Enzyme-aided Wool Dyeing: Influence of Internal Lipids

Dyeing and diffusion properties of dyes into wool fiber are governed by a membranous structure which is formed by a matrix protein and lipid components. External lipids (wool wax) are mainly non-polar, while internal lipids consist mainly of sterols, polar lipids (ceramides), and free fatty acids. These components constitute a real hydrophobic barrier to the diffusion of dye molecules and in fact conventional wool dyeing methods are based on long times at temperature near the boil in order to ensure good levels of dye penetration. To limit the action of this barrier and to achieve higher values of dye bath exhaustion operating at temperatures lower than 98 oC, wool fabric was subjected to three different pre-treatments. The first pre-treatment consisted of the removal of internal lipids by extraction with solvents in order to obtain a higher affinity of the fiber towards the dyes. The second involved hydrolysis with a protease, which leads to the formation of access routes within the fiber to improve the uptake of dyes or other reagents. Finally, the third took into account the combined action of the two previous pre-treatments. The influence of each individual pre-treatment and their combinations on the kinetics and final exhaustion of the dye bath were studied, and assessment of color fastness (to washing and to light) were carried out.