394 JOURNAL OF COSMETIC SCIENCE A new test methodology has been developed to determine "Hair Moisturization/ Humidity Resistance." By measuring changes in hair elasticity with different equilib- rium period at a constant RH, we are able to evaluate the penetrating rates of moisture into hair fibers. Comparing the average ratios of hair elasticity of a set of hair fibers at 50% and 80% RH before and after cosmetic treatments, we can define and determine the "Hair Humidity Resistance Factor" (HHRF). EXPERIMENT AL MATERIALS Shampoo samples la. SH-1 Shampoo (formulation is listed in Table I) 1 b. SH-1 Shampoo with additional 1 % active Polyquaternium-70 (Croda Inc) le. SH-1 Shampoo with additional 0.5% active Guar Hydroxypropyltrimonium Chlo- ride (Hercules) ld. SH-1 Shampoo with additional 0.5% active Polyquaternium-67 (Dow) le. SH-1 Shampoo with 0.2% active Polyquaternium-10 (Dow) Hair samples. Virgin dark brown and naturally curly hairs were purchased from Inter- national Hair Importers, Inc., New York [Lab bleached hair (30 minutes and 60 minutes bleaching time)}. TEST METHODS Measurement of hair elasticity. Forces at 1 % extension of single hair fibers were measured using a Dia-Stron MTT-670 (Dia-Stron Limited, UK) attached with an Autosampler, which was placed in an environmentally controlled chamber with a constant temperature of 23°C and a fixed relative humidity. The cross-sectional area of each tested hair fiber was determined by a Laser Scanning Micrometer LSM-5000 (Mitutoyo, Japan) and the data were transferred into MTTWIN software for calculations of elasticity of each hair fiber. Image analysis. Hair tresses were placed in an environmentally controlled chamber at room temperature of 23°C and a fixed relative humidity for at least four hours for equilibration. Digital images of hair tresses were taken using a Sony DSC-717 digital camera. Table I SH-1 Shampoo Formulation Ingredient Sodium lauryl sulfate (30.0% active) Sodium loureth sulfate (30.0% active) Cocamidopropyl hydroxysultaine Cocamide DEA Propylene glycol (and diazolidinyl urea (and) methylparaben (and) propylparaben Deionized water Weight(%) 23.33 10.00 3.00 2.00 1.00 60.67

2006 TRI/PRINCETON CONFERENCE 395 RES UL TS AND DISCUSSION CORRELATION BETWEEN WATER GAIN PERCENT AND RH The water regain percent in hair samples was determined using a gravimetric method. Around 1.5 grams of hair sample were equilibrated at various RH levels for 8 hours and then weighed using an electronic analytical balance (precision 0.00001 gram) in a sealed weighing bottle. Plots of water gain (%) of hair samples vs. the environmental RH are presented in Figure 1. It is observed that the water regain percent of human hair increases with an increase in the environmental relative humidity (RH). The bleached hair showed more water regain than the virgin hair at the same level of RH and the water regain slightly increases with an increase in the bleaching time. This can be attributed to the increased hair hydrophilicity after oxidation. It is found that the hair water re- gain increases linearly with an increase in RH in the range of 40-85%, and the water regain increases more rapidly after 85% RH due to capillary condensation in the swollen fiber. CHANGE IN HAIR ELASTICITY It has been known that hair elasticity decreases with an increase in the environmental relative humidity. The plots of hair elasticity vs. environmental RH are presented in Figure 2. It is seen that the hair elasticity decreases linearly with an increase in the range of 50-80% RH and drops quickly after 80% RH. This is consistent with the results showed in Figure 1, which exhibits a rapid increase in water gain after 85% RH. Since the absorbed water molecules break and replace hydrogen bonding inside hair, which is responsible for approximately 50% of the hair elasticity. More water content inside hair, less hydrogen bonding between the coils of the alpha helix, smaller the elasticity of hair should be. 28 26 24 - 22 � C 20 ca 18 (!) ... a., 16 ca 14 12 10 8 40 -+-Virgin ......,_ Bleached (30') _._ Bleached (60') 45 50 55 60 65 70 75 RH(%) ------- 't --------�------ 80 85 90 95 100 Figure 1. Correlation between water gain and RH for human hair.