1. SOUTHEAST UNIVERSITY, Bangladesh
Department of Textile ENGINEERING
Name:MD Mehedi Hasan
Batch:2nd(Evening)
Major:Wet Processing Technology
Vat Dyes with properties and
chemical structure
2. Textile Dyes And Chemical Structure
A substance that is used to impart color to substrate. it may be textiles or fibers.
textile dye is used to coloration of textile fiber or textile goods.
History of dyes:
We know that, first Egyptians people starts dyeing process for textile materials with
different dyes. and Egyptian people produced different types of dyes before many
year ago. this dyes is windly used in textile industry. Different oldest dyes are made
from natural source such as plants, animals and some dyes are made from natural
plants this dyes is called indigo dyes. In 1869 an artificial dyes was successfully
created. Young scientist or chemist name is William parkin is created synthetic dyes.
then this dyes is come around the world and this dye are windily used in textile
industry and develop the growth of fabric production. Germans company also be
produced high production of dyes. it is also be stand for high production of dyes.
Specially in a textile industry lots of requirement of dyes for dyeing. but synthetic
dyes can cause problems because the solution of synthetic dyes is very dangerous
for human body as well as environment. So cleaning of solutions or water must be
required before drain out side of industry.
3. So, the waste water is very important to cleaning for environment because wast
solutions is very harmful or pollutant around the world. So, cleaning (ETP) process is
done with very carefully. Some Chemical or some substance is widily used during
textile dyeing process such as alkali, HCl and more. We know that textile dyes is
organic substance and inorganic substance. the tendency of textile dyes is to absorb
light and reflect light to show color. and dye have also tendency to properly soluble in
water. this are the best tendency of dyes. that is reason dyes are used for coloration
of textile materials.
the basic concepts of textile dyeing is, the interaction between a dye and a fiber
(textile materials/textile goods). and it consist several steps. and in textile dyeing
process, involved follow terms, such as,
Disaggregation of the dye
Exhaustion – dye uptake
Adsorption – transfer of dye from aquods solution onto fibre surface.
Diffusion – Textile dye is diffused into the fiber.
Fixation – dye is fixed on to the fiber
4. Types Of Dyes:
Pigment Dye Mordent Dye
Developed Dye
Synthetic Dye
Sulpher Dye Natural Dye
5. Different Types Of Dyes:
Now, I will discuss about different types of dyes with their properties:
Vat dyes
1. Vat dyes 10. Mordant dyes
2. Basic dyes 11. Synthetic dyes
3. Direct dyes 12. Disperse dyes
4. Reactive dyes 13. Develop dyes
5. Azo dyes 14. Aniline dyes
6. Acid dyes 15. Nitro dyes
7. Azoic dyes 16. Anthraquinone dyes
8. Sulphur dyes 17. Turmeric dyes (Natural dyes)
9. Pigment dyes
6. 1)Vat dye:
Vat dye is made from natural plants. So, Vat dye is also called indigo dyes. Vat dye is insoluble in
water but soluble by vetting process. Vat dyes is windily used in cellulose materials for dyeing
purpose. Vat dye have good overall fastness properties.
Vat dye is not directly use for dyeing process. Vatting is must be required before dyeing. Because
vat dye is insoluble in water but it Solubilized by vetting process and then dyeing is done
Properties:
1. Vat dye are insoluble in water.
2. The particle size of vat dye is very small.
3. Vat dye are Applied in alkaline condition PH 12-14
4. vat dye mostly belong to indigoid, and Anthraquinone class.
5. vat dyes can’t be directly applied on cotton material for dyeing.
7. 6. In vat dyeing process, first need vatting process.
7. First vetting process is done then it can apply on textile materials for dyeing purpose.
8. After dyeing it gives different shade.
9. wet fastness is very good but rubbing fastness is not good.
10. wet fastness is very good around 4-5.
Vatting Process:
It converting insoluble vat dyes into soluble form is known as vetting. It is given more solubility in
water. they are reduced to soluble leuco compound. this process is called vatting process. vat dye
are more difficult to reduced then Sulphur dye. vat dye displays no substantively towards cellulose
but with the help of suitable reducing agent and alkali convert the insoluble vat dye to its soluble
leuco form results in change of color. Sodium dithionite (work as a reducing agent) they are
windily use in vetting. Sodium dithionite are more popular reducing agent are mostly used in case
of vetting process. Dihydropyrane, Na2S2O4.2H2O and hydrose are mostly used in case of vat
dyeing.
After Treatment:
After dyeing some pigment particles is present on the surface of materials. this is carryout with the
help of detergent at boiling temp. But removing pigment particles is necessary with the surface of
the fabric because these treatment gives final or proper shade. Soaping are required for removing
pigment particles with the surface of the fabric. Which gives the material final shade and improved
the fastness properties typical of vat dye. It gives different type of shade.
8. Common Phases of Vat Dyeing (Exhaust Method):
follow these 4 steps to know how to how to used vat dyes:
Reduction
Insoluble Vat Pigment Are Converted Into Soluble Anions
Diffusion
Leuco Vat Anions Get Into The Cellulosic Fiber
Oxidation
Soluble Dyes Are Oxidized Into The Pigment From
Soaping
Dye Crystallize From Big Stable Aggregates And Can not
Come Out Due To Mechanical Entrapment
9. Classification of Vat Dyes:
Vat dyes can be classified based on the following –
1.Chemical Constitution
2.Application Condition
1. Classification Based on Chemical Structure-
Vat Dyes
Polycyclic
Indigoid &
Thonithiniodigo
Anthraquinones
Benzanthrones
Benzanthrones
Acridones
Miscellaneous
Carbazoles
10. 1.Polycyclic Vat Dyes:
These class of dyes based on anthraquinone & related polycyclic systems generally exhibit
outstanding fastness properties.
Provides hues covering the whole of the visible spectrum
Main commercial products are found within the blue, green, brown and black sectors
Some of the relatively simple yellow and orange dyes cause photo tendering
High stability permits many of them to be used as pigments
Many of them are suitable for use on cellulosic fibers for infrared camouflage[4]
a)Anthraquinones:
Over 200 anthraquinone vat dyes are at present in commercial use, and the constitutions of about
130 of them have been disclosed. They represent a wide variety of chemical types.
*Provide shades ranging from yellow to black
*Complex dyes with structures that may contain up to 19 condensed rings
*Chiefly important in application to cellulosic fibers by dyeing and printing processes
*Varying of vatting conditions, but the only reducing agent of practical importance is alkaline
sodium hydrosulphite (Hydrose)
11. Let’s take a look at one of the many anthraquinone vat dye structures –
Anthraquinones Vat Dyes
12. b).Indanthrones:
The discovery of the first vat dye, Indanthrone, is a landmark in the history of synthetic dyes. It was
named indanthrene, a name coined from those of Indigo and anthracene.
Based on anthraquinone
Marketed by BASF as Indanthren Blue R (CI Vat Blue 4)
Excellent fastness properties[4]
Indanthrones vat dye structure-
Indanthrones vat dye
13. c).Benzanthrones:
Dyes from benzanthrone are actually substituted indanthrone, which is used as a dye. Several
important vat dyes have been manufactured from benzanthrone. Among these are dibenzanthrone
(CI Vat Blue 20) and Caledon jade green (CI Vat Green 1 or violanthrone) [5]. These dyeclass is
particularly important for the green vat dyes.
*Good levelling properties
*Excellent fastness to light and wet treatments
*Some colors (mainly green) with these excellent fastness properties cannot be produced by any
other means[6]
Benzanthrones vat dye structure-
Benzanthrones vat dye
14. d)Carbazoles:
Diphthaloylcarbazole derivatives constitute this important group of vat dyes.
*Good all-round fastness properties
*Provide hues ranging from yellow to black
Carbazoles dye Structure-
e)Acridones:
The first anthraquinone vat dye containing an acridone ring system was synthesized in 1909 by Ullmann.
Excellent lightfastness
Only moderate resistance to alkali due to the keto-enol equilibrium
15. f)Miscellaneous Polycyclic Quinones:
Flavanthrone, Pyranthrone, Anthrathrone, etc. are also of commercial interest.
Flavanthrone boasts excellent lightfastness but is prone to slow oxidation, lower wash fastness,
photochromism
Pyranthrone, a phototenderer, sports brilliant orange hues of good fastness properties [4]
16. II. Indigoid & Thioindigo Vat Dyes:
This is the dye that was produced from the plant of Indigofera genus. It was called
Indigo. The first commercially successful operation was achieved by BASF in 1897
using a process based on the fusion of o-carboxyphenylaglycine with caustic
potash and oxidation of the resulting indoxyl.
Gives a bluish shade
The dye is of considerable commercial importance, especially in warp dyeing for
woven cotton denim
Moderate light fastness, but even when it fades, it stays in tone
17. Classification Based on Application Condition
I.The IN (Indanthrene Normal) Group of Dyes
Dyes require the use of concentrated NaOH and high vatting (60°C) and dyeing
temperature (60°C)
No salt is added to the dyebath because of the high substantivity of the leuco dyes
for cotton fibres
18. II. IW (Indanthrene Warm) Group of Dyes
Require only moderate amounts of NaOH and lower vatting (50°C) and dyeing
temperature (50°C)
The leuco forms of these dyes have moderate substantivity for cotton
Some addition of salt is needed during dyeing to aid exhaustion
19. III. IK (Indanthrene Cold)
Dyes only need a low concentration of NaOH with low vatting (40°C) and dyeing
temperature (20°C)
Have low substantivity for cotton
Needs considerable salt for good dyebath exhaustion
Some have an amide group that would be hydrolyzed under fine the vatting and
dyeing conditions used for IN and IW dyes
20. IV. The IN Special Group
Only difference with IN group is that these dyes require more amount of alkali [7]
21. Vat Dyeing Recipe:
Chemically/parameter Depth of shade
Shade(%) 1.5 3 4.5
Hydros(g/l) 5 8 10
Extra Hydros(gm) 0.12 0.12 0.12
Caustic Soda(g/l) 15 20 25
Extra Caustic Soda(gm) 0.05 0.05 0.05
Temperature 60 60 60
pH 13 13 13
Time 50 50 50
M:L 1:10 1:10 1:10
22. Reduction of Dyes
As you already know, in this stage, the insoluble dye will change into soluble
leuco by reduction with suitable reducing agent & alkali combination. And for this
instance, they are Hydrose and Caustic Soda, respectively.
For the anthraquinone type of dyes, the above change takes place while reacting
with Hydros or Sodium Dithionite.
Here the hue change takes place because the conjugation of the dye molecule
changes.
Transformation from Insoluble to Soluble Form by Reduction
23. Stereochemistry of Vat Dyes:
Leuco Oxidizing:
Once the leuco vat dye has entered the fibre, all that remains is to convert the dye from the water-
soluble, or leuco form, back to the pigment, or water-insoluble form.
This is usually accomplished by placing the cellulosic fibre in an oxidizing bath. These small ions
enter the fibre quickly, and the pigment form of the vat dye is locked in the fibre both mechanically
and through secondary or hydrogen bonding.
Oxidations can be carried out in two ways
24. I. Air Oxidation:
The dyed material is subjected to oxidation by atmospheric oxygen. This is known
as air oxidation, airing or skying.
Advantages
The oxygen in the air is an adequate oxidizing agent for returning the reduced
form of vat dyes to the original pigmentary form
Disadvantages
Slow action
Non-uniform
Not ideal for compact structures like yarn packages or beams
Unwanted side reaction can change the final shade
I. Chemical Oxidation
Here, the dyed material treated with a suitable chemical oxidizing agent.
25. Advantages:
Rapid action
Less possibility of unwanted hue change
Uniform oxidation
Ideal for any form of material
Disadvantages:
Costly compared to air oxidation
Accelerated chemical oxidation may be carried out by acidified sodium or
potassium dichromate (now obsolete), sodium hypochlorite or peroxygen
compounds such as hydrogen peroxide (most commonly used).
Now you have to know that alkali carried forward by the substrate does not allow
oxidizing agents to release free oxygen, so shades produced in this way will lack
desired fastness.
26. That’s why before applying the oxidizing agent, a thorough wash needs to be
ensured. Otherwise, part of the peroxide gets wasted by the following reaction –
Na2S2O4 + 2NaOH + 3H2O2 = 2Na2SO4 + 4H2O
A typical chemical soaping with Hydrogen Peroxide can be –
Hydrogen Peroxide 5g/l
Temperature room temperature
Time 10 minute
Precautions in Vat Dyeing:
Here are some things we need to be careful about –
• To get uniform level dyeing results, the concentration of sodium hydrosulfite and
caustic soda must be in exact quantity to reduce the dye bath during the whole process.
• The presence of little excess reducing agent, which is a must, can be tested by vat
yellow paper in dyebath. Change in yellow color to deep blue shows the presence of
excess reducing agent.
27. Excessive quantity of reducing agent and alkali decrease the exhaustion rate of
the dyeing.
And in extreme cases will over-reduce the vat dyes.
Excess amount of oxidizing agent can lead to over-oxidation as well.
USE OF VAT DYES:
As you already know, vat dyes exhibit excellent wash fastness and resistance to
cross-staining, they are extensively used in places where these properties are the
primary concerns. Here are some examples –
Workwear and uniforms for armed forces, police, fire, nursing services, etc., which
are subjected to severe laundry washing and bleaching with hypochlorite and long
exposure to sunlight.
Clothing and household articles such as shirtings, sportswear, toweling, bed
sheets, tablecloths.
28. Furnishing requiring high fastness to light.
Outdoor fabrics requiring high weather fastness such as parasols, tenting, tarpaulins.
Yarns like sewing threads and for colored threads for weaving, which are subsequently
piece – bleached with hypochlorite.
Shirting fabrics with white stripe go to mercerizing in fabric stage after weaving with dyed
and grey yarn.
Yarns used for the border of dhoti, towel, etc.
Military Uniform Dyed with Vat Dyes
29. Vat Dyes Advantages and Disadvantages:
Advantages of Vat Dyes:
Excellent cross-staining fastness
Can sustain intense washing & hypochloride bleaching
Good resistance to sunlight fading
Finds application in sewing thread
Disadvantages of Vat Dyes:
Requires extra preparatory process, i.e, vatting
The dyeing vessel needs to be air-tight
Lengthy dyeing process
Prone to over-reduction and poor dyeing if ORP value is not monitored
Difficult to use for printing as it’s susceptible to
Very costly
