Indian Journal of Fibre & Textile Research Vol. 21 , March 1996, pp. 1-29

Advances in direct dyes

John Shore

I Cromley Road, High Lane, Stockport, Cheshire SK6 8SP, UK

Current trends in direct dyes research include: structural designs to minimize health risks from intermediates; improved sorbents and decolourising chemicals for dye residues; factors influencing dye sorption by cellulose; origins of dyeability variation in cellulosic materials; activation of cellulose to enhance dyeability; introduction of activated sites for nucleophilic dyes; and dyeability of cellulose crosslinked with N-methylol or polycarboxylic acid reactants.

Keywords: Amine intermediates, Cationised cellulose, Cellulose reactants, Direct dyes, Dyeing theory, Dye sorption

I Introduction The distinction between the classes of

water-soluble dyes for cellulose is becoming less clear as a result c;>f recent developments in dyeing and finishing. In the early 1980s, Sandoz I introduced a range of reactant-fi~able substantive dyes, the Indosol SF series. Initially, these were all copper-complex direct dyes selected from the existing Solar(S) range for good light fastness when aftertreated with the special I ndosol(S) fixing agents used with them. Now, however, the Indosol range includes brighter unmetallized dyes that are unable to form co-ordinate linkages with the fixing agent and must become linked to the agent or to cellulose by other means2

•

Another trend in the 1980s was the interest of retailers of fashion garments in improving their response to consumer demand by deferring the decision on colour as late as possible. This was facilitated by dyeing as made-up garments or garment blanks, rather than fabric or yarn. Much research has been undertaken, mainly in the USA, into techniques for improving the dyeability of cotton that has already been given a crosslin king finish in fabric form. A successful outcome to these efforts will be highly dependent on integrating the requirements of dye and finish.

Increasing concern about residual colour and electrolyte in effluents from direct or reactive dyeing also led in the 1980s to numerous attempts to modify cellulose using reactive cationic agents with a view to enhancing uptake of anionic dyes and minimizing the need for added electrolyte. Many of these treatments brought their own disadvantages, none being entirely susccessful. More recently, a parallel development

has been the concept of incorporating the reactive function into cellulose3 , either by pretreatment or in situ reaction , and selecting or de"igning dyes with nucleophilic amino substituents able to react covalently with the activated substrate.

2 Developments in Organic Chemistry No dyer can afford to ignore the environmental

consequences of his activities. A major study4 was undertaken by ET AD (Ecological and Toxicological Association of the Dyestuff Manufacturing Industry) to identify and assess the risks to health attributable to dyes and the~r intermediates. More than 90% of over 4000 dyes tested in the survey had LDso values greater than 2 x 103 mg/kg. The highest values for acute toxicity were found among the basic dyes and disazo direct dyes .

In July 1994, the German government banned the use of azo dyes that yield on reduction any of twenty named arylamines, including benzidine (1 ; R = H) and its disubstituted congeners (1; R = CI, CH 3,

OCH3)' These amines are classified in Germany as

R R

HN 0 h NH2 2~ (11

substances that have been proved unequivocally to be carcinogenic5 . Most European dye makers no longer make dyes that break down to form these specific ammes.

2.1 Replacements for Dyes Derived from Hazardous Amines

The main potential risks to health from dyes and intermediates are acute toxicity, carcinogenicity and

2 INDIAN 1. FIBRE TEXT. RES., MARCH 1996

allergic sensltlsation. Certain disazo structures derived from benzidine are known to be carcinogenic, including Congo Red (2), the first direct dye to be discovered. Early epidemiological studies revealed an increased incidence of bladder cancer in workers exposed to 2-naphthylamine. Later, benzidine was also identified as a causitive agent but it was not until the 1970s that the major dye makers agreed to phase out the manufacture of benzidine dyes. An analytical stud y6 of over 40 direct dyes derived from benzidine revealed that all contained at least 2 mg/kg benzidine as impurity and three contained more than 50 mg/kg.

Thin-layer chromatography has been used to isolate and identify benzidine and o ther unsulphonated diamines(l). The dye is reduced with dithionite and the products separated on silica gel with a methanol-chloroform eluant. The diamine spots are rendered visible by uv irradiation or exposure to nitric oxide vapour. Strict sa fety procedures are essential in view of the toxic nature of the contaminated eluant 7

• An alternative procedure is chloroform extraction followed by gas chromato­graphy. Reduction of certain disazo and trisazo dyes for leather such as c.1. Direct Brown 2(3) and Black 3l:l(4) yielded peaks with retention times characteristiC of benzidine, whereas the benzidine­free tetrazo dye c.1. Direct Black 22 (5) did not 8

.

A notable trend in research on novel direct dyes has been attempts to find satisfactory alternatives to these hazardous diamines as middle components. An example was the synthesis and use of 7-amino-3-(4' -aminophenyl)quinoline (6) to prepare disazo and

~OOC OH

HOb-N;N---©--(lrN'N~NH2 - Na<l:JS~

(3)

trisazo dyes. The differential reactIvIty of the teterazonium salt of 6 was helpful , the diazonium cation on the phenyl ring being more reactive, but unfortunately the derived dyes were only moderate in colour strength and light fastness9 .

Replacing benzene or naphtha lene nuclei by heterocyclic analogues often enhances substantivity as well as avoiding the use of hazardous amines. Thus, in a series of azostilbenes and related dyes (7; Ar= phenyl or 2-thiophenyl, X = CO, CONH or CH = CH), the affinity values increased in the order of increasing electron mobility (vinylene > amide> keto) and were greater for the thiophenyls than the corresponding phenyl-suhstituted dyes 'o .

The important contribution of hydrogen bonding to the substantivity of direct dyes was explored by the synthesis of red (8; X = CHO) and violet (8; X = PhNHCSNH2) monoazo derivatives of R-acid . The existence of hydrogen bonding between the X group and hydroxy groups in cellulose was demonstrated . This research was followed up by a more comprehensive comparison of various disazo R-acid dyes derived from various alternatives to benzidine [9; Y = 0, NH, CH 2, CO, S02, CH = CH, CONH, NHCONH, NHCSNH, CONHNHCO, NHCOCONH, NHCOCH2 CONH, NHC( = NH)NH, and CONHC (= NH)NHCO]. The significance of such central functional groups with scope for hydrogen bonding or dipolar interaction with the cellulose OH groups was clearly evident II.

HO S~Na

X-©-N;N~ Q

(8) SO)Na

SHORE: ADVANCES IN DIRECT DYES 3

Analogous disazo dyes from 4,4'-diamino-benza­nilide, -benzophenone, -di phenyla mi ne, and -diphenylurea were synthesized as we ll as simil a r d yes derived from di amines co ntaining cyclic carbazole, f1u o reno ne a nd phenanthrid o ne systems, for comparison with the corresponding benzidine analogues. It was found that 3,8-di a min ophenan­thrid one showed the Illos t favourable proper ti es 12.

Derivatives of ben 7. idi ne and 4,4' -diami nodi phcnyl­urea containing sulph o o r carboxy substituents were also incorpo ra ted into di sazo ana logues of establi shed benzidine d yes. Arylamines containin g cyclic imido systems were used as diazo o r te trazo components for mo noazo, di sazo o r tri sazo d yes. These had marked ly hi gher affini ty for ce llul ose than the analogous acycl ic d yes l3 .

Primuline base res ult s from the thionation of p-toluidine and conta ins threc main compo nents: mono- , bi s- a nd tri s-dchyd ro thi o-p-to luidine (10). Thi s mixture is sulpho na ted a nd marketed as c. 1. Direct Yellow 59, a diazotisa ble direct dye. I n a recent study ' 4, the components were sepa ra ted before sulphonation and application to cotton . The increase in the number ofbenzothiazole units had a powerful bathochro mic influence o n hue as we ll as inc reas ing the substantivity fo r ce llul ose.

2.2 Dyes from Non-genotoxic Intermediates

A more fundamental approach to no n-h azardo us azo dyes is to identify and utili 7.c precursor intermedi a tes that have been shown to be non-genotox ic . Increasi ng reli a nce o n publi shed data for the mutagenicity a nd carcinogenicity ofazo dyes and their intermedi a tes sho uld ensure th a t the se lected intermediates are non-m utagenic a nd will take account of the potential geno toxic ity of any metabo li tes result ing fro m reducti ve clca vage of the azo groups. Incorpo ra tion of butyl or butoxy substituents ortho to the NH group of the pa rent amine eliminates mutagenicity, pres umably by blocking N-hydroxy lati o n . Although bulk y a lkoxy gro ups

we re useful in lowe ring the mutagenicity of certain analogues or c. 1. Direct Bl ack 17, the decrease observed was less than that seen in a series of monoa7.o disperse d yes '5

Replacement or a C a to m in the a ryl rin gs of benzidine by a n N a tom leads to significant lowering of the muta genic it y exhibited by the pa rent amine in the standard .IO/lI/ lIllc I/O assay (Ames test). The above results hi ghlighted the impor ta nce of the Pri va l mod ilica ti o n of the sta ndard A mes mut agenicit y assay in eva lua ting azo dyes ' s . A related project in vo lved the design a nd synthesis of J-acid derivatives as potential magen ta components for jet printing. The dyes had to be no n-geno toxic in the Ames tes t and I ~ l s t to light on paper. A disazo dye deri ved from .I -acid and a suitab le hyd roxya mino­quinoline ex hibited the best a ll-ro und properties ' 6

2.] [}~l· EHlul'I1t Trl'atml'nt and Recycling

A ltho ugh direct dyes are particularly easy to apply, the need fo r e lect ro lyte additio n , the presence of chel a ted copper in many structures of high li ght fas tness a nd the need to apply a ca ti oni c a ftertrea tmen t for high we t fastness mea ns tha t careful a ttenti o n must be given to final trea tment of the exhau st liquo rs. Reviews of water suppl y and recovery for ce llulosic dye ing ' 7. ' B have specified the main contaminants a nd summa rized me thod s of dealing wi th them .

The ri si ng costs of water supply a nd effluent di sposa l are fo'rcing dye rs to re-examine the possibilities of repeated use of d yeba ths. Equatio ns have been derived to show how elec tro lytes build up · during repeated use of dyebaths. The initial recycle of a direct cotton dyebath can give the same quality as a conventional fresh-bath d yeing', but meta i ion build-up may modify the shade of dyeings after multiple recyc\es I 9 . A simple sc reening test has been devised 20 using over 50 direct a nd acid d yes to assess whethe r they a re precipitated by a typical hard water concentra ti on of calcium salts. Ten of the dyes proved sensItI ve; so lubility prod uc t cons tant s were dete rmined for some of them.

Res idua l sa lt levels in exhaust d yeba th s must be lowered on enviro nmental gro unds. Several direct and reacti ve dyes were evaluated to determine the minimum sa lt required for an acceptable yield . Most direct dyes ex hau st well a t 2-5 gi L sa lt but reactive dyes need a t least 20 gi L. Dyei ng at the lowes t practicable liquor ratio sho uld be an integra l ai m of efforts to minimi ze the sa lt con tent of dyehouse e ffluen t 2 1 . Resid ua l sodi um chl o ride o r sulphate ca n be harmful to fres h water orga ni sms. Less tox ic and

4 INDIAN J. FIBRE TE XT. RES., MARCH 1996

mo re readil y precipitabk a lte rna tives have been evaluated. Direct d yes applied with a patented o rga nic sa lt of magnesium ha ve given results equal to those obtained in the prese nce o f sodium chloride22

.

Methods of meas uring the colour of wa ste dye liquors have been reviewed. A survey2 3 fo und that reac tive red s and sulphur blacks caused most difficulty in thi s regard , but direct d yes can be readil y removed by adsorption or precipitation. Detailed invesligation by cyclic voltamet ry 24 of the mechanism of reductive strippingofC.1. Direct Red I (II), Red 79( 12), Violet 47( 13) and Violet 51 (14) has revealed tha t complete reduction of both azo groups in each dye, even the copper complex Violet 47, was achieved in sodium dithio'lite solution at pH 9.5 and 25°C.

Details have been given of dithionite reduction tests carried out on the azostilbene C. I. Direct Yellow

4{ 15) and eight other anionic dyes. Adsorption capacities a nd rates of adsorption of these dyes on activated ca rbon have been determined 25 . Studies of the carbon sorption of direc t d yes from dyehouse wastes ha ve demonstrated that the saturation adsorption increased with ': (i) the relative molecula'r mass (rmm) of the dye, (ii) the electrolyte concentration in the waste water, and (iii) the integral pore volume of the carbon20 .

Cheap and readily ava ilable sorbents fo r d yes are of great interest for this purpose. Fly ash is a finel y powdered waste from thermal power pl a nts and is a rich source of silica , alumina, ferric oxide and other inorganics. T he chemica l composition ofay ash from va rious sources has been tabulated . The application of thi s ma terial to remove colour from direct dye effluents is reported 27

. Cellulose prepared from sugar cane bagasse pulp was reac ted with acrylamide at

CH3 H~ OH

H3C~ N=N / \ N=N~' '-.~ - J

50:3 No OCH3 No~5 '- ,/ NH-{)

( 14)

503 Na

HO--©--N ~ N-O-CH ~ CH V-N: N-@-OH No0:35

(15 )

SHORE: ADVANCES IN DIRECf DYES 5

Nao,S-©-N=N-d;:N~ N mO~ " roO: N :a:bN=N{='>so,Na ,,/ "I /

Na03S NHCO NH S03Na

(16)

WS~Na N=Ni}\' N=N~_\ N=NmO

H

/" - /1 " "I / " /

\ / \ / N 0°3 S N H 2

S03Na NaO 5 3

(17)

S03 Na

",C¥O-©-N'N-©-CH= CH9 N=N-@-OCH,CH, NaOJS

(18)

alkaline pH and the effects of treatment conditions on contents of Nand COOH groups were examined. The uptake of c.1. Direct Red 79(12) was evaluated spectrophotometrically28 . A pilot plant has been developed recently at the Denkendorf Institute29 for decolorisation and partial recycling of dyehouse effluents. Three flocculants for direct dyes were exmined:

• an amide-amine condensation product, • a dicyandiamide-HCHO condensate and

ammOnilllTI salls, and • a mixture of a polyelectrolyte and aluminium

chloride. Recent evaluationJO of the macrocyclic ligand

cucurbituril in powder form as a precipitant for direct dyes varying in molecular size, including c.I. Direct Red 79 (12; disazo) , Red 80 (16; tetrazo) and Blue 71 (17; trisazo), established the influence of pH and ligand concentration on adsorption. Near-quanti­tative removal of dyes is only possible by passing the effluent through a column filled with the curcurbituriP'. The effects of non ionic and anionic surfactants , as well as inorganic electrolytes , on the formation of insoluble complexes of the li gand with these dyes were examined. Anionic surfactants compete with direct dyes for the available cucurbiturip 2. Most of the copper in direct dyeing effluents is from copper-complex dyes. Selective removal of dye from the liquor by this ligand eliminates almost all of the heavy metal contamina tion33 .

The reductive biodegradation of Congo Red (2) and eight monoazo dyes by a cell-free extract from

Pseudomonas sfufzeri was evaluated34. Six of the dyes were appreciably degraded. The extract was quite specific for three of them (all N-substituted orthanilic acid-->aniline dyes) with the lowest redox potential.

Catalytic oxidation is probably the simplest approach to decolorisation of residual direct dyes. Poly-p-phenylene-I ,3,4-oxadiazole may be used to induce oxidative decomposition under uv irradia­tion3s . The influence of substituents in arylazo H-acid dyes on the rate of oxidation in hydrogen peroxide solution has been studied36 . The dissociated form of the 2-hydroxyazo grouping undergoes degradation by perhydroxyl radicals (·OOH) that are formed. The mechanism of oxidation of sulphonated amino- and hydroxy-arylazo dyes in sodium percarbonate solution at pH 10.6 was also examined37. The initial rate and apparent activation energy of the reaction were determined. The quinone hydrazone form of such dyes is more susceptible to attack than the hydroxyazo tautomer.

.ozone treatment has potential as a powerful means of decolourising.exhaust dyebaths for recycling. Large-scale trials38 on dyehouse effluents have established a relationship between colour removal , pH and ozone consumption. Fundamental studies of the ozonolysis mechanism have demonstrted tha t the azostilbene c.I. Direct Yellow 12(18) yields mainl y 4-carboxy-4! -ethoxyazobenzene-3-sulphonate (19) and hydrogen peroxide39 . The stability to ozone of 2-arylazo- l-naphthol-3,6-disulphonates was investigated . Electron.withdrawing nitro or bulky perfluorobutyl substituents in the 2~aryl nucleus gave improved stability40.

6 IN DIAN J . FIBRE TEXT. R ES., M A RC H 1996

3 Developments in Physical Chemistry The transfer of a direc t dye fro m an aqueo us

ciec tro lyte soluti o n to the inte rior' of a cell ul osic fibre is a n esse nti a ll y simple process, ye t it co ntinues to stimul a te resea rch o n the mechani sm involved . A comprehensive trea tment o f the sorpti o n equilibrium mu st ta ke accoun t o f the io nic composition of the so luti o n ph ase a nd the mo rph o logica l a nd surface cha rac te ri sti cs o f the substra te .

3.1 Generalizl'd Donnall Equilihrium and the Gouy-Chapman Theory

A genera li zed a fTini ty eq ua tio n was develo ped4 1 by elabo ra ti o n o rthe classica l D o nna n theory. Thi s was ex tended to ta ke account of the influence o f multi valent ions o n the eq uilibrium as we ll as the effect o f a lk a line pH conditi o ns o n the ioni sa ti o n o f hydroxy a nd ca rboxy gro ups in the ce llulosic substra te. These rdinements lead to some fa irl y complex eq uati o ns fo r the compu ta ti o n o f a ffini ty. A . prac ti ca l limitati o n to their use fo r predicti ve purposes is the need to de te rmine by a na lysis the concentrati ons o f a ll the io nic species present in both phases o f the sys tem . The content of ion is a ble groups a nd the vo lume of the interna l aqueo us phase o f the

1I9)

fibre must be "sta bli shed , as well as the fmm, bas icity and purity o f each dye present, including the na ture of the io ni sa ble impurities. M o reover, it has bee n po intecl O Ut'~ 2 th a t ad va nces in definin g the cha racteri stics of the electrica l d ouble layer a t the fi bre surface h ave shown the Do nna n di stribut ion of ions betwee n the inte rna l a nd externa l p hases to be inco rrect.

Acco rding to the G o uy-Cha pm a n theory. d ye in g equilibria with direct d yes can be cha racte ri zed with rega rd to three co nsta nts that a re readil y o bta ina ble expe rimentally. These arc the sta ndard a ffinity (Ao) and two terms tha t defin e the elec trosta ti c interaction between the dye a nd the dyed substra te. The term A I is rela ted to the cha rge density on the substra te and A2 is rela ted to the specific surface accessible to d ye a ni o ns. The ra ti o A I/A1 represents the sta te o f cha rge a t the inne r sur face, i.e. the cha rge co ncentration o f the surface accessible to d ye. D yeings o f va rio us co mbina tio ns of c. 1. Direct Yellow 50(20), Red 81 (21), Blue 15(22) o r Blue 106(23) demo nstra ted tha t the inte rac ti o ns be tween com ponent d yes ca n be quanti fi ed in a simple ma nner using thi s a pp roach43.

Mo re recently, the merits o f the D o nna n theory a nd the G o uy-C ha pman model ha ve bee n co mpared 44

. Bo th method s o ffer useful ad vantages and have some fea tures in co mmon , such as the representa ti o n of adsorption behavio ur in term s o f three paramete rs: affi nity, fix ed cha rge a nd inte rna l vo lume in the D o nna n treatme nt: , o r a ffinit y, ch a rge density a nd accessible surface in the G o uy-Chapma il equa tions. Da ta for the co pper-complex di sazo c. 1.

OH

NoO S-~N=N~N=Nro 3 "c..r \=r ~ I~ ~

NoO)S NHC0-0

(21)

SHORE: ADVANCES IN DIRECT DYES 7

( 24)

NoO 5 3 S No035 503 No / \ OH OCH3 ",..... . _ ..... I 1./ ~ONo

N-N / \ N-N \ / _ A - W N NH I/\'LN:N ~OOOH ~ OH NH~ ~ \:=:J ~

Nol1..5 H...C \I -, . _] . _j N "" N (25) 'rH-@

Direct Red ~3(24) at various concentrations of Glauber's salt were used to illustrate the Gouy-Chapman approach.

3.2 Sorption and Accessibility of Cellulose Structure Two direct dyes of markedly different molecular

sizes are widely used in the red-green test to reveal different degrees of maturity in raw cotton: c.1. Direct Red 81(21; rmm 675) and Green 26(25; rmm 1350). Adsorption isotherms for both dyes or unmercerized cotton and viscose yarns were measured . Reciprocal plots suggested Langmuir­type sorption onto a limited number of sites and saturation values that were higher on viscose:Both dyes showed evidence of sorption as a monomolecular layer. The cotton yarn was subjected to controlled acid hydrolysis to leave a crystalline residue and dye sorption was again determined . As the time of hydrolysis increased, the sorption of Red 81 decreased, ultimately to approximately half that of the intact fibre. With Green 26, on the other hand, accessibility initially increased but later fell slowly to a level about double that of the control. Presumably, this internal increase is attributable to improved access of the bulky Green 26 molecules to previously inaccessible internal surfaces45.

3.3 lnfluence of Electrolytes on Dye Sorption In a study of the kinetics of direct dye uptake46.47,

cotton yarns were dyed continuously by a column chromatographic technique . The influence of control parameters on the initial rate of strike was

examined. ~elevant variables included dye type and concentratIOn, electrolyte concentration and temperature. The trisazo c.1. Direct·Blue 7\(17) wa s one of ~he dyes tested. The role of electrolytes in promotmg exhaustion was examined48 in relation to dye structural features. Cotton was dyed with two direct dy~s ?iffering in rmm and degree of sui phonatIOn m the presence of various electrolytes and a phosphate buffer. Under these conditions the un i-divalent electrolytes, e .g. calcium chloride, ~e~e the most effective in boosting exhaustion , presumably by forming calcium dye sulphonate aggrega tes.

The e.ffects of sodium chloride in direct dyeing have been mterpreted using 5% ethanol as a disaggregating agent. The Nernst equation was u~ed49 to describe adsorption equilibria for two dlsazo dyes derived from 4,4'-diaminodiphenyl­m~thane and 4,4' -diaminostilbene-2,2' -disulphonic aCId. A related study of the symmetrical disazo c.I. Dir~ct Blue I (26) demonstrated th,at ethanol exerted a dlsaggregating effect at low salt concentration decreasing the saturation uptake of dye, but at high salt the solvent favoured the electrostatic association of dye molecules via protonated amino and sulphonate groups with enhanced adsorption of the aggregat.ed dye. The Langmuir equation was appropriate to describe the ' adsorption equilibrium50.

The .effe~ts of al~ali-metal ions, quaternary ammOnIum Ions and bIvalent and trivalent cations on

8 INDIAN J. FmRE TEXT. RES., MARCH 1996

_ *~.., OH N=H~COh d e:

3=NwOH ~"H1 SO) OS ~ /1"

3 /1 ....... ....... ./ ....... ./

(26) S03NO S03 No

0- Cu++ Cu++ O-

J 0- O-'-q f[ir' N=Nm mN=N 1_' - ./....... :;..-- .......

....... 1./ "I ./ Sn.... N H ~N~S No0

3S NH S03 No ~L 2

(27)

H2N-d-~~N-©-N=N~N=N-©-N~:bNH2 ~ NoO,S SO,No

(29)

the adsorption of the copper-complex disazo C.I. Direct Violet 66(27) by viscose have been investigated 5 1.52. The size of the cation is much more important 'than its valency. A linear relationship was found between dye saturation values in the presnce of various ions and their ionic radii. The rate of sorption also increased with the size of the cation, particularly at lower temperatures.

Equilibrium isotherms and rates of uptake of the symmetrical disazo c.1. Direct Blue 1(26) on visco~e were determined in the presence of electrolytes with predictably different capabilities to modify water structural characteristics. Saturation values at 45°C increased in the order: tetraethylammonium CI < tetramethylammonium CI < propylamine HCl < ethylamine HCl < NaCl < KCl < guanidinium Cl. These results clearly demonstrated 5 3 that variations in water molecules clustering around the hydrophobic groups in dye molecules influence the dye-binding mechanism in cellulose. In the presence of alkali-meta I chlorides the absorption of Blue I by viscose and dyeing rate at constant salt concentration both increased in the order: LiCI < NaCI < KCI. In binary mixtures of these electrolytes,

the (larger) cation with the greater ability to disrupt cslustering in water considerably enhanced the ability of the smaller cation to influence dye uptake54 .

When another symmetrical disazo Congo Red(2), a dye that readily aggregates by electrostatic attraction between protonated amino and sulphonate groups, is applied to viscose in the presence of electrolytes capable of modifying the clustering of water molecules in a predictable manner, the adsorption and rate of dyeing are similar to those for much less aggregated anionic dyes. Thus, although Congo Red readily forms aggregates, the influence of electrolyte cations on water clustering around the dye ions is unaffected ss .

3.4 Influence of Organic Additives on Dye Sorption

Most inorganic salts enhance the uptake of direct dyes but the effects of organic additives are more difficult to predict. The influence of pH and various concentrations of auxiliaries on the dyeing of cotton with the disazo C.I. Direct Blue 67(28) and the tetrazo C .1. Direct Black 19(29) was examined by spectrophotometry of the dyebaths56. Urea, pyridine and. amyl acetate markedly increased exhaustion by

SHORE: ADVANCES IN DIRECT DYES 9

disaggregating the dyes, whereas gelatin and carboxymethylcellulose had a restraining effect by forming dye-agent aggregates. Strongly acidic liquors decreased uptake of dye, as did alkali above pH 8.5

In aqueous media the phosphonic acid groups in the sequestering agent ethylenediaminetetramethyl­phosphonic acid (EDTMP; 30) are ionised and the N atoms exert a weakly basic effect. The presence of small amounts of EDTMP in the dyeing of cotton with the copper-complex disazo CI. Direct Red 79( 13) accelerated the rate of uptake and improved the fastness to washing. Similar effects were observed when the cotton was pretreated overnight with small amounts ( ~ 0.03 giL) of the aminoacids alanine (31), valine (32), phenylalanine (33) and histidine (34). This was attributed to protonation of the amino group of the aminoacid which is hydrogen bonded to cellulose57

, facilitating uptake of the copper-complex anionic dye.

3.5 Pore Size and Diffusion Kinetics

A variable porosity model was adopted to describe the diffusion of the symmetrical disazo dyes CI. Direct Yellow 12(18), Red 2(35), Blue 1(26) and Blue 15(22) in water-swollen cellophane at various ionic strengths. The validity of this model was tested by adsorption experiments58 . The discrepancies observed between apparent diffusivities obtained by sorption rate and steady-state methods were attri buted 59 to the concen tration dependence of the diffusion process. The influence of the crosslinking of cellulose film using bis(hydroxyethyl)sulphone and

dimethylolethyleneurea on the diffusion behaviour of Yellow 12(18) was examined . Crosslinking reduced the steady-state diffusivity by almost twice the decrease in equilibrium adsorption . The diffusivities were calculated by the time-lag technique and from permeability measurements. The results were interpreted60 in terms of the pore model and the gel model for water-swollen cellulose. Diffusion rates of four direct dyes were measured in cellophane at various concentrations of dye and electrolyte. The apparent diffusion coefficient and another coefficient expressing diffusion of the free form of the dye, unrestrict~d by immobilisation effects, were derived . The free diffusion values were two or three orders of magnitude larger than the overall values61

•

The pore structure of cellulosic. fibres is decisive for direct dyeing. It can be defined using probe molecules of specific graduated sizes, measurement being by either the stationary non-solute water method or by chromatographic: elution on a cellulose column. The distribution of pores can be determined from chromatographic measurements, revealing the accessibility of the inner voids to dye molecules of different sizes62

. Pore structure data have been related to the adsorption and kinetics of the disazo dyes CI.Direct Red 81 (21) and Blue 1(26). The specific pore surface can be decisive for equilibrium uptake, whereas the porosity or the amount of free water can be important when inte'rpreting differences in diffusion rate63 .

In a recent detailed study64 of the kinetics of direct dyeing from finite baths, curves of adsorption against

o 0

~N-CH-COOH I

CH3

(31)

II II HO-~-CH2 /CH2 -~-OH

OH ~ OH N-CH2 CH2 -N 0

R / "II HO- ~- CH2 CH2- ~ -OH

OH OH ( 30)

H2N -CH - COOH I CH

/ '\ H;C CH 3

(32)

~N-CH-COOH I

CH 2

~N NH-iJ

(34)

10 INDIAN J. FIBRE TEXT. RES., MARCH 1996

time formed the basis for determining sorption equilibria, spccific rate constants, diffusion coefficients, resistance to diffusion, steady-state equilibria, adsorbent capacities, finite bath exhaustions, activation energies and interaction enthalpies. The kindic constants were correlated with the number of aryl rings and ionisable sulpho groups in the direct dye molecules.

3.6 Influence of Energy Fields on Direct Dyeing

An interesting trend in recent years has been the application of certain novel energy systems to the dyeing process. Direct dyeing is particularly convenient for this because of its essential simplicity. By selecting dyeing conditions that give a slow rate of dyeing or only moderate exhaustion in the absence of the specific energy input, the positive influence of the treatment can be sensit ive ly assessed.

The diffusion behaviour and affinity values of the symmetrical di sazo dyes c.I. Direct Yellow 12(18), Red 2(35) and Blue I (26) on cellophane under hydrostatic pressures up to 600 MPa have been measured 65 at 5YC. The uptake of Yeilow 12 increased slightl y but those of the other two d yes decreased considerably with increasi ng hydrostatic pressure. The central sulpho groups in the Yellow 12 molecule tend to inhibit aggregation, whereas Red 2 and Blue I aggregate much more readily. The small increase in affinity observed with Yellow 12 may indicate that cis-trans isomerisation is favoured as the pressure increases.

The effects of ultrasonic cavitation (the formation and violent coliapse of micro bubbles) onthe dyeing of cotton fabrics with Yellow 12(18) a nd Blue 1(26) have been studied in detaiI 66 .67 . Ultrasonic waves heat the medium of propagation appreciably. The dyeing rate and equilibrium adsorption are both increased to an extent dependent on the cavitation intensity68 . Determination of the combined effects of ultrasound-induced heat and cavitation66 has shown that external heat requirements are much lower. Both cavitation and induced heat accelerate the dyeing rate but the efTect of cavi tation is dominant. In a recent study of three direct blue d yes on cotton6 9 , the influence of dye type, electrolyte concentration, temperature' and ultrasonic intensi ty on dyeing kinetics was examined .

A direct d ye solution was passed through a magnetic field a nd immediately used to dye cotton fabrics 70 . The degree of exhaustion varied with the strength of the magnetic field. the temperature and the rate of flow of the d ye solution . The relation between exhaustion and field strength was complex, which explained inconsistencies in previous work.

The trea tment was more effective at lower temperatures and higher flo w rates, providing the flow was not turbulent. The effect of the magnetic pretreatment was lost after storage for about 6 h at ambient temperature .

Electrochemical activation of the aqueous medium 7l allows the direct dyeing process to be accelerated and the equilibrium exhaustion increased. The effect of such acti va tion o n the state of aggregation of the dyes in solution ha-s only recently been clarified . The electrochemical loading of the dyebaths required for optimum sol ubility characteristics of the dyes has been determined.

Applications of radio-freq uency energy, y-rays, uv radiation, plasma and laser treatments in dyeing and finishing have been reviewed 72. Six disazo direct dyes were applied to cotton fabrics tha t had been irradiated for 4-8 h with y-rays 73 . Some dyeings were aftertreated with a cationic fi xing agent. The irradiation resulted in enhanced uptake or dye, better fastness to washing and partial resis tance to extraction with 50% aqueous dimethylformamide, perhaps as a result of covalent reaction of the dye with activated sites in the irradiated substrate. After treatment with the fixing agent, however, was a more effective method of improving wash fastness .

4 Effect of Preparation on Dyeing Behaviour Cellulosic fibres require thorough preparation

before dyeing and direct dyes are quite sensitive to differences in qegree of penetration. There is a need for more selective and specific dyeing tests to be developed that will reveal the effects o f inadequately controlled preparation processes on these fibres.

4.1 Mercerisation and Liquid Ammonia Treatment

The relationship between fibre porosity and direct dye uptake was examined 74 by pre-swelling with causti·c soda or zinc chloride and measu rement or pore size di stribution and porosity. Substantial d ye savings were demonstrated by trea tment of cotton fabrics with 20% NaOH solution for I min at ambient temperature, followed by washing, neutra lisation and dyeing with c.I. Direct Yellow 28 (36; monoazo), Red 81 (21 ; disazo) or Blue 781(37; trisazo). The improved colour yield was attributed to increased dye uptakc, the optical effect offibre swelling and internal light scattering influenced by the change in total pore volume. Dyeings of the disazo dyes Red 81(21) and Blue I (26) on bleached cotton fabrics tha t had been mercerised in various ways7S provided further evidence that the dye saving is related to the reduction in diffuse light scattering a nd depends on the pretreatment given. The reduced light scattcring

SHORE: ADVANCES IN DIRECT DYES 11

(36 )

(37 )

CI H3C OH

CI-fit-" N=N %N=N ml ...... ...... ./ ~

S03Na NaOJS NH CONH~ NHCOCH3

(38)

occurs at the interface between the fibre seco nda ry wa ll and the ce ll lumen.

Grey a nd merceri sed samples o f cotto n were compa red with viscose staple fo r steam so rpti o n a nd wa ter retentio n. So rpti on measurements with suga rs a nd dextra ns o f gradua ted sizes?6 were used to dete rmine cha nges in pore structure caused by merce ri sing . By correla ting these res ult s with the upt a ke o f the symmetri ca l di sazo C. I.Direc t Blue 1(26) it was deduced tha t tra nsiti o n po res in the cellul os ic fibres with a di ameter o f a bo ut 20-60 nm a re respo n<; ible fo r d ye so rpti o n. C ha racte ri sti cs o f the pore structure o f co tt o n and viscose in the wa te r- swo llen sta te?? ena bled new volume terms to be es timated fo r ca lcul a ti o n o f thermodyna mic affinit y. Substanti vity parameters fo r Blue 1(26) o n co tton un de r va ri o us conditi o ns a ft er ho t merceri sing a t 60 a nd 90°C have bee n determined ?s . The effec t '> o f a lk a li co ncentra ti o n a nd tempera ture , additi o n o f surfac ta nt s. vac uum impregnati o n and the Therrn o tex sa tura ti o n process o n the meree ri singa t 60° a nd 90°C have been determined ?S symll1etrica l di sazo c. 1. Direct Red 2(35) a t 10: I liquo r ra ti o we re in ves ti ga ted " ' .

Wa rmmerce risa ti o n of grey co tt o n fa bri cs be low 50°C res ul ted in little diffe rencc in a bso rp tio n of the symmctrica l di sa70 c. 1. Direc t Blue 15( 22). a lth o ugh trea tll1ent a t hi gher tempera tures did produce a mca ';urahl e increaseHo . The relati ve effecti ve ness o r hot a nd cold methods o f ll1ereeri sa ti o n was assessed H I hy tcs ts o r wate r retenti o n. iodin e

a bsorption a nd d ye ing tri a ls using c. 1. Direct Green 26(25) a nd c. 1. Reacti ve Red 2 .

. Pretrea tment with liquid ammo nia is a hi ghl y ef"lec tl ve and well contro lled a lterna tive to ca usti c soda merceri sa ti o n, but the hi gh ca pita l cos t o f the eq ui pment necessary fo r recovery of the a mmo nia as well as the a pplica tio n step limits the ado pti o n of thi s sophisticated process mo re widely. Bleached cott on fa brics trea ted in th ese two ways were exa mined for cha nges in morphol ogy by X-ray a nalysis, fibre c ro~s- section a nd measurements of the sorptio n o f IodIne, steam a nd c. 1. Direct Blue 1(26). M a rked diffe rences between the two treatments were fo und a nd liquid a mmo nia swelling does no t a lways yield a sta ble fi bre structure82 . In la te r wo rk s3, trea tmen t with liquid ammoni a a nd then ca ustic soda was compa red to trea tment with a mmo ni a a lo ne. The changes in fibre s tructur~ were aga in examined by X~ ray analYSIS a nd sorpti on of the di sazo dyes C. I. DIrect Red 110(38) a nd Blue 1(26).

More recentl y84, untrea ted and merceri sed cotto n were trea ted with liquid a mmo nia a nd then tes ted fo r a bsorbency, mo isture rega in a nd d yea bility with the symmetri ca l disazo d yes c. 1. Direct Red 2(35) a nd Rille 1(26). The d ye ing properti es o f th e merceri sed co tto n ~ere ad verse ly affec ted by subsequent liquid a mmo nI a trea tment. The mo re o pen structure achi eved by merceri sa ti o n is evidentl y converted back to a mo re compact a rra ngement by a mmo nia, whIch apparentl y induces cha nges offine struc ture especially in the a mo rpho us regio ns of the mercerised cotto n.

12 INDIAN 1. FIBRE TEXT. RES ., MARCH 1996

An important a rea for liquid ammo nia treatment is prior to crosslinking with cellulose reacta nt fini shes. Hi gh-qua lity cotto n shirting subjected to thi s pretrea tment a nd then given a dura ble press fini sh shows good easy-ca re pro perties with o nly modest strength loss . C ha nges in morpho logy during thi s sequence have been evalua ted 8 5 with the direct d yes o f ma rkedly different mo lecula r sizes (21 a nd 25) used in the red-green test for immature co tto n (see Section 3.2).

4.2 Coverage of Immature Ncps in Cotton Fabrics

Pa le fl ecks in d yed cotton fa brics ca n be caused by immature o r dead cotton. C lumps of immature fibres tend to exhibit poo r dyeability a nd the fl a ttening o f such clumps may fo rm sma ll , highly re fl ec ti ve surfaces. Poo r dye penetrati o n may leave undyed spots if the clumps o f loose ly a tt ached imma ture fibres cha nge positi o n a ft e r d yeing.

The d yea bility o f imma ture cotto n ca n be improved by merceri sa ti o n butthe lack of seconda ry ce ll wa ll develo pment in dead co tt o n ma kes such trea tment ineffec ti ve86 Co tt o n fab rics co nta ini ng both immature fibre neps and p rocess neps composed o f damaged ma tu re fi bres were given va rio us merce ri sing trea tments . After d ye ing with ten direc t dyes , full y mercerised fa brics showed 95% increase in visua l coverage of neps, but ca ustic ised fa brics showed o nly 85 % increase. A fter liquid ammo ni a trea tment , a significa nt improvement in nep cove rage occurred with o nly fi ve o f the ten d yes87. The differences betwee n d yes in their behaviour towards nep coverage a re most evident with those neps composed of immature fi bres with some seco nda ry wa ll develo pment. Aggregation and mi gra tion properties o f direc t d yes appea r to be re la ted to nep covcrage88 .

Careful dye selection is the best way to deal with the pro blem of dead cotton . Direct dyes conta ining more tha n one amino or amido group in their structure tend to achieve rela ti vely good co verage o f neps88 .89 . The content o f prima ry amino gro ups is no t the o nly crite ri o n9 0 , since ca rbona mido , sulphona mido a nd ureido a re also powerful hydrogen bo nding sites89.9 1

.

Mo re than 100 dyes o f known structures were evaluated92 fo r coverage pro perties. T he most efTective dyes in each hue ca tegory were identified and

co rrelatio ns be tween structure and coverage a bility were analyzed.

A test has been developed93 to distingui sh between imma ture fi bre neps a nd neps composed o f thin ma ture fibres. Webs made from lint processed to form mechanical neps we re d yed with c.I. Direct Red 81 (21), selected as yieldi ng · pa rti cul a rly poo r coverage of imma ture cotton88 . Neps that showed contras t aga inst the web back gro und were ident ified as immature ra ther tha n thin ma ture fib res . Thi s tes t was compa ll'ed94 with o ther fibre-level eva lua ti on procedures to ident ify clo th pro blems. Exce llent co rrela tion was found be tween undyea ble neps seen in d yed webs a nd in dyed clo th made fro m the same fibres. The web-nep tes t ga ve bette r p redictio n ' of cl o th neps tha n did instrumenta l measurements of ave rage fibre qua lity, including micronaire, maturity a nd linea r density.

It has been c1a imed 95 tha t a pre trea tment with chitosa n (pa rti a ll y' deacetyla ted po ly-N-ace tyl-D­glucosa mine) o n co tto n containing imma ture fibre neps improves the cove rage in subsequent dyeing with Indoso f. SF(S) d yes. as well as o the r direct a nd reac ti ve dyes. Mo re recently, the po lyethyleneimine a uxilia ry Polymin P(BASF) was a pplied in a similar wayQ6. Both o f these wea kly ca tionic po lymers can be . used in conjunctio n with cellulose reactant fini shes but tfie trea tment may ad verseiyaffect tne subsequent penetration a nd light fas tness o f direct o r reacti ve dyes.

4.3 Diagnostic Dyeing Tests for Undyed Cellulose

Ma ny la tent fa ults in tex tile ma teria ls only beco me a ppa rent du ring d yeing. The sensitivity o f dyes to inherent va ri a ti o ns in pro perties o f a n un~ed substra te ca n be explo ited in developing , diagnostic dye ing o r staining tes ts9 7 to define the na ture a nd extent o f such diffe rences . A lo ng es ta blished stain tes t is based o n [he viole t co lo ur fo rmed by spo tting iodine o n co tto n conta ining residual sta rch size. Durable vio le t sca les produced with direc t dyes, vat dyes or pigments98 ca n be used to quantify the degree of sta ining in the iodine test, which fades rat he r quickly o n sto rage.

Two meth ods have been compa red Q<) to assess the

degree of wetta bility o f enzyme-desized co tt o n fabrics: The Tegewa Drop Test and a dyeing test using 10 gi L C. I. Direct Red 23(39). Vario us si ngeing a nd stea ming trea tments l OO ha ve ben appli ed to co tto n

SHORE: ADVANCES IN DIRECT DYES 13

yarns, which were then dyed with se lected dyes . The influence of these thermal treatments on the problem of streaky dyeings has been distinguished from other possible causes such as the presence of immature fibres.

Consistent dyeability in cotton fibres may be estimated using a specific concentration of the sensitive tetrazo dye c.1. Direct Green 27(40). After spectropho tometric measurements the results are expressed as % variation ; shade variations less than 5% a re too slight for visual pe rception . C ritical mixtures of reactive d yes were applied to test yarns containing known dyeabiJily variations. Typical direct dyes covering all chemical types were evaluated on the same ya rn s. Certain d yes, including the symmetrical disazo c. 1. Direc t Red 79(12), showed good correlation with the reactive mixture recipes 10 I.

Several dyeing tests a re available to assess the degree of maturity within colto n S<l lilples a nd their respon se to a lk a line treatme nt s. A comprehensive series of tests for matu ri ty has been reviewed I 02 in rel a tion to d yeability response. The potentia l exploitation of ma turity test data to cont ro l bulk dyeing has been assessed . The red-green test at the boil with two dyes differing widely in rmm has already been mentioned (see SectionI3.2). Ripe cotton is stained violet red a nd immature o r dead cotton fibres show up as green I 0 3 .

Another sensitive test of thi s kind is based on a mixt~re of the monosulphonated c.1. Acid Red 151(41) and the tetrasulphonated c.I. Direct Blue 10(42). Untreated cotton is stained red but an increa se in alkali concentration during me rce ri sin g or causticising results in progress ively bluer staining 104 . Fully mature colton is stained dull viole t but immature or dead cotton fibres appear as navy blue 10s . In a recent study l06 of the trea tment o f colton with cellulase enzymes'i the mixture of dyes 41 and 42 was used to follow the kinetics of swelling. Merceri sed cotton is hydro iysed much more readi ly by cellulase enzymes than an unmercerised control. These changes were followed by monitoring the uptake of the trisazo tetrasulphonate c.I. Direc t Blue 71(17) as well as tests of various physical properties I OJ.

5 Exhaust Dyeing with Direct Dyes A comprehensive account I 08 of the mechanisms of

dye exhaustion and levelling in batchwise conditions included valuable insight into the significance of electrolytes in direct dyeing. Direct dye adsorption isotherms were measured on cotton fabric forming the . stationary phase in a liquid chromatography column 109

. Frontal analysis gave similar results to standard eq uilibrium sorption techniques and yielded a reli a ble quantitative measure of dye compatibility. Experience of the controlled dosage of

14 INDIAN 1. FIBRE TEXT. RES., MARCH 1996

salt in solid fonn in the dyeing of cotton yarn packages has been reported I 10 . The effects on levelness of the dosing technique, machine design and type of salt were elucidated. Electrical resistance measurements were used to estimate salt concentrations in the dyebath.

5.1 Influence of Surfactants on Direct Dyeing

Studies of the interaction between dyes and auxiliaries have stimulated much research but one of the attractions of direct dyes is that they can be dyed level simply by control of dyebath temperature and electrolyte addition . Complexes of direct dyes and polyvinylpyrrolidone are thermally stable and can be used for the fugitive tinting of wool or cellulosics but casein-dye complexes become unstable after a few days of storage II I .

The interaction between three direct dyes and a series of dodecylpolyoxyethylenes (penta to octa) wa~ investigated by filter paper capillary analysis 11 2.

The effects were dependent oil dye structure, Qxyethylene chain length and loss of water structure associated with the hydrophobic groups in dye and agent. The interaction between c.I. Direct Red 1(11) and several anionic , cationic and nonionic surfactants was examined by spectrophotometry I 13 .

Anionic agents do not interact with fully solubilised dye molecules but a specific equilibrium is established with nonionic types. Cationic products interact

. strongly, resulting in neutralisation and further solubilisation. Spectrophotometry was also applied 114 to the stoichiometery of interaction between two stearylamine polyoxyethylenes (II and 22 EO units/mol) and the disazo dyes C. I. Direct Red 23(39) and Blue 2(43) . Maximum dye uptake was observed at the highest mole ratio of dye to surfactant.

5.2 Interaction between Direct Dyes in Mixtures

An important practical objective of theories of dyeing has always been the reliable prediction of behaviour in mixtures from data assembled for individual members of a range of dyes. Sorption data for individual dyeings and binary mixtures of the disazo disulphonates C. I. Direct Yellow 12( 18), Red 2(35), Red 81 (21) and Blue I (26) were analyzed 115. A modified Langmuir equation accounted for positive

and negative dye interactions on the fibre. Factors influencing selectivity in mixture recipes include:

• competition of dye anions fo r the available adsorbing surfaces,

• decrease in sorption of either dye anion because· of increase in total concentration of sodium ions on the fibre ,

• electrical repulsion of incoming dye anions by those of like charge already adsorbed ,

• ' attraction of dye anions for one another on the adsorbing surface, and

• I interaction between different dye anions in the dyebath.

Equilibrium sorption isotherms of three direct dyes and their binary and ternary mixtures were determined on cotton 116. Sorption of an individua l dye from any mixture was invariably lower than sorption alone at any given dye and salt concentration. A recent detailed study l1 7 - 11 9

involved the trichromatic combination of c.I. Direct Orange 46, Red 79(12) and Blue 71(17) on mercerised cotton yarn in the presence ofa non ionic surfac tant o r a mixture of linear and cyclic dextrins. The initial strike and ultimate exhaustion values depended on the individua l dyes, auxiliaries a nd the interactions between them. Six direct dyes of various types were applied in self shades and mixtures on cotton fabric 12 0 . The effects of nonylpnenolethoxy­late and tridecylethoxylate surfactants on the kinetics of dyeing were also investi.gated .

5.3 Dyeing of Bast Fibres

Direct dyes are particularly useful for the dyeing of jute. The effects of dye and electrolyte concentrations , time and temperature on the uptake of such dyes by jute were studied 12 1 . Selected products to achieve optimum fastness to light , washing and chemical treatments were recommen­ded. The ability of various aftertreatments to improve these fastness properties and the resistance to photodegration of jute dyed with direct dyes has been evaluated 122. The photostability was enhanced by aftertreatment with copper sulphate and potassium permanganate and the washing fastness by subsequent appliCation of a cationic fixing agent. Dyes with peak wavelengths in the range 590-670 nm showed low light fastness on jute. So, the hues that

OH MOH NH2

¥roN=N~N=N;' ....... ;' I....... \=i \::::J, I;, '- ;' NO'1S so, No

SO,No

(4"3 )

SHORE: ADVANCES IN DIRECT DYES 15

depend on dyes that absorb mainly below 560 nm are preferred.

The surface morphology of raw sisal fibres , as well as after alkaline or acid treatment and grafting with styrene and ethyl acrylate , was investigated by electron microscopyl 23. Dyeabaility tests with e.I. Direct Green I (44) and with blue disperse and basic dyes on the grafted fibres are reported. The common milkweed plant yields cellulosic fibres with interesting thermal insulation and absorption properties l24. Direct, disperse and basic dyes were evaluated to achieve satisfactory fastness ratings on milkweed fibres.

5.4 Dyeing of Regenerated Cellulosic Fibres

Comparisons of the structural characteristics of regenerated cellulosic fibres with the fine structure of cotton yield valuable insight into dyeability differences between them. Four high wet modulus modal fibres were compared with cotton and viscose for dyeability with typical direct dyes l2s . The fibres varied in cross-section and in skin-core ratio. Cotton contains more ordered material inaccessible to direct dyes than do the regenerated fibres. Prima modal fibres showed higher exhaustion than viscose, but exhaustron values on the hollow fibre Viloft were intermediate between those on cotton and viscose.

Substantivity values for several Sol~r(S) direct dyes , including the symmetrical dyes e.1. Direct Yellow 28(36; monoazo disulphonate) and Red 80(16; tetrazo hexasulphonate) , were determined on cotton, viscose and modal fibres. The sulphonated phthalocyanine Blue 199 was anomalous in showing much lower substantivity on the regenerated fibres, despite thei r larger accessi ble surface area 126. Increasing the electrolyte conte.nt of the dyebath brought the substrates closer in dye uptake . Analysis of these results in terms of the Gouy-Chapman theory (see Section 3.1) yielded an exceptionally high A2 value (specific surface accessible to dye) for Blue 199, typical of an unusually large dye anion .

In another recent investigation 12 7, e.I. Direct Blue 1(26; disazo) , Blue 86 (phthalocyanine) and Blue 106(23; triphenodioxazine) were applied to cotton , viscose, modal and carbamate-spun fibres. Initial

(l, l,)

strike and final exhaustion values were related to ultimate levelness. Factors with a bearing on dyeability were evaluated by scanning electron microscopy, porosity and crystallinity. Exhaustion values decreased in the order: viscose and carbamate-spun > high tenacity > modal and cotton. The structural characteristics, moisture sorption and swelling behaviour of viscose fibres have been discussed 128 in the context of the dyeing and finishing of outerwear fabrics woven from filament yarns .

6 Continuous Dyeing with Direct Dyes Direct dyes are much less suitable for continuous

dyeing than for exhaust methods. Tailing and migration problems are encountered and prolonged diffusion is necessary in pad-batch methods . The pad-roll process is probably the most appropriate semi-continuous method for direct dyes at 80-1 OWe. Recommendations have been given 129 for control o f fabric moisture and pad liquor temperature, d ye selection for optimum compatibility and the use o f suitable auxiliaries . The p<l-d-roll system is more versatIle than steaming methods with direct dyes but the development of compact pad-steam ranges has enabled more valid cost comparisons to be reached against the semi-continuous alternatives 130.

Many water-soluble dyes show undesirable migration in continuous dyeing. In a recent work on this problem 131 , mercerised cotton was pretreated with wetting agent and then padded with various direct dyes , including Red 81 (21) and Blue 78(37). Factors identified as influential in this context include:

• liquor retention and swelling of the substrate, • dye substantivity and solubility during padding

and drying, • presence of electrolytes and migration

inhibitors, and

• design of dryer and conditions of drying.

There is a tendency for migration of direct dyes to increase as substantivity decreases, but reactive dyes migrate less than this trend because of the immobilisingeffect of reaction with the substrate l32 .

16 INDIAN J. FIBRE TEXT. .RES., MARCH 1996

7 Activation of Cellulose to Enhance Dyeability The sta tus of co tton cellulose as a na tura lly

occurring biodegrada ble polymer is in tune with the times but that does no t mean that cellulosic dyeing is free from environmental problems. Direct dyes ha ve high inherent susbsta nti vity but they still need electrolyte addition to ensure high exha ustion in full depths. Reacti ve dyes a re less substantive a nd thus need more salt. There has been a surge of inte rest recently1 33 in techniques to introduce ca tionic groups into cellul ose, neutra lising the negati ve cha rge on the fi bre surface a nd boos ting the substantivity of a ni onic dyes .

7.1 Cationic Epoxy or Azetidinium Reactants

There has been much ac ti vity in this a rea, ma ny o f the a ttempts to incorpora te quaterna ry N sites in cellulose being dependent on epoxy deri va tives. The fir st prod uct o f thi s type on the ma rket 134.13 5 was Glytac A (Protex ; 45). This is readily ava ilable 136

from epichlorohydrin a nd trimethylamine (Eq . I) . Glytac reacts with cellulose via the glycidyl group

at a lk a line pH. Cellulose modified in thi s way ca n b e dyed with acid dyes a nd shows enha nced uptake o f direct or reacti ve dyes, a lthough some earl y claims of improved wet fas tness were exaggera tedI 37 .138.

Reacti ve dyes can be applied a t neutra l pH without sa lt , co nditions tha t a re environmentally a ttracti ve. Thi s behaviour has been a ttributed to predomina ti on of the zwitterionic form of the Glytac side cha in a fter a lka line fi xa tion (Eq .2).

Thus, the a nionic dye is a bsorbed on the quaternary N site a nd, ifreactive, it is attacked by the nucleophilic ionised alcoholic gro up nearby! 39.

A reagent exhibiting some features in common with Glytac is I , l-dimethyl-3-hydroxyazetidinium chloride (DMAC)I33 ·140. It reacts with cellulose by a similar a lka li-ca ta lysed ring-opening etherification . T he modified substra te conta ins ma inly the zwitterionic form of a seconda ry amine a na logue o f Glytac (Eq .3):

The results from the two q uaternised cellulose ethers are simila r, but there is ma rginally better reactive dye fi xati on to the DMAC grouping.

An a lterna ti ve approach1 41 to arnini sation of cotton fabric invol ves padding with ca ustic soda solution, then immersion overnight in an acetone soluti on of epichlorohydrin and trietha nolamine (mole ra ti o , 3: I) . The etherifying agent is assumed to be mainly the reacti ve tertia ry a mine (46) fo rmed by condensati on between the sta rting ma teri a ls( Eq.4).

7.2 Cationic N-Methylol Reactants The N-metlhy lola tion reaction that has been so

impo rta nt in traditional chemica l fini shing ca n be exploited as a first step to the aminisa tion of cellulose us i~g N-methylo lacrylamide (NMA; 47) (Eq .S).

Thi s acryla midomethylated cellu lose reacts readil y with ammonia or a lkylamines to yield cellulose deriva ti ves3 containing a mine o r quaterna ry N groups (Eq .6).

CH) 1+

+ N(CH)) ~ CH2--CHC~-N- CH) CI-"0/ I

Cellulose-OCH2 CH I

OH

Cellulose-OC~ CfH

OH

OH­CI---+Cellulose-OCH2

CH)

1(45)

H20

H..,O L

ZnCI2 Cel\ul0ge-OH +HOCH2NHCOCH=CH2 6" Cellulose - OCH NH COCH -CH

150 C 2 - 2

(47)

... ... .. ( I )

... ..... (2)

....... (3)

..... ... . (4 )

.(5 )

SHORE: ADVANCES IN DIRECT DYES 17

Dyeing tests on these derivatives showed generally good colour yields and high fixation , but reactive dyes on those aminised with di- or tri- methylamine gave poor fixation . The dye-fibre linkage is labile owing to the strongly electron-withdrawing quaternary groupl39 (Eqs 7&8).

7.3 Cationic Active Halogen Reactants Groups of the haloheterocyclic type found in

traditional reactive dyes , such as aminochloro­tri~zine or diftuoropyrimidine, have been exploited in aminising agents that also contain mono- or bis-quaternary N groups to boost the uptake of anionic dyes by theaminised substrate. Such agents react more readily with cellulose and show higher thermal stability than the ring-opening types such as Glytac or DMAC. Both classes of monofunctional reactive system, however, share the disadvantages of low substantivity for cellulose and must be applied by padding. More complex multifunctiona l structures were designed for exhaust application 142 and these gave impressive colour yields. There are practical drawbacks to all these agents, however, including lower light fastness l3 J, hue changes and poor penetration into the fibre 142.

An alternative approach to the aminisation of cellulose involves esterification usmg chloropropionyl chloride (48) (Eq.9).

Chloropropionylated cellulose condenses readil y at 50°C with ammonia or alkylamines to yield aminised cellulose derivatives l43 (Eq.IO).

If arriinisation is carried out at the boil , however, chloropropionic acid is eliminated and the cellulose derivatives do not contain ester groups. The ester bond is still intact after reactive dyeing but it is hydrolysed during alkaline soaping at the boil (Eqs 11&12).

7.4 Polymeric Cationic Reactants Many cationic polymers have been applied to

cellulose with a view to enhancing uptake of anionic dyes. It is considerably more difficult in those instances to interpret the precise mechanisms involved , apart from the obvious participation of electrostatic:~ interaction between dye anions and basic groups in the polymer. Recent studies have included the application to cotton 133 of the polyamide-epichlorohydrin resin Hercosett 125 (Hercules): originally marketed as a shrink-resist treatment for wool. The essential objective was the ab.sorption and fixation of reactive dyes at neutral pH

Na~P04 C.llulos.-OCH

2NHCOCH =CH2 + H-R • C.llulos~OCH2NH COCH2CH2-R

+ R=-N~,-NHCH)I-NHCH2CH20H ,-N(CH)2 or -N(CH))CI-

OH-Cellulose - OH + CICOCH2CH2CI - Cellulose-OCOCH 2CH2CI

(48)

soOc Cellulose-OCOCH2CH 2CI + H -R~·Cellulose-OCOCH2CH2R

+ R=-NH2 ,-NHCH3 ) -N (CH)2 or-N(CH))CI-

......... (6)

.. .. ..... (8)

.......... (9)

..... .... ( I 0)

......... ( I I )

.. .... ... ( 12)

18 INDIAN 1. FIBRE TEXT. RES., MARCH 1996

in the absence of sa ltl 44. Improved dyeabihty and good wet fa stness were obtained, but dullness of hue and impaired light fastness were disadvantages.

Incorporation of thiourea into the Hercosett polymer during application 145 was intended to overcome deficiences when using low-reactivity dyes on Hercosett alone. Thiourea reacts with azetidinium groups in the resll1 to form iso thiouronium groups (Eq. 13).

These are more strongly nucleophilic and improve the fixation oflow-reactivity dyes. Some of the isothiouronium groups decompose during dyeing to yield thiol groups, which form further sites for dye fixation and may also react with remaining azetidinium groups to form thioether crosslinks in the resin (Eqs 14 & 15).

Differences in colour yield were still observed between dyes of high and low reactivity and therefore ethylenediamine was evaluated as an additive to the Hercosett resin l46. This reacts readily with azetidinium groups to form primary, secondary and tertiary amino sites for fixation of reactive dyes (Eq. 16).

Enhanced substantivity for direct and reactive dyes , good bri ghtness a nd excellent fa stness to

" + ...... NH2 N - C~CH CH -5=C

/ I 2 "NH 2 OH CI-

washing were achieved but the light fastness was still impaired in most cases.

Epichlorohydrin can be polymeri sed using the ring-openi-ng catalyst boron trifluoride etherate (BF30Et2) in carbon tetrachloride. Quaternised derivatives of polyepichlorohydrin (PECH) were prepared by reaction with dimethylamine (Eq. 17).

Cotton was treated with polymers of this kind (rmm 400-2000)136.147 and dyed with c.l. Direct Ora nge 39 (azostilbene), Blue 78(37; trisazo tetrasulphonate) and Blue 86 (sulphonated phthalocyanine). Residual chloromethyl groups in the PECH derivative are capable of reac ting with cellulose under alkaline conditions. T he higher the rmm of the polymer, . the higher the direct dye exhaustion as a result of complex formation l47. Cofour yield on the treated cotton in 2 giL NaCI solution is higher than on an untreated control at 25 giL NaCI cQrlcentration. Perspiration fastl1ess is excellent but fastness to washing is not improved . Reactive dyes show high fixation on the treated cotton even when d yed without salt or a lkali .

7.5 Simultaneolls Application of Reactants and Nucleophilic Dyes

A relatively uncontrolled attempt to enhance the colour yield and wash fastness of selected direct dyes involved add ition to the dyebath of a colourless reactant that would react with nucleophilic groups in

· . . (13)

· .. (14)

· . . (15)

\ -./N CH21HCH2NH CH2CH2NH CH2)H 0v(

OH OH · .. (16)

[-C~-TH-O-J + C~CI

n CI--]

. n · . . (17)

SHORE: ADVANCES IN DIRECT DYES 19

the dyes and hydroxy groups in.celiulose. Most of the dyes selected 14H contained at least two primary arhino groups in aminonaphth ol residues, as in c.I. Direct Red 2(35), Red 28(2) and Blue 2(43). The reactants eva luated were cyanuric chloride (49), l , l-diethyl-3-hydroxyazetidinium ch loride (DEAC; 50) and 2,4-d ichloro-6-( 4' -sulphoanilino )-.s·-tri azine (5 1), which will indeed reac t readil y with primary arylamines. Some of the dyes selected, however, contained onl y sa licylic acid residues, as in c. 1. Direct Brown 2(3), or diphenylurea components, as in Yellow 50(20), and these are most unlikely to react efficient ly under dye ing conditions .

In a later developmentI 49. 150, cyanuric chloride was proposed as an aftertreatment of cotton already dyed with <.l mino- containing direct dyes. This approach appears even less likely to succeed than in situ. addition to the dyebath . Seri ous hazards are associated wi th the handling of cyanuric chloride under these conditions. Dye-agent reaction will be inefficien t because of hydrolytic deactivation of these reactants and uptake of cyanuric ch loride (or its hydrolysis products) will be poor on the pre-dyed substrate.

7.6 Introduction of Al·tivated Si ll's for Nucleophilic Dyes

Thi s is a much more controlled approach to tile cuncept of incurporating the reacti ve function into the substrate and ca rrying out a reacti ve dyeing with a

CI'f~CL NyN

CI

(49)

Na01S~NH N CI \::::J ~ I(

N" N Y CI

( 5')

'non-reactive' dye co ntaining nucleophilic gro ups3 A model dye of this kind was prepared by rec!c ting the aminoch lorotri azine dye c. 1. Reac ti ve Red 58 wit h ethylenediamine to form a 2-a minoethylamino­triazine derivati ve (Eq . 18) .

Acryl amidomethylated cellulose prepared by condensation ot'N-methylolacrylamide with Collon cel lulose (see Section 7.2) reacts readi ly wi th nucleophilic dyes of this kind which show no hydrolysis during dyeing. High fixat ion is achieved either by exhaustion at pH 10.5 in 80 g{ L salt so lution or by pad-batch at the same pH for 24 h (ref.139). These aminoalkyl dyes show zwitterionic charac­teristics below pH 8 and this lowers the nucleophilicity of the primary amino group (Eq . 19).

Nucleophilic dyes containing thi ol groups would be more reac ti ve than aminoalk yl analogues hut there wou ld be problems of toxicity. odour and a tendency to ox idi se to di sulphide. Aminoaryl and hydroxy­alkyl analogues wo uld be less reacti ve than these am inoalky l deri va ti ves .

The novel reac tant 2.4-dichloro-6-(.2'-pyridino­cthylamino)-s-tri azi ne (DCPEAT; 52) was eva lua ted 151 as a mea ns of acti va ting cellulose by pad-batch application at pH 8.5 for 24 h. After a cold water wash, the modified substrate was dyed with aminoalk yl dyes prepared by reacting c.1. Reacti ve Red 58 (monofunctional) and the bi s(aminochloro­triazine) Red 120 with ethylenediamine. Both dyes .

(50)

.. ........ ( 1 X)

..... .. . ( 19 )

20 INDIAN J. FIBRE TEXT. RES., MARCH 1996

(5'3 )

especially the latter, gave high fixation by exhaust dyeing at pH9 without salt.

Nucleophilic aminoalkyl dyes can also be fixed on either cotton I 5 2 or nylon 1 53 that have been pretreated with the trifunctional reactant 2-chloro-4,6-bis{4'­sui pha toethylsulphonylani lino )-.I-triazi ne (53).

Developments in this area seem to be leading to daunting complexity rather tban elegant simplicity. Certain aspects of this concept inspire unease rather than confidence: • the risk of premature hydrolysis leading to impaired fixation has been transferred from the dye to the substrate, • the pretreatment with a colourless reactant necessary to activate the substrate must be exceptionally uniform if dye fixation is to be consisten t, • if penetration of the reactant is poor (more likely the higher the rmm), ring dyeing will follow and the fastness properties will be adversely affected, • only the aminoalkyl dyes will react with the activated substrate and other classes of dyes for unmodified cellulose may be inapplicable, and • cost implication:- give concern because both dye and substrate must be specially modified befo"re the desired reaction can occur.

8 Cationic Aftertreatment of Direct Dyeings The aftertreatment of direct dyeings to improve

their fastness performance has been a perennial objectiye of research in this fieldI 54 .1 55.

8.1 Conventional Aftertreatments

Recent developments in this area have not been spectacular. Five direct dyes on cotton were aftertreated with a cationic fixing agent. Addition of formic or acetic acid surprisingly impaired the effectiveness of the agent 156. Efficiency indices have been devised to assist users offixing agents to evaluate their cost-effectiveness in improving wet fastness, as well as adverse effects on shade and light fastness I 57 . Fastness to wet rubbing can be a serious problem in full depths of direct dyes aftertreated.with a cationic

agent. Mechanical destructi o n of the dyed fibres produces microscopically small fragments that stain the adjacent white fabric l58 . Six proprietary aftertreatments marketed for cotton dyed under domestic conditions have been evaluated with c.I. Direct Red 81(21). None of the agents was satisfactory and colour loss was increased in some instances l 59

. Chitosan (see Sectibn 4.2) has been applied to dyed viscose, cupro and polynosic fabrics by a pad-rinse technique. There was a marked increase in fabric stiffness and lower moisture absorbency. Effects on fastness of reactives were negligible but fastness of direct dyes to wet treatments was impaired l60.

8.2 Reactant-fixable Direct Dyes

Probably the most sigl)iticant development in direct dyes during the 1980s was the introduction of the Indosol SF(S) dyes and fixing agentsl . The original range of twelve dyes, c.I. Direct Violet 66(27) being a typical member, were all copper-complex types selected for good light fastness when aftertreated. The patent literature revealed that Indos'ol CR was a mixture of three components designed for simultaneous crosslin king and dye fixation. The components were:

• a polybasic condensate of diethylenetriamine and an amide, e.g. cyanamide, dicyandiamide, guanidine or biguanide, • an N-methylol precondensa te of the dicyandiamide-formaldehyde type, and • an acid catalyst, e.g. lactic acid .

The polybasic condensate was la ter marketed alone as I ndasal E-50 far the exhaust aftertreatment of Indosol d·yeings. This agent does not confer any improvement in crease recovery.

Compared with reactive dyes , Indosols offered savings in dyes, chemicals, water and process time. Treatment with Indosol CR eliminated the need for any subseq uent resin finishing. Partial replacement of Indosol CR by dimethylold ihydroxyethyleneurea (DMDHEU) offered a further saving l61 , but this was' accompanied by higher fo rmaldehyde release.

SHORE: ADVANCES IN DIRECT DYES 21

Trends in washing. and laundering practice were shown to be favourab le for the Indosol system l62 .

The originallndosol SF range was strong in blues and greys but somewhat deficient in the yeliow to vio let sector. Novel reactive yellow and red dyes were later added, blurring the distinction between the reactive and reactant-fixable classes. A third type of aftertreating agent was introduced to give even better fastness to washing. Indosol E-F forms a similar dye-agent complex to that produced by Ind osol E-50, but it is held more securely by virtue of covalent bonds between agent and fibre l63 that resemble those fo rmed in conventional reactive d ye ing.

9 Interaction between Crosslinking Finishes and Direct Dyes ' The influence of DMDHEU.on co tto n dyed with

several classes of dyes , includihg directs, ha s been studied 164. Dye structure/.inorganic ca ta lyst type and curing conditions were taken int o account. Differences in colour yield , fixa tion , light fastness and crosslinking were interpreted in terms of the extent of interaction between fibre , d ye and fini sh. The formaldeh yde-induced discoloura tion of twice­coupled H-acid dyes, i.e. those containing a l -amino-2, 7-bis(phenylazo)-8-naphthol grouping, by N-methylol reactants was investigated recentlyl 65. Electrophilie attack at the amino group by the + CH 20H ca tion initiates the hue change. Bulky and/or electron-withdrawing groups close to the I-amino position have a retardin g effec t.

9.1 Simultaneous Dyeing and Finishing

An obvious way to minimize processi ng costs in dyeing a nd finishing is to operate two stages simultaneously rather than in sequence. Unfortuna­tely, the moist/wet a lkaline fixation that is necessary for most cellulosic d ye classes (reactive, sulphur, vat, azoic coupling) is highly incompatible with dry curing of a cellulose reactant finish in the presence of a latent acid catalyst. Direct dyes, on the other.hand, do not need aH<ali addition and they benefit grea tly from the improved wet fastness conferred by a cross linked finish.

Cotton fabrics were padded with acid, direct or disperse d yes, resin and ammonium chloride, dried and cured at 16ete. In general, increasing the number of nucleophilic groups in the dye molecule gave higher colour yield within each dye class, but rmm was also significant. Fastness to rubbing and perspiration was good but light fastness varied widely, depending on dye structure a nd resin type l66. C.I. Direct Orange 61 (azostilbene), Red 80 (16; letrazo hexasulphonate) or Red 81 (21; di sazo di sulphonate) was applied to

cotton simultaneously with DMDHEU and a ca ta lyst. Colour yield increased with curing tempera ture and the deepest dyeings were achieved using amm.onium persulphate as catalyst '67 .

The phthalocyanine c.l. Direct Blue 86 was applied with DMDHEU and magnesi um chloride on untrea ted , alKali-treated 'and dieth ylaminoethylated cotton fabrics. The substrate containing cationic dyeing sites invariably showed the highest colour yield and orease recovery , irrespective of the DMDHEU concentration and curingconditions '68 .

Bleached viscose fabrics were padded with various direct dyes, including c.1. Direct Red 79(12; disazo tetrasulphonate) and Red 81 (2L disazo disulphonate), N-methylol reactant and inorganic catalyst, dried and cured under various condi­tions l69 . The extent of c rosslinking and interaction with the d yes depended on the reactant and catalyst combination, as well as curing conditions.

9.2 Dyeing after N-Methylol Crosslinkihg

The reorganization by retailers of fashion garments in recent years to bring their garment orders closer in line with customer demands in terms of colour and style has resulted in a revival of interest in dyeing after making-up asgannents. If a resin finish is required to provide easy-care performance, howevcr, thi s is normally only feasible as a continuous treatment of the fabric before ga rment manufacture. Accordingly, there has been a grea t dea l of interest in the garment dyeing of cotton that has already been cross linked and is therefore ditl1cult to d ye convemionally . Nevertheless, it is possible to achieve a nea t dura ble press look after garment dyeing of cotton twill or corduroy, for example, by soaking the dyed garments in a resin furmulation, vacuum extraction, tumble drying, pressing and oven curing l70.

If trimethylolmelamine (54) is used to crosslink cotton, remarkably enhanced atl1nity for direct dyes without salt is observed 171. There is mueh less wastage of dye in the effluent than from salt-assisted dyeings on conventionally finished fabrics . DialdehYge reactants varylllg in challllength between the aldehyde groups were used to crosslink cotton. Sorption curves for direct dyes demonstrated how the type and extent of crosslinking reduced the rate constants, diffu~ion coetl1cients a nd equilibrium adsorption of all the dyes tested 17 2.

A compromise approach to the problem of lower dyeability is to partially hydrolyse the resin finish . Thus, aftertreatment of a urea-formaldehyde finish with 5% acetic acid solution at 60°C improves dye uptake with sacrifice of some crease recovery.

22 INDIAN.I . FIBRE TEXT. RES ., MARCH 1996

{ 54)

CH) I

HO'CH"N, , C=O

...... CH / HO '- N

I CH 3

(56) (57)

Bleached cotton crosslinked with dimethylolethylene­urea (DMEU), DMDHEU , meth yla ted DMDHEU or dimethyloiisopropyl carbamate (55) was subjected to pa rtial hydrolysisl 73 in various ways (liquid ammo ni .. , NaOH mercerisation, acetic acid, urea­phosphate). All gave some improvement in dyeability wi th the disazo disulphonate C. I. Direct Red 81 (21).

Co tton fabrics crosslinked with formaldehyde , DM EU or DMDHEU were dyed with c.I. Direct Red 81 (21 ; disazo di sulphona te) or Blue 78(37; trisazo tetrasulphona te). Dye upta ke depended on whether the cotton had been merceri sed , the type of crosslin king agent and the dye structure , as well as curing and dyeing conditions l74. In general, sorption of the larger Blue 18 was favoured by formaldehyde­trea ted cellulose, whereas sorption by the fibres crosslinked with DMEU or DMDHEU was greater for the smaller Red 81. The po re structure of cotton crosslinked with DMDHEU or 4,5-dihydroxy-I ,3-dimcthylimidazolidone (DHDMI; 56) was investiga­ted using reverse ge l permeati on chromatography 175. The results were interpreted in terms of the receptivity of these subst rates toward s Red 8 i(21) . Although cross lin king reduced accessibility , samples reacted with DH DMI retai ned substantially more accessible internal volume across th~ entire range of pore sizes . Post-mercerisa tion of DH OM I-treated cotton before dyeing co nfers a further improvement 176. Direct dyes of high rmm that nonnaliy give poor yields are strongly absorbed . Such d yeings on the post-mercerised finish are substantially deeper than on an untrea ted but mercerised control. Yields are best at pH 8 because acidic dyebaths ca use partial st rippillg of the DHDMI finish.

Much more progress has been made by incorpora­ting a cationic m(loit1er into the resin finish

(55)

(58)

formulation . Thus, trimethylolacetylenediurein (T ACD; 57) , choline chloride (58) a nd a catalyst were applied to mercerised cotton a nd cured in the usual way. Tests with the symmetrical disazo c.I. Direct Blue I (26) and a reactive dye demonstra ted that thi s route provided an easy .. care finish tha t could be readily dyed in full depths after crosslinking177 .

Mono-, di- a nd tri-ethanolamines were compared as additIves for a DMDHEU fini sh on cotton . Triethanolamine was the most effectives in enhancing dyeability, giving results approximately equivalent to direct and reactive d yes on the untreated fibre. The DMDHEU reacts with the OH gro ups in the alkanolamine and the N atoms in the latte r provide sites for dye sorption 17S. Various salts of triethanolamine with organic and ino rganic acids were compared as additives to the DMDHEU finish 1 79. The dyeing characteristics of cotton crosslinked with DMDHEU in the presence a nd a bsence of triethanolamine were compared with those of mercerised a nd unmerceri sed controls. Crosslinking decreased all the dyeing kine tic constants hu t incorporation of the alkanolamine reversed these effects and enhanced d yeabilityl so.

The inclusion of an alkylene glycol or polyethylene glycol ill a DMDH EU formulation that already contai ns a ca ti o nic modifier such as choline chloride or triethanola mine greatly improves the dyeability, even with direct dyes of high rmm in full depths l 78. Cotton fabrics were given d urable press finishes fonnulated in this way and then dyed with c.I. Direct Red 79(12; disazo tetrasulphonate), Red 80(16; tetrazo hexas ulphonate) a nd ot her direct and acid d yes. Cross .. sec tiona l microscopy confirmed good penetra lion and di stribu li o n of a 1\ the dyes applied 181. Two carball10ylctbylamine add tlct s,

SHORE: ADVANCES IN DIRECT DYES 23

prepared by reaction of acrylamide with diethyl­amine 0r die thanolamine, were evalua ted 178 as ca tionic modifiers with DMDH E U. In thi s case, the DMDH EU reacts with the amide grouping a nd the a lkylami no centre becomes the site fo r dye adsorption .

9.3 Dyeing after Polycarboxylic Acid Crosslinking

The N-methylo la ted cyclic ureas , no ta bl y DMDHEU, have dominated chemical fini shing since the 1950s but the haza rds associa ted with release of loosely bound fo rmaldehyde from the fini shed fabric stimula ted a sea rch in the 1980s fo r crosslinking reactants tha t a re incapable of yielding fo rma ldehyde as a product of decomposition. One of the first of these was the cyclic urea deri va ti ve DHDMI (56) , which condenses with cellul ose vi a the 4,5-dih ydroxy gro ups. This was followed by an entirely new class of formaldehyde-free cross linking reacta nts, the po ly­ca rboxylic acids 182. 18 3 .

Cellulose is readily este ri fied with po lycarboxylic acids such as 1,2,3,4-butanetetraca rboxylic acid (BTCA; 59), 1,2,3-propa netricarboxylic aci.d (PT A; 60), citric acid (61 ) and succinic acid (62). ACidic sa lts o f phosph orus oxyacids a re the pre~e rred ca ta ­lysts 184. 185 , their effectiveness decreasll1g 111 the o rder: NaH?PO? > NaH,P04 > Nal HP04. The ca ta lyst has a butferil;g effect t-ha t minimizes the acidic hydro lysis of cellulose . Po lyca rboxylic acids a re of considerable interes t as crosslinking reac ta nts fo r fo rma ldehyde­free durable press fi nishing, giving exce llent

appearance and high strength retenti on. Dyeing trials were carried out using c. I. Direc t Red 79 (12; symmetrical disazo te trasulphonate), Red 80 (16; symmetrica l tetrazo hexasulphonate) a nd Red 81 (21 ; asymmetrica l disazo disulpho na te) to assess the degree o f cross linking 18 6.

Thermoanalytical techn iques have revea led 182.187

tha t the esterifica tion proceeds by initia l formation of cyclic,a nhydrides (e. g. 63) as the actua l esterifying agents (Eq .20) .

The hypophosphite ca ta lys t is be lieved to promote the ra te of anh ydride form a ti on, as well as acce lera ting the este rifica ti on o f cellul ose OH groups by the a nhydride. I n the case of citric acid , then~ is a ri sk of yellowing as the dehydrating conditi ons l 88

may result in the fo rmation of aconitic acid (64) and its a nhydride (Eq .2 1).

As ;n the case o r DMDHEU, incorpora ti on of a ca tio nic modifier considera bly enha nces dyea bility. Merceri sed cotton fa brics were cross linked by padding with BTCA (59). sodium hypophosphite and va ri o us additi ves l 8 9

: 1110no-, di- a nd tri-e tha no l­a mines, tri s( hydroxymethyl)ami nometha ne (65), thei r hydrochlo rides, a nd the qua terna ry compound 2-hydroxye thyltriethyla mmonium chloride (66). Acid , basic, reactive a nd severa l direct dyes, including c. 1. Direct Red 80(16) and Red 81(21 ), were applied a t pH 3 to eva lua te the rela ti ve effecti veness of the ca tionic modi fie rs. Trie tha nolamine proved pa rti­cul a rl y suita ble fo r thi s purpose beca use it con ta ins three hyd roxyethyl gro ups per molecule. In a simila r eva lua ti on 190, tr ietha nolamine compared favo ura -

COOH COOH CH 2 - COOH CH2COOH CH 2COOH

I I I I I CH1CH CHCH2 COOH CH - COOH HO-(-COOH CH2COOH

I I I C~COOH COOH CH 2-COOH

(59) (60)

eOOH COOH NoH P02 I I 2 C~CH CH CH.zCOOH ---••

I COOH

( 59)

(6 i)

( 61) (62)

a 0, ,\ "-C- CH2 / C = 0

I '- I o CH - CH C "C /' "CH{ ~O II (61) o

CH COOH II C -COOH I

CH2COOH

( 64 )

.......... (2())

.. .... .... (2 1)

24 INDIAN 1. FIBRE TEXT. RES., MARCH 1996

CH2CH20H 1+

HOH2CH2C -7-CH2CH20H CI-

CH2

CH2

0H

( 68)

bly with N-methyldiethanolamine (MDEA; 67). The BTCA anhydride reacts with the OH group(s) in the N-hydroxyethyl compound, hence incorporating N atoms to provide dyeable sites in the finished fabric . The use of these additives also gives improved durable press performance, allowing a decrease in the amounts of BTCA and hypophosphite catalyst required l90 .

The dyeing properties of cotton finished with citric acid (61) and a series of N-hydroxyethyl additives were investigated 191 using acid, reactive and direct dyes. The most effective cationic modifiers were triethanolamine hydrochloride and tetrakis(2-hydroxyethyl)ammonium chloride (THEAC; 68). The presence of these additives has an inhibiting effect on the dehydration of citric acid to aconitic acid (64), thus giving improved brightness of pastel shades 188. The inclusion of an alkylene glycol or polyethylene glyco1'89.192 in a BTCA or citric acid formulation containing an N-hydroxyethyl modifier markedly enhances the dyeability , even'with direct dyes of high rmm l88 .

Recent research 193.194 has reveaJed that unsatura­ted dicarboxylic acids, such as maleic (69; cis), fumaric (69; trans) and itaconic (70), can be used as crosslinking reactants instead of the saturated acids, provided a free radical initiator (e.g. sodium persulphate) is included as well as the esterification catalyst (e.g. sodium hypophosphite). Alternatively, mono- or di-sodium salts of these unsaturated acids are themselves effective cata lysts for the BTCA (59) esterification of cellulose. FTIR and FT-Raman analyses revealed that these salts do not form part of the esterification complex l95 . Likewise, the sodium salts of certain hydroxyacids were found l96 to be useful catalysts of the BTCA reaction . Sodium salts of citric acid (61) gave BTCA-finished fabrics with the best durable press ratings.

CH-COOH II CH - COOH

(69)

HOH2CH2C \

N -CH) /

HOH2

CH2

C

( 67)

H2C = C ·- COOH I CH2CO OH

( 70)

Certain N -containing heterocyclic compounds have been shown to accelerate the crosslinking of cellulose with BTCA . Imidazole and jts 2-alky\ derivatives were evaluated in BTCA formulations for their effects on hue changes of direct dyes. It was concluded 197 ,( 98 that these compounds can be used as catalysts instead of sodium hypophosphite in durable press finishes based on BTCA. Another interesting possibility is to use sodium bromide as a co-catalyst, for BTCA esterifica,tion. As much as 75% of the sodium hyponhosphite can be replaced l99 by the bromide without significant loss of effectiveness.

A recent comprehensi ve comparison 188 of BTCA and citric acid finishes , incorporating several types of cationic modifier, hypophosphite cata lyst and polyethylene glycol to boost the effect of the modifier, demonstrated the importance of pH control in the subsequent dyeing stage. The c<:llionic modifiers were: triethanolamine hydrochloride, MDEA (67) hydrochloride, choline chloride (58), THEAC (68) and bis(2-hydroxyethyl)dimethylammonium chloride (BHEDMAC). Acid, reactive and several direct dyes, includingC.I. Direct Red 80(16; symmetrical tetrazo hexasulphona te) and Red 81 (21 ; asymmetrical disazo disul phonate), were applied at various pH. Finishes based on DMDHEU, magnesium chloride catalyst and the same series of cationic modifiers were included as controls.

The citric acid fini shes were inferior to those based on BTCA or DMDHEU for durable press rating and dyeability . With. the a lkanolamine hydrochloride additives , BTCA gave higher N content and dye­ability than the corresponding ' citric acid fini sh , presumably because BTCA anhydride (63) reacts more readil y with OH group(s) in the N-hydroxy­ethyl compound and in cellcJlose . With either polycarboxylic acid . triethanolamine (three HOEt groups) boosted the dyea bilit y and N content more

SHORE: ADVANCES IN DIRECT DYES 25

effec tive ly tha n MDEA (o nl y two) . A gents with quaternary N atoms, vi z. chohne chloride, THEAC a nd BH E DMAC, co nfe rred hi gher fas tness to washing th a n the te rtiary a mine hyd rochl o ride. Sa ti sfacto ry washing fastness of BTC A-treated co tto n is a tta ina ble fo r a wider ra nge of dyes than on co tto n trea ted with citric acid . DMDH EU fini shes, however, yield bette r wash fastness ra tings than those based o n either of the po lyca rboxylic acidszoo .

Contro l o f d yeba th pH is pa rticularly impo rtant when d yeing on fabrics fini shed with a polyca rboxylic acid a nd a n N -hydroxyeth yl additive. Fo r example l B8

, d ye ings o f c. 1. Direct Red 8 1(21 ) o n BTC A with BH EDMAC, cho line chlo ride (58)" o r tri etha no la mine hydrochl o ride gave Kubelka ­Munk Kj5 va lues o f 15-20 a t p H 3 but only 5-7 a tpH 4.7. Finishes based o n DMDH E U a nd cho lin~

chl o ride20 1 show optimum upta ke when dyed a tpH 4-5. With a polyca rboxylic acid and an a lkanolamine hydrochlo ride, howeve r, the ca rboxy groups sho uld be undi ssocia ted to minimi ze repulsio n o f direct d ye anio ns and the te rti a ry amine N a to ms sho uld be pro tona ted to a ttrac t them 188 ; thus, op timum dyeabilit y is fo und bel ow pH 3.S.

10 Direct Dyes on Non-Cellulosic Substrates Direct dyes a re de igned fo r effi c ient a bso rpti o n by

a ny o f the c;e llulos ic fi bres. The ir a.nio nic cha rac ter , however, a lso impa rt s good a ffinit y fo r wool, silk , nylo n a nd lea the r. Reviews o f the bleachin g a nd colo ra ti on o f silk usua lly include recommc nd a ti o ns fo r ex ha ust d yeing with direc t d yesZOZ - Z04. N a tura l silk warp ya rns ca n be d yed continu o usly by inco rpo ra ting direct o r reac ti ve d yes in the size ba th Zo s. Red ox sys tems (perox id ~jg lucose o r persulpha te/glucose) have bee n inco rpo rated in dyeba th s o f the di sazo di sulph o na tes c. 1. Direc t Yell ow 12(18) a nd Red 23(39) fo r d ye in g silk at va rio us tempera tures. Colo ur yields dcpcndc(j 'O n the substra te, dye a nd redox sys tem . Fastness to washin g wa s good a nd s treng th losses insignificant ZU (,. In a recent wo rk o n the d yea bilit y o f silk fa bri cs givcn a BTCA-cross link ed dura hl e press lini sh zo 7, ('. 1. Di rect Red 8 1 (21 ) as we ll as acid a nd basic d yes were used to eva lua te the effec ts o f the polyca rboxylic ac id and N-h ydroxyethyl modifie r"o n d ye ing hehav io ur.

Acid , direc t a nd reac ti ve d yes showed good exha ustio n a t 30"C o n silk a nd a t SO°C o n nylo n when d yed fro m a glyo xa l/ pe roxide red ox sys tcm 2UH. In similar studies. nylo n a nd wool we re d yed with direc t d yes. including c. 1. Direc t Red 79( 12). Red 8 1(21 ) a nd Blue 67(28). in the prcsence of ammo nium persulpha tc al o ne and together with vari o us reducing agentsZOl) The in fluence of the red uci ng agcnt on the

enha ncement o t" colour yield increased in the o rder: sodium thi osulpha te < potassium pyrosulpha te < thio urea < glucose. The initi a l strike on nyl o n wa s extremely rapid , 80°C being the o ptimum d ye ing tempera ture o n thi s fibre, but co lo ur yield o n woo l inc reased progressively fro m SO°C to 90°C. The exha ustion of selected direct dyes o n nylo n a t 70-90°C co uld be acce le ra ted ma rkedl y by additi o n o f benzyl chl o ride to the d yeba th 2lO. Radia ti o n grafting of nylo n with acrylonitrile a nd styrene was assessed 211

using C t. Direct Orange liS and o ther dyes a t va rio us levels of po lymer add-o n .

Direct d yes a re widely used o n chro me-ta nned lea thers but they give gene ra ll y poo r yie lds on vegeta ble-tanned maleri a lz'2 . Penetra ti o n IS

norma lly lo w but C I. Direct Blue 2(43) and certa in copper-complex d yes will give d yed-thro ugh e lTec ts. When combined with toning dyes o f mo re penetra ting cha racter, the conventi o na l low-penet ra ti o n direct d yes impa rt good surface co lo ur yield a t modera te cost. The effects o ffa tliquo ring o n direc t dye ings were reviewed recentl yZI3. The type. co lo ur a nd concen­tra ti o n o f d yes presen t are all relc\an t. Di rect dyes of high rmm a nd ex tensive hyd rogcn-bo nding po tentia l tend to pro duce a firmer lea the r than d oes a s impl e mo nosulph o na ted acid d ye. Ra isin g the d yc co ncen­tra ti o n fo r th ro ugh-dyed lea thers dcmand s a higher sa lt concentra tio n with ad ve rse e fTec ts o n emulsi o n sta bility, d epending o n whethe r the ratliquo r is sulphated , sulphited , ca ti o ni c o r no ni o nic.

T ypica l lea the r d yes . such as the tri sazo te tras ulpho nate C I. Direc t Blue 78(37). possess good wa le r so lubility and sa ti sfacto ry eas tness to migra ti o n . Poo r migra ti o n is often a ttributed to colo urcd impurities. Meta l-complex d yes have good wei fastness b ut o nl y moderale fastness to mi grati on . The la tte r is usua ll y ad equ a te if two o r mo re sulph o gro ups a re present but the fas tness to pe rspirati o n may be lower. C ati o nic a ftertrea tment usuall y provides a ma rk ed a nd las ting impro vement in pe rspira ti o n fas tness. The need fo r ca re ful d ye se lec ti on to minimize metameri sm in shade ma tching a na to achi eve adequa te fas lness to li ght. pe rspirati o n , mi gra ti o n and dry clea ning ha s bee n hi ghlighted in rela tio n to dema nds fo r improved perfo rma nce o n ca r upho lstery lea the rs2 12.

11 Oefinitions Required Traditi onally. direct dyes (as the name implies) a re

abso rbed a nd reta ined within the cellul os ic substrate by o perati o n o f the fo rces o f substanti vit y al o ne. with o llt the fo rmati o n o f cova lent d ye- libre ho nds. Reacti ve d yes (a ga in implicit in .the name) arc fundament a ll y dependent o n cova lent dye-fibre

26 INDIAN J. FIBRE TEXT. RES., MARCH 1996

bond formati on. But what of the reactant-fixable dyes (Section 8.2)'1 Originally , these were renamed direct dyes th ~lt had to be linked to the fibre by means ora n ;lgen t designed ror the purpose. Moreover. the initial ra nge ha s be.en su ppiclllen ted \\'i th selected react i ve dyes in order to atta in a rull gamut or b:'ighter hues . !\re rcactant-Il xable dyes direcb o r re;lcti\es')

COll\ent ional reactive dyeing proce~se s Oil

ce llulo:-;e in\'o lve nucleo phil ic attack by ion ised OH gro ups oleellulose on an active centre in tile reacti ve dye Ill olec uk. such as a r olari sed carbon- Iwl oge n bond o r a vinyl gro up . Recent rese,lrch on the inco rporat ion ot's uch active ce ntres in cellulose an d tile use on these ll1 0ciilied libres or suhst<lnti\ 'e d)es co ntaining nucleophilic primary amino gro ups 'is n:portcc! (Section 7.6). Man y convention:!1 direct dyes co ntain groups of this kind . Are the new nucleophilic dyes d irect s o r reac ti ves')

In the last few ycms, much research eITort has heen dCH)ted to th e problem or ove rcoming the poo r dyea bili ty of ga rments made from colton fa hric t ha t has a lre~ld y been given a durable press trea tment. The best so luti on so far is to incorporate in the lalter a tertiary amine o r quate rn a ry sa lt eontalnlilg N-hydroxyct hyl groups that enable it to react with the cross linking agent (Sections 9.2 and 9.3) . What shlwld we ca ll this combination orcell ulose reactant and cati onic modifier'? The term 'pretrea ting fini sh' (or ' Iinishing pretreatment') is an oxymoron. We need a hette r description of a process that achieves efTective crosslinkillg and durable press perfo rmance while avoiding the serious loss ofaecessibility to dyes that no rmally accompanies resin fini shing. Perhaps 'substanti ve cross l!nk ing' wo uld serve to di stingui sh the new process from tradition al chemica l finishing and signal that it is intended to precede substantive dye ing.

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32 (t986) 584 l. 49 Amat o M E & Fisichella S, Colourage AIIIlUil l, (1986) 51.

SHORE: ADVANCES IN DiRECT DYES 27

50 Ama to M E. Fisichc ll a S & Occ hipin ti S. O ITS Pigill . 7 \ 1986) I .

51 Dc Giorgi M R. Albert i G & Seu G. AIIII Chilli (RolII£,). 71. ( 1983) 635 .

52 De G io rgi M R. Albe rti G & Cern ia ni A. Alii f}1 'cSI Rcp. 74 (March 191; 5) 33.

53 Si va ra;a Iyer S R & Subrama nian K. J Soc O I'C'rs CO/OII /, . 96 ( 1980) 185.

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59 Ibe E C & Ibe S . Acta PO/Ylllerim . 37 ( 1986) 15 1. 60 Ibe E C. ACIU Po!rllleriCli. 39 (1 986) 549. 61 Birger B N. Melnikov B N & Livadonova A V. Z hllr Prik/lld

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(1988 ) 208; Am Dyesl Rep . 79 (May 1990) 45; 79 (June 1990) 38.

67 Thakore K A. Smith C B & Hite D. TeXI Chem C% r. 22 (November 1990) 2 1.

(i8 Smith B. Mcin tosh G & Shanpi ng S. Am 01'('.1' 1 Rep. 77 (October 1988) 15.

6'} Denter U. Poul<l kis K & Schollmeyer E, Texl-Prox. 49 (1994) 2$ 1.

70 D<lvidzon M 1& Mahsev<l TN, Tek.\'1 Promsi. 8 (August 198 1) 58; Kol/oid Z hllr. 43 (September/Oc to be r 198 1) 970.

71 Marinich T L. Koka reva I A & Ovchinnikov Y K, I~v VI 0 11'

Khimil 'a i Khilll 7·l'khllo/. 5 (1 993) 110. 72 Krichevsky G E. 151h I FA TCC Congress. Lucerne (J une 1990)

Poster. 73 Shakra S. Kharadly E A & Ibrahim M. Am Dyesl Rep. 71 (Jul y

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16 1. 75 Bredereck K & Wolf J . Me/liand T('x ti/her. 64 (1983) 16 1. 76 S<la fan A A. Mel/iond Tn Ii/her . 65 (1984) 534; 68 (1 987) 678. 77 Saafan A A & Habib A M. Me/liand Tr:oi/her, 68 (1987) 845. 78 Saafan A A & Abdul-Halim ST. Mel/iond Ji!xli/her. 69(1988)

51\. 79 Reicher J & Rusznak I. Texli/ vered/ung . 22 ( 1987) 95 . 80 Ahmed N & Tahir K D. Texl Hori::ons. 5 (Februa ry 1985) 20. 81 Hermanutz H. Herli nger H & Bechter D. Tcxl- Prax. 49 ( 1994)

495. 82 Bredereck K & Saafa n A A. MI'I/ialld Tcrti/her. 63 ( 1982) 510 83 Saa fan A A & Sa kran M. Mel/iwu/ Texli/ha . 69 (1 988 ) 20 I. R4 Wakida T. Lee M. Niu S,Yanai Y. Yoshioka H. Kahayashi S.

Bac S & Kim K. J SIIC Dre/'S C% llr . III ( 1995 ) 154. 85 Brederec k K & Buschle-Dille r G. Me /lialld Tl!x li!her. 70

(1989) 11 6. 86 Walson M D & Jones 13 W. T('xl Ch"11 1 C(I /(lr . 17 (M arch 19R5)

37.

X7 Chee k L. Wilcock A & HSlI L II. 1"1'11< ... \ .1 . :; ('1 I <) XI, ) 56'): :; 7 (I<)X 7) (,'10.

88 Chee k L & Wilcock A .J S(/c f).I'ersC(/I(/ur. 104(1 988) 477. X<) Wilcock A & L\oyd-( Jraham D . .I Soc Or e/'.\ ( '0/11111'. 106 ( I ')')Il )

104. 90 Ja in A K. J Soc /).1'('/'.1' C%llr . 10(, ( 1<)<)0) 24X. 9 1 .l ai n A K & Dweltz E. A lii /)n 'sl R,,/, . X I ( \)l'l:,'mhcr I 'N2)

48. <)2 Smith B. 7i'x l Red . 6 1 (I <)<) I ) 226. 93 Chee k L Hsu L H & Thibodea ux D P. h \l Rl's .f. 60 (1990)

1m. .

<)4 C heck L. Tnl Rn J . 60 ( 1<)<)0) 75<) . 95 Mehta R D & Combs R N. P/'I){'eetlillgs . A A TCC IlI le/'l/ali(/lIu/

CIIII/c'rellce & l::x hihilioll (DC I(/ha 1(90) 214. A lii D.I'esl Ref/. RO (Septemher 19(1) 74.

96 Mehta R D & Sa lame P A. Te.\'I Asia . 24 (.Iune 1 9<)~) 41 . <)7 Park J & Sho re J . R('I' h llg CII /II/'. 12 ( 19K2) 4.1. 98 Deschler U & Schmid t G. Te.I' I-Pm .\. 36 (1<)8 1) 133 1. 99 Fiebig D. Herli nge r H & So lt ~l u D. -f(-I' I-I'm.\. 4X (1<)<)3) 974. 100 Krucker W. Texl i/rer('(/illllg . IX ( 1<)83) ::X9. 10 I Cooper P & Taylor J M. J S"c Drers ( ',,1,,"1'. 10K (199:: ) 4X(, . 102 Smith B. Te.1'1 Res J . 6 1 (199 1) 137. 103 Schollmeyer E & Dent er U. Te.\'I-P m .\ . 38 ( 19R3) Ins. 104 Duga l S. Dellt er U & Scho llmeyer E. Me/liul/(ll l'.\'I ili",r . 64

(1983) 494. 105 Denter U. Pfluger G & Schollmeyer f. Mel/ialld Tnliliwr. 67

(1 986) 671. 106 Bach F & Scho llmeyer E. Tex li/reretl/lIl1g . 29 ( 1994) 2X4. 107 Almeid a L & Cavacc-Pa ul o A. Me/liollt/ l "xli/her. 74 ( 19(3 )

404 . 108 Hoffmann F. 7i'x liit·er('( l/lIl1g. 24 (1 989) 340. 109 Lacli sch C M & Y<lng Y. Tn l Re.\' .!. 62 ( 1<) <)2 ) 4X I. 11 0 Lubbers A. Souren 1& Ro uct te H K. Me/lial/{/ Te.\li/h('/' . 71

(1990) 371. III Achwa l W R & Samvatsark a r R. Illdiall J 7i'xl Res . 12 ( 1')1\7)

6. 11 2 Iwadara Y. Sell-i Cakkaisil i. 39 (1 983 ) .14. 113 Navarro A, ~is M & Valldeperas J. 15111 IFA TCC COllgress .

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11 6 Bairathi A. Prol'eedillgs. A A TCC III/e/'l/aliollu/ COII/i'rell(,( ' & Exhihilioll . (October 19(3) 85; Texl ('tt('//I C%r. 25 (December 1993) 4 1. •

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11 8 Denter U. Duffner H & Schollmeyer E. Texliit'ered/11I tg. 2<) (1994)238.

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·123 EI-Nayger A M. EI-Hosamy M B. Zahran A H & Zohdy M H. Am Dyesl Rep. 8 1 (Ja nua ry 1992 ) 40.

124 Weltrowski M. Lombard G . Tliorr F & Drea n J Y. Proceedings. AA TCC Inlerrwliono! Con/ercnce & Exhihilion (Octuber 1993) 303. . .

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10 15: J Soc Dyers C%llr . l OX ( 1992) 2 15.

28 INDIAN 1. FIBRE TEXT. RES., MARCH 1996

In No usia nen P. I S/II I FA TCC COl/g ress. Lucerne (June 1990) Lecture .

1 2~ Schlicht mann G. Cllemie(asern / Tex/-Ind. 39/9 1 (1989) 462. 129 Lehmann H. Me/liand Te:({i/ber . 67 (1986) 189. 130 Somm F & Buser R, Tex/i/ l'ered/ulIg, 17 (1982) 15. 13 I Fiehig D. Herlinger H & Schafer p, Tex /-Prax . 46 (199 1)

550. 132 Hcrlinge r H. Me/liand Tl'x/i/her . 72 ( 199 1) 784. 13.1 Lewis D M & Lei X P, Tex/ ('hem C% r , 21 (1989) 23. 134 Rupin M. Veaute G & Ba lland J, Tex/i/veredlllllg , 5 (1970)

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58. 141 Waly A, Rafai R. EI-Ratie M H & Hebeish A. A m Dres/ Ref! .

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(1984) 304. 143 Lei X P & Lewis D M. Dres P~f!. III . 16 ( 199 1) 273. 144 Burkinsha w SM. Lei X P & Lewis D M . .1 Soc Dras C%llr .

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Phillips D A S . .1 So, ' Dre!'s C%llr . 106 ( 1990) .107. 146 Lei X P & Lewis D M . .1 Soc /)rl'l's C%llr. 106 ( 1990) 352. 147 Wu T S & Chen K M . .I Soc Drers C%llr , 109 (1993) 15.1 .

.165 .

148 Kamel M. YousscfB M & Kamel MM . Dres Pigm , 16(1991) 57: 7', ·.\ /-Pw.\. 46 (199 1) U24 .

I.N Y,)llsset'B M. Kamel M M & Kamel M. Dres Piglll . 19( 1992) 22 _1.

ISO Kamel M M & Kame'! M . .1 Soc Drl' rsC% llr. 108 ( 1992)450. l SI Lell'is D M & Lci X P. P/'(}c('edillgs. AA T CC IlIIe/'lw/iollo/

COIl /i' re// l'l ' & /:.'xllihi/ ioll. (October 1992) 259. 152 LL'llis D M. Parton B & Tapley K . III/e/'lUi/ioll' " COII/i'rellce

(}II Cill'lIl is /rr & App/ica/iOlI o(Rc{lcil'l' Drcs. Harroga te (1992 ) Poster.

1) 3 Lewi s D M Ho Y C. Proceedillgs , AATCC 11I/('/'1I1IliOlw/

COII /i' r cllc(' & 1::.\'IIihi/illII . (Octohe r 1994) 419. 154 Cook C C. ReI' Prog Cn/" r . 12 ( 1982) D. 155 risc her H. Tl '.\' /i/l'ered/lIl1g. 25 (1990} '54. 156 Shaha S & Ibrahim M. A lii /)rcs / Rcp. n (April 1988) 38. 157 Ett ers J . A lii Dres / Rep . 78 (Se ptember 1989 ) 19. ISII Hc:rlinl!er H & Schul/. G. I'v/el/iollt/ Tn/iI/wI', 71 (I 99() 126. 159 C rcws - P C & Th orso n L Proccedillgs, ' A A TeC

III /el'lJ(lIiollll/ COII/i' r('ll ce & £.\'hihi/itlll. (Oct oner 19X7) 285 . 160 Kak o T & Katayama A . .1 .Il1PlllI Res Assoc o/7'e.1'I Elld-Ilses,

(Fenruary 19(3) 95.

161 Reinh a rdt R M. Varghese J & Pat el S K. Alii /).I'es/ Ref!. 80 (Oc tober 1(9 1) 34.

162 Egger W B & Rohinson T. Tl'.\'/i/rered/Illlg . III ( 1983) 41: Te.Y/ Chelll C% r . 15 (October 1983) 189.

16.1 Ro binson T. Mel/illlJ(/ Te.l'li/her . 68 (198 7) 1.17. 164 Rafai R & Ibrah im N A. A lii Dres/ Rep , 79 (October 1990)

20. 165 Omura T. Dri'S Piglll , 22 ( 1993) 99 . 166 Kamel M M. Kharadly E A & Yo ussef B M. Alii DJ'es/ Rcp . T2

(December 198.1) 40. 167 Ibrahim A & Haggag K. A lii D.I'c.VI Rcp . 75 (ApriI19X6) 20. 168 Hebeish A. EI-Alfy E A & Mardini M H A. Alii Dies/ RCf! . 76

(Oct ober 1987) 42.

169 Ha ggag K & Ibrahim N A. J Tex/ III.I/ . 62 (199 1) 9. 170 Barbery J . A lls/m/illil 7,'.1'1 , 10 (J anuary .. Februa ry 1990)28. 171 Yang Y & Li S. Te l' / Res .f , 64 (1994) 4.13. 172 Lian g T Y. Hwa ng J Y. Ju D S& Chen Cc. 1'1'.1'1 Res } . 62

{19(2)S47.

173 Reinha rdt R M & Blancha rd E J . Alii DJ'es/ Rep . 8 1 (December 1992) 37.

174 Gonzales E J & Blanchard E J. Alii DJ'es / Rep . 77 (March 1988) IS.

175 Berto niere N R & King W D. Te.\' / Res .I . 59 ( I n9) 608 . 176 Welch C M. ReI' Prog C% r . 22 ( 1991) 32. In Harrd R J & Stone R L Tc.y/ ChclII C% j·. 18 (Novcmner

1996) .n 178 Blanchard E J & Rcinh.ardt R M. A lii /).1'1'.1/ Rep. 79 (June

1990) 15: 79 (Jul y 1990) 27: SO (August 199 1) 7.\ : Proceedillgs. .4.4 T CC I ll/erllll/iollll/ COll fio r ell ce & t :xhihi/ioll , (Octo ber 1991) 211.

179 Reinhardt R M. Bl anchard E J & Gra ves E E. Am Dyes /

Rep. 82 (Octobe r 1993) 46. 1110 Cllra , til.l. Reinh a rdt R M & Blanchard F J. Tn / Res .l . 60

( 1990) 441. III I Blancha rd E J & Graves E E. A lii DJ'es / Rep. 81 (N ovcl11 nc:r

1993) 4 1. 1112 Weich C M & Andrews BA K. Te.\'/OIl'1II C%r. 11 (Fenru;lry

1989) 1.1 . 183 Andrews B A K. Tcx / C/I('III C% r . 12 (Sep tcmner 19(0) 63. 1114 Tra~k-Mnrrell B.I & Andrews B A K. Te.Y/ Res .J. 62 ( 19(2)

144.

ISS Brown R 0 & Tomasino C. Proccct/illgs . AATCC 11I/,'m lllioll,,1 COII/i'rmcc & E.\'liihi/ioll . (Octoher 1(9 1) 168 .

186 Andr~w, BA K . 13iandlard E J& Reinh;,rdt R M . AIII /).1'('.\ /

Rep. 79 (Se ptemner 1990) 4X. 1117 Andrews B A K & Trask-Morrell B J. A lii /).1'<'-' / Ref! . 80 (J Lil y

19( 1) 26. 18X Blanchard 1::.1 . I{einharcit I{ M & Gra ves I:: I::..f Soc Ihas

C"lolll' . (ill press ). IX9 Blanchard E J . Reinhardt R M & And rews B A K.

P/'(I('( 'I'dillgS. AA TCC Ill/em illiollll / COIl /i ' /'ell f'( ' & /:'yh ihi/ioll. (Octoner 1990) 149: 7".\' / C hl'lII Color, 23 (Ma\ 199 1) 25.

190 Welch C M. Te.1'I CII('III Coio/'. 23 (March 1991) 29. 191 Bbnchard E J. Reinhardt R M . Graves E E & Andrews B A K .

P/'(Iceetfill,!!.s. A .-' TCC I llIe /'llIlJilillll/ COll li ' rellce & I::.rhihi/ion . (Octo ner 1<)92) 270.

192 Blanchard EJ & Reinhardt R M. Te.Y/ C11l'1II C%r. 24( 1992) 1.\.

193 C lwi H M . '/" '.1'1 Cllelll CO/"I' , 24 ( 1992) 6 14 . 194 Choi H M & Welch C M. Prof'( ,,'dill,!!.s . . " A TC C III /,'m ll/ioll"/

COIl/i '/'{ 'IICl' (~ 1:.'.I'IIihi/i(l ll . (Octobe r 1992) 287. 1<)5 Clwi H M. Welch C M & M'lI'ri s N M. 1'1'.1'1 Res .f , 64 ( )994 )

SOl. 196 A ndrews B A K & Morri s N M . .1 TI,.\·,.'II.I/ . 84 (1994)63 1 197 C hoi H M . Welch C M & Morri s M. T('x/ Res./. 6.' ( I ' )l) .I)

650.

19X Choi H M. Li J D. Goodin R D & Pratt T D. Alii n J'es / Nel " S3 (February 1994) 38.

199 Welch C M & Peters J G. 7" .11 Chelll CO/Oi' . 25 (Octuhc: r 1<)93) 25.

200 Blanchard E J. Reinhardt R M. Gra ves E E & Andrews B A K. Illd Ellg C/Ji'1II Res, 3.1 (1993) 1030.

201 Harper R J . Tn / Chelll C%r . 10 (19XX) 25. 202 Shankarachary R R. C%llrage, .I I (Octo ber 19X4) .1.1 . 203 Hofstetter R. Tex/-Pra.r. 40 (19115) 12.13 .

SHORE: ADVANCES IN DIRECT DYES 29

204 Flensburg H. Tex /- Prax . 43 (1988) 739. 205 Baitsel G K. Baritdi nova F G & Kalo nta rov 1 Y. SheIk

(Tashkel1l ). 6 (1985) 2 1. 206 Sa ligram A N. Singh S. Shrivas tava R P & Shukla S R. Arn

Ores / Rep. 82 (May 1993 ) 30. 207 Yang Y & Li S, A lii Dyes/ Rep, S2 (A ugust 1993) 22; 83

(Februa ry 1994) 26. 208 Shenai V A & Joshi S B. Tex / Drer Pril1ler, 18 (October 1985)

16.

209 Ibrahim N A & Dawoud M A. Alii Ores/ Rep. 77 (March Il}RR) 35; 77 (June 19X9) 35.

210 Abdou L A & Benda k A. Am Dl'es / Rep. 71 (November 1(82) 35.

211 EI-Sakma wi K. EI-Hosa my M B. EI-Naggar A M & EI-Gend y E. Alii Ores/ Rep. 82 (May 1993) 47.

212 Wachsman., H M. J A m L('{/ Ih C h(,111 Assoc. R2 ( 19K7) 277: R4 (1989) I gO.

213 Burgess D. J Soc Le(//h Tec/Ill o/ C/I£'III . 75 ( 19<)4) 39.