3.1. Dye extraction
CH and US extractions of lac dye were reported previously
to reveal the effectiveness of US over CH by about 41% enhancement
[15].
3.2. Dyeing
3.2.1. Effect of dye bath pH
Fig. 2 shows that the pH values of the dye bath have a considerable
effect on the dyeability of cationised cotton fabrics
with lac dye under both US and CH conditions. It is clear
that US has improved the dyeability of the fabrics at pH 1.5
and 2.5 values. As the pH increases the dyeability, under
both CH and US conditions, decreases. The effect of dye
bath pH can be attributed to the correlation between dye structure
and cationised cotton fibres. Since the lac dye used is a water-
soluble dye containing carboxyl groups, it would interact
ionically with the protonated terminal amino groups of cationised
cotton fibres at acidic pH via ion exchange reaction. The
anion of the dye has a complex character, and when it is bound
on fibre, further kinds of interactions take place together with
ionic forces. This ionic attraction would increase the dyeability
of the fibre as clearly observed in Fig. 2.