Thursday, April 27, 2017

Textile Chemicals and Auxiliaries Used in Wet Processing

At various stages of textile wet processing different types of chemicals and auxiliaries are used. Though all are actually chemicals, in practice the materials without which a process cannot be complete are termed as “chemicals” and the other substances which facilitate or improve the performance of that process are termed as “auxiliaries”.
Textile chemicals and auxiliaries
Fig: Textile chemicals and auxiliaries
List of wet processing chemicals and auxiliaries:
Following are some of the chemical and auxiliaries used in practice:
  1. Acid
  2. Alkali
  3. Salt
  4. Oxidizing agent
  5. Reducing agent
  6. Detergent
  7. Wetting agent
  8. Leveling agent
  9. Anti-creasing agent
  10. Sequestering agent
  11. De-foaming agent
  12. Dispersing agent
  13. Carrier
  14. Emulsifier
  15. Anti static agent
  16. Resin
  17. Catalyst
  18. Softener
  19. Milling agent etc.
Functions and uses of chemicals and auxiliaries in dyeing and finishing are described briefly at below:

1. Acid:
According to the team 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.

In textile processing, acid is considered one of the most important chemical. For example, the uses of some most common acids are listed here:


Acids
Uses
H2SO4
Widely used in washing and mordanting, carbonizing of wool, acid dyeing on wool, etc. Salts of this acid are also used.

HCI
Used in washing and dyeing, in diazotization, in souring, etc. salts of this acid are also used.
CH3COOH
Used for dyeing and for neutralization
C2H2O4
To remove the metallic stain from fabric and garments etc.
2. Alkali:
According to the 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 and indigo vat etc.
3. 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 discussed here:

Salts
Uses
NaCl
Widely used as electrolyte in reactive dyeing etc.

NaOCl
Used for bleaching
NaNO2
Used for azoic color dyeing and diazotization, also used in direct, azo and vat dyeing.
Na2S
Used as reducing agent, for the preparation of sulphur dye.
Na2SO4
Used for finishing of cotton, direct, acid and sulphur dyeing.
NaHSO3
To remove chlorine form silk and wool after bleaching.
Na2S2O4
Used in vat dyeing, washing of protein fibre.
CH3COONa
Used in wool dyeing with direct and acid dyes and also during stripping of wool and silk.
Ca(OCl)Cl
Used in cotton bleaching, discharge printing.
4. Buffer:
  • It is saturated solution of acid salt or alkali-salt mixture.
  • It resists the change of PH on addition of acid alkali.
  • Usually used to control PH of any bath solution.
  • Buffer solution are solutions containing mixture of a weak acid or base and a salt of that acid or base.
E.g. The mixture of acetic acid or sodium acetate, which dissociates as:

CH
3COOH-----------CH3COO- + H+
CH
3COONA---------CH3COO- + Na+

5. Oxidizing agent:
The chemical compound which provides oxygen during chemical reaction and then itself converted to oxides. They gain electron in a redox chemical reaction, e.g. O3
, H2O2, and CaOCl2.

6. Reducing agent:
The chemical compound which losses electron during chemical reaction. It reduce other substances chemically, especially by donating electron, e.g. Hydrose (Na
2S2O4), Rongolite C.

7. 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
8. Wetting agent:
It accelerates wet ability of material in solution, thus helps to easy penetration of chemicals into substrate. Usually used in scouring, bleaching, and dyeing. It is available in the form of clear or yellowish liquid in market.

9. Detergent:
Detergents are one kind of surface active agent (but, the reverse is not true). Surfactants that have detergency power and number of carbon in the aliphatic chain are not less than 9. These are usually used in textile to clean the materials by removing undesirable substances. These products are either soap/synthetic detergents.

10. 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.

11. Anti-foaming agents:
Another type surfactant that is able to reduce or prevent foam. Usually used in dyeing bath and in printing paste to hinder foam generation. Excess foam generation can create adverse effect in processing and product.

12. Anti creasing agent:
Usually used in dye-bath or finishing stage to prevent creasing of fabric or garments.

13. Anti pilling agent:
Some MMF and 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.

14. Leveling agent:
Leveling agents are used in textile coloration process to achieve uniform dyeing over the whole substance by controlling the rate of dyeing. Generally, it is a non-ionic surfactants type compounds either fibre substantive or dye substantive. These are available in liquid form.

15. Retarding agent:
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.

16. Dispersing agent:
Dispersing agents are usually used in disperse and vat dyeing process. It helps to distribute the dye molecules in the dye bath. It also helps to penetrate the dye molecules into the substrate. This is available in power form.

17. 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.