Physico chemical aspects of the dyeing process

Dye dispersed in the dye bath ↓↑Convective diffusion Dye in the diffusion layerboundary layer ↓↑ Molecular diffusion Dye in the electrical double layer ↓↑ Adsorption Dye absorbed on t

Physico-Chemical Aspect of the Dyeing Process

Prepared By : Mazadul Hasan sheshir ID: 2010000400008

13th Batch (session 2009-2013) Department : Wet Processing Technology Email: mazadulhasan@yahoo.com

Blog : www Textilelab.blogspot.com (visit)

Southeast University

Department Of Textile Engineering I/A 251,252 Tejgaon Dhaka Banglade sh

Prepared By :

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Physico-chemical aspect of the dyeing process is one kind of system or way which shows how to a dye penetrates or enter into the fiber It also describes how many process and time a dye molecule follow to enter completely onto the fiber

The dyeing process is essentially a distribution process The dye is distributed over at least two phase systems, the dye bath and textile materials When equilibrium dyeing is reached, the following subsidiary equilibrium is established

Dye dispersed in the dye bath

↓↑(Convective diffusion) Dye in the diffusion layer(boundary layer) ↓↑ (Molecular diffusion)

Dye in the electrical double layer

↓↑ (Adsorption)

Dye absorbed on the fiber surface

↓↑ (Diffusion)

Dye diffused in the fiber

↓↑ (Fixation)

Dye physically or chemically bond in the fiber

Successive Stage in the Dyeing:

1 Dye Dispersed in the Dye Bath:

Most of the dyes in solution are in molecular and partially ionized state or exist in the form of ionic micells

2 Dye in the Diffusion Layer:

When a substrate is brought into a dye bath, a concentration gradient is created which will-make the dye molecules move or diffuse to the fiber The dye which approaches the fiber surface must eventually diffuse through a thin liquid layer, the so-called diffusion layer, towards or onto the fiber surface

3 Dye in the Electrical Double Layer:

All textile fibers when immersed in water or aqueous solution, acquire an electrical potential after referred to as Beta potential At the fiber surface the dye molecules must pass the electrical double layer, consists of non-solvated anions (mostly) and solvated cat ions These positive and negative ions try to approach the fiber surface as close as possible This layer is about 1nm thin

4 Dye Absorbed on the Fiber Surface:

The dye molecules reach the fiber surface (and the first layer of the fiber) This dye take-up at the fiber surface (absorption) occurs very rapidly and leads to a reduction of dye molecules in the immediate vicinity of this surface

5 Dye Diffused in the Fiber:

After absorption, dye diffused in the fiber Owing to the high temperature, there is always an abundance of dye stuff molecules in the vicinity of the fiber and agitation has little effect upon the time of half dyeing

6 Dye Physically or Chemically Bond in the Fiber:

The last step of dyeing is fixation In case of reactive dyes, the fixation is one-way Because here dye molecules become attached to the fiber polymer by strong co-valiant bonds In case of all other dyes this fixation is two ways Because they are fixed with fiber by weak hydrogen or salt linkage

The following factors are responsible for the anchoring of the dye molecules to the fiber:

1. Salt linkage/ionic bonds for protein fibers

2. Co-ordination linkage

3. Hydrogen bonds

4. Co-valent bonds ; for cellulose fibers Physical forces & Dispersion forces

Fig: Dyeing Mechanism

Here, Cf = Cone of dye in fibre

Cs = Cone of dye in solution EDL = Electrical Double Layer

DL = Diffusion Layer

Affinity: The attraction of the dyes to the textile materials It is related to the heat or tempeture.

Substantivity: The attraction of the textile materials to the dyes

Diffusion: Diffusion can be define as the spontaneous spreading of any material through any medium

Adsorption: When the dye molecules comes contact to the surface of the fiber by passing of EDL

Exhaustion: when three processes has completed (Adsorption→ Sorption→ Absorption) then total amount of dye molecules remain

in the fiber is called Exhaustion Mathematically

Exhaustion % = (IDC – FDC) x 100% / IDC

Absorption: The process by which dye molecules enter into the fiber.

Fixation: It is nothing but the physical & chemical bonding of dye molecules & fiber After washing which amount of dyes are contact with the fiber that is called fixation Fixation = Exhaustion – (Wash + Soap Wash)

Shade%: shade is express in percentage of dye amount in unit weight of fiber Light → 0.5% Medium → 1.5% Deep → more than 1.5%

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