Cotton Fabric Coating by Cationic Starches to Aim for Salt‐Free Reactive Dyeing.

Cationic starch (CatS) coating of cellulose fabrics enables salt‐free reactive dyeing. However, the relation of the degree of substitution and CatS concentration in the dyeing procedure are open issues. Accordingly, three cationic starches of increasing degree of substitution were used at different concentrations for the coating of cotton fabrics. Fabrics were evaluated for stiffness, dye uptake, dye exhaustion, wash fastness and nitrogen content. With an increasing degree of substitution coating solutions become more viscous, resulting in increased wet pick‐up and less stiff coated fabrics. These fabrics show increasing dye absorption and color generation. Due to the molecular size of the cationic starch, yarn/fiber ring dyeing is supposed present. Specifically, color generation can be adjusted by initial cationic starch coating concentration. Above 5 % CatS concentration ceases to have an increasing coloration effect. Pre‐treating a cellulose fabric with approximately 2.2 % CatS (Ds=0.7) enables similar coloration to a standard reactive dyeing protocol. Light fastness is reduced by 1–1.5 compared to salt‐based reactive dyeing. Rub fastness decreases by 1–2 only for higher substituted cationic starches (Ds=0.7). Nitrogen analysis reveals that a share of the CatS elutes off the fabrics into the dye bath. [ABSTRACT FROM AUTHOR]