THE DYEING OF NATURAL COTTON WITH DIRECT DYES: SOME EFFECTS DUE TO TEMPERATURE, DYE CONCENTRATION, AND ANIONIC SURFACE-ACTIVE AGENTS

The presence of an anionic surface-active agent in the dyeing of natural cotton yarn with a purified direct dye, using a dye-bath containing sodium chloride, is shown to increase the rate of dyeing, and to increase the amount of dye sorbed at equilibrium. The rate-accelerating effect has been studied as a function of the concentration of surface-active agent, using both commercial materials and methanol-extractable fractions of the latter. The effect exerted by an anionic surface-active agent, both on the equilibrium sorption and on the rate of dyeing, decreases as the temperature is increased. An explanation of the data, in terms of an interaction between the fibre and surface-active agent, is advanced.Studies carried out in the absence of a surface-active agent show that with increased temperature of dyeing the rate of dye sorption is increased, but the value of the equilibrium sorption is decreased; the dyeing process in exothermic. The relation between equilibrium sorption and residual dye-bath concentration is expressible by a Freundlich equation, and that between equilibrium sorption and initial dye-bath concentration is linear, at least over the range of concentration studied. The time required to reach a state of equilibrium increases as the initial concentration of dye in the bath is increased.