STUDY OF THE SOFTNESS OF HUMAN HAIR (1) Development Of The Softness Measurement By Means Of The Bending Length

Softness of human hair plays a big roll on the manageability of it. Therefore, it is important to measure the softness quantitatively. It is well known that the softness of long shaped materials can be obtained from tensile young's modulus and bending modulus. The tensile young's modulus is most generally empolyed as a parameter of softness, but is usually obtained by destructive way. Bending elasticity can be obtained by nondestructive way and is suitable for the study of the natural mate rials with scattered properties such as hair. But accurate measurement on hair bending may be difficult because of its hygroscopy and curl, and there is little informations about the bending of hair within authors' knowledge. In this paper, the bending length measurement, which is one of the possible way to measure the bending elasticity, is applied to study the softness of hair. The incre ased bending length with the enviromental humidity is arised from the increase of the bending elas ticity and that of the weight caused by the absorption of water, and the latter can be reduced by peirce's equation. The effect of curl can be minimized by the average of the bending length's of two opposite situations along the axis of the hair. As the result, the softness of hair is obtained with good accuracy by means of the bending length.