The Torsional Properties of Normal and Sulfur-Enriched Wool Fibers

The mechanical properties in torsion of single wool fibers of biologically produced high- and low-sulfur content have been studied to determine the effects on torsional behavior. The modulus of rigidity and the torsional relaxation, i.e., the decay in torque with time at a constant degree of twist, were determined in fibers tested in glycerol (~0% RH), distilled water, and aqueous solutions of HCl at pH 0.8, 1.8, and 2.9. The sulfur content had no significant effect on the modulus of ridigidy or on the magnitude of the torsional relaxation of dry fibers. Again, for fibers tested in distilled water, no significant effect of sulfur content on the modulus of rigidity was observed, but the percent decay in torque was measurably affected. The decay in torque in 1 hr for fibers of normal wool amounted to 23% of the initial torque and that for fibers of sulfur-enriched wool amounted to 15%. This difference in torsional relaxation behavior of wet fibers of the two wools was not thought to be due to the difference in sulfur content but may partly be linked with the aspartic acid content of the two wools. The modulus of rigidity and the torsional relaxation of fibers in aqueous HCl decreased with decreasing pH to as little as one third of the values obtained in distilled water, presumably due to the breaking of salt links, the decrease being greater for the sulfur-enriched wools.