Leather is a durable and flexible material made by raw tannery, mostly cow leather. These can be produced on a manufacturing scale ranging from home-based industries to heavy industries.
Leather is used for making various items, including clothing (especially shoes), in bookbinding, and as a furniture cover. It is produced in various types and styles, decorated by various techniques. The earliest records of leather artefacts date back to 1300 BC.
Video Leather
Production process
The skin-making process is divided into three basic subprocesses: preparation, tanning, and hardening. Further subprocess, surface coating, can be added to the skin process sequence, but not all skins receive surface treatment.
The preparation stage is when hide is prepared for tanning. The preparatory stage may include: calcification, termination, hair removal, degreasing, bleaching, and preservation.
Tanning is a process that stabilizes protein from raw skin so it does not rot, making it suitable for a wide variety of end applications. The main difference between raw leather and tanned skin is that the raw skin dries to form a hard and non-supple material which, when immersed, becomes porridge, while the disguised ingredients dry up into a flexible form that does not become rotten when moistened.
Many methods and tannery exist. The typical process of seeing the tanner loads the skin into the drum and puts it in a tank containing "liquor" tanning. The straw soaked while the drum slowly spun around its axis, and the tanning fluid slowly penetrated through the full thickness of the skin. Once the process reaches penetration even, workers slowly raise the pH of liquor in a process called improvement, which improves the tannery. The more tanning materials are improved, the higher the hydrothermal stability of the skin and the shrinkage temperature resistance.
Crusting is a process that dilutes and lubricates the skin. This often includes staining operations. Chemicals added during hardening of the skin should be repaired. Crusting culminates with drying and softening operations, and may include separation, shearing, immersion, bleaching or other methods.
For some skins, tanners use a surface layer, called "finishing". Finishing operations may include oiling, brushing, rubbing, coating, polishing, embossing, glazing, or tumbling, among others.
Skin can be oiled to improve water resistance. This process of tanning after tanning supplements the remaining natural oils in the skin itself, which can be washed out through repeated exposure to water. Oiling oil frequently, with feather oil, neatsfoot oil, or similar materials keeps it supple and dramatically improves its lifespan.
Tannery method
The tanning process is very different in which chemicals are used in tanning liquids. Some common types include:
- using tannins extracted from vegetable materials, such as bark prepared in a bark factory. This is the oldest known method. The color is supple and brown, with the right color depending on the mixture of ingredients and skin color. Vegetable leather is unstable in water; it tends to discolor, and if it is left submerged and then dries, it shrinks and becomes harder. This is a leather tanned leather feature that is utilized in traditional shoe making. In hot water, it shrinks drastically and partially thickens, becomes stiff and ultimately fragile. Boiled skin is an example of this, in which the skin has hardened by soaking in hot water, or in boiled candles or similar substances. Historically, it was sometimes used as an armor after hardening, and it has also been used to bind books.
- Chrome's Chrome skin , discovered in 1858, was tanned using chromium sulphate and other chromium salts. It is also known as "wet blue" for the pale blue color of the loose skin. The chrome tanning method usually takes about a day to complete, making it most suitable for large-scale industrial use. This is the most common method in modern use. It is more pliable and supple than vegetable leather and does not darken or deform as drastically in water as the vegetables are browned. However, there are environmental problems with this tanning method, because chromium is a heavy metal.
- Aldehyde-tanned skin tanned using glutaraldehyde or oxazolidin compounds. This is referred to as "white wet" because of its pale cream color. It is the main type of "chrome-free" skin, often seen on shoes for babies and cars. Formaldehyde has been used for tanning in the past; it is being phased out because of the danger to workers and the sensitivity of many people to formaldehyde.
- Chamois skin is a form of aldehyde tanning that results in absorbent and highly absorbing skin. The chamois skin is made using marine oil (traditional cod oil) that oxidizes to produce aldehydes that tan the skin to color it.
- Bronze-colored skin is made by a labor-intensive process that uses emulsified oil, often from animal brains such as deer, cattle, and buffalo. They are known for their extraordinary softness and endurance.
- Aluminum is altered using aluminum salt mixed with various binders and protein sources, such as flour and egg yolks. The skin of alum is not really tanned; but this process is called "tawing", and the resulting material returns to raw skin if immersed in water long enough to remove alum salt.
Maps Leather
Value
In general, leather is produced in the following classes:
- The top-grain skin includes an outer layer of skin, known as wheat, which features finer, denser fibers that produce strength and endurance. Depending on the thickness, it may also contain some of the more fibrous lower layers, known as corium. Grain skin types include:
- The full grain skin contains all layers of grain, without removing the surface. Instead of running out, he develops patina during his useful life. Usually regarded as the highest quality leather. Furniture and footwear are often made from full grain leather. Full-grain skin is usually finished with aniline dye. The russian skin is a form of full-grain skin.
- Corrected grain leather has a surface that is subjected to final treatment to create a more uniform look. This usually involves buffing or sanding deficiencies in grains, then coloring and scattering the surface.
- Nubuck is grain leather that has been sanded or rubbed on the side of the grain to produce a short bit of protein fiber, producing a velvety surface.
- Split skin is created from the left corium after the top grain has been separated from hide, known as the drop split. In thicker skin, split drop can be subdivided into split middle and split meat. Splits are often used to make suede. The split skin can also have a polyurethane or vinyl coating applied to the surface and embossed to give the appearance of the grain, known as the basted leather, which is slightly stiffer than the grain skin but has a more consistent texture.
- Patent Skin is a skin that has been finishing high-gloss with the addition of layers. Inventor Seth Boyden developed the first mass-production process, using linseed linseed oil varnish, in Newark, New Jersey, in 1818. Modern versions typically have a plastic coating, similar to a bicast leather.
- bonded leather , also called dissolved skin , is an ingredient that uses shredded leather pieces and is bonded together with polyurethane or latex into a fiber net. The amount of skin fibers in the mixture varies from 10% to 90%, affecting the properties of the product.
From other animals
Currently, most of the skin is made of cowhide, but there are many exceptions.
Horse skin is used to make skin that is very durable. The cordovan shell is a horse skin that is made not of the outer shell but the undercoat is found only in a species of horse called a shell. This is very valuable for mirror-like look and anti-wrinkle properties. Sheep and deer skins are used for soft leather with more expensive clothing. Deer and elkskin are widely used in work gloves and indoor shoes. Pig skin is used in clothing, and in saddle chairs. Buffalo, goat, cow, and yak skin can also be used for the skin.
Reptile skins, such as crocodiles, crocodiles, and snakes, are noted for their distinct patterns that reflect the scale of their species. This leads to the hunting and cultivation of this species partly to their skin.
Kangaroo skin is used to make goods that must be strong and flexible. This is the most common material used in bullwhips. Some motorcyclists love kangaroo skin for motorcycle leather because of its light weight and abrasion resistance. The kangaroo skin is also used for jesses falconry, football footwear, and boxing speed bags.
Although originally bred for their feathers in the 19th century, ostriches are now more popular for meat and skin. The ostrich's skin has a distinctive "lump gum" because of the large follicles in which the hair grows. Different processes result in different solutions for many applications, including coatings, footwear, automotive products, accessories, and clothing.
In Thailand, stingray skin is used in purses and belts. Stingray skin is very strong and durable. The skin is often dyed black and covered with small rounded bulges in the natural pattern of the animal's back. These bumps are usually white to highlight the decor. Stingray rawhide is also used as a handle on Chinese swords, Scottish basketball-backed swords, and Japanese katana. Stingray skin is also used for high abrasion areas on motor racing skin (especially in gloves, where high abrasion resistance helps prevent wear during crashes).
Environmental impact
Skin produces environmental impact, mainly because:
- The carbon footprint of livestock raising
- The use of chemicals in the tanning process (eg, chromium, formic acid, mercury and solvents)
- Air pollution due to the transformation process (hydrogen sulfide during dehairing and ammonia during deliming, steam solvent)
Carbon footprint
An estimated carbon footprint of leather goods is 0.51 kg CO 2 equivalent per × 1,010 output at retail price 2010, or 0.71 kg CO 2 eq per à ,  £ 1 output at industry prices 2010.
Water trail
One ton of skin or skin generally produces 20 to 80 m 3 of wastewater, including chromium levels of 100-400 mg/l, sulfide content of 200-800 mg/l, high fat levels and other solid waste , and leading pathogen contamination. Manufacturers often add pesticides to protect the skin during transportation. With solid waste representing up to 70% of the wet weight of the original leather, the tanning process is a considerable strain on the water treatment plant.
Disposal
Biodegradation of the skin slowly - takes 25 to 40 years to decompose. However, materials derived from vinyl and petrochemical take 500 years or more to decompose.
Chemicals used in tanning
Tanning mainly pollutes in countries where loose environmental regulations, such as in India, the world's third largest leather manufacturer and exporter. To provide an example of an efficient pollution prevention system, the chromium-per-ton load produced generally subsides from 8 kg to 1.5 kg. VOC emissions typically decrease from 30 kg/t to 2 kg/t in well-managed facilities. A review of the reduction in total pollution burden that can be achieved by the United Nations Industrial Development Organization posts accurate data on reductions that can be achieved through industry-proven waste-forward methods, while noting, "although chromium contamination expenses may be reduced by 94% advanced technology, a minimum load of 0.15 kg/t of raw leather can still cause difficulties when using landfills and composting sludge from wastewater treatment due to regulations applicable in some countries. "
In Kanpur, the self-proclaimed "World Leather City" - with 10,000 tannery in 2011 and a city of three million on the banks of the Ganges River - the level of pollution is so high that, despite the industrial crisis, pollution control of the Council decided to close 49 tannery high pollution from 404 in July 2009. In 2003 for example, the main waste disposal tadahies' waste dumped 22 tons of chromium solid waste per day in the open. Scientists at the Central Leather Research Institute in India have developed biological methods for preting, as well as better chromium management.
In Hazaribagh Dhaka neighborhood in Bangladesh, chemicals from tannery ends in the main river Dhaka. In addition to environmental damage, the health of local factory workers and end-consumers is also negatively affected. After about 15 years of ignoring high court decisions, the government closed more than 100 tannery on the weekend of April 8, 2017 in the neighborhood.
The higher costs associated with waste treatment compared to unprocessed waste disposal lead to illegal disposal to save costs. For example, in Croatia in 2001, decent pollution reductions cost US $ 70-100 per tonne of raw materials processed against $ 43/t for irresponsible behavior. In November 2009, one of Uganda's main skinmakers was caught directly discharging wastewater to a wetland adjacent to Lake Victoria.
The role of enzyme
Enzymes such as proteases, lipases, and amylases have an important role in soaking, dehairing, degreasing, and bating operations in leather manufacturing. Protease is the most commonly used enzyme in skin production. Enzymes should not damage or dissolve collagen or keratin, but must hydrolyze casein, elastin, albumin, globulin-like proteins, and nonstructural proteins that are not essential for the manufacture of the skin. This process is called bating.
Lipase is used in degreasing operations to hydrolyze fat particles embedded in the skin.
Amylase is used to soften the skin, to remove grains, and give strength and elasticity to the skin. This enzyme is rarely used.
Preservation and conditioning
The natural fibers of the skin are damaged with the passage of time. Acidic skin is particularly susceptible to red decay, which causes surface powders and consistency changes. Damage from red rot is exacerbated by high temperatures and relative humidity. Although chemically irreversible, treatments can add strength to handling and prevent red rotted skin disintegration.
Long term exposure to low relative humidity (below 40%) can cause the skin to become dry, irreversibly alter the fibrous structure of the skin. Chemical damage can also occur from exposure to environmental factors, including ultraviolet light, ozone, acids from sulfur and nitrogen pollutants in the air, or through chemical action after treatment with fat or oil compounds. Both oxidation and chemical damage occur more rapidly at higher temperatures.
Various treatments are available such as conditioner. Saddle soap is used to clean, condition, and soften the skin. Leather shoes are widely conditioned with shoe polish.
In modern culture
Because of its excellent resistance to abrasion and wind, the skin finds its use in manual labor. The eternal image of a cowboy in the leather gave way to the leather-bound and leather-jackged aviators. When a motorcycle is found, some riders use thick leather jackets to protect from road rashes and gusts of wind; some also wear full chapters or leather pants to protect the lower body. Many sports still use leather equipment. Its flexibility facilitates forming and shaping it into balls and protective gear.
Skin fetishism is a popular name used to describe fetishistic appeal for people who wear leather, or in certain cases, on the clothes themselves.
Many rock groups (especially heavy metal and punk groups in the 1980s) are famous for wearing leather clothing. Extreme metal bands (especially black metal bands) and Goth rock groups have extensive leather garments. Skin has become less common in punk communities over the last three decades, as there is a rejection of leather use from punk that supports animal rights.
Many cars and trucks come with optional or standard "leather" seats.
Religious sensitivity
In countries with significant populations of religious observers who place restrictions on material choices, leather sellers usually clarify skin types in their products. For example, leather shoes have labels that identify the animal from which the skin originated. It helps a Muslim accidentally buy a pig's skin, and a Hindu avoids cattle. Many vegetarian Hindus do not use any kind of skin. Such taboos increase the demand for religiously neutral skins such as ostriches and deer.
Judaism forbade the comfort of wearing leather shoes at Yom Kippur, Tisha B'Av, and during mourning. Also, see Teffilin and Torah Scroll.
Jainism prohibits the use of the skin, as it is obtained by killing animals.
Alternative
Many artificial skin substitutes have been developed, usually involving a polyurethane or vinyl coating applied to the fabric base. Many names and brands for such artificial skins exist, including "pleather", portmanteau "plastic leather", and the brand name Naugahyde.
References
Further reading
- Beeby, K.J. The Wonderful Story of Leather (PDF) . UK: Harmatan.
- Lefroy, George Alfred (1884). Daryaganj skin worker . Delhi: Cambridge mission to Delhi.
- Skin for Binding and Binding (PDF) . UK: Harmatan. 2002.
- Skin for Library (PDF) . UK: Harmatan.
Source of the article : Wikipedia
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