HAIR STRAIGHTENING USING AN AUTOMATED FLAT IRON 131 temperature exceeded 150°C. Disulfi de bond scissions facilitated the keratin denaturation, as suggested by Istrade (14). Therefore, the straightening occurred more rapidly at 175°C than at lower temperatures. Interestingly, at low temperature, provided the fi bers were held straight multiple times, change in the microfi lament organization (decrease of bire- fringence) and the fi ber reshaping occurred despite the low number of disulfi de scissions (small Td shift). An amino acid analysis would be useful to determine whether the scis- sion of disulfi de bonds was indeed different between the samples produced at low and high temperatures. Progressive thermal straightening may be a promising method to achieve permanent smoothing of curly hair without chemical treatment. Ironing at the onset temperature (~154°C), before substantial disulfi de bond scission occurred, seemed to be a good com- promise between process speed, straightening performance, and hair integrity (i.e., re- duced loss of cross-linking). In that transition region, the silicone increased the process effi ciency, allowing the hair to be straightened at lower temperature. REFERENCES (1) C. R. Robbins, Chemical and Physical behavior of Human Hair, 4th Ed. (Springer-Verlag, New York, 2002). (2) S. Ogawa, K. Fujii, K. Kaeyama, K. Arai, and K. Joko, A curing method for permanent straightening using thioglycolic and dithioglycolic acids, J. Cosmet. Sci., 51, 379–399 (2000). (3) W. Von Bergen, Wool Handbook, 3rd Ed. (John Wiley & Sons, New York, 1963). (4) M. Feughelman, A. R. Haly, and J. W. Snaith, Permanent set and keratin structure, Text. Res. J. 32, 913–917 (1962). (5) F. J. Wortmann, C. Springob, and G. Sendelbach, Investigations of cosmetically treated human hair by differential scanning calorimetry in water, J. Cosmet. Sci., 53, 219–228 (2002). (6) F. J. Wortmann, G. Sendelbach, and C. Popescu, Fundamental DSC investigations of α-keratinous materials as basis for the interpretation of specifi c effects of chemical, cosmetic treatments on human hair, J. Cosmet. Sci., 58, 311–317 (2007). (7) J. Cao, Melting study of α-form crystallites in human hair keratin by DSC, Thermochim. Acta, 335, 5–9 (1999). (8) J. Cao and F. Leroy, Depression of the melting temperature by moisture for a-form crystallites in human hair keratin, Biopolymers, 77, 38–43 (2005). (9) R. G. Jones, W Ando, and J. Chojnowski, Silicone-Containing Polymers (Kluwer Academic Publishers, Dordrecht, The Netherlands, 2000). (10) A. Dussaud and L. Fieschi-Corso, Infl uence of functionalized silicones on hair fi ber-fi ber interactions and on the relationship with the macroscopic behavior of hair assembly, J. Cosmet. Sci., 60, 261–271 (2009). (11) L. B. Rockland, Saturated salt solutions for static control of relative humidity between 5 and 40 C, Anal. Chem., 32, 10, 1375–1976 (1960). (12) W. C McCrone, L. B. McCrone, and J. G. Delly, Polarized Light Microscopy (McCrone Research Institute, Chicago, 1987), pp. 147–149. (13) J. M. Marsh, C. J. Clarke, K. Meinert, and R. M. Dahlgreen, Investigations of cosmetic treatments on high-pressure differential scanning calorimetry, J. Cosmet. Sci., 58, 319–327 (2007). (14) D. Istrate, “Heat induced denaturation of fi brous hard α-keratin and their reaction with various chemi- cal reagents,” PhD thesis, Aachens University, DWI (Germany), 2011.