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Abstract:
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Hydrolyzed reactive dyebaths present dyers with a major problem. Recently it
has been estimated that effluent treatment costs incurred for the batchwise reactive
dyeing of cotton are virtually identical to the cost of water used in dyeing. This is a
result of increasing environmental legislation which has lead to an increase in dyeing
costs. An exhausted reactive dyebath may contain as much as 50 percent of the
original dye used as well as auxiliary chemicals such as inorganic salts which do not
exhaust during the dyeing process. Current treatment systems to remove hydrolyzed
reactive dyes from the effluent have been proven costly and ineffective for some dye
classes.
Recent research has shown that hydrolyzed reactive dyebaths cannot be reused
to dye cotton because of the change in dyeing behavior and fastness characteristics.
However, this does not eliminate the possibility of using hydrolyzed reactive dyebaths
to dye other fibers such as nylon and wool. The objectives of this thesis were to
determine if it is technically feasible to dye nylon 66, nylon 6, and wool with
hydrolyzed reactive dye baths and to determine if this method of reuse could be used
as an alternative to current wastewater decolorization methods. This was
accomplished by investigating the adsorption characteristics of four hydrolyzed
reactive dyes under various conditions, comparing the washfastness and lightfastness
characteristics of selected hydrolyzed reactive dyes to acid dyes with similar parent dye structures, by illustrating the percent exhaustion of hydrolyzed reactive dyes into
selected fibers, and by comparing initial and final ADMI values.
The results of this thesis revealed that hydrolyzed reactive dyes can be used to
dye nylon 66, nylon 6, and wool under acidic conditions. The highest percent
exhaustion values were attained when fibers were dyed at a pH of 4.0. In general,
dye adsorption increased as sodium sulfate concentration increased. Lightfastness and
washfastness characteristics were comparable to acid dyes, however, the modified dye
structure resulted in poorer fastness in some cases. ADMI values were reasonably
low for some dyes, but were dependent on the initial dye concentration as well as the
fiber that was dyed. In all cases, there was a definite reduction in dye concentration
after using the hydrolyzed reactive dyebath to dye the selected fibers. This factor
coupled with the relatively low capital and operating costs of the reuse process would
result in a decrease in treatment costs. In addition, there is the potential to recover
the value of the reactive dye.
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