Abstract
Formulations of thermal/hygral viscoelasticity of the keratin composite are presented by applying an analogy with the theory of uncoupled elasticity. The anisotropic mois ture swelling and thermal expansion are expressed in terms of the mechanical and thermal/hygral properties of the constituent phases and filament volume fraction. The calculated moisture swelling/hygral expansion of the matrix phase in the keratin fiber increases nonlinearly with fiber regain. From dry to wet, the matrix volume increases by 83% (the wet filament volume fraction = 0.5). The filament or microfibril phase changes in dimension only slightly compared with the matrix phase. The analysis using the estimated phase thermal expansion coefficients yields a value of the volumetric thermal expansion coefficient for wet keratin equal to 5.18 × 10-4/deg, which is in good agreement with the value measured by Mason for the volume thermal expansion of wet wool.