In-depth analysis of potassium peroxysulfate based oxidation of wool fibre by advanced infrared spectroscopy

• The extent of oxidation of wool fibre was investigate by surface sensitive photothermal induced infrared spectroscopy. • The combination of different IR techniques reveals chemical information from different layers of the wool fibre structure. • Desired surface modification and fibre strength can be controlled by the extent of oxidation. A systematic study of the influence of potassium peroxysulfate oxidation treatment under aqueous conditions on the proteinaceous structure of wool is presented in this work. The combination of different infrared spectroscopy techniques, including the surface sensitive photothermal induced infrared spectroscopy coupled with atomic force microscopy, enables the evaluation of the chemical information from different layers of the wool fibre structure. We are able to show that infrared absorption intensities for cysteic acid are detected at all layers measured. The presence of anionic groups on wool was proven by methylene blue absorption studies, UV–VIS investigation and colour measurement. The increase in infrared absorption intensities related to cysteic acid as a function of treatment intensity appears to be more continuous when measured with the more surface sensitive technique, whereas there is considerable variation when measured in deeper wool fibre layers. With additional chemical and structural analysis, the study thus provides new insights into the oxidation treatment of wool fibres.