2. Unit 1
INTRODUCTION
Sturcture and composition of animal skin-terminology involved in leather tanneries-chemistry of
beam house processes-soaking, liming, unhairing, deliming, bating and pickling-preservation of
animal skin-salt curing and brine curing
UNIT II
MATERIALS AND METHODS OF TANNING
Vegetable tans –catechol tans-pyrogallol tans-vegetable tanning process and applications of
vegetable tanned leather-Chrome tanning-chemicals used-method-type of leather obtained and
its uses-aldehyde tanning-Artificial leather-Corfam-synthetic tans
UNIT III
POLLUTION AND TREATMENT OF TANNERY EFFLUNT
Various finishing process in tanneries – drying – bleaching – fat liquoring – dyeing – calendaring
Pollution caused by leather tanneries –Treatment of tannery effluents – primary , secondary and
tertiary treatment.
UNIT IV
TEXTILE FIBRES
Classification fo textile fibres – difference between celllulosic and synthetic fibres –identification
of fibres by burning and solubility tests – chemical structure-physical and– chemical properties
of cotton-silk.
UNIT V
BLEACHING ,DYEING & FINISHING
Bleaching of cotton fabrics –peroxide bleaching –hypochlorite bleaching –dyeing of cotton with
vat dyes-dyeing of wool acid dyes-dyeing of polyester with disperse dyes-textile finishing –
mercerization – water repellent and water proof finish.
3. UNIT 1
Sturcture and composition of animal skin
It is nothing but the skin of the animals were usually chosen for clothing since they wer bigger
,stronger and warmer. the tanned skin does not become hard or britting material. And is know as
leather.
skin-terminology involved in leather tanneries
There are two types of leathers tannage first one is Before tannage another one is After tannge . The
before tannage process is normal sequence .The After tannage is a order is a varies considerly for
different types of leathers one is Heavy leathers another one is Light leather.
chemistry of beam house processes-soaking, liming
Soaking is the process of putting the skin in water to bring the dried skin back to flaccid. Liming
may be carried out at the same time by immersing the hides and skins completely in lime and water.
Unharing
Leathe processing involves a series of unit operating of unharing is the first major step in the leather
making.
Deliming
The deliming operation in leather processing is a drum paddle or pit based operation where two main
objective are met.removal of alkali from the pelt and the consequent dewelling of the fibres.
bating and pickling
It is the further step in the purification of the hide prior to tanning making it cleaner, smoother
and fine.Pickling is a process to treat the hide with salt and acid to bring the skin to the desired pH
for either preservation or tanning.
Preservation of animal skin Curing and brine curing
The method is used to prevent putrefaction or damage of the skin before tanning is called curing.
Brine curing is a one of the most efficient method of curing.it can be done in less time.
4. Sturcture and composition of animal skin
It is nothing but the skin of the animals were usually chosen for clothing since they wer bigger
stronger and warmer. the tanned skin does not become hard or britting material. And is know as
leather.
Other animal coverings such as the arthropod exoskeleton have different developmental origin
structure and chemical composition T he adjective cutaneous means "of the skin" (from Latin
cutis, skin).
In mammals the skin is an organ of the integumentary systemmade up of multiple layers of
ectodermal tissue and guards the underlying muscles bones ligaments and internal organs.
Skin of a different nature exists in amphibians reptiles
and birds All mammals have some hair on their skin, even marine mammals like whales dolphins
and porpoise which appear to be hairless. The skin interfaces with the environment and is the
first line of defense from external factors.
For example, the skin plays a key role in protecting the body against pathogens and excessive
water loss. Its other functions are insulation, temperature ,egulation, sensation, and the
production of vitamin D folates. Severely damaged skin may heal by forming scar tissue
This is sometimes discoloured and depigmented. The thickness of skin also varies from location
to location on an organism. In humans for example, the skin located under the eyes and around
the eyelids is the thinnest skin in the body at 0.5 mm thick, and is one of the first areas to show
signs of aging such as "crows feet" and wrinkles.
The skin on the palms and the soles of the feet is 4 mm thick and is the thickest skin on the body.
The speed and quality of wound healing in skin is promoted by the reception of estrogen
5. TANNING
Tanning is the process of treating skins and hides of animals to
produce leather A tannery is the place where the skins are processed.
Tanning hide into leather involves a process which permanently alters
the protein structure of skin, making it more durable and less
susceptible to decomposition and also possibly coloring it.
Before tanning, the skins are unhaired, degreased, desalted and soaked
in water over a period of 6 hours to 2 days. Historically this process was
considered a noxious or "odoriferous trade" and relegated to the
outskirts of town.
Traditionally, tanning used tannin an acidic chemical compoundfrom
which the tanning process draws its name (tannin is in turn named
after an old German word for oak or fir trees, from which the
compound was derived). The use of a chromium (III) solution was
adopted by tanners in the Industrial Revolution
6. Soaking
In soaking, the hides are soaked in clean water to remove the salt left
over from curing and increase the moisture so that the hide or skin can
be further treated.
To prevent damage of the skin by bacterial growth during the soaking
period, biocides, typically dithiocarbamates, may be used. Fungicides
such as 2-thiocyanomethylthiobenzothiazole may also be added later
in the process, to protect wet leathers from mold growth.
After 1980, the use of pentachlorophenol and mercury-based biocides
and their derivatives was forbidden
7. Liming
Main article: Liming (leather processing)
After soaking, the hides and skins are taken for liming: treatment with milk of lime (a basic agent)
that may involve the addition of "sharpening agents" (disulfide reducing agents) such as sodium
sulfide, cyanides, aminesetc. The objectives of this operation are mainly to:
Remove the hair and other keratinous matter
Remove some of the interfibrillary soluble proteins such as mucins
Swell up and split up the fibres to the desired extent
Remove the natural grease and fats to some extent
Bring the collagen in the hide to a proper condition for satisfactory tannage
The weakening of hair is dependent on the breakdown of the disulfide link of the amino acid cystine,
which is the characteristic of the keratin class of proteins that gives strength to hair and wools(keratin
typically makes up 90% of the dry weight of hair).
The hydrogen atoms supplied by the sharpening agent weaken the cystine molecular link whereby the
covalent disulfide bond links are ultimately ruptured, weakening the keratin.
To some extent, sharpening also contributes to unhairing, as it tends to break down the hair proteins.
The isoelectric point of the collagen in the hide (this is a tissue-strengthening protein unrelated to
keratin) is also shifted to around pH 4.7 due to liming.
8. Unhairing and scudding
Peeling hemlock bark for the tannery in Prattsville, New York during
the 1840s, when it was the largest in the world
Unhairing agents used at this time include sodium sulfide sodium
hydroxide sodium hydrosulfite calcium hydrosulfide, dimethyl amine
and sodium sulfhydrate The majority of hair is then removed
mechanically, initially with a machine and then by hand using a dull
knife, a process known as scudding.
9. Deliming and bating
Main article: Deliming
The pH of the collagen is brought down to a lower level so the enzymes
may act on it, in a process known as deliming.
Depending on the end use of the leather, hides may be treated with
enzymes to soften them, a process called bating.
In modern tanning, these enzymes are purified agents, and the process
no longer requires bacterial fermentation (as from dung-water
soaking) to produce them.
Pickling
Once bating is complete, the hides and skins are treated first with salt
and then with sulfuric acid in case a mineral tanning is to be done.
This is done to bring down the pH of collagen to a very low level so as
to facilitate the penetration of mineral tanning agent into the
substance.
This process is known as pickling. The common salt (sodium chloride)
penetrates the hide twice as fast as the acid and checks the ill effect of
sudden drop of pH.
10. The standard values of moisture content and salt saturation of
salted hides and skins were noted as 40-48% and ≥ 85%,
respectively.
34,36 According to these standart values, moisture contents of
our skin samples were determined low (<40%) for 4 sheep and 6
goat skin samples; normal (40-48%) for 7 sheep and 8 goat skin
samples; high (>48%) for 14 sheep and 11 goat skin samples.
However, the growth of both moderately halophilic bacteria,
proteolytic and lipolytic moderately halophilic bacteria was not
affected by low moisture content. ...
.Minimum and maximum ash content of salted hides and skins
were respectively stated as 14% and 48%.
34 While ash contents of the salted sheep skins ranged from 12
to 30%, ash contents of goat skins were between 11-32% (Tables I-
II).
Our experimental results showed that ash contents of the all
skins, which are mostly related to NaCl, were sufficient for the
growth of moderately halophilic bacterial populations. ...
11. BRINE CURING
Curing and shipment. Because raw hides and skins decay rapidly, they are
preserved and disinfected prior to shipment to the tannery.
The hide or skin is flayed from the carcass and then preserved by curing.
Curing can be accomplished by a variety of means. Curing by drying is
suitable in regions where hot and dry climatic conditions prevail.
Drying consists of stretching the hides on frames or spreading them on
the ground in the sun.
Dry-salting, another method of curing hides, consists of rubbing the fleshy
side of the hide with salt. Brine curing, or brining, consists of submerging
the hides in a solution of sodium chloride to which naphthalene may have
been added.
Brining is the most common form of preservation in developed countries.
Prior to shipment, hides are generally treated with DDT, zinc chloride,
mercury chloride, chlorophenols or other agents for disinfection.
These substances may represent hazards both at the site of curing and on
receipt at the tannery.
