Introduction
Cotton is an abundant natural fibre which consists of practically
pure cellulose (about 88e96%) [1]. Cotton may be
described chemically as poly(1,4-b-D-anhydroglucopyranose)
(Fig. 1) [2]. Natural cellulose fibres carry a small negative
charge (zplateauZ11 mV) due to the presence of some carboxylic
Lac dye is used extensively as a natural food additive
[9,10], and in cosmetics [9], as well as a colourant for silk
and cotton dyeings [11]. In the north and northeast of Thailand,
lac dye is a natural red dyestuff extracted for cotton and silk
dyeings [11]. However, lac dye has a low affinity for cotton
because cotton does not have any cationic sites for the attachment
[12]. An alternative way to overcome this problem is the
pretreatment of cotton with cationic agents. Rastogi et al. [13]
created affinity in cotton for lac dye by introducing cationic
sites in the fibre. Cotton fabrics were treated with a cationic
agent, Discofix DBA, and then they were dyed with lac
dye. It was found that the cationised cotton which was dyed
with lac dye exhibited a good colour yield and wet fastness
properties even without mordanting. In addition, poly(ethyleneimine)
(PEI) has been used as a cationic agent in cotton
dyeing with lac dye [14]. It was found that PEI increased
the dye adsorbed on cotton and also decreased the dye desorption
from the fibre.