Study of the interaction between hair protein and organic acid that improves hair-set durability by near-infrared spectroscopy.

In this study, hydrogen bonds around hair proteins were analyzed by near-infrared spectroscopy to reveal the mechanism of improving hair-set durability by treatment with a specific organic acid. The improvement of set durability was confirmed by measurement on single hair fibers, suggesting that improvement is not because of the surface adhesion increase but because of the internal changes in the hair. Through analysis by two-dimensional near-infrared correlation spectroscopy, it was found that a combination band of stretching NH and amide II is deconvoluted into three bands interacting with different hydrogen bonds. From the assignment of the three bands, the behavior of the organic acid in the hair was clarified as follows: it absorbs at the site where water originally binds, even in extremely dry conditions, prevents water penetration, and makes strong and stable hydrogen bonds with hair proteins. The formation of such strong and stable hydrogen bonds suppresses the exchange of hydrogen bonds that is the cause of the breakage of set durability.