A universal structural model for human hair to understand the physical properties 1

A universal structural model for human hair has been proposed in order to u nderstand the physical properties of hair. The model consists of two struct ural parts, both of which have two states (Two-part/two-state model). The t ransition temperature (T-c) between the two states of one part is about 70 degrees C, and that of the other part is about 0 degrees C in a water mediu m. These transition temperatures depend highly upon the water content of th e hair. A higher transition temperature is observed in hair having a lower water content. Above the transition temperatures, both parts of the hair ar e soft and plastic (a melted state); they are hard and elastic (a solid sta te) below the transition points. One part of hair which has a higher transi tion temperature (ca. 70 degrees C in water) is assigned to be macrofibril and exo-cuticle consisting of keratinous proteins; the other part with a lo wer T-c (ca. 0 degrees C) is inter-macrofibrillar materials, a cell-membran e complex (CMC), and the endocuticle of non-keratinous proteins and lipids. This structural model was derived from the results of thermal-setting and relaxation experiments as well as TEM observations after permeating a dye w ith a high electron density (Erythrosin B).