deposit on the negatively charged surface of hair and render it hydrophilic. The binding is strong enough to resist removal by simple rinsing (solubilization). On the other hand, low molecular weight cationic actives such as CETAB penetrate the hair in signifi cant amounts and also deposit on the surface of hair by form- ing salt links with the negative charges of cysteic acid groups, forming a monolayer of C-18 lipid chains and rendering the surface hydrophobic. Rinse-off formulations based on these actives had negligible effect that can be quantifi ed. This was viewed to be due to lack of deposition or penetration of actives. To ensure adeq uate deposition of the actives, a rather unconventional method of treat- ment (compared with normal rinse-off washing) was adopted. The actives were used on hair tresses in their pure form as 0.5% aqueous solutions at 50°C for 10 min followed by fi ve 1-min rinses with distilled water. This treatment was repeated 10 times, after which the tresses were air-dried at 65% RH and 21°C. About 20 mg of hair from each of the tresses was used in the sorption–desorption experiments as described earlier. The sorption– desorption isotherms of hair treated with these conditioners are shown in Figure 2. Figure 2. So r p tion–desorption isotherms of hair treated with different conditioners.
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