Silk



Silk is a fiber made from the silk threads created by the silk worm. It is mainly used to make clothing and similar fabrics. It is a soft white substance similar to cotton strands. Silk is much softer and more expensive to produce than cotton. To make silk factory workers have to take the strands of silk that are produced by the silk worm and weave multiple strands together to get a thicker strand of silk. They then send strands to clothing companies who create clothes. In general, silk is used to make many different things.

History
The production of silk has an long history that most people do not know about. For centuries the West did not know much about silk or the people who made it. The reason for this was because the Chinese kept it a secret for more than two thousand years. It was one of the most protected secrets in history. The Chinese legend says there was a goddess of silk who was named Lady Hsi-Ling-Shih who was the wife of the Yellow Emporor who ruled China in 3000 BC. The Chinese give her credit for finding the silkworm to make the silk and inventing the loom.

In 1927, half a silkworm cocoon was found in the Yellow River in Shanxi Province in northern China. It was dated to be from 2300 and 2600 BC. Also, a group of ribbons, woven fragments, and threads have been found at Qianshanyang in Zhejiang province and has been said to be between 6000 and 7000 years old. Spinning tools, silk thread, and fabric have been found along the Yangzi River and are believed to show the origins of silk production to be even earlier.

Properties
In general silk filament is strong. This is because it is configured in a very crystalline linear polymer system. This way more hydrogen is able to form in a more frequent manner. Silk is known for losing its strength when it gets wet. This is because water molecules hydrolize many hydrogen bonds which weakens the silk polymer. Silk that has been degummed is less dense than flax, rayon, cotton or wool. Its specific gravity is 1.25. Silk fibers are weighed by having the filaments absorb in heavy metallic salts. This increases the density of the material and gives it its draping property.

The feel of silk is described to be a medium. Its crystalline polymer system creates a bit of stiffness due to the filaments. Many people misinterpret this as soft because of the smooth, soft and regular surface of the silk filaments. Silk fiber is very flexible. It is mostly used for clothing so it can be tailored easily. Silk does not do a good job when it comes to conducting electricity. It tends to to create a static charge when it is handled. Because of this, it causes problems during shipping, especially in dry areas.

Production
Sericulture is the production of the silkworm cocoon specifically for their filament. The most popular species of silkworm used for silk is the Bombyx. It is usually cultivated and raised under a controlled environment with a specific nutrition diet. There are four stages to the life cycle of a silkworm. The egg, the silk worm, the pupa and the moth. The silk worm covers itself in a cocoon by secreting a protein like substance from its head. The most desirable stage for silk producers is the cocoon stage. When the silk worms form cocoons, the farmer delivers them to the factory, which is called a filature. This is where the silk is unwrapped from the cocoons and the silk is collected.

The filatures perform specific tasks. Their jobs go as follows: sorting cocoons, softening the sericin, reeling the filament, and bailing. First, the cocoons get sorted according to their size, shape, texture, and color since all of these categories affect the end result of the silk. The color of the cocoons range from white all the way to yellow to grayish. The next step is softening the sericin. The strands of silk are double strands of fibroin, which is kept shut by a sticky substance known as sericin. After the cocoons are sorted, they are immersed in hot and cold liquid. This is because the sericin needs to be softened so the strands can unwind to make one long thread. The third step is reeling the strands. Reeling means to unwind the silk strands from the cocoon to combine them all together so it can form a thread of raw silk. Because one strand of raw silk is too thin for commercial use, they need to use three to ten strands at a time to create the desired thickness of silk. This is known as "reeled silk". The final length ends up to be around 300 to 600 m. The final step of creating silk is bailing it. The silk threads are reeled into skeins, which are then compressed into small packages called books which usually weigh between 2 to 4.5 kg. The books are then put into bales that weigh around 60 kg. In this final form, the silk is shipped to silk mills all over the world.

Uses
Silk is mostly used to make clothing such as pajamas, shirts, ties, trousers, dresses, underwear and folk costumes. Because silk has the ability to retain heat in cold temperatures, it is often used in skiing garments to keep the skier warm. It is also used to make duvets or comforters because it is hypoallergenic and lightweight. It can also be used to make fabrics for curtains, rugs, upholstery and sheets for bedding. Sometimes silk is used to make parachutes and parachute cords, although most parachutes are made from nylon.

Silk is also occasionally used to make bicycle tires' casing. Cotton and nylon can also be used in the process of making bicycle tries along with silk. Silk thread is used as sutures that are non-absorbent during surgeries at hospitals. It has been used to make non-reusable cups and utensils. Since silk has a refractive personality to it, it has been used to make holograms. It has also been used to make capsules to put medicine inside of. A different type of silk that has been gaining popularity is spider silk. Spider silk has been used to create cross hairs in instruments such as microscopes.