FTIR Analysis to Study Chemical Changes in Wool Following a Sulfitolysis Treatment

Abstract

Sulfitolysis of wool keratin is important to many industrial processes, including shrink resistance, setting, and bleaching; its extent therefore requires rapid estimation. Currently, time consuming chemical analysis is used to convert the cysteine-S-sulfonate to cysteine and then to measure total cysteine colorimetricaily. Using ftir and the attenuated total reflectance (atr) method, our experiments quantify the relative amount of cysteine-S-sulfonate on the wool fiber surface. The cysteine-S-sulfonate (Bunte salt) shows a strong symmetrical stretching vibration at 1022 cm−1; working in the absorbance mode and taking second derivatives to enhance resolution allows changes in the amount of Bunte salt to be followed. The keratin Bunte salt is stable to acid but labile in alkali; a treatment with ammonium thioglycolate at pH 7.6 completely removes the Bunte salt. Results show the same trend as those obtained using the classical chemical method.