EVALUATION OF HAIR DAMAGE 351 Evaluation of fiber structure Dye diffusion studies. The diffusion behavior of a fluorescent dye into hair fiber cross sections was measured using microfluorometry. The samples were treated for 3-5.5 hours at 50øC in 0.1% uranin solution, rinsed, dried, embedded and cured, microtomed to 10 •m thickness, and scanned cross-sectionally at a wavelength of 540 nm, using an excitation wavelength range of 450-495 nm. Amino acid analysis. The amino acid analysis was performed by Wella, AG, Darmstadt, on the untreated and bleached samples prepared at TRI/Princeton. Hair samples were hydrolyzed with 6 N HCI at 110øC for 24 hours. After multiple evaporations to dryness until the solution became neutral, a 5 •1 aliquot was withdrawn for derivatization. A pre-column derivatization method reported by Bidlingmeyer et al. (9) was used. A 5 aliquot was finally injected into the chromatograph. A programmed elution procedure with variable mixtures was used for optimum separation. Mechanicalproperties. Wet mechanical properties of single fibers were determined with an Instron tensile tester at a rate of extension of 40% per minute. Cross-sectional areas were assessed by use of an electronic vibroscope. Fatigue behavior. Constant load fatiguing was carried out on an apparatus that accom- modates 40 fibers in an impact-loading mode of fatiguing. The fatigue apparatus was described by Kamath et al. (10). Each 3 cm long fiber is mounted on a hook that is adjustable for fiber creep during the fatiguing procedure. A weight of 40 g is attached to the lower end of the fiber. The lower platform oscillates at approximately one cycle per second, and the fibers were fatigued for 100,000 cycles at 65% RH and 2 IøC. The weights mounted on the fibers clear the lower platform at its lowest position, thereby impact-loading the fibers. Each of the 40 positions has a microswitch counter that stops when the fiber fails. The conditions were the same for the bleached, permed, and groomed hair studies. A sample size of 60 replicates was used in each case. This type of fatiguing is known as constant load fatiguing rather than constant strain fatiguing. Strain levels in these measurements were well within the Hookean range. RESULTS AND DISCUSSION PRIMARY DAMAGE IN BLEACHED AND PERMED HAIR Surface changes Fiber surfaces of bleached hair were studied by microfluorometry and SEM. Wettability measurements were made on bleached hair and also on permed samples. Microfluorometry. Previous work with the fluorescent tracer Rhodamine B (CI Basic Violet 10) suggested that this compound would be suitable for exploring aspects of oxidative damage of the fiber surface and the cuticular region. Rhodamine B is a cationic dye that would be expected to show interactions with the sulfonic acid groups produced by oxidative treatments of hair the dye structure is shown in Figure 1. Longitudinal views of characteristic filaments of the four bleach treatments with Rhodamine B are shown in Figure 2. Rhodamine B deposited at the scale edges of unbleached hair (Figure 2a), with the possibility of some slight penetration into either the endocuticle or the intercuticular cell membrane. Oxidation for one hour (Figure 2b)

352 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS HsC • (•)• C 2H 5 2j N • O• HsC2 Calls O COOH Rhodamine B Figure 1. Structure ooe Rhodamine B. produced a significant increase in scale penetration and scale face deposition. This is much more pronounced after four hours of bleaching (Figure 2c), where the scale face appears to be extensively marked by the tracer. In the 30 minute bleach creme treat- ment, the scale faces show slightly less fluorescence intensity (FI) than in the four hour peroxide treatment. In order to quantify this behavior, longitudinal scans of fluorescence intensity were made along 2.2 mm of fiber surface, as seen in Figure 3. Fluorescence intensity levels were quite uniform in all samples. The outlining of scale edges in the untreated and the one hour hydrogen peroxide treated, and the extensive scale penetration, as shown for the four hour treated fiber, are clearly noticeable. In Figure 4, average values of fluorescence intensity show a considerable increase as a result of oxidative damage. In general, the fluorescence intensity increased with increas- ing peroxide treatment times, and a major level of oxidative surface damage occurred already within one hour. The 30 minute bleach creme treatment produced essentially the same level of oxidative surface damage as the four hour 6% H202 treatment. Scanning electron microscopy. When viewed by SEM, untreated and bleached hair showed a variety of features in their surface topography, as seen in Figure 5. Besides the normal cuticles of untreated fibers, loose and broken-off cuticle edges were observed. Fibers of all four categories displayed cuticles with holes in them, although hole formation was most extensive in bleached hair. Erosion of the cuticle face was observed after the four hour bleach treatment prior to subsequent combing. The bleach creme treatment produced the least topographical damage among the bleaching conditions we investi- gated. Wettability. The surface of intact untreated hair is dominated by the hydrophobic epicuticle, while bleaching produces a hydrophilic hair fiber surface. Figure 6 illustrates the factors involved in solid-liquid interactions. A hydrophilic fiber (a) shows a low contact angle (0) with a hydrophilic liquid such as water, which has a surface tension CrLV of --72 mN/m. This results in a concave meniscus at the fiber-liquid contact line and a positive wetting force, F w. A hydrophobic fiber (b), such as the root end of an untreated hair fiber, forms an obtuse contact angle with water, resulting in a convex meniscus and a corresponding negative wetting force.