Dyeing assistants (1)

Dyeing assistants

Chemicals that aid in producing the desired colour during dyeing is known as dyeing assistants.

Additionally known as dyeing auxiliaries. Some typical dyeing assistants are briefly discussed below -

Dyeing assistants -

(1) Water softening agents
(2) Exhausting agents
(3) Dispersing agents
(4) Levelling agents
(5) Regarding agents

Softening agents

Explanation -

(1) Water softening agents (Sequestic agents or chelating agents) -

The chemicals are mostly utilised in dyeing processes that use hard water. They combine with

metallic ions to form a complex ion as a result of their reaction. Additionally, they are referred to as sequester or cheating agents.
Commonly used softening agents are -

(a) Calgon(Sodium hexa-metaphosphate)- Calogen reacts with calcium or magnesium in the following way

Reaction - Na2[Na2(PO3)6] + Ca++---> Na2[Ca(PO3)6]+2Na+

(b) ethylene-diamine-tetra acetic acid
Formula - (COOH.CH2)2N.CH2CH2.N(CH2COOH)2, often abbreviated as EDTA

This formation of complexes is referred to as chelation and it manifests in what are called chelating compounds.

(2) Exhausting agents - (NaCl)

Exhausting agents are important from the purpose of view of economical dyeing because they facilitate the movement of the dye molecules to the fibre and thereby exhaust the dye bath.

In all these cases, the dyes act as anionic dyes(splitting up into dye anions and sodium or other metal cation in water). When a cellulosic fibre is immersed in water it acquires a negative electrical charge (Zeta potential).

As a result, the charged fibre surface repels the charged anions present within the water(i.e during the dyeing of cellulosic fibre from a solution of the anionic dye).

When common salt or Glauber's salt is added to the dye bath the Sodium ions released by it try and neutralize or reduce the charge of the fibre surface, thereby reducing the repulsion of the dye-anion at the fibre surface.

As a result, the approach of the dye anions towards the fibre surface is facilitated.
In other words, more dye is preoccupied with the fibre within the presence of salt than in its absence.

However, the extent of increase in exhaustion caused by salts varies from dye to dye. also with other dye-fibre combinations, other chemicals are used as Exhausting agents.

Common salt(NaCl) or Glauber salt(Sodium sulphate-Na2SO4) is predominantly used as an Exhausting agent within the dyeing of cellulose fibres with direct, azoic, vat, solubilised vat and reactive dyes.

(3) Dispersing agents -

To keep water in insoluble or suspension or dispersed form dispersing agents are used Dispersing agents are described as sodium salts of -

(i) A naphthalene sulfonic acid condensation product
(ii) An aromatic acid condensation product
(iii) Highly condensed NS acid or
(iv) Disodium salt of methylene dinaphthalene disulphonic acid etc.

These are available in the style of yellowing brown powder, light powder, light beige coloured powder, and dark brown mobile Liquid then on.

The powder brand may be a non-hygroscopic powder that's -
(i) It is quickly soluble in water with any degree of hardness (it is stable in hard water),

(ii) proof against Alkalis, acid and salts and has dispersing and protective colloid properties It finds use within the dyeing of vat dyes by the vat-acid process and also in dyeing with Disperse dyes, solubilised vat dyes and azoic (naphtol) colours.

In the dyeing of polyester and polyamide with Disperse dyes, the use of dispersing agent results in the assembly of a fine dispersion of the dye thanks to its non-foaming nature it's recommended for the heat dyeing of yard goods or yarn struggling.

When added to developing baths(to extents within the range of 0.5 to 2 GPL) azoic dyeing dispersing agents increase the clarity of the baths and yield dyeing of Improved rubbing fastness.

Preparation of Dispersing agents

Other dyeing assistants

Questions -

Which chemical agents are used as dying assistants?
Explain Water softening agents for dyes.
Explain Exhausting agents for dyes.
Explain Dispersing agents for dyes.
Explain Levelling agents for dyes.
Explain Regarding agents for dyes.

References

Dyes and dyeing. (n.d.). Gov.uk. from https://www.hse.gov.uk/textiles/dyes-dyeing.htm

eBook, T. (2021, February 22). Textile dyeing PDF by Dr. N. n. mahapatra. Textile EBook. https://www.textileebook.com/2021/02/textile-dyeing-pdf-by-dr-n-n-mahapatra.html

Introduction to dyeing and dyehouse automation. (2014). In Modelling, Simulation and Control of the Dyeing Process (pp. 1–30). Elsevier.

Rana, M. B. (2015). Textile dyes and their application process. https://www.academia.edu/17283292/Textile_dyes_and_their_application_process

textile - Dyeing and printing. (n.d.). In Encyclopedia Britannica.

Textile dyes and dyeing. (n.d.). Pdfdrive.com. from https://www.pdfdrive.com/textile-dyes-and-dyeing-e176024633.html

(N.d.-a). from http://chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://www.cottonworks.com/wp-content/uploads/2018/01/Dyeing_Booklet.pdf

(N.d.-b). Researchgate.net. from https://www.researchgate.net/publication/338450346_Fabric_Dyeing_Process

(N.d.-c). Researchgate.net. from https://www.researchgate.net/publication/321085555_Handbook_of_Textile_Coloration_and_Finishing

(N.d.-d). Researchgate.net. from https://www.researchgate.net/publication/257956500_Textile_Dyeing

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