Dyeing rate

At HOY speeds, the rate of increase in orientation levels off but the rate of crystallization increases dramatically. Air drag and inertial contributions to the threadline stress become large. Under these conditions, crystallization occurs very rapidly over a small filament length and a phenomenon called neck-draw occurs (68,75,76). The molecular stmcture is stable, fiber tensde strength is adequate for many uses, thermal shrinkage is low, and dye rates are higher than traditional slow speed spun, drawn, and heat-set products (77). 

Diffusion coefficients [115] and dyeing rate constants [116] for the same fifteen dyes on nylon are given in Table 3.19, confirming many of the trends already noted above. Yellow 1, Orange 3 and Violet 4 are again the three most rapidly absorbed dyes, in the same order. The diffusion coefficients place the first two dyes in reverse order, however, suggesting that the terminal phenolic group in Yellow 1 interacts more effectively with proton-acceptor sites... 

Table 3.19 Diffusion coefficients [115] and dyeing rate constants [116] for disperse dyes on nylon at 80 °C...

A common method to increase the dyeing rate is to inhibit the formation of crystalline regions during fiber manufacture. To this end, it suffices to break up... 

The eventual dispersion process consists of grinding the moist dye, generally in a ball, bead, or sand mill, in the presence of dispersing agents. Since the dyeing rate depends on particle size, the aim is to reduce the particle size to <1 qm. A narrow particle-size distribution is important to minimize recrystallization during storage and application. 

Dye affinity to polyacrylonitrile and hence the dyeing rate can be enhanced by introducing an aralkyl residue [33] or an aryloxyalkyl residue [34] in place of an alkyl group at the trialkylammonium group. 

High dyeing rates bear the danger of unlevel dyeings. Therefore, dyes have to be carefully selected when used together in one recipe. The dye producers readily communicate their knowledge on dyeing characteristics of their dyes and on the particular requirements for all textile fibers. 

Dye selection in view of compatibility, fastness properties, dyeing rate, time requirements, and cost. 

Microfibers. PAC microfibers (single titer less than 1 dtex) behave differently in some respects from normal acrylic fibers [171], First, more dye is required for the desired shade in each case because of the greater light scattering of the fiber. This requirement increases more than twofold with increasing depth of color (similar to pore fibers). For this reason, the fiber saturation is usually adjusted to a higher value by the fiber producer. The characteristic dyeing rate of the fiber is... 

Joseph JM, Destaillats H, Hung H-M, Hoffmann MR. The sonochemical degradation of azobenzene and related azo dyes rate enhancements via Fenton s reaction. J Phys Chem A 2000 104 301-307. 

Vat Stripping CNC LEVELER 45 retards the dyeing rate of vat colors in direct proportion to the concentration used. 

This material is a mildly cationic organic condensate retarder specifically designed for use with acrylic fibers to obtain a level dyeing and to reduce the dyeing rate. 

The dyeing of cotton fiber is accomplished by three principal processes. Cotton may be chemically reacted with fiber-reactive dyes in solution. The dyeing takes place by reaction with hydroxyl groups in cotton. A second method is the use of substantive dyes that diffuse directly into fiber from a dye solution. The dyeing rate is increased by the addition of electrolytes. The third method is referred to as mordant dyeing in which the dye in solution reacts with metals previously applied to the fiber to form insoluble colored compounds on the cotton. Vat dyes are another important class of dyes for cotton. These are applied in a soluble reduced form and after application they are oxidized, forming an insoluble molecule [8]. 

Balmforth et al. (jf.S.D.C., 1966, 82, 408) showed that there is a ma.xi-mum concentration of the carrier above which the take-up of the dye by the fibre decreases. This optimum carrier concentration corresponds approximately with the amount necessary to saturate both fibre and dyebath phases of the system. Excess will introduce a third phase, namely undissolved carrier, which will compete with the fibre for the dye. Increase in adsorption at equilibrium is brought about by bisphenyl, orthophcnyl-phenol and phenyl salicylate in the order in which they are set out. Benzoic acid, on the other hand, decreases the adsorption by the fibre at equilibrium and only increases the dyeing rate, probably by promoting the solubility of the dye. It is suggested, in fact, that water soluble carriers such as benzoic acid really act as extremely efficient dispersing agents. 

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