The Formation of Cysteine-S-sulphonate Groups in Wool and the Effect on Shrink-resistance

The different stages of wool oxidation during the Dylan XCP permonosulphuric acid based shrinkproofing process have been followed using second-order derivative Fourier transform infra-red (FT-IR) analysis. After oxidising wool with Caro’s salt, some of the cystine residues present were oxidised to cysteic acid, but cystine-S-monoxide and cystine-S-dioxide concentrations remained the same. After treating the oxidised wool with bisulphite, cysteine-S-sulphonate groups were formed and the fibre acquired significant shrink-resistance to washing. The effect on shrink-resistance of reducing the concentration of cysteine-S-sulphonate groups was determined. It was found that when these residues were reconverted to disulphide bonds the shrink-resist effect was lost