140
P. S. Kumar et al.
remove subcutaneous material and weighed. Sodium sulfide, lime, and/or an enzyme
is used during the dehairing stage, whereas only 3–3.5% is used during the reliming
process. The final product obtained after the liming operation consumes 4,000–6,000
L water/t hide.
Deliming-Cum-Bating
In order to neutralize and remove the lime from pelt, ammonium sulfate or ammonium
chloride is used. Phenolphthalein is used indicator to confirm the elimination of lime
in water by the absence of pink color. This step is following by the bating stage which
is the treatment of delimed hides with enzymatic precaution for the removal of short
hair, scud and enhances grain characteristics. During this process, 4,500–5,000 L
water/t is used.
Pickling
Pickling is defined as a process of conditioning delimed and bated pelts for chrome
tanning. A pH in the range of 2.8–3.0 is required to reach the equilibrium by using
sulphuric acid. This helps to bring the pH of collagen to a very low level to ease
the penetration of mineral tanning agent into the substance. A range of volume of
800–1,000 L water/t is used during this process.
4 Tanning Process
Tanning is a chemical process of converting raw hides or skins into leather through
stabilizing agents against heat and enzymatic attack [8]. Also, this process tends the
raw material to change their chemical, physical, and mechanic properties. Different
agents such as aldehydes, synthetic tannins, mineral tanning salts, vegetable tannins
materials are used to stabilize hides or skins. The most common tanning methods are
chrome, vegetable, or a combination of both. The choice of a method and any agent
depend on raw material, cost of materials, and the quality of the final product. In the
chromium process, chromium(III) sulfate is ([Cr(H2O) 6 ] 2 (SO 4 ) 3 ) has always been
used as the most adequate tanning agent. The increase of pH in a particular range is
being possible by using sodium bicarbonate leading to a cross-linkage between the
collagen and the chromium. In vegetable tanning, tannins naturally occur in the bark
or leaves of many plants are used as a class of polyphenol chemicals. Collagen is
then coated by tannins, render them less-water soluble and more resistant to bacterial
attack, finally, the hides are more flexible. This second step consumes around 1,500–
2,000 L water/t pelt. Nevertheless, recent studies have stated the chrome tanning as
the most used, but chromium tends to be noxious for human health when its uptake
value is beyond 13.4 µg 1,000 kcal
−1 [9], and also for various types of cancer [10].
P. S. Kumar et al.
remove subcutaneous material and weighed. Sodium sulfide, lime, and/or an enzyme
is used during the dehairing stage, whereas only 3–3.5% is used during the reliming
process. The final product obtained after the liming operation consumes 4,000–6,000
L water/t hide.
Deliming-Cum-Bating
In order to neutralize and remove the lime from pelt, ammonium sulfate or ammonium
chloride is used. Phenolphthalein is used indicator to confirm the elimination of lime
in water by the absence of pink color. This step is following by the bating stage which
is the treatment of delimed hides with enzymatic precaution for the removal of short
hair, scud and enhances grain characteristics. During this process, 4,500–5,000 L
water/t is used.
Pickling
Pickling is defined as a process of conditioning delimed and bated pelts for chrome
tanning. A pH in the range of 2.8–3.0 is required to reach the equilibrium by using
sulphuric acid. This helps to bring the pH of collagen to a very low level to ease
the penetration of mineral tanning agent into the substance. A range of volume of
800–1,000 L water/t is used during this process.
4 Tanning Process
Tanning is a chemical process of converting raw hides or skins into leather through
stabilizing agents against heat and enzymatic attack [8]. Also, this process tends the
raw material to change their chemical, physical, and mechanic properties. Different
agents such as aldehydes, synthetic tannins, mineral tanning salts, vegetable tannins
materials are used to stabilize hides or skins. The most common tanning methods are
chrome, vegetable, or a combination of both. The choice of a method and any agent
depend on raw material, cost of materials, and the quality of the final product. In the
chromium process, chromium(III) sulfate is ([Cr(H2O) 6 ] 2 (SO 4 ) 3 ) has always been
used as the most adequate tanning agent. The increase of pH in a particular range is
being possible by using sodium bicarbonate leading to a cross-linkage between the
collagen and the chromium. In vegetable tanning, tannins naturally occur in the bark
or leaves of many plants are used as a class of polyphenol chemicals. Collagen is
then coated by tannins, render them less-water soluble and more resistant to bacterial
attack, finally, the hides are more flexible. This second step consumes around 1,500–
2,000 L water/t pelt. Nevertheless, recent studies have stated the chrome tanning as
the most used, but chromium tends to be noxious for human health when its uptake
value is beyond 13.4 µg 1,000 kcal
−1 [9], and also for various types of cancer [10].