Leather technology

Leather Technology
Name : Parth M. Ka.patel
Sem. : 3rd
Roll no.: 12
Department of Materials
science
Date : 12/9/2014

Outline
 Introduction
 Production of leather
1. Preparatory stages
2. Tanning
3. Crusting
 Forms of leather
 Types of leather
 Less-common leathers
 Leather Products
 Environmental impact
 References

Introduction
 Leather is a durable and flexible material
created by the tanning of animal rawhide and
skin, often cattle hide. It can be produced
through manufacturing processes ranging from
cottage industry to heavy industry.

Production of Leather
 The leather manufacturing process is
divided into three fundamental sub-processes:
2. Tanning
3. Crusting

 In the preparatory stages the raw hide/skin is
cleaned and sterilized, under this process all the
unwanted matter like Flesh and blood stains are
removed.
 Preparatory stages may includes :
(A) Soaking : under which the raw hide is washed
and is put in water temporarily.
(B) Unhairing : Just includes removal of hair
(C) Splitting : It includes cutting the raw hide into
many pieces of horizontal layers.

(D) Degreasing : Under this, non-chemically most
of the fats and oil are removed.
(E) Bleaching : Chemical modification of dark
pigments and stains to yield lighter colored
raw hide.
(F)Saline treatment : under this, all the harmful
bacterias are neutralized with the help of salt
solution.

2. Tanning
 Tanning is the process that converts the raw
hide into more stable form.
 In this process the proteins and fibers of the
raw hide is reacted with certain
chemicals(Ex. Chromium, formic acid)
which changes the property of the materials
and makes it more stable for the longer
usability
 In this process leather is treated with
chromium which tanns the leather and
change the color to Light Blue for this the
product is commercial called “Wet Blue”.
 Tanning increases the hydrothermal stability
and also resistance to the abrasion.

3. Crusting
 Crusting is the process by which the
hide/skin is thinned, retanned, lubricated,
soften and simultaneously coloured by the
use of chemical.
 The precautions which are to be taken by
crusting are as below :
(A) Amount of chemicals used
(B) Temperature & Pressure
(C) pH i.e. Maintain between 4.5 to 6.5
(D) Drying : The leather is dried to various
moisture levels
Removal of moisture i.e. 40% to 55%
water is squeezed out of leather

 For some leathers, a surface coating is
applied
 Surface coating is one of the most
important process which includes the final
toning of the finished leather.
 It includes treatments like
 Oiling
 Brushing
 Buffing : It is the mechanical rubbing of
the final leather with soft material which
smoothens the surfaces.
 Polishing
 Ironing : it is done to remove the wrinkles.

Forms of Leather
 Several tanning processes transform hides
and skins into leather:
1. Vegetable-tanned leather is tanned using
tannins and other ingredients found in
different vegetable matter, such as tree bark
prepared in bark mills, wood, leaves, fruits
and roots and other similar sources. It is
supple and brown in color, with the exact
shade depending on the mix of chemicals
and the color of the skin. It is the only form
of leather suitable for use in leather carving
or stamping.

2. Chrome-tanned leather is tanned using
chromium sulphate and other salts of chromium.
It is more flexible and pliable than vegetable-tanned
leather and does not discolor or lose
shape as drastically in water as vegetable-tanned.
3. Brain tanned leathers are made by a labor-intensive
process which uses emulsified oils,
often those of animal brains. They are known for
their exceptional softness and their ability to be
washed.
4. Alum-tawed leather is transformed using
aluminium salts mixed with a variety of binders
and protein sources, such as flour and egg yolk.
5. Rawhide is made by scraping the skin thin,
soaking it in lime, and then stretching it while it

Types of Leather
 Full-grain leather refers to the leather which has not
had the upper “top grain” and “split” layers separated.
 Top-grain leather is the second highest quality and has
had the “split” layers separated away, making it thinner
and more pliable than full grain.

 Corrected-grain leather is any leather that has
had an artificial grain applied to its surface.
 Split leather is leather created from the fibrous
part of the hide left once the top-grain of the
rawhide has been separated from the hide.

Less-common leathers
 Buckskin or brained leather is manufactured by tanning
process that uses animal brains or other fatty materials to
alter the leather.
 Patent leather is leather that has been given a high-gloss
finish.
 Vachetta leather is used in the trimmings of luggage and
handbags. The leather is left untreated and is therefore
susceptible to water and stains.
 Slink is leather made from the skin of unborn calves. It is
particularly soft and is valued for use in making gloves.
 Deerskin is a tough leather, possibly due to the animal's
adaptations to its thorny and thicket-filled habitats.
 Nubuck is top-grain cattle hide leather that has been sanded
or buffed on the grain side, or outside, to give a slight nap of
short protein fibers, producing a velvet-like surface.

Leather used in specialty products, such
as briefcases, wallets, and luggage
 Belting leather is a full-grain leather that was
originally used in driving pulley belts and other
machinery. It is found on the surface of
briefcases, portfolios, and wallets, and can be
identified by its thick, firm feel and smooth
finish. Belting leather is generally a heavy-weight
of full-grain, vegetable-tanned leather.
Ex.

 Napa leather is chrome-tanned and is soft and
supple. It is commonly found in wallets,
toiletry kits, and other personal leather goods.
 Bycast leather is a split leather with a layer of
polyurethane applied to the surface and then
embossed. Bycast was originally made for the
shoe industry and it was also adopted by the
furniture industry.

Examples of Napa leather
Ladies Pouch Mobile cover
Examples Of Bycast leather
Tronchetto boots

Leather Products
Product group Description
Handbags Handbags with or without shoulder
strap
Pocket or small leather goods Wallet, purses, key pouches, credit-card
cases, pen cases and other small
articles
Travel goods Suitcases, casual travel bags, beauty
cases, sports bags and other travel
articles
Stationary articles and special
cases
Writing pads, book covers, camera
cases, spectacles cases, jewel cases,
mobile phone holsters etc.
Military equipments Various holsters for fire arms
Belts Women's and Men's belts
Watch straps Watch straps made of leather and
synthetics
Sports articles Balls for football, rugby

Environmental impact
 Addition to the environmental impact of
leather, the production processes have a
high environmental impact, most notably
due to:
 The heavy use of chemicals in the tanning
process (e.g. chromium, formic acid,
mercury and solvents etc.)
 Air pollution due to the transformation
process (hydrogen sulphide during
dehairing and ammonia during deliming,
solvent vapours)

References
 Introduction to the principles of leather
Manufacture
By-S. S. Dutta, 4th edition, I.L.T.A., Calcutta
 Theory and practice of leather manufacture
By- K. T. Sarkar, Macmillan Indian Press,
Madras.
 Google Images

Leather technology

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