The Stabilization of Irreversibly Deformed Keratin Fibers

Abstract

The significance and relative contribution of the various factors that contribute to the stabilization of the extended state of the keratin fibers have been investigated. In this context, the stress relaxation of extended keratin fibers in 7.2 M LiBr solutions, as well as their recovery and recrystallization behavior, were studied. A kinetic analysis of stress relaxation in 7.2 M LiBr at a strain of 60% indicated that the controlling mechanism is an SH-catalyzed disulfide inter change with an activation energy of 22.9 kcal/mole. The recrystallization in a stable β-configuration of the chemically molten and extended keratin fibers is only possible after a structural rearrangement which removes disulfide bonds from stressed positions. If this rearrangement is prevented, the β-crystallites remain unstable even after an extended re crystallization time. Stabilization of the extended state by the formation of stable covalent cross links is not possible, unless crystallization of β-crystallites is permitted. The formation of β-crystallites alone, on the other hand, is also not sufficient to stabilize the extended state, unless the β-configuration is supported by stable covalent cross links. After a melting-extension-recrystallization cycle at 96°C, the total longitudinal deformation of the keratin fibers approaches 125%, which would correspond to the theoretical α-β-translation distance.