Indian Journal of Fibre & Tex tile Research Vol. 26. March-June 200 I. pp. 108- 11 5

Cationization of cotton for low-salt or salt-free dyeing

D P Chatlopadhyay"

Department of Textile Chemi stry. The Technolog ica l Institute of Textile & Sciences. Bhiwani 12702 I. India

Cotton acquires negative charge in aqueous med ium and thus repels negati vely charged dye ani on during dyeing. Such repul sion between fibre and dye is offset by using large quantity of salt in dye bath. particularly for reacti ve dyes. A low dye bath ex haustion also leads to low dye fixation of reactive dyes on cotton. Thus. the use of hi gh salt concentration and low reactive dye fixation lead to environmental problems related to hi ghly coloured efnu ent with high salt content. These problems can be overcome by improving the dye substantivity of cotton in the absence of salt or with low salt additions. One such approach is cation ization of cotton which is criti ca lly reviewed in the present paper. Majori ty of the chemica ls used for in troducing cat ionic si tes in cotton are themselves not sa fe environmentall y. Therefore. there is a need to explore the potentiality of the cationi za ti on route using eco fri endly chemicals. The use of chitosan. a polymer derived from chitin . is a step forward in this direc tion.

Keywords: Cati oni zat ion. Cotton. Dyeing. Reactive dyes

1 Introduction Cellu losic fibres when come in contact with water

produce slightly negati ve charge due to the ion ization of hydroxy l groups, whereas most of the dye classes sui table fo r cotton are an ioni c in solution. The slightly negative charge on the fibre results in repulsion of anionic dyestuffs and thus the ex haustion of the bath in limited t

• However, by adding an electrolyte like sodium chloride or sod ium sulphate, the charge repul sion factor can be offset and thus increased dye ex haustion is achieved. The reacti ve dyes, in particular, require large quantities of electrolyte for its ex haust application, leading to environmental problems. In addition, inadequate dye bath exhaustion and dye fixation pose the problem of colour effluents. Therefore, a dyeing procedure leading to high dye fixation could be of great benefit to minimize the environmental problems. Different approaches, such as modification of the dye structure to make it more substantive to cellulose, cationization of cellulose through chemical reaction with compounds containing cation ic groups or controlled dos ing of dye and salt duri ng the exhaustion process, have been recommended to control the above mentioned effluent prob lem. The approach of producing fabrics from yarns of cationic and normal cotton has been commercialized by Japanese companies such as

"Preselll address: Department of Textile Chemi stry, Facu lty of Technology & Engineering. M S University of Baroda, Vadodara 390001. India Phone: 0091-0265-434188/423898 Extn. 210; E-mail: dpchattopadhyay@ ilashmail.colll

Kurabo Industries, Kanebo Textiles and Toyobo. On subsequent dyeing, these fabrics give a differential colour and cross-dye effect. Cottum, Colo-cotto and Viewline are some of the brand names of cationic cotton sold in the international market by the Japanese manufactures2

.J

.

In this paper, an attempt has been made to review critically some of the developments in the fi eld of cationization of cotton.

2 Treatment with Epoxy Compounds Compounds containing epoxy radicals find various

applications in the textile industry due to their ab il ity to react with cellulose, especially in an alkaline medium, with the formation of an ether bridge4

•o. The

poss ibility of using epoxyamine or quaternary epoxyammonioum compounds for introducti on of a cationic site in cellulose through reaction of an epoxy radical in alkaline medium and, therefore, modi fyi ng the reactivity of cellulose towards anionic dyes attracted the attention of many scientists for quite a long time. Schlack7 was the first to report improved affinity of acid dyes towards cellulose modified through the introduction of epoxy derivatives. Champetier el al.8 and Merle9 modified cellulose by a reaction with epoxy diethylamine-3-propane fo ll owed by an ethyl iodide quaternization and reported the dyeability of the modified cellulose towards acid dyes. The most popularly used epoxy chemical. at that time, for the cationization of cellulose was glyc idyl trimethylammonium chloride, commonly known as Glytac (Fig . I). Japanese rescarcher'o investigated

CHATTOPADHYAY: CATIONIZATION OF COTTON FOR LOW-SALT OR SALT-FREE DYEING 109

Fig. l -Glycidyltri methy lammonium chloride (G lytac A)

closely the improvement in fastness properties of acid dyes on Glytac-pretreated cellulose. Rupin et a /. 11

-12

studied the dyeability of cell ulose towards reactive and direct dyes after pretreatment with Gyltac and simultaneous modificati on and dyeing by exhaust, pad-batch and pad-cure processes. Glytac-pretreated cellulose showed improved dyeability , in exhaust appl ication, towards reactive dyes in presence of alkali and salt, whereas si multaneous Glytac treatment and dyei ng were not found effective for exhaust application. The dyeability in case of pad-batch and pad-cure processes was improved for the both pre­and simultaneous Glytac treatments. The wash fastness of Glytac-pretreated and direct dyed materi al was excellent, which is claimed to be due to strong ionic bond formation between the positi ve charge of Glytac modified cellul ose and the anionic dye molecules. In a later paper, Van Rensburg l3 reported that some of these claims for the effectiveness and versatility of Glytac were greatly exaggerated. Rupin et 0/.

11.12 reported considerable improvement in wet

fas tness, claimed to be much superior to ratings obtained on similar direct dyeings after-treated with conventional fixing agents . On the other hand, Rensburg fo und little or no improvement in fastness to alkaline perspirati on or ISO 3 washing. He also found that fixation of reacti ve dyes by pad-batch application to Glytac-pretreated cotton was decreased relative to contro l dyeings. The improved colour yield obtai ned by Rupin et 01.11.12 was due to the absorption of hydrolyzed dyes on account of electrostatic attraction rendered by cationic sites . Evidence for this was obtai ned by solven t extraction l4

. Glytac type of compounds have low substantivi ty , unpleasant odour and poor thermal stability, and thus they are only suitable for pad applications.

3 Treatment with Epichlorohydrin Precursor of Glytac Rudolf ls studied the dyeability of cellulose

substrates modified with epichlorohydrin precursor of Glytac (Fig.2). When treated with alkali , this precursor is converted to Glytac and the epoxy group reacts wi th cellulose. Trimethylamine released during

CH 3

'+ CI-CH -CH-CH -N-CH CI 2 I 2 I 3

OH CH3

Fig. 2-Epichlorohydrin pecursor of Glytac

Fig. 3-Mono reacti ve bi s quaternary agent

the reaction suffers form toxicity problem. Selected direct dyes can be applied to the quaternized cellulose without salt, yielding satisfactory fastness to ISO 3 washing IS.

4 Treatment with Chlorotriazine Type Quaternary Compounds

Mono- and bi s-reactive halogenoheterocycli c compounds containing one or two quarternary groups likewise are effective for producing cationi c sites in cotton 14 . Evans et 01 . 14 modified cotton with

monoreactive bi s-quaternary agent (Fig. 3) by pad­batch method. Such pretreatment caused substantial improvements in both neutral and alkaline exhaustion with reactive dyes in the presence of salt. The alkali ne exhaustion and fixation on pretreated cotton was

reported to be approximately double compared to that on the untreated cotton fabric. The fixation efficiency was also found to be considerably better on the pretreated substrate. They worked with various monochlorotriazine bis-quaternary compounds of symmetrical structures (Fig. 4) and concl uded that ary laminotriazine type of compounds were more effective in enhancing dyeability than alkylamino­triazine types due to the higher substanti vity and

fix ation of the former. They further reported that a para substituted arylamine compound was slightly more effective than its meta substituted isomer and a trimethylammonium alkyl group was slightly superior to a pyridinium alkyl group. An extremely good acid dye exhaustion in absence of an electrolyte was found on cotton fabric pretreated with monoreacti ve bis­quaternary agent by pad-batch sequence. However, addition of sodium chloride as an electrolyte in thi s sys tem sharply reduced exhaustion. The reduction in exhaustion is reported to be due to the competition of

110 INDIAN J . FIBRE TEXT. RES., MARCH-JUNE 2001

+ + R - NH 'Y-N yNH- R

X- NyN X

CI

Compund R

A

Fig . 4. - Vari ous monchlorotriazine bis quaternary cationizing agents

the ch loride ion and dye anions for the bis-quaternary sites in the modified fibre. Evans et al. 14 also tried to apply monoreactive bis-quaternary agent to cotton fab rics in a conventional pretreatment sequence, viz. continuous pad-steam peroxide bleaching, but the effectiveness of the agent in enhancing the dyeability was largely destroyed by the steaming in presence of hydrogen peroxide. According to Van Rensburg 13,

reactive dyes applied by the pad-batch process to Glytac-treated cotton showed inferior fixation compared wi th conventional controls, whereas Evans et al.14 confirmed that such problem was absent for reactive dyes applied by pad-batch method on cotton mod ified with monoreactive bi s-quaternary agent (Fig. 3). He claimed that the quaternary chlorotriazine type of agents react with cellulose more readily than do the epoxypropy l types. Moreover, the discolouration of the fibre can occur during the alkaline cure necessary for epoxy fixation. The loss of trimethylamine destroys the effectiveness of Glytac and its precursor and simultaneously gives rise to objectionable odour in the treated fabric. It is reported 14 that the alkali ne perspiration fas tness of reactive dyes on cotton pretreated with epoxypropyl type quaternary agent and dyed in presence or absence of alkali is often signi ficantly inferior to control dyeings on untreated cotton. The most serious limitation raised against the epoxypropyl agents was its low substantivi ty which makes it unsuitable for exhaust application and shows migration problems on drying subsequent to padding. On the other hand, the

CH 3 I

HO-CH2- CH2- N-CH3 CI I CH3

Fig. 5-Choline chloride

higher reactivity of chlorotriazine type of agents made them suitable for pad-batch and exhaust application rather than the alkaline pad-cure process used fo r the epoxy type of compounds.

5 Treatment with Choline chloride Another concept l6

.17 of cationizing cotton , using a

compound that contains both a quaternary group and an alcohol moiety as a reactive additive and a crosslinking agent, was evolved by Harper. He used choline chloride (Fig. 5) and various crosslinking agents with an object to produce cationic fabric with easy care performance and enhanced dyeability. Such approach provided a method of producing post­dyeable garments and fabrics and allowed dyeing subsequent to crosslinking. The treated fabric is reported to be dyed substantially with reactive dyes from an acidic bath whereas the reactive dye uptake of untreated or conventionally treated fabric was very low and, therefore, opened route of producing cross dyeing effects in fabric containing mixtures of yarns of cationic and untreated cotton. The various crosslinking agents used for this purpose were tri methy 101 melamine, tri meth y lolacety lene di urei ne, dimethyloldihydroxyethylene urea and dimethyl propyl carbamate. Trimethylacetylene diureine and choline chloride combination produced a good DP rating and colour yield.

6 Treatment with Polyamide Epichlorohydrin Type Polymers Hercosett 125, a product of Hercules Powder

Corporation, is a reacti ve polymer which can introduce a cationic charge to cotton. This polymer can be prepared by partial condensation of adi pic acid and diethylenetriamine, followed by crosslinking with epichlorohydrin. Thus, it is a polyamide epichlorohydrin (PAE) type of polymer. It is sparingly soluble in water and stable up to six months at pH 4-5 as a 12.5% aq ueous solution is. It was proved by NM R studies I? that the polymer can introduce an azetid ini um cation (Fig. 6). On drying.

CHA TTOPADHYA Y: CATIONIZATION OF COTTON FOR LOW-SALT OR SALT-FREE DYEING I II

"" + /CH 2'-..... C/ OH

N /"-/ . "CH H CI 2

Fi g. 6-Azetidin ium cati on

Hercosett 125 can react with nucleophilic sites in cotton or in the polymer itself, thus fixi ng the polymer to the substrate. Pretreatment of cotton with thi s polymer offered the opportunity for increasing both the substantivity and reactivity towards reactive dyes under neutral or acidic condi tions due to the introduction of cationic azetidinium group and unmodified highly nucleophi lic secondary and terti ary amino groups (Fig. 7). Pretreatment of cotton with PAE polymer resulted excellent exhaustion and fixation of reactive dyes from neutral bath in absence of salt, in comparison to the untreated cotton sample. Both the exhaustion and fixation reached the maximum values for 2% (owf) polymer application. For a variation of pH from 6 to 8 the dye exhaustion was found to be more in acidic pH, whereas dye fixation was maximum at pH 7. The improvement in dye exhaustion in acidic dye bath was attributed to the fact that besides azetidinium groups the polymer also contains secondary and tertiary amino groups which get protonated under acidic condi tions and thus produce a positively charged cotton surface which attracts more dye anions. But as the nature of the dye­fibre reaction is one of nucleophilic substitution, the reactivity of the treated cotton was found to be decreased with the decreasing application pH. While invest igating the effect on various types of reactive dyes, Burkinshaw et al?O found higher fixation for high reactivity dyes such as ditluorochloropyrimidine and dichlorotriazine dyes . The high fixation of high reactivity dyes was attributed to the fact that Hercosett is fixed to cotton mainly by means of cross linking and since the reactive side chain of the polymer partially loses mobility when water is removed, crosslinking is incomplete in some part of the resin film. As Hercosett has a large molecular structure, it is not extracted from cotton under neutral dyeing conditions, but during dyeing the highly reacti ve dyes react with Hercosett on the cotton surface fo rming further cross links and reducing the solubil ity of the res in . As a result. both dye and Hcrcosett are fi rmly fixed to the cotton . During dyeing, the reactive groups of the reacti ve dye compete with the azetidinium cations for the available highly lllC!eophi li c imino sites in the resin. Low

--......+ __ NHCH2

Secondary amine

OH

l~+ tertiary amine

+ -­CH - CH2-NH __

! OH

Fi g. 7 - Vari ous amines present in Hercoset polymer

"" + /CH ; '-..,. ./' OH

./ N _ .......... / C"'" Azetidinium ./ CI CH 2 H

/NH2 + S = C Thiourea

~ NH 2 I '-.. + ..- NH 2

./ N - CH 2 - CH - CH 2 - S = C ..-..-

I '-..,. NH ? CI -

OH

Isothiouranium salt

Fig. 8-Reacti on of PAE with thiourea

reactivity dyes thus lose out and show lower fixati on efficiency . The fact that the PAE resin could not improve the fixation of low reactivity dyes directed Burkinshaw to develop newer system for the introduction of highly nucleophilic sites in cotton so that better fixation of both high and low reactivity dyes mi ght be achieved . Under mild condition , the azetidinium cation can react with strong nucleophiles like amines and thiols by ring opening (Fig. 8)21.

Burkinshaw et al.22 therefore pretreated cotton with PAE resi n (200 giL) and thiourea (10 giL) using a simple pad-dry procedure. The treated fab ric was dyed with reactive dyes from an acidic bath in the absence of salt. whereas the untreated control was dyed by the dye manufacturer' s recommended method (i.e. with salt and alkali ). Incorpo ration of thiourea improved both the exhausti on and fixat ion of high reactiv ity dyes significant ly. Such improvement was believed to he due to the fonnation of

112 INDIAN J. FIBRE TEXT. RES .. MARCH-JUNE 2001

isothiouronium salt residues (Fig. 8) in the substrate, following reaction of thiourea with azetidinium cation. These not only impart a strong cationic character to the substrate but also supply highly nucleophi lic thiol groups during the dyeing process due to hydrolytic decompositi on of isothiouronium salt at elevated temperature. Evidence for the presence of isothiouronium salt residues in the PAE/thiourea treated fabrics was obtained from f t i r spectroscopy22.

Lei and Lewis23 introduced 10 milL ethyl enediamine (EDA ) in the PAE (Hercosett 125, 200 giL) pad bath and applied by si mple pad-dry procedure to improve the dyeability of cotton towards low reactivity dyes. The various advantages claimed of using EDA are as follows:

• EDA promotes the crosslinking of PAE resin because of its tetrafunctionality .

• The dyeability of PAE/EDA treated cotton is improved due to the fact that an increased number of highly nucleophilic amino groups are made available for reaction with the dyes.

• The substanti vity of the treated substrate towards the anionic dyes increases, as in the acidic condition the amino groups get protonated and act as reservoir for the generation of cationic si tes. PAE/EDA treated cotton is reported23 to show a

strong f t i r absorbance band at 1591 cm' ), which ind icates that the number of amino groups was increased due to EDA addition to the PAE pad liquor.

The treated cotton was dyed in a slightly acidic bath (pH 5) in absence of salt, whereas the untreated control was dyed as per the manufacturer's recommendation. The EDA addition could improve the dye build up for both low and high reactivity dyes to a very great extent and was found to be much superior to either PAE or PAE/thiourea treatment. However, the light fastness was badly affected due to EDA incorporation in the PAE pad liquor. The poor light fastness was attributed to the presence of dye mainly on the surface of the fibre, a phenomenon commonly called as ring dyeing.

7 Treatment with N, N'-dimethylazetidinium chloride The problem of ring dyeing and low light fastness

associated with PAE/EDA system was resolved by using low molecular weight species to pretreat cotton by a pad thermosol fixation technique24.25 , Better results were obtained using N, N-methylazetidinium chloride (DMAC). DMAC reacts with cotton in presence of alkali as shown in Fig. 9. The modified

cellulose was found to have excellent substanti vity for reactive dyes form a neutral bath in the absence of

24 electrolyte . Guo and Chen26 found that the dyeablility of the

DMAC-treated cotton can be further enhanced when the DMAC treatment is preceded by alkali pretreatment. It is reported that a pretreatment with 200 giL sodium hydroxide solution and then with an aqueous solution of DMAC (40- 100 giL) could improve both the colour yield and fixation of reactive dyes to a very hi gh extent. The alkali pretreatment prior to DMAC treatment was believed to promote the formation of the nucl eophilic cellulosate anion and thus increased the chances of the reaction between DMAC or its oligomers and cellulose. DM AC treatment after alkali pretreatment was found to yield much stronger colour than the pad thermosol method proposed for DMAC application earlier24 .

8 Treatment with N-methylolacrylamide Lewis and Lei 27 modified cotton with N­

methylolacrylamide (NMA). The NMA-treated cotton was further aminated using ammonia and various amines (Fig. 10), e.g. methylamine, dimethylamine, trimethylamine and ethano lamine. After the treatment , the substrate was dyed with reactive dye in a slightly acidic bath without an electrolyte. It was found that

Ceil-OH

Me CI "'" + /CH 2'-...... /"OH

N C

/ " / "'"

1

Me CH 2 H _ (OMAC)

OH , 200°C

_____ Me

Cell-O-CH2-CH-CH 2-N ............ +HCI I Me

OH

Me -+ 1+ CI

Ceil- OH Me- N - CH2-CH - CH 2

I '" /

1 - Me (Glytac A) 0

OH, 120°C

OH Me I 1+ _

Ceil- O- CH2- CH - CH 2- N - Me- CI I

Me

Fig. 9-Rcaction of DMAC and Glytac with cotton

CHA TTOPADHY A Y: CATIONIZATION OF COTTON FOR LOW-SALT OR SAL T-r !{EE DYEING 113

the dye build up and fixation were improved with the introduction of primary and secondary amino groups (for substrates I,ll and V), which, in turn , improved both the substantivity of the dye towards the substrate and the reactivity of the substrate. The presence of tertiary amino groups was found to cause a high improvement in exhaustion, but fixation was badly affected under mild acidic conditions. Under acidic conditions, a reasonable number of tertiary amine sites got protonated, thus offering a cationic site for the anionic dye and increas ing the substantivity. On the other hand, a terti ary amino group can react with the dye to form a product as shown Fig. 11 . The onium group is strongly electron withdrawing and also a very easy leavi ng group. Its elimination occurs in the alkaline soaping bath . This accounts for the low fixation value observed on substrate III.

The effect of modifi cation of cotton using various N-methylolacrylamide derivati ves, viz. bis (N­

methylol-2-carbamoy lethyl ) butylamine, N-(N, N'-di­methylol-2-carbamoylethyl) diethylamine and N-(N, N'­dimethylol -2-carbamoylethyl) dimethylamine, on ac id dyeability has been investigated by EI-kharadly et al.28

. These agents were prepared by lI1ethylolation of bis (2-carbamoylethyl)29, N-(2-carbamoylethyl)­diethylamine30 and N-(2-carbamoylethyl) dimethyl­amine3

! respectively and applied by pad-dry-cure procedure to cotton fabric. Such treatments were found to improve the crease recovery angle and acid dyeability. But these agents release hazardous formaldehyde during curing as well as on storage.

9 Treatment with Polyepichlorohydrin dimethylamine Wu and Chen32 treated cotton with polyepichloro­

hydrin (PECH) dimethylarnine which wa<; manufactured by initial polymerization of epichlorohydrin, followed by amination with dimethylamine. The epichlorohydrin was polymerized in carbon tetrachloride using boron trifluoride etherate as catalyst (Fig. 12). The dyeability of treated cotton towards direct dyes was investigated and it was fo und that PECH-amine could improve the direct dyeability of modified cotton. The pretreatment could improve the perspiration fast ness, whereas the wash and light fastness were not improved.

Wu and Chen33 also reported the effect of PECH­amine treatment on the reactive dyeability of cotton. It was found that the modified cotton can be dyed with selected low reactivity dyes under neutral condition using li mited salt concentrations or with selected high reacti vity dyc~ wi thou t salt.

o II

Cell - OH • HO-{;H,- NH-<:- CH =CH,

\ '"'", "oc o " Cell-O- CH,- NH- C- CH-CH, • H,O

I I Ammonia 0 C .t, II 'e

Cell - O- CHC NH-C-CH2- CH2- NH2 ~

o II

~

~ :I;

Cell - O- CH,- NH- C-CH2- CH2 - NHMe

U

~ ~ Cell-Q-CH2- NH-C-<:H2 - CH2- NMe2

III

~ W +_ Cell- Q- CH,- NH- C-CH2- CH2 N Mel X

IV

~ ?t

N' melhylolacrylamide

.. " ·e .. :;, £ .. E i5

Cell-Q- CH2- NH- C- CH2 - CH2 - NH- CH2- CH2- CH

v

Fig. 10- Various cellulose derivati ves obtained by reaction o f cellulose with N-methylolacrylamide fol lowed by ami nation wi th different amines

o CH,

II I. C! CI Cell - O- CH 2 - NH - C - CH 2'CH 2 - N-/I

I "-L NH - @

CH ,

Fig, 11 - Derivati ves fo rmed by reaction of terti ary amino groups with reacti ve dyes

SF OEI CH, - CH-CH2 CI ' 2 ~ (- CH2- CH- O-)n ,, - / CCI. I "0 CH

2

CI Polyeplchlorohydrin

lMe2NH

(- CH2- CH-O-)n

I + _ CH 2NH (Mel,CI

Polyepichlorohydrin-amine

Fig , 12-Formation o f polyep ichlorohyd rin and po lyephi chloro­hydrin-am ine

In a recent work34 , sc ienti sts of German Wool Research Institute reported the modi ficat ion of Iyocell fibres using epichlorohydrin catalyzed with Zn (BF4h fo llowed by ami nation with e thlenedi amine di hydrochloride at a lkaline conditions. The modification was aimed at improving the acid dyeability of Iyocell for one-bath dyeing of blends with wool. Intense colorati on was achieved on modified Iyor;ell using both ac id and reactive dyes ,

114 INDIAN J. FIBRE TEXT. RES., MARCH-JUNE 2001

10 Treatment with DCPEA T Lewis and Lei35

, in an attempt to improve the substantivity of cotton in the no-salt dyeing, studied another novel compound 2,4-dichloro-6-(2-pyridino ethylamino)-s-triazine(DCPEAT), as in Fig. 13.When cellulose is treated with DCPEA T under weakly alkaline conditions, one of the chlorine atoms of DC PEAT reacts with cellulose. The modified cotton becomes much more reactive than the original one towards aminoalkyl dyes. It has been found that the reaction of DC PEAT with co tton takes place effic iently through cold pad batch application at pH 8.5 followed by thorough cold washing.

Recently, Seong and K036 prepared different cationizing agents by reacting trialkyl amines of variable alkyl groups with epichlorohydrin and these compounds were treated with cotton. The modified cotton was found to be dyeable with acid dyes, but the amount of dye absorbed decreased as the length of the hydrocarbon chain increased. They also reported that the cationic cotton showed excellent antimicrobial activity in spite of the small amount of cationizing agent introduced.

11 Miscellaneous Approaches Chavan et al. 37

.38 reported a new method of

cat ionizing cellulosic fibres by a reaction of alkali­pretreated cotton or jute with 1,2-dichloroethane followed by amination with methylamine. They found excellent improvement in the exhaustion of cold brand and HE reactive dyes on cotton and jute when dyed from slightly acidic bath without an electrolyte. The dye fixation was from usual alkaline bath . Low reactivity hot brand dyes can also be applied, in absence of salt, for producing light shade on cationized cotton or jute. The fixation of all these classes of dyes was found to be improved considerably due to the cationization treatment.

Cotton yarn was treated with a non-reactive polymeric quarternary ammonium compound by the

d· b '1 39 exhaust method in an aqueous me IUm at 01 .

During dyeing, a large number of cationic sites were thus made available by the polymer on the cotton surface. After dyeing, vigorous soaping completely removed the polymeric film from the fabric. Such treatment could improve the reactive dye bath exhaustion greatly and opened up the possibility of producing various woven designs by using cationized and uncationized yarns. The removal of cationic polymeric film helps in retaining the brightness and the light fast lless of the shade.

CI

- NJ- N

C +CI -l:: II r; _ N- CH 2 - CH 2 - NH ~N~ CI

2,4-dichloro-6-(2-pyridino ethylamino)-S-triazine (DCPEAT)

Fig. 13-DC PEAT, DC PEAT-colton and dyed substrate obtained in dyeing with amino alkyl dyes

Majority of the chemicals used for imparting cationic sites in cellulosic fibres to reduce the amount of salt used in dyeing for controlling the effluent problems are themselves not safe environmentally. Most of the amines are highly toxic in nature and they cause irritation to eyes, skin and respiratory organs which may result in headache, dizziness, shortness of breathing, nausea and vomiting. Chlorine containing agents, on the other hand, arise AOX problem. The various routes for cationization of cotton discussed here are therefore to be modified to make them free from eco-hazards. Chitosan, a polymer derived from chitin, may be a possible substitute for various hazardous chemicals used for the cat ionization of cotton. The main difference between the chitosan and the cellulose molecule is that in chitosan, the hydroxyl group at C-2 has been replaced by an amino group. The amino group in chitosan molecule can accept a proton from a slightly acidic dye bath and thus creates a route to dye cellulose material , pretreated with chitosan, by anionic dyes in the absence of an electrolyte. Bandyopandyay et al.40 reported one such attempt. The treatment of cotton fabric with a solution of chitosan in 2% aqueous acetic acid by pad-dry technique could cut down the amount of salt required by about 50% in the dyeing with vinylsulphone and cold brand reactive dyes. An increase of 15-50% in dye fixation on chitosan-treated fabric was found in case of cold brand reactive dyes, as compared with untreated fab ric.

CHATTOPADHYAY: CATIONIZATION OF COTTON FOR LOW-SALT OR SALT-FREE DYEING liS

Cationization treatment of cotton for improved dyeabi lity thus provides an enormous scope for further investigation to suit the today 's need of greener technology .

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