Developed in ancient China, where its use was reserved for royalty, silk remains the "queen of fabrics"
Silk is produced by the silkworm, Bombyx mori. Fed on mulberry leaves, it produces liquid silk that hardens into filaments to form its cocoon. The larva is then killed, and heat is used to soften the hardened filaments so they can be unwound. Single filaments are combined with a slight twist into one strand, a process known as filature or "silk reeling".
A silk filament is a continuous thread of great tensile strength measuring from 500 to 1 500 metres in length, with a diameter of 10-13 microns. In woven silk, the fibre's triangular structure acts as a prism that refracts light, giving silk cloth its highly prized "natural shimmer". It has good absorbency, low conductivity and dyes easily.
CNR-ISMAC, Biella, Italy
Silk is produced in more than 20 countries. While the major producers are in Asia, sericulture industries have been established in Brazil, Bulgaria, Egypt and Madagascar. Sericulture is labour-intensive. About 1 million workers are employed in the silk sector in China. Sericulture provides income for 700 000 households in India, and 20 000 weaving families in Thailand.
Production and trade
Global silk production rose from around 100 000 tonnes in 2000 to 150 000 tonnes in 2006, thanks mainly to growth of China's output. China produces about 70% of the world's silk, followed by Brazil, India, Thailand and Viet Nam, with minor production in Turkmenistan and Uzbekistan. India, Italy and Japan are the main importers of raw silk for processing. The unit price for raw silk is around twenty times that of raw cotton.
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Uses of silk
Silk's natural beauty and other properties - such as comfort in warm weather and warmth during colder months - have made it sought after for use in high-fashion clothes, lingerie and underwear.
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It is used in sewing thread for high quality articles, particularly silk apparel, and in a range of household textiles, including upholstery, wall coverings and rugs and carpets.
It is also being used as surgical sutures (below) - silk does not cause inflammatory reactions and is absorbed or degraded after wounds heal.
Other promising medical uses are as biodegradable microtubes for repair of blood vessels, and as moulded inserts for bone, cartilege and teeth reconstruction.