Dyeing Properties of Acrylic Fibers

The roles of elevated temperature and carriers in the dyeing of polyester fibres using disperse dyes: Part 2. Analysis of conventional models of dye adsorption

“…From the perspective of the disperse dye/PET fibre system, in 1954, Schuler and Remington 18 observed that rectilinear, Nernst (aka partition) adsorption isotherms were obtained for the aqueous CI Disperse Red 15/PET fibre system which took the generic form of line I in Figure 1. These findings were subsequently confirmed by other workers for the disperse dye/PET fibre system 19,[22][23][24] as well as for the adsorption of disperse dyes on other types of fibre (e.g., PA, 22,25,26 PP, 27 CA 8,19,[28][29][30] PAN, 31,32 CV, 33 CTA 30 and wool 34 ; see Burkinshaw 5 for a summary).…”

“…Firstly, linear adsorption isotherms of the type represented by line I in Figure 1 have been secured for the equilibrium uptake of disperse dyes on a wide range of different types of textile fibre (e.g., PET, cotton, wool, PAN, CV, etc. ), 15,18,27,[31][32][33][34] which of course contain a broad assortment of potential adsorption sites (e.g., -OH, -NH 2 , -COOH, -SO 3 H, -OCOCH 3 , etc.) with which sorbed dye molecules can interact and eventually become adsorbed onto.…”

“…Figure 9a reveals that as dyeing temperature increases from T 1 to T 2 , so the partition coefficient of the dye, as given by the slope of the straight lines in Figure 9a, decreases, as observed by Schuler and Remington 18 for the CI Disperse Red 15/PET fibre system, and by other workers for various disperse dye/fibre systems. 15,27,[31][32][33][34]82 This means that as dyeing temperature increases, the partition of the dye between the fibre phase, [D] f , and the solution (dyebath) phase, [D] s , shifts in favour of the latter phase, which means that, according to Equation (1), the partition coefficient, K, will therefore decrease concomitantly, as a function of increasing temperature.…”

“…The earlier analysis of the effect of temperature on disperse dye adsorption shows that conventional thermodynamic analysis, expressed in terms of Equations ( 2) and ( 6), is unable to account for the thermally-induced increase in uptake of CI Disperse Red 15 at saturation observed by Schuler and Remington 18 on PET fibre and by various workers for disperse dye adsorption on various types of fibre. 15,27,[31][32][33][34]82 More significantly, such conventional thermodynamic analysis cannot account for the characteristic, substantial promotional effect that increasing temperature exerts upon disperse dye uptake during HT dyeing processes, as depicted in Figure 10.…”

“…This will then provide the reasons for the anomalous temperature dependent dyeing behaviour observed for the equilibrium adsorption of disperse dyes on PET and other types of fibre. 15,18,27,[31][32][33][34]82 T A B L E 3 Aqueous solubility of various types of pure dye 92,98,[114][115][116] The equilibrium adsorption data for the CI Direct Yellow 12/CV sheet system discussed above 86 was reported for dyeings undertaken in the presence of 1 g L À1 added NaCl, since this reflects the widespread usage of added inorganic electrolyte, in the guise of either NaCl or Na 2 SO 4 , to promote the uptake of the five classes of dye (namely direct dyes, reactive dyes, vat dyes, sulfur dyes and azoic colourants) that are used on CV and other types of cellulosic fibre. 40,112 In terms of the mechanism by which added inorganic electrolyte promotes anionic dye uptake on cellulosic fibres, it was recently demonstrated that added NaCl or Na 2 SO 4 promotes dye-fibre substantivity by reducing the solubility of the anionic dye/dye precursor anion in the dyebath phase, which enhances the fundamental inclination of the planar dye molecules to self-associate and thereby shifts the intrinsic preference of the high solubility dye/dye precursor anion away from the aqueous phase and towards the fibre phase.…”