Kinetic Modeling of Salt Mediated Dye Penetration Boundaries in Heavy Ring Spun Twills
Linear salt dosing coupled with controlled liquor flow balances surface exhaustion and pore diffusion to eliminate core pale zones in heavy ring spun twills.
Salt Mediated Sorption
Charge Neutralisation
Chemical interactions between dyes and cellulose fibres in aqueous baths are driven by the electrical charges of both the substrate and the dye molecules. The process of salt mediated sorption relies on the addition of electrolytes to neutralise the negative surface charge of cotton, allowing anionic dyes to approach and bind to the fibres. This mechanism is fundamental to achieving deep shades in reactive and dyeing processes, as it increases the affinity of the dye for the textile material.
Electrolyte Function
Cellulose fibres develop a negative surface potential when immersed in water, which repels similarly charged dye molecules. Through salt mediated sorption, the addition of sodium chloride or sodium sulfate screens these charges. This reduction in the energy barrier allows the dye to migrate from the liquor onto the fibre.
Shade Consistency
Controlling the concentration of salt prevents uneven dye absorption. If the salt mediated sorption occurs too rapidly, the dye deposits unevenly, causing spotty defects. Gradual dosing ensures a level distribution.
Environmental Impact
High electrolyte concentrations in dyehouse effluent present disposal challenges for textile mills. Although salt mediated sorption is necessary for efficient dyeing, the resulting wastewater must be treated to reduce salinity before discharge. Some mills are adopting low-salt or salt-free reactive dyes to mitigate this issue.