Power Ultrasound-Assisted Cleaner Leather Dyeing Technique

Environ. Sci. Technol. 2004, 38, 1616-1621

Power Ultrasound-Assisted Cleaner Leather Dyeing Technique: Influence of Process Parameters VENKATASUBRAMANIAN SIVAKUMAR* AND PARUCHURI GANGADHAR RAO Chemical Engineering Division, Central Leather Research Institute, Adyar, Chennai 600 020, India

The application of power ultrasound to leather processing has a significant role in the concept of “clean technology” for leather production. The effect of power ultrasound in leather dyeing has been compared with dyeing in the absence of ultrasound and conventional drumming. The power ultrasound source used in these experiments was ultrasonic cleaner (150 W and 33 kHz). The effect of various process parameters such as amount of dye offer, temperature, and type of dye has been experimentally found out. The effect of presonication of dye solution as well as leather has been studied. Experiments at ultrasonic bath temperature were carried out to find out the combined thermal as well as stirring effects of ultrasound. Dyeing in the presence of ultrasound affords about 37.5 (1.8 times) difference as increase in % dye exhaustion or about 50% decrease in the time required for dyeing compared to dyeing in the absence of ultrasound for 4% acid red dye. About 29 (1.55 times) increase in % dye exhaustion or 30% reduction in time required for dyeing was observed using ultrasound at stationary condition compared with conventional dynamic drumming conditions. The effect of ultrasound at constant temperature conditions with a control experiment has also been studied. The dye exhaustion increases as the temperature increases (30-60 °C) and better results are observed at higher temperature due to the use of ultrasound. Presonication of dye solution or crust leather prior to the dyeing process has no significant improvement in dye exhaustion, suggesting ultrasound effect is realized when it is applied during the dyeing process. The results indicate that 1697 and 1416 ppm of dye can be reduced in the spent liquor due to the use of ultrasound for acid red (for 100 min) and acid black (for 3 h) dyes, respectively, thereby reducing the pollution load in the effluent stream. The color yield of the leather as inferred from the reflectance measurement indicates that dye offer can be halved when ultrasound is employed to promote dyeing. Scanning electron microscopy analysis of the cross section of the dyed leather indicates that fiber structure is not affected due to the use of ultrasound under the given process conditions. The present study clearly demonstrates that ultrasound can be used as a tool to improve the rate of exhaustion of dye, reduce pollution load in the spent effluent liquor, and improve the quality of leather produced. The study also offered provision to employ optimum levels of chemicals and increases percentage exhaustion for a given * Corresponding author phone: 91-044-24916706; fax: 91-04424911589; e-mail: [email protected]. 1616

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time, thereby limiting the pollution load in the tannery effluent, which is of great social concern.

Introduction Ultrasound is a sound wave with a frequency above the human audible range (16 Hz to 16 kHz). Power ultrasound having a frequency range of 20-100 kHz is commonly employed for enhancing physical processes such as cleaning, emulsification, degassing, crystallization, extraction, etc. and for accelerating/performing chemical reactions (1, 2). The potential uses of ultrasound with the aim to reduce process time and pollution load and to obtain improvement in the product quality are being studied extensively. In this work, the use of power ultrasound in leather dyeing has been studied. The main advantage of physical methods such as use of power ultrasound over chemical means of activation is that they do not contribute to pollution load in the form of chemical entities (3). The applications of power ultrasound in leather processing were studied earlier for its potential benefits in some of the process stages such as soaking and liming (4-9), degreasing (10), chrome tanning (10-12), vegetable tanning (13-17), and dyeing (18-21) and in fatliquoring (22-24). The application of power ultrasound to textile dyeing has also been reported for the possible benefits (25, 26). Recently, Sivakumar and Rao have made a detailed analysis on the application of power ultrasound in leather processing as an eco-friendly approach (27) and our earlier papers (28, 29) show beneficial effects of ultrasound in leather dyeing and dye uptake followed the square root dependence on time. An earlier investigation by Ding et al. (21) in leather dyeing with ultrasound employed 700-W (1.36 W/cm2) ultrasonic output power with 38-kHz frequency. In the present study lower ultrasonic output power of 150 W (0. 47 W/cm2) has been used with 33-kHz frequency. Even though investigations have been carried out earlier in leather dyeing, systematic investigations on the effect of important process parameters such as amount of dye offer, effect of temperature, pre-sonication effect on substrate as well as substance, quantification of color value of leather, and the effect of ultrasound on fiber structure of leather dyed with ultrasound have not been made so far. Hence, a detailed study has been made to cover these aspects and are presented in this paper. The objectives of the present study include the following: (a) Study the exhaustion of dye with and without ultrasound, thus reducing the unspent dye in the spent effluent liquor. (b) Study the effect of various process parameters and understand the enhancement obtained with ultrasound. (c) Quantify the improvement in color value of the leathers obtained with ultrasound and study the fiber structure of the leather dyed with ultrasound. (d) Achieve environmental benefits through improved dye exhaustion levels. Acoustic Cavitation. The sonochemical activity arises mainly from acoustic cavitation in liquid media. The cavitation can be explained as follows: when a liquid is irradiated by ultrasound, microbubbles can appear, grow, and oscillate extremely fast and even collapse violently if the acoustic intensity is high enough, that is, >1-3 W/cm2 (30). In the case of low ultrasonic intensities less than 3 W/cm2, generally experienced in the case of ultrasonic cleaner, stable cavitation bubbles are formed (31). Stable cavities are bubbles that oscillate often nonlinearly around some equilibrium size. 10.1021/es034853d CCC: $27.50

 2004 American Chemical Society Published on Web 01/23/2004

FIGURE 1. Schematic representation of ultrasonic cleaner experimental setup. They are relatively permanent and can continue to oscillate for many cycles of acoustic pressure. There is an acoustic streaming effect associated with the stable cavitation. Streaming action reduces the concentration gradient in the immediate neighborhood of the membrane (32). The increase in the amount of materials diffused in the ultrasonic field is mainly due to acoustic microcurrents, which increase the velocity of the particles of the medium (33).

Experimental Section Experimental Setup. Ultrasonic cleaner (4-L capacity) generating maximum available output power of 150 W as quoted by the manufacturer (Roop Telsonic-ultrasonics, India) at 33-kHz frequency was used in the present study for experiments in the presence of ultrasound. Schematic representation of the experimental setup used is shown in Figure 1. Experiments were carried out in a glass beaker with a flat bottom, clamped inside the ultrasonic cleaner filled with 2.5 L of water. A piezo-electric ultrasonic transducer fixed below the bottom wall at the center of the ultrasonic cleaner generates ultrasound at the specified frequency. The actual power dissipated in the dye vessel has been calculated to be 76 W by the calorimetric method (29, 34). The process beaker was positioned exactly at the center of the tank at a distance d above the transducer. The flat bottom surface of the process beaker was aligned parallel to the transducer face and the distance between the faces h. Control experiments in stationary condition were carried out in a water bath (Buchi, Switzerland) having a temperature controller. Drumming experiments were carried out using a dyeing drum (Ronald, India) having 22-cm diameter × 8.5-cm width and having temperature and rpm control. Drumming experiments were carried out at 45 rpm with temperature control. Process Details. Wet-blue cow leathers shaved to 1.2mm thickness were used for the experiments. Wet-blue leathers were rechrome-tanned with 5% BCS and neutralized to pH 6.0-6.5 and then retanned with 12% syntan and fatliquored with 10% fatliquor. Then the leathers were hooked to dry, staked, trimmed, and buffed. The full chrome cow crust leathers so processed were used for the dyeing experiments. Circular samples of 9-cm diameter were cut parallel to the backbone at corresponding portions from both sides of the leather for comparison of the experiments with and without ultrasound. The percentage of chemicals used and mentioned here is based on the crust leather weight. For the experiments carried out, typically the circular leather sample weight was 6 ( 0.5 g and exact weight of the leather samples taken were recorded. Each experiment was carried out with a single circular leather sample. Then the leathers were wetbacked

for 16 h with 1% ammonia solution and 1000% water. Then they were neutralized to the pH of 6-6.5 with 1% sodium formate and 1% sodium bicarbonate for 2 h. Then dyeing was carried out with X% acid red dye (X ) 2-10%) and 1000% water. Fixing of dye was carried out with X/2% formic acid. The dyes used for the experiments were acid red (Sandopel IGN, Clariant, India) and acid black 1 (Atul dyestuffs Ltd., India). All other chemicals used were LR grade. Distilled water was used for the dyeing experiments and double-distilled water for the dye analysis. To find out the effect of ultrasound, experiments with ultrasound at stationary condition have been compared with those in the absence of ultrasound at stationary condition. To find out the benefits over the conventional process, experiments with ultrasound at stationary condition have also been compared with conventional drumming condition. Various process parameters such as amount of dye offer (210%), temperature (30-60 °C), type of dye, and dyeing time have been studied.

Methods Analysis of Dye in the Spent Dye Liquor. The spent dye liquor samples were collected at regular time intervals from the dye bath and analyzed for the dye content using spectrophotometric method by measuring the absorbance value at the wavelength λmax of the dye used, after filtering and suitably diluting the sample. A Shimadzu UV-visible spectrophotometer UV-2101PC was used for the analysis. The % dye exhaustion and other calculations were made using the formula

% dye exhaustion ) dye offered - dye in the spent liquor × 100 dye offered mg of dye uptake per gram of leather ) dye uptake in mg weight of leather in g difference or increase in % dye exhaustion due to ultrasound ) (% dye exhaustion)us (% dye exhaustion)without us decrease in time due to ultrasound ) time taken for the given dye exhaustion (without ultrasound - with ultrasound) Color Value of the Dyed Leather. Quantification of color of the dyed leather was made according to the Commission Internationale de l’Eclairage (CIE) system of color measurement with 10° standard observer data (35). L* and a* values for both the grain as well as the flesh side of the dyed leathers were obtained using a Milton Roy color mate HDS spectrophotometer. The reflectance curves were also obtained and compared for the process with and without ultrasound. A more negative value of L* denotes darker shades and a more positive value of L* for lighter shades of the color. A more negative value of a* implies greener color and a more positive value of a* indicates higher red hue. Scanning Electron Microscopic (SEM) Analysis. Leather fiber structure from the cross section of the leather dyed with and without ultrasound has been studied using SEM analysis. Leather samples without any pretreatment were cut into uniform sizes and then gold-coated using an Edwards sputtering device. Analysis was performed using a Leica Cambridge Stereoscan 440 Scanning Electron Microscope.

Results and Discussions Effect of Amount of Dye Offer. The effect of variation in amount of dye given 2-10% (% based on crust leather weight) has been studied using acid red dye. Total dyeing time was VOL. 38, NO. 5, 2004 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 2. Increase in temperature inside the ultrasonic dye bath (Tus) during the course of the dyeing process fixed at 100 min. Formic acid fixing was carried out after 1 h in three feeds. The temperature inside the ultrasonic dye bath during the course of the dyeing process was measured using a thermocouple with digital display. There is a gradual rise in temperature due to localized heating effect of ultrasound (Figure 2). The beneficial effects of ultrasound in leather dyeing are due to a combination of thermal as well as stirring effects of ultrasound. To find out the influence of ultrasound including the temperature effects, ultrasonic experiments were carried out without external cooling or heating, under room-temperature condition, and from this point onward this temperature condition is mentioned as Tus in this paper. The temperature inside the ultrasonic bath rises from room temperature (30 °C) to 49.7 °C from the start of the experiment until 100 min of dyeing time. Control experiments were carried out under room-temperature conditions at 30 °C. The results indicate an increase in the dye exhaustion levels for ultrasound-aided dyeing in comparison to dyeing without ultrasound as well as conventional drumming for 2-10% acid red dye offer. The amount of dye uptake per gram of leather increases as the percentage dye offer increases (Figure 3). The percentage exhaustion of dye decreases as the percentage dye offer increases from 2 to 10%. The increase in dye uptake with dye offer follows an equilibrium trend as the amount of dye offer increases from 2% to 10%. The order of dye uptake for the three processes is ultrasound > drum > without ultrasound. The values for % dye exhaustion for 4% dye offer are 82.42, 44.96, and 53.22 respectively for the processes with ultrasound, without ultrasound, and conventional drumming. Therefore, the difference or increase in % dye exhaustion due to ultrasound is found to be 37.5 (1.8 times) compared to the process without ultrasound in stationary condition and 29.2 (1.55 times) as compared to conventional drumming condition. The photograph of the spent liquor for 2% dye offer for the process with and without ultrasound shows that spent liquor is relatively colorless for the ultrasound-aided process (Figure 4). This is because 99.99% dye exhaustion is achieved with the aid of ultrasound when the dye offer is 2%. The corresponding value is 48.5% under identical conditions but without the use of ultrasound. Effect of Temperature. The temperature of the dye bath was maintained throughout the process at pre-selected values 1618

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FIGURE 3. Effect of amount of dye offer on dye uptake per gram of leather with ultrasound (at Tus), without ultrasound (at 30 °C), and conventional drumming (at 30 °C).

FIGURE 4. Photograph of the spent dye liquor for the process with and without ultrasound for 2% dye offer. Left: with ultrasound. Right: without ultrasound. by circulating cold/hot water from a thermostatic water bath. The effect of temperature (30, 40, 50, and 60 °C) of the process has been studied using 4% acid red dye. Since 4% dye offer is generally employed for dyeing various types of leathers and lies in the medium offer range, different parameters were studied, keeping the dye offer at the 4% level. Total dyeing time was fixed at 100 min. Formic acid fixing was carried out after 1 h in three feeds. The results indicate an increase in the dye exhaustion levels for ultrasound-aided dyeing in comparison to dyeing without ultrasound as well as conventional drumming for 30-60 °C (Figure 5). The percentage exhaustion of dye increases as the temperature of the dye bath increases from 30 to 60 °C. The order of dye uptake for the three processes is ultrasound > drum > without ultrasound. The difference in the dye uptake on account of the ultrasound-aided process is higher when the dyeing temperature was 60 °C in comparison to that at 30 °C. This difference may well arise from the variations of cavitation processes at 60 and 30 °C. At 60 °C, a relatively more stable cavitation effect leading to concomitant increase in dye uptake is feasible.

FIGURE 5. Effect of temperature on % exhaustion of acid red dye for 4% dye offer with ultrasound, without ultrasound, and conventional drumming for 100 min of dyeing.

FIGURE 7. % exhaustion of acid black 1 dye during the course of dyeing with (at Tus) and without ultrasound (at 30 °C) for 4% dye offer.

FIGURE 8. Effect of presonication (at Tus) of crust leather compared to dyeing with ultrasound during the process for 100 min of dyeing.

FIGURE 6. % exhaustion of acid red dye during the course of dyeing with (at Tus) and without ultrasound (at 30 °C) for 4% dye offer. Effect of Dyeing Time and Type of Dye. Experiments were carried out to study the effect of ultrasound during the course of the dyeing process using 4% acid red as well as acid black 1 dye. Since the penetration of acid black 1 dye is difficult as compared to that of acid red dye, the total dyeing time for acid black dye was set at 3 h. The temperature was maintained as Tus as explained in the section for the effect of amount of dye offer experiments. The temperature rises from 30 to 53.2 °C from the start of the experiment to 3 h time (Figure 2). A control experiment was carried out at 30 °C. There is a significant improvement in the percentage exhaustion of dye during the course of the dyeing process due to ultrasound for acid red and acid black 1 dye (Figure 6 and Figure 7). About 50% dyeing time can be saved due to the use of ultrasound as inferred from the time taken for 30% exhaustion level for ultrasound-aided dyeing in comparison to the control dyeing process. Effect of Presonication of Dye Solution. To understand the ultrasound-aided dyeing process, dye solution alone was

presonicated and subsequently used for dyeing in the absence of ultrasound. The dyeing experiment was carried out using 1% (w/v) dye solution and presonicated for 30 min (at Tus) with subsequent dyeing without ultrasound at 30 °C using 4% acid red dye for 100 min. The results indicate that presonication of the dye solution and subsequent dyeing without ultrasound has no appreciable improvement in the exhaustion of dye. In contrast, the use of ultrasound during the dyeing process has improved the exhaustion of dye significantly. Therefore, it is clear that the improvement observed in dyeing using ultrasound is realized when it is applied during the course of the dyeing. Absence of any effect of presonication of dye solution on the exhaustion levels indicates that there is no remarkable change in the dye particles during sonication since the dye selected was totally soluble in water under the conditions employed. This trend is not unexpected. Effect of Presonication of Crust Leather. Experiment was carried out by presonicating the crust leather (at Tus) for 1 h with 2000% water and subsequent dyeing without ultrasound at 30 °C using 4% acid red dye for 100 min. Dye liquor sample was taken every 30 min and analyzed for dye content. The results indicate that presonication of the crust leather and subsequent dyeing without ultrasound has no significant improvement in the percentage exhaustion of dye for 100 min of the dyeing process (Figure 8). Therefore, under the given conditions, presonication of crust leather does not bring about an irreversible change in the pore structure of the substrate such that the dyeing behavior of presonicated leather is altered. There may be reversible expansion and VOL. 38, NO. 5, 2004 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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TABLE 1. Color Measurement Values for the Leathers Dyed with Ultrasound, without Ultrasound, and Conventional Drumming Using Acid Red Dye for 100 min with ultrasound % grain/ dye flesh L* a* 2 3 4 5 6 7

FIGURE 9. Reflectance curves for the grain side of the leather dyed with 3% acid red dye, with ultrasound and without ultrasound.

FIGURE 10. Photograph of the grain side of the leathers dyed with 3% acid red dye, with ultrasound (left) and without ultrasound (right) for 100 min. contraction of pores during sonication, which help in dye diffusion process. Therefore, the studies indicate that presonication of leather or dye solution has no significant effect on leather dyeing and ultrasound effect is realized when applied during the dyeing process. Color Value of Leather. To quantify the influence of ultrasound on color value of dyed leathers, reflectance measurements have been made for leathers dyed with various amount of dye offer. The color values of leathers for dyeing experiments using 2-7% acid red dye with and without ultrasound indicate that leathers dyed in the presence of

G F G F G F G F G F G F

56.6 44 51.6 43.3 49.3 38.6 49.1 42.1 49.2 39.9 53.9 42.7

27 41.2 33.3 42.1 35.2 41.8 33.7 40.2 34.6 38.8 30.6 40.5

without ultrasound

L* 65.1 51.2 60.9 49.9 56 47.4 64.4 49.8 58.1 49.9 49.7 48.6

a*

L

da

conventional drum

L*

a*

dL

da

15 8.5 -12 54.2 24.7 -2.4 -2.3 37.2 7.2 -4 47.3 36.7 3.3 -4.5 20.1 9.4 -13.2 37.9 6.6 -4.2 27.2 6.7 -8.0 58.4 22.8 9.1 -12.4 39.3 8.8 -2.5 46.9 32.9 8.3 -8.9 14.6 15.3 -19.1 36.4 7.8 -3.8 22.8 8.9 -11.8 34.9 10 -4 33.1 -4.2 2.6 50.2 32.3 -3.7 1.8 35.1 5.9 -5.4 41.9 35.4 -0.8 -5.1

ultrasound have higher color values compared to the control leathers as presented in Table 1. It can be seen that 2 and 3% dye offer using ultrasound has better color value compared to 4 and 6% dye offer without ultrasound, respectively. Therefore, 50% of dye can be reduced under the given process conditions by using ultrasound to achieve the same color value obtained without ultrasound. These results can be further confirmed by the reflectance curves for the grain side of the leathers dyed with 3% dye offer, % reflectance vs wavelength (Figure 9). The leather with higher color value has lower % reflectance at the wavelength corresponding to that of color of the leather. The results indicate that leathers dyed with ultrasound have better color values compared to the leathers dyed without ultrasound. A photograph of the leathers dyed with 3% acid red dye offer (Figure 10) shows that leather dyed in the presence of ultrasound has better color intensity. Scanning Electron Microscopic (SEM) Analysis. Leather fiber structure, which is another important property for final leather and effect of ultrasound on the same, has been studied using SEM analysis. SEM analysis of the dyed crust leather dyed with ultrasound (at Tus) and without ultrasound (30 °C) for 4% acid red dye offer for 100 min have been made. The SEM photographs of the fiber bundles of the leather dyed with and without ultrasound at 1500× magnification were analyzed (Figure 11a, b). The photographs show that fiber bundles are intact for the leathers dyed with and without ultrasound. Therefore, SEM analysis results indicate that leather fiber structures are not affected due to the use of ultrasound in the dyeing process under the given process conditions.

FIGURE 11. Scanning electron micrographs of fiber bundles for the leathers dyed with 4% acid red dye (a) with ultrasound (at Tus) and (b) without ultrasound (at 30 °C) for 4% acid red dye offer for 100 min. 1620

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TABLE 2. Amount of Dye Present in the Spent Dye Liquor for Dyeing with and without Ultrasound for 4% Acid Dye Offer amount of dye in the spent dye liquor (ppm) dyeing with without reduction type of dye time (min) ultrasound ultrasound due to ultrasound acid red acid black

100 180

805.95 92.13

2502.7 1507.7

1696.75 1415.57

Environmental Benefits. The results indicate that 1697 and 1416 ppm of dye can be reduced in the spent liquor due to the use of ultrasound for acid red (for 100 min) and acid black (for 3 h) dyes, respectively, as presented in Table 2. Therefore, there is about 68% and 94% reduction in dye in the effluent stream due to the use of ultrasound for the dyeing process using acid red and acid black dyes, respectively, thereby resulting in lower pollution load for the ultrasoundaided dyeing process compared to that for the control process. Techno Economic Feasibility Study. Preliminary cost analysis indicated that savings in dyeing due to ultrasound could compensate electrical energy cost for the ultrasonic process (3). Savings in dyeing time can compensate for the ultrasonic equipment cost over a payback period. Additional benefit can be obtained due to potential reduction in effluent treatment cost due to significant reduction of dye in the spent dye liquor. Further experiment on a large scale with optimum design of the ultrasonic process equipment will lead to ultrasound application on an industrial scale. Mechanisms for the Enhancement with Ultrasound. The possible reasons for the enhancement in leather dyeing due to the use of ultrasound are as follows: (a) Presonication studies as well as SEM analysis results give a clue for the reversible opening and closing of the pores in the leather matrix during the compression and rarefaction cycle of the ultrasonic wave propagation aiding penetration of dye. (b) Ultrasound propagation through the leather matrix causes internal stirring action. (c) In the case of low ultrasonic intensity, ∼0.5 W/cm2 employed in the present study, stable cavitation is produced. Stable cavitation induced effects such as microjet formation, which increase the velocity of the dye molecules present. (d) Enhanced molecular motion causes frictional heat and produces a localized rise in temperature.

Acknowledgments One of the authors (V.S.) is grateful for the financial assistance and fellowship provided by the Council of Scientific and Industrial Research (CSIR), India. The authors thank Dr. T. Ramasami, Director, C.L.R.I, for his scientific stimulation. Prof. R. Kumar and Prof. K. S. Gandhi, I.I.Sc, Bangalore, are thanked for their valuable suggestions regarding the project. Dr. N. R. Rajagopal, Faculty, Bits Pilani for his valuable help. Mr. G. Swaminathan, Mr. B. V. Ramabrahmam, Dr. C. Muralidharan, Scientists CLRI, and Entire Staff Chemical Engineering Division are also thanked for their valuable help.

Literature Cited (1) Contamine, F.; Faid, F.; Wilhelm, A. M.; Berlan, J.; Delmas, H. Chem. Eng. Sci. 1994, 49 (24B), 5865-5873. (2) Ando, T.; Ichihara, J.; Hanafusa, T. Mem. Int. Sci. Res. 1985, 42, 27-39. (3) Sivakumar, V. Studies on the application power ultrasound in leather processing, Ph.D. Thesis submitted to Anna University, Chennai, India, 2001. (4) Fridman, V. M.; Zaider, A. L.; Dolgopolov, V.; Mikhailov, A. M. Legk. Promst. 1954, 14 (2), 43-44. (5) Herfeld, H. Gerbereiniss. Pranis 1978, 30, 144-166. (6) Renaut. U.S. Patent 2965435, 1958. (7) Mieczyslaw, T. Rev. Technol. Ind. Cuir. 1958, 50 (12), 261-267. (8) British Patent No. 683105, 1953, British Thompson Houston Company. (9) Alpa, Spa. World Leather 1995, 8 (7), 89-91. (10) Herfeld, H. Leder Haeutemarkt 1978, 30, 232-237, 271-274. (11) Akseband, A. M.; Grif, M. G.; Nozhenko, A. N. Kozh. Obuvn. Promst. 1961, 3 (8), 24-26. (12) Timochin, N. A.; Barinov, I. G.; Kraminora, K. G. Kozh. Obuvn. Promst. 1961, 3 (8), 15-16. (13) Ernst, R. L.; Gutmann, F. J. Soc. Leather Technol. Soc. 1950, 34, 454-459. (14) Simoncini, E.; Criscuolo, I. Cuio Pelli Mater Concianti 1953, 29, 82-91. (15) Fridmann, V. M.; Zaider, A. L.; Dogopolov, V.; Mikhailov, A. M. Legk. Promst. 1958, 18 (3), 13-14. (16) Karpman, M. J. Kozh. Obuvn. Promst. 1962, 4 (5), 34-35. (17) Witke, F. Ost. Leder. Ztg. 1952, 7, 165-166. (18) Cujan, Z.; Kolomaznik, K.; Mladek, M. Leder. Waren. 1984, 19 (4), 180-182. (19) Xie, J. P.; Ding, J. F.; Mason, T. J.; Attenburrow, G. E.; Mason, T. J. J. Am. Leather Technol. Assoc. 1999, 94, 146-157. (20) Sivakumar, V.; Rao, P. G. In Proceedings of the XXV IULTCS Congress; CLRI: Chennai, 1999; p 146. (21) Ding, J. F.; Xie, J. P.; Attenburrow, G. E. In Advances in Sonochemistry; Mason, T. J., Ed.; JAI Press: London, 1999; Vol. 5, p 249. (22) Senilov, B. V.; Obuklov, D. USSR Patent 133160, 1960. (23) Xie, J. P.; Ding, J. F.; Mason, T. J.; Attenburrow, G. E.; Mason, T. J. J. Am. Leather Technol. Assoc. 2000, 95, 85-91. (24) Sivakumar, V.; Rao, P. G. In Proceedings of Chemcon-2000, Indian Institute of Chemical Engineers IIChE: Calcutta, PDD, 2000; Vol. II, p 29. (25) Thakore, K. A. Indian J. Text. Res. 1988, 13, 133-139, 208-212. (26) Saligram, A. M.; Shukla, S. R. J. Soc. Dyers. Colour. 1993, 109, 41-43. (27) Sivakumar, V.; Rao, P. G. J. Cleaner Prod. 2001, 9 (1), 25-33. (28) Sivakumar, V.; Rao, P. G. Ultrason. Sonochem. 2003, 10 (2), 8594. (29) Sivakumar, V.; Rao, P. G. J. Am. Leather Chem. Assoc. 2003, 98 (6), 230-237. (30) Suslick, K. S. Sci. Am. 1989, 260 (2), 62-68. (31) Mason, T. J. The Uses of Ultrasound in Chemistry; Royal Society of Chemistry: Cambridge, 1990. (32) Mortimer, A. J.; Trollope, B. J.; Villeneuve, E. J.; Roy, O. Z. Ultrasonics 1988, 26, 348-351. (33) Lenart, I.; Auslander, D. Ultrasonics 1980, 18, 216-218. (34) Hagenson, L. C.; Doraiswamy, L. K. Chem. Eng. Sci. 1998, 53, 131-147. (35) McLaren, K The Colour Science of Dyes and Pigments; Adam Hilger Ltd: Bristol, 1983.

Received for review August 1, 2003. Revised manuscript received November 16, 2003. Accepted December 17, 2003. ES034853D

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