Chitosan‐assisted dyeing of cotton with sodium copper chlorophyllin: Effects of process parameters on colour yield and fastness

Sodium copper chlorophyllin (SCC), a food‐grade green pigment, offers potential for sustainable textile coloration; however, its application to cotton is hindered by electrostatic repulsion with the negatively charged cellulose surface. In this study, chitosan was used to modify cotton, thereby promoting a more cationic fibre interface for SCC binding. We systematically evaluated the effects of chitosan concentration, pH, NaCl dosage, temperature, time, SCC concentration on colour yield ( K / S at the Soret band) and chromatic properties and assessed colour fastness before and after tannin fixation. Under selected conditions (chitosan 15 g/L, SCC 2% owf, pH 4, NaCl 10 g/L, 90°C, 60 min), the modified cotton achieved a pastel green shade with K / S values of 2.4 ± 0.11 at the Soret band (410 nm) and 0.35 ± 0.02 at the visible Q‐band (626 nm) versus 0.29 ± 0.04 (Soret) and 0.04 ± 0.01 (Q‐band) for unmodified cotton. The hue angle remained nearly constant (~137–139°) across dye concentrations, facilitating reproducible colour control. Tannin fixation improved wash and rubbing fastness to grade 3–4 or higher, while light fastness stayed at grade 3. This study provides practical guidance for pastel dyeing of cotton with a food‐grade natural colourant.