A Kinetic Study of the Supercontraction of Wool Fibers in Solutions of Salts, Acids, and Alkalies

Abstract

Wool fibers contract in hot solutions of acids or alkalies, the initial rate of contraction increasing with increasing concentration of the acid or alkali. At the higher concentra tions contraction is followed by elongation of the fibers to lengths which may exceed the original length. The maximum contraction obtained decreases with increasing con centration of acid or alkali used. Comparison of the rates of contraction of wool fibers in solutions of different salts in 1 or 4 N HCl shows that cations and anions fall in the fol lowing order of decreasing contraction rate: Li+ > Na+ > K+ and I- > Br - > Cl-. Kinetic curves for the contraction of wool fibers in 1 N HCl containing salts show well- defined two-stage contraction. With 4 M LiBr or NaI this appears as a shelf in the curve at 25-30% contraction, and with many fibers the final level of contraction exceeds 70%. With 5 or 6 M LiI or 6 M NaI the fibers contract by about 25%, elongate to a length which may approach the original, and then again contract; in such solutions a con siderable proportion of the wool protein is dissolved, leaving a sulfur-rich residue. Two-stage contraction kinetics have been observed only when using solutions with pH values in the lower range. As the pH is increased the rate of contraction also increases, particularly at pH values greater than about 8. The two-stage contraction kinetics have been interpreted in terms of the contraction at different rates of two structures in the wool fiber.