Social Media Policy

31 Pages·2010·0.35 MB·English

CHAPTER 8
DYES: THE CHEMISTRY AND
APPLICATIONS
CHAPTER 8
OBJECTIVES
(cid:132) INTRODUCTION
(cid:132) COLORANTS
(cid:132) CLASSIFICATION OF DYES
(cid:132) TEXTILE FIBERS
(cid:132) THE APPLICATION OF DYES
(cid:132) INTERMEDIATES
(cid:132) MANUFACTURE OF DYES
Professor Bassam El Ali 2
INTRODUCTION
(cid:132) Dyes are colored organic compounds that are used to
impart color to various substrates, including paper,
leather, fur, hair, drugs, cosmetics, waxes, greases,
plastics and textile materials.
(cid:132) Indigo, the oldest known dye was used by the ancient
Egyptians to dye mummy clothes.
(cid:132) Tyrianpurple, obtained from Murex snails found near
the city of Tyre, was used by the Romans to dye the
togas of the emperors.
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INTRODUCTION
(cid:132) The dye industry has always been highly competitive; the
industry has lately experienced major setbacks in terms of
profitability and overall attractiveness particularly in
Europe and the United States.
(cid:132) Major changes have taken place during the last 20 years,
and today Asia (India, Japan, Korea and China) has
become the largest dyestuff market, accounting for about
42% of the value of the global dyestuff market.
(cid:132) World demand for dyes and organic pigments is forecast
to increase 5.1% per year to more than $ 14 billion in
2004.
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CHAPTER 8
OBJECTIVES
(cid:132) INTRODUCTION
(cid:132) COLORANTS
(cid:132) CLASSIFICATION OF DYES
(cid:132) TEXTILE FIBERS
(cid:132) THE APPLICATION OF DYES
(cid:132) INTERMEDIATES
(cid:132) MANUFACTURE OF DYES
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COLORANTS
(cid:132) The two major types of colorants produced today are
dyes and pigments.
(cid:132) Pigments both inorganic and organic types, are
almost always applied in an aggregated or crystalline-
insoluble form that requires a binder to form a coating
on the surface of a substrate.
(cid:132) Pigments do not interact with the substrate and hence
do not destroy the crystal structure of the substrate.
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COLORANTS
(cid:132) Dyes are normally water-soluble or water dispersible
organic compounds that are capable of being
absorbed into the substrate destroying the crystal
structure of the substance.
(cid:132) The dye molecules are usually chemically bonded to
the surface and become a part of the material on
which it is applied.
(cid:132) The primary use of dyes is in the textile industry,
although substantial quantities are consumed for
coloring, such diverse materials as leather, paper,
plastics, petroleum products, and food.
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COLORANTS
(cid:132) To be of commercial interest, dyes must have high
color intensity and produce dyeing of some
permanence.
(cid:132) The color intensity of the dye molecule depends on
how strongly it absorbs radiation in the visible region,
which extends from 400 to 700 nm.
(cid:132) It was observed earlier that only some types of
organic structures give rise to color.
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COLORANTS
(cid:132) The partial structures necessary for color (unsaturated groups
that can undergo π-π* and n-π* transitions) were called
chromophores:
C C , C C , , ,
O
N N , NO2 , C
(cid:132) It was also observed that the presence of some other groups
caused an intensification of color. These groups are called
auxochromes.
(cid:132) The auxochromesare groups that can not undergo π-π*
transitions, but can undergo transition of n electrons:
-OH, -OR, -NH, -NHR, -NR, -X
2 2
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CHAPTER 8
OBJECTIVES
(cid:132) INTRODUCTION
(cid:132) COLORANTS
(cid:132) CLASSIFICATION OF DYES
(cid:132) TEXTILE FIBERS
(cid:132) THE APPLICATION OF DYES
(cid:132) INTERMEDIATES
(cid:132) MANUFACTURE OF DYES
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CLASSIFICATION OF DYES
(cid:132) Dyes may be classified according to their chemical
structure or by the method by which they are applied to
the substrate.
(cid:132) The dye manufacturers and dye chemists prefer the
former approach of classifying dyes according to chemical
type. The dye users, however, prefer the latter approach
to of classification according to application method.
(cid:132) Classification by application or usage is the principal
system adopted by the Color Index (C.I.).
(cid:132) The classification of dyes according to their usage is
summarized in Table 8.1, which is arranged according to
the C.I. application classification.
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CLASSIFICATION OF DYES
Table 8.1. Application Classification of Dyes
Class Principal substrates Method of application Chemical Types
Acid Nylon, wool, silk, paper, Usually from neutral to Azo(including premetalized),
inks, and leather acidic dyebaths anthraquinone, triphenylmethane,
azine, xanthene, nitro and nitroso
Azoic Cotton, rayon, cellulose Fiber impregnated with Azo
components and acetate and polyester coupling component and
compositions treated with a solution of
stabilized diazonium salt
Basic Paper, polyacrylonitrile, Applied from acidic Cyanine, hemicyanine,
modified nylon, dyebaths diazahemicyanine,
polyester and inks diphenylmethane, triarylmethane,
azo, azine, xanthene, acridine,
oxazine and anthraquinone
Direct Cotton, rayon, paper, Applied from neutral or Azo, phthalocyanine, stilbene, and
leather and nylon slightly alkaline baths oxazine
containing additional
electrolyte
Disperse Polyester, polyamide, Fine aqueous dispersions Azo, anthraquinone, styryl, nitro,
acetate, acrylic and often applied by high and benzodifuranone
plastics temperature/pressure or
lower temperature carrier
methods; dye may be
padded on cloth and
baked on or thermofixed
Fluorescent Soaps and detergents, From solution, dispersion Stilbene, pyrazoles, coumarin, and
brighteners and all fibers, oils, or suspension in a mass naphthalimides
paints, and plastics Professor Bassam El Ali 12

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CLASSIFICATION OF DYES
Food, drug, and Foods, drugs, and Azo, anthraquinone, carotenoid
cosmetic cosmetics and triarylmethane
Mordant Wool, leather, and Applied in conjunction Azo and anthraquinone
anodized aluminum with Cr salts
Oxidation bases Hair, fur, and cotton Aromatic amines and Aniline black and indeterminate
phenols oxidized on the structures
substrate
Reactive Cotton, wool, silk, and Reactive site on dye Azo, anthraquinone,
nylon reacts with functional phthalocyanine, formazan, oxazine
group on fiber to bind dye and basic
covalently under
influence of heat and pH
(alkaline)
Solvent Plastics, gasoline, Dissolution in the Azo, triphenylmethane,
varnishes, lacquers, substrate anthraquinone, and phthalocyanine
stains, inks, fats, oils,
and waxes
Sulfur Cotton and rayon Aromatic substrate vatted Indeterminate structures
with sodium sulfide and
reoxidized to insoluble
sulfur-containing products
on fiber
Vat Cotton, rayon, and wool Water-insoluble dyes Anthraquinone (including
solubilized by reducing polycyclic quinines) and indigoids
with sodium
hydrogensulfite, then
exhaPursotefeds soonr Bafisbsearm aEnl dA li 13
reoxidized

Acid Dyes
(cid:132) Acid dyes are water-soluble anionic dyes, containing one or
more sulfonic acid substituents or other acidic groups. An
example of the class is Acid Yellow 36.
H
N N N
SO3H
(cid:132) Acid dyes are applied from acidic dye baths to nylon, silk, wool,
and modified acrylics. They are also used to some extent for
paper, leather, ink-jet printing, food, and cosmetics.
(cid:132) The dyeing process is reversible and may be described as
follows:
Dye- + H+ + Fiber Dye- H+ Fiber
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Acid Dyes
(cid:132) The ionic bonding between the dye and the fiber is
the result of reaction of the amino groups on the fiber
with acid groups on the dye.
(cid:132) Generally the fastness of this dye depends on the
rate with which the dye can diffuse through the fiber
under the conditions of washing.
(cid:132) Metal complex (cobalt or chromium) acid dyes are
used mainly on wool for improved fastness.
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Azoic Dyes
(cid:132) Azodyes contain at least one azogroup (-N=N-)
attached to one or often two aromatic rings.
(cid:132) They are produced on textile fibers (usually cotton,
rayon and polyester), by diazotization of a primary
aromatic amine followed by coupling of the resulting
diazoniumsalt with an electron-rich nucleophile (azo
coupling).
(cid:132) A variety of hues can be obtained by proper choice of
diazoand coupling components.
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Azoic Dyes
(cid:132) The production of bluish red azoic dye from the
following two components is an example.
N O 2 N O 2
C H 3 O N H 2 + CH 3 O N N
H H
A z o i c D i a z o C o m p o n e n t 1 H O C N H O C N
O H
A z o i c C o u p l i n g C o m p o n e n t 2 B l u i s h R e d A z o i c D ye
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Basic (Cationic) Dyes
(cid:132) Basic dyes are water-soluble and produce colored
cationsin solution.
(cid:132) They are mostly amino and substituted amino
compounds soluble in acid and made insoluble by the
solution being made basic.
(cid:132) They become attached to the fibers by formation of
salt linkages (ionic bonds) with anionic groups in the
fiber.
(cid:132) They are used to dye paper, polyacrylonitrile,
modified nylons, and modified polyesters.
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Basic (Cationic) Dyes
(cid:132) In solvents other than water, they form writing and printing
inks. The principal chemical classes are triarylmethane or
xanthenes.
(cid:132) Basic Brown 1 is an example of a cationic dye that is
readily protonatedunder the pH 2 to 5 conditions of
dyeing.
NH2 H2N
H2N N N N N NH2
Basic Brown 1
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Direct Dyes
(cid:132) Direct dyes are water-soluble anionic dyes, but are not
classifiedas acid dyes because the acid groups are not
the means of attachment to the fiber.
(cid:132) They are used for the direct dyeing of cotton and
regenerated cellulose, paper and leather.
(cid:132) They are also used to dye union goods (mixed cotton, and
wool or silk) and to a lesser extent nylon fiber.
(cid:132) Most of the dyes in this class are polyazocompounds,
along with some stilbenes, phthalocyaninesand oxazines.
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Direct Dyes
(cid:132) The solubility of the dye in the dye bath is often reduced by
adding common salt or Glauber’ssalt.
(cid:132) The presence of excess sodium ions favors establishment of
equilibrium with a minimum of dye remaining in the dye bath.
Direct orange 26 is a typical direct dye.
HO OH
N N N N
NH CO HN
Na O3 S SO 3 N a
Di r e c t O r a n g e 26
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Disperse Dyes
(cid:132) Disperse dyes are substantially water-insoluble nonionic
dyes for application to synthetic hydrophobic fibers from
aqueous dispersions.
(cid:132) Disperse dyes are applied as very finely divided materials
which are adsorbed onto the fibers with which they then
form a solid solution.
(cid:132) Dispersed dyes are primarily used for polyester and
acetate fibers. Simple soluble azo, styrylbenzodi
furanone, and insoluble anthraquinone are the most
common disperse dyes.
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Disperse Dyes
(cid:132) Disperse yellow 3, Disperse Red 4, and Disperse Blue 27
are good examples of disperse dyes:
OH O NH2 HO O OH
CH3COHN N N OCH3
CH3 O OH O2N O NH C2H4OH
Disperse Yellow 3 Disperse Red 4 Disperse Blue 27
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Fiber-Reactive Dyes
(cid:132) These dyes react with the cellulosicfiber to form a covalent
bond. This produces dyed fiber with extremely high wash
fastness properties.
(cid:132) Cotton, rayon, and some nylons are dyed by this relatively
simple dye. The principal chemical classes of reactive dyes are
azo, triphendioxazine, phthalocyanine, formazan, and
anthraquinone.
(cid:132) An example of this type is the Reactive Blue 5 dye shown below:
O NH2
SO3Na Cl
N C N SO3Na
O NH NH C C
N
SO3Na
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Reactive Blue 5
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Mordant Dyes
(cid:132) Some dyes combine with metal salts (mordanting) to
form insoluble colored complexes (lakes). These
materials are usually used for the dyeing of cotton,
wool or other protein fiber.
(cid:132) The fiber is first treated with an aluminum, chromium
and iron salt and then contacted with a lake forming
dye (azoand anthraquinone derivatives).
(cid:132) The metallic precipitate is formed in the fiber
producing very fast colors highly resistant to both light
and washing.
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Mordant Dyes
(cid:132) Alizarin is the best-known anthraquinone derivative as an
example of a mordant dye as shown in the following
reaction.
(cid:132) The hydroxyl groups attached to anthraquinone nuclei are
capable of reaction with metals in the mordant material
(aluminum hydroxide) to form mordant dyes (aluminum
“lake”).
O OH
OH
O
Mordant Red 11
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Sulfur Dyes
(cid:132) Sulfur dyes are applied to cotton from an alkaline reducing bath
with sodium sulfide as the reducing agent.
(cid:132) These dyes are water-insoluble but they are soluble in their
reduced form and exhibit affinity for cellulose.
(cid:132) They dye by adsorption but on exposure to air they are oxidized
to reform the original insoluble dye inside the fiber.
(cid:132) They are low cost and have good fastness to light, washings and
acids.
(cid:132) The actual structures of sulfur dyes are largely unknown
although it is considered that they possess sulfur-containing
heterocyclic rings.
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Vat Dyes
(cid:132) The vat dyes are insoluble complex polycyclic
molecules based on the quinonestructure (keto-
forms).
(cid:132) They are reduced with sodium hydrosulfite in a
strongly alkaline medium to give soluble leucoforms
that have a great affinity for cellulose.
(cid:132) After the reduced dye has been absorbed on the
fiber, the leucoforms are reoxidizedto the insoluble
ketoforms.
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Vat Dyes
(cid:132) The dyeingsproduced in this way have high wash
and light fastness. An example of a vat dye is Vat
Blue 4 (Indanthrene).
O
NH O
O HN
O
Vat Blue 4
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Solvent Dyes
(cid:132) These dyes are water-insoluble but soluble in
alcohols, chlorinated hydrocarbons, or liquid
ammonia.
(cid:132) They are used for coloring synthetics, plastics,
gasoline, oils and waxes.
(cid:132) The dyes are predominantly azoand anthraquinone,
but phthalocyanineand triarylmethanedyes are also
used. Perchloroethyleneis the preferred solvent.
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