Time-of-flight secondary ion mass spectrometry (ToF-SIMS) analysis of the bleaching of keratin fibres and the application of cationic alkyl protein softeners to bleached cashmere

Studies using ToF-SIMS have demonstrated that the 18-methyleicosanoic acid (18-MEA) bound to the fibre, via a thioester linkage, is the major lipid present at keratin fibre surfaces. Relatively higher levels of eicosanoic acid were detected by ToF-SIMS than has been observed by wet chemical analysis. Hydrogen peroxide bleaching of keratin fibres cleaves the 18-MEA, the level of loss being related to the severity of oxidative attack. The adsorption of a wetting agent, nonyl phenol ethoxylate (NPE-8), onto the fibre occurs during bleaching with preferential adsorption of the more hydrophobic short ethoxymer species observed. Characterization of protein softeners indicated complex ToF-SIMS spectra, with the surface analysis data agreeing with the wet chemical bulk analysis. Surface analysis of the 'softened' cashmere indicated that the cationic alkyl protein softeners are highly substantive and that enrichment of the more hydrophobic softener components has occurred. A distribution model for the cationic protein softener over the anionic fibre surface has been proposed.