Mau 1941 WHITT.AIUGR-“THE INDIVIDUALISM O F DYES” 146

The Individualism of Dyes C . M. WHITTAKER

The views expressed in this conimunication are the personal views of the present author and must, under no circumstances, be connected with the Company of whose staff he is a member.

The dictionary assigns many meanings to the word “individualism”, amongst which is

personal peculiarity”; it is in this sense that tnhe word is used in this communication.

The present tiuthor’s experience in a very debiled study of viscosc. rayon dyeing during the last 20 years. c+oupled with his previous experience with other fibres and dyes, has convinced him with ever-increasing emphmis that unless the individualism of the dyes used by a dyer is known to that dyer, he cannot use them intelligently. The present author has appealed to the dye manufacturers to extend this information in their publications, but the response up to the preAent time has been disappointing. It is worthy of comment that hhe individualism of the group of azoic dyes has been studied in the greatest detail, and the results have been distributed to the dye user in the most complete form. The other groups of dyes could, in the present author’s opinion, be treated in a similar detailed manner to the advantage of both dye manufacturer and user. On the contrary, the determination and publication of the individualism of many of the direct cotton and vat dyes have been carried out by the research staffs of the manufacturers of specific synthetic fibres.

The determination of the behaviour of the direct cotton dyes with viscose rayon of variable dyeing affinity proceeded through empirical stages from 1921 onwards until the publication of the work of Boulton and Reading1 (1934), based on an accurate determination of the time of half dyeing, which finally placed the classi- fication on an exact basis. The published Table also gives a most exact classification of the direct cotton dyes from the point of view of their levelling properties.

When the empirical so-called “temperature range” test was published in 1931, the present author made a personal tour of the laboratories of the British and Continental dye makers, and asked the responsible officials t o use i t in the determination of the suitability of their direct cotton dyes for viscose rayon, and to broadcast the results. The reception of the suggestion in one quarter remains one of the humorous memories of the prevent author, because the opinion was backed with voluminous notes on why the test failed in their several laboratories: subsequently, it was adopted as the method used for this purpose in discussing the properties of new direct cotton dyes at their periodical conferences.

I 6

AY

Boulton and Morton2 (1939) have published a most valuable study of the vat dyes, and from the classification therein it niay be seen why vat dyes are more difficult to apply than direct cotton dyes.

The necessity for determining the indi- vidualism of dyes is clearly illustrated by the fact that there is a variation in the time of half dyeing of the two extremes in Boulton and Reading’s’ Table of 1:4(HM). Any dyer who mixes dyes from the two extreme ends of the Table is sure to encounter trouble. The golden rule in choosing dyes for compound shades is, of course, to choose those dyes which dye on at as near the same rate as possible.

The information to be derived from Boulton and Reading’s Table is of the highest value, but it requires to be supplemented by informa- tion on the salt sensitivity and effect of the dyeing temperature on the individual dyes, because these do not necessarily follow the order of Boulton and Reading’s Table, which specifically relates to the behaviour towards variable dyeing viscose rayon.

Salt sensitivity varies very widely with the different direct cotton dyes. Neale has shown that pure cellulose and a pure direct cotton dye free from electrolytes have no affinity one for the other. Commercial dyes are usually standardised to type with common salt in Great Britain and with sodium sulphate on the Continent. It is advisable, therefore, for those whose dyeing processes take place in a small liquor-material ratio that they should use dyes of the highest possible concentration. Fortun- ately, war conditions and shortage of packages have recently compelled the general supply of more concentrated brands. It is to be hoped that these will be retained after the war as a contribution to the more intelligent control of dyeing with direct cotton dyes in short liquors. The rate of exhaustion and salt sensitivity of two strengths of the same dye are illustrated by the following examples-

If dyed at 90” C. for 20 min. in 10 volumes without salt on “Fibro” (13 denier per filament) 1% Diphenyl Blue M2B shows an exhaustion of SOYO, whereas 0*33O/, Diphenyl Blue M2B 300% shows an exhaustion of only 19%; in other words, the presence of 67 parts electrolytes in 100 parts of Diphenyl Blue M2B as delivered to the dyer increases the degree of exhaustion under the above conditions by 40% as compared with a corresponding equivalent of Diphenyl Blue M2B 3000/,. 1% Dipheriyl Fast Red 7BL dyed under the same conditions gives an exhaustion of 64o/b, but an equivalent strength of Diphenyl Fast Red 7BL lSO%, viz. O*5S3/bt gives an exhaustion of only 33%; in other

146 WHITTAKER-“THE INDIVIDUALISM OF DYES” May 1941

words, 0.44% common salt added to 0.56y0 Diphenyl Fast Red 7BL 18070 increases the degree of exhaustion 31%.

These facts show the imperative necessity of strict control of salt additions when dyeing direct cotton dyes in short liquor-material ratios. In the cases quoted above, this means only 0*5y0 salt calculated on the weight of material, so it will readily be seen that the addition of 5% in one lot would be liable to cause serious troubie.

In contrast, 0.66% Benzopurpurine 4B 1800/, gives an exhaustion of 91% under the above conditions of dyeing, as against only 33Y0 for 066% Diphenyl Fast Red 7BL lSO%, a very striking example of the varying individualism of two direct cotton dyes, which immediately indicates that Benzopurpurine 4B is much more difficult to apply in small liquor-material ratios than Diphenyl Fast Red 7BL.

The present author’s contention is that, if the dyer is not in possession of the variation in the different individualism of the various members of the same group of dyes, he is, inevitably, incapable of dyeing them with that best of all dyeing assistants, viz. common sense.

The group of cellulose acetate rayon dyes includes dyes of the most varying individualism; there may be enumerated, for example, the variation in the building-up property of. the dye when dyeing heavy shades. Duranol Brilliant Blue G and Duranol Blue CB show a great contrast in this respect. The varying susceptibility of some cellulose acetate rayon dyes, particularly blues, to the nitrous acid present in burnt gas fumes3 (Rowe and Chamber- lain, 1937) is a striking example of individualism which has been a great source of trouble and expenee to the dyers of cellulose acetate rayon. The migration test devised by the present author4 is one more illustration of the widely varying degree of ease with which solid solution occurs in cellulose acetate rayon.

If the class of vat dyes is considered, it is found that its members possess most pronounced individualism. Indeed, the differences in their individual peculiarities are so wide that some refuse to mix with others, whilst if some vat dyes condescend to agree in the dyebath sufficiently well t o give an acceptable compound shade, it may be found that one of the dyes will destroy the other on exposure to light, although the destroyed dye, if exposed in a self shade, is faster than its destroyer. More than one yellow vat dye, all of which are inferior to Caledon Jade Green in fastness to light as self shades, will, when mixed with Caledon Jade Green, destroy the fastness to light of the latter colour. Paradone Yellow GC and Hydron Yellow NF are examples of this type of yellow, whereas Paradone Yellow G does not impair the fastness to light of Caledon Jade Green. Even the aristocrats of the vat series will occasionally reveal astonishing

weakness to some subsequent processing. The present author receivcd a complaint from Australia that a dyeing of Caledon Jade Green was not fast to bleaching. This complaint was received by him with scepticism, until further details were availuble. These revealed that the bleaching process had been carried out in an acid permanganate bath and, true enough, Caledon Jade Green breaks down under the test, but if the alkali which develops in bleaching with pernianganate is “killed” with magnesium fiulphate instead of sulphuric acid, the shade withstands the treatment.

The vat dyes, like the direct cotton dyes, show wide variation in their rate of dyeing on cellulosic fibres so that, unless these variations are known, it is impossible to obey the golden rule of dyeing that compound shades should be dyed with dyes which dye on at the same rate. The present author always avoids the use in the same dyebath of Rtrong and weak alkali vat dyes, because of the wide variation in their rate of dyeing. This precaution is particularly necessary when dyeing viscose rayon. It is also his experience that the individualism of the vat dyes is so pronounced in their rate of dyeing that no product recommended as a retardent in the dyeing of these dyes has yet been marketed which is capable of retarding their different individual affinity to uniform rate of dyeing; a retardent fulfilling these ideal conditions would find a ready sale.

Another direction in which vat dyes show marked individualism is the fact that some of them tender cellulosic material during the actual dyeing, unless the appropriate precautions are taken by adding tannic. acid or sulphite cellulose waste liquor. The present author has more than once had the disconcerting experience of seeing viscose rayon yarn almost drop off the rollers during dyeing when using such vat dyes, until he found that sulphite cellulose waste liquor prevented it. Subsequently, I.G. Farben- industrie A.-G. patented the use of tannic acid for the same purpose.

Individualism of the vat dyes is just as pronounced in their behaviour on exposure to light and atmosphere. The work of Scholefield, Haller, and the present author and his colleagues in this field has resulted in the tendering vat dyes being segregated from the non-tendering dyes, so that no dyer can plead ignorance nowadays if he uses a tendering vat dye for casement fabrics.

The most recent developments in textile chemistry, such as the Tootal anti-crease process, the introduction of special auxiliary products, e.g. Fixanol, and the basified fibres, e.g. “Rayolanda” X, have all shown strikingly different effects on the fastness to light of the dyes available, which has compelled a rigorous selection of the dyes, the fastness to light of which is not depreciated by the above develop- ments.

M5tl1941 WILCOCK & TATTERSFIELD-“TESTS FOR IDENTIFICATION OF ‘RAYOLANDA’ X” 147

The real cause of these differences still requires further elucidation; in fact, it may be confidently stated that a study of the reasons of varying individualism in dyes offers a wide variety of research problems, the solution of which would be valuable, both to the manu- facturers and users of dyes.

It is a curious fact that the destructive effect of one dye on another, when used in compound shades, on exposure to light, is confined to dyes of the yellow portion of the spectrum as the destructive factor, e.g. Oxyphenine 2 6 amongst the direct cotton dyes, and Anthraflavone GC amongst the vat dyes.

Another curious fact is that in the group of direct cotton dyes, the yellows include the fastest-to-light members of the group, whereas in the group of vat dyes and the group of

sulphur dyes, the yellow members are the weakest in light fastness. On the other hand, direct cotton blues, greens, and greys are, in general, inferior in fastness to light to the direct cotton yellows, whereas the vat blues, greens, and greys are, in general, very much superior in light fastness to the vat yellows; in other words, they show a complete reversal in relative light fastness properties when compared with those exhibited by the direct cotton dyes. (Received 6th March, 1941)

REFERENCES Boulton and Reading, t,hia Jour., 1934, 60, 381.

Rowe and Chamberlain, ibid., 1937, 58, 268. * Boulton and Morton, ibid., 1939, 66, 481.

‘ Whittaker and Wilcock, Dyeing with Coal Tay Dyeatuffa, 3rd edition, p. 234.

Tests for the Identification of “Ravolanda” X C. C. WILOOOK and

Within the last few years there has been considerable research activity on methods for basifying or animalising cellulose. At the present time, however, the only fibre of this type commercially available in this country is “Rayolanda” X, produced by Courtaulds Ltd. by a patented process.

As “Rayolanda” X is being used to an increasing extent to produce novel effects in conjunction with other fibres, it is of some importance that its presence in blended yarns and fabrics should be easily recognisable. The blends which are most likely to be met with in practice are those with wool, “Fibro”, cellulose acetate “Fibro”, and cotton. Providing the blended material iR undyed or only dyed to a light shade, the presence of “Rayolanda” X may be recognised by immersing for 5 min. in a cold solution of 0.5 g. of level dyeing acid dye and 0.5 C.C. of 80% sulphuric acid per 100 C.C. water, and then well rinsing. Suitable dyes are Xylene Light Yellow 2 6 (Colour Index, No. 639), Aao Gerariine 2GS (Colour Index, No. 31), and Erio Fast Cyanine 5 conc. (Colour Index, No. 1054); the choice of dye should be made so that it contrasts with the ground shade of the dyed material. Under these conditions “Rayolanda” X and casein fibre (cf. this Jour., 1937, 63, 468) are heavily stained, whereas wool, “Fibro”, cellulose acetate “Fibro” and cotton are only slightly stained, if stained at all. The presence of wool or casein fibre can be confirmed by a burning test or by Millon’s reagent, and cellulose acetate “Fibro” by its solubility in acetone.

It will be readily appreciated that staining tests fail when heavily dyed material has to be examined. Microscopical examination enables wool and cotton to be readily identified, but

4

C. P. TATTERSFIELD lt DENIER FIBRES

(a) Before i m w r e h in (%prammoniuni SdzUim

does not distinguish between “Rayolanda” X and “Fibro” and, therefore, a further test to distinguish between these two latter fibres is required. If, however, the material nuspected