Silk - Animal Fibres

SILK

Biological Source

Fibres obtained from the cocoons spun by the larvae Bombyx mori Linn., belonging to family Bombycidae/Moraceae.

Geographical Source

China, France, Iran, Italy, Japan, and India.

History

It is native to northern China and Persia presently known as Iran. Bombyx mori is a member of a small family of about 300 moth species.

The credit for the discovery of silkworm’s silk goes to an ancient empress in China, who while walking around accidentally, noticed the worms. When she touched it with her fingers, the silk came out and surrounded her finger. When the full silk had come out, she saw the small cocoon inside it; which was responsible for the formation of silk. It is even said that the Chinese princess smuggled eggs to Japan by hiding them in her hair and thus they began their love affair with silk. Due to its captivity for thousands of years, Bombyx mori is fully domesticated and cannot survive without the support of mankind.

The silkworm is the larva of a moth. Larvae are monophagous which takes only mulberry leaves as its diet. The cocoon is made of a single continuous thread of raw silk from 300 to 900 metre long. The fibres are very fine and lustrous, about l/2500th of an inch in diameter. One pound of silt can be made from about 2,000 to 3,000 cocoons, and it is estimated that almost 70 million pound of raw silk are produced each year. It requires about 1 billion pounds of mulberry leaves to produced 7 million pounds of raw silk and one pound of silk is almost equivalent to 1,000 miles of filament.

Preparation

One gram of silk-worm egg consists of around 15,000 eggs which are kept at 0°C to overcome the immature development. The silkworms eat mulberry leaves day and night and they grow very fast. When the colour of their heads changes darker, it indicates that the time for them to moult has come. It require almost a month time for its development into full size. During this period it takes four moulds and their body turns slightly yellow reaching a size of 4 cm long. The silk-worm finally eats a meal which is about twenty to twenty five times its weight of leaves and attains a size of 9 cm length and 10 mm thick. The skin becomes tight and all these symptoms indicate that it is going to cover itself with a silky cocoon. The process of spinning cocoon continues for almost three days. After 7–8 days, the larvae changes into chrysalides, and the cocoons are collected by throwing them into boiling water, this kills the silkworms and also makes the cocoons easier to unravel. If the caterpillar is left to eat its way out of the cocoon naturally, the threads will be cut short and the silk will be useless. The cocoons are kept in hike warm water to remove the gum. Since all the eggs hatch almost the same time, the cocoons also be collected together and treated at the same period. Some amount of cocoons are retained and allowed to come out for fertilization. The females lay nearly 500 eggs and these eggs are stored till further requirement is wanted.

Description

Chemical Constituents

Silk mainly consists of protein known as fibrion. Fibrion is soluble in warm water and on hydrolysis yields two main amino acids, glycine and alanine.

Uses

Silk is used pharmaceutically in the preparation of sutures, sieves, and ligatures. The ‘stiff silkworm’ (dried body in the four to fifth stage of larva, which dies due to infection of the fungus Beauveria bassiana) is used in the traditional Chinese medicine.