The Effect of Hydration on the Mechanical Behaviour of Hair

Human hair is a biological material constantly exposed to different external factors,such as humidity, sunrays, temperature, chemical treatments, etc. All these treatments influence and modify its physical behaviour. Studying the biophysical properties of human hair is very important in both dermatology to provide useful markers for the diagnosis of hair disorders and in cosmetics to develop better hair-care products. Water is one of the external factors whose action on the mechanical behaviour of hair is the most visible. To understand the role of water in the biophysical behaviour of hair, it is essential to study its influence on alpha-keratin, which composes the major part of the structure of hair. The influence of water on the biomechanical behaviour of hair has been studied using relaxation tests. The generalised Maxwell model was used to analyse rheological results. The results indicate a modification of the rheological behaviour of hair before and after immersion in water and during ambient air-drying. Finally, a correlation between the rheological results and the chemical bond structure of hair is discussed.