INTERACTION BETWEEN HAIR PROTEIN AND ORGANIC ACID 141 for 30 sec, then naturally dried. For control samples, the hair was also treated with deionized water or an aqueous solution of 0.001 N HCl/BOE (10%)/ethanol (15%) in the same manner. CURL RETENTION MEASUREMENT IN HIGH HUMIDITY Single fibers (ca. 10-cm long) were wound around glass rods (10 mm p) under a constant tension by pending a small weight at the tip end of the fibers. The samples were then wetted with a small amount of water and blow-dried. After storage under ambient conditions (ca. 25°C, 30% RH) overnight, the hair fibers were removed from the rods. All of the hair fibers were water set in the shape of the glass rods, taking the appearance of "springs." By being cut at one side of the spring, some single fibers, having an almost round shape, were obtained. About ten curls were obtained from five hair fibers. Their shape was recorded by a digital camera, and they were kept in a glove box controlled at 26°C, 90% RH. The fibers' shape was again recorded at time t: the time left in the box. After repeating series of the process above, the radii of the curvature of the hair fibers at t, R n were measured and the hair set index, 5/Rl' where 5 is the radius of the glass rod in millimeters, was calculated. Since most of the hairs were not completely straight, the corrected hair set index was calculated according to the following equation (1) Here, R' is the radius of curvature of the hair fiber after being immersed into water, followed by natural drying. NIR SPECTROSCOPY NIR spectra were measured with a Y okogawa Infra Spec NR800 spectrometer. A total of 1024 scans were accumulated at an 8 cm- 1 resolution for each measurement. The cell of the NIR was set under dry nitrogen atmosphere at 25°C. Hair samples, untreated and treated by an aqueous solution of MA/BOE/ethanol for 20, 40, and 60 min, were dried under vacuum overnight before the NIR measurement. The NIR spectra obtained were subjected to smoothing, baseline correction, and inten- sity correction before further analysis. For the data processing, Grams software (Thermo Electron Corp.) was used. GENERALIZED 2D CORRELATION SPECTROSCOPY The mathematical background for 2D correlation spectroscopy has been described in detail by Noda (12). For the generalized 2D correlation analysis, we used a program named 2D POCHA composed by D. Adachi (Kwansei-Gakuin University). RES UL TS AND DISCUSSION HAIR-SET DURABILITY Figure 1 shows the results of the curl retention measurement for untreated hairs and for those treated with aqueous solutions of MA/BOE/ethanol or HCl/BOE/ethanol. For the

142 JOURNAL OF COSMETIC SCIENCE 0.9 0.8 0.7 .... 0.6 - 0.5 a: -... LO 0.4 - 0.3 0.2 0.1 0 0 5 10 15 t I min Figure 1. Change of the corrected hair-set index plotted against the time left, t, in the box controlled at 26 ° C, 90% RH. 0: untreated. L,., □, e: treated by an aqueous solution of malic acid (MA)/ benzyloxyethanol (BOE)/ethanol for 20, 40, and 60 min, respectively. ♦: treated by an aqueous solution of HO/BOE/ethanol for 60 min. untreated hair, the initial curl set rapidly relaxed and returned to the original, almost straight, shape. Such change is seen as a rapid decrease of the hair set index in Figure 1. This means that the water set of hair is broken. For the MA/BOE/ethanol-treated hairs, the set durability improved with treatment time. It is again worth noting that this measurement was done on single fibers, not on a hair bundle. This suggests that the durability improvement comes from changes in the internal properties of the hair fiber. In Figure 1 the result for the HCl/BOE/ethanol-treated hair is also plotted, showing that setting durability did not improve. This means that the improvement of the set dura- bility comes from MA, not from BOE. NIR SPECTRUM OF THE UNTREATED HAIR Figure 2 displays an NIR spectrum from 7000 to 4000 cm- 1 of the untreated hair after smoothing and baseline correction. Five main bands are observed. Three bands in the regions of 6800-6400 cm-1, 6000-5600 cm,- 1 and 4950--4750 cm- 1 have been as- signed to be a first overtone of NH stretching, first overtones of CH stretching for CH2 and CH 3 groups, and a combination of NH stretching and amide II, respectively (9,10). The band in the 4700-4500 cm- 1 region has two possibilities (10): one is due to the combination of NH stretching and amide III, and the other is due to the ternary