[Chemistry Class Notes] on Silk Pdf for Exam

Silk is a luxurious fabric spun from the cocoons of a moth, Bombyx mori.  These cocoons are spun to produce a continuous silk filament with a natural gum that lends it to have an appealing sheen. Silk fibers are made from a protein produced by the silkworm, Bombyx Mori. The protein is called Sericanin and is solely produced by this insect. It is secreted as a fluid from two glands situated on the side of the worm. These glands produce a protein called sericin which is converted into a fluid silk plasma.

The fluid travels along with a system of many tiny tubes that the worm has a series of fine small spigots that can be opened or closed, which release a precise amount of silk fluid. The threads are collected by a series of sticky hairs on the worm’s head. A few minutes after the initial striking, the larva has spun a cocoon around itself in the air, an amazing feat of engineering that actually propels it into the air when the wrap is tight.  The moth then emerges from the cocoon as it sheds its final, now useless, insect outer layers.

List of Advantages of Silk Fibers

1) Inexpensive to store as silk doesn’t ignite as easily as cotton as a result of the low heat released from the burning of the silk.

2) They are antibacterial which can be beneficial as they resist bacteria found in sweat or water.

3) Silk is a natural material so they are very breathable.

4) They are a durable material.

5) Silk clothing helps with personal hygiene as they wick away dirt and sweat from the skin.

6) Silk can improve the body’s circulation and therefore, help with discomfort from having poor circulation.

7) Silk slows down the process of frizzy, dry hair.   Silk fibers have a naturally high level of hydrogen peroxide.

8) Silk no longer requires harsh chemicals so they are ideal for those who have sensitive skin.

Disadvantages of Silk Fibers

1) The production of silk requires the life of thousands of silkworms, B. Mori.

2) It requires more land to produce silk than cotton, which is more costly.

3) They are more expensive and can get expensive depending on the grade.

4)   They are more difficult to dye.

5) Silk needs more labor intensive work to produce but can last up to three times the amount of time of other clothing materials.

How is Silk Made?

Usually, you choose to wear the most expensive fabric like silk to a wedding and function. Do you know how and where silk is obtained from? The most lustrous fabric of all times, silk, is a natural fiber like cotton and wool. Silk is obtained from Bombyx mori’s cocoon, a type of silkworm. The larvae of the mulberry silkworms produce the most popular mulberry silk.  Silk is produced by rearing silkworms in captivity. Thus, the fabric is a natural animal fiber. The process by which silk is produced is called sericulture. Here you will learn in-depth about how  silk is obtained from silkworm, and different types of silk.

How is Silk Obtained from the Cocoon of Silkworms?

Let us find out in detail how silk is obtained from the cocoon of silkworms in detail.  Here is a step by step process of silk production. 

1. At the larva stage, the silkworms produce fibers of silk.  The larva weaves a cocoon in two or three days to protect itself for the development of pupae. 

2. Silk is obtained from the silkworm before it matures into an adult silk moth.  Furthermore, the farmer extracts silk fiber in its pupa stage. 

3. Then, he submerges the cocoons in boiling water to soften the layers of the cocoons.

4.  The silk workers brush the cocoons to untangle the silk strands. 

5. Subsequently, they reel the silk strands into a continuous string. Reeling is the process of exposing the cocoons to extreme heat to separate the silk fibers.  These fibers are twisted to become silk yarn.

6. Thereafter, the silk workers roll the silk yarn under the roller to make it uniform.

7. Henceforth, the manufacturers dye the yarns to produce colorful silk fabric.

8. Finally, the producers can construct a garment from the silk yarn.

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What is the Silk Structure?

Silk is made up of protein fiber, namely, 70% of fibroin (the filament) and 30% of sericin.  The mulberry silkworms produce these two proteins in its cocoon. Fibroin consists of the sequence of long-chain amino acids Gly-Ser-Gly-Ala-Gly-Ala.  Furthermore, it forms beta-keratin.  Fibroin is protected with a sticky layer of sericin.   The coating of sericin results in intramolecular and intermolecular hydrogen bonding between the amino acid groups which provides large forces of attraction. Thus, sericin makes the silk strand of high-tensile strength and holds the silk structure together.

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Position of sericin and fibroin in silk structure

 

Types of Silk Fibers

Different varieties of silkworms produce different types of silk.  However, the quality differs based on the chemical composition of silk.  Furthermore, silk formations are of two types – natural and artificial silk.  Basically, natural silk is obtained from the cocoons of silkworms.  Such silk is made up of protein. On the other hand, artificial silk is made up of wood pulp, such as rayon.  Here are some examples of silk.

1. Mulberry Silk – It is the most substantial textile.  Mulberry silk is the softest and the most durable fabric.

2. Eri Silk – Another name for eri silk is peace silk because its production does not include the killing of silkworms.  It is heavier and more durable in comparison to mulberry silk.

3. Tasar Silk – India and Japan produce this variety of silk.  Green silkworms are the producer of Tasar silk.

4. Spider Silk – It is the most expensive variety of silk.  Manufacturers use spider silk to produce microscopes, bulletproof vests, etc.

5. Muga Silk – The natives of Assam produce this variety of fabric using semi-domesticated muga silkworms.

6. Sea Silk – Another name for sea silk is mussel silk since species of mussel of the Mediterranean Sea produce it.

7. Coan Silk – Silkworms, which feed on oak, pine, and juniper trees produce coan silk.  You will find this variety in Greece, Turkey, and Italy. 

Fu
n Facts on Silk

1. As much as 1.5 km of silk filament can be drawn from a single cocoon of a silkworm.

2. Apart from silkworms, other insects like raspy crickets and web spinners can also produce silk.

3. The emperors kept the production of silk as a guarded secret for more than two thousand years.

4. In ancient times, ordinary people were prohibited from wearing silk garments.