Mechanical hysteresis in wool keratin fibers

By comparison of the mechanical hysteresis behavior of Lincoln wool fibers in distilled water and in aqueous HCl at pH 1, it has been demonstrated that a large proportion of the mechanical hysteresis in water arises from the breakdown of Coulombic interactions during extension. These latter interactions, once broken, are slow in reforming. In aqueous HCl at pH 1 the mechanical behavior of the wool fibers indicates that stress at any strain during extension and retraction corresponds to an equilibrium stress required to maintain equilibrium between the folded α-state and the unfolded β-state of the keratin wool fiber, together with a viscoelastic stress resulting from the resistance to the chain movement concomitant with the α ⇆ β transformation. Results from the variation of stress in a fiber held at a fixed extension of 0.8% in a number of media suggest that the Coulombic interactions play an important role in stabilizing the α-helices within the wool keratin structure, and that these interactions act laterally within the fiber.