Sorption of an acid dye by silk fibre in the presence of bolaform electrolytes containing pyridine rings

The sorption behaviour of the acid dye, sodium 1‐phenylazo‐2‐hydroxy‐6‐naphthalenesulphonate, by silk fibre was investigated in the presence and absence of cationic bolaform electrolytes containing pyridine rings. These electrolytes were found to influence dye sorption to an extent depending on the pH of the dyebath. At pH 3, sorption decreased slightly with increasing electrolyte concentration, but in pure water it increased. It was found that although the number of binding sites and the intrinsic binding constant for Langmuir‐type sorption were hardly affected by the presence of bolaform electrolytes, the partition coefficient was significantly enhanced both at pH 3 and in pure water. This result is explained by the sorption of a dye–bolaform electrolyte complex by the silk. The influence on the sorption by the terminal groups on the bolaform electrolyte are discussed and compared with that of an aliphatic analogue.