The effect of water molecules on viscoelastic properties of human hair

Abstract

The effects of water on viscoelastic properties of human hair were investigated by dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). Dynamic modulus (E′) of dry human hair decreased linearly with increasing temperature. On the other hand, E′ of wet human hair showed an inflection point near 0 °C. Moreover, a new dispersion peak was observed in tan δ curves of human hair containing water molecules. The DMA curves of thioglicolic acid-treated human hair were similar to those of untreated human hair. Therefore, it was found that hydrogen bonds between protein chains in human hair acted more prominently than disulfide linkage (S-S linkage). The glass transition temperature (Tg) of human hair decreased with increasing absorbed water content (Wc) and then saturated at about 30% of Wc. The non-freezing water content (Wnf) of human hair measured by DSC was about 30%. This means that physical properties of human hair such as Tg and strength are controlled by bound water which is strongly restricted by hydrophilic groups of proteins.