Indian Journal of Fibre & Textile ResearchVol. 20, March 1995, pp. 23-26

Studies on mechanical properties and atmospheric dyeing of solventpretreated polyester multifilament yam

A K Samanta, D Sur, D P Chattapadhaya", S K Ghosh & S N Mondal"Fibre Science & Technology Department, Institute of Jute Technology, 35 Ballygunge Circular Road,

Calcutta 700 019, India

Received 26 July 1993; revised received 11 May 1994; accepted 31 May 1994

Polyester multifilament yams were subjected to swelling treatment with different solvents andsubsequently dyed with a commercial disperse dye (Dispersol Red-B-3B; Cd. Disperse Red 11) atdifferent temperatures in the range 70-100oe with a view to save thermal energy. It is observed thatwithout much sacrificing the tensile and other mechanical properties of PET and some increase inbreaking extension, disperse dye uptake reaches the desirable level.at lOOoe for pretreatments withnH:resol, dichloromethane, nitrobenzene and phenol at their optimum concentrations of either aque-ous or non-aqueous solutions.

Keywords: Dyeing, HT-HP dyeing, Polyester multifilament yarn, Solvent pretreatment

1 IntroductionOn commercial polyester fibre, having very

compact structure and no dye sites, it is difficultto achieve satisfactory dye depth without the useof high temperature/pressure (HT-HP) or carrierchemicals. HT-HP dyeing is high energy expensiveand the use of carrier chemicals has known disad-vantages. Besides the use of carrier chemicals,low-temperature or atmospheric dyeing of polyes-ter filaments through solvent pretreatment haspotential to gain attention as a energy saving ap-proach. With this in view, the present work wasundertaken to study the atmospheric dyeing ofPET yarn after different solvent pretreatments.Brennecke and Richter) studied the shrinkage andtensile behaviour of fifteen different swellingagents on polyester yarn, but not the dyeing ofpolyester. Ribnick et aU studied interaction of 26solvents with different textile fibres, but not thetensile properties and dyeing. The progressiveswelling of continuous filament of polyester inphenol is explained by Bobeth". Reports are avail-able in literature= on solvent-assisted sequencialdrawing and its effect on structure of PET fila-ment/fibre. Gulrajani? studied the effect of phenolpretreatment on disperse dyeing of PET. Mooreand Sheldon 7 have shown a correlation between

"The Technologicallnstitute of Textile and Sciences,Bhiwani 125 021, IndiabPolyester Filament Texturing Division, Garden Vareli SilkMiUs, Surat, India

solubility parameters, shrinkage and swelling ofunoriented amorphous polyester by differentswelling agents. Dyeing of PET through solventpretreatment has not been studied in detail andonly a few reports" are available in literature.

The solvents selected for the present investiga-tion were phenol, m-cresol, nitrobenzene, dichlo-romethane and chloroform. The selection wasmade on the basis of shrinkage values'-" and theresults of a preliminary study on the shrinkagebehaviour of PET in different solvent pretreat-ments carried out in our laboratory. Phenol andm-cresol were used in aqueous medium while theother three solvents were diluted in trichloro-ethylene.

2 Materials and Methods2.1 Materials

Fully drawn, 50 denier, 24 filaments. polyestermultifilament yarn of Mis Petrofil CooperativeLtd, India, was used. The yarn in small hankform wrapped in cotton cloth was soxhlet extract-ed in methanol for 4h, air dried and stored inCaCl2 desiccator for 24h. All the chemicals, in-cluding the solvents, used were of LR grade (MisS D Fine Chemicals).

2.2 Solvent PretreatmentMethanol-extracted, dried PET yarns were sub-

jected to solvent pretreatment in small hank formwrapped in cotton cloth. They were dipped in dif-

24 INDIAN J. FIBRE TEXT. RES., MARCH 1995

ferent solvents of the specified concentration atroom temperature for 24h, keeping the material-to-liquor ratio at 1:100. After the solvent treat-ment, the yams were first neutralized and thenprolong-washed with dil. NaOH solution in caseof phenol and m-cresol pretreatments and withtrichloroethylene in case of dichloromethane,chloroform and nitrobenzene pretreatments. Fi-nally, the yams were washed with hot water anddried at room temperature.

2.3 Measurement of ShrinkageThe length of the PET filament yams in hank

form was measured, with 0.2 g1den pretension,before and after the solvent pretreatment for cal-culating the shrinkage (%) consequent to changein length on given solvent treatment.

2.4 Measurement of Tensile PropertiesBreaking load and breaking elongation for se-

lected yam samples were measured in Zwick1445 CRT Universal Tensile Testing Machine us-ing 100 mm test length and 0.1 N pretension.Tenacity was calculated on the basis of actualdenier before and after the solvent pretreatment.Initial modulus was calculated using the stress va-lues corresponding to 1% extension for eachsample.

2.5 DyeingA commercial disperse dye, Dispersol Red-Be

3B (C.!. disperse Red 11; mol. wt, 268), obtainedfrom M/s ATIC Industries (Atul), Valsad, wasused without further purification to simulate com-mercial/industrial dyeing procedure. However, forexperimental and scientific need, the purity of thedye was tested through repeated soxhlet extrac-tion as suggested by Shenai and Parekh".

Each dye bath contained: disperse dye, 1% (onthe weight of goods, but considering the purity ofthe dye, the dye percentage in the bath was 0.6);dispersing agent (Setamol-WS), 0.1%; and a fewdrops of glacial acetic acid to obtain pH 4-4.5.The material-to-liquor ratio was kept at 1:100.The dyeing temperatures used were 70°, 80°, 90°,100° and 130°C and the duration of dyeing ineach case was 60 min. After the dyeing was over,the dyed yams were washed with water and sub-jected to usual reduction clearing, soaping andwashing and finally air drying at room tempera-ture.

2.6 Measurement of Optical Density and Dye UptakeThe optical density of the dye solution (after

extracting the dye from the dyed PET filament

yam using chlorobenzene extraction at 125°C)was measured using U-2000 Hitachi UV/VISSpectrophotometer by the usual procedure andthe dye uptake (g dye/kg of fibre) was noted.

3 Results and DiscussionThe solvents act on polyester either by plasti-

cising or swelling action with or without some de-gradation and lowering of glass transition temper-ature2,4,5 and, therefore, atmospheric dyeing ofPET may become possible. The swelling agentdiffuses into polymer matrix, swells the polymerand breaks and rebuilts some weak intermolecularforces between polymer chains, causing somestructural rearrangemenr'f and permissible shrin-kage7,IO-12 with or without tensile strength loss.At the same time, there is an increase in accessib-ility in non-crystalline zone for better segregationof crystallites and non-crystallites as observed byWarwicker':'. Therefore, the effect of solvent pre-treatment is somewhat analogous to thermal sett-ing in polyester fibre. With the above backgroundinformation, the results of the present investig-ations are discussed.

3. t Mechanical PropertiesTable 1 shows the tenacity, breaking extension,

initial modulus and shrinkage values before andafter the solvent pretreatment of polyester yamswith different concentrations of aqueous and non-aqueous solutions of the five selected solvents.The concentration ranges used were selected aftera number of trial studies with a view to keep abalance among strength loss, breaking extensionand moderate to high shrinkage values. For phe-nol and m-cresol, with increase in solvent concen-tration above 3%, strength loss becomes higher,breaking extension increase becomes marginaland rate of increase in shrinkage values becomeslesser. At about 3% concentration of the abovetwo solvents, the initial modulus decreases to alarge extent. Considering the above studies andthe changes in mechanical properties with thesetwo solvents, the concentration for the pretreat-ment before atmospheric disperse dyeing is select-ed as 3% for phenol and m-cresol.

The increase in breaking extension in all thepretreatments studied may be explained by highshrinkage with relaxation of the structure (stressrelaxation) with chain folding and structural rear-rangement on solvent swelling of PET, as report-ed earlier':"!'. In case of nitrobenzene, thestrength loss is lowest at all the concentration le-vels used when compared with that for other sol-vents (at the comparable concentration level). At

SAMANTA et al.: SOLVENT PRETREATED POLYESTER MULTIFILAMENT YARN 25

Table I-Effect of solvent (with varying concentration)pretreatment on mechanical properties of polyester

multifilament yam

Solvent Tenacity" Breaking Initial Shrinkage% (w/w) g/den" extension modulus on solvent

% g/den pre-treat-ment, %

Nil 4~94 18.80 0.68Aqueous phenol

1 4.74 18.60 0.62 3.22 4.55 20.40 0.53 5.53 4.40 25.76 0.46 lO.ot4 4.19 26.56 0.3..9 12.205 4.02 28.22 0.38 14.10

10 3.52 32.12 0.33 17.09

Aqueous metacresol1 4.79 18.59 0.59 2.832 4.63 28.21 0.43 lO.753 4.20 31.62 0.41 16.36

10 4.04 3l.99 0.39 17.3499 3.28 35.68 0.36 22.78

Nitrobenzene in TCEc

10 4.88 20.22 0.64 4.325 4.82 21.53 0.89 5.950 4.75 22.82 0.51 9.8275 4.69 24.35 0.47 l3.34100 4.54 25.94 0.44 16.33

Dichloromethane in TCE

10 4.72 24.69 0.43 9.2425 4.56 27.57 0.42 11.3150 4.44 33.00 0.40 14.7475 4.12 35.49 0.39 16.34

98 3.90 40.14 0.32 i9.64

Chloroform in TCE

10 4.80 25.45 0.49 7.5625 4.62 27.62 0.46 10.5050 4.45 27.92 0.42 12.7375 3.89 27.93 0.39 14.44

99 3.77 28.24 0.35 18.79

"Tenacity results were calculated on the basis of actual denierobserved after solvent pretreatment."To convert g/den to SI units (kN-m.kg) the given results areto be multiplied by 88.26.<TCE- Trichloroethylene.

100% concentration, nitrobenzene gives 16.33%shrinkage, marginal strength loss, about 7% in-crease in breaking extension and initial modulusvalue of 0.44 glden. In case of dichloromethaneand chloroform in trichloroethylene, the optimumconcentration chosen is 50% considering andoptimizing the strength retension level (at least

90%), increase in breaking extension (at leastmore than 35%) and loss of initial modulus (notmore than 40-45%). The marginal loss in tenacityon controlled solvent pretreatment and some re-duction in initial modulus .were as expected fromearlier reports4,lO-12.

3.2 Atmospheric Disperse DyeingDisperse dye uptake (g dye/kg of fibre) values

of untreated and solvent pretreated PET at 70-100°C for atmospheric dyeing and at 130°C forHT-HP dyeing are shown in Table 2. A compari-son of mechanical properties (Table 1) and dis-perse dye uptake (Table 2) indicates that there isminimum degradation of PET polymer pretreatedwith 3% aqueous solution of phenol or m-cresoland considerable increase in disperse dye uptakeat 100°C (as compared to that at 100°C in the sameprocess for untreated PET yams). The increase indisperse dye uptake is 48.5% for 3% aqueous m-cresol pretreatment and 17.2% for 3% aqueousphenol pretreatment. But it is difficult to removem-cresol from PET on washing, even after pro-long alkali wash, and it may degrade the polymerlater on and leaves brownish colour on PETwhich is undesirable. Also, it is known that pres-ence of m-cresol type of compound impairs lightfastness for dyed fibres.

Increase in disperse dye uptake at 100°C fordichloromethane pretreatment is > 32% and fornitrobenzene pretreatment, > 26% (Table 2). Thisincrease+' in dye uptake may be explained bylowering of ~ and plasticizing effect of the swell-ing agents on PET and also by increase in acces-sibility by structural rearrangement on stress-re-laxation and better segregation of crystalline andnon-crystalline parts. Chloroform pretreatmentnot only has health hazards but also gives mini-mum increase in disperse dye uptake and, there-fore, it can also be excluded from the possibility.A comparison of the results of conventional HT-HP dyeing of untreated PET filament at 130°Cwith those of dyeing at 100°C of PET filamentspretreated with 100% nitrobenzene, 50:50 dich-loromethane/TCE and 3% aqueous m-cresolshows that disperse dye uptake is higher in caseof dyeing of pretreated PET at 100°e. For 3%phenol pretreated PET, disperse dye uptake is al-most similar to that for untreated PET dyed at130°C by HT-HP process. However, it may benoted that the disperse dye exhaustion is appar-ently much at lower side in all the cases, probablydue to the use of commercial dye directly withoutfurther purification. Determination of purity ofthe commercial dye used revealed that the dye

26 INDIAN J ..FIBRE TEXT. RES., MARCH 1995

Table 2-Effect of solvent pretreatment on disperse dye uptake of polyester multifilament yam

Pretreatment Dye uptake (glkg of fibre"t

901.201.67

2.752.40

2.892.12

100

2.683.193.983.48.

3.54

2.98

Lab HT-HPdyeing at

130'C

3.38

Increase indye uptake(at 100°C)

%Atmospheric Lab-beaker dyeing at temperature" (0C)

Nil3% Aqueous phenol3% Aqueous metacresol100% Nitrobenzene50% Dichloromethane in TCE<

50% Chloroform in TCE

70

0.240.571.72

0.861.23

0.87

80

0.540.971.871.821.92

1.68

17.248.5

26.132.111.1

'Dye used was Dispersol Red-B-3B (C.!. disperse Red 11) from Atul, India. 1% disperse dye was used on the weight of fibre.The purity of dye was 60%. 100% exhaustion of bath will give 6 g dye/kg of fibre. Maximum exhaustion observed was 56%.bTemperature used was within ± 2°C.<TCE- Trichloroethylene.

purity was 60% and therefore the dye uptake re-sults (Table 2) must be read keeping the per centpurity of the dye in mind.

4 ConclusionsSolvent pretreatment route of dyeing polyester

(atmospheric dyeing of solvent pretreated PET)with disperse dye using 3% aqueous phenol, 3%aqueous m-cresol, 100% nitrobenzene and 50:50dichloromethane/trichloroethylene (particularlythe last two solvents) with success paves the wayof effectively dyeing PET fibre in open bath at100°C, without much sacrificing tensile and othermechanical properties on solvent pretreatmentand ensuring substantial energy. saving in polyes-ter dyeing. However, m-cresol and chloroformpretreatments have shown some disadvantages. Adetailed study involving some more solvents isneeded to work out the commercial viability ofthis route.

AcknowledgementThe authors are thankful to Dr P C Dasgupta,

Ex-Principal, Institute of Jute Technology, Calcut-

ta, for his valuable suggestions and encourage-ment during this work.

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