Dynamic mechanical study of hair viscoelasticity and softness

IFSCC Magazine , 12 (2009) (2) 93–98 Dynamic mechanical analysis (DMA) has been widely used to investigate material properties such as thermal transitions and complex modulus of polymers. Until now, only a few articles have been published to discuss applications of DMA in studying human hair and evaluating hair care products due to difficulties in handling hair samples. In DMA, a complex modulus (E*), an elastic (storage) modulus (E’) and an imaginary (loss) modulus (E’’) are determined which give a better characterization of viscoelastic properties of hair than regular tensile strength. A new DMA test methodology including a hair bundle preparation and sample clamping technique was developed and applied to study human hair samples. Effects of hair type (Caucasian vs. Asian), bleaching time, environmental relative humidity (RH), and cosmetic treatments on hair viscoelasticity and storage bending modulus/stiffness were investigated. Average complex modulus and Young's modulus of single hair fibers and storage bending modulus of hair bundles before and after cosmetic treatments at various relative humidity levels were determined. Subjective evaluations of hair soft feel by salon panelists were conducted and the results compared with those of objective measurements (changes in hair storage bending modulus). Keywords: Dynamic mechanical analysis, hair, viscoelasticity, softness, quaternium‐91 This paper was presented at the 25th IFSCC Congress 2008, Barcelona, Spain