The Theory of Dyeing Cellulosic Fibers

Abstract

The theory of dyeing was developed in the last 25 years, rather lately compared with the history of the synthetic dye industry. This delay was, to a certain extent, unavoidable, since sufficient knowledge of the submicroscopic structure of fibers and of the nature of aqueous dye solutions was not previously available. More recent develop- . ments of the theory are characterized by refinements in details and by its application to specific problems.A complete theory of substantivity has still to await the elucidation of molecular attraction forces by chemical physics, but this does not hinder the basic understanding of the dyeing phenomena. As a main achievement of the theory, mass action laws are formulated which explain and describe the equilibrium of dye absorption. Since the cellulose dyes are ionized and absorbed as ions, cellulose dyeing from the standpoint of absorption equilibrium is more complex than the dyeing of acetate and synthetic fibers with non-ionic disperse dyes. This fact fully explains the tremendous effect of salt observed in direct dyeing of cellulose. It also defines the place of cellulose dyeing in the general framework of a unitary theory of dyeing.The kinetics of dyeing is based on the concept that the rate-determining process in dyeing is the diffusion of the dye from the surface of the fiber into its interior. It can be considered as the second main achievement of the theory that it gives a satis factory description and explanation of the rate of dyeing.The third achievement of the theory of dyeing is the explanation of the trans formations of the dye in the fiber. This was studied by X-ray diffraction and light absorption measurements. The results indicate that soluble dyes and dye-formers are absorbed in monomolecular form by the fiber, but after they are insolubilized, they exhibit in many cases a tendency to crystallize. This explains the behavior of azoic and vat dyes on aftertreatment.The theory provides the dyer with an understanding of his everyday problems, and enables him to supplant empirical craft by scientifically controlled methods. This will be accelerated as the validity of the theory is generally recognized and accepted as a basis for teaching and learning the technology of textile dyeing.