i i FIRST PLACE WINNER: Quebec Section Effects of Dye Substantiv ity in Dyeing Cotton with Reactiv :?Dyes n dyeing cotton with fiber reactive the material. The dyebath exhaustion at In almost any range of commercial 1 dyes, the addition of alkali to the the end of this phase is called the primary reactive dyes, there is a graduation of dyebath not only promotes formation of exhaustion. substantivity from very low to medium, or the covalent bond between the dye and the 0 The fixation phase. This begins when even quite high substantivity, particularly cellulose but also causes hydrolysis of the alkali is added to the dyebath to raise the in the presence of salt. The dyer is thus reactive group of the dye. Unfixed hydro- pH to the point where the dissociated faced with the problem of deciding how lyzed dye remaining in the fabric after the hydroxyl groups of the cellulose begin to severe the washing conditions should be dyeing process must be removed by wash- react with the dye. Migration of the fixed for removal of unfixed dye from the ing, otherwise the optimal fastness to dye is impossible. During this stage, more material since he must decrease the resid- washing and crocking of the final fabric dye is absorbed from the solution and ual amount to the level that his client is will not be realized. The batch dyeing reacts with the cellulose. The exhaustion satisfied with the fastness properties of the process thus consists of three stages: of the dyebath at the end of the process is final product. To achieve the best product The migration phase. In this first called the secondary or final exhaustion. quality, the dyer can wash the goods stage, the cotton is treated with dye The washing phase. Once dyeing is repeatedly, consuming more hot water solution in the presence of salt at about pH completed, the material is washed several than may be absolutely necessary. On the 6, but little reaction with the cellulose times to remove unfixed dye. The fixation other hand, from the point of view of cost occurs. The dye is free to migrate from the is calculated using a simple mass balance and productivity, it is important to keep more heavily to the lightly dyed areas of based on the total amount of dye added to hot water consumption to a minimum. the initial dyebath, the amount remaining The problem of dyeing on shade with in the final bath and the amount removed trichromatic mixtures of reactive dyes is by washing. also related to the substantivity of the .S The primary and final dyebath exhaus- dyes. The best color control results by If :e ABSTRACT tion and the fixation yield are defined as using dyes which all have the same reac- follows: tive group, and which also have compara- .h Fiber reactive dyes for cotton were 70 Exhaustion ble rates of dye absorption and fixation. Jl shown to vary widely in their substan- = 100 x (C,- Cf)/ c, The dyer then only needs to be concerned 'P tivity for the fiber. Substantivity also where C, = initial concentration of dye about the gradual development of the :h depended on dyebath temperature and (g/L) and CJ = final concentration of dye depth of the particular shade. When using cs salt concentration, as expected. The dyes of quite different reactivity or sub- er relative substantivities of the hydrolyzed WL). %Fixation stantivity towards the cellulose, there will id forms of the reactive dyes were assessed = loox(Mi-Mf-M,)/M, in the laboratory by means of a simple, be pronounced color changes during the quick and inexpensive paper chrom- where Mi = mass of dye in the initial dyeing operation, as well as the usual build atography test. Correlation of the sub- dyebath (g), MI = mass of dye in the final up in depth. This makes color matching stantivity of the dye with the amount dyebath (g) and M, = mass of dye re- very difficult. removed from the cotton under various moved by washing (g). This project was developed in response washing conditions indicated that it The primary dyebath exhaustion, and to these practical problems related to the should be possible to select higher or the ease with which unfixed dye can be substantivity of reactive dyes. The objec- lower washing temperatures based on removed by washing after dyeing, depend tive was to examine how the substantivity the substantivity of the dye to be re- on the substantivity of the reactive dye, or of these dyes influences dyeing with tri- 'es . moved. In addition, the paper chroma- 1 or of its hydrolysis product, for the cotton. In chromatic mixtures, and the ease with tography test was useful for quick .be general, the two forms have almost identi- which unfixed dye can be washed off the selection of dyes of about the same Idi- substantivity. Mixtures of such dyes cal substantivities. Many of the early cotton after dyeing is completed. It was dyed cotton with little change in hue reactive dyes for cotton were, by design, also decided that it would be valuable to We- re. during the dyeing process; dyes of dyes of low substantivity whose chemical have some simple laboratory test which different substantivity gave pronounced structures resembled low molecular the dyer might use to evaluate the substan- pn- color changes. weight acid dyes rather than the more tivity of reactive dyes. The results of such a rely ub- complex direct dyes. It was not possible, test might be used to select dyes for dyeing 1 in- however, to provide a complete range of in combination and also for establishing Key Terms pg colors, including navy blues for example, more or less severe washing conditions, me Dyeing Cotton without introducing at least some dyes and thus contribute to energy savings I as Fiber Reactive Dyes which had substantially higher substantiv- where this is possible. Paper Chromatography ity for cotton. Some of the newer bifunc- Reactive Dyes tional reactive dyes, such as those synthe- Experimental Techniques , 41 Reactive Groups sized by coupling two monofunctional For paper chromatography of the dyes, a Su bstantivity reactivedye molecules together, are also of solution of dye (1 .OO g/L) was prepared in increased substantivity. aqueous NaOH solution (1 .OO g/L). The November 1991 Ca, 21 --.. -- c Dye Substantivity 2-propanol/water/concentrated aqueous trations were determined by absorbance ammonia (9%: 1 by volume). measurements at the wavelength of maxi- All analyses of dye solutions were per- mum absorption and calculation from the solution was allowed to stand for several formed using standard spectrophotomet- slope of the Beer-Lambert calibration days to ensure that the reactive groups of ric techniques (3).Transmission measure- graph prepared using dye solutions con- the dyes were hydrolyzed and then neu- ments were carried out using a Diano taining the same amount of phosphate tralized to pH 6 with acetic acid. Small Match Scan I1 double beam reflectance buffer. volumes of the dye solutions were then spectrophotometer with matched 1.00 cm The material used was a bleached cot- spotted onto a small piece (2 X 4 in.) of glass cuvettes. To ensure that the dye in ton jersey knit (I63 g/m2). The reactive Whatman $1 filter paper. After drying, the solution always had the same environ- dyes were applied at a depth of 1 .OO% owf the papers were developed by standing ment, and thus did not undergo changes in at temperatures, and salt and alkali con- them in a shallow pool of solvent in a closed extinction coefficient. samples of the dye- centrations, according to the recommen- jar and the chromatograms developed by bath to be analyzed were mixed with dations of the manufacturers (see Table the ascending technique (I,2). The devel- phosphate buffer solution (0.10M I). All dyeings were carried out in sealed oping solvents used were 2-propanol/wa- Na2HPO4X7H20, 0.10 M KH~POJ)and stainless steel pots using a Zeltex Poly- ter/acetic acid (18: 17: 1 by volume) and diluted by a factor of five (4).Dye concen- color laboratory dyeing machine equipped with a Szdo PC 1000 microprocessor controller. In all cases, a liquor-to-goods Table 1. Dyeing Conditions for the Exhaustion and Fixation Data ratio of 20: 1 was used (5.00 g cotton plus 100 mL dye solution). The alkali was added in the form of powdered sodium Salt N a2C03 Time of Time of carbonate. or a very small volume of Dyeing Conc. Conc. Migration Fixation concentrated sodium hydroxide solution. Dye Temp (C) (P/U (g/L) (min.) (min.) After dyeing, the cotton was washed six 40 50 5a 30 15a times in clean water, for 5 min. at 30C and + 0.5 NaOHa 45a then for 15 min. at temperatures of 60,60, 30 40 10 40 60 100 1 45 30 10 30 60 100, and 60C using a 16: liquor ratio. 30 40 10 30 60 In trials to measure the exhaustion of 5O-8OQ 20 15 40b 453 the hydrolyzed forms of the dyes, stock 50-80' 40 15 40° 453 solutions were prepared as described foi 30 40 10 30 60 paper chromatography. The dyebath ea- 40 40 10 40 60 haustion after 60 min. was measured for 50-80' 20 15 40° 453 1 .OO% owf dyeings carried out at either 30, Gation with soda ash for 15 min followed by NaOH for 45 min b50C/10 min plus salt. 50-80C/30 50.75 or IOOC, in the presence of either 0, min.. add alkali. fixation at 80C/45 min IO.