Wool hydrolysates as coadjuvants in wool dyeing with anthraquinones and flavonoid derivatives natural dyes

Wool that is unsuitable for use in clothes and household applications represents a special category of waste whose discharge causes a cost. Quite a few works in the literature studied the possibility of employing this type of wool in different fields. However, some by-products, such as wool hydrolysates, might be formed anyway, which need to be managed. In the present work, we studied the possibility of utilizing wool hydrolysates (WH), obtained as a by-product after the alkaline treatment of wool for adsorbent panels, in the dyeing process of wool fabrics with natural dyes. Two categories of natural dyes were selected, one from anthraquinones, the Carmine, and one from flavonoids, the Anthocyanin. A traditional dyeing recipe was carried out on pure wool fabrics to verify the affinity between the dyes and the fibers. Further, dyeing processes were carried out on the wool fabrics treated with the WH. Three different procedures were studied to optimize the effect of the WH on the dyeing; in the first two methodologies, the WH were applied as fabrics pretreatment; in the last method, they were dispersed directly into the dyeing liquor. The dyeing performance was evaluated through the measurement of dye exhaustion, color coordinates, and color strength K/S (Fig.1). The analysis evidenced that the WH efficiently improved the dyeing of the wool fabrics with the natural dyes and can, therefore, be considered as an alternative dyeing methodology for wool. In addition, the thermal, physical, and morphological characterization as well as the mechanical properties of the dyed fabrics, evidenced a very similar behavior for the fabrics dyed with or without the WH.