👉Adsorption
Dye molecules when come to the contact of the textile fibre. Dyes do not penetrate into fibres rather stay on the surfaces of textile materials.
Dye molecules when entered into the fibre.
👉Desorption
The removal of the adsorbed atoms, molecules or ions from a substrate is called desorption. When the dye molecules come out from the fibre, the condition is termed as desorption.
The removal of the adsorbed atoms, molecules or ions from a substrate is called desorption. When the dye molecules come out from the fibre, the condition is termed as desorption.
👉Exhaustion
In exhaust dyeing, all the material contacts all the due liquor and the fibres absorb the dyes. The dye concentration in the bath therefore gradually decreases. The degree of dye bath exhaustion as a function of time describes the rate and extent of the dyeing process. For a single dye, the exhaustion is defined as the mass of dye taken by the material (after the adsorption, sorption & desorption is completed) in ratio of the initial mass of dye in the bath. It is expressed as E%.
[Where Co and Cs are the concentrations of dye in the bath initially and at some time during the process respectively]
👉Fixation
Total amount of dyes finally fixed (after washing) with the fibres in a dyeing process. It is expressed by F%.
So,
Fixation, F % = Exhaustion % – Loss % (due to washing, soaping or any other treatment).
The slope of a dyeing exhaustion curve defines the rate of dyeing at any instant during the process. The rate of dyeing gradually decreases until, if dyeing is continued long enough, an equilibrium is reached where no more dye is taken up by the fibres. There is now a balance between the rate s of dye adsorption and desorption.
👉Rate of dyeing
Dyeing rates are of greater practical significance than exhaustion at equilibrium. This is because continuation of dyeing to equilibrium is uneconomic. Dyeing should be neither too slow nor too fast. Slow dyeing involves: (a) Long dyeing times with increased risk of fibre damage and dye decomposition, (b) It is too costly. On the other hand, very rapid dyeing will usually result in uneven colour.
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