Indian Journal of Textile ResearchVol. 11, December 1986, Pp. 181-187

Effect of Solvent Pretreatment on Dyeability and Mo phologyofPoly(ethylene terephthalate)

V H PATEL and N V BHAT

Centre of Advanced Studies in Applied Chemistry, Department of Chemical Technology, Univers ty of Bombay, Matunga,Bombay 400019, India

Received 3 February 1986; accepted 27 February 1986

The effect of pretreatment of polyesters with dimethylformamide (DMF), dichloromethane (DCM) and perchloroethylene(PCE) on dyeability of poly(ethylene terephthalate) (PET) with a disperse dye was investigated. Thd dye uptake depended onthe nature of solvent as well as duration and temperature of pretreatment. All pretreated samples shbwed a higher dye uptakethan the untreated ones. However, DMF-treated samples acquired the highest dye uptake followed b~ DCM- and PCE-treatedsamples. A temperature close to the boiling point was the best for all the three solvent pretreatmentlfrom the point of view ofdyeing. Dyeing studies showed quite promising results without the addition of carrier to the dyebath. Solvent pretreatment didnot have any adverse effect on the other textile properties of polyester. The enhanced dyeabili,y brought about by thepretreatment was associated with the plasticization and reduction in glass transition temperature 0jPET as evident from thestudy of per cent elongation at break and loss modulus.

Keywords: Disperse dye, Dye uptake, Polyester, Poly(ethylene terephthalate), Solvent pretreatme t

1 Introduction \to determine the changes in the structural andMany investigations 1 -5 have been carried out on mechanical properties by using an Instron tensile tester

interaction of the organic solvents with polyester fibres and a Rheovibron DDV -II viscoelastometer. Thewith a view to understanding the morphological and changes in the morphology of fibres as a result ofstructural changes taking place owing to the solvent pretreatment and the mode of dyeing were studied withpretreatment. The effect of pretreatment on dyeabilityhas also been studied" -9 . The main aim in all these a scanning electron microsc pe.

studies was to increase dye uptake. Also, some of the 2 Materials and Methodsworkers!" -12 have studied the effect of solventpretreatment on the morphology of poly(ethylene 2.] Materialsterephthalate) (PEn. 2.1.1 Fibre substrate- 76 denier (76/34/0) continuous

The use of non-aqueous organic solvents in textile polyester filament yarn sUP~lied by Nirlon Syntheticwet finishing has been emphasized 13.14. The presence Fibres & Chemicals Ltd WJ used. It is a hot-drawnof organic solvents in aqueous dyebaths improved dye semicrystalline fibre with 2.235 denier for eachuptake, lowered dyeing temperature and shortened the monofilament.duration of dyeing for both natural and synthetic 2.12 DMF, DCM, PCE an acetic acid used were offibres. However, solvent dyeing has posed problems, Analar grade. Lycol 01 (po Ider) was used as the non-such as extra installation cost, effluent treatments, ionic dispersing agent.requirement of new dyestuffs and recovery of 2.].3 Two disperse dyes, C.I. Disperse Blue 56 and c.!.

Isolvent 15 . Polyester shrinkage has been related to the Disperse Yellow 23, purified and recrystallized fromvarious changes in the structure and it is mainly benzene, were used. Icorrelated to the relaxation of built-in strains. Inaddition, plasticization of the amorphous regions 2.2 Pretreatment Iaccompanied by chain-folding and crystallization Samples weighing one ~ram were immersed inunder the influence of organic solvents results in the solvent (50 ml of solvent n a conical flask). Theobserved shrinkage. Attention has been given in recent pretreatment was carried out at three differentyears to the pretreatment of polyester fibres to increase temperatures and durations ranging from 5 to 60 minthe dye uptake without many of the problems for all the three solvents. Pr,treatment was done in aencountered during carrier and solvent dyeing. temperature-controlled wate5-bath for lower tempera-

This work was undertaken with a view to studying tures and in an oil-bath for ~igher temperatures. Thethe effect of solvent pretreatment on dyeability and samples were later thoroughly washed with water andmorphology of PET fibres. Attempts have been made dried in vacuum for 4 h. I

I181

INDIAN J. TEXT. RES., VOL. 11, DECEMBER 1986

2.3 DyeingThe treated fibres (100 mg) were dyed in a conical

flask in the water-bath maintained at 98 ± 2ee. Also,in each set, the control samples were dyed in thesame bath. Dyeing was ~one at pH 5.5-6 (maintainedby adding acetic acid) for 60 min. The dye content inbath was 2% of the weig,ht of the fibre. The sampleswere later washed and reduction-cleared with 5 g/litreof caustic and 2 g/litre of hydrosulphite for 15 min at60' e. Dyed and redu)tion-c1eared samples werewashed thoroughly and dried in vacuum for 4 handwere used for further analysis.

2.4 Analysis2.4.1 The tenacity and e~Ongation at break of driedsamples were determined by an Instron tensile tester.2.4.2 The tan (5 (dynai ic mechanical loss) wasmeasured by a Rheovibron DDV-lI viscoelastometerand the loss modulus E" tnd storage modulus E' werecalculated.2.4.3 A calibration curve of the dye in chlorobenzenewas prepared, and the dye uptake of the dyed fibreswas found from the optical densities measured with aspectrophotometer.2.4.4 Scanning electron microscopic studies werecarried out with an ISI DS-130 SEM.

3 Results and DiscussionFigs. 1, 2 and 3 showl the effect of pretreatmentduration on the dye uptake of PET fibres for varioustemperatures of pretreatment with DMF, DCM andPCE respectively.

With all the three solvents the dye uptake increaseswith duration as well as emperature of pretreatmentand the effect of trea ment temperature is morepronounced. Also, pr longing the duration ofpretreatment up to 30 m n brings about a substantialincrease in dye uptake. For a given pretreatmentduration DMF is much more effective in improvingthe dye uptake than DC and peE.

The improvement of d e uptake due to pretreatmentof PET fibres by solvent indicates that these solventsalter the microstructure of polyester and the alteredmicrostructure cannot be reversed to the original state.It is likely that the solvent diffuses in the polyester,breaks the hydrogen bonds between the adjacentmacromolecules, interacts with the ester groupingsand leads ultimately to he loosening up of the fibrestructure. thereby incrersing the dye uptake. Thedependence of dye uptake on duration of pretreatmentand temperature ofpretratment and also nature of thesolvent is clear from Fi s. 1-3.

A higher dye uptake 1'0 the fibres treated with DMFas compared to that pre reated with DeM and peEsuggests that DMF alter the fibre structure greatly. It

182

is an active plasticizing agent and thus gives permanentchanges in the structure which leads to the higher dyeuptake. In such pretreatments the temperature ofpretreatment may also help chemical action so thatboth the thermal and chemical energy take part inchanging the microstructure. The comparison ofDeM with peE shows higher values for DeM thanpeE. This may be due to the high penetration capacityand plasticizing action of DeM than peE, which isreflected in the per cent elongation at break.

13 •••.•---------e6-~

12-_ C.1. DISPERSE awE 56

----- C.I.DISPERSEYELLOW 23

-e--G- 140C~'2D'C

~'OO't

11

10

9

-----•. 8••.!.. 7

~.." 6~0

5

_--i:-------.-A",I!f'~

/'

_----J:>--_ ~- -0- --

4 CONTIJPI:'O'"

."VY"3 Q -- CONTRO~ 5 7530 45 60

T'ME OF PRETREATMENT, mm

Fig. I-Effect of DMF pretreatment on dye uptake of PETfilaments (Dyeing at 38±2aC)

8

-- C.I. QtSP,RSE BLUE 56

-----C.I.DISPERSE YEL1.OWZl

~40'C____ 30'C

___ 23'C

:~t- _--_::::.=..;i;;.;:;:-:.:.: :.:!:.-

UtOL

2

°O~--~1~5----~3~0----~4~5----760~--~7S'-TIME OF PRETREATMENT, nun

Fig. 2-Effect of DCM pretreatment on dye uptake of PETfilaments (Dyeing at 38± 2aC)

PATEL and BHAT:EFFECT OF SOLVENT PRETREATMENT ON DYEABILITY AND MbRPHOLOGY OF PET

Fig. 4 shows the rate of dyeing for control and the maximum increase. This mJy be due to the effect offibres treated at the maximum temperature of pretreatment temperature dn the structure of PETpretreatment selected in this study. The rate of dyeing fibres. Raising the temperature of treatment seems tofor treated fibres is higher than that for the control and enhance the segmental =in PET via breaking theis maximum for fibres treated with OMF. The H-bonds under the influenc of thermal and chemicalsaturation in dye uptake is achieved in a dyeing of 1 h. energy supplied. Also, T ble 1 shows. that theAlso, changes brought about by OMF are drastic as elongation at break (%) incrases with duration andcompared to those due to OCM and PCE. temperature of pretreatment f~r all the three solvents

The extent and the rate of dyeing for the samples used and the order of i creasing the per centtreated near the boiling points of the solvents show I

14

UJ

~ 4•..Q.

:>UJ 3>Cl

roNTR~ .A- -- = = =::2: =~-=--:,l'}_ -- -0-

--0- ----<'>- ------~--- °co"NrR""8'L 4

•--c.1. 0 isp.rw BI""5'6-- --- C.I.Disp@rse v..Uow 23

13

6~

120'C100'C80'C

12

11

10

8

__ Dt.4F,lI.0t.l1>

-+-G- PCM, 4O'C,I"

•••..•.••••• peE ,120·C,lh___ CONTROL

9

'"c;. 5E

~ 7

W 6~•.:>

~ 5o

3

15 30 60TIM E OF PRETREATMENT. mln

o 7 90 105 120TIMe OF DyeiNG, min

Fig. 4-Kinetics of dyeing for vari~s pretreatments of PET (dyeused-CI disperse blue 561dyeing at 38± 2°C)

Fig. 3-Etfect of PCE pretreatment on dye uptake of PET filaments(Dyeing at 38± 2°C)

Table I-Effect of Pretreatment on Elongation at Break and Tenacity at Break 0lPET Filaments

Treatment Treatment temp.cC Elongation at break, ~. Tenacity at br ak, g/deniertimemin DMF DCM PCE DMF DCM PCE DMF DCM PCE

Control Control Control 14.86 14.86 14.86 4.59 4.5~ 4.595 80 23 80 16.04 28.87 19.94 4.73 4.9 4.88

15 80 23 80 16.08 34.69 22.31 4.46 50~ 5.2230 80 23 80 16.55 36.94 25.81 4.39 5.1~ 5.3960 80 23 80 16.88 32.94 25.31 4.47 4.9p 5.21

5 100 30 100 28.75 32.69 25.47 4.61 5.1i? 5.1715 100 30 100 35.93 38.69 25.62 4.63 4.9[3 5.1130 100 30 100 36.44 37.75 26.50 4.86 5.W 5.3960 100 30 100 36.00 37.03 26.40 5.15 5.112 5.075 120 40 120 33.75 35.81 26.25 4.93 5.04 4.95

15 120 40 120 36.18 35.73 27.00 4.74 4.98 5.0530 120 40 120 43.69 37.06 27.68 4.80 4.9~ 5.1360 120 40 120 40.00 37.55 30.00 4.89 4.9 5.245 140 35.25 4.44

15 140 39.31 4.6730 140 41.81 4.5460 140 43.50 4.59

181

INDIAN J. TEXT. RES., VOL. 11, DECEMBER 1986

elongation at break is O~F > OCM > PCE. Thisalso reflects the interaction of these three solvents withPET. I

Tenacity (Table 1) I is not affected by thepretreatment and shows an increase in some cases(except at 14OCC, 1 h, 0rytF treatment) which may bedue to the solvent induced crystallization. Figs. 5, 6and 7 show the temperature dependence of lossmodulus E" for the PET fibres treated with OMF,OCM and PCE at differe9t temperatures for 1 h. Thesefigures show that the curves for loss modulus E" forthe PET fibres treated with OMF, OCM and PCE at100c, 23c and 80cC re~pectively become sharp incomparison with the cUfve for the control. On theother hand, the curves fO~the samples treated with theabove-mentioned solven s at slightly higher tempera-tures (140C

, 40° and 120c) show the broadening of the

curves to some extent. The temperatures at which theE" curve attains a maxirmim are given in Table 2. The

~140'C,lh

-A--+- 100'C,lh

~COHTROL

l.l18,,~----:,7, -~,,;----t;12:--+-'"''10--±'OO;--~,;t,26---;77----;h-TEMP RATURE,·C

" ,rJa

-e--a-- 4O·C. 1 h TREATMENT

~ 23·C.lh TREA'JoIENl

~- CONTROL

Fig. 5-E' and E" versus tempe ature for PET pretreated with DMF

-w

71), 10

-E '

,ll~,~,---!,-'-, ---f";----="71c-+-+.90;---'~O.;----;'c:,26;-----:~-~TEMPE FlATU FlE;C

184

Fig. 6--E' and E" versus tempe ature for PET pretreated with DCM

table shows that E" for control occurs at 108°C,max

which increases to l ltr'C for the samples treated withOMF at lOoce. In contrast, when the samples aretreated with OMF at 140°C, E" occurs at 94°C, a

maxtemperature much lower than that of the control. Asimilar reduction in the-E" temperature is observedmaxfor PET treated with OCM at 40cC and PCE at 120°Cbut to a lesser extent.

The broadening of the peak corresponding toE:axtemperature and the reduction in the temperature atwhich this occurs show that the fibre has undergoneplasticization, which helps in increasing the dyeuptake. The trend in the reduction ofE:ax temperatureis OMF > OCM > PCE and a similar trend isobserved in the increase of the dye uptake.

,The scanning electron micrograph of the controlPET filaments (Fig, 8) shows that the structure is notvery smooth as expected but reveals a large number oftiny particulates. A careful study throughout provedthat this grainy structure is a structural parameterassociated with the fibre, The commercial PET fibre, ingeneral, does not show a very smooth structure. Thesurface may be accompanied by some crystallites. It isalso possible that a high viscosity liquid exudate

1.1~

~ vurc t v«........,.,. eo·c 11h

~ CONTROL PET

- ,••: ,E<! 2

-w

",r!9s

I:l1

1.,~'· ':..1 ---!',----,C'---f.;'--t;;' -_c:,' ;__--;*'" _--;-!-:-' _~'- )6 ~ n 98 108 116 ,l.i"

TE MIlERATURE,'C

Fig. 7-E' and E" versus temperature for PET pretreated with PCE

Table 2-Effect of Pretreatment on E"max

Solvent Treatmenttemp.r'C

E" x 10·max

dynes/em?

Temp. ofE"

max°C10811094

112106122110

ControlDMFDMFDCMDCMPCEPCE

100140234080

120

0.00520.00350.00420.00330.00320.00450.0047

PATEL and BHAT:EFFECTOF SOLVENT PRETREATMENT ON DYEABILITY AND MORPHOLOGY OF PET

containing some 'crystalline material may come to the When the fibres were treate TWith DMF for 60 min atsurface. It.is equally likely. that the .exposure of PET 100°C, the grainy structure1till prevailed but its sizefibre to heat gives rise to sublimation of cyclic trimers reduced to 0.35 pm and showed a very minutefrom the interior of the fibres which eventually set on appearance of fibrils (Fig. 9 .the surface. In the micrograph (Fig. 8), the grainy The fibre structure obse ved for samples treatedparticles observed have a more or less circular with DCM for 60 min at 40 C do not reveal a drasticsymmetry and the size varies from about 0.5 {1m to 4.0 change from that of the co rol (Fig. 10). The grainypm with an average of about 1.9 pm. On this basis it isconcluded that this surface characteristic is formedowing to the high viscosity liquid exuding to thesurface. Hence, they represent the low-molecular-weight fractions.

The morphological changes occurring as a result ofsolvent treatment are shown in Figs. 9, 10 and 11.

Fig. 8-Scanning electron micrograph of control PET filament

Fig. IO-Scanning electron microg aph of PET filament treatedwith DCM for h at 40°C

I

Fig. 9-Scanning electron micrograph of PET filament treated with Fig. l l+-Scanning electron micrograph of PET filament treatedDME for 1 h at 100°C with PCE for 1 It at 100°C

185

INDIAN 1. TEXT. RES., VOL. 11, DECEMBER 1986

structure still persists, th9 size of which reduced to 0.30pm for 60 min treatmen~.

The morphology observed for the samples treatedwith peE reveals very Interesting features. Fig. 11shows that for the sampler treated with peE for 60 minfibrillar structure appea~s and some bulging is alsoobserved presumably dU9 to the oligomer exuding outto the surface in the presence of peE. In this treatmentalso the size of grainy structure reduces to 0.15 11m for60 min treatment.

Thus, the morphological observations support ourconclusion from the st~'dies using other physicaltechniques that there is a structural transformationtaking place owing to th solvent pretreatment.

The studies on the dfle uptake described earlierrevealed that the dye uptake increases as a result ofsolvent treatment. To u derstand the mechanism ofdye uptake, the dyed fi~res were examined with ascanning electron microscope. In Figs. 12-15 are

186

Fig. 13-Scanni~g electron mi 'rograph of PET filament dyed (C IDisperse Blue 56) after pret eatment with DMF (I h; 100°C)

shown the scanning electron micrographs of thecontrol as well' as solvent-treated and subsequentlydyed PET fibres. In the case of the control dyed samplethere is no change in structure and it is more or less thesame as that of the control undyed. But in the case ofall other treated dyed fibres an elongated rod-like

..,I

Fig. 14--Scanning electron micrograph of PET filament dyed (C IDisperse Blue 56) after pretreatment with DCM (1 h; 40°C)

Fig. 15-Scanning electron micrograph of PET filament dyed (C IDisperse Blue 56) after pretreatment with PCE (I h; 40°C)

1,PATEL and BHAT: EFFECT OF SOLVENT PRETREATMENT ON DYEABlLITY AND M RPHOLOGY OF PET

structural feature is observed on the surface: Thesestructures are needle-shaped, of a width of about 0.3pm. A photograph of these structures at highmagnification does not reveal any further internalorganization. These rod-shaped structures must be theresult of crystallization of dye molecules on the fibresubstrate. Such a crystallization of anthraquinone vatdyes for cellulose has been reported on the basis of X-ray diffraction studies1Q•17. Similarly, recent work oncellulose has proved the existence and formation ofsuch dye crystallites+f!". In the case of samplestreated with OMF the length of needle-shaped crystalswas higher than in the case of samples treated withOCM and PCE.

This direct observation of aggregates andcrystallization of dye molecules on the fibrespretreated with solvents reveals that the morphologyof PET is altered significantly. Further, the formationof such crystalline aggregates proves the existence ofspecific sites on the fibre surface which act asnucleating centres. The higher dye uptake of thepretreated fibres, therefore, can be understood.

AcknowledgementThe authors wish to express their gratitude to Or

V.G. Karnath ofNirlon Synthetic Fibres & ChemicalsLtd, Bombay, for supplying the polyester filamentyarn. They are grateful to the Surface ScienceLaboratory at the University of Western Ontario,Canada, for permitting them to use the scanningelectron microscope. One of the authors (VHP) wishes

to thank the University Grants Commission, NewDelhi, for the award of a fe lowship.

References1 Kulshreshtha A K, Khan A H and Madan G L, Polymer, 19

(1978) 819.2 Lawton F L and Cates D M, Text Res J, 48 (19.78)478.3 Makarewicz P J and Wiltees Gt' Text Res J, 48 (1978) 132.4 Makarewicz P J and Wiltees G L, J Appl Polym Sci, 22 (1978)

3347.5 Padhye M R and Machi Raju I V, Proc Centre of Advanced

Studies in Appl Chem (UDfT, Bombay) 1978,48.' •6 Matakowsky R D, Weigmann D and Scott M G, Text Chem

Color, 12(3)(1980) 55.7 Moore R A F and Weigmann H D, 7ext Chem Color, 13(3)(1981)

70. I8 Robert J p, Charles D C and Ga y N M, Text Chem Color, 15(4)

(1983) 15.9 Basu A K, Deb T K, Gandhi R B and Shroff J J, Proceedings,

38ih All india Textile Conf~rence on Blended Textiles (TheTextile Association of India, Bombay) 1981,282.

10 Rewicz F M, Cates D M and Rutherford H A, Am DyestuffReptr, 50 (1961) 320. I

II Moore W R and Sheldon R P, Polymer, 2 (1961) 315..12 Sadat M A and Taiyo Aogogi, 11 m Dyestuff Reptr, 69(3) (1980)

46.13 McGregor Rand Adeimy J A'fext Res J, 47 (1977) 477.14 Ritter R E, Texl Chem Color, 1 (1969) 7234.15 Derbyshire A N and Harvey F ,J Soc Dyers Colour, 91 (1975)

106.16 Warwicker J 0, J Text Inst, 49 1958) T148.17 Warwicker J 0, J Text lnst, 50 (t959) T404.18 Chaudhuri N K, Arvindnath S ]nd Betrabet S M, J Polym Sci,

Polymer Leu Ed, 19 (1981) 131.19 Chaudhuri N K, Arvindnath S nd Betrabet S M, J Polym Sci,

Polymer Leu Ed, 22 (1984) .

187