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Topics - Tanvir Ahmed Chowdhury

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Textile Engineering / Mechanism of disperse dyeing
« on: January 18, 2017, 10:37:23 AM »
The dyeing of hydrophobic fibers like polyester fibers with disperse dyes may be considered as a process of dye transfer from liquid solvent (water) to a solid organic solvent (fiber).
Disperse dyes are added to water with a surface active agent to form an aqueous dispersion. The insolubility of disperse dyes enables them to leave the dye liquor as they are more substantive to the organic fiber than to the inorganic dye liquor. The application of heat to the dye liquor increases the energy of dye molecules and accelerates the dyeing of textile fibers.


Heating of dye liquor swells the fiber to some extent and assists the dye to penetrate the fiber polymer system. Thus the dye molecule takes its place in the amorphous regions of the fiber. Once taking place within the fiber polymer system, the dye molecules are held by hydrogen bonds and Van Dar Waals’ force.
Dyeing of hydrophobic fibers like polyester fibers with disperse dyes may be considered as a process of dye transfer from a liquid (water) to a solid organic solvent (fiber) and the dyeing takes place in the following stages—

a) Dispersion of the dye into water by breaking up into molecules (Dissolution in water): The dissolution depends on the disposability and solubility of the dyestuff further aided by the presence of dispersing agents and Raise the temp.

b) Adsorption of the dissolved dye form the solution on to the fiber surface: The dye staff adsorption by the fiber surface is influenced by the solubility of the dye in the dye bath and that in the fiber.

c) Diffusion of the dye molecules from the fiber surface into the interior of the fiber substance towards the center: The diffusion rate governs the overall rate of dyeing. When equilibrium state is reached, the following subsidiary equilibrium are established-
i) Dye dispersion in the dye bath   dye dissolved in the dye bath
ii) Dye dispersion in the dye bath  dye absorbed on the fiber surface.
iii) Dye absorbed on the fiber surface dye diffused in the fibro
iv) dye diffused in the fiber  dye diffused fiber to dye bath.

Textile Engineering / Commercial Name of disperse dyes
« on: January 18, 2017, 10:36:15 AM »
   Name   Manufacturer   Country
1.   Terasil    Cibageigy    Switzerland
2.   Foron    Sandoz    Switzerland
3.   Palanil    BASF   Germany
4.   Resonil    Bayer    Germany
5.   Samaron    Herchst    Germany
6.   Dispersol    ICI    UK

Textile Engineering / Properties of disperse dyes
« on: January 18, 2017, 10:35:50 AM »
i) Disperse dyes are molecularly dispersed.
ii) Disperse dyes are very less soluble in water which makes fine dispersion.
iii) The light fastness of disperse dye is fair to good and light fastness rating 4-5.
iv) Washing fasters is mode rate to good. The washing fastress rating is about 3-4.
v) Sublimation- Disperse dye have good sublimation power due to its stable electron arrangement. The sublimation fastness of disperse dye is related to
•   Low molecular size of dye stuff
•   Non ionic group
•   No sulphonatod group.
vi) Color will be fade due to heat application on disperse dye.
vii) In the presence of nitrous oxide, textile mlt dyed with certain blue and violet disperse dyes with anthraquinone dye structure will be fade.

Textile Engineering / Definition of Disperse dye
« on: January 18, 2017, 10:35:28 AM »
The term ‘disperse dyes’ have been applied to organic coloring substances, which are free from ionizing groups are of low water solubility and are suitable for dyeing hydrophobic textile mils from colloid dispersion.
It is a special class of dyestuff which is used for dyeing man-made fibers eg acetate, polyamide, polyesters etc.
The dye is so called because it is non soluble, non ionic dye and molecularly dispersed, farther dispersing agents are used with the dye. The size of the dye molecule is very small.

Textile Engineering / Full stripping
« on: January 18, 2017, 10:34:10 AM »
For complete stripping, the goods are firstly treated with Na2S2O4 Sodium hydrosulfite at boil. Then treatment is done at room temperature for 30 min.

Textile Engineering / Partial stripping methods
« on: January 18, 2017, 10:33:47 AM »
Partial stripping is obtained by treating the dyed fabric with dilute acetic acid or formic acid. The commanded conc. is betn 5 to 10 parts glacial aid or 2.5 –10 parts of formic acid per 1000 parts of water
Recipe: Glacial acetic acid = 5 – 10 parts
   Water   --> 1000 parts
   Formic acid   --> 2.5 to 10 parts
   Water   --> 1000 parts
   Temp   --> 70-100oC
   Time   --> Until the desired shade is obtained.
Process- The goods are entered and temp is raise to 70-100oC and the treatment is continued until the shade has been reduced to the desired amount thoroughly washing is then necessary to remove the products of hydrolysis.

Textile Engineering / Sequence of Dyeing with reactive dye
« on: January 18, 2017, 10:32:05 AM »
Grey textile mtls

Pre treatment


Washing (Cold)




Washing (Cold)

I)   PH
II)   Temperature
III)   Dyeing time.
IV)   Liquor Ratio.
V)   Concentration of electrolyte (salt)

Textile Engineering / Dyeing mechanism of reactive dye
« on: January 18, 2017, 10:30:36 AM »
The dyeing mechanism of material with reactive dye takes place in 3 stages:-
1.   Exhaustion of dye in presence of electrolyte or dye absorption.
2.   Fixation under the influence of alkali.
3.   wash-off the unfixed dye from material surface.
Now they are mentioned below:
1.   Dye absorption:
When fiber is immersed in dye liquor, an electrolyte is added to assist the exhaustion of dye. Here NaCl is used as the electrolyte. This electrolyte neutralize the negative charge formed in the fiber surface and puts extra energy to increase dye absorption. So when the textile material is introduces to dye liquor the dye is exhausted on to the fiber.
2.   Fixation:
Fixation of dye means the reaction of reactive group of dye with terminal –OH or-NH2 group of fiber and thus forming strong covalent bond with the fiber. This is an important phase, which is controlled by maintaining proper pH by adding alkali. The alkali used for this purpose depends on brand of dye and dyeing temperature. Here generally caustic soda, soda ash or NaHCO3 is used as alkali depending upon reactivity of dye. They create proper pH in dye bath and do as the dye-fixing agent. The reaction takes place in this stage is shown below: -

1. D-SO2-CH2-CH2-OSO3Na + OH-Cell                          D-SO2-CH2-CH2-O-Cell + NaHSO3

2. D-SO2-CH2-CH2-OSO3Na + OH-Wool                       D-SO2-CH2-CH2-O-Wool + NaHSO3
3.     Wash-off:
   As the dyeing is completed, a good wash must be applied to the material to remove extra and unfixed dyes from material surface. This is necessary for level dyeing and good wash-fastness. It is done by a series of hot wash, cold wash and soap solution wash.

Under alkaline condition, Reactive dyes react with the terminal hydroxyl group of cellulose. But if the soln of the dye is kept for long time, its concentration drops. Then the dye reacts with the hydroxyl group of water. The reaction of dye with water is called Hydrolysis of reactive dye.

I)   Halogenated heteroycles
(a)   Triazine group :
Example: Procoin, Cibacron


b   Pyrimidine
c   Quinoxaline
II)   Activated Vinyl compounds:
a   Vinyl Sulphone (D-SO2-CH2-CH2-) Ex: Ramazol.
b   Vinyl Sulphonamide (D-SO2-NH-CH2-CH2-) Ex. Levafix
c   Vinyl acrylamide (D-NH CO-CH2-CH2-) Ex: Primazine

Textile Engineering / Reactive dyes so popular
« on: January 18, 2017, 10:26:54 AM »
•   Good washing fastness (Rating 4-5)
•   very good light fastness (Rating 6)
•   Lower cost.
•   Simple dyeing method
•   Good reproducibility.
•   Low dyeing temp (below 100oC)
•   Ability to produce bright shade
•   Dye molecular composition
•   Easily applicable to cellulosic fiber as well as protein
•   All kinds of shade are found.

Textile Engineering / Properties of Reactive dyes
« on: January 18, 2017, 10:26:27 AM »
1.   Water Soluble dyes.
2.   Makes covalent bonds with the fibers.
3.   A certain amount of dye is hydrolyzed during dyeing (10-60%)
4.   Dyeing is carried out in alkaline condition (PH = 11.5).
5.   Huge electrolyte is necessary for dyeing with reactive dyes.
6.   Fastness (wash, light, Rubbing, perspiration) properties are generally good.
7.   Easy applicable to cellulosic as well as protein fibers. (Wool & Silk)
8.   Very popular and wide used in the wet processing industry in Bangladesh.
9.   Comparatively cheap.
10.   All kinds of shade are found.
11.   Dyeing method is easy.

Textile Engineering / Reactive Dye: Why so called?
« on: January 18, 2017, 10:25:56 AM »
Reactive dyes react with the fibers.
   Mainly react with cellulosic fibers
   e.g. cotton, jute, bast fibers, viscose, flax
It can be applied to protein fibers e.g. wool & silk.
Reactive dye contains reactive group and this reactive group makes covalent bonds with the fibers and becomes part of the fiber.
The general formula of Reactive dye can be written as follows:
Here    D --> Chromophore of Dye post
   X --> Bridge
   Y --> Functional group
D-X-Y + Fiber --> D-X-Y-Fiber Covalent bond.
Reactive dyes water soluble
D-F + Cell-OH --> Dye-F-O-cell   F = Functional group
D-F + H-OH --> Dye-F-OH

Textile Engineering / Cleansing Action of Soap
« on: January 12, 2017, 03:01:55 PM »
A soap has two dissimilar ends. At one end it has the hydrocarbon chain that is non-polar and hydrophobic (soluble in oil/dirt). At the other end there is the carboxylate ion that is polar and hydrophilic (water soluble).
When soap is added to water, its molecules make a unimolecular film on the surface of water with their carboxyl groups dissolved in water and the hydrocarbon chains standing on end to form a hydrocarbon layer as shown in the figure below.

When a dirty cloth is soaked into a soap solution, soap dissolves fat or oil with dust by micelle formation. The fat or oil with dust is dissolved in water by hydrophobic hydrocarbon chains of soap. The water soluble carboxylate ions make a hydrophilic surface in water and render the micelles of oil or fat from the cloth to the water. Thus, the micelle is dissolved in water and is washed away. Soap tends to concentrate on the solution surface and therefore lowers its surface tension, causing foaming. This helps it to penetrate the fabric. It emulsifies fat and dirt to form micelles and make all the micelles water-soluble. Thus, the water washes the dirt away.

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