Water sorption performance of human hair and the influences of cosmetic products and processes

Water Sorption Performance of Human Hair and the Influences of Cosmetic Processes and ProductsFranz-J.Wortmann, School of Materials, University of Manchester, Sackville Street, Manchester M60 1QD Alexandra Hullmann, Kao Professional Salon Services GmbH, Pfungst??dter Str. 92 100, D-64297 DarmstadtCrisan Popescu, DWI at RWTH Aachen University, Pauwelsstrasse 8, D-52056 AachenAbstractUnder normal conditions of humidity and temperature ??-keratinous materials, such as human or animal hair, can take up to about 30-35% water before feeling wet, while undergoing changes in a wide variety of their properties. Investigations of the hair/water system are therefore of fundamental interest as well as of elementary technical relevance for their cosmetic or textile performance, respectively. However, whereas the water sorption for wool is well documented comparatively little data are available for human hair. The determination of a water sorption isotherm, e.g., for hair by isothermally applying discrete, cumulative humidity changes comprises a dynamic and a static aspect, from which diffusion coefficients and equilibrium water contents are obtained. Temperature dependent isotherms for the water ab- and desorption of human hair were determined (25-65oC) together with the related diffusion coefficients and hysteresis effects. Special care was taken to standardize the physical history of the samples. With increasing temperature, isotherms, while preserving their shape, shift to lower regains. In parallel the hysteresis effect decreases. This is in accordance with expectations derived from the Rosenbaum-model for water sorption. The differential heat of water sorption changes from dry to wet hair between 1020 and 50 J/g H2O. Diffusion coefficients are of the order of 10-9cm2/s. The coefficients increase with temperature and show a pronounced maximum in the range of medium regains. The temperature dependence follows the Arrhenius equation and exhibits activation energies that change from dry to wet hair between 55 and 30kJ/mol. The sorption performance of hair after treatment with a variety of cosmetic processes and ingredients was investigated, finding very few relevant effects. It is concluded that human hair exhibits a rather robust static and dynamic water sorption performance that, against initial expectations, is not readily changed, namely, by cosmetic processes and products.