Permanent Set and Keratin Structure

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Abstract
When a normal wool fiber is held extended in boiling distilled water, the force due to bonds opposing the extension falls rapidly in the first few minutes to a steady value of force, which has been shown to he purely entropic. Accompanying this breakdown of bonds opposing extension is the reduction of the ability of the fiber to return, on release, to its native configuration. The loss of organization in the released fiber suggested by mechanical fiber tests is confirmed by birefringence measurements and also by the irrecoverability of the a-keratin structure, as measured by the x-ray diffraction pattern. The longitudinal swelling on wetting dry fibers increases as the setting exten sion increases and with increased time of setting; these observations are also consistent with structural disorganization of the fiber. The equilibrium state after release of the keratin fiber changes in the first few minutes of being held extended in the boiling water from the native state to a supercontracted state. This state, on further boiling, is replaced by that of the set fiber.