DYEING OF POLYAMIDE FIBRES
WOOL, SILK AND NYLON
• DYEING MECHANISM
• POLYAMIDE STRUCTURE
NH2---X—COOH
• NH2
• COOH
• X
END AMINO GROUP
END CARBOXYL GROUP
POLYAMIDE CHAIN (CONH)
EFFECT OF pH
• END GROUP ISONIZATION IS pH DEPENDENT
H20
•
NH2----X----COOH ------ +NH3 ---X---COO-
(IN WATER)
•
H+
+NH3---X---COO- ---------- +NH3 ---X---COOH
(IN ACIDIC SOLUTION)
•
OH
+NH3---X---COOH ------- NH2---X---COO- (IN ALKALINE SOLUTION)
DYEING MECHANISM WITH ANIONIC
DYES
UNDER NEUTRAL OR ACID CONDITIONS
•
H+ DIFFUSE RAPIDLY AND GET ADSORBED ON WOOL FIBRE
•
•
•
BECOME ASSOCIATED WITH END NH2 GROUP OF FIBRE TO GIVE
CATIONIC NH3+ GROUP
DYE IONISES TO DSO3- Na+
ELECTROSTATIC ATTRACTION BETWEEN DSO3 – AND NH3+
•
H20/H
NH2—X—COOH ---- +NH3— X— COO- (Fibre in water))
•
H2O
DSO3Na ---- DSO3- + Na+ (Dye in water)
•
NH2—X—COOH + DSO3Na - DSO3- +NH3---X---COO- +Na (Dyed fibre)
DYEING MECHANISM
• THE HYPOTHESIS THAT ANIONIC DYE IS
ATTRACTED TO CATIONIC DYE SITE IS OVER
SIPLIFICATION
• WATER SOLUBLE DYES HAVE
• HYDROPHILIC WATER SOLUBILIZING GROUP
• HYDROPHOBIC REGIONS IN THE FORM OF
BENZENE RING WITH GROUPS LIKE OH, NH2 ETC
CAPABLE FORMING H BONDS AND VANDER WAALS
INTERACTION WITH FIBRE
• NATURE OF INTERACTION WILL VERY FROM DYE
TO DYE
SCHEMATIC DYE-FIBRE INTERACTION
SUITABLE DYE CLASSES
1.
Acid dyes: are cheaper and produce bright shades,
generally show low wash fastness
2.
Chrome mordant dyes: expensive. Produce dull shades of
good all round fastness
3.
Metal-complex dyes: Are pre-metallized dyes . easy to
apply and produce dyeings of reasonably good fastness
4.
Reactive dyes: comparatively new entrants. Give bright
dyeings with good fastness properties.
DYE UNIFORMITY AND WASH FASTNESS
MIGRATION AND FASTNESS
• MIGRATION DECREASESS WITH mol.wt OF DYE
(rmm)
• AFFINITY AND WET FASTNESS INCREASES WITH
mol. Wt
• LEVELLING OR MIGRATION CAN BE IMPROVED
USING SUITABLE DYEING AUXILIARY PRODUCTS
ACID DYES
• produce wide shade range.
• Acid dyes are so called because the original members of the
dye class were applied in a bath containing mineral or
organic acid
• most of the acid dyes are sulphonic acid salts but there are
few containing carboxylic acid groups.
• Acid dyes have direct affinity to wool silk and nylon but no
affinity to cellulosic fibres.
CLASSIFICATION
•
APPLICATION POINT VIEW
•
LEVEL DYEING OR EQUALIZING ACID DYES
•
MILLING ACID DYES
•
SUPER MILLING ACID DYES
LEVEL DYEING ACID DYES
• TWO SUB DIVISIONS
• MONOSULPHONATED DYES (r.m.m 300-500)
• DISULPHONATED DYES (r.m.m 400-600)
• POSSESS VERY GOOD LEVELING / MIGRATION
PROPERTIES AT BOIL
•
WET FASTNESS IS NOT SATISFACTORY.
• THE LIGHT FASTNESS IS GENERALLY GOOD.
DYEING METHOD
• These are applied at low pH value (2.5-4) using sulphuric
acid(5% owm)
• there is danger of fibre damage at such a low pH.
• Glaubers salt (10-20% owm) must be added to assist
leveling by competition between sulphate ions and dye
anions for the positive sites.
• The goods are entered at 600C, raised to boil in 30 min. and
boiled for 45 min, cool, wash and dry.
• Level dyeing acid dyes are most appropriate when uniform
dyeing is critically important with moderate wet fastness.
• used for dyeing of bright shades in pale and medium depth
with high light fastness on woolen fabrics for ladies wear,
upholstery and furnishings.
DYEING CYCLE
• acid is essential to achieve the optimum pH (2.5-4)
• sulphate ions are necessary to assist migration and levelness
• sulphate and dye anions compete for cationic sites on wool
fibre.
W-SO4 + D2-  W-D + SO4 2-
• W represents a cationic site in the fibre
• D is the dye anion having 2 SO3- groups.
• Protonated amine groups in fibre are considered to be the
primary sites of absorption but other groups such as amides
may be involved at these low pH value.
DYEING CYCLE
DYEING PRECAUTIONS
•
•
•
•
•
•
•
To achieve good levelness it is essential to give
sufficient time at the boil to permit the dyes to migrate
this is the main mechanism by which levelness is
achieved.
Procedure of dye additions for shade adjustment
Turn off the steam supply
Add the previously dissolved dyes
Run for 5 min.
Return to boil and boil for 30 min.
ACID MILLING DYES
• These dyes are so named because they have some degree of fastness to
milling process, which indicates a higher level of wet fastness than other
acid dyes.
• Two main subdivisions.
• A. Monosulphonted dyes (mol.Wt 500-600), these have been described
as half acid milling dyes since they migrate and cover well but are little
inferior to traditional acid milling dyes in terms of wet fastness.
• B. Disulphonated dyes of high mol. Wt (r.m.m) 600-900. These dyes
diffuse much more slowly than typical leveling acid dyes and exhibit
correspondingly higher wet fastness. However, migration and coverage
properties are inferior and the addition of leveling agent is necessary.
• Non-polar Vander Waals forces are involved between these dyes and
wool. Resulting in relatively poor migration properties.
• Hydrophobic interactions lead to reduced migration but increased wet
fastness
DYEING BEHAVIOUR
• These dyes also tend to be more tippy- dyeing than leveling dyes i.e. the
affinity of the dyes for weathered tip of the wool fibre is different from
that for the bulk of the fibre.
• For this reason and to obtain a slower and more uniform rate of
absorption, dye leveling agents are normally used
• These products form complexes with dyes and allow solid, nonskittery
dyeing with improved levelness
• Control of recommended temp and pH is essential
• Milling dyes are not easily combinable; they are therefore most suitable
for self-shades.
• Typical dyeing recipe for milling dyes is
• Leveling agent
1-2%
• Sodium acetate
2 g/l
• Acetic acid
to pH 5-6.5
DYEING BEHAVIOUR
• There is no significant migration at boil, therefore uniform
dye uptake right from beginning must be ensured.
• The effect of sodium sulphate on level dyeing performance of
milling dyes is negligible
• The dyeing pH will depend on depth of shade .
• pH 5-6.5 may be used
APPLICATION AREAS
• Milling dyes are used where good wet fastness properties are
necessary.
• Loose fibre or slubbing for multicolour yarns or
• yarns for coloured woven fabrics.
• or for fabrics which are subjected to wet finishing
particularly milling,
• machine washable fabrics.
• Milling dyes are employed primarily for bright shades.
• Milling dyes have also been used for black and navy shades
in piece dyeing since levelness is less critical in this shade
areas and fastness of leveling dyes is not adequate.
SUPER MILLING ACID DYES
• Super milling acid dyes are similar to disulphonated milling acid dyes
but contain higher alkyl substituents (e.g. butyl, octyl, dodecyl) to impart
more hydrophobic character to the dye molecule.
• These dyes show exceptionally good wet fastness.
• They are used for bright colours on loose wool or slubbing where any
batch to batch variations can be eliminated by blending
• These dyes are applied with a leveling agent and dyeing method is
carefully designed to ensure uniform uptake since the dyes do not
migrate readily. .
• This group comprises the dyes of high anion affinity which require
minimum of acid. These are sometimes called neural dyeing acid dyes.
The dyeing procedure is
• The material is entered at 600C into dyebath containing 2-5% of
ammonium acetate The temp. is raised to boil in 45 min. It may be
necessary to add 1-2% of acetic acid (30%) after boiling for 30 min. in
order to exhaust the dye bath.
•
CHROME MORDANT DYES
• Chemically chrome mordant dyes are closely related to acid dyes but
their molecules contain additional groups in O,O’ position ( such as OH
OH, OH NH2, COOH COOH etc) which enables the dye to form stable
co-ordination complex with chromium within the fibre.
CHROME MORDANT DYES
•
•
•
•
Mordant dyes show good wet fastness property.
The salts of Al, Cr, Cu, Fe and Sn are suitable as mordants.
Of these the salts of Cr are of importance to wool dyeing.
Hence mordant dyes for wool are usually referred to as
chrome dyes.
•
1.
2.
3.
Methods of application
Chrome mordant method
Metachrome method
Afterchrome method
CHROME MORDANT METHOD
• Wool is first treated with Cr compound like Sod. Or Potassium
dichromate and then dyed.
• This is the oldest method but now not very popular because it involves
two bath process,
• lengthy and expensive in terms of time and energy
• Mordanting
•
The material is entered at 600C into a bath containing dichromate
(1.5% owm) and formic acid (2% owm).
• The temperature is raised to boil in 45 min. and boiling continued for
60-75 min.
• The fabric is then washed with hot and cold water.
• Dyeing
•
The well-rinsed material is entered into the dye bath containing
• 1-5% acetic acid (30%) at 500C,
• the temperature is raised to boil and boiling continued for 60-90 min.
• The fabric is then washed with hot and cold water.
METACHROME METHOD
• With many chrome dyes it is possible to combine
mordanting and dyeing in the same bath.
• The necessary requirement being the dye must exhaust well
from the bath of pH 6-7.
• This obviously restricted the method to those dyes which
had reasonable neutral affinity for wool
• Disadvantage
• Chances of metal complex formation in the dye bath
• The limited number of suitable dyes.
• The inability to achieve very heavy shades because of
limited exhaustion at neutral pH values. Not suitable for
dyeing Blacks and navy blues.
• High residual levels of chromium because of limited
exhaustion of chromium at neutral pH
AFTER CHROME METHOD
• Most widely adopted method.
• The dyeing and chroming processes although separate steps are often
carried out in the same bath, thereby reducing dyeing times, water and
energy requirements.
• Additionally there is no restriction on shades as there is with the
metachrome process.
• After chroming, dyeing gives better fastness properties than either of the
other two chrome-dyeing techniques.
• The main disadvantage of after chrome dyeing is the difficulty in shade
matching,
• since the final colour is not developed until the chroming stage.
• For this reason, shading additions are often made with milling or 1:2
metal complex dyes.
• Shading dyes must be suitably resistant to chromate or dichromate anions
in the bath.
DYEING CYCLE
DYENG METHOD
• The dyeing is carried out as follows.
• The goods are entered at 45 0C into a bath containing dye, 2% acetic
acid (30%) and 10% Glauber’s salt,
• the temp. is raised to boil in 45 min.
• kept at boil for 30 min. the dyebath is then exhausted.
• If necessary by adding more acetic acid or 0.5-1% or formic acid and
boiling for a further 30 min..
• When the dyebath has been exhausted completely it is cooled slightly,
• Add dichromate
• Continue dyeing for a further 30-60 min.
• Boiling must be continued sufficiently long to ensure complete reduction
of the chromate on the fibre.
• This method provides best fastness properties.
METAL COMPLEX DYES
• These dyes are also referred to as premetallized dyes.
• Earlier members of this class of dyes were produced from
the premetallisable acid dyes.
• Therefore these dyes are also classified as acid dyes in the
Colour Index.
• Though most of the transition metals can form complex
with the dye, commercially, chromium complex dyes are
mostly synthesized and marketed.
1:1 METAL COMPLEX DYES
• the 1:1 metal complex dyes are prepared from dyes
possessing chelating groups e.g O O’ dihydroxy azo dyes
containing one or two sulphonic groups to render them
water solubility
1:1 METAL COMPLEX DYES
• Besides o o’dihydroxyazo compounds, the 1:1 metal complex dyes
include o-amino-o’-hydroxy azo compounds and derivatives of salicylic
acid. (COOH COOH groups).
• These dyes are mostly monosulphonates of mol.Wt. 400-500.
• This gives them dyeing properties somewhat similar to those of monosulphonated leveling acid dyes.
• In spite of the decline in recent years in the use of 1:1 metal complex
dyes, the dyes continue to be used in the dyeing of loose stock and yarn
for floor coverings, hand knitting yarns and piece goods.
• They exhibit excellent level dyeing and penetration characteristics.
• The dyes have good light fastness and moderate wet fastness.
DYEING METHOD
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•
•
•
•
•
•
•
•
1:1 metal complex dyes are usually applied to wool from a strongly acidic (pH 2)
dye bath ( hence dyes some times are referred to as acid dyeing metal complex
dyes).
Under these conditions the dyes possess excellent migrating and leveling
properties.
Since wool absorbs approximately 4% owf of sulphuric acid (96%), an excess of
acid is required in order to maintain a suitably acidic dyebath.
Chelating agents for water softening should not be used owing to demetallization
of some dyes.
Because prolonged boiling under such low pH conditions can cause fibre damage,
either reduced amounts of sulphuric acid or other acids such as formic acid (810%) owf) or proprietory leveling agent can be used.
The dyes can also be applied at 80 0C so as to reduce fibre damage.
BASF suggest the use of sulphamic acid in place of sulphuric acid.
The pH of the dye bath at the beginning is 1.8,
but as the temp. rises to boil the pH increases between 3 – 3.5 owing to hydrolysis
of sulphamic acid leading to less fibre damage compared to sulphuric acid.
NH2SO3H + H2O  NH4HSO4
DYEING CYCLE
1:2 METAL COMPLEX DYES
•
The wet fastness properties of 1:1 metal complex dyes are
lower than those of mordant dyes
• their excellent migrating and penetration character, ease of
application, good light fastness and comparatively bright
shades made them popular till the introduction of 1:2 metal
complex dyes in 1951.
• Owing to the weakly acid or neutral pH conditions used for
application of 1:2 metal complex dyes they are sometimes
referred as neutral dyeing metal complex dyes.
These dyes are classified into two groups
1. unsulphonated 1:2 metal complex dyes
2. sulphonated 1:2 metal complex dyes
UN-SULPHONATED 1:2 METAL COMPLEX
DYES
UN-SULPHONATED 1:2 METAL COMPLEX
DYES
• These dyes are free of strongly polar ionic water solubilizing group like
SO3Na.
• Water solubility is conferred by the inherent anionicity of the 1:2
structure (arising from the loss of four protons from the two dye ligands)
and the
• presence of non-ionic, hydrophilic substituents such as methyl sulphone
(SO2CH3), sulphonamide (SO2NH2), methyl sulphonamide (
SO2NHCH3).
• these dyes are salts of strong acid
• dissociate completely in dilute solutions to give a –Vely charged dye
molecule.
• They show high neutral dyeing affinity and very good fastness to light
and wet treatments.
• Their high affinity can cause rapid initial strike
• have slow diffusion and migration properties.
SULPHONATED 1:2 METAL COMPLEX DYES
• Introduction of sulphonic solubilizing group leads to dyes having poor
leveling properties and lower fastness to wet treatments.
• Over the last 30 years great advances have been made in developing
auxiliary products which improve the level dyeing properties of
sulphonated 1:2 metal complex dyes
• Sulphonated 1:2 metal complex dyes are divided into two sub-classes
• Unsymemetrical monosulphonated dyes: The two dye molecules in the
complex may be different
• Disulphonated dyes: Many of these dyes are symmetrical in structure
and are cheaper than unsymmetrical monosulphonated dyes.
• They are slow in dyeing and do not cover irregularities well.
• They can be applied on wool using amphoteric or weakly cationic leveling
agent with control of pH and temperture, but their intrinsic migration
properties are poor.
DYE STRUCTURE
DYEING METHOD
• Dyeing is carried out at pH 5-6 using ammonium acetate.
• The usual method of application typically is as follows.
• The yarn or cloth is treated at 40 0C for 10 min. in a bath
set with 2-4% ammonium acetate.
• Dissolved dye is then added
• the temperature is raised to boil in 45 min.
• After 30-60 min at boil the bath should have exhausted to
the extent of 90%
• After dyeing rinse with hot and cold water
DYEING pH FOR DYE CLASSES FOR WOOL
• Typical dyeing pH for different dye classes for
wool
Dye bath pH for 80-85% exhaustion
dye class
pH
Leveling acid dyes
2.5-4
Milling acid dyes
4.5-5.5
Super-milling acid dyes
5-6
1:1 metal complex dyes
2- 4
1:2 metal complex dyes
5-6
REACTIVE DYES
Following ranges of reactive dyes available for dyeing of wool
CHARACTERISTICS
• High degree of dye-fibre covalent bonding at the end of
dyeing operation, minimizing the washing treatment
required to give maximum wet fastness.
• The rates of adsorption is higher than rate of reaction to
avoid uneven dyeing.
• A highly reactive dye will react rapidly with the fibre during
exhaust dyeing reducing its chances of migration to get
uniform dyeing.
• Whereas a low reactive dye will require extended dyeing
time for the reaction to complete
CHEMISTRY OF REACTIVE DYES
• In theory dyes are capable of reacting with sites in the fibre
such as OH in cellulose and NH2, SH (Thiol), OH in wool or
silk.
• The dye fibre reaction can take place either by
•
• nucleophilic substitution or
•
nucleophilic addition.
LANASOL DYES
• These have been introduced as compatible trichromatic
system based on Lanasol Yellow 4 G, Lanasol Blue 3 G, and
Red 6 G.
• Lanasol dyes based on -bromo acrylamido reactive group
• were introduced in 1966
• are known for their brightness of shade, high reactivity
and good all round fastness properties.
• These dyes are capable of reacting with polypeptides
through both nucleophilicsubstitution and nucleophilic
addition reactions.
• The rate of fixation of these dyes on merino wool is 3 times
higher than that of boiled silk.
LANASOL DYES
DRIMALAN F DYES
• These dyes were specially synthesized for wool and are
among the most important reactive dyes for machine
washable wool.
• They are distinguished by brilliance of shade, high
efficiency of reaction with the fibre and good wet and light
fastness.
• The reactive group in these dyes is 2,4, difluoro- 5chloropydimidine.
• The reasons for the success of these dyes is the resistance to
hydrolysis and high degree of reaction with fibre.
• The fluorine atom in position 4 reacts first because of its
high reactivity but the reactivity of fluorine atom in position
2 is also high enough to further react with wool.
• Their excellent wet fastness is due to their high fixation ratio
of the order of 95% and above.
DRIMALAN F DYES
• The high fixation ratio has been attributed to the high reactivity of
partially hydrolyzed dye, since the reactivity of second fluorine -carbon is
only slightly decreased after the first fluorine has reacted with wool.
• These findings indicate that the dye molecule has two reactive centers,
which can react independently with the nucleophiles in protein fibres.
• There is also evidence that these dyes form cross-links both with wool
and silk.
• In silk tyrosine OH group also takes part in the reaction.
• Levelling agents Drimagen F (S) and Avolan RE (BAY) are
recommended to get uniform dyeing.
DRIMALAN F DYES
HOSTALAN AND PROCILAN E DYES
• The novelty of this class of dyes lies in the controlled nature of the
reaction with fibre.
• The actual reactive group is formed only gradually during the
exhaustion dyeing, so that in the early stages of dyeing these dyes behave
more like an acid level dyes, offering a real chance of sufficient dye
migration to obtain level dyeings.
• These dyes are blocked vinyl sulphone derivatives which gradually
activate to the reactive vinyl sulphone at elevated temperature.even
under slightly acidic conditions.
• The main advantage of such system is an improvement in dye levelness,
due to suppression of dye-fibre covalent bonding at temp. below boil.
• It is believed that Hostalan E brands are the most level dyeing Nmethyltaurine adducts,
• other Hostalans are -sulphatoethyl sulphone specially selected for their
ready formation of the reactive vinyl sulphone form under the weakly
acidic boiling conditions required for wool dyeing.
•
HOSTALAN OR PROCILAN E DYES
• DSO2CH2CH2OS03- Na+ 
PEPTIDE
Beta Sulphatoethyl sulphone
DSO2CH=CH2 + NH2—
Vinyl Sulphone
- DSO2CH2CH2NH--PEPTIDE
CHEMISTRY OF HOSTALAN DYES
CONVENTIONAL REACTIVE DYES
• Wool can be dyed with conventional rective dyes
namely Procion M, H and vinyl sulphone (Remazol).
• These dyes produce shades with good wet fastness
and brilliance when dyed at pH 8-9.
REACTIVE DYE REACTION WITH SILK
• Reactive dyes also form covalent bond with silk giving good wet
fastness just as with wool or cellulose. Their preferred applications are
• in the yarn sector for coloured wovens
• in prints on washable goods and shirtings
• for dyeing discharge grounds on woven fabrics due to their good
dischargeability
• for dyeing knit goods especially washable articles.
REACTION WITH SILK
• The reaction partners are mainly the terminal amino groups of the
lysine, especially when dyeing is carried out in the neutral to weakly
acidic region.
• In the alkaline region the phenol group of the tyrosine side chain may
also react with the dye.
REACTION WITH SILK