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.
Vinylsulfone Dye
Colorant Chemistry
A group of reactive colorants that incorporate a masked vinylsulfone group as their electrophilic reactive site forms strong covalent bonds with cellulosic fibers. The vinylsulfone dye is applied under alkaline conditions, where the precursor sulfate group is eliminated to yield the reactive vinylsulfone moiety. This moiety then reacts via nucleophilic addition with the hydroxyl groups of the cellulose.
Chemical Reaction
The activation of this chemical group requires the addition of an alkali, typically sodium carbonate or trisodium phosphate, to the dye bath. This alkali raises the pH of the bath to a range between ten and eleven, which triggers the elimination reaction and generates the highly reactive vinylsulfone form. This active form quickly reacts with the cellulose fibers to create a stable ether linkage that is resistant to enzymatic and mechanical action.
This covalent bond provides high fastness to wet treatments, chlorine exposure, and household laundering.
Dyeing Performance
These dyes are highly valued for their bright colors, excellent build-up properties, and high reactivity at moderate temperatures, usually around sixty degrees Celsius. This moderate temperature requirement saves energy compared to high-temperature triazine dyes. The high reactivity also leads to high fixation rates, which reduces the amount of washing needed to remove unreacted dye from the fabric.
Application Limit
The ether bond formed between the dye and the cellulose is susceptible to acid hydrolysis, which can cause the color to fade if the dyed textile is stored under acidic conditions. Additionally, if the temperature or pH of the dye bath is too high during the cycle, the reactive dye will hydrolyze rapidly, reducing its fixation efficiency.