Quantification and prevention of hair damage

M. L. Tate; Y. K. Kamath; S. B. Ruetsch; H.-D. Weigmann

EVALUATION OF HAIR DAMAGE 353

354 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS FI(% 100- 20' (a) Unbleached 0.4 0.9 1 '3 118 212 DISTANCE ( mm ) FI(%) 1 2O 0 0.0 0.4 0.9 1.3 1.8 2.2 DISTANCE (mm ) FI(%) 100' (C) 6% H202, 4 h FI(%) 100 t 40' 20' (d) Bleach creme, 30 min o o.o 0.4 0.9 1.3 1.8 2,2 o. 0.4 0.9 1,3 1.8 2,2 DISTANCE (mm ) DISTANCE (mm ) Figure 3. Longitudinal fluorescence intensity scans of unbleached and bleached hair fibers treated with Rhodamine B. The wetting force is given by equation 1: F w = PCrzv COS0 a (1) where P is the fiber perimeter, Crzv the liquid surface tension, and 0a the advancing contact angle. The fiber perimeter is measured with hexadecane in a separate experi- ment, and the liquid surface tension is measured with a platinum wire. Work of adhesion, W, used in this work as an index of surface energy, is defined in the present context as the work required to separate a solid/liquid system at the interface: W = Crzv (1 + COS0a) (2) Figure 7 shows the effects of various oxidative treatments on the wettability of hair fibers. The repeated short time treatment in 6% H202 (2' X 10) and the bleach creme treatment are similar in their effects on water wettability, approaching surface energy levels close to that of the one hour treatment in 6% H202. The two minute bleach treatment repeated ten times has a total bleaching time of 20 minutes. Since the bleaching solution is most effective at the start of the bleaching treatment, and a fresh solution was used at each of the ten treatments, it seems reasonable that this sample would show greater change than one subjected to a single 30 minute bleach treatment. The bleach creme treated sample had a W value in agreement with other 9% H202

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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.

EVALUATION OF HAIR DAMAGE 353

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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.

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EVALUATION OF HAIR DAMAGE 355 FI (%) lOO 8O 6O 4O 2O Untr I h 4h Treatment Bleach creme Figure 4. Average fluorescence intensity for five each of longitudinally scanned unbleached and bleached fibers treated with Rhodamine B. treatments done in our labs under similar conditions. Although the surface of the hair shows a relatively low level of wettability, we have seen that damage to the fiber interior is more extensive than one might expect from the observed change in surface properties. We also studied the water wettability of unbleached and bleached hair permed one, two, and three times. In contrast to the increased wettability of bleached hair, after bleaching even repeated perm treatments did not produce a major increase in wettability. This observation was somewhat surprising since reductive scission of disulfide bonds leads to the formation of two hydrophilic sulfydryl groups that would be expected to produce an increase in the hydrophilicity of the hair fiber surface. In previous (8) studies of the effect of reduction without subsequent reoxidation (neutralization) on the wettability of hair, we observed that wettability increased rapidly and leveled off at W values of 85-90 mN/m. This difference from the previously observed behavior must be attributed to the fact that the neutralization step (3% H202) following the perming apparently leads to extensive reformation of the original disulfide bonds in the surface regions of the hair. Although bond reformation with peroxide is known not to be complete, the surface sulfydryl groups are the most accessible to reformation and would be the first and most easily affected. Structural changes Dye diffusion. The rate of dye transport in keratin fibers is strongly affected by the nature of the fiber structure. Any decrease in the disulfide crosslink density in the matrix and

356 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Untreated I h H202 4 h H202 Bleach creme, 30 min Figure 5. SEMs of bleached hair, showing cuticle damage, hole formation, and abrasion effects. introduction of highly hydrophilic sulfonic acid groups lead to an increase in swelling, and with it to higher transport rates. One way to characterize the effect of bleaching on hair structure is, therefore, to determine the change in diffusion of dyes into the hair fiber cross section. Diffusion studies were carried out using the strongly fluorescent molecule uranin, the sodium salt of fluorescein (CI Acid Yellow 73) shown in Figure 8. The following treatment conditions were evaluated: one hour and four hours in 6% H202 and 30 minutes with bleach creme. Figure 9 shows micrographs of the cross sections of the dyed fibers and the corresponding cross-sectional scans that were used for the calculation of diffusion coefficients. The ring dyeing of the cuticular region appears to be due to the rapid penetration of the dye solution into the intercellular ,regions or the endocuticular domains. Dye concen- tration profiles (which are not shown) in the cortex in the early stages of diffusion seem to indicate Fickian kinetics, as shown by the solutions of Fick's second equation for radial diffusion in a cylindrical geometry. A typical solution is given in equation 3 (11). The diffusion coefficients are calculated using the Bessel functions. Concentration- dependent coefficients will be obtained by this procedure however, in this case, the concentration dependence of the diffusion coefficients seems to be negligible.

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