The Physical State of Direct Dyes in Viscose and its Influence on Lightfastness

Abstract

As part of a study on the factors determining the lightfastness of dyes on cellulosic materials, a means of examining the physical state of direct dyes in viscose was developed which makes use of dyed ultrathin films as primary specimens in the electron microscope. When this method was used to examine the physical state of two direct dyes in viscose, their physical state was found to differ markedly. Aggregates of one dye could not be detected in the viscose films at a resolution limit of about 30 Å, whereas aggre gates of the other dye were plainly visible in viscose films dyed under the same conditions. The apparently unaggregated dye exhibited considerably poorer lightfastness on rayon than the one which aggregated in viscose. The results suggest the use of this method of study to investigate the influence of the physical state of direct dyes in viscose on their lightfastness.