Affinity Property
Thermodynamic attraction forces that cause dye molecules to leave the aqueous bath and attach to the textile fiber govern the initial phase of the dyeing process. The dyestuff substantivity describes the distribution of dye between the fiber and the bath at equilibrium. It determines the rate of dye uptake and the level of exhaustion achieved during the cycle.
This property varies with temperature, salt concentration, and fiber type.
Equilibrium Distribution
High molecular attraction between the dye and the polymer chains results in rapid absorption and minimizes the amount of residual chemical in the wastewater. With high dyestuff substantivity, the dye moves quickly to the fiber surface, which requires careful temperature control to prevent uneven coloring. Slow, controlled heating allows the dye molecules to distribute evenly before permanent bonds are formed.
This prevents localized spots and band patterns.
Dyeing Method
In continuous pad application, the level of attraction must be balanced to avoid depletion of the dye bath over time. When dyestuff substantivity is too high, the fabric takes up more dye than liquor, causing the concentration of the remaining bath to decrease. This leads to a gradual reduction in the depth of shade of the produced fabric.
Formulators add chemicals to modify this attraction and maintain a stable bath concentration.
Fixation Limit
Very low molecular attraction requires large amounts of electrolyte to force the dye onto the fiber. This increases the chemical load of the effluent treatment plant.
