Thioglycolic acid, with wool

A development reported recently [519] involves reduction of the cystine disulphide bonds in wool with either thioglycolic acid or tetrakis(hydroxymethyl)phosphonium chloride to form thiol groups, followed by crosslinking with bifunctional reactive dyes. This gave improved insect resistance but had adverse effects on physical properties such as strength, shrinkage and stiffness, thus limiting the potential of the process for commercial use. 

Leach and O Donnell [15] have shown that the complete reduction of wool fiber with thioglycolic acid can be approached at pH 6.9 by employing extremely large concentrations of mercaptan (II) relative to keratin cystine (I). Similar results have been reported for the reduction of wool fiber with mercaptoethanol [16]. 

Recent structural studies have shown that the 8-layer in the CMC often appears to have a laminated ultrastructure. After polymer grafting into thioglycolic-acid-reduced hair [176], the cuticle 8-layer indicated a nonstaining central band surrounded by two densely stained bands. After staining with osmium, the 8-layers in the cuticle CMC of human hair and developing wool fiber cuticle cells have also shown a series of laminations [41,72,177] (Figure 5.11). 

Hartsuch descrit d modifications through wool s -NH2 groups and -S-S-linkages by crosslinking with formaldehyde (Eq. 1) or benzoquinione, by the addition of an amino group to a ketone (5) The reduction of disulfide bonds with thioglycolic acid and the subsequent formation of new crosslinks between two adjacent chains by dihalogen compounds (Eq. 2,3) is shown below ... 

The amount of protein extracted from wool or hair with thioglycolate at pH 10 can be increased by pretreatment with concentrated sulfuric acid (Lustig and Kondritzer, 1945). Some fractionation of the protein extracted from the cortex was achieved by Lustig et al. (1945). 

The reaction of mercaptans with keratin hbers is a relatively specihc reaction in mild acid. However, in alkaline media, peptide bond hydrolysis and the formation of lanthionyl residues can also occur [42]. Zahn et al. [43] have suggested that mercaptides such as thioglycolate or cysteinate can accelerate the rate of formation of lanthionyl residues in wool hber. (A more detailed discussion of the formation of lanthionyl residues in keratin fibers is described later in this chapter.)... 

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