Short-cutting cationic fabric pre-treatments in reactive dyeing: addition of cationic starches into the dye bath

Cationization of a plain weave cellulose fabric was conducted indirectly via cationic starch (CatS) absorption in the dye bath. The cationic agent was pipetted into the dye bath from solution. Three different cationic starches and polydiallyldimethylammonium chloride (Pdadmac) were compared for their efficacy in salt-free reactive dyeing by reactive black 5. Dyeing was performed at pH 7 and pH 12. Fabric nitrogen content increased with increasing addition of cationic agent in the dye bath as with pH. The cationisation enables dye exhaustion of up to 30 % for a 3 % dye shade at an M:L of 1:100 before precipitation induction in the dye bath. Cationised fabrics develop higher shades at higher pH due to increased cationic agent absorption and dye exhaustion. The indirect cationisation approach does not achieve the same coloration as a conventional reactive dyeing approach with 45 g/l NaCl. Nevertheless, pH 12 cationic samples with a degree of substitution ≥1 enable similar or better coloration compared to the conventional approach at pH 7. Due to the size of the cationic agent fibre and yarn ring dyeing is encountered. Despite chemical savings the dyeing protocol has to be ameliorated.