Analysis of structural changes in permanent waved human hair using Raman spectroscopy

To investigate the mechanism leading to the reduction in tensile strength of permanent waved human hair, the structure of cross-sections at various depths of permanent waved white human hair was directly analyzed without isolating the cuticle and cortex, using Raman spectroscopy. The beta-sheet and/or random coil content (beta/R) and the Amide III(unordered) band intensity existing throughout the cortex region of virgin white human hair remarkably increased, while the alpha-helix (alpha) content slightly decreased by performing the permanent waving treatment. This suggests a secondary structural change from the alpha-helix form to the random coil form in the proteins existing in the microfibril of the cortex region. On the other hand, the S-S band intensity existing in the matrix of the cortex region almost did not change, despite the reduction in the tensile strength of the white human hair following the permanent waving treatment. Moreover, the transmission electron microscope observation shows that the macrofibril (the microfibril and matrix) existing in the cortex region of the virgin white human hair was remarkably disturbed, while the cuticle region was almost unchanged by performing the permanent waving treatment. From these experiments, the authors concluded that some of proteins existing in the cortex region (the microfibril and matrix) of the virgin white human hair were changed, thereby leading to the remarkable reduction in the tensile strength of the white human hair after the permanent waving treatment.