Important Chemicals & Auxiliaries for the dyehouses

1. Mashrur Wasity Shovon
Bangladesh University of Business &
Technology

2. Special chemicals &
Auxalaries
in
Wet Processing

3. Title
Introduction :
Most of the operations in the textile
processing such as scouring, bleaching, dyeing and
printing are carried out by use of basic chemicals like
acid, alkalis oxidizing, reducing agents dyestuffs etc.
Besides this other chemical are also used in relatively
small quantity proportion to increase the efficiency
of above process. These substances are called
Auxiliaries.

4. WHAT IS THE NEED OF TEXTILE CHEMICAL PROCESSING?
• In Textile Chemical Processing the chemical treatments are given to
the fabric after being manufactured.
Actually the fabric coming from the loom is not having properties like
absorbency, softness etc and the most important is that the
appearance of the fabric is dirty or pale yellow; we cannot use
it directly for making apparels or clothing. So, it is necessary to go
for chemical processing of the material to make it wearable.

5. Title
It is defined as a chemical or a formulated chemical product which
enables a processing operation. The various processing operations
may be in the functions of preparation, dyeing, printing or finishing.
Auxiliaries help by speeding up these processes or carry out the
processes in a more efficient manner. This is necessary to obtain the
desired effect.
What Does Auxiliary
Mean in
Textiles?

6. Title

7. The chemicals used can be subdivided into:
• Textile auxiliaries – covers a wide range of functions, from
cleaning natural fibers and smoothing agents to improving
easy care properties.
Included are such things as:
o Complexing agents, which form stable water-soluble complexes
o Surfactants, which lowers the surface tension of water so grease
and oil to be removed more easily.
o Wetting agents, which accelerates the penetration of finishing
liquors
o Sequestering agents
o Dispersing agents
o Emulsifiers
o Water

8. • Textile chemicals (basic chemicals such as acids, bases and
salts)
such as:
o Dyes
o Dye-protective agents
o Fixing agents
o Leveling agents
o pH regulators
o Carriers
o UV absorbers

9. • Acid: Acid is used to control PH
. Acid decrease the pH of the
solution. If PH
1-7 then it is called Acidic solution.
• Basic: Basic is used for increase the PH
of the solution. PH
range of
basic is 7-14. This also used as scouring agent.
• pH:
pH is a scale between 0 and 14 used to express the concentration
of hydronium (H3O+, or H+) ions in a solution. It is defined by
Equation .
pH = – log [H+]

10. Acetic Acid
• Acetic acid is a colorless and corrosive liquid with pungent smell of
its own. It is miscible with water, alcohol and ether in all proportions.
Acetic acid is used in garment industry for dyeing purposes
Oxalic Acid
• Oxalic is a colorless, crystalline solid with two molecules of water of
crystallization. Oxalic acid is used in garment and textile industry for
the removal of ink stains from cloths and bleaching of straw for hats.
Its antimony salts are used as mordant for dyeing and printing.

11. Soda Ash
• Sodium carbonate is a white crystalline solid containing water of
crystallization. It is used in laundry as washing soda. It is also used
for softening water.
Caustic Soda ( Sodium Hydroxide), NaOH :
Function :
 Caustic soda is the strong alkali used in garments washing to
introduce an alkaline condition.
 Caustic created the role in bleach technique without color change
the garments.
 Caustic has a cleaning power which is more powerful than soda
Ash.

12. Wetting agent :
This is used to reduction of surface tension of water and increase the
penetration of chemicals on fabric surface.
It also increase the absorbency.
Sequestering Agent :
This agent is used to remove hardness of water so that the scouring
can be done without any wastage of soaps & detergents.
If chelating agents are not used, then hard water can cause wastage of
soaps and detergents. As a result scouring efficiency decreased.

13. Peroxide Killer:
This chemical is used to kill per oxide which is remaining in the
material. Peroxide is harmful for the material. A test is carried out to
measure the amount of peroxide present in the solution.
Oxidising agents and reducing agents :
Oxidising agents are mainly used for bleaching and reducing agents
are mainly used for vat dyeing in textile wet processes. These
agents are often strong chemicals and need to be handled with
care.
Hydrogen peroxide (H2O2), Sodium Hypochlorite etc are some
oxidising agents & Sodium hydrosulphite (Na2S2O4), Sodium
thiosulphate (Na2S2O3•5H2O) etc are some of the reducing agents.

14. Dispersing Agent:
This agent is used for disperse dyes. We know, disperse dye is
insoluble in water and dye present in disperse form. By applying this
agent dye molecule breaks and become soluble in the solution.
Bleaching Agent :
Bleaching is carried out before dyeing or printing operation. Better
absorption of dyes depends on better bleaching. Absorbency test is
carried out to test the bleaching performance. Absorbency time
should lie under 5 second.
Function:
It is used for removing natural color from the grey yarn or fabric.

15. Wash/Soaping Agent: Soaping agent is used for washing. It needs to
wash dyed material to remove unfix dye from the material. Dark
material needs double wash. Sometimes no wash is carried out for
light shade. It also increases the reflecting properties.
Function :
 Disperse the unfixed substanted hydrolyzed dyes, and solubilize and
emulsify these into the aqueous medium and keep these substances
in suspension.
 Prevent re-deposition of hydrolyzed dyes and other particles of
colloidal substance into the textile material.
 Prevent the precipitation of insoluble calcium or magnesium salt.

16. Salts :
Salts are the products of the acid-base neutralisation reaction.
The salts used most in textile wet processes are common salt (NaCl,
sodium chloride) and Glauber’s salt (Na2SO4, sodium sulphate).
Function :
Salt increase the exhaustion rate of the dyeing process.

17. Scouring Agent: Scouring agent is used to remove fat, waxes,
fragments of cotton etc.
Antifoaming Agent: A defoamer or an anti-foaming agent is a
chemical additive that reduces and hinders the formation of foam in
industrial process liquids.
Foam is formed during bleaching and dyeing process. Anti foaming
agent is used to resist foam formation. If foam formed it reduces the
dyeing uptake percentage.
Alkyl poly acrylates , Castor Oil , Fatty Acids, Paraffin Oil are some of
the example of antifoaming agents.

18. Neutralization Agent: This agent is used to neutral the PH
of the
solution.
Fixing Agent : It is an excellent agent and is widely used as fixing
agent for direct & reactive dyestuffs on cellulose fiber. Fixing agents
is used for improving the rubbing fastness of the direct colours to
light and washing. It enhances wet fastness for heavy shade but
usually reduce light fastness.
This agent is also used for removing the unfix dye.

19. Surfactants
Surfactants are widely used in textile wet processes for the
purpose of wetting, dispersing, emulsifying and cleaning. The
molecular structures of surfactants have a distinctive hydrophilic
moiety and a distinctive hydrophobic moiety. When they are used at
a sufficient concentration, the surface tension of the solution is
lowered and micelles are formed, which give the solution extra
properties.

20. • Surfactants are four types
1. Anionic surfactants
2. Cationic surfactants,
3. Non-ionic surfactants and
4. Amphoteric surfactants
Functions :

21. Dye: A coloured organic comp. or mixture that may be used for
imparting colour to a substrate such as cloth, paper, plastic or
leather.
 Requisites of a True Dye:
 Suitable & attractive colour
 Able to attach itself.
 Must be water soluble
 Substrates being dyes must be affinity to dye.
 After fixation of dye, it must be fast to washing, cleaning etc.
 Shade & fastness of a given dye may vary depending on the
substrate.

22. Classification of Dyes by Use or Application Method
1. Reactive Dyes:
 It possible to achieve extremely high wash fastness properties by
relatively simple dyeing methods .
 Chemical structures are much simpler, their absorption spectra
show narrower absorption bands, and the dyeing are brighter.
• EX. Azo (including metallized azo), triphendioxazine,
phthalocyanine, formazan, and anthraquinone .
• High-purity reactive dyes are used in the ink-jet printing of textiles,
especially cotton.

23. 2. Disperse Dyes:
 Water-insoluble non-ionic dyes for application to hydrophobic fibers
from aqueous dispersion.
 Used predominantly on polyester and to a lesser extent on nylon,
cellulose, cellulose acetate, and acrylic fibres.
 Used in Thermal transfer printing and dye diffusion thermal transfer
processes for electronic photography.

24. 3. Direct Dyes.
 Water-soluble anionic dyes, when dyed from aqueous solution in the
presence of electrolytes, are substantive to, i.e., have high affinity
for, cellulosic fibres.
 Applicable for cotton, linen, viscose, silk. Simple diffusion into the
fibre, from aqueous solution. It has relatively poor fastness
properties to light, washing and perspiration. These fastness
properties can be improved by after treatment.
 After treatments, frequently applied to the dyed material to improve
wash fastness properties.

25. 4. Vat Dyes :
• Water-insoluble dyes are applied mainly to cellulosic fibres as
soluble leuco salts after reduction in an alkaline bath, usually with
sodium hydrogen sulfite.
• The leuco forms are reoxidized to the insoluble keto forms and after
treated, usually by soaping, to redevelop the crystal structure.
• The principal chemical classes of vat dyes are anthraquinone and
indigoid.
• It has high fastness to washing, chlorine, boiling, light, weather,
rubbing and perspiration.

26. 5. Sulfur Dyes:
• These dyes are applied to cotton from an alkaline reducing bath with
sodium sulfide as the reducing agent. Numerically this is a relatively
small group of dyes.
• The low cost and good wash fastness properties of the dyeing make
this class important from an economic standpoint.
6. Acid Dyes:
Water-soluble anionic dyes
Applicable for wool, silk, nylon. Applied from an acidic dyebath. The
fastness properties of this dye-stuff depends on the fibre type.

27. 7. Basic Dye:
 It is suitable for acrylic fibres (other fibres by mordanting)
 It reacts with acidic groups, or mordants (a chemical which can
react or complex with a chromophore to form an insoluble color) in
the fibre.
 It has good fastness properties on acrylic fibres.

28. Brightening Agent:
This agent is used to increase the brightness of the material. This
agent increases the reflecting property of the material. Standard
reflecting value is 85%. Sometimes it is possible to increase it up to
95%. But it is risk because it needs high kier boiler temperature,
which reduces the strength of material.
Ethylenediamine tetraacetate (EDTA)
Ethylenediamine tetraacetate (EDTA) can form a few different water
soluble salts with calcium, potassium and sodium, for example,
calcium disodium, trisodium and tetrasodium salts. EDTA
tetrasodium salt is used most widely in many industrial applications
as a powerful chelating agent. Its 1% solution has a pH of 11.3. It
can chelate with many divalent and trivalent metal ions to form
watersoluble metal complexes.

29. Fluorescent whitening agents :
Fluorescent whitening agents (FWA) are a special type of chemical
that can significantly increase the apparent whiteness of treated
fabrics. They absorb UV radiation and re-emit the absorbed energy
in the blue visible light range which makes the treated fabrics
appear whiter.
The easiest test for the effect of FWAs is simply a visual examination of
the whiteness of treated fabrics. Manufacturer’s recommendations
should be followed in order to achieve the best whitening effect.

30. Carriers :
The extreme crystalline nature of polyester fibres creates problems
in obtaining dark shades by conventional dyeing methods even at
high temperature. The carriers are found to assist the disperse dyes
to enter the polyester polymer, enabling dark shades to be
produced.
The carriers swell the polyester fibres, increase inter polymer space
and let the dye molecules to enter the polymer system easily.