Surface Analysis of Wool by X-Ray Photoelectron Spectroscopy and Static Secondary Ion Mass Spectrometry

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 C ₂₀ , C ₂₁ , and hydroxylated C ₂₁ 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%.