| In order to achieve reduced load on the environment, textile manufacturers need to optimize and standardize the entire supply chain and resources, according to DyStar Ecology Solutions |
At every stage of textile production, large amounts of energy, clean water and chemicals are used to process the textiles and apparel which we consumers demand. In turn these processes generate air, water and soil pollution through often-untreated effluent disposal and waste generation which place a heavy burden on the environment.
In order to achieve reduced load on environment, we need to optimize and standardize the entire supply chain and resources. This article discusses two major fibers processed today and show how the advanced process optimization can minimize resource use and pollution load.
- Exhaust dyeing of cellulosic fibers with reactive dyes
- Exhaust dyeing of polyester with disperse dyes
Exhaust dyeing of cellulosic fibers with reactive dyes
Build up of Remazol Ultra Orange RGB and Remazol Ultra Yellow RGBN vs. C.I. Reactive Yellow 176 | 
Build up of Remazol Ultra Carmine RGB and Remazol Ultra Red RGB vs. C.I. Reactive Red 239 | 
Dyes consumed in tonnes at a model small/medium sized dye house operating 50 weeks per year |
The main effluent control parameters of textile dye house wastewater include volume, total dissolved solids, chemical oxygen demand (COD), biological oxygen demand (BOD), colour and pH. Each is quantifiable and in many industrialised countries concentration or total load limits are established which may not be exceeded in effluent discharge to either independently operated waste water treatment plants (WWTP) or to surface waters. The permitted limits for discharge to a WWTP are typically higher than those allowed for surface waters such as rivers and lakes.
However, perhaps the single most important focus for coloration of cellulosic fibres is the elimination of non-conformance by using reactive dye technology engineered to support right-first-time production incorporating laboratory to bulk transferability and production lot repeatability.
For medium to deep shades the impact on the environment can be significantly reduced by exploiting the properties of the Remazol Ultra RGB reactive dyes.
The key targets of this reactive dye were:
- High tinctorial strength of the individual dyes
- High degree of fixation on the cellulosic fibre
- Minimised dye-dye interaction which causes "blocking".
Blocking is typical in many commodity reactive dye combinations based on a golden yellow, red and navy/black reactive dye ternary leading to poor reproducibility and overloading of dye in an attempt to reach the desired depth of shade. Dye overload results in poor right-first-time performance, very low fixation efficiency and consequently a high pollution load in the dye house effluent due to unfixed dye hydrolysis.
The key to avoiding dye overload is to form the covalent bonds with the cellulose fibre at a percentage of dye application where the graph is steep, because the rate of fixation levels off with saturation of the available sites in the fibre.
Dye recipes formulated to the same visual deep shade has indicated a reduction in quantity of dye required by the Remazol Ultra RGB combination compared with commodity dyes approaching about 50%
This dye demonstrates outstanding build-up and tinctorial value by exhaust, cold pad batch and continuous application methods to achieve deep shades from a lower concentration of dyes and chemicals than is currently available from competitive systems.
In exhaust application the electrolyte required is dependent on the percentage of reactive dye applied in order to neutralise the negative ions when alkali is added to effect the dye-fibre fixation stage. The electrolyte concentration used for the application of this dye may be reduced by up to 40% compar
ed with similar visual depth shades dyed with lower efficiency commodity dyes.
By forming the dye-fibre covalent bonds at the steep part of the fixation curve, the amount of dye hydrolysate formed in competition with water is reduced. This contributes to a saving in water usage during washing off and a significant reduction in total colour loading of the effluent.
The following charts illustrate the reduction in quantity of dye required by the Remazol Ultra RGB combination compared with commodity dyes approaching approximately 50%. The figures are derived from a model small/medium sized dye house operating 50 weeks per year and indicate the dye applied and hydrolysed dye discharged on an annual basis calculated for both unmercerised cotton and Tencel A100 lyocell fibre in knitted fabric constructions.
Colour in effluent
Dyes released in tonnes at a model small/medium sized dye house operating 50 weeks per year |
The unfixed colour removal in the model was calculated from controlled dyeings, and the?optical density of total colour to be removed and discharged in effluent was measured with the following calculated results:
Impact on effluent loading
As an illustration of the impact on the dye house effluent load, we have taken the above dye house model processing by exhaust application on knitted cotton interlock and Tencel A100 using an overflow jet at 10:1 liquor ratio and a carry-over of liquor 300% between drain and fill baths.
A typical procedure uses three baths for preparation/rinsing of cotton, two baths for preparation/rinsing of Tencel, one bath for dyeing each fibre, and five baths for the rinsing/ soaping stages of cotton and four rinsing/soaping stages for Tencel A100 giving a total water consumption of about 66 litres per kilo of cotton fabric and 52 litres per kilo of Tencel respectively.
Chemical Oxygen Demand
COD in mg/l normalised to one litre of solution | 
Salt consumed in tonnes |
COD values are normalised to one litre of solution of the different fibres and dyes (as shown in the chart). If the fixation yield is not optimal -- illustrated by commodity ternary -- the remaining colour in the exhaust dye bath produces a high COD.
Reduction in total dissolved solids
Electrolyte consumption largely contributes to the TDS loading, which is significantly reduced by use of the Remazol reactive dye technology compared to use of commodity dyes particularly in deep shades, and can be further reduced by the use of Tencel A100 compared with unmercerised cotton, according to DyStar.
Disperse dyes for exhaust dyeing of polyester fibre
Due to limited availability of clean water and the ever increasing cost of oil-derived raw materials, polyester fiber production which is growing at a rapid pace has a considerable environmental footprint. Hence, we need to minimize the resources used for the coloration of polyester fibers irrespective of whether the fiber is virgin or recycled.
There are ways of reducing resource use in exhaust dyeing of polyester fiber using DyStar’s Dianix disperse dyes and Sera processing auxiliaries by the intelligent application of process optimization software (Optidye P).
Build Conventional processing for medium to dark shades process time (415 min) | 
Optimized processing with Scour dyeing, opt dye PES calculation and reductive clearing in dyeing bath process time (225 min) | | (/tbody> |
Two primary concerns in dyeing processes, namely energy and water use the following minimization options were identified.
Energy saving options can best be achieved through:
• Frequency-regulated motors for reels and pumps
• Optimized dyeing processes and temperature / time optimization
• Compatible, level-dyeing dyes for reliable dyeing
• High Right-First-Time performance (RFT)
• Heat recovery from hot discharge liquors
• Low liquor ratio
Water saving can best be achieved through:
• Optimized machinery loading
• Lowest possible liquor ratio
• Combined washing and dyeing processes
• Optimized rinsing processes
• Reuse of rinsing baths
• Compatible, level-dyeing dyes for reliable dyeing
According to DyStar Ecology Solutions, a number of benefits can be achieved by using this greener disperse dye, Sera process auxiliaries and DyStar’s Optidye PES program, including high reproducibility (RFT), level dyeing, energy saving, reduction of water and dyes/auxiliaries cost, and increased productivity. By using Dianix Yellow Brown S-4R 150%, which is designed to comply with all requirements outlined by the Restricted Substances List (RSL) and ecological requirements of major brands, retailers and independent ecolabels as an alternative to the old commodity dye C.I.Disperse Orange 30.
A process evaluation program from DyStar Textile Services found that the optimized process using DyStar products and process technology leads to the following benefits:
• 43% electricity
• 46% steam
• 50% water
• 39% process time
• 38% cost in total
• 58% increase in production.
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