Leather industries in Pakistan

APPLIEDCHEMISTRY
ASSIGNMENT
Leather Industry
Group 2
8/16/2017
Submittedto MissAnam
Group-2,BS-III,VI Semester, ChemistryDeppartment

BS-III AppliedChemistryAssignment RABIA AZIZ
Contents and Group Members:
1. Bi Bi Rabia (Introduction)
2. Iqra Akram (Types of leather)
3. Rabia Aziz (Leather Manufacturing Process
Technology with Flow Sheets, Flaying, Curing,
Beamhouse Operations)
4. Sara Fayyaz (CHROME TANNING (AND WET
BLUE)
5. Areeba Rahat ( )
6. Shakila Yasmeen ( )

LEATHER INDUSTRY
INTRODUCTION
Leather is a durable and flexible material created by tanning animal rawhide and skin,
often cattle hide. It can be produced at manufacturing scales ranging from cottage
industry to heavy industry.
People use leather to make various goods—including clothing (e.g., shoes, hats, jackets,
skirts, trousers, and belts), bookbinding, leather wallpaper, and as a furniture covering. It is
produced in a wide variety of types and styles, decorated by a wide range of techniques.
Leather is also made from kangaroos, zebras, seals, snakes, lizards, and even sharks, dolphi
ns, and stingrays, many of whom are either raised or hunted specifically for their skins. A pi
ece of skin that is not tanned (treated) is biodegradeable, which means it would rot away in
your closet or on your feet. To prevent this natural breakdown, a number of dangerous toxi
ns are used in the production and treatment of leather. For example, most leather is chrom
etanned, even though the Environmental Protection Agency considers chromium waste haz
ardous., the leather processing procedures have three phases, including preparation, tanni
ng, and finishing. During the first phase, raw hides are cleaned, wet salted, soaked, limed, a
nd base split.
Wetblue leathers are generated after deliming, tanning, pickling, sammying, and dyeing in t
he phase of tanning. The third processing phase contains fatliquoring, vacuum dry, texturin
g, and polishing.
HISTORY OF LEATHER
Leather is one of man’s earliest and most useful discoveries. Our ancestors used leather to
protect themselves from the elements. Primitive man hunted wild animals for food, then
made clothing, footwear and crude tents from the hides. Like then, hides used today are a
by-product. Animals are raised for the meat, dairy and wool industries, not for their hides.
Roughly half of all leather produced today is used to make shoes, and about 25% for
clothing. Upholstery demands only around 15% of the total product.

The tanning process from the early 1900’s.
Wall paintings and artifacts in Egyptian tombs dating back to 5000 B.C. indicate that leather
was used for sandals, clothes, gloves, buckets, bottles, shrouds for burying the dead and for
military equipment. The ancient Greeks are credited with developing tanning formulas
using certain tree barks and leaves soaked in water to preserve the leather. This was the
first record of vegetable tanned leather, which became a well-established trade in Greece
around 500 B.C. Vegetable tanned leathers are still produced today and remain an active
ingredient in modern tannages. The Romans made extensive use of leather for footwear,
clothes, and military equipment including shields, saddles and harnesses.
Due to its durability and comfort, leather has been used for seating throughout the history
of transportation and furniture. It has always been the ideal material for making saddles
and tack, as well as footwear. During the Middle Ages, leather became the cover of choice
for dining chairs, because it was easy to maintain and did not absorb the odor of food.
The spread of industrialization in the 18th and 19th centuries created a demand for new
kinds of leathers, such as belting leathers to drive machinery. The invention of the
automobile, the demand for softer, lightweight footwear with a fashionable appearance,
and a general rise in the standard of living created a demand for soft, supple, colorful
leather. The traditional vegetable tanned leather was too hard and thick for these
requirements and thus, the use of chromium salt was adopted and chrome tanning became
the standard for modern footwear, fashion and upholstery leathers.
Modern technology has allowed for innovation in the leather industry, as the development
of chemicals and sophisticated processing methods have greatly expanded the aesthetics
and feel of leather as well as the possible applications. Leather continues to be the material

of choice, not just for commercial and residential furniture but for automotive, aviation and
marine applications as well.
Here are some definitions of some glossaries:
a) Tanning: is the process by which the proteins in the skin are stabilised, and transfor
ms hide into leather with strong resistance to water and bacteria.
b) Crust leather: is leather which is yet to undergo the tanning process.
c) Wet..blue leather: is the type of leather produced from chrome tanning. It is versatil
e and can be easily dyed.
d) Leather: is the durable and water-
resistant material produced by tanning animal skin.
FORMS OF LEATHER
 Chrome-tanned leather, invented in 1858, is tanned using chromium
sulfate and other chromium salts. It is more supple and pliable than vegetable-
tanned leather and does not discolor or lose shape as drastically in water as
vegetable-tanned. It is also known as wet-blue for its color derived from the
chromium. More exotic colors are possible when using chrome tanning. The chrome
tanning method usually only takes a day to finish, and the ease and agility of this
method make it a popular choice. However there are environmental concerns with
this tanning method. It is reported that chrome-tanned leather adds up to 80% of
the global leather supply.

 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. 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. Vegetable-tanned leather
is not stable in water; it tends to discolor, so if left to soak and then dried 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 armour after hardening,
and it has also been used for book binding.
 Aldehyde-tannedleather is tanned
using glutaraldehyde or oxazolidine compounds. This is the leather that most
tanners refer to as wet-white leather due to its pale cream or white color. It is the
main type of "chrome-free" leather, often seen in shoes for infants and automobiles.
 Brain tanned leathers are made by a labor-intensive process that uses
emulsified oils, often those of animal brains such as deer, cattle, and buffaloes. They
are known for their exceptional softness and washability.
 Rose-tanned leather is a variation of vegetable oil tanning and brain tanning,
where pure rose otto replaces the vegetable oil and emulsified oils. Rose-tanned
leather tanned leaves a powerful rose fragrance even years from when it is
manufactured. It has been called the most valuable leather on earth, but this is
mostly due to the high cost of rose otto and its labor-intensive tanning process.
 Synthetic-tanned leather is tanned using aromatic polymers such as
the Novolac or Neradol types (syntans, contraction for synthetic tannins). This
leather is white in color and was invented when vegetable tannins were in short
supply during the Second World War. Melamine and other amino-functional resins
fall into this category, as well, and they provide the filling that modern leathers often
require. Urea-formaldehyde resins were also used in this tanning method before
people realized the hazards that formaldehyde presents to tanners and consumers.
 Alum-tanned leather is transformed using aluminium salts mixed with a
variety of binders and protein sources, such as flour and egg yolk. Alum-tanned
leather is technically not tanned, as tannic acid is not used, and the resulting
material reverts to rawhide if soaked in water long enough to remove the alum salts.
 Rawhide is made by scraping the skin thin, soaking it in lime, and then stretching
it while it dries. Like alum-tanning, rawhide is not technically "leather",[citation
needed] but is usually lumped in with the other forms.[citation needed] Rawhide is
stiffer and more brittle than other forms of leather; it is primarily found in uses such

as drum heads and parchment where it does not need to flex significantly; it is also
cut up into cords for use in lacing or stitching and for making many varieties of dog
chews.
TYPES OF LEATHER
In general, leather is sold in these four forms:
 Full-grain leather refers to hides that have not been sanded, buffed, or snuffed (as
opposed to top-grain or corrected leather) to remove imperfections (or natural
marks) on the surface of the hide. The grain remains allowing the fiber strength and
durability. The grain also has breathability, resulting in less moisture from
prolonged contact. Rather than wearing out, it develops a patina during its expected
useful lifetime. High quality leather furniture and footwear are often made from full-
grain leather. Full-grain leathers are typically available in two finish
types: aniline, semi-aniline.
 Top-grain leather (the most common type in high-end leather products) is the
second-highest quality. It has had the "split" layer separated away, making it thinner
and more pliable than full-grain. Its surface has been sanded and a finish coat added,
which produces a colder, plastic feel with less breathability, and it does not develop
a natural patina. It is typically less expensive and has greater stain resistance than
full-grain leather if the finish remains unbroken.
 Corrected-grain leather is any leather that has had an artificial grain applied to
its surface. The hides used to create corrected leather do not meet the standards for
use in creating vegetable-tanned or aniline leather. The imperfections are corrected
or sanded off, and an artificial grain embossed into the surface and dressed with
stain or dyes. Most corrected-grain leather is used to make pigmented leather as the
solid pigment helps hide the corrections or imperfections. Corrected grain leathers
can mainly be bought as two finish types: semi-aniline and pigmented.
 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. During the splitting
operation, the top-grain and drop split are separated. The drop split can be further
split (thickness allowing) into a middle split and a flesh split. In very thick hides, the
middle split can be separated into multiple layers until the thickness prevents
further splitting. Split leather then has an artificial layer applied to the surface of the
split and is embossed with a leather grain (bycast leather). Splits are also used to
create suede. The strongest suedes are usually made from grain splits (that have the
grain completely removed) or from the flesh split that has been shaved to the
correct thickness. Suede is "fuzzy" on both sides. Manufacturers use a variety of
techniques to make suede from full-grain. A reversed suede is a grained leather that
has been designed into the leather article with the grain facing away from the visible
surface. It is not considered a true suede.[3]

There are two other types of leather commonly used in specialty products, such as
briefcases, wallets, and luggage:
 Belting leather is a full-grain leather 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.
 Napa leather is chrome-tanned and is soft and supple. It is commonly found in
wallets, toiletry kits, and other personal leather goods.
STAGES IN THE LEATHER PROCESSING
The processing of leather involves three distinct sets of unit operations. These are
 beamhouse or pre-tanning operations
 tanning process and
 post-tanning operations including finishing.
ENVIRONMENTAL IMPACT
 Use of chemicals in the tanning process (e.g., chromium, formic
acid, mercury and solvents)
 Air pollution due to the transformation process (hydrogen sulfide during dehairing
and ammonia during deliming, solvent vapors)
 The carbon footprint of cattle rearing
ROLE OF ENZYMES
Enzymes like proteases, lipases, and amylases have an important role in the soaking,
dehairing, degreasing, and bating operations of leather manufacturing. Proteases are the
most commonly used enzymes in leather production. The enzyme must not damage or
dissolve collagen or keratin, but should hydrolyze casein, elastin, albumin, globulin-like
proteins, and nonstructural proteins that are not essential for leather making. This process
is called bating.
Lipases are used in the degreasing operation to hydrolyze fat particles embedded in the
skin.
Amylases are used to soften skin, to bring out the grain, and to impart strength and
flexibility to the skin. These enzymes are rarely used.

CHEMICAL CONSUMPTION PATTERN IN LEATHER INDUSTRY
The chemicals used in leather processing are classified as bulk and performance chemicals.
Bulk chemicals are sodium chloride, lime, sodium sulphide, ammonium salts, formic acid,
sulphuric acid, sodium formate, sodium bicarbonate, ammonia etc., which are used in many
other industries as well. On the other hand, tanning materials, formulations of fatliquors,
retanning, finishing agents etc., are performance chemicals.These are used to add to the
performance of leather in usage and limited to use in leather sector alone.
The consumption pattern of chemicals in leather processing per ton of hides or skins is
presented in following Table :
Sl.No . Chemical In Kg per ton of hide/skin process
1 Soaking aids 0-2.5
2 Preservative 2.5-5.0
3 Lime 80-200
4 Sodium sulphide 20-30
5 Sodium chloride 80-100
6 Ammonium salts 10-15
7 Sulphuric acid 12-20
8 Sodium formate 5-12.5
9 BCS 60-120
10 A1 (A1203) 1-20
11 Zr(Zr02) 0-15
12 Vegetable tannins 10-220
13 Synthetic tanning agents 20-60
14 Fatliquors 25-100
15 Dyes 2.5 -20
16 Binders 20-45
17 Pigments 10-25
18 Top coats 20-45
19 Wax emulsions 2.5-5.0
20 Feel modifiers 1-2
USES OF LEATHER
There are many different uses for leather as it is a versatile material. It is both durable and
fashionable, and therefore its applications are nearly endless..
Here are some different uses for leather, some of which are currently
prevalent while others are more historical in nature.

1) BINDING
Leather is often used to bind or finish books.
2) CLOTHING
It is often used to make clothing, including pants, skirt, raincoats, and
jackets.
3) SADDLES
In fact, leather has been used for all types of equestrian related products,
including horse hoof boots.
4) FOOTWEAR
Fashionable footwear is one of the most common uses for leather,
including boots, shoes, slippers, and more.
5) FURNITURE
Couches, chairs, recliners, and even automotive interiors are made from
leather.
6) GLOVES
From fashionable winter gloves to durable work gloves, leather is often
used.
7) WATCHES
Leather wrist watch straps are very common, as well as bangles and
other jewelry.
8) SPORTS
Leather has a number of uses in sports, such as producing footballs
and baseball gloves.
9) BAGS
Satchels, backpacks, wallets, and purses are all made from leather.
10) CASES

A case for your eyeglasses or a protective enclosure for your smartphone may be made
from leather.
11) HOLSTERS
Leather is commonly used to make arrow quivers, knife sheaths, and
gun holsters.
12) ACCESSORIES
Leather is commonly used to manufacturer personal accessories, such
as belts.
PRESERVATION AND CONDITIONING
The natural fibers of leather break down with the passage of time. Acidic leathers are
particularly vulnerable to red rot, which causes powdering of the surface and a change in
consistency. Damage from red rot is aggravated by high temperatures and relative
humidities. Although it is chemically irreversible, treatments can add handling strength and
prevent disintegration of red rotted leather.
Exposure to long periods of low relative humidities (below 40%) can cause leather to
become desiccated, irreversibly changing the fibrous structure of the leather. Chemical
damage can also occur from exposure to environmental factors, including ultraviolet light,
ozone, acid from sulfurous and nitrous pollutants in the air, or through a chemical action
following any treatment with tallow or oil compounds. Both oxidation and chemical
damage occur faster at higher temperatures.
Various treatments are available such as conditioners. Saddle soap is used for cleaning,
conditioning, and softening leather. Leather shoes are widely conditioned with shoe polish
Types of Leather
In general, leather is sold in these four forms:
Full-grain leather;
The strongest and most durable part of the hide of an animal is just below the hair. The
grain pattern in this part of the hide is very tight, and the leather made from here is called
"full-grain" leather. Full-grain leather is the strongest and most durable leather.
Additionally, since the grain is so tight, it resists moisture very well. Over time, full-grain
leather will look nicer and nicer and develop a patina from being handled.

Among grain leathers there are three general categories:
aniline, semi-aniline, and protected.
 Analine leathers (like Horween’s Chromexcel) are processed using soluble dyes
to maintain their natural markings and texture, and do not have a surface pigment or
coating. This makes them the most natural-looking leathers, but also more
susceptible to scratching, fading and staining.
 Semi-analine leathers (like most bridle leathers) are treated with pigments and thus
conceal more blemishes and have a more uniform coating, as well as staying more
protected.
 Protected leathers have a non-leather coating sprayed or attached to the leather as a
protectant.
Top grain leather;
The next best—and second strongest—leather is called "top-grain" leather. Top grain
leather is similar to full-grain leather, except that the top couple millimeters have been
sanded and buffed to take away imperfections. With the top layer removed, the leather will
have a more uniform finish, but it won't be as durable—and it will break down much faster.
This is more of a "cookie cutter" leather that most leather wallets and handbags are made
of, which lends to their generic appearance. Top-grain leather can be good leather, but its
strength and durability is not even close to the strength of full-grain leather.
Correctedgrainleather:
Corrected grain is a special type of leather that’s been fixed, or corrected, by a professional
leatherworker to improve its aesthetics and functional qualities. If a leather worker deems
a piece of leather as having too many flaws, it’s used as corrected leather instead of full-
grain. The leatherworker will attempt to remove as many of these flaws as possible before
using the material in a product. When the flaws are removed, the material is dubbed
“corrected grain,” at which point it’s used in the production of a jacket, handbag, shoes, belt,
furniture, etc.
For a better understanding of corrected grain, you must first look at the physical qualities
of leather.
Normally, leather has a rough, almost sandpaper-like grain on the surface (to a lesser
degree, of course). This helps to create its appealing characteristics. With corrected grain,
however, the leather grain’s is below the necessary standards for the leatherworker to use
it as a full-grain. Instead of throwing it away, however, the leatherworker removes the

flawed grain on the surface and replaces it with an artificial grain. The exact process for
this varies depending on the leatherworker’s preferences.
Advantages and Disadvantages;
There are both advantages and disadvantages to choosing corrected grain leather
 Because it’s derived from lower quality leather,
 it tends to cost less than full or top-grain.
 If you’re looking for an inexpensive piece of leather, corrected grain is the way to
go. Furthermore, it’s often produced in different finish types, such as semi-aniline
and pigmented, adding an extra layer of appeal.
Split leather:
The leather created from the fibrous part of the hide left once the top-grain of
the rawhide has been separated from the hide. During the splitting operation, the top-grain
and drop split are separated. The drop split can be further split (thickness allowing) into a
middle split and a flesh split. In very thick hides, the middle split can be separated into
multiple layers until the thickness prevents further splitting. Split leather then has an
artificial layer applied to the surface of the split and is embossed with a leather
grain (bycast leather).
 Splits are also used to create suede. The strongest suedes are usually made from
grain splits (that have the grain completely removed) or from the flesh split that has
been shaved to the correct thickness. Suede is "fuzzy" on both sides
 Manufacturers use a variety of techniques to make suede from full-grain. A reversed
suede is a grained leather that has been designed into the leather article with the
grain facing away from the visible surface. It is not considered a true suede.
Another use for split leather is suede, which has been textured to have a napped finish.
Suede is often confused with nubuck, which is a grain leather that is textured to have a
similar nap finish. The difference is that nubuck is much stronger and more durable than
suede, though suede’s softness and pliability make it useful for certain applications.
Less-commonleathers include:
 Buckskin or brained leather:
The tanning process that uses animal brains or other fatty materials to alter the leather.
The resulting supple, suede-like hide is usually smoked heavily to prevent it from returning
to a rawhide state, if wetted. It is easier to soften, and helps repel leather-eating bugs.

 Patent leather; is leather that has been given a high-gloss finish. Inventor Seth
Boyden developed the original process, in Newark New Jersey in 1818. Patent
leather usually has a plastic coating.
 Fish leather:is popular for its motifs and its pigmentation. Mainly used for making
shoes and bags, the fish skin is tanned like other animal skins.The species used
include salmon, perch, sturgeon, etc.
 Slink: is leather made from the skin of unborn calves. It is particularly soft and is
valued for making gloves.
 Deerskin: is a tough, water-resistant leather, possibly due to the animal's
adaptations to its thorny and thicket-filled habitats. Deerskin has been used by
many societies, including indigenous Americans.
Most modern deerskin is no longer procured from the wild, with deer farms
breeding the animals specifically for the purpose of their skins. Large quantities are
still tanned from wild deer hides in historic tanning towns such
as Gloversville and Johnstown in upstate New York.
Deerskin is used in jackets and overcoats, martial arts equipment such
as kendo bogu, as well as personal accessories such as handbags and wallets.
 Goatskin; is soft but tough, and is used for items such as thorn-resistant gardener's
gloves.
 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.
 Russia leather: is a particular form of bark-tanned cow leather. It is distinguished
by an oiling step, after tanning, where birch oil is worked into the leather to make it
particularly hard-wearing, flexible and resistant to water.
There are other types of leather commonly used in specialty products, such as briefcases,
wallets, and luggage:
 Belting leather; is a full-grain leather 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.
 Bonded leather or reconstituted leather;is an economical material that uses leftover
organic leather (from tanneries or workshops) that are shredded and bonded together
with polyurethane or latex on to a fiber sheet. The varying degree of organic leather in
the mix (10% to 90%) affects the smell and texture. Its reduced cost makes it popular

for furniture upholstery, especially for commercial furniture that requires durability—
though durability can vary widely depending on the formulation.
 Bycast leather; is a split leather with a layer of polyurethane laminated to the surface
and then embossed. Bycast was originally made for the shoe industry, and later
adopted by the furniture industry. The original formula created by Bayerwas strong
but expensive. The result is a material that is slightly stiffer but cheaper than top-grain
leather but has a much more consistent texture. Because its surface is completely
covered in plastic, is easier to clean and maintain, but is not easily repaire.
Leather Manufacturing Process Technology
with Flow Sheets
Raw Materials
The following are the types of basic raw materials which are being used by this industry:
1. Buffalo:
Buffalo is considered as the specialty of Pakistan in World, because of its ample availability
in Pakistan.
2. Cow:
The cow hide is considered a superior raw material upon buffalo because of its fine, tight
and comparatively uniform structure.
3. Goat:
It is good for making shoe upper leathers, garment and goods leather.
4. Sheep:
Leather made from sheep skin has a very good and softer touch and is considered best for
leather garments.
The industry meets 75% of its needs of raw hides from local sources while rest is met
through imports. Pakistan imports raw hides from Saudi Arabia, Iran, and China, Dubai,
Sudan, Kenya, Australia and Italy.

Flaying: The technical term is used to denote the
removal of hides and skins from the parental body is
called Flaying.
Curing (Dehydate the
Hides/Skins): The temporary preservation of
hides or skin is known as curing. Curing can be done
using by solid salt or brine. The solid salt method is the
more general and is used worldwide. NaCl used to
remove Hyaloglunic acid.
BEAMHOUSE OPERATIONS:
The steps in the production of leather between curing and tanning are collectively referred
to as beamhouse operations. They include, in order, soaking, liming, removal of extraneous
tissues (unhairing, scudding and fleshing), deliming, bating (including puering) , and
pickling.
Trimming: The trimming is done by hand to
remove any portion of the hide that could interfere
with the subsequent machine processes, e.g.: the
shanks, ears, and snout.
Batch: Trimed hides are sorted for size and weight and formed into batches.
Soaking: It is a process of rehydration of
preserved raw hides or skins.
Objectives:
• The preserved raw hides regain their normal
water contents.
• Dirt, manure, blood, preservatives
(sodiumchloride, bactericides) etc. are removed.
Soaking Paddles:
Onlywell-curedhidesandskinsproduce highquality
leather.

Chemicals:
• Soda Ash or Na2CO3- It increases the pH & works as bleaching agent. It helps to
keep pH within 6.5 to 7.0 of raw hides/skins
• Caustic Soda or NaOH- It works as Soda ash
• Wetting agent-It wets back wet or dry salted leather during soaking. Some wetting
agents are:-
• 1.LD600(buckman) 2.Lissapol EF(ACI) 3.Eusapon FB(BASF) 4.Sinteral
BD(Alpha) 5.Metapol WA 6.7794
• Bactericide- It prevents bacteria's growth in raw hides/skins.
• Soaking Enzyme- It works as catalyst to return the wet condition completely in
hides/skins just like green condition and also remove loose plunk which grows
during mechanical agitation of soaking. It also assists to control the pH in optimum
level.
Operation:
1. Soaking is carried out in quanity of water which is double the weigth of hides/skins.
In this stage bacterial spores, dirt, blood and salt are washed out.
2. Then soaking is carried out in quanity of water which is four to five times the
weight of hides/skins, and soaking agents and bactericides are used.
Quality Control:
1. Soaking time depend upon the condition of raw stock.
Freshly slaughtered hides require minium soaking time.
Cured hides require 36-48 hours soaking time.
2. Water used for soaking should be soft to medium hard and free of dissolved organic
matter.
Hard water softens hides more slowly than soft water and will pricipitate soaps
from wetting agents.
Organic matter accelerates the bacterial growth.
3. pH Check-9.0 to 9.5(if pH is 10,no problem). If the pH goes over 11, it is called
immunization of soaking. In this case hair gets fixed in its root and cause problem in
liming process.
4. Cross Section Check: Take cross section, if the entire part feel wet uniformly then
soaking has done.

Liming: Liming is a process in which hides are soaked in an alkali solution. It is
performed using a drum and paddle or a pit.
Objectives:
 Unhairing to remove the epidermic layer
 Swelling of fibre bundles into individual fibres and
splitting of fibres into fibrils
 To remove the natural fats and grease by soponification
Turbo Mixture for Liming:
Chemicals & Use condition:
Chemicals
1. Sodium Sulfide (Na2S)
2. Calcium Oxide (CaO)
Conditions
 If the hide has great thickness and area
Sodium Sulfide (Na2S)-3.5%
Calcium Oxide (CaO) -3.25%
 If the hide has mediocre thickness and area
Calcium Oxide (CaO)-3.5%
 If the hide is thin and small in size
Sodium Sulfide (Na2S)-3.5% to 3.75%
Calcium Oxide (CaO)-4.0%

 In case of goat skin(Any size and thickness)
Calcium Oxide (CaO)-7.0% to 7.5%
Operation:
When lime is sharpening with sodium sulphide, the sodium sulphydrate (sharpening agent)
formed in the bath, causes rapid loosening of hair, whereas caustic soda solution causes
vigorous plumbing of hide fibres due to its strong alkalinity and also saponifies the natural
fat in the hides and skins.
Quality Controls:
 pH-12 to12.5
 Cross section test-Drip phenolphthalein in the cross section of limed pelt, if deep
pink color appears, liming is confirmed.
 Layer- If double layer appears in the cross section of limed pelt, and then liming has
done.
 Swelling & Plumping- If the pelt uniformly distended then that’s plumping, it needs
8000lb pressure to bring the water from inside. If the pelt inflates in different place
that’s called swelling, it requires 48000lb pressure to bring out the water.
 Duration- 24 hours in industries, but it varies in laboratory.
 Hair Slip test-Before soaking we should test hair slipness, if hair slips then the raw
stock is putrefied.
 Temperature, concentration of chemicals, time period of liming should be
controlled.
Fleshing: The process of
removal of sticky flesh from the side
of the skin or hide on fleshing
machine or by hand is called
fleshing.
Limedhidesandskinsare calledpelts

Deliming: It is an intermediate process between liming and pickling. The deliming
operation in leather processing is a drum/paddle or pit based operation. Fully delimed
pelts produce softer leather while half delimed pelts produce hard types leather.
Objectives:
 Lowering the pH from 12-12.5 to 8.5-9.0
 Remove the lime
 Remove swelling and plumping
 Depleting the pelt
Deliming Chemicals:
• Water
• Acids: Hydrochloric acid (diluted), Sulfuric acid (diluted), Boric acid, Lactic acid,
Formic acid, Acetic acid
• Ammonium salts: ammounium chloride, ammonium sulfate
• Carbon dioxide
Condition:
• If the pelt is thick and large
(NH4)2SO4- 2.75% to 3.0% (duration-75 mins)
• Medium thick and medium size pelt
(NH4)2SO4- 2.5% (duration-75 mins)
• Less thick and small pelt
(NH4)2SO4- 2.0% to 2.25% (duration-50 min-60min)
• For all types and sizes goat and sheep skin
(NH4)2SO4- 1.5% (duration- 45 min)
• If bath falls down, upload the pelts in the drum, add 80% water and 0.25%
(NH4)2SO4 then run the drum for 10 minutes
Operation:

In deliming process, the free alkali, which is soluble in water, is removed by washing the
pelts in water. After washing, chemically combined alkali is removed by neutalising it with
acids, acid salts, ammonium salts or substances with acidic reaction.
Quality Control:
 pH- 8.2 to 8.8
 Cross section test-Drip phenolphthalein in the cross-section, if light pink color
appears or the pelt become colorless deliming has done
 After deliming we press the pelt by hand, if it feels soft, then it does mean the
protein inside pelt has prepared for fixation reaction.
Bating:
Bating is an enzymetic process in which non-leather making
constitutes such as degraded proteins, colour pigments, grease and
lime soap are reomoved by pancreatic enzymes or proteolytic
enzymes.
Enzymes:
 Theoretically there are three types bating enzymes. They are:-
1. Weak bating enzymes-
2. Mid strong bating enzymes-
 Strong bating enzymes- There are two types available commercially, they are:-
1. Alkali bate
2. Acid bate
Operation:
Wash the pelts and then to carry out partial deliming. In final deliming, the temperature is
raised and the bate is added.
Features of Bating in Acidic Condition:
1. Bating operation can be carried out in 25-32°C.
2. Deliming, bating, pickling and chrome tanning can be carried out in the same drum.
3. Reduces the operation cost.

4. Manual scuding can be avoided.
5. The grain remains tight after finishing.
Sign ofbating:
1. The grain of the bated pelts should feel silky and slippery.
2. The thumb impression should be retained on the grain when pressed.
3. The pelt should be perfectly fallen and flaccid.
4. The pelt should be white, clean and porous.
5. The scud should be easily removable.
6. The flesh should be come off easily when scratched with finger.
After bating the skins and hides are rinsed for 10-12 minutes to reomve lime salt and also
to cool down the pelts.
Pickling: The treatment of delimed or bated pelt with a solution of acid and salt is
known as pickling.
Objectives:
 Preserve the pelt for further treatment
 Acidify the pelt, the pH bring down from 7.8 to 2.8
 Oxidize hair root and remove if hair remains after liming
 Remove all swelling and plumping
 Produce softer, thinner white pelt
 Reduce astringency of chrome tanned leather
Operation:
Pelts are introduced into the pickle liquor (salt and diluted acid in water) for 10 minutes.
The starting pH is 1.7-2 of pickle bath which gradually increases 2.7-3 due to absorption of
acid by the pelts.
Salts & Acids:
• Salts
1. Common salt – NaCl
The pickle anddegree of picklingare of greatimportance indeterminigthe qualityof leather
and the speedof the tannage.

2. Sodium Sulfate – NaSO4
3. Sodium Formate - HCOONa
4. Sodium Acetate – CH3COONa
• Acids
1. Sulfuric acid- H2SO4
2. Formic acid- HCOOH
Quality Controls:
• pH- 2.6 to 2.9
• Cross section test- If yellow color appear pickling done
• Moulds grow on pickled stock and cause decolouration in the finished leather and
even produce stains.
Vegetable Tanning:
Vegetable tanning is a tanning method that uses natural ingredients such as the bark of
chestnut trees to tan the leather. Plant extracts are used for the purpose of tanning in this
process. This means the finished product colour is usually warm, rich tones of natural
browns. Vegetable tanning is usually done by tanneries that have a rich heritage of tanning
hides. Unlike chrome tanning, vegetable tanning can take up to 40 days to produce a piece
of dyed leather.
Wet white tanning refers to organic tanning methods. The biosynthetic is used to tan
the leather, which result in a semi-finished leather that looks white-tinted.
This fairly new method of tanning has been gaining popularity, partially due to increased
concern for water treatment systems and the environment.
The off-cuts from wet white tanned leather in the form of shavings can be recycled or used
as fertilizer, in contrast to wet blue tanning methods.
Advantages and Disadvantages of Vegetable tanning:
Advantages:
 Only natural ingredients (no harmful chemicals) are used when dying the hides
 Lighter in color and can be converted into pastel Shade leathers

 High softness
 Good lightness
 Natural sensation
 Pleasant touch
 Beauty over the time
 Environmentally friendly and can be recycled.
 Each leather product that is dyed using vegetable tanning is completely unique.
 Rich, warm-tone colors which look completely natural.
 High performance leather can be obtained, often better than chrome tanning
Disadvantages:
 The process of vegetable tanning takes a long time, and can take up to 60 days.
 Vegetable tanning doesn’t react well with water and can stain easily.
 Products that have been vegetable tanned are more expensive.
 The colors you can produce from vegetable tanning are limited.
 Direct heat can cause vegetable tanned products to shrink or crack.
CHROME TANNING (AND WET BLUE)
80-90% of leathers in the world are tanned by chrome (also known as mineral) tanning.
Chrome tanning uses a solution of chemicals, acids and salts (including chromium
sulphate) to dye the hide. It’s a very quick process, taking about a day to produce a piece of
tanned leather. First the hide is ‘pickled’ by being left in the acid salt mixture, before being
placed into the chromium sulphate. All hides then come out looking light blue (known as
‘wet blue’) and then have a finishing colour applied.
Wet Blue is the tanning process where chromes are used to process the leather from raw
hide to finished leathers. This process causes the semi-finished leather to look blue-tinted.
Advantages and Disadvantages of Chrome tanning
Advantages:
 Quick and easy to produce, usually only taking up to a day.
 Stain resistant and water can roll off the surface easily.
 Soft and supple to the touch.
 Colour remains the same throughout the products life.
 It’s cheaper to buy than vegetable tanned leather, which means it is also easier to find.
 It has a high degree of thermal resistance.
Disadvantages:

 Chrome tanning is very bad for the environment.
 It’s produced with little skill and very often mass produced.
 It doesn’t wear very well or last long and can crack after a few months of use.
 Chrome tanning often smells of chemicals.
 It doesn’t appear (neither is it) very natural.
HOW TO TELL THE DIFFERENCE
Do you want to buy a vegetable or chrome tanned leather product but aren’t sure how to
tell the difference? Or do you have a ladies leather handbag and want to know how it’s been
tanned? There are a couple of things you can do to test the type of leather it is.
Firstly; if you are shopping for a leather product you can smell the product. If the product
smells chemically then it’s probably been chrome tanned. Vegetable tanned leather smells
sweeter and not at all like chemicals.
Secondly; you can scratch the leather product (but do not do this in shops!), if the scratches
can be easily buffed out with minimum effort then it is probably vegetable tanned leather.
Thirdly; the burn test! You can burn the leather product to find out what type of leather it
is. Simply hold a lighter up against the product; if it has no effect on the leather then it is
vegetable tanned! If it produces any ash at all it will be grey, chrome tanned will be a
distinctive green. Note: never do this in a shop or with a much loved piece! Only do this test
if you know of the quality leather or you do not care that much about the product you are
testing.
Tanning:
Tanning is the process that converts the protein of the raw hide or skin into a stable
material which will not putrefy and is suitable for a wide variety of end applications. The
principal difference between raw hides and tanned hides is that raw hides dry out to form a
hard inflexible material that can putrefy when re-wetted (wetted back), while tanned
material dries out to a flexible form that does not become putrid when wetted back. A large
number of different tanning methods and materials can be used; the choice is ultimately
dependent on the end application of the leather. The most commonly used tanning material
is chromium, which leaves the leather, once tanned, a pale blue colour (due to the
chromium), this product is commonly called “wet blue”.
The acidity of hides once they have finished pickling will typically be between pH of 2.8-3.2.
At this point the hides are loaded in a drum and immersed in a float containing the tanning
liquor. The hides are allowed to soak (while the drum slowly rotates about its axle) and the
tanning liquor slowly penetrates through the full substance of the hide. Regular checks will
be made to see the penetration by cutting the cross section of a hide and observing the
degree of penetration. Once an even degree of penetration is observed, the pH of the float is
slowly raised in a process called basification. This basification process fixes the tanning

material to the leather, and the more tanning material fixed, the higher the hydrothermal
stability and increased shrinkage temperature resistance of the leather. The pH of the
leather when chrome tanned would typically finish somewhere between
Define wet processing:
Processing Engineering is one of the major streams in textile engineering refers to textile
chemicals process engineering and applied science. The other three streams in textile
engineering are yarn engineering, fabric engineering and apparel engineering. ... In other
words, wet process is done on manufactured fabric.
Wet Processing Engineering: is one of the major streams in textile engineering refers to
textile chemicals process engineering and applied science. The other three streams in
textile engineering are yarn engineering, fabric engineering and apparel engineering.
Wet process is usually done on the manufactured assembly of interlacing fibers, filaments,
and/or yarns having substantial surface (planar) area in relation to its thickness, and
adequate mechanical strength to give it a cohesive structure. In other words, wet process is
done on manufactured fabric. The processes of this stream is involved or carried out in
aqueous stage and thus it is called wet process which usually covers pretreatment, dyeing,
printing and finishing.
All of these stages are required aqueous medium which is created by water. A massive
amount of water is required in these processes per day. It is estimated that, on an average,
almost 100 liter of water is used to process only 1 kg of textile goods.[citation needed]
Water can be of various quality and attributes. Not all water can be used in the textile
process, it must have some certain properties, quality, color & attributes for being used in
textile processes. This is why water is a prime concern in wet process engineering.
Water:
Most water used in the textile industry is from deep well water which is found 800 ft below
the surface level. The main problem which is concerned in using water in textile processes
is water hardness caused by the presence of soluble salts of metals including calcium and
magnesium. Iron, aluminum and copper salts may also contribute to the hardness, but their
effects are much less. Using hard water in wet process can cause problems such as the
formation of scale in boilers, reactions with soap and detergents, reaction with dyes and
problems due to Iron.
Water hardness can be removed by boiling process, liming process, sodalime process, base
exchange process or synthetic ion exchange process. Recently some companies have
started harvesting rain water for use in wet processes as it is less likely to cause the
problems associated with water hardness.
Pretreatment:
Wet Process Engineering (WPE) is the most significant division in the textile
preparation and processing. It is a major stream in textile engineering which is
under the section of textile chemical processingengineering and applied science.
Textile manufacturing covers everything from fiber to apparel; covering with yarn,

fabric, fabric dyeing, printing, finishing, garments or apparel manufacturing. There
are many variable processes available at the spinning and fabric-forming stages
coupled with the complexities of the finishing and coloration processes to the
production of a wide ranges of products.
In Bangladesh, textile manufacturing is a major industry. In this industry, wet
processing plays a vital role in the area of pre-treatment, dyeing, printing and
finishing of both fabrics and apparels. But coloration in fiber stage or yarn stage is
also included in the wet processing division.
All the processes ofthis stream are carried out in an aqueous state or aqueous
medium. The main processes ofthis section include;
 Singeing
 Desizing
 Scouring
 Bleaching
 Mercerizing
 Dyeing
 Printing
 Finishing
Singeing:
The process ofsingeing is carried out for the purposeof removing the loose hairy
fibers protruding from the surface of the cloth, thereby giving it a smooth, even
and clean looking face. Singeing is an essential process forthe goods ortextile
material which will be subjected to mercerizing, dyeing and printing to obtain best
results from these processes.
The fabric passes over brushes to raise the fibers, then passes over a plate heated
by gas flames. When done to fabrics containing cotton, this results in increased
wetability, better dyeing characteristics, improved reflection, no "frosty"
appearance, a smoother surface, better clarity in printing, improved visibility of the
fabric structure, less pilling and decreased contamination through removal of fluff
and lint.
Singeing machines can be of three types: plate singeing, roller singeing, or gas
singeing. Gas singeing is widely used in the textile industry. In gas singeing, a
flame comes into direct contact to the fabric and burn the protruding fiber. Here,
flame height and fabric speed is the main concern to minimize the fabric damage.
Singeing is performed only in the woven fabric. But in case of knit fabric, similar

process ofsingeing is known as biopolishing where enzyme is used to remove the
protruding fibres.
Singeing is a mechanical process bywhich hairy, loose fibers are removed from
the surface of the textile material either by heating or burning to make the material
smoother and lustrous.
Importance: same to bio-polishing without point 5
Desizing:
Desizing is the process ofremoving sizing materials from the fabric, which is
applied in order to increase the strength of the yarn which can withstand with the
friction of loom. Fabric which has not been desized is very stiff and causes
difficulty in its treatment with different solution in subsequentprocesses.
After singeing operation the sizing material is removed by making it water-soluble
and washing it with warm water. Desizing can be done by either the hydrolytic
method (rot steep, acid steep, enzymatic steep) or the oxidative method (chlorine,
chloride, bromite, hydrogen peroxide)
Depending on the sizing materials that has been used, the cloth may be steeped in a
dilute acid and then rinsed, or enzymes may be used to break down the sizing
material. Enzymes are applied in the desizing process if starch is used as sizing
materials. Carboxymethyl cellulose (CMC) and Poly vinyl alcohol (PVA) are often
used as sizing materials.
Scouring:
Scouring is a chemical washing process carried out on cotton fabric to remove
natural wax and non-fibrous impurities (e.g. the remains of seed fragments) from
the fibers and any added soiling or dirt. Scouring is usually carried in iron vessels
called kiers. The fabric is boiled in an alkali, which forms a soap with free fatty
acids (saponification). A kier is usually enclosed, so the solution of sodium
hydroxide can be boiled under pressure, excluding oxygen which would degrade
the cellulose in the fiber. If the appropriate reagents are used, scouring will also
remove size from the fabric although desizing often precedes scouring and is
considered to be a separate process known as fabric preparation. Preparation and
scouring are prerequisites to most of the other finishing processes. At this stage
even the most naturally white cottonfibers are yellowish, and bleaching, the next
process, is required.
The three main processesinvolved in the scouring are saponification,
emulsification and detergency.
The main chemical reagent used in the cottonscouring is sodium hydroxide which
converts saponifiable fats and oils into soaps, dissolves mineral matter and

converts pectoseand pectin into their soluble salts.
Another scouring chemical is detergent which is an emulsifying agent and removes
dust and dirt particles from the fabric.
Since damage can be caused to the cottonsubstrate by sodium hydroxide. Due to
this, and in order to reduce alkali content in the effluent, Bio-scouring is introduced
in the scouring process in which biological agent is used, such as an enzyme.
Bleaching:
Bleaching improves whiteness by removing natural coloration and remaining trace
impurities from the cotton;the degree of bleaching necessary is determined by the
required whiteness and absorbency. Cottonbeing a vegetable fiber will be
bleached using an oxidizing agent, such as dilute sodium hypochlorite or dilute
hydrogen peroxide. If the fabric is to be dyed a deep shade, then lower levels of
bleaching are acceptable. However, for white bed sheets and medical applications,
the highest levels of whiteness and absorbencyare essential.
Reductive bleaching is also carried out, using sodium hydrosulphite. Fibers like
polyamide, polyacrylics and polyacetates can be bleached using reductive
bleaching technology.
After scouring and bleaching, optical brightening agents (OBA), are applied to
make the textile material appear more white. These OBAs are available in different
tints such as blue, violet and red.
Mercerizing:
Mercerization is a treatment for cottonfabric and thread that gives fabric or yarns a
lustrous appearance and strengthens them. The process is applied to cellulosic
materials like cottonor hemp. A further possibility is mercerizing during which the
fabric is treated with sodium hydroxide solution to cause swelling of the fibres.
This results in improved lustre, strength and dye affinity. Cottonis mercerized
under tension, and all alkali must be washed out before the tension is released or
shrinkage will take place. Mercerizing can take place directly on greige cloth, or
after bleaching.
Dyeing:
Dyeing is the process ofadding color to textile products like fibers, yarns, and
fabrics. Dyeing is normally done in a special solution containing dyes and
particular chemical material. After dyeing, dye molecules have uncut chemical
bond with fiber molecules. The temperature and time controlling are two key
factors in dyeing. There are mainly two classes of dye, natural and man-made.

Solution dyeing:
Solution dyeing, also known as dopeor spun dyeing, is the process ofadding
pigments or insoluble dyes to the spinning solution before the solution is extruded
through the spinneret. Only manufactured fibers can be solution-dyed. It is used for
difficult-to-dye fibers, such as olefin fibers, and for dyeing fibers for end uses that
require excellent colorfastness properties. Because the color pigments become a
part of the fiber, solution-dyed materials have excellent colorfastness to light,
washing, crocking (rubbing), perspiration, and bleach. Dyeing at the solution stage
is more expensive, since the equipment has to be cleaned thoroughly each time a
different color is produced. Thus, the variety of colors and shades produced is
limited. In addition, it is difficult to stockthe inventory for each color. Decisions
regarding color have to be made very early in the manufacturing process. Thus,
this stage of dyeing is usually not used for apparel fabrics.
Filament fibers that are produced using the wet spinning method can be dyed while
the fibers are still in the coagulating bath. The dye penetration at this stage is high,
as the fibers are still soft. This method is known as gel dyeing.
Fiber dyeing:
Stockdyeing, top dyeing, and tow dyeing are used to dye fibers at various stages of
the manufacturing process prior to the fibers being spun into yarns. The names
refer to the stage at which the fiber is when it is dyed. All three are included under
the broad category of fiber dyeing.
Stockdyeing is dyeing raw fibers, also called stock, before they are aligned,
blended, and spun into yarns.
Top dyeing is dyeing worsted wool fibers after they have been combed to
straighten and remove the short fibers. The wool fiber at this stage is known as top.
Top dyeing is preferred for worsted wools as the dye does not have to be wasted on
the short fibers that are removed during the combing process.
Tow dyeing is dyeing filament fibers before they are cut into short staple fibers.
The filament fibers at this stage are known as tow.
The dye penetration is excellent in fiber dyeing, therefore the amount of dye used
to dye at this stage is also higher. Fiber dyeing is comparatively more costly than
yarn, fabric, and productdyeing. The decision regarding the selection of colors has
to be made early in the manufacturing process. Fiber dyeing is typically used to
dye wool and other fibers that are used to produceyarns with two or more colors.
Fibers for tweeds and fabrics with a “heather” look are often fiber dyed.
Yarn dyeing:
Yarn dyeing adds colorat the yarn stage. Skein, package, beam, and space dyeing

methods are used to dye yarns.
In skein dyeing the yarns are loosely wound into hanks or skein and then dyed. The
yarns have good dye penetration, but the process is slow and comparatively more
expensive.
In package dyeing yarns that have been wound on perforated spools are dyed in a
pressurized tank. The process is comparatively faster, but the dye uniformity may
not be as good as that of skein dyed yarn.
In beam dyeing a perforated warp beam is used instead of the spools used in
package dyeing.
Spacedyeing is used to produceyarns with multiple colors.
In general, yarn dyeing provides adequate color absorptionand penetration for
most materials. Thick and highly twisted yarns may not have good dye penetration.
This process is typically used when different colored yarns are used in the
construction of fabrics (e.g. plaids, checks, iridescent fabrics).
Fabric dyeing:
Fabric dyeing, also known as piece dyeing, is dyeing fabric after it has been
constructed. It is economical and the most common method of dyeing solid colored
fabrics. The decision regarding color can be made after the fabric has been
manufactured. Thus, it is suitable for quick responseorders. Dye penetration may
not be good in thicker fabrics, so yarn dyeing is sometimes used to dye thick
fabrics in solid colors. Various types of dyeing machines are used for piece dyeing.
The selection of the equipment is based on factors such as dye and fabric
characteristics, cost, and the intended end use.
Union dyeing:
Union dyeing is “a method of dyeing a fabric containing two or more types of
fibers or yarns to the same shade so as to achieve the appearance of a solid colored
fabric”.[1] Fabrics can be dyed using a single or multiple step process.Union
dyeing is used to dye solid colored blends and combination fabrics commonly used
for apparel and home furnishings.
Cross dyeing:
Cross dyeing is “a method of dyeing blend or combination fabrics to two or more
shades by the use of dyes with different affinities for the different fibers”.[1] The
cross dyeing process canbe used to create heather effects, and plaid, check, or
striped fabrics. Cross dyed fabrics may be mistaken for fiber or yarn dyed
materials as the fabric is not a solid color, a characteristic considered typical of
piece dyed fabrics. It is not possible to visually differentiate between cross dyed

fabrics and those dyed at the fiber or yarn stage. An example is cross dyeing blue
worsted wool fabric with polyester pin stripes. When dyed, the wool yarns are
dyed blue, whereas the polyester yarns remain white.
Cross dyeing is commonly used with piece or fabric dyed materials. However, the
same conceptis applicable to yarn and productdyeing. Forexample, silk fabric
embroidered with white yarn can be embroidered prior to dyeing and productdyed
when an order is placed.
Product dyeing:
Productdyeing, also known as garment dyeing, is the process ofdyeing products
such as hosiery, sweaters, and carpet after they have been produced. This stage of
dyeing is suitable when all components dye the same shade (including threads).
This method is used to dye sheer hosiery since it is knitted using tubular knitting
machines and then stitched prior to dyeing. Tufted carpets, with the exception of
carpets produced using solution dyed fibers, are often dyed after they have been
tufted. This method is not suitable for apparel with many components such as
lining, zippers, and sewing thread, as each component may dye differently. The
exception is tinting jeans with pigments for a “vintage” look. In tinting, color is
used, whereas in other treatments such as acid-wash and stone-wash, chemical or
mechanical processesare used. After garment construction, these products are
given the "faded" or "used" look by finishing methods as opposed to dyeing.
Dyeing at this stage is ideal for quick response. Many T-shirts, sweaters, and other
types of casual clothing are productdyed for maximum responseto fashion’s
demand for certain popular colors. Thousands of garments are constructed from
prepared-for-dye (PFD) fabric, and then dyed to colors that sell best.
Dye types:
Acid dyes are water-soluble anionic dyes that are applied to fibers such as silk,
wool, nylon and modified acrylic fibers using neutral to acid dye baths.
Attachment to the fiber is attributed, at least partly, to salt formation between
anionic groups in the dyes and cationic groups in the fiber. Acid dyes are not
substantive to cellulosic fibers.
Basic dyes are water-soluble cationic dyes that are mainly applied to acrylic fibers,
but find some use for wool and silk. Usually acetic acid is added to the dyebath to
help the uptake of the dye onto the fiber.
Direct or substantive dyeing is normally carried out in a neutral or slightly alkaline
dyebath, at or near boiling point, with the addition of either sodium chloride,
sodium sulfate or sodium carbonate. Direct dyes are used on cotton, paper, leather,
wool, silk and nylon.

Mordant dyes require a mordant, which improves the fastness of the dye against
water, light and perspiration. The choice of mordant is very important as different
mordants can change the final color significantly. Most natural dyes are mordant
dyes and there is therefore a large literature base describing dyeing techniques. The
most important mordant dyes are the synthetic mordant dyes, or chrome dyes, used
for wool; these comprise some 30% of dyes used for wool, and are especially
useful for black and navy shades. The mordant, potassium dichromate, is applied
as an after-treatment. Many mordants, particularly those in the heavy metal
category, can be hazardous to health and extreme care must be taken in using them.
Vat dyes are essentially insoluble in water and incapable of dyeing fibers directly.
However, reduction in alkaline liquor produces the water-soluble alkali metal salt
of the dye, which, in this leuco form, has an affinity for the textile fiber.
Subsequent oxidation reforms the original insoluble dye. The color of denim is due
to indigo, the original vat dye.
Reactive dyes utilize a chromophoreattached to a substituent that is capable of
directly reacting with the fiber substrate. The covalent bonds that attach reactive
dye to natural fibers make them among the most permanent of dyes. "Cold"
reactive dyes, such as Procion MX, Cibacron F, and Drimarene K, are very easy to
use becausethe dye can be applied at room temperature. Reactive dyes are by far
the best choice for dyeing cottonand other cellulose fibers at home or in the art
studio.
Disperse dyes were originally developed for the dyeing of cellulose acetate, and
are water-insoluble. The dyes are finely ground in the presence of a dispersing
agent and sold as a paste, or spray-dried and sold as a powder. Their main use is to
dye polyester but they can also be used to dye nylon, cellulose triacetate, and
acrylic fibers. In some cases, a dyeing temperature of 130 °C is required, and a
pressurised dyebath is used. The very fine particle size gives a large surface area
that aids dissolution to allow uptake by the fiber. The dyeing rate can be
significantly influenced by the choice of dispersing agent used during the grinding.
Azoic dyeing is a technique in which an insoluble azo dye is produced directly
onto or within the fiber. This is achieved by treating a fiber with both diazoic and
coupling components. With suitable adjustment of dyebath conditions the two
components react to producethe required insoluble azo dye. This technique of
dyeing is unique, in that the final color is controlled by the choice of the diazoic
and coupling components. This method of dyeing cottonis declining in importance
due to the toxic nature of the chemicals used.
Sulfur dyes are two part "developed" dyes used to dye cotton with dark colors. The
initial bath imparts a yellow or pale chartreuse color, This is after–treated with a

sulfur compound in place to producethe dark black we are familiar with in socks
for instance. Sulfur Black 1 is the largest selling dye by volume.
Printing:
Textile printing is referred as localized dyeing. It is the application of color in the
form of a paste or ink to the surface of a fabric, in a predetermined pattern. Printing
designs onto already dyed fabric is also possible. In properly printed fabrics the
color is bonded with the fiber, so as to resist washing and friction. Textile printing
is related to dyeing but, whereas in dyeing properthe whole fabric is uniformly
covered with one color, in printing one or more colors are applied to it in certain
parts only, and in sharply defined patterns. In printing, wooden blocks, stencils,
engraved plates, rollers, or silkscreens can be used to place colors on the fabric.
Colorants used in printing contain dyes thickened to prevent the color from
spreading by capillary attraction beyond the limits of the pattern or design.
Finishing:
Textile finishing is the term used for a series of processesto which all bleached,
dyed, printed and certain greige fabrics are subjected before they are put on the
market. The object of textile finishing is to render textile goods fit for their purpose
or end-use and/or improve serviceability of the fabric.
Finishing on fabric is carried out for both aesthetic and functional purposes to
improve the quality and look of a fabric. Fabric may receive considerable added
value by applying one or more finishing processes. Finishing processesinclude
 Raising
 Calendering
 Crease resistance
 Filling
 Softening
 Stiffening
 Water repellency
 Moth proofing
 Mildew-proofing
 Flame retardant
 Anti-static
 soil resistance

Calendering:
Calendering is an operation carried out on a fabric to improve its aesthetics. The
fabric passes through a series of calender rollers by wrapping; the face in contact
with a roller alternates from one roller to the next. An ordinary calender consists of
a series of hard and soft (resilient) bowls (rollers) placed in a definite order. The
soft roller may be compressed with either cottonor wool-paper, linen paper or flax
paper. The hard metal bowl is either of chilled iron or castiron or steel. The
calender may consistof 3, 5, 6, 7 and 10 rollers. The sequence of the rollers is that
no two hard rollers are in contact with each other. Pressure may be applied by
compound levers and weights, or hydraulic pressure may be used as an alternative.
The pressure and heat applied in calendering depend on the type of the finish
required.
The purposes ofcalendering are to upgrade the fabric hand and to impart a smooth,
silky touch to the fabric, to compress the fabric and reduce its thickness, to
improve the opacity of the fabric, to reduce the air permeability of the fabric by
changing its porosity, to impart different degree of luster of the fabric, and to
reduce the yarn slippage.
Raising:
An important and oldest textile finishing is brushing or raising. Using this process
a wide variety of fabrics including blankets, flannelettes and industrial fabrics can
be produced. The process ofraising consists of lifting from the bodyof the fabric a
layer of fibers which stands out from the surface which is termed as "pile". The
formation of pile on a fabric results in a "lofty" handle and may also subdue the
weave or pattern and color of the cloth.
There are to types of raising machine; Teasel machine and Card-wire machine. The
speed of the card-wire raising machine varies from 12-15 yards per minute, which
is 20-30% higher than that of teasel-raising. That is why the card-wire raising
machine is widely used.
Crease resistance:
Crease formation in woven or knitted fabric composed ofcellulose during washing
or folding is the main drawback of cottonfabrics. The molecular chains of the
cottonfibers are attached with each other by weak hydrogen bonds. During
washing or folding, the hydrogen bonds break easily and after drying new
hydrogen bonds form with the chains in their new position and the creases are
stabilized. If crosslinking between the polymer chains can be introduced by
crosslinking chemicals, then it reinforces the cottonfibers and prevents the
permanent displacement of the polymer chains when the fibers are stressed. It is
therefore much more difficult for creases to form or for the fabric to shrink on

washing.
In crease-resist finishing of cotton, the following steps are followed
1. Padding the material with a solution containing a condensation polymer
precursorand a suitable polymerization catalyst.
2. Drying and curing in a stenter frame to form crosslink between the polymer
chain and adjacent polymer chain.
The catalyst allows the reaction to be carried out 130-180 degree temperature
range usually employed in the textile industry and within the usual curing
time(within 3 minutes, maximum).
Mainly three classes of catalysts are commonly used now a day.
 Ammonium salts, e.g. Ammonium chloride, sulphate and nitrate.
 Metal salts e.g. Magnesium chloride, Zinc nitrate, Zinc chloride.
 Catalyst mixture e.g. magnesium chloride with added organic and inorganic
acids or acid donors.
The purposeof the additives is to offset or counterbalance partly or completely the
adverse effect of the crosslinking agent. Thus softening and smoothing agents are
applied not only to improve the handle, but also to compensate as much as possible
for losses in tear strength and abrasion resistance. Every resin finish recipe
contains surfactants as emulsifiers, wetting agents and stabilizers. these surface-
active substances are necessary to ensure that the fabric is wet rapidly and
thoroughly during padding and the components are stable in the liquor.
Textile wetprocessing:
In which way grey fabric is dyed is called wet process technology. Normally wet
processing depends on buyer's demand. Supposeyour buyer wants the more
precised dyed fabric; so in this fact you should mercerize your fabric during the
dyeing pre-treatment process. Basically if the buyer don’twant that so called
particular fabric there is no need to mercerize your fabric.
Flow Chart of Textile Wet ProcessTechnology:
Grey Fabric Inspection

↓
Sewing or Stitching
↓
Brushing
↓
Croping
↓
Singeing
↓
Desizing
↓
Scouring
↓
Bleaching
↓
Mercerizing
↓
Dyeing
↓
Printing
↓
Finishing
↓
Final Inspection
↓
Delivery
All above process are describedbriefly:
Grey Fabric Inspection:
After manufacturing fabric it is inspected in an inspection Table. It is the process to
remove neps, warp end breakage, weft end breakage, hole spot.
Stitching:
To increase the length of the fabric for making suitable for processing is called
stitching. It is done by plain sewing m/c.
Brushing:
To remove the dirt, dust, loose fibre & loose ends of the warp & weft threads is
known as brushing.

Shearing / Cropping:
The process bywhich the attached ends of the warp & weft thread is removed by
cutting by the knives or blades is called shearing. Shearing is done for cotton&
cropping for jute. After Shearing or cropping fabrics goes under singeing process.
Singeing:
The process bywhich the protruding / projecting fibres are removed from the
fabrics by burning / heat to increase the smoothness of the fabric is called singeing.
If required both sides of fabric are singed.
Desizing:
The process bywhich the sizing mtls (starch) are removed from the fabric is
known as desizing. This must be done before printing.
Scouring:
The process bywhich the natural impurities (oil, wax, fat etc) &
added/external/adventitious impurities (dirt, dust etc) are removed from the fabric
is called scouring. It is done by strong NaOH.
Souring:
The process bywhich the alkali are removed from the scoured fabric with dilute
acid solution is known as souring.
Bleaching:
The process bywhich the natural colours (nitrogenous substance)are removed
from the fabric to make the fabric pure & permanent white is known asbleaching.
It is done by bleaching agent.
Mercerizing:
The process bywhich the cellulosic mtls/substance are treated with highly
conc.NaOHto impart some properties such as strength, absorbencycapacity,
lusture is known as mercerizing. It is optional. If the fabrics are 100% export
oriented then it is done by highly conc. NaOH (48-52° Tw).
Dyeing:
A process ofcoloring fibers, yarns, or fabrics with either natural or synthetic dyes.
Printing:
A process forproducing a pattern on yarns, warp, fabric, or carpet by any of a large

number of printing methods. The color or other treating material, usually in the
form of a paste, is deposited onto the fabric which is then usually treated with
steam, heat, or chemicals for fixation.
Finishing:
Then finishing treatment are done according to buyer requirements and then
folding, packaging, and at last delivery.
Define Finishing process:
finishing refers to the processes that convert the woven or knitted cloth
into a usable material and more specifically to any process performed
after dyeing the yarn or fabric to improve the look, performance, or
"hand" (feel) of the finish textile or clothing.
finishing refers to the processes that convert the woven or knitted cloth into a
usable material and more specifically to any process performed after dyeing the
yarn or fabric to improve the look, performance, or "hand" (feel) of the finish
textile or clothing.[1][2] The precise meaning depends on context.
Some finishing techniques such as bleaching and dyeing are applied to yarn before
it is woven while others are applied to the grey cloth directly after it is woven or
knitted.[3] Some finishing techniques, such as fulling, have been in use with hand-
weaving for centuries; others, such as mercerisation, are byproducts ofthe
Industries.
Introduction:
In order to impart the required functional properties to the fiber or fabric, it is
customary to subject the material to different types of physical and chemical
treatments. For example, wash and wear finish for a cottonfabric is necessary to
make it crease-free or wrinkle-free. In a similar way, mercerising, singeing, flame
retardant, water repellent, waterproof, anti-static and peach finishing achieve
various fabric properties desired by consumers.
The use of 100% synthetic textiles has increased considerably since the
development of textured yarns made of filaments, and the growing productionof
knit goods. Theuse of open weave has enabled productionof lighter, breathable,
fabrics to ensure better wearing comfort.
The properties of petroleum-based synthetic fibers, most important among them
being polyamide, polyester and polyacrylonitrile, are essentially different from
those of natural cellulosic and protein/wool fibers. Hence the sequence of finishing

operations is likely to be different. While cellulosic fabrics require a resin finishing
treatment to impart easy-care properties, synthetic fibers already exhibit these
easy-care criteria and require only a heat setting operation.
Finishing- processing ofcotton:
Purification and preliminary processes:
The grey cloth,woven cotton fabric in its loom-state, not only contains impurities,
including warp size, but requires further treatment in order to develop its full
textile potential. Furthermore, it may receive considerable added value by applying
one or more finishing processes.
 Singeing
Main article: Singe § Textiles
Singeing is designed to burn off the surface fibres from the fabric to produce
smoothness. The fabric passes over brushes to raise the fibres, then passes over
a plate heated by gas flames.
 Desizing
Depending on the size that has been used, the cloth may be steeped in a dilute
acid and then rinsed, or enzymes may be used to break down the size.
 Scouring
Scouring, is a chemical washing process carried out on cottonfabric to remove
natural wax and non-fibrous impurities (e.g. the remains of seed fragments)
from the fibres and any added soiling or dirt. Scouring is usually carried in iron
vessels called kiers. The fabric is boiled in an alkali, which forms a soap with
free fatty acids (saponification). A kier is usually enclosed, so the solution of
sodium hydroxide can be boiled under pressure, excluding oxygen which would
degrade the cellulose in the fibre. If the appropriate reagents are used, scouring
will also remove size from the fabric although desizing often precedes scouring
and is considered to be a separate process known as fabric preparation.
Preparation and scouring are prerequisites to most of the other finishing
processes.At this stage even the most naturally white cottonfibres are
yellowish, and bleaching, the next process, is required.
 Bleaching
Main article: Textile bleaching
Bleaching improves whiteness by removing natural coloration and remaining
trace impurities from the cotton;the degree of bleaching necessary is
determined by the required whiteness and absorbency. Cottonbeing a vegetable

fibre will be bleached using an oxidizing agent, such as dilute sodium
hypochlorite or dilute hydrogen peroxide. If the fabric is to be dyed a deep
shade, then lower levels of bleaching are acceptable, for example. However, for
white bed sheetings and medical applications, the highest levels of whiteness
and absorbencyare essential.
 Mercerising
Main article: Mercerized cotton
A further possibility is mercerizing during which the fabric is treated with
caustic sodasolution to cause swelling of the fibres. This results in improved
lustre, strength and dye affinity. Cotton is mercerized under tension, and all
alkali must be washed out before the tension is released or shrinkage will take
place. Mercerizing can take place directly on grey cloth, or after bleaching.
Coloration:
Color is a sensation caused when white light from a sourcesuch as the sun is
reflected off a pigment on the surface. The pigment selectively reflects certain
wavelengths of light while absorbing others. A dye can be considered as a
substancethat can be fixed to a material that has these properties. The colour it
reflects is defined by the structure of the molecule, and particular the parts of the
chromogen molecule called the chromophoregroup. [9] There are two processes
used to apply colour:
 Dyeing
Main article: Dyeing
Finally, cotton is an absorbentfibre which responds readily to colouration
processes.Dyeing, for instance, is commonly carried out with an anionic direct
dye by completely immersing the fabric (or yarn) in an aqueous dyebath
according to a prescribed procedure. For improved fastness to washing, rubbing
and light, other dyes such as vats and reactives are commonly used. These
require more complex chemistry during processing and are thus more expensive
to apply.[10]
 Printing
Main article: Textile printing
Printing, on the other hand, is the application of colour in the form of a paste or
ink to the surface of a fabric, in a predetermined pattern. It may be considered
as localised dyeing. Printing designs on to already dyed fabric is also possible.
The common processesare block printing, roller printing and screen printing

Finishing
Mechanicalfinishing
 Raising
Another finishing process is raising. During raising, the fabric surface is treated
with sharp teeth to lift the surface fibres, thereby imparting hairiness, softness
and warmth, as in flannelette.
 Calendering
Main article: Calender
Calendering is the third important mechanical process, in which the fabric is
passed between heated rollers to generate smooth, polished or embossed effects
depending on roller surface properties and relative speeds.
Chemicalfinishing
Many other chemical treatments may be applied to cottonfabrics to producelow
flammability, crease resist and other special effects.
 Shrinking (Sanforizing)
Main article: Sanforization
Mechanical shrinking (sometimes referred to as sanforizing), whereby the
fabric is forced to shrink width and/or lengthwise, creates a fabric in which any
residual tendency to shrink after subsequent laundering is minimal.
Standard finishes:
Quality-oriented:
 Calendering
 Decatising
 Desizing for woven fabrics.
 Pressing
 Scouring with detergents, alkaline solutions, or enzymes removes foreign
matter.
 Shrinking, Sanforization
 Shearing or singeing smooths the fabric by removing the fine protruding fibers
on the surface of the fabric. Flame singeing is the standard process:the wet
fabric is passed through an array of gas burners at a suitable distance to burn the
pills off of its surface.

Design-oriented:
 Bleaching of woven fabrics removes any prior color in order to obtain a
uniform color during the dying process.
 Dyeing adds color.
 Printing adds color and pattern.
 Watering adds moiré patterns.
Handle-oriented:
 Fulling or waulking adds weight and density.
 Hydrophobic finishing produces a fabric that repels stains or water.
 Weighting silk with metallic salts or polymer adds weight and improves
handle.
Specialfinishes for natural fibers:
Bio-polishing removes the protruding fibers of a fabric through the action of an
enzyme. Enzymes, such as cellulase for cotton, selectively remove protruding
fibers. These enzymes may be deactivated by an increase in temperature.
Mercerisationmakes woven cottonfabric stronger, more lustrous, to have better
dye affinity, and to be less abrasive.
Raising lifts the surface fibers to improve the softness and warmth, as in
flannelette.
PeachFinish subjects the fabric (either cottonor its synthetic blends) to emery
wheels, making the surface velvet-like. This is a special finish used mostly in
garments.
Fulling or waulking is a method of thickening woollen material to make it more
water-resistant.
Decatising to bring dimension stability to woollen fabrics.
Calendering makes one or both surfaces of the fabric smooth and shiny. The
fabric is passed to through hot, fast-moving stainless steel cylinders.
Sanforizing or Pre-shrinking prevents a fabric and the produced garment from
shrinking after production. This is also a mechanical finish, acquired by feeding
the fabric between a roller and rubber blanket, in such a way the rubber blanket
compresses the weft threads and imparts compressive shrinkage.
Crease-Resistfinish or "wash-and-wear" or "wrinkle-free" finishes are achieved
by the addition of a chemical resin finish that makes the fiber take on a quality
similar to that of synthetic fibers.

Anti-microbial finish causes a fabric to inhibit the growth of microbes. The humid
and warm environment found in textile fibers encourages the growth of the
microbes. Infestation by microbes can cause cross-infection by pathogens and the
development of odorwhere the fabric is worn next to skin. In addition, stains and
loss of fiber quality of textile substrates can also take place. With an aim to protect
the skin of the wearer and the textile substrate itself, an anti-microbial finish is
applied to textile materials.
Specialfinishes for synthetic fibers:
Heat-setting of synthetic fabrics eliminates the internal tensions within the fiber,
generated during manufacturing, and the new state can be fixed by rapid cooling.
This heat setting fixes the fabrics in the relaxed state, and thus avoids subsequent
shrinkage or creasing of the fabric. Presetting of goods makes it possible to use
higher temperature for setting without considering the sublimation properties of
dyes and also has a favorable effect on dyeing behavior and the running properties
of the fabric. On the other hand, post-setting can be combined with some other
operations such as Thermasol dyeing or optical brightening of polyester. Post-
setting as a final finish is useful to achieve high dimensional stability, along with
desired handle. Heat-setting is an important part in textile finishing.
Stiffening and filling process:A stiffening effect is desirable in certain
polyamides and polyester materials (e.g. petticoats, collar inner linings), which can
be done by reducing the mutual independence of structural elements of fabric by
polymer deposition on coating as a fine film.
Hydrophilic finishes compensate for lower moisture and water absorption
capacity in synthetic fiber materials, which become uncomfortable in contactwith
skin. Certain products, based onmodified (oxy-ethylated) polyamides, make the
fabric more pleasant by reducing the cohesion of water so that it spreads over a
larger area and thus evaporates more readily.
Anti-pilling finish alleviates pilling, an unpleasant phenomenon associated with
spun yarn fabrics, especially when they contain synthetics. Synthetic fibers are
more readily brought to the surface of a fabric due to their smoothsurface and
circular cross-section, and due to their higher tensile strength and abrasion
resistance. With knit "picking" also occurs:by abrasion, individual fibers work
themselves out of yarn loops onto the surface, and the garment catches on a
pointed or rough object. Knitting is susceptible to these effects due to the open
weave and bulky yarn.
Anti-static finish prevents dust from clinging to the fabric. Anti-static effective
chemicals are largely chemically inert and require Thermasol or heat treatment for
fixing on polyester fabrics. Polyether agents have been found to be useful but

should not affect the dye-equilibrium on fiber, lest they impair the rubbing
fastness.[citation needed] In general, Thermasol anti-static agents also have a good
soil release action, which is as permanent as the anti-static effect. Anti-static
finishes may also be of polyamide type, being curable at moderate temperatures.
Non-slip finishes give the filaments a rougher surface. Synthetic warp and weft
threads in loosely woven fabrics are particularly prone to slip because of their
surface smoothness when the structure of fabric is disturbed and appearance is no
longer attractive. Silica gel dispersions or silicic acid colloidal solutions are used in
combination with latex polymer or acrylates dispersions to get more permanent
effect, along with simultaneous improvement in resistance to pilling or snagging.
These polymer finishes are also capable of imparting a soft and smoothhandle to
synthetic fabric without making it water repellent.
Fire ResistantorFlame Retardant finish: to reduce flammability.
Anti-microbial finish: with the increasing use of synthetic fibers for carpets and
other materials in public places, anti-microbial finishes have gained importance.
Products which are commonly applied are brominated phenols, quaternary
ammonium compounds, organo-silver and tin compounds, which can be applied as
solutions or dispersions. They can also be incorporated in a polymeric film
deposited on the surface to achieve controlled release.
Emissions
The discharge of solid waste and wastewater containing chromium is the main environmental
problem. Chromium is a highly toxic compound and the dumping of chromium containing
material is in most countries restricted to a few special dumping grounds. Reduction of
chromium discharge is therefore essential. Emissions into the air are primarily related to energy
use, but also the use of organic solvents and dyes causes emissions into the air.
1. Solid waste
The production of fresh hides has been estimated at about 8-9 million tonnes per year (FAO,
1990a). During the processing of these hides a total of 1.4 million tonnes of solid waste is
produced (El Boushy and Van der Poel, 1994). This means that in all likelihood ca 16% of the
processed hides is leather waste. Buljan (1994) puts the figures for trimmings and splittings (i.e.
leather waste) at a total of 225 kg/ton hide (i.e. ca 23%). This is almost the same amount of waste
produced as meat from fleshing activities (7 - 23%). For every ton of raw hide processed, the
amounts of solid waste and by-products may be produced as given in Table 14 (Buljan, 1994).
These figures show that the solid waste produced per ton of raw hide is about 450-600 kg. About
half of this contains 3% chrome on a dry matter basis.

Pretanning Tanning Finishing
Trimmings 120* 110 32
Fleshings 70-230
Wet blue split 115
Buffing dust 2
Total 190-350 225 34
GRAND TOTAL Approx. 450-600
*: hides not trimmed in the abattoir itself
Buljan (1994) states:
“Collection and safe disposal of solid waste, especially chrome containing solid waste and sludge
is normally monitored by environmental authorities and associated with costs. Conversion of
solid waste into by-products not only reduce pollution load, it can also be commercially
beneficial. This represents great potential for producing increased returns to tannery processing
through deriving value from wastes. In any event, reduction of waste is essential in order to meet
demands for reduced pollution load from tanneries.”
2. Wastewater
As for the production of wastewater, over 80 per cent of the organic pollution load in BOD terms
emanates from the beamhouse (pretanning); much of this comes from degraded hide/skin and
hair matter. The beamhouse is also the source of all non-limed and limed solid waste such as
fleshing, trimming and waste split. As already mentioned, during the tanning process at least ca
300 kg of chemicals (lime, salt etc.) are added per ton of hides. Excess of non-used salts will
appear in the wastewater. Because of the changing pH, these compounds can precipitate and
contribute to the amount of solid waste or suspended solids (Department of the Environment,
1978).
Every tanning process step, with exception of the crust finishing operations, produces
wastewater. An average of 35 m3 is produced per ton of raw hide. This wastewater contains:
- salts (Cl), fat, protein, preservatives (soaking);
- lime and ammonium salts, ammonia, protein (hair), and sulphides (fleshing, trimming, bating);
- chromium(salts) and polyphenolic compounds (tanning); and
- dye and solvent chemicals (wet-finishing).
Solid waste produced consists of fleshings containing lime, chromium containing ‘wet-blue’
shavings and of trimmings (leather).
Water will not only have a diluting effect, it also increases the number of kg of BOD per ton of
hides. Rajamani (1987) gives a BOD range of 1000 - 3000 mg/l depending upon the volume of
water used and on other impurities. TNO gives BOD and COD values both for precipitated and

mixed wastewater. BOD- and COD-values for precipitated wastewater show a reduction of BOD
and COD of ca 50% (Pelckmans, undated). This implies that it is worth precipitating dissolved
organic compounds and treating this as solid waste. It is known that treatment of solid waste can
in general be undertaken without too many efforts and that the costs and energy required are
lower than those for the treatment of wastewater.
Tanneries that perform the complete tanning procedure, produce mixed wastewater. The
composition of this wastewater is not solely the result of separate waste streams that merge
together. The different pH’s and the different compounds influence each others’ solubility. In
composite wastewater, compounds precipitate while they stay dissolved in the wastewater from
the separate processes (Pelckmans, undated). Most reports give reliable values for composite
wastewater. Some reports only give data for the separate wastewater streams. These values
should be used with great care and should not be merely added in order to arrive at a compound
value.
In Table 15 high and low values for BOD, COD, SS and Cr3+ are given. This variation might be
caused by a high amount (45 m3 per ton of hide) or low amount (25 m3 per ton of hide) of water
used during the tanning process. Mulder and Buijssen (1994) give values of 50 m3 per ton of hide
for traditional manufacturing processes of Wet-blue and 20 m3 per ton of hide when water saving
actions are applied.
(1) (2) (3)
BOD 110 40-100 80
COD 265 120-280
SS 216 70-200
Cr 8.8 5
Values are estimated from data from:
(1): Rajamani (1987); values from Kanpur, Pakistan.
(2): Clonfero (1990); refering to a UNIDO-study (1975).
(3): Taiganides (1987); an average and quit general value.
In Table 16, RIVM (1992) presents the quantity and composition of wastewater for every step of
the tanning process in a Dutch situation. Per ton of hide a total of 35 m3 wastewater is produced.
The Dutch figures of the COD produced during the pretanning process are higher than the
figures mentioned in Table 15. RIVM noted that measured chromium-concentrations were 3-7
times higher than the estimated figures. Moreover, in the Netherlands about 50% of the hides
processed in tanneries have already been pretanned or tanned.
Process step Amount of water pH COD NKj Cr
(m3/ton) - kg COD/m3 kg N/m3 kg Cr/m3
Pretanning:
Soaking 4-6 6-9 30-40 1-1.5 -

Unhairing, liming 5-9 12-13 40-60 3-5 -
Fleshing 1-3 - - - -
Deliming, bating 5-7 8.5-9 5-8 3.5-4 -
Tanning:
Chrome tanning 0.5-1 3.8-4 2-3 0.3-0.6 0.5-5
Pressing 0.4-0.6 3.6-4.5 1.2-1.8 0.11-0.22 0.5-5
Neutralisation 1-1.5 4.5-4.7 2.5-3 0.5-0.8 0-1.0
Painting, fatting 3-4.5 3.8-4.5 5-6 0.2-0.3 0-5.0
Finishing:
Drying 3-6
Finishing 1-2
Cleaning 5
Clonfero (1990) gives in annex 1 the characteristics of the wastewater of each step of the tanning
process for an Italian tannery. This tannery had produced a huge amount of water (about 310 m3
wastewater per ton of raw hides), and high amounts of SS and a COD of 2500 kg per ton of raw
hides. No explanation is given for the differences between the figures of UNIDO (table 15) and
the figures of the Italian tannery (annex 1).
3. Air pollution
Table 17 gives the emissions into the air during the tanning process. Few figures are available
about the amount of air pollution.
An important part of the air pollution by leather tanneries is caused by the need for energy.
RIVM (1992) estimated the need for the Dutch tanneries at: 439 kWh (electricity) per ton of raw
hides and 108 m3 of gas per ton of raw hides. Gas is used for heating. Table 17 gives the
emissions into the air as a result of gas-combustion. No figures are available about the emissions
into the air as resulting from the use of electricity.
Process-step Air pollutants kg/ton raw hide
Unhairing/liming H2S
Deliming/Bating NH3
Finishing solvents, formaldehyde 25*
heating with gas CO 0.033*
CO2 190*
NO2 0.17*
*: Netherlands situation, based on figures of RIVM (1992)
H2S may be emitted into the air when the pH of the processwater is less then 7. During the
finishing-process volatile organic compounds are used.
Prevention of waste production

Considerations for the reduction of the amount of polluting value of the produced wastewater
are:
- a reduction of the total water use by re-use of produced wastewater and by the development of
technologies that minimize the quantity of water needed during the tanning process; and
- a reduction of the used chemicals such as lime, salt, sulphide etc and a reduction of chromium.
The following gives a more detailed discussion (from Higham, 1991).
Water conservation
A reduction of water use can lead to a reduction of the total waste load. Re-use of wastewater
with a minimal harmful or even a moderately beneficial effect on earlier processes may be
considered as an option.
Curing hides and skins
A reduction of the use of salt for preservation can be considered as an option. Fifteen percent of
salt on weight basis may preserve the hides for even 6 weeks, and 5 per cent of salt plus biocide
lead to a preservation for two months. Chilling without salt can preserve hides for a few days.
Another alternative preservation method is radiation by electron beam or gamma rays. Where
possible, biodegradable preservatives (insecticides etc.) should be used instead of derivatives of
chlorinated aromatic hydrocarbons. The latter persist in the waste and are highly toxic to the
environment.
Beamhouse processes
Hair saving methods are recommended to prevent degraded keratin from entering the waste
streams. Unhairing/liming fluids can be recycled after recharging. It is also recommended that
the unhairing and liming stages should be seperated. Both liquids can be recharged and hair can
be screened out. The intermediate wash can be re-used as a soak liquid.
Tanning
Low chrome systems, possibly requiring an aluminium salt for pretannage will produce a wet-
white leather. Splitting and shaving wastes will contain less chromium. Alternative mineral salts
such as aluminium, zirconium, titanium and iron are might be used as substitutes for chromium
salts. However, under certain conditions aluminium is known to be more poisonous to aquatic
life than trivalent and even hexavelant chromium. Re-use of chromium is a more realistic
alternative (see par. 5.2.2). The unused tanning fluids which contain chromium can be collected
separately. From these fluids and from the solids that contain chromium, chromium can be
recovered. The remainder may be used as source material for glue and animal feedstuff. In
countries where discharge of chromium is strictly prohibited, great efforts are made to recover
and re-use chrome.

Alternative vegetable tanning methods can replace chrome tanning to a high degree. An example
is the ‘Liritan’ process, developed in South Africa. A high chemical uptake, low pollution load,
uniform penetration of the tan and a shortened process time with consequent financial efficiency
are claimed to be the main advantages of this process (Higham, 1991), but little is known on the
practical implications.
Finishing
A reduction of volatile organic compounds (VOC) can be accomplished by using aqueous
finishes for base and middle finishing coatings.
Leather Industry In Pakistan
Profile:
Pakistan's leather industry is one of the major foreign exchange earners for the country. About
90% of its products are exported in finished form. There are some 600 tanneries in the formal
sector and an equally large number of tanneries in the informal sector. These are concentrated
in a few clusters of which Kasur (180 tanneries), Karachi (170), and Sialkot (135) are the most
important.
The Environmental Challenge:
Leather tanneries in Pakistan produce all three categories of waste: wastewater, solid waste
and air emissions. However, wastewater is by far the most important environmental challenge
being faced by Pakistan's tanneries.
Wastewater:
Although the exact quantity varies widely between tanneries, a normal requirement of around
50-60 liters of water per kilogram of hide is suggested.
Tannery wastewater is highly polluted and the contamination observed is many times beyond
the limits set by the National Environmental Quality Standards (NEQS) for all important
wastewater parameters. The high level of settle able matter is a major reason for the sludge in
composite tannery wastewater. This sludge contains between 3.5-6.5% of solid content, 20-
48% of volatile matter, and 51-74% of inorganic matter.
Solid Waste:

Leather industries in Pakistan

Leather industries in Pakistan

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