John A. Rippon

Effects of Plasma Treatment of Wool on the Uptake of Sulfonated Dyes with Different Hydrophobic Properties

A wool fabric has been subjected to an atmospheric-pressure treatment with a helium plasma for 30 seconds. X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry confirmed removal of the covalently-bound fatty acid layer (F-layer) from the surface of the wool fibers, resulting in exposure of the underlying, hydrophilic protein material. Dye uptake experiments were carried out at 50°C to evaluate the effects of plasma on the rate of dye uptake by the fiber surface, as well as give an indication of the adsorption characteristics in the early stages of a typical dyeing cycle. The dyes used were typical, sulfonated wool dyes with a range of hydrophobic characteristics, as determined by their partitioning behavior between water and n-butanol. No significant effects of plasma on the rate of dye adsorption were observed with relatively hydrophobic dyes. In contrast, the relatively hydrophilic dyes were adsorbed more rapidly (and uniformly) by the plasma-treated fabric. It was concluded that adsorption of hydrophobic dyes on plasma-treated wool was influenced by hydrophobic interactions, whereas electrostatic effects predominated for dyes of more hydrophilic character. On heating the dyebath to 90°C in order to achieve fiber penetration, no significant effect of the plasma treatment on the extent of uptake or levelness of a relatively hydrophilic dye was observed as equilibrium conditions were approached.

Effects of leveling agent on the uptake of reactive dyes by untreated and plasma-treated wool

Atmospheric-pressure plasma treatment of wool fabric produced a significantly higher level of adsorbed fiber-reactive dye when applied at 50 °C (pH 3.0—6.0) in the absence of any organic leveling agent. In addition, color yields indicated that dye was more uniformly adsorbed by the plasma-treated fabric compared with the untreated material. When untreated fabric was dyed in the presence of a leveling agent (Albegal B), the extent and levelness of dye sorption were enhanced. These enhancements were, however, relatively small on the plasma-treated wool compared with those on untreated wool. A ‘surface’ mechanism, similar to that proposed when plasma-treated wool is dyed in the absence of leveling agent, can explain the leveling ability of Albegal B under adsorption conditions. Increasing the dyebath temperature to 90 °C resulted in dye penetration of the fibers. Under these conditions, any enhancements of dye uptake produced by the plasma treatment, as well as the use of Albegal B, were relatively small, in contrast to the behavior at 50 °C. Improvements in the uniformity of dye sorption observed at 50 °C were, however, maintained at the higher temperature. It is concluded that the inability of reactive dyes to migrate (and so promote leveling and uniformity) once they have reacted with the fiber, means that differences in the uniformity of dye sorbed at 50 °C are still apparent at equilibrium.

Comments on "Pathways for Dye Diffusion in Wool Fibers"

Wortmann et al. recently reviewed some of the studies on the mechanism of dye diffusion into wool and gave their interpretation of the experimental data ( 6 ] . They agreed substantially with our earlier work ( Leeder et al. [3]), where we used the transmission electron microscope to follow the diffusion into wool of specially synthesized dyes containing nuclear-dense atoms. The mechanism, described in my review (Rippon [ 4 ] ) , is summarized’below. After entering the fiber between cuticle cells, dye diffuses throughout all the nonkeratinous regions,,including the cell membrane complex (cmc), endocuticle, and intermacrofibrillar material. Dye also appears in the nuclear remnants early in the dyeing cycle. Dye molecules progressively transfer from the nonkerati-