The leather manufacturing process are the operations taken to create leather from hides. The procedure is divided into three sub-processes: preparatory stages, tanning, and crusting. All true leathers will undergo these sub-processes. A further sub-process, surface coating, may be added into the sequence. The list of operations that leathers undergo vary with the type of leather. There are environmental impacts associated with the process.
The preparatory stages are when the hide is prepared for tanning. [1] During the preparatory stages many of the unwanted raw skin components are removed. Many options for pretreatment of the skin exist. Not all of the options may be performed. Preparatory stages may include: [2]
Tanning is the process that converts the protein of the raw hide or skin into a stable material which will not putrefy and is suitable for a wide variety of end applications. The principal difference between raw hides and tanned hides is that raw hides dry out to form a hard inflexible material that can putrefy when re-wetted (wetted back), while tanned material dries out to a flexible form that does not become putrid when wetted back. A large number of different tanning methods and materials can be used; the choice is ultimately dependent on the end application of the leather. The most commonly used tanning material is chromium, which leaves the leather, once tanned, a pale blue colour. This product is commonly called “wet blue”.
The acidity (pH) of hides once they have finished pickling will typically be between 2.8 and 3.2. At this point the hides are loaded in a drum and immersed in a float containing the tanning liquor. The hides are allowed to soak (while the drum slowly rotates about its axle) and the tanning liquor slowly penetrates through the full substance of the hide. Regular checks will be made to see the penetration by cutting the cross section of a hide and observing the degree of penetration. Once an even degree of penetration is observed, the pH of the float is slowly raised in a process called basification. This basification process fixes the tanning material to the leather, and the more tanning material fixed, the higher the hydrothermal stability and increased shrinkage temperature resistance of the leather. The pH of the leather when chrome tanned would typically finish somewhere between 3.8 and 4.2. [6]
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Crusting is when the hide/skin is thinned, retanned and lubricated. Often a coloring operation is included in the crusting sub-process. The chemicals added during crusting have to be fixed in place. The culmination of the crusting sub-process is the drying and softening operations. Crusting may include the following operations:
For some leathers a surface coating is applied. Tanners refer to this as finishing. Finishing operations may include:
The leather making process is in general restricted to batch processing, but if the surface coating sub-process is added, then some continuous processing can be included. The operation flow has to follow the preparatory → tanning → crusting → surface coating sub-process order without deviation, but some of the sub-processes can be omitted to make certain leathers (or partially tanned/ untanned products).
In addition to the other environmental impacts of leather, the production processes have a high environmental impact, most notably due to:
One tonne of hide or skin generally leads to the production of 20 to 80 m3 of turbid and foul-smelling wastewater, including chromium levels of 100–400 mg/L, sulfide levels of 200–800 mg/L and high levels of fat and other solid wastes, as well as notable pathogen contamination. Pesticides are also often added for hide conservation during transport. With solid wastes representing up to 70% of the wet weight of the original hides, the tanning process comes at a considerable strain on water treatment installations. [7]
Tanning is especially polluting in countries where environmental norms are lax, such as in India - the world's 3rd largest producer and exporter of leather. To give an example of an efficient pollution prevention system, chromium loads per produced tonne are generally abated from 8 kg to 1.5 kg. VOC emissions are typically reduced from 30 kg/t to 2 kg/t in a properly managed facility. Very clearly, the process remains highly polluting all the same. A review of the total pollution load decrease achievable according to the United Nations Industrial Development Organization [8] posts precise data on the abatement achievable through industrially proven low-waste advanced methods, while noting that « Even though the chrome pollution load can be decreased by 94% on introducing advanced technologies, the minimum residual load 0.15 kg/t raw hide can still cause difficulties when using landfills and composting sludge from wastewater treatment on account of the regulations currently in force in some countries. »
In Kanpur, the self-proclaimed "Leather City of the World" and a city of 3 million people on the banks of the river Ganges, pollution levels were so high that, despite an industry crisis, the pollution control board has decided to seal 49 high-polluting tanneries out of 404 in July 2009. [9] In 2003 for instance, the main tannery's effluent disposal unit was dumping 22 tonnes of chromium-laden solid waste per day in the open. [10]
The higher cost associated to the treatment of effluents as compared to untreated effluent discharging leads to environmental dumping to reduce costs. For instance, in Croatia in 2001, proper pollution abatement cost 70-100 USD/t of raw hides processed against US$43/t for irresponsible behaviour. [11]
No general study seems to exist, but the current news is rife with documented examples of untreated effluent discharge. In November 2009 for instance, it was discovered that one of Uganda's main leather producing companies directly dumped its waste water in a wetland adjacent to Lake Victoria. [12]
Nevertheless, several researchers have developed cleaner leather processing methodologies to reduce the environmental impact of conventional leather processing and to lower the burden of end-of-pipe treatment. They include salt-free preservation systems, enzyme-assisted low-sulfide hair removal processes, [13] chemical-free enzymatic fiber opening, [14] ammonia-free deliming systems, pickle-free chrome tanning process, waterless chrome tanning technology, [15] chrome-free tanning methods, formaldehyde-free syntans [16] and solvent-free finishing systems. [17] Some of these processes have found commercial acceptance.
Chromium is a chemical element; it has symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal.
Leather is a strong, flexible and durable material obtained from the tanning, or chemical treatment, of animal skins and hides to prevent decay. The most common leathers come from cattle, sheep, goats, equine animals, buffalo, pigs and hogs, and aquatic animals such as seals and alligators.
Tanning, or hide tanning, is the process of treating skins and hides of animals to produce leather. A tannery is the place where the skins are processed.
Chrome plating is a technique of electroplating a thin layer of chromium onto a metal object. A chrome plated part is called chrome, or is said to have been chromed. The chromium layer can be decorative, provide corrosion resistance, facilitate cleaning, and increase surface hardness. Sometimes, a less expensive substitute for chrome, such as nickel may be used for aesthetic purposes.
Industrial wastewater treatment describes the processes used for treating wastewater that is produced by industries as an undesirable by-product. After treatment, the treated industrial wastewater may be reused or released to a sanitary sewer or to a surface water in the environment. Some industrial facilities generate wastewater that can be treated in sewage treatment plants. Most industrial processes, such as petroleum refineries, chemical and petrochemical plants have their own specialized facilities to treat their wastewaters so that the pollutant concentrations in the treated wastewater comply with the regulations regarding disposal of wastewaters into sewers or into rivers, lakes or oceans. This applies to industries that generate wastewater with high concentrations of organic matter, toxic pollutants or nutrients such as ammonia. Some industries install a pre-treatment system to remove some pollutants, and then discharge the partially treated wastewater to the municipal sewer system.
Buckskin is the soft, pliable, porous preserved hide of an animal – usually deer – tanned in the same way as deerskin clothing worn by Native Americans. Some leather sold as "buckskin" may now be sheepskin tanned with modern chromate tanning chemicals and dyed to resemble real buckskin.
Ostrich leather is the result of tanning skins taken from African ostriches farmed for their feathers, skin and meat. The leather is distinctive for its pattern of vacant quill follicles, forming bumps ranged across a smooth field in varying densities. It requires an intricate, specialised, and expensive production process making its aesthetic value costly.
Robert Hermann Foerderer was an American businessman and politician who served as a Republican member of the U.S. House of Representatives for Pennsylvania's at-large congressional district from 1901 to 1903 and Pennsylvania's 4th congressional district in 1903.
Liming is a process used for parchment or leather processing, in which hides are soaked in an alkali solution. It is performed using a drum and paddle or a pit. Its objectives are:
Title 40 is a part of the United States Code of Federal Regulations. Title 40 arranges mainly environmental regulations that were promulgated by the US Environmental Protection Agency (EPA), based on the provisions of United States laws. Parts of the regulation may be updated annually on July 1.
This article discusses topics related to the environment of Pakistan.
S.B. Foot Tanning Company is a leather production facility located in Red Wing, Minnesota. It processes leather for use in the crafting of shoes, boots, belts, and leather accessories. In 2010, the factory processed nearly 6 million linear feet of hides. S.B. Foot Tanning Company is a wholly owned subsidiary of Red Wing Shoes Company, Inc. and is the principal supplier of leather to their shoe manufacturing plants. The company also supplies over 1.5 million linear feet of leather for use in the production of military footwear per year, extending a tradition that began with World War I, when the tannery supplied boot leathers for the construction of soldier boots.
Latigo leather is cowhide leather that is combination tanned. First it is chrome tanned, then it is vegetable tanned. Before modern combination tanning, latigo had been combination tanned with alum and gambier.
Karachi has many environmental issues, severely affecting its biophysical environment as well as human health. The industrialization as well as lax environmental oversight have contributed to the problems. The various forms of pollution have increased as Karachi which has caused widespread environmental and health problems. Air pollution, lack of proper waste management infrastructure and degradation of water bodies are the major environmental issues in Karachi.
The conservation and restoration of leather objects is the process of determining the causes of deterioration, followed by deciding the best course of action for preserving the leather objects for the future.
Chouara Tannery is one of the three tanneries in the city of Fez, Morocco. It is the largest tannery in the city and one of the oldest. It is located in Fes el Bali, the oldest medina quarter of the city, near the Saffarin Madrasa along the Oued Fes. Since the inception of the city, the tanning industry has been continually operating in the same fashion as it did in the early centuries. Today, the tanning industry in the city is considered one of the main tourist attractions. The tanneries are packed with round stone vessels filled with dye or white liquids for softening the hides. The leather goods produced in the tanneries are exported around the world.
Leather is created when an animal skin or hide is chemically treated in a process called tanning to preserve them for long term use as material for clothing, handbags, footwear, furniture, sports equipment and tools. Alligator leather is also commonly used to create similar items as mentioned above.
Carl Erengisle Hyltén-Cavallius, born 19 February 1817 in Vislanda; died 29 October 1853 in Gothenburg, was a Swedish pharmacist and chemist; he invented the now dominating technology of tanning by using chromium salts.
Palanisamy Thanikaivelan is a leather technologist and material scientist. He joined the Central Leather Research Institute in Chennai, India in 2002 and currently working as the Chief Scientist. In 2006, he won the Young Scientist and Young Engineer Awards from Council of Scientific and Industrial Research and Indian National Academy of Engineering for his work on innovative and cleaner zero discharge tanning methods. He is a Young Associate of the Indian Academy of Sciences and Indian National Academy of Engineering.
Catherine Anne Money is an Australian biochemist whose discoveries have changed leather making. By introducing a freezing process, she simplified the preparation of hides in Australian tanneries. Her simplified approach which minimise tannery effluents and maximises hide quality is now used globally.
Media related to Leather processing at Wikimedia Commons