Investigation of the Effect of Self-Crosslinking Acrylate on Naturally Dyed Cotton Fabric

Onion-skin waste is a readily available source of flavonoid-based natural colourants; however, their limited affinity for cotton can restrict practical application. This study investigated a self-crosslinking acrylate post-treatment for improving the colour properties and fastness of cotton exhaust-dyed with red onion-skin extract. Unmordanted fabrics were treated with 10, 30, or 50 g/L self-crosslinking acrylate by a pad–dry–cure process and compared with untreated and aluminium sulfate-mordanted samples. SEM revealed film-like coverage and localised inter-fibre polymer bridges, while FTIR supported acrylate deposition through a characteristic ester carbonyl band at approximately 1730 cm−1. Aluminium sulfate mordanting produced a darker, more saturated yellow shade but resulted in the greatest washing-induced colour difference (= 22.14). In contrast, 10 g/L self-crosslinking acrylate increased K/S from 3.44 to 5.31 and provided the lowest post-washing colour difference (= 6.63). All acrylate-treated fabrics exhibited dry and wet rubbing fastness ratings of 5 and 4–5, respectively. Increasing the self-crosslinking acrylate concentration above 10 g/L provided no additional improvement. Overall, treatment with a low concentration of self-crosslinking acrylate improved colour retention and rubbing fastness of onion-skin-dyed cotton without metallic mordanting, with no benefit from increasing the treatment concentration.