الفهرس 
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Abstract
The work presented in this thesis is undertaken with a view of :
(a) studying factors affecting the dyeability of wool, nylon-6, cotton
and mercerized cotton fabrics with direct dyes in presence and absence
of redox systems, (b) understanding the role of re~ox systems as well as
the mode of interaction, and (c) improving the dyeing properties of
direct dyes on the given substrates.
Results obtained along with conclusions arrived at from this thesis
are summarized and given below under three main headings :
(I) Utilization of redox systems for improving fixation of direct
dyes on wool fabric.
(II) The role of redox systems in dyeing nylon-6 fabric with direct
dyes, and
(III) Factors affecting the dyeability of cotton and mercerized cotton
fabrics with direct dyes in presence of redox systems.
I. Utilization of Redox Systems for Improving Fixation of Direct Dyes on
Wool Fabric
With a view to enhance the dyeability of wool fabric with direct dyes,
attempts have been made to incorporate different redox systems in the dyeing
bath. Redox systems used include ammonium persulphate as oxidant and glucose,
thiourea or potassium pyrosulphite as reductant. Given below dre the main
conclusions arrived at from these studies - vi -
1. The colour strength, expressed as K/5, is much greater in the
presence than in the absence of the redox system. This is observed irrespective
of the reductant used. Nevertheless, for a glven set of dyeing
conditions, the magnitude of colour strength is determined by the kind
of reductant used along with (NH4) 2N2o8, and it follows the order
(NH4)2 s2o8/c6H12o6 > (NH4 ) 2s 2os~cH 4N 2S > (NH 4) 2s 2os~K 2s 2o 5 >
(NH4) 2s2o8 ~None,
2. Presence of c6H12o6 along with (NH4) 2s2o8 (0.025 mol/1 each)
enhances significantly the colour strength.
3. Dyeing proceeds much faster in presence than in absence of
(NH4)2 s2o8/C6H12o6 redox system. Needless to say that the colour strength
increases initslly very fast then slows down with time.
4. Raising the dyeing temperature (from 50° to 90°C) is accompanied
by a signi ficnat enhancement in colour strength of dyeings.
5. At lower liquor ratios the availability of the dye, redox
system in the vicinity of the wool macromolecules is greater thereby leading
to higher dyeing.
6. Increasing the concentration up to 2~o (owf) is accompanied by
a significant improvement in the colour strength of the wool fabric. Moreover,
the highest colour strength is obtained in the presence of (NH4) 2s2o8;
c6H12o6 redox system.
7. The enhancement in the dye fixation before and after DMF extraction
as well as the improvement in the fasters properties of dyeings via- vii -
incorporation of the redox system in the dyeing formulation indicates that
presence of the redox system alters the mode of dye attachment to the wool
substrate.
8. In the presence of the redox system, i.e. (NH4l 2s2o8;c6
H12o6
,it
is postulated that dyeing involves covalent bonds and that there is a freeradical
mechanism in bonding between wool and direct dye in addition to their
conventional attachment.
II. The Role of Redox System in Dyeing Nylon-6 Fabric with Direct Dyes
Factors affecting dyeing of nylon-6 fabric with direct dyes in the
absence and presence of certain redox systems were investigated under different
conditions. The variables studied were : type and concentration of
redox system, dyeing conditions, i.e. time and temperature, material to liquor
ratio 8S well as type and concentration of direct dye. The obtained results
indicate that :
1. The colour strength is outstandingly higher in presence than in
absence of the oxidant, i.e. (NH4) 2s2o8, alone or along with reductant. A
comparison between the colour strength values of such dyeings obtained along
with four reductants would call for the following order :
(NH4) 2s2o8;c6H12o6 > (NH4) 2s2o8 > (NH4)2s2DgiCH4N2S > (NH4) 2s2o8/K2s2o5
>(NH4) 2s2o8/Na 2s2o3. 5H 2D ~None.
2. In absence of the redox system, dyeing proceeds via electrostatic
bonds between the dye anion and the protonated amino group, hydrogen
bonds and/or Van der Waals fources, but in presence of redox system, free
radical are supposed to be formed in both the fibre and the dye and the inter- viii -
action between these free radicals brings about covalent fixation beside
the usual physical bonds. This rather supported by the significant
value of colour strength after DMF extraction for dyeings obtained using
(NH4) 2s2o8/C6H12o6 (0.025/0.025 mol/1) redox system.
3. The rate of dyeing increases initially very fast then slows
down with time to level off. A perusal of result indicates that, 80°C
constitutes the optimal temperature for dyeing nylon-6, for a given set
of dyeing conditions. Nevertheless, the rate of dyeing is far greater in
presence than in absence of (NH4) 2s2o8;c6H12o6 redox system.
4. Increasing material to liquor ratio up to 1 : 40 is accompanied
by a significant decrease in colour strength.
5. The enhancement of colour strength as the dye concentration
increases could be attributed to greater availability of dye molecules
and/or dye free radicals in the vicinity of nylon-6 immobile macroradicals.
6. The magnitude of the colour strength and the fastness properties
of the dyeings are determined by the nature of the dye, i.e. size, shape,
configuration, number of dye sites, the fibre dye capacity, as well as by
the mode of interaction.
III. Factors Affecting the Dyeability of Cotton and Mercerized Cotton
Fabrics with Direct Dyes in Presence of Redox Systems
The work was further extended with a view of studying factors affecting
the dyeability of cotton and mercerized cotton fabrics with direct dyes and
understanding the mode of interaction in presence of certain redox systems.- ix -
Results obtained led to the following conclusions :
1. Presence of c6
H
12o6 along with (NH4) 2s2o8 in the dyeing bath
enhances significantly the colour strength. This suggests that (a) glucose
assists decomposition of (NH4
) 2s2o8 , (b) glucose radicals takes part in
creating a reactive sites located along the cellulose backbone as well as
on the dye capable of combination to form covalent bond in addition to their
conventional attachment via physical bond.
2. Mercerized cotton showed higher extent of dyeing than unmercerized
cotton. This is a a direct consequence of increased accessibility and
availability of the cellulose active centers for dye adsorption, i.e. hydroxyl
groups, under the influence of mercerization.
3. The rate of dyeing is much better in presence than in absence of
the redox system. On the other hand, raising the dyeing temperature from
50° to 70°C is accompanied by a considerable increase in colour strength
irrespective of the substrate used. This could be ascribed to the greater
activiation energy, and the greater mobility of the macromolecular chains in
the fibre as well as the greater solubility and mobility of the dye.
4. The colour strength, expressed as K/S, decreases by increasing
the material-to-liquor ratio up to 1 : 40. Nevertheless, the colour strength
is much better in presence than in absence of the redox system as well as
with mercerized than unmercerized cotton fabric as already emphasized.
5. The colour strength increases initially very fast by increasing
the dye concentration up to 1% owf, then almost levels off by further increase- X -
in concentration irrespective of the substrate used. On the other hand,
the nature of direct dye exerts a considerable effect on the magnitude of
the colour strength as well as the fastness properties of the dyeings.