Indian Journal of Textile ResearchVol. 4, June 1979, pp. 49-52

Studies in Dyeing of Polyamides: Part III-Improvement in Light Fastness ofDyed Polyamide Fibres by Grafting at Low Add-on

W B ACHWAL & M R NAGARDepartment of Chemical Technology, University of Bombay, Bombay 400019

Received 8 January 1979; accepted 4 April 1979

The effectof grafting on the light fastness of cationic dyeings on nylon and basic as well as reactive dyeings on wool has beeninvestigated. Cationic dyes were applied to nylon after chemical modification to increase the number of acidic sites. Graftingwas done by v-ray irradiation in the presence of acrylonitrile and acrylamide to get low add-on (< 3%)to maintain the physicaland mechanical properties of the dyed fibres. With acrylonitrile, the light fastness of dyeings was improved appreciably, whileacrylamide gave only a marginal improvement.

In spite of the introduction of brilliant cationicdyestuffs which have very good light fastnessproperties on acrylics, it is well known that the lightfastness of dyeings of nylon with these dyestuffs isgenerally not adequate. In the present investigation,the condensation product of cyanuric chloride andsulphanilic acid has been used to enhance the affinity ofnylon for cationic dyestuffs. The details of theprocedures used for modifying nylon and itssubsequent dyeing have been given in earlierpublications 1.2.

Normally grafting is carried out to get sufficient add-on with a view to changing the physical or dyeingproperties of textile materials. However, in thisinvestigation, grafting of predyed substrate wascontrolled to get a low add-on (2-3%), so that otherproperties of the fibres were not affected. Acrylonitrileand acrylamide have been grafted on nylon filamentsdyed with Sandocryl B dyestuffs using y-rays from acobalt-60 source. Grafting of wool yam samples dyedwith normal basic and Remazol dyestuffs was alsocarried out for comparison.

Materials and MethodsSubstrate-The following polyamide samples were

used:

Substrate type Denier Remarks(1) Century Enka

multifilament nylon 44/10' Sparkling(2) Australian Merino

wool 2500 4 ply, worsted

Purification of samples-Nylon and wool sampleswere scoured using a detergent (Lissapol N), washed,dried and conditioned.

Initiator system usedfor grafting-All samples weregrafted using y-rays from a cobalt-60 source. Thegamma irradiation unit holding up to several thousandcuries of cobalt-60 has been developed at the BhabhaAtomic Research Centre for radiation research indifferent fields. The sample chamber of this unit is10 cm in diameter and 14.3 em in height.'. The dose ratewas a little less than 0.5 M rad/hr.

Method of grafting-Conditioned samples (afterapplying suitable corrections for moisture content)were used in the form of skeins. The required amountsof the monomer, water, etc. were thoroughly mixed intest tubes of fixed dimensions and the skeins wereintroduced. The test tubes were then taken in a beakerwhich was kept at the centre of the y-irradiation unit.The height of each test tube was such that it occupiedmore than three-fourths the height of the samplechamber. The swollen samples were irradiated for68 min to give a known dose (0.5 M rad). Afterirradiation, the samples were suitably washed toremove most of homopolymer, dried and conditioned.

Moisture content of grafted samples-A knownweight of the conditioned sample was heated in aweighing bottle at 110DC till a constant weight wasobtained. Moisture content (M.C.) of the sample wascalculated as follows:

M C 0/ __ WI - W2•. , /0 X

WI100

where WI is the weight of the conditioned sample, g;and W2, the weight of the dried sample, g.

Add-on- The percentage add-on was calculated asfollows:

W2-WIAdd-on, %= x 100WI

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INDIAN J. TEXT. RES., VOL. 4, JUNE 1979

where W 1 is the weight of the dried sample beforegrafting; and W2, the weight of the dried sample aftergrafting.

ResultsOptimizatiOll of Coaditioas for GraftiDg of MeriDo Wool

Grafting of acrylonitrile-Preliminary trials for thedetermination of optimum conditions for grafting werecarried out on undyed wool samples by varying theconcentration of the monomer at a fixed dose of "1-

radiation. Samples were grafted from a systemcontaining acrylonitrile, water and dimethylforma-mide (DMF). The irradiated samples were first washedwith water followed by repeated extraction with DMFto remove as much of the homopolymer as possible,again thoroughly washed with water, dried andconditioned.

The same procedure was adopted for grafting ofacrylonitrile on predyed wool skeins dyed with twobasic dyestuffs, viz. Rhodamine B and Methylene BlueB, and two Remazol dyestuffs, viz. Remazol Brill.Violet SR and Remazol Brill Orange 3R. Basic dyeswere extracted to a great extent by DMF used both forgrafting and removal of the homopolymer. MethyleneBlue B was found to be almost completely destroyedafter grafting and was, therefore, not used insubsequent experiments. Remazol dyestuffs were alsofound to be stripped to some extent. However, this maybe due to the extraction of the hydrolyzed dye byDMF. From these experiments it was concluded thatsome other method has to be used for grafting becauseof the fact that DMF extracts basic dyestuffs, resultingin loss of colour value.

When grafting was carried out in the absence ofDMF, homopolymerization was of a very high order.Copper salts have been suggested to be effective inreducing homopolymerization". When 10-2 moles ofcopper sulphate per mole of acrylonitrile wereincorporated into an aqueous solution of acrylonitrile,the extent of homopolymerization was found to be less.However, the samples were stained by copper sulphate.

It has been reported in literature that irradiationgrafting of polyamide fibres can be carried out from abath containing acrylonitrile, methanol and water". Inthe preliminary experiments, wool samples weregrafted using a mixture of acrylonitrile, methanol andwater. After exposure, the samples were washed withhot water (~ 70°C), till no turbidity appeared, toremove the homopolymer, dried and conditioned. Thepercentage add-on was found to increase with increasein the concentration of acrylonitrile. The percentagemoisture content, on the other hand, was found todecrease slightly from 11.1% for unmodified wool to10.5% for the sample grafted using 10% (vol.zvol.)acrylonitrile.

so

On the basis of the results of these experiments, thefollowing optimum conditions were standardized forgetting 3% grafting add-on on dyed wool samples.Aqueous solution of acrylonitrile 3.75% (vol.zvol.)+ methanol 30% at a material-liquor (M: L) ratio 1:20,preswelling for 30 min, followed by irradiation for68 min at a dose rate of 0.5 M rad/hr.

During subsequent washing with hot water or D MFonly a small fraction of acrylonitrile was removed. Thisindicates that most of polyacrylonitrile is grafted to theirradiated fibres. The samples were, therefore, notextracted with DMF to remove the homopolymer. Thesoft hand of the samples indicated that very littlesurface homopolymer was present.

Grafting of aerylamide-In the preliminaryexperiments, wool skeins were grafted with acrylamidefrom an aqueous bath. After irradiation, the sampleswere repeatedly washed with hot water to remove thehomopolymer, dried and conditioned. The percentageadd-on was found to increase with the concentration ofacrylamide. When a solution containing l()01o (wt/vol.)acrylamide was used, it was extremely difficult toremove the homopolymer completely even afterprolonged washing with boiling water. On the basis ofthe results of these experiments, the following optimumconditions were selected for grafting of dyed woolsamples with acrylamide to get an add-on of about 3%:Acrylamide 5% (wt/vol.) in water at M:L::l:10;samples preswollen for 30 min and irradiated for68 min.

The feel and tensile strength ofthe samples remainedunaltered at this level of grafting. The moisture contentof acrylonitrile and acrylamide grafted samples was of.the order of 10.6% and 11.4% respectively.

To find out whether there is an appreciable loss incolour value of the samples during grafting or furtherextraction with hot water, a known weight of thesample was dissolved in a fixed volume of cadoxen andzincoxen. The difference in optical density values ofungrafted and grafted samples in these two solventswas insignificant, indicating that the dyes were notaffected by irradiation.

In the case of wool samples dyed with basic dyestuffs,a lot of bleeding of the dye was observed duringgrafting and subsequent washing with hot water.However, optical densuy measurements could not becarried out on these samples, as dyes on grafted samplewere found to be destroyed during extraction withalcohol. Further, cadoxen and zincoxen solvents couldnot be used for the estimation of basic dyestuffs, asduring the period of dissolution (8 and 72 hrrespectively), the dyes were found to get destroyed.Similar observations were made by Achwal andMohite earlier".

ACHWAL & NAGAR: STUDIES IN DYEING OF POLYAMIDES: PART III

Optimization of Cooditioas for GnftiD& of Nyloo Filameots

Grafting of acrylonitrile-The following optimumconditions were standardized for grafting of dyednylon filaments with acrylonitrile to get an add-on ofabout 3%: Aqueous solution of acrylonitrile 2.0%+methanol 30% (vol.jvol.) used at M: L :: 1: 10; after30 min preswelling, irradiation was done for 68 min.

Grafting of acrylamide- The following optimumconditions were standardized for grafting of dyednylon filaments with acrylamide to get an add-on ofabout 3%:Solution of acrylamide 2.5%(wt/vol.) used atM:L:: 1:10; the preswelling and irradiation periodssame as for wool. The feel and tensile strength of nylonfilaments remained unaltered at this level of grafting.

Dyed nylon filament samples were then grafted withacrylonitrile and acrylamide respectively under theabove optimum conditions, at graft add-or. of the olderof 3%. The moisture content of acrylonitrile andacrylamide grafted samples was 3.5% and 3.7%respectively in comparison to 3.6% for ungraftednylon. To assess the extent of loss of colour valueduring grafting as well as extraction with hot water, aknown weight of sample was dissolved in a fixedvolume of 85% formic acid. Decrease in optical densityvalues (about 15%) was due to bleeding of cationicdyestuffs during grafting and subsequent treatment ofthe samples with hot water to remove thehomopolymer.

Determination of lightfastness of dyed samples-Thelight fastness of grafted and ungrafted samples of dyedwool and nylon, as prepared above, was assessed byexposing them in Atlas Model Fade-o-meter. The lightfastness grades of the dyed samples were assigned bycomparing the first change in shade or tone of thesamples with those of simultaneously exposed lightfastness standards. The light fastness grades of dyedand grafted wool samples are summarized in Table 1.The results indicate that there is an improvement inlight fastness of wool samples grafted withacrylonitrile. Acrylamide grafting, on the other hand,confers a comparatively lesser improvement in the lightfastness.

The light fastness grades of grafted and ungraftednylon filaments are summarized in Table 2. As the lightfastness of a dyed material depends upon the amount ofdyestuff present, unmodified nylon filaments which willtake up comparatively less amount of dyestuff ascompared to the amounts taken by half blocked andfull blocked nylon samples, will have a poor lightfastness compared to that of modified nylon samples.For this reason, the light fastness grades of unblockednylon samples are not given in Table 2. It is apparentthat there is an improvement in the light fastness aftergrafting, irrespective of the nature of the dye selected.

Table I-Light Fastness of Dyed Wool Samples

Dye Ungrafted Grafted with

Rhodamine BMethyl VioletMalachite GreenMagenta PNSRemazol Brill. Violet 5 RRemazol Brill. Orange 3 RRemazol Blue RRemazol Rubine R

Acrylonitrile Acrylamide3 4 3-43 4 3~4 5-6 4-5

3~ 4 3~6-7 7 , 76-7 7 6-76-7 7 6-76-7 7 6-7

Table 2-Light Fastness of Dyed Nylon Filament Samples

Dye Amino Ungrafted Grafted withgroup

blocked Acrylonitrile Acrylamide%

Sandocryl [ 50 2-3 3 2-3Violet B-2RLE 100 2-3 2-3 2-3Sandocryl Brill. [ 50 1-2 4 3-4Red BF (200"1.) 100 1-2 4 3~Sandocryl Blue [ 50 6-7 7 6-7B-FE 100 6-7 7 6Sandocryl Orange [ 50 6-7 7 6-7B-3RLE 100 6-7 6-7 6

DiSClmiODIn the present investigation, predyed samples were

used for grafting. Batty and Guthrie 7 have reportedthat the light fastness of wool dyed with Remazoldyestuffs can be improved by grafting withacrylonitrile at 2-3% add-on. As generally cationicdyestuffs have a poor light fastness on nylon ascompared to that on acrylics, the effect of grafting aswell as blocking of amino groups on the light fastnessof such dyeings was studied. The effect of grafting ofwool dyed with basic and Remazol dyestuffs on thelight fastness of the dyeings was also studied. The effectof the nature of the monomer and the nature of thedyestuff was investigated. Two monomers, viz. acry-lonitrile and acrylamide, were selected for grafting ofdyed nylon and wool samples. For wool, four basicdyestuffs (having poor light fastness) and four Rema-zol dyestuffs (having very good light fastness) wereselected. It is clear from the results that, as a generalrule, the light fastness increases in all cases. Whenacrylonitrile was used as the monomer, there was asubstantial improvement in the light fastness of basicdyestuffs on wool. On the other hand, as Remazoldyestuffs have very good light fastness, theimprovement in the same was marginal. When.acrylamide was used as the monomer, it caused onlymarginal improvements in the light fastness of the

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dyeings irrespective of the nature of the dyestuffpresent on wool.

Two cationic dyestuffs having low light fastness onacrylics, viz. Sandocryl Brill. Red. BF and SandocrylViolet B-2 RLE, and two having good light fastness,viz. Sandocryl Blue B-FE and Sandocryl Orange B-3RLE, were selected. The light fastness of the dyeingswas marginally improved when half blocked or fullblocked nylon samples were used for grafting.Acrylonitrile on grafting improved the light fastness ofthe dyeings. However, acrylamide on grafting gaveonly a marginal improvement in the light fastness ofthe dyeings. Moreover, the improvement in the lightfastness was more marked, when a dye ofcomparatively lower light fastness was used.

The moisture content of acrylonitrile graftedsamples was slightly less due to the fact thatpolyacrylonitrile is hydrophobic in nature. On theother hand, the moisture content of acrylamide grafted

52

samples increases slightly due to hydrophilic nature ofpolyacrylamide.

However, changes in the moisture content are notsignificant at. the level of grafting, i.e. 2-3%, and,therefore, the improvement in light fastness ofacrylonitrile grafted samples cannot be attributed todecrease in moisture content. Enhancement of lightfastness, therefore, takes place as a result of grafting atlow add-on, which possibly alters the nature of energyabsorption by the fibre surface.References1 Achwal W B & Nagar M R, Indian J Text Res, :z (1977) 82.2 Achwal W B & Nagar M R, Indian J Text Res, 3 (1978) 50.3 Nagar M R, M.Sc. (Tech.) thesis, University of Bombay, 1976.4 U.S. Pat 3,488,268 (1970); Chern Abstr, 72 (1970) 68149x.5 Proceedings, 18th Hungarian Textile Conference, Sept. 15-18,

Budapest, Vo!.I, edited by E. Jakab, 1970,211.6 Achwal W B & Mohite V P, J Soc Dyers Colour, 88 (1972) 437.7 Batty N S & Guthrie J T, Internationale Wolletextif

Forschungskonferenz, Kurzfassungen der Originalbeitrage,Aachan, 2-11 Sept., 1975,341.