IndianJournalofFibre& TextileResearchVol.22, March1997, pp. 53-60

Reactive dyeing behaviour of ramie fabrics pretreated with differentswellingagents and their rub fastness property

n Oas,A K Samanta' & P C DasguptaTextileChemistrySection,InstituteofJuteTechnology,35 BallygungeCircularRoad,Calcutta700 019, India

Received14 June 1995; first revisedreceived12 April 1996; secondrevisedreceivedandaccepted31 October1996

Scoured and bleached ramie fabrics were pretreated separately with four swe1lidg agents, viz.NaOH, EDTA, urea and phosphoric acid, and the consequent changes in tensile properties, extentof decrystallization, absorbency, dye uptake and fastness to washing light and rubbing for a monoch-lorotriazine reactive dye (Cl. Reactive Orange 13) were evaluated. Pretreatment with 20% urea or20% NaOH under slack condition resulted in a more desirable balance in the above-mentioned pro-perties including the improved dye uptake. Fastness to rubbing was poor and it was more pro-nounced at higher number of rub cycles. Both ring dyeing and higher coefficient of friction of ramiehave been found to be responsible for this. To improve the rub fastness of reactive-dyed ramie fa-bric, post-treatment was carried out separately with catasoftener, silicone and polyethylene emulsion.Post-treatment with the last two finishing agents improved the rub fastness significantly on \bothNaOH (slack) and urea (slack) pretreated and reactive-dyed ramie fabrics.

Keywords: Dyeing, Polymeric finish, Ramie, Ring-dyeing, Rub fastness, Swellingpretreatment

1 IntroductionRecently, ramie has regained importance be-

cause of its increased share in the apparel and up-holstery textiles 1 in Asia and its sub-continents.Degummed ramie, in comparison with the rele-vant properties of cotton, is coarser, more heat-resistant, rapidly dryable, more durable, more lus-trous, more rigid, less extensible with highly crys-talline and highly oriented fine structure and hashigher coefficient of friction, less moisture regain,higher tensile strength and improved wetstrength!", Highly crystalline and highly orientedfine structure of ramie makes the required dyediffusion difficult in comparison to that for cot-ton. In most of the cases, ring dyeing of ramiegives lower rub fastness. A few reports are avail-able on the rub fastness study for pure cellulosics"but little information is available on such studyfor ramie and that for reactive-dyed ramie pre-treated with different swelling agents. Merceriza-tion of ramie as pretreatment before dyeing hasbeen investigated earlier by many workers-". Re-cently, Cheek and Rousellf-? have also made com-parative studies on the dyeing of mercerized ra-mie, cotton and flax with low and high molecularweight direct dyes. But most of the azo direct

"Towhom allcorrespondenceshouldbe addressed.

dyes are now banned in European countries fortheir carcinogenic nature or possible harmfulnessto human body. Therefore, reactive dyeing of ra-mie becomes much important in today's context.The present work was, therefore, undertaken toinvestigate the dyeing behaviour of ramie fabricsand their fastness properties when dyed withreactive dye with or without suitable pretreat-ments using different swelling agents and selectivepost-treatments subsequent to dyeing of pretreat-ed ramie fabric.

2 Materials and Methods

2.1 Materials

2.1.1 FabricsScoured and bleached plain-woven ramie fabric

having the following specifications was used:weight, 130 g/m-; warp, 52.9 tex; weft, 25.6 tex;ends/dm,190; and picks/dm, 230. For compara-tive purposes, plain weave cotton fabric havingthe following specifications was also used: weight,109 g/m''; ends/dm, 315; picks/dm, 315; warp, 47tex; and weft, 47 tex.

2.1.2 Dyes andChemicalsA monochlorotriazine reactive dye (0 Reactive

Orange-13) obtained from a local dye supplier

54 INDIAN J. FIBRE TEXT. RES., MARCH 1997

was used after necessary purification. Sodiumchloride, sodium hydroxide, sodium carbonate,urea, phosphoric acid, EDTA (disodium salt ofethylenediamine tetraacetic acid), ammonium hy-droxide, pyridine and acetic acid, all of AR grade,were used.

2.2 Methods2.2.1 Pretreatment with Different Swelling Agents

The ramie fabric was pretreated by dipping in20% (w/w) aqueous solution of urea or in 15%(w/w) aqueous solution of EDTA, keeping thematerial-to-liquor ratio (MLR) at 1:10, at roomtemperature (30 ± 2°C) for 30 min after which itwas thoroughly washed with cold water and driedin air.

The phosphoric acid pretreatment of the ramiefabric was similarly done with 81% (wIw) aque-ous phosphoric acid using same MLR and tem-perature for 30 min. The fabric was then washedthoroughly with water, neutralized with dilute am-monium hydroxide solution, rinsed, washed anddried in air.

Caustic pretreatment of the experimental cottonand ramie fabrics was carried out by dipping thefabric piece in 20% (w/w) aqueous NaOH for 30min at room temperature (30 ± 2°C). The material-to-liquor ratio was kept at 1:10. The fabric was thenwashed with water, neutralized with 1.5% aceticacid solution, rinsed, washed and air dried. Mer-cerization of ramie fabric for extended time peri-od (30 min) was also done using the same causticliquor and same treatment condition but undertension by dipping the pretensioned ramie fabricheld on the pin of a celluloid frame throughoutthe treatment period and .the fabric was unloadedbefore air drying.

2.2.2 Dyeing with Reactive DyeDyeing of ramie and cotton fabrics with a reac-

tive dye (CI Reactive Orange-13) was carried outusing a material-to-liquor ratio of 1:50 and sodi-um chloride (70 gIl) and sodium carbonate (20gIl) as additives to be added subsequently in thedyebath. The dyebath was initially set at 50°Cwith dye and the material was put in the dyebath.The temperature was gradually raised to 80°Cand then sodium chloride was added in three in-stalments within 30 min, keeping the dyebathtemperature at 80 ± S°e. Finally, sodium carbon-ate was added in two instalments and dyeing wascontinued for further 45 min. After the dyeingwas over, the material was rinsed cold, soapedwith 5 gIl commercial grade detergent at 50°C for15 min, washed in cold water and dried in air.

2.2.3 Post-treatment with SoftenerlPolymeric EmulsionsThe dyed fabrics were padded in a two-bowl

laboratory padder containing 5% (solid basis) po-lyethylene emulsion, adjusting the wet pick up at80%. The fabrics were then touch dried at 80°Cfor 10 min and further subjected to a higher tem-perature (110°C) treatment for another 5 min in alaboratory hot air-drying and curing chamber.

For silicone emulsion treatment, the fabricswere similarly padded with 40 gIl silicone emul-sion containing 4 gIl zinc acetate, adjusting thewet pick up at 80%. The fabrics were then touchdried at 80°C for 10 min and cured in a laborato-ry drying and curing chamber at 150°C for 4 min.

Catasoftener was applied by exhaustion processon the fabrics by dipping the fabric pieces in a so-lution containing 2.5% (solid basis) catasoftener atpH 4 (adjusted by acetic acid), keeping the mate-rial-to-liquor ratio at 1:20.

2.2.4 Physical and Chemical TestingsAbsorbency of treated and untreated ramie fa-

brics was determined by measuring the iodinesorption value (ISV) following the procedure de-scribed by Marie'". X-ray crystallinity (%) of treat-ed and untreated (controJ) ramie as well as cottonfibres was determined after separating the fibresfrom the respective fabrics to obtain the wideangle diffraction pattern with rotation powdermethod by nickel filtered CuKa radiation for 28values between 10° and 30°, and the crystallinecontents were evaluated using Segal's crystallinityindex". Weight losses were determined by usualoven dry'weight basis.

Area shrinkage of the fabrics was determinedfollowing the usual method described elsewhere".

The linear density (tex) of warp and weftyams of the untreated (control) and treated ramiefabrics was determined after separating the warpand weft yam from the corresponding fabric fol-lowing the conventional procedure'? as given byASTM D1059-87.

The coefficient of friction of treated and un-treated (control) ramie fibres was measured fol-lowing the conventional procedure':' using an in-clined plane fibre friction testing instrument.

Breaking load und breaking elongation of un-treated (control) and treated ramie fabrics were de-termined'! as per IS: 1969-1968 using Zwick-1445 CRT universal tensile testing machine.

The dye uptake of treated and untreated cottonand ramie fabrics, expressed as mglg (dye in mili-gram per gram of fibre) was determined from thedifference of initial dye concentration taken in thedyebath and the final dye concentration remained

DASet al.: REACTIVEDYEINGBEHAVIOUROF RAMIEFABRICS 55

in the dyebath (including wash liquor) after ex-haustion. The dye concentrations were estimatedin the usual way" by the absorbence spectropho-tometry analysis using U-2000-Hitachi-UV-Visabsorbence spectrophotometer at the maximumabsorbence wavelength of the respective dye solu-tion using a calibration curve prepared for thispurpose.

Fastness to washing of the reactive-dyed ramiefabrics was determined using ~ Launder-o-meteras per ISO- 2 wash method 16 and was assessed bygrey scale as per ISO-105-AD2 (loss of depth) andISO-105-AD3 (staining).

Colour fastness to rubbing was determined 15

using SDL-electronic crockmeter as per IS: 766-1956 and the grey scale as per ISO-105-AD2and AD3. Colour fastness to light was determinedas per BS-1-6 : BOI-1978, using SDL-MBTFLamp-microscallight fastness tester".

KlS values computed by Kubelka-Munk equa-tion 16 were obtained by measuring the reflectanceof the dyed and subsequently rubbed fabrics onMacbeth 2020 plus computer-aided reflectancespectrophotometer using the necessary softwares.

3 Results and Discussion3.1 EffectofPretreatment withDifferentSwellingAgents

on Mechanical Properties and Fine Structure

3.1.1 BreakingLoad and ExtensionFrom Table 1, it is observed that phosphoric

acid (PA) pretreatment lowers the breaking loadto the highest extent (29.7%). The best effect isobtained in the case of NaOH (tension) pretreat-ment, where a measurable increase in breakingload is evident. In the case of EDTA and ureapretreatments, the loss of breaking load is onlymarginal. In all the pretreatments, breaking exten-sion increases, except for NaOH (tension) pre-

treatment where the change is insignificant. Boththe loss in breaking load and increase in breakingextension must be viewed as a consequence of theeffect of decrystallization, partial loss of orienta-tion and possible structural rearrangement .set af-ter swelling.

3.1.2 FrictionalBehaviourTable 1 shows that the frictional behaviour of

the ramie fibre remains almost unchanged irre-spective of the type of swelling pretreatments,keeping the surface behaviour almost same.

3.1.3 Area Shrinkageand YarnLinear DensityThe area shrinkage values of ramie fabrics pre-

treated with different swelling agents are given inTable 1. For each of the pretreatments, the areashrinkage value is higher than that for the controlsample and it is maximum for PA pretreatment,showing maximum relaxation. The changes in thetex values of the warp and weft yams of the pre-treated ramie fabric are much in tune with the ul-timate area shrinkage values obtained as a resultof warp-way and weft-way yam shrinkage in thefabric, except in the case of phosphoric acid pre-treated sample, where the changes in the tex va-lues of the yams in both the directions are notcommensurate with the extent of shrinkage. Thelower extent of tex change, in spite of highest areashrinkage, in case of phosphoric acid treatmentmay be explained by some loss in mass from ra-mie' in PA treatment due to hydrolysis, supersed-ing the effect of reduction in the length of theyam by shrinkage.

3.1.4 DecrystaUizationIn all the pretreatments to ramie fabric, phos-

phoric acid pretreatment results in maximum de-crystallization, reducing the X-ray crystallinityfrom 63.3 to 39.2%. The extent of decrystalliza-

Table I-Effect of pretreatmentswith different swellingagents on mechanicalproperties and fine structure of ramieTreatment Breaking Breaking Coefficient Area Lineardensityofyarn,tex Crystallinityi'

load extension of friction' shrinkage %N % % Warp Weft

Untreated (Control) 568.00 9.15 0.63 1.2 53.0 26.0 63.320%NaOH (tension) 583.21 8.93 0.64 6.0 54.3 26.6 53.220%NaOH (slack) 570.34 11.27 0.64 8.0 54.6 27.0 52.315%EDTA(slack) 558.24 12.23 0.63 11.0 55.0 27.8 51.320%Urea (slack) 519.68 15.52 0.61 18.0 55.4 28.5 46.181%Phosphoricacid(slack) 399.04 19.43 0.62 24.0 56.0 29.0 39.2"Coefficientoffrictionfor controlcotton,0.24.bCrystallinityfor controlcotton,63.0%.

56 INDIAN J. FmRE TEXT. RES., MARCH 1997

tion for different swelling pretreatments is in theorder: NaOH (tension)<NaOH (slack) <ED-TA < urea < phosphoric acid (Table 1). Preferably,the small crystallites in the non-crystalline regionare dissolved by the action of different swellingagents on ramie and thus non-crystalline regioncan be more accessible to external reagents ordyes for possible increase in intercrystalline freespace in this region. In case of phosphoric acidpretreatment, the chances of some decrystalliza-tion even in crystalline region and some chain de-gradation can not be ruled out.

3.2 Effect of Pretreatment with Different Swelling Agentson Absorbency, DyeabiJity and Dye Fastness Properties

3.2.1 AbsorbencyAbsorbency .data in terms of iodine sorption

value (ISV) of differently pretreated ramie fabric(Table 2) follow the same trend as the extent ofdecrystallization after the same pretreatments,showing the highest iodine absorbency (more thanfour times of thai for the control sample) for PApretreated sample. Urea pretreatment shows con-siderable increase (more than three times of thatfor the control sample) in absorbency with only8.6% loss in breaking load, about 70% increase inbreaking extension and 27% decrystallization(Tables 1 and 2).

3.2.2 DyeabiHtyThe reactive dye uptake (mg/g of fibre) for

the control ramie fabric is much lower than thatfor the control cotton fabric. The ramie fabricspretreated with different swelling agents show a

noticeable increase in dye uptake when comparedwith that for the control ramie fabric. This maybe due to creation of more accessibility of reac-tive dye sites by decrystallization and opening upof 'the compact structure of ramie by swellingagents.

NaOH pretreatments (both slack and tension)of ramie though show notable increase in reactivedye uptake, but the dye uptake level is lower thanthat for the control cotton fabric. 20% EDTA so-lution pretreatment shows reactive dye uptakemore or less at the same level as for the controlcotton.

20% urea solution pretreatment, without caus-ing much sacrifice of mechanical properties,shows a reactive dye uptake level higher than thatfor the control cotton fabric, while 81% phos-phoric acid pretreatment gives highest reactivedye uptake but with appreciable strength loss.

For the different swelling pretreatments studied,the observed trend of increase in reactive dye up-take (Table 2) is much in tune with the increase iniodine absorbency (Table 1) for the same pretreat-ments.

3.2.3 Dye Fastness Properties

3.2.3.1 Wash FastnessData presented in Table 2' show that the differ-

ent pretreatment'S on ramie fabric have little ormarginal effect on the fastness of reactive dyes towashing. Wash fastness for reactive dyes on ramieis fairly good like that on cotton, as expected dueto the formation of covalent bond between reac-tive dye and ramie-cellulose.

Table 2-Effect of pretreatment with different swelling agents on absorbency, dyeability (reactive dyes) and dye fastnessproperties of ramie fabric ' ,

Absorbency Dye uptake Wash fastness R¥b fastness(Iodine sorp- mglgtion value)

mglg

Treatment Lightfastness

10 Cycles 100 Cycles

Staining" Staining"Ramie Fabric

Untreated (Control) 28 7.2 S 5 3 4-5 2 4-5 3-420% NaOH (tension) 89 11.1 5 5 3-4 4-5 2-3 4-5 3-420% NaOH (slack) 99 13.6 5 4-5 4 5 3 4-5 3-415% EDTA (slack) 101 lS.2 5 5 3-4 5 2-3 4.5 3-420% Urea {slack) 121 19.2 5 5 4-5 5 3-4 4-5 381 % phosphoric acid (slack) 132 21.3 5 5 4-5 5 3-4 4-5 2Cotton Fabric

Untreated (control) 34 15.2 5 5 5 5 4-S 4-5 3-4"Loss of depth or change in colour was assessed as per ISO 105 AD2 grey scale."Staining was assessed as per ISO 105 AD3 grey scale.

DAS et al: REACTIVE DYEING BEHAVIOUR OF RAMIE FABRICS

3.2.3.2 Light FastnessThe light fastness of reactive dyes on both con-

trol ramie fabric and control cotton fabric is al-most same, showing that there is little effect of thetype of fibre. In the case of urea and phosphoricacid pretreated and subsequently reactive-dyedramie samples, the light fastness ratings are 3 and2 respectively (Table 2). This may be attributed tothe increased absorbency or accessibility in thenon-crystalline region after decrystallization byswelling agents, possibly facilitating the ease ofdiffusion of more moisture and oxygen for initiat-ing the light fading mechanism'".

3.2.3.3 Rub FastnessRub fastness ratings as assessed from the loss

of depth of shade and from the extent of stainingto the abrader cloth from ramie fabric are differ-ent, the former (loss of depth) being poorer ineach case (Table 2), while the corresponding datain case of dyed control cotton fabric show thesame rub fastness rating on assessment by boththe methods. However, on pretreatments with dif-ferent swelling agents, the poor rub fastness (as-sessed by loss of depth of shade) of ramie im-proves bymore than one unit for phosphoric acid-andurea-pretreated and dyed ramie fabrics.This may beattributed to mare diffusionand fixationofdyes to thecore rather than surface after swellingpretreatmentscreate easy dye diffusion facility and increaseddye-accessible sites on decrystallization by thehigh swelling action of these two reagents. Theother two swelling reagents, NaOH and EDTA,show little or marginal improvement in rub fast-ness (loss of depth) of ramie. However, when theNaOH pretreatment is carried out under slackcondition, a small but measurable improvement inrub fastness (loss of depth) for reactive-dyed ra-mie is noticed (Table 2). Rub fastness ratings as-sessed from the extent of staining to the abradercloth show almost no bearing on the type of pre-treatments done.

On the extensive rubbing, i.e. for rubbing up to100 cycles instead of 10 cycles, the rub fastnessrating for reactive-dyed control ramie came downto 2 from 3 when assessed from the losss ofdepth of shade. But interestingly the rub fastnessratings assessed from the extent of staining toabrader cloth for 10 rub cycles-and for 100 rubcycles do not show any significantdifference.

Fig. 1 shows the KlS values of the reactive-dy-ed ramie and cotton fabrics as well as of thecorresponding stained abrader clothes for differ-ent number of rub cycles. It is observed that the

57

change in the K/S value of reactive-dyed cottonfabric almost ceases (curve 5) at about 20 rub cy-cles, with no significant increase in the KlS valueof the corresponding stained abrader cloth (curve8), indicating neither further dye transfer tostained abrader cloth on rubbing after 20 rub cy-cles, nor loss of depth of shade (i.e. no alterationof KlS values is observed for both the originaldyed cotton and stained abrader cloth from 20 to100 rub cycles). But in case of reactive-dyed ra-mie, rubbing on the crockmeter up to 100 rub cy-cles showed that though the transfer of dye ontostained abrader (ramie) cloth almost ceases(curve 4) after 20 rub cycles, but the loss ofcolour from original dyed ramie fabric continued(curve 1) up to 100 rub cycles without further in-crease in stain on the abrader (ramie) cloth. Thisloss of depth of shade of reactive-dyed ramie fa-bric on rubbing was found to continue even with-out any measurable loss of dyed fibre mass, as ex-perimented separately (Data not shown here).

These interesting observations about the rubfastness of reactive-dyed ramie fabric led us to

Romill Fobr ie

21

--------"'-I'I---¥.' 4

Cotton Fobr ie

20 40 so .0030Number of rub eye'"

Fig. l-K/S values of reactive-dyed ramie and cotton fabricssuQjected to different number of rubbing cycles vis-a-viscorresponding abrader cloth. (1 & S-without pyridine ex- .traction; 2 & 6-with pyridine extraction; 3 & 7-.bradercloth for pyridine-extracted samples; and 4 & 8- abrader

cloth for without pyridine-extracted samples]

58 INDIAN J. FIBRE TEXT. RES., MARCH 1997

extend this study for Iinvestigating the causes andremedies for this continual loss of depth of shadewithout staining to the abrader cloth,particularlyon extensive rubbing.

3.3 Causes of Poor Rub Fastness (Loss of Depth) ofReactive-dyed Ramie on E'lltensive Rubbing

The observed poo~ rub fastness with continualloss of depth of shade without staining the abrad-er cloth on extensive rubbing (20-100 rub cycles)for reactive-dyed ramie fabric may be due to anyone or possible combination of the followings:

(i) Relatively strongly held loose (unreacted)and hydrolyzed reactive dyes deposited on fabricsurface may show poor rub fastness on higher rub

cyc(.~e)sHi·igh ffi . Iff" (063) f .11 er coe cient 0 .ncnon . 0 ranue(Table 1) with more irregular surface structure-?as compared to that of cotton (p.24) may producehigher abrasive force on the fabric surface duringextensive rubbing and may cause breaking and ul-timately loss of some ~yed fibre mass.

(ill) The same as in (ii) may also happen with-out showing any loss of fibre mass, if the long-sta-ple ramie fibres (on the fabric surface) are torn orbroken on extensive rubbing, but still remain an-chored, holding the broken fibres at the other endto the yarn structure in ramie fabric. The socalled free broken ends of the dyed ramie fibreswith ring dyed cross-sections may be exposed tothe dyed fabric surface and thereby may alter thereflectance of the rubbed portion, showing the ap-parent loss of depth without staining to theabrader cloth.

(iv) In consequent to ring dyeing (as observedin microscopic examination) for highly oriented andordered structure of ramie fibre, the surface of thering-dyed ramie fibre is when abraded forhigher number of rub cycles, it may cause ex-posing of inner undyed layer progressively withthe increase in rubbing cycles, which may lead toalteration of KlS valub of the rubbed portion of thedyed ramie fabric accordingly.

To test if reason (i) has any bearing on the poorrub fastness, the pyridine-extracted reactive-dyedramie and cotton fabrics were also subjected toextensive rubbing (from 0 to 100 rub cycles) andthe corresponding changes in KlS values weremeasured after 10, 20, 30, 50 and 100 rub cycles.The results are presented in Fig. 1 (curves 2 & 6).It is observed from Fig. 1 that the loss of depth ofshade, in terms of decrease in KlS value, onrubbing for 0 to 100 rub cycles, is very marginalfor pyridine-extracted reactive-dyed cotton sam-ple (curve 6) while that for corresponding reac-

tive-dyed ramie fabric, continual loss of depth issignificant (curve 2). However, it is also observedthat the ultimate rate of decrease of KlS value, onrubbing for 0 to 100 rub cycles, for pyridine-ex-tracted reactive-dyed ramie fabric .(curve 2) ismuch lower than that found for the sample with-out pyridine extraction (curve v'I ). Also, theabrader cloths for pyridine-extracted samples ofboth ramie and cotton show no significant changes inKlS values on extensive rubbing (curves 3 and 1).These observations establish that the poor rubfastness of reactive-dyed ramie fabric is not go-verned at least by relatively strongly held loose(unreacted) or hydrolyzed reactive dyes depositedon ramie.

It is already mentioned in the last para of3.2.3.3 that the loss of depth of shade of reac-tive-dyed ramie fabric continued without anymeasurable loss of dyed fibre mass and hence amongthe above-said possible reasons, the reason (ii)may be considered to be negligible but there isevery chance that phenomenon explained in thereason' (iii) may playa major role in this case. Onmicroscopical examination, the presence of bro-ken long-staple ramie fibre, anchored to the yarnassembly even after 100 cycles of rubbing, indi-cated that the reason (ill) is atleast partly respon-sible for showing poor rub fastness (loss of depth)of reactive-dyed ramie on extensive rubbing.

Microscopical examination of the cross-sectionsof dyed control ramie showed ring dyeing effect,which may ultimately cause exposition of the innerundyed layer on higher abrasion on extensive rubb-ing and thus continual loss of depth of shade andconsequent change in K/S value may be ob-served. Therefore, ring dyeing [reason (iv)] due tohighly ordered and oriented fine structure of ra-mie is another factor responsible for such poorrub fastness (loss of depth) on extensive rubbingwithout staining to the abrader cloth.

Therefore, it may be concluded that the reasons(ill) and (iv) in mutual combination are responsi-ble for the poor rub fastness of dyed ramie, parti-cularly on extensive rubbing, showing continualloss of depth of shade without increasing stain tothe abrader cloth.

The ring dyeing phenomenon can be reducedby swelling pretreatment allowing more dye diffu-sion, particularly when urea or phosphoric acid isused as swelling agent, as discussed in 1st para ofsection 3.2.3.3. Phosphoric acid pretreatmentgives inferior mechanical properties of ramie and,therefore, 20% urea or 20% NaOHpretreatment(under slack condition) may be considered as aprospective pretreatment for ramie, which is even

DAS et al: REACTIVE DYEING BEHAVIOUR OF RAMIE FABRICS 59

better than NaOH pretreatment (under tension)or mercerization considering the overall balanceof mechanical properties, dyeability and dye fast-ness (particularly rub fastness).

3.4 Effect of Selective Post-treatment with DifferentSofteners/Polymeric emulsions on Rub Fastness ofReactive-dyed Ramie

To mitigate or reduce the poor rub fastness(loss of depth of shade) problem of reactive-dyedramie on extensive rubbing and consequent phe-nomenon explained in reason (ill) of section 3.3 .•attempts were made to suitably modify the sur-face characteristic of 20% NaOH (slack) pretreat-ed and 20% urea pretreated ramie fabrics usingselective softeners/polymeric emulsions such ascatasoftener, silicone emulsion and polyethyleneemulsion. Relevant rub fastness results (after thesepost-treatments ),in terms of change in KlS values,are graphicallypresented in Fig. 2.

Catasoftener (cationic softener) post-treatment(curve 2) on NaOH-pretreated (slack) and dyed ra-mie, though deposited the fatty matters on the sur-face of the fibre to lubricate and soften the fibresurface it showed little improvement in rubfastness over slack-causticised ramie sample and athigher number of rub cycles, the improvement wasvery marginal as indicated by the correspondingcurves 1 and 2. Catasoftener treatment on urea-pretreated ramie rather showed deterioration inrub fastness (corresponding curves 6 and 5), thereason for which is not understood from thisstudy. Silicone finish suitable for producing a sof-ter handle alongwith moderate film forming ca-pacity showed a marked improvement (curves 3and 7) in rub fastness for both NaOH (slack) andurea-pretreated ramie, even on extensive rubbing.From Fig. 2, it may also be observed that polye-thylene emulsion, probably producing a smoothfilm over the fibre surface, showed orily marginalloss of KlS value at the rubbed portion for bothNaOH (slack) and urea-pretreated dyed ramie, re-taining the physical appearance of the cloth al-most intact even after 100 rub cycles (curves 4and 8). This further supports the view [reason (ill)in section 3.31 that the surface frictional behav-iour is one of the important factors responsiblefor poor rub fastness of reactive-dyed ramie fa-bric which can be reduced by post-treatment withsilicone or polyethylene emulsion forming a softand smooth surface film over the dyed ramie sur-face. Therefore, post-treatment, either with sili-cone or polyethylene emulsion, of reactive-dyedramie fabric pretreated with either 20% NaOH orpreferably with 20% urea, both in slack condition,

1·6 Pretreated with NaOH

1·4

"2

Control•• 0~"0:> 1·8~ 1'6

Pretreated with urea>C

"4 ~ e'·2 ~ 7

'·0 ~S~6

0-8 ~0 Control

0 10 20 30 40 SO 100Numberof rub cycln

Fig. 2-K/S values on extensive rubbing for differently finishedreactive-dyed ramie fabrics pretreated separately with aqueoussolution of NaOH (20%) and urea (20%), both in slack conditionprior to dyeing [Control-without any pretreatment or finishingpost-treatment; I-NaOH-pretreated without any finishing post-treatment; 5-urea-pretreated without any finishing post-treat-ment; 2 & 6-finished with catasoftener; 3 & 7-finished with sili-cone emulsion; and 4 &8-finished with polyethylene emulsion]

can be considered to be a useful practical propo-sition if higher rub fastness is desired.

4 Conclusions4.1 All the pretreatments, considered for the en-hancement ·of accessibility, improve the reactivedye uptake of ramie fabric to different extents.Phosphoric acid though improves the accessibilityto the highest extent but results in high loss(about 30%) of tensile strength. Pretreatment with20% NaOH or 20% urea under slack conditionshows appreciable amount of decrystallization[more than that obtained for NaOH (under ten-sion) or mercerization process], considerable im-provement in reactive dye uptake with low tomoderate strength loss, iridicating practical im-portance for possible industrial application.4.2 Fastness to washing and light for reactive-dyedramie are almost at par with those for similarlydyed cotton. However, the fastness to rubbing isgenerally poor for ramie, particularly at highernumber of rub cycles, in comparison to that forcotton.4.3 Highly oriented and ordered structure of ra-mie offers less dye accessibility (consequently lessdye sites), resulting in (i) ring dyeing phenomenonand (ii) high coefficient of friction of the ramie fi-

60 INDIAN J. FmRE TEXT. RES., MARCH 1997

bre, causing break of long-staple ramie fibre onextensive rubbing without detaching from fabric;these two reasons have been found to be the ma-jor responsible factors for lowering the rub fast-ness of reactive-dyed ramie.4.4 Post-dyeing treatments with selective softenersor polymeric emulsions like silicone and polyethy-lene emulsion of suitably pretreated (particularly20% NaOH or 20% urea pretreatment underslack condition at room temperature) ramie fabricimprove the fastness to rubbing significantly forreactive-dyed ramie fabric and these pre- andpost-treatments may be considered useful forpractical application.

AcknowledgementThe authors gratefully acknowledge the help

rendered by Dr Swadesh Sett, College of TextileTechnology, Serampore, in determination of X-raycrystallinity. They are also thankful to Dr U. Mu-khopadhyay, Dr D. Sur and Mr. D.K. Sinha of lIT fortheir advice, help and keen interest. The authors ex-press their indebtedness to the Ministry of Human Re-source Department, Govt. of· India, and AICTE,Govt.of India, for grant in-aid to this department;the equipment purchased from these grants werevery useful in this work.

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