The Stress Relaxation of Fibrous Materials

Abstract

The relaxation of stress in single wool fibers (Columbia 56's) held at fixed extension in water and in dilute salt solutions was studied by techniques described previously. The early portion of the stress relaxation in water did not change much with temperature, and this stress decay may be ascribed to scission of hydrogen bonds. The later portion depended more strongly on temperature, and here the decay is ascribed to hydrolysis of cystine bonds. The relaxation in salt solutions (0.1N) proceeded faster than in water. The rate and extent of relaxation varied strongly from fiber to fiber, and it was not possible to detect any systematic differences due to anion size, cation size, anion charge, or cation charge. The action of FeCl₃ differed from that of the other salts, not an unexpected behavior in view of the oxidizing, acidic, and catalytic effects of this salt. Because the effects of dilute HCl and of cysteine on stress relaxation are not altered by previous treatment with salt solutions, it appears that the salt-sensitive linkages are neither the acid-sensitive bonds nor the cystine bonds; tentatively we ascribe the salt-sensitive linkages to highly ordered regions of hydrogen bondings.