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

Abstract

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.

Characterisation of the bound lipids at the wool fibre surface by time of flight secondary ion mass spectrometry (ToF-SIMS)

“…The dominant peaks at m/z = 325 À , 327 À , 339 À , 341 À (and peaks related to 341 À at 342 À , 343 À and 344 À ; see later text) in untreated wool fabric 1 and fabric 2 were assigned to aC 20 H 41 COO À , C 19 H 39 -COS À , an unknown thiolate ion, and aC 20 H 41 COS À ions, respectively, largely in agreement with previous reports (Peet et al, 1995;Shao et al, 1997;Volooj et al, 2000;Ward et al, 1993). In contrast, for fabric given a 2 h KOH treatment, all the surface bound lipids were expected to be removed (Negri et al, 1993), and as expected none of these peaks were detected experimentally, Table 1 and Figure 1.…”

“…Negative ion ToF-SIMS analyses of wool Positive and negative ion ToF-SIMS spectra of both untreated wool fabrics were similar to one another and those reported previously (Peet, Wettenhall, Rivett, & Allen, 1992;Shao et al, 1997;Volooj et al, 2000;Ward et al, 1993). However, unless samples were exhaustively extracted with solvent and appropriately handled prior to ToF-SIMS measurement (Vickerman & Briggs, 2001), PDMS and detergent residues were visible in both positive and negative ion spectra of all untreated and treated fabrics.…”

“…The assignment of many ToF-SIMS peaks to acyl species confirms previous assignments (Peet et al, 1995;Shao et al, 1997;Volooj et al, 2000;Ward et al, 1993) and confirms fatty acids are bound to the fibre surface by both acyl and thioester linkages (Evans et al, 1985;Peet, 1994). Relative amounts of the different species were calculated by subtracting the signal at each respective mass for the 2 h KOH-treated fabric from the respective signals for the different fabric samples to yield a 'corrected' estimate of the relative peak intensity for each respective species.…”

“…Previously, untreated wool ToF-SIMS spectral peaks at m/z = 297 À and 281 À have been assigned to C 17 H 33 COS À and C 17 H 33 COO À species from octadecenoic (oleic) acid (Volooj et al, 2000). However, with surfactant and other residues effectively removed from the fabric surface, as in this study, only a very small signal, barely above background levels, was observed at m/z = 281 À for untreated fabric.…”

“…ToF-SIMS has been used in the past to identify lipids at the untreated wool fibre surface (Peet, Wettenhall, & Rivett, 1995;Shao, Jones, Mitchell, Vickerman, & Carr, 1997;Volooj, Carr, Mitchell, & Vickerman, 2000;Ward et al, 1993) and to reveal information about protein surfaces (Batts & Paul, 1994;Mantus, Ratner, Carlson, & Moulder, 1993) and it was hoped in this study that it could confirm the presence of cysteine residues at the fibre surface after hydroxylamine treatments and potentially exploit this selective route to functionalise the wool surface. Meade, Dyer, et al (2008) have suggested on the basis of atomic force microscopy (AFM) measurements that significant degradation of the wool fibre surface occurs during hydroxylamine treatment, raising doubts about the production of a cysteine rich surface following lipid removal with this treatment.…”