Linear and nonlinear relations between DSC parameters and elastic moduli for chemically and thermally treated human hair

Abstract

Against the practical context of thermal straightening, hair samples were obtained with a chemical (bleaching) as well as a cumulative thermal history (0-800 s, 200°C). On these samples, tensile testing and DSC analysis, both in the wet state, were conducted to obtain the elastic moduli E w as well as denaturation temperatures T D and enthalpies DH D . 3D plots show overall linearity for the relationships between the parameters for natural hair. For bleached hair, pronounced nonlinearities develop beyond 300 s of thermal treatment. At this stage, T D as well as E w approaches limiting values, consistent with the state of a highly cross-linked, thermoset polymer. 2D projections are used to investigate the correlations between pairs of parameters. The results show that bleaching imparts a specific sensitivity for thermal damage, namely, to the matrix proteins, which more readily than the intermediate filaments (IF) turn into a thermoset. Overall, correlations between parameters hold well prior to the thermoset range. It is thus suggested that tensile testing to determine the elastic modulus and DSC come to consistent and equivalent results, at least, for the current experimental context. However, while E w combines contributions of IFs and matrix, DSC differentiates the specific property changes of these components.

Influence of water and temperature on the electrical conductivity of the human nail

“…Our previous dielectric studies of the human nail with about 11% water [4][5][6][7] also revealed the process of removing water, but at a lower temperature of 80°C. Release of water in other a-keratin fibers using the DSC method [14][15][16][17] was also observed in a similar temperature range. In addition, plots for wet nail show that during the aging test for 1 h at 150°C, the values of e 0 and e 00 are in the ranges 7.30-5.71 and 0.99-0.24, respectively.…”

Perm-waved human hair: a thermorheologically complex shape memory composite

“…The additional, perceived loss of shape towards the hair tips is, in our view, not associated with a genuine lack of stability of hair shape or the action of special trigger stimuli (23). We rather attribute it to changes/damage imparted to the morphological structures of the hair through natural weathering processes [a combination of UV-exposure, humidity and heat: (68)] or further common grooming practices [bleaching, dyeing: (69)].…”

Effect of equilibrium pH on the structure and properties of bleach‐damaged human hair fibers

“…The literature suggests that DSC and tensile parameters correlated well while studying bleached and thermal damage levels. [ 19 ] These treatments permanently changed the hair structure. pH treatment, excluding extreme values, cosmetically modified hair proteins (recoverable changes), thus, it is useful to understand if (a) large observed changes in hair matrix crosslinking and (b) integrity of IF across the pH range, can translate into significant changes in the mechanical properties of hair.…”

“…The literature suggests that DSC and tensile parameters correlated well while studying bleached and thermal damage levels. [19] These treatments permanently changed the hair structure. pH treatment, to acidic treatments such as lemon juice, vinegars or certain patented hair care formulations.…”