Synthesis and Measurement of Solubilities of Reactive Disperse Dyes

Article pubs.acs.org/IECR

Synthesis and Measurement of Solubilities of Reactive Disperse Dyes for Dyeing Cotton Fabrics in Supercritical Carbon Dioxide Dan Gao, Da-fa Yang, Hong-sheng Cui, Ting-ting Huang, and Jin-xin Lin* Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002, People’s Republic of China S Supporting Information *

ABSTRACT: Solubilities of the reactive disperse dyes synthesized with the reactive group of 1,3,5-trichloro-2,4,6-triazine were investigated in supercritical carbon dioxide (SC-CO2) at pressures of 10.0−25.0 MPa, temperatures of 333.2−393.2 K, and equilibrium contact time of 60 min. Meanwhile, dyeing experiments of cotton fabrics by using these dyes were performed at 373.2 K and 20.0 MPa for 60 min with a dye concentration of 0.5% owf in SC-CO2. Solubilities of these dyes increased with increasing pressure and decreasing temperature. Additionally, the color strength and the color fastness of dyed cotton fabrics were measured, and reasonably good dyeing effects were obtained. Furthermore, the color characteristics of dyed cotton fabrics were studied in terms of the reflectance spectra, and their surface morphologies were investigated by SEM as well.

1. INTRODUCTION Supercritical carbon dioxide (SC-CO2) dyeing technology has received extensive attention in the textile industry due to sustainable development and environmental concerns, as reflected by a number of research papers dedicated in this field.1−4 This dyeing method has many advantages over conventional aqueous dyeing. Notably, carbon dioxide is nontoxic, nonflammable, and recyclable; dyes can be collected for reuse, and no other chemical is required; in addition, energy can be saved because no substrate-drying process is needed, and the dyeing cycle is shorter than that of traditional methods.5,6 The solubility of a dye has a direct impact on the design and economy of dye in SC-CO2 and determines the transport rate from the SC-CO2 to the textile, thus greatly affecting the velocity of dye diffusion into the textile as well as the rate of dye adsorption, uptake, color strength, and final coloration quality on the textile.7 Basically, a higher solubility of dye in SC-CO2 favorably promotes dyeing efficiency. To design and develop a proper dyeing process, systemic and competent solubility data of dyes are necessary. Therefore, it is a prerequisite to measure a reliable solubility of dye for application of SC-CO2 dyeing technology in the textile industry. Solubility data for different dyes in SC-CO2 have been reported by several groups,8−14 most reports describing solubilities of disperse dyes in dyeing synthetic fibers.15−23 However, a greater challenge in SC-CO2 dyeing is the coloration of natural fibers, especially cotton fabrics. To achieve a good dyeing performance for cotton fibers, one strategy is the development of CO2-soluble reactive disperse dyes with reactive groups that are able to react with the cotton fibers by forming chemical bonds. Whereas the conventional reactive dyes generally have poor solubility in SCCO2, the reactive disperse dyes manifest not only sufficient dye solubility in SC-CO2 but also increased power of permanent dyestuff fixation on fibers and improved color fastness properties. Solubilities of reactive disperse dyes, however, have been rarely documented.24 © 2014 American Chemical Society

So far, many different reactive groups (triazine, bromoacrylic acid, vinylsulfone, halogenated acetamide) on reactive disperse dyes have been researched,25−28 and the dyeing effect of cotton was improved when dyed by the above reactive disperse dyes, but important reactive groups used in dyeing processes for cotton in SC-CO2 were based on triazine. In this work, reactive disperse dyes with a 1,3,5-trichloro2,4,6-triazine group were synthesized and their solubilities in SC-CO 2 were subsequently measured by a dynamic− recirculation apparatus having a visible window for real-time observation of the dissolution situation of dyes. The solubilities of these dyes in SC-CO2 were investigated at pressures from 10.0 to 25.0 MPa, temperatures from 333.2 to 393.2 K, and an equilibrium contact time of 60 min, respectively. In addition, dyeing experiments for cotton fabrics with these dyes in SCCO2 were carried out at 373.2 K and 20.0 MPa for 60 min with a dye concentration of 0.5% owf (percent on weight of cotton fabric).

2. EXPERIMENTAL SECTION 2.1. Materials. All chemicals used for synthesis of the reactive disperse dyes were purchased from Energy Chemical Co. The carbon dioxide gas (99.6 vol %) obtained from Fuzhou Huaxinda Industrial Gases Co., Ltd., was used for SC-CO2 dyeing and measurement of solubility. Cotton fabric (20.0 g of fabric sample with a dimension of about 10.0 cm × 200.0 cm) used in this study was obtained from Shandong Weiqiao Pioneering Group Co., Ltd. The reactive disperse dyes were synthesized in our laboratory and were carefully isolated, purified, and characterized by 1H NMR and MS. 2.2. Instruments. 1H NMR spectra were recorded on Bruker-Biospin 400 spectrometer using DMSO-d6 as the solvent and TMS as internal standard. Mass spectra were Received: Revised: Accepted: Published: 13862

June 24, 2014 August 14, 2014 August 24, 2014 August 24, 2014 dx.doi.org/10.1021/ie5025497 | Ind. Eng. Chem. Res. 2014, 53, 13862−13870

Industrial & Engineering Chemistry Research

Article

Scheme 1. Synthesis of Dye 1


Compound 1a (0.01 mol, 2.98 g) dissolved in ethanol (200 mL) was added dropwise to a solution of Na2S·9H2O (0.02 mol, 4.8 g) in water (100 mL). The mixture solution was refluxed for 3−4 h. On completion of the reaction, it was poured into 200 mL of cold water to obtain a precipitate. The precipitate was filtered off, washed with water, and dried, and a deep orange powder, 1b, was obtained, 2.04 g (yield = 76%). Compound 1b (0.005 mol, 1.35 g) was dissolved in a mixture of 1,4-dioxane (150 mL) and water (50 mL), and the mixture was cooled to 0 °C. A solution of 1,3,5-trichloro-2,4,6-triazine (0.005 mol, 0.92 g) in 1,4-dioxane (20 mL) was added dropwise to the mixture, while the temperature was maintained at 0 °C, and the pH value of the mixture solution was adjusted to 6−7 by adding sodium carbonate. Over 2−3 h, the reaction was completed and the mixture solution was restored to room temperature. Precipitate was obtained by adding 300 mL of water, then was filtered, washed with water, and dried. Finally, the product was collected and purified by recrystallization with DMF to obtain a deep yellow powder, dye 1, 1.95 g (yield = 94%, purity = 98%). The IUPAC name is (4,6-dichloro-

performed employing a Thermo-Finnigan ion trap mass spectrometer. Reflectance spectra were measured via a Lambda 900 UV−vis spectrophotometer using BaSO4 as a white standard. The surface morphologies were observed on a scanning electron microscope (SEM) of Phenom G 2. The melting points were measured by a Netzsch differential scanning calorimeter. 2.3. Dye Synthesis. 2.3.1. Synthesis of Dye 1. The synthesis of dye 1 is shown in Scheme 1. 4-Nitroaniline (0.02 mol, 2.76 g), NaNO2 (0.022 mol, 1.52 g), and concentrated HCl (4.8 mL) in 200 mL of water were vigorously stirred at a temperature of 0−5 °C. After 3−4 h, the diazotization completed, the pH value of the diazonium salt solution was adjusted to 5−6 by adding sodium acetate. After that, a corresponding coupling component N,N-diethylaniline (0.02 mol, 3.0 g) in 20 mL of methanol was added dropwise to the solution and stirred for 3−4 h at 0−5 °C until the reaction finished. A precipitate was obtained by adding 400 mL of water. Then, the precipitate was filtered, washed with water, and dried to obtained a red powder, 1a, 5.42 g (yield = 91%). 13863

dx.doi.org/10.1021/ie5025497 | Ind. Eng. Chem. Res. 2014, 53, 13862−13870


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Figure 1. SC-CO2 apparatus: (1) CO2 cylinder; (2) refrigerating machine; (3) heat exchanger; (4) cooling unit; (5) liquid pump; (6) high-pressure syringe pump; (7, 11) preheater; (8) dyeing autoclave/dyestuff vessel; (9) flow gauge; (10) CO2 circulating pump; (12) cold trap; (13−21) valves; (22) main controller.

= 91%, purity = 95%). The IUPAC name is 4-[4-(4,6-dichloro[1,3,5]triazin-2-ylamino)-phenylazo]-5-methyl-2-phenyl-2,4-dihydro-pyrazol-3-one. TLC analysis showed one product spot (Rf = 0.32; ethyl acetate/hexane = 1:2): 1H NMR (400 MHz, DMSO-d6), δ 1.23 (s, 3H), 2.77 (s, 1H), 7.20−7.24 (t, 1H), 7.44−7.48 (t, 2H), 7.65−7.69 (d, 4H), 7.92−7.94 (d, 2H), 11.24 (s, 1H); MS, m/z 439.0 (M+); melting point, 513.2 K. 2.3.3. Synthesis of Dye 3. The synthesis of dye 3 is shown in Scheme 3. Disperse orange 3 (0.01 mol, 2.42 g) was dissolved in ethanol (200 mL), and then Na2S·9H2O (0.02 mol, 4.8 g) in water (100 mL) was added dropwise to the ethanol solution and refluxed for 3−4 h. After the reaction reached completion, the mixture solution was concentrated and then diluted with 100 mL of water. The aqueous solution was extracted with ethyl acetate three times. The combined organic phase was concentrated and dried to obtain a deep yellow powder, 1c, 1.51 g (yield = 71%). Compound 1c (0.005 mol, 1.06 g) was dissolved in a mixture of 1,4-dioxane (150 mL) and water (50 mL), and the mixture was cooled to 0 °C. A solution of 1,3,5-trichloro-2,4,6-triazine (0.01 mol, 1.85 g) in 1,4-dioxane (40 mL) was added dropwise to this mixture, which was kept at 0 °C and adjusted to pH 6−7 by using sodium carbonate. After 3−4 h, the reaction was completed and restored to room temperature. The precipitate was obtained by adding 300 mL of water and then was filtered, washed with water, and dried. The pure dye was obtained by recrystallization in DMF and was a yellow powder, dye 3, 2.28 g

[1,3,5]triazin-2-yl)-[4-(4-diethylamino-phenylazo)-phenyl]amine. TLC analysis showed one product spot (Rf = 0.63; ethyl acetate/hexane = 1:2): 1H NMR (400 MHz, DMSO-d6), δ 1.12−1.15 (t, 6H), 3.44−3.46 (m, 4H), 6.80 (s, 2H), 7.74−7.82 (m, 6H), 11.39 (s, 1H); MS, m/z 414.3 (M+); melting point, 427.1 K. 2.3.2. Synthesis of Dye 2. The synthesis of dye 2 is shown in Scheme 2. The same procedure by the diazotization reaction was performed as described above. Then, a corresponding coupling component, 3-methyl-1-phenyl-5-pyrazolone (0.02 mol, 3.5 g), in 30 mL of methanol was added dropwise to a diazonium salt solution and stirred for 3−4 h at 0−5 °C. On completion of the reaction, the mixture solution was poured into 400 mL of water to obtain a precipitate, and then the precipitate was filtered, washed with water, and dried to obtained an orange-red powder, 2a, 5.62 g (yield = 87%). Compound 2b was synthesized according to a procedure similar to that usef for 1b. Upon completion of the reaction, the mixture solution was concentrated to remove ethanol and then diluted with 100 mL of water. The aqueous solution was extracted with dichloromethane three times. The combined organic phase was concentrated and dried to obtain a red powder, 2b, 2.14 (yield = 73%). The last procedure by the condensation reaction of compound 2b and 1,3,5-trichloro2,4,6-triazine was similar to that of 1b. The purification was achieved by recrystallization with DMF and gave a solid, dried. The final compound was an orange powder, dye 2, 2.01 g (yield 13864



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concentration of 0.5% owf. After the dyeing autoclave had been sealed, high-pressure CO2 was introduced into the whole system before it was heated and circulated. The dyeing pressure in the autoclave was initially 5.0 MPa and, after a period of approximately 20 min, adjusted to the desired pressure of 20.0 MPa for another 60 min at 373.2 K. When the dyeing was completed, the SC-CO2 equipment was stopped and allowed to cool to normal temperature and pressure. Finally, the autoclave was opened and the dyed cotton fabric was removed from the vessel to measure the color fastness and color strength. Figure 2 is a photograph of three synthesized reactive disperse dyes and cotton fabrics dyed with these dyes.

(yield = 90%, purity = 93%). The IUPAC name is {4-[4-(4,6dichloro-[1,3,5]triazin-2-ylamino)-phenylazo]-phenyl}-(4,6-dichloro-[1,3,5]triazin-2-yl)-amine. TLC analysis showed one product spot (Rf = 0.54; ethyl acetate/hexane = 1:2): 1H NMR (400 MHz, DMSO-d6), δ 7.85−7.88 (d, 4H), 7.93−7.96 (d, 4H), 11.51 (s, 1H); MS, m/z 505.6 (M+); melting point, 451.4 K. 2.4. SC-CO2 Apparatus and Procedures. Measurement of solubilities of synthesized reactive disperse dyes was carried out, and these dyes were employed to dye cotton fabric on our homemade dynamic-recirculation apparatus of SC-CO2 containing systems of refrigeration, pressurization, temperature control, dyeing/equilibrium, and SC-CO2 circulation sections. Figure 1 is a diagram of the whole apparatus. The CO2 leaving from a cylinder (1) was passed through a cooling unit (4) and heat exchanger (3) and then introduced into a high-pressure syringe pump (6); the high-pressure CO2 eventually flowed into the dyeing autoclave (8). The dyeing autoclave was a stainless steel vessel of 500 cm3 volume equipped with a visible window for observing the dissolution state of dyes. The pressure and temperature of experiments were monitored by main controller (22) equipped with a digital indicator in a cabinet, and the estimated errors of the temperature and pressure measurements were ±0.05 K and ±0.02 MPa, respectively. Moreover, SC-CO2 was circulated by a circulating pump (10), and its flow velocity and volume were recorded with a flow gauge (9). However, for measuring solubilities of dyes, the dyes packed into the top groove of the stainless steel shaft were placed into this autoclave (8) after being preheated by the preheater (7). When SC-CO2 in the system reached the equilibrium pressure and temperature, the valve (13) was opened to divert the saturated SC-CO2 instantaneously into a cold trap (12), which was a stainless steel vessel of 200 cm3 volume, before being preheated by the preheater (11). Finally, the dissolved dyes were collected by the cold trap, which was depressurized and cooled for the separation of CO2 and dyes. 2.5. Measurement of Solubilities. Synthesized dyes (0.1 g) were put into and kept in the middle of the top groove of a perforated stainless steel shaft and then placed into the autoclave before it was sealed. About 20 min after this autoclave had been filled with SC-CO2, the CO2 circulation pump was opened and the dyes were dissolved and circulated in the system. After equilibrium of dye solubility at desired temperatures (333.2, 353.2, 373.2, 393.2 K), pressures (10.0, 15.0, 20.0, 25.0 MPa), and an equilibrium contact time (60 min), the mixture of SC-CO2 and dissolved dyes in the autoclave was immediately released to the cold trap to collect a certain volume of this mixture. Finally, after the cold trap was depressurized and cooled, CO2 was removed, and the dissolved dyes were precipitated. The precipitated dyes were dissolved in acetone, and the absorbance of the solution was measured using a UV−visible spectrophotometer to determine the concentration of dyes. The solubilities of the dyes were calculated from the dye concentration and the volume of carbon dioxide used to fill the cold trap of (200 cm3). At least three replicates were taken at each experimental condition. The solubilities were obtained by an arithmetic mean value of several measurements. The uncertainty of the solubility measurements was estimated to be approximately ±4.0−6.0%. 2.6. Dyeing Experiments. The cotton fabrics were wrapped around the stainless steel shaft and then placed into the dyeing autoclave together with the synthesized dye

Figure 2. Photograph of dye 1 (A), dye 2 (B), dye 3 (C), and cotton fabrics dyed with these dyes.

3. RESULTS AND DISCUSSION 3.1. Effects of Pressure and Temperature on the Solubilities of Reactive Disperse Dyes. Solubility is typically defined as mole fraction (y2) of solute in SC-CO2, and the experimental solubility data for our reactive disperse dyes are presented in Table 1, along with the supercritical pure Table 1. Solubilities of Three Dyes at Various Temperatures and Pressures y ( × 10−6)

parameters

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T (K)

P (bar)

ρ (mol/L)

dye 1

dye 2

dye 3

333.2

10.0 15.0 20.0 25.0

6.59 13.73 16.44 17.87

6.74 10.41 12.1 12.79

0.86 2.19 3.48 3.96

4.21 6.33 7.23 7.65

393.2

10.0 15.0 20.0 25.0

5.04 9.71 13.50 15.59

6.28 9.12 11.52 12.51

0.74 1.82 3.01 3.67

3.89 5.44 6.79 7.48

353.2

10.0 15.0 20.0 25.0

4.28 7.55 10.92 13.71

6.05 8.43 11.21 12.41

0.71 1.63 2.86 3.45

3.82 5.13 6.47 7.36

373.2

10.0 15.0 20.0 25.0

3.80 6.37 9.12 11.49

5.97 8.07 10.64 11.89

0.7 1.48 2.76 3.26

3.8 5.09 6.22 7.13



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Figure 3. Solubility of dye 1 (A), dye 2 (B), and dye 3 (C) in SC-CO2 as a function of the density of pure CO2 at 333.2, 353.2, 373.2, and 393.2 K and fitting of the data to the Chrastil model (eq 1).

CO2 density (ρ) calculated by an online program.29 As shown in Table 1, most solubilities were within the range of 10−6− 10−5 mole fraction for each dye, and the solubilities increased with increasing pressure from 10.0 to 25.0 MPa, which was correlated with the density of the SC-CO2 under the same temperature conditions. However, the solubilities decreased with increasing temperature from 333.2 to 393.2 K at the same pressure conditions. Theoretically, the increase of pressure will result in increased density of SC-CO2 and therefore an increased solvent power toward dyes that facilitates the improvement of dye solubilities at the same temperature. On the other hand, the density and the solvent power of the SC-CO2 decrease with the increase of temperature and, thus, lead to decreased solubilities of dyes with temperature enhancement at constant pressure. 24 However, it is also true that increasing temperature increases the vapor pressure of the solute, thus leading to an increase in solubility. Temperature, in fact, has a two-fold effect versus solubility, and this leads to the well-known crossover pressure. Below this pressure the solubility decreases with increasing temperature, whereas an opposite trend is observed at pressures higher than the crossover pressure. The fact that the solubilities of our dyes always decrease in value when the temperature increases at constant pressure may be due to the fact that they are below the crossover pressure and the negative effect of temperature versus solubility prevails. Furthermore, dye structure is one of the most significant factors that determines SC-CO2 solubility. We observed that dyes of higher polarity and larger molecular weight generally had lower solubilities in SC-CO2. At the same conditions of temperature and pressure, dyes 1 and 3 had higher solubilities in SC-CO2 than dye 2, with dye 1 to a larger extent. Dye 1 was similar to dye 3 in structure, but had a higher solubility than dye 3 due to the smaller molecular weight of dye 1. Meanwhile, dye 1 was also structurally similar to dye 2, which has a much lower solubility than dye 1. This may result from the higher polarity of dye 2 than of dye 1. 3.2. Experimental Solubility Data Correlation with the Chrastil Model. To understand the capability in representing the solubility of dye in SC-CO2, the experimental solubility data of reactive disperse dyes were correlated by the density-based model Chrastil equation (eq 1) as a function of the density (ρ) of pure carbon dioxide fluid as shown below:

ln y2 = A +

B + C ln ρ T

(1)

A, B, and C are temperature-independent adjustable parameters obtained by fitting eq 1 to the experimental results. For the three dyes examined, the model parameters were obtained by average absolute relative deviation (AARD) between the experimental solubilities (y2exptl) and calculated values (y2calcd), according to eq 2 AARD (%) =

100 N

N

∑

− y2,calcd y2,exptl n n y2,exptl n

n=1

(2)

where N is the number of data points. As depicted in Figure 3, good agreements between the experimental solubilities and the calculated values by the Chrastil model in the form of isotherms were obtained at system temperatures from 333.2 to 393.2 K. Moreover, as shown in Table 2, satisfactory correlation results were achieved from the experimental data at various temperatures and pressures with a low AARD (%) value and association number (C). Table 2. Parameters of the Chrastil Equation and Average Absolute Relative Deviations (AARD %) between the Experimental and Calculated Values parameters compound

A

B

C

AARD (%)

dye 1 dye 2 dye 3

1.971 0.540 0.886

−468.986 −598.129 −249.158

0.630 1.443 0.576

1.44 4.41 0.94

3.3. Color Strength Test. The color strength (K/S) of the dyed cotton fabric was determined by the Kubelka−Munk equation (eq 3), where Rmin is the minimum value of the reflectance curve, which was determined by measuring the dyed cotton fabric with a Lambda 900 UV−vis-spectrophotometer. The reflectance (R) was obtained at 10 nm intervals in the range of 300−650 nm. K /S = 13866

(1 − R min)2 2R min

(3)



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The K/S value of the extracted cotton fabric ((K/S)extracted) was determined and used to calculate the percentage of dye molecules that was fixed to cotton fabric (F). The dyed fabric was extracted for 1 h with acetone at 80 °C by a Soxhlet extraction method for the removal of unfixed reactive disperse dyes. The (K/S)dyed (after dyeing) and (K/S)extracted (after extraction) of the dyed cotton fabric were measured and then put into eq 4 to calculate the F value. F=

(K /S)extracted × 100% (K /S)dyed

were probably responsible for the enhanced permanent dye fixation on cotton fabric. Meanwhile, the highest F value of dyed cotton fabric with dye 3, 92%, was achieved under this dyeing condition. 3.4. Color Fastness Test. The washing fastness of dyed cotton fabric was examined by a washing-fastness apparatus (SW-12A II), and multifiber adjacent fabrics (acetate, cotton, polyamide, polyester, acrylic, and wool) were used for staining fastness assessment according to China textile criteria GB/ T3921-2008 (method C).30 The rubbing fastness of dyed cotton fabric was performed at a rubbing tester (11219) with dry and wet samples according to China textile criteria GB/T 3920-2008.31 Color fastness of China textile is rated at nine levels (1, 1−2, 2, 2−3, 3, 3−4, 4, 4−5, 5); the best level is 5, and the worst is 1. Generally, the dry rub fastness reached the 4−5 level; wet rub fastness, 4; staining fastness, 4; and fading fastness, 3−4, respectively, conforming to the standards of garment dyes. As summarized in Table 3, our results exhibited good grades for all kinds of fastnesses. The dry, wet rub fastness and staining fastness showed excellent levels at 4−5 and 5, which met the requirements for industrial use, although the fading fastness of dye 2 was slightly low at 3−4, which should be further improved. 3.5. Color Characteristics. The synthesized reactive disperse dyes with different colors successfully dyed cotton fabrics. As depicted in Figure 2, the colors of the cotton fabrics dyed with three dyes were close to those of the dyes themselves. The colors of cotton fabrics dyed with dyes 1 and 3 were apparently deeper than that dyed with dye 2. This phenomenon could be attributed to dyes 1 and 3 having higher solubilities in SC-CO2 than dye 2, and therefore they displayed better capabilities in cotton fabric dyeing. In addition, reflectance spectra of dyed cotton fabrics were measured using a Lambda 900 UV−vis spectrophotometer in the wavelength range of 300−650 nm to observe their color characteristics. As shown in Figure 5, reflectance spectra were recorded by adopting white standard BaSO4; the minimum values of the reflectance curve were centered around 450, 415, and 378 nm for these cotton fabrics dyed with the three dyes, respectively. Compared with dye 3, dye 2 tended to red, which was correlated with a slight bathochromic shift in the reflectance curve of dye 2. However, the peak wavelength of dye 1 was slightly greater than that of dye 2, probably due to the high dyeing power of dye 1 compared with that of dye 2. 3.6. Microscopic Studies. The surface morphologies of cotton fabrics were investigated by SEM technique, and our results revealed remarkable morphological alterations before and after dyeing using three dyes. As shown in Figure 6, the surface of pristine cotton fabric appeared fairly smooth and clean (Figure 6A), whereas when treated by SC-CO2 alone, the surface of the fabric was noticeably rough and swollen (Figure 6B). After dyeing, the fabric samples were rough with a great

(4)

Actually, higher solubility of dye in SC-CO2 is favorable to promote the efficiency of the dyeing process. Observed from solubility data of our dyes, the solubility increased with increasing pressure and decreased with increasing temperature. Nevertheless, color strength increased favorably with increasing temperature.28 In conclusion, an appropriate dyeing process for cotton fabric in SC-CO2 was operated at a temperature of 373.2 K and a pressure of 20.0 MPa, which ensured a relatively high solubility and color strength and a moderate temperature and pressure to save energy. As shown in Figure 4, (K/S)dyed, (K/S)extracted, and F values of dyed cotton fabrics with the three reactive disperse dyes were

Figure 4. (K/S)dyed, (K/S)extracted, and F values of dyed cotton fabrics with three dyes at a constant dyeing temperature of 373.2 K, pressure of 20.0 MPa, time of 60 min, and dye concentration of 0.5% owf.

investigated at a dyeing temperature of 373.2 K, a pressure of 20.0 MPa, a time of 60 min, and a dye concentration of 0.5% owf. The (K/S)dyed values with these dyes ranked in the following order: dye 1 > dye 3 > dye 2, which was nicely consistent with dye solubilities in SC-CO2. One explanation for this result could be that high dye solubilities improved the color strength of the dyed cotton fabrics. Nevertheless, a larger (K/ S)extracted value was observed for dye 3 than for dyes 1 and 2. The two 1,3,5-trichloro-2,4,6-triazine reactive groups in dye 3

Table 3. Fastness Data of Dyed Cotton Fabrics with Three Dyes in SC-CO2 at Conditions of 373.2 K, 20.0 MPa, 60 min, and 0.5% owf wash fastness

rub fastness

staining dye

fading

acetate

cotton

nylon

polyester

acrylic

wool

dry

wet

1 2 3

4 3−4 4

4−5 4−5 4−5

4−5 4−5 4−5

4−5 4−5 4−5

4−5 4−5 4−5

4−5 4−5 4−5

4−5 4−5 4−5

5 5 5

4−5 4−5 4−5

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Figure 5. Reflectance spectra at short wavelength of dyed cotton fabrics with dye 1 (A), dye 2 (B), and dye 3 (C), respectively.

pores were uniformly distributed on fabric sample with dye 1, suggesting a good combination of dye 1 and cotton fabric relative to the other two dyes. Furthermore, measurement of the pore size diameter was 200−500 nm (Figure 6F). 3.7. Disperse Dye Dyeing Cotton Fabrics. For comparison, the cotton fabrics were also dyed with the disperse orange 3 (CAS Registry No. 730-40-5). The dyeing procedure (373.2 K and 20.0 MPa for 60 min with dye concentration of 0.5% owf in SC-CO2) was the same as that with the reactive disperse dyes. Under all conditions used, the (K/S)dyed and (K/ S)extracted values of dyed cotton fabrics with the disperse orange 3 and dye 3 were compared (Figure 7). As is shown by the (K/

Figure 7. (K/S)dyed and (K/S)extracted values of dyed cotton fabrics with dye 3 and disperse orange 3 at a dyeing temperature of 373.2 K, pressure of 20.0 MPa, time of 60 min, and dye concentration of 0.5% owf. Figure 6. SEM images of samples: pristine cotton fabric (A); cotton fabric treated with SC-CO2 alone (B); cotton fabric dyed with dye 1 (C); cotton fabric dyed with dye 2 (D); cotton fabric dyed with dye 3 (E); pore size diameter (F).

S)dyed and (K/S)extracted, the color strength was substantially unchanged before and after extraction with dye 3 on cotton fabrics, indicating that dye 3 by reactive groups was able to react with the cotton fiber by forming a covalent bond between this dye and the fiber. However, as for disperse orange 3, remarkable changes in (K/S)dyed and (K/S)extracted were observed, implying some weak and noncovalent dye−fiber interactions in this case. To further confirm the dyeing effect of reactive groups in SCCO2, we soaped the dyed cotton fabrics with disperse orange 3 and dye 3 to evaluate the washing fastness of the fabrics. As

many pores appearing on their surface (Figure 6C−E). The surface roughness of dyed fabric was further compared. The formation of the pore on the surface of the fabric was probably due to an interaction between the dye and cotton fabric. More pores were found in the fabric dyed with dye 1 (Figure 6C) than in those dyed with dyes 2 and 3 (Figure 6D,E), and the 13868



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staining 4−5, and fading 3−4 and 4, respectively, meeting the standards of garment dyes. Finally, different colors and dyeing effects of our dyes result in the observation of differential reflectance spectra of dyed cotton fabrics. In this study, by comparing disperse dye and reactive disperse dye, our research highlights the high efficiency of the reactive disperse dyes in the dyeing of cotton fabrics.

shown in Figure 8, under the soaping condition, the decolorization was not obvious for dye 3, implying good

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ASSOCIATED CONTENT

* Supporting Information S

1 H NMR spectra and mass spectra of three reactive disperse dyes. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*(J.L.) E-mail: [email protected]. Tel: 86-0591-83833016. Notes

The authors declare no competing financial interest.

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Figure 8. Photograph of before and after soaping of cotton fabrics dyed with dye 3 (A, B) and disperse orange 3 (C, D).

ACKNOWLEDGMENTS This work was supported by the Science and Technology Planning Project of Fujian Province (No. 2012H0051) and the Natural Science Foundation of Fujian Province (No. 2012J01059).

washing fastness of the dyeing with the reactive disperse dyes. Again, this observation indicated that the reactive groups of dye 3 were able to react with the cotton fibers by forming covalent bonds. The cotton fabrics dyed with disperse orange 3, however, were almost completely discolored by soaping, as the noncovalent interactions between the disperse dye and the fiber resulted in poor washing fastness. In contrast to the disperse dye, the reactive disperse dye is able to preferably fix to cotton fabric in SC-CO2 as shown by color strength and washing fastness. The possible dyeing mechanism of reactive disperse dye is a description of the following: adsorption of the dye onto and diffusion of the dye into the fiber are likely the limiting steps of the dyeing process of cotton. Therefore, primarily the cotton fabric is impregnated in SC-CO2 after about 20 min in the autoclave to swell the fiber; then reactive disperse dye can be dissolved and react with the cotton fiber. To further propose the dyeing mechanism, the reactive disperse dye introducing a reactive group (1,3,5trichloro-2,4,6-triazine) is able to react with hydroxy groups of the cotton fiber via substitution reaction to form covalent bonds.

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REFERENCES

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4. CONCLUSIONS In summary, solubilities of synthesized reactive disperse dyes with a 1,3,5 trichloro-2,4,6-triazine group were investigated, and these dyes were applied to dye cotton fabrics in SC-CO2. The results indicated that the solubilities of the dyes increased with increasing pressure at the same temperature, and decreased with increasing temperature at a given pressure. Meanwhile, the solubilities for these dyes were also influenced by the polarity of the dye molecules, in such a manner that higher solubility was displayed by less polar molecules and lower solubility by more polar molecules. In this study, an appropriate dyeing condition in SC-CO2 was adopted at a dyeing temperature of 373.2 K, pressure of 20.0 MPa, time of 60 min, and dye concentration of 0.5% owf. The (K/S)dyed value of dyed cotton fabric reached 14.9 for dye 1, and the (K/S)extracted value of that reached 13.1 for dye 3; the highest F value achieved for dye 3 was 92% at this dyeing condition. Moreover, the rub fastness values for wet and dry dyed cotton fabrics were 4−5 and 5, wash fastness of 13869



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Synthesis and Measurement of Solubilities of Reactive Disperse Dyes

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