Leather fabric is commercially obtained from cattle, calf, goat, sheep, lamb, horse, pig, kangaroo, deer, reptile, seal, and walrus. The major exporters of goatskin leather in the world are India, China and Pakistan. In sheepskin leather, China, New Zealand, Australia and Iran are the important exporters. USA, Europe, Brazil and USSR are key players in exporting leathers obtained from bovine.
Process of making Leather Fabric
Pre-tanning
- Animal skin is cleaned and salted to prevent decay.
- The hide or pelt then is sent to tannery for trimming and sorting.
- Next, it is soaked in water to restore moisture content, which is lost during salting process.
- It is treated mechanically with rollers and blades to remove fat/muscle and flesh (Fleshing).
- During liming the skin is soaked in lime solution to remove the hair, inter-fibrillary protein and epidermis.
- In De-liming the hide or pelt is washed in water containing ammonium chloride or ammonium sulphate to neutralise it.
- Bating involves treating the leather with digestive enzymes to remove non-fibrous protein.
- Scudding is done with a blunt knife to remove remaining hair roots, skin pigmentation, and surface fats.
- Lastly, it is put in sulphuric acid to lower the pH.
Tanning is the process where the leather gets the necessary feel and physical characteristics. In this process, the collagen, an insoluble fibrous protein, which carries the major property of the hide or pelt gets less susceptible to decay and are kept flexible. This is done by removing the water molecules from the gap of protein molecules and replacing it with chemicals that retain flexibility.
The main tanning processes are mineral/chrome tanning, vegetable tanning and oil tanning.
- Mineral/chrome tanning is the most common and modern method, which uses chromium salts. This makes leather water proof and stretchable.
- Vegetable tanning, or bark tanning is the process where the hide is soaked in a solution of bark of oak/chestnut which is chopped or boiled. The leather becomes moldable and can be tooled. Moreover when dry, the leather will not stretch.
- Oil tanning is a process where fish and animal oil is used. The leather becomes very soft and flexible. It cope up with wetted condition without causing damage to the leather. Chamois leather is best example of oil tanning.
After tanning, the leather undergoes different processes according to the use of the final product.
- Vegetable-tanned leather which are used for shoe soles is bleached, lubricated and then run through rolling machines to make it firm and glossy.
- Chrome-tanned leather, for shoe uppers, is split and shaved and then placed in a rotating drum for the dyeing process using several types of coloring materials to give color fastness and durability.
- Before or after dyeing, it is rolled in a fat liquor containing emulsified oils and greases. Next, the leather is pasted on glass or ceramic frames and then passed through drying tunnels with controlled heat and humidity.
Characteristics of Leather Fabric
- It has porosity and breathability.
- It is waterproof to a great extent.
- It is firm, soft and elastic.
- It retains its shape.
- It resists the aging process.
- It is durable.
- It is abrasion and wind resistant.
- It absorbs water vapour upto 30% of its weight without loss of dryness.
- Leather fabric is very versatile. It is widely used. Soft leather is used in clothing and hard leather in products like shoe soles, machine belts, engine gaskets and harnesses. Calfskin leather, which is lighter and finer grained, is used in shoe uppers. Sheepskin leather, which is soft and supple is generally used in products like gloves, jackets, and other apparel.
- Leather fabric is also used in upholstery, sofa, wallets, purses, bags, belts, rugs, tents, tepees, shields and weapon sheathes.
