Reactive Exhaustion Dyeing

In the name Procion Red H-E 7B, Procion is the Zeneca trade name for its range of reactive dyes for cotton. Red denotes the main color of the dye. H-E denotes the dye to be hot dyeing and an exhaust dye (high fixation), and 7B denotes it to be a very bluish red dye, ie, a magenta. 

Cold Exhaust Dyeings Fiber-Reactive Dyes. Start at 25—30°C optionally with a sequestrant and maintain. The dye is added over 5 min, then there is portionwise addition of salt every 10—15 min, increasing the size of the addition each time over 1 h. The amount of salt used (10—100 g/L) depends on the depth of shade. After the final addition of salt, wait 15 min, portionwise add soda ash (10—20 g/L) over 15 min, and continue dyeing for 30—45 min. Drop dyebath, cold water rinse, and use a sequence of hot washes to remove all loose "unfixed" dye. 

Figure 12.17 Dye exhaustion and fixation profiles in exhaust dyeing with atypical reactive dye [141]...

Washing Exhaust dyeing of Cl Reactive Red 123 on bleached cotton Continuous dyeing of Cl Reactive Blue 104 on mercerised cotton ... 

The kinetics of reaction of DABCO (7.66) and nicotinic acid (7.67 R = COOH) with the aminochlorotriazine dye Cl Reactive Red 3 (7.2) were studied under neutral conditions at temperatures in the range 100-130 °C. Quaternisation by DABCO was much more rapid than by nicotinic acid under these conditions. Neutral exhaust dyeing tests at 130 °C using the bis(aminochlorotriazine) analogue Cl Reactive Red 120 (7.48 X = Cl) with the two catalysts confirmed these trends, in that the degree of fixation was greatly increased by DABCO but nicotinic acid showed no appreciable catalytic effect [60]. This difference may be attributable to steric strain of the C-N+ bond in the quaternised triazine structure by the non-planar DABCO substituent. 

Silk can be readily dyed with conventional high-reactivity dyes of the dichlorotriazine, dichloroquinoxaline or difluoropyrimidine classes. Exhaust dyeing at 60-70 °C and pH 5-6 gives satisfactory results, especially if a mildly alkaline aftertreatment is given to enhance fixation. Dichlorotriazine dyes can also be applied by pad-batch dyeing with bicarbonate and a batching time of 4-6 hours. The relatively low reactivity of aminochlorotriazine dyes, however, results in moderate to poor build-up on silk. Tertiary amine catalysts such as DABCO (7.66) can be used to accelerate the dye-fibre reaction and increase the fixation substantially [116], but it is difficult to achieve satisfactory compatibility in mixture dyeings by this method (section 7.4.2). 

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. 

Application Methods. There are many detailed application methods used for applying reactive dyes, and all have been described in detail. Examples of the main methods include cold exhaust dyeing fiber-reactive dyes, warm, hot exhaust dyeing dyes, migration exhaust technique for less than 0.5% depth of shade, all-in method, continuous dyeing, and cold pad-batch dyeing. 

When two of the chlorine atoms are substituted, for example with amino or alkoxyl groups, monochlorotriazinyl dyes 2 are obtained. These are considerably less reactive, and hence react with cellulose in the exhaust dyeing process only at relatively high temperature (80°C). Such dyes are especially advantageous for printing [14],... 

Figure 4.1 Reactivities of established anchor systems and optimum dyeing temperatures in exhaustion dyeing.

About 20% of reactive dyes are used in textile printing, 30% in pad dyeing, and 50% in exhaustion dyeing processes. 

In the exhaustion dyeing process, highly or moderately substantive dyes are usually employed. The optimum dyeing conditions depend on the reactivity of the dyes. Cold dyers are dyed at 30-50°C and a pH of 10-11 hot dyers at 70-90°C and a pH of 11-12. For pH control normally mixtures of sodium carbonate and sodium hydroxide are used. To enhance substantivity of the dye sodium sulfate or sodium chloride is added. For less than 0.5 % dye based on textile weight, salt concentrations of 10-30 g/L are recommended. For deep shades (more than 4%), ca. 50 g/L is used with vinylsulfone dyes having low substantivity, up to 80 g/L. 

The salt load and discoloration of wastewater from dyeworks using reactive dyes often attract criticism on environmental grounds. With mono functional dyes, the fixation yield in exhaustion dyeing processes is in the region of 60 %. 

Reactive dyes based on a nicotinic acid residue allow dye-fiber reaction at a neutral pH of 7-7.5 (Morimura and Ojima, 1985). These dyes are particularly suitable for neutral, high-temperature exhaust dyeing, and for one-bath dyeing of polyester/ cotton-blended fabrics (Lewis, 1993). This continues to be an active area for R D (Lewis and Vo, 2007 Lewis et al., 2008). 

Uses Fixing agent for reactive dyeings improves wetfastness props, of Indosol SF dyes and Drimarene dyes in exhaust dyeing Properties Liq./powd. 

A reactive dye for ceUulose contains a chemical group that reacts with ionized hydroxyl ions in the ceUulose to form a covalent bond. When alkaH is added to a dyebath containing ceUulose and a reactive dye, ionization of ceUulose and the reaction between dye and fiber is initiated. As this destroys the equihbrium more dye is then absorbed by the fiber in order to re-estabUsh the equUibrium between active dye in the dyebath and fiber phases. At the same time the addition of extra cations, eg, Na+ from using Na2C02 as alkaH, has the same effect as adding extra salt to a direct dye. Thus the addition of alkaH produces a secondary exhaustion. 

Electrolyte therefore plays three important roles increasing absorption in the neutral state, preventing desorption/promoting secondary exhaustion, and increasing the amount of ioni2ed ceHulose. Thus the amounts of salt used in the apphcation of fiber-reactive dyes are larger than for direct dyes. 

Eig. 3. Amounts and forms of fiber-reactive dye on the fiber as a function of time for a low affinity dye, where X represents the reactive group. Point A represents the amount of dye exhausted in neutral conditions B is the total amount of dye exhausted at the end of the dyeing process, ie, [dye—OH] +... 

Alkali is usually added in a second stage. However, with low reactivity high affinity dyes it is possible to add the alkah at the beginning of the dyeing process and control the rate of uptake and chemical reaction by temperature control. With high affinity dyes the exhaustion takes place at low temperature rapidly before the chemical reaction becomes significant. If dyes are carefully selected or synthesized to have identical dye uptake it is possible to include all the electrolyte from the beginning and operate an "ah-in" technique. 

Migration Exhaust Technique for Less than 0.5% Depth of Shade. Start at 50°C with sequestrant at pH 7.0. Add dye over 20 min and raise temperature to highest safe level depending on the dye (95°C with monochlorotriazinyl reactive system) at a rate of 1.5°C/min. Hold for 20 min and cool back to dyeing temperature. Alkali is portionwise added, or mechanically dosed, over 20 min and after a further 30 min the dyebath is dropped and the washing sequence begun. 

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