Lac dye is used extensively as a natural food additive
Chitosan is a deacetylated derivative of chitin, a natural
polymer found in the shell of crabs and shrimps [15]. Structurally,
chitosan contains two main functional groups, namely hydroxyl
and amino groups, as well as ether linkages (Fig. 2). It
has also been used to treat cotton in lac dyeing processes [12].
It was found that chitosan enhanced the uptake of lac dye and
increased lac dye sorption on cotton. However, the adsorption
isotherm was not reported in the study of Saxena et al. [12].
We have now investigated the adsorption and thermodynamics
of lac dyeing of cotton pretreated with chitosan compared
with untreated cotton. The effect of sodium chloride
(NaCl) on the dyeing process with, and without, pH control
was also studied. In addition, the thermodynamics of adsorption
of lac dye on cotton in the presence of NaCl was investigated.
These results were compared with the results from the
lac dyeing of pretreated and untreated cotton with chitosan,
and the findings are now reported in this paper.