Silk:
Silk is the queen of all fiber. In old English, silk was “sioloc”.
the name has thought to have originated from the Greek “seres”, meaning the
people from eastern Asia, namely Chinese.
Silk is a natural protein filament which is wound from the
cocoon of a moth caterpillar known as silk worm. for thousands of years silk
has originated as the queen of fiber. “With time and patience the mulberry leaf
becomes a silk gown” ancient Chinese proverb.
Silk was first developed in early china, possibly as early
as6000Bc and definitely by 3000BC. Legend gives credit to a Chinese empress Xi
Ling Shi.
Perhaps the first evidence of the silk trade is that of an
Egyptian mummy of 1070BC.
By 1100BC silk had
arrived to the Middle East, Europe and Africa and the silk trade has formed the
famous Silk Road to use as its main route between the cultures and continents.
It is believed that silk was introduced into Europe bu
Alexander the great in the fourth century B.C.
Spain began to produce silk in the eight century.
Italy began silk production in the twelfth century and was
the leader for five hundred years.
In the sixteenth century, France became the rival of Italy
in the production of silk fabrics of excellence and beauty.
James I of England introduced silk growing to the American
colonies around 1619.
In the 1800s a new attempt at a silk industry
began with European-born workers.
Properties of silk:
Physical properties:
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Silk fibers have a triangular cross section with
rounded corners and allows light to hit at different angles and it has a
natural shine.
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The denier becomes when wet then 4.0g/d and when
dry then 4.5g/d.
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Smooth, soft texture that is not slippery.
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Good moisture regain of about 11%
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Strongest natural fibers and up to 20% losses of
its strength when wet.
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Poor elasticity.
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The ironing temperature is moderate.
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Silk is sensitive to light than other natural
fibers.
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Yellowing of the fiber is generally accompanied
by photo degradation that is mainly occurred due to action of UV radition of
light.
Chemical properties:
Acid: Silk is readily decomposes by hot
concentrated acids. The degree of hydrolysis is much greater with acid than
with alkali & is pH dependent. There is no harmful of weak and
cold hydrofluoric acid. Dilute organic acids contain little effect on silk at
room temperature.
Alkali: Dilute alkali at room temperature
does not cause any considerable chemical and structural damage of silk, but the
luster of the fiber may be decreased depending on the exposure time. Caustic
soda, when it is hot and strong, dissolves the silk fiber.
Oxidizing agent: Silk fibroin is not
severely affected by H2O2 solution.
The action of chlorine solution on the silk
fibroin is more harmful than hypochlorite solution.
Reducing agent: The reducing agents that are
commonly found in use in textile processing such as hyposulphite, sulfurous
acids and their salts do no exercise any constructed action on the silk fiber.
Silk producing country:
When famers in the Asiatic countries first raised silkworms,
the many diseased worms and defective cocoons resulted in poor grades of
finished goods. The farmers were raising silkworms only as an additional means
of support. Japan was the first country producing silk in large quantities to
use scientific methods in cultivating the silk worms.
Other silk producing countries are:
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France
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Spain
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China
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India
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Italy
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Brazil
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Bulgaria
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Austria
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Turkey
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Iran
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Greece
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Syria
Chemical composition:
Fibroin--------- 72-75%
Sericin -------- 22-23%
Wax and fat ---1.4-2.7%
Mineral salts ---0.3-1.6%
Ash---------------0.1-0.5%
Composition of silk fibroin:
Glycine ----------40.5%
Alanine----------25%
Tyrosine-------11%
Arginine -------1.5%
Lysine ---------0.9%
Histidine -------0.8%
Proline --------1%
Leucine -------2.5%
Serine --------1.8%
Phenyl alanine –1.5%
Chemical structure of silk:
R
R
Where R= a radical, which is different for each of the known
amino acid.
Flow chart of silk filament extraction:
The caterpillar spins a cocoon from
two liquidsfibron(protein) and sericin(gum). It secrets them through a hole
called spinneret. This liquid sets in to silk fiber which the caterpillar winds
round itself.
Cocoon is harvested before the
caterpillar becomes a moth(approx. 10 days)
Cocoon is subjected to dry or wet heat
which kills the insects inside.
Filaments ends are found and would on
to a reel. A single filament is too fine; therefore a number of cocoon are
would together, which results in raw silk or grease silk.
Reels are made up of a continuous
filament around 5000 meters long.
Several bundle are twisted together in
a throwing process which increase strength.
Spinning will determine the fabrics end use.
Manufacturing process of silk:
·
Sericulture
·
Sorting cocoons
·
Softening and sericin
·
Reeling
·
Throwing
1 ) Sericulture:
The cultivation of silkworms for the purpose of producing
silk is called sericulture. The best raw silk is obtained from the species of
moth called Bombyx Mori. Breeding of silkworm occurs once in a year but under
scientific conditions, they may be hatched three times a year. Larvae of about
3mm are hatched from the eggs. For about 20 to 30 days they are carefully
nurtured and are fed five times a day on chopped mulberry leaves. In the
meantime, the larvae charge their skin for four times and are formed into
caterpillar of about 9cm long. Now they are ready to spin cocoon for which
racks, clusters of twigs or straw are provided.
The caterpillar have small openings under their jaws called
spinnerets through which they secret a protein like substance. This substance
solidifies when it comes in contact with air and the filament thus formed is
spun around the silkworm in the figure resembling the digit 8.
2 ) Sorting cocoon:
The cocoon is sorted according to color, shape and texture,
as all these affect the final quality of the silk. Cocoons may range from white
or yellow to grayish, depending on the source abd the type of food consumed
during the worm stage.
Cocoon from China are white, Japanese cocoons are creamy
white and yellow, Italian cocoons are yellow.
3 ) Softening the sericin:
After the cocoons have been sorted, they are put through a
series of hot and cold immersions, as the sericin must be softened to permit
the unwinding of the filament as one continuous thread.
4 ) Reeling:
Reeling may be
achieved manually or automatically. The cocoon is brushed to locate the end of
the fiber. The method is as simple as it is laborious. It is threaded through a
porcelain eyelet, and the fiber is reeled onto a wheel. Meanwhile, diligent
operators check for flaws in the filaments as they are being reeled.
As each filament is nearly finished being reeled, a new
fiber is twisted onto it, thereby forming one long, continuous thread. Sericin contributes
to the adhesion of the fibers to each others. The average cocoon reels off
about three hundred yards in a single thread.
5 ) Throwing:
The production of yarn from reeled silk known as throwing
consists of adding twist or of doubling and further twisting these strands in
to desired size.
Different types of silk:
I.
Mulberry silk:
Produce by silk worm(Bombyx Mori) fed on
Mulberry leaves.
II.
Tussar silk:
Larvae of several species of moth such as
Antheraea mylitta, Antheraca proylei, Antherea pernyi and Antheraca yamamai
produce this silk. The insects mostly live in the wild on bushes and trees on
which they feed.
III.
Katiya silk:
The portion of Tussar cocoons leftover
after about 60% reelable silk is spun into katiya yarn.
IV.
Balkal silk:
The peduncle(silk that anchors the cocoon,
it is very week) are utilized for production of Balkal yarn.
V.
Muga silk:
It belong to same family as Tussar. It is
popular for its natural golden color, glossy fine textures and durability. Muga
silk is produced by Antheraea assama westwood which is an endemic species
prevent in the Brahmaputra valley and adjoining hills.
Muga silkworm is a polyhageous insect which
feeds on leaves of Som, Soalu and other plants which grow abundantly in
Brahmaputra valley.
VI.
Eri silk:
The word eri is a derivative from Sanskrit
nomenclature for Castor Plant, eranada. Castor leaf is the main food for the
Eri silkworms and so names as Eri. This is the only completely domesticated
non-mulberry variety. Its silk is as it cannot be reeled.
VII.
Spun silk:
A silk yarn made of short lengths of silk
obtained from silk wastes, pierced cocoon or floss which gives yarn its
characteristic brilliance. There are two grades of yarn Schappe and Bourette. It
is spun on special machinery which in some ways is akin to cotton and worsted.
VIII.
Noil silk/waste silk:
A noil short fiber removed in combing
operation of yarn making of spun silk is spun into Noil yarn. Noil is mostly
produced in Karnataka and Madras.
IX.
Dupion silk:
An irregular, riugh silk reeled double
cocoons or cocoons spun side-by-side which are interlocked, making it necessary
to reel them together. The unevenness of the yarn confines its use.
X.
Filature silk:
A raw silk which is reeled by machine as
distinct from silk prepared by hand in cottage industry.
XI.
Matka silk:
Mutka silk is obtained from waste Mulberry
silk by hand spinning without removing the gum. Cocoons required to produce
Matka are mainly obtained from Karnataka and Kashmir but spinning is mostly
done in the villages of malda and Murshidabad districts in west Bengal by hand
spinning.
XII.
Spider silk:
The silken filament spun by spders is so fine
that they can often be seen only with difficult. The golden garden spider spins
a filament only 0.0001 in diameter. Many attempts have been made to use spider
silk as a textile fiber.
Source of different silk fiber:
The difference is in the type of worms producing the yarn
and the types of leaves they eat.
Mulberry silk is obtained from Bombyx Mori feeding on
Mulberry leaves.
Tussar silk is obtained from Antherea Mylitta feeding on
Arjun and Asan leaves.
Muga silk is obtained from Antherea Assamensis feeding on
Som and Sualu leaves.
Eri silk is obtained from Cynthia Ricini feeding on Castor
Oil leaves.
The Eri silk is the only completely domesticated silkworm
other than Bombyx Mori.
End users of silks:
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Apparel:
Dresses, blouses, lingerie, scarves, men’s
ties, long underwear, socks etc
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Home Furnishings:
Upholstery, draperies, wall coverings, bed
sheet, lamp shades etc.
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Industrial application:
Sewing threads, embroidery threads, type
writer ribbons etc
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Silk is also used as scarf’s, ties, hats,
artificial flowers, umbrella etc.
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Silk is cool and comfortable in underwear.
