Physical Properties of Human Hair. 1. Evaluation of Bending Stress by Measuring the Major and the Minor Axis of Human Hair.

Abstract

A thick or stiff feeling of hair is thought to be due to a complex combination of several physical properties including the bending stress, the torsional stress, and the friction among hair fibers. Rigidity of hair is one of these basic factors. Rigidity as Young's modulus from a material dynamics viewpoint was evaluated accurately by measuring a minor and a major axis of hair. An experimental instrument equipped with laser beam emission for hair diameter measurements has been developed to estimate the minor and the major axis of hair, A two- phase structure model which has different Young's modulus (cuticle and cortex) was assumed. Evaluations of Young's modulus of an intact hair and a delaminated hair from which the cuticle was removed by physical stripping were carried out. The results showed that the cuticle Young's modulus of normal hair was approxi mately four times than that of the cortex. The contribution of the cuticle to the bending stress of whole hair was also evaluated by the minor axis, the major axis, and the thickness of the cuticle. Since the contribution of the cuticle to the bending stress of whole hair was up to 60%, it was concluded that the cuticle could play an important role in the thick or stiff feeling of hair