Wool hydrolysates as eco-compatible resources in wool fabrics dyeing

Textile dyeing is a crucial phase in textile manufacturing. Since ancient times, it was realised by extracting natural pigments from plants and animals, but at the expense of the washing fastness of the dyed fabrics. Technology developments allowed synthesising dye molecules easier to handle and with better washing fastness. To obtain a durable effect, however, mordants, generally metal ion solutions, need to be introduced into the dyeing liquor to favour the link between the dye molecule and the textile substrate. Nevertheless, synthetic dyes and their mordants contribute to increasing wastewater pollution and environmental concern. As a consequence, natural dyes are getting renewed interest, as well as the search for more sustainable mordants. Among the wastes produced by the textile companies, wool by-products and poor quality wool represent a significant concern, classified as special waste by the European Union. On the other hand, thanks to its amino acidic structure, which allows the formation of hydrogen bonds and electrostatic interactions with many molecules, the hydrolysed wool may have high potential also in textile dyeing. In our study, low-quality wool was hydrolysed in alkaline solutions, to obtain a fine suspension of wool hydrolysates, mainly composed of peptides with nine amino acids chains. Different process conditions were tested to optimize the hydrolysis; afterwards, the produced hydrolysates were employed in wool fabrics dyeing according to various procedures. For comparison, a wool fabric was dyed without the use of hydrolysates. The results showed that dyed fabrics with a higher color strength could be prepared after wool fabrics treatment with the hydrolysates. The test performed demonstrated the possibility of dyeing the fabrics at a lower temperature as well, if compared to that normally set during the industrial processes. In addition, fabrics characterization revealed that the physico-mechanical properties of the pristine samples were not remarkably affected.