3.3. Adsorption and desorption studies of lac dye on
cotton pretreated with chitosan and on untreated
cotton, and on cotton in the presence of 0.5 M
NaCl without pH control
The cotton yarn, prepared as noted in Section 2.1.1., with
and without the pretreatment with a 0.3% (v/v) of aqueous
solution of chitosan was dyed with an initial dye concentration
of 473 mg/L in a thermostatted shaker bath operated at
75 rpm. The adsorption conditions were pH 3.0, MLR of
1:100 and 30 -
C. The absorbance of the dye solutions was
monitored until constant absorbance values were obtained.The dyed cotton samples were then taken out and dried at
room temperature. To study the desorption of lac dye at
30 -
C, deionized water (50 mL) in each conical flask
(125 mL) was shaken in a thermostatted shaker bath operated
at 75 rpm. After 30 min, the dried cotton sample (0.50 g),
which had been pre-warmed in the thermostatted bath at
30 -
C for 30 min, was immersed in deionized water. The
cotton samples were then rapidly withdrawn after different
immersion times. The desorbed dye concentrations (qde)
were determined using a calibration curve based on absorbance
at lmax 487 nm (Cary 1E UVevisible spectrophotometer)
versus dye concentration in standard lac dye solutions.
The amount of dye adsorbed on cotton after desorption was
calculated by subtraction.
The adsorption and desorption of lac dyeing onto cotton
(initial dye concentration of 479 mg/L) in the presence of
0.5 M NaCl was investigated in a similar way. The absorbance
of the dye solution was measured at lmax 487 nm to monitor
the amount of lac dye adsorbed and desorbed from the cotton,
respectively