The surface of untreated wool has been investigated using x-ray photoelectron spec troscopy (XPS) and static secondary ion mass spectrometry (SSIMS). The wool surface is covered in a thin layer of lipid estimated to be approximately 0.9 nm thick. Mass spectral peaks are consistent with the presence in the lipid layer of saturated C20, C21, and hydroxylated C21 fatty acids, presumably bound as esters. This lipid layer can be partially, but not completely, removed by treatment with potassium tert-butoxide in tert-butanol or potassium hydroxide, reagents that cause oxidation of the surface cys tine. XPS indicates that the surface protein (epicuticle) is rich in sulfur, suggesting a half-cystine content of about 35%.
As part of a program directed at zero-AOX shrinkproofing treatments, we have compared the reactivity of different oxidants with wool by following their disappearance under similar conditions. The reactivity series was as follows: aqueous chlorine > DCCA ~ permonosulfate > permanganate / salt > peracetic acid > permanganate > persulfate ~ hydrogen peroxide. This series was not related to redox potentials but generally followed the level of shrink resistance imparted by the oxidant. Fourier transform infrared spectroscopy using the attenuated total reflectance technique showed significant differences in the amounts of cystine oxidation products formed in the oxidations above. One new finding was the direct formation of low concentrations of Bunte salts by the oxidation of wool with persulfate. We further studied the surface of permonosulfate-treated fibers with scanning electron microscopy and frictional measurements. Permonosulfate treated wool fibers produce Allwörden sacs with chlo rine water, whereas aqueous chlorinated fibers do not. We suggest that the most likely mechanism for shrink resistance in permonosulfate treatments is the removal of de graded protein from below the exocuticle, producing a modified surface with a reduced differential friction between the "for" and "against" scale directions.
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