Thursday, 2 September 2010

More about Silkworms and Silk fiber- Mulberry, Muga, Tasar and Eri

Silkworm belong to the order Lepidoptera. They belong to family of Bombycidae and Saturniidae. Under Bomycidae, we have Bombyx Mori or commonly known as Mulberry Silkworm. Under Saturniidae family the eri silk worm is called Philosamia Ricine, Muga is called Anthrerea Assamensis and Tasar is called A. Mylitta

Silk filament is made up of 75-80 percent fibroin and 20-25% sericin or gum. Fibroin is insoluble but sericin may be removed by boiling. 

The Muga and Tasar varieties of the worm also secrete a cement which causes a drab color to develop, making bleaching a very laborious process. 

Silk of the B. Mori variety is triangular in cross section. It has a capacity to reflect light and the layers of protein impart it with a pearly sheen. Tasar silk has a flatter structure which is a reason for its dull appearance. 

Muga is rounder and more lustrous. 

The B.Mori and Muga imagos cut their way through one end of the cocoon, thus making the filament discontinuous. The Tasar moth secrets an enzyme called cocoonase, which softens the cocoon shell facilitating  emergence. The eri moth spins an open ended cocoon through which the imago can fly to full term. 

In silk only male worm can fly. 

During the process of boiling of silk 75% of the sericin is removed. Care is taken to retain the 25% of the gum to prevent tangling. If the boiling is insufficient, filaments tend to snap during weaving, while excess boiling increases the amount of waste silk. 

The thread drawn from the cocoon is of uneven consistency, being finer at the beginning and the end. In order to provide uniformity in consistency, additionaly filaments are drawn in course of reeling, the process is called throwing. 

Because of the structure of cocoon, the process of reeling also generates a residue of waste fiber. In B. Mori, about 45% of the product is floss. This material is spun. This is called Matka. In the case of muga worm 25 to 50 percent may be spun. With regard to tasar only about 10 per cent of the filament can be reeled

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