CHLORINATION OF HAIR AND pH 383 Table IV Effect of pH and Cycles of Chlorination on the Ratio of Knot Breaking-to-Fiber Tenacity (K/T) of Blond Hair Cycles pH K/T s* 0 10 0.575 0.055 7 O.6OO 0. 134 2 0.591 0.155 15 10 0.594 0.063 7 O.924 O.O77 2 O.796 0.07! 30 10 0.648 0.084 7 O.955 0. 148 2 0.850 0.122 * s = standard deviation for eight observations. tended, the crosslinked matrix offers resistance to the unfolding of the microfibrils (10b). Treatment with chlorine reduces the number of disulfide crosslinks in the matrix material, thus leading to a •lecrease in the force necessary to extend the fibers. The values of the ratio of knot breaking-to-fiber tenacity (K/T) of fibers tested under standard laboratory conditions are shown in Table IV. The values of K/T were generally affected by both pH and cycles of treatment. The effects of cycles at pH I0 and the effect of pH on control samples are not significant. At pH 2 and 7, increase in cycles from 0 to 15 resulted in a highly significant increase in the value of K/T. Increase in cycles beyond I5 produced little further change. Decrease in pH from I0 to 7 resulted in a significant increase in the"value of K/T, but further decrease in pH to 2 did not result in a significant change in K/T. The above results of the knot strength in chlori- nated fibers give no evidence of brittleness. Rather, the results indicate an increase in flexibility with chlorination at pH 7 and 2. Consequently, the harsh feel commonly associated with chlorinated hair may be attributed more appropriately to altered surface morphology and increased interfiber friction than to increased rigidity of the fibers. CONCLUSIONS This study has demonstrated that the effects of mild chlorination on various properties of human hair are dependent on the pH of the reaction medium. The two hair types, the natural blond and the dark brown, reacted similarly to the chlorination treatment. Acid chlorination produced the greatest and most rapid change in interfiber friction, surface morphology, weight loss, and the reduction in force required to extend wet fibers 20%. Chlorination at pH 7 produced a more gradual change in these properties, and alkaline chlorination produced little significant change. The results of this study generally agree well with the effects found from the chlorina- tion of wool in more highly concentrated solutions. Both systems produce similar changes in frictional properties, surface morphology, and wet tensile properties under acidic and neutral conditions. Under alkaline conditions, however, some dissimilarities exist. There was little apparent effect of chlorination in dilute alkaline solutions on the various fiber properties studied. This lack of effect could be the result of limited pene- tration of hypochlorite ions into the hair.

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