The role of auxiliaries in the immersion dyeing of textile fibres: Part 5 practical aspects of the role of inorganic electrolytes in dyeing cellulosic fibres with direct dyes

Both the colour strength of 2% omf dyeings and the extent of dye exhaustion achieved for three commercial grade direct dyes on cotton were promoted by the addition of 20 gl−1 NaCl at each of eight liquor ratios (1:50, 1:20, 1:10, 1:6, 1:3, 1:2, 1:1.5 and 1:1). The extent of electrolyte-enhanced dye uptake decreased with decreasing liquor ratio. For each of the three dyes, unlevel dyeings were obtained at 1:1 liquor ratio only in the presence of added electrolyte, whereas level dyeings were secured even at 1:1 liquor ratio in the complete absence of added electrolyte. The depth of the dyeings obtained in the absence of added electrolyte using both 1:1 and 1:1.5 liquor ratios were of similar magnitude to those secured using 1:10, 1:20 and 1:50 liquor ratios in the presence of 20 gl−1 NaCl. The promotion of dye uptake imparted by both added electrolyte and reduced liquor ratio were interpreted in terms of their effects on the substantivity of the direct dyes towards the cotton substrate. It is proposed that adding electrolyte to the dyebath and reducing the liquor ratio employed for dyeing have the same consequence in terms of enhancing dye uptake, namely that of encouraging dye aggregation in the dyebath which reduces the aqueous solubility of the anionic dye, which, in turn, results in the inherent preference of the dye to favour the aqueous phase shifting towards the fibre phase

The role of auxiliaries in the immersion dyeing of textile fibres: Part 7 theoretical models to describe the mechanism by which inorganic electrolytes promote reactive dye uptake on cellulosic fibres

A model is proposed to explain the manner by which the uptake of reactive dyes on cellulosic fibres is promoted by the addition of NaCl or Na2SO4 to the dyebath. The theoretical model invokes the concept of interstitial water in dyeing and suggest that increased dye uptake occurs because the added inorganic electrolyte promotes dye aggregation which reduces the solubility of the dye in the dyebath, so that the inherent preference of the highly soluble dye to favour the aqueous phase shifts towards the fibre phase. It is proposed that the same model can account for the promotion of direct dye uptake imparted by the reduction in the liquor ratio utilised for dyeing. As such, added inorganic electrolyte and reduced liquor ratio are considered to exert a combinatorial promotional effect on reactive dye uptake

The role of auxiliaries in the immersion dyeing of textile fibres: Part 9 practical aspects of the role of inorganic electrolytes in dyeing cellulosic fibres with pure reactive dyes

The colour strength, as well as the extents of both exhaustion and fixation, achieved for three pure reactive dyes on cotton were promoted by the addition of 50 gl⁻¹ NaCl at each of seven liquor ratios employed (1:50, 1:20, 1:10, 1:6, 1:3, 1:2 and 1:1.5). The depth of shade of dyeings obtained in the absence of added electrolyte using a1:1.5 liquor ratio were of similar magnitude to those secured using 1:10–1:20 liquor ratios in the presence of 50 gl⁻¹ NaCl. The promotional effect on dye uptake imparted by both added electrolyte and reduced liquor ratio was interpreted in terms of their effects on the substantivity of the reactive dyes towards the cotton substrate. The two, seemingly different actions of adding electrolyte such as NaCl or Na₂SO₄ to the reactive dye dyebath and reducing the liquor ratio used for immersion dyeing have the same result, namely that of encouraging dye aggregation in the dyebath, which reduces the solubility of the direct dye in the dyebath, which, in turn, shifts the inherent preference of the dye to favour the aqueous phase towards the fibre phase. It is thus possible to dye cotton using pure reactive dyes in the complete (ie 100%) absence of added inorganic electrolyte. The ensuing dyeings were of realistic depths of shade and displayed excellent levels of wash fastness

The role of auxiliaries in the immersion dyeing of textile fibres: Part 4 theoretical model to describe the role of liquor ratio in dyeing cellulosic fibres with direct dyes in the absence and presence of inorganic electrolyte

A model is proposed to explain the manner by which the uptake of direct dyes on cellulosic fibres is promoted by a reduction in the liquor ratio used for dyeing. According to the model, which invokes the concept of interstitial water in dyeing, reducing the liquor ratio promotes dye aggregation which reduces the solubility of the dye in the bulk dyebath phase, so that the inherent preference of the dye to favour the aqueous phase shifts towards the fibre phase. It is suggested that the same mechanism accounts for the promotion of direct dye uptake imparted by the addition of inorganic electrolyte to direct dye dyebaths. As such, reduced liquor ratio and added inorganic electrolyte exert a combinatorial promotional effect on direct dye uptake

The role of auxiliaries in the immersion dyeing of textile fibres: Part 6 analysis of conventional models that describe the manner by which inorganic electrolytes promote reactive dye uptake on cellulosic fibres

An analysis is provided of the various models that have been proposed to account for the manner by which added NaCl or Na2SO4 promotes the uptake of reactive on cellulosic fibres. Although conventionally, mathematical interpretations of isothermal equilibrium dye adsorption data are employed to describe the mechanism by which reactive dye adsorption occurs, such an approach does not satisfactorily explain why reactive dyes display inherently low uptake on cellulosic fibres in the absence of added inorganic electrolyte, nor does it explain why added inorganic electrolyte is so effective in promoting dye uptake

The role of auxiliaries in the immersion dyeing of textile fibres: Part 5 practical aspects of the role of inorganic electrolytes in dyeing cellulosic fibres with direct dyes

Both the colour strength of 2% omf dyeings and the extent of dye exhaustion achieved for three commercial grade direct dyes on cotton were promoted by the addition of 20 gl−1 NaCl at each of eight liquor ratios (1:50, 1:20, 1:10, 1:6, 1:3, 1:2, 1:1.5 and 1:1). The extent of electrolyte-enhanced dye uptake decreased with decreasing liquor ratio. For each of the three dyes, unlevel dyeings were obtained at 1:1 liquor ratio only in the presence of added electrolyte, whereas level dyeings were secured even at 1:1 liquor ratio in the complete absence of added electrolyte. The depth of the dyeings obtained in the absence of added electrolyte using both 1:1 and 1:1.5 liquor ratios were of similar magnitude to those secured using 1:10, 1:20 and 1:50 liquor ratios in the presence of 20 gl−1 NaCl. The promotion of dye uptake imparted by both added electrolyte and reduced liquor ratio were interpreted in terms of their effects on the substantivity of the direct dyes towards the cotton substrate. It is proposed that adding electrolyte to the dyebath and reducing the liquor ratio employed for dyeing have the same consequence in terms of enhancing dye uptake, namely that of encouraging dye aggregation in the dyebath which reduces the aqueous solubility of the anionic dye, which, in turn, results in the inherent preference of the dye to favour the aqueous phase shifting towards the fibre phase

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

The role of auxiliaries in the immersion dyeing of textile fibres: Part 1 an overview

Although auxiliaries have been a key component of immersion dyeing processes for many years the precise mode of action of many auxiliaries has not been fully resolved. This part of the paper discusses the various types of auxiliary available and the nature of the assistance they provide in immersion dyeing processes, together with both environmental and financial aspects associated with their use, as well as a discussion of the relationship between liquor ratio and the use of auxiliaries in immersion dyeing