Indian Journal of Fibre & Textile Research Vol. 30, September 2005, pp. 324-330

Dyeing of microdenier polyester fabric in supercritical carbon dioxide

She n Kung Liaoa

Department of Fiber and Composite Materials, Feng Chi a Uni versity, Taichung 40724, Taiwan

Received 5 April 2004; revised received 26 August 2004; accepted 10 November 2004

Supercrit ical flu id dyeing technology has been used to dye microdeni er polyethylene terephthalate fibres at elevated pressure and temperature simultaneously. It is observed that the dye speck disappears when pressure increases beyond 200bar and dye uptake increases when pressure increases above 250bar. Temperatures above 120°C are fo und to be suitab le fo r the dyeing of polyester fabrics. As the pressure re leases step by step, a deeper shade is obtained because of the incrementa l mi xing of the fluid , dyestuff and substrate. Di sperse Reel 60, which own anthraquinonid structure, could be di sso lved more eas ily in supercritical fluid system. Reaucti on cleaning is not req uired and the fas tness propert ies of dyed samples st ill meet commercial requirements. The results also show that the dye uptake could be ra ised with solvents such as dimethyl fo rmamide and dimethy l sulfox ide in combinati on with dyestu ffs. DSC and X-ray anal yses also indicate no obvious damage when polyester fab ri cs are dyed at 250bar pressure and 120°C temperature fo r 10mi n in superc ritical flu id carbon diox ide.

Keywords: Dyei ng, Microdenier fabric, Po lyethylene terephthalate, Supercritical flui d

IPC Code: In t. C I7 D06PI /OO

1 Introduction Polyethylene terephthalate (polyester) must be dyed

with di sperse dyes because it has no hydrophilic group which can react with other dyes and these dyes can diffuse only at high temperatures using ass istant agents such as surfactants l

. Supercritical fluid , which is indistinguishable as liquids or gases, is defined as the fluid processed beyond the critical point2

.

Supercri tical carbon di ox ide dyeing method has several benefits, such as nonflammable, nontoxic, easy to use, economical and environmentally acceptable. The study became attracti ve since Saus et al.3

.4 studied the dyeing of polyester and modi fied natural fi bres with disperse dyes in supercritical

. . 5 .. 67 carbon dIoxide. Then, Beltrame et at. , Ozcan et al . . and Schmidt et at.s studied the dyei ng of cotton and modified cotton in supercri tical carbon diox ide. They reported that the temperature and pressure are the mai n fac tors which could affect dyeing perfo rmance. It has been demonstrated that the supercritical carbon dioxide is a good medium fo r hydrophobic polymer dyeing, but some factors which affect the results, such as pressure. temperature, dye concentration, pH value and addition of assistant agents, sti ll need to be

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studied. In the present study, supercritical fluid dyeing technology9 has been used to dye microdenier polyester fabric in a 180ml capacity dye pot by raising pressure and temperature simultaneously.

Dyeing theory for polyester is accepted in accordance with free volume theory. When a fi bre is heated up to glass transformation temperature, the thermal acti vi ty of molecular chains is more vigorous which increases the free volume of molecules and dye di ffu sion. As the temperature is reduced, dyestuffs are fixed inside the molecul ar chain and stay in the fibre. Disperse dyes di ssol ved in dyeing systems diffuse rapidly because of the low viscosi ty of supercri tical fl uid which shortens the dyeing time lo

. Dye is preserved in the resealing procedure. The density of carbon dioxide can be contro llable upon changing pressure. Raisi ng pressure increases the solubili ty and high temperature increases the diffusion of dye. Polyes ter can be dyed without vigorous convecti on, and the carbon dioxide can be reused with a recycling process wi th no pollution 11 .12. It has been demonstrated that the supercri tical carbon dioxide is a good medium fo r hydrophobic polymer dyeing, but some factors, such as addition of organ ic solvent, sti ll need to be understood. Solubility of disperse dyes in supercritical carbon dioxide was also measured.

LIAO: DYEING OF MICRODENIER POLYESTER FABRIC TN SUPERCRTTICAL CARaON DIOXIDE 325

2 Materials and Methods 2.1 Materials

211 drill microdenier polyester woven fabric (warp: 90 threadslinch, 75 denier, and 72 filaments; and weft: 100 threadslinch, 150 denier and 288 filaments) was used for the study. The commercial dyes, namely c.1. Disperse Red 60, c.l. Disperse Yellow 3 and c.l. Disperse Orange 76, were purchased from Yi-Whia and supplied by the Yong-Kuang company. Their structures are shown in Fig. I . The dyes were purified by extraction and recrystallization. Firstly, each dye was dissolved in saturated sodium chloride solution which was boiled for Ih. Secondly, the dispersing agent was removed using a filtration step, and dried for 24 h at 50°C, then extracted with acetone to get pure dye. The fabrics were separately impregnated with different solvents, namely acetone, 2-methoxy ethanol, dimethyl formamide (DMF) and dimethyl sulfoxide (DMSO), all of extra grade. Industrial grade perchloroethylene and a commercial reagent (carrier SP) were also used.13

-15

The dyed sample's apparent colour yield (KIS) was tested with an ICS Gain spectrophotometer. Dyed materials were also tested for the reflectance (R) and apparent color yield using a color matching system and the following formula:

KIS=(l_R) 2 2R

The dye uptake was measured using DMF by extractive method. Fastness testing was subjected to a simulated rS02 and ISO 105 B05 standards before and after reducing wash. The colour fastness was measured by an rcs Gain Macbeth20/20 plus spectrophotometer. To observe the microstructure variation in microdenier polyester fibre , an X-ray diffraction pattern was observed using a SIEMENS D5000 apparatus. Thermal properties were observed using a Seiko SSC5000 DSC.

2.2 Dyeing Procedure The specifications of the dyeing apparatus,

manufactured by Zaar Technical Company, have been reported in a previous publication 16. The dyeing apparatus can be compressed and heated up to 400bar and 200°C respectively. A measured amount of dye was placed into a dye vessel and a microdenier polyester fabric was cut to a 40mmx200mm size and wound on an iron wire before dyeing. Then, the fabric

C.l. Disperse Red 60

o < > o OH

C.r. Disperse Yellow 3

C.1. Disperse Orange 76

Fig. l--Structures of disperse dyes

was put into the dye speck and the tubes were sealed to make a closed system. In the dyeing procedure, pressure and temperature were raised at the same time with 4°C/min rate. The dyeing was carried out for 10 min and then pressure was released step by step. At each step, 25bar of pressure was reduced and the temperature was still kept at dyeing temperature for 2' min until the pressure comes down to atmosphere. As the dyeing process was completed, reducing wash was performed. For reducing wash, specimen was treated with 2g/L sodium hydroxide and 2g/L sodium hydrosulfite solution at 80°Cfor 10 min and then dried at 60°C.

2.3 Solubility of Dye Dye dissolved in carbon dioxide was extracted by

dimethyl formamide in solvent container as carbon dioxide passes through it. Dye particles deposited in tube were also washed with dimethyl formamide and collected in solvent container. Second solvent container was cooled with ice to reduce the volatility of dimethyl formamide. Finally, the volume of carbon dioxide, collected over the water container, was detected by wet flow meter to calculate the mole of

326 INDIAN J. FIBRE TEXT. RES. , SEPTEMBER 2005

carbon dioxide In accordance with the following formula '7,'8:

11 co, RT

where 17('0 is the mole of carbon dioxide; P , the pres-2 WII '

sure of atmosphere; p;;:~ , the saturated vapour pressure

of water in water container; ~;;;I , the saturated vapour

pressure of solvent (dimethy l formamide) in solvent container; Vco, ' the volume of carbon dioxide detected

by wet flow meter; R, the gas constant; and T, the absolute temperature of wet flow meter.

Vapour pressure of dimethyl formamide and water was calculated using the following formula:

u 8 10gP =A---

T+C

where pO is the vapour pressure of dimethyl formamide or water; A, the constant (dimethyl formamide: 6.03823, water: 7.61171); 8, the constant (dimethyl formamide : 1393.225, water: 1948.271); and C, the constant (dimethyl formamide: 195.722, water: 249.201).

The mole of dye (ndye ) may be determined by visible spectra. Hence, the solubi lity of dye was calculated from the following formula:

where Xdye is the solubility of dye expressed in mole fraction .

The solubility of disperse dyes in carbon dioxide was tested using the apparatus shown in Fig. 2.

3 Results and Discussion 3.1 Microscopic .-\nalysis

The woven microdenier polyester fabric was wound into the dyepot, the apparatus was sealed and then heated to 120°C, whilst carbon dioxide was pumped at the pressure of 250bar. The temperature was maintained at 120°C with 4% (owf) dyes for 10 min separately. The cross-section of dyed microdenier polyester fibres observed by the optical microscopy is shown in Fig. 3. The figures indicate that the dye

Cooling system

Liquid carbon dioxide

Pressure gauge

Heat exchanger Glass ball conta iner

Fig. 2- Apparatus used for testing the so lubility of dye

particles have penetrated throughly into fibres within 10 min when carbon dioxide is the transport medium. Thus, dyeing of microdenier polyester fibres in supercritical fluid is feasible.

3.2 Dye Solubility The solubility of disperse dyes in supercritical

carbon dioxide was measured. (Table I) Disperse Red 60 shows better solubility than the others. Besides, comparison of solubility of dyes indicates that the eyes have better solubility in supercritical fluid than in water. 19 Both Disperse Yellow 3 and Disperse Red 60 dyes have similar solubility parameter or dye's density. Both Disperse Orange 76 and Disperse Red 60 dyes have similar E value. Hence, the Disperse Red 60 can be dissolved more easily . On the other hand, anthraquinonid based disperse dye shows higher solubility than azo based disperse dye.

3.3 Dyeing Analysis Comparative account of dye uptake at different

pressures using temperature of 120°C and dye concentration of 4% (owf) is shown in Fig. 4. Results show that the specimens dyed at higher pressures have increased dye uptake, especially at pressures above 200bar. At pressures exceeding 275bar, the dye uptake becomes lower but more even . As soon as the carbon dioxide reaches its supercritical state, disperse dye begins to dissolve and stain the fabric. It is uneven because dye particles are not dispersed evenly and most of the dye I?articles precipitate to the bottom of the fabric to form a deeper shade at the bottom and dye spots. This phenomena can be observed on the specimen dyed a( low pressure «150bar) . When pressure is raised above 200bar, the particles staining the fabric dissolve into the fluid state and penetrate into the fibres. Leveling efficiency is greatly improved as pressure rises above 250bar. Higher

LIAO: DY EING OF MIC RODENIER POLY ESTER FABR IC IN SUPERCRITICAL CARBON DIOXID E 327

pressures dissolve dye more efficiently which makes the dye uptake greater. But at pressures greater than 275bar, superior solubil ity allows dye particles in stains to be dissolved back into the fluid. When the

Fig ~ptical microscopic photographs of dyed microdenier po lyester fibres [(a) Di sperse Red 60, (b) Di sperse Orange 76, and (c)Di sperse Yellow 31

system is released, the di ssolved dyed particles excluded out into the dyeing system and this reduces the dye uptake. . In second set of experiment, the dyeing was carri ed

out at different temperatures (50, 70, 90, I 10, 120 and 130°C) using 250bar pressure and 4% (owf) dye concentration. Fig . 5 shows that the dye exhaustion increases upon reaching the glass transitIOn temperature of 80°C and reaches maximum at 120°C­I30°C, wh ich is simi lar to the traditi()nal water dyeing method. But at 90°C, supercritical fluid dyeing methods get better results than water dyeing methods at the same temperatures. It is known that the fluid density of carbon dioxide in supercritical fi eld is dependent on temperature when pressure is constant. When the temperature is higher, the fluid density will be lower. This shows that the Disperse Red 60 and Disperse Yellow 3 have better dye uptake at 90°C than that at lOO°e. It is obvious that the dyes would be released from the interior of the fibre when dyeing temperature is rai sed, except showing the good compatibility. As shown in Table 1, Disperse Orange 76 has so lubility parameter close to that of fibre . In

6

r ~ o;'f'."'" Red 60 I fa Disrcrse Yell ow 3 t=i Disperse Orangl: 76

~ ~

~ i) rn

~

L .- ~ '--o 100 150 200 250 275 300

Pressure, bar

Fi g. 4--Relationship between pressure and dye uptake of mi crodenier po lyester fabrics

Table l- Solubil ity of di sperse dyes in supercritical carbon di oxide

Dye Density g/cm3

E valuea

Llcm-mole So lubility paramete r

(cal/cm' ) 112

Solubility in CO2

(X2), mole/mole

c.l. Disperse Red 60 1.24 12768 14.77 1.28x 10·5

c.l. Disperse Yellow 3 1.26 2 16 11 14.89 1.03x \0 6 c.l. Disperse Orange 76 1.38 12987 13.22 4.95x \0·6 "Characteristic of dye at the spec ified wave length ()"max) according to Beer-Lambert law (Dye was di sso lved in dimethyl formam ide).

328 INDIAN J. FfBRE TEXT. RES., SEPTEMBER 2005

6 r-------------------------------------~

90 100 120 140

Temperature, °C

Fig. 5--Relationship between dyeing temperature and dye uptake of microdenier polyester fabrics

other words, there is more compatibility between Disperse Orange 76 and microdenier polyester fibre. Disperse Orange 76 dyed microdenier polyester fibre shows the highest uptake. Only at temperatures beyond 110°C, the leveling efficiency satisfies our requirements. Using the results from the sublimation fastness test, it is found that the samples which are dyed above 90°C have the same grade of fastness. It is believed that the supercritical carbon dioxide can plasticize the polymer and makes it dyeable at 90°C, but this phenomenon is limited and temperature is the major factor affecting fibre swelling and dye diffusion.

In third set of experiment, dye concentration was varied from 1.0% (owf) to 8.0% (owf) using 250bar pressure and l20°C temperature to observe the dyeing results. As shown in Fig. 6, the dye uptake increases as the dye concentration increases. Dye shades can be controlled using dye concentration adjustments. Dyers can also change pressure under suitable conditions simultaneously to get a sati sfactory results.

3.4 Effects of Solvent Perchloroethylene is thought to be the best choice

in solvent dyeing because it can swell polyester to increase the diffusion rate of dye part icles and hence indecates the dye ability of the fibre. Carrier SP is also used in dyeing processes for polyester which acts like perchloroethylene. Both the perchloroethylene and carrier SP show the solubility parameters 9.3 (callcm3

) 1/2 and 11.1 (callcm3) 112 respectively which is near to polyester solubility parameter 10.0 (cal/cm3)1 /2

2 4 6 8

Concentration, %o.w.f.

Fig. 6--Relationship between dye concentrations and dye uptake on microdenier polyester fabrics

Table 2-Boiling point, solubility parameter and solubility of Disperse Orange 76 in solvents and assistant agent

Solvent/fibre

Polyester Perchloroethylene Carrier SP Acetone 2-methoxy ethanol DMF DMSO

Boiling point/melting

point

°C

255 121.0 245.0 56.1 124.5 152.8 189.0

Solubil ity Solubility x IO-J

parameter g dye/ml (cal/cm3) 112

10.0 9.3 11.1 9.8 40.0 10.1 7.1 1 12.1 34.3 12.9 9.4

(refs 19-21). Table 2 shows some data of solvent and assistant agent. In the experiment, the dyeing was carried out at 250barx l20°Cx 1 Omin in supercritical fluid, using the concentration of 4% (owf) and carrier SP/water mixture of 1: 1 ratio. The results show that the carrier SP and acetone reduce the dyeing efficiency. The solvents 2-methoxyethanol, DMF and DMSO give better colour yield (Fig. 7.) These results can be attributed to the excellent dispersion of dye

L1AO: DYEING OF MTCRODENIER POLYESTER FABRlC IN SUPERCRITICAL CARBO DIOXIDE 329

10 9 8

g 7 co ;> 6 ;2 5

4 3 2

Untreated I'crchloro- larrier SP Aectone 2-mcthoxy OMr DMSO ethylene

Solvent l.1hanol

Fi g. 7-Effect of solvents on color yie ld (K/S ) of Disperse Orange 76 dyed microdenier polyester fabrics

() '- " ,--A 'E Q; .c '0 x lJ.J B

I \ <l

I -C

co E

\. Q; ~D .c

"" '0 '0 c

lJ.J

, . 20 76 132 188 244 300

Temperature , DC

Fig . 8--DSC anal ysis of microden ier polyester fib res dyed with Disperse Orange 76 [A--untreated raw fibre, B- ribre treated at 250barxI20°Cxdye4%x IOmin in SFD, C- fibre trea ted wi th DMF at 250barx I20°Cxdye4%x IOmin in SFD, and D--fibre treated with DMSO at 250barx 120°Cxdye4%x 10min in SFD]

particles which causes the molecules to penetrate well. Solvents, like acetone, will vaporize under dyeing conditions and then reduce the solubility power.

3.5 Fibre Analysis The curves obtained from DSC analysis and X-ray

diffraction of microdenier polyester fibres are shown in Figs 8 and 9 respectively . It is observed that the melting temperature variation is not clear for the treatment conditions 250barx l20°Cxdye4%xlOmin in supercritical fluid . The melting point calculated by DSC is found to be 253 .0-253.I °C but the X-ray diffraction curves show a little change in crystal

.s::::. ~--------~-----A 0, c: 0,) '-(ii c: 0

n ----....... ---,B co '-:e 0 ......... --------c

-------------D ( 5.000 x:2 theta 60 .000 )

2 e (deg)

Fig 9--X-ray diffraction pattern of microdenier polyester fibres wi th Disperse Orange 76 [A- untreated raw fibre , B- fibre treated at 250barx I20°Cxdye4%x IOlllin in SFD, C-fibre treated with DMF at 250barx 120°Cxclye4%x IOmin in SFD, and D--fi bre treated with DMSO at 250barx 120°Cxdye4%x 10min in SFD]

Table 3--Colour fastness on Di sperse Orange 76 dyed microdenier pol yester fabrics before and after reducti on clea ning

Parameter Fastness to Dry heating Washing Organi c solvent Rubbing Xenon arc lamp

light

Non-reduction clean ing 4-5 4-5 4-5 4-5 5 Reduction cleaning 4-5 4-5 4-5 4-5 5

330 INDIAN J. FIBRE TEXT. RES., SEPTEMBER 2005

Table 4- Dye quantity in residual so luti on after reducing wash 0 11 Di sperse Orange 76 dyed mi crodeni er polyester fabri cs

Parameter 90°C 100°C 120°C 140°C

Dye quantity pmole/g 0.044 0.026 0.030 0.027

Per cent" 0.63 0.34 0.29 0 .25

"( Dye quantity in residual solution I dye quantity on fibres)x I 00%

degree. Untreated raw polyester fibre shows 41.5 % degree of crystal, fibre treared at 250barx l20°Cx dye4%x lOmin in supercritical fluid shows 38.3% degree of crystal, fibre treated with DMF at 250barx I20°Cxdye4%xlOmin in super-critical fluid shows 36.2% degree of crystal, and fibre treated with DMSO at 250barx 120°Cxdye4%x lOmin in super­critical fluid shows 37.8% degree of crystal.

3.6 Colour Fastness Data on colour fastness to dry heating, washing, organic solvent, rubbing, xenon arc lamp light are shown in Table 3. For all the above fastness conditions, specimens show the same fastness for non-reduction and reduction cleaning. The residual solution after reducing wash was also measured using a Milton Roy 3000 spectrophotometer. Table 4 shows the dye quantity in the residual solution after reducing wash . The dye quantity of the washing solution is found to be <0.3% above 120°C. This indicates that the post-treatment is not necessary in the supercritical fluid dyeing processes.

4 Conclusions It is observed that the dyeing conditions for

microdenier polyester fabric are suitable at 250bar, 120°C and with suitable dye concentration by using decompress-compressing procedure. The solvents DMF and DMSO cou ld be the better choice as their boiling points are greater than dyeing temperature with better solvolysis power to selected dye. The DSC and X-ray analyses indicate no obvious damage for fabrics dyed at 250barxJ20°Cx 10min in the super­critical fluid . Dye fastness is satisfactory and reducing wash is not necessary. The proposed processes have

the potential for substantial energy sav ings and waste reduction as compared to existing methods. ft is ev ident that these researches are still a long way from the performance of existing process. The potenti al benefits of another hydrophobic material' s dyeing are great and the combination of materials and application techniques needs to be explored.

Acknowledgement The author would like to thank Ms Y C Ho for her

assistance during the experimental work and the National Science Council for financia lly supporting this research under Contract Number NSC 90-2216-E-035-007.

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