Investigations of cosmetically treated human hair by differential scanning calorimetry in water.

By applying differential scanning calorimetry (DSC) on human hair in water, the thermal stability of hair' major morphological components is determined. Against the background of the two-phase model for alpha-keratins, these components are identified as the partially helical, fibrous intermediate filaments (IF) and the intermediate filament associated-proteins (IFAP) as a cross-linked, amorphous matrix. DSC yields the denaturation enthalpy deltaH(D), which depends on the amount and structural integrity of the alpha-helical material, and the temperature T(D), which is kinetically controlled by the cross-link density of the matrix. To assess the effects of cosmetic treatments, hairs were investigated that had undergone either multiple bleaching or perm-waving treatments. The respective dependencies between denaturation temperature and enthalpy show that both morphological components are similarly affected by bleaching, while reductive damage, in comparison, is more pronounced in the IFs. For both types of treatments, changes in enthalpy follow apparent first-order kinetics with respect to the number of treatments as well as treatment time (perm-waving), yielding characteristic reaction rate constants. It appears that DSC in water is an especially suitable method to determine the kinetics of damage formation in human hair resulting from cosmetic treatments.