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Silk . . . Seide . . . Soie . . . Seda
History
According to legend, almost 5000 years ago the Chinese Empress Si Ling Shi (or Lie Zu) observed a silk caterpillar spinning itself into a cocoon. She unravelled the filaments and made a fabric from them.
The Romans paid one pound for silk fabric. Caterpillar eggs were smuggled into Europe in about 555 AD and, form then on it was possible to produce silk in the Mediterranean region.
Production and Sources
The world production of raw silk is about 70 000 tons. This is less than 0.2% of the world textile fibre production. Silk can be produced only where the mulberry tree grows.
The most important producing areas are:
1 China
2 India
3 Japan
4 former USSR
5 Brazil
6 Korea
7 Thailand
8 Turkey
9 France
The Mulberry Silkworm
On emerging from its egg, the mulberry silkworm is only about 2 mm long. It feeds on a large quantity of mulberry leaves.
After about 30 days, and after moulting four times, it will be as large as a middle finger and begins to pupate. The fibroin is extruded from a spinneret. The emerging filaments are coated with sericin. Spinning takes about 3 days (filament production of 3000m). The silkworm moves its head in a figure-of-eight pattern to create a cocoon.
The transition form pupae to moth takes about 14 days. The moth dissolves a portion of the cocoon wall and crawls out. The moths mate, the female lays, and both die immediately.
The harvest from 50 000 silkworms is about 1000 kg of cocoons, which yield about 120 kg of raw silk.
Wild Silk
Beside the mulberry silkworm, there are many wild species. The most important of these is the Tussah. So far, this type of silkworm has not been bred in Europe.
Construction of the Silk Filament
The basic fibre substance is fibroin. Like wool, it is made from long-chain protein molecules. Each of the two individual fibroin filaments is constructed form fibrillar bundles (tiny fibres) which themselves are made from microfibrils.
The physical, chemical, and clothing-comfort properties of silk are determined by the molecular chains, and their orientation in the fibre interior. These are disposed in crystalline layers, somewhat like the leaves of a book. This results in high strength and good resilience.
The silk gum, or sericin, surrounds the two filaments and holds them together. It is a transparent, water-soluble protein, which may be more or less pigmented in the usual silk-cocoon colours of natural white to yellow or orange-yellow, for mulberry silk, or light brown to reddish-brown or dark brown, for tussah.
Production of Cultivated (Mulberry) Silk
Raw silk (Net silk):
The silk cultivator needs to have undamaged cocoons. He kills the pupae with steam or dry heat. The cocoons are placed in hot water, to soften the gum, to find the filament ends. The filaments are then wound up onto a reel. An individual filament is too fine to wound separately, so 7 to 10 of them are wounded to form the raw silk. The reeled silk is a bundle of continuous filaments, about 1000m long, coming from the middle part of the cocoon, and still cemented together by the gum. Later, several of these bundles will be twisted together in the silk throwing process.
Spun silk:
Unwindable remnants form the cocoons, are converted into spun yarns by the usual methods. Spun yarns are made form the longer fibres, separated at a combing machine. They are fine, smooth and regular. Also known as Schappe silk.
Noil silk:
The shorter waste fibres, in the form of comber noils from spun silk processing, are spun into coarser, irregular neppy yarns using the woollen spinning system. Also known as Bourette silk.
Recovery of Wild Silk (Tussah Silk)
The wild Tussah cocoons are gathered from trees and bushes. Wild silk is not easy to degum and usually can not be reeled. Therefore, it retains its natural reddish or brownish colouring. The filaments exhibit variations in their fineness, which may look like irregular pencilled streaks.
Clothing Comfort
Thermal insulation:
Silk is cool and warm. Filament silk is made into fine fabrics. These fine, compact silk fabrics are good insulators because warm air, between fabric and skin, can not escape easily.
Moisture absorption:
Like wool, it can absorb and hold about 33% of its weight of water vapour without feeling wet.
Next-to-skin comfort:
Silk is very pleasant to wear, because of its fineness and softness.
Other Important Properties
Lustre, Fineness, Handle
The most important properties of degummed silk are its typical lustre, its fineness and its pleasant handle.
Strength
Silk has a very good tenacity.
Extensibility
It is very good; it lies between 10% and 30%.
Elasticity
Silk has outstanding resilience. It does not crease badly and the wrinkles tend to fall out.
Sensitivity
Perspiration, deodorant sprays and perfumes can cause colour changes and can embrittle the fibre.
Improvement of Properties by Finishing
Degumming
The natural silk gum makes knitted and woven raw silk fabrics harsh and rough. The sericin gum is removed by a gentle boiling in mild soap solution.
Weighting
The degummed silk can be made heavier again by addition of metallic salts or other chemicals.
Typical Silk Fabrics
Bourette
Chiffon
Crêpe
Crêpe de Chine
Damask
Duchesse
Organza
Pongé
Satin
Satin crêpe
Taffeta
Twill
Wild silk:
Doupion
Honan
Shantung
Aftercare Properties and Labelling
Aftercare Properties
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