DSC ANALYSIS OF HAIR IN WATER 225 c 4,6 0 ._• 4,4 It: 4,2 4,0 y = 4.55 - 0.069 x r = 0.91 o -' -*--.._ I ................... ,...,.. 0 1 2 3 4 5 6 7 8 Number of Bleachings Figure 4. Plot of/n(HXr•/) vs number of bleachings, according to the assumption of first-order denaturation kinetics. The linear regression line is shown as described by the equation on the graph. In the wet state, furthermore, the increase in the content of anionic groups induces an increase in water content. This leads to a continuous decrease of matrix viscosity and thus of To, in contrast to a less oxidative treatment such as perm-waving, where an expo- nential relationship is observed, as discussed below. In agreement with our results, Leroy et al. (13) observed a decrease in denaturation peak area through bleaching. This can be attributed to a loss of crystalline material, as observed by SAXS (small angle X-ray scattering) (16) or to a general decrease in native o•-helical material, which can be denatured (11). PERM-WAVING EFFECTS Figure 5 summarizes the results for the peak temperature and the denaturation enthalpy for the perm-waved samples in the form of a "box & whisker" plot. Data are given for the start material for this study and the once-bleached material. The latter material, considered as representing an average type of common hair damage, was submitted to the perm-waving treatments. With respect to the scaling of the x-axis of Figure 5, the first number, characterizing a treatment, gives the number of treatments and the second one the duration in minutes. 3 x 30 is thus a sample perm-waved three times for 30 min each. One notes a consistent decrease in T o as well as for AH D with increasing numbers of treatments. This is in agreement with common hairdressers' knowledge, that multiple permanent waving treatments are more effective than a single treatment of equivalent duration.

226 JOURNAL OF COSMETIC SCIENCE 160 (.,1 155 o ß - 150 ß ,-, 145 ,-, 140 E !- 135 0 130 :3 125 e 120 115 0 1 i i f i i i i start bleach lx10 lx20 lx30 3x10 3x20 3x30 5x10 5x20 5x30 16 14 12 I= 10 8 "' 6 ._o 4 ::3 2 Code for Hair Treatment Figure 5. Denaturation temperatures and enthalpies of the perm-waved samples as multiple "box & whisker" plot (see Figure 2). For the definition of codes see text. Vertical lines separate data groups that have undergone the same number of treatments. 18 = 14 a. 12 -= 10 4,-I LU 8 • 6 ß 2 0 1 10 115 120 125 130 135 140 145 150 155 160 Denaturation Temperature in øC Figure 6, Plot of AH o vs T o for the perm-waved samples, As a guide for the eye, an exponential fit (solid line) is drawn through the data,