A comparison of the colour strength and fastness to repeated washing of acid dyes on standard and deep dyeable nylon 6,6

Five acid dyes were applied at 0.5%, 1%, 2% and 5% omf depths of shade to both standard (amino end group [AEG]: 45 meq kg−1) and deep dyeable (AEG: 70 meq kg−1) nylon 6,6 fibres. The colour strength (K/S) of the dyeings as well as their fastness to repeated washing at 60 °C was determined. The finding that the K/S of dyeings on the deep dyeing variant was higher than that on its standard dyeable counterpart supports the accepted mechanism of dyeing nylon 6,6 with anionic dyes, that dye–fibre substantivity occurs predominantly via ion–ion forces operating between anionic groups in the dye and the protonated amino end groups in the fibre. However, the small difference in colour strength observed between dyeings on the deep dyeable and the standard dyeable fibre types implies that forces of interaction (e.g. H-bonding, dispersion forces and polar van der Waals' forces) other than ion–ion contribute to dye–fibre substantivity. When subjected to repeated ISOC06/C2S (60 °C) wash fastness testing, the five dyes displayed similar behaviour insofar as at each of the four depths of shade used, the dyeings underwent a reduction in colour strength due to loss of dye during. The extent of this reduction in colour strength increased with increasing depth of shade and with increasing number of washes; the reduction in K/S that accompanied an increase in number of washes was similar for both the standard and deep dyeable nylon 6,6 variants. The corresponding colorimetric data revealed that the standard dyeable and deep dyeable fabrics were very similar in colour at each of the four depths of shade used, both before and after repeated wash testing, which can be attributed to the polymers that were used in the two fibre types being similar.