Water Footprint in Leather Tanning and Steel Production
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5 Post-Tanning Operations
This last stage is also considered as the finishing process which consists of rechrome
tanning, neutralization, retanning, dyeing, and fatliquoring.
Rechrome Tanning
In this step, a basic chromium sulfate is used to treat and level the tanned hides. A
volume per chrome-tanned leather produce is between 2,000 and 3,000 L.
Neutralization
The neutralization consists of the reduction of the cationic surface charge of chrometanned leather so that the uptake of dyestuffs, fat liquors, and anionic retanning agents
will be monitored. A better and uniform distribution of processing agents during
successive steps is then achieved. A total volume of 5,000–6,000 L water/t tanned
leather is required to accomplish the neutralization process.
Retanning
Due to the lessened molecular weight of chrome complexes, the tanned leather
produced are generally not saturated, then retaining is always required. Different
retannage and retanning materials are available, and are used together or by combination according to the final of the desired product. Acrylic syntan, vegetable tannins
(quebracho, wattle, phenol–formaldehyde condensates), and resins syntan based on
melanine are the various retanning materials generally used.
Dyeing
Leather dyeing is a transition process between tanning and finishing. This process
is in relation to retanning and fatliquoring, as well as these materials are anionic
in nature, and one can act as a regulator to the other. The final physical properties
required in the leather such as light fastness, rub fastness, resistance to solvents,
perspiration resistance, etc., determine the choice of dyestuffs.
Fat Liquoring
In this step, leather is lubricated and softens. The nature of substrates, the stage of
the application, the nature of the fat liquor, and the type of finished leather are the
parameters to be considered for the affinity of fat liquor to tanned leather and its
efficiency in lubricating fibers. Generally, retanning, dyeing, and fat liquoring are
implemented together, with a water requirement of 2,500–3,500 L/t tanned leather
(Fig. 1).
The leather industry is therefore a sector of both public and private economies
on which many countries depend. Also, in agreement with the Food and Agriculture
Organization (FAO) of the United Nations, the interest in leather products, in general,
is expected to continue in the world especially in developing countries as presented
by recent findings throughout different regions in the world [6]:
141
5 Post-Tanning Operations
This last stage is also considered as the finishing process which consists of rechrome
tanning, neutralization, retanning, dyeing, and fatliquoring.
Rechrome Tanning
In this step, a basic chromium sulfate is used to treat and level the tanned hides. A
volume per chrome-tanned leather produce is between 2,000 and 3,000 L.
Neutralization
The neutralization consists of the reduction of the cationic surface charge of chrometanned leather so that the uptake of dyestuffs, fat liquors, and anionic retanning agents
will be monitored. A better and uniform distribution of processing agents during
successive steps is then achieved. A total volume of 5,000–6,000 L water/t tanned
leather is required to accomplish the neutralization process.
Retanning
Due to the lessened molecular weight of chrome complexes, the tanned leather
produced are generally not saturated, then retaining is always required. Different
retannage and retanning materials are available, and are used together or by combination according to the final of the desired product. Acrylic syntan, vegetable tannins
(quebracho, wattle, phenol–formaldehyde condensates), and resins syntan based on
melanine are the various retanning materials generally used.
Dyeing
Leather dyeing is a transition process between tanning and finishing. This process
is in relation to retanning and fatliquoring, as well as these materials are anionic
in nature, and one can act as a regulator to the other. The final physical properties
required in the leather such as light fastness, rub fastness, resistance to solvents,
perspiration resistance, etc., determine the choice of dyestuffs.
Fat Liquoring
In this step, leather is lubricated and softens. The nature of substrates, the stage of
the application, the nature of the fat liquor, and the type of finished leather are the
parameters to be considered for the affinity of fat liquor to tanned leather and its
efficiency in lubricating fibers. Generally, retanning, dyeing, and fat liquoring are
implemented together, with a water requirement of 2,500–3,500 L/t tanned leather
(Fig. 1).
The leather industry is therefore a sector of both public and private economies
on which many countries depend. Also, in agreement with the Food and Agriculture
Organization (FAO) of the United Nations, the interest in leather products, in general,
is expected to continue in the world especially in developing countries as presented
by recent findings throughout different regions in the world [6]: