J O U R N A L OF THE SOCIETY OF DYERS A N D COLOURISTS Volume 81 February 1965 Number 2

We remember with gratitude the life, and record with deep regret the death, of

The Right Honourable Sir Winston Leonard Spencer Churchill K.G., O.M., C.H., F.R.S.

British and Honorary American Citizen and World Statesman

A dynamic and inspiring leader

'Never in the course of human history has so much been owed by so many to one man'

1874 1965 I Proceedings of the Society

Cold-pad Desizing and Bleaching for Dyeing and Printing H. S. GARDNER AND S. E. KALINOWSKI

Cotton Silk and Man-made Fibres Research Association, Shirley Institute, Didsbury, Manchester 20

Meetings of the Midlands Region, held at the King's Head Hotel, Loughborough, on 26th November 1963, Mr J. Saunders in the chair; of the Northern Ireland Region, held in the Grosvenor Rooms, Belfast, on 14th January 1964, Mr N . Hindshaw in the chair; and of the Manchester Region (One-day Symposium), held at the College of Science and Technology, Manchester,

on 6th March 1964, Mr F. V. Davis in the chair

Existing cold-pad processes, and new methods developed to overcome their defects, are discussed in the light of laboratory experiments and full-scale works trials; the processes examined in detail are bromite desizing, peroxide bleaching, and chlorite

bleaching; mention is made of a new cheap solvent-detergent for use with enzymes and scouring liquors.

Introduction Cold-pad processes are attractive to finishers who wish to

experiment in a new field without purchasing new machinery; they are useful for increasing output where the existing machinery is working near its limit, convenient for dealing with small specialised orders which must be treated in open width, and outstanding for cloth made from heat- or alkali-sensitive fibres. The machinery used for desizing and bleaching consists only of a pad-mangle with a low-capacity trough and a batching device, stillage space, and some means for washing-off the cloth after the storage period. Unexpected fluctuations in the temperature of the croft or dyehouse during the storage period can alter the final result, and cold-pad processes generally are unsatisfactory below 10°C; for this reason mention will also be made of alternative warm-pad processes where these are applicable.

Desizing of Cotton Cloth Much of the starch-sized grey cloth in Britain is desized by

impregnating it at the quench-box in warm bacterial or malt

enzyme solution, transferring it in rope form to uncovered pits, open wagons, or unenclosed piles on the croft floor for a storage period of 2-20 h, and washing-off in cold or lukewarm water. Exothermic hydrolysis warms the inside of the load, but the outside or top of the load cools and may also dry out, giving uneven results.

New enzymes giving good desizing in a reasonable time at 10-20°C may soon be available, but at present only oxidising systems can be used for strictly cold-pad desizing. Persulphate and hypochlorite (1) are less efficient and require rather longer storage times than sodium bromite, which is fully consumed in 10-30 min at 3&10"C and causes virtually no chemical break- down of cellulose (2 ,3) . BROMITE DESIZING

The cloth is singed, cooled, padded at 50 % pick-up with 0.08 % sodium bromite solution buffered to pH 10 and containing a special wetting agent, stored briefly until the bromite is consumed, and washed-off on the jig or open soaper in boiling 1 % or 0.5 % sodium hydroxide, respectively.

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42 JSDC FEBRUARY 1965; GARDNER AND KALINOWSKI

TABLE 1 Pilot-scale Bromite Desizing*

Alkali in Padding Storage Residual starch (%) after pad-liquor temp. conditions washing in

temp. time water 5 g/l. 5 g/l. (“C) (min) Na,CO, NaOH

Buffer (PH 10) 20 20 20 0.70 0.75 0.31 20 g/l. NaOH 50 50 I20 0.45 0.49 0.30 Control (no bromite) - - - 1.15 1.11 0.47

(“C)

* Material: heavy cotton cambric (4.5 oz/ydz) containing 4.4% sago starch and tallow. Washer contains the stated liquors at 95°C in boxes 1 and 2, cold water in boxes 3 and 4. Immersion time in each solution- 15 s.

Pilot-scale experiments show that on a typical British cloth a one-hour caustic boil-off on the jig may leave as much as 0.7 % starch on the cloth. More of the digested starch is removed in an open soaper, as shown in Table 1, because of the mechanical action at the nip. If water or dilute soda solution is used for washing-off, a less complete desize is effected; this is partly offset by adding 2% sodium hydroxide to the padding bath and storing the cloth for 2 h at 50°C before the water rinse, but washing in caustic soda is essential for a moderate desize (0.3% residual starch).

Industrial experiments on short runs of cloth (5-20 pieces) originally containing 4.5-8 % size show the same general trend, but desizing efficiency is lower and a second alkali treatment is essential for adequate desizing (< 0.15 % residual starch), as shown in Table 2.

In our opinion the bromite desize will not be widely adopted in the near future in this country for the following reasons.

(1) It is inconvenient in many works to dry-quench singed cloth and leave it to cool before padding. The pH-10 bromite solution cannot be used in a quench-box, since temperatures above 40°C lead to tendering of cellulose, poor desizing, and wasteful consumption of bromite on colouring matter.

( 2 ) A bromite solution containing 2 ”/, caustic soda, which is stable in a quench-box at 50”C, will exhaust on cotton cloth in 2 h at this temperature, but poor desizing at the selvedge will result from allowing the cloth to lie in open trucks; this is a disadvantage common to quench-box enzyme desizing.

(3) A hot alkaline wash in open width is not easily arranged in rope-kier bleaching ranges.

(4) The striking results reported by French workers are not repeatable on British cloth; their success was due to there being little or no tallow mixed with starch on the French cloth, enabling better penetration of the cold liquor.

( 5 ) The second alkali treatment (which is common to all oxidative desizing treatments) is inconvenient in single-stage chlorite bleaching ranges, as it must be followed by thorough neutralisation of the cloth.

The inventors of the process have recently stated in reply to point 3 that cotton cloth padded in bromite solution at pH 10 and stored briefly as above can be kier-boiled without an inter- mediate wash-off; and in reply to point 5 that a modified sequence, consisting in padding with bromite solution, storing, rinsing out the pH-10 buffer, chlorite bleaching, and washing-off with sodium hydroxide solution, desizes the cloth efficiently and avoids the neutralisation step. Bromite used correctly causes no loss of strength of cotton (fluidity 3-33); its attack on starch is rapid,

even, non-specific, and unaffected by antifungal agents detri- mental to enzymes. But it appears to give better results on French cloth sized with potato starch than on British cloth sized with sago-tallow mixture; at present it seems best suited to continuous and semi-continuous pad-steam peroxide bleaching ranges. PAD AND QUENCH-BOX DESIZING WITH ENZYMES

A recurring problem in the desizing of cotton fabric is pene- tration of size films, especially where paraffin wax or spermaceti has been used as lubricant. A rapid initial rate of wetting-out can be secured without detriment to the enzymes by adding non- ionic surfactants, but the total process involves several physical processes, and the later stages may be retarded by their presence (4 ) ; indeed, some manufacturers of enzymes hold that wetting agents confer no advantages (5). Wetting of the yarn surface is accompanied by penetration of the size film when a solvent- detergent is present; we have established on the pilot scale that a British cloth, padded with a bacterial enzyme and BRRASK PS 5*, stored on the roll at 60°C for 30 min, and passed down a washing range with 0.5% sodium hydroxide in the first two boxes, was desized more completely than a similar piece padded with enzyme and wetting agent at the same pick-up, in spite of the fact that the enzyme showed some loss of activity when tested with BRRASK PS 5 in a starch sol.

B 1 each i n g Cold bleaching of cotton cloth with chlorite or peroxide gives a

poor white which is unstable to dry heat, but nevertheless adequate for dyeing to all but the palest depths. Removal of cotton seed is good, and the wettability may be good enough for pad-dyeing or printing. One cold chlorite process can be used with solvent-detergent for removal of oil stains, and another is useful for stripping dyeings of disperse, direct, acid, and sulphur dyes. PEROXIDE BLEACHING

The cold process requires rather more sodium hydroxide than does the pad-steam peroxide bleach. The effects of varying a Laporte recipe are shown in Table 3, which summarises small- scale experiments on a seedy Indian drill containing 4.9% of starch; the samples were padded at 80% pick-up, stored over- night at 20”C, and scalded for 5 min in 0.5 % soda ash.

Addition of pyrophosphate gave the best mote removal, but the residual motes were least noticeable when BRRASK PS 5 was present; this additive reduced the fat and wax content (6) and gave outstanding wettability (7) and the best white for an extra

This is a solvent-detergent containing 70% of a high-boiling white spirit obtainable from Booth & Openshaw Ltd, Blackburn.

TABLE 2 Industrial-scale Bromite Desizing

Cotton Alkali in Contents of Starch (%) Subsequent NaOH Residual fabric pad-liquor washer boxes after process (% 0.w.f.) starch

1 and2 washing-off ( %I 4-oz poplin buffer (pH 10) water, 70°C 1.90 } kier, 1 ha t 5 0 4-OZ poplin 20 g/l. NaOH water, 70°C 0.89 35 Ib/in2 5 0 4-oz plain buffer (pH 10) 5 g/l. Na,CO,, 95°C 1 4 3 pad-steam, 1.h 4 0.1 3 6-oz gaberdine buffer (PH 10) 5 ell. NaOH, 95°C 0.77 jig, 1 h 3 0.13

COLD-PAD DESlZlNG AND BLEACHING 43

TABLE 3 Cold-pad Bleaching with Peroxide

Recipe*, per liire Sodium hydroxide (9) 5 20 20 20 20 Sodium pyrophosphate (g) - - 5 - - Bontex 25 (g)t 1 I 1 - -

2 5 BRRASK PS 5 (ml) - - -

Properties of bleached cloth Reflectance factor 0.77 0.81 0.82 0.83 0.84 Motes removed (%) 80 92 98 94 95 Mote colour brown buff yellow cream cream Fat and wax (%) 0.79 0.67 0.55 - 0.23 Wettability v6s (s-l) 0,001 0.005 0,008 0,037 0.132 Water absorbency (calc.) (s) 23 5 3 0.6 0.2 * All recipes contained 20 g/l. sodium silicate (Pyramid No. l), 5 g/l. sodium carbonate,

t Aconventional bacteriallysoft alkarylsulphonate detergent made by Industrial Soaps 15 g/l. hydrogen peroxide (i.e. 5 vol)

Ltd

0.4d per Ib of cotton (4% on weight of fibre). By using double this quantity (8 o.w.f.), all traces of rings caused by the hand spotting of oil stains were obliterated.

The peroxide bleach works well on all-cotton fabric, and is effective in the presence of starch size; the padding liquor is innocuous and there are no washing-off or effluent problems. However, copper- or iron-contaminated cloth cannot be bleached with complete safety, and unions of cotton with alkali-sensitive material (acetate) are more difficult to deal with, since patchy delustring and surface saponification may occur when sufficient alkali is used to activate the solution. Some synthetic-polymer materials may be degraded (polyamides, Orlon, Darvan) or yellowed (Verel) by alkaline peroxide solutions designed for bleaching cotton, and mixtures or unions of these fibres with cotton must be bleached by other means.

CHLORITE BLEACHING

Formaldehyde Activation A typical industrial solution (Table 4) includes sodium chlorite,

formaldehyde, and sodium carbonate. When these react, the products can be analysed to give some indication of the reaction route. In dilute solution in a closed vessel (column 1 of Table 5) , all the formaldehyde is converted to formic acid overnight, and the overall reaction is

2NaC10, + HCHO --f NaCIO, + HCOOH + NaCl This might be construed as representing the activation reaction. However, acidified chlorite solutions prepared at pH 4 with sodium chlorite and formic acid do not bleach cotton fabric as

TABLE 4 Chlorite-Formaldehyde Bleaching Recipe

Commercial Pure Molar materials materials ratio

NaCIO, 251b 20 6.63 Na,CO, 1 Ib 2.2* 0.61 HCHO 2 pints 1 .oo 1 .oo

(per 100 gal) (sil.)

* Includes soda present in chlorite powder

TABLE 5 Chlorite-Formaldehyde Chemicals Balance (Molar Ratio)

After 16 h After 1 h After 16 h (encloscd) (scavenged) (cloth bleach)

Reagents consumed NaCIO, 1 .96 2.00 3.8 HCHO 1 .oo 1 .oo 1 .oo

NaCIO, 0.98 0.53 0.3 Products

CIO, 0 0.37 0

rapidly as chlorite solutions activated with the equivalent amount of formaldehyde; further, the equation takes no account of the intermediate production of chlorine dioxide, and predicts a much greater wasteful production of chlorate than is found in practice.

The solution described in Table 4 produces chlorine dioxide very slowly, and it is difficult to remove it quantitatively by means of an air stream; but in concentrated solution the reagents give a rapid evolution of the gas, which can be absorbed quantitatively in potassium iodide solution and titrated. The results of one such experiment are shown in the middle column of Table 5; removal of some of the chlorine dioxide has caused less chlorate to be produced. The figures do not fit a simple equation, and another molecular species (e.g. oxygen) may be involved.

The last column of Table 5 is a summary of several bleaching experiments with the industrial recipe. Chlorine dioxide is absorbed by the cotton impurities at almost the same rate as it is produced (see later) and the amount of chlorate produced is still lower; in fact, the molar ratio of chlorate produced to chlorite consumed (0.08) is similar to that observed (8) in pad-steam bleaching at pH 5.5. The results suggest that the production of chlorine dioxide is linked with the wasteful production of chlorate via a disproportionation reaction with chlorite.

Two processes are concerned in the activation, neutralisation of excess alkalinity by production of formic acid, permitting the reaction of chlorous acid with colouring matter, and evolution of chlorine dioxide; evolution of gas commences after an induction period, when the pH value falls to 10, continuing as the pH falls to between 4 and 5; when it ceases, the rate of bleaching assumes the low value expected with cold acidified chlorite. This is borne out by the upper two curves of Figure 1. The induction period is absent when no soda ash has been added to the recipe; the system is unstable. By altering the proportions of formaldehyde and soda ash, a whole range of solution stability and bleaching activity can be covered. Actual bleaching results on a desized Egyptian poplin (Figure 2 ) show that excess of formaldehyde does not noticeably improve the bleach ; also, the pad-liquor becomes less stable. The disadvantage of low liquor pick-up is stressed by the white circle and triangle, which are results obtained by padding at 60% pick-up with all concen- trations increased bv one-half. Both the Dad-liauor and the liquor on the cloth generate chlorine dioxide more rapidly higher concentration.

0

at

6 I2 Time, h

I8 24

Upper curves: Bottom curve:

20 g/l. NaClCz. I g/l. NaZCOJ lOg/l . NaCICZ. no NalCOS

Figure I - Rate of consumpiion of chlorite on cloth

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44 JSDC FEBRUARY 1965; GARDNER AND KALINOWSKI

0'9 I

0.6 ' I I

I 2 3 Formalin concentration, pints/100 gal

A after 7 h 0 after 24 h OA results at 60% pick-up; all concn. increased by 50%

100 gal of pad-liquor contain 25 Ib of 80% chlorite and I Ib soda ash; pick-up = 90%

Figure 2- Effect of Formalin concentration on reflectance factor of desized cotton fabric

With desized Egyptian cotton fabrics, the bleach is well on the way to completion at 20°C in 7 h, but with seedy American or Indian fabrics longer storage is necessary. It can be seen from Figure I that chlorite consumption on cloth is not proportional to formaldehyde concentration; there is evidence that a constant amount of formaldehyde is absorbed by nitrogenous material in cotton. Much more is absorbed if gelatin size is present, as on some cotton unions with acetate or viscose warps; for these the recipe is altered to 33 pints Formalin solution (38% form- aldehyde) and 16 Ib soda ash, but, since the cloth warms up in the roll and chlorine dioxide is evolved only 10 min after padding, the size of batch is restricted, and immediate wrapping in polythene is essential. Further, the pad-liquor is stable for only 20-30 min, compared with twice this time for the conventional recipe.

On condenser-weft union cloths, the formaldehyde-chlorite system frequently gives adequate seed removal and a white sufficient for dyeing; measurement of reflectance is difficult on these cloths, but a reflectance factor of 0.8 is typical. However, grey all-cotton cloths bleach to a poorer white (0.75) and more chlorite is required than in the recipe of Table 4; moreover, the low efficiency of chlorite utilisation (see Figure 1) is a challenge to a cost-conscious bleacher. Pad-liquor stability is better at lower temperatures, as might be expected, but a low batching or storage temperature introduces a further complication ; after storage overnight, the batch still contains unreacted chlorine dioxide, which is harmful to operatives unrolling the batch before rinsing and dyeing. Several firms regularly use this system for bleaching union fabrics, but they have made special arrangements for fume extraction during padding, storage, and unrolling (see later). Chlorite-formaldehyde with BRRASK PS 5 is useful for removal of oil stains from continuous-filament fabrics.

Permanganate Acceleration Small quantities of manganous salts accelerate chlorite

bleaching, but direct padding of cloth with manganese salts and chlorite is impossible because of precipitation of manganous hydroxide. Potassium permanganate reacts slowly with chlorite to give higher hydrated oxides, but, if a suspending agent is added, their precipitation is retarded sufficiently to ensure a stable pad-liquor and a uniform catalytic effect. The curves of Figure 3 summarise three series of cold-bleaching experiments in which solutions containing 20 gjl. sodium chlorite and the additions shown in the key were applied to desized Egyptian

0.95

0.9

0 ._ - n a PI u .- b z 0.8

E . 0

2 8

5

m u L .- -

0.5

0 6 I 2 I8 Time, h

a b I g/I. KMnO, c

I g/l. each of KMn04. HCHO, Cellofas B 300, Na2C03

I g/l. each of H C H O and Na2COJ

Figure 3- Rate of consumption of chlorite on cloth

24

cotton poplin at 80 % pick-up; the chlorite consumption has been plotted on a logarithmic scale in order to obtain information about the reaction kinetics.

Both solutions containing permanganate were stable for some hours at 20°C, and on the cloth, after an initial fast reaction, both showed rates which were first order with respect to chlorite; longer storage gave progressively better bleaching. Perman- ganate-chlorite at first appeared to be a particularly attractive system, since no chlorine dioxide appeared at any stage. This proved to be a disadvantage, however, because seed removal was very slow on the desized Egyptian cotton fabric. Moreover, neither system was suitable for desized cotton fabrics containing much seed, or for any cotton fabrics sized with starch, and union fabrics were bleached only with varying degrees of success; this was in part due to the mode of precipitation of manganese oxides in the fabric. Gelatin size inhibited the rapid reaction of the permanganate-formaldehyde system.

0 20 40 60 80 Time, rnin

a 50 811. persulphate b 10 811. formaldehyde

Figure 4- Activation of sodium chlorite

COLD-PAD DESlZlNG AND BLEACHING 45

TABLE 6 Bleaching Condenser-weft Union Fabrics

( O W 2 ) used (%I factor residual motes Fabric Warp Weight Size Chlorite Reflectance Colour of

Satin Acetate 1 1 - 97 0.81 orange Poplin brocade Acetate 6 PVA 95 0.80 cream Satin brocade Acetate 16 PVA 98 0.75 (none) Fancy repp Acetate 8 PVA 97 0.87 orange Satin Viscose 8 gelatin 94 0.79 (none)

Persulphate Activation Hydrogen peroxide and a number of organic and inorganic

persalts inhibit the generation of chlorine dioxide in hot chlorite bleaching solutions, and some are constituents of commercial activators and stabilisers. But permono- and perdi-sulphates cause generation of chlorine dioxide at high pH values; thus ammonium perdisulphate liberates chlorine dioxide from a cold concentrated solution of sodium chlorite (120 g/L) at a similar rate to that obtained in activation by the same molar concentra- tion of formaldehyde (Figure 4), but without an induction period. Mixtures of Laporte liquid chlorite with ammonium per- disulphate (pH 9-2) and potassium perdisulphate (pH 12.1) show no induction period. Thus the pad-liquor cannot be stabilised merely by adding soda, as with the formaldehyde system; a suitable fume suppressor is sodium perborate, but this eliminates chlorine dioxide and inhibits bleaching at 20°C.

Stability of pad-liquor and acceleration of bleaching are achieved in the following recipe -

Concn. (g/I.)

80% sodium chlorite 20-30 Cellofas B 300 (sodium carboxymethylcellulose) 1 soda ash 0- 1 potassium permanganate 2 ammonium perdisulphate 4 wetting agent 1-3

When permanganate is present, the stability of the pad- liquor can be controlled simply by the amount of sodium carbonate added, and varies from 1 to 8 h at 20°C in this con- centration range; this permits some compensation for seasonal variations in padding and storage temperatures. For Laporte chlorite solution (324 g/l.), the recipe is altered to 50-75 rnW chlorite solution and 0.5-1.5 g/l. soda ash; the remainder of the recipe is unchanged. Cellofas B 300 (or other forms of sodium carboxymethylcellulose of similar viscosity) acts as a suspending agent for the hydrated manganese oxides; persulphate is thought to act by simultaneous oxidation of chlorite to chlorine dioxide and decomposition to sulphuric acid and ammonium sulphate, which together cause the pH of the liquor on the cloth to fall to around 4. The reaction is unaffected by gelatin size and starch; it goes virtually to completion (because of the accelerator), so that less chlorite is required than in the formaldehyde system (16-24 g/l. for grey cottons, at 80% pick-up). Chlorine dioxide is generated later, enabling larger batches to be made, and after storage the batches are free from fumes.

Cloth stored overnight after padding with this solution has a brown colour (from the manganese oxides) which is then removed by a short hot treatment in a mixture of reducing and sequester- ing agents (see later). The cloth can be rinsed and dyed, or given an alkali boil to remove fat and wax, and to promote wettability before dyeing.

Some typical results on grey union and all-cotton fabrics are shown in Tables 6 and 7. The whites obtained were considered suitable for dyeing; mote colour was light enough for all colours demanded by converters of union brocades; fluidity was very low (2-3.4), and wettability (7) of some cotton samples after a short soda boil and ironing at 150°C was as high as v&= 0.4.

TABLE 7 Bleaching Starch-sized Cotton Fabrics

Fabric Weight Chlorite Reflectance Colour of (oz/yd2) used (%) factor residual motes

American 5 96 0.77 (none)

American 5 98 0.82 (none)

American 10 98 0.75 (none)

Indian drill 9 97 0.82 cream Egyptian 3.5 92 0.78 (none)

Miscellaneous uses The formula has no advantage over chlorite-formaldehyde for clearing oil stains, but is far superior for stripping anthraquinone dyes from cellulose acetate and nylon, and also from Terylene if they were applied by means of a carrier. On these materials most of the manganese oxide rinses off, and clearing with bisulphite-EDTA is much more rapid than it is with cotton.

It must be conceded that, on all-cotton and cotton union fabrics, clearing of the brown colour is the main disadvantage; this frequently requires 4 ends (40min) on the jig. But this disadvantage is small compared with the advantages.

Practica I Points 1. Padding

Cold-pad chlorite systems rely on generation of chlorine dioxide in the roll and, in order to cope with occasional irregularities in formulation, it is usual to provide a fan at or near floor level at the pad-mangle and the stillage. If fumes develop in the pad-box, this should be emptied at once and rinsed out well before proceeding. Chlorite-formaldehyde pad-liquor has limited life, and a cheap way of ensuring continuity is to use two storage tanks alternately. More economical use of chlorite is possible if it is applied by proportionate feed, in a wet-on-wet pad-box, to cloth that has been rinsed well; if the components are metered separately from two tanks, more concentrated mixtures can be used safely. It is important to prepare the pad-liquor carefully, by mixing each component thoroughly with plenty of water in a bucket and tipping them in the order shown into the bulk of the water, with efficient stirring. It is imperative that the temperature be kept below 30°C (86°F). On no account must brass or copper parts be allowed to come into contact with the permanganate-persulphate-chlorite solution, since they catalyse decomposition of persulphate, causing generation of gas. Stainless-steel padding boxes are not corroded by alkaline chlorite solutions.

Some types of rubber bowls will disintegrate if solvent- detergent (e.g. BRRASK PS 5 ) is used with chlorite for removal of cleaning rings or of actual oil stains; a chlorinated rubber withstands this double attack.

2. Batching-up After padding with chlorite, the batches should be covered

with polythene or, failing this, several layers of wet cloth, the outer layer being saturated with weak bisulphite. In peroxide bleaching, thermal insulation and prevention of drying-out are important; polythene sheeting is again suitable.

sheeting

sheeting

drill

poplin

46 JSDC FEBRUARY 1965; FOX

3. Washing-off Peroxide-bleached batches require a hot soda boil for

maximum whiteness (reflectance factor 0.84-0.87). Cloth bleached with chlorite-formaldehyde may retain fumes and must be unrolled from under the surface of bisulphite solution. Cloth treated with permanganate-persulphate-chlorite needs washing- off in hot bisulphite, oxalic acid, or neutral hydrosulphite, together with sequestering agent; this is particularly suitable where an alkali scald to confer wettability follows, or where a size is present which coagulates in acid solutions.

CHEMICAL COSTS

Cold bleaching of 100 lb of grey all-cotton fabric is likely to cost 5s. if 5-volume peroxide (improved pyrophosphate recipe) is used and 6s. for chlorite-formaldehyde (25 g/l. 80% chlorite) or accelerated permanganate-persulphate-chlorite (20 g/l. 80 % chlorite); there is a small extra cost for reducing agent in the

chlorite processes. By comparison, the chemicals for a pad- steam peroxide or chlorite bleach would cost only 3s.-4s., but to this must be added the cost of steam, the high cost of special equipment, and the fact that heat-sensitive material may be damaged. * * *

We thank Mrs P. Thiele and Miss S. Whitelegge for their help with the experimental work. (MS. received 14th August 1964)

References I Chesner, L., J.S.D.C., 79 (1963) 139. 2 Freytag, R., Teintex, 25 (1960) 323. 3 Idem, Bull. Inst. Text. France, 17 (1963) 541. 4 Nuessle, A. C., Amer. Dyestuff Rep., 52 (1963) P565. 5 Hall, J. A. D., Dyer, 126 (1961) 295. 6 ‘British Standards Handbook No. 1 l’, 1963 edition, p. 376. 7 Ref. 6, p. 334. 8 Leigh, R. A., J. Textile Inst., 52 (1962) T 557.

Com municati on S

Wet and Dry Boundaries on Cellulosic Textiles and their Influence on Dyes and Dyeing-II

M. R. FOX Imperial Chemical Industries Ltd, Dyestuffs Division, Hexagon House, Blackley, Manchester 9

In Part I ( I ) , previous studies of the formation of brown evaporation marks on cellulosic textiles were discussed. Experimental work is now described which relates to the dyeing of cellulosic textiles with (a) reactive, (b) direct, (c) vat and azoic, and@) phthalocyanine dyes. The colour reactions produced at wet-dry boundaries are interpreted in terms of the initial formation of the free dye-acid, apparent local loss of effective sodium ions, and subsequent reduction of the dye; the cellulose in the boundary area is physically and chemically modified. Reaction is not confined to dyes covalently linked with cellulose. The presence of sulphonic acid groups can be a significant factor in the course of reactions at the boundary; non-sulphonated dyes, although capable of undergoing colour changes at the time, do not give rise to discharge effects or fibre re-wetting problems. On the basis of this work a tentative explanation of the tendering of cotton by Sulphur Black is advanced. Experiments on the dyeing of cotton

suggest that these could lead to a better understanding of listing problems in jig dyeing.

Experimental REACTIVE DYES

Since reactive dyes are covalently linked to cellulosic fibres through the hydroxyl groups of the cellulose and the boundary effect is clearly caused by a chemical reaction at the hydroxyl sites in the fibre, cotton dyed with reactive dyes was examined at an early stage in this investigation.

A pattern 24-in. square was taken from a year-old 1.5% jig dyeing of Procion Brilliant Red M-2BS (C.I. Reactive Red 1) on bleached mercerised cotton. This was suspended at room temperature in open width over distilled water in a stainless-steel vessel so that the lower edge of the cloth made free contact with the water. About one hour after the start of the experiment it was found that the cloth was no longer in contact with the water and wicking had occurred upwards for only two or three inches. A primary boundary was formed which will be referred to later as X; its significance was not recognised at the time. The pattern was lowered to the water surface again and the boundary eventually became static for about 6 h, roughly 8 in. from the bottom of the cloth. The water supply was removed and the pattern allowed to dry at room temperature overnight. The boundary line was clearly marked by a narrow zone of soluble red dye which readily transferred to wet cloth pressed on to it. Collection of hydrolysed dye in this way was not unexpected, because (a) the dyeing was an old one and this particular dye is prone to bleeding on storage and (b) no precautions to avoid this defect, e.g. by treatment with Triamine PR (ICI) (2) or Fixanol PN (ICI) (3), had been taken at the time the dyeing was made.

Immediately above the region where soluble dye had collected was a paler bluish red zone about 2 mm wide, which fluoresced

strongly under U.V. radiation. The cloth was ironed (surface temperature of electric iron 120°C) over both back and face for 30 s and allowed to age over steam in air for about 1 min, until the original colour was restored. This process of ironing and ageing was repeated six times in an attempt to accelerate the normal regain of moisture and its loss by drying which occurs during the life of cotton materials. By this time the original bluish red zone had discharged almost completely to white and, furthermore, the primary boundary X- quite unexpectedly, since the presence of this line had been forgotten and it could not be observed in daylight before ironing and ageing- became completely discharged to a white line across the piece (Figure I ) . The discharged lines still fluoresced under U.V. radiation. It should be noted that the free-acid form of Procion Brilliant Red M-2BS is bluish red and is particularly easily destroyed by reduction.

The above experiment was repeated on another piece of the same dyeing after it had been re-soaped to remove the hydrolysed dye produced by long storage; completely new jig dyeings and pad-steam dyeings were included in parallel tests. All these behaved similarly, except that very little unfixed dye was collected by capillarity; the bluish red zones were present at the boundaries, however, and these formed the white discharge lines on acceler- ated ageing by ironing and steam-airing. It was also found possible to produce the discharge effects by replacing the ironing and ageing treatments by two 15-min bakings at 120°C, ageing over steam in air between each baking. Similar, but less specta- cular, behaviour was found with dyeings of Procion Brilliant Orange M-GS (C.I. Reactive Orange 1); here the original boundary was marked by a yellower zone, which gave a partial discharge when ironed and aged six times as above.