EFFECTS OF CHLORINE ON HAIR 237 Figure 5e. 20 cycles of chlorination at 50 pprn and pH 8, showing "against" scale rubbing. Figure 5g. 60 cycles of chlorination of 50 ppm and pH 8, showing "against" scale rubbing. scale structure more pronounced. This would accentuate the ratchet effect experienced in the "against" scale direction while not greatly affecting the "with" scale friction. An important property of visoelastic fibers is that, under suitable conditions of testing, they produce a stick-slip profile. The effect of a treatment on frictional behavior may appear more sensitively in the nature of this trace than in the average values of the parameters. A typical example illustrating this is included in Figure 4 The difference in

238 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS stick-slip generally increased with an increase in the number of chlorination cycles. Similar results were found with an increase in chlorine concentration. Since all friction tests were carried out at a constant speed of traverse, the load traces reflect a change in the state of the surface. This change involves a transition from a hard and elastic surface of the control and the less severely chlorinated specimens to a softened and plastic surface of the more severely chlorinated specimens. Similar results have been reported in chlorination of wool keratin (7-10). Disulfide bond scission and peptide link cleavage (11) described for the chemical attack of wool keratin would also be expected to occur in hair keratin, with consequent softening of the fiber surface. The transition from hard elastic to soft plastic surface is verified by examination of surface morphology of friction tested samples in the scanning electron microscope (Figures 5a-5g). The specific areas on the fiber surfaces examined were those in which fibers had actually rubbed during friction tests. The 60 cycle control sample (Figure 5a) still has a definite scale structure and the damage due to the friction test is minimal. With the samples subjected to chlorination at 10 ppm, the transition from hard to soft surface is gradual. After 20 cycles of chlorination at 10 ppm, the stick-slip profiles in the "with" scale direction are still essentially straight (Figure 4), although the average values of friction (Table II) are significantly higher than those of control samples. When viewed under SEM, the samples are still found to have a scaly surface (Figure 5b), although somewhat muted and the depth of deformation due to friction still shallow. At 60 cycles of chlorination treatment at 10 ppm (Figure 5c), the fibers exhibit a greater damage with friction as well as a generally more highly altered surface. In the 20 cycles, 50 ppm samples (Figures 5d and e), however, the scale structure has lost its character, and the surface has been equally deformed by the friction tests in both the "with" and the "against" scale directions. At 60 cycles of treatment with 50 ppm chlorine solution (Figures 5f and g), the fiber surfaces have apparently lost all scale definition. The bulk deformation due to rubbing on fiber surfaces is found to be very similar in both Table III Effect of pH and Number of Cycles at a Constant ppm of 50 on Values of Friction "With" Scale "Against" Scale DFE (Static) Cycles pH 3t, 3tk 3rs 3tk 3ta - 3tw 10 20 8 0.181 0.175 0.246 0.226 0.065 (.0124)* (.0123) (.0076) (.0050) 8 0.226 0.226 0.283 0.283 0.057 (.0251) (.0251) (.0223) (.0226) 4 0.336 0.336 0.375 0.367 0.039 (.0166) (.0170) (.0231) (.0113) 2 0.374 0.359 0.401 0.374 0.027 (.0171) (.0119) (.0278) (.0062) 8 0.341 0.337 0.357 0.346 0.016 (.0341) (.0315) (.0076) (.0112) 4 0.360 0.358 0.390 0.386 0.030 (.0188) (.0187) (.0202) (.0186) 2 0.399 0.367 0.409 0.358 0.010 (.0197) (.0069) (.0385) (.0196) *Values in parentheses are standard deviations for n = 5.