Silk Fibre

SILK

Silk is commonly known as the “Queen of Fabric”. It is a very fine long smooth protein fibre. It is a secretion of silkworm. Silk was first found by the Chinese Princess and after many years the technique was passed on to other countries. Silk can be cultivated or it is found in forests as wild silk. Cultivated silk variety is the Mulberry silk. The common wild silk varieties are Eri, Tasar and Muga silk. The process of cultivation of silkworm for silk production is called as sericulture.

Principle Origin : Natural

Generic Name : Proteinaceous

Chemical : Secretion of silk worm

Common Name : Silk

Production of Silk

The production of silk involves many sub division,

·           Sericulture.

·           Silkworm egg hatching.

·           Feeding the silkworm.

·           Spinning silk thread from cocoon.

·           Silk filament reeling.

·           Silk throwing.

·           Weighting of silk.

Sericulture

Sericulture is a process in which silkworms are cultivated. Bombyx mori is the species used by most of the commercial silk indus-try. Silk worms are fed with mulberry leaves. Therefore mulberry trees are grown. The mulberry leaves are cut into small parts and given as feed to silk worms.

Egg Hatching

As per modern scientific methods, eggs are produced for fertilization from mul-berry silkworms. The produced eggs are collected and stored under suitable con-ditions so that it will be used whenever it is needed.

Feeding the Silkworm

The collected eggs are kept in the incu-bator for hatching at 18°C to 28°C. Heat is required for hatching of the eggs, which takes about one week to 10 days. Eggs are hatched into larva or caterpil-lars of quarter inch lag. The tiny hatched worms are kept with the mulberry leaves in a plate. Care is taken to feed the worms at regular intervals. After eating more and more leaves, the worm becomes bigger in size of 3 inches. After the full growth, it stops eating and there is change in colour of the silkworm. It takes approximately one month for the silk worm to achieve the full growth. The fully grown worm swings its head and secretes a substance from the ends of its mouth, and the secreted substance solidifies on contact with air. Using this substance the silk worm forms a cocoon around its body. This substance is a con-tinuous, thin filament made of sericin and fiberoin. The silkworm takes two to three days for formation of the cocoon. The well grown cocoons are selected for the fertilization and the others are used for the making of silk fibre. Cocoons are put in hot chamber and steam is passed. This process is called staving or stifling to destroy chrysalis inside the cocoon. This process would prevent silk filament breakage (Figure 2.8).

Spinning Silk Thread from Cocoon

The cocoons (Figure 2.9) are put in hot water, so that the gum on the outer shell is removed. After that, using a stick the loose fibres is slowly unreeled.

Silk Filament Reeling

It is passed through an eyelet and reeled on to a wheel. The fibres are moved from left to right hand slowly and rolled up. This pro-cess is called reeling. Three to ten fibres are combined to make a suitable silk filament.

Throwing

The reeled silk is known as raw silk. The process of transferring silk fibre to yarn is known as throwing. This is sorted based upon size, colour, length or quantity. The raw silk skeins are soaked in warm water with soap or oil. This softens the sericin and helps in the movement of the threads. The skeins are placed on light reels and the silk is wound on the bobbins after mechanical­ drying. When the strands are wound, desired amount of twist can be given. If two or more yarns are wound it is called doubling. Based on the require-ments the twist may be given in the same or opposite direction. In order to make yarns into fabrics, the yarns are dyed first. The yarns are washed with soap water to remove sericin. This process is called degumming. The silk filaments are reeled into skeins. This is packed into small bun-dles called books, which is kept ready for marketing.

Weighing of Silk

The silk fabric manufactures buy silk yarns in kilograms for cloth production. During degumming process the silk weight is lost. In order to increase the weight of silk which was lost in degumming the silk yarns are treated with chemical and metals. This process increases the weight of fabric and is called weighting of silk. This processes increase the weight of the silk but the natu-ral elasticity is lost.

The silk also gets deteriorated on exposure to sunlight, perspiration and dry cleaning.

Characteristics of the Silk Fibre

Shape : Like glass rod

Length : 30,000 – 39,000 cm

Elasticity : More

Stretch ability : More

Flexibility : Medium

Density : 1.25 g/cm3

Reaction : Causes less damage with acid

To flame : Burns with a sputtering flame

Sunlight : Increased exposures will breakdown the fibres

Insects : Destroyed by carpet beetles

Drying : Quick and good

Dyeing : Good absorption for acid and basic dyes

Common Uses of Silk

·           Clothing (Scarfs, Silk Sari, Dothi, Towel, Dress Materials).

·           Household textiles (Bed Spread, Wall Hangers, Table Cloths).

·           Medical Textiles (Suture Threads).