increased. However, when the amount of dye increased from 12 to
16 g/L, the chromatic parameters reached a plateau, as the fibers
started to reach adsorption saturation.
As shown in Table 2, the K/S value reached maximum at a liquor
ratio of 25:1. Table 2 also shows that the lightness of the dyed
fabrics was lowest, leading to optimal dyeing results. At a lower
liquor ratio, therewas unevenness of the fabric surface; but after an
increase in the liquor ratio, the unevenness did not return. At a
higher liquor ratio, the concentration of the spent dye solution was
less than that of the initial solution because of more water in the
solution. The amount of dye remaining in the dye bath increased
with liquor ratio increasing. In view of technical and economical
considerations, we found that that the liquor ratio 25:1 was
suitable.
With the increase in dyeing temperature, more pigment molecules
overcome the diffusion barrier. The pervasion rate of the
pigment increases with the dyeing temperature. In particular, high
dyeing temperature facilitates diffusion of the dye. Results in
Table 3 suggest that as the temperature increased to 95 C, the dye
uptake reached a maximum value, and then decreased with further
increase in temperature. This trend may be explained by the
increased molecular movement at high temperature, and the
consequent desorption of more pigment from the fibers. Correspondingly,
the K/S value of fabric was also optimal at 95 C. The
color of the dyed fabric was yellowish-brown.
The effects of dyeing time on the depth of shade (K/S), dye
exhaustion rate and colorimetric parameters of the dyed flax fabric
are shown in Table 4. The K/S values increased with the dyeing time
up to 50 min, and then reached a plateau. This behavior is a
consequence of the balance in the amounts of pigment that
diffused to the interior of fibers and escaped from fibers at 50 min
dyeing time. Color coordinate values shown in Table 4 indicate that
the change in shade with dyeing time from 50 to 60 min was very
small. The dyeing system apparently reached equilibrium at
50 min. The lightness value of fabric reached the minimum when
the dyeing time was 50 min, indicating that 50 min was a suitable
duration for dyeing with EFCS.
Addition of salt to flax fabric being dyed is necessary in the case
of application of natural dyes. The uneven distribution of negative