The effect of various anti-setting systems in wool dyeing. Part 2: Sodium maleate based systems

Wool is subject to permanent setting reactions during dyeing at the boil. Sodium maleate additions to the dyebath exert an anti-setting effect, and in the case of wool piece-goods dyeing, the magnitude of anti-setting was evaluated using the crease angle method. To achieve anti-setting, the key reactions are the nucleophilic addition of the activated double bond in sodium maleate with wool thiolate anion groups and with free hydrosulphide anions generated by cysteine thiol decomposition. Optimum antisetting effects were achieved when wool fabric was treated with sodium maleate at pH 3. Fourier transform infrared reflectance spectroscopy was used to monitor chemical changes to the wool fibre. Compared to untreated wool, two new frequencies at 1354 and 865 cm^?1 were apparent; the highest intensity values for these bands were obtained for wool treated at pH 3, which indicates that wool, being positively charged in this acidic solution, adsorbed more sodium maleate, thus enhancing the chances for nucleophilic addition reactions.