j. Soc. Cosmet. Chem., 38, 371-384 (November/December 1987) The chlorine-hair interaction. II. Effect of chlorination at varied pH levels on hair properties N. B. FAIR and B. S. GUPTA, University of Missouri-Columbia, Columbia, MO 65211 (N.B.F.), and North Carolina State University, Raleigh, NC 27695-8301 (B.S.G.). Received April 23, 1987. Synopsis The results of a study of the effect of chlorination at varied pH on selected physical properties of human hair fibers are presented. The hair was treated in 10 ppm chlorine solutions at either pH 2, 7, or 10 for durations of up to 30 hours. Acid chlorination produced the greatest and most rapid change in interfiber friction, surface morphology, weight loss, and the greatest reduction in the force required to extend wet fibers 20%. Chlorination at pH 7 produced a more gradual change in these properties. Alkaline chlorina- tion produced little significant change in the properties examined. INTRODUCTION A review of the literature (1) has provided an insight into the mechanisms by which chlorine affects wool and the general consequences of the reaction. It has also provided specific information on the changes that take place in some of the properties of wool during commercial shrinkproofing treatments involving this reagent. Although both wool and human hair are keratin fibers, when analyzing the effect of chlorine on the latter, in light of the published work on the former, it is important to consider the differences which exist between the two fibers. A wool fiber is generally smaller in diameter (10-30 Ixm) and is covered by cuticle cells which overlap singly. A human head hair is relatively thicker (60- 100 Ixm in diameter) and is covered by 6- 10 layers of overlapping cuticular cells. Additionally, human hair has a considerably higher cys- tine content than wool. Also important to consider are the differences that exist between the treatment condi- tions to which the two fibers are exposed, conditions of shrinkproofing in the case of wool and those of swimming in the case of hair. In shrinkproofing wool, the chlorine concentration is generally 2-4 percent (based on the weight of wool), the pH of the treatment solution is below 6, and reaction times are usually short (of the order of minutes) (2,3). Under these conditions, chlorination could be expected to be restricted essentially to the surface, with little effect expected on the cortex (4). On the other hand, in swimming pools, in which hair is exposed to chlorine, the conditions are much milder. The pH level of the water generally lies between 6 and 8, and the available 371

372 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS chlorine concentration is only about 0.5-2.5 ppm (5,6). However, the liquor-to-hair ratio is very large, the exposure times are long (of the order of hours), and the resultant damage to the hair can be significant if the effects are cumulative. Thus, although in both swimming and shrinkproofing, keratin is exposed to chlorine, the conditions under which this happens are widely different. Therefore, the results of chlorination found in wool, which were reviewed earlier (1), could not be taken directly to represent the behavior expected in human hair. Reported here are the results of a study in which human hair fibers were exposed to dilute concentrations of chlorine for extended periods of time. The hair fibers were treated with 10 ppm chlorine solutions adjusted to pH levels of 2, 7, and 10 for dura- tions of up to 30 hours. The concentration of 10 ppm was selected, being only slightly higher than concentrations found in swimming pools. The pH levels were chosen to correlate with conditions used in studies of the chlorination of wool. The effects of these treatments were examined on the surface morphology, interhair friction, weight loss, and tensile properties. The results obtained were compared with those generally found on wool and interpreted in light of the mechanisms proposed for the latter. MATERIALS AND METHODS SAMPLE PREPARATION Natural blond and dark brown Caucasian hair were used in this study, with samples prepared to suit the physical property being studied. For friction, morphological, and knot strength tests, both types of hair were mounted onto polytetrafluoroethylene frames and held in place with waterproof tape. The hair was aligned in an array so that each fiber was separate from its neighbor. The root ends of the fibers were mounted on the same end of the frame and clearly marked. For the measurement of weight loss, full-length blond hair fibers were wound into loops and secured with a separate hair fiber. The loops weighed between 6 and 12 mg. For the measurement of force required to extend fibers 20%, hair fibers were cemented onto acetate tabs using a gauge length of 2.5 cm. CHLORINATION PROCEDURE Solutions with chlorine concentrations of 10 ppm were prepared by dilution of a sodium hypochlorite solution with deionized water. The chlorine concentration was analyzed by iodometric analysis with KI and Na2S203. The pH level of the solutions was adjusted to 2, 7, and 10 with HC1 and NaOH. The treatments were carried out at room tempera- ture using a ratio of 2000 ml liquor to 1 g hair. Two chlorination procedures were used, one for the hair mounted on frames for friction, morphological, and knot strength tests, and the other for hair wound into loops or mounted onto tabs for weight loss or tensile tests, respectively. The hair mounted onto frames was subjected to 5, 10, 15, and 30 cycles of chlorination. Each cycle consisted of soaking the hair for one hour in the chlorine solution, rinsing in water, and drying it for 15 minutes in an air-circulating oven at 40-50øC. The samples for weight loss and tensile tests were subjected to 10, 20, and 30 cycles of treatment. Each cycle consisted