HAIR SHAPE AND DAMAGE FROM RE-SHAPING HAIR 407 Table IV Tensile Strength Data for Chemically Treated Hair Measured in the Fully Hydrated State (48) Hair sample Tensile strength (N·m)/1000) Untreated 1.21 Hair color (30 vol. developer) 1.14 Acid wave 0.99 Hair relaxer (NaOH) 0.78 Hair relaxer (guanidine) 0.70 Hair bleach (30 vol. developer) 0.48 even a slight increase in some of the tensile parameters. Similar to the case of wool, heat- ing to elevated temperatures may result in the formation of cross-links within the inter- nal structure of hair thereby requiring greater forces to extend and break the fi ber (50). CONCLUDING REMARKS Chemical and physical treatments intended to change the shape of hair often result in changes to fi ber shape, which is often accompanied by damage to structural proteins of the fi ber. Photographic imaging techniques in conjunction with image analysis provide accurate measurements of fi ber shape as manifested in fi ber alignment and curl. In addi- tion, using laser stereometry we characterize the three-dimensional structure of the fi ber assembly and its occupied volume, allowing for comparison of the initial state with that of the reshaped hair. On the other hand, many other tools are available to assist in deter- mining the location and extent of damage associated with reshaping hair. Spectroscopic techniques are the best tools at providing us with real chemical information as to the health state of hair. These changes can be probed by monitoring specifi c amino acid resi- dues utilizing fl uorescence spectroscopy, Raman spectroscopic imaging, or IR spectro- scopic imaging. As an example, one may monitor tryptophan degradation with fl uorescence, or conversion of cystine to cysteic acid residues by IR spectroscopic imag- ing. In all of the IR imaging data presented, we examined cross sections of hair fi bers, providing specifi c chemical information in a spatially resolved manner. All of the spectro- scopic techniques are advantageous however, Raman confocal imaging is extremely pow- erful since it permits us to noninvasively dissect the fi ber providing a z-line (through the fi ber cross section) of functional group or secondary structure information. Both spectro- scopic imaging methods also allow for the determination of beta keratin, and its local- ization in the morphological components of hair. In this way, we monitored the conversion of alpha keratin to beta keratin. More common techniques to measure hair damage—especially due to perming, straight- ening, and fl at ironing—include DSC and tensile property measurements. The increased utility of these techniques stems from their ease of use and instrument accessibility (e.g., budgetary factors). DSC provides us with a quick look at the health state of the crystalline (alpha-helical component) and amorphous (the matrix located in cortical cells) regions of hair by monitoring ΔHD and TD. Tensile strength measurements, on the other hand, are normally used to generate data about the tensile properties of hair. These data are typically presented in the form of stress–strain curves that provide a fi ngerprint of the

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