How do hydrogen bonds help dyes attach to wool, silk, and synthetic fibres?

In the process of dyeing, hydrogen bonding serves as one of the four primary forces that anchor dye molecules to textile fibres, ensuring the coloration is relatively permanent and resistant to washing.1

In wool, silk, and various synthetic fibres, hydrogen bonds are formed between specific functional groups on the dye molecule and the fibre itself. These bonds typically occur between the amido groups (-CO-NH-) present in the fibre and groups on the dye such as azo, amino, and alkylamino groups.1

At a molecular level, this interaction arises because elements like oxygen and nitrogen are more electronegative than carbon and hydrogen, creating polarized sites within the molecules. When a weakly acidic hydrogen atom on one molecule is positioned near an electronegative atom (such as oxygen or nitrogen) on a neighbouring molecule, a strong attractive force—the hydrogen bond—is established. While these interactions do not involve the formation of a formal chemical bond, they provide significant attractive forces that contribute to the substantivity, or affinity, of the dye for the substrate.2