XPS and SIMS Investigation of Covalently Bound Lipid on the Wool Fibre Surface

Alcoholic alkali solutions, such as potassiumt-butoxide int-butanol and potassium hydroxide in ethanol, have been known to remove the covalently bound lipid from the wool fibre surface. In this study, x-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS) have been used to investigate the surface characteristics of unprocessed wool fibres (both base section and weathered tips), wool fabric and the relative effects of potassiumt-butoxide and potassium hydroxide treatments. Results comparing the fibre base and tip confirm that the weathering may result in partial loss of the covalently bound lipid from the tip. In addition, a loss of sulphur has been observed. While the extent of sulphur oxidation on the surface of the base section is insignificant, the tip section may have up to 30% oxidized sulphur. There is no apparent difference between the fibres and the fabric used in this study regarding the levels of carbon, sulphur and oxidation. Potassiumt-butoxide is found to be less effective than potassium hydroxide in removing the surface bound lipid. An explanation is given which supports a hypothesis that the bound lipid is located not only at the outer most surface, but that it is also trapped within the underlying protein layer. The potassiumt-butoxide, due to its bulky molecular structure, may not have easy access to the trapped lipid. While the extent of oxidation of surface sulphur after potassiumt-butoxide treatment is higher compared to that after potassium hydroxide treatment, the levels of sulphur loss caused by these two reagents are similar. The removal of bound surface lipid for fabric is more effective than for fibres. It is suggested that fine-scale damage to the fibre, which has been observed to occur during physical processing, is responsible for this difference.