History of the
use of silk:
The Chinese has used silk since the 27th
century B.C.. Silk is mentioned by Aristotle and became a valuable
commodity both in Greece and Rome. During the Roman Empire, silk was sold for
its weight in gold. The Chinese domesticated silk worms and fed them with
mulberry leaves. They unwound the silkworms' cocoons to produce long
strands of silk fiber.
Farm women in China at that period were
supposed to raise such silkworms as one of their chores. Silk was used in
China and exported along the Silk Road (the ancient trade route linking
China and the Roman Empire). This trade brought China great wealth, but the
Chinese did not give away the secret on how silk was formed.
Christian monks finally broke China’s
monopoly of the silk production by smuggling silkworm eggs out of the
country, and soon other countries started to produce their own silk.
Production of
silk:
Silkworms are cultivated and fed with
mulberry leaves. Some of these eggs are hatched by artificial means such as
an incubator, and in the olden times, the people carried it close to their
bodies so that it would remain warm.
Silkworms that feed on smaller, domestic
tree leaves produce the finer silk, while the coarser silk is produced by
silkworms that have fed on oak leaves. From the time they hatch to the time
they start to spin cocoons, they are very carefully tended to. Noise is
believed to affect the process, thus the cultivators try not to startle the
silkworms.
Their cocoons are spun from the tops of
loose straw. It will be completed in two to three days' time. The
cultivators then gather the cocoons and the chrysales are killed by heating
and drying the cocoons.
In the olden days, they were packed with
leaves and salt in a jar, and then buried in the ground, or else other
insects might bite holes in it. Modern machines and modern methods can be
used to produce silk but the old-fashioned hand-reels and looms can also
produce equally beautiful silk.
Care of your silk
garment:
It is best to dry clean your silk garment
either by individual or bulk method, in order to maintain the
characteristic of the silk.
Dry clean: Sending it to the dry cleaners may be done but
make sure that you inform the dry cleaner that your garment is made of
silk.
Hand wash:
1) Make sure you wash in cool water.
2) Use a small amount of soap or mild detergent to wash the silk.
3) After washing it, rinse in cold water.
4) Hang it or lay it flat in a shaded area to dry.
5) If pressing is needed, use an all cotton iron board cover, a low or
moderate steam setting, and press on the wrong side of the fabric while
ironing.
Other Tips:
- To keep
white silk white, add peroxide and ammonia to the wash.
- Do not
use bleach or any washing detergent with bleach
- To
remove yellow from white silk, add a few teaspoons of white vinegar to
the wash.
Properties of
the silk:
1)It is versatile and very comfortable.
2)It absorbs moisture.
3)It is cool to wear in the summer yet warm to wear in winter.
4)It can be easily dyed.
5)It retains its shape and is relatively smooth.
6)It has a poor resistance to sunlight exposure.
7)It is the strongest natural fiber and is lustrous.
Physical
Properties of Silk Fiber:
Tenacity - The silk filament is strong. This strength is due to its
linear, beta configuration polymers and very crystalline polymer system.
These two factors permit many more hydrogen bonds to be formed in a much
more regular manner. Silk loses strength on wetting. This is due to water
molecules hydrolyzing a significant number of hydrogen bonds and in the
process weakening the silk polymer.
Specific gravity - Degummed silk is less dense than cotton, flax, rayon or wool. It has a
specific gravity of 1.25. Silk fibres are often weighted by allowing filaments to absorb
heavy metallic salts; this increases the density of the material and
increases its draping property.
Elastic-plastic nature - Silk is considered to be more plastic than
elastic because it’s very crystalline polymer system does not permit the
amount of polymer movement which could occur in a more amorphous system.
Hence, if the silk material is stretched excessively, the silk polymers
that are already in a stretched state (They have a betaconfiguration) will
slide past each other. The process of stretching ruptures a significant
number of hydrogen bonds.
Elongation - Silk fibre has an elongation at break of 20-25% under
normal condition. At 100% R.H. the extension at break is 33%.
Hygroscopic nature - Because silk has a very crystalline polymer
system, it is less absorbent than wool but it is more absorbent than
cotton. The greater crystallinity of silk's polymer system allows fewer
water molecules to enter than do the amorphous polymer system of wool. It
absorbs water well (M.R.11%), but it dries fairly quickly.
Thermal properties - Silk is more sensitive to heat than wool. This is
considered to be partly due to the lack of any covalent cross links in the
polymer system of silk, compared with the disulphide bonds which occur in
the polymer system of wool. The existing peptide bonds, salt linkages and
hydrogen bonds of the silk polymer system tend to break down once the
temperature exceeds 1000C.
Electrical properties - Silk is a poor conductor of electricity and
tends to form static charge when it is handled. This causes difficulties
during processing, particularly in dry atmosphere.
Hand feel - The handle of the silk is described as a medium and its
very crystalline polymer system imparts a certain amount of stiffness to
the filaments. This is often misinterpreted, in that the handle is regarded
as a soft, because of the smooth, even
and regular surface of silk filaments.
Drapes Property - Silk fibre is flexible enough and if silk fibre is
used to make garments, then the fabric drapes well and this is why it can
be tailored well too.
Abrasion resistance - Silk fabric possess good abrasion resistance as well as resistance
to pilling.
Effect of sunlight - Silk is more sensitive light than any other
natural fibre. Prolonged exposure to sunlight can cause partially spotted
color change. Yellowing of silk fibre is generally occurred due to photo
degradation by the action of UV radiation of sunlight. The mechanism of
degradation is due to the breaking of hydrogen bonds followed by the
oxidation and the eventual hydrolytic fission of the polypeptide chains.
Chemical Properties of Silk Fiber:
Action of water - The absorption of water molecules takes place in
the amorphous regions of the fibre, where the water molecules compete with
the free active side groups in the polymer system to form cross links with
the fibroin chains. As a result, loosening of the total infrastructure
takes place accompanied by a decrease in the force required to rupture the
fibre and increase extensibility. Treatment of silk in boiling water for a
short period of time does not cause any detrimental effect on the
properties of silk fibre. But on prolonged boiling, silk fibre tends to
loss its strength to some degree, which thought to occur because of
hydrolysis action of water. Silk fibre withstands, however, the effect of
boiling better than wool.
Effect of acids - Silk is degraded more readily by acids than wool.
Concentrated sulfuric and hydrochloric acids, especially when hot, cause
hydrolysis of peptide linkages and readily dissolve silk. Nitric acid turns
the color of silk into yellow. Dilute organic acids show little effect on
silk fibre at room temperature, but when concentrated, the dissolution of
fibroin may take place. On treating of silk with formic acid of
concentrated about 90% for a few minutes, a swelling and contraction of
silk fibre occur. Like wool, silk is also amphoteric substance, which
possesses the ability to appear as a function of the pH value either as an
acid or as a base.
Effect of alkalis - Alkaline solutions cause the silk filament to
swell. This is due to partial separation of the silk polymers by the
molecules of alkali. Salt linkages, hydrogen bonds and Van der Waals'
forces hold the polymer system of silk together. Since these inter-polymer
forces of attraction are all hydrolyzed by the alkali, dissolution of the silk
filament occurs readily in the alkaline solution. Initially this
dissolution means only a separation of the silk polymers from each other.
However, prolonged exposure would result in peptide bond hydrolysis,
resulting in a polymer degradation and complete destruction of the silk
polymer. Whatever, silk can be treated with a 16-18% solution of sodium
hydroxide at low temperature to produce crepe effects in mixed fabric
containing cotton. Caustic soda, when it is hot and strong, dissolves the
silk fibre.
Action of oxidizing agent - Silk fibre is highly sensitive to
oxidizing agents. The attack of oxidizing agents may take place in three
possible points of the protein 1. At the peptide bonds of adjacent amino
groups,
1.
At the
N-terminal residues and
2.
At the
side chains
Though fibroin is not severely
affected by hydrogen peroxide solution, nevertheless may suffer from the
reduction of nitrogen and tyrosine content of silk indicate that hydrogen
peroxide may cause breakage of peptide bonds at the tyrosine residues
resulting in the weight loss of the fibre. The action of chlorine solution
on the silk fibroin is more harmful than does the solution of hypochlorite.
These solutions, even at their lower concentration, cause damage to
fibroin.
Action of reducing agents - The action of reducing agents on silk
fibre is still a little bit obscure. It is, however, reported that the
reducing agents that are commonly found in use in textile processing such
as hydrosulfite, sulfurous acids and their salts do not exercise any
destructive action on the silk fibre.
Silk is used to make blouses, dresses,
scarves, pants and ties. It can also be made into curtains, draperies,
cushion covers and sofa covers.
The length of the silk is
important in creating high quality fabric. Long fibers make long, smooth
surfaces, which is why silk reflects light and has that special luster we
value. But, short fibers and broken fibers may also be spun to create lower
quality fabrics.
For all its delicacy, silk is as
strong as wire of equal thickness. However, it deteriorates over time. As
silk ages, it becomes dry and brittle and will literally fall to pieces in
one’s hands. Much like shattered glass, silk will develop fissures,
crumble, and fall off in chunks. Feeding all those hungry caterpillars is
expensive – so silk fabric is expensive and used primarily in high-end
apparel and furnishings.
|
|
According to Chinese legend,
around 2700 B.C. Empress Hsi Ling Shi [Sigh-Ling-She] sat under a mulberry
tree drinking tea. She began playing with a silkworm cocoon and discovered
it was made of a delicate thread. The Empress learned to spin the silk and to
make luxurious fabric.
Archeological evidence indicates
that silk production may have begun as early as 5000BC – that’s more than
seven thousand years ago. Sericulture is the raising of silkworms and the
production of silk. The ancient Chinese kept the details of sericulture a
secret – a secret coveted by the rest of the world. Today silk is produced
mostly in China, India, and Japan.
Silkworms, which are really
caterpillars, are fed mulberry leaves, mulberry leaves, and only mulberry
leaves. They never stop eating. That means feedings every four hours.
|
Comments
Post a Comment