Introduction:
silk is a natural protein fiber, obtained from the silkworm. The scientific name of the silkworm is Bombyx mori. Silk produced from Bombyx mori is known as Bombyx Silk. The history of silk is started in china in the 4th millennium BC. In India, the first trace of silk was found in the Vedic period (i.e., 5000 BC). States like Karnataka, Andrapradesh, Tamilnadu, Bengal, Assam, Jammu & Kashmir, Uttar Pradesh, Manipur, and Bihar, etc.. are producing Domesticated silk.
Types of silk Worm:
Mulberry Silk Worm
Tasar Silk Worm
Oak Tasar Silk Worm
Eri Silk Worm
Muga Silk Worm
Color of Silk: White, Yellow, Light Green, Grey, Light or Dark Brown, Pale Green, Pale Pink, Pale blue, Red, Ruby, and Emerald.
**The natural color of silk is due to the type of leaf upon which the silkworm feed. For example:
Silk Worms Fed by White mulberry leaves will give “White silk”.
Domesticated Silk Worms will Give “Yellow Silk”.
Green Silk is produced due to the presence of Chlorophyll.
Domesticated Silk: To domesticate Silk some Special conditions are required like:
Suitable climate for the growth of silkworm.
Availability of Mulberry plants/ leaves.
Intensive care of cocoons for better quality of silk.
Production of silk filaments consist of
Sericulture – Production of reeling cocoons.
Reeling – Production of raw silk.
Sericulture: It is the process of cultivating the silk cocoons or silkworms. Types of mulberry silk cocoons.
Univoltime cocoons (which hatches once per year).
Bivoltime cocoons (which hatches twice per year).
Multivoltime cocoons (which hatches several times in an year).
**Most of the domesticated silks are Multivoltime type. Life cycle of the silkworm:
Each Female moth lays about 500 eggs.
Eggs are hatched by silk moths in incubating room at 20-25oc.
Eggs laid by silkworm are used for
Reproduction.
Cocoon production.
Moths lay eggs on a sheet which contains gummy substance.
After placing on the sheet eggs change their color rapidly from bluish brown to black.
These egg sheets are placed in cold storage, later transferred into an incubator which is at 25-27oc.
Eggs are placed in the incubator for 8 to 10 days till the caterpillars are hatched out of the eggs.
1 gm of eggs will yield about 1500 to 2000 caterpillars.
After the incubation period, the caterpillar weighs about 5mg and length about 2-3mm long.
For the next 20-30 days, silkworm continuously eats mulberry leaves, so that the weight of the worm will be 2-5gm and length will be around 5-9cm.
Generally, silkworms will increase in weight about 10,000 times in their lifetime.
After few days worm will stop eating and changes its color from greenish-white to creamy white color.
Now that silkworm starts secreting a liquid-like substance called sericin and forms cocoon around it.
Now the caterpillar will transform into a pupa and then to a moth.
In general, the life of a silk moth is about 1-4 days.
Production of raw Silk: The production of raw silk will be processed in 4 stages,
Drying (Stifling).
Sorting.
Cooking.
Reeling.
Drying:
This process is also known as Stifling.
During this process pupa is killed.
Cocoons are stifled either by a direct method like sun drying (or) heating (or) indirect methods like steam (or) hot air drying.
After this process this cocoons are preserved for a while.
Sorting:
In this process good cocoons are sorted and stained cocoons, irregular cocoons, flossy cocoons and thin cocoons are removed.
In sorting some physical properties of the cocoon are considered.
color due to sericin & other impurities.
Weight of cocoon.
Filament length.
Filament diameter.
Cooking:
The main objective of this process is to swell and soften the sericin.
There are various methods of cooking.
Open pan ( single basin).
Three pan.
Pressurized cocoon boiling
Circular type manually operated.
Conveyor system.
Reeling:
In this process continuous silk filament is extracted from cocoons without any break. For this process first cocoons are immersed in a hot water bath to soften the cocoon, once the cocoons become soft it floats on the hot water. Later the winder picks the filament by means of tension guide, pressure, and yarn guide, then the yarn is winded.
** Throughout this process cocoon remains in hot water.
Types of reeling systems: In general, there are two types of reeling systems like
The French system, in this system two threads will be twisted to form a filament.
Italian system, in this system the threads are twisted themselves by the process of crossing to give a high cohesion and uniform thread.
Types of reeling:
Charaka reeling (handloom industry).
Cottage based system.
Filature system.
Charaka Reeling:
This is the Italian system.
In this type of reeling cooking and reeling are done in one basin.
After cooking, the cooked cocoons floats in the basin at high temperatures.
The reeling ends are taken out of the cocoons and twist around themselves by crossing to give the high cohesion and uniform speed.
Generally, 4 to 5 threads are twisted at once.
Cottage basin system:
In this process cooking and reeling is done separately.
Cooking is done in boiling water basin and reeling is done in hot water basin, present near the cooking basin.
Filature system:
This is power-driven multi-end reeling device.
In this system cooking and reeling are done separately.
Sometimes the system is continuous.
The multi-end filature basin is a modern reeling device.
The silk produced through this process is also known as filature silk.
After a certain length, the filaments are nonuniform, these filaments cannot be separated by reeling.
The spun silk principle is generally used to separate out these fibers.