152 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table VII Dry and Wet Curvature Data on Different Hair Types/Treatments Single Fiber Tress Round Off Hair Type/Treatment C C C DRY WET " O-Oil * 0.0 0 O-SAC 1.55 + 0.60 No change 1.6 O-SLS 1.59 ñ .81 No change 1.6 O-Bleached 1.47 ñ .95 No change 1.5 Cau-Oil * 0.0 0 Cau- SAC 2.50 --- . 61 No change 2.5 Cau-SLS 2.74 q- .84 No change 2.7 Cau-Bleached 2.58 ñ 1.5 No change 2.6 KI-Oil 17.81 --- .8 18.32-• 17.8 KI-SAC 18.02 q- .62 -- 18.0 KI-SLS 18.10 ñ .66 17.36-• 18.1 KI-Bleached 18. l 1 ñ .74 -- 18.1 KII-Bleached 16.32 ñ 1.1 16.08-• 16.3 KII-SLS 16.08 ñ 2.2 16.55 q- 0.88:• 16.1 KII-SAC 15.82 ñ 1.4 -- 15.8 KII-Oil 15.96 + 1.8 16.08-• 16.0 •' KII-Bleach/Oil 15.88 ñ 1.6 16.43 ñ 0.48•: 15.9 r' O-SAC * 0 0 O-SLS * 0 0 O-Bleached * 0 0 Cau-SAC * 0 0 Cau- SLS * 0 0 Cau- Bleached * 0 0 KI-SAC (no rinse) -- 14.41.• 14.4 KI-SAC (rinse) -- 14.035 14.0 KI-SLS -- 14.78-• 14.8 KI-Bleached -- 14.38-• 14.4 * Visual inspection revealed obvious discrepancy between measurement in single fiber and actual curvature in tress which was virtually straight therefore C in single fibers not measured. In tress N goes to zero therefore C = O. -• Only L c measured in tress. N and Lr taken from single-fiber measurement. No change means only Lc of tresses measured and no significant difference between Lc in tress vs L c of fibers. For wet hair, curvature was visually different than dry hair (see Table VII). For wet O and Cau hair, the tresses were virtually straight due to high friction, weight of water, and cohesive forces of water in the capillary spaces between hairs. Therefore for these systems N = O and C = O (see Table VII). Water had less of an effect on the kinky hair however, the weight of water and interfiber forces did lengthen the relaxed hair. Therefore L c had to be estimated in tresses rather than from single hairs. For KI hair, N did not appear to change in the tresses compared to single hairs, although the ampli- tude and wavelength of the curls did change as noted by the differences in L c measure- ments of single hairs vs tresses. Therefore to adjust for curvature changes in wet kinky hair, L c was measured in the tresses, as indicated in the experimental section, and used to calculate C using N and L T from dry measurements on single hairs (see column labeled Tress C of Table VII). Fiber stiffness. Bending, stretching, and torsional stiffness are all involved in combing hair. However, if these three stiffness parameters are collinear or correlate with each

HAIR ASSEMBLY CHARACTERISTICS 15 3 other, then only one measurement is necessary to assess stiffness. For Caucasian hair, bending stiffness has been shown to correlate with stretching stiffness (16). It therefore seemed reasonable to consider only one stiffness parameter to test the relationship of single fiber properties to combing behavior. Our first attempt to measure fiber stiffness employed the hanging fiber method of Scott and Robbins (16). A few exploratory measurements with KI and KII hair indicated that this method would not work for kinky hair. The curvature was too great and the hair could not be straightened sufficiently to obtain a meaningful measurement with the weights ordinarily used. Heavier weights were tried, but the results were still unsatis- factory. A cantilever beam method was not tried because of similar anticipated diffi- culties with the high-curvature fibers. Scott and Robbins (16) have shown that the bending stiffness of human hair determined by the hanging fiber method correlates with Hookean slopes estimated from tensile measurements. Therefore, this approach to estimate stiffness from the initial part of load-extension curves was adopted to assess hair fiber stiffness. Table VIII summarizes stiffness data for fibers taken from tresses of SLS-treated and bleached hair of all hair types. The data shows highest stiffness values for O hair, the thickest hair, and lowest stiffness values for kinky hair, which is thinner than the O but thicker than the Cau hair. The kinky hair, however, was steam-set, which might de- crease its stretching resistance. Although all bleached hair samples are not significantly lower in stiffness than the corresponding unbleached hair (SLS), each sample is numeri- cally lower and there is a significant overall stiffness reduction by bleaching (17). The data of Table VIII also show lower stiffness values for wet vs dry hair, a well known fact demonstrated by others for stretching (18), bending (16), and torsional measure- ments (19). For the "surface treatments," namely SAC and the oil, we anticipated no changes in stiffness. Nevertheless, experiments were conducted to determine the stiffness effects of SAC and oil. The results of these experiments are summarized in Table IX. For each experiment, twenty hair fibers, from another lot of Oriental hair, were extended as indicated in the experimental section and separated into two equivalent groups. These calibrated hairs were then soaked in water for 1 hour and allowed to relax for 24 hours, then treated, and after drying, restretched except in the case of experiment II when the hairs were rewet for 1 hour and restretched. The data for each experiment were analyzed by Analysis of Covariance, indicating no significant treatment effects, i.e., no significant effect of SAC or oil on stiffness. There- fore the stiffness values for SAC and oil treatments used in the regression analysis were the corresponding values for the SLS-treated hair. The data of Table IX shows a significant increase in stiffness for the second stretching evaluation compared to the calibration. Apparently 1 hour in water and 24 hours at 60 q- 5% RH is not sufficient time to permit complete relaxation of the hair. Diameter. The data of Table X summarizes diameter measurements of the different hair types by linear density and microscopic methods. The diameter values determined by microscopy are higher than those obtained using the linear density method. This differ- ence may be an inherent difference in these two procedures, since the linear density method assumes circularity while the microscopic method averages diameter across the elliptical fibers.