DYEING OF POLYAMIDE FIBRES WOOL, SILK AND NYLON

1
DYEING OF POLYAMIDE FIBRESWOOL, SILK AND NYLON

• DYEING MECHANISM
• POLYAMIDE STRUCTURE
• NH2---XCOOH
• NH2 END AMINO GROUP
• COOH END CARBOXYL GROUP
• X POLYAMIDE CHAIN (CONH)

2
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)

3
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 ----? NH3 X COO- (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

• Acid dyes are cheaper and produce bright shades,
  generally show low wash fastness
•  
• Chrome mordant dyes expensive. Produce dull
  shades of good all round fastness
•  
• Metal-complex dyes Are pre-metallized dyes .
  easy to apply and produce dyeings of reasonably
  good fastness
•  
• Reactive dyes comparatively new entrants. Give
  bright dyeings with good fastness properties.
•  

7
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

9
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
  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.

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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 amides may be involved at these
  low pH value.

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DYEING CYCLE
15
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.

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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

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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

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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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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.

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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.
•  

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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
• Chrome mordant method
• Metachrome method
• 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 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.

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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

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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 12 metal complex dyes.
• Shading dyes must be suitably resistant to
  chromate or dichromate anions in the bath.

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DYEING CYCLE
27
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 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.

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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
  complex with the dye, commercially, chromium
  complex dyes are mostly synthesized and marketed.
  

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11 METAL COMPLEX DYES

• the 11 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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11 METAL COMPLEX DYES

• Besides o odihydroxyazo compounds, the 11 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 mono-sulphonated leveling
  acid dyes.
• In spite of the decline in recent years in the
  use of 11 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.
•  

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DYEING METHOD

• 11 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 (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 hydrolysis of sulphamic
  acid leading to less fibre damage compared to
  sulphuric acid.
• NH2SO3H H2O ? NH4HSO4
•  

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DYEING CYCLE
33
12 METAL COMPLEX DYES

•  The wet fastness properties of 11 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 12 metal
  complex dyes in 1951.
• Owing to the weakly acid or neutral pH conditions
  used for application of 12 metal complex dyes
  they are sometimes referred as neutral dyeing
  metal complex dyes.
• These dyes are classified into two groups
• unsulphonated 12 metal complex dyes
• sulphonated 12 metal complex dyes

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UN-SULPHONATED 12 METAL COMPLEX DYES
35
UN-SULPHONATED 12 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 12 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.

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SULPHONATED 12 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 12 metal complex dyes
• Sulphonated 12 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
38
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 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
• 11 metal complex dyes 2- 4
• 12 metal complex dyes 5-6

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REACTIVE DYES

• Following ranges of reactive dyes available for
  dyeing of wool
•  

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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.

43
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
45
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- 5-chloropydimidine.
• 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.

46
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.

47
DRIMALAN F DYES
48
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 N-methyltaurine 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.
•  

49
HOSTALAN OR PROCILAN E DYES

• DSO2CH2CH2OS03- Na ? DSO2CHCH2
  NH2PEPTIDE
• Beta Sulphatoethyl sulphone Vinyl Sulphone
•  
• -? DSO2CH2CH2NH--PEPTIDE
•  

50
CHEMISTRY OF HOSTALAN DYES
51
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.

52
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.
•  
•  

53
REACTION WITH SILK