396 JOURNAL OF COSMETIC SCIENCE 100.00 � 90.00 ·u 80.00 70.00 w - 60.00 a, -.-virgin Hair 50.00 a, -II-Bleached Hair 40.00 50.00 60.00 70.00 80.00 90.00 100.00 RH(%) Figure 2. Percent changes in Young's modulus of human hair with RH. Combining Figures 1 and 2, we find that the differences in hair elasticity at 50% and 80% RH can provide information about the change in water contents inside hair fiber. Larger the difference, more sensitive to the environmental RH the hair sample is. Smaller the difference, more resistant to the environmental RH the hair sample should be. Comparing these differences before and after cosmetic treatments on the same hair sample, we are able to evaluate effects of cosmetic treatments on hair water ad- sorption behavior-improvement in humidity resistance or enhancement in hair mois- turization. EFFECTS OF COSMETIC TREATMENTS ON HAIR ELASTICITY Cosmetic treatments usually modify the hair surface and sometimes hair cortex as well. A lot of cosmetic treatments make hair more hydrophilic and improve hair moisturi- zation-more water regain under the same RH than that before the treatment. Some cosmetic treatments make hair more hydrophobic and improve hair humidity re- sistance-less water regain under the same RH than that before the treatment. Few treatments may not show any significant effects on hair water adsorption be- havior. Typical force-extension curves of a single fiber at 50% and 80% RH, respectively, before and after a treatment with a personal care formula containing hydrolyzed wheat protein are presented in Figure 3. It can be seen that at 50% RH, the slope of the line, which corresponds to the hair elasticity, E(50), decreased from 18.35 to 16.49 after the treat- ment. The lower E(50) value of the treated hair fiber indicated higher water content inside the hair compared to that of the same fiber before the treatment. This suggests that the treatment protected the hair fiber from loss of moisture under 50% RH. It is also found that at high RH of 80%, hair elasticity, E(S0) increased from 10.05 to 12.87 after the treatment. This implied that the treated hair fiber absorbed less water under 80% RH compared to that of the same untreated hair fiber, and the treatment protected the hair from gain of moisture under high humidity. The differences in elasticity of the

20 18 16 14 iii 12 � 10 8 6 4 2 0 0 2006 TRI/PRINCETON CONFERENCE • RH 50 RH 80 A RH 50T , RH 80T 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Extension (%) 397 !Y = 10.047x + 0.3811 [ 0.8 0.9 Figure 3. Change in Young's modulus of a hair fiber after a cosmetic treatment. hair fiber at 50% and 80% RH were 7.85 (18.35-10.05) before the treatment and 3.62 (16.49-12.87) after the treatment, respectively. This difference was reduced after the treatment, and it indicated that the treatment improved hair moisture balance and provided hair humidity resistance. It is assumed that the determined difference in hair elasticity under the same RH at a fixed equilibrium time period (from 15 minutes to 4 hours) before and after cosmetic treatments is mainly attributed to the change in hair moisture content. Therefore, by comparing differences between the average hair elasticity at 50% and 80% RH before and after cosmetic treatments, we are able to evaluate effects of cosmetic treatments on the hair: hair moisturization or hair humidity resistance (anti-frizz). If the average difference between hair elasticity at 50% and 80% RH increases after a cosmetic treat- ment, this indicates that the difference in moisture contents inside hair fibers becomes larger, and the cosmetic treatment enhances hair moisturization. If the difference be- tween hair elasticity at 50% and 80% RH decreases after a cosmetic treatment, it implies that the difference in moisture contents inside hair fibers turns smaller, and the cosmetic treatment improves hair humidity resistance. We may use another way to measure these changes in hair elasticity. As seen in Figure 3, the remaining percent (ratio) of hair elasticity (the slope of the force-extension curve) at 80% RH to the one of the same hair fiber at 50% RH (10.5/18.35 = 57.2%) was greatly reduced after the cosmetic treatment (12.87/16.49 = 78.0%). The value of this ratio reflects the effect of the environmental RH on hair elasticity at a fixed equilibrium time period. Higher the ratio, less effect of the environmental RH on hair elasticity, and better the humidity resistance. Lower the ratio, stronger effect of environmental RH on hair elasticity, and easier the hair moisturization. Therefore, comparing these ratios of hair elasticity at 50% to that at 80% RH before and after cosmetic treatments of hair samples, we are able to evaluate the effects of cosmetic treatments on hair water ad- sorption behavior-Hair Humidity Resistance/Moisturization