Chapter 7 235 and represents the elastic component that stores energy elastically on each cycle and the out of phase modulus, E’’,is called the “loss modulus” and represents the energy that is dissipated as heat on each cycle through viscous processes. The modulus can be expressed as a complex variable: where i2 = -1. it can be shown that The loss tangent, tan( ), is an important parameter in the analysis of viscoelastic materials, as it reflects the relative tendency of the material to either dissipate or store energy on deformation. Gao42 recently reported DMA measurements on virgin and bleached Asian and Caucasian hair at 40%, 60% and 80% RH. Gao’s DMA data from virgin hair are shown in Table 4. Table 4. DMA data on Asian and Caucasian hair versus RH at 1 Hz 15 hairs per group RH Storage Modulus, E’ (GPA) Loss Modulus, E’’ (GPA) Tan( ) Asian Caucasian Asian Caucasian Asian Caucasian 40% 4.98 5.24 0.121 0.109 0.0243 0.0208 60% 4.45 4.79 0.138 0.129 0.0310 0.0269 80% 3.68 4.15 0.143 0.138 0.0388 0.0335 The storage modulus was found to decrease with RH as the loss modulus increased. Both effects contribute to increased tan(δ) with RH. The lower storage modulus and higher loss modulus for Asian hair was reported to be statistically significant below 80% RH, and the author hypothesized that this may be due to increased medulla in Asian hair.45 Torsion and bending measurements: Resistance to twisting and bending deformations may influence properties of hair important to