Abstract
The mechanism of recovery of keratin fibers from deformation in aqueous solutions was investigated. Above a transition temperature of ~70°C the deformation of the fibers became at least partially irreversible and the reversibility of the α-β-transformation was completely destroyed. Various levels of an irreversible disorientation of the native structure could also be obtained by holding the fibers in the extended state above the transition temperature for various lengths of time. The level of disorientation obtained under these conditions is reflected in the stress level reached during stress relaxation. Upon release of the fibers, instantaneous recovery occurred which was proportional to the stress just prior to release. The total recovery can be kept at this level if an SH-blocking reagent is added prior to the release of the fibers, indicating that the second, slower phase of recovery is controlled by an SH-catalyzed disulfide interchange mechanism. A similar behavior could be observed for highly reduced fibers, in which case the formation of stable thioether linkages during setting presumably prevents the second phase of recovery. The removal of disulfide bonds from contraction-opposing positions is the rate-determining factor of the second phase of recovery