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:

1. Preparatory stages

2. Tanning

3. Crusting

1. Preparatory stages

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

dries.

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.

Schematic of types of leather

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 Bycast leather

Examples of Napa leather

Ladies Pouch Mobile coverTronchetto boots

Leather ProductsProduct 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.

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