Abstract
At the outermost layer of cuticle, fatty acids [mainly 18-methyleicosanoic acid (18-MEA)] are connected with fibrous protein under these acids. This layer is called the F-layer. The F-layer allows the hair surface to be hydrophobic and have a good smoothness under normal conditions. After the F-layer is broken, the hairs lose 18-MEA from the surface, leading to the hydrophilization of the hair surface and the deterioration of the protective-barrier function against outside stresses, resulting in the hair surface developing an uncomfortable friction and rough texture. For keeping the healthy and beautiful hair, the lost F-layer need to be recovered with some cosmetic materials. We have developed Cetearamidoethyl diethonium hydrolyzed protein (CDHP), an ionic complex material consisting of rice peptide and aliphatic cationic compounds. This compound was designed by focusing on the F-layer structure. CDHP has simulated the F-layer structure of which the alkyl and peptide moieties correspond to 18-MEA and the protein parts of healthy hair surface, respectively. We previously investigated the properties of CDHP against damaged hair using fluorescence microscope observation. This observation revealed that CDHP selectively adsorbs to the damaged part of the hair surface. In this study, to investigate the physical character changes to the hair surface that occur with CDHP adsorption, we evaluated contact angle and frictional measurements of hair surfaces. These analyses revealed that CDHP restores the deteriorated physicochemical properties to the state of healthy hair. Furthermore, we found, with combing tests and sensory evaluation, that silicone-free hair conditioner containing CDHP improved hair texture significantly and maintained a good sensory character, respectively, over the long term.
