The role of auxiliaries in the immersion dyeing of textile fibres part 2: Analysis of conventional models that describe the manner by which inorganic electrolytes promote direct dye uptake on cellulosic fibres

An analysis is provided of the various concepts and theories that have been proposed to account for the manner by which added NaCl or Na2SO4 promotes the uptake of direct dyes on cellulosic fibres. Although conventional approaches to describe the mechanism by which direct dye adsorption occurs entail the use of complex mathematical interpretations of isothermal equilibrium dye adsorption data, such interpretations are unable to satisfactorily explain not only why direct dyes display inherently low uptake on cellulosic fibres in the absence of added inorganic electrolyte but also why added inorganic electrolyte is so effective in promoting dye uptake.