Keywords (Extracted from title, table of contents and
abstract of thesis)
Acids, Based, Textile, Chemicals,
Dyestuff, Dyeing, Reduction, Method, Experimental, Technology,
Conservation, Ozon, Development, Aops, Reference, Environmental,
Water, Pollution, Novel |
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Abstract
This study discusses
the application of a newly developed method capable to decolorize
liquor by ozone and re-use it to rinse dyed materials for the
removal of unfixed dyes simultaneously. After successful application
of the new method on a laboratory scale, the method was upgraded
using a pilot plant and more than 100 runs were carried out
employing a variety of reactive, disperse and vat dyes.The quality
of textile materials treated with new method was determined in terms
of color evenness, fastness properties, color differences, and total
color difference with respect to reference.The new method was also
patented as “Method and device for dyeing a textile substrate” in
various Intellectual Property Offices (IPOs) of the world.
Initially, the effects of process parameters (pH, treatment time,
type of dyestuff, dye contents and proprietary chemicals) on the
color removal efficiency of ozonation process were studied for
synthetic effluents of reactive, disperse and vat dyes on a
bench-scale. In the case of reactive dyes, the color removal
efficiency of the process was significantly increased in an alkaline
environment. For effluents containing disperse and vat dyes, the
efficiency of the process though enhanced with increasing pH of the
effluent and ozone exposure time but that increase in the efficiency
was negligible as compared to the increase observed in the effluents
containing reactive dyes. The deceolorization performance of ozone
was significantly dropped for effluents of higher dye contents. The
addition of chemicals like salts and leveling agents showed no
noticeable effect on the color removal efficiency of ozone. However,
addition of sequestering agent (EDTA) slightly reduced (2-3%) the
efficiency of the process.
CI Reactive Black 5, CI Reactive Blue 19, and CI Reactive Orange 7
dyed fabrics were then treated with new method using a bench scale
experimental set-up. It was observed that an increase in treatment
time (40-50 minutes) improved the fastness properties of all three
dyes due to the decolorization of surface deposited unfixed dyes by
ozone. CI Reactive Blue 19 dyed fabric samples appeared to be
resistant to ozone decolorization, and best wash fastness (4.5) was
obtained after 50 minutes ozone treatment. The shade of ozone
treated fabric was almost identical to reference, and the minor
differences in terms of lightness (ΔL*= 0.03), hue (Δh*=0.01), and
total color difference (ΔE*=0.10) between reference and fabric
treated using new method were observed. In case of CI Reactive Black
5, 30 minutes washing-off by ozone assigned color properties (ΔL*=
-0.07, Δh*= -0.18, ΔE*=0.32) similar to reference. On contrary, CI
Reactive Orange 7 behaved differently and showed wash fastness
rating half point less than that of reference. The shade was darker
(ΔL*= -0.51), slightly brighter (Δc*= 0.34) and yellower (Δb*=0.31)
than reference. Total color difference (ΔE*= 0.91) was, however,
within permissible limit (ΔE*<1.0). This implies that unfixed dyes
are still present on the fabric surface, which is required to be
removed either by extending the ozonation time or by increasing the
ozone dose. The application of ozone treatment also resulted into a
gradual decline in the pH of the bath water, which owes to the
formation of organic ions in the form of their corresponding acids.
Since dyed materials are extremely sensitive to ozone dose, it was
essential to determine an optimal dose before applying new method on
a pilot scale. An ozone dose of 10 g/hr was found to be optimum for
very dark shade (7% owf). The new method was then extensively tested
using a pilot plant, and more than 100 trial runs were carried out
using a wide range of dyes from various classes of dyestuff
(predominantly reactive dyes) obtained from world renowned dye
manufacturers (Dystar, Clariant, Ciba, and Sumitomo).
Vinylsulfone dyes were prone to rapid degradation by ozone, and
liquor was almost colorless after 20 minutes of ozone treatment. For
all shades such as Black (16), Indigo (18), M.Blue (21) and Navy
(24), wash fastness (4.5) was similar to reference after 20-30
minutes ozone treatment. Total color difference values (ΔE*=
0.83-1.0) were in the acceptable limit (ΔE*<1.0). However, the color
differences (ΔL*, Δa*, Δb*, Δc*, and Δh*) between reference fabric
and those washed-off using new method showed the occurrence of
unfixed dyes on the surface of fabric.
In case of monochlorotriazine (MCT) reactive dyes, the color removal
of bath water was in the range of 85-99% after 30 minutes ozonation
treatment. The wash fastness of ozone treated fabric was excellent
(4.5) for all shades including Yellow (11), Orange (19), Dark Blue
(32) and Light Blue (37). However, color differences in terms of ΔL*,
Δa*, Δb*, Δc*, and Δh* between ozone treated fabric and reference
showed that shades of ozone treated fabrics were darker, which
implied that surface deposited loose dyes were still there. Total
color difference values (ΔE* = 0.69 - 1.26) were in the acceptable
limit (ΔE*<1.0).
For bi-functional reactive dyes (Green (17), Burgandy (25) and Dark
Grey (27)) bathwater was almost colorless after 30 minutes of ozone
treatment. Wash fastness of all fabrics was similar to reference
fabric. Total color difference values (ΔE*= 0.58-1.23) were also in
the acceptable limit (ΔE*<1.0).
Fabric samples of Blue (10) and Dark Pink (26) shades of
monoflourotriazine reactive dyes showed excellent wash fastness
(4.5) after 10-40 minutes ozone treatment. The color removal of bath
water was in the range of 82-99% after 40 minutes of ozonation. For
all shades, the total color difference values (ΔE*= 0.43- 1.50) were
closer to the acceptable limit. However, color differences (ΔL*, Δa*,
Δb*, Δc*, and Δh*) between ozone treated fabric and reference showed
the presence of some surface deposited unfixed dyes.
Similarly, the wash fastness properties of fabrics (Choco (31) and
Slate (33)) treated with new method were excellent (4.5), and total
color difference values (ΔE*= 1.10 - 1.14) were near to allowable
limit.
Overall, most of the shades of ozone treated fabrics were a bit
darker with respect to reference indicating the presence of surface
deposited unfixed dyes, however, these unfixed dyes can be removed
by either extending ozone treatment time or by increasing ozone
dose.
The new method was proved to be very economical because it reduces
the water consumption (50% water saving), is less energy intensive
(applicable at ambient temperature), and is environmental-friendly
(involves no chemicals).
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