Dynamic humidity curl retention as a method for the evaluation of hair fixative components

Hair fixative components enhance the bending recovery stability of a water wave, which is formed by the breakage and reformation of hydrogen and salt bonds in hair. By treating the hair with a setting film, the humidity-dependent behaviour exhibits a dependence on the properties of the fixative components as such and, namely, on their surface characteristics. The ability of the fixative polymer to form inter-hair bonds, its glass transition temperature, its hydrophilic as well as elastic properties, combined with the crystalline to amorphous ratio, determine the performance of a styling product. High Humidity Curl Retention (HHRC) is a suitable method to investigate such polymer characteristics on hair. As a further development Dynamic Humidity Curl Retention (DHRC) is introduced. It is a method to determine the time-dependent ability of treated hair tresses to retain a certain hair style under defined changes of climatic conditions. The recovery of keratin fibres from cohesive set, which is governed by the general principles of viscoelasticity, is determined as the ratio of the length of the curled hair tress at any time compared to its maximum, original length.The results for different hair fixative components after an abrupt relative humidity change and the implications with respect to water absorption and changes of the glass transition temperature, respectively, are discussed.