..C

OPTIMIZING APPLICATION PROCESSES TO

REDUCE ENVIRONMENTAL IMPACT

Femand Schlaeppi, ESQU Corporation Management Consultant for the Textile Wet Processing Industry

lnt rod uct ion

Escalating costs of effluent treatments due to increasingly stringent governmental regulations pose a major economic problem for the textile industry. Costs of generating effluent are water usage, waste water treatment and associated equipment, discharge fees, effluent monitoring and toxicity testing.

The most effective means to curb these costs is waste minimization at the source, i.e. optimizing application processes to reduce waste water and pollutants.

Successful process optimization involves one or more of the following:

0 Product substitution

Process analysis

Effluent reduction 0

0 Chemical use reduction

0 Process modification

0 Application techniques based on existing technologlek

Application techniques not widely accepted by industry

0 Automation

0 Developing Technologies

Some specific examples will be given to illustrate employment of these strategies for potential reduction of effluent and chemical pollutants.

Product Substitution

Examples:

Substitution of formic acid for acetic acid reduces the biologicai oxygen demand in the effluent.

In bleaching, active chlorine can be replaced with peroxide compounds. This eliminates significant amounts of AOX (activated carbon absorbable organohalogens) and trichloromethane compounds typically found in spent hypochlorite bleaching liquors').

Substitution of sodium carbonate/sodium hydroxide buffer for trisodium phosphate in the fixation of high temperature reactive dyes reduces phosphate pollution.

Reactive dyes applied by exhaust methods require large amounts of sodium sulfate to attain an acceptable degree of fixation. Recently ClBA introduced Cibacron LS dyes which can be applied with about one quarter the amount of salt needed by other reactive dyes. Reduction of salt in the effluent reduces pollution of rivers and streams, where the biological equilibrium depends to a large extent on the salt content of the water.

Commercial acid metal complex dyes, despite their toxic metal content, are used for dyeing automotive nylon fabrics to meet high lightfastness requirements. The National Textile Center recently announced the synthesis of iron complexed formazan dyes by research chemists at N. C. State University2'. Dyes based on the chemistry contain a non-toxic metal and, having excellent lightfastness on nylon, could replace the existing metal complex dyes, thus alleviating metal pollutants in the effluent stream. Until such dyes are commercially available, dyeing methods yielding 100% exhaustion of the current metal complex dyes should be developed.

Processes Analysis and Modification to Reduce Waste Discharge from Dyeing Cotton Fabrics with Direct Dyes in Deep Shades

Effluent, chemical and dyestuff discharge are analyzed for three procedures:

Conventional beck dyeing

Conventional jet dyeing

Modified jet dyeing

The chemicals used for these procedures and the resulting waste water discharge are shown in table I .

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I Table I. Comparison of Waste Water Discharge from Direct Dyeing Processes I

Procedure Conventional Beck Conventional Jet Modified Jet Dyeing L.R. 20:l Dyeing L.R. 8:1 Dyeing L.R. 8:l

Dyes Salt Wettin agent

Dye exhaustion Wate; P

4% 25 OIL

1 glL 60 Ukg

65%

4% 25 gIL

1 glL 24 Ukg

70%

~~~

4% 25 OIL

24 Ukg 80%

_ _

WASTE WATER DISCHARGE FOR 1000 KILOGRAMS FABRIC

Active dyestuff s7 5.6 kg 4.8 kg 3.2 kg

Chemical discharge-) 544 kg 232 kg 224 kg

Effluent volume 60,000 L 24,000 L 24,000 L

*) 1 dye, 2 rinse baths **) Assumes an average active dye content of 40%

***) includes diluent from dyes

Conventional Beck Dyeing

At a typical liquor to goods ratio of 20:1, dye exhaustion for heavy shades is around 65%. To ensure a level dyeing, the conventional procedure calls for starting at a low temperature, followed by a gradual increase to 90 - 95OC. The temperature profile is shown in Figure 1.

Conventional Jet Dyeing

The liquor ratio on older jet dyeing machines is between 6 : l and 8: l . Dyeing at low liquor ratios saves water and concentration based chemicals. There is also a saving in dyes due to the equilibrium between the concentrations of dye in the fiber and in the bath at the end of the dyeing process. Direct dyes follow the Langmuir exhaustion isotherm and, therefore, the concentration of the dye on the fiber gradually approaches a limit with increasing dye concentration in the solution. This explains the relatively small improvement in dye exhaustion from 65% to 70% which, nevertheless, amounts to a 14% reduction of color in the effluent.

In jet dyeing the temperature profile is essentially the same as for beck dyeing, except the dyeing time may be shortened due to increased dyebath/fabric interchange at lower liquor ratios.

Modification of Conventional Jet Dyeing

The modified jet dyeing procedure differs from the conventional procedure in that dyeing is started at 95OC, and the bath is cooled to 5OoC. (See

3

I

figure 2). Cooling the bath to 5OoC increases the degree of dyestuff exhaustion to about 80%, thus further reducing color in the effluent by 339/0.

Increased direct dye exhaustion at 5OoC was recently confirmed by rasearchers at N. C. State university3).

100

980 1: I-

O

100 4

Q 8 0 1' 20 I-

0

Fig. 1 Temperature profile for .conventional beck dyeing

Fig. 2 Temperature profile for modified jet dyeing

In addition to improved waste discharge, the modified procedure offers advantages in improved levelness and dye penetration when dyeing heavy, tightly woven fabrics. This allows the use of SDC classification type B and C dyes, which are poorer in leveling and penetration, but which generally have better wet and lightfastness than class A dyes. This is also the only procedure by which heavy spun viscose rayon fabrics can be dyed level and without crack marks.

FOUR PROCESSES WITH VARYING ENVIRONMENTAL IMPACT - WHICH IS THE BEST CHOICE?

Four different processes, based on existing technologies, can be used for dyeing and/or bleaching of cotton knit goods with reactive dyes. The processes vary greatly in the volume of effluent generated and in the amount of chemicals discharged. Choosing the best process depends on environmental considerations, available equipment, volume of annual production and customer requirements.

The processes are:

Conventional Beck Process

. Conventional Pad-Batch Process

Pad-Batch Process on Greige Goods with Post Bleach

Pad-Batch Process on Greige Goods without Bleaching

4

The concentrations of chemicals used for these procedures are based on a medium depth of shade with monochloro triazine reactive dyes. The resulting waste water and chemical discharge are shown in table II.

Table 11. Comparison of Waste Water Discharge from Reactive' Dyeing Processes

Procedures Exhaust Pad-Batch Pad-Batch Pad-Batch L.R. 1 5 1 L.R. 1:l Grey Goods Grey Goods

L.R. 1 : l L.R. 1:l Pretreatment L.R. 15:l Post-Bleach Chemicals

L.R. 1 5 1 Soda ash 4 gIL 4 glL 4 glL Wettinglscouring 3 gIL 3 OIL 3 OIL Seq uest ra nt 1 glL 1 glL 1 glL Stabilizer 1 glL 1 OIL 1 OIL Water 60 Ukg 60 Llkg 90 Ukg

Dyeing Glauber's salt anh. 60 gIL Soda ash 1 OIL 20 glL 20 OIL 20 OIL So. Silicate (dry base) 15 OIL 15 glL 15 glL Caustic soda (dry) 0.8 glL 2.4 OIL 2.4 gIL 2.4 gIL Wettingldeaerating 1 glL 2 gIL 2 glL Water 105Ukg 60 Ukg 60 Ukg

WASTE WATER DISCHARGE FOR 1000 KILOGRAMS FABRIC

Chemical discharge 1,062 kg 173 kg 174 kg 39 kg

Effluent volume 165,000 L 120,000 L 90,000 L 60,000 L

Water Usage

The volume of water used for the different processes is based on the number of treatment baths at 15 liters per kilogram fabric per bath.

Pretreatment on a dye beck: 60 L/kg Treatment bath, overflow rinse, hot and cold rinse.

Exhaust dyeing and washing on the dye beck: 105 Ukg Dye bath: 15Ukg Washing off of hydrolyzed dye: 90 Ukg Overflow rinse, hot rinse, scour at 95OC, hot, warm and cold rinse.

Pad-batch dyeing: 60 Ukg Water used for washing off of hydrolyzed dye is based on a beam wash- off unit4) which is more efficient and saves one third of the water needed for washing on a beck.

Pad-batch dyeing with post-bleach on a dye beck: 90 L/kg Overflow rinse, hot rinse, bleach and scour at 95OC, hot, warm, and cold rinse. 5

Assessment of Results

Conventional Beck Process

The effluent volume is very high due to the large number of baths for pretreatment, dyeing, and washing off. The chemical discharge is also very high due to the substantial quantity of salt required for acceptable dye fixation.

This procedure should only be chosen when the annual production is small, and the capital investment for batch dyeing equipment can not be justified.

Conventional Pad-Batch Process

The effluent volume is 25% lower than that for beck processing, because the dye bath is eliminated and washing off on a beam washing unit is more efficient. The total quantity of chemicals used is approximately 1/6 of that needed for exhaust dyeing, because in pad-batch dyeing salt is eliminated. The very low liquor ratio in pad-batch dyeing is the main reason salt is not required for'this process. Analysis of the procedures clearly illustrates the magnitude of the savings in waste water volume and chemical discharge when using the pad- batch process.

It is not surprising that pad-batch is the preferred procedure for the application of reactive dyes on knit goods. Larger mills usually employ continuous preparation machines, which use less water and lower amounts of chemicals than beck dyeing machines, thus further reducing waste water and chemical discharge.

Pad-Batch Process on Grey Goods with Post-bleach

Additional improvements in waste discharge are attainable by combining washing-off of unfixed reactive dyes with bleaching Qpost-bleach), thereby realizing substantial savings in effluent treatment costs, as well as in chemical and energy costs.

This process is suitable for most shades, except where the ultimate in brightness is essential. The dyestuff yield may be somewhat lower due to alcoholysis from impurities in the cotton and especially from knitting oils. It has been shown that the type of needle oil can affect the dye yield').

Practical application of this process was demonstrated at ITMA 1983 by Jawetex on their newly developed padder for tubular knit goods. The fabrics were padded with monochlorotriarine dyes (Cibacron F dyes). The goods were washed at a nearby textile mill, and half of each batch was bleached. The next day the goods were displayed on the Jawetex stand.

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Pad-Batch Process on Grey Goods without Post Bleach

This process has the lowest effluent yolume and the chemical discharge is insignificant. The applicability of the process depends on the quality of the cotton used, and on the type of shade. A European manufacturer uses this method for dyeing of corduroy in dark brown, bottle green, maroon, navy, and black shades. The fabric has an exceptionally rich, full hand, because the natural waxes and pectins in the cotton are not removed. This approach was rejected in the U.S., since the stylists demanded a full range of shades.

ANALYSIS OF DISCHARGE FROM PROCESSES FOR DYEING POLYESTEWCOTTON BLENDS WITH DISPERSE AND REACTIVE DYES

Four procedures may be used for dyeing polyesterkotton knit goods with disperse and reactive dyes. The choice of one procedure over another is contingent on the quantity of waste discharge relative to customers’ fastness and shade requirements.

The procedures are:

Conventional Two-Bath

Reverse Two-bath

Reverse Two-bath with Pad-Batch on Grey Goods

One-Bath Two Step

Table Ill. illustrates reduction in effluent volume by modifications of the conventional two-bath procedure, and reduction of chemical discharge by pad- batch, where salt is eliminated for dyeing the cotton portion in the blend.

Table 111. Comparison of Waste Water Discharge from PESICO Dyeing Processes

WASTE WATER DISCHARGE FOR 1000 KILOGRAMS FABRIC

Procedures Conventional Reverse Reverse Two- One-Bath Two Two-Bath Two-Bath Bath Pad-Batch Step

Chemical Discharge.) 1,175 kg 1,115 kg 227 kg 1,115 kg

Effluent Volume 225,000 L 165,000 L 120,000 L 165,000 L

9 Chemicals are calculated in the same manner as shown in Table 11, assuming a L.R. of 1 5 1 for all processes, except for pad-batch which is calculated on the basis of L.R. 1:l . HT-dyeing of polyester: 0.5 g/L sequestrant, 1 g/L auxiliary, 2 g/L ammonium sulfate. Reductive clearing: 3 glL hydrosulfite, 2 g/L sodium hydroxide (dry)

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Processing Sequence and Water Usage

Conventional Two-Bath Procedure: Total 225 Ukg

1. Pretreatment in a beck: 60 Ukg Water usage: Treatment bath, overflow rinse, hot and cold rinse

2. HT dyeing of polyester in a beck: 30 Ukg Water usage: Dyebath and rinse

3. Reduction clear: 30 Ukg Water usage: Treatment bath and rinse.

4. Exhaust dyeing and washing of cotton: 105 Ukg Water usage: Dye bath, overflow rinse, scour at 95'C, hot, warm, and cold rinse.

Reverse Two-Bath Procedure: Total 165 Ukg

1. Pretreatment: 60 Ukg

2. Dyeing of cotton: 45 Ukg Water usage: Dyebath and two warm rinse baths.

3. HT dyeing of polyester: 60 Ukg Water usage: Dyebath (simultaneous scouring of unfixed reactive dye), hot, warm, and cold rinse baths

Reverse Two-Bath with Pad-Batch on Grey Goods: Total 120 Ukg

1. Pretreatment replaced by post bleach

2. Pad-batch dyeing of cotton: 30 L/kg Water usage: Removal of chemicals on a beam wash-off unit.

3. HT dyeing of polyester: 30 L/kg Water usage: Dyebath (simultaneous scouring of unfixed reactive dye), and one warm rinse bath

4. Post-bleach: 60 Ukg Water usage: Bleach bath at 95' C, hot, warm, and one cold rinse baths.

One Bath Two Step: Total 165 L/kg

1. Pretreatment: 60 Ukg

2. HT dyeing of polyester, followed by dyeing of cotton in the same bath: 105 L/kg Water usage: Dyebath, overflow rinse, hot rinse, scouring at 95OC, hot, warm and cold rinse baths.

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Assessment of Results

Conventional Two-Bath Procedure

This procedure generates the highest effluent and chemical discharge, but it gives best results in terms of brightness of shade and fastness to washing, because reduction clearing eliminates the disperse dye stain on the cotton.

Reverse Two-Bath Procedure

In this procedure the hydrolyzed reactive dye is effectively removed during the polyester dyeing cycle, reducing total effluent by 25%.

Reduction clearing of the disperse dye stain on the cotton is not possible, because the reactive dye would also be destroyed. Disperse dyes remaining on the cotton may cause some staining of nylon in wet fastness tests. Where optimum wet fastness is required, such as demanded by Marks & SRencer, this procedure can not be used.

Reverse Two-Bath with Pad-Batch on Grey Goods

This procedure generates the least effluent and the lowest chemical discharge. It should always be used when pad-batch equipment is available. The only limitation may be some staining of nylon by wet fastness tests.

One-bath two-step process

Total discharge for this procedure is the same as for the reverse two- bath procedure. Reduction clearing is also not possible but Dispersol PC dyes (ICI) may be used. These dyes are saponified by alkali during the fixation of the reactive dyes. The saponified species are water soluble and have no affinity to cellulose’’. Staining of nylon in wet fastness tests therefore should not be a problem.

WASTE WATER AND CHEMICAL DISCHARGE FROM POLYESTER DYEING PROCESSES

Rapid HT-Dyeing Procedure for Polyester

During the 1970’s polyester double knit fabrics were highly fashionable and large yardages were dyed by exhaust processes. Various rapid dyeing systems were proposed to save time and snergy. The success of such a system depends on controlling the rate of exhaustion of disperse dyes during the exhaustion phase prior to diffusion of the dyes into the polyester.

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An optimized system, developed at Ciba, meets the following criteria7):

Butyl Benzoate Emulsifier Nonionic leveling agent Ammonium sulfate. Acetic acid (BOD 0.64)** Formic acid (BOD 0.12)** Trimer

0 Leveling during the exhaustion phase.

Conventional Process Optimized Process Yes no Yes no no Yes no Yes no no Yes Yes ves no

Maximum dye exhaustion to ensure repeatability and to minimize dye

in the effluent

0 Minimum discharge of chemicals

Chemical contamination of the effluent is given in Table IV.

* Ammonium sulfate is a nutrient in an activated sludge process. .. Pound for pound BOD equivalent".

Thermosol Process Saves Effluent and Chemical Discharge

Prior to the advent of thermosol dyeing it was firmly believed that penetration of dyes into fibers could only occur in the presence of water. In 1947, Joe Gibson used dry heat for dyeing the new hydrophobic synthetic fibers. He placed a fabric, padded with a disperse dye, between two flat irons for five seconds at 200'C. A dyed fabric in the shape of an iron was obtained') and the principle of thermosol dyeing was discovered.

This radical departure from conventional exhaust procedures made continuous dyeing of large yardages of polyesterkotton blends feasible, and saved enormous quantities of effluent and chemicals from being discharged into the environment.

Continuous Dyeing of Textured Polyester by High Temperature Steam

The Thermosol process is not suitable for dyeing texturized polyester fabric, because the aesthetic properties, such as bulk and texturizing crimp are lost under dry heat fixation conditions at 200' to 220'C. This is largely avoided by high temperature steam fixation at 16OoC to 18OoC for 3 to 6 minutes")"') in an Airoli, Stork, Artos, or SACM festoon ager. Discharge generated by continuous and by exhaust processes is shown in Table V.

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Table V. Comparison of Waste Water Discharge from Continuous and Exhaust Dyeing Processes

Chemicals Pad: 70% pickup HT steam

HT exhaust 1 5 1 L.R.

Disperse dye 50% liq. Disperse dye pdr. Antimigrant Wetting agent Sequestrant Dyeing assistant Ammonium sulfatelformic acid Water for reductive clear and rinsing

57 glL

10 glL 2 glL

10 Ukg

2%

0.5 glL

60 Ukg')

1 glL 2 glL

WASTE WATER DISCHARGE FOR 1000 KILOGRAMS FABRIC

C he mica1 disc ha rg e")

Effluent Volume 10,000 L 60,000 L

20 kg 65 kg

7. Includes 1 dye bath, 1 reduction clear, and 2 rinse baths. ") Includes dispersants from dyes, assuming an active dye content of 40% for powder and 20% for liquid

dyes.

Continuous dyeing at a very low liquor ratio of 1:0.7 (due to condensation in the steamer the liquor ratio during dyeing is around 1:l.l) saves considerable quantities of chemicals and effluent. When large yardages of textured polyester are being dyed, the capital investment for a high temperature steamer is justified.

CHEMICAL DISCHARGE FROM CONTINUOUS DYEING OF COTTON WITH REACTIVE DYES

Three processes based on established technology, and a process based on new technology are compared for their effect on effluent and chemical discharge. The processes are:

Pad-Steam Process Sequence: Pad - Dry - Chemical Pad - Steam - Wash

Single Pad - Steam Process Sequence: Pad - Steam - Wash

Thermofix Process Sequence: Pad - Dry - Thermofix - Wash

Econtrol Process Sequence: Pad - Steam - Wash

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Table VI. Comparison of Chemical Discharge from Continuous Dyeing Processes for Cotton with Reactive Dyes

Pad-Steam Single Pad- Pad Econtrol Steam Thermofix

Dve Pad wetting agent m-Nitrobenr. Sulf. So. Sulfate anh. Urea Dicyandiamide So. carbonate calc. Sodium bicarbonate Pickup Chemical Pad So. Sulfate anh. Sodium hydroxide Pickup

2 glL 3 gll 10 glL

- -

70%

250 glL

80% 4 g/L

2 glL 3 gIL

50 glL

20 glL

80%

2 g1L 3 glL

70 glL 30 glL

10 glL

-

70%

2 glL

10 glL 70%

CHEMICAL DISCHARGE FOR 1000 KILOGRAMS FABRIC

Chemical Discharge 214 kg 60 kg 81 kg 8.1 kg

The effluent volume is the same for all four processes and depends on the efficiency of the washing equipment used. The recipes for all three established processes are based on monochlorotriazine dyes. In contrast to exhaust dyeing the chemical discharge is greatly reduced and is comparable to the semi-continuous pad-batch process.

The Econtrol Process

This process is a recent joint development of Zeneca Colours and Montforts Textilmaschinen'2). Highly reactive dichlorotriazine dyes, such as Procion MX types, are padded with 10 g/L sodium bicarbonate and fixed in a hot flue for approximately two minutes. The hot flue has a temperature of 12OoC with a 25% voiume steam content. Under these conditions the fabric temperature reaches 68OC, which is sufficient for fixation.

The chemical discharge for 1000 kilograms fabric from the Econtrol process is reduced to eight kilograms, mainly from sodium bicarbonate.

AIR AS DILUENT FOR AQUEOUS LIQUORS

Foam Finishing

Various foam finishing systems are in use throughout the world. In these systems, air is used to dilute the water content of a finishing liquor between 50% to 75% 13)*14)*15). Finishing processes cause no effluent unless the fabric is washed after curing. Foam finishing is widely used, because of large savings in en erg y consumption .

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Continuous Foam Dyeing

Continuous foam dyeing of textured polyester fabrics with Terasil X dyes (concentrated nonionic dispersions) has been attempted, using the FFT process, developed jointly by Union Carbide Corp. and Gaston County Dyeing Machine Co."). Precise control of the foam and its application to the fabric proved too difficult for a perfectly level dyeing. Continuous foam dyeing with soluble dyes is not practical, because of insufficient water available to dissolve the dyes.

0 Exhaust Dyeing with Foamed Dye Liquors - The SancowadQ Process

The Sancowad process was developed by Sandoz, Ltd. around 1970i7). Aqueous dye baths are diluted with air using a foaming agent, thus reducing the liquor ratio and the amount of chemicals.

The process was proposed for beck dyeing of cotton, using a 3% foaming agent (Sancowad and reducing the liquor ratio from 20:l to 8:l. An oval reel to plate the goods in wide folds, and a driven lifting roller were required for adequate circulation of the goods in the foamed dye liquor. Modern jet dyeing machines allow dyeing of cotton below a liquor ratio of 8:1, and further reduction with foam is not practical, because there would be insufficient water for dissolving the dyes and chemicals.

Hydrophobic fibers are dyed with essentially water insoluble disperse dyes, and dyeing at much lower liquor ratios is practical. Dyeing of textured polyester on a one port Gaston County jet was successful at a liquor ratio of 21 , but on a multi port jet there was insufficient bath to ensure even distribution of the dyes throughout all the tubes.

! / - *

The best use of the Sancowad process is to dye hydrophobic materials, such as texture nylon hosiery, on rotary drum dyeing machines. Such a machine was first installed in New Hampshire in 1973"'. Table VI1 shows the $6 b- effluent of the conventional versus Sancowad procedure. bbiy I

Table VII. Effluent from the Conventional versus the Sancowad Process

/- 100 POUNDS NYLON

Processes Scouring Dyeing Rinsing Afte r-trea ti ng Softening

Conventional Mill Process 1,080 gals. 360 gals. 720 gals. 18 gals.

1,080 gals. 36 gals. 360 gals. 18 gals.

Total Effluent 3,600 gals. 90 gals.

Data calculated from Table I l l in the American Dyestuff Reporter of June 1973, p. 56

Low liquor ratio foam dyeing of nylon garments is feasible and should be used more widely

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DYEBATHREUSEFORBECKDYEINGNYLONCARPET

Reusing spent dyebaths is a potentially attractive technique for effluent reduction at the source. It has been explored in the mid 1970's and early 1980's by researchers from the Georgia Institute of Technology20)s2'). It has yet to be widely adopted, because there are several difficulties and disadvantages.

Dyebath reuse is easiest to manage when the same shade is produced with the same dyes. The amounts of the remaining dyes in the spent dyebath are measured with a spectrophotometer, and the bath is replenished with the appropriate amounts of the same dyes required to match the shade for the next dyeing cycle. After a few cycles, the bath becomes turbid from spin finishes and from loose fibers. It is then necessary to filter a sample of the bath for photometric analysis.

Dyebath reuse becomes practically impossible when new shades have to be produced with dyes other than those used in the previous cycle, due to difficulties in shade matching and potential metamerism.

These severe limitations are eliminated with a dyeing system which yields 100% dyestuff exhaustion.

Dosacid@ System for Multiple Dyebath Reuse

In 1980 Ciba-Geigy introduced the Dosacid system which allows for complete exhaustion of the dyes and of the leveling agent. Under these conditions multiple reuse cycles are possible regardless of the shade to be dyed.

At the start of the dyeing the pH is adjusted with dilute sodium hydroxide solution to the alkaline region. The pH is then reduced at a controlled rate with dilute sulfuric acid solution until the dyebath is completely exhausted. During dyeing the liquor is circulated through filters (to remove loose fibers), then past the pH measuring probes and past the caustic and acid feeding devices, back into the dye vessel. The initial and final pH levels, and the pH gradient are programmed on a pH measuring closed loop control and dispensing unit. The unit was developed by Polymetron AG, Switzerland.

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The temperature and pH profiles for the first dyeing are shown in figure 3., and those for the second and subsequent dyeings in figure 4.

0 30 75 120 150 180 Tima [mln)

PH - Temperature .--- 1 Fig. 3 Temperature and pH profile

for first dyeing

0 30 75 120 150 180 Tim. (mln)

PH - Temperature - - * I

Fig. 4 Temperature and pH profile for second and subsequent dyeings

At the end of each dye cycle the spent bath is pumped into a storage vessel, the carpet is rinsed and unloaded.

Build-up of salt from the acid and caustic and from the diluents in the dyes and build-up of spin finishes from the fibers determines the limit of reusable cycles. Ten cycles are attainable without any problems.

Practical Trial

A practical trial was conducted at a nylon carpet yarn dyehouse in the U.S. on a Hussong skein dyeing machine. A beige shade was dyed with C.I. Acid Yellow 21 9, Red 361 , Blue 277 and dodecylated oxidibenzene disulfonate as a leveling agent. A pH measuring probe was borrowed from Polymetron. The alkali and acid solutions were added manually to attain the proper pH gradient. Six consecutive dyeings were made, reusing the spent bath five times. The reproduction of the shade from lot to lot was perfect, and the skeins were level throughout. Despite this success the system was not implemented, because there was no means of pumping the dyebath to a storage vessel, and the tracks for the hoist of the yarn carrier did not permit moving the skeins to an adjacent machine for rinsing.

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Calculation of Effluent Savings

With the Dosacid system it is possible to reuse 80% of the spent dye liquors nine times for ten dye cycles, assuming that 20% of the bath is retained by the carpet after the bath is pumped to the storage vessel. The savings in water usage are calculated as follows:

Water used for the first dyebath: Water used to replenish 9 spent baths: (9 x 0.2 gal.) Total water used for 10 dye cycles:

1.0 gal. 1.0 gal. 2.0 gal.

Without dyebath reuse water used for 10 dye cycles: 10.0 gal.

Water savings with Dosacid system: 72%

Potential Annual Savings in Effluent by the U.S. Carpet Industry

In 1994, U.S. shipments of tufted broadloom carpet totaled 1.3 billion square yards22). Based on 1976 data23) about 60% was nylon, and 37% of the nylon was beck dyed. This amounts to approximately 290 million square yards. While today this figure may not be entirely accurate, the following is intended merely to illustrate an order of magnitude of the potential effluent savings, if the Dosacid system were used.

Water consumption for beck dyeing of carpet is estimated at 25 gallons per square yard23). Assuming that half of this water is used for rinsing, the water consumption for the actual dyeing of 290 million square yards is 3.625 billion gallons. The potential savings in effluent are well over 2 W billion gailons per annum. Moreover the effluent is completely colorless and contains no chemicals other than salt from the diluent in the dyes and from neutralizing of sodium hydroxide with sulfuric acid.

A system of this type, if adopted by only half the carpet industry, could save over 1 % billion gallons of effluent each year. Comparison of effluent generated with and without dyebath reuse is shown in figure 5.

4

3 .5

I 3 3 2.5

6 2

1 5

T 1 0 . 5

0

- =

W Jthout Dyebath Dyebath Dyebath R e u s e by Reuse by Reuse E ntlre H .It the

Industry Industry

~~

Fig. 5 Effluent generated from dyeing nylon carpet 16

COMBINED DYEING AND FINISHING

The idea of combining dyeing and finishing into one operatim is not new. Simultaneous dyeing and finishing could , /eliminate substantial quantities of waste water and chemical discharge generated by dyeing. Despite tremendous potential advantages combined dyeing and finishing has not yet been widely implemented.

Some Proposed Systems

Following the introduction of fiber reactive dyes attempts were made to simultaneously react the dyes and resins with cellulose.

The Procion Resin Process is based on applying reactive dyes with reactant resins in conjunction with a special acid donating ~ a t a l y s t ~ ~ ) ’ ~ ~ ) .

Co-application of reactive dyes with urea-formaldehyde, using alkaline catalysis for fixation of the dyes and simultaneous polymerization of the resin was also proposed26).

In 1968, American Cyanamide Co. announced the Calcobond reactive dyes which react with cellulose under acidic conditions and could be co-applied with acid catalyzed resin systems2’). However, these dyes were soon discon tin ued for other reasons .

Reactive dyes, containing an activated vinyl moiety, can be fixed on cellulose by high energy electron irradiati~n~*)*~’). When co-applied with N- methylol acrylamide and subjected to irradiation, simultaneous dye fixation and resin polymerization take place. Dye fixation as high as 60% is attainable. By replacing ionizing radiation with other means of generating free radicals a greater fixation efficiency may be achieved.

A more recent publication points to the possibility of dyeing polyester/cotton blends using disperse dyes in conjunction with trimethyol melamine and styrene-butadien latex3’). Should this approach prove feasible, it would be a technological breakthrough for dyeing and finishing cotton/polyester fabrics.

Combined pigment dyeing and resin finishing (pad - dry - cure)31) is a completely effluent free process and could be realized without undue technical problems, at the very least for dyeing cotton fabrics in light and medium shades.

Adoption of such a process in the wet processing industry is difficult, because it would require reorganizing two separate departments, located in two separate areas in a building, and sometimes even in different buildings, into a single department.

Elimination of environmental pollution and enormous savings in production costs should provide sufficient incentive for continued development and for implementation of combined dyeing and finishing.

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PROCESSES FOR EFFLUENT-FREE COLORATION OF TEXTILES

Pigment Printing

Pigment printing is by far the most important textile printing process, amounting to 46% of the total print market worldwide3*). The process consists of printing, drying, and curing.

Advantages: Simple and safe

0 No waste water and chemical discharge from the process itself

Disadvantages: Limited colorfastness to crocking in heavy shades

0 Some stiffening of the fabric in printed areas

Waste water originates from the cleaning of the machine and associated eqqipment. Residual print pastes, which are not suitable for reformulation, need to be disposed. These wastes can be minimized by computer based automation in preparing print pastes, reducing print paste losses at the printing machine, and accurate calculation of the quantities of the print pastes needed for a given run.

Transfer Printing

Heat transfer printing was invented by Noel de Plasse in 195833). It is a two-step process consisting of printing the paper with low energy disperse dyes and transferring the design from the paper to the fabric on a transfer printing calendar34). The share of transfer printing in the print market today is estimated at 4 YO w o r I d w i d e35).

Advantages: Increased design capabilities (effects not attainable by conventional printing methods)

0 No water and no steam required

0 No waste water and chemical discharge

Disadvantages: 0 Limited colorfastness

0 Wasted paper

Printing of Polyester without Washing

In transfer printing only the pure dyestuffs sublime from the paper to the fabric. Thickener and other chemicals do not and remain on the y p e r , hence washing of the fabric is eliminated. The paper printing step can be circumvented by printing the fabric directly, using a thickener with minimal dry content and nearly pure dyestuffs. High molecular weight polymers3'), such as ethylene/maleic anhydride copolymers (EMA 91), methyl vinyl ethdmaleic

18

anhydride (Gantrez AN), or carboxy polymethylene polymers (Carbopol), yield thickening vehicles of extremely low dry content. Conventional disperse dyes are not compatible with these polymers, because they contain large amounts of anionic dispersants which adversely affect the viscosity of the polymers. Specially prepared liquid disperse dyes, such as Terasil X dyes (Ciba), are dispersed with small amounts of nonionic dispersants and are compatible with polymer thickeners. A system based on high molecular weight polymers and nonionic disperse dyes is printed on polyester and the fabric is dried and thermofixed, or HT-steamed, but does not require washing. This process is used in Europe and to a limited extent in the U.S.

Advantages: 0 Elimination of t b paper printing step

0 No wasted paper

0 100% dye fixation

0 Practically no chemicals deposited on the printed fabric

0 Excellent colorfastness

0 No discharge of waste water and chemicals

Disadvantage: 0 Limited design capability compared to transfer printing

AUTOMATION

Automation is an important strategy in optimizing application processes to reduce environmental impact. Water, chemical, and dyestuff usage are precisely controlled, thus reducing waste.

Automation requires data acquisition and recording of important variables which affect a particular process, such as temperature, time, and pH. The variables, and the limits which they need to be controlled, must be established to ensure reproducibility of the process.

A control device initiates a warning signal when a measured value is outside a programmed acceptable range and requires intervention3’’. The ultimate in automation is total control and automatic adjustment through feedback loops to controllers, ensuring that the process variables fall within predetermined limits.

In autcrmated exhaust dyeing variables that can be controlled are liquor ratio, rate of rise of temperature, pH, electrolyte and dyestuff concentration. An automated dyeing machine is equipped with temperature, pH, and conductivity probes and fiber optical sensors, which feed data into a computer, where it is

19

compared with preprogrammed values. Control devices then regulate the steam intake, or activate measuring and dispensing units to feed alkali, acid, salt, and dyes to the machine.

In automated continuous dyeing, wet pickup can be measured across the width and throughout the fabric run, using microwave measuring allowing for precise adjustments at the padder. Control of temperature, air circulation, and humidity in flue dryers minimizes dye migration and, therefore, the use of antimigrants.

In the not too distant future, complete automation in preparation, dyeing, printing and finishing, and robotics in material handling will be cost effective and significantly reduce the environmental impact from the textile industry.

DEVELOPING TECHNOLOGIES

Supercritical Fluid Dyeing (SDF)

Dyeing with supercritical carbon dioxide is at the leading edge of emerging technological developments. Research is being conducted at the North West German Textile Research Center in Krefeld, Germany3’). A pilot plant for dyeing eight kilograms of yarn is in operation. Research in the U.S. on supercritical fluid technology as a processing fluid is ongoing under the auspices of the National Textile Center at Clemson and North Carolina State Universities and at the Georgia Institute of Techn~logy~~’ .

Supercritical carbon dioxide as a dyeing medium for polyester and polyamide, using unadulterated disperse dyes, may become an effluent-free dyeing process.

Potential advantages are:

0 Excellent leveling

Short dyeing cycle

0 Water-free dyeing

0 Elimination of a reductive clearing process

0 Elimination of energy intensive drying

C02 is recyclable

No waste effluent

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I

Calculated Dot Printing

In calculated multicolor dot printing, developed jointly by Ciba Basle, SST Thai and Schwitter AG4", a design is resolved into individual dots and digitalized. The desired shades are obtained by mixing print pastes on the material. Four print pastes containing four different dyes (colors) are printed with four screens. The dot size controls the amount of each individual color component. A single print paste concentration is used. With a screen ruling value of 100% full shades are produced and with a value of 1% extremely pale shades are obtained. Effluent pollution from wasted unused print pastes is eliminated, because leftover print pastes can be used the next day, whereas in traditional screen printing print paste losses average about 20 pounds per screen.

Jet Printing on Flat Goods

Stork & Co. in conjunction with Zeneca Colours developed the TruColorQ system, a sample print machine based on jet printing and using high purity liquid Procion dyes. At ITMA in Milan Stork unveiled Fashion Jet, a production scale jet printing demonstrator developed jointly with the German printer KBC and Zeneca CoIours4*). These systems usually operate with only four colors which are mixed on the substrate. This eliminates disposal of wasted print pastes and effluent contamination from washing of equipment.

Eco-friendly Bleaching and Mercerizing

A novel system for scouring, bleaching, and mercerizing has been invented at the University of Ca l i f~ rn ia~~) . It is based on electrochemistry. The fabric passes through a cathode chamber and via a roller to the anode chamber. The two chambers are separated by a liquid-impervious membrane. The electrolyte filling the cell is a one-molsr sodium sulfate solution. Electric current passing, from the cathode to the anode, produces sodium hydroxide at the cathode, where the fabric is mercerized, and sulfuric acid at the anode, where the fabric is neutralized. So far the amount of electrical energy required for practical processing speeds is not known. The inventors claim that the system is eco-friendly.

Advances in Indigo Dyeing

The indigo concentration in the dyebath can be reduced by lowering the pH from 13 to 1144) without affecting the depth of shade. Less indigo is washed off the yarn, reducing the amount of indigo in the effluent and lowering the alkalinity of the waste water.

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CONCLUSION

A properly constructed program for optimizing application processes to reduce environmental impact includes the following strategies:

Product substitution to eliminate harmful pollutants.

Analysis, comparison, and modification of related procedures to facilitate selection of the best processes to reduce effluent volume and chemical waste.

Utilization of waste saving processes based on proven technology.

Experimentation with known application techniques, which are not yet in wide use, but which could lessen detrimental impact on the environment .

Automation to reduce water, chemical, and dye usage and waste caused by human error.

Implementation of modified or new processes despite resistance to change.

Benefits through Process Optimization

Benefits derived from source reduction through process optimization are three fo Id:

Abatement of environmental impact.

0 Cost reduction in effluent treatment and disposal.

0 Improved profitability from savings in raw materials and energy and from increased productivity.

Expenditures for waste treatment and treatment facilities decrease profitability. Process optimization offers economic benefits which can be quantified to justify capital expenditures for equipment modifications, or for new and more efficient machinery.

22

References:

1) Steiner N., TC&C, 27/8, 1995

2) Freeman H.S., Sokolowska-Gajda, and J. Reifa A., TC&C, 27/2, 1995

3) Lu J., Spiekermann R., McGregor R., and Smith B., TCCLC, 27/3, 1995

4) Stone R.L., TCLC, 1314, 1981

5) Elliott M.S., and Whittlestone D., JSDC, 110/9, 1994

6) Menzies I.D., and Leatherbetter, P.W., AATCC Nat. Tech. Conf., Book of Papers,

7) Schlaeppi, F., Wagner R.D., McNeil J.L., TC&C, 14/12, 1982

8) Brandon T.W. and Grindley S., Sewage Wks. Journ. 17, 652, 1945

9) Gibson, Jr. J.W., TC&C, 2812, 1996

I O ) Leube H. and Richter P., TC&C, 5/3, 1973

17) 1980 ITPC, TC&C, 1314, 1981

12) van Wersch K., International Dyer, 1/1996

13) Valchem Division, U.M. & M, ADR, July 1979

14) Turner G.R., TC&C, 17/10, 1985

15) Gregorian R.S., TC&C, 1914, 1987

16) Clifford F.G., ADR, April 1980

17) Davenport R., ADR, Nov. 1977

18) Skoufis J., ADR, July 1979

19) ADR Report, June 1973

20) Cook F.L. and Tincher W.C., TC&C, lO/l , 1978

21) Carr W.W. and Cook F.L., TC&C, 1215, 1980

22) Source: 1990-94 U.S. Department of Commerce

23) Black B., James L.D. and Tincher W.C., ADR, June 1976

24) Senger N.G., Text. Rundschau, Jahrgang 16, Sept. - Oct., 1961

25) Rattee I.D., JSDC, 7812, 1962

26) Nuessle A.C., JSDC, 8111, 1965

27) Copeland A.F., ADR, April, 1968

28) German Patent 2,046,736 (1971)

2.9) 1970 ITPC, TC&C, 2/24, 1970

30) Flath H.-J., Melliand 6/1993

31) Kothe W., Melliand 9/1988

32) International Dyer, 3/1995

33) French Patent, 1,223,330 (1958)

1985

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i P

34) Stork Brabant M.V., Market Research, 1996

35) Schlaeppi, F., Text. Research Journal, 4713, 1977

36) U.S. Patent 4,095,942 (1978)

37) Fretland W.D., TC&C, 27/1, 1995

38) Pleva R., TC&C, 2715, 1995

39) Knitel D. and Schollmeyer E., Melliand, 911995

40) Drew M.J. et. al., TC&C, 2616, 1994

41) Hermann H., ADR, Aug. 1995

42) Textile Printing, International Dyer, 311 996

43) Lennox-Kerr P., International Dyer, 6/1996

44) Etters J.N., TC&C, 27/2, 1995

\

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SYMPOSIUM COMMllTEE

S u e D. Wagner Ciba

Symposium Chairman 4

Russell J. Ruggieri Springs Industries Inc. - James T. Swicegood

FMC Corporation - 0 Arthur J. Toompas C s e Mills Corporation

Copies available from

AATCC P.O. Box 12215

Research Triangle Park, NC 27709-221 5

fax: 91 9/549-8933 91 9/549-8 1 41