Ind. Eng. Chem. Res. 2006, 45, 3425-3433
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Solubility Measurement and Dyeing Performance Evaluation of Aramid NOMEX Yarn by Dispersed Dyes in Supercritical Carbon Dioxide Taehyoung Kim,† Gwansoo Kim,† Ji-Young Park,‡ Jong Sung Lim,† and Ki-Pung Yoo*,† Department of Chemical and Biomolecular Engineering, Sogang UniVersity, Seoul 121-742, South Korea, and Department of Chemistry, UniVersity of North Carolina, Chapel Hill, North Carolina 27599-3290
The solubility of various dispersed dyes in supercritical carbon dioxide was measured and, subsequently, based on the solubility data, the dry dyeing was conducted in a temperature range of 363.15-423.15 K and at pressures of 10-30 MPa. The target fibers are Aramid NOMEX yarn obtained from Du Pont, which is known to be difficult to use to perform wet dyeing, and the dispersed dyes include E-types of C. I. Dis Red 60, Blue 56, and Yellow 54 and S-types of C. I. Dis Red 360, Blue 79, and Yellow 114. Solubility data of the dispersed dyes in CO2 were correlated in terms of the density of carbon dioxide, using an empirical equation of Bartle et al. The highest color depth (K/S) of the dyed Aramid spun yarn was obtained when the experiment was performed at 423.15 K and 30 MPa. The adsorption isotherms were measured using the concentration of the three dyestuffs (E-types). These adsorption isotherms follow the Langmuir type. As a result of the supercritical fluid dyeing (SFD) for Aramid yarn with the three different dyestuffs, the dyeing stability of SFD was on the order of C. I. Dis Yellow 54, Blue 56, and Red 60. The mechanical properties (tensile strength, elongation, shrinkage) of Aramid spun yarn was only rarely changed by SFD. 1. Introduction Conventional water-based dyeing has been widely used in coloring synthetic textiles and yarn such as polyester, nylon, acetate, etc. However, this process has intrinsic environmental problems, because of the inevitable use of a large amount of water and the addition of various chemical additives.1 Recently, new dyeing technologies such as ultralow liquor ratio dyeing or foam dyeing have been studied to reduce wastewater. Among these modern technologies, supercritical fluid dyeing (SFD) is an unique method in which no water is used. SFD has been actively tested as a possible alternative process of the traditional water-based dyeing.2-4 Supercritical fluid, especially carbon dioxide, is a very attractive medium, because it is easily recyclable, nontoxic, chemically stable, and less expensive than conventionally used materials. Therefore, an increasing number of papers has been reported on the basic studies relating to SFD, such as solubility measurements of disperse dyes5-8 and the thermal and mechanical properties measurements9-12 of synthetic polymer textiles and yarns in supercritical carbon dioxide. For the past decade, much of the attention of government, industrial research and development (R&D) groups, and universities in Korea has been placed on the use of supercritical carbon dioxide for new environmental benign dyeing. In this work, the solubility of disperse dyestuffs in supercritical carbon dioxide was measured in situ, using a modified ultravioletvisible light (UV-Vis) spectroscopy method, along with optical fibers. Using these data, the dyeing was performed for the aramid yarn, which is well-known to be a nondyeable fiber with a newly designed bench-scale SFD system. Also, process variables on the dyeing level were evaluated at temperatures in the range of 365.15-423.15 K and pressures in the range of 10-30 MPa. Based on these results, a 50-L pilot-scale SFD has been designed and constructed. * To whom correspondence should be addressed. Tel.: (822)7057898. Fax: (822)781-0550. E-mail:
[email protected]. † Sogang University. ‡ University of North Carolina.
The most common dyeing process is the aqueous process, in which a dye is dispersed into water and dyed in the wet state. However, this wet dye process creates various problems. For example, strong basic chemicals and weak acids are added into the water in the preliminary dyeing process. Thus, the wastewater in dyeing process contains a significant amount of toxic chemicals and coloring agents. The inevitable polluting aspects of the textile industry have discouraged its further technological advancement. Therefore, one of the technological alternatives to solve pollution problem in traditional wet dyeing is dry dyeing in a supercritical solvent medium. Dry dyeing under a supercritical CO2 medium can be conducted without using basic and acidic chemicals.2,3 The SFD method is basically a nonaqueous procedure and, as a result, the discharge of wastewater can be completely prevented.4,5 Also, supercritical carbon dioxide dyeing is also possible for a hydrophobic fiber.6 We studied the dyeing properties of supercritical carbon dioxide using disperse dyes and aramid (Nomex) spun yarn that is generally known to be difficult to dye. To acquire dyeing property on Aramid (Nomex) spun yarn in the SFD, the SFD machine with a capacity of 0.5 L was designed and manufactured. C. I. Disperse Red 60, Yellow 54, and Blue 56 were used. The supercritical dyeing experiment was performed at temperatures and pressures ranging from 10 MPa and 363.15 K to 30 MPa and 423.15 K.7 In this work, the solubility of disperse dyestuffs in supercritical carbon dioxide was measured using modified in situ UV-Vis spectroscopy, along with optical fibers. Using these data, the dyeing was performed for the Aramid yarn, which is well-known to be a nondyeable fiber with a newly designed bench-scale SFD system. Also, the process variables on the dyeing level were evaluated at temperatures in the range of 363.15-423.15 K and pressures in the range of 10-30 MPa. 2. Theory 2.1. Beer-Lambert’s Law. It can be seen intuitively that the amount of light absorbed by a spectra in solution will be
10.1021/ie0507171 CCC: $33.50 © 2006 American Chemical Society Published on Web 12/06/2005
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dependent on the number of ions or molecules of the species in the pathway (light path) of a photon beam. It follows that more light will be absorbed as the concentration of the absorbing species increases. Similarly, the longer the light path followed by the photon beam through the solution, the more photons that are absorbed. The third factor that governs the amount of light absorbed is the probability of a photon being absorbed and causing an electronic transition in a chemical species. Different chemical species have different probabilities; the species with the highest probability will absorb more light than another species at the same concentration. These facts are the basis of the fundamental law of spectroscopy, which is known as the Beer-Lambert law or simply as Beer’s law. This law states that the amount of light or ultraviolet or infrared radiant energy absorbed or transmitted by a solution is an exponential function of the concentration of absorbing substance present and the sample path length. Suppose that a beam of light of radiant power P is passed through a solution containing N absorbing ions or molecules. The amount of light absorbed will be directly proportional to the number of absorbing species in the light path. If we divide the solution into a number of small, equal sections, the change in radiant power (∆P) will be dependent on the number of absorbing species in this section (∆N). The radiant power of the beam that enters succeeding sections will be diminished by the absorption by the preceding sections of solution. The amount of light absorbed by each section is dependent on the number of absorbing species in that section and is proportional to the radiant power of light entering that section. If the sections are infinitely small, the equation can be expressed as follows:
dP - ) kP dN
(1)
where k is a proportional constant. The minus sign indicates a decrease in the radiant power of the beam. If we rearrange and integrate between the limits P0 and P (the initial and final radiant power of the light beam) and between zero and N for the number of absorbing species in the light path, the following results are obtained: N ) -k∫0 dN ∫PP dP P
(2)
P ln ) -kN P0
(3)
0
(4)
If eq 2 is converted to base 10 logarithms and combined with eq 3, we get the following expression for Beer’s law:
log
P ) -abc P0
(5a)
P0 ) abc P
(5b)
log
solvent
wavelength (nm)
solvent
wavelength (nm)
acetic acid acetone acentonitrile benzene 1-butanol butyl acetate carbon disulfide cyclohexane ethanol ethyl acetate
260 330 190 280 210 254 380 210 210 255
glycerol heptane hexadecane hexane isobutyl alcohol methanol pentane pyridine toluene water
207 197 200 210 230 210 210 330 286 191
a Data from ref 14. Absorbance of 1.00 in a 10.0 mm cell versus distilled water.
as the wavelength changes. In other words, Beer’s law applies only to monochromatic radiant energy. The term log(P0/P) is commonly called the absorbance (or the optical density in older literature) and given the symbol A. Thus, eq 5b becomes The numerical value of the molar
A ) abc
(6)
extinction coefficient, a, is dependent on the units used to express the concentration of the absorbing solution. Concentration units such as parts per million (ppm), which is milligrams per liter or grams per 1000L, are often used. However, a different symbol, , is used in place of a when the concentration is expressed as molarity:
A ) lc
(7)
where is the molar extinction coefficient (known as the molar absorptivity), l the light path (in centimeters), and c the molar concentration of the absorbing species.13 2.2. Choice of Solvents. The solvent chosen must dissolve the sample, yet be relatively transparent in the spectral region of interest. To avoid poor resolution and difficulties in spectrum interpretation, a solvent should not be used for measurements that are near the wavelength of (or are shorter than) the wavelength of its ultraviolet cutoff, that is the wavelength at which absorbance for the solvent alone approaches one absorbance unit. Ultraviolet cutoffs for solvents commonly used are given in Table 1.14 3. Experiments
N is dependent on the concentration of absorbing species in solution (c) and the thickness of absorbing solution traversed by the light beam (b):
N ) k′cb
Table 1. Ultraviolet Cutoffs of Spectrograde Solventsa
where a is the proportionality constant, b the length of light path (in centimeters) through the solution, and c the concentration of absorbing species in the solution. The absorptivity a is characteristic of a particular absorbing species and will change
3.1. Reagents. C. I. Disperse dyes that contained neither dispersing agents nor surfactants supplied by Kyong-In Co. (Korea) were used. Aramid fiber was purchased from Dupont Co. (NOMEX type 450, USA). Carbon dioxide (purity 99%) was obtained from Daewoo Gas Co. (Kyonggi, Korea). 3.2. Solubility of Disperse Dye in Supercritical CO2. The concentration of disperse dyestuffs in supercritical CO2 (SCCO2) was determined from the absorbance using the BeerLambert law. To measure the absorbance of the dye solution through optical fibers (Thorlab Co., USA) in situ, a conventional UV-Vis spectrophotometer (S2000-UV-Vis, Ocean Optics, Inc., USA) with a pulsed xenon light source (PX-2, USA) and a fiber optic interface was used. The experimental apparatus is depicted in Figure 1. Hexane was used as the solvent to obtain the optical density of carbon dioxide, because it has a polarity similar to that of carbon dioxide. Hexane has been shown to exhibit a similar extinction coefficient and negligible shifts in the position of absorption maxima.
Ind. Eng. Chem. Res., Vol. 45, No. 10, 2006 3427
Figure 1. Schematic diagram of the experimental apparatus for in situ measurement of ultraviolet-visible-light (UV-Vis) absorbance.
3.3. Correlation with Calculated Data. 3.3.1. MF-NFL Equation of State. The configurational Helmholtz free energy for a general mixture is written as c
βAc ) z
∑ i)1
Ni ln Fi + No ln(1 - F) -
[ ( ) ] ( )∑
Nq ln 1 +
2
qM rM
-1 F -
zNq
c
2
i)1
θjτji) + βii] ∑ j)0
(8)
where [qM ) ∑ xiqi], [rM ) ∑ xir]i, [F ) ∑ Fi], [Fi ) Vi*/V], [Vi* ) NariVH], and xi is the mole fraction of species i. The summation covers all molecular species. From the Helmholtz free energy given by eq 8, expressions of other thermodynamic properties can be obtained in a straightforward manner. Because the volume V is represented by the relation V ) VH(No + ∑iNiri), the equation of state (EOS) is obtained by
P) z
{ [ ( )] ∑ ( ) ∑ (∑ ∑ z
1
ln 1 +
βVH 2 c
2 i)1
θi
qM rM
τ0i
c k)0
- 1 F - ln(1 - F) +
-1 +
θkτki
z
c
2 i)1
θi
τ0i
c k)0
-1 θkτki
)}
(9)
If we set the subscripts i ) 1 and j ) 0, eqs 8 and 9 are reduced to the expressions for pure fluids. Because the system volume V is represented by the relation V ) VH(No + N1r1), the EOS for pure fluids is obtained from the relation described by eq 9:
P)
{ [ ( )]
q1 1 z - 1 F - ln(1 - F) + ln 1 + βVH 2 r1 z 2 τ01 - 1 θ 2 1 θ0τ01 + θ1
(
)}
[ () [ ()
11 T0 ) Ea + Eb(T - T0) + Ec T ln + (T - T0) k T ri ) Ra + Rb(T - T0) + Rc T ln
c
θi[ln(
size parameters (), which are determined using the critical conditions of a pure component:
where θ0 ) 1 - θq. The model EOS basically required four pure parameters, such as the coordination number (z), the unit lattice cell volume (VH), the molecular size (V/i ), and energy (ii). However, in practice, the authors set the coordination number to a value of z ) 10 and the unit lattice cell volume to a value of VH ) 9.75 cm3/ mol, following previous studies. Then, there are two molecular
T0 + (T - T0) T
(11) (12)
where T0, which has a value of 273.15 K, is a reference temperature.15 3.3.2. Empirical Equation. Although the prediction of solubility in supercritical fluids is difficult and not very accurate, a simple semiempirical method16 was used for the correlation of the experimental data. The correlation equation is given in eq 13:
ln
( )
xP ) A + c(F - Fref) Pref
(13)
where x is the mole fraction (solubility), P is the system pressure, A and c are constants, Pref is a reference pressure (Pref ) 1 bar), F is the density of the solution, and Fref is a reference density (Fref ) 700 kg/m3). The reason for using Fref is to make the value of A much less sensitive to experimental error in the data and to avoid the large variations caused by extrapolation to zero density. A is given by
A)a+
b T
(14)
where T is the absolute temperature. Combining eqs 13 and 14, the correlation equation becomes
ln (10)
] ]
( )
b xP ) a + + c(F - Fref) Pref T
(15)
From the experimental data, each isotherm must be fitted using eq 13 to obtain the values of A and c. The values of c were then averaged for each dye. Afterward, the isotherms are refitted to obtain new value of A, using the averaged values of c. 3.4. Supercritical Fluid Dyeing. A newly designed system for SFD is presented in Figure 2. The system consists of a gas booster (Haskel Co., USA), a dyeing vessel, a dye storage vessel (RTI Eng. Co., Ltd., Korea), and high pressure/temperature centrifugal pump (Autoclave Engineers, USA).
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Figure 2. Schematic diagram of the bench-scale supercritical fluid dyeing (SFD) system used in this study. Table 2. Physical Properties and Formula of C. I. Disperse Dyestuffs
dyestuff
chemical constitution
melting temperature, Tm (°C)
molecular weight, Mw
C.I. Disperse Red 60 C.I. Disperse Blue 56 C.I. Disperse Yellow 54
E Type (Mild) anthraquinone anthraquinone quinoline
187 199 270
331.32 365.18 289.28
C.I. Disperse Red 360 C.I. Disperse Blue 79.1 C.I. Disperse Yellow 114
S Type (Thick) monoazoic monoazoic monoazoic
146 146 205
440.45 530 424.43
The dyeing carrier winded by Aramid yarn was connected to the bottom of the dyeing vessel, and the dye vessel was filled with glass beads and dyestuff. After the vessel was sealed, carbon dioxide was fed into the entire system, using a gas booster, and the temperature of the system was increased to the required value, using a heating jacket (attached to the dyeing vessel) and a heating band (attached to the process line) with the proportional integral derivative (PID) controller. The circulation pump then was operated for 1 h. 3.5. Properties of Aramid Yarn after Supercritical Fluid Dyeing. To examine the change in mechanical properties of the Aramid yarn before and after SFD, UTM (Instron 5565, Instron Co., USA) was used. After the Aramid yarn was dyed in SC-CO2, a reductive post-treatment was performed. The color strength (K/S) of the dyed Aramid yarn, using SFD, then was estimated from the reflectances of the fibers measured with a spectrophotometer (Datacolor SF-600, USA). The K/S value was calculated using the Kubelka-Munk equation: K/S ) (1 - R)2/2R, where R is the reflectance of the fiber, K the coefficient of absorption of the dye, and S the coefficient of scattering.8 Also, various types of fastness of dyed yarn were measured. Weather-O-Meter (CI 4000, Atlas Electric Devices Co., USA) was used for light fastness, Launder-O-Meter (LP2, Atlas Electric Devices Co., USA) was used for washing fastness, Crock meter (CM-5, Atlas Electric Devices Co., USA) was used for rubbing fastness, and Scorch Tester (DL-2014, Daelim Starlet, Korea) was used for sublimation fastness. 3.6. Materials. Presscakes of C. I. Disperse dyestuffs, which did not include any additives such as dispersant, anti-static agent, etc., were obtained from Kyung In Yang Heang Co. (Seoul, Korea) and used directly without further purification. Its physical properties and formula of disperse dyestuffs are listed in Table
Figure 3. Chemical structures of E-type C. I. Disperse dyestuffs used in this work.
Figure 4. Chemical structures of S-type C. I. Disperse dyestuffs used in this work.
2 and described in Figures 3 and 4. CO2 (>99.9% purity) was purchased from Dae Woo Gas Co. (Seoul, Korea). n-Hexane (HPLC grade, >99.9% purity) was purchased from Mallinckrodt Baker Inc. (Phillipsburg, NJ). Acetone (high-performance liquid chromatography (HPLC) grade, >99.9% purity) was purchased from Aldrich Chemical Company (Milwaukee, WI). They were used directly without further purification. The physical properties and formula of solvents are listed in Table 3. 4. Results and Discussion 4.1. Solubility of Disperse Dye in Supercritical CO2. The solubility of C.I Disperse dyes in CO2 were measured at
Ind. Eng. Chem. Res., Vol. 45, No. 10, 2006 3429 Table 3. Physical Properties and Formula of Solvents solvent
formula
Mw
F
TC (K)
PC (MPa)
Tb (K)
dipolar moment (debye)
acetone benzene ethanol n-hexane carbon dioxide
CH3COCH3 C6H6 CH3CH2OH CH3(CH2)4CH3 CO2
58.08 78.11 46.07 86.17 44.01
0.792 0.879 0.789 0.659 0.713a
508.2 562.16 513.92 507.6 304.19
4.71 4.88 6.12 3.04 7.38
329.65 353.25 351.55 342.15
2.9 0.0 1.7 0.0 0.0
a
Data obtained at 298.15 K and 0.43 MPa.
Figure 5. Comparison of measured data with correlated values calculated with MF-NLF EOS for CO2 + C. I. Disperse Yellow 54.
temperatures of 333.15, 363.15, and 393.15 K and pressures in the range of 10-30 MPa. They were compared with calculated values using the MF-NLF EOS in Figures 5 and 6. To confirm the reliability of experimental data obtained from newly designed apparatus for measuring the in-situ solubility of disperse dyestuffs in SC-CO2, we compared the experimental solubility data of C. I. Disperse Red 60 with the literature values.7 As shown in Figure 7, our experimental data agreed well with the literature data from Shim et al.7 The results of the measurement for C. I. Disperse Yellow 54 are shown in Figure 8. The solubility of disperse dye in SC-CO2 increased as the density of the carbon dioxide increased. 4.2. Process Optimization and Adsorption Isotherms of SFD. To obtain the optimum conditions of pressure and temperature, SFD with C. I. Disperse Red 60 was performed at
various pressures and temperatures, in the ranges of 10-30 MPa and 363.15-423.15 K, respectively. The results were shown in Figures 9 and 10, respectively. The color strength (K/S) has a tendency to increase with increasing pressure and temperature of the dyeing condition. Especially, the most deep dyeing result was obtained at 423.15 K and 30 MPa. The K/S value under these conditions is 0.57, which is much more than the value of 0.2-0.25 observed for other conditions. This seems to be due to two reasons: one is higher solubility of the dyes at high pressure and temperature of carbon dioxide, and the other is the mobility and free volume of a polymer. At higher temperature, the free volume of a polymer increases and it is easier to adsorb a molecule of a dyestuff under these conditions than at lower temperature. Also, SFD experiments at 423.15 K and 30 MPa were performed with various concentration of a dye (denoted as owf, which means “on the weight of fiber”). In addition, three adsorption isotherms for three types of disperse dyes were obtained (DR60, DY54, and DB56). The dyeing process that is being considered is dyesolute f dyesolution f dyefiber, where the rate of dyeing is controlled by the adsorption rate constant. This rate constant is dependent on the time, the dyeing temperature, the dye used, the type of fiber, and circulation rate.9 In addition, there are three types of adsorption isotherms in the dyeing process: the Henry, Freundlich, and Langmuir isotherms.10 As shown in Figures 11-13, the color strength increases with the concentration of dye and, above a certain concentration of dye, a constant K/S value were observed. Therefore, SFD studied in this work seems to follow the Langmuir isotherm. The higher color strength was obtained in the following order: DY54 > DB56 > DR60. It was found that the K/S value (color strength) is dependent on temperature, pressure, and dye concentration. Figure 14 shows the K/S value versus pressure at four different temperatures. It was found that the highest K/S
Figure 6. Comparison of measured data with correlated values calculated with MF-NLF EOS for CO2 + C. I. Disperse Red 60.
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Figure 7. Comparison of solubility of dye C. I. Disperse Red 60 in supercritical fluids measured in this work with literature data: (2) data reported by Shim et al.19 and (O) data obtained in this work.
Figure 8. Solubility data for C. I. Disperse Yellow 54 (DY54) in SCCO2.
Figure 9. Relationship between color strength (K/S) and pressure (given in units of MPa) with 0.5% (owf) of C. I. Disperse Red 60 (DR60) in SFD (150 °C, 60 min).
value was obtained at 30 MPa and 423.15 K. Therefore, we could decide that, among our experimental conditions, the best conditions for SFD are 30 MPa and 423.15 K. 4.3. Properties of Aramid Yarn after Supercritical Fluid Dyeing. Recently, an increasing number of papers has been reported on the effect of SC-CO2 on synthetic polymeric fibers.
Figure 10. Relationship between color strength (K/S) and temperature (given in units of °C) with 0.5% (owf) of DR60 in SFD (30 MPa, 60 min).
Figure 11. Relationship between color strength (K/S) and concentration of DR60 for Aramid yarn in SFD (30 MPa, 150 °C, 0.5% owf).
Figure 12. Relationship between color strength (K/S) and concentration of DY54 for Aramid yarn in SFD (30 MPa, 150 °C, 0.5% owf).
A greater amount of shrinkage of polypropylene (PP) and poly(ethylene terephthalate (PET) fiber was observed in carbon dioxide than in air. Carbon dioxide is able to penetrate into hydrophobic fibers such as PP, polyethylene (PE), and PET and acts as a good solvent. Moreover, carbon dioxide can increase the crystallinity of a various polymers without changing the melting temperature.
Ind. Eng. Chem. Res., Vol. 45, No. 10, 2006 3431 Table 4. Fastness Properties of Aramid Yarn Dyed by SFD with Driperse Dyes Washing Staining
Rubbing
sample
A
C
N
P
Ac
W
fade
C. I. Disperse Red 60, 0.5% (ARAMID) C. I. Disperse Blue 56, 0.1% (ARAMID) C. I. Disperse Yellow 54, 0.5% (ARAMID) C. I. Disperse Red 60 Wet dyeing, 0.5% (ARAMID)
5 4-5 4-5 4-5
5 5 4 5
5 4 4 4-5
5 4-5 4-5 5
5 5 5 5
5 4-5 5 5
4-5 4-5 5 4
4-5 4-5 4-5 4-5
light
sublimation
1 1 1 1
4-5 4-5 3-4 3-4
5 4 4 4-5
Table 5. Fastness Properties of Aramid Yarn Dyed by SFD with Disperse Red 60 Red 60 fastness washing stain acetate cotton nylon PET acrylic wool fade rubbing dry wet light sublimation Figure 13. Relationship between color strength (K/S) and concentration of DB56 for Aramid yarn in SFD (30 MPa, 150 °C, 0.5% owf).
0.5% (owf)
3.0% (owf)
4 5 4 4-5 5 5 4-5
3 4-5 3 4-5 5 5 3-4
4-5 4-5 1 3
4 4 1 2-3
Table 6. Fastness Properties of Aramid Yarn Dyed by SFD with Disperse Yellow 54 Yellow 54 fastness washing stain acetate cotton nylon PET acrylic wool fade rubbing dry wet light sublimation
0.5% (owf)
3.0% (owf)
4 5 4 4-5 4 4-5 4-5
3-4 5 3-4 4-5 4 4-5 4
5 5 1 3-4
4-5 4-5 1 3
Table 7. Fastness Properties of Aramid Yarn Dyed by SFD with Disperse Blue 56 Figure 14. Change of K/S value (color strength), relative to changes in pressure and temperature, in DR60 (0.5 owf).
To determine the optimum conditions for SFD without causing damage to the fiber properties, the mechanical properties of Aramid fiber before and after SFD were measured. The amount of change in tenacity and elongation of Aramid fiber is not significant. Especially, it is very difficult to obtain a reproducible mechanical property of spun yarn. In addition, the weight change and shrinkage by SFD were not observed, unlike PET. It can be concluded that SFD did not give any mechanical damage to Aramid yarn. The fastness properties of Aramid spun yarn dyed in SC-CO2 are summarized in Tables 4-7. As shown in these tables, most of fastness properties are >4. However, the light-fastness of Aramid (NOMEX) spun yarn dyed is 1. It is caused by the intrinsic characteristic of NOMEX spun yarn. When the light fastness of the undyed NOMEX spun yarn was tested, the result is shown in Figure 15. It is concluded that the color fastnesses for the sublimation of the dyes from the dyed Aramid spun yarn are not good.
Blue 56 fastness washing stain acetate cotton nylon PET acrylic wool fade rubbing dry wet light sublimation
0.5% (owf)
3.0% (owf)
4 4-5 3-4 4-5 5 4-5 3-4
4 4-5 3-4 4-5 5 4-5 3-4
5 4-5 1 3-4
4-5 4-5 1 4-5
4.4. Design Consideration and Construction of a PilotScale Supercritical Fluid Dyeing System. As studied on a bench-scale SFD for Aramid (NOMEX) spun yarn with E-type disperse dye, when the SFD was performed at 150 °C and 30 MPa, the deepest dyed yarn could be obtained. Therefore, the newly designed pilot-scale SFD system can be used safely at
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Figure 15. Tenacity (in units of g/den) and elongation (expressed as a percentage) of Aramid yarn before and after SFD.
180 °C and 35 MPa. The capacity of the dyeing vessel is 50 L. The SFD system consists of a dyeing vessel, a dye-dissolving vessel, a centrifugal pump, a two-stage separator, a gas booster, and a carbon dioxide storage tank. It is possible to recycle the carbon dioxide used for dyeing by using a separator and a carbon dioxide storage tank. In the previous work,17,18 it was confirmed that the circulation flow rate of dye solution was the one of most important variable for SFD. When the piston-type metering pump was used for SFD, it is easy to be out of order in the piston O-ring. In addition, it is very difficult to obtain an even dyeing, especially for a filament yarn such as polyester. The outside of the fiber, which was wound to a carrier, was dyed deeply, but the inside of the fiber was not. It seems to be due to small capacity of the pump. This problem could partly be solved by the pretreatment of the fiber and enlargement of the process line size. When the heat-setting of the fiber was performed before SFD, more uniformly dyed fiber could be obtained. In addition, the piston pump was replaced with a centrifugal pump, which had higher capacity and greater resistance to high pressure and temperature. Therefore, when the pilot-scale SFD system was designed and constructed, the centrifugal pump was used. A continuously stirred tank reactor (CSTR) with a size of 1 L was used as the dye storage vessel in front of the centrifugal pump. Because of the high mixing power of the CSTR, a faster dissolution time of the dye was accomplished. It has reported that a nonuniform and light dyeing could be caused by the melting of the disperse dyestuff.19 These problems can be overcome when the CSTR (the dye storage vessel) was connected to the suction line of the pump. 5. Conclusions The bench-scale supercritical fluid dyeing (SFD) for Aramid (NOMEX) with disperse dyestuffs was performed under various conditions. Based on the experiments in this work, the following conclusions were obtained:
(1) An in situ measurement apparatus that used optical fiber for the solubility of dyestuffs in supercritical CO2 (SC-CO2) was manufactured. (2) The solubility of C. I. Disperse Yellow 54 in SC-CO2 was experimentally determined. (3) The highest color strength (K/S, where K is the coefficient of absorption of the dye and S is the coefficient of scattering) of the dyed Aramid spun yarn was obtained when the experiment was performed at 150 °C and 30 MPa. (4) The adsorption isotherms were obtained with the concentration of the three dyestuffs. (5) These adsorption isotherms are Langmuir type. (6) The dyeability of SFD with dyestuffs was better, in the order of DY54 > DB56 > DR60. (7) Mechanical properties (tensile strength, elongation, shrinkage) of Nomex spun yarn were rarely changed in SFD. (8) The fastness properties of the dyed yarn were fair, except for light fastness and color fastness for sublimation. (9) The light fastness of undyed NOMEX yarn was 1. The pilot-scale SFD system was newly designed and constructed. The design data needed for a SFD pilot were obtained from the experiments of a bench-scale SFD system: (1) The design pressure and temperature of the pilot-scale SFD system are 35 MPa and 180 °C, respectively. (2) The capacity of the dyeing vessel was designed to be 50 L, and shape of the dyeing vessel was the vertical type. (3) A centrifugal pump with high capacity (70 L/min) and great resistance to high pressure and temperature was used as a circulation pump. (4) It is possible to change the circulation direction of the dye solution and recycle the carbon dioxide used for SFD. Acknowledgment The authors gratefully acknowledge financial support from the Korea Ministry of Commerce, Industry and Energy and the Korea Energy Management Corporation. The authors also gratefully acknowledge financial support from the ERC program from the Korea Ministry of Science and Technology. Literature Cited (1) Kim, N. S. The Chemistry of Dyes; Korea, 1994; p 387. (2) Bach, E.; Cleve, E.; Schollmeyer, E. The Dyeing of Polyolefin Fibers in Supercritical Carbon Dioxide, Part I: Thermo-mechanical Properties of Polyolefin Fibers after Treatment in CO2 under Dyeing Conditions.J. Text. Inst. 1998, 89, 647. (3) Kawahara, Y.; Kikutani, T.; Sugiura, K.; Ogawa, S. Dyeing Behaviour of Poly(ethylene terephthalate) Fibres in Supercritical Carbon Dioxide. Color. Technol. 2001, 117, 266. (4) Guzel, B.; Akgerman, A. Mordant Dyeing of Wool by Supercritical Processing. J. Supercritical Fluids 2000, 18, 247. (5) Joung, S. N.; Yoo, K. P. Solubility of Disperse Anthraquinone and Azo Dyes in Supercritical Carbon Dioxide at 313.15 to 393.15 K and from 10 to 25 MPa. J. Chem. Eng. Data 1997, 42, 9. (6) Ozcan, A. S.; Clifford, A. A.; Bartle, K. D. Solubility of Disperse Dyes in Supercritical Carbon Dioxide. J. Chem. Eng. Data 1997, 42, 590. (7) Sung, H. D.; Shim, J. J. Solubillity of C. I. Disperse Red 60 and C. I. Disperse Blue 60 in Supercritical Carbon Dioxide. J. Chem. Eng. Data 1999, 44, 985. (8) Muthukumaran, P.; Gupta, R. B.; Sung, H. D.; Shim, J. J.; Bae, H. K. Dye Solubility in Supercritical Carbon Dioxide. Effect of Hydrogen Bonding with Cosolvents. Korean J. Chem. Eng. 1999, 16, 111. (9) Hohne, G. W. H. High pressure differential scanning calorimetry on polymers. Thermochim. Acta 1999, 332, 115. (10) von Schnitzler, J.; Eggers, R. Mass Transfer in Polymers in a Supercritical CO2-atmosphere. J. Supercritical Fluids 1999, 16, 81. (11) Kim, H. S.; Lee, J. H.; Joung, S. N.; Yong, K. J.; Park, Y. H.; Yoo, K. P. Effect of Supercritical Carbon Dioxide Environment on the Mechanical Properties of Synthetic Fibrous Materials. In Proceedings of
Ind. Eng. Chem. Res., Vol. 45, No. 10, 2006 3433 the 5th Kyushu-Sogang International Conference on Thermodynamics and Supercritical Fluids; 2002, Vol. 5, p 59. (12) Lee, J. H.; Kim, K. S.; Kim, S. Y.; Yoo, K. P. Effect of Supercritical Carbon Dioxide State Conditions on the Alteration of Thermal Properties of Solid State Polymers. In Proceedings of the 5th Kyushu-Sogang International Conference on Thermodynamics and Supercritical Fluids; 2002, Vol. 5, p 68. (13) Frits, J. S.; Schenk, G. H. QuantitatiVe Analytical Chemistry, 5th Edition; Allyn and Bacon: Boston, 1996; pp 340-343. (14) Dean, J. A. Lange’s Handbook of Chemistry, 5th Edition; McGrawHill: New York, 1999; pp 718-720. (15) Joung, S. N.; Yoo, C. W.; Shin, H. Y.; Kim, S. Y.; Yoo, K-. P.; Lee, C. S. and Huh, W. S. Measurements and correlation of high-pressure VLE of binary CO2-alcohol systems (methanol, ethanol, 2-methoxyethanol and 2-ethoxyethanol). Fluid Phase Equilib. 2001, 185, 219. (16) Bartle, K. D.; Clifford, A. A.; Jafer, S. A. Solubilities of solids and liquids of low volatility in supercritical carbon dioxide. J. Phys. Chem. Ref. Data 1991, 20, 713.
(17) Joung, S. N.; Kim, H. S.; Yoo, K.-P.; Park, Y. H. Dry Dyeing of Polyester Textile and Fiber in Supercritical Carbon Dioxide. In Proceedings of the 5th Kyushu-Sogang International Conference on Thermodynamics and Supercritical Fluids; 2002, Vol. 5, p 39. (18) Joung, S. N.; Kim, H. S.; Yoo, K.-P.; Kim, S. Y.; Yong, K. J.; Park, Y. H. The dyeing of polyester Textile in Supercritical Carbon Dioxide. In The 6th Annual Green Chemistry and Engineering Conference Proceedings, Georgetown University, Washington, DC, 2002; p 161. (19) Bach, E.; Cleve, E.; Schollmeyer, E. Experience with the Uhde CO2-Dyeing plant on technical scale. Melliand Int. 1998, 192.
ReceiVed for reView June 15, 2005 ReVised manuscript receiVed October 25, 2005 Accepted October 27, 2005 IE0507171
