Mechanism of Dyeing and chemical bonds for textile

Mechanism of Dyeing -

The process of dyeing is also divided into three phases
(A) Adsorption of the dyestuff at the fibre surface
(B) Diffusion of the dyestuff through the internal structure of fibre and
(C) Fixation or Anchoring of the dye molecules at an appropriate location or dye site.

Explanation -

(A) Adsorption -
within the first phase or step, the dye molecules within the dye bath move towards the fibre and people that are nearest to the fibre get adsorbed on the fibre surface
They form an awfully thin layer of molecules on the fibre surface.

Other dye molecules still within the dye bath will be adsorbed as long as this adsorbed layer moves further into the fibre.

A schematic representation of a fibre showing the adsorption of dye molecules on the surface of the fibre -

(B) Penetration -

The adsorbed dye molecules enter the fibre structure and typically disperse into the pores or channels in the structure in the second stage.

The chemical features of the dye, the molecular arrangement in the fibre, and the dying circumstances will all affect how quickly and how deeply they penetrate.

Almost all of the dying time is spent on dye diffusion or dye penetration in the fibre.
The colouring gets brighter and better the deeper the dye has penetrated the fibre.

Therefore, good penetration is essential for effective dyeing.

Effectiveness of dyeing

As shown in a dig. of dyed fibre, one with good dye penetration and the other with poor penetration, poor penetration causes dull, uneven dyeing with unsatisfactory colour fastness properties.

(C) fixation-

Fixation is the last stage, in which the dye molecules locate suitable places or locations and get fixed or anchored there.

The nature and degree of the forces used to hold the dye molecules inside the fibre vary depending on the dye-fibre connection.

Bonds between the fibre and the dye -

Although the exact nature of the forces holding the dye particles to the surface of the fibre is not fully known, they could be categorised as follows:

(i) Van der Waals forces
(ii) Hydrogen bonds
(iii)Salt linkages or Ionic bonds
(iv) Covalent bonds

Explanation -

(i) Van der Waals forces -

Very weak forces of attraction are always present between the electrons of 1 atom and the nucleus of another in close enough proximity.

Individually these are very weak forces, collectively they're considered to be of sufficient strength to be the foremost important attractive forces between dye and fibre.

These forces are called Van der Waals forces. Disperse dyes are held in a very Polyester fibre using van der Waals forces.

Van der Waals forces

(ii) Hydrogen bonds -

These forces of attraction are weak forces found between certain atoms within the dyestuff molecules after they are close enough to other atoms within the fibre.

One of these atoms is the atom hence, the term chemical bond some direct and vat dyes are hydrogen-bonded in cellulose fibres.

(iii) Salt linkages or Ionic bonds -

In solution, dyestuff molecules get divorced into positive and negative charged particles called ions one of which is coloured.

Depending upon the actual class of dyestuff being considered the coloured ion is also cationic (carried a positive charge) or anionic (where the charge is negative).
When strong electrostatic forces of attraction develop between the ions in a very fibre and oppositely charged dyestuff ions, salt linkages or ionic bonds are said to be formed.

Ex: When the anionic (-SO3) groups in an acid dyestuff get close enough to draw in a cationic (-NH3+) group in wool, silk or nylon the resulting bond could be salt linkages or a bond or bond.

(iv) Covalent bonds -

Bonds leading to very strong chemical forces that don't seem to be easy to interrupt except under server conditions are called covalent bonds.

The classic example is that the mixture of cellulose is covalently bonded to the appropriate atom within the reactive dye.

Bond type	Relative strength
(1) Van der Waal force	1.0
(2) Hydrogen bond	3.0
(3) Ionic bond (salt linkages)	7.0
(4) Covalent bonds	30.0

Fibre	Dye class having Affinity	Type of dye fibre bonds
Cellulosic: cotton, jute, Rayon etc	Direct,vat, solubilised vat and sulphur	Van der Waals forces and hydrogen bonds
	Reactive	Covalent
Protein, polyamide: wool, silk, nylon	Direct,acid, metal, complex and basic	Ionic or electrostatic bonds
	Reactive	Covalent bond
Polyester	Disperse	Van der Waal forces and hydrogen bonding
Cationic dyeable polyester (CDP)	Cationic	Ionic or electrostatic bonds
	Disperse	Van der Waals forces and hydrogen bonding
Acrylic	Cationic	Ionic or electrostatic bonds
	Disperse	Van der Waals forces and hydrogen bonding

Questions -

Which mechanism works behind the process of dying?
Explain the absorption process for textile dying.
Explain the penetration process for textile dying.
Explain the fixation process for textile dying.
Which bonds are generated between fibres and dyes during chemical processing?
Explain Van der Waals forces between fibres and dyes.
Explain Hydrogen bonds between fibres and dyes.
Explain Salt linkages or Ionic bonds between fibres and dyes.
Explain Covalent bonds between fibres and 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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