Some mechanical changes during sorption of water by dry keratin fibers in atmospheres near saturation

If a wool fiber is held at a small fixed strain in water (∼1%) the stress in the fiber relaxes and reaches a steady value in about 1 hr. If, while the fiber is still held extended, it is dried and subsequently rewetted, the stress in the fiber after rewetting drops rapidly to a minimum and then slowly rises. This rise in stress in the fiber was previously interpreted as a rebuilding of hydrogen bonds under strain in the matrix of the wool fiber. Recent torsional measurements on fibers during the absorption of moisture from dry to a high humidity throw doubt on this conclusion. It appears that the rise in stress after moisture sorption is due to the reformation of the structure of the microfibrils, which have been partially disrupted by the swelling of the keratin structure due to the entrance of moisture. Infrared evidence of increased deuterium oxide penetration of the keratin structure during sorption of deuterium oxide agrees with this interpretation. A mechanism is suggested for this disruption of the microfibrils based on the difference of swelling of matrix and microfibril with the sorption of water into the wool fiber.