Effects of reduction on the denaturation kinetics of human hair

Although human hair as an α-keratinous fiber exhibits a complex morphology, it can be considered as a nano-structured filament/matrix composite for the context of thermal analysis. Using differential scanning calorimetry (DSC) in water, the denaturation performance of the α-helical protein fraction and the effects of reductive treatments were studied. The results are viewed in the context of a previous study for oxidative treatments. It was found that the course of the denaturation process remains generally unperturbed by the treatment, following an irreversible, one-step, first-order process. Arrhenius activation energies and pre-exponential factors were determined from the DSC-curves by applying the principles of the Friedman-method. Comparing activation energy values between reductive and oxidative processes shows the differences of the effects on the components of the composite. In contrast, the values of the rate constant at the denaturation temperature, though showing differences in their trends with cumulative treatments, are very similar. This further emphasizes the theory that the viscosity of the matrix affects strict kinetic control over the denaturation of the α-helical segments. Once the viscosity of the matrix has decreased enough for the denaturation process to occur, this follows a path that is largely independent of the temperature range and of the chemical pre-history. © 2008 Wiley Periodicals, Inc.