Reactive dyeing systems for wool fibres Coloration based on hetero-bifunctional reactive dyes. Technology Part 2: Investigation of dyeing properties during the dyeing cycle Ho Jung Cho*,† and David M Lewis Department of Colour Chemistry, University of Leeds, Leeds LS2 9JT, UK Society of Dyers and Colourists The dyeing behaviour during the dyeing cycle of a Sumifix Supra dye and some other commercial reactive dyes under various dyebath pH conditions was investigated. Studies of the dyeing of wool serge fabric indicated that the diffusion properties of hetero-bifunctional Sumifix Supra dyes generally lie between those of b-sulphatoethylsulphone (Remazol dyes) and monochlorotriazine (Procion H dyes). Introduction Experimental Some of the common faults encountered in the dyeing Materials industry are off-shade dyeings, inadequate wash and light All dyeings were carried out on wool serge (2/2 twill) fastness and unlevelness. Of these, unlevelness can fabrics, supplied by Parkland (Bradford). Albegal B, an represent the biggest problem in wool dyeing. When the amphoteric surface active agent, was supplied by Ciba dark and light places are numerous and close together the (UK). The reactive dyes used were commercial samples patchiness is called skitteriness and it is commonly provided by Dystar, Ciba and Sumitomo. All other experienced in wool dyeing due to dyeability variations chemical reagents were of laboratory grade. The VS form from the root to the tip of the individual fibres [1]. of the β-SES dyes were prepared by reaction with sodium Wool reactive dyes represent an extreme example of carbonate, adjusted to pH 8 and heated at 60−70°C, as dyes which emphasise unlevelness when dyeing tippy described previously [9]. All dyeings were carried out wool, since they are usually di- or tri-sulphonated (there- using a Mathis Labomat IR dyeing machine (Werner Mathis fore hydrophilic) and mainly non-migrating. It is generally AG, Switzerland). accepted that reactive dyes are more difficult to apply in a level manner than other classes of dyes, mainly due to Study of dyeing behaviour of various types of reactive the irreversible fixation of the dye inhibiting the migration dyes with wool during the dyeing cycle and diffusion process [2]. In particular, vinylsulphone (VS) A series of dyeings (2% owf) was produced using three dyes show reduced levelling properties compared to their types of dye in order to compare the dyeing behaviour, precursor sulphatoethylsulphone (SES) dyes, due to the depending on each reactive group, during the dyeing cycle high reactivity of the vinylsulphone dyes. at pH 4. Dyeings at pH 5.5 were also carried out using the Many attempts have therefore been made to establish Sumifix Supra dye to assess the influence of a change of reactive systems that do not covalently fix to the wool fibre pH. The dyebaths were set at the required pH using a citric until they are activated by a change in dyeing conditions, acid/disodium hydrogen phosphate buffer, the McIlvaine such as a change of pH or increase in temperature [3–5], buffer system. Buffered solutions covering the range of pH as well as by using crosslinking agents [6–8]. were prepared using 0.2 M disodium hydrogen phosphate The exhaustion and fixation profiles of several types of and 0.1 M citric acid. Each pH buffer solution (20 ml) was dye with different functional groups were measured to com- prepared and diluted with distilled water to 40 ml. The pare the dyeing behaviour during the dyeing cycle, assum- dyeing commenced at 30 °C and the temperature was ing that the levelling properties depend on the reactive raised to the boil over 60 min at a rate of 1.5 °C/min until groups. Also an electrophile was introduced into the 60 °C was reached and then at 1.0 °C/min until the dyebath in an attempt to improve the migration properties temperature reached 100 °C. The dyebath was maintained by reacting rapidly with cysteine thiol thus reducing the rate at the boil for a further 80 min. The liquor-to-goods ratio of reaction of the fibre with the reactive dye. was 20:1 (2 g fabric sample size). A series of dyeings using the selected Sumifix Supra dye was carried out in the presence of sodium maleate at pH 5.5. The dyebath was set at the required pH using sodium carbonate. The dyeing cycle used was the same as described previously. For the fabric samples pretreated with maleic acid, the bath was raised to 80 °C over 30 min † Present address: Division of Textile Technology Center, KITECH, 35-3 Hongchon-Ri, Ibjang-Myun, Chonan-Si 330-825, and the pretreatment was continued for a further 30 min. South Korea. Email: [email protected] After the pretreatment, the wool samples were rinsed with 220 © Color. Technol., 118 (2002) Web ref: 20020503 20020503_j1302.pmd 220 01/10/02, 10:30 water and introduced into fresh dyebaths, and then the group (Remazol dye) or a MCT group (Procion H dye), dyeing and sampling were carried out as described above. respectively. The uptake of dye by the wool was measured by The fixation values for the Remazol dye increased sampling the dyebath every 10 min during the dyeing gradually, although the initial fixation was much higher cycle. Measurements of exhaustion, fixation and total than that of the Procion dye and a slow reaction with the fixation efficiency of each sample were carried out using the methods described previously [9]. 100 Microscopy investigation (a) Dyeings (3% owf) were produced using the selected Remazol, Procion HE and Sumifix Supra dyes having a β- 80 sulphatoethylsulphone (SES) group or a monochloro- triazine (MCT) group, or a β-SES group and a MCT group, F 60 respectively, at pH 5 and 100 °C on wool fibres. , % E Fibres from each dyed sample were embedded in % 40 cellulose acetate. Cross sections were then prepared using a Hardy microtome and these were mounted in a Gurr %E 20 mounting medium. Cross sections were viewed using an %F Olympus optical microscope. The camera body used was %T a Pentax LX, which was attached to the microscope via a 0 Hama T2 adapter. Kodak Ektachrome 64T was used for 0 20 40 60 80 100 120 140 developing the pictures and the pictures were printed on 30 60 80 100 100 100 100 100 × Ilfochrome Classic paper. The magnification ratio was Time, min/Temp., oC 400. 100 (b) Results and Discussion 80 Dyeing behaviour of different functional groups with wool A series of dyeings was produced using three types of dyes 60 F having different reactive groups in order to compare the , % E dyeing behaviour, depending on each reactive group, % 40 during the dyeing cycle. A dyed fabric sample was removed from the dyebath every 10 min and the %E 20 percentage exhaustion (%E), percentage dye fixation (%F) %F and total percentage fixation (%T) was calculated for each %T sample. Figure 1 shows the exhaustion and fixation curves 0 for 2% owf Sumifix Supra Brilliant Red 3BF dyed at pH 4. 0 20 40 60 80 100 120 140 30 60 80 100 100 100 100 100 It can be seen that the dye fixation occurred more o rapidly in the case of the VS form of the dye whilst the Time, min/Temp., C exhaustion values for both types were similar. It was shown in Part 1 of this study that the VS group is available Figure 1 Exhaustion and fixation of Sumifix Supra Brilliant Red 3BF at pH 4 in (a) SES form and (b) VS form to covalently bond with nucleophiles in the wool even under acidic conditions, and the MCT groups are able to react with nucleophiles below pH 4 [9]. Thus, in the case 100 of Sumifix Supra dyes, the VS form of these dyes reacts much faster than the SES form, which may indicate that 80 it would be difficult to achieve level dyeings using the VS dyes because there is little chance for the fixed dye to 60 diffuse and to migrate within the wool fibre. The results F show that for the VS dye ca. 90% of the exhausted dye had , % E been covalently bonded at the beginning of boiling (60 min % 40 dyeing time) and there is a difference of ca. 10% between the fixation of the two forms of the dye. In addition, in 20 the case of the VS dye, reaction with the fibre nucleophiles was almost complete after 90 min whereas, in the case of 0 the SES dye, the reaction seemed to be continuing even 0 20 40 60 80 100 120 140 at the end of dyeing cycle. It can be assumed therefore that 30 60 80 100 100 100 100 100 the SES dyes could have more chance to migrate within o the fibre to produce level dyeings. Time, min/Temp., C Figures 2 and 3 show the exhaustion and fixation curves Figure 2 Exhaustion and fixation of Remazol Brilliant Red BB at of two other types of reactive dye, which have either a SES pH 4; for key see Figure 1 Web ref: 20020503 © Color. Technol., 118 (2002) 221 20020503_j1302.pmd 221 01/10/02, 10:30 100 substrate as well as within the substrate, making it harder to achieve complete diffusion and exhaustion of the dye. Figure 4 shows the exhaustion and fixation curves for 80 Sumifix Supra Brilliant Red 3BF (in the SES form and the VS form) dyed at pH 5.5. 60 F The exhaustion values were lower than those at pH 4 , % (Figure 1) due to the decreased physical adsorption of the E % 40 dyes.