Eco-friendly dyeing of cationised cotton with reactive dyes: mechanism of bonding reactive dyes with CHPTAC cationised cellulose

The linkage between the dye and the cellulose is generally responsible for obtaining good washing and rubbing fastness properties of dyed materials. For reactive dyes this linkage is formed in reaction between reactive group of the dye with hydroxyl group of the cellulose. This reaction can go through nucleophilic substitution or an addition mechanism. Introducing the cationic groups to the chain of cellulose in the modification process completely changes the cotton surface charge from negative to partially or totally positive. Electrostatic interaction between the cation modifiers and sulfo group of anionic dye leads to the formation a strong ionic bond and rapid exhaustion the dye from the bath without addition of electrolytes. It was found and experimentally confirmed that when the cotton was cationised with 3-chloro-2-hydroxypropyltrimethylammonium chloride ([CHPTA]⁺Cl⁻) reactive dye creates a covalent bond with hydroxyl group located in modification agent instead of with hydroxyl group in a glucopyranose ring. This reaction can be done without salt and alkali and at room temperature. The analysis using particle optimisation with MM + molecular mechanics and quantum-chemical calculations PM3 by the method of all valence orbitals confirmed the experimental results of high activity of the nucleophile being formed on the hydroxyl group in the chain of modificator.