Urea in Reactive Dyeing

The effect of urea on formation and cleavage of a covalent bond between a reactive dye and cellulose has been investigated. The evidence presented is consistent with the view that urea increases the bonded dye yield by keeping the reactive dye in solution during the diffusion of the dye to its reaction site. Urea does not increase the water content of the fabric by retarding evaporation during drying; with urea, the water content of the fabric is lower. Urea can also decrease the bonded dye yield. In combination with alkali and heat, urea enhances cleavage of an ether-type dye-cellulose bond, but has only a slight effect on an ester-type bond. The over-all effect of urea on reactive dyeing is shown to depend upon the solvolytic stability of a dye-fiber bond under specific dyeing conditions.