Dyeing of Polyamide Fibres

8/13/2019 Dyeing of Polyamide Fibres

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DYEING OF POLYAMIDE FIBRES

WOOL, SILK AND NYLON

DYEING MECHANISM

POLYAMIDE STRUCTURE

NH2---XCOOH

NH2 END AMINO GROUP

COOH END CARBOXYL GROUP

X POLYAMIDE CHAIN (CONH)


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EFFECT OF pH

END GROUP ISONIZATION IS pH DEPENDENTH20

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)


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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

NH2XCOOH ---- +NH3XCOO- (Fibre in water))

H2O DSO3Na ---- DSO3-+ Na+ (Dye in water)

NH2XCOOH + DSO3Na - DSO3- +NH3---X---COO-+Na (Dyed fibre)


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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


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SCHEMATIC DYE-FIBRE INTERACTION


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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.


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DYE UNIFORMITY AND WASH FASTNESS


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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


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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.


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CLASSIFICATION

APPLICATION POINT VIEW

LEVEL DYEING OR EQUALIZING ACID DYES

MILLING ACID DYES

SUPER MILLING ACID DYES


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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.


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DYEING METHOD

These are applied at low pH value (2.5-4) using sulphuricacid(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 dyeanions 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 uniformdyeing 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.


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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 amidesmay be involved at these low pH value.


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DYEING CYCLE


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DYEING PRECAUTIONS

To achieve good levelness it is essential to givesufficient 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.


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ACID MILLING DYES

These dyes are so named because they have some degree of fastness tomilling 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 littleinferior 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


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DYEING BEHAVIOUR

These dyes also tend to be more tippy- dyeing than leveling dyes i.e. theaffinity 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, nonskitterydyeing 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


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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


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SUPER MILLING ACID DYES

Super milling acid dyes are similar to disulphonated milling acid dyesbut contain higher alkyl substituents (e.g. butyl, octyl, dodecyl) to impartmore 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 anybatch to batch variations can be eliminated by blending

These dyes are applied with a leveling agent and dyeing method iscarefully designed to ensure uniform uptake since the dyes do notmigrate readily. .

This group comprises the dyes of high anion affinity which requireminimum 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 benecessary to add 1-2% of acetic acid (30%) after boiling for 30 min. inorder to exhaust the dye bath.


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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.


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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.

Methods of application

1. Chrome mordant method

2. Metachrome method

3. Afterchrome method


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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 600

C 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 for60-75 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.


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AFTER CHROME METHOD

Most widely adopted method.

The dyeing and chroming processes although separate steps are oftencarried 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 theother 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.


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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% Glaubers 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 andboiling 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.


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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 complexwith the dye, commercially, chromium complex dyes are

mostly synthesized and marketed.


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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


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Besides o odihydroxyazo compounds, the 1:1 metal complex dyes

include o-amino-o-hydroxy azo compounds and derivatives of salicylicacid. (COOH COOH groups).

These dyes are mostly monosulphonates of mol.Wt. 400-500.

This gives them dyeing properties somewhat similar to those of mono-sulphonated leveling acid dyes.

In spite of the decline in recent years in the use of 1:1 metal complexdyes, the dyes continue to be used in the dyeing of loose stock and yarnfor 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.


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DYEING METHOD

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 complexdyes).

Under these conditions the dyes possess excellent migrating and levelingproperties.

Since wool absorbs approximately 4% owf of sulphuric acid (96%), an excess ofacid is required in order to maintain a suitably acidic dyebath.

Chelating agents for water softening should not be used owing to demetallizationof 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 (8-10%) 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 hydrolysisof sulphamic acid leading to less fibre damage compared to sulphuric acid.

NH2SO3H + H2O NH4HSO4


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DYEING CYCLE


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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


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UN-SULPHONATED 1:2 METAL COMPLEX

DYES


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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 1:2structure (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 aVely 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.


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SULPHONATED 1:2 METAL COMPLEX

DYES

Introduction of sulphonic solubilizing group leads to dyes having poorleveling 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.


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DYE STRUCTURE


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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


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DYEING pH FOR DYE CLASSES FOR WOOL

Typical dyeing pH for different dye classes forwool

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


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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


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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.


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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.


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LANASOL DYES


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DRIMALAN F DYES

These dyes were specially synthesized for wool and areamong the most important reactive dyes for machine

washable wool.

They are distinguished by brilliance of shade, highefficiency of reaction with the fibre and good wet and lightfastness.

The reactive group in these dyes is 2,4, difluoro- 5-chloropydimidine.

The reasons for the success of these dyes is the resistance tohydrolysis and high degree of reaction with fibre.

The fluorine atom in position 4 reacts first because of itshigh reactivity but the reactivity of fluorine atom in position2 is also high enough to further react with wool.

Their excellent wet fastness is due to their high fixation ratioof the order of 95% and above.


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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.


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DRIMALAN F DYES


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HOSTALAN OR PROCILAN E DYES

DSO2CH2CH2OS03

-

Na

+

DSO2CH=CH2 + NH2PEPTIDEBeta Sulphatoethyl sulphone Vinyl Sulphone

- DSO2CH2CH2NH--PEPTIDE


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CHEMISTRY OF HOSTALAN DYES


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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.


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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 gooddischargeability

for dyeing knit goods especially washable articles.

REACTION WITH SILK

The reaction partners are mainly the terminal amino groups of thelysine, 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.


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REACTION WITH SILK

Documents

Dyeing of Polyamide Fibres