Michael addition with a variety of amines, a number of modified celldoses ...... D M Lewis and P A Broadbent, IFATCC congress book of papers,. Vienna (1996) ...
The chemical modification of cellulosicfibres to enhance dyeability D M kwis and K A McIlroy Department of Colour Chemistry and Dyeing, The University ofkds, Leeds, LS2 911;UK
undesirable, as increased salinity in rivers upsets the delicate balance of aquatic flora and fauna. Sodium The ingenuity of fibre and colour chemists to develop natural and synthetic fibres with enhanced coloration chloride is an electrolyte commonly used, but the properties is legendary. These developments often require alternative sodium sulphate is even more suspect, as it chemical modifications, applicable during the fibre attacks concrete pipes [5], and also has been associated production stage, prior to dyeing or, more desirably, with increased acidity of waterways. Reactive dyes in particular use very high concentrations of salt, so are during dyeing. under the most scrutiny The sodium and potassium salts The worlds demand for textiles continues to grow [l]; of polycarboxylic acids have shown some promise as the annual consumption of textile fibres rose by 2% in 1995 alternatives to sodium chloride, but their use is likely to and that rate of growth is expected to continue. Most of the growth is from the synthetic fibre sedol; particularly prove too costly [6]. Colour in dyehouse effluent also raises environmental polyester. However, cotton consumption still represents concern these days. Although colorants are generally the largest market share at 45%; it is estimated that this considered to be of low toxicity, there have been many figure will have remained constant during 1996 and 1997. compIaints of coIour in rivers in the LJK, particularly in the This paper focuses on cellulose, reviewing older and u p Severn Trent region [q.The Environment Agency has set todate methods for improving its dyeability by chemical modification. Consideration is also given to polyesterl colour consent limits in some regions, and surcharges cotton blends, which at present require long and complex must be paid if these are exceeded [8]. Improving the substantivity of cellulose towards dyeing processes owing to the individual chemical and physical properties of different fibres. The demand for anionic dyes will greatly reduce the need for electrolyte in polyesterlcotton fibre blends continues because they offer the dyebath, and also improve dyebath exhaustion, serving to lessen colour in dyehouse effluent. Hence a a combination of desirable properties. This review review of the chemical modification of cellulosic materials, examines possible novel dyeing processes for the dyeing as a means of providing improved dyeability,is timely of such blends.
INTRODUCI'ION
PROBLEMS ASSOCIATED WITH CELLULOSICS DYEING In a rwiew of recent developments in cellulosic dyes and dyeing processes, Phillips gave figures which indicated that reactive dyes are at present the most popular dye class for cellulosic fibre dyeing, and that their annual consumption is set to greatly inmase in coming years [2]. Complete domination by reactive dyes is, however, prevented by the complementary properties of the other dye classes suitable for cellulose; these other classes variously offer advantages of low cost, ease of application, wide gamut of colours, shade reproducibility, low environmental impact, plus good levelness, and good fastness to light, washing, bleaching and rubbing. Increased awareness of environmental issues in the dyeing industry has been brought about by public concern and tougher legislation based on the 'polluter pays' principle [3]. Regulatory developments will eventually demand low-salt dyeing of cellulosics [4]. High electrolyte concentrations in dyebath discharges are
CHEMICALMODIFICATIONTO IMPROVE DYEABILITYWITHANIONICDYES Aminoa&ylceIlulose!s Introduction of amine groups into the cellulose structure produces a fibre that may be considered analogous to wool. Unlike cellulose, wool has a natural substantivity towards anionic dyes, espeaally under aadic conditions. Methods for amination of cellulose have been known for quite some time. In 1926 Karrer and Wehrli tosylated cotton, then reacted this modified cotton with various amines to produce fibres containing primary, secondary, tertiary and quaternary aliphatic amines, as well as aromatic amines and quaternary nitrogen heterocyclics [9]. Scheme 1 shows the tosylation of cotton with ptoluenesulphonyl chloride, followed by nucleophilic displacement of ptoluenesulphonic aad with ammonia, to give cotton aminated with primary amino residues. Karrer and Wehrli have described the preparation of an
REV.PROG.COLORATION VOLUME 27 1997 5
cell-OH
+
-
CI-SOp-(&CH3
+
cell-O-SOp~CH3
HCI
I
1""'
+H
cell-NHz
schema 1
cell-OH
+
Cl-$
-
+NO2
0
O - S O p o C H 3
+
+NO2
cell-O-$
HCI
0
I
C ~ I I - O - $ G N H ~+ Hp0
0
sch.nw2
cell-OH
+
-
CI--S&+NHWCH3
cell-0-Sop
..1
cell-0-so2
cell-OH
+ HN2-CH&HflS03-Na+
+
NaOH
aminated cotton by reaction with pnitrobenzoyl chloride followed by reduction of the nitro group (Scheme 2). Another route to aminated cotton mentioned by Karrer and Wehrli is the reaction of cotton with acetylaminobenzenesulphonyl chloride in nitrobenzene or chloroform,followed by hydrolysis of the amide bond (scheme 3). Hartmann described the preparation of Zaminoethylcellulose by reacting &&lomethylamine and similar compounds with soda cellulose or cellulose hated with 18% sodium hydroxide [lo]. 'katment of cotton with Z aminoethylsulphuricacid in an aqueous alkaline medium was found to be more efficient at producing a 2aminoethylcellulose and had the added advantages over the Hartmam p'ocess of being relatively inexpensiveand not requiring organic solvents, thereby simplifymg the application process [ll].Compounds related to Zaminoethylsulphuric acid were examined and found to produce celluloses of varying nitrogen content; treated celluloses with lower nitrogen content were obtained for sulphato compounds possessing low solubility in concentrated sodium hydroxide (121. Aminoalkylcelluloses were recognised to be capable of enhancing dyeability with
6 REV.PROG.COLORATION VOLUME 27 1997
130°C. 15 min
o N H C O C H 3
O
N
cell-0-CHpCHpNHp 2-minoethyl celluloee
H
p
+
+
HCI
CH3COOH
+ Naps04 + Hp0
most cotton dyes, especially direct dyes [13]. They also offered the opportunity for introduction of compounds which gave properties of flame retardancy, rot resistance and increased ion-exchange capacity. Simple addition of sodium borohydride to the Zaminoethylsulphuric acid sodium hydroxide pad liquor allowed a white aminated cotton to be produced, since borohydride reduces any yellow Schiff's bases formed by the reaction of aldehyde groups in the cellulosewith amino groups (Scheme4) [14]. The application of 2aminoethylsulphuric acid to cellulose, as well as forming the desired aminoalkylcellulose, produces polyethyleneiminesand ethanolamine [15]. More recently, Herlinger et ul. suggested a new twostage dry fixation process for the production of aminoethylated cellulose with Zaminoethylsulphuric acid; if vinylsulphone dyes were added to the pad liquor excellent colour yields were obtained, and even hydrolysed vinylsulphone dyes were covalently bound to the fibre [16]. Ethyleneimine when applied as a vapour or solution to cotton produces a cotton of enhanced dyeability. Polymerisation of ethyleneimine occurs in and on the fibre [ l q . Drake et d. found that treatment with ethyleneimine
Clcell-OH
+
+IC2H5 CI-CH2CH2-N-H
C2H5
scheme5
had no apparent effect on fibre properties, other than improved dyeability, and proposed that little covalent reaction actually took place between the imine and cellulose [18]. Cooper and Smith presented evidence for graft polymerisation of the imine onto the cellulose chain [19]. Segal and Eggerton recognised that various workers were treating cotton with ethyleneimine by different methods, and hence products of a different nature could result [20].They found that acetic acid catalysed the imine reaction during treatment of cotton with ethyleneimine dissolved in benzene. The ethyleneimine-treated cotton contained polymer that was easily removed by water washing, although some nitrogen remained behind in the treated cotton after an alkaline extraction. Ma-red studies of the ethyleneimine-treated cotton showed its structure to strongly resemble that of aminoethylcellulose. Soignet et al. found that the tertiary amino groups contained in diethylaminoethylcellulose (DEAE cellulose) acted as a 'built-in' catalyst to increase the reactivity of epoxides (in the absence of external catalysts) and effectively quaternised the fibre [21,22]. Tertiary amino groups have been incorporated into cellulose by reaction of cotton with &chloroethyldiethylamine hydrochloride according to the Hartmann process, producing DEAE cellulose (Scheme5)[23]. The DEAE cotton could be dyed, in the absence of salt, with dired,reactive and acid dyes. Interestingly, covalent fixation of a Drimarene K (5-chloro-2,4difluoropyrimidine or FCP type) reactive dye occurred under neutral and slightly acidic dyebath conditions. El-Alfy et al. explained the phenomenon of covalent bonding between the reactive dye and cellulosic hydroxyl groups under neutral and acidic conditions by proposing that the tertiary amino groups of the DEAE cotton were behaving as a 'built-in catalyst' (Scheme 6, where D is the dye chromophore)[231.
-
/C2H5
NaOH
cell-O-CH2CH2-N.
The action of a 'built-in' catalyst was again used to
explain reactive dye fixation at pH 7 with a monofluoro-striazine (MFT) dye by Hebeish and Higazy in the preparation of DEAE flax/polyester fabric [XI. Kratz et al. examined reactive dyeing of aminoethylated linedwool blends [25]. Ethylenediamine (EDA) was found in the wash liquors, thus such a modification process was considered unsatisfactory for use in industry. Cellulose can be esterified with most inorganic and organic acids. Many of the products have practical applications and discussion of these lies beyond the scope of this paper [%,27l.lkuji and colleaguesacetylated cotton and showed improved uptake of direct dye without adversely affecting fastness to laundering [B].Enhanced dyeability of the acetylated cotton was presumably due to changes in the cellulose's crystalline structure and hence dye accessibilitywithin the fibre. Lewis and Lei esterified cotton with chloropropionyl chloride (CPC),and then aminated the modified cotton by nucleophilic substitution of the chloropropionate residue with various amines to produce cotton fabrics containing primary, secondary, tertiary and quaternary amines [29]. It was initially assumed that the reactions would take the course of Scheme 7,where Rl, Rzl R3 = H or CH3 cell-OH
cell-O-~-CH2CH2-N(CH3)2
+!?
F-
C~II-O-C-CH~CHZ-N+(CH~)~ClC2H5
D-NH ,f,$~;~H2-O-cell CI
Schema 6
scheme7
Dyeing was carried out with reactive dyes under neutral to slightly acidic conditions in the absence of salt. The aminated cotton containing secondary amino residues (treatment with methylamine) gave the highest colour yields. When dyed with CI Reactive Red 5 (2% o.w.f., pH 5, at the boil, no salt) the apparent amino residue efficiency, in terms of dye uptake, was ranked as: secondary > tertiary > quaternary > primary
REV.PROG.COLORATION VOLUME27 1997 7
? cell-O-C-CH2CH2-CI
+
NR1R2R3
Schema 8 cell-0-
+
CI-
CH3 H2C-CH-CH2-y-CH3 CH3
0
/ \
+I
100°C
Cl-
cell--+NR1R2R3
+
?
HO-C-CH2CH2-CI
OH-
Cl-
Y CH3 cell-O-CHp-CH-CH2-(ll-CH3 +I
CH3
schema9
Alkali washing showed the propionate ester stability to be poor, but this problem was overcome as it was discovered that a more severe amination step (amine treatment at lOOT)did not produce modified cotton containing an ester linkage. Instead bonds of the type cell-N+R1R2R3 were obtained, which gave reactive dyeings of excellent alkali stability. Supporting evidence from FI'IR suggested that during the reaction of the amine and the chloropropionate esterified substrate at the boil, the amine attaches directly to the cellulose by a nucleophilic displacement of either chloropropanoic acid or the &elimination product, acrylic acid (scheme 8). This is a similar reaction to that proposed by Karrer and Wehrli for tosylated cotton treated with amines (91. Many investigations have assessed the reaction of various epoxides with cellulose (30,311.Amines may be introduced into cellulose by reaction with epoxides. Stahn reacted epichlorohydrin with cotton in the presence of ethanolamine and sodium hydroxide [32].Alternatively glycerol-dichlorohydrin can be used in place of epichlorohydrinas it reacts to form the glycerol-diepoxide in the presence of sodium hydroxide. Lawrie, Reynolds and Ward published results from their work with epoxides (ethylene oxide, propylene oxide and glycidol), showing there was no reaction with cellulose until concentrations of sodium hydroxide had reached a level of 9.5% (331. Most epoxides with a strained ring will react with cellulose in the presence of sodium hydroxide, but reaction is unlikely in the absence of a catalyst (341. A quaternary, amino-epoxy derivative, glycidyltrimethylammonium chloride, was marketed by Protex as Glytac A, and its application chemistry has been described by Rupin and co-workers, emphasising its use as a compound which offered enhanced dyeability of cotton with reactive and direct dyes (Scheme 9) [35,36].The use of Glytac A was particularly useful in conjunction with direct dyes as it could be added to the dyebath without precipitation of the dye, to produce dyeings of higher tinctorial strength and higher wash fastness than conventional dyeing of directs. A later paper by Van Rensberg critically reassessed the experimental work of Rupin and co-workerson Glytac A [37. Cellulose may be treated with the less toxic chlorohydrin precursor of glycidylhimethylammonium chloride, since in the presence of sodium hydroxide 1trime thylammonium-2-hydroxy-3-chloropropane chloride is converted to the fibre-reactive epoxide form (Scheme 10). Dyeing cotton pretreated with Glytac A in
8
REV.PROG.COLORATION VOLUME 27 1997
the absence of electrolyte with reactives dyes gave a high degree of covalent bonding under boiling, neutral dyebath conditions along with high dyebath exhaustion (381.
kH3
schema 10
Cotton was modified with the low molecular mass reactive species l,l-dimethyl-3-hydroxyazetidinium chloride (DMA-AC) in order to study the light fastness of subsequent dyeings (391. DMA-AC has similar characteristics to the Hercosett polymer (Hercules)in that it is water soluble and consists of cationic, reactive azetidinium groups capable of reaction with the hydroxyl nucleophiles of cellulose. The compound may be prepared by reaction of dimethylamine and epichlorohydrin (Scheme11)[MI.
DMA-AC
scheme 11
DMA-AC was applied to cotton fabric by pad-bake methods. The presence of a strong alkali was necessary to provide sufficient levels of covalent bonding between DMA-AC and the cellulose. There is an equilibrium formed between DMA-AC and l-N,N-dimethylamino-2 hydroxy-3-chloropropane which provides an environment in which the tertiary amino group is capable of undergoing attack with the azetidinium cation or ychloro group to form oligomeric compounds. Dyeing of cotton treated with DMA-AC took place with reactive dyes at the boil, at pH 7 in the absence of salt. Dye fixation was extremely high, thereby eliminating the need for a long soaping-off process. Results showed almost the same dyeing behaviour as cotton treated with Glytac A. It was therefore concluded that the introduction of tertiary and quaternary groups into cotton by low molecular mass species improves the neutral fixation of reactive dyes by increasing cellulose hydroxyl ionisation due to the proximity of strongly basic groups. It is also worth noting
that terhary amino residues in the cellulose are capable of undergoing quaternisation with a halotriazyl and halopyrimidyl reactive dyes, further encouraging neutral substantivity and fixation with anionic reactive dyes. Evans et al. carried out a comprehensive evaluation of three types of quaternary colourless compound, capable of covalently bonding to cellulose to impart cationic character which should enhance cotton's dyeability with reactive and simple acid dyes (Figure 1)[41]: Type 1 was the chlorohydrin precursor to glycidyltrimethylammonium chloride, i.e. 1-trimethylammonium-Z hydroxy-3-chloropropanechloride T i 2 compounds were monochloro-s-triazines containing bisquaternary amines ?spe 3 compounds were bis-monochloro-s-triazines containing bis-quaternary amines.
CH3
or fully continuous process, and the compounds also showed poor penetration of the fibre due to migration of the agents to the surface during drying. Type 3 compounds are readily reactive and exhibit high substantivity towards cotton, but react preferentially at the surface of the fibre. On subsequent dyeing this results in ring dyeing. The quatemised cellulose exhibits a Langmuir type mechanism due to the saturation of quaternary sites, which become neutralised by absorbed dye anions. Therefore reactive dyes with a low number of sulphonated groups are best for the dyeing of quaternised cellulose. Twelve reactive dyes were tested, resulting in some extreme hue changes, which could be either agentspecific and/or dye-specific, but were impossible to predict. Lewis and McIlroy synthesised nicotinoyl-thioglycollate (NTG)as a novel acylating agent for cotton. They observed that NTG could react with cotton under alkaline pad-thermofix conditions (60 s, 2oo"c, pH 8) (Scheme 12)[a].
Type 1
Reaction with the fibre
cell-0-
+Na+
X-
xType2
~2 +
\COOcell
\
N Y N
COSCH2COO-+Na
CI
Na+ -SCH&OO- +Na
Hydrolysis
NaOH Cl
Figure 1 Quaternary compounds capable of bonding covalently to cellulose to enhance dyeability; R represents an aliphatic amine, aromatic amine or pyridinium moiety, Q an aliphatic amine or aromatic amine and M pphenylenediamine,4,4'-diaminodiphenylurea or piperazinebridging species (411
The three compounds were applied to cotton by different methods owing to differences in their reactivity and substantivity.Type 2 compounds, recognised to have low substantivity for cellulose, were applied by a pad-batch method at room temperature. Type 3 compounds, recognised to have higher substantivity for cellulose were applied by exhaustion in the presence of sodium carbonate. Type 1 compounds, being less reactive than chlorotriazines, required harsher application conditions; application with the chlorohydrin compound was under highly alkaline conditions by both a pad-dry-bake method and an exhaustion method, although the latter proved ineffective at incorporating quaternary groups in the cotton. Instability of the type 1 compound during application was evident by the release of an undesirable odour of trimethylamine. This problem may be somewhat overcome by the introduction of bulkier 1groups onto the nitrogen atom, but at greater expense. Owing to the low substantivity of type 1 and type 2 compounds, their application to cotton demanded a semi-
kOSCH2COO- +Na
N
q
+
Na+ SCHzCOO- +Na
'COOH
scheme 12
Surprisingly monochloro-s-triazineswere found to give excellent uptake and covalent fixation when applied at the boil in the absence of salt, at pH 3 on the modified fibre. It was proposed that initially the dye quaternised with the tertiary amine residue and then, under boiling, neutral soaping-off conditions, the quaternised dye reacted with cellulosichydmxyl groups to give normal dyefibre bonds (Scheme 13, where D is the D chromophore). Reaction of a quaternised triazine with cellulosate nucleophiles is the principle mechanism for the fixation of Kayacelon React dyes (Nippon Kayaku) on cotton [43,44]. These dyes react with cellulose at the boil, under neutral conditions (hence the term 'neutral-fixing dye') or at lower temperatures with a small addition of alkali.Croft et al. investigated the use of various tertiary amines in the synthesis and application of neutral fixing, quaternised striazinyl reactive dyes. They found derivatives of diazabicyclo-octane (DABCO), nicotinic acid and isonicotinic acid to offer the most potential as neutral-fixing reactive dyes [&I. Dyeing on NTG cotton were carried out in the absence of salt. The most successful dyeings were with a monochloro-s-triazine reactive dye, which gave optimum dye fixation and exhaustion under dyebath conditions of
REV.PROG.COLORATION VOLUME 27 1997 9
Scheme 13
Formation of epichlorohydriw?riethanolamine composite
C2H40H N,-C2H4OH CzH40H
+
-OH, N-(C2H40-CHy-HC,-PH2)3
3 CICHp-HC\-/CHp 0
0
Intermolecular reaction withcellulose
N-(CZH~O-CHZ-HC\-/CH~)~ Scheme 14
+ 3 Cell-OH
0
-
pH 3 and 80°C. The resulting dyeings had similar light fastness to the conventional dyeing, and wash fastness was only slightlyinferior.Higher-reactivity dyes (dichloros-triazineand dichlooquinoxaline)gave excellent dyebath exhaustion. However,dye fixation was poor, probably due to the instability, under acid dyeing conditions, of the quaternised triazine. Non-reactive anionic dyes had good substantivity for the NTG cotton but wash fastness properties of the dyeings were poor. Clearly approaches of this nature would necessitate the use of pad-thermofix equipment, which would restrict such a procedure to fabric processors only. Investigations to deliver substantivesystems are required. Waly ef al. introduced tertiary amino groups by impregnating cotton fabric with a solution of epichlorohydrin and triethanolamine (3:l)in acetone and curing [MI.The treated cotton showed considerable crease recovery, suggesting the reaction to be intermolecular crosslinking (Scheme14)[47,48].Dyeing was carried out by a pad-drybake process using various temperaWtime parameters (1-5 min, lW140"c).There was marked dye uptake on the treated cotton containing tertiary amino residues in the case of an acid dye and a dichloro-s-triazine 0 reactive dye. Acid dye uptake was attributed to cationic, protonated tertiary amino groups in the molecular structure of the modified cellulose undergoing ionic bonding with the anionic sulphonate groups of the dye. Unlike the acid dyeing, the reactive dyeing retained most of its colour strength after laundering. The authors explained this covalent fixation by proposing that the tertiary amino groups performed as 'built-in' catalysts, promoting reaction between the reactive dye and the hydroxyl groups of the cellulose [MI.This explanation
10 REV. PROG. COLORATION VOLUME27 1997
N-(C2H40-CH2-CH-CH2-O-cell)3 AH
seems unlikely, since triethylamine does not easily quaternise monohalotriazine dyes because of steric effects. A more likely explanation is the 'neighbouring group effect'. The proximity of the protonated, cationic nitrogen to the secondary hydroxyl group might encourage ionisation of the hydroxyl group, thus creating a nudeophile that promotes the fixation of DCT dyes under mild pH conditions. The 'neighbouring group effect' was postulated by Lewis and Lei as an explanation of the excellent, neutral fixation of reactive dyes on cotton treated with Glytac A (491. To investigate systematically the effect of attaching a variety of amines to the cellulose fibre by a simple pretreatment, Lewis and Lei modified cotton with N rnethylolacrylamide (NMA) [N].This reagent is a versatile, commercially available crosslinking agent formerly employed in the Visa process for producing durable-press cellulosic fabrics [51].Cotton will react with NMA in the presence of a Lewis acid catalyst according to Scheme 15. Using the pendant double bond as a site for Michael addition with a variety of amines, a number of modified celldosescould be readily prepared. The amine-modified substrates were dyed with a dichloro-s-triazine reactive dye, CI Reactive Red 5,at pH 5; dyeings were produced in the absence of salt by raising to the boil and boiling for an hour. Typical results including measured before and after soaping (5g/l colour yield (US) nonionic detergent plus 5 g/l sodium carbonate, 15 min at the boil) are reproduced in Table 1. Colour yields obtainable on the modified substrates (ammonia and methylamine) are much greater than those achieved by the conventional dyeing method, and dye fixation is high (99%).
cell-OH
+
R
HO-CH2-NH-C-CH=CH2
i-l cell-0-CH2-NH-C-CH=CH2
+
H20
Flgure 2 4,5-Dihydroxy-l,3-dimethyl-2-imidazolidinone
Substrate summary
R R cell-O-CH2-NH-C-CH2-CH2-NH2 cell-0-CH2-NH-C-CH=CH2
NHCH20H
1
A 2
N
HOCH2HNANANHCH20H
I! I1
cell-O-CH2-NH-C-CH2-CH2-NHMe
R R + C~I~-O-CH~-NH-C-CH~-CH~-N(M~)~ Xc~II-O-CH~-NH-C-CH~-CH~-N(M~)~
3
Figure3 Trimethylolmelamine
4
pH values below 6 TMM hydrolysis occurs, resulting in reduced crease resistance; at pH values of 4 and below 5 crease resistance effects are negligible. Dyeing of the TMM-treated cotton with direct and acid dyes in the cell-O-CH2-NH-C-CH2-CH2-NHCH2CH20H 6 absence of salt gives higher colour strengths than with control dyeings, although fastness to- rubbing and Schema 15 washing is worse. Work on modification of electrical resistivity of durableTabk 1 Colour yield and fixation of CI Reactive Red press finishes showed it is possible to introduce cationic 5 (2% 0.w.f.) on different substrates derived from groups into the finished cotton by covalent attachment of NMA choline along with a crosslinking agent [59]. The crosslinking agents TMM, trimethylolacetylenediureine Colour yield (3ACD), DMDHEU and dimethylolpropylcarbamate (DMPC), normally associated with durable-pressfinishing After soaping Substrate Before soaping processes, were used to bind choline chloride by a paddry cure application to cotton fabric, producing a fabric NMA only (1) 0.51 0.12 13.77 13.64 Ammonia (2) which gave good uptake of CI Reactive Red 2 under acidic Methylamine (3) 14.64 14.45 conditionsin the absence of salt [ a ] . Dimethylamine (4) 15.60 1.94 Cotton treated by thermal fixation (3 min, 15O"c, plus Trimethylamine(5) 10.32 8.93 Ethanolamine (6) 12.61 11.52 Lewis acid catalyst) with DMDHEU in combination with Untreated. 14.31 14.10 hydroxyalkylamines gave substrates with high anionic dye substantivity, especially under acidic (pH 3.0-3.5) a Conventionaldyeing, 4% 0.w.f. dye dyebath conditions(Scheme 16) [61,62]. Monoethanolamine, diethanolamine and triethanolCrosslinking agents of the N-methylol type [52], such as amine were evaluated with the latter giving the best dimethyloldihydroxyethylene urea (DMDHEU) (or more results in terms of dyeability and whiteness after curing. formally 1,3-bis(hydroxymethyl)-4,5-dihydroxy-2imid- The dyebath set at pH 3.CL3.5 was found to be the most effective at producing a modified fabric giving good azolidinone), produce a material with smooth-drying properties and are applied to cotton after dyeing [53], as colour yield. The study was extended by combination of pretreatment usually renders the material undyeable. DMDHEU with several primary and tertiary amines with Cotton fabric treated with 4,5dihydroxy-l,3-dimethyl-2 hydroxyalkyl functionality (lhble 2) [63]. imidazolidinone (DHDMI, Figure 2), a non-methylol type The treated fabrics had excellent substantivity towards agent, shows some substantivity for reactive and direct direct dyes, and compared with untreated cotton the dyes, espeaally low molecular mass directs [54,55]. Yang et amine-treated cotton had higher colour strengths after al. used the pore model to explain the differences in washing. More detailed studies in this area by Blanchard substantivity exhibited between DMDHEU- and DHDMI- et al. used 3ACD with three different reagents: choline finished cotton [%I. The acidic conditionsemployed in the chloride (CC), methylpolyoxyethylencocoammonium dyebath resulted in the hydrolysis of the DHDMI finish chloride (C-25) and a water-soluble quaternary ammoand hence reduced its smooth-drymg performance [57l. nium compound containing pendant hydroxyl groups (PSimilar problems were seen for the durable-press finish l), in the presence of a magnesium chloride catalyst trimethylolmelamine(TMM,Figure 3) [%I. [64,65]. On CC-treated fabrics exhaustion of reactive dyes TMM-treated cotton gives good colour yields when was possible without salt; in fact salt was found to reduce dyed with direct dyes from dyebaths at pH 3, although at dye uptake. Dyeing under acidic conditions gave the
R
REV.PROG.COLORATION VOLUME 27 1997 11
OH
+
HO-CH2-CH2-NHR
+
cell-OH
-Ho)+
cell-O-CHp
HoCHl/N'fi0N%H20H 0
N ,,
fi0N. CH2-0-CH2-CH2-NHR 0
Scheme 1I3 Table 2 Amines employed with durable press resins Abbreviation Chemical name AEPD
Structure
2-amino-ethyl-1-9propanediol
y
HOCH2-Y-
2
CHPH
C2H5
AMP
2-amino-2-methyl-1-propanediol
YH2
CH3-F-CH20H CH3
y(CHd2 DMAMP
2dimethylamino-2-1-propano1
CH3-?-
THAM
tris(hydroxmethy1)aminomethane
(HOCH,), CNH,
HBO
7-hydroxymethyl-bicyclo-oxazolidine
OH CH3
YH2OH
7 C l
4CH,ACH,P highest colour yields, with the best fastness to laundering being achieved with CC-grafted cotton. Fastness to laundering could be further improved by a second fixation step with an alkaline catalyst. All three quaternary cottons gave improved dye uptake with direct dyes, although the dyed cotton fabrics treated with P-1 exhibited less dye uptake than the others. Generally light fastness properties of the dyed cotton treated with P-1 were poor, the dyed CC-treated cotton giving the best light fastness properties. Of the three quaternary cottons, the CC-grafted moiety gave superior performance in terms of high colour strength, brightness, fastness to washing and light, but an undesirable odour was released, probably himethylamine chloride, during application, so an after-washingstep was necessary. Stone and Harper explored the wide application versatility of such a cationic cotton produced by treatment with CC and 3ACD [a]. However, it is recognised that light fastness is a continuing problem with this system, although it can be somewhat improved by using mercerised cotton and higher concentrations of CC in the pad-liquor. The tetra-functional polycarboxylic acid crosslinking agent butanetetracarboxylic acid (BTCA) in combination with hydroxyalkylamine additives, such as monoethanolamine (MEA), diethanolamine (DEA), hiethanolamine (TEA) and tris(hydroxymethy1)aminomethane (THAM), were applied to cotton to determine if dyeable estercrosslinked fabrics could be obtained [67l. Dyeing with acid, direct and reactive dyes was good to very good in most cases. Fabric properties depended on the type and concentration of amine relative to the concentration of the crosslinking agent.
12 REV.PROG.COLORATION VOLUME 27 1997
Finally, a comparison was made of dyeable crosslinked cotton with the low-formaldehyde crosslinker DMDHEU and the non-formaldehyde crosslinker BTCA [MI. The crosslinking agents were used in conjunction with the three additives: TEA, 2hydroxyethyltrimethylammonium chloride and tetrakis(2hydroxethyl)ammonium chloride; all the additives were found to be effective in reducing formaldehyde release in DMDHEU finishing. In summary, DMDHEU- and BTCA-crosslinked cotton textiles containing amine additives exhibited increased anionic dye sorption without the need for salt in the dyebath. Dye retention on washing was influenced by several factors in the finishing process, such as the amount and type of crosslinking agent, catalyst and additives used. Modificationof cellulose with amino polymers In an attempt to minimise the speckling effect of immature fibres in dyed fabrics, cotton fabric containing substantial amounts of immature fibres was pretreated with chitosan [69]. Chitosan is a longchain unbranched polymer similar to cellulose except that the hydroxyl groups in the C2 position of cellulose-D-glucopyranoseunit are replaced by either an acetylaminoor an amino group. The preparation of chitosan is achieved by partial deacetylation of chitin, poly(N-acetyl-D-glucosamine),in hot alkali.The chitosantreated cotton gave improved dye coverage with direct dyes as well as increased dyebath exhaustion and colour strength. However, the chitosan pretreatment also decreased wash fastness and rub fastness, demanding a further treatment with a fibre-reactive, quaternary compound if fastness levels were to be similar to those of untreated cotton. The Sandene process was developed by Courtaulds and Clariant (formally Sandoz) and involved the application of a cationic polymer, Sandene 8425, to cellulosic fibres under alkaline conditions by an exhaust method to enhance the fibre's dyeability with anionic and reactive dyes [70].Ease of application made Sandene 8425 particularly attractive as a pretreatment for cotton. The polymeric pretreated cotton provided a substrate that had high neutral substantivity for anionic dyes; reactive dyes could be covalently bound to the resin from neutral to slightly acidic dyebaths. Reduced light fastness and a marked dulling effect in the case of some dyes were regarded as the main draw-backs of the Sandene process. Kratz et al. pretreated linen with Sandene 8425 and successfully produced solid shades on hedwool blends with selected reactive dyes under conditions normally adopted for wool dyeing [Z]. Hercosett 125 (Hercules) is a cationic, reactive polymer prepared by a condensation reaction of adipic acid and
triazine (Mn) and dichloroquinoxaline (DCQ) reactive dyes, but did work well for highly reactive dichloro-striazine (DCT) and difluorochloropyrimidine (FCP) reactive types. The wash fastness properties of the PAEtreated and dyed cotton were excellent, although light fastness was down by 1-2 points compared with control dyeings on untreated cotton. Hercosett has a high molecular mass and low substantivity for cellulose, but during the drylns stage it is cured and insolubilised at the surface of the fibre. The location of the resin encourages subsequent surface coloration, and this makes the dyeing particularly susceptible to photofading. Further investigations into the PAE midcotton system were carried out in an attempt to improve the dyeability of PAE-treated cotton with low-reactivity reactive dyes and to increase the light fastness of dyeings. A thiourea derivative of Hercosett was applied to cotton fabric (731. The azetidinium cations of the PAE resin reacted with thiourea to produce the isothiouronium salt, which should impart extra cationic charge to the treated PAW thiourea cotton (Scheme 18).It was proposed that during dyeing at elevated temperatures the isothiouronium salt undergoes hydrolytic decomposition to produce cotton containing a polymer with highly nucleophilic thiol groups (Scheme 19).The highly nucleophilic nature of the PAWthiourea-treated cotton promotes covalent bonding with dyes of low reactivity [73]. The effect of dye build-up on the PiWthiourea-treated cotton was good for highly reactive DCT dyes, although with dyes of lower reactivity (MCT, FCP, DCQ) good colour yields and fixation were only obtained at up to 2% 0.w.f. depths. The authors suggested that during dyeing there is a competitive reaction between the dye and residual azetidinium cations for secondary amino groups in the PAE resin. The dyes possessing high reactivity compete successfully for secondary amino sites and thus their build-up properties are good, the opposite being the case for dyes of lower reactivity. To improve the build-up properties of dyes of both low and high reactivity, cotton was pretreated with P W D A mixture [74]; EDA produces a different crosslink on drymg, having surplus nucleophilic amino sites (Scheme 20). EDA not only greatly modified the azetidinium sites of the PAE resin to incorporate a large number of nucleophilic primary, secondary and tertiary amino sites
diethylenetriamine, followed by partial crosslinkingof the polyamide with epichlorohydrin. Burkinshaw et al. applied Hercosett 125to cotton by a pad-dry(3 min, 100°C)process [71].NMR studies have shown Hercosett to contain a mixture of 3-hydroxyazetidinium chloride, epoxypropyl and chlorohydrin groups in the ratio 3:l:l [72]. The main reactive group is 3-hydroxyazetidinium chloride, which on drying reacts with secondary nucleophilic sites in the polymer itself, thus insolubilising it on the substrate. Scheme 17 represents the reactive and nucleophilic sites that may exist on the surface of the polyamide-epichlorohydrintreated cellulose. It is most unlikely that covalent bonding can take place between Hercosett and the cotton substrate under neutral conditions, because the nucleophilicity of the secondary amino groups in the polymer is much higher than that of the cellulose hydroxyl group. The pretreated polyamideepichlorohydrin (PAE) cotton could be dyed from neutral dyebaths, in the absence of salt, to give high exhaustion and fixation values for reactive dyes of high reactivity. The system did not work well for low reactivity monochloro-s-
Fbm phwr
Polymer (fibre surface) phase ClAzetidinium
catlon
5 5
+ NH2
)H -L
J ,
'
N-CH2yHCH2-N OH
x
-a
mine
Terbaryamine. secondary hydro@
11 -OH
-0-CH2CHCH2-N AH
-b
Covalent link to polymer
Schema 17
/ Azetidinium cation
lsothiouronium salt
Schema 18
schema 19
REV.PROG.COLORATION VOLUME 27 1997 13
r, -\N.+/\/"+
NH2--CH2-CH2-NH2
\+
ct
,N.-CH2-CH(OH)-CH2-NH-CH2-CH2-NH2
,N-CH2-CH(OH)-CH2-NH-CH2-CH2-NH-CH2-CH(OH)-CH2~~,
/s
Scheme 20
(with a preponderance of secondary amino groups), but also promoted more efficient crosslinking of the PAE resin with cellulose. Under slightly acidic dyeing conditions some of the amino groups are protonated, providing good substantivity for the reactive dyes in the absence of salt. Excellent build-up properties were achieved with dyes of both low and high reactivity. Dye fixation was in the region of 95% and wash fastness properties were excellent. However, the problem of reduced light fastness remained unresolved. Wu and Chen applied polyepichlorohydrin-dimethylamine (PECH-amine) to cotton to improve its dyeability with directs and reactives [75-771. The first step in the polymer's preparation was polymerisation of epichlorohydrin by a ring-opening mechanism in carbon tetrachloride with a boron trifluoride etherate catalyst to produce polyepichlorohydrin (PECH). The amine derivative was achieved by adding dimethylamine to PECH at 95°C (Scheme21).
Scheme 21
The PECH-amine can be applied to cotton by an exhaustion method. Higher total nitrogen content on the fibre resulted in dyeings of higher colour yield. Dyeing with CI Direct Blue 78 showed that the molecular mass and nitrogen content of the prepared polymer can have an influence on the colour yield of the dyeings produced on the pretreated cotton. Polymers containing similar nitrogen content but different molecular mass when applied to cotton showed the higher molecular mass species to give better colour yields, presumably due to the higher substantivity of the higher molecular mass polymer. Polymers of similar molecular mass but of different nitrogen content when applied to cotton showed that the polymer containing less nitrogen gave better
14 REV.PROG.COLORATION VOLUME 27 1997
colour yields, presumably due to its higher content of chloromethyl groups. PECH-aminecan also be applied to cotton by a pad+ method; thisis probably best for the smaller molecular mass polymers. Dyeing studies with direct dyes revealed that, compared with untreated cotton, higher colour yield for the PECH-amine treated cotton could be achieved with small amounts of salt (2 gA),but the PECH-amine cotton dyeings were duller with lower wash and light fastness. Excellent build-up properties were achieved with dyes of both low and high reactivity under neutral dyeing conditions; lowreactivity dyes required only 10%of the normal salt usage and high reactivity dyes required no salt. The wash fastness of dyed PECH-amine-treatedcotton was excellent, although a drop in light fastness of 1-2 points was reported. Evidence shows that increases in light fastness can be achieved through increased covalent bonding of reactive dye to cellulose (rather than the polymeric resin) [78]. Thus Wu and Chen proposed that light fastness of dyeings was related to penetration and distribution of the dyes. A recent publication promoted Texamin ECO (VutzInotex) as a substantive, cationisingagent for cellulose [79]. Unfortunately, little is known of the compounds chemistry.
Nucleophilic dyes on a modified 'activated cellulose "MA is well known as a crosslinking agent for imparting crease-resistantproperties to cotton fabrics [51]. It has two well defined modes of reaction. (a) Lewis acid catalysed etherificationof hydroxyl groups (b) Alkali-promotedMichael addition to nucleophiles. Lewis and Lei have shown that the activated substrate reacts well with aminoakyl dyes, prepared by the reaction of a monochloro-s-triazinedye with ethylenediamine [49]. The alkylamino dyes have the advantage over conventional reactive dyes in that they do not hydrolyse in the dyebath. NMA-treated cotton was dyed with akylamino dyes at pH 10.5 in the presence of 80 gA salt producing dyeings of excellent colour yield, with fastness unsurpassed by conventional reactive dyeings on untreated cotton. Further work demonstrated that the system suffered from reduced dye build-up with shades greater than 4% 0.w.f. Amide bond hydrolysis during dyeing, decreasing the number of active sites available for
reduction in colour discharge in the effluent. The preparation of thisactivated substrate is shown in Scheme 23.
dye fixation and fixed sulphonate anion build-up, may be responsible for reduced dye build-up with heavier shades. Scheme 22 (where D is the dye chromophore) describes fixed sulphonate anion build-up; the already-fixed dye on the substrate behaves as a dye resist, preventing further dye from being absorbed and fixing on the substrate. To overcome the problem of sulphonate anion repulsion effects, cotton was treated with 2,4dichloro-& (2’-pyridiniumethylamino)-s-triaz,ine(DCPEAT), as this compound incorporates a cationic centre neutralising the negative charge imparted by the fixed sulphonate p u p s of the dye [80].DCPEAT contains two reactive chlorines and when applied to cotton under mild conditions one of the chlorines reacts with cellulose; at the same time the reactivity of the other chlorine is reduced. The treated fibre contains monochloro-s-triazine residues that can undergo reaction with aminoallcyl dyes (stronger nucleophiles) but not with cellulose hydroxyl groups. DCPEAT was applied to cotton both by exhaustion and pad-batch processes, although exhaust application did not give adequate levels of efficiency. Dyeing was carried out at the boil, pH 9, in the absence of salt. The resulting dyeings were bright, of similar hue to that of the respective parent dye applied by the classical method to untreated cotton; similar washing and light fastness levels were achieved as in conventional dyeing. Advantages of this system, apart from the quality of dyeing obtained, are that full use of the dye is made in the dyebath because no dye hydrolysis can occur. Furthermore, environmental benefits include no salt, reduced wash-off times and a
Improving dyeabilityby other methods So far, the methods discussed for improving the dyeability of cellulosics with anionic dyes have involved the introduction of nitrogencontaining compounds into the cellulose substrate. Sakamoto et al. looked at the introduction of sulphonium derivatives into cotton [81]. The cotton was treated with bis-p-isocyanatoethyldisulphide in dimethylformamide at 80°C followed by reduction with tri-n-butylphosphine in methanol containing 10% water to give cellulose pmercaptoethylaminocarboxylate (RDTC). The RDTC cellulose was then treated with methyl iodide to form the sulphonium salts (Scheme24). The sulphonium derivatives were dyed with Direct Sky Blue A and gave increased dye uptake due to ionic interaction; dye uptake increased with increasing sulphonium content. Clearly this approach is one of theoretical value only since it involves modification from organic solvents with toxic substances. Vigo and Blanchard immersed soda cellulose in an arylsulphonium salt solution [82]. Dyeing of the arylsulphonium cellulose was carried out at pH 5.0 with direct, reactive, sulphur and disperse dyes. Improved colour strength was seen for all the aforementioned dye classes but dyebath exhaustion levels and fastness results are not reported.
0
+ (SO3-),-D-NH
L N + L + R
I
Aminoalkyl dye
ClCly,NYNH-CH2-CH2-N
NYN 6
n
cell-O-CH2NH-C-CH=CH2
DCPEAT
3-
+/
\
+
cell-0
NMA treated cotton containing ‘acthrated‘ double bond
ClNH-CH2-CH2-h2
NY-N CI
REV.PROG. COLORATION VOLUME27 1997 15
cell-O-$-NHCH2-CH2SH 0
CH31
cell-OCNHCH2CH2SCH3
&Mercaptoethylaminorboxylatecelluiose or RCTC cellulose
Schema 24
@-SCH2COO-Na+
+
ceII-O-Na+
-
@O-cell
+
Na+-SCH2COONa+
Sodium benzoylthiilycdlate
)"
Na+-0Oc
>-/
Na+-0Oc
Sodium benzoylsalkylate
Schema 25
Kratz et al. esterified linen with thioglycollic acid to incorporate thiol groups [El. Thiols are stronger nucleophiles than hydroxyl p u p s [83], so it was expected that the thiol-modified cellulose would react more efficiently with reactive dyes. Subsequent dyeing gave improved colour yields but dye uptake was not increased sufficientlyto give solid shades in linenhvoolblends.
CHEMICAL MODIFICATIONTO ENHANCE DYEABILITY WITH DISPERSE DYES Unmodified cellulosic fibres cannot be dyed with nonionic, disperse dyes. A modified cotton that could be dyed with disperse dyes would offer two main benefits. Firstly it could be amenable to printing using sublimation heat-transfer methods, and secondly one dye class could be used to dye polyester/cotton blends. Several workers have demonstrated that by introducing bulky aryl residues into cellulosic fibres, the hydrophobic character of the fibre is increased thus improving substantivity towards disperse dyes. In the 1920s Tootal, Broadhurst and Lee pretreated cotton with benzoyl chloride to improve easy-care properties of the cotton fabric. The Shikibo-Uni process also used benzoyl chloride to treat cotton with the intention of producing a substrate for transfer printing with disperse dyes [84,85]. The Shikibo-Uni process involved acetylation of cotton by the Schotten-Baumann method. Fabric was treated with 20% sodium hydroxide solution and then with benzoyl chloride, followed by washing-off. The benzoylated cotton substrate can be transfer printed using disperse dyes, giving prints of a quality similar to those produced on 100% polyester. Benzoyl chloride is, however, not a desirable chemical for use in the mill environment due to its lachrymatory properties. Thomas used water-soluble active esters, which are more acceptable to working mill conditions, for the arylation of cotton [&I. Water-soluble activated salicylate
16 REV.PROG. COLORATION VOLUME27 1997
or thioglycollate esters were reacted with cotton at high temperatures (150-200°C). Typical esters are sodium benzoylthioglycollate (BTG) and sodium benzoylsalicylate (Scheme 25). Optimum application conditions for BTG modification of cotton were achieved with a pad-liquor containing 200 g/l BTG and 20 gA sodium carbonate, thennofixing for 60 s at 200°C [871. Higher temperatures discoloured the fabric. Baumann and Korte modified cellulose with aliphatic acid chlorides and demonstrated that increasing the chain length of the aliphatic chain resulted in increased substantivity towards disperse dyes [88]. Maximum substantivity was achieved with a chain length of at least eleven carbon atoms. Einsele et al. demonstrated that aromatic substituents in the cellulose fibre give greater disperse dye substantivity than do aliphatic residues (89,901. For benzyolated cotton an optimum dyeablity is accomplished at a degree of substitution of 0.15425, while to obtain good wash fastness properties a degree of substitution in the range 0.3-0.4 is required [91]. The ester bond linkages are unstable during alkaline washing, resulting in a loss of approximately 30% of the on@ ester group content of the substrate [92]. After five washes this ester bond loss is increased to 60-70%, until after ten washes no appreciable further hydrolysis is apparent. Hebeish et al. carried out a graft copolymerisation with styrene on partially carboxymethylated cotton using gamma radiation [93]. The hydrophobic nature of the polystyrene bound to the cotton substrate enhanced its dyeability with disperse dyes. Furthermore, the higher the graft yield of polystyrene, the greater the colour strength of the subsequent dyeing.
CONCLUDING SUMMARY Clearly the chemical modification of cellulose (cotton) to obtain enhanced dyeing properties has attracted much
research interest. It is pleasing to note that auxiliary manufacturers are already selling reactive aminating compounds for the purpose of improving dyeing properties; the Vicotone ECO System developed in the US is a commercially used process and does not interfere with the handle and physical properties of the fibre. Other processes which are on trial include the Hydrocol EP 155 System from Rudolf and the Tscamine System from ViitzInotex. Whether or not these attempts have a sigruficant market impact depends on a number of issues [94], not least the cost of the treatment. Modification during the dyeing process itself would be an ideal and researchers should be encouraged to thinkalong these lines.
42. D M Lewis and K A McIlroy, Dyes Pigments,in press. 43. N Morimura and M Ojima, A m . Dyestuff Rep., 74 (1985) 28. 44. M Miyumoto and R Parham, AATCC conj book of papers, Atlanta (1986) 153. 45. S N Croft,D M Lewis, R Orita and T Sugimoto,J.S.D.C.,108 (1992) 195. 46. A Waly, R Rafia, M H El-Rafie and A Hebeish, A m Dyestuff Rep., 79 (1990)34. 47. J L Gardon and R Steele, Text. Res.J., 31 (1%1)160. 48. D D Gagiardi and F B Shippee, Text. Res. J., 31 (1%1) 316. 49. DMLewisandXPLei,J.S.D.C.,lW(1991)102. 50. D M Lewis and X P Lei, IFATCC congress book of papers, Lucerne,
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