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Ultrasound for low temperature dyeing of wool with acid dye
Ultrasonics Sonochemistry 19 (2012) 601–606
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Ultrasonics Sonochemistry journal homepage: www.elsevier.com/locate/ultsonch
Ultrasound for low temperature dyeing of wool with acid dye F. Ferrero ⇑, M. Periolatto Dipartimento di Scienza dei Materiali e Ingegneria Chimica, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy
a r t i c l e
i n f o
Article history: Received 28 June 2011 Received in revised form 30 September 2011 Accepted 9 October 2011 Available online 20 October 2011 Keywords: Ultrasound Wool Dyeing kinetics
a b s t r a c t The possibility of reducing the temperature of conventional wool dyeing with an acid levelling dye using ultrasound was studied in order to reach exhaustion values comparable to those obtained with the standard procedure at 98 °C, obtaining dyed samples of good quality. The aim was to develop a laboratory method that could be transferred at industrial level, reducing both the energy consumption and fiber damage caused by the prolonged exposure to high temperature without the use of polluting auxiliary agents. Dyeings of wool fabrics were carried out in the temperature range between 60 °C and 80 °C using either mechanical or ultrasound agitation of the bath and coupling the two methods to compare the results. For each dyeing, the exhaustion curves of the dye bath were determined and the better results of dyeing kinetics were obtained with ultrasound coupled with mechanical stirring. Hence the corresponding half dyeing times, absorption rate constants according to Cegarra–Puente modified equation and ultrasonic efficiency were calculated in comparison with mechanical stirring alone. In the presence of ultrasound the absorption rate constants increased by at least 50%, at each temperature, confirming the synergic effect of sonication on the dyeing kinetics. Moreover the apparent activation energies were also evaluated and the positive effect of ultrasound was ascribed to the pre-exponential factor of the Arrhenius equation. It was also shown that the effect of ultrasound at 60 °C was just on the dye bath, practically unaffecting the wool fiber surface, as confirmed by the results of SEM analysis. Finally, fastness tests to rubbing and domestic laundering yielded good values for samples dyed in ultrasound assisted process even at the lower temperature. These results suggest the possibility, thanks to the use of ultrasound, to obtain a well equalized dyeing on wool working yet at 60 °C, a temperature process strongly lower than 98 °C, currently used in industry, which damages the mechanical properties of the fibers. Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction In literature it has been reported that ultrasonic energy can be successfully applied to the textile wet processes, for example laundering [1], desizing, scouring, bleaching, mercerization of cotton fabric [2], enzymatic treatment [2,3], dyeing [4], leather processing [5], together with decoloration/mineralization of textile dyes in waste water [6]. Acoustic cavitations and the related effects, such as the formation of microjets are the physical mechanisms behind the ultrasonic textile wet processes [7]. Dyeing is a solid/liquid phase process which proceeds through the migration of the dye molecules from the bath to the solid surface of the fiber. Once the dye molecules get into the fiber, a slow process, which is diffusion controlled, starts to take place. The basic idea in ultrasound-assisted dyeing processes was that ultrasound can enhance the mass transfer by reducing the stagnant cores in the yarns. Improvements observed are generally attributed to cavita⇑ Corresponding author. Tel.: +39 011 564 4653; fax: +39 011 564 4699. E-mail address: [email protected] (F. Ferrero). 1350-4177/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.ultsonch.2011.10.006
tions phenomena and to other consequent physical effects such as dye dispersion (breaking up of aggregates with high relative molecular mass), degassing (expulsion of dissolved or entrapped air from fiber capillaries), strong agitation of the liquid (thickness reduction of fiber-liquid boundary layer), swelling (enhancement of dye diffusion rate inside the fiber). The acceleration in dyeing rates observed by many authors might be the cumulative effect of the above. The behavior of ultrasonic waves in dye baths containing different fabrics was also studied. Waves transmission, reflectance and adsorption by fabrics were measured and it was found that textile fabrics transmit very little high intensity ultrasound, reflecting most of the sound energy. Even very light fabrics allow less than 4% of the high intensity ultrasonic energy to pass through. The ultrasonic energy transmitted through the fabric was slightly greater at 25 kHz than at 40 kHz or with fabrics not too hairy. It means that fabrics absorb negligible ultrasonic vibrational energy since most of the waves are reflected or transmitted [8] and the effects on their morphology are limited. Moreover, approaches to the transfer of the process at industrial level were reported and design requirements for industrial size
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ultrasound bath for textile treatments were determined. Finite element analysis (FEA) was applied to investigate spacing and alignment of the ultrasound source transducers to reach effective and homogenous acoustic pressure distribution in the bath. Effects of sound pressure level, bath temperature, bath volume, textile material type and hydrophilicity degree of fabric were taken into account [9]. For what concern the environmental impact after dyeing, some authors monitored the selected pollution parameters in dye bath effluents, i.e. pH, total organic carbon (TOC), chemical oxygen demand (COD), and biochemical oxygen demand (BOD5). The obtained results indicated higher exhaustion level of dyestuffs during ultrasound assistance in comparison to conventional dyeing, enabling a reduction in dyeing time and energy consumption. Moreover, the selected pollution parameters were diminished in all the dye-baths effluents after ultrasonic dyeing, with environmental protection improvement [10]. The effect of ultrasonic energy on dyeing processes was already widely investigated on cotton [11], cationized cotton [12], silk [13], acrylic [14], nylon [15] and polyester fibers [16–18] with good effects in all cases. However the wool structure is more complex than that of such fibers, since it can be represented as a set of compact protein units, cuticular and cortical cells, surrounded by a keratin cell membrane, held together by intercellular cement. Cuticle constitutes a real barrier to the transfer of dye molecules from aqueous solution causing a significant deviation from the theoretic model of dye diffusion (Fick’s law) [19]. A good wool dyeing process must provide a satisfactory exhaustion of dye bath and an adequate penetration of dye into the fiber, with the practical advantages of good wet fastness and uniform coloration. The conventional methods for wool dyeing are based on long times at temperature of the bath close to the boiling point, in order to ensure good results of dye penetration and levelling. These conditions can damage the fibers, with bad effects on the characteristics of the finished material. The extent of the damage that can be caused to dyed wool depends on pH and time–temperature profile of the dyeing cycle. When the wool is maintained at temperatures near 100 °C in acid ambient for long times, the structure of the fiber is gradually damaged by hydrolysis of peptide bonds. Such damage can be minimized by reducing the operation time or, better yet, by reducing the dyeing temperature. Therefore many low temperature wool dyeing processes were proposed by introducing specific auxiliary agents [20,21] and enzyme or plasma pre-treatments [22–24]. Recently, ultrasound assisted wool dyeing was studied with the aim to reduce temperature or dyeing time with respect to the conventional dyeing technique. Kamel et al. [25] found a significant improvement of kinetics in wool dyeing with natural dye. McNeil and McCall [26] reported that ultrasound show potential to reduce the chemical and energy requirements in wool dyeing with reactive and acid milling dyes, but not with acid levelling dyes. Furthermore, Battù et al. [27] observed that in wool dyeing at 85 °C with acid dyes ultrasound caused an enhancement of the dyebath exhaustion as high as about 25%, or vice versa a dyeing time nearly 20% shorter than conventional dyeing. Yükselog˘lu and Bolat [28] confirmed these improvements using ultrasound in dyeing of wool fabrics at 80–90 °C with a pre-metallized dye. In the present work the possibility of reducing the temperature of conventional wool dyeing with a typical acid levelling dye using ultrasound was further investigated, in order to reach exhaustion values comparable to those of the standard procedure, obtaining dyed samples of good quality. The aim was to develop a laboratory method that could be transferred at industrial level, reducing both the energy consumption and fiber damage caused by the prolonged exposure to high temperature without the use of polluting auxiliary agents which are commonly used to improve the mass transfer kinetics of dyes onto the fiber surface.
2. Experimental 2.1. Materials Textile material was pure wool knitted fabric EMPA Mousseline, 200 g/m2, yarn 2/48 Nm (2 fibers) 550 tors/mz, single fiber 360 tors/ ms, previously washed for 10 min with 1 g/l solution of ECE surfactant and 10 ml/l NH3 (33%), followed by rinsing first in lukewarm, then in cool water to completely eliminate foam which might affect the uniform migration of dye on the fabric. The dye chosen was Telon Blue 100% (Acid Blue 80) by Dystar. It is a disulfonate acid dye that presents a maximum absorbance peak at 626 nm. Acetic acid of laboratory grade by Sigma–Aldrich was used for acidification. 2.2. Dyeing process The first aim of this study was the determination of isothermal exhaustion curves of the dyebath, with mechanically or ultrasound alone agitation and coupling both, at different dyeing temperatures: 60, 70 and 80 °C. The experiments were performed without auxiliary chemicals. An Elmasonic S60H (Elma GmbH & Co., Singen, Germany) ultrasonic and thermo-controlled bath was used. It can generate ultrasound at 37 kHz with effective ultrasound power of 150 W and heating power of 400 W. The dyeings were made on 2.00 g wool samples introduced in a beaker containing the dyebath. Then the beaker was immersed in the water bath of the ultrasonic equipment. Mechanical agitation was provided by a magnetic stirrer turning at 110–120 rpm, plunged in the same bath. Tests without ultrasound were carried out with the sonication turned off. A 1:50 material to liquor ratio was chosen, with 1% o.w.f. (over weight fiber) dye amount at pH adjusted to 4 by acetic acid addition. The dyeing temperature was maintained for 110 min, analyzing bath samples every 10 min to monitor dye exhaustion. The measurements were performed with an UV–VIS spectrophotometer UNICAM UV2 (ATI Unicam, Cambridge, UK) and evaluated by ‘‘Vision 32’’ software basing on Lambert–Beer law. Finally, the dyed samples were squeezed, thoroughly rinsed with cold water, and dried at 100 °C. 2.3. Ultrasound effect evaluation From exhaustion curves, besides the final bath exhaustion reached, times of half dyeing were also determined. It is the time required by a fabric to adsorb half the amount of dye adsorbed at equilibrium, so as it is small, the more dyeing process is fast. Moreover, to evaluate the effect on wool dyeing produced by ultrasound, absorption rate constants and apparent activation energies were determined. Adsorption rate constants were calculated from the exhaustion curves, by fitting the experimental values according to Cegarra– Puente modified kinetic equation [17]:
" ln ln 1
E2t E21
!# ¼ a ln t þ a ln K
ð1Þ
where Et is the dye concentration in the fiber at the time t, E1 the dye concentration at the equilibrium, K the absorption rate constant, and t is the dyeing time. Arrhenius equation was used for apparent activation energy calculation: E
K T ¼ K 0 eRT
ð2Þ
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ðK US K ST Þ DK% ¼ 100 K ST
ð3Þ
where KUS and KST are the rate constants of dyeing with ultrasonic and stirring alone process, respectively [14]. For each sample dyed with the different dyeing processes, color fastness to domestic washing (UNI-EN ISO 105-C01), and rubbing (UNI-EN ISO 105-X12) were carried out. Moreover, to evidence a possible damage of wool fibers caused by ultrasound, the surface morphology was examined by SEM with a Leica (Cambridge, UK) Electron Optics 435 VP scanning electron microscope with an acceleration voltage of 15 kV, a current probe of 400 pA, and a working distance of 20 mm. The samples were mounted on aluminum specimen stubs with double-sided adhesive tape and sputter-coated with gold in rarefied argon with an Emitech (Kent, UK) K550 sputter coater with a current of 20 mA for 180 s.
120 100
Exhaustion (%)
where KT is the absorption rate constant at the absolute temperature T, E the apparent activation energy, K0 the frequency factor, and R is the ideal gas constant (R = 8.314 J/mol K). Finally, ultrasonic efficiency (DK%) to accelerate the dyeing rate was calculated by introducing the following equation:
stirring + us
120 100
Exhaustion (%)
stirring alone us alone
0
0
20
40
60
80
100
120
time (min) Fig. 2. Comparison between the exhaustion kinetics of wool dyeing at 70 °C.
120
80 60 40 stirring + us us alone
20
stirring alone 0
60
80
100
120
time (min) Fig. 1. Comparison between the exhaustion kinetics of wool dyeing at 60 °C.
Exhaustion (%)
In Figs. 1–3 the comparison of the exhaustion curves was made between mechanically or ultrasound alone agitated dyeing and coupling both at 60, 70 and 80 °C, respectively. In Fig. 1 it is evident that at 60 °C with mechanical stirring alone the complete exhaustion is not reached even after 110 min, while in the presence of ultrasound the final exhaustion was complete. However coupling mechanical stirring and ultrasound the complete exhaustion was reached already after 60 min. At 70 °C (Fig. 2) 90 min were needed to obtain 100% exhaustion with mechanical stirring or ultrasound alone while ultrasound coupled with mechanical agitation reduced this time to 40 min. Finally at 80 °C these times were further reduced to 80 and 30 min, respectively. Hence the ultrasonic energy coupled with mechanical stirring showed a synergic effect strongly improving the kinetics of the process even at the higher temperature. However ultrasound agitation alone in the adopted experimental conditions did not show an improvement of the dyeing kinetics and the corresponding exhaustion curves were practically unaffected by temperature increase. This could be due to the fact that ultrasound alone at the power applied did not induce
40
40
100
3.1. Exhaustion curves
20
60
20
3. Results and discussion
0
80
80 60 40 stirring + us stirring alone
20
us alone 0 0
20
40
60
80
100
120
time (min) Fig. 3. Comparison between the exhaustion kinetics of wool dyeing at 80 °C.
convective movements into the bath enough to assure a fast supply of dye molecules onto the fiber surface. Hence half dyeing times and absorption rate constants were evaluated only from the exhaustion curves related to mechanically stirred dyeing with or without ultrasound. These values are compared in Table 1. The absorption rate constants K increased with temperature in both the processes thanks to the positive effect of the temperature on dye diffusion into the fibers, but increased by at least 50%, at each temperature, in the presence of ultrasound. This increase confirmed the great importance of sonication effect on the dyeing kinetics, as highlighted by the ultrasonic efficiency values reported also in Table 1. The sonication effect is relevant at all the investigated temperatures, but the higher efficiency was found at the higher temperature, where the rate constant becomes more than double. The apparent activation energy values for both the processes were evaluated and the Arrhenius plot is reported in Fig. 4. The slope of the graph related to ultrasound-assisted process resulted slightly higher than that of stirring alone, hence the apparent activation energy values were calculated as 62.2 and 49.8 kJ/mol, respectively. However the values of ln K0 were 18.9 and 13.9, respectively showing that the strong enhancement of the kinetic constants in the presence of ultrasound is due to the increase of the pre-exponential factor K0. This effect on the kinetics was observed in many heterogeneous reactions carried out with ultrasound [29–31].
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Table 1 Times of half dyeing, absorption rate constants K and ultrasound efficiency DK. Temperature (°C)
Half dyeing time (min)
K (min1)
Stirring alone
Stirring and sonication
Stirring alone
Stirring and sonication
60 70 80
40 20 14
19 12 5
0.017 0.029 0.045
0.028 0.048 0.102
DK (%)
64.7 65.5 126.7
-2 stirring + us Fig. 7. Comparison between wool fabric dyed at 60 °C: (a) with ultrasound and stirring; (b) with stirring alone.
stirring alone
-2.5
ln(K T )
-3
Table 2 Dyeing fastness to rubbing. Fastness type
Dyeing process
-3.5
-4
-4.5 2.80
2.85
2.90
2.95
3.00
80
Stirring alone Stirring and sonication
3/4 5
4 5
4/5 5
Dry rubbing (degree)
Stirring alone Stirring and sonication
4/5 5
5 5
5 5
In order to evaluate if sonication effect could affect also the surface of wool fibers, another test was carried out at the lower temperature (60 °C). In this case wool was subjected to sonication for 120 min in acid solution, but in absence of dye. After this time sonication was turned off, the dye was introduced and the process went only with mechanical stirring. The resulting exhaustion curve was compared with the corresponding obtained without sonication and no enhancement in dyeing kinetics was observed with ultrasound pre-treatment, as reported in Fig. 5. This means that the effect of ultrasound was just on dye dispersion, mass transfer and diffusion, unaffecting the wool fiber structure, according to the results founded by McNeil and McCall in dyeing wool pre-treated with ultrasound [26].
Fig. 4. Arrhenius plot.
100
80
Exhaustion (%)
70
Wet rubbing (degree)
3.05
1000/T
60
40
3.2. Characterization of dyed samples
original
20
Dyeing temperature (°C) 60
pre-sonicated 0 40
60
80
100
120
time (min) Fig. 5. Comparison between the exhaustion kinetics of wool dyeing at 60 °C carried out with stirring alone on original and pre-sonicated fabrics.
The importance of dyeing at temperature lower than that commonly used in industry was demonstrated in our previous work carried out on wool yarn dyed at different temperatures [23]. Loss of tensile strength and elongation determined by Uster Tensorapid Tester dynamometer according to UNI-EN ISO 2062 showed that both tensile strength and elongation suffered a great loss after
Fig. 6. SEM images of undyed wool fabrics at magnification ratio of 800: (a) without any treatment; (b) after 110 min of ultrasound at 60 °C; (c) after 110 min of ultrasound at 80 °C.
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F. Ferrero, M. Periolatto / Ultrasonics Sonochemistry 19 (2012) 601–606 Table 3 Dyeing fastness to domestic laundering. Fastness type
Dyeing process
60
70
80
Staining on cotton (degree)
Stirring alone Stirring and sonication
4/5 5
5 5
5 5
Staining on wool (degree)
Stirring alone Stirring and sonication
2/3 5
5 5
5 5
Color degradation (degree)
Stirring alone Stirring and sonication
3/4 5
5 5
5 5
Dye released in washings (mg/100 ml)
Stirring alone Stirring and sonication
3.55 1.21
1.66 1.02
1.21 0.92
dyeing at 98 °C while at lower temperature the degradation was reduced. In particular, wool yarn submitted to dyeing process at 98 °C showed a loss of mechanical performances of 24% for tensile strength and of 51% for elongation while at 65 °C the losses became 11% and 9%, respectively. Images of SEM analysis performed on undyed wool fabrics treated at 60 and 80 °C for 110 min at pH 4 under sonication are compared in Fig. 6 with that of untreated fabric. At 60 °C the surface of wool fibers appears to be practically undamaged by ultrasonic treatment, according to McNeil and McCall [26] which treated a wool fabrics at about the same frequency applied in our experiments. However at 80 °C some detachment of scales from the fibers is observed, hence at this temperature the treatment time should be reduced to avoid fiber degradation. At 60 °C sonication coupled with stirring gives dyed fabrics of good quality as shown in Fig. 7, where a sample dyed for 110 min under sonication and stirring is compared with another dyed under stirring alone for the same time. The coloration of the former is evidently uniform and more intense. Optimal fastness values at all the investigated temperatures are shown by the results reported in Tables 2 and 3. The most pronounced enhancement with respect to the process without sonication was shown by rubbing test in wet conditions and, in general, at the lower temperature. Moreover, in the case of washing fastness, no staining was revealed either on wool or cotton white standards, but dye release in washing liquids was evident. Hence these liquids were spectrophotometrically analyzed revealing great differences in dye concentrations. For each process, the amount of released dye was greater at the lower temperature according to a decrease in dyeing quality, but the dye release from the samples dyed with sonication was greatly reduced, confirming the good effect also on the fastness. It can be ascribed to a deeper penetration of the dye into the fiber as a consequence of diffusion improvement. All the dyeing tests were performed without auxiliary levelling agents so it can be said that ultrasound could replace these auxiliaries in dyeing processes. 4. Conclusions Comparing the results, a wool dyeing process with an acid levelling dye even at 60 °C with both mechanical stirring and sonication can be indicated as an ecofriendly alternative to traditional one, carried out at 98 °C. In this way, in fact, total bath exhaustion is coupled with low mechanical properties loss and great energy savings due to the lower process temperature involved. The positive effect of sonication on dyeing process was confirmed by the evaluation of all the kinetic parameters. Dyed fabrics showed optimal fastness values even in absence of levelling agents. Finally it was verified that ultrasound acts just on dye dispersion, mass transfer and diffusion, unaffecting the fiber structure.
Dyeing temperature (°C)
Moreover at 60 °C no surface fiber damage due to ultrasound was evidenced by SEM analysis. Acknowledgements This work was developed with the financial support of Regione Piemonte, Italy, Applied Scientific Research 2004, Project C46. The authors are gratefully to Dr. Raffaella Mossotti of CNR-ISMAC of Biella, Italy, for SEM analyzes. References [1] C. Hurren, P. Cookson, X. Wang, The effects of ultrasonic agitation in laundering on the properties of wool fabrics, Ultrason. Sonochem. 15 (2008) 1069–1074. [2] C. Basto, T. Tzanov, A. Cavaco-Paulo, Combined ultrasound-laccase assisted bleaching of cotton, Ultrason. Sonochem. 14 (2007) 350–354. [3] H.B.M. Lenting, E. Zwier, V.A. Nierstrasz, Identifying important parameters for a continuous bioscouring process, Text. Res. J. 72 (2002) 825–831. [4] D. Sun, Q. Guo, X. Liu, Investigation into dyeing acceleration efficiency of ultrasound energy, Ultrasonics 50 (2010) 441–446. [5] V. Sivakumar, P.G. Rao, Application of power ultrasound in leather processing: an ecofriendly approach, Ultrason. Sonochem. 9 (2001) 25–33. [6] S. Vajnhandl, A.M. Le Marechal, Ultrasound in textile dyeing and the decolouration/mineralization of textile dyes, Dyes Pigm. 65 (2005) 89–101. [7] V.S. Moholkar, M.M.C.G. Warmoeskerken, Investigations in mass transfer enhancement in textiles with ultrasound, Chem. Eng. Sci. 59 (2004) 299–311. [8] G.V. Datar, P. Banks-Lee, P.L. Grady, Acoustical properties of fabrics in highintensity ultrasound, Appl. Acoust. 48 (1996) 33–45. [9] S. Perincek, A.E. Uzgur, K. Duran, A. Dogan, A.E. Korlu, I.M. Bahtiyari, Design parameter investigation of industrial size ultrasound textile treatment bath, Ultrason. Sonochem. 16 (2009) 184–189. [10] A. Ojstršek, D. Fakin, The impact of ultrasonic-assisted dyeing on ecological parameters, in: Proceedings of the Eighth Autex Conference, Biella, Italy, June 24– 26, 2008.. [11] P.S. Vankar, R. Shanker, J. Srivastava, Ultrasonic dyeing of cotton fabric with aqueous extract of Eclipta alba, Dyes Pigm. 72 (2007) 33–37. [12] M.M. Kamel, M.M. El Zawahry, N.S.E. Ahmed, F. Abdelghaffar, Ultrasonic dyeing of cationized cotton fabric with natural dye. Part 1: Cationization of cotton using Solfix E, Ultrason. Sonochem. 16 (2009) 243–249. [13] S.R. Shukla, M.R. Mathur, Low-temperature ultrasonic dyeing of silk, J. Soc. Dyers Colour. 111 (1995) 342–345. [14] M.M. Kamel, H.M. Helmy, H.M. Mashaly, H.H. Kafafy, Ultrasonic assisted dyeing: dyeing of acrylic fabrics C.I. Astrazon Basic Red 5BL 200%, Ultrason. Sonochem. 17 (2010) 92–97. [15] M.M. Kamel, R.M. El-Shishtawy, H.L. Hanna, N.S.E. Ahmed, Ultrasonic-assisted dyeing: I. Nylon dyeability with reactive dyes, Polym. Int. 52 (2003) 373–380. [16] A.N. Saligram, S.R. Shukla, M. Mathur, Dyeing of polyester fibres using ultrasound, J. Soc. Dyers Colour. 109 (1993) 263–266. [17] F.J. Carrión Fité, Dyeing polyester at low temperatures: kinetics of dyeing with disperse dyes, Text. Res. J. 65 (1995) 362–368. [18] K.W. Lee, Y.S. Chung, J.P. Kim, Characteristic of ultrasonic dyeing on poly(ethylene terephthalate), Text. Res. J. 73 (2003) 751–755. [19] J.A. Rippon, The structure of wool, in: D.M. Lewis (Ed.), Wool Dyeing, Society of Dyers and Colourists, Bradford, 1992, pp. 1–51. [20] J.A. Rippon, F.J. Harrigan, New method for dyeing wool at temperature below the boil, Wool Rec. 4 (1994) 53–55. [21] M. Martí, A. De la Maza, J.L. Parra, L. Coderch, S. Serra, Dyeing wool at low temperatures: new method using liposomes, Text. Res. J. 71 (2001) 678–682. [22] A. Riva, I. Algaba, R. Prieto, Dyeing kinetics of wool fabrics pretreated with a protease, Color. Technol. 118 (2002) 59–63. [23] M. Periolatto, F. Ferrero, M. Giansetti, R. Mossotti, R. Innocenti, Enzyme-aided wool dyeing with a neutral protease at reduced temperatures, Eng. Life Sci. 10 (2010) 474–479.
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[24] C.W. Kan, Dyeing behavior of low temperature plasma treated wool, Fibers Polym. 7 (2006) 262–269. [25] M.M. Kamel, R.M. El-Shishtawy, B.M. Yussef, H. Mashaly, Ultrasonic assisted dyeing III. Dyeing of wool with lac as a natural dye, Dyes Pigm. 65 (2005) 103–110. [26] S.J. McNeil, R.A. McCall, Ultrasound for wool dyeing and finishing, Ultrason. Sonochem. 18 (2011) 401–406. [27] A. Battù, M. Giansetti, G. Rovero, S. Sicardi, Intensification of wet textile processing by ultrasound application, in: Proceedings of the 22nd IFATCC International Congress, Stresa, Italy, CD_E11, May 5–7, 2010.
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Contents lists available at SciVerse ScienceDirect
Ultrasonics Sonochemistry journal homepage: www.elsevier.com/locate/ultsonch
Ultrasound for low temperature dyeing of wool with acid dye F. Ferrero ⇑, M. Periolatto Dipartimento di Scienza dei Materiali e Ingegneria Chimica, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy
a r t i c l e
i n f o
Article history: Received 28 June 2011 Received in revised form 30 September 2011 Accepted 9 October 2011 Available online 20 October 2011 Keywords: Ultrasound Wool Dyeing kinetics
a b s t r a c t The possibility of reducing the temperature of conventional wool dyeing with an acid levelling dye using ultrasound was studied in order to reach exhaustion values comparable to those obtained with the standard procedure at 98 °C, obtaining dyed samples of good quality. The aim was to develop a laboratory method that could be transferred at industrial level, reducing both the energy consumption and fiber damage caused by the prolonged exposure to high temperature without the use of polluting auxiliary agents. Dyeings of wool fabrics were carried out in the temperature range between 60 °C and 80 °C using either mechanical or ultrasound agitation of the bath and coupling the two methods to compare the results. For each dyeing, the exhaustion curves of the dye bath were determined and the better results of dyeing kinetics were obtained with ultrasound coupled with mechanical stirring. Hence the corresponding half dyeing times, absorption rate constants according to Cegarra–Puente modified equation and ultrasonic efficiency were calculated in comparison with mechanical stirring alone. In the presence of ultrasound the absorption rate constants increased by at least 50%, at each temperature, confirming the synergic effect of sonication on the dyeing kinetics. Moreover the apparent activation energies were also evaluated and the positive effect of ultrasound was ascribed to the pre-exponential factor of the Arrhenius equation. It was also shown that the effect of ultrasound at 60 °C was just on the dye bath, practically unaffecting the wool fiber surface, as confirmed by the results of SEM analysis. Finally, fastness tests to rubbing and domestic laundering yielded good values for samples dyed in ultrasound assisted process even at the lower temperature. These results suggest the possibility, thanks to the use of ultrasound, to obtain a well equalized dyeing on wool working yet at 60 °C, a temperature process strongly lower than 98 °C, currently used in industry, which damages the mechanical properties of the fibers. Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction In literature it has been reported that ultrasonic energy can be successfully applied to the textile wet processes, for example laundering [1], desizing, scouring, bleaching, mercerization of cotton fabric [2], enzymatic treatment [2,3], dyeing [4], leather processing [5], together with decoloration/mineralization of textile dyes in waste water [6]. Acoustic cavitations and the related effects, such as the formation of microjets are the physical mechanisms behind the ultrasonic textile wet processes [7]. Dyeing is a solid/liquid phase process which proceeds through the migration of the dye molecules from the bath to the solid surface of the fiber. Once the dye molecules get into the fiber, a slow process, which is diffusion controlled, starts to take place. The basic idea in ultrasound-assisted dyeing processes was that ultrasound can enhance the mass transfer by reducing the stagnant cores in the yarns. Improvements observed are generally attributed to cavita⇑ Corresponding author. Tel.: +39 011 564 4653; fax: +39 011 564 4699. E-mail address: [email protected] (F. Ferrero). 1350-4177/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.ultsonch.2011.10.006
tions phenomena and to other consequent physical effects such as dye dispersion (breaking up of aggregates with high relative molecular mass), degassing (expulsion of dissolved or entrapped air from fiber capillaries), strong agitation of the liquid (thickness reduction of fiber-liquid boundary layer), swelling (enhancement of dye diffusion rate inside the fiber). The acceleration in dyeing rates observed by many authors might be the cumulative effect of the above. The behavior of ultrasonic waves in dye baths containing different fabrics was also studied. Waves transmission, reflectance and adsorption by fabrics were measured and it was found that textile fabrics transmit very little high intensity ultrasound, reflecting most of the sound energy. Even very light fabrics allow less than 4% of the high intensity ultrasonic energy to pass through. The ultrasonic energy transmitted through the fabric was slightly greater at 25 kHz than at 40 kHz or with fabrics not too hairy. It means that fabrics absorb negligible ultrasonic vibrational energy since most of the waves are reflected or transmitted [8] and the effects on their morphology are limited. Moreover, approaches to the transfer of the process at industrial level were reported and design requirements for industrial size
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ultrasound bath for textile treatments were determined. Finite element analysis (FEA) was applied to investigate spacing and alignment of the ultrasound source transducers to reach effective and homogenous acoustic pressure distribution in the bath. Effects of sound pressure level, bath temperature, bath volume, textile material type and hydrophilicity degree of fabric were taken into account [9]. For what concern the environmental impact after dyeing, some authors monitored the selected pollution parameters in dye bath effluents, i.e. pH, total organic carbon (TOC), chemical oxygen demand (COD), and biochemical oxygen demand (BOD5). The obtained results indicated higher exhaustion level of dyestuffs during ultrasound assistance in comparison to conventional dyeing, enabling a reduction in dyeing time and energy consumption. Moreover, the selected pollution parameters were diminished in all the dye-baths effluents after ultrasonic dyeing, with environmental protection improvement [10]. The effect of ultrasonic energy on dyeing processes was already widely investigated on cotton [11], cationized cotton [12], silk [13], acrylic [14], nylon [15] and polyester fibers [16–18] with good effects in all cases. However the wool structure is more complex than that of such fibers, since it can be represented as a set of compact protein units, cuticular and cortical cells, surrounded by a keratin cell membrane, held together by intercellular cement. Cuticle constitutes a real barrier to the transfer of dye molecules from aqueous solution causing a significant deviation from the theoretic model of dye diffusion (Fick’s law) [19]. A good wool dyeing process must provide a satisfactory exhaustion of dye bath and an adequate penetration of dye into the fiber, with the practical advantages of good wet fastness and uniform coloration. The conventional methods for wool dyeing are based on long times at temperature of the bath close to the boiling point, in order to ensure good results of dye penetration and levelling. These conditions can damage the fibers, with bad effects on the characteristics of the finished material. The extent of the damage that can be caused to dyed wool depends on pH and time–temperature profile of the dyeing cycle. When the wool is maintained at temperatures near 100 °C in acid ambient for long times, the structure of the fiber is gradually damaged by hydrolysis of peptide bonds. Such damage can be minimized by reducing the operation time or, better yet, by reducing the dyeing temperature. Therefore many low temperature wool dyeing processes were proposed by introducing specific auxiliary agents [20,21] and enzyme or plasma pre-treatments [22–24]. Recently, ultrasound assisted wool dyeing was studied with the aim to reduce temperature or dyeing time with respect to the conventional dyeing technique. Kamel et al. [25] found a significant improvement of kinetics in wool dyeing with natural dye. McNeil and McCall [26] reported that ultrasound show potential to reduce the chemical and energy requirements in wool dyeing with reactive and acid milling dyes, but not with acid levelling dyes. Furthermore, Battù et al. [27] observed that in wool dyeing at 85 °C with acid dyes ultrasound caused an enhancement of the dyebath exhaustion as high as about 25%, or vice versa a dyeing time nearly 20% shorter than conventional dyeing. Yükselog˘lu and Bolat [28] confirmed these improvements using ultrasound in dyeing of wool fabrics at 80–90 °C with a pre-metallized dye. In the present work the possibility of reducing the temperature of conventional wool dyeing with a typical acid levelling dye using ultrasound was further investigated, in order to reach exhaustion values comparable to those of the standard procedure, obtaining dyed samples of good quality. The aim was to develop a laboratory method that could be transferred at industrial level, reducing both the energy consumption and fiber damage caused by the prolonged exposure to high temperature without the use of polluting auxiliary agents which are commonly used to improve the mass transfer kinetics of dyes onto the fiber surface.
2. Experimental 2.1. Materials Textile material was pure wool knitted fabric EMPA Mousseline, 200 g/m2, yarn 2/48 Nm (2 fibers) 550 tors/mz, single fiber 360 tors/ ms, previously washed for 10 min with 1 g/l solution of ECE surfactant and 10 ml/l NH3 (33%), followed by rinsing first in lukewarm, then in cool water to completely eliminate foam which might affect the uniform migration of dye on the fabric. The dye chosen was Telon Blue 100% (Acid Blue 80) by Dystar. It is a disulfonate acid dye that presents a maximum absorbance peak at 626 nm. Acetic acid of laboratory grade by Sigma–Aldrich was used for acidification. 2.2. Dyeing process The first aim of this study was the determination of isothermal exhaustion curves of the dyebath, with mechanically or ultrasound alone agitation and coupling both, at different dyeing temperatures: 60, 70 and 80 °C. The experiments were performed without auxiliary chemicals. An Elmasonic S60H (Elma GmbH & Co., Singen, Germany) ultrasonic and thermo-controlled bath was used. It can generate ultrasound at 37 kHz with effective ultrasound power of 150 W and heating power of 400 W. The dyeings were made on 2.00 g wool samples introduced in a beaker containing the dyebath. Then the beaker was immersed in the water bath of the ultrasonic equipment. Mechanical agitation was provided by a magnetic stirrer turning at 110–120 rpm, plunged in the same bath. Tests without ultrasound were carried out with the sonication turned off. A 1:50 material to liquor ratio was chosen, with 1% o.w.f. (over weight fiber) dye amount at pH adjusted to 4 by acetic acid addition. The dyeing temperature was maintained for 110 min, analyzing bath samples every 10 min to monitor dye exhaustion. The measurements were performed with an UV–VIS spectrophotometer UNICAM UV2 (ATI Unicam, Cambridge, UK) and evaluated by ‘‘Vision 32’’ software basing on Lambert–Beer law. Finally, the dyed samples were squeezed, thoroughly rinsed with cold water, and dried at 100 °C. 2.3. Ultrasound effect evaluation From exhaustion curves, besides the final bath exhaustion reached, times of half dyeing were also determined. It is the time required by a fabric to adsorb half the amount of dye adsorbed at equilibrium, so as it is small, the more dyeing process is fast. Moreover, to evaluate the effect on wool dyeing produced by ultrasound, absorption rate constants and apparent activation energies were determined. Adsorption rate constants were calculated from the exhaustion curves, by fitting the experimental values according to Cegarra– Puente modified kinetic equation [17]:
" ln ln 1
E2t E21
!# ¼ a ln t þ a ln K
ð1Þ
where Et is the dye concentration in the fiber at the time t, E1 the dye concentration at the equilibrium, K the absorption rate constant, and t is the dyeing time. Arrhenius equation was used for apparent activation energy calculation: E
K T ¼ K 0 eRT
ð2Þ
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ðK US K ST Þ DK% ¼ 100 K ST
ð3Þ
where KUS and KST are the rate constants of dyeing with ultrasonic and stirring alone process, respectively [14]. For each sample dyed with the different dyeing processes, color fastness to domestic washing (UNI-EN ISO 105-C01), and rubbing (UNI-EN ISO 105-X12) were carried out. Moreover, to evidence a possible damage of wool fibers caused by ultrasound, the surface morphology was examined by SEM with a Leica (Cambridge, UK) Electron Optics 435 VP scanning electron microscope with an acceleration voltage of 15 kV, a current probe of 400 pA, and a working distance of 20 mm. The samples were mounted on aluminum specimen stubs with double-sided adhesive tape and sputter-coated with gold in rarefied argon with an Emitech (Kent, UK) K550 sputter coater with a current of 20 mA for 180 s.
120 100
Exhaustion (%)
where KT is the absorption rate constant at the absolute temperature T, E the apparent activation energy, K0 the frequency factor, and R is the ideal gas constant (R = 8.314 J/mol K). Finally, ultrasonic efficiency (DK%) to accelerate the dyeing rate was calculated by introducing the following equation:
stirring + us
120 100
Exhaustion (%)
stirring alone us alone
0
0
20
40
60
80
100
120
time (min) Fig. 2. Comparison between the exhaustion kinetics of wool dyeing at 70 °C.
120
80 60 40 stirring + us us alone
20
stirring alone 0
60
80
100
120
time (min) Fig. 1. Comparison between the exhaustion kinetics of wool dyeing at 60 °C.
Exhaustion (%)
In Figs. 1–3 the comparison of the exhaustion curves was made between mechanically or ultrasound alone agitated dyeing and coupling both at 60, 70 and 80 °C, respectively. In Fig. 1 it is evident that at 60 °C with mechanical stirring alone the complete exhaustion is not reached even after 110 min, while in the presence of ultrasound the final exhaustion was complete. However coupling mechanical stirring and ultrasound the complete exhaustion was reached already after 60 min. At 70 °C (Fig. 2) 90 min were needed to obtain 100% exhaustion with mechanical stirring or ultrasound alone while ultrasound coupled with mechanical agitation reduced this time to 40 min. Finally at 80 °C these times were further reduced to 80 and 30 min, respectively. Hence the ultrasonic energy coupled with mechanical stirring showed a synergic effect strongly improving the kinetics of the process even at the higher temperature. However ultrasound agitation alone in the adopted experimental conditions did not show an improvement of the dyeing kinetics and the corresponding exhaustion curves were practically unaffected by temperature increase. This could be due to the fact that ultrasound alone at the power applied did not induce
40
40
100
3.1. Exhaustion curves
20
60
20
3. Results and discussion
0
80
80 60 40 stirring + us stirring alone
20
us alone 0 0
20
40
60
80
100
120
time (min) Fig. 3. Comparison between the exhaustion kinetics of wool dyeing at 80 °C.
convective movements into the bath enough to assure a fast supply of dye molecules onto the fiber surface. Hence half dyeing times and absorption rate constants were evaluated only from the exhaustion curves related to mechanically stirred dyeing with or without ultrasound. These values are compared in Table 1. The absorption rate constants K increased with temperature in both the processes thanks to the positive effect of the temperature on dye diffusion into the fibers, but increased by at least 50%, at each temperature, in the presence of ultrasound. This increase confirmed the great importance of sonication effect on the dyeing kinetics, as highlighted by the ultrasonic efficiency values reported also in Table 1. The sonication effect is relevant at all the investigated temperatures, but the higher efficiency was found at the higher temperature, where the rate constant becomes more than double. The apparent activation energy values for both the processes were evaluated and the Arrhenius plot is reported in Fig. 4. The slope of the graph related to ultrasound-assisted process resulted slightly higher than that of stirring alone, hence the apparent activation energy values were calculated as 62.2 and 49.8 kJ/mol, respectively. However the values of ln K0 were 18.9 and 13.9, respectively showing that the strong enhancement of the kinetic constants in the presence of ultrasound is due to the increase of the pre-exponential factor K0. This effect on the kinetics was observed in many heterogeneous reactions carried out with ultrasound [29–31].
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Table 1 Times of half dyeing, absorption rate constants K and ultrasound efficiency DK. Temperature (°C)
Half dyeing time (min)
K (min1)
Stirring alone
Stirring and sonication
Stirring alone
Stirring and sonication
60 70 80
40 20 14
19 12 5
0.017 0.029 0.045
0.028 0.048 0.102
DK (%)
64.7 65.5 126.7
-2 stirring + us Fig. 7. Comparison between wool fabric dyed at 60 °C: (a) with ultrasound and stirring; (b) with stirring alone.
stirring alone
-2.5
ln(K T )
-3
Table 2 Dyeing fastness to rubbing. Fastness type
Dyeing process
-3.5
-4
-4.5 2.80
2.85
2.90
2.95
3.00
80
Stirring alone Stirring and sonication
3/4 5
4 5
4/5 5
Dry rubbing (degree)
Stirring alone Stirring and sonication
4/5 5
5 5
5 5
In order to evaluate if sonication effect could affect also the surface of wool fibers, another test was carried out at the lower temperature (60 °C). In this case wool was subjected to sonication for 120 min in acid solution, but in absence of dye. After this time sonication was turned off, the dye was introduced and the process went only with mechanical stirring. The resulting exhaustion curve was compared with the corresponding obtained without sonication and no enhancement in dyeing kinetics was observed with ultrasound pre-treatment, as reported in Fig. 5. This means that the effect of ultrasound was just on dye dispersion, mass transfer and diffusion, unaffecting the wool fiber structure, according to the results founded by McNeil and McCall in dyeing wool pre-treated with ultrasound [26].
Fig. 4. Arrhenius plot.
100
80
Exhaustion (%)
70
Wet rubbing (degree)
3.05
1000/T
60
40
3.2. Characterization of dyed samples
original
20
Dyeing temperature (°C) 60
pre-sonicated 0 40
60
80
100
120
time (min) Fig. 5. Comparison between the exhaustion kinetics of wool dyeing at 60 °C carried out with stirring alone on original and pre-sonicated fabrics.
The importance of dyeing at temperature lower than that commonly used in industry was demonstrated in our previous work carried out on wool yarn dyed at different temperatures [23]. Loss of tensile strength and elongation determined by Uster Tensorapid Tester dynamometer according to UNI-EN ISO 2062 showed that both tensile strength and elongation suffered a great loss after
Fig. 6. SEM images of undyed wool fabrics at magnification ratio of 800: (a) without any treatment; (b) after 110 min of ultrasound at 60 °C; (c) after 110 min of ultrasound at 80 °C.
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Dyeing process
60
70
80
Staining on cotton (degree)
Stirring alone Stirring and sonication
4/5 5
5 5
5 5
Staining on wool (degree)
Stirring alone Stirring and sonication
2/3 5
5 5
5 5
Color degradation (degree)
Stirring alone Stirring and sonication
3/4 5
5 5
5 5
Dye released in washings (mg/100 ml)
Stirring alone Stirring and sonication
3.55 1.21
1.66 1.02
1.21 0.92
dyeing at 98 °C while at lower temperature the degradation was reduced. In particular, wool yarn submitted to dyeing process at 98 °C showed a loss of mechanical performances of 24% for tensile strength and of 51% for elongation while at 65 °C the losses became 11% and 9%, respectively. Images of SEM analysis performed on undyed wool fabrics treated at 60 and 80 °C for 110 min at pH 4 under sonication are compared in Fig. 6 with that of untreated fabric. At 60 °C the surface of wool fibers appears to be practically undamaged by ultrasonic treatment, according to McNeil and McCall [26] which treated a wool fabrics at about the same frequency applied in our experiments. However at 80 °C some detachment of scales from the fibers is observed, hence at this temperature the treatment time should be reduced to avoid fiber degradation. At 60 °C sonication coupled with stirring gives dyed fabrics of good quality as shown in Fig. 7, where a sample dyed for 110 min under sonication and stirring is compared with another dyed under stirring alone for the same time. The coloration of the former is evidently uniform and more intense. Optimal fastness values at all the investigated temperatures are shown by the results reported in Tables 2 and 3. The most pronounced enhancement with respect to the process without sonication was shown by rubbing test in wet conditions and, in general, at the lower temperature. Moreover, in the case of washing fastness, no staining was revealed either on wool or cotton white standards, but dye release in washing liquids was evident. Hence these liquids were spectrophotometrically analyzed revealing great differences in dye concentrations. For each process, the amount of released dye was greater at the lower temperature according to a decrease in dyeing quality, but the dye release from the samples dyed with sonication was greatly reduced, confirming the good effect also on the fastness. It can be ascribed to a deeper penetration of the dye into the fiber as a consequence of diffusion improvement. All the dyeing tests were performed without auxiliary levelling agents so it can be said that ultrasound could replace these auxiliaries in dyeing processes. 4. Conclusions Comparing the results, a wool dyeing process with an acid levelling dye even at 60 °C with both mechanical stirring and sonication can be indicated as an ecofriendly alternative to traditional one, carried out at 98 °C. In this way, in fact, total bath exhaustion is coupled with low mechanical properties loss and great energy savings due to the lower process temperature involved. The positive effect of sonication on dyeing process was confirmed by the evaluation of all the kinetic parameters. Dyed fabrics showed optimal fastness values even in absence of levelling agents. Finally it was verified that ultrasound acts just on dye dispersion, mass transfer and diffusion, unaffecting the fiber structure.
Dyeing temperature (°C)
Moreover at 60 °C no surface fiber damage due to ultrasound was evidenced by SEM analysis. Acknowledgements This work was developed with the financial support of Regione Piemonte, Italy, Applied Scientific Research 2004, Project C46. The authors are gratefully to Dr. Raffaella Mossotti of CNR-ISMAC of Biella, Italy, for SEM analyzes. References [1] C. Hurren, P. Cookson, X. Wang, The effects of ultrasonic agitation in laundering on the properties of wool fabrics, Ultrason. Sonochem. 15 (2008) 1069–1074. [2] C. Basto, T. Tzanov, A. Cavaco-Paulo, Combined ultrasound-laccase assisted bleaching of cotton, Ultrason. Sonochem. 14 (2007) 350–354. [3] H.B.M. Lenting, E. Zwier, V.A. Nierstrasz, Identifying important parameters for a continuous bioscouring process, Text. Res. J. 72 (2002) 825–831. [4] D. Sun, Q. Guo, X. Liu, Investigation into dyeing acceleration efficiency of ultrasound energy, Ultrasonics 50 (2010) 441–446. [5] V. Sivakumar, P.G. Rao, Application of power ultrasound in leather processing: an ecofriendly approach, Ultrason. Sonochem. 9 (2001) 25–33. [6] S. Vajnhandl, A.M. Le Marechal, Ultrasound in textile dyeing and the decolouration/mineralization of textile dyes, Dyes Pigm. 65 (2005) 89–101. [7] V.S. Moholkar, M.M.C.G. Warmoeskerken, Investigations in mass transfer enhancement in textiles with ultrasound, Chem. Eng. Sci. 59 (2004) 299–311. [8] G.V. Datar, P. Banks-Lee, P.L. Grady, Acoustical properties of fabrics in highintensity ultrasound, Appl. Acoust. 48 (1996) 33–45. [9] S. Perincek, A.E. Uzgur, K. Duran, A. Dogan, A.E. Korlu, I.M. Bahtiyari, Design parameter investigation of industrial size ultrasound textile treatment bath, Ultrason. Sonochem. 16 (2009) 184–189. [10] A. Ojstršek, D. Fakin, The impact of ultrasonic-assisted dyeing on ecological parameters, in: Proceedings of the Eighth Autex Conference, Biella, Italy, June 24– 26, 2008.
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