The affinity of the dye
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The affinity of the dye for the fibre depends upon the molecular structure of the dye. It relates mostly to the chromophoric group in the dye and partly with the reactive system.
With higher affinity of the dye, the exhaustion will be more, while less affinity dyes will give less exhaustion. In case of batch dyeing, where dyeing takes place by exhaustion, the dyes of higher affinity are preferred. For continuous method we require dyes which do not give tailing effect, hence dyes of less affinity are preferree for continuous method.
In case of reactive dyes, hydrolysis takes place due to reaction with water while dyeing and such (hydrolysed part) decomposed part must be removed for better wet fastness properties. The hydrolysed part of the dye behaves like a direct colour and it does not react with cellulose. but gets adsorbed on the fibre due to physical affinity. In case of higher affinity dyes, hydrolysed part has also more affinity and hence it is difficult to remove from the fibre, While in case of less affinity dyes, hydrolysed part has less affinity hence it can be easily washed off.
