Dynamic mechanical properties of α-keratin fibers during extension

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Abstract
Lincoln wool fibers have been tested for their dynamic modulus E' and loss angle 5 at various values of strain in the “Hookean”, yield, and postyield regions by applying various rates of extension, and in atmospheres varying from 0 to 100% relative humidity. An estimate of the energy loss per cycle for the whole fiber exhibits only minor change over the complete range of change of the humidity and strain. The dynamic modulus E' and loss angle 8 change considerably with overall strain of the fiber, especially under more moist conditions. The variation of E' and 6 can be interpreted in terms of the microfibril-matrix composite which forms the major component of α-keratin fibers. In particular, the mechanical effect of the unfolding of the α-helical structure contained within the microfibrils is shown to be independent of relative humidity. The results indicate that the α-helical component is responsible for a fixed amount of the Young's modulus of the initial stiff region (the Hookean region) of the stress-strain curve of Lincoln wool fibers. This fixed amount of 1.2 × 109 Newtons m2 is confirmed from other independent mechanical estimates.