Studies on dyeing wool with indigo

Abstract

Wool fabric was dyed with indigo through an exhaust technique at various pH values. The non-ionic form of indigo showed the highest substantivity, while the ionic ones exhibited relatively poor substantivity for wool. The wool fibres were best dyed in the appropriate acidic pH range. The chemistry of the indigo dyebath and wool fibres was taken into account to explain the effects of pH on colour strength. The results suggested that hydrogen bonding and ionic interactions were the main reasons for the exhaustion of indigo dye on wool fibres. The hydrogen bonding were established between the hydroxyl groups and amide groups of the dye and the fibres, respectively. The ionic interactions worked in the low pH range between the end-amino and ionized groups of the wool fibres and indigo dye, respectively.