the use of indicator-dyed wool to control certain textile operations

OC~. 19271 KING-“USE OF INDICATOR WOOL TO CONTROL TEXTILE OPERATIONS” 321 - ~-

Application to Oi2s and Varnishes.-& in the textile trade so in the oil and varnish trade, the same crying need for fastness soon made itself apparent by the increasing volume of inquiries for colours capable of forming fast lakes soluble in various solvents.

It is very doubtful whether the vat colours form stable lakes with aluminium, calcium, or barium salts. The need for forming the lake, however, does not arise, since these colours, being insoluble in water and dilute acids, perform the functions of ordinary lakes. The lake maker purchases Alizarin and forms the aluminium lake to give a red pigment, and Caledon Red BN, when dried, provides a similar pigment, although much faster. Un- fortunately, most of the vat colours are marketed in the form of aqueous suspensions, and these cannot be used for mixing with oils and varnishes. Also when these aqueous sus- pensions arc filtered and dried, most of the covering power of the pigment is lost, because the dried pigment is not in the same h e state of division as the aqueous suspension. If an ordinary vat colour paste is upset on the floor, a heavy coloured stain results, but if the colour paste is dried and then mixed with the same amount of water as previously, no stain will be obtained if a portion is upset on the floor.

The problem before the colour maker was thus to supply these fast vat colours in the form of pastes suspended in some other medium, such as linseed oil, turpentine, butyl alcohol, or ethyl acetate. This has now been done.

In studying this problem some interesting points emerged. A colour such as Caledon Red BN will only give one shade of varnish, varying in body according to the amount of colour used and the number of coats given. In order to obtain lighter shades of pink, this pigment must be mixed with a white pigment; the light pink cannot be obtained by using less colour. This, of course, limits very much the range of shades available.

For dopes and other forms of varnish, solution of the colour in the solvent is not necessary, the colour being produced BUS- pended in the required medium and mixed intimately to form the coloured dope. The use of these fast colours for oils and varnishes is still incompletely explored. The demand for increased fastness, however, will force the market to adopt this suitable and extremely fast series of colours. They are admittedly much more expensive than ordinary metallic lakes, but the cost is decreasing, and as the scope of their application is widened, and the demand thus increased, they will undoubtedly be economically introduced into this branch of the colour trade.

COMMUNICATIONS

The Use of Indicator-Dyed Wool to Control Certain Textile Operations*

A. T. Kma, B.Sc., F.I.C. (British Research Association for the Woollen and

Worsted Industries)

The work described in this paper is a practical outcome of an investigation, not yet fully completed, on the sorption of sulphuric acid by wool.

The idea occurred in the course of this work that if acid- or alkali-sensitive indicators could be dyed on the wool, a valuable means might be afforded of directly estimating, from a com- parison of the colour change against standards prepared once and for all, the amount of acid or alkali absorbed by wool from any given solution; and in view of the great simplification which such a device would achieve in the study of numerous problems connected with acid or alkali on wool, search was made to find dye- s t d s suitable for this purpose.

Experiments have been made with a large number of substances which possess the pro- perty of both dyeing wool and of changing colour on the dyed wool in presence of acids or alkalis. These have been termed indicator- dyestuffs. The great majority were found to be lacking either in sensitiveness or in fastness, but after eliminating these it has been found possible to construct a series in which each member undergoes its colour change a t a different strength of acid or alkali. In this way, on placing the dyed patterns in solutions of gradually increasing strength, e.g. of sul- phuric acid, before the most sensitive has com- pletely changed in colour the next in sensitive- ness begins to change, and so on throughout the series. Thus from a colour chart the amount of sulphuric acid or of alkali taken up by wool or cloth in a given treatment can be estimated by matching an indicator-dyed test piece put through at the same time.

Also, these indicator-dyestuffs will show automatically any uneven distribution of acid or alkali, and thus the causes underlying numerous technical problems in which acid and alkali are concerned may be ascertained. Valuable results have already been obtained (see p. 324, A, B, and C).

Characteristics of Indicator-Dyestuffs.-The first two requirements, fastness on wool and sensitiveness to acids and alkalis when dyed on wool, are rarely met with in the same substance.

The usual indicators employed in titration of acid and alkali, e.g., Litmus, Phenolphthalein, Methyl Orange, or Methyl Red, are useless, as they are incapable of being dyed satisfac- torily upon wool; and most commercial dye- stuffs, although in numerous instances quite

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Published privately, fjeptember 1923.

322 KING-“USE OF INDICATOR WOOL TO CONTROL TEXTILE OPERATIONS” [Oct. 1917

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sensitive in solution to acids and alkalis, are almost inert to these reagents when dyed on wool. This, naturally, is a requisite for good commercial dyes. In fact, although a large number of dyes known to be sensitive in solution have been examined, only a few, mostly of the Congo Red type, were found to have any reasonable degree of sensitiveiness to acids when dyed on wool. Congo Red itself was found to be the most sensitive of these, but like its congeners, Benzopurpurin &c., it has the defect of slowly bleaching when left standing in sulphuric acid solution.

In addition, the behaviour has been examined of the class of pH indicators,* which are used in the measurement of hydrogen ion concentra- tion (see Clark’s “Determination of Hydrogen

I Thymol Blue Thymol sulphon-

Broin Phenol Tetrabrorno-

phthnieln

]Hue phenol sulphon- P phthalein

8 1,acmoid ... % Brom Cresol Dibromo-o-cresol M Purple siilphon-

- e

pht halein

Brom Thyniol Dibromo-thymol Blne sulphon-

I phthalein

Indicator Constitution

Tons,” 1920).

A

I3

C

D

E

Ref.

Indicator

Carbonising

H2S04 In dye- bath

Acid milling

Yellow, orange-red, t,o 4.5-7 N/lO-N/1.2 O.G%-4% magenta red

Blue, greenish-blue, to 3-5 N/SOO-N/lO 0.01 %-0.5”/, yellow

Slate blue to puce red 1.5-3.5 N/l,OOO-N/GO 0~005”:,-0~1%

Rrom Thymol See above E Blue

0 2 Plieriol R P ~ ... Phenol sulphon- F 0“ phthalein 0 2 Cresol Rrd % .

Thymol Bhic ...

Rrom Tiiymol See above

9 I 1 Blue

o-Crewoi sulphon- 0

See above A

phthalein

- 2 Plieriol R P ~ ... Phenol sulphon- F 0“ I phthalein I

do.

Plece scouring with alkali

NaeCOa solution. Y~llow to purplish red

Yellow to slate blue

.-

indicators themselves towards acids or alkalis as the case may be. These are eminently suitable indicators for the purpose in view.

The third requirement, that a series of indicator-dyestuffs should be found of such change-points (see footnote) that a wide range on both the acid and alkaline sides of the neutral point can be controlled by pach indicator of the series coming successively into play, when dyed upon the wool, is also fulfilled by the series of sulphonphthalein indicators.

Scheme of Indicator-Dyestuffs 8elected.-The range eventually adopted is made up from the Clark and Lubs series of indicators, with the addition of Lacmoid (see Table I.).

For the more exact relation of the amount of reagent taken up to the tint produced on the

TABLE I.

Neutral-N/1,000 NeiitraI4~005Y, I o-E I For leaving Purpllsh, dirty blue to WMJI faintly yellow acid

Neutrailslng Blulsh-green to yellow Neutral-N/10,000 Neutrsl-0’0005%

Colonr Change with Applications Increasing Strength

of nlkall

Scouring and Bluish-green to brighl washing-off, blue soap mlliing

Many of these proved valueless for the purpose, being devoid of, or very deficient in, dyeing properties, but some, notably those of the sulphonphthalein type introduced by Clark and Lubs, possess excellent dyeing properties, and wool dyed with them retains, although in diminished degree, the sensitiveness of the

‘With ordinary Indicators the change point (“neutral” or “end-polnt”) is not that of ahsolute neutrality as scientlflcully understood. but is suficlently near it for general work. Aim no Indicxtor gives a perfectly shnrp change p ~ l n t , be t for each thpre I s a small range of alteration In strength of the solution either on the acid side or the alkaline slde of absolute neutrality: over which t h ~ enlour of the Indlcator progressively changes.

With the p H indicators a series can be arranged with thelr change points occurring successively the first in thr series changing rnlour a t a point well on the alkali& widp nnd the last a t a point well on the arid side. Their purpose ls’thus rather to indicate within narrow llniits, the degree of acidity or alkalinity of a 8 0 1 ~ . tlon than to nRcertain the point of approximate neutrality Uener- ally’speaking the further the change point I s from the ‘absolute nentr~ti point’ the Less sensitive Is the Indlcator i.e the greater the rhnnge 11; strength of the solution necessary’ to ‘domplete the colour change.

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indicator-dyed wool a colour chart is in course of preparation.

Thus Thymol Blue dyed cloth registers, by means of its change of colour from yellow to red, over a range of 4.5 g. to 7 g. of sulphuric acid sorbed by 100 g. of (dry) cloth, and also gives the strength of d p h u r i c acid solutions with which i t is in equilibrium, from 0.5% up to 4% acid.

Different Behaviour of Free and Dyed Indi- cator.-A much greater range of acidity is given by the indicators when dyed on wool than when used in solution in the ordinary way, e.g., Thymol Blue in solution is completely changed with 0.25% sulphuric acid, whereas to produce the same change on the dyed wool requires a solution of nearly 4y0, or 15 times the strength. This difference in behaviour is of considerable

Oct. 29271 KING-"USE OF INDICATOR WOOL TO CONTROL TEXTILE OPERATIONS" 323

significance theoretically in connection with the question of how the acid and dyestuff are attached to the wool, and the theory of dyeing generally.

From the practical standpoint the device of utilising the colour change of indicator-dyed wool as an automatic register of the progress, as well as the completion, of operations involving treatment with wide ranges of strengths of acid or alkali represents a new departure in methods of control and of analysis. The eye soon becomes practised to the colour values, and observation of the control sample, which is passed through the process along with the goods under treatment, shows when the re- quired change is completed.

Automatic Record of Unevenness of Treatment. -The method is especially valuable in auto- matically demonstrating any unevenness of acidity or alkalinity which may be developed in a given treatment; this being impossible by any other known method.

The accompanying photograph of a piece of Brom Thymol Blue dyed cloth wetted out,

BIG. 1-Brom Thymol Blur Indlrator Cloth, showing unequal dis- tribution of Alkali.

dropped into ho/" potash olive oil soap, and left immersed for an hour, illustrates the sensitive- ness of the indicator. The dark parts are blue (alkaline), the light parts yellow (still acid with acetic acid from the dyebath). Intermediate tones correspond to bluish-green and yellowish- green shades. The contrasts are quite well marked in the photograph, but less striking than those in the original.

Attempts to discover such unevenncss by chemical analysis are always of uncertain value, since the samples have to be taken haphazard, and in any case the result cannot show the

-4 5

extremes of variation, but only the average over the sample taken.

Tating Carbcmised Wool.-Reference will be found in the literature to the testing of carbon- ised wool by pressing the moist wool with litmus paper or the like, the wool being considered fully neutralised if the litmus paper is turned blue. Such tests may be entirely misleading. Carbonised wool after scouring will have sufficient surface soap and alkali to give the alkaline reaction, and yet may contain much free acid in the interior of the fibre. Such, in fact, is usually the case. The same objec- tion applies to spotting the wool or cloth with indicator solution. Even with homo- geneously acid or alkaline wool, on pressing with wet indicator test paper, or spotting with indicator solution, th? indicator only notes the acid or alkali removed from the surface of the wool by the solution or wet test paper applied, and gives a t best only the roughest approxi- mation to the quantity actually present in the wool fibre. Thus out of a dozen different samples of scoured carbonised wool, placed in water with Brom Thymol Blue, one showed a momentary alkaline reaction, the remainder a definite to strong alkalinity. On standing they all eventually turned acid in reaction, showing that the fibres themselves were acid, although covered with an alkaline soap layer. Indi- cator-dyed wool or cloth, however, registers an acid condition of the fibre in spite of surface soap and alkali, and also registers the gradual removal of acid as the process of neutralisation proceeds, The slowness of neutralisation of sulphuric acid sorbed by wool needs emphasis. Carbonised cloth has been observed to retain acid after agitating for half an hour either in 4% sodium carbonate, or in soap solution which was lathering strongly.

Method of Dyeing the Indicators.-All the indicators can be satisfactorily dyed from an acetic acid bath (1% acetic acid on the weight of cloth) starting in the cold, and raising very slowly to the boil, as the colours tend to rush on, especially in the case of Brom Phenol Blue.

It is desirable from the scientific standpoint to use the minimum amount of indicator commensurate with a good colour change on making acid or alkaline, and also to use chemic- ally equivalent quantities rather than equal weights, in order to have the same reacting quantity of each indicator per unit weight of wool; but for use in technical operations the percentage of dyestuff is, within reasonable limits, immaterial, so long as the same amount is adhered to for both the recording and match- ing samples.

A convenient basis is 0.02% of Phenol Red (which has the lowest molecular weight of the series), and for the other sulphonphthalein colours this quantity is multiplied by the ratio of the molecular weights (see table below) in order to have chemically equivalent quantities

324 BARKER, HIRST & WARDLE-“FADING POWER OF SUNLIGHT &c.” rod. 1927 __-.

Brom Phenol Blue Brom CresolPu le Brnm Thymol B7)ue Phenol Bed... ... Cresol Red ... ...

in each case. For the small scale dyeings the colour was dissolved with slightly more than its equivalent of caustic soda and made up to 0.2 g. per l., so that 100 g. of cloth require 100 C.C. of Phenol Red, or 100~-=176 c c. of Brom Thymol Blue, and

so on, as in Table 11.

024 354

TABLE 11.

670 I 1.89 16 j 189 540 1.62 I 20 152 624 1 1.16 , 364 1.0 382 1 1.08 ~ 28 108

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Degree of Fading

Negllgiblc

Marked

Veryslight

Negligible

Negligible Negligible

_ _ ~ Negligible

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For Lacmoid a heavier shade is necessary, and 0.8y0 on the cloth is a suitable quantity. Its behaviour depends, however, on the method of preparing the solution. For the present work the commercial product was extracted with hot water and the sparingly soluble residue rejected. The solution was made up to 0.2% and allowed to stand a few days. A precipitate separates, which must be filtered off, as i t dyes the wool but is practically non-sensitive, and if left in the solution alters the shade and reduces t4he ~lensitiveness of the Lacmoid itself.

Fatness of Indicator-Dyutuffs on Wool,- (1) Fastness to A&&-All the indicator dyes in Table I. are reasonably fast to sulphuric acid in cold solutions up to 5%. (2) F a a t w e to AlkaliSodium carbonate up to 0.5% is without serious effect on the indicators A to E during one hour’s contact, but colour is lost if the period is prolonged. With ordinary soap solutions the loss is negligibly small. F and G indicators are definitely loose to 0.5% alkali, and lose colour appreciably even with weak alkali and soap. Efforts to find more suitable substitutes with the same ranges of sensitiveness have so far been unsuccessful. Indicator A, however, overlaps E sufficiently well for most practical purposes. (3) Fastness to Light-It will be noted that with the exception of indi- cator C (Lacmoid) all the indicators can be made yellow on cloth with an appropriate amount of acid. In this form the dyed cloth is reasonably fast to light, and can be stored without deterioration. Table 111. shows roughly

__ Alkaline Degreeof I F a n g

Dirty bull Sllght

Full blue Deflnite Slate-blue Slight

Purplish-blue Strong

Blue strong

Mauve Marked Dull purple Slight

TABLE I11

Indicator AcldlIled I - Thymol Blue ... Brom Phenol

Blue ... Orauge-yellou

Bluish-grey

Lacmold ... Brom Cresol

Purple ... Brom Thymol

Blue ... Phenol Red . . . Dull yellow

Cresol -&a,. . Yellow

Reddlsh- brow11

Dull yellow Pale yellow

;he vari&ion in fastness to light (on wool) after iwelve hours’ exposure to direct sunlight.

The exposed parts of the yellow test pieces tame up equally well with the unexposed parts )n developing to another colour. The looseness ;o light of other forms than yellow introduces :omplications as regards the preparation of tccurate standards for matching. It is im- naterial, however, for practical purposes, since che control sample does not suffer during the ihort time it is in use, and can be returned to the yellow form until required for use again.

Some Technical ’ Applications.-Valuable re- sults have been obtained on the following- [A) Faults due to migration of alkali during the hying-off of moist cloth or yarn, e.g., in cuttled piece goods and in various types of yarn winding. (B) Scouring and washing-off, i.e., degree of alkalinity developed in the fibre during the gcour, and of residual alkalinity after washing- off. (C) Carbonising and neutralising wool and piece goods.

Mr. R. J. Smith (Chemical Assistant) has rendered valuable assistance in the experi- mental work.

himption of the Fading Power of Sunlight through- out the Year

5. G. BARKER and H. R. HIRST, in co-operation with G. C. WARDLE (Messrs. J. Wardle

and Sons, Leek) In a previous paper (J. Text. Inst., 1920,17,

495), it was indicated that G. C. Wardle, in a private communication, had shown that on exposure to sunlight of patterns dyed with Victoria Blue the results gave values which showed that the fading of the pattern was in close agreement with the variation of sunlight. In ful l sunshine throughout the year the amount of fading was in good agreement with Scott’s light values, whilst for dull light the agreement, though not so good as for full sun, was tolerably good. The results showed that sunlight gives a fairly constant relative fading under all conditions in the case of Victoria Blue. Since this publication further work has been carried out by Wardle, and observations of sunlight have been made daily throughout a whole year, using a Photographic Bee Meter. The results were all related to June midday sun as unit, and expressed as a percentage of this unit. Thus June midday sun became 100 units, whilst January midday sun was found to be 25 units. The table thus obtained is shown in Fig. 1. From this table the hourly values of the light to which the patterns are exposed can be calculated in terms of June midday sun. To allow for variations of latitude similar t+bles can be constructed for any particular place. The photographic light tables issued by Messrs. Burroughs & Wellcome and other firms are sufficient for this purpose.