The Influence of NaCl Concentration on the Build-Up Properties and Aggregation of Reactive Dyes

Abstract

This research investigated the influence of NaCl salt concentrations on the build-up properties of the selected warm- (Remazol Red RGB and Sumifix Supra Red 3BF) and hot- (Procion Red H-E3B and Drimarene Red X-6BN) dyeing reactive dyes on cotton. The results showed that an increment in the
NaCl salt concentration in the dyebath influenced the visual color yields of the dyes on cotton. Too high a salt content led to a decline in the visual color yields. This may have been explained by the formation of larger dye aggregates, being enhanced by the higher salt content. Too large aggregates were considered to lead to a lower number of dyes diffusing into the fiber and so they would mostly remain on the fiber surface, thereby reducing the visual color yield. A significant reduction in visual color yield of the dyes on cotton occurred at 300 g/l salt. Among the dyes studied, Drimarene Red X-6BN was less affected by the salt concentration changes. From the study of the aggregation of the dye molecules in solution, it was found that increasing the salt concentrations enhanced the aggregation of the dye molecules. In the presence of salt, less dye in monomeric form existed in the solutions. When salt concentrations increased, the absorbance peaks responsible for the dye aggregates increased compared with those of the dyes in monomeric form. In addition, a bathochromic shift was also observed. With increasing salt concentrations,
Drimarene Red X-6BN exhibited less reduction in the absorbance peak of the dye aggregates compared with the other dyes. This was in agreement with the build-up results. From this research, it showed that almost all recommended salt concentrations used in the reactive dyeing were not the optimum concentrations delivering the ultimate build-up of the dyes on cotton.