This document discusses chemicals and auxiliaries used in textile wet processing. It provides an overview of various chemicals like acids, alkalis, salts, oxidizing agents, reducing agents, detergents, wetting agents, and others. For each chemical or auxiliary, common examples and their uses in processes like scouring, bleaching, dyeing, and finishing are described. Successful wet processing requires the proper use of dyes and chemicals, as operations cannot be satisfactorily completed without things like alkalis for dyeing or sequestering agents to remove water hardness.

1. An Assignment
On
“Study on the chemical auxiliaries used in textile wet processing?”
Course Title: Wet Processing III
Course Code: WPE 411
Submitted To:
Dr. A K M Saiful Islam
Assistant Professor & Head
Department of Textile Engineering
City University
Submitted by:
SL Name ID Batch
01 Md. Zahid Hasan 173317179 37th
(Day)
02 Md. Mahirul Islam 173375037 37th
(Day)
03 Md. Wadud Miah 173375051 37th
(Day)
04 Arif Miah 173375063 37th
(Day)
05 Md. Obidul 173375075 37th
(Day)
06 Mohammad Sharif Ahmmed 173375101 37th
(Day)
07 Md. Rakibul 173375102 37th
(Day)
08 Md. Anisur Rahman 173375106 37th
(Day)
09 Md.Abdur Rahman 173375124 37th
(Day)
10 Mohammad Emon Hasan 173375147 37th
(Day)
11 Mominur Islam 173375150 37th
(Day)
12 Rakibul Islam 173375166 37th
(Day)
13 Rakib Billah Tamjid 173375026 37th
(Day)
14 Md.Atiqur Rahman 173375076 37th
(Day)
Submission Date: 11th
March, 2021

2. Introduction
Coloration is the main stage of chemical application for attractiveness or
decoration of textile end product. But to get the best result of coloration, some
preparatory steps are necessary for grey textiles. Dyeing is the process of adding
color to textile products like fibers, yarns, and fabrics. We know that dyes and
chemicals are the main factor for producing color in yarn of fabric. Different types
of chemicals are used during dyeing. In different stages of dyeing processing,
various chemicals are used. Every chemical have their own characteristics and they
are used in different stages of wet processing.
Wet processing Chemicals & Auxiliaries
At various stages of textile wet processing different types of chemicals and
auxiliaries are used. Through all are actually chemicals, in practice the materials
without which a process cannot be completed are termed as “chemicals” & the
other substances which facilitate or improve the performance of that process are
termed as “auxiliaries”.
Following are some of the chemicals & auxiliaries used in practice:
i. Acid
ii. Alkali
iii. Salt
iv. Oxidizing agent
v. Reducing agent
vi. Detergent
vii. Wetting agent
viii. Leveling agent
ix. Anti-creasing agent
x. Sequestering agent
xi. De-foaming agent
xii. Dispersing agent
xiii. Carrier
xiv. Emulsifier

3. xv. Anti-static agent
xvi. Resin
xvii. Catalyst
xviii. Softener
xix. Milling agent etc.
i. Acid
According to term of chemistry, the compound that dissolves in water and
provide H+
(proton) is called acid. Some of the examples are HCl, H2SO4,
HNO3, CH3COOH etc.
Uses of some common acids are:
Acids Uses
H2SO4 Widely used in washing & mordanting, carbonizing of wool, acid
dyeing on wool, etc. Salts of this acid are also used.
HCl Used in washing & dyeing, in diazotization, in scouring, etc. Salts
of this acid are also used.
CH3COOH Used for dyeing & for neutralization.
C2H2O2 To remove the metallic stain from fabric & garments, etc.
ii. Alkali
According to term of chemistry, the compound that provides OH-
(hydroxyl ion)
is called alkali. Some of the examples are NaOH, Na2CO3, CaO, Na2O etc.
Uses of some common alkalis are:
Alkalis Uses
NaOH Used in scouring, mercerizing, dyeing, soap formation, washing,
etc.
Na2CO3 Widely used in reactive dyeing.
Ca(OH)2 To remove the hardness of water, formation of bleaching
chemicals, mordant & indigo vat, etc.

4. iii. Salt
In textile wet processing salt is of maximum use. Different types of salts are
used in different processes for different purposes. Some of them are discusses
here:
Salts Uses
NaCl Widely use as electrolyte in reactive dyeing, etc.
NaOCl Used for bleaching.
NaNO2 Used for azoic color dyeing & diazotization, also used in direct,
azo & vat dyeing.
Na2S Used as reducing agent, for the preparation of sulphur dye.
Na2SO4 Used for finishing of cotton, direct, acid & sulphur dyeing.
NaHSO3 To remove chlorine from silk & wool after bleaching.
Na2S2O4 Used in vat dyeing, washing of protein fibre.
CH3COONa Used in wool dyeing with direct & acid dyes and also during
stripping of wool & silk.
Ca(OCl)Cl Used in cotton bleaching, discharge printing.
iv. Buffer
 It is saturated solution of acid salt or alkali-salt mixture.
 It resists the charge of PH
on addition of acid alkali.
 Usually used to control PH
of any bath solution.
 Buffer solutions are solutions containing mixture of a week acid or base
and a salt of that acid or base.
E.g. The mixture of acetic acid or sodium acetate, which dissociates as:
CH3COOH --------- CH3COO-
+ H+
CH3COONA ------- CH3COO-
+ Na+
v. Oxidizing agent
The chemical compound which provides oxygen during chemical reaction and
the itself converted to oxides. They gain electrons in a redox chemical reaction.

5. vi. Reducing agent
It is used for stripping of dyed material and reduction purpose where insoluble
substances need to be convert into soluble form. E.g. Hydrose (Na2S2O4),
Rongolite C.
vii. Surfactant
Surfactants or surface-active agents act in solid-liquid, solid-gas, or liquid-gas
interfaces and reduces the interfacial tension.
In textile wet processing it works in between solid-liquid interface and reduce
the surface tension of liquid.
It has a versatile application in textile industries especially in coloration. For
example,
 Wetting agent,
 Detergent,
 Lubricant,
 Foaming agent,
 Anti-foaming agent,
 Leveling agent,
 Dispersing agent.
vii. Wetting agent
It accelerates wet ability of material in solution, thus helps to easy penetration
of chemicals into substrate. Usually used in scouring, bleaching & dyeing. It is
available in the form of clear or yellowish liquid in market.
viii. Detergent
Detergents are one kind of surface active agent (but, the reverse is not true).
Surfactants that have detergency power & number of carbon in the aliphatic
chain are not less than 9. These are usually used in textile to clean the materials

6. by removing undesirable substances. These products are either soap/synthetic
detergents.
ix. Lubricant
The chemical compounds used to prevent contact between solid surfaces in
relative motion in order to reduce friction, wear, overheating and rusting. They
are very good coolants provide the appropriate range of viscosities and are
thermally stable.
x. Anti-foaming agents
Another type surfactant that is able to reduce or prevent foam. Usually used in
dyeing bath & in printing paste to hinder foam generation. Excess foam
generation can create adverse effect in processing & product.
xi. Anti-creasing agent
Usually used in dye-bath or in finishing stage to prevent creasing of fabric or
garments.
xii. Anti-pilling agents
Some Man-made fibre (MMF) & blended fibre fabrics can easily form pills in
their surface. Thus it reduces the aesthetic value of the fabric or garments. Anti-
pilling agents are used to prevent such kind of pills formation during wearing of
cloth.
xiii. Leveling agents
Leveling agents are used in textile coloration process to achieve uniform dyeing
over the whole substrate by controlling the rate of dyeing. Generally, it is a non-

7. ionic surfactants type compound either fibre substantive or dye substantive.
These are available in liquid form.
xiv. Retarding agents
The chemical compound that is able to retard or control the dye uptake inside of
the fibre. Use of retarding agent is common in acrylic dyeing with cationic
dyes.
xv. Disperse agent
It is used to prevent aggregation of dyestuff molecules in the highly
concentrated paste or solution of the dye. For example, Aceton, Diethylene
glycol.
xvi. Carrier
Carriers are relatively small organic substances that usually have affinity for
polyester. They act as catalysts to accelerate the dye penetration into the fibre
during disperse dyeing process.
Conclusion
Wet processing engineering is one of the major streams in textile engineering
refers to textile chemical processing engineering and applied science. For
successful wet processing operation different dyes, chemicals or chemical
auxiliaries plays an important role. Without these chemicals dyeing operation
will not be satisfactory (like without alkali no dyeing will be taken place,
without salt proper fixation or sometimes better can’t be achieved, without
sequestering agent-EDTA,NTA is mostly used dye bath water hardness can’t be
removed, etc.).
So we should use the chemicals according to their scope of use.