The Microfibril-Matrix Relationships in the Mechanical .Properties of Keratin Fibers

The torsional modulus of wool fibers in water is unaffected by extension right up to break (∼50% strain). This result, taken in conjunction with other mechanical data, suggests that the rapid in crease in stress in an α-keratin fiber with extension in the post-yield region (>30% strain) comes from opposition to extension within the microfibrils of α-keratin fibers. When a fiber undergoes longitudinal extension, the matrix goes from a "gel" to a "sol" state while the fiber is extending and reverts to the "gel" state when extension ceases. The behavior of the matrix appears independent of the extension of the wool fiber, and this is confirmed by dynamic measurements carried out on fibers during low rates of longitudinal extension. The energy loss per cycle remains practically unaltered at all strains during the slow extension of a wool fiber in water.