Technical terms of textile dyeing

Presentation on: Technical terms of Textile Dyeing
Prepared By:
Tanvir Ahammed Rana
Id. 2012000400038
19th Batch, Textile Department.
SouthEast University.

Introduction to dyeing
Dyeing is process in which textile substrate is colored by
suitable substances that is dyes or pigment (pigment
dyeing). The former is widely used in textile wet processing.
A basic knowledge of dyeing process and related terms are
quite important to understand dyeing theory. Dyeing can be
done at any stage of the manufacturing of textile- fiber, yarn,
fabric or a finished textile product including garments and
apparels. Textile materials can be dyed using batch,
continuous or semi-continuous processes. The type of
process used depends on several things including type of
material (fiber, yarn, fabric, fabric construction, and
garment), generic type of fiber, size of dye lots and quality
requirements in the dyed fabric.

Dye
A dye is an organic colored compound which when applies to textile for
imparting color & strictly adheres with the textile substrate [5]. Dyes should
resistant to light, heat and wet agencies. In textile terms, a soluble colorant
that attaches in molecular form to the fibers. All dye is a colored substance
whereas all colored substances are not dyes. The dyes applied to textile fibers
should possess the following characteristics,
1. Stable & attractive color i.e. should not undergo structural changes easily
2. Posses affinity to the fibers
3. Soluble in water or any suitable medium otherwise it should form stable
dispersion with water or solvents
4. Fastness to light, washing, perspiration, dry cleaning agents and rubbing
Dyestuff consist of the constituents named as chromophores and
Auxochrome. Chromophores give the dye molecule its particular colour,
while the Auxochrome intensify the hue of the dye molecule’s colour, makes
the dye molecule more water soluble, and improve the colour fastness of the
dyed fabric or printed fabric. Some common chromophores groups are azo,
quinonoid, nitro and nitroso groups whereas Auxochrome are acidic such as
carboxylic and Sulphonic groups and in basic Auxochrome includes amino
and hydroxyl groups.

Substantivity
Tendency of a dye to move from a
solution out of fibers in the dye
solution. It is a quality of dye.
Without substantivity, most of
dyes would simply remain in
solution or dispersion in the bath.
The substantivity of dyes depend
upon,
i. Molecular structure (shape)
ii. Size of molecule dye
iii. Dye bath conditions
This property of a dye determines
how much dye is exhausted on to
the fiber under neutral conditions.
More substantive
dye
 Planar structure
 Less soluble
 Poor leveling
 High wash
fastness
 High r.m.m*
Less substantive
dye
 Less Planar
 More soluble
 Good leveling
 Low wash
fastness
 Low r.m.m*

Affinity
Attraction between two items, in dyeing affinity
essentially means the preferential attraction of the
dye for the fiber rather than for the solution of the
dye bath. It is quantitative expressing of
substantivity. Technically, affinity is expressed in
term of energy. Generally, more substantivity dyes
have low affinity characteristic, it is due strike or
rush of dye molecule.

Exhaustion
The process of transfer of dyestuff from the dye bath on to the fiber or material is
known as exhaustion. The ratio between the amount of dye taken up by the
substrate and the amount of dye originally available.
Relative molecular mass
Where,
Co = initial concentration of dye in dye bath
Cs = concentration during the process
The exhaustion of dyestuff is depend on,
i. Concentration of dye
ii. Concentration of salt
iii. Temperature
iv. Agitation
v. liquor ratio

Adsorption Absorption
Dyes molecules from solution are
taken up by certain textile
substrates which have porous
surface i.e. cotton by the process
adsorption. Distribution of the dye
stuff on to the surface of the fiber
is known as adsorption.
Adsorption is depend on
i. Concentration
ii. Temperature
iii. Dye nature
iv. Pressure
v. Surface area
Distribution of liquor containing
is dye stuff on to the whole of the
fiber that is on to the surface and
inside of the fiber surface.
The some factor are mentioned
below which affects the rate of
absorption,
i. Time
ii. Temperature.
iii. Alkalis
iv. Electrolytes
v. Dyeing Auxiliaries
vi. Liquor ratio

Desorption Diffusion
Transfer of dyestuff from
the surface of the fiber in
the liquor is known as
desorption. Desorption is
reverse of dyeing process.
This is a process by which dye move from a
surface of the fiber in to the fiber itself and vise
versa. The diffusion of given dyestuff is
heavily influenced by temperature the higher
the temperature the greater the degree and rate
of diffusion. Diffusion rate is also depending
on the crystallinity of the fabric structure.
The expression is known as Fick’s law and it
gives a quantitative value to the diffusion of
dye molecules from the outside layers into the
interior of the fiber:
ds/dt = -D dc/dx
Where,
s = amount of dye diffusing across unit area;
t = a small interval of time;
c = concentration of dye at a specified point x;
x = the distance diffused;
D diffusion coefficient – it is preceded by a
negative charge b/c the amount of diffusion is
inversely proportional to the value of dc/dx.

Migration
Migration is the process by which are
dye move around the fiber or level
itself. Transfer of dyestuff from heavily
dye to light dye portion of the same
material during dyeing is known as
migration. The migration process
comprises adsorption of dye on to the
fiber surface, migration through the dye
liquor, re-adsorption onto the fiber
surface since diffusion is the rate
determining step, in this dynamic
process, migration itself is also heavily
influenced by temperature.
Dye stuff in a solution
(Desorption)
↓↑
Dyestuff on the surface of fiber
(Diffusion & Absorption)
↓↑
Dyestuff in to the inside and whole the fiber
The above complete process of
absorption, diffusion and desorption is
known as migration. The migration
properties of dyestuff depend on dyes
nature.

Zeta potential Strike
It is a difference in the
electrical potential across
the interface (a diffuse
double layer) of a solid
surface contact with a
liquid.
The initial rate of dyeing (the
initial slope of exhaustion
versus time). Rapid strike by a
dye often results in initial
unevenness and must be avoided
for those dyes that cannot
subsequently migrate from
heavily to lightly dyed areas of
the fabric.
The strike depends on:
i. Dyeing temperature
ii. Dyeing pH
iii. Addition of chemicals.

Fixation Reactivity
Formation of the “final” bond
between the dye and the fiber with
the mechanisms such as ionic
bonding and hydrophobic forces.
Disperse and vat dyes are fixed in
the fibre largely by physical
entrapment of insoluble dye
within the fibre. The bond that
causes final fixation is not
necessarily the same type of bond
is first made as the dye exhaust
onto the fibre.
This term describes the rate at
which a dye reacts with fibre.
High reactivity dyes react rapidly
at relatively low temperature,
where as low reactivity dyes
generally require relatively high
temperature for dye fixation.
Dye uptake
Dye-uptake is a property or
ability of textile fiber to capture
the given amount of dye. This
property varies fiber to fiber and
depends on dye sites, orientation
in a fiber.

Dyeing rate
Rate of dyeing under any set of conditions (i.e.
temperature, pH and time) is proportional to
concentration of dye in the solution at given time
t. rate of dyeing can be written as
Rate of dyeing = [Dye]s,t . kdye
Where,
s means ‘solution’
t means ‘time after the start of dyeing’
kdye, it is a proportionality constant called the
dyeing rate constant for the particular set of
conditions of dyebath.
Rate of dyeing curves can then be constructed
similar to that shown in figure below, in which
different dyeing rates of three reactive Remazol
dyes. By plotting percentage exhaustion against
time of dyeing; these are very useful indicators of
dyeing efficiency.
Fig. Rate of dyeing of different dyes

Dyeing equilibrium Rate of dyeing reaction
Dyeing can be perceived as a two way
process or equilibrium reaction, in
which dye (D) and the fiber (F) are in
equilibrium with dyed-fiber (DF).
i.e.
D + F ↔ DF
dyeing reaches the equilibrium point,
where there is no further in dye on
tAs dyeing proceeds, more dye is
taken up by the fiber than is lost from
it back into bath; i.e. there is net
increase of dye on fiber. Eventually he
fiber. However, this does not imply
that dye movement has now ceased; at
the equilibrium point; dye still enter
and leave the fiber but it does not at
the same rate.
The rate of reaction of dyes
means the rate at which chemical
bonds between dyes and textile
fibers are formed. Although the
rate of reaction varies with dyes,
it is largely affected by ,
i. temperature,
ii. pH
iii. time
In practical dyeing, the
dye/water/cellulose system is
heterogeneous, and affinity and
diffusion should be considered,
so that there is much difficulty in
measuring the rate of reaction.

Heat of dyeing
The heat of dyeing is the measure of the strength of the bonds by
which the dye is held to the fiber. Since the transfer of dye from the
solution to the fiber involves a decrease in free energy of the system,
heat is given out, and the heat of dyeing is therefore a negative
quantity. the converser is, of course, also true, namely that the
migration of dye from the fiber to the liquid phase is accompanied by
the absorption of heat. Thus an increase of temperature favors
desorption and consequently decreases the concentration of the dye
molecules in the fibre at equilibrium.
It is difficult to measure the direct calorimetric measurement of heat of
dyeing b/c the thermal change is so small.
Tinctorial strength:
The effectiveness of a given amount of dye in coloring a given mass of
fiber.

Compatibility
This decrease the ability of a dye combination usually with similar
substantivity, exhaustion and fixation profile to behave as a single dye
combination of compatible dye will generally give good
reproducibility and sustainability to variable in the process.
Generally it can never be predicted whether the high or low
substantive dyes will produce better result the overall result are always
based on S.E.F profiles of the combination use for desire shades.
A dye would never be appropriate if it highly reactive and low in
substantivity most importantly there should be a minimum difference
between the exhaustion and fixation curve irrespective of its high or
low substantive character.
Cloud point
The cloud point is the temperature at which the detergent reaches its
limiting solubility and start to precipitate out, causing the solution to
appear cloudy. In general when comparing two detergents with similar
structures, the one have more hydrophilic will have higher cloud point
than the other. This is most common in nonionic surfactants.

Depth of shade (dos)
It is a ratio of weight of dye to weight of goods dyed, usually expressed as
percentage; amount of dye, owf (over the weight of fabric). Depth of shade (DOS),
in these terms, is not really a very good way of comparing the darkness or intensity
of color of finished fabrics, due to inherent differences in the hues of different dyes
within a family, difference between dye families, and differences due to the nature of
the fabric. Dye manufacturers’ shade cards are typically show one or two depths of
shade for a particular dye, often between 1% and 4%, except for black, which is
typically 3% to 6%.
Anti migration
It is a reverse of migration, the dyestuff is move out from the fiber surface and goes
into the dye bath solution
Anti-migration → decrease in affinity
Each dye class have its critical temperature, above this critical temperature the dye
stuff anti-migrate instead of migration.
An additive use in dye or pigment mixture to prevent undesired movement or
spreading of the wet dye on fabric. Sodium alginate is the anti-migrating agent used
in reactive dyeing, retard the rate of migration by producing physical hindrance and
by increase of viscosity of solution. The function of levelling agent or retarder is
antimigration.

Dispersion
A system consisting of finely divided particles and the medium in which
they are distributed.
Color fastness
The resistance ability of dye molecule to any agency named as washing.
Light, rubbing and crocking. The different terms comes under this term
such as wash fastness, light fastness etc.
Fading
Fading is seen as a colour loss by the dyed or printed fabric textile material.
It is result of some changes in the structure of dye molecule due to
absorption of light, reaction with air pollutants, laundering, dry cleaning
and other agency.
Gas fading
Fabrics dyed with certain blue & violets disperse dyes containing
Anthraquinone structure become fade in presence of nitrous oxide. This
nitrous oxide may be made in nature from various sources such as open gas
fire, electric heating arrangement.

Oligomers
During the exhaust dyeing process the oligomers may diffuse out of the Polyester
fiber and form grey deposits (white dust) on the fiber surface and also on machinery
and pipes during cooling down of the dyebath.
During the production of poly ethyl enter phthalate (PET) fibers short chains,
consisting of only a few monomers units, are also formed, these are so called
oligomers. The main component is a cyclic trimmer. All Polyester fibers contain
small quantities of oligomers, Approx. 0.5% - 3% of the fiber.
Level dyeing
Uniform in shade over the surface of a piece of dyed fabric or along the length of
dyed yarn Level dyeing is usually the objective in commercial processes.
Some dyes, such as leveling acid dyes, are easy to accomplish level results with.
They do not bind tightly to the fabric in the dye bath, and dye can leave the fibre
and re-enter the dye bath. Other dyes, such as reactive dyes, don’t level as easily,
and greater care is required to achieve level results. In general, level dyeing is
promoted by good agitation, careful control of the rate of rise of the temperature of
the dye bath, control of pH, and sometimes by use of special leveling agents or
retarders. It is often the case that the dyes that level most easily are the least
washfastness.

Reserving agent
It is also called restraining agents; a dye bath auxiliary that is
typically used to prevent one fiber in a blend from taking up dye
intended for the other fiber, or to equalize the uptake When blends
are dyed, one fiber may be truly dyed while the other is stained
(colored, but with very poor fastness). Reserving agents can be
used to significantly reduce the undesired staining. In blends such
as wool nylon, reserving agents can act to reduce the dye uptake by
the nylon, so that the nylon and wool ultimately are colored
similarly.
OWB (or O.W.B)
On weight of bath; usually expressed as percentage; omb is on
mass of bath - preferred modern usage. The amount of some
constituent of a dyebath or other process bath based on the weight
of the bath. For example, something specified as 6% owb would
require 0.06 pounds of that item per pound of bath. Since the bath
is invariably mostly water, which weighs 1 kilogram per liter,
calculations in the metric system is much easier.

OWF (or O.W.F.)
On weight of fibre, usually expressed as percentage; omf is on mass of fibre -
preferred modern usage often this is synonymous with owg but distinction
may be appropriate when considering a particular fibre in a blend.
OWG (or O.W.G.)
On weight of goods; usually specified as percentage; omg is on mass of goods
preferred modern usage. The amount of dye or auxiliary chemicals used is
often based on ratio to the weight of the goods to be dyed. For example, if a
formula calls for 3% dye owg, and 400 grams of fabric are to be dyed, the
required amount of dye would be 3% of 400 grams, or 12 grams. Owf may be
more accurate when blended fibres are considered.
Padding
This is the most important component of semi or continuous dyeing machines.
It is a dyeing method with very low liquor to goods ratio, where typically only
enough strong dye solution is used to saturate the fabric. Padding can have the
advantage of high dye yield. Padded goods are usually “batched” - wrapped in
plastic and left for some period of time for the dye to attach to the fibre, or
steamed to fix the dye quickly.

Pick up%
It is a ratio of amount pick or uptake by fabric when it passes through the
solution or dye liquor.
Pick up % = [ (W2 – W1 ) / W1] X 100
Where,
W2 = after padding weight of fabric
W1 = before padding weight of fabric
Liquor ratio
It is the ratio of the weight of the dyebath or other processing bath to the
weight of the goods being dyed or processed for immersion dyeing in art
dyeing processes, common liquor to goods ratio is 20:1. That is, for each
kilogram of fiber to be dyed, 20 kilograms
of dyebath are used. In the metric system, this is easy to calculate, since one
liter of water weighs one kilogram. High liquor ratios are generally avoided,
since they often cause poor exhaustion of the dye, though this is not true for
all dye types. Modern commercial dyeing equipment often works with low
liquor ratios. Very low ratios may be used for methods where essentially all
of the dye solution is to be absorbed by the fiber, such as padding .

Stock solution
A solution of known strength, made up with the intent of
dilution or mixing before final use Stock solutions are a
convenient way of avoiding the need to weigh chemicals each
time you need to use some. For example, you need 2% shade
of Red of 5 gram of fabric and you have 1% stock solution of
dye. Use this formula and take amount of dye in ml.
Dye (ml) = (Wt. Of fabric * Shade %) / Stock Solution %
Dye blocking
The term dye blocking is used when one dyestuff blocks the
exhaustion of the other dyestuff on to the fabric when
combined in the same bath. It is due to the different r.m.m and
affinities of dyes molecules in combination shades.
Topping
It is a process of redyeing of dyed fabric in response of faulty
dyeing or increase the depth of shade.

Tailing
Tailing is refers to a phenomenon in which depth & shade occur on
dyed fabric owing to worst distribution of dyes from top to bottom
(first meters and last meters). This is a problem of semi &
continuous dyeing. Tailing behavior is dependent upon the
following factors,
i. Kind of fibers
ii. Padding operation & substantivity of dyes
iii. Particle size of dyes
iv. Concentration of dyes
v. Dispersibility or solubility of dyes
Tailing is also cause by incompatibility of dyes with auxiliaries.
High substantive dyes are liable to tailing. In vat/disperse dyeing
the dispersion stability; change in concentration is very important
to avoid this problem. In blends fabric such as polyester/cotton the
chances of tailing is reduced as only in cotton, it also depend on
the blend ratio.

Listing
Listing refers to a phenomenon in which variations in depth & shade occur
on dyed fabric owing to uneven dye uptake from side to side and side to
center. As causes of listing, the following may be given:
i. Uneven drying before padding of the fabric from side to center
ii. Uneven squeezing
iii. Inadequate pretreatment
iv. Uneven padding liquor temperature
v. Uneven fabric temperature
vi. Variation in dye migration due to air speed
vii. Temperature dependence of dyes of thermo soling
For preventing listing during padding, padding liquor should be taken up
uniformly onto t5extile substrate from side to center, while the textile
substrate are immersed in padding liquor for a very short time & then
squeezed. Inadequate pretreatment is hot issue for listing problem; the low
absorbency rate can influence this problem. In drying by means of heat, air
speed has large effect on the rate of drying, and as a result, it has also effect
on migration. As the air speed increased the rate of migration increased.

Specks
This problem occurs due to improper dissolution of dye powder while
preparing the dye solution [8]. Formation of specks during padding is mostly
attribute to the particle size of dyes, compatibility with migration inhibitor &
penetrating agents, re-dispersibilty of dispersion liquor (Vat/disperse dyes).
A larger factor causing specks in practical dyeing is compatibility of dyes
with auxiliaries used together. When poor compatibility, dye aggregation is
caused and solubility or Dispersibility of dyes markedly lowered, a
formation of specks but also the tailing are caused.
Colour spots / blotches
This is formation of dark colored area on the dyed fabric, which causes
faulty dyeing. The probable reasons are,
i. Filtration of dye solution is not carried out, especially when mixture of
dyes are used, before adding into the machine or padding trough.
ii. Inadequate pretreatment
iii. Presence of contaminants in water, salt, alkali etc.
iv. Incompatibility of dyes with auxiliaries

Photochromism
Photochroism is refers to the phenomenon in which dyed substrate
changes in color under irradiation of light but returns to original color
when the irradiation stops. This is said to be tautomerism occurring to
molecules under exposure to light. However, the color is restored after
the substrates are left overnight.
This phenomenon appears markedly in viscose rayon and tends to
occurs increasingly easily as the concentration of urea formaldehyde
resin increases. The reversion of color is depending on the relative
humidity and light intensity.
Thermochromism
Thermochromism is refers to phenomenon in which dyed substrate
changes in color under application of heat but returns to original color
when the heat stops or reduced.
As to reactive dyes, this phenomenon varies from dye to dye.

Stripping
Stripping is refers to the removal of dyestuff either partial or complete from the dyed
fabric in case of too high dye in depth, unlevel dyed or faulty dyeing.
Complete removal of dyestuff is generally difficult. The stripping of dyes can be
done by reducing agents or oxidizing agents, in most cases reducing agents are
preferable.
Washing off
As the name indicate the term washing off is to remove the unfix dyes and other
auxiliaries from the dyed substrate. Substances in the second category can often be
swollen & removed quite quickly by vigorous washing at low temperature, but
removal of dyes from within the fiber will be much slower unless high temperature
are used. The removal of soluble materials from the fabric is accomplished by two
mechanisms,
i. Diffusion
ii. Liquid interchange
The following factors are unfavorable for washing off,
i. Hard water
ii. Electrolyte content of water
iii. Washing process at a low liquor ratio
iv. Too Low temperatures

Aggregation
Clustering of individual particles of a substance that is dyes or pigment
to colloidal properties. Aggregation of dyes is the dye-dye self
association in solution, called dye aggregation, which is important term
where dye molecules or ions takes part. In general, the term
aggregation is used for dye-dye interaction & dye association for
interaction of dyes with other compounds e.g. polymers.
The reasons of aggregation of dyes are,
i. Dyes are consists of, a. Hydrophobic aromatic portion b. Polar
groups for water solubility and charged groups (sulfonic or positive
charged groups) for rendering molecule water soluble
ii. When dye molecules dissolved in water a new interface is created
between the hydrophobic portion and water. Dye can reduce the size
of the interfacial water by overlapping of the hydrophobic areas and
there will be a tendency to aggregate.
iii. Usually linear and planar dye molecules should tend to stack one
molecule upon another with the ionized groups arranged so as to
give minimum free energy condition causes aggregation.

iv. Dyes with long aliphatic chains
form micelles of a spherical form in
which the flexible chains associate
in the interior with the sulfonic acid
groups exposed on the surface of
sphere.
v. Aggregation of dimer is more
obvious as aromatic ring system
have maximum overlap (van der
Waals forces) because the distance
between the anionic charges is larger
(minimum electrostatic repulsion).
As dye concentration increases there
will be an increased tendency for
trimmers, tetramers etc. to be formed.

Union dye
A dye that is a mixture of two or more different classes
of dye, used typically to dye blends of fibres
“Household” dyes, of the sort sold in grocery stores, are
usually union dyes containing a direct dye which will
work on cellulose fibres, and an acid dye which will
work on wool or nylon. Industrially, union dyes may be
other combinations, such as reactive and disperse dyes
for dyeing cotton-polyester blends.
Prepared for dyeing
It is a term used for a fabric or garment that is specially
made to be dyed; sometimes “preferred for dyeing”;
usually abbreviated pfd or p.f.d. PFD fabrics have been
desized, scoured, and fully bleached, but have been
processed without optical brighteners or softeners which
can interfere with dye uptake.

Some miscellaneous dyeing method
Color is applied to fabric by different methods and at different stages
of the textile manufacturing process. The processes are given below,
Solution pigmenting or dope dyeing
Dye is added to the solution before it is extruded through the
spinnerets for making synthetic filaments. Simply, Coloration of the
polymer prior to manufacturing of fibers.
Stock dyeing
Stock dyeing is used to dye fibers. In this process, the staple fibers are
packed into a vessel and then dye liquid is forced through them.
Although the dye solution is pumped in large quantities, the dye may
not penetrate completely into the fibers and some areas may be left
without dyeing. However, the following blending and spinning
processes mix up the fibers in such a thorough way that it results in an
overall even color. Woolens are usually stock dyed.

Top dyeing
Top is the combed wool sliver. It is wound on perforated spools and the dye
solution is circulated through it. This method results in very even dyeing.
Yarn dyeing
When dyeing is done after the fiber has been spun into yarn, it is called yarn
dyeing. In this method, the dyestuff penetrates the fibers to the core of the
yarn. There are many forms of yarn dyeing- Skein (Hank) Dyeing, Package
Dyeing, Warp-beam Dyeing, and Space Dyeing.
Skein (hank) dyeing
The yarns are loosely arranged in skeins or coils. These are then hung over a
rung and immersed in a dyebath in a large container. In this method, the
colour penetration is the best and the yarns retain a softer, loftier feel. It is
mostly used for bulky acrylic and wool yarns.
Package dyeing
The yarns are wound on spools, cones or similar units and these packages of
yarn are stacked on perforated rods in a rack and then immersed in a tank. In
the tank, the dye is forced outward from the rods under pressure through the
spools and then back to the packages towards the center to penetrate the
entire yarn as thoroughly as possible. Mostly, the carded and combed cotton
which are used for knitted outerwear is dyed through this method.

Warp-beam dyeing
It is similar to package dyeing but more economical. Here, the yarn is wound
on to a perforated warp beam and then immersed in a tank for dyeing it
applying pressure.
Space dyeing
In this method, the yarn is dyed at intervals along its length. For these two
procedures- knit- deknit method and OPI Space-Dye Applicator- are
adopted. In the first method, the yarn is knitted on either a circular or flat-
bed knitting machine and the knitted cloth is then dyed and subsequently it is
deknitted. Since the dye does not readily penetrate the areas of the yarn
where it crosses itself, alternated dyed and undyed spaces appear. The OPI
Space-Dye Applicator technique produces multi coloured space- dyed yarns.
The yarns are dyed intermittently as they run at very high speeds through
spaced dye baths. They are continuously subjected to shock waves produced
by compressed air having supersonic velocities.
Piece dyeing
The constructed fabrics are piece dyed for the flexibility they provide. The
textile manufacturer can dye the whole fabric in batches according to the
fashion demands of the time thus avoiding wastage and resultantly loss.
There are several methods prevalent or piece dyeing.

Garment dyeing
Garment dyeing dye is applied to finished products such
as apparels and garments.
Piece dyeing
In this method, small batches of constructed natural
colored fabric are dyed according to the demands for a
given color.
Beck dyeing
It is used for dyeing long yards of fabric. The fabric is
passed in rope form through the dyebath. This rope of
the fabric moves over a rail onto a reel which immerses
it into the dye and then draws the fabric up and forward
and brings it to the front of the machine. This process is
repeated many times until the desired color intensity is
obtained.

Recent dyeing terminologies
Ultrasonic assisted dyeing
The use of ultrasound in the dyeing of textile can be explained as: when ultrasound
waves are absorbed in the liquid system the phenomenon of cavitations takes place.
Cavitation's can liberate entrapped gases from liquid or porous material like textiles,
dyebath etc. The influence of ultrasound on dyeing is explained to have thee-ways
effects:
 Dispersion
 Degassing
 Diffusion
Microwave dyeing
Microwave dyeing takes into account only the dielectric and the thermal properties.
The dielectric property refers to the intrinsic electrical properties that affects the
dyeing by polar rotation of the dye & influences the microwave field upon the
dipoles.
The aqueous solution of dye has two components which are polar, in the high
frequency microwave field oscillating at 2450MHz. It influences the vibrational
energy in the water molecules and the dye molecules. The heating mechanism is
through ionic conduction, which is a type of resistance heating. Depending on the
acceleration of the ions through the dye solution, it results in collision of dye
molecules with the molecules of the fiber. The mordant helps and affects the
penetration of the dye and also the depth to which the penetration takes place in the
fabric. This makes microwave superior to conventional dyeing techniques.

Electrochemical dyeing
The vat and Sulphur dyes are insoluble in water; therefore for their
application it is necessary to convert them into water-soluble form using
suitable reducing agent and alkali. Different reducing agents use for vat and
Sulphur dyes are briefly reviewed with emphasis on the emerging technique
of electro chemical reduction.
Plasma application for dyeing of textile substrate
Dyeability of Cotton Substrate
It has been reported that plasma treatment on cotton in presence of air or
argon gas increases its water absorbency. This report was concerned with the
effect of air and oxygen plasma on the rate and extent of dye uptake of
Chloramine Fast Red K on cotton print cloth. The effect of plasma treatment
in two different gas atmospheres (air and oxygen) for different treatment
times was studied by applying 2% of Chloramine Fast Red K.
The effect of plasma treatment in air and oxygen appears to increase both the
rate of dyeing and the direct dye uptake in the absence of electrolyte in the
dye bath. Oxygen treatment is more effective than air plasma treatment. This
shows that the increase in the rate and extent of dye uptake for the direct dye
studied depends more on the oxygen component of the air than on the
nitrogen component, which supports an oxidative mechanism of attack on the
cotton.

The contributory factors leading to this increase in dye uptake can be:
i. The change of the fabric surface area per unit volume due to
the surface erosion.
ii. The etching effect of the plasma effect on the fibred mages
the fiber surface and also removes surface fiber impurities
(e.g. cotton wsax or any remaining warp size, etc.)
iii. The chemical changes in the cotton fiber surface (leading
to carbonyl and carboxyl groups in the fiber.
iv. The possibility of the formation of free radicals on the
cellulosic chains of cotton.
v. Thus the action of oxygen and air plasma treatments
modifies the surface properties of cotton and leads to an
increase in the rate and extent of uptake of direct dye.

Supercritical carbon dioxide (CO2) dyeing
Water is a valuable raw material which is not unlimitedly available. It must
be protected by appropriate legal measures. Usage of water as solvent for
chemicals is mostly because of its abundant availability and low cost.
Problems associated with usage of water are effluent generation and
additional step is needed to dry the fabrics after each step. The amount of
energy spent to remove the water is also huge adding to the woes of
processors, making processing the weakest link among the entire textile
chain. The unspent dyestuffs remain in liquor, thus polluting the effluent. It
leads to additional pollution of waste water.
To eliminate the disadvantages it is proposed that certain gases can replace
water as solvating medium. High pressure and temperature are needed to
dissolve the dyes. Of all the gases being possible of converted into super
critical fluids, CO2 is the most versatile and prominently used. Because of
their high diffusion rates and low viscosities that allow the dye to penetrate
into the fiber. Moreover, by reducing the pressure at the end of the process,
dye and CO2 can be recycled.

Technical terms of textile dyeing

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