Learning about types of tannaries and chemicals used for tanning factories and application of tannaries.

1. Vegetable tans
The vegetable tans are water extracted from plant barks ,leaves etc. It
consists of large polyphenol molecules with some acidic groups and
high secondary valency of potential.
catechol tans
The catechol process is a increases in molecular size when boiled in an
acid solution.
pyrogallol tans
The pyrogallol tans are usually more yellow brown catehols.its sugar
content often leads to acid fermentation during long tannage.
vegetable tanning process and applications of vegetable tanned leather
Vegetable tanning is one of the oldest methods known. Primitive people
have developed vegetable tanning system based on meterials available
locally.
Application of vegetable tanned leather
The process is used in order to stabilise the skin and be able to process
the resulting leather.

2. Chrome tanning
There are two process of chrome tanning i) One bath process ii) Two
bath process.
Chemicals used-method type of leather
The chemical name is sodium sulphate, sodium hydrosulphide, causdic
soda soda ash ammonium sulphate, ammonium chloride ,fomic acid,
sulphuric acid
Leather uses
Leather isoften used to bind or finish books,foot wear fashionable foot
wear is one of the most common uses for leather,including
boots,shoes,sillpers, gloves, watches, cases,acessories.
Artificial leather
It is a material intended to substitute for leather in fields such as
clothing, footwear, and fabrics
Synthetic tans
It is used in tanneries as replacement syntans ,to compliment the
tanning action made by the natural tanning.
Aldehyde tannage
This type of tannage is done by Formalin solution contanning 40%,
formaldehyde 8-10%, methanol.It is used for tanning white,
washable leather.

3.  Vegetable tanning uses tannins(a class of polyphenol
astringent chemicals), which occur naturally in the bark and
leaves of many plants.
 Tannins bind to the collagen proteins in the hide and coat
them, causing them to become less water-soluble and more
resistant to bacterial attack The process also causes the hide
to become more flexible.
 The primary barks processed in bark mill and used in modern
times are chestnut oak redoul, tanoak, hemlock, quebracho
mangrove, wattle (acacia; see catecholand myrobalans from
Terminalia spp., such as Terminalia chebula.
 Hides are stretched on frames and immersed for several
weeks in vats of increasing concentrations of tannin.
 Vegetable-tanned hide is not very flexible and is used for
luggage, furniture, footwear, belts, and other clothing
accessories.

4.  Chromium(III) sulfate ([Cr(H2O)6]2(SO4)3) has long been regarded as the most
efficient and effective tanning agent. Chromium(III) compounds of the sort
used in tanning are significantly less toxic than hexavalent chromium.
Chromium(III) sulfate dissolves to give the hexaaquachromium(III) cation,
[Cr(H2O)6]3+, which at higher pH undergoes processes called olationto give
polychromium(III) compounds that are active in tanning, being the cross-
linking of the collagen subunits.
 The chemistry of [Cr(H2O)6]3+ is more complex in the tanning bath rather
than in water due to the presence of a variety of ligands. Some ligands
include the sulfate anion, the collagen's carboxyl groups, amine groups from
the side chains of the amino acids and masking agents.
 Masking agents are carboxylic acids, such as acetic acid, used to suppress
formation of polychromium(III) chains. Masking agents allow the tanner to
further increase the pH to increase collagen's reactivity without inhibiting the
penetration of the chromium(III) complexes.
 Collagen is characterized by a high content of glycine proline, and
hydroxyproline usually in the repeat -gly-pro-hypro-gly-.[These residues
give rise to collagen's helical structure. Collagen's high content of
hydroxyproline allows for significant cross-linking by hydrogen bonding
within the helical structure.
 Ionized carboxyl groups (RCO2
−) are formed by hydrolysis of the collagen by
the action of hydroxide. This conversion occurs during the liming process,
before introduction of the tanning agent (chromium salts). The ionized
carboxyl groups coordinate as ligands to the chromium(III) centers of the
oxo-hydroxide clusters.
 Tanning increases the spacing between protein chains in collagen from 10 to
17 Å.]The difference is consistent with cross-linking by polychromium
species, of the sort arising from olation and oxolation.

5.  Vegetable-tanned leather is tanned using tannins extracted from vegetable
mattersuch as tree barkprepared in bark mills. It is the oldest known method.
It is supple and brown in color, with the exact shade depending on the mix
of materials and the color of the skin.
 The color tan derives its name from the appearance of undyed vegetable-
tanned leather. Vegetable-tanned leather is not stable in water; it tends to
discolor, and if left to soak and then dry, it shrinks and becomes harder.
 This is a feature of oak-bark-tanned leather that is exploited in traditional
shoemaking. In hot water, it shrinks drastically and partly congeals,
becoming rigid and eventually brittle. Boiled leather is an example of this,
where the leather has been hardened by being immersed in hot water, or in
boiled wax or similar substances.
 Historically, it was occasionally used as armorafter hardening, and it has
also been used for book binding.
 Chrome-tanned leather, invented in 1858, 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.
 The chrome tanning method usually takes approximately one day to
complete, making it best suited for large-scale industrial use. This is the
most common method in modern use.
 It is more supple and pliable than vegetable-tanned leather and does not
discolor or lose shape as drastically in water as vegetable-tanned. However,
there are environmental concerns with this tanning method, as chromium is a
heavy metal.

6.  Aldehyde-tanned leather is tanned using glutaraldehyde or
oxazolidine compounds. It is referred to as "wet white" due to
its pale cream color.
 It is the main type of "chrome-free" leather, often seen in
shoes for infants and automobiles. Formaldehyde has been
used for tanning in the past; it is being phased out due to
danger to workers and sensitivity of many people to
formaldehyde.
 This type of tannage is done by formalin solution containing
40% foramaldehyde 8-10% methanol. It is used for tanning
white washable leather.
 The skin are prepared toapH of 4.0 or 5.0 in any suitable
manner heavily picked skin requires de pickling to attain the
correct pH’
 A suitable de picking bath is prepared by sodium acetate.salt
and water.
 The skin are well in the closed drum overnight and the ashed
up.in this process ½-1 ½% of soda ash is dissolved in 50-
100% water and added to the drum until the pH of the skin is
not less than 8.

8.  Artificial leathers are often used in clothing fabrics, furniture
upholstery, and automotive uses.One disadvantage of plastic-
coated artificial leather is that it is not porous and does not allow
air to pass through; thus, sweat can accumulate if it is used for
clothing, car seat coverings, etc. One of its primary advantages,
especially in cars, is that it requires little maintenance in
comparison to leather, and does not crack or fade easily.
 Synthetic tan
 They are products made by the condensation of formaldehyde
with the sulphonic acids of phenol and naphthalene.
 Recently, Silvateam has invested significant resources developing
products with a low environmental impact by reducing the
content of phenol and free formaldehyde.
 Synthetic tannins, Blancotan, are used in tanneries as
replacement syntans, to compliment the tanning action made by
the natural tanning extracts. They are used as auxiliaries for
pretanning, retanning and combined tanning and as dispersing
agents for vegetable tannins and dyestuffs.

9.  Leather is often used to bind or finish books.
 . Clothing
 It is often used to make clothing, including pants, skirt,
raincoats, and jackets.
 3. Cuir Bouilli
 Cuir bouilli, French for boiled leather, was historically used to
create body armor and flasks.

10.  Couches, chairs, recliners, and even automotive interiors are
made from leather.
 . Gloves
 From fashionable winter gloves to durable work gloves,
leather is often used.

11.  Leather is commonly used to make arrow quivers, knife
sheaths, and gun holsters.
 10. Bags
 Satchels, backpacks, wallets, and purses are all made from
leather.