Chapter 11 385 An investigation of keratins in water shows a single endothermic peak at around 150‑160°C. Its nature is also under controversy. The peak is shifted to lower temperatures by certain cosmetic treatments. Various studies concluded that DSC of “wet” samples yields the denaturation enthalpy (ΔH D ) which depend on the amount and structural integrity of the α-helical material in the intermediate filaments (IF), and the temperature (T D ) which is kinetically controlled by the cross-link density of the matrix (IFAPs) in which the IFs are embedded. Research48 has indicated that the mechanism of fiber morphology change is more complicated, and further involves the participation of the “inter-phase” between intermediate filaments, IF, and the matrix, as well as the participation of the disulphide bonds and hydrogen bonds to the thermal degradation process. The model developed to answer the experimental data is a three-phase model, with an important role attributed to the inter-phase between crystalline intermediate filaments (IF) and the amorphous matrix (KAP). This explains why, after breaking the disulphide bonds, the temperature of denaturation for a hair fiber decreases dramatically, as seen in Figure 7, below 100°C.49 Figure 7. DSC analysis of hair fibers reduced for breaking the disulphide bonds
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