T H E PHYSICAL CHEMISTRY O F DYEING: SUBSTANTIVE DYES
BY T. R. BRIGGb
The term ‘‘substantive” as applied to dyes was introduced originally by Edward Bancroft’ in the following words. ‘ L T me, ~ however, colouring matters seem to fall naturally under two general classes; the first including those matters, which, when placed into a state of solution, may be fixed with all the permanency of which they are susceptible, and made fully to exhibit their colours in or on the dyed substance, without the interposition of any earthy or metallic basis; and the second, comprehending all those matters which are incapable of being so fixed, and made to display their proper colours, without the mediation of some such basis. The colours of the first class I shall denominate substantive; using the term in the same sense as it was employed by the great Lord Verulam, as denoting a thing solid by, or depending only upon, itself; and colours of the second class I shall call adjectiw, as implying that their lustre and permanency are acquired by their being adjected upon a suitablc basis.” Having thus defined the term and having pointed out that certain coloring matters, adjective to cotton, might be, and actually were, substantive to wool, Bancroft proceeded to describe the substantive colors which m r e available a t that time. His list included Tyrian Purple (the secretion of a certain shellfish), Indigo, Turmeric, Safflower, and the various mineral colors. I n regard to the latter colors it is interesting to read“ that “the afinity between cotton and the oxide of iron is so strong, that by simply moving the former about in water, wherein the sulphate of iron has been dissolved and left exposed to atmospheric air for a few days, it will gradually attract and take to itself every particle of the metallic oxide.” None of the early coal tar colors appears to have been substantive to cotton, and it was not until 1884, when Bottiger discovered Congo Red, that an artificial dye, definitely substantive to cotton, as well as t o wool and silk, became available. Since the introduction of Congo Red, many other substantive cotton dyes have been brought into use, notably the Mikado colors and the Primulines. The majority of these dyes are also substantive to wool and silk. In the modern classification of dyes, adopted by technical colorists, the term “substantive dye” has taken on a rather specialized and narrow meaning. According to Matthew9 the so-called substantive dyes “include derivatives of benzidine, tolidine, diamidostilbene, and various azoxydiamines; they also include certain derivatives of stilbene, such as the Mikado colors. Another class of direct cotton or substantive dyes is not included in the azo dyes
...
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“Philosophy of Permanent Colours,” 1, 118 (1813). ZBancroft: Ibid., 1, 313 (1813). 3 “Application of Dyestuffs,” 275 (1920). 1
SZTBSTANTIVE DYES
3 69
at all, but is derived from certain bases made from sidphur compounds of paratoluidine or its homologues: these form the primuline group of dyes.” The members of this group of dyes, all more or less ‘soluble’ in water, are similar‘ chemically to the acid dyes, being employed in the dyebath in the form of their sodium salts or as the free dye acid; they differ markeclly, however, from the acid dyes in their mode of application to the fiber? In the broad sense of Bancroft’s definition, and because of their marked similarity to the substantive dyes, (as defined by Matthews), in respect of their behavior in the dyebath and toward the fiber, one should include among the substantive dyes the Immedial or Sulphur dyes,3the Vat dyes (such as the leuco form of in dig^),^ suspensions of the inorganic colors,5 and certain colloidal developing agents, such as those of the Naphthol AS series6, Under certain circumstances some of the acid7 and bssic dyess appear t o behave likr substantive dyes. Dyeing with Substantive Dyes, Comparison with Acid Dyes In p r a ~ t i c e the , ~ substantive dyes are employed in either. neutral, acid, or alkaline dyebaths, usually with the addition of an assistant, the action of which is to effect an increase in the amount of color adsorbed by the fiber and to further the exhaustion of the dyebsth. These assistants are stated to be salts, such as sodium chloride or sodium sulphate, though as a matter of fact acids and bases act in the same way. Thus we have found that both hydrochloric acid and sodium hydroxide, in moderate amounts, cause an increase in the quantity of Buffalo Direct Red adsorbed by cotton, precisely as is done by sodium chloride or by sodium sulphate. Because of the rather striking assisting action of salts, the substantive colors are often spoken of as ‘salt’ dyes. The substantive dyes differ distinctly from the acid dyes in the effect produced on the dyeing process by bases and salts containing univalent cations, even though the two classes of dyes are chemically similar. Sodium hydroxide acts normally as a restrainer10with acid dyes, but as an assistant with suhstantive dyes, while hydrochloric acid may act as assistant with both. Sodium chloride is without much effect in the case of acid dyes, but is an active assistant with the substantive class. The difference is marked in the case of sodium Cf. Haller: Kolloid-Z., 29, 95 (1921). Cf. Mntthews: “Application of Dyestuffs”, 595 (1920). 3 Cf. Biltz and Behre: Ber., 6 38, 2973 (1905). 4 Cf. Haller and Nowak: Kolloidchem. Reihefte, 13,94 (1921). Bilte: Ber., 37, 1771 (1904); 38, 2963 (1905). 6 Rath: J. SOC.Dyers and Colourists, 39, 334 (1923). 3 Cf. Haller: Kolloid-Z., 29, 95 (1921). 8 Cf. Briggs and Bull: J. Phys. Chem., 26, 873 (1922). 9 Knecht,, Rawson and Loewenthal: “A Manual of Dyeing”, 377 (1910); Whittkcr: er
Depth of Color (Arbitrary Scale) N o Gelatin I percent Gelatin
None
I2
IO
1/32
12.5
10.5
I3 14
10.5
118
114
I5
I2
112
I4
I3
111
12.5 0
I3 I1
1/16
211
I1
411 7 7 The numbers of Table VI1 show that the expectation of the previous p a r s graph was realized by experiment. In the absence of gelatin, the point of maximum dyeing occurred in the bath containing 1/4 mol sodium chloride per liter. When gelatin was added, the point was shifted and occurred somewhere between the half molar and the one molar solutions. Besides this, the gelatin had the effect of causing less color to be adsorbed at the maximum, but more color for some distance beyond this point. The action of gelatin as restrainer was also brought out very strikingly by experiments in which the procedure of Method z was used. Erie Red (0.05 percent) was again employed and the least number of inch-square pieces of cotton needed to exhaust the dyebath was determined. The results follow.
TABLE VI11 Influence of Gelatin on dyeing with Erie Red 4B Composition of Dyebath I 2 ,j
4
Pieces to Derolorizc Dyebath
25cc Dye plus 2 5 cc Water. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I7 Same plus 2 5 cc 2 . 5 percent Gelatin.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Same plus 2 5 cc M/z Sodium Chloride.. . . . . . . . . . . . . . . . . . . . . . . . . 7 Same plus 2 5 cc M/2 Sodium Chloride containing 2.5 percent Gelatin 2 0
386
T. R. BRIGGS
It was thought that sodium oleate might have the same effect as gelatin, but this was found not to be the case. Addition of sodium oleate up to one percent in dyebaths containing 0.1 percent of Erie Red caused a progressive increase in the amount of color shown by dyed cotton, though the actual amount of this increase was not very large. The color was brighter and more evenly distributed. It seems probable that something in the soap solution is adsorbed by the fiber and acts as a mordant for the dye, but this is only a guess at present. Conclusions and Summary The experiments reported in the preceding pages, while admittedly of a somewhat preliminary nature, appear to be in complete agreement with the general theory of substantive dyes as stated in detail in the introduction to this paper. It is gratifying to note that the results, derived independently and in some cases as early as the summer of I 9 I 7 , confirm and amplify those of Auerbach previously mentioned. An effort has been made in this paper, however, to show that the phenomena met with in dyeing with predominantly' colloidal dyes may be explained with the aid of what is known about the distribution of colloids in suspension between an interface and the suspending medium. The results of this paper may be summarized as follows: I . The evidence collected by previous investigators shows conclusively that the process of dyeing with substantive or colloidal dyes is simply a case of adsorbing a colloid from its suspension, in which the dispersion and stahility are capable of being greatly varied. 2 . The adsorption of a colloid from suspension has been considered as a process of distribution between an interface and the suspending medium. Factors which affect this process have been considered. 3 . From a consideration of the general process of colloid distribution, a special theory of substantive dyeing has been formulated and tested by experiment. 4. A substance which destabilizes the suspension of the dye will act as an assistant in the dyebath up to the point of actual flocculation. 5 . A substance which stabilizes the suspension of the dye will act as a restrainer, providing it does not act as a mordant toward fiber and dye. 6. A stabilizing substtarice and a destabilizing substance may each exert their specific effects in the same dyebath. 7. Transition dyes undoubtedly exist which combine with their properties of acid or basic dyes the characteristics of substantive dyes. 8. The experiments are being continued. Cornell University. 1 A substantive dye of the sodium salt type which is wholly colloidal in water will behave in accordance with the theory outlined in this paper. If, ,however, the dye is a semi-colloid (partly in true solution) it will behave partly as an acid dye and artly as a colloidal dye, one or the other behavior possibly predominating. Such a dye mi&t be called a transition dye, and it is very probable, so I am told by Dr. A. W. Bull, that Niagara Violet is an example. Likewise, a semi-colloidal basic dye will behave partly as a basic dye and partly as a colloidal dye, as Briggs and Bull have noted in the case of Methylene Blue.
