Isotherms were measured for the distribution of three pure non-ionic dyes and their binary mixtures between polyethylene terephthalate and water in the presence and absence of benzoic acid. In each case, the equilibrium concentration of dye in the fibre was directly proportional to the concentration in the water. For a binary mixture of greatly dissimilar dyes, each behaved completely independently of the other, while for a mixture of two closely related dyes some interference was noted. The solubilities of the dyes in both the fibre and the water increased with a temperature increase and the isotherm was displaced toward the water. The presence of benzoic acid displaced all isotherms toward the water.It is concluded that sorption of non-ionic dyes by polyethylene terephthalate takes place by a solution mechanism.

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These two fiber classes are similar in that both are dyed by disperse-type dyes; however, polyacrylic fibers can be dyed with anionic dyes if positive sites are provided. This can be done, for example, by using fiber containing ammonium groups. Alterna tively, positive sites in the form of bound cuprous ions can be produced by treatment of the fiber with cuprous salts. In either case, ion exchange occurs in which colorless anions and dye amons compete for positive sites in the fiber. In contrast, disperse dyes, which are used on all common fibers except cellulose and wool, require no specific dyeing sites. In polyethylene terephthalate, the dyeing reac tion behaves like a simple solution in the tiber, with dipole interactions and dispersion forces probably very important. The rate of dyeing of polyethylene terephthalate tends to be inconveniently slow, and organic compounds called carriers are used frequently to increase the rate. They are effective by mcreasing the diffusion rate of dye through the fiber.

The mechanism of dyeing polyacrylonitrile fibres is discussed for two cases in which the fibre, through its affinity for H+ and Cu+ respectively, acquires cationic centres capable of permitting absorption of dye anions. In the first, affinity for H+ is created by basic sites introduced through copolymerization and the dyeing reactions are best described by a mechanism involving sites differing in basicity. In the other, every cyan0 group in polyacrylonitrile appears inherently capable of absorbing cuprous copper through formation of a complex of the type (RCN)Cu+, which acts as a site for fixation of dye * Throughout this paper subscripts f and s indicate fibre and solution respectively.