More efficient usage of natural dyes through incorporation of cationic polymer into viscose fibres

Abstract

Natural colorants could serve as a bio-based alternative for synthetic textile dyes. Most natural colorants exhibit limited affinity to cellulosic fibres. As a result only light shades are obtained and the efficiency in use of the valuable plant extracts is low. By addition of a cationic polymer to the viscose spin dope regenerated cellulose, fibres with incorporated cationic groups are obtained. The presence of accessible cationic sites increases sorption of natural dyes substantially. In dyeing experiments with extracts from canadian goldenrod, green nut shell and ashes bark darker dyeings were obtained the modified viscose fibres compared to results on cotton or viscose fibres. The higher sorption of the natural dyes can be explained with dissociation of the extracted natural dye molecules under dyebath conditions. The formation of negatively charged dye molecules was confirmed with model calculations for species distribution using representative natural dye molecules as examples. The results indicate a strategy for a more economic use of plant based colorants, which is a condition for wider use of this renewable dye source.