WOOL FABRICS DYEING WITH METAL-COMPLEX DYES AFTER UV IRRADIATION

Wool fabrics were treated by ultraviolet radiations, using a medium pressure Hg lamp, in order to obtain a strong modification onto fibers surface. As consequence, UV treated wool showed a decrease of water contact angle, then an increase of hydrophilicity, together with a better kinetics of dye absorption under the same conditions of dyeing, obtaining a dye-bath exhaustion nearly complete. The interaction between the metal cation and new ligand groups formed on irradiated wool (such as cystine oxides and cysteic acid) is responsible for the significantly increased depth of shade with 1:1 metal-complex dyes. In support of this hypothesis, UV-C-treated wool soaked in solutions of various transition metal salts (namely Mohr’s salt, copper sulphate and silver nitrate) at room temperature gave a grey/brown colour in the irradiated regions, denouncing the increased affinity. Experimental results showed that different kind of dyes are able to give differential dyeing after irradiation, but not all members of the same dyeing class have similar behavior. Then, a selection of 1:1 metal-complex dyes was chosen to evidence the maximum of colour difference between irradiated and not irradiated areas. The purpose of this study was to find the best conditions for differential dyeing in terms of pH, temperature, liquor ratio, dyeing time. The main interests on wool fabrics were focused on two effects: a) one colour, double face same shade but different depth, higher on treated side; b) two shades, double face – different colours. Fastness evaluations toward dry rubbing and washing at 50°C were also carried out to confirm the feasibility of this alternative dyeing technique; in all experiments carried out with selected 1:1 metal-complex dyes the same score of conventional premetallised 1:1 dyeings was obtained.