Silk.is a natural fiber that can be woven into textiles. It is
obtained from the cocoon of the silkworm larva, in the process known as
sericulture, which kills the larvae.
Silk was first developed in early China, possibly as early as 6000 BC and definitely by 3000 BC. Legend gives credit to a Chinese Empress Xi Ling Shi. Though first reserved for the Emperors of China, its use spread gradually through Chinese culture both geographically and socially. From there, silken garments began to reach regions throughout Asia. Silk rapidly became a popular luxury fabric in the many areas accessible to Chinese merchants, because of its texture and lustre. Because of the high demand for the fabric, silk was one of the staples of international trade prior to industrialization.
Perhaps the first evidence of the silk trade is that of an Egyptian mummy of 1070 BC. In subsequent centuries, the silk trade reached as far as the Indian subcontinent, the Middle East, Europe, and North Africa. This trade was so extensive that the major set of trade routes between Europe and Asia has become known as the Silk Road.
Uses of Silk
Cultivation of Silk
Silk moths lay eggs on specially prepared paper. The eggs
hatch and the caterpillars (silkworms) are fed fresh mulberry leaves.
After about 35 days and 4 moltings, the caterpillars are 10,000 times
heavier than when hatched, and are ready to begin spinning a cocoon. A
straw frame is placed over the tray of caterpillars, and each
caterpillar begins spinning a cocoon by moving its head in a "figure 8"
pattern. Two glands produce liquid silk and force it through openings
in the head called spinnerets. Liquid silk is coated in sericin, a
water-soluble protective gum, and solidifies on contact with the air.
Within 2-3 days, the caterpillar spins about 1 mile of filament and is
completely encased in a cocoon. The silk farmers then kill most
caterpillars by heat, leaving some to metamorphose into moths to breed
the next generation of caterpillars.
Silk was first developed in early China, possibly as early as 6000 BC and definitely by 3000 BC. Legend gives credit to a Chinese Empress Xi Ling Shi. Though first reserved for the Emperors of China, its use spread gradually through Chinese culture both geographically and socially. From there, silken garments began to reach regions throughout Asia. Silk rapidly became a popular luxury fabric in the many areas accessible to Chinese merchants, because of its texture and lustre. Because of the high demand for the fabric, silk was one of the staples of international trade prior to industrialization.
Perhaps the first evidence of the silk trade is that of an Egyptian mummy of 1070 BC. In subsequent centuries, the silk trade reached as far as the Indian subcontinent, the Middle East, Europe, and North Africa. This trade was so extensive that the major set of trade routes between Europe and Asia has become known as the Silk Road.
Uses of Silk
- Silk's good absorbency makes it comfortable to wear in warm weather and while active. Its low conductivity keeps warm air close to the skin during cold weather. It is often used for clothing such as shirts, blouses, formal dresses, high fashion clothes, negligees, pyjamas, robes, skirtsuits, sun dresses and underwear.
- Silk's elegant, soft luster and beautiful drape makes it perfect for many furnishing applications. It is used for upholstery, wall coverings, window treatments (if blended with another fiber), rugs, bedding and wall hangings
- While on the decline now, due to artificial fibers, silk has had many uses; parachutes, bicycle tires, comforter filling and artillery gunpowder bagsFrom the blackpowder era, until roughly World War I, early bulletproof vests were made from silk
- A special manufacturing process which removes the outer irritant sericin coating of the silk makes it suitable as non-absorbable surgical sutures. This process has also recently led to the introduction of specialist silk underclothing for children and adults with eczema where it can significantly reduce itch
- Silk cloth is also used as a material on which to write and paint.
- Physical Properties of Silk
- Silk fibers have a triangular cross section with rounded corners. This reflects light at many different angles, giving silk a natural shine. It has a smooth, soft texture that is not slippery, unlike many synthetic fibers. Its denier is 4.5 g/d when dry and 2.8-4.0 g/d when moist.
- Silk is one of the strongest natural fibers but loses up to 20% of its strength when wet. It has a good moisture regain of 11%. Its elasticity is moderate to poor: if elongated even a small amount it remains stretched. It can be weakened if exposed to too much sunlight. It may also be attacked by insects, especially if left dirty.
- Silk is a poor conductor of electricity and thus susceptible to static cling.
- Unwashed silk chiffon may shrink up to 8% due to a relaxation of the fiber macrostructure. So silk should either be pre-washed prior to garment construction, or dry cleaned. Dry cleaning may still shrink the chiffon up to 4%. Occasionally, this shrinkage can be reversed by a gentle steaming with a press cloth. There is almost no gradual shrinkage or shrinkage due to molecular-level deformation.
- Chemical Properties of Silk
- Silk is made up of the amino acids GLY-SER-GLY-ALA-GLY and forms Beta pleated sheets. Interchain H-bonds are formed while side chains are above and below the plane of the H-bond network.
- The high proportion (50%) of glycine, which is small, allows tight packing and the fibers are strong and resistant to stretching. The tensile strength is due to covalent peptide bonds. Since the protein forms a Beta sheet, when stretched the force is applied to these strong bonds and they do not break.
- Silk is resistant to most mineral acids but will dissolve in sulfuric acid. It is yellowed by perspiration.