Differential Dyeing of Cotton. Part 2 – Stoichiometry of Interaction With Acid and Direct Dyes

The stoiciometry of interaction of both acid and direct dyes with cotton modified with a reactive cationic reagent has been examined. In the case of the acid dyes adsorption is principally by a specific site mechanism and gives a 1:1 ration between cationic sites on the cotton and sulphonate groups on the dyes, although some diffuse adsorption occurs with the more hydrophobic dyes. The direct dyes show a much greater amount of diffuse adsorption in addition to specific site adsorption. The results show that the presence of the cationic sites enhance the amount of dye taken up by diffuse adsorption and a mechanism for this is proposed