Leather is a durable and flexible material created by tanning the animal rawhide. The mainly used raw material is cattle hide and skin. Leather usage has come under criticism in the 20th and 21st centuries by Animal Rights groups. These groups claim that buying or wearing leather is unethical because producing leather requires animals to be killed. However, according to the LCA report for the United Nations Industrial Development Organization, most of the raw hides and skins used in the production of leather were derived from animals that are raised for meat and/or dairy production. The skin and hide from the meat industry may create a major pollution. It can be either burnt or buried in landfill. Leather production utilizesthe non-usable part of dead animals, so that, there will no waste of animals’ skin. It helps to decrease dead animal waste and improveseconomic growth of India by maximizing export of leather goods.
Leather is processed by tanning animal rawhide and skins to make it durable and flexible. It can be produced at manufacturing scales ranging from artisan to modern industrial scale. Leather making has been practiced for more than 7,000 years; the earliest record of leather artifacts dates to 2200 BCE. Leather is used to make a variety of articles. It is produced in a wide variety of types and styles and decorated by a wide range of techniques as in Fig. No.1.
Figure No. 1. Leather fabric
Leather usage has come under criticism in the 20th and 21st centuries by animal rights groups. These groups claim that buying or wearing leather is unethical because producing leather requires animals to be killed. However, according to the LCA report for the United Nations Industrial Development Organization, 99% of the raw hides and skins used in the production of leather derive from animals raised for meat and/or dairy production.
The leather manufacturing process is divided into three fundamental sub-processes: 1. Preparatory stages, 2. Tanning, and 3. Crusting. A further sub-process of finishing can be added into the leather processing sequence, but not all leathers receive finishing.
- The preparatory stages are when the hide is prepared for tanning. Preparatory stages may include soaking, hair removal, liming, deliming, bating, bleaching, and pickling.
- Tanning is a process that stabilizes the proteins, particularly collagen, of the raw hide to increase the thermal, chemical, and microbiological stability of the hides and skins. Thus, making it suitable for a wide variety of end applications. The principal difference between raw and tanned hides is that raw hides dry out to form a hard, inflexible material that, when rewetted, will putrefy, while tanned material dries to a flexible form that does not become putrid whenMany tanning methods and materials exist. The typical process sees tanners load the hides into a drum and immerse them in a tank that contains the tanning “liquor.” The hides soak while the drum slowly rotates about its axis, and the tanning liquor slowly penetrates through the full thickness of the hide. Once the process achieves even penetration, workers slowly raise the liquor’s pH in a process called basification, which fixes the tanning material to the leather. The more tanning material fixed, the higher the leather’s hydrothermal stability and shrinkage temperature resistance.
- Crusting is a process that thins and lubricates leather. It often includes a coloring Chemicals added during crusting must be fixed in place. Crusting culminates with a drying and softening operation, and may include splitting, shaving, dyeing, whitening or other methods.
Finishing Process for some leathers, tanners apply a surface coating, called finishing. Finishing operations can include oiling, brushing, buffing, coating, polishing, embossing, glazing, or tumbling, among others.
Leather can be oiled to improve its water resistance. This currying process after tanning supplements the natural oils remaining in the leather itself, which can be washed out through repeated exposure to water. Frequent oiling of leather, with mink oil, neat’s-foot oil, or a similar material keeps it supple and improves its lifespan dramatically.
Tanning processes largely differ in which chemicals are used in the tanning liquor. Some common types include:
Vegetable-tanned leather is tanned using tannins extracted from vegetable matter, such as tree bark prepared in bark mills. It is the oldestknown method.
Chrome-tanned leather is tanned using chromium sulfate and other chromium salts. It is also known as “wet blue” for the pale blue color of the undyed leather
Aldehyde-tanned leather is tanned using glutaraldehyde or oxazolidine compounds. It is referred to as “wet white” due to its pale cream color.
Chamois leather is a form of aldehyde tanning that produces a porousand highly water-absorbent leather. Chamois leather is made using marine oils.
Brain tanned leathers are made by a labor-intensive process that uses emulsified oils, often those of animal brains such as deer, cattle, and buffalo.
Alum leather is transformed using aluminum salts mixed with a variety of binders and protein sources, such as flour and egg yolk. Alum leather is not actually tanned; rather the process is called tawing.
Grades of Leather
- Top grain leather
- Full grain leather
- Corrected grain leather
- Split leather
- Bicast leather
- Patent leather
- Suede leather
- Bonded leather
Properties of Leather
- Leather hasHigh tensile strength i.e., cow leather is between 8 – 25 N / mm². Leather with higher fat content has a higher tear strength. But there are many other parameters that influence the tear strength,the tanning method, the finish, the stiffness, or the age of the leather.Since leather is a natural product, every skin behaves differently.Resistance to tear is an important property. Good leather is stable and resistant to tearing, whereas suede, nubuck or extremely soft lambskin will not have the same stability as, for example, a belted leather.
- High resistance to flexing i.e.,the ability to withstand numerous flexing cycles without damage or deterioration. Better mouldability, it can be molded into a certain shape and then remolded into another shape later.
- Permeability to water vapori.e., enables leather to absorb water and perspiration.
- Good thermostatic properties i.e. The leather is warm in winter and cool in summer. It is resistant to heat and fire.Leather provides good heat insulation.
- The leather is resistant to abrasion in both wet and dry environments. This makes leather an excellent protector of skin.
- Resistant to Fire, fungi, and chemical attack.
Advantages of Leather
Leather is truly sustainable and natural fiber. Good leather ages well and can keep for long period. Leather is easy to repair and easy to maintenance. Leather products can be recycled and have natural comfort.Leather is more luxurious and have beautiful surface area. It has many endsuses as follows-
Leather can be used as binder for finished books. It is often used to make clothing including pants, skirt, raincoats,and jackets.Leather has been used for all types of equestrian related products, including horse hoof boots. also, From fashionable winter gloves to durable work gloves.Fashionable footwear is one of the most common uses for leather, including boots, shoes, slippers, and more.Couches, chairs, recliners, and even automotive interiors are made from leather.Leather can be used for accessories like wristwatch straps, jewellery, belts, wallets, bags,and purses etc.
Leather is more sensitive to fluctuations in temperature, where itcan feel warmer in summer and cold in winter. When it comes to color and patterns, combinations of color and patterns are limited. It has maindrawback i.e., producing leather requires animals to be killed.
This study gives us basic information of leather i.e., history, manufacturing process, applications, etc. Which shows leather is a natural, biodegradable fabric. It is made from tanning of animal skin. The rawhide and skin used for leather manufacturing is comes from, 99% of the raw hides and skins used in the production of leather derive from animals raised for meat and/or dairy production. Leather productions utilize non usable part of dead animals, so that there will no waste of animals.
Author – AVHAD PRADNYA DASHARATH,
Student, DKTE Society’s Textile and Engineering Institute, Ichalkaranji