The Influence of Chemical Treatment on the Properties of Wool

Abstract

The view that the cortex of the wool fiber consists of a resistant fraction, the paracortex, and a less resistant fraction, the orthocortex, which extend in the form of two twisted hemi cylinders from one end of the fiber to the other, is used to explain the mechanism of the alkali- solubility test on acid-damaged wool. The effects of acid damage on several single-fiber prop erties and on the resistance of fabrics to flex abrasion have been measured for correlation with alkali-solubility data. During the initial exposure of the wool to acid damage, alkali solubility is observed to in crease rapidly, corresponding to damage chiefly to the orthocortex; during the later stages, as the damage proceeds into the paracortex, the alkali solubility increases at a much slower rate with time of exposure. The decreases observed in the values for physical properties of the wool with increasing exposure to acid correspond generally with the changes in alkali solubility. Wool treated with formaldehyde, either preceding or following a series of progressive expo sures to acid, exhibits greatly decreased alkali solubility, but fails to show a corresponding im provement in physical properties. It is suggested that the acid acts to degrade the wool fiber by hydrolyzing peptide bonds, and that the formaldehyde treatments decrease alkali solubility by a cross-linking mechanism that does little to improve the physical properties of the wool. A good correlation was found between the flex-abrasion resistance of the variously treated fabrics and the energy to break of the corresponding single fibers. The product of breaking stress and breaking extension, a fiber property related to energy to break, was also found to correlate well with the fabric flex-abrasion resistance.