2010 TRI/PRINCETON CONFERENCE 115 fi ber excessive elongation, its exposure to high temperatures, exposure to alcoholic solu- tions, and also after chemical changes that destabilize its structure, i.e. breakage of hydrogen and disulfi de bonds (11–14). According to the ongoing considerations it is straightforward that pore formation is as- sociated to the following phenomena: 1) Protein denaturation involving chemical changes due to hydrogen and disulfi de bond breakage, 2) Water evaporation, and 3) Fiber elonga- tion and super-contraction. The fact that pores start to form at around ~150°C, and that water and mechanical elongation/contraction are necessary for their creation, suggests that pore formation involves a process of protein denaturation. During this process a frac- tion of the hair crystalline structure will undergo a transition into a disordered structure. The denatured regions will be further disrupted by the explosive evaporation of water and by protein motion activated, either, by elongation or contraction creating, thus, the ob- served pores. Also, it is quite likely that at these temperatures superheated steam is Figure 9. Graph showing total count of number of pores in an area of ~ 0.06 mm2 as a function of temper- ature while keeping the number of hot-iron treatments constant at fi ve. The data represent counts of three fi bers ~ 68 μm in diameter. Table I Average Degrees of Super-Contraction Associated with Fiber Elongation for Sets of Five Fibers Subjected to Three Hot-Iron Treatments at a Temperature of 180°C with a Hot-Iron Speed of 1.0 in/s Fiber no. % Extension % Super-contraction 1 15.7 3.1 2 13.2 2.6 3 12.4 2.8 4 11.2 2.4 5 10.7 2.7 6 10.3 3.1 7 9.8 2.5 8 9.5 1.7 9 8.7 2.3 10 8.4 1.9 The hair fi bers showed pore formation immediately after hot-iron treatment. Super-contraction was produced in these fi bers after they were wet for 3 min and then heated again at 150°C.

JOURNAL OF COSMETIC SCIENCE 116 Figure 10. Micrograph of a hair fi ber (φ ~ 72 μm) showing the formation of larger voids (inside circles) deeper inside the cortex at a distance of ~ 24 μm from the hair surface. The fi ber was subjected to fi ve hot- iron treatments at 180°C using a hot-iron speed of ~ 1 in/s. involved, both, in the process of protein denaturation and hair straightening. Super- heated steam is steam at a temperature higher than water’s boiling point and it is quite possible that the hair moisture inside the cortex rapidly vaporizes and superheats when the hot iron temperature is higher than 150°C. EFFECTS OF TEMPERATURES HIGHER THAN 180°C AND LOW HOT-IRON SPEEDS Thus far the effects of temperatures ≤180 C and normal hot iron speeds (~1 in/s) on pore formation have been analyzed. In the following sections the effects of hot iron tempera- tures in the range of 180 210°C but with lower speeds (~0.2 inch/s) will be analyzed. When the hot-iron speeds were reduced to ~ 0.2 inch/s and the temperature was kept at 180°C a few pores started to appear deeper inside the cortex. These deeper pores were observed to coexist with a few voids of larger size (see Figure 10). Further increases in temperature to ~ 210°C while still maintaining low hot iron speeds, resulted in the appearance of larger voids approximately 3 to 10 μm inside the cortex. For instance, Figure 11a shows the image of a hair fi ber hot ironed at 210 °C and obtained without shift in plane of focus. The level of cuticle sheath integrity observed in this image indicates again that, when the microscope's plane of focus is at the hair surface, no apparent damage in the fi ber is de- tected. However, when the microscope's plane of focus is shifted to regions inside the cortex, the presence of large voids becomes apparent (see Figures 11b and 11c). Further increases in the hot iron temperature to ~ 220°C and above with low speeds re- sulted in the formation of air bubbles approximately 20 to 30 μm in size. The appearance of these air bubbles inside the cortex could easily be detected by optical microscopy as they produced bright large spots due to their diffuse pattern of light scattering. Further- more, the appearance of these air bubbles was invariably accompanied by severe fi ber shape deformation (see Figures 12a, 12b, 12c, and 12d) and by a brittle transformation of the whole hair fi ber. After this process the fi ber broke into small fragments with a minimum force. This type of protein transformation in the hair fi bers constitutes the most severe