Environmental aspects of textile processing

WilliamSHiCkman Solvay lnterox Research 6 Development, Widnes Laboratory, PO Box 51, Moorfield Road, Widnes, Cheshire WA8 OFE, UK

The paper outlines some developments in ‘clean’ textile technology and discusses opportunities for effluent treatment with peroxy compounds. Particular aspects dealt with are elimination of organohalogen compounds (AOX) from cotton bleaching and wool shrinkproofing, energy and COD reduction in the continuous preparation of cotton and its blends, dye oxidation without chromium com- pounds, and the removal of colour from dyehouse effluent.

INTRODUCTION There are a multitude of processes covered in textile pro- duction, including fibre growth and harvesting, synthetic fibre manufacture, carding, combing, spinning, fabric pro- duction (weaving and knitting), preparation - the area with which Interox is most familiar and which includes desizing, scouring and bleaching - dyeing, finishing and making-up. Each particular aspect can have its own en- vironmental problems as shown in Table 1. From these few examples it can be seen that two solutions to the problems exist, i.e. clean technology or effluent treatment, in other words prevention or cure. In dyeing, for example, sulphur dyes can be oxidised by non-chromium-containing oxi- dants or the chromium in the effluent can be adsorbed onto some active material (carbon and casein have both been suggested).

The background to this paper is chemistry, particularly applied to the textile wet-processing sector, and so it is not the intention to examine all of the above topics. Those ar- eas have been selected in which Interox can make a useful contribution. These include: (a) AOX in cotton bleaching and wool shrinkproofing (b) Energy reduction in bleaching (c) COD reduction in desizing (d) Dye oxidation (e) Colour removal from dye effluent.

ADSORBABLE ORGANOHALOGEN COMPOUNDS The abbreviation AOX covers organohalogen compounds that are adsorbable on activated carbon. Such materials were of academic interest not so many years ago but dis- covery of dioxin in effluent from pulp treated with chlorine-containing bleaching agents has resulted in in- creased awareness of their toxicity. In fact, they are re- garded as so highly toxic that laws were introduced in Germany limiting or banning their discharge. Legislation is now being implemented throughout the EC and will have implications worldwide.

This paper was originally presented at the Nordisk Fageriteknisk Konferanse, Bergen, Norway, in June 1991.

Table 1 Some environmental problems associated with various textile processes

Textile Example Problem process

Fibre production Viscose production Flax harvesting Retting Cotton spinning Dusting Bleaching Cotton with NaOCl Dyeing Sulphur dye oxidation

Any dyeing Finishing Crease resist resins

Wool shrinkproofing

Sulphur compounds High COD/BOD Byssynosis AOX Cr(iii) Coloured effluent Formaldehyde AOX

Bleaching of cotton and AOX It was against this background that Interox’s German laboratories treated grey, desized, scoured and desized and scoured cotton fabric with sodium hypochlorite, sodium chlorite and hydrogen peroxide in the presence and in the absence of common salt [l]. The latter was added as it is often found at high concentrations in the work‘s balancing tanks as an aftermath of reactive dyeing. It was possible that chlorine could be generated by admix- ture of such process waters with oxidants, and this could lead to high AOX levels under conditions where no chlorine-containing bleaching agent was used. Hypochlorite was found to be a prime source of AOX whereas sodium chlorite generated much less. Peroxide, either in the presence or in the absence of salt, gave negli- gible increase of background AOX levels.

This work was extended by Schultz who examined the effect of various aspects oi hypochlorite bleaching on AOX in the effluent [2] . It was found that the purity of the substrate being bleached decreased the AOX content of the effluent. The results are summarised in Figure 1, the knitted cotton being made with less cleaner combed cot- ton and the loose stock having the usual high content of vegetable matter. Clearly the more impurities present in the substrate, the higher the AOX content.

Wool shrinkproofing and AOX The sources of AOX in the wool textile industry have re-

32 JSDC VOLUME 109 JANUARY 1993

cently been identified [3]. A major source is the treatment of wool with chlorine which forms part of the shrink-resist process. These chlorination agents can be replaced with peroxy compounds. Tables 2 and 3 show the use of mag- nesium monoperoxyphthalate (MMPP), an experimental peracid salt produced for use in organic synthesis, and potassium monoperoxysulphate (Kh4PS or Curox) in batch systems with and without resin [4].

-

Table 2 Shrink resistance with magnesium monoperoxyphthalate (MMPP) alone and with resin treatment

-

Area felting shrinkage (%)(a)

MMPP(b) (g/lOO 9

Fabric wool) Resin 1 2 3 4 5

Shetland 2 2 3 3 4 4

Lambswool 3 4 5 5 2.5 3 4 5

4% Crosil R

4% Crosil R

4% Crosil R

4% Crosil R 3% Basolan SW 3% Basolan SW 3% Basolan SW 3% Basolan SW

2 4 -1 1 2 3

-2 -6 0 -2

-2 -3

9 21 7 18 3 11

-3 -1 -1 -2 -1 1 -1 0

0 -1

11 1 5

-5 -4 -6

39 32 22 4 1

-1 0 2

15 4 9

-6 -1 -6 45 41 33 6 2 0

-1 0

21 8

10 -7 -2 -4

49 47 39 10 0 2

-2 1

(a) IWS wash TM 31 (b) MMPP applied at 30°C, liquor ratio 30:1, pH 4, with formic acid; develop 5%

sodium sulphite, pH 8, 25 min, 30°C (resin applied in fresh bath)

Table 3 Shrink resistance with Curox (KMPS) alone and with resin treatment

Area felting shrinkage

KMPS(b) (9/100 9

Fabric wool) Resin 1 2 3 4 -~ ~~~

Shetland 2 2 3 3 4 4 5

Lambswool 4 4 5 5 2 3

28 4% Crosil R 4

12 4% Crosil R 0

7 4% Crosil R -2

0

5 16 34 41 4% Crosil R 1 3 19 31

5 12 24 32 4% Crosil R 0 1 9 1 8 3% Basolan SW 1 6 18 25 3%BasolanSW -1 0 3 4

(a) IWS wash TM 31 (b) KMPS applied at 30% liquor ratio 30:l ; develop 5% sodium sulphite. pH 8,

25 rnin. 30°C (resin applied in fresh bath)

80

60

- . i? 2

40

20

0 PC CPI CP2 CT

PC - pure cellulose CT - cotton twill CPI -cotton poplin 1 CP2 - cotton poplin 2

KC -knitted cotton LS - loose stock

Figure 1 AOX in hypochlorite bleach liquors from the processing of various cotton-containing textiles [2]

Table 2 shows that MMPP alone can produce zero per- centage area felting shrinkage and that aftertreatment with resin allows this to be achieved with lower levels of oxidant. This is true even if the wool is a more difficult to treat worsted lambswool. Table 3 illustrates similar find- ings for Curox to those obtained for MMPE

ENERGY USE IN COTTON BLEACHING In the processing of cotton via open-width and rope routes some American researchers, including those at the Institute of Textile Technology in Charlotteville, Virginia [5], carried out energy measurements on bleaching ranges. One group produced values that are shown as histograms in Figures 2 and 3. These express two different ideas: the energy usage of a stage and of the operations within each stage. Two points are clearly demonstrated by Figures 2 and 3: firstly that washing operations are by far the largest consumer of energy and secondly that each stage con- sumes an approximately equal amount of energy.

Alternative routes Obviously a considerable amount of energy could be saved if the number of stages were cut from three to two, or even to a single stage. This reduction in energy con- sumption would simply result from the use of less water heating (which implies less water usage and discharge, both aspects being important environmentally). The con- sequences of lower energy consumption include less steam raising, fuel burning and effluent gas, and hence re- duced atmospheric pollution, with all that that implies.

The savings in energy are important but such savings will yield improved economy only if they are not offset by higher chemical costs, and if there is no loss in preparation quality resulting in more reprocessing.

JSDC VOLUME 109 JANUARY 1993 33

0" I I

8 60- i

$ tj 40- 5

P E 20-

.- c

x

w

I J-box 0 Open-width range

Figure 2 Distribution of energy in continuous preparation processes [51

I J-box 0 Open-width range . n

Desizing Scouring Bleaching

Figure 3 Distribution of energy in continuous preparation processes [51

Oxidative desizing Many early attempts to reduce processing stages under pad-steam conditions failed because of inadequate seed and size removal. Interox's first attempt to combine stages concentrated on combining scouring with desizing in a so- called oxidative desize. The currently used, successful processes add hydrogen peroxide or a peroxodisulphate (persulphate) to the scour liquor. This unstable system favours desizing over bleaching, and so the oxidatively desized fabric must have a bleaching stage to achieve the optimum degree of whiteness. A typical formulation for this combined desizehcour is shown in Table 4. The pro- cess can be carried out either hot or cold, and with or with- out the addition of sodium silicate or organic stabiliser.

Increasing the amount of stabiliser reduces desizing ef- ficiency. Suitable oxidants include sodium percarbonate, hydrogen peroxide and persulphate. Interox normally rec- ommends hydrogen peroxide for the following reasons:

Table 4 Typical formulae for oxidative desizing of 100% cotton (all quantities g/100 g fabric)

Cold dwell Pad-steam

Caustic soda (solid) 1 .O-5.0 2.5-4.0 Stabiliser 0.0-1 .o 0.0-1 .o

(or sodium perdisulphate) 0.2-0.5 0.2-0.5 Hydrogen peroxide (35%) 1.0-4.0 0.5-1.5

(a) It is a liquid product (b) It is already on site (c) Some whitening also occurs during desizing.

The first item implies that no predissolving is necessary. The second means that a bleacher who is already using hydrogen peroxide need not buy extra chemicals. The third emphasises the fact that hydrogen peroxide, unlike the persulphates, does whiten the fabric slightly. Perhaps the old adage 'well bottomed is half bleached should now read 'well oxidatively desized is half bleached.

Not only does oxidative desizing enable the number of stages to be reduced, it also has two other major advan- tages: (a) A wide range of sizes (poly(viny1 alcohol), starch from

all sources, carboxymethyl cellulose, polyacrylates) can be removed

(b) The CODBOD of the effluent is reduced.

The former is often the more important to textile wet pro- cessors as they seldom know where the fabric comes from, let alone which size it contains. Table 5 illustrates the sec- ond advantage using published data from Hoechst [6 ] . This aspect, the environmental one, is becoming ever more important. The heaviest effluent load, in terms of CODBOD, is usually associated with preparation [q, and the fact that there is a reduction of any degree at this stage can be not only environmentally friendly but also money saving. The story would be incomplete without mention- ing the work carried out by the auxiliary makers to im- prove effluent loads by getting rid of alkylphenol ethoxylates (APEOs), and replacing them without loss of performance.

Table 5 Reduction in COD (in mg/l) as a result of oxidative desizing PI

Three stage Two stage Single stage

Enzyme desize 95 800 Scour/oxidative desize 59 400 91 290 Bleach 11 000 22100 191 000 Total 166 200 113390 191 000

BASF has reviewed the environmental impact of toxic metabolites and offered replacements in the form of alco- hol ethoxylates, quoting performance comparisons [8]. Henkel, in slight contrast, offers not only alcohol ethoxylates but also hydroxyether sulphates and ether sulphonates which have somewhat different environmen- tal (fish toxicity, biodegradability, etc.) and performance properties [9].

Table 6 shows how oxidative desizing can be integrated into a shortened route. In this particular case cold desizing was selected as there was only one steamer and all of its running time was required for pad-steam bleaching.

34 JSDC VOLUME 109 JANUARY 1993

Table 6 Commercial two-stage processes incorporating oxidative desizing

Process Chemical Amount (gil00 g fabric)

~~ ~

Oxidative desize(a) Wetting agent Caustic soda (solid) Hydrogen peroxide (35%)

Wash-off Bleach@) Wetting agent

Emulsifier Organic stabiliser Caustic soda (solid) Hydrogen peroxide (35%)

0.1 -0.3 2.5-4.0 0.5-1.2

0.1-0.2 0.3-0.4 0.6-1 .O 1 .o-1.5 4.0-5.0

(a) 4 h at room temperature (b) 10 min at 100°C

DYE OXIDATION The continuous application of vat and sulphur dyes to cot- ton and its blends with polyester is one area where clean technology can be applied. The process starts with apply- ing dye to fabric using a low-volume padder. The fabric has its moisture content significantly reduced in an infra- red drier; this minimises surface contact of the wet fabric in order to reduce dye migration. The residual moisture is removed in a conventional drier. The fabric is then padded with reducing agent and steamed to promote dye diffu- sion, and finally washed and dried. The reduced dye is reoxidised in the washer.

Traditionally the oxidant was sodium or potassium dichromate. In the case of vats this was superseded by hy- drogen peroxide. Typically boxes three and four on a open soaper are set at 55 and 100°C respectively, each contain- ing 4 ml/l hydrogen peroxide (35%) and 4 ml/l acetic acid (60%). Sodium perborate tetrahydrate has been used to some extent but is disappearing fast, presumably as boron becomes more suspect. ’Chrome’ is still used for oxidising sulphur dyes but environmental pressure is mounting for its replacement; alternatively alkaline or acid hydrogen peroxide can be used [lo].

COLOUR REMOVAL Hydrogen peroxide, as supplied, is not only a very versa- tile oxidising agent, it is also very stable during long peri- ods of storage, as is illustrated in Figure 4. For bleaching or other oxidative processes to occur, this innate stability must be overcome by the use of an activator. Possibilities for doing this are shown in Figure 5. The normal activator for textile bleaching is alkali, usually the hydroxy ion. However, efficient bleaching requires the correct balance of four factors: (a) Activator concentration (b) Stabiliser concentration (c) Bleaching temperature (d) Bleaching time.

Activation using sulphuric acid to form peroxomono- sulphuric acid, or Caro’s acid, and its salts has been recom-

2.5

8 a; 9

1.5 L

Lo

0 1

0.5

0

Time, days

Figure 4 Stability of hydrogen peroxide at 20 and 40°C

Figure 5 Role of activators in overcoming stability of hydrogen per- oxide

mended, e.g. for the bleaching of coloured wovens, but nowadays permonosulphates are rarely used, except for Curox to make wool machine washable. Caro’s acid is much used in the mining industry for recovery or separa- tion of metals.

The generation of hydroxy radicals, using heavy metal ions, was something that textile cotton processors feared most as radicals lead to chemical damage. Research in the detergent industry has shown that this route can give in- creased stain removal, or bleaching, in domestic washing machines [lo], but as yet no industrial process has emerged. The method is, however, used for bleaching of pigmented wools, cashmere, camel hair, etc., and also the decolorisation of waste water using Fenton’s reagent. UV irradiation of peroxide solutions also produces hydroxy radicals that are used in effluent treatment, but special re- actors are required [ll].

Interox’s interest in colour removal from effluent started some time ago in its Japanese laboratories [12]. It had been noticed that, with increased usage of reactive dyes, the traditional precipitatiodflocculation processes were not removing colour completely. As a peroxide pro- ducer, it wondered, not unreasonably, if peroxide addition

JSDC VOLUME 109 JANUARY 1993 35

to the iron($ sulphate treatment stage would improve matters. Nine direct dyes were also chosen for investiga- tion since, compared with reactives, they are easy to decolorise.

For both reactive and direct dyes, 100 mgA dye liquors were used and their hues covered the whole spectrum. Between 20 and 100 mgA hydrogen peroxide (35%) were added to 60 mgA iron as iron@) sulphate solution. The pH was adjusted to 6 with sulphuric acid and the liquor aer- ated for 30 min at 30"C, and then the pH was adjusted to either 8.5 with caustic soda (for direct dyes) or pH 10 with

-

100

80

J 2 60 I

2

4 40

E L

0

20

0

-

- 0

-

r

-

7

100

-

-

60 mgll Fe 0 60 mg/l Fe + Kayaflok

Figure 6 Colour removal from solutions of Procion Navy H-NF (ICI), assessed from ratio of absorbances at wavelength of maximum ab- sorption

100

80

J -- 60 J 2

8 40

E L

0 I 20 I 40 60

Hydrogen peroxide (35%) added, mg/l

60 mgll Fe 0 60 mg/l Fe + Kayaflok

Figure 7 Colour removal from solutions of Mikacion Red RS (KYK), assessed from ratio of absorbances at wavelength of maximum ab- sorption

calcium hydroxide (for reactive dyes). An organic flocculant was added to the reactive dye liquors because the iron flocs were poorly formed.

The majority of the direct dyes were decolorised by this treatment; in fact the results were better than those ob- tained from chlorination. The twelve reactive dyes gave variable results from non-peroxide processes, but in all cases the peroxide process produced complete colour re- moval. Typical results are summarised in Figures 6 and 7, in which the left bar of each pair represents flocculaton with iron(1r) sulphate alone and the right-hand bar repre- sents flocculation with iron followed by a flocculant (Kayaflok) for the reasons given. Figure 6 represents a 'best case', i.e. one which needs least help from added oxi- dant to achieve 100% colour removal, while Figure 7 shows a 'worst case'.

As public disapproval to discharged colour increases in vigour, legislation will become tougher. For this reason Interox's Germany company reinvestigated some of the earlier Japanese findings but extended it to a wider range of dye classes [13]. The work consisted of making dye liquors from red or blue dyes (alone or in admixture) from the reactive, direct, metal-complex, pigment, disperse and vat classes, with the appropriate dyebath auxiliaries. Eeat- ment of these liquors consisted of pH adjustment to about 3, addition of quantities of iron(@ sulphate and hydrogen peroxide, which were calculated on the starting COD of the liquor, reaction for 60 min at 20°C ,followed by pH ad- justment with either caustic soda or calcium hydroxide. The concentration of dye was 10 mgA. Any precipitate was filtered off. Colour removal was assessed by measuring spectra of the solutions before and after treatment and then calculating the area under each of the two resultant curves. The percentage colour removal was determined by comparing the two areas.

Typical colour removal data for the individual dye solu- tions are shown in Figure 8. In only one case (Palanil Blue 3RT) neither physical nor chemical treatment removed the colour. When this dye was a component of the mixture of dyes, however, colour removal from the mixture was good.

0 20 40 60 80 100 Colour removal, % = Ca(OH), precipitation

A Remazol Brill. Blue B (HOE) B Sirius Fast Blue BRR (BAY) C lrgalan Blue FGL (CGY)

0 NaOH precipitation

D Helizarin Blue BGT E Palanil Blue 3RT (BASF) F lndanthren Blue GCD (BASF)

Figure 8 Colour removal from some dyebath effluents

36 JSDC VOLUME 109 JANUARY 1993

CONCLUSION This paper has discussed the versatility of peroxy com- pounds and attempted to highlight their environmental friendliness. They can be used, for example, to remove a wide range of sizes from woven cotton fabrics, often with reduced energy consumption and effluent load. If hydro- gen peroxide is the oxidant then desizing gives a better start for bleaching.

If the cotton goes on for dyeing with dyes that need oxi- dation, then peroxy compounds can be used to replace ’chrome’ oxidation. For vat dyes hydrogen peroxide is nearly always used, but for sulphur dyes there is a wider choice of oxidants, which is often affected by those dyes that are difficult to oxidise, such as CI Sulphur Red 10. Hy- drogen peroxide is nearly always used for sulphur blacks on package machines.

Wool processors concerned with machine-washable wool should also be aware that there are replacements for the chlorination of wool.

Finally, whether cotton or wool is processed, there is an

alternative to ‘chlorine’, i.e. Fenton’s reagent, for decolorising the effluent from the dyehouse.

* * *

This paper would not have been possible without the help of my German and Belgian colleagues.

REFERENCES 1. W Sebb, Textil Praxis Internat., 44 (1989) 841. 2. G Schultz, Textil Praxis Internat., 45 (1990) 40. 3. UK Dept of Environment circular 110.7 (1989). 4. IWS, Private communication. 5. D Balmforth, Amer. Dyestuff: Rep., (Aug 1985) 13. 6. E Rosch, Melliand Textilber., 63 (1982) 790. 7. K Schliiter, Melliand Textilber., 71 (1990) 182. 8. BASF technical information TI/T 208e. 9. B Wahle, Textilueredlung, 25 (1990) 199.

10. EP 0 082 563; EP 0 072 166. 11. K H Gregor et al., Melliand Textilber., 73 (1992) 526. 12. I Kato eta/., Sen-i Kako, 27 (1975) 449. 13. K H Gregor, Melliand Texfifber., 71 (1990) 976.

REPORT OF THE EXAMINATIONS BOARD (1992)

Following four annual increases in the number of candi- dates for the ASDC examination, the number this year fell, by approximately 20%, to below the average for the last ten years (117). Moreover, the drop-out rate this year at 22% is the highest on record; these entrants either with- drew in advance or simply failed to turn up for the exami- nation. Nevertheless, 20 of the 84 candidates examined passed the written examination, all in Branch 1 (textile op- tion).

The examination was held at five centres in the UK and in South Afnca and Hong Kong. Table 1 shows a break-

Table 1

Number of examinees passing in all papers for which they entered

Number Taking Taking Taking completing

Total Number whole papers to part of written Year entries examined exam complete exam exam

1992 108 84 1 ( 4%) 19 (58%) 6 (25%) 20 1991 135 127 2 ( 5%) 10 (22%) 3 ( 7%) 12 1990 130 117 2 ( 6Yo) 15(31%) O ( Oo/o) 17 1989 120 109 4 (1 OYo) 16 (44%) 4 (1 3%) 20 1988 84 78 7 (25%) 7 (22%) 5 (31%) 14 1987 117 98 15 (38%) 20 (61%) 3 (13%) 35

Figures in parentheses refer to the percentage of examinees in each group passing all the papers for which they entered

down of the 1992 examination results, together with those for the previous five years.

The 31% of examinees passing all the papers for which they entered represents a marked improvement in overall success. This could be attributed to the higher proportion of entrants taking papers to complete the examination but the following factors may also be contributory: (a) Candidates being allowed 15 minutes to read the ex-

amination papers before commencing writing, for the first time

(b) The high number of drop-outs, which may have re- sulted in a greater proportion of better prepared and motivated candidates

(c) The disclosure of graded marks to previous candi- dates, which has enabled them to quantify any areas of weakness.

Only one entrant passed all six papers at the first attempt, but eight passed after two attempts, and nine more of the 20 successful candidates had passed five papers after their second attempt at the examination.

Turning to the individual papers, there was a substan- tial improvement over last years performance in respect of both pass rate and average mark. In Papers A, C, D and G the percentage passes (1991 figures bracketed) were A 90% (53%), C 54% (4%), D 55% (35%), G 86% (53%). The pass rates in the remaining papers continue to be disappoint- ing: B 36% (47%), F 40% (39%); but the main cause for con- cern this year was Paper E in which only 19% of examinees were successful (compared with 40% in 1991).

The board extends its congratulations to the 20 candi-

JSDC VOLUME 109 JANUARY 1993 37