Environ. Sci. Technol. 2006, 40, 1069-1075
Reversing the Conventional Leather Processing Sequence for Cleaner Leather Production SUBRAMANI SARAVANABHAVAN,† PALANISAMY THANIKAIVELAN,‡ J O N N A L A G A D D A R A G H A V A R A O , * ,† BALACHANDRAN UNNI NAIR,† AND THIRUMALACHARI RAMASAMI† Chemical Laboratory, Centre for Leather Apparels & Accessories Development, Central Leather Research Institute, Adyar, Chennai 600 020, India
Conventional leather processing generally involves a combination of single and multistep processes that employs as well as expels various biological, inorganic, and organic materials. It involves nearly 14-15 steps and discharges a huge amount of pollutants. This is primarily due to the fact that conventional leather processing employs a “do-undo” process logic. In this study, the conventional leather processing steps have been reversed to overcome the problems associated with the conventional method. The charges of the skin matrix and of the chemicals and pH profiles of the process have been judiciously used for reversing the process steps. This reversed process eventually avoids several acidification and basification/neutralization steps used in conventional leather processing. The developed process has been validated through various analyses such as chromium content, shrinkage temperature, softness measurements, scanning electron microscopy, and physical testing of the leathers. Further, the performance of the leathers is shown to be on par with conventionally processed leathers through bulk property evaluation. The process enjoys a significant reduction in COD and TS by 53 and 79%, respectively. Water consumption and discharge is reduced by 65 and 64%, respectively. Also, the process benefits from significant reduction in chemicals, time, power, and cost compared to the conventional process.
Introduction Conventional leather processing involves four important sets of processes, viz., pre-tanning, tanning, post-tanning, and finishing. It includes a combination of single and multistep processes that employs as well as expels various organic and inorganic materials (1). The conventional method of leather making involves 14-15 steps comprising soaking, liming, reliming, deliming, bating, pickling, chrome tanning, basification, rechroming, basification, neutralization, washing, retanning, dyeing, fatliquoring, and fixing. This conventional technique discharges enormous amounts of wastewater along with pollutants (2). This includes BOD, COD, TDS, sulfides, chlorides, sulfates, chromium, etc. * Corresponding author phone: +91 44 2441 1630; fax: +91 44 2441 1630; e-mail:
[email protected]. † Chemical Laboratory. ‡ Centre for Leather Apparels & Accessories Development. 10.1021/es051385u CCC: $33.50 Published on Web 12/23/2005
2006 American Chemical Society
This is primarily due to the fact that the conventional leather processing employs “do-undo” process schemes such as swell-deswell (liming-deliming), pickle-depickle (pickling-basification), rechroming-basification (acidification-basification), and neutralization-fixing (basificationacidification) (3). In other words, conventional methods employed in leather processing subject the skin/hide to wide variations in pH (4). Such pH changes demand the use of acids and alkalis, which results in the generation of salts of calcium, sodium, and chromium ions. This results in a net increase in COD, TDS, chlorides, sulfates, and other minerals in tannery wastewaters (5). Conventional chrome tanning generally involves pickling, tanning using basic chromium sulfate (BCS), and followed by basification processes. Spent pickle liquor has high TDS and a considerable amount of COD, since pickling involves the use of 8-10% sodium chloride salt along with sulfuric acid (2). Spent chrome liquor contains significant amount of chromium, sulfates, and TDS. The conventional method of post-tanning involves 7-8 major steps comprising rechroming, basification, neutralization, washing, retanning, dyeing, fatliquoring, and fixing. Post-tanning processes employ a pH range of 4.0-6.5 and a variety of chemicals. The post-tanning processes contribute significantly to TDS, COD, and heavy metal pollution, as reported by Simoncini and Sammarco (6). Several attempts have been made to render the leather processing steps cleaner (7, 8). However, these improvements are specific to a unit operation. Implementation of all the advanced technologies and eco-friendly chemicals involves financial input and machinery requirements as well. This calls for the development of integrated leather processing methods and revamping the process sequence. Very few attempts have been made to revamp the whole or part of leather processing steps. Thanikaivelan et al. have attempted to process leather in a narrow pH range from 4 to 8.0 (5, 9). Later, a three-step tanning process was developed which involves enzymatic dehairing, fiber opening using enzyme or alkali, and pickleless chrome tanning at pH 8.0 (10, 11). Recently, integrated one-step wet finishing processes have been developed (12, 13). Further, process integration has been attempted by combining tanning and post-tanning steps in one bath (14). In this study, an attempt has been made to reverse the conventional leather processing steps. This is by treating the delimed pelts with post-tanning chemicals such as syntans, dye, and fatliquors, followed by chrome tanning at pH 5.05.2 (15). The percentage of post-tanning chemicals have been carefully designed and calculated, taking into account the shaved weight parameters. The performance of the final leathers has been evaluated in terms of physical as well as organoleptic properties. Softness of the leathers has been quantified and compared with that of conventionally processed leathers. The pollution parameters, such as COD and TS, have been quantified and analyzed. Technoeconomic viability of the developed process has also been discussed.
Experimental Methods Materials. Conventionally delimed/bated goatskins were chosen as the raw material. The chemicals employed for leather processing were of commercial grade. The chemicals used for analytical techniques were of laboratory grade. Process Chemistry of Conventional and Reversed Leather Processes. In this study, delimed goatskin was chosen as the starting material for conventional and reversed leather VOL. 40, NO. 3, 2006 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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processing. The delimed goatskin is partially anionic in charge. In the conventional leather process, the delimed goatskin is treated with sulfuric acid in order to convert the matrix charge into a cationic charge, prior to chrome tanning to avoid surface deposition as shown in eq 1. Salt is used to suppress the swelling by maintaining the ionic balance of the skin matrix.
During chrome tanning, chromium is irreversibly bound with the collagen matrix by cross linking with collagen carboxylic groups through coordinate covalent linkage, as illustrated in eq 2. Chrome-tanned leather is positive in charge.
The modified leather making process reverses the conventional process sequence by making use of the charge character of the delimed pelt. The charge of the delimed pelt is partially negative. Interestingly, the chemicals used for post-tanning are also negative in charge. Hence, the posttanning chemicals are treated with the delimed pelt without any problem in penetration, as shown in eq 6.
After treating with post-tanning chemicals, the pH is brought down to 5.0-5.2 (eq 7); this would not only facilitate the fixation of the post-tanning chemicals but also provides proper conditions for the application of basic chromium sulfate salt for pickleless tanning (16). The mechanism of chrome tanning at this condition is similar to that of pickleless tanning (16). In other words, a simultaneous penetration cum fixation of chromium molecules would take place (16). The final pH of leather as well as the spent liquor is around 3.8-4.0, due to the hydrolysis of chromium molecules. Hence, the amino groups of the collagen matrix, if any, are ionized and form electro static linkage with the negatively charged post-tanning chemicals (eq 8).
Chrome-tanned leathers are neutralized in order to avoid the surface fixation of negatively charged post-tanning chemicals on the positively charged chromium cross linked matrix. This is achieved by using mild alkalis such as sodium bicarbonate. During neutralization, the pH of the chromium cross linked matrix is raised to 5.0-5.2 (eq 3). Hence, the penetration of negatively charged post-tanning chemicals is achieved on a neutral matrix (eq 4).
To fix the post-tanning chemicals, the amino group of the chromium cross-linked leather matrix is ionized by bringing down the pH to 3.5-4.0 using formic acid (eq 5). The positively charged amino groups form an electrostatic linkage with the negatively charged post-tanning chemicals, such as syntans (R(S)-), dyes (R(D)-), and fatliquors (R(F)-), as shown in eq 5.
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Hence, it is seen that the crust leathers processed from conventional and modified methods are basically similar in character (see eqs 5 and 8). Process Description. Twenty delimed/bated goatskins were converted into shoe softy upper leathers through conventional and reversed processes. Ten skins were used for each process (for process details and comparative flowchart for conventional and reversed leather process, see the Supporting Information). Objective Assessment of Softness Through Compressibility Measurements. Softness of leathers can be numerically measured based on their compressibility (17). Circular leather pieces (2 cm2 area) from experimental and control crust leathers were obtained per IUP method (18) and conditioned at 80° ( 4° F and 65 ( 2% relative humidity over a period of 48 h. The samples were spread uniformly over the solid base of the C & R (compressibility and resilience) tester. The initial load acting on the grain surface was 100 g. The thickness at this load was measured 60 s after the load was applied. Subsequent loads were added and the change in thickness was recorded one minute after the addition of each load. Logarithm of change in leather thickness (Y axis) was plotted against logarithm of load (X axis).
TABLE 1. Comparison of Chromium Content and Shrinkage Temperature of Leathers and Percent Exhaustion of Chromium from Conventional (C) and Reversed (E) Processesa sample
% Cr2O3 (dry weight basis)
% exhaustion
Ts (°C)
C E
3.05 ( 0.10 3.84 ( 0.08
78 92
>120 >120
a
Moisture free tanned leather weight.
Physical Testing and Hand Evaluation of Leathers. Samples for various physical tests from experimental and control crust leathers (five each) were obtained per IUP method (18). Specimens were conditioned at 80° ( 4°F and 65 ( 2% relative humidity over a period of 48 h. Physical properties such as tensile strength, % elongation at break, tear strength, and grain crack strength were examined as per the standard procedures (19-21). Five crust leathers from the control and five from the experiment were assessed for softness, fullness, grain tightness, grain smoothness, and general appearance by hand and visual examination. The leathers were rated on a scale of 0-10 for each functional property by two experienced tanners; higher scores indicate a better property. Chromium Content and Shrinkage Temperature of Leathers. Samples from the official butt portion (18) of experimental (wet processed stage) and control wet blue leathers were taken for chromium estimation. A known weight (∼1 g) of the sample was taken, and the amount of chromium was estimated as per standard procedures (22). Samples were initially analyzed for moisture content (23), and chrome content was expressed on the dry weight basis of leather. The shrinkage temperature of the leathers was measured using a Theis shrinkage tester (24). Scanning Electron Microscopic Analysis. Samples from experimental and control leathers after crust stage were cut from the official sampling position (18). Samples were cut into specimens with uniform thickness. All specimens were then coated with gold using an Edwards E306 sputter coater. A JEOL JSM-840A scanning electron microscope (SEM) was used for the analysis. The micrographs for the grain surface and cross section were obtained by operating the SEM at high vacuum with an accelerating voltage of 15 KV in different lower and higher magnification levels. Chromium Exhaustion. Chrome liquor collected from the control chrome tanning process was analyzed for chromium content per the standard procedure, and uptake of chromium was calculated (25). In the case of the reversed leather process, the final liquor was collected and used for the analysis. Analysis of Composite Waste Liquor. Composite liquors from control and experimental processes were collected from all the unit operations except pre-tanning processes (soaking to deliming) and analyzed for COD and TS (dried at 103-105 °C for 1 h) per the standard procedures (26). From this, emission loads were calculated by multiplying concentration (mg/L) with volume of effluent (L) per metric ton of raw skins processed.
Results and Discussion Chromium in Leather and Spent Tan Liquor. The amount of chromium present in the leather and spent tan liquor has been analyzed to assess the chromium uptake behavior of the reversed process. The amount of chromium present in the leathers is given in Table 1. The leathers from the reversed process possess a higher amount of chromium compared to the control leathers. This is due to the presence of carboxyl groups of collagen in ionized form during the entire course of chrome tanning of the reversed process, as shown in eqs
FIGURE 1. Plot of log of change in load vs log of change in thickness for conventional and reverse processed leathers. 7-8. The mechanism of this process is similar to that of a pickle-basification-free chrome tanning process (16). The chromium uptake values of conventional and reversed processes are presented in Table 1. It is seen that the uptake of chromium is significantly increased in the reversed process compared to the conventional process. This is in accordance with the trend observed in the chrome content of leathers. The chromium concentration of the spent tan liquor from conventional and reversed process is 2286 and 528 ppm, respectively. The shrinkage temperature of leathers from both control and reversed processes is more than 120 °C. Softness Measurement. Objective assessment of softness for both control and experimental leathers has been made through compressibility measurements. Softness is directly proportional to compressibility of the leather. Hence, the logarithm of change in thickness was plotted against logarithm of change in load for the control and experimental leathers, which exhibited a linear fit (17). The plots are shown in Figure 1. The line equation was obtained from the fit. The negative slope angles were calculated from the line equation and the values are 8.40 and 8.46° for control and experimental leathers. It has been reported that the negative slope angle of a very soft sheep-based glove leather and for a soft grain garment leather was 8.56° and 5.69°, respectively (17). Higher negative slope angles imply more softness in the leather. In this study, it is seen that both the control and the experimental leathers exhibit a higher negative slope angle comparable to the values of very soft leathers. In other words, the reversed leather processing is capable of producing leathers with a softness similar to that of the conventional process. Strength and Organoleptic Properties. The average strength values of five leathers from both the conventional and the reversed processes are given in Table 2 along with the standard deviation. Strength properties of the leathers obtained from the reversed process are comparable to that of conventionally processed leathers, and all of them meet the Bureau of Indian Standards (BIS) specifications (27). The average rating for the five leathers from control and experiment, evaluated by two independent tanners, were calculated for each functional property and is given Figure 2 along with the standard deviation. Softness, fullness, grain smoothness, and grain tightness of the leathers from the reversed process are comparable or even better than the conventionally processed leathers. This is because of the improved uptake of chemicals. Generally, the appearance and overall performance of the leathers from reversed process is comparable to the conventionally processed leathers. Scanning Electron Microscopic Analysis. Scanning electron micrographs of crust leather samples from conventional and reversed processes showing the grain surface at a VOL. 40, NO. 3, 2006 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 2. Physical Strength Data of Control (C) and Experimental (E) Leathers tensile strength (kg/cm2)
% elongation at break
tear strength (kg/cm)
sample
average valuea
average valuea
average valuea
load (kg)
distension (mm)
load (kg)
distension (mm)
C E BIS norms27
223 ( 8 216 ( 6 200
65 ( 2 62 ( 3 40-65
57 ( 2 62 ( 2 30
45 ( 0.5 45 ( 1.0 20
11.2 ( 0.2 10.8 ( 0.4 7
46 ( 0.5 47 ( 0.5
12.3 ( 0.2 12.0 ( 0.3
a
grain crack strength (average valueb)
bursting strength (average valueb)
Average of mean of along and across backbone values for five leathers. b Average of load and distension values for five leathers.
FIGURE 2. Bulk properties of conventional and reverse processed leathers. Values in each property are the average rating for five leathers as evaluated by two tanners. Error bars indicate the standard deviation.
FIGURE 3. Scanning electron micrographs of crust leather samples showing the grain surface at a magnification of ×50 from (a) conventional and (b) reversed leather processing; cross section at a magnification of ×100 from (c) conventional and (d) reversed leather processing. magnification of ×50 are given in Figure 3a and b. The grain surface and the hair pores of both control and experimental crust leather samples are clean without any solid foreign particles. This shows that there is no surface deposition of chromium or any other performance auxiliaries. There is no 1072
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change in the surface morphology of the leather upon reversing the conventional leather process steps. Scanning electron micrographs of crust leather samples from conventional and experimental processes showing the cross section at a magnification of ×100 are given in Figure 3c and
TABLE 3. Comparison of Water Consumption and Discharge for Conventional (C) and Reversed (E) Leather Processing of 1 Kg Raw Skinsa C
E
unit processes
input (L)
output (L)
pickling chrome tanning/reversed process washing washing neutralization washing I washing II retanning, dyeing and fatliquoring washing dilution of acids/alkalis and emulsification of fatliquors total
0.80 0.40 1.60 0.60 0.30 0.60 0.60 0.30 0.60 0.30
0.40 0.78 1.60 0.48 0.28 0.58 0.60 0.29 0.60 0.30
6.10
5.91
input (L)
output (L)
0.40 1.60
0.38 1.58
0.16
0.16
2.16
2.12
a
Weight of skins before soaking; water audit was not made from soaking to deliming because they were constant for both conventional and reversed process.
TABLE 4. Spent Liquor Analysisa emission load (kg/ton of raw skinsc processed)
c
process
COD (ppm)b
TS (ppm)b
volume of effluent (L/ton of raw skinsc)
COD
TS
C E
6483 ( 18 8150 ( 22
32432 ( 32 18672 ( 36
5910 2120
38 18
192 40
a Composite liquors were collected from all the unit operations expect from soaking, liming, and deliming. b Average of three measurements. Weight of skins before soaking; C is conventional leather processing and E is reversed leather processing.
d. The fiber bundle weave pattern from grain to corium for both the samples seems to be similar. Higher magnification (×500) micrographs show that the splitting of fiber bundles after the mechanical operations is similar for leathers from both conventional and reversed processes (see Figure 3e and f, in the Supporting Information). Water Consumption. In principle, the reversed process enables significant reduction in the consumption of water because it avoids several acidification, deacidification and washing steps. Hence, a water audit has been made for conventional and reversed processes. The quantity of water employed and discharged for processing 1 kg of raw skin through conventional and reversed methods is given in Table 3. It is apparent that the reversed process enjoys a reduction in water consumption and effluent discharge by 65 and 64% for processing 1 kg of raw goatskin. It has been reported that, by 2025 AD, 1.8 billion people will live in countries or regions with absolute water scarcity (28). In this context, the ability of the reversed process to reduce the water consumption is one of the significant achievements. Environmental Benefits. The composite liquors have been collected from all the unit operations except soaking, liming, and deliming. COD and TS have been chosen to analyze the environmental impact of the conventional and reversed processes. A direct comparison of the observed COD and TS values may not give proper consequences on the environmental impact. Hence, these values have been converted into emission loads. The COD and TS values and the calculated emission loads are given in Table 4. It is interesting to note that the concentration of TS is significantly lower in the effluent from reversed process compared to the conventional process, despite the low hydraulic load. This is primarily due to the fact that the reversed process eliminates several acidification-deacidification steps that are practiced in conventional leather processing, as seen in eqs 1-8. It is known that acidification-deacidification steps would lead to the formation of neutral salts that contribute to dissolved
or total solids. It is seen that the concentration of COD in the effluent from the reversed process is slightly higher than the conventional process. This is due to the presence of pollutants in a significantly low amount of water. There is, however, a significant reduction in the COD and TS parameters when they are converted into emission loads. The reduction in COD and TS loads are 53 and 79%, respectively. These reductions are not only due to the elimination of several processes but also due to the better uptake of chemicals such as chromium, syntans, dyes, and fatliquors. It is intriguing to note that these reductions are without altering the process chemicals or using any speciality chemicals. Techno-Economic Viability. Implementation of any developed process in the industry demands technical feasibility and cost-effectiveness. In this study, a reversed leather process has been developed to achieve reductions in water, time, power, as well as better quality of leather and effluent. It is already shown (Table 3) that the reversed leather process enjoys a reduction in water consumption by 65% compared to the control process, which provides savings in water cost. This reduction in water consumption lowers the hydraulic load by 64%, and thereby reduces the operating cost of ETP. The consumption of process time and power for the control and experimental processes is shown in Table 5. Time consumption of the reversed process (drumming time) is 42% lower than the control process. Furthermore, there is also a significant reduction in the time lag between conventional chrome tanning and wet finishing, which is usually a minimum of 12 h (overnight aging). The reduction in the energy consumption for the reversed process is about 42%, compared to the control process, which leads to a savings of about US$ 16 for processing 1 metric ton of raw skins. The total chemical consumption for the conventional and reversed processes is given in Table 6. It is seen that the reversed process reduces the total chemical consumption by 54%. The chemical cost was not carried out for BCS, syntans, dyes, and fatliquors because there is no change in VOL. 40, NO. 3, 2006 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 5. Time and Power Consumption for the Conventional (C) and Reverse (E) Processesa time (h) unit operations
C
pickling chrome tanning/reversed process washing washing neutralization washing I washing II retanning, dyeing and fatliquoring fixing washing total total power consumption (kwh) cost (US$)
1.5 3.83 0.16 0.16 1.83 0.16 0.16 3.16 1.33 0.16 12.45 373.5 37.35
a
Glossary 1 metric ton
1000 kg
Bating
Treating the unhaired hides or skins with a commercial enzyme formulation in order to remove certain undesirable proteinous constituents
BCS
Basic chromium sulfate
BIS
Bureau of Indian standards
BOD
Biochemical oxygen demand
COD
Chemical oxygen demand
Control leather
Leather made using conventional process sequence
Crust
Dried and flexed leather after post tanning
Drum
Rotating cylindrical container (usually made of wood) used in leather production
ETP
Effluent treatment plant
E 7.0 0.16
7.16 214.8 21.48
1 h running ) 30 KWh; 1 KWh ) US$ 0.1.
TABLE 6. Table 6. Chemical Consumption for the Conventional (C) and Reversed (E) Leather Processing kg/ton of raw skins processed chemicals
C
sodium chloride sulfuric acid basic chromium sulfate sodium formate sodium bicarbonate syntans dyes fatliquors formic acid total
80 9.6 40 11 11 36 9 24 6 226.6
E
Experimental leather Leather made using reversed process sequence Fatliquor
An emulsion of oils or greases in water, usually with an emulsifying agent, used to lubricate the fibers of leather
Fatliquoring
It is a process in which the leather is treated with fatliquors for lubricating the fibers
IUP
International Physical Testing Commission
40 32 8 21.3 4 105.3
the type and percentage of chemicals between the two processes. However, the reversed process provides a considerable reduction in chemical cost by about US$ 20 for processing 1 metric ton of raw skins by avoiding the acids and alkalis required for several acidification and deacidification processes. Hence, it is evident that there is a significant reduction in the consumption of water, time, energy, and chemicals. This would provide an overall reduction in the cost of leather processing. The global leather industry is looking for a viable cleaner leather processing methodology to overcome environmental and economic constraints. The sustainability of leather production would depend on the development of an alternative system for leather making. In this scenario, the development of reversed leather processing by rationally changing the order of the conventional process sequence provides a technically as well as economically viable alternative. However, a commercial level study may be required to validate the perceived economic and technical benefits.
Official butt portion That part of the hide or skin covering the rump or hind part of the animal, where the samples are cut for physical or chemical testing Pelt
Skin/hide without hair
Sammying
Removal of free water by pressing the wet chrome tanned leather between two felt rollers
Syntan
Synthetic tanning agent used to fill the voids of leather matrix
TDS
Total dissolved solids, comprise inorganic salts and small amounts of organic matter that are dissolved in water
TS
Total solids, which includes dissolved and suspended solids
Acknowledgments
Upper
The authors thank Dr. R. Rajaram for physical testing measurements. S.S. thanks the CSIR, New Delhi for providing a senior research fellowship.
Leather meant for top portion of footwear
Wet blue
Chrome tanned leather in wet condition
Supporting Information Available Process details, comparative flowchart for conventional and reversed leather process, and scanning electron micrographs of the crust leather samples at higher magnification (×500) from conventional and reversed process. This material is available free of charge via the Internet at http://pubs.acs.org. 1074
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(3) Bienkiewicz, K. Physical Chemistry of Leather Making; Krieger Publishing: Malabar, FL, 1983. (4) Heidemann, E. Fundamentals of Leather Manufacture; Eduard Roether KG: Darmstadt, 1993. (5) Thanikaivelan, P.; Rao, J. R.; Nair, B. U. Development of a leather processing method in narrow pH profile. Part 1. Standardisation of unhairing process. J. Soc. Leather Technol. Chem. 2000, 84, 276-284. (6) Simoncini, A.; Sammarco, U. The possibility of reducing the CODs deriving from the fatliquoring of the softy leathers in residual baths; Proceedings of the XXIII IULTCS Congress: Germany, 1995. (7) Thanikaivelan, P.; Rao, J. R.; Nair, B. U.; Ramasami, T. Progress and recent trends in biotechnological methods for leather processing. Trends Biotechnol. 2004, 22, 181188. (8) Thanikaivelan, P.; Rao, J. R.; Nair, B. U.; Ramasami, T. Recent trends in leather making: processes, problems, and pathways. Crit. Rev. Environ. Sci. Technol. 2005, 35, 37-79. (9) Thanikaivelan, P.; Rao, J. R.; Nair, B. U. Development of a leather processing method in narrow pH profile. Part 2. Standardisation of tanning process. J. Soc. Leather Technol. Chem. 2001, 85, 106-115. (10) Thanikaivelan, P.; Rao, J. R.; Nair, B. U.; Ramasami, T. Stepping into third millennium: third generation leather processing A three step tanning technique. J. Am. Leather Chem. Assoc. 2003, 98, 173-184. (11) Thanikaivelan, P.; Rao, J. R.; Nair, B. U.; Ramasami, T. Biointervention makes leather processing greener: An integrated cleansing and tanning system. Environ. Sci. Technol. 2003, 37, 2609-2617. (12) Ayyasamy, T.; Thanikaivelan, P.; Chandrasekaran, B.; Rao, J. R.; Nair, B. U. Development of an integrated wet finishing process: Manufacture of garment leathers. J. Am. Leather Chem. Assoc. 2004, 99, 367-375. (13) Ayyasamy, T.; Thanikaivelan, P.; Rao, J. R.; Nair, B. U. The development of an integrated rechroming-neutralization-post tanning process: Manufacture of upper leathers from goatskins. J. Soc. Leather Technol. Chem. 2005, 89, 71-79. (14) Thanikaivelan, P.; Saravanabhavan, S.; Rao, J. R.; Nair, B. U. Integration of chrome tanning and wet finishing process for making garment leathers. J. Am. Leather Chem. Assoc. 2005, 100, 225-232.
(15) Saravanabhavan, S.; Thanikaivelan, P.; Rao, J. R.; Nair, B. U.; Ramasami, T. Transposed process for making leather. US Patent Application 20050138738, 2005. (16) Thanikaivelan, P.; Rao, J. R.; Nair, B. U.; Ramasami, T. Underlying principles in chrome tanning: Part 2. Underpinning mechanism in pickle-less tanning. J. Am. Leather Chem. Assoc. 2004, 99, 82-94. (17) Lokanadam, B.; Subramaniam, V.; Nayar, R. C.; Compressibility measurement and the objective assessment of softness of light leathers. J. Soc. Leather Technol. Chem. 1989, 73, 115-119. (18) IUP 2, Sampling. J. Soc. Leather Technol. Chem. 2000, 84, 303309. (19) IUP 6, Measurement of tensile strength and percentage elongation. J. Soc. Leather Technol. Chem. 2000, 84, 317-321. (20) IUP 8, Measurement of tear load - Double edge tear. J. Soc. Leather Technol. Chem. 2000, 84, 327-329. (21) SLP 9 (IUP 9), Measurement of distension and strength of grain by the ball burst test. In Official Methods of Analysis; The Society of Leather Technologists and Chemists: Northampton, 1996. (22) IUC 8, Determination of chromic oxide content. J. Soc. Leather Technol. Chem. 1998, 82, 200-208. (23) IUC 5, Determination of volatile matter. J. Soc. Leather Technol. Chem. 2002, 86, 277-278. (24) McLaughlin, G. D.; Theis, E. R. The Chemistry of Leather Manufacture, Reinhold Publishing Corp.: New York, 1945. (25) O’Flaherty, F.; Roddy, W. T.; Lollar, R. M. The Chemistry and Technology of Leather; Krieger Publishing Company: Florida, 1977; Vol IV. (26) Standard Methods for the Examination of Water and Wastewater, 17th ed.; Clesceri, L. S., Greenberg, A. E., Trussell, R. R., Eds.; American Public Health Association: Washington, DC, 1989. (27) Specification for glaze kid upper leather; IS 576. Bureau of Indian Standards New Delhi, India, 1989. (28) International Water Management Institute, Projected Water Scarcity in 2025. http://www.iwmi.cgiar.org/home/wsmap.htm (accessed November 2005).
Received for review July 17, 2005. Revised manuscript received November 20, 2005. Accepted November 28, 2005. ES051385U
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