Physical Properties of Shinayaka Hair and Fine Technology to Control Internal Hair Properties

One of main factors for beautiful hair for Japanese women is the smooth movement of hair strands. The motion of the beautiful hair is flexible, but those strands smoothly return to the original shape, like an elastic material. Such flexible and elastic behavior is preferred in Japan and described as Shinayaka in Japanese. We have found that the Shinayaka hair fiber has a two-layered cortex with different physical properties. The relatively softer ortho-ike cortex tends to distribute in the outer layer of the hair fiber （ near hair surface ）， while stiffer para-like cortex tends to be distributed in the inner layer （ near the center of the fiber ）． On the other hand, non-Shinayaka hair exhibits almost no difference in physical properties between the inner and outer layers of the hair fiber because of its structure or damage by a chemical treatment. In this research, we have developed a new technology to selectively soften the outer layer of the non-Shinayaka hair to realize flexible and elastic behavior through two-layered distribution of physical properties. We have found out that the elasticity of the outer layer of the hair is reduced by a treatment with succinic acid, while the elasticity of the inner layer is kept at constant value. Then, we have confirmed the hair strands become more flexible while keeping their elasticity after the treatment.