A Mechanical Model for Wool

Abstract

A model is presented which seems to account more fully for wool properties. This model contains two axially parallel parts: a microfibril made up largely of low-stability alpha-keratin and a matrix consisting of a series arrangement of high-stability alpha- keratin chains and amorphous protein partly extended in the axial direction. The matrix, which contains most of the cross links of the cortex, has a modulus considerably higher than that of the microfibrils. On extension, beta-keratin may originate from both the alpha chains and the amorphous chains. In solvents, the fiber is considered to have little tendency to swell longitudinally, because of restraints imposed by both amor phous and crystalline phases. Heretofore, it has been thought that the amorphous phase strives to swell isotropically but is restricted by the crystalline phase to swelling in the radial direction. Because of the high modulus now attributed to the matrix, the fiber structure appears to correspond mechanically to a honeycomb, at least with respect to tensile properties. I n compression, the microfibrils exhibit a high modulus, so that the composite structure also has some of the features of prestressed concrete. An example of the use of the model is given for the modulus of wool swollen in water and in water/formic acid mixtures.