543 CHARACTERIZATION OF BLEACHED HAIR linearly with increases in cysteic acid (R2=0.95). More specifically, the onsets to thermal denaturation/pyrolysis increased with increasing bleaching damage, where the 240 min bleached sample exhibited pyrolysis at 248°C, which was 11°C higher than demonstrated by the nonbleached fibers. Interestingly, E a magnitudes show a curvilinear correlation with Raman EDF, with a peak E a corresponding to 60–90 min bleaching. Hence, the energy barrier required to denature the IFKPs and pyrolyze the cortex was increased with minor increases in cortical ionic character. However, after 90 min of chemical bleaching, the E a barrier began decreasing. Finally, at 240 min of bleaching, where cystine bonds are lessened by 40−50%, the barrier to pyrolysis was nearly equivalent to that of unbleached hair (1). Comparing the E a and onset temperatures by MTGA to the Ozawa activation energy values and T D determined by HPDSC, the trends are generally disparate, where the E a values and temperatures to break ionic cross-links were lower when the fibers were heated under increasing pressure in excess water. For the virgin European dark brown fibers, the MTGA derived activation energy values for dry fibers (358 ± 6 kJ/mol) agree with published E a results (416 ± 8 kJ/mol) determined using the non-reversing signal in modulated DSC further, our E a results (251 ± 7 kJ/mol) from HPDSC also followed Wortmann’s results (263 ± 16 kJ/mol), where the E a for the untreated dry fibers was 43% higher than the results obtained in wet HPDSC studies (14). DVS OF BLEACHED FIBERS Modifying the cross-link density, hydrophilicity, and porosity of the hair fibers induces subtle changes to the water management properties of hair. For example, chemical bleaching cleaves structural lipids from the F-layer of the cuticle and oxidizes cystine cross- links throughout the fiber. Consequently, bleaching increases whole fiber cysteic acid salt concentrations with commensurate increases in whole fiber wettability. In dry environments, secondary structuring between complementary side chains in oxidized keratin is strong however, at higher humidity, water vapor solvates hydrogen bonds and ionic cross-links and accordingly influences the temporal dynamics of water vapor sorption. To establish connections between water-regain properties and cystine oxidation, Figures 15 and 22 together associate decreases in cross-link density (i.e., lower T D ) with greater steady-state moisture regains (R2=0.94). For convenience, Figure 22 includes the inversely proportional DVS (R2=0.94) and HPDSC (R2=0.92) results against the Raman 509/1003 cm−1 band Figure 21. Activation energy (± 8 kJ/mol) from MTGA studies as a function of Raman EDF. The values next to the Ea data are the MTGA pyrolysis extrapolated onset values, which are in units of ± 0.5°C.

544 JOURNAL OF COSMETIC SCIENCE area intensity. Noting that dm/dt control with hair fibers produces kinetical and not fully equilibrated outcomes, Figure 22 details the maximum regains for the bleached samples at 90% RH, where the maximum adsorption difference between virgin and the 240 min bleached sample was approximately 6% (w/w) (30). CONCLUDING REMARKS Several instrumental techniques were applied to monitor physicochemical changes in hair fibers resulting from repetitive bleaching treatments. FTIR imaging provided a 2D map of the cysteic acid composition across the volume of individual fiber cross-sections. By operating in transmission mode, FTIR imaging demonstrated a visual footprint of chemical damage caused by oxidative bleaching, including compositional and conformational modifications to the cuticular, cortical, and medullar components of the fiber, while leveraging all aspects of the mid-IR spectrum for the entire thickness of each discrete cross-section. FTIR-ATR and Raman spectroscopy were used to probe collections of hair cross-sections and whole fibers for average cysteic acid and cystine changes. Marrying the spectroscopic techniques presented a means to correlate spectra from individual pixels in the cortex of single cross- sections with average spectra from multiple cross-sections obtained from FTIR-ATR and Raman spectroscopy studies. Further, by simply glancing at the concatenated FTIR image, color changes in adjacent panels were used to qualitatively describe the spatial progress of timed chemical bleaching, whereas EDF indices from FTIR-ATR and Raman spectroscopy facilitated quantitative associations between global chemical changes and thermomechanical outcomes, including correlations with Fickian diffusion. Most striking, as shown in Figure 8, is the stark difference between cuticle and cortex EDF kinetics that have been elucidated with these experiments. Additionally, colorimetry and fluorescence spectroscopy were used to quantify hair tress color changes and to correlate oxidative tryptophan degradation with increased bleaching time. Thermal measurements, including HPDSC, dry DSC, TGA, and DVS provided supportive physical characterization of the bleaching process and allowed us to better resolve the effects of chemical bleaching on the amorphous and crystalline Figure 22. DVS maximum moisture regain (90% RH) and TD against normalized disulfide content (normalized Raman 509 cm−1 band area intensity).