Heterogeneous Chemical Modification of Cotton Cellulose with Vinyl Sulfone Dyes in Non-Nucleophilic Organic Solvents

Hydrolysis-free heterogeneous modification of cotton cellulose with vinyl sulfone (VS) dyes in non-nucleophilic organic solvents was investigated. Dimethyl sulfoxide was selected to be used in the process based on its superior ability to swell cotton. Dimethylcarbonate was used as a cosolvent to enable dye substantivity adjustment so that dye sorption could be promoted without using inorganic salts. Both solvents are green solvents with excellent environmental health and safety profiles. It was found that the nucleophilic addition of cellulosic hydroxyls to the VS dye required the formation of an activated intermediate of the dye and an amine base, which was distinctive from the general base catalysis observed in conventional wet processing. Diazabicyclo[2.2.2]octane was identified as the most effective base for promoting the reaction. The spent liquor from the solvent-based process was confirmed to be free of hydrolyzed dyes, and multicycle dye bath reuse was demonstrated. The process was also found to be generally applicable to vinyl sulfone dyes with consistently good shade build-up and colorfastness. The problems of insufficient swelling and dye fixation commonly associated with nonaqueous processes were solved without compromising the recyclability.