Effects of Water on Glass Transition and Enthalpy Relaxation of Human Hair

Glass transition and enthalpy relaxation behavior of human hair and their dependent on water content and aging time were investigated by means of differential scanning calorimetry (DSC). The obtained values of heat capacity change (Delta Cp) and of execs enthalpy (Delta H) determined by DSC were used for analyzing the glass transition and the enthalpy relaxation process, respectively. In the relationship between the value of Delta Cp and Delta H and the water content of hair samples aged for 4 days at various relative humidity, the value of Delta Cp and Delta H increased to a maximum around 10%-15% water content, and then decreased. when the water content was over 15%. However, in the case of the long storage under the conditions of the constant temperature and humidity, the different relationship was found from that mentioned above. This indicates that Delta Cp and Delta H at glass transition of hair depend on both the water content and the aging time. So, for the hair samples aged under three storage conditions with the different humidity, the values of Delta Cp and Delta H for all aged samples was found to change periodically during isothermal aging, and their changes tended to be opposite phase, indicating that the increase of polymer chain mobility increased the extent of the enthalpy relaxation but decreased the extent of heat capacity change. These results suggest that the polymer chain network of glassy state repeated periodically a stable double left right arrow unstable structural transformation through plasticization by water, and that the mobility of the macromolecular chain Occurred mainly in a lower cross-linked and higher hydrophilic region of the amorphous components, such as endocuticle, cell membrane complex, intermacrofibril material and nuclear remnants, in hair fiber.