Rayon

Rayon Dyeing and Acetate, Synthetic Dyeing Difficulties

When rayon or acetate fibers were first produced very few of the dyes, then available could  used for dyeing them. Even those dyes which showed some affinity for this new rayon fiber failed to yield shades of satisfactory fastness. So, new dyes had to be discovered. But curiously enough, the new dyes were quite different from any previously used in they were insoluble n water. Even today most of the dyes used for acetate are of this so-called disperse type as it seems that acetate/ rayon has little or no affinity for water soluble dyes.


Study of the manner in which acetate fibre absorbed various swear soluble substances applied to it from aqueous suspension showed that he absorption was really a ease of the substance being dissolved by the fibres. Cross section of the fibres revealed that the absorbed substance was uniformly distributed throughout the fibre, whereas when other textile fibres are dyed it is often the case that that the dye is present mainly on the outside of each fibre. Thus it seemed that to dye acetate finer it would be necessary to discover colored substances which were soluble in cellulose acetate.
Such special dyes were soon found. To apply them t the acetate fibres it was found most convenient to grind them very finely and then paste them with soap or turkey red oil and so make a dye liquor in which the dye was in the room of highly dispersed insoluble particles. In the dyeing process the dye particles quickly com into contact with the surface of each fibre to form a thin layer. Afterwards they pass slowly by solution from it. This is an instance of the solution f one solid in another.
In recent years it has been found that nylon or rayon and other synthetic fibres behave similarly to acetate fibres in that they dissolve the dyes applied to them and in fact the special dyes found suitable for acetate fibres, and now termed disperse dyes, are now proving very useful for coloring these synthetic fibres. Mention has been made earlier of certain modifications of synthetic fibres made by introducing acid or basic groups into their molecules and thus making them receptive to commonly used dyes for cotton and wool.
Today the disperse dyes have become very much more important that formerly, and increasing numbers of them are being manufactured. This importance arises from the fact that they are bow being used for the coloring if practically all the synthetic rayon fibres now available.