aftertreatments for improving the fastness of dyes on textile fibres

for Fastness of Dyes on Christopher C Cook Postgraduate School of Studies in Colour Chemistry and Colour Technology University of Bradford Bradford West Yorkshire ED7 1 DP

Chemical aftertreatments available over the last 100 years for improving the fastness to wet treatments, to washing and to light, of dyes on textile fibres are fully reviewed. Particular attention is given to the use of metal salts, tanning agents (both natural and synthetic) and to cationic 'fixing' agents.

INTRODUCTION The purpose of this review is to survey the chemistry involved in aftertreatments and the use of these processes for improving the fastness properties of dyes on textile fibres. As such a review appears to be unique, some historical material, for example that concerned with the use of tanning agents in the coloration of cotton, has been included so as to give the background to other processes such as the classical backtanning of dyed nylon. As a result of this inclusion, the knowledge surveyed extends over the period 1880-1 980.

In considering improvements in fastness properties, these have been restricted to those covered by the terms 'fastness to light', 'fastness to wet treatments and to washing'. Gas-fume fading considerations have been excluded as have, in the main, those aftertreatments involving processes fundamental to the production of a level, well-penetrated dyeing, for example, the fixation of reactive dyes by changes in pH, steaming processes, oxidation of reduced forms of vat and sulphur dyes, soaping-off and reduction-clearing techniques or any process which is used to develop the true hue of a dye by surface modification of its state within the fibre. With regard to light fastness improvements the use of ultra- violet (u.v.) absorbers has had to be excluded.

Every effort has been made, wherever possible, to include all useful aftertreatments but, in some areas, once the use of a particular treatment has been established, those references to the same general method, which add no further knowledge, have been omitted. It must also be stressed that, in many cases, examples of suitable chemicals have been taken from patented claims and the examples selected are not necessarily those which found commercial use.

GENERAL DEVELOPMENT Most early dyeing processes using naturally occurring coloured compounds, for example the dyewoods [l 1, which have no significant affinity for cotton or silk, required a metal salt mordant before dyeing and, after coloration, fixation with tannin. Following the discovery in 1856 of Mauveine, the first synthetic dye, Perkin and Pullar [2], presumably utilizing observations that tannins precipitated basic dyes from their solution and that basic dyes padded onto cotton were removed when treated with tannin, initiated the 'tan-metal' mordant technique of precipitating these dyes on cotton mordanted with natural tannin. Metal salts were also necessary for adequate fastness to soaping and light [3]. Thus, cotton

Improving the Textile Fibres

was steeped [4] in tannin extract 1561 (gall-nuts, sumac, myrobalans, chestnut, oakwood, quebracho, divi-divi, etc.), then in a metal-salt solution [7], and finally acid-rinsed before dyeing. In 1882 commercial use was made of the discovery [2,3] by John Dale that antimonyl tannate treatment gave significant improvements in the fastness to light, and especially in fastness to soaping, milling and perspiration. This approach became extremely popular [8,9] in the aftertreatment of printed cotton and of tannin-mordanted, basic-dyed silk.

In the 1880s, with the appearance of substantive direct dyes which required no previous mordanting of the cotton, use of basic dyes and hence use of antimony aftertreatments declined, although the use of bright basic dyes for 'topping' duller direct or sulphur dyes gained in importance [lo]. Substantive polyazo basic dyes for cotton [ll] and dye mixtures for wool/cotton blends [12] became available, but they still required antimonyl tannate aftertreatment.

Potassium dichromate [13] or copper salts [14, i 51 had been applied to dyeings of natural dyes so as to enhance fastness to light or to wet treatments, and Fayolle extended the use of dichromate aftertreatment to a synthetic basic dye, Rosaniline Brown [16]. Nietzki and others also observed that many mordant dyes, particularly those derived from salicylic acid, could be bound to wool by adding dichromate to the exhausted dyebath, giving marked improvements in fastness properties [17-191.

Despite initial claims that some early direct dyeings were fast to soaping [20], it was soon appreciated that fastness to light and to wet treatments left much to be desired. Increasing the molecular weight of the dye and reducing the degree of sulphonation improved substantivity to some extent, but the unavoidable reduction of solubility, especially in salt solution, made such dyes very difficult to apply. A partial solution of the fastness problem was offered by suitable aftertreatment to render the dye less soluble, thereby improving the wet fastness, sometimes significantly. New pattern cards produced at the dawn of the twentieth century reveal many direct and some sulphur dyes that showed improved wet fastness when aftertreated with metal salts, although colour and fastness to light were often adversely affected. Early methods of aftertreatment, entailing the formation of additional azo links, crosslinking with formaldehyde or reaction with metal ions, although giving improved resistance to water, gave no substantial improvement in fastness to washing [21].

From 1930 onwards the complexing of direct (anionic) dyes, present on the fibre, with aqueous solutions of cationic 'fixing agents' began to be fully exploited. The importance and use of these agents was greatly extended by the development of products rising from the condensation of cyanamide or similar compounds with formaldehyde. These 'resin-fixatives' [22] of which Fi- brofix [23] was a classical example, could be applied by a simple, finishing technique to cellulosic fibres dyed or printed with direct dyes. The resulting fastness properties were still inferior to those of vat dyeings but were adequate for many requirements on viscose fabrics, enabling material so treated to withstand normal wash-

REV. PROG. COLORATION VOL. 12 1982 73

ing treatments without discoloration of special effects

Shortly after the introduction of polyamides in the 1940s, it was discovered that the wet fastness of certain acid dyes applied to them could be improved by two types of aftertreatment. Firstly, the afterchrome method, previously restricted to the treatment of acid dyes on wool, was applied with great success to those dyes capable of reacting, on the fibre, with chromium. Sec- ondly, the formation of a sparingly water-soluble antimonyl tannate was employed so as to restrict outward diffusion of dye during washing treatments, but problems associated with this technique (the full backtan aftertreatment of dyed nylon) gave rise to a demand for a simpler process. A great deal of work had already been carried out to produce a large number of synthetic tanning agents (syntans), which were useful alternatives to natural tanning agents for the transformation of skin or hide to leather. Thus, when considering the possibility of replacing a natural tanning agent used in aftertreatment of dyed nylon, it seemed logical to investigate the use of syntans for this purpose. The results were so promising that a range of syntans, specifically recommended for application to dyed polyamides to increase wet fastness properties of dyeings, is now available.

The production, in the 1960s, of polyfunctional, cross- linking fixing agents capable of reacting with both dye and fibre was a significant development in aftertreatments. These agents have been used to aftertreat dyes on cellulosic, polyamide and wool fibres but a study of current literature does not indicate a mass exploitation of this development, and the concept of a cheap, quick treatment to give outstanding fastness properties would still appear to be too ambitious.

Dyers and printers have continually aimed at reduced dye-cycle times and improved reproducibility, wherever possible. As a direct consequence, the use of aftertreatments has been avoided to an increasing extent over the years. Thus, much of the work published over the period 1880-1960 is now only of historic interest and some of the processes developed since 1960 have become obsolete. At present, reactive dyes are often used instead of aftertreated direct dyes, and the use of acid milling dyes has tended to replace that of aftertreated acid levelling dyes. However, a declining, but nevertheless continuing, requirement is anticipated in the future. Aftertreatment still remains an extremely useful way of improving, sometimes temporarily, the wet fastness properties of a deep dyeing that fails to meet the necessary standard. Thus a brief, batchwise rinsing treatment with a suitable agent to increase the fastness slightly above the required level still finds use in those continuous dyeing and printing processes where washing efficiency may be inadequate.

AFTERTREATMENT OF DYES O N CELLULOSIC FIBRES

Basic Dyes

Ahertreatments for Improving Fastness to Wet Treat- ments It had become common practice [3], not only in the printing of cotton [24], but also in silk dyeing [8] to form a weakly held, insoluble tannin-dye complex on the fibre and to transform it to the less water-soluble antimonyl derivative before washing. Another variation involved the 'backtanning' of mordanted and dyed cotton in the previously used antimonyl tannate mordanting liquors. As a result, aftertreatment of basic dyes with antimony salts and/or with tannins became firmly estab-

WI. lished as a necessary part of the coloration process. Cotton and silk, unlike wool, are capable [4,25,26] of absorbing substantial quantities of tannins. Partial hydrolysis of these compounds could occur during application [27], with the formation of simpler phenolic acids. Studies [4,25,28] of the sorption of gallic acids and related phenols by cotton revealed not only surpris- ing differences in relative affinities, but also significant increases in uptake in the presence of certain electrolytes [4,25,29].

In the dyeing of cotton the dye (base)-tannin (acid)- antimony balance was delicate and problematical r26.301. Excess tannic acid gave dye loss on washing and the tannin-dye lake was soluble in concentrated tannin [9]. Although it was known [3] that, when no excess tannin or antimony was present, the resulting complex [29,31] was insoluble in boiling water, the achievement of this ideal was impossible and, despite argument [30] against this practice, excess antimony was always used.

Despite the suggested use of salts of titanium [32], cobalt or nickel [33], antimony was preferred. Potassium antimonyl tartrate (tartar emetic), obtained by boiling antimony oxide with potassium tartrate, was the most common source [9,24,27,34], but certain disadvantages (toxicity, cost, instability) were 'found, leading to adul- teration with zinc salts or the alternative use of zinc lactate [35]. Furthermore, tartar emetic, in the presence of tannin, reverts to antimony oxide [27] and to acid tartrate salts. As both antimony oxide [9] and the dye-antimony-tannin complex [36] are soluble in solutions of potassium hydrogen tartrate, the tartar emetic became useless and was discarded, even though excess antimony was still present. Increases in the acidity of the fixation bath caused by accumulation of acid tartrates could be offset by addition of chalk [37], but it was assumed [9] that only 30-40% of the antimony applied actually entered the fibre and alternative antimony compounds were evaluated [38].

It was claimed that potassium antimonyl oxalate [39] could replace an equal weight of tartar emetic [3,37,40], but the acidity problem remained [41,42]. Certain mixed halides of antimony and ammonia or alkali metals at- tracted attention, especially antimony sodium fluoride (double antimony fluoride) and antimony fluoride-ammonium sulphate double salt (antimony salt) [36,43]. Both contained more available antimony but could be harmful [44]. Calcium antimonyl tartrate (antimonelle) and certain other organic salts of antimony were investigated [42,44-481 but, despite all attempts, no acceptable alternative to tartar emetic was found.

A ftertreatmen ts for Improving Fastness to Light In many cases the light fastness of early basic dyes on cotton was appalling, but certain selected aftertreatments intended to improve this property may be listed: zinc polyglucoside [49], phosphotungstic, phosphomo- lybdic or phosphomolybdotungstic [50,51] acids (known [52] also as powerful mordants for basic dyes, not only on cotton but on chrome-tanned leather), water- soluble esters (e.g. the monophenyl ester) of phosphoric acid [53] and sodium thiosulphate [33,54].

Direct Dyes

Formation of Additional Azo Links Two important developments arose from the early discovery by Griess of diazonium compounds: the ingrain formation of insoluble azoic dyes within the fibre by Read Holliday in 1880, and Green's discovery [55] in

74 REV. PROG. COLORATION VOL. 12 1982

1887 that Primuline could not only be oxidized on the fibre with alkaline hypochlorite [56] but could be diazotized on the fibre and developed with suitable coupling components [57,58]. Subsequently, many amino-containing direct dyes capable of diazotization and development became available [59]. The reverse process, whereby direct dyes containing a phenolic hydroxy group were treated with diazotized amines was also employed [60]. Of particular interest was the claim [61] of improving fastness, either by diazotizing on the fibre and coupling with hydroxynaphthyltrialkyl ammonium salts, or by coupling suitable dyes on the fibre with diazotized trialkylammonium phenylamines.

Formation of additional azo links generally gave significant improvement in fastness to milling, washing, crabbing and cross-dyeing but the fastness to light was often reduced. The most popular demand for this treatment was in the production of black sewing thread and mercerized yarn, but with increasing use of sulphur blacks this demand was greatly reduced.

Cross-linking with Formaldehyde Aftertreatment of certain direct dyes, especially those bis- and polyazo dyes containing m-amino or m- hydroxyl groups, with formaldehyde (or acetaldehyde, benzaldehyde or glyoxal, although the use of formaldehyde was stated [62] to be unique) was first claimed in 1899, to give substantial improvements in fastness to perspiration and to washing [63]. Despite a theory described by Whittaker [64] that formaldehyde linked amino groups on the dye to give a closed ring ( l ) , it is now believed that combination with formaldehyde takes place through a methylene link formed at a reactive site on each of two adjacent dye molecules giving rise to a new dye (2) which, by virtue of its greatly increased molecular weight, has reduced solubility in water or in aqueous alkali [65,66].

The additional possibility of modification of the substrate by its reaction with formaldehyde appears to have been dismissed, as this would demand conditions considered to be remote from those employed in the aftertreatment [66]. Nevertheless, treatment of cotton with formaldehyde could decrease its swelling capacity [67] when subsequently wet-treated. Formyl groups [68] capable of acting as new dye sites showing greater attraction towards direct dyes than do hydroxyl groups could be introduced into the cellulose molecule during the aftertreatment.

This aftertreatment [54a,69] became increasingly popular over the period 191 4-1 925, particularly for black direct dyes, and still finds use today, but often causes a decrease in light fastness. This can be partially compensated for by the use of formaldehyde in conjunction with copper salts [70].

There is, additionally, an observation [71] that aftertreatment of metallized, aminohydroxyazo dyes (on wool) with formaldehyde removes dull impurities and gives brightness but this does not appear to have been extended to other dye classes or to other fibres.

Use of Metal Salts for Improving Fastness to Wet Treatments By 1910, the treatment of direct [70,72], azoic and developed direct [73], oxidation black [74] and sulphur [75] dyes with various metal salts had become common practice. Chromium compounds appear to have been the most successful in terms of improvement in wet-fastness properties [62], particularly with dyes containing salicylic or hydroxynaphthoic acid groups readily chelatable with metal ions [76].

Use of Metal Salts for Improving Fastness to Light Improvements in fastness to light were claimed for direct dyeings aftertreated with salts of nickel, zinc and especially copper [77]; some azoic and developed direct dyes also benefitted [78]. Whilst the oxide, glycollate, tartrate, diethanolamine acetate, sulphide, sulphate, acetate or chlorate of copper ( 1 1 ) could be used, apparently the ferrocyanide [79] and cuprous salts [80] could not. Treatment with cupric salts apparently produces chefates [62] with improved light fastness, but excess copper can accelerate fading [81] and, in the case of vat dyes [82], phototendering. Certain chelated dyes are unstable to concentrated alkali and oxalic or sulphuric acid [62, 80, 831. Histidine, an amino acid found in human perspiration, readily forms stable copper complexes and by abstraction of copper, may cause breakdown of the chelate [84]. There is also a belief that dye-copper complexes can be degraded by anionic detergent solutions. Improvement in fastness to light is now largely obtained by modification of dye structure rather than by aftertreatment and the number of direct dyes now available for complexing with copper after their application to cotton is small. Aftertreatment with copper has been recommended for dyeings on wool/cellulosic blends [56,85,86] where all-round fastness, except possibly to milling, is required and commercial fixing agents for use in the copper [84] or in the nickel [87] aftertreatment of direct dyes have been marketed.

Use of Cationic, Surface-active and Non -surface-active Dye- fixing Agents The first cationic fixing agents to be made available for the aftertreatment of dyed cellulosic fibres were substantive to these fibres and were thought to form colourless, sparingly soluble complexes with direct dyes, thereby increasing the fastness of the dyeings to wet treatments.

Ammonium compounds found to be of use in this context included [88-931 fatty acid-diamine condensates such as the hydrochloride, acetate, methosulphate and benzyl hydrochloride of oleyldiethylaminoethylam- ide, oleylmethyldiethylenediamine methosulphate, mo- nostearylethylenediaminotrimethylammonium methosulphate and oxidized products of tertiary amines. A typical reaction scheme [go] for the preparation of this type of compound is as follows:

CH~C(CH,),CH:CH(CH,),COOH + H2NCH&H,N(C&)2 Amine I -H@

I Fatty acid

CH3(CH2),CH:CH(CH2~CONHCH2CH2N(C,H,),

(CH3)+0,

[CH,(CH ,),CH:CH(CH2),CONHCH ,CHJJCH3(C2H5 *SO,CH j Cationic agent

Heterocyclic ammonium 'salts or copper complexes obtained from, for example, reactions involving pyridine


[93-951 (Type I), picoline [95], piperidine [96], imida- zoles [97] and cyanuric chloride [98] were also fully exploited and the more useful and important reactions were extended [99] to cover ternary sulphonium (Type II and quaternary phosphonium (Type 111) or even antimony [91] salts, some containing alkyl groups consisting of at least ten carbon atoms.

Those products that were acid salts of free bases were not fully converted to the quaternary state, were sensi- tive to changes in pH and were of little use when in aqueous solutions having pH values greater than 10 [22]. A few of the early, cationic compounds, classified [22] as being surface active, also found use as water- proofing agents. Mention should be made here of the use [loo] of specified aminoalkyl silicones for improving the wash fastness of direct dyes on cotton. Others were also softening [ l o l l or wetting agents and the early Sapamines, for example, were considered to be better softening agents than they were 'dye-fixing agents' [90,102]. Modified products tended to reverse this state of affairs [ lo31 and early patents for these included derivatives of polymeric alkyldiamines (Type IV) [104], polyamine-cyanuric chloride condensates (Type V) [lo51 and aminated glycerol dichlorohydrins [106].

I HN I Highly

ci I I NH

c b + NAN + H& - cross-linked polymer

I NH

I I

Members of this 'non-surface-active' class were thought to have highly cross-linked, three-dimensional structures [22].

The casual reader of claims patented over the period 1932-1945 can perhaps be excused for gaining the impression that, with the possible exception of condensations involving the use of formaldehyde, alkylation was the key to the door of everlasting employment as a research and development chemist. It was, no doubt, observed with some relief that the introduction of long, alkyl chains into both anion and cation, for example using triethylcetylammonium cetyl sulphate, gave water- insoluble products which were condemned as having ineffective dye-fixing properties [107].

The history of the provision and development of cationic auxiliaries of the type described generally relates to improvement in fastness to wet treatments [lo21 other than soap washing [21] viz. fastness to hot water, perspiration, wet rubbing, acid cross-dyeing or wet, hot pressing. Certainly, with the simpler types of cationic compounds, such improvements must have been due to the formation of a cation-anion complex having limited solubility in water, either within the fibre or at the fibre surface [22,90]. A study [91] of the interaction of direct dyes and long-chain, quaternary compounds in aqueous solution did show that the precipitated complex contained the reactants in stoichiometric proportions:

0-(SO;), + XC+ - [D-bo;c'lm]l

Direct Fixing Precipitated dye agent complex

In some cases, wet-fastness properties were improved still further if sulphate ions were present in the aftertreatment bath [108].

Unfortunately, the force of attraction between soap molecules and the fixing agent appeared to be greater than that between dye and agent. Thus, in boiling, aqueous, soap solution, the complex formed between dye and agent became unstable. At the same time it was found that treatment of dyed material in aqueous, alkaline, detergent solutions containing certain quaternary compounds gave loss of that dye which had been loosely deposited at the fibre surface. With certain agents [log], cetyltrimethylammonium bromide for example, some dye classes were completely removed from the fibre and these observations led to the use of suitable agents in washing-off procedures [l l o ] and in stripping baths [93,111].

The effect of cationic agents on both the colour and the fastness to light of the aftertreated dyeings provided a further limitation to their use [22,112]. Changes in colour, varying from slight to significant, often took place and were invariably accompanied by a reduction in light fastness proportional to the colour change, those dyeings undergoing the most pronounced colour changes being the most fugitive in light.

Despite the known instability of these agents in the presence of aqueous soap solution, some claims of improved fastness to washing processes were made for this type of aftertreatment of dyed cellulosic fibres (and also in some cases, of dyed cellulose acetate fibres). One such technique entailed the mordanting with the agent, prior to dyeing, followed by aftertreatment of the dyeing with chromium [113]. Alternatively, application of agent could be followed by metallization with copper [114]. An interesting claim was made whereby those direct dyes containing diazotizable amino groups were coupled, within the fibre, with components containing a trimethylammonium ion [115].

Use of Resin - fixatives It is not intended in this review to survey the use of polymers and resins in textile-finishing treatments [116], but the reaction of cotton with resin finishes is known to modify its absorbency sufficiently to improve the fastness of non-reactive ionic dyes [117]. Also, cationic groups present in typical crease-resist resins can provide additional sites for electrostatic association with anionic dyes, thus giving the potential for improved fastness properties of dyed and crease-resist finished cotton [118]. The term suggested [22] for early examples of suitable agents was resin-fixatives and the uses of these and of certain pre-condensates, condensates and polymers have been combined in this section.

Following a claim [119] in 1935 of improved colour fastness resulting from the aftertreatment of dyed fabric with dicyandiamide-formaldehyde condensates, a distinct advance towards improved fastness to washing of direct dyes on both cellulosic and silk fibres was made with the introduction of Fibrofix [23, 561. This was apparently a cyanamide-formaldehyde condensation product developed [120] from observations that cellulosic fibres, impregnated with reaction products of cyanamide, guanidine, etc. with formaldehyde, had increased substantivity towards acid dyes [121].


* NH2C(:NH)NH2 NH2CN NH3

Cyanamide (neutral) Guanidine (strongly basic)

NH2C(:NH)NHCONH2 Dicyandiamidine (strongly basic)

NH&NH)NHCN .

NH2C(: NH)NHC(:NH)NH,

Dicyindiarnide (neutral)

Biguanide (strongly basic)

Either cyanamide or dicyandiamide could be converted to strongly basic guanidine derivatives prior to or during the course of condensation. Since aqueous washing solutions are often strongly alkaline, only those bases that were ionized under these conditions were found to be of use in giving cation-anion complexes reasonably stable to aqueous alkaline solutions of soap or anionic deter- gents [22]. Although Fibrofix wasclassed asa basic, dye- fixing agent, a constituent in its production was undoubt- edly formaldehyde, and its mode of action in improving wet-fastness properties was considered to be different from that of the more common, quaternary, cationic, dye- fixing agents already described. The resin-fixative class, first exemplified by Fibrofix and possibly by a Russian product, Fixer DCU, which, in 1948, was claimed as having been available since 1936, [122,123] was rapidly extended to provide a large number of agents [89,124]. These were generally available as water-soluble precondensates based on those products of the reaction of formaldehyde with cyanamide derivatives (including melamine [125]) which were suitable for the aftertreatment of direct dyes on cellulose and, to some extent, of anionic dyes on wool/viscose blends. The observation that Fibrofix readily formed ionic complexes with anionic fluorescent whitening agents, thus protecting dyed and aftertreated material against changes of colour on subsequent washing in the presence of substantive fluorescent compounds, is perhaps still of current interest [126]. It should also be mentioned here that some of these dye- fixing agents and fixatives found use for modifying the substantivity of nylon for direct dyes [127] whilst other similar types (resin syntans) were claimed [128] to be leather-tanning agents. In addition, certain condensates of formaldehyde with sulphurized phenols or with urea, referred to as 'fixing agents' but now perhaps better classified as syntans, were claimed to be of use in improving the wet-fastness properties of direct dyes present on cotton [ 1 291.

Improvement in the fastness to chlorine treatments of some dyes was observed as a result of aftertreatment with urea-formaldehyde or with melamine-formaldehyde condensates, the protective action afforded being due to preferential absorption of chlorine by the resin with the formation of chlorine-resistant chloramine derivatives [130]. Unfortunately, however, for the vast majority of agents based on systems using formaldehyde with cyanamide, dicyandiamide, guanidine, or melamine there was an adverse effect on the fastness to light of aftertreated dyeings attributed to the reaction between the dye and formaldehyde released from the condensate as a result of irradiation [122]. This reduction in light fastness was often accompanied by hypsochromic shifts in the absorption spectra of susceptible dyes [131]. Both dicyandiamidine and biguanide readily form metal complexes [22] and the incorporation of copper salts [23,131,132] (e.g. cupric acetate, chloride or sulphate) copper derivatives [84] and resin complexes [122,133] or application of these fixatives to dyes that had already

been after-coppered [134] was usually recommended to avoid decreases in fastness to light and, sometimes, to enhance the increase in wet-fastness properties. It is possible that complex formation, between fixative and copper, on the fibre could inhibit any photosensitized reaction between agent and dye that might lead to destruction of the dye [22]. However, it is more likely that complex formation between copper ions and chelatable groups present in the dye would take place, giving rise to a dye complex more resistant to irradiation [135]. Despite this increased resistance, there was still the disadvantage that copper, even in the complexed form, could be stripped from the fibre by aqueous solutions of histidine, natural perspiration for example, thus giving drastic reductions in the fastness to light [84].

Further reaction of cyanamide or cyanamide derivatives or resins with alkylene amines, diamines, tetramines or polyalkylene polyamines was possible [136] and condensates of these amines with formaldehyde [137], other precondensates [138] or with aliphatic dihalides [139] were also of use in improving fastness properties. Vinyl- imidazole polymers or copolymers [140], polysulpho- nium compounds [141], vinyloxazolidinone polymers [142] (applied during a soaping or washing treatment), copolymers of quaternized esters or amidestvith unsatu- rated compounds [143], isocyanate adducts [144], methylol derivatives of alkylated compounds [145] and condensates [146] of formaldehyde and triazine or triazinyl derivatives were of use for the same purpose.

Condensation products derived from formaldehyde and phenol [147] or urea [70,148] (as used in well- known anti-crease-finishing processes [149]) or formaldehyde and aromatic diamines [150] or acetone [151] often gave resins [152] of use not only in finishing but in the simultaneous improvement of wet fastness and, in some cases, washing fastness of direct dyes on cellulosic fibres. Acid catalysts could be incor- porated with preparations of the resin fixatives described and, during curing, further condensation and cross- linking within and upon the fibre took place [153]. In many cases there was still evidence of instability towards boiling, aqueous, alkaline, soap solution and the improvements in the fastness obtained from aftertreatment with, for example, alkylated methylol melamine resins were said to be superior to those obtained from aftertreatment with urea-formaldehyde systems [154]. Presumably amino groups present in the dye molecule were capable of reacting with methylol or dimethylol groups present in the resin, or witil formaldehyde itself. Further, primary amines could in some cases be split from ?he dye molecule giving greatly reduced substantivity [155]. Nevertheless, the use of quaternary compounds, in conjunction with formaldehyde and urea (a formaldehyde 'acceptor' or scavenger') [156], was claimed to give substantial improvements in water-and wash-fastness properties [157].

For many of the resin fixatives, and particularly for those based on urea-formaldehyde systems, the reductions in light fastness resulting from resin aftertreatment presented a problem. Whilst the fastness to light of a limited number of direct dyes was found to have been improved, the majority of direct dyes did appear to show a reduced fastness after such a treatment. Recent work has shown that when cotton, dyed and then crease- resist finished, is exposed to light photodegradation involving photo-oxidation of dye molecules can occur. N-methylol derivatives are thought to be involved in the oxidation. Thus, in theory, light fastness can be improved by restricting the N-methylol species to ones that are stable to oxidation [158].


Use of Polyfunctional, Cross-linking Fixing Agents In the 1960s serious attention was also given to methods of dyeing employing a mixture of a non-reactive dye and a reactive assistant, which could enter into chemical combination with both dye and fibre. These assistants [153,159,160], referred to as polyfunctional, cross-linking agents, or simply as fixing agents, were developed as a result of progress in the resin finishing of cellulosic- fibre goods. Such agents, e.g. trivinylsulphonyl-s-triazine derivatives, triethylenemelamine and epoxyalkylam- monium compounds, are of use in this context, not simply to cross-link cellulose molecules in cotton or viscose fibres, but to also cross-link such molecules with dyes containing -NH, (primary or secondary, aromatic), , N-H (heterocyclic), -SH, -COCH,COCH,, -CONH-, -OH, -SO,NH,, -CH,CH,OH or -CH,CH,NH, groups, resulting in improved overall fastness to wet treatments. In fixing a dye to cellulosic fibres by this means it is usual to pad or print the textile with a liquor containing dye, cross-linking agent and an alkali such as sodium or potassium carbonate or bicarbonate and then to give a heat treatment to promote rapid fixation of dye. Alterna- tively, the process can be split into two stages whereby the padding with cross-linking agents becomes an aftertreatment, carried out specifically to confer improvements in fastness properties [153]. Aftertreatment of selected, direct dyes with a cross-linking agent of the type described has been shown to improve the wash-fastness properties to a level equivalent to that obtained for dyeings with reactive dyes [160]. Additionally, the use of polyfunctional agents in aftertreatments is claimed to give no appreciable decrease in light fastness, in contrast to resin aftertreatment, which usually impairs it [160].

The Present Position Cationic, quaternary fixing agents and cationic, resin fixatives still find use throughout the world for improving the fastness of direct dyeings and prints on cellulosic (including viscose and bast) fibres towards exposure to water, sea water and perspiration. Cationic products are used in discharge printing of direct-dyed grounds to prevent the staining of discharge effects; many are used in the aftertreatment of reactive dyes on cotton and also find use in the treatment of lining fabrics. Suitable agents, many still based on dicyandiamide or its derivatives, can be applied by batchwise or continuous techniques or from resin-finishing baths (with perhaps, in certain cases, some limitation in the choice of catalyst and other electrolytes that may also be present). Some products have high substantivity for cotton; other modified types, having reduced substantivity and therefore being taken up evenly throughout entire wound packages, are more suitable for use in circulating-liquor machines and in continuous processes. The effect of modern cationic compounds on the colour and light-fastness properties of some dyeings can be minimal, but decreased light fastness is always a possibility, particularly when excessive amounts of cationic agents are used. As a result copper salts, complexes and blends of cationic resins and copper salts are still used to compensate for any reduction in the light fastness of after-copperable direct dyeings and can find use in specialized areas such as the production of dyed velvet, although their use may be restricted to those locations where problems associated with the eff luent are no; important [335].

\

Sulphur and Vat Dyes The oxidation of reduced forms of sulphur, vat and sulphurized vat dyes using, for example, acidic bichromate, alkaline perborate, hydrogen peroxide [161,162]

or sodium bromite or iodate [163] solutions is such a fundamental part [62] of the application process that it cannot be considered as being an aftertreatment; without this stage the parent dye cannot be reformed within the cellulosic fibre. Nevertheless, an aftertreatment with an alkylating agent can effectively replace bichromate oxidation since, not only does it avoid the use of chromium salts, which might present effluent disposal problems, but it also leads to brighter dyeings with improved washfastness properties [162].

In Europe, the application of alkylating agents has mainly been directed towards improvement in the fastness to washing, kier boiling, mercerizing and peroxide treatments of sulphur dyeings or prints [161,162,164,165]. The dye, present on the fibre, is alkylated and simultaneously cross-linked with substantive cationic reactive compounds, e.g. polyhalogenohy- drins [166] or polyhalogenoalkylcarboxylic acid amides [167] that are activated by alkali in a manner similar to that in the reactions of reactive dyes [162]. Those sulphur dyes having characteristics of vat dyes, including, for example, those containing quinonimine groups, are usually selectively preoxidized to prevent the fully reduced form being linked to the cotton by the alkylating agent [l68], which reacts with unoxidized mercapto groups to complete the oxidation and permit development of the optimum fastness properties [164].

Other aftertreating agents [169] recommended for improving the wash- and wet-fastness properties of sulphur dyes and some vat dyes include quaternary ammonium alkyl compounds [170,171], e.g. peral- kylated polyalkylenepolyamines, and resins [171], e.g. acetone-formaldehyde condensates [161,172]. Prod- ucts that have either high or reduced substantivity (for use in circulating-liquor machines) are now available. An additional problem which can be encountered with black sulphur dyes is the degradation of dyed cotton caused by the formation of mineral acid during drying and storage under unfavourable conditions. This can be compensated for either by aftertreatment with amine condensation products prior to oxidation [173] or by the use of an alkaline finishing treatment [174].

For 'obvious reasons, the improvement of the light fastness of vat dyes on cellulosic fibres does not appear to have been a particularly important consideration, but it can be achieved by the formation of metal chelates within the dyed fibre, using, for example, 2-hydroxy-4- methylacetophenone oxime and suitable nickel salts [175]. The aftertreatment of sulphur dyeings with metals is well known.

Aftertreatment of solubilized vat dyes that have been applied to cotton with aqueous alkaline soap solution, perhaps by completing the hydrolysis of the leuco ester (although Johnson's mechanism casts doubt on this possibility) and simultaneously modifying the physical state of the dye in the fibre, significantly improves the light fastness of the dyeings [176] but this is obviously only one example of the advantages to be gained from the use of conventional soaping-off aftertreatments.

The presence of small quantities of copper is known to diminish the phototendering effects observed when cotton that has been dyed with the more susceptible types of vat dye is exposed to light, although the presence of copper can increase the phototendering taking place when vat dyes of lower phototendering activity are present [177,178]. Some protective action is also afforded when mixtures of coppered direct dyes and vat dyes are used resulting in less 'photo-active' tendering of the substrate and a decreased fading of the dye. Cop- per-chrome aftertreatment of sulphur dyeings also gives


some resistance to those degradative reactions initiated by exposure to light [178]. The use of U.V. absorbers in improving the light fastness of sulphur dyes on cotton has been specifically recommended as an aftertreatment rather than as a treatment to be carried out during the application of the dye [I 791.

Reactive Dyes As is the case for the oxidation of leuco forms of vat dyes, for example, the fixation of reactive dyes and their efficient washing-off to remove unfixed (either unreacted or hydrolysed) dye are both fundamental stages [180] in the production of fast dyeings on cellulosic fibres. Thus, in the context of this review, they have not been considered as representing separate aftertreatments following dye application. However, the production of reactive dyeings and prints that can withstand prolonged treatment in boiling aqueous alkaline soap solutions has presented problems and aftertreatment with selected cationic dye-fixing agents or resins (as used in durable- press finishes) has been recommended for improving the perspiration- and wet-fastness properties of reactive dyes on cellulosic (including bast) fibres [ I81 3. Poly- functional cross-linking agents [153,182], of use in the production of crease- and shrink-resist finishes [183], can be applied by an aftertreatment to cotton dyed or printed with reactive dyes. However, although alkaline conditions are necessary for conventional reactive dye fixation and acid catalysts are used in typical easy-care finishing processes, special attention has been directed towards simultaneous reaction of cellulose with both reactive dyes and cross-linking reactants [184]. Thus, by selection of suitable systems, catalysts and conditions, the required reaction takes place between dye and fibre and does not take place between dye and finishing agent [I 531. In this context a study of the coloration of cotton fabrics before, during and after crease-resist finishing with respect to the attainment of optimum fastness of dyed material and the mechanisms of reaction of cellulose and the cross-linking agent is of interest [185]. The light fastness of many reactive dyeings treated in this way does not appear to be adversely affected [186]. Cationic agents are also of use in the aftertreatment of dyeings with reactive dyes and give complexes with residual unreacted dye, irrespective of chemical type. They thereby reduce the staining resulting from hydrolysis of dye-fibre bonds or from loss of hydrolysed unreacted dye, but are perhaps considered to be of greater use with dyes of low reactivity where the presence of unreacted dye is more likely.

Exposure of dyeings and prints of some reactive dyes, particularly those of high reactivity applied in full depths, to damp acidic conditions leads, through protonation of bridging oxygen atoms, to eventual hydrolytic rupture [187] of the dye-fibre link giving rise to the release of 'loose' dye from the fibre with consequent reduction in wet fastness [188]. This fault can be avoided by aftertreatment at the soaping stage with primary or secondary amines, e.g. ethylenediamine, triethylenetetramine or hexamethylenediamine, which are believed to react with any unhydrolysed, reactive groups remaining in the covalently-bound dye, thereby increasing the stability of the dye-fibre bonds already in existence [I 881. Tertiary amines have been examined to determine whether qua- ternization reactions with reactive dyes are possible for increasing reactivity [I 891. However, reactive dyes that do not require this aftertreatment with amines are now available.

The effect of the formation of covalent bonds between the dye and the substrate on the fastness to light of the

resultant dyeing still remains unresolved; some dyes show improvement, some do not and, for many, the results are inconclusive [190].

AFTERTREATMENT OF DYES O N NATURAL PROTEiN AND POLYAMiDE FIBRES

Acid Dyes

Use of Metal Salts Despite early suggestions that salts derived from metals such as copper [191], titanium [32] or tin [192] could improve the fastness properties of certain dyes on wool, the extent to which these (particularly copper salts) can actually achieve improvements has not been clarified. For this and other reasons, aftertreatment with metal salts has been restricted to those employing salts of chromium. The afterchrome dyeing process (initially called a 'saddening' method), defined [193] as a method of dyeing in which the fibre is dyed with a mordant dye and afterwards treated with a chromium compound to form a dye-chromium complex within the fibre, is considered to be one of the most important aftertreatments in present use. Acid dyes present on silk can be reacted in a similar manner [194] but the bulk of the general literature on the chroming of dyed fibres relates to the treatment of dyed wool [195-1981.

The afterchroming of dyed wool, which entails the addition of chromium, usually as the dichromate or, in some cases, the fluoride, to the exhausted acidic (acetic acid) dye-liquor results in improved fastness to wet treatments, to potting and to milling. During the treatment, dichromate anions are absorbed by wool and are reduced to chromic anions with simultaneous oxidation of cystine and, perhaps, other amino acids. Chelation of Cr(lll) with dye molecules gives 1 :1 or, perhaps more predominantly, 1 :2 complexes, both of which have a greatly reduced mobility within the fibre [195,196].

1 1 :::: . . . . I j Dye - Dyed wool Wool +

Dyed wool + Chromium - 1.2 dygchromium complex on wool

The absorbed chromium can be divided into that present as a dye-metal complex held to the fibre by electrostatic and non-polar forces, a constant amount of which is firmly bound to either dyed or undyed wool, and that participating in cross-linking, probably by coordination with carboxyl groups of, for example, glutamic and aspartic acids [I 991. Incomplete reaction, initially a problem, was partly solved by the incorporation [200] of reducing agents, e.g. lactic, tartaric or citric acids or sodium bisulphite, and some dull impurities could be removed by aftertreatment with formaldehyde [201]. Naturally, the rate and extent of chromium uptake [202]


by wool has been of interest, as has the effect of pH on this uptake and on the final fastness properties [198, 2031. At elevated temperatures processing variations are less significant [198] and attempts to reduce the processing time have been described [204]. Recently, much progress has been made with regard to the reduction of the chromium content of afterchrome effluent to levels that are ecologically acceptable without impairing the efficiency of the aftertreatment [203,205,206]. In this connection Meier has emphasized that, although it has been known since the early 1950s that most chrome dyes require less than the quantity calculated by the '50% rule' (which states [195] that the amount of potassium dichromate employed should normally be half the amount of dye used, but not less than 0.25% or not more than 2.5% of the weight of the goods), authors of modern textbooks on dyeing still persist in recommending this too-generalized method for calculating the amount of dichromate to be employed. A method to reduce chromium wastage [195], based on thestoichometric relation between chromium and mordant dyes, which improves the quality of :he afterchromed wool as compared to that of wool dyed by conventional afterchrome processes has been made available. Methods that utilize a reducing agent and a complex-forming agent capable of forming a substantive, water-soluble, chromium complex have been described [207].

Application of metal salts to acid-dyed nylon was investigated soon after the fibre was introduced. Interest has been shown in the aftertreatment of materials dyed using basic [208] and anionic [208-2101 dyes with copper and manganese salts to give some improvement in fastness to light and to wet treatments, but the use of chromium for this purpose is well established. Cobalt complexes of chrome dyes yield a few interesting colours but in general these possess low light fastness and the sodium cobaltinitrite used for complex formation can also give oxidative degradation of the dye [210]. In contrast to wool, nylon is incapable of readily reducing dichromate ions [210] and it was to be expected that early dyeings had disappointing fastness properties due to incomplete chroming of dye on the fibre. Improved complex formation could be achieved by adding a reducing agent to the metallization bath [210-2121. but problems are still presented by the relatively low absorp- tive capacity [210] of nylon for dichromate and chromic ions. Thus, 'clearing' treatments are often a necessary requirement [212] to remove any undiffused complex remaining at the fibre surface.

It should be mentioned here that acid dyes present on nylon that contains poly(ethy1ene oxide) have improved fastness to light if the dyeings are aftertreated with cupric salts [213], but copper salts are not normally applied to dyed nylon.

Use of Natural Tanning Agents The term 'tanning agent' was given initially [214] to those water-soluble cellulosic materials that precipitated gelatin from solution and were also irreversibly absorbed by putrescible animal collagen (hide), thus producing a material (leather) rendered resistant to fermentative or hydrolytic decomposition processes. However, it was pointed out in a rather confusing way [215] that the gelatin precipitation test did not necessarily identify a tanning agent. It now seems usual to classify these polyphenolic compounds as: (a) hydrolysable pyrogallol tannins (galloylated saccharides giving gallic acid (3) on hydrolysis with acids, alkalis or enzymes), exemplified by 'tannic acid', by Chinese or Turkish gallotannins (galls) and by Sicilian and Stagshorn sumac, (b) hydrolysable

ellagitannins that give ellagic acid (4) or similar acids on hydrolysis, exemplified by valonea, chestnut, divi-divi and gambier, and (c) condensed or catechol tannins that contain little or no carbohydrates and are converted to acids to insoluble amorphous polymers.

(3) (4)

Catechol tannins, exemplified by catechin and phlo- baphen, although finding use in the heavy tannage of leather to give shoe soles and belts, are unsuitable for application to textile fibres.

The work [216] of Nierenstein, Freudenberg, Fischer, Haslam, Haworth and others has established that the major constituents of gallotannins are polygalloylated glucoses and not galloylated polysaccharides and has suggested that they are derivatives of glucose, substituted through ester links by four or five galloyl groups. This core is further substituted by between two and five such groups, either attached to the inner ring of galloyl residues through depside bonds or existing as a short chain of up to four galloyl groups. Shore [217] has shown that the 1,2,4,6-tetragalIoyl ester of D-glucose can exist as a remarkably flat and stable structure and insertion of four additional galloyl groups could give either a flexible chain, which is attached to a relatively flat and rigid plate-like core, or could give a flat and compact swastika-shaped molecule (5).

H----9/":. I ti, p-H

(5)

Haslam [218] has briefly but succinctly reviewed current theory regarding the mechanism of collagen tanning that suggests that multi-layer adsorption associated with restricted diffusion is mainly brought about by attraction between phenolic groups in the tanning agent and collagen peptide groups [219].

It is known that cotton and silk, unlike wool, are capable of absorbing appreciable quantities of natural tannins. Nevertheless, the high molecular weight gallotannin constituents of tannic acid have moderately high substantivities for wool and the sorption of these has been of interest in the development of acid-dye resists on this fibre. There is also some indication that treatments of tannic acid, e.g. chlorination or acetylation, which are likely to increase the number of charged groups present or which are likely to decrease the number of free phenolic groups, enhance the substantitivity [220].


Rates of diffusion of tannins into normal homogene- ous polyamides are relatively slow owing to the tight packing of the polymer chains [217,221-2231. As a result of this compactness of structure, the majority of amide groups are internally compensated by hydrogen bonding. This, in turn, results in a distinct shortage of available sites (mainly carbonyl groups) for attachment of tannin molecules and in a lack of access to these sites. The limits of effectiveness of natural tannins for the tanning of collagen [224] approximate to the molecular weight range 600-2 000. Comparison of the effectiveness of hydrolysable tannins relative to that of gallic acid and those related polyphenols, which have molecular weights less than 600, or of those condensed tannins or other polyphenols, which have molecular weights greater than 2000, confirms that a similar range of tannins with similar molecular weights exists for the aftertreatment of dyed nylon [217,225]. Apparent diffusion coefficients for tannic acid have been calculated [217] from rate of adsorption curves making use of Crank's equation for a finite bath. The addition of urea considerably increased the apparent diffusion coeff ici- ent, perhaps due to fibre swelling, but did not increase the equilibrium exhaustion. Formic acid, however, increased both factors, suggesting that it is capable of 'opening out' inaccessible parts of the substrate as well as facilitating transfer of larger molecules through the more randomly orientated regions of the fibre. Alterna- tively, the increases observed could indicate the release of more amine end groups by acidic hydrolysis of the polyamide.

The classical full backtan aftertreatment, which was developed to overcome the problems of inadequate wash fastness [211] of acid dyes on polyamide fibres, entailed successive treatments with tannic acid, potassium antimonyl tartrate and stannous chloride [217,222,226]. Subsequently this method, a modification of an earlier process for treating silk, was simplified by omitting the use of tin. The optimum application process involved the exhaustion of tannic acid onto previously dyed and rinsed nylon in the presence of acetic or formic acid at 85-95" C for nylon 6.6 or at 60-70°C for nylon 6 [217,226-2281. For treatment of nylon 6 the temperature of application was critical and the use of temperatures below 55°C or above 75°C gave negligible improvements in the fastness to washing, thus implying that much less tannin was absorbed at these extremes [229,230]. As no anionic dye-antimony1 tannate complexing effect is thought to contribute to the improvement in wash fastness [217,222,231], the result of the process could well be the formation of a surface skin of the sparingly water-soluble antimonyl tannate, which would be expected to have decreased diffusion properties and decreased oxidative tendencies compared with uncomplexed tannic acid. Film-forming aggregates of the complex, located at the fibre periphery, block the diffusion pores, occupy dye sites and reduce diffusion [217,222,232] of dye into nylon during the attempted dyeing of pretreated material, or out of nylon during the subsequent washing of dyed and aftertreated material. Opinions differ on the complex's chemical composition. Whilst five moles of potassium antimonyl tartrate are required to precipitate one mole of gallotannin from aqueous solution [217], there is some evidence [233] tosuggest the formation of a 1 :1 complex in solution. However, reaction within the substrate does not obey the same stoichiometric ratio and complexing of gallotannin in the outer polymer layers with incoming antimony preventsfurther uptake of antimony, so that free gatlotannin remains within the core of the filament [217].

The full backtan process was found to improve the

wet, crocking and sublimation fastness properties of acid dyes and of some direct and disperse classes present on polyamides significantly [223,229]. Acid dyes of low molecular weight [229] and some disperse dyes 12231 could be upgraded to I S 0 3 washing-fastness standards, but there were distinct disadvantages associated with the process that made acceptance difficult [223,227,229,230,234,235]. Apart from factors such as high cost, toxicity, instability to hot alkali, effect on handle and subsequent light-fastness properties, changes in colour, and incomplete exhaustion of tannin in single-bath application, the most serious fault was the diffusion, or even complete rupture, of the complex that took place during after steam- or heat-setting operations. The chemistry associated with the degradation processes has been fully investigated [217,230]. The influence of the concentration of tannic acid and of the temperature of treatment on the yellowing of nylon and on the subsequent wet fastness properties oi the aftertreated dyeings has been described [223]. Of interest in this context was the claimed replacement of antimony by stannous, bismuth, chromic or zinc salts to give tannate complexes, the presence of which gave rise to good initial fastness properties that were not significantly changed by further heat treatments [236].

Tannins applied to wool fibres and then c'omplexed with metals found some use as acid-dye-resist treatments but, as the restraining effect exerted by antimonyl tannates. towards these dyes was low [217], the final complexing on the fibre was achieved using salts of tin, aluminium or chromium [220,237].

Use of Syntans The term synthetic tanning agent (syntan) implies that the agent has hide- or skin-tanning properties and does not necessarily imply that the same agent is substantive to nylon or that it will improve the fastness properties of dyes already present on nylon. However, it would appear that an organic chemical that is a useful replacement to natural tanning agents in the manufacture of leather may well be, at least partly, substantive to polyamides and could well be capable of improving the fastness to wet treatments of acid dyes on the fibre. On the other hand, syntans specifically designed for aftertreating dyed nylon may not be alternatives to hide-tanning agents. Thus, the term 'syntanning' used to describe a treatment of nylon, although preferable to 'dye fixing', is confusing. The descriptions 'syntans for leather' or 'syntans for nylon' should always be used.

In 1875 Schiff [238,239] obtained a water-soluble compound (6), with the general properties of a leather-tanning agent, from the dehydration of phenol- sulphonic acids and early patents covered the similar dehydration of naphtholsulphonic acids [239]. The development of this discovery of a method of linking

&rw2-oow,H

together phenols to give water-soluble compounds appears to have been divided into two main sections

Firstly, a new class of syntans for leather, originally produced by Stiasny, was developed by BASF and was based on the acidic (usually sulphuric acid) condensation of phenols and their sulphonic acids with formaldehyde or other aldehydes [215,241]. The con-

[238-2401.


densations were rapidly extended to include those of naphthalene and naphtholsulphonic acids, salicylic and cresotinic acids, resorcinol and chlorophenols and gave rise to water-soluble, novolac syntans [242] which had an essentially linear, chain-like structure (7).

OH

/cH1+H2@*H+3H

(7b) / / /

y 1 :HI

s0,Na so* Omission of water solubilizing groups led to the

formation of resins, the resinous properties being attributed to the presence of a number of isomerides [243]. It was usual, therefore, to confer water solubility by the use of sulphonic acid groups, either present in the phenol or naphthol before condensation, or introduced after the condensation by sulphonation [244] or by the use of aqueous alkaline sulphite solutions [245].

In the 1 930s stepwise condensations using alkaline conditions (employing ammonia, sodium hydroxide, me- thylamine or hexamethylenetetramine [246,247] followed by further condensation under acidic conditions became popular, and this technique was extended to include stepwise condensations of hydroxydiaryl sulphones and sulphonic acids [248]. The useof urea [249] and thiourea [250] in conjunction with aldehydes, phenols, aromatic sulphonic acids and sulphones also became popular; metal (chromium, iron, aluminium and tin) salts [251] were employed and some of the condensations described were also carried out in the presence of natural tanning agents [252]. In addition, resin systems (resin syntans) based on condensates of cyanamide derivatives, e.g. with formaldehyde, were claimed to be tanning agents [128]. The impression gained from exam- ination of patents filed in the period 191 5-1 940 is that anything that showed the slightest indication of reacting with formaldehyde was exploited to the fullest extent and to this day a wide range of syntans is available for the manufacture of leathers.

Secondly, a new class of sulphurized phenols (thiophenols), for example the Katanol class of compounds, was developed, not from the dehydration of sulphonic acids, which became a useful method for preparing heterocyclic sulphoxides [253], but from the reaction between phenols and sulphur or sulphur monochloride or dichloride [254]. The products of the reaction were either monothiobisphenols (8) or oligomeric thiophenols, de- pending upon the ratio of phenol to sulphur employed [255].

OH OH

RI-&.Q R'. Rz = H. alkyl, halogen, etc 9

(8) It was also common practice to react aqueous alkaline

solutions of these 'sulphurized products' with sulphites (possibly from sulphite waste liquors) in the presence of an oxidizing agent, usually a stream of air [256]. Metallization of the products with tin, molybdenum, chromium, antimony, lead or aluminium was also common [257].

Attempts to combine the preparation of the two classes of compound to produce phenol molecules linked together with both -S- and -CH,- groups were successful

and examples are seen of the condensation of sulphurized naphthols with aldehydes [258], the linking of water- soluble phenol-formaldehyde syntans with sulphur [259] and the use of thioaldehydes [260]. Later claims specifically concerned with the improvement in fastness to wet treatments of acid dyes (or, in one example, of cationic dyes) on nylon fibres utilized modified systems such as condensates of formaldehyde and alkylated diphenylethers [261], substantive adducts of nonyl phenol and ethylene oxide [262] or even novel complexes of antimony with polyamine-gallic acid condensates [263].

All the sulphurized phenols and some of the phenol- formaldehyde condensates (the latter being termed 'syntans for leather') were claimed to be substantive to both cellulosic and natural protein fibres. On cotton they formed anionic-cationic complexes with basic dyes and thus found use [264] as synthetic mordants, e.g. Tamol (BASF), Katanol 0 (IG) and Taninol B M (ICI). These readily replaced tannic acid as no aftertreatment with antimony appeared to be necessary, and some were also reported to be of use in the aftertreatment of direct dyes for improving the fastness to wet treatments of dyed cotton [265]. Whilst a few of these compounds found use for weighting silk, others, including metallized (tin or antimony), sulphurized phenols, sulphurized naphthols and phenol-formaldehyde condensates, were claimed [266] to be reserving agents towards acid dyes when present on wool and silk; they found use for preventing the staining of protein fibres during the burl dyeing of cotton blends with direct dyes [267]. Improved fastness properties for this type of agent, which had been applied as an aftertreatment to acid-dyed wool, were first claimed in the late 1930s [268] and the aftertreatment of basic- dyed silk with sulphurized phenols was also found to give considerable improvement in wash fastness [269].

However, by far the greatest textile demand for syntans was in the improvement, by aftertreatment, of the wet fastness of nylon dyed with unmetallized anionic dyes. Disadvantages associated with the expensive, full backtan treatment have been described earlier and these, in some cases, were so serious that they initiated a renewed interest in the use of the anionic compounds described above. It was known [270] that treatment of nylon with sulphonated naphthalene derivatives gave resist effects towards the uptake of direct dyes, but those claims [271] relating to the application of these agents to polyamides were, in the main, cautious. Some described either the prevention of staining of nylon during the washing of prints or the reservation towards some acid, chrome or direct classes, the latter property being of use in the dyeing of nylon/cellulosic or nylon/wool blends using mixtures of dye classes. However, many patents [272] claim an improvement in wet-fastness properties. The majority of products currently available have been selected from the compounds described in this section. As a result, the chemical details regarding the structures and syntheses of many of these products now remain hidden within those patents pertaining to the production of syntans for leather and to the production of synthetic mordants for use in cotton dyeing.

Application and Mechanism of Action of Syntans The majority of syntans of use in aftertreatments are applied to dyed nylon under neutral to acidic conditions [217,223,227-229,234,235,2731 (alkaline conditions [274] lead to loss of anionic dyes) by a single bath, one-stage technique. They can be applied from the exhausted dyebath but a small number of agents, e.g. glyoxal-phenol condensates [275] and some sulphurized phenols, are applied from aqueous alkaline solutions.


A second-stage metallization process involving treatment with stannous, bismuth, chromic or zinc salts has been recommended, but if metallization is used it is usually carried out during the manufacture of the agent [276]. In attempts to improve the fastness to wet treatments of anionic syntans, the possibility of forming ionic complexes with cationic compounds has also been studied

There has been much speculation and little proof on their mechanism of action. It has been postulated that an attractive force exists between those amino groups present in animal collagen and syntans of use in the tanning of hide [278]. The combined effect of allforcesattracting syntan molecules to the surface of leather is greater than the sum of the forces responsible for the attraction and retention of acid, direct or chrome dyes. Thus, aftertreatment of dyed leather with a syntan results in the rapid replacement of dye molecules situated at the surface by a layer of more strongly retained syntan molecules [279]. A similar situation could well exist in the application of syntans to polyamides. Anionic syntans are rapidly absorbed by nylon, particularly under acidic conditions. Hydrogen bonding between uncharged polar groups, electrostatic attraction between negatively charged groups in the syntan and protonated amino groups in the fibre [217] and non-polar forces [217,280,281] operat- ing between aromatic hydrophobic regions in both agent and fibre al l contribute to the formation of aggregates, situated mainly at the fibre periphery. Diffusion of syntan molecules [277,280,282,283] is possibly greater than that observed for the antimony1 tannate complex and there is no evidence for the formation of a surface skin as was the case for the full backtan treatment. Although dye loss [280,281,283] can be observed during an aftertreatment of some dyeings with syntans, suggesting that dye molecules are replaced by syntan molecules, the extent of diffusion can be controlled by restricting the time of the treatment. Longer treatments lead to extended diffusion of the surface layer of syntan molecules with a corresponding reduction in the improvement of fastness properties. Shorter treatments, which lead to near 'precipitation' of the syntan at the fibre surface, tend to produce maximum improvements in fastness. Dry-heat or steam- setting treatments are known [217,227,229,230, 2351 to reduce the overall extent to which the agent improves the fastness properties. This is believed to be due to a disruption of the surface layer of syntan, possibly entailing either further diffusion into the fibre interior or physical loss from the fibre by degradative or non- degradative sublimation (during dry heat treatments), or by the partitioning of syntan molecules from the fibre into an aqueous phase (during some steam-setting processes). Once present, the surface layer of syntan molecules is believed to reduce the diffusion (desorption) of dye out of dyed, treated fibre during a washing process and to restrict diffusion (adsorption of dye into undyed, treated fibre during a process which, without the treatment, would lead to stairiing of white backgrounds. If this theory is correct the fastness properties of the syntan itself are of supreme importance. In addition, negatively charged groups on syntan molecules could repel similarly charged groups on dye molecules resulting in reduced diffusion of dye through a 'boundary' layer of syntan. Observations [217,281] that a syntan was less effective than tannic acid in retarding or restraining absorption of disperse dyes by nylon and that syntanned leather had little substantivity for most acid dyes, (although this substantivity increased as the number of anionic groups on the dye molecule was decreased [284]) are of interest.

[277].

The possible formation of dye-syntan complexes re- quires further investigation. Dawson and Todd [231] observed colour changes during aftertreatment with syntans that were not due to complexing, whilst Shore [217] obtained some evidence of molecular association between one acid dye and a sulphonated sulphurized phenolic syntan. Formaldehyde or compounds containing free hydroxymethyl groups could be present in, or liberated from, some syntans during their application. These are certainly capable of reacting with amino groups present in collagen [285], possibly by a Mannich reaction, and can also react with disperse dyes containing amino or aliphatic hydroxyl groups when dyeings with these dyes are aftertreated with formaldehyde resins [135]. If reactive entities were present in syntans, reaction with and blocking of amino-end-group dye sites could lead to chemical retention of the syntan and to reduced mobility of the dye during either sorption or desorption. Unfortunately, an early observation by Stiasny and others [286] that, whilst formaldehyde treatment lowered the substantivity of hide powder for acids and acid dyes, in the similar treatment of wool no difference in uptake before and after the application could be detected, does cast doubt on the possibility of such reactions taking place on nylon.

With syntans for leather the anion affinitiesare reduced with increasing degree of sulphonation and with decreasing molecular weight but no direct relationship between anion affinity and tanning power [287] has yet been established. However, it appears that tanning power may increase with decreasing degree of sulphonation and with increasing extent of condensation to a maximum value followed by a reduction in tanning power with over-condensation [288]. In general, the Gilbert-Rideal theory of acid binding by proteins appears to explain the sorption of sulphonic acids by hide much more satisfac- torily than does the Donnan theory [287]. The measurement of the relative efficiencies of syntans for nylon is not easy. Visual assessments of dye loss from dyeings, or dye uptake of adjacent undyed material, during a washing cycle cannot be used with any degree of accuracy in forecasting the ability of the syntan to withstand prolonged washing treatments over, say, a three-year period. Continuous monitoring of washing liquors is of some use [281] but alkaline soap solutions can give troublesome flocculations and turbid hazes that interfere with colour measurement. Alternatively, restraining effects exerted by a syntan present on undyed fibre towards incoming dye could be considered to indicate its efficiency in reducing dye loss when it is applied after the dye. Restraining effects exerted towards simple acid dyes do not steadily increase with increasing degree of condensation but a general decrease in restraint was observed [280] beyond molecular weights of 1 500. Thus an efficient syntan of the phenol-formaldehyde-resin type appears to be based on a system consisting of between five and ten condensed sulphonated phenol molecules [280,283]. Phe- nol-formaldehyde condensates of relatively low molecular weight and having relatively high degrees of sulphonation tend to be more useful as levelling or blocking agents in controlling the uptake of anionic dyes by nylon, for example in single-bath dyeings of nylon/wool and nylon/cellulosic blends [217,289]. Appreciable restraining effects towards simple acid dyes are exerted by sulphonated, phenol-formaldehyde resins present on undyed nylon, anions derived from these resins occupy- ing potential dye sites [217,280,283]. On the other hand, the absence of anionic solubilizing groups in the syntan molecule results in a reduction of the restraining effect. In contrast, some naphthols that do not contain such groups


can show considerable restraining effects towards anionic dyes and can give improvements in wash fastness when they are used in aftertreatments [280,281]. How- ever, the relationship between the degree of improvement in fastness properties resulting from an aftertreatment and the degree of restraint exerted towards incoming dye anions when the syntan is present on undyed nylon is unclear, but it would appear that the two properties are not directly related [281, 2831. Some agents, whilst exhibiting little influence on the sorption of acid dyes if applied to undyed fibre, can, when applied after the dye, reduce dye loss from the fibre and dye migration to white backgrounds during subsequent wet treatments.

Aftertreatment with syntans does not improve the wet fastness of anionic dyes on nylon to quite the same extent as does a full backtan. Despite tendencies [217,227,229] to reduce the fastness to light of aftertreated dyeings, to give slight changes in hue, to give a firm handle to the fabric or to cause difficulties when used in foam laminat- ing, the use of syntans is widely recommended by many manufacturers [290]. Costs associated with their application are significantly lower than those involved in the use of natural tanning agents requiring complexing with antimony or other metal salts. Syntan treatment of acid dyes on nylon, especially polycaprolactam, is still the major economical route to deep colours of acceptable wet fastness. Nevertheless, instability to dry-heat, post- boarding and steam-setting trearments remains as a major problem.

Miscellaneous methods Acid dyes present on wool can be aftertreated either with epichlorohydrin [291] to improve [21,292] the fastness to washing, or with alkylated sulphanilic acid to reduce dye loss and marking-off onto undyed wool during subsequent wet treatments [293].

Polyhalogenoquinones [294], when applied to certain acid dyes present on nylon, are capable of reacting with amino groups present in the dye molecule to give significant improvements in wet fastness. For better wash fastness on protein and polyamide fibres the dyes present on the fibre can be reacted with colourless fixing-agents. Amino groups present in acid dyes on nylon, wool and silk. fibres can be reacted with esters of poiycarboxylic or carbothioic acids to give acyl derivatives [295] and acid dyes which contain hydroxyl or amino groups can, when present on wool, be coupled with diazonium compounds to give additional azo groups [296], both treatments giving enhanced fastness to washing processes. Acid dyes containing hydroxyl, amino or carboxylic acid groups can be readily reacted, by aftertreatment with carbodi-imides [297] such as N,N-dicyclohexyl- and dibutyl-carbodi-imides in ethanol or dioxan solution. With this reaction the improvement in fastness to washing of dyed wool and nylon is attributed to the formation of amide or ester links between amino or carboxylic acids in the fibre and suitable groups in the dye [297]. With o- hydroxyazo dyes, which are likely to exist in the hydrazdne form, N-acylation of the nitrogen atom in the dye is possible:

LJ

coo- @ tcm t tNH2

Fibre

@ =Dye

However, when other hydroxyl groups are available other reactions are possible and this could explain the reduced sensitivity to alkaline treatment observed for dyes derived from chromotropic acid [297]. Although no effect on the light fastness of the aftertreated dyeings can be detected, some dye loss can take place.

Cationic aftertreating agents have been found to be useful in improving the wet and perspiration fastness of anionic dyes on leather [298], the perspiration fastness of acid dyes on nylon/Lycra fabrics [299], the fastness to washing (with a corresponding reduction in associated staining problems) of some acid and metal-complex dyes present on machine-washable or Hercosett Superwash wool [299,300] and the fastness to wet treatments of animal hair [301] dyed with certain black direct dyes. However, in this last instance it was pointed out that the result is not as good as that for hair dyed with a black chromed dye.

Reactive Dyes When reactive dyes are applied to wool there always remains a fraction of adsorbed dye, present in a non- covalently bound form, that can lead to poor wet fastness [302] as revealed by the alkaline perspiration test. The usual practice is to increase the pH of the dyebath using ammonia or perhaps ammonia-formaldehyde complexes [153] or sodium salts of chlorinated carboxylic acids [303] towards the end of the dyeing process. This causes a reduction in the substantivity of loosely bound dye [153,302] and, at the same time, might promote further reaction between dye and fibre, although this second possibilitjl is considered [304] to be unlikely. It is currently claimed [304,305] that the extent of any reaction with wool is not improved by increasing the pH above the value used in dyeing since the dye tends to desorb before it reacts. The removal of loosely attached dye from the fibre by this means does not seem to depend on the specific action of any particular chemical but is merely governed by such factors as pH, time and temperature [304]. Treatment of dyed wool with aqueous solutions of reducing agents [306], sodium sulphite for example, capable of breaking -S-S- bonds removes much unreacted dye [302,307]. The use of sulphites, which could lead to the formation of dye derivatives having decreased substantivities towards wool, is now regarded as being more effective than the use of aqueous ammonia [302], but high concentrations should perhaps be avoided [308]. A stepwise aftertreatment for wool, in particular for that which has been given a shrink-proof finish, entailing treatment at pH 9, then with a reducing agent at pH 5, followed by an oxidizing stage and finally with a fabric softener, has recently been claimed to improve the fastness properties of reactive dyes [309].

In addition, aftertreatment of reactive dyes on wool with aqueous solutions of cationic dye-fixing agents has been claimed [310] to give good improvements in wet fastness.

The use of substantive adducts of nonylphenol and ethylene oxide [311], of condensates of dicyandiamide


or urea [312], or of naphthalene sulphonic acid and dihydroxydiphenylsulphone, with formaldehyde has been recommended for improving the fixation of reactive dyes on nylon.

An early claim [313] stated that water-imoluble reactive dyes, when applied to nylon, could be aftertreated with aqueous solutions of amines, phenols or thiophenols. More recent work [314] has shown that tertiary amines, e.g. triethanolamine, by forming quaternary derivatives with an increased reactivity towards amine groups, can improve the covalent fixation of reactive dyes during their application to nylon fibres. Primary aqd secondary amines exert no such catalytic influence and often reduce the extent of covalent bond formation.

Disperse Dyes Several dye manufacturers have suggested that the wet fastness of dyeings of some disperse dyes can be improved by backtanning with tannic acid and tartar emetic, to the extent that medium depth dyeings on nylon can withstand an I S 0 3 wash test. Alternatively, simultaneous application (by padding or by printing) of tanning agents and those disperse dyes containing carboxylic acid groups is claimed to give improved fastness to wet treatments [315]. It would appear that thosedyeingsthat show an improvement after backtanning also show some response to aftertreatment with syntans but it is generally accepted that syntans are not as effective as is the full backtan aftertreatment for this purpose. Apart from one claim [295] recommending that dispersedyes containing at least one amino group could, by reaction with an ester of a polycarboxylic or carbothioic acid, be converted on nylon, all other references to the aftertreatment of disperse dyes appear to describe occasional uses of tanning agents.

AFTERTREATMENT OF DYES ON CELLULOSE ACETATE FIBRES The use of chromium salts for the treatment of disperse dyes on secondary acetate fibres has been recommended [316], but the majority of aftertreatments for improving the fastness to wet treatments or to washing of dyeings on these fibres entail the use of formaldehyde resins or condensates. Certain anthraquinone disperse dyes can be aftertreated with polyhalogenoquinones to improve their wash fastness [294]. Disperse dyes containing amino or aliphatic hydroxyl groups are believed [317] to react with methylol groups present in formaldehyde resins; reactive disperse dyes present on acetate fibres can be reacted with amidogen-formaldehyde condensates in the presence of a copper complex and a catalyst [318], whilst aftertreatment with melamine or N-substituted derivatives can give improvements in fastness to gas-fume fading as well as in light fastness [319]. In the case of azo dyeings or prints on acetate fibres this last property can also be improved by aftertreating with alkylated aromatic amines such as alkylated phenylenediamines [320].

AFTERTREATMENT OF DYES ON POLYESTER FIBRES Dyes that are substantive to polyester fibres and form chelates with copper may be aftertreated on the fibre with an aqueous solution of a copper salt and an oxime-copper coordination complex, e.g. from salicylaldoxime, to give excellent fastness to washing and to light [321]. The genoral fastness properties of disperse dyes present on these and other fibres can also be improved, not only by treatment with aromatic compounds containing long alkyl chains [322] or by exposure to a mixture of steam and furfural vapour [323], but by the use of many

aliphatic, aromatic or masked isocyanates, acid halides or anhydrides [324].

AFTERTREATMENT OF DYES ON POLYALKENE FIBRES The general fastness properties of dyes on acid-dyeable propylene yarn can be improved by aftertreatment with water-insoluble fatty acid esters [325]. Light fastness can be improved, often significantly, either by aftertreating dyeings of metallizable dyes (on fibres containing metals such as zinc, calcium, magnesium or aluminium) with metal complexes of cnelating agents [326] or by aftertreating basic and acid dyes on the fibre with iodine or hydrogen iodide [327].

AFTERTREATMENT OF DYES ON ACRYLIC FIBRES Aftertreatment of acid dyes on acrylic fibres [328] or of basic dyes on vinylidene cyanide copolymer fibres [329] with sulphurized phenols has been recommended for improving fastness to washing processes. Direct, acid or chrome dyes can be aftertreated with aqueous solutions of cupric salts and a reducing agent can give improvement in light fastness [330].

GENERAL METHODS FOR IMPROVING FASTNESS TO WET TREATMENTS Dyes, on acetate, natural protein, polyamide or cellvlose- derived fibres, that contain at least one amino group, a hydrogen atom of which can be readily replaced by treatment with cyanuric chloride, can be aftertreated in cold aqueous dispersions of compourids having a mono- or di-halogenated 1,3,5-triazine ring to give improvements in their fastness to wet treatments [331].

Aftertreatment of water-soluble dyes on natural protein or cellulosic fibres with sulphonium compounds gives improvement in the fastness to alkaline milling, in the case of acid dyes on wool. Such treatments also improve the wet fastness of direct dyes on cotton [332]. Suitable dyes, when present on polyester, wool, silk, acetate, nylon, acrylic and cellulosic fibres, can also be aftertreated with polymerization initiators, resulting in the formation of polymerized dyes having improved fastness to washing processes [333].

GENERAL METHODS FOR IMPROVING FASTNESS TO LIGHT The use of U.V. absorbers in improving the fastness to light of dyed textile fibres has been excluded from this review but has been reviewed arid discussed elsewhere [334].

I am grateful to Mr D M Nunn and Mr J Shore for their patient assistance, and to those dye manufacturers who so kindly supplied details of their products and comments on their use. The mariuscript was prepared during a period spent in the Department of Chemistry, Bayero University, Kano, Nigeria and not only do I thank. Professor B J Salter-Duke for the facilities provided in his colour chemistry section, but also wish staff and students of his depaitment every success in the future.

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130. Landolt. J.S.D.C., 64 (1 948) 93; Landolt, Textil Rund. 11 (1 947) 201.

131, Ishii, Sen-i-Gakkaishi, 13 (1 957) 1 10. 132. SCI, BP 536480 (1941); Sokolov and Frolova, Tekstil Prom., 6

(1946) 33; Fedorova and Vorobova, Tekstil Prom., 18 (1958) 42. 133. Legkun, Zhur. Priklad. Khim., 34 (1 961 ) 1 126; Ciba, BP 61 9 969;

J.S.D.C., 66 (1950) 90; Ciba, BP 691 686; J.S.D.C., 69 (1953) 310; S, BP 620257 (1949); S, BP 611 235 (1948); Streck and General Aniline, USP 2 741 535 (1 956); CGY, Manufacturer's Pattern Card, J.S.D.C., 90 (1974) 208; Ciba, BP 722321; J.S.D.C., 71 (1 955) 268; General Aniline, BP 73561 9; J.S.D.C., 71 (1955) 688; Ciba, BP738647(1955); J.S.D.C.,72(1956) 30; Buddicker-Lons, Z. gas. Textilind., 58 (1 956) 93; American Cyanamid, USP3000863 (1956); J.S.D.C.,78(1962) 509; BAY, BP 767 152; J.S.D.C., 73 (1957) 231.

134. Ciba, BP 599830; J.S.D.C., 64 (1948) 295. 135. Salvin et al., Amer. Dyestuff Rep., 43 (1 954) 764. 136. ICI, BP 798061 (1958); S. BP 1299335 (1970); J.S.D.C., 89

(1973) 100; Ciba, BP 814288 (1959); J.S.D.C. 75 (1959) 466; Ciba. BP 823405 (1 959); S, BP 657 753; J.S.D.C., 68 (1 952) 29; IG. BP 522 539 (1 940); BAY, BP 767 152; J.S.D.C., 73 (1 957) 231.

137. Sun Chemical Corpn., BP638323; J.S.D.C., 66 (1950) 488; Geigy, BP 540 822 (1 941 ) .

138. BAY, BP 897 276 (1 959); J.S.D.C., 78 (1 962) 523. 139. BAY, BP 887358 (1957); J.S.D.C., 78 (1962) 184; Geigy, BP

140. BASF, BP 1067 102 (1965); J.S.D.C., 83 (1967) 353; BASF, BP

141. BAY, BP 895674 (1957); J.S.D.C., 78 (1962) 473. 142. Dow Chemical, USP 3067143 (1958); J.S.D.C., 80 (1964)

143. Ciba, BP 796 543 (1 958); J.S.D.C., 74 (1 958) 659. 144. Bradford Dyers' Association, BP 729643; J.S.D.C., 71 (1955)

481. 145. BAY, BP 969 159 (1962); J.S.D.C., 81 (1965) 33; CGY, BP

1368712 (1971); J.S.D.C., 91 (1975) 54. 146. Geigy, BP 865686 (1957); J.S.D.C., 77 (1961) 375; Geigy, BP

595 065 (1 947). 147. Marsh, Norbury and Tootal Broadhurst Lee, BP 590684 (1947);

Umarova and Stamler, Mater. Resp. Kont. Tekst. Khim. 3rd (1 974) 33; J.S.D.C., 93 (1 927) 151.

148. bntz, Morrison and Calico Printers' Association, BP 437 642 (1935); SCI, BP 550663 (1943).

149. Foulds et al. and Tootal Broadhurst Lee, BP 291 473 (1926); Foulds. Marsh, Wood and Tootal Broadhurst Lee, BP 291 474 (1926).

150. Partridge, Key, Stevenson and Stevensons (Dyers), BP 590 536 (1947).

Prog. Coloration, 2 (1971) 51.

702 695; J.S.D.C., 70 (1 954) 127.

735 557; J.S.D.C., 71 (1 955) 688.

209.

151. Ingham, Miller, Burawoy and Calico Printers' Association, BP 551 693 (1943); IG, BP 506050 (1939).

152. Landells, J.S.D.C.. 72 (1956) 137; Smith, J.S.D.C., 61 (1945) 269; Wilcock, J.S.D.C., 63 (1947) 41; Cameron and Morton, J.S.D.C.. 64 (1 948) 329; Thomas, Amer. Dyestuff Rep., 38 (1 949) 413; Clayton. J.S.D.C..48(1932)295;Smith,J.S.D.C..70(1954) 381; Smith, J.S.D.C., 77 (1961) 416; Smith, Rev. Prog. Colora- tion, 6 (1 975) 38; Lantz. lngham and Calico Printers' Association, BP 555 575 (1 943).

153. Dorset, Text. Manuf., 90 (1964) 51 1. 154. Nute, Amer. Dyestuff Rep., 34 (1 945) 230. 155. Braun, Textil Praxis, 16 (1 961 ) 728, 792, 938. 156. Roth and American Cyanamid, USP 2 833 670 (1 958); Northern

157. Evans et al. and ICI, BP 503 168 (1 939); Comp. Nat. Mat. Col.

158. Fiebig and Hohewel, Melliand Textilber., 57 (1 976) 837. 159. Lutzel, J.S.D.C., 82 (1966) 293; Lutzel and Hensel, Angew.

Chem., 77 (1965) 303; Ellis, Gantz and General Aniline, USP 3178250 (1961); BAY, BP 1445317 (1974); J.S.D.C., 93 (1977) 66.

160. Kamel. Kamel and El-Kashouti, Amer. Dyestuff Rep., 60 (Mar 1971 ) 33; (Apr 1971 ) 44.

161. Heid, Melliand Textilber., 59 (1 978) 247. 162. Sternberger, Amer. Dyestuff Rep., 63 (Sept 1974) 88. 163. Tigler, Amer. Dyestuff Rep., 61 (Sept 1972) 46, 107. 164. Heid, Melliand Textilber., 51 (1 970) 322. 165. Wood, Rev. Prog. Coloration, 7 (1 976) 80; Heid, Holoubek and

Klein, Melliand Textilber., 54 (1 973) 131 4; Schreiner and Kemter. Textiltechnik, 25 (1 975) 47; Prenzel, Chemiefasern, 76 (1974) 293.

Piedmont Section, Text. Chem. Colorist, 13 (1981) 29.

Nord, BP 543092 (1942).

166. CFM, BP 1114036 (1965); J.S.D.C., 84 (1968) 536. 167. CFM, BP 1009643 (1963); J.S.D.C., 82 (1966) 39. 168. Zerweck, Ritter and Schubert, Angew. Chem., 60 (1 948) 141. 169. CFM, BP 1504830 (1975); J.S.D.C., 95 (1979) 377. 170. CFM, BP 715532; J.S.D.C., 70 (1954) 521; CFM, BP683251;

J.S.D.C., 69 (1 953) 103; HOE Data Sheet, Solidogen FGA, 4327e TH/T (Feb 1978); HOE Data Sheet, Solidogen FFL, 4326e TH/T (Mar 1978).

171. Rizzo and Bailey, Amer. Dyestuff Rep., 42 (1 953) 492. 172. Ciba, BP 1113737 (1965); J.S.D.C., 84 (1968) 536. 173. HOE Data Sheet, Fibradurit FSN, 4279e TH/T (Dec 1978). 174. Tigler, Text. Chem. Colorist, 12 (1 980) 146. 175. ICI, BP 1321 645 (1970); J.S.D.C., 89 (1973) 444. 176. Johnson, 'The Theory of Coloration of Textiles', Ed. Bird and

Boston, (Bradford: Dyers Company Publications Trust, 1975); Rakhlina, Strunina and Kozlova, Tekstil Prom., No. 2 (1 962) 56.

177. Niederhauser, Teintex, 15 (1 950) 109. 178. Little, J.S.D.C., 80 (1 964) 527. 179. Rhim et al., Kisul Yon'guso Pogo, 2 (1 963) 122. 180. Hildebrand, Textil Praxis, 25 (1 970) 621 ; Walsh, Dyer, 157 (1 977)

232. 181. ICI, BP 952680 (1961); J.S.D.C. 80 (1964) 343; Schmidt,

Textilveredlung, 13 (1 978) 293; Roberts, SAWTRl Tech. Rept. No. 417 (1978); J.S.D.C., 95 (1979) 71; von der Eltz, Melliand Textilber., 42 (1 961 ) 929; Brunnschweiler, Textilveredlung, 13 (1978) 298; Ciba, BP 877948 (1958); J.S.D.C., 78 (1962) 60; ICI. Tech. Inf. Dyehouse, 11 95; J.S.D.C., 87 (1 971 ) 282; ICI. Tech. Inf. Dyehouse, 961; J.S.D.C., 83 (1967) 457; ICI, Tech. Inf. Dyehouse. 1294; J.S.D.C., 89 (1973) 186; ICI, BP 890518 (1959); J.S.D.C., 78 (1962) 306.

182. Hebeish, Kamel, El-Rafie, El-Alfy and Kamel, Cell. Chem. Tech., 12 (1978) 317.

183. Smith, Rev. Prog. Coloration, 6 (1 975) 38. 184. Shore, Rev. Prog. Coloration, 10 (1979) 33. 185. Farag, Bull. Fac. Eng. Univ. Alexandria, 14 (Jan 1976) 1, 43. 186. von der Eltz, Melliand Textilber., 42 (1 961 ) 929. 187. Rattee, J.S.D.C.. 85 (1969) 23. 188. Ferguson, J.S.D.C., 89 (1973) 281; ICI, Tech. Inf. Dyehouse,

1294; J.S.D.C.,89(1973) 186;ICI,BP879980(1959);J.S.D.C., 78 (1962) 150; ICI,Tech. Inf.Dyehouse,961;J.S.D.C.,83(1967) 457; ICI, Tech. Inf. Dyehouse, 640 J.S.D.C., 78 (1962) 293.

189. Dawson, J.S.D.C., 80 (1 964) 134; Badertscher, Amer. Dyestuff Rep., 52 (1963) 859.

190. Datyner, Nicholls and Pailthorpe, J.S.D.C., 93 (1 977) 21 3. 191. Text. World, (Sept 1901) 527; J.S.D.C.,17(1901)265;Text.Col.,

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200. h a y et al., BP 12614 (1899); J.S.D.C., 16 (1900) 132. 201. Ciba, BP 655712; J.S.D.C., 67 (1951) 477. 202. Millson, Amer. Dyestuff Rep., 32 (1943) 502; Meckel, Textil

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208. Cho, Chosen Shoyakkai Gakujutsu Rombunshu, 6 (1976) 187; J.S.D.C., 94 (1978) 543.

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255. Cherubim, Kautschuk u Gummi, 19 (1966) 676; Kuntstoff Rund- schau. 13 (1966) 291; Kuntstoff Rundschau, 13 (1966) 235; Neale, Bain and Rawlings, Tetrahedron, 25 (1 969) 4583, 4593.

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265. BASF, BP 244104 (1924); SCI. BP 429209 (1935); Geigy, BP 51 1 676 (1 939).

266. IG, BP 393011 (1933); IG, GP 432111; Geigy, BP 388936 (1933); IG, BP 370458 (1931); IG, BP 467998 (1937); Elliott,


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272. BAY, BP 975307 (1962); J.S.D.C., 81 (1965) 84; Diamond Alkali, USP 3480379 (1968); J.S.D.C., 87 (1971) 131; Schuf- fenhauer, Chemiefasern, 22 (1972) 407; BAY, BP 1291 784 (1969). J.S.D.C., 89 (1973) 27; ICI, Tech. Inf. Dyehouse, 1318, J.S.D.C.. 89 (1973) 186; S, BP 1377218 (1970); J.S.D.C., 91 (1975) 155; BAY, BP 1283284 (1969); J.S.D.C., 88 (1972) 381; S. BP 1299335 (1970); J.S.D.C., 89 (1973) 100; ICI, BP 715919; J.S.D.C., 70 (1954) 592.

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aftertreatments for improving the fastness of dyes on textile fibres

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