Abstract
Most dyes used for cellulose fibres today are reactive dyes, due to performance features such as higher fastness properties, brighter colour effects and a wider colour palette1. The range of available reactive dyes is wide, and enables a large number of dyeing techniques to be used2. This research was undertaken with a view to improving value addition to the substrate and reducing dyeing cost. In order to reduce the cost structure in the cotton-dyeing process, six dyes were selected and applied on cotton yarn, with 1% dye concentration, using selected exhaustion agents common salt, vacuum salt and Glauber’s salt, with 40gpl concentration and 16gpl concentration soda ash as a fixation agent. The process was followed by rinsing, washing and drying, and CIE Lab values of the samples were measured with a DataMaster V2.0 spectrophotometer, with a 10° normal observer and norm light D65. On yarn dyed with three shades, samples exhausted with Glauber’s salt exhibited high strength value and also showed a lower consumption of dyes as compared to the other two exhaustion agents.
Keywords: Exhaustion agent, fixation agent, washing fastness, effluent load, dye consumption
Introduction
Glauber’s salt is important in the manufacture of textiles. Glauber’s salt helps in ‘levelling’, reducing negative charges on fibres so that dyes can penetrate evenly in to substrate, so depth of colour with Glauber’s salt is more than with common salt and vacuum salt. Glauber’s salt is also environmentally friendly.
Methodology (Cold and Hot Brand Method)
Three different reactive dyes, sourced from a commercial dye manufacturer, were selected from both cold brand ranges (RedM5B, Blue MR, Yellow M3R) and hot brand ranges (Red HE3B, Blue HERD, Yellow HE4R) and were used for reactive dyeing. Dyeing processes were carried out with dye concentrations of 1%. The dyeing procedure was followed by the addition of calculated amounts of salt solution (common salt/vacuum salt/Glauber’s salt) 40gpl and soda ash 16gpl after a regular interval. After dyeing the samples underwent washing and soaping.
For cold brand reactive dyes, dyeing was carried out with a laboratory-scale dyeing machine with a liquor ratio of 1:10 at 30°C room temperature. The dyeing process was started with liquor containing alkaline, salt and dyestuff at 30°C, and the samples were then treated for 60 minutes, then rinsed at 60°C for 10 minutes, and 5 minutes in cold water. And samples were dried. The reflectance (%R) and CIE Lab values of the samples were measured with a Datacolor spectrophotometer with a 10° normal observer and norm light D65.
For hot brand reactive dyes, the dyeing process was started with liquor containing alkaline, salt and dyestuff at 30°C, and after 15 minutes the temperature was raised to 80°C with a 2°C/min temperature rise ratio; the samples were then treated for 60 minutes. After dyeing, the samples were rinsed and neutralised (10 min at 80°C with 0.5 g/l acetic acid), and then rinsed at 80°C for 10 minutes, 95°C for 15 minutes (twice for 2% dyeing), 80°C for 10 minutes, and 5 minutes in cold water. The reflectance (%R) and CIE Lab values of the samples were measured with a DataMaster V2.0 spectrophotometer with a 10° normal observer and norm light D65.
Method of Testing
Standard testing procedures were followed for the assessment of colour-fastness properties and colour-difference values were recorded by the ISO- 1 method.
Results and Discussion
Effects of Dyeing Exhaustion Agents on Colour Depth (Strength %)
Tables 1 represents the values calculated with reference to the samples of reactive-dyed fabrics, in which the sample dyed with common salt as the exhaustion agent was treated as standard sample and the samples treated with the exhaustion agents vacuum salt and Glauber’s salt were compared with the standard sample by DataMaster V 2.0 spectrophotometer. The values colour-strength % values obtained by spectrophotometer (Table 1) show that by changing the exhaustion agent (common salt, vacuum salt, Glauber’s salt), colour-strength % value increases significantly for the three shades of reactive-dyed yarn with 1% dye concentrations.
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| Table 1: Washing fastness properties of cotton yarn, with cold and hot brand reactive colours; by ISO-1 method |
In reference to Figures 1 and 2, it was observed that In all three cold-brand colours (1 = Red M5B, 2 = Blue MR, 3 = Yellow M3R) and hot brand colours (Red He3B, Blue HERD, Yellow HE4R) the same trend was observed. Common salt exhaustion produced low colour depth while vacuum salt gave comparable shade strength and Glauber’s salt recorded the highest strength. The above study reveals that, as the exhaustion agent changes from common salt to vacuum salt and Glauber’s salt, shade strength significantly increases, which leads to a reduce cost structure and consumption of dye and improves the efficiency of cotton-dyeing plant. If suitable exhaustion agents are not selected during the dyeing process, depth of colour reduces and the substrate requires additional processing, which consumes extra time leads to a reduction in the efficiency of dyeing plant.
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| Figure 1: Effect of different exhaustion values on colour strength for cold brand (1= Red M5B, 2 = Blue MR, 3 = Yellow M3R) |
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| Figure 2: Effect of different exhaustion values on colour strength for hot brand |
Practices Suggested for Obtaining Correct Shade in Dyeing
1. Before consumption of any dye, the colour strength received from the supplier should be compared with running colour because, in the dye manufacturing, batch-to-batch variations are introduced. In order to minimise these effects, the strength should be evaluated and compared with supplied dye. If the strength of the supplied dye is higher, the consumption of the dye must be reduced.
2. Selection of exhaustion agents is very important in obtaining shade strength. From Figures 1 and 2 it was observed that the shade produced with Glauber’s salt recorded highest strength with both cold and hot brand colours. Almost same trend was observed with both cold and hot brands in the three basic colours (ie. red, blue and yellow) and there is dominant effect of Glauber’s salt exhaustion on shade strength.
3. Effect of MLR on shed depth: lowering the liquor ratio leads to improve in shade strength. In reactive dyeing, lowering the liquor ratio brings down the volume of water used and the waste generated. Apart from the easier handling of lower volume of effluent, the dosing of chemicals and auxiliaries in the dye bath is done on the basis of g/litre of liquor. This significantly reduces the quantities of chemicals and auxiliaries and finally the effluent load.
4. Right-first-time approach : Carefully following the dyestuff manufacturer's recommendations for salt, alkali usage, temperature, time, etc, ensures the optimum fixation levels and right-first-time production, thereby avoiding the need to make shading additions. Computer colour matching is helpful in this regard.
Conclusions
This research study revealed the effects of exhaustion agents on colour strength %. Using Glauber’s salt in dyeing instead of common salt and vacuum salt significantly reduced dyeing cost, which is cost-effective and important for both small and large-scale industries.
In effluent treatment, only a small quantity of salt is removed. Thus a major quantity of salt enters the environment on discharge of wastewater. High salt concentration in the effluent has a number of disadvantages, such as toxicity to organisms, and also causes land infertility. Using of Glauber’s salt with reactive dyeing leads to reduced effluent load, produces brighter shades also reduces consumption of dye.
From the study it was confirmed that the variety of shades produced on yarn exhibited adequate all-round washing fastness and high colour strength was reported with Glauber’s salt. Dyeing in the presence of Glauber’s salt improves the properties of the cotton substrate. Use of Glauber’s salt in reactive dyeing reduces the effluent load and, saves the consumption of dyes and produces bright shade, with an improvement in cost structures. Using a short liquor ratio reduces the use of electrolyte and the amount of energy required to heat the dye bath as well as the water consumption.
References
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