2010 TRI/PRINCETON CONFERENCE 275 In addition to the protein conformation change, hair protein modifi cation from thermal treat- ment was further assessed using a band at 2960 cm−1, a C-H asymmetric stretching mode of the CH3 group. This CH3 band is mainly attributed to the terminal amino residues of hair proteins with minor lipid contribution. Figure 6 shows the spatial IR images of the hair cross section which depict the concentration profi le of hair protein with minor lipid contribution obtained from the CH3 band area. The intensity color bar at the right side with higher num- bers and corresponding colors indicates higher protein concentration. It is observed from the fi ber cross sections that there is an overall protein and lipid loss for the thermally treated hair as indicated by a reduction in the integrated area of the bond. Pretreatment with all three polymers tested effectively prevents the overall protein and lipid loss. FTIR results support the DSC analysis and provide additional insights to the total helical protein degradation. As little is known about the molecular conformational state of other protein components in hair (8), other protein components besides the β-sheet structure, such as other uncoiled, random coil, or denatured cross linking structures that α-helix can transform to but are undetected by this FTIR analysis, may exist. THERMAL PROTECTION OF THE HAIR SURFACE BY COSMETIC PRETREATMENT Figure 7 shows atomic force microscopy (AFM) images of the surface of the hair cuticle with and without thermal treatment. The AFM images indicate that thermal treatment at 232°C causes damage on the cuticle surface, including cracks, holes from over-heating, and formation of micropores. These surface damages will increase the hair permeability resulting in faster water loss during drying. Figure 6. IR images of a thermally treated hair cross section at 232°C with and without polymer pretreat- ment. Maps were developed from the peak area of 2960 cm-1 band, representing the relative protein concen- tration in the hair cross section. European dark brown hair.

JOURNAL OF COSMETIC SCIENCE 276 Figure 8 shows the scanning electron microscopy (SEM) images of European hair fi bers with and without thermal treatment at 232°C and with the pretreatment of the tested polymers. Four to fi ve fi bers were examined for each hair sample to ensure reproducibility. Thermal treatment causes severe cuticle damage to the hair fi ber surface by showing cu- ticle disintegration with missing cuticle pieces and jagged cuticle layers. The 0.5% HEC (hydroxyethylcellulose) solution pretreated hair has damage on cuticle layers and shows the fusion of some cuticle cells. Once the cuticle is damaged, hair breaks easily since there is no protection for the cortex. The SEM images also show that polymer pretreatment prevents signifi cant cuticle damage due to thermal treatment. Among them, VP/acry- lates/lauryl methacrylate copolymer-treated hair fi bers have well defi ned cuticle layer. This result is consistent with the polymer’s high anti-breakage effect, 55%. Therefore, hair surface protection to ensure good cuticle integrity and surface smoothness also plays an important role in their anti-breakage effect besides protecting cortex protein from thermal damage. WATER VAPOR SORPTION AND DESORPTION OF THERMALLY TREATED HAIR AND THE ROLE OF WATER RESTORATION IN HEAT CONTROL Water changes the properties of human keratin fi bers and, therefore, plays an important role in cosmetic performance. Hot fl at irons that lack heat control can destroy the hair Figure 7. AFM Images of the hair cuticle surface with and without thermal treatment. (a) Not thermally treated. (b, c, d) Thermally treated at 232°C.