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Studies on the application of natural dye extract from Bixa orellana seeds for dyeing and finishing of leather
Industrial Crops and Products 43 (2013) 84–86
Contents lists available at SciVerse ScienceDirect
Industrial Crops and Products journal homepage: www.elsevier.com/locate/indcrop
Short communication
Studies on the application of natural dye extract from Bixa orellana seeds for dyeing and finishing of leather A. Tamil Selvi a , R. Aravindhan b , B. Madhan a , J. Raghava Rao c,∗ a b c
Centre for Human and Organizational Resources Development, Central Leather Research Institute, Council of Scientific and Industrial Research, Adyar, Chennai 600 020, India Leather Process Technology Division, Central Leather Research Institute, Council of Scientific and Industrial Research, Adyar, Chennai 600 020, India Chemical Laboratory, Central Leather Research Institute, Council of Scientific and Industrial Research, Adyar, Chennai 600 020, India
a r t i c l e
i n f o
Article history: Received 4 June 2012 Received in revised form 9 July 2012 Accepted 10 July 2012 Keywords: Natural dye Bixa orellana Leather application Dyeing Finishing Eco benign
a b s t r a c t The types of dyestuff that are used by tanneries generally vary depending on the product range needed along with the dictates of the fashion world. It is a fact that each tannery uses between 50 and 100 different types of dyestuffs. Leather industry primarily uses dyestuffs such as acid, basic, metal complex, reactive and sulfur dyes. Many of the synthetic dyes used for leather dyeing are difficult to degrade due to their complex structure and xenobiotic properties. Hence, there is a need for development of more degradable or natural materials for use as a coloring agent for leathers, which would eco benign. Thus, the present study aims at extraction of color from Bixa orellana seeds and employing the same in dyeing and finishing of leather. The leathers dyed and finished using the natural dye extract showed better coloring properties. It is the first time, where this material is reported for their use in leather processing. © 2012 Elsevier B.V. All rights reserved.
1. Introduction Nowadays there is a growing demand for eco-friendly/non-toxic colorants, for application in dyeing of food, textile and leathers. Natural dyes and pigments have emerged as an important alternative to potentially harmful synthetic dyes (Chavan, 1995). In the present study, colorants extracted from the seeds of the Bixa orellana tree have been chosen for its dye ability to leather substrate. The fruit of the B. orellana tree consists of bur-like red; similar to sweet chestnut, containing from 10 to 50 seeds at a size of grape seeds covered with a thin layer of soft, slightly sticky vermilion pulp. The extract from the seed is rich in tannin but contains a mixture of eight colorants of carotenoids group; the major colorants are bixin and nor-bixin (Gulrajani et al., 2002; Das et al., 2007). The dye extracted from the B. orellana finds a wide range of utility as coloring agent for foods and beverages. Recently, the dye extracted from the seed covering has been used in dyeing of cotton, silk and wool samples (Hallagan et al., 1995). However, the application of these seed extract (B. orellana) for dyeing of leather has not been attempted. The main objective of the present study is extractions of colorants from the seeds (B. orellana) and employs them in the dyeing and finishing of leathers. Very scanty attempts have been
∗ Corresponding author. Fax: +91 44 24411630. E-mail address: rao [email protected] (J. Raghava Rao). 0926-6690/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.indcrop.2012.07.015
made on the use of natural dyes for leather manufacture (Rao et al., 2008; Velmurugan and Kannan, 2010). 2. Materials and methods 2.1. Materials Dried B. orellana seeds were collected from Forest Department, Dharmapuri district, Tamil Nadu, India. The intact material was stored in the dark at room temperature and used for the experiments. All the chemicals used in this study were of laboratory reagent grade. 2.2. Extraction and characterization of colorants from B. orellana seeds The dye from the seed material was extracted using water. Known amount (5 g) of B. orellana seeds were crushed in a mortar and pestle and soaked in water (100 mL) for 10 min and refluxed at 80 ◦ C (in water bath) for an hour. During this period, the colorants get extracted. The extracted solution was filtered through Watt man No. 1 filter paper. The pH of the extracted dye solution is 6.5. The extracted dye solution was subsequently employed for dyeing and finishing of leathers. The water extract of the B. orellana seed has been subjected to column chromatography using silica gel (60–120 mesh) and eluted stepwise using (100:13.5:10) methanol:chloroform:water as a
A. Tamil Selvi et al. / Industrial Crops and Products 43 (2013) 84–86
85
Table 1 Post tanning, dyeing and finishing process for manufacture of upper leathers. Process
Chemicals
%
Duration (min)
Remarks
Wash
Water
200
20
Drain
Acid wash
Water Acetic acid
100 0.5
60
pH = 3.0–3.2; drain/wash
Re-chroming
Water Chrome syntan
50 5
60
Basification
Sodium formate Sodium bicabonate
1 1
15 3 × 10 + 45
pH = 3.8–4.0; drain/wash/pile
Water Neutralization syntan Sodium formate Sodium bicabonate
100 1 1 1
20 15 3 × 10 + 45
pH = 4.8–5.0; drain/wash
Water Acrylic resin syntan Synthetic fatliquor Dye extract Phenolic syntan Melamine resin syntan Synthetic fatliquor Semi synthetic fatliquor
100 3 3 (x) 8 6 2 4
30 30 60
Check penetration
Formic acid
2
Neutralization
Retanning/dyeing/fatliquoring
Fixing
30 60 3 × 15 + 45
pH = 3.8–4.0; drain/wash/pile
Finishing formulation employing the seed extract colorant Coat
Chemical
Base
Polyurethane binder Water Penetrator
100 50 5
Dye (seed extract) Resin binder Protein binder Wax emulsion Penetrator
100 80 10 10 10
Lacquer emulsion Water
100 50
Intermediate
Top
Quantity (mL)
Remarks
Two cross coat, dry
Four cross coat, dry Two cross coat, dry
mobile phase. The purified samples have been further analyzed by Cary 100 UV-spectrophotometer. FT-IR of samples was analyzed using Perkin-Elmer RX I FT-IR spectrophotometer and particle size analysis of the dye solution was characterized using Malvern Instruments, UK.
where Co is the concentration of the colorant offered and Cs is the concentration of colorant in the spent liquor.
2.3. Experiments using the extracted dyes
Dyed leathers processed in this study were subjected to the reflectance measurements using a Milton Roy color Mate HDS instrument. Color measurements (L, a and b) were recorded, where ‘L’ represents lightness factor, ‘a’ represents the red and green axes and ‘b’ represents the yellow and blue axes. Samples of appropriate size (5 cm × 14 cm) were cut from both experimental dyed and finished leathers and were tested for dry and wet rub resistance (IUF 450, 1993). This method uses a SATRA-TM 167 crock meter. Samples were also tested for perspiration resistance (IS 6191, 1971) under the action of artificial perspiration solution. Finish film adhesion test was also carried out on the experimental finished leather (SATRA-TM 411, 1992).
The extracted dye solution was employed for dyeing of chrome tanned goat skins. Also, the possibility of utilizing colored seed extract in finishing operation was investigated. The dyeing and finishing process employed is shown in Table 1. 2.4. Analysis of B. orellana seed extracts exhaustion in the process liquor Calibration graph for the B. orellana seed extract colorant was prepared and the same was used for the determination of the concentration of the colorant in the spent wastewater. The spent wastewater from experimental dyeing process was collected and analyzed for the color using Cary 100 Perkin-Elmer UV-visible spectrophotometer at the absorbance value of (max ) 487 nm and the respective concentration was estimated from the calibration graph. The dye exhaustion was calculated based on the following equation: % Dye extract exhaustion =
C − C o s Co
× 100
2.5. Analysis of leathers dyed and finished with B. orellana dye extract
3. Results and discussions 3.1. Column chromatography The water extract of the B. orellana seed has been subjected to column chromatography using silica gel and eluted stepwise using methanol:chloroform:water as a mobile phase. Three bands of yellow color separated in the column. Similarly, when chloroform extract of the seed has been eluted using the mobile phase
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A. Tamil Selvi et al. / Industrial Crops and Products 43 (2013) 84–86
three bands of yellowish orange color and a single band of yellow color has been separated in the column. For acetone extract of the seed, two bands of reddish orange and two bands of orange color has been separated in the column. 3.2. Spectroscopic analysis of purified samples The infrared (IR) spectrums of the water elute were obtained and analyzed. The main absorbance peaks observed are 3367.47 cm−1 for OH group in Alcohol, Phenol; 2977.87 cm−1 for OH stretch for COOH group; 1650.95 cm−1 for NH group in Primary amines. This may be because of low intensity physical bond formation between the compounds. These functional groups are present in the B. orellana seed color components like bixin and nor-bixin. Hence, from IR spectroscopic study, it was found that there was no evidence of interaction between the colors. 3.3. Determination of particle size
Fig. 1. Picture of the leathers (a) dyed and (b) finished using B. orellana seed extracts.
The particle size measurements were carried out using a Malvern Zetasizer 3000 HSA. The measurements were performed and the distribution curve obtained. The particle size was measured using the method of photon correlation spectroscopy, (PCS). The result of the particle size analysis showed that there are two different size distribution ranging around 225 nm and 965 nm, respectively. Thus it could be inferred that the penetration of dye will be better or enhanced because of the smaller particle size of the dye molecules.
covering and uniform color throughout the leathers. The wet and dry rub fastness of the finished leather showed a grey scale rating of 4/5. Also, the light fastness rating equivalent to the blue-wool standards 4–5 has been obtained. The film adhesion test results showed that the film formed is strong with 1864 g (requirement min. 300 g in dry). The leathers also passed the perspiration resistance test. Fig. 1a and b, shows the photos of leathers dyed and finished using B. orellana seed extracts, respectively.
3.4. Application of dye Wet blue sheep skins have been dyed using the water extract of the B. orellana seed. Uniform intense shade on both grain and flesh side of the leathers have been observed. This clearly indicates that the dispersion and distribution of dye has been uniform, and the dye can be used for dyeing of leathers. 3.5. Color measurement of dyed crust Leathers colored using the seed extract have been subjected to reflectance measurement. The color measurement parameters viz., L, a and b have been recorded. The L, a and b values from different regions of the leather have found to be similar. The ‘L’ value was found to be 61, proving that the leathers are lighter in shade. Positive values of ‘a’ around 14 and ‘b’ around 52, show that the leathers are yellowish red in color. 3.6. Analysis of exhaustion in the spent liquor and rub fastness of leathers The % exhaustion of the dye has been determined and is around 81 ± 1%. This proves the efficiency of the dye employed in this study. The fastness to dry and wet rub of the naturally colored leathers is extremely good (rating 4/5 on grey scale). Leathers also showed moderately better light fastness (rating 3 on grey scale), equivalent to the blue-wool standards 4–5. 3.7. Investigation of seed extract for finishing The B. orellana seed extracts were used in the finishing process instead of synthetic pigments. The resulting leathers showed better
4. Conclusions The B. orellana seed extract have been characterized and chemical compound nor-bixin, which is yellow in color, was found maximum in the extract. The process of dyeing has rendered satisfactory results. Leathers dyed and finished using B. orellana extract showed better rub fastness characteristics. Film adhesion was found to be good. Hence, dyeing and finishing of leather to different shades and with better properties using, B. orellana extract appears to be a viable option for commercial exploitations as a replacement for synthetic dyes and pigments. References Chavan., R.B., 1995. Revival of natural dyes: a word of caution to environmentalists. Colourage 142, 27–30. Das., D., Maulik, S.R., Bhattacharya, S.C., 2007. Dyeing of wool and silk with Bixa orellana. Indian J. Fibre Text. Res. 32, 366–372. Gulrajani., M.L., Gupta, G., Gupta, P., 2002. Application of natural dyes on bleached in wool dyeing. J. Text. Assoc. 63, 119–124. Hallagan., J.B., Allen, D.C., Borelleca, J.F., 1995. The safety and regulatory status of food, drug and cosmetics colour additives exempt from certification. Food Chem. Toxicol. 33, 515–528. IS 6191 (LF:7), 1971. Determination of fastness to artificial perspiration of colored leather. Indian standards. IUF 450 (DIN EN ISO 11640), 1993. Determination of fastness to rubbing (wet and dry) of colored leather. Rao, J.R., Prakash, A., Thangaraj, L., Sreeram, K.J., Saravanabhavan, S., Nair, B.U., 2008. Natural dyeing of leathers using natural material. J. Am. Leather Chem. Assoc. 103, 68–75. SATRA-TM 411, 1992. Sole bond strength test. Velmurugan., P., Kannan, S.K., 2010. Natural pigment extraction from five filamentous fungi for industrial application and dyeing of leather. Carbohydr. Polym. 79, 262–268.
Contents lists available at SciVerse ScienceDirect
Industrial Crops and Products journal homepage: www.elsevier.com/locate/indcrop
Short communication
Studies on the application of natural dye extract from Bixa orellana seeds for dyeing and finishing of leather A. Tamil Selvi a , R. Aravindhan b , B. Madhan a , J. Raghava Rao c,∗ a b c
Centre for Human and Organizational Resources Development, Central Leather Research Institute, Council of Scientific and Industrial Research, Adyar, Chennai 600 020, India Leather Process Technology Division, Central Leather Research Institute, Council of Scientific and Industrial Research, Adyar, Chennai 600 020, India Chemical Laboratory, Central Leather Research Institute, Council of Scientific and Industrial Research, Adyar, Chennai 600 020, India
a r t i c l e
i n f o
Article history: Received 4 June 2012 Received in revised form 9 July 2012 Accepted 10 July 2012 Keywords: Natural dye Bixa orellana Leather application Dyeing Finishing Eco benign
a b s t r a c t The types of dyestuff that are used by tanneries generally vary depending on the product range needed along with the dictates of the fashion world. It is a fact that each tannery uses between 50 and 100 different types of dyestuffs. Leather industry primarily uses dyestuffs such as acid, basic, metal complex, reactive and sulfur dyes. Many of the synthetic dyes used for leather dyeing are difficult to degrade due to their complex structure and xenobiotic properties. Hence, there is a need for development of more degradable or natural materials for use as a coloring agent for leathers, which would eco benign. Thus, the present study aims at extraction of color from Bixa orellana seeds and employing the same in dyeing and finishing of leather. The leathers dyed and finished using the natural dye extract showed better coloring properties. It is the first time, where this material is reported for their use in leather processing. © 2012 Elsevier B.V. All rights reserved.
1. Introduction Nowadays there is a growing demand for eco-friendly/non-toxic colorants, for application in dyeing of food, textile and leathers. Natural dyes and pigments have emerged as an important alternative to potentially harmful synthetic dyes (Chavan, 1995). In the present study, colorants extracted from the seeds of the Bixa orellana tree have been chosen for its dye ability to leather substrate. The fruit of the B. orellana tree consists of bur-like red; similar to sweet chestnut, containing from 10 to 50 seeds at a size of grape seeds covered with a thin layer of soft, slightly sticky vermilion pulp. The extract from the seed is rich in tannin but contains a mixture of eight colorants of carotenoids group; the major colorants are bixin and nor-bixin (Gulrajani et al., 2002; Das et al., 2007). The dye extracted from the B. orellana finds a wide range of utility as coloring agent for foods and beverages. Recently, the dye extracted from the seed covering has been used in dyeing of cotton, silk and wool samples (Hallagan et al., 1995). However, the application of these seed extract (B. orellana) for dyeing of leather has not been attempted. The main objective of the present study is extractions of colorants from the seeds (B. orellana) and employs them in the dyeing and finishing of leathers. Very scanty attempts have been
∗ Corresponding author. Fax: +91 44 24411630. E-mail address: rao [email protected] (J. Raghava Rao). 0926-6690/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.indcrop.2012.07.015
made on the use of natural dyes for leather manufacture (Rao et al., 2008; Velmurugan and Kannan, 2010). 2. Materials and methods 2.1. Materials Dried B. orellana seeds were collected from Forest Department, Dharmapuri district, Tamil Nadu, India. The intact material was stored in the dark at room temperature and used for the experiments. All the chemicals used in this study were of laboratory reagent grade. 2.2. Extraction and characterization of colorants from B. orellana seeds The dye from the seed material was extracted using water. Known amount (5 g) of B. orellana seeds were crushed in a mortar and pestle and soaked in water (100 mL) for 10 min and refluxed at 80 ◦ C (in water bath) for an hour. During this period, the colorants get extracted. The extracted solution was filtered through Watt man No. 1 filter paper. The pH of the extracted dye solution is 6.5. The extracted dye solution was subsequently employed for dyeing and finishing of leathers. The water extract of the B. orellana seed has been subjected to column chromatography using silica gel (60–120 mesh) and eluted stepwise using (100:13.5:10) methanol:chloroform:water as a
A. Tamil Selvi et al. / Industrial Crops and Products 43 (2013) 84–86
85
Table 1 Post tanning, dyeing and finishing process for manufacture of upper leathers. Process
Chemicals
%
Duration (min)
Remarks
Wash
Water
200
20
Drain
Acid wash
Water Acetic acid
100 0.5
60
pH = 3.0–3.2; drain/wash
Re-chroming
Water Chrome syntan
50 5
60
Basification
Sodium formate Sodium bicabonate
1 1
15 3 × 10 + 45
pH = 3.8–4.0; drain/wash/pile
Water Neutralization syntan Sodium formate Sodium bicabonate
100 1 1 1
20 15 3 × 10 + 45
pH = 4.8–5.0; drain/wash
Water Acrylic resin syntan Synthetic fatliquor Dye extract Phenolic syntan Melamine resin syntan Synthetic fatliquor Semi synthetic fatliquor
100 3 3 (x) 8 6 2 4
30 30 60
Check penetration
Formic acid
2
Neutralization
Retanning/dyeing/fatliquoring
Fixing
30 60 3 × 15 + 45
pH = 3.8–4.0; drain/wash/pile
Finishing formulation employing the seed extract colorant Coat
Chemical
Base
Polyurethane binder Water Penetrator
100 50 5
Dye (seed extract) Resin binder Protein binder Wax emulsion Penetrator
100 80 10 10 10
Lacquer emulsion Water
100 50
Intermediate
Top
Quantity (mL)
Remarks
Two cross coat, dry
Four cross coat, dry Two cross coat, dry
mobile phase. The purified samples have been further analyzed by Cary 100 UV-spectrophotometer. FT-IR of samples was analyzed using Perkin-Elmer RX I FT-IR spectrophotometer and particle size analysis of the dye solution was characterized using Malvern Instruments, UK.
where Co is the concentration of the colorant offered and Cs is the concentration of colorant in the spent liquor.
2.3. Experiments using the extracted dyes
Dyed leathers processed in this study were subjected to the reflectance measurements using a Milton Roy color Mate HDS instrument. Color measurements (L, a and b) were recorded, where ‘L’ represents lightness factor, ‘a’ represents the red and green axes and ‘b’ represents the yellow and blue axes. Samples of appropriate size (5 cm × 14 cm) were cut from both experimental dyed and finished leathers and were tested for dry and wet rub resistance (IUF 450, 1993). This method uses a SATRA-TM 167 crock meter. Samples were also tested for perspiration resistance (IS 6191, 1971) under the action of artificial perspiration solution. Finish film adhesion test was also carried out on the experimental finished leather (SATRA-TM 411, 1992).
The extracted dye solution was employed for dyeing of chrome tanned goat skins. Also, the possibility of utilizing colored seed extract in finishing operation was investigated. The dyeing and finishing process employed is shown in Table 1. 2.4. Analysis of B. orellana seed extracts exhaustion in the process liquor Calibration graph for the B. orellana seed extract colorant was prepared and the same was used for the determination of the concentration of the colorant in the spent wastewater. The spent wastewater from experimental dyeing process was collected and analyzed for the color using Cary 100 Perkin-Elmer UV-visible spectrophotometer at the absorbance value of (max ) 487 nm and the respective concentration was estimated from the calibration graph. The dye exhaustion was calculated based on the following equation: % Dye extract exhaustion =
C − C o s Co
× 100
2.5. Analysis of leathers dyed and finished with B. orellana dye extract
3. Results and discussions 3.1. Column chromatography The water extract of the B. orellana seed has been subjected to column chromatography using silica gel and eluted stepwise using methanol:chloroform:water as a mobile phase. Three bands of yellow color separated in the column. Similarly, when chloroform extract of the seed has been eluted using the mobile phase
86
A. Tamil Selvi et al. / Industrial Crops and Products 43 (2013) 84–86
three bands of yellowish orange color and a single band of yellow color has been separated in the column. For acetone extract of the seed, two bands of reddish orange and two bands of orange color has been separated in the column. 3.2. Spectroscopic analysis of purified samples The infrared (IR) spectrums of the water elute were obtained and analyzed. The main absorbance peaks observed are 3367.47 cm−1 for OH group in Alcohol, Phenol; 2977.87 cm−1 for OH stretch for COOH group; 1650.95 cm−1 for NH group in Primary amines. This may be because of low intensity physical bond formation between the compounds. These functional groups are present in the B. orellana seed color components like bixin and nor-bixin. Hence, from IR spectroscopic study, it was found that there was no evidence of interaction between the colors. 3.3. Determination of particle size
Fig. 1. Picture of the leathers (a) dyed and (b) finished using B. orellana seed extracts.
The particle size measurements were carried out using a Malvern Zetasizer 3000 HSA. The measurements were performed and the distribution curve obtained. The particle size was measured using the method of photon correlation spectroscopy, (PCS). The result of the particle size analysis showed that there are two different size distribution ranging around 225 nm and 965 nm, respectively. Thus it could be inferred that the penetration of dye will be better or enhanced because of the smaller particle size of the dye molecules.
covering and uniform color throughout the leathers. The wet and dry rub fastness of the finished leather showed a grey scale rating of 4/5. Also, the light fastness rating equivalent to the blue-wool standards 4–5 has been obtained. The film adhesion test results showed that the film formed is strong with 1864 g (requirement min. 300 g in dry). The leathers also passed the perspiration resistance test. Fig. 1a and b, shows the photos of leathers dyed and finished using B. orellana seed extracts, respectively.
3.4. Application of dye Wet blue sheep skins have been dyed using the water extract of the B. orellana seed. Uniform intense shade on both grain and flesh side of the leathers have been observed. This clearly indicates that the dispersion and distribution of dye has been uniform, and the dye can be used for dyeing of leathers. 3.5. Color measurement of dyed crust Leathers colored using the seed extract have been subjected to reflectance measurement. The color measurement parameters viz., L, a and b have been recorded. The L, a and b values from different regions of the leather have found to be similar. The ‘L’ value was found to be 61, proving that the leathers are lighter in shade. Positive values of ‘a’ around 14 and ‘b’ around 52, show that the leathers are yellowish red in color. 3.6. Analysis of exhaustion in the spent liquor and rub fastness of leathers The % exhaustion of the dye has been determined and is around 81 ± 1%. This proves the efficiency of the dye employed in this study. The fastness to dry and wet rub of the naturally colored leathers is extremely good (rating 4/5 on grey scale). Leathers also showed moderately better light fastness (rating 3 on grey scale), equivalent to the blue-wool standards 4–5. 3.7. Investigation of seed extract for finishing The B. orellana seed extracts were used in the finishing process instead of synthetic pigments. The resulting leathers showed better
4. Conclusions The B. orellana seed extract have been characterized and chemical compound nor-bixin, which is yellow in color, was found maximum in the extract. The process of dyeing has rendered satisfactory results. Leathers dyed and finished using B. orellana extract showed better rub fastness characteristics. Film adhesion was found to be good. Hence, dyeing and finishing of leather to different shades and with better properties using, B. orellana extract appears to be a viable option for commercial exploitations as a replacement for synthetic dyes and pigments. References Chavan., R.B., 1995. Revival of natural dyes: a word of caution to environmentalists. Colourage 142, 27–30. Das., D., Maulik, S.R., Bhattacharya, S.C., 2007. Dyeing of wool and silk with Bixa orellana. Indian J. Fibre Text. Res. 32, 366–372. Gulrajani., M.L., Gupta, G., Gupta, P., 2002. Application of natural dyes on bleached in wool dyeing. J. Text. Assoc. 63, 119–124. Hallagan., J.B., Allen, D.C., Borelleca, J.F., 1995. The safety and regulatory status of food, drug and cosmetics colour additives exempt from certification. Food Chem. Toxicol. 33, 515–528. IS 6191 (LF:7), 1971. Determination of fastness to artificial perspiration of colored leather. Indian standards. IUF 450 (DIN EN ISO 11640), 1993. Determination of fastness to rubbing (wet and dry) of colored leather. Rao, J.R., Prakash, A., Thangaraj, L., Sreeram, K.J., Saravanabhavan, S., Nair, B.U., 2008. Natural dyeing of leathers using natural material. J. Am. Leather Chem. Assoc. 103, 68–75. SATRA-TM 411, 1992. Sole bond strength test. Velmurugan., P., Kannan, S.K., 2010. Natural pigment extraction from five filamentous fungi for industrial application and dyeing of leather. Carbohydr. Polym. 79, 262–268.