Thermodynamic Modeling of Bifunctional Dye Hydrolysis under High Shear Boundary Layer Flow
High fluid shear compresses boundary layers, accelerating hydroxyl mass transfer and driving hydrolytic dyestuff loss in bifunctional reactive dyeing.
Unfixed Dye Wash-off
Surface Removal
Removal of hydrolyzed or unreacted dye molecules from the fibre surface ensures that the finished textile meets standard colorfastness requirements. During the reactive dyeing process, some dye fails to form a covalent bond and remains loosely associated with the yarn. Efficient unfixed dye wash-off is necessary to prevent this excess color from bleeding during subsequent consumer laundering.
Fastness Achievement
Wet fastness and rub fastness ratings depend heavily on the thoroughness of the cleaning steps following fixation. The unfixed dye wash-off stage typically involves several cycles of rinsing at varying temperatures to extract the chemicals from the interior of the fabric. If this process is incomplete, the fabric will fail quality control tests for staining.
Water Temperature
Hot rinsing is more effective than cold rinsing because it increases the solubility of the waste dye and opens the fibre structure. Optimized wash-off protocols use surfactants and temperature control.
Effluent Load
Management of the wastewater stream is complicated by the high concentration of color removed during the initial rinsing phases. Identifying the point at which the unfixed dye wash-off is complete allows mills to stop the process as soon as the water runs clear, saving both time and resources.