Dyebath dyeing with

Hydrophobic fibers are difficult to dye with ionic (hydrophilic) dyes. The dyes prefer to remain in the dyebath where they have a lower chemical potential. Therefore nonionic, hydrophobic dyes are used for these fibers. The exceptions to the rule are polyamide and modified polyacrylonitriles and modified polyester where the presence of a limited number of ionic groups in the polymer, or at the end of polymer chains, makes these fibers capable of being dyed by water-soluble dyes. 

Isotherms. When a fibei is immersed, in a dyebath, dye moves fiom the external phase into the fibei. Initially the late is quick but with time this slows and eventually an equiUbrium is reached between the concentration of dye in the fiber and the concentration of dye in the dyebath. For a given initial dyebath concentration of a dye under given dyebath conditions, eg, temperature, pH, and conductivity, there is an equiUbrium concentration of dye in fiber, Dj and dye in the dyebath external solution, D. Three models describe this relationship simple partition isotherm, Freundhch isotherm, and Langmuir isotherm. 

The compatibihty value is mainly related to the affinity of the dye for the particular fiber because for basic dyes on modified acryhc fibers there is htde possibihty for migration and therefore this does not play a significant part in determining compatibihty. The rate of dyeing of a specific mixture of dyes of the same compatibihty value is not determined by the value itself. The adsorption of cationic dyes is induenced by the presence of others in the dyebath the presence of cationic retarding agents and electrolytes also induences the rate of exhaustion. It is therefore possible to have a combination of dyes with a compatibihty value 5 that under specific dyebath conditions exhausts more rapidly than a combination based on dyes of compatibihty value 3. 

A feature of the chemistry of triazinyl reactive dyes, which is in fact common to all reactive dye systems, is that they undergo, to a certain extent, a hydrolysis reaction that involves reaction of the dye with OH anions present in the aqueous alkaline dyebath in competition with the dye-fibre reaction. The hydrolysis reaction is also illustrated in Scheme 8.1. Reactive dye hydrolysis is a highly undesirable feature of reactive dyeing for a variety of reasons. In the first instance, the hydrolysed dye 175b which is formed is no longer capable of reacting with the fibre and so must be washed out of the fibre after dyeing is complete, to ensure the... 

Dithionite and derivatives Minimising the concentration by optimising Oxidation of sulphite to sulphate (isothermal dyeing with oxidation in the dyebath for pale shades)... 

These are defined as anionic dyes with substantivity for cellulosic fibres applied from an aqueous dyebath containing an electrolyte. The forces that operate between a direct dye and cellulose include hydrogen bonding, dipolar forces and non-specific hydrophobic interaction, depending on the chemical structure and polarity of the dye. Apparently multiple attachments are important, since linearity and coplanarity of molecular structure seem to be desirable features (section 3.2.1). The sorption process is reversible and numerous attempts have been made to minimise desorption by suitable aftertreatments (section 10.9.5). The two most significant non-textile outlets for direct dyes are the batchwise dyeing of leather and the continuous coloration of paper. 

As shown in Table 1 the wastewater limit for chromium is 0.5-1 mg/L and Cr is 0.1 mg/L. While conventional 1 2 and 1 1 dyes permit chromium concentrations in the dyebath at the end of the dyeing process of 3.0-13.0 mg/L Cr, the application of modem dyestuffs and optimized processes permits final concentrations to approximately 1 ppm. By general optimization of the process (e.g., dosage of acid), use of dyes with a high degree of exhaustion, and minimal concentration of free chromium [15], final bath concentrations below 4 ppm can be reached, even for black shades. By application of such procedures the exhaustion of the chromium should reach values of better than 95% of the initial value. 

Particularly in the case of dyes with a limited degree of fixation the dyestuff content in the wasted water leads to intensively colored wastewater. As the reactive group of the unfixed dyestuff is hydrolyzed into an inactive form, a reuse is not possible. On the basis of an exhaust dyeing with 5% color depth, a liquor ratio of 1 10, and a degree of dyestuff fixation of 70-80% corresponding to 3.5-4 g/L of dye are fixed on the goods and 1.5-1 g/L of hydrolyzed dyes are released with the dyebath. 

It is possible to tailor dyes, by use of the stepwise reactivity of the chlorine atoms in cyanuric chloride (B-59MI11200), to a variety of applications. For example, in structure (16), two molecules of cyanuric chloride may be reacted with one molecule of a suitable diamine, such as 4,4 -diaminostilbene-2,2 -disulfonic acid, at 0-5 °C and then the subsequent bis-dichlorotriazinyl product condensed with two molecules of an azo dye with a primary amino group at 35-40 °C. The resultant dyes are applied very efficiently to cellulosic fibres at 85-90 °C with very little dye remaining in the dyebath. The same molecule may also be prepared by condensation of the dye with cyanuric chloride at 0-5 °C and then with the diamine at higher temperature. Dyes more suitable for printing application may be prepared by condensation of a dye-amino group with cyanuric chloride followed by a diamine and then a further molecule of cyanuric chloride. The various applications are manifested in the various ranges of ICI s Procion dyes. 

The most recent development in this area is the 1 2 metal-complex dyes with two sulfonic acid groups. Contrary to the opinion frequently expressed in the literature that such dyes would exhibit inadequate levelness when applied in a weakly acid bath and inadequate stability to acid in a strongly acidic dyebath,... 

Table III. Color Uniformity in Polyester Carpet Dyeings with Dyebath Reuse...

The presence of BURCOLEV PBF in the dyebath together with careful selection of acid dyestuffs insures extremely level dyeing with good coverage of barre and warpiness. 

Carthamin enters commerce in a nearly pure state as safflower extract. For dyeing, the extract is dissolved in soda and the dyebath acidified with citric or other acid. In place of this extract the soda solution from safflower, which has been extracted with water, may be directly employed. 

The choice, until recently, has been between a disperse dye with wetfastness which is not all that could be desired, accompanied by coverage of yarn variations, and faster colours which show up differences in physical and chemical properties of the polymer. When, in 1959, I.C.I. placed the Procinyl dyes on the market an advance of considerable importance was made. They are reactive dyes based on disperse dyestuff molecules containing chlorotriazinyl groups. Under neutral conditions the pattern of behaviour is that of a disperse dye and yarn irregularities are covered up to a great extent. When alkali is added to the dyebath, fixation takes place, giving wet-fastness of a high order. 

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