What is Silk Its Chemical Structure Properties and Applications
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.
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.
Silk is obtained from the silkworm before it matures into an adult silk moth. Furthermore, the farmer extracts silk fiber in its pupa stage.
Then, he submerges the cocoons in boiling water to soften the layers of the cocoons.
The silk workers brush the cocoons to untangle the silk strands.
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.
Thereafter, the silk workers roll the silk yarn under the roller to make it uniform.
Henceforth, the manufacturers dye the yarns to produce colorful silk fabric.
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.
Mulberry Silk – It is the most substantial textile. Mulberry silk is the softest and the most durable fabric.
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.
Tasar Silk – India and Japan produce this variety of silk. Green silkworms are the producer of Tasar silk.
Spider Silk – It is the most expensive variety of silk. Manufacturers use spider silk to produce microscopes, bulletproof vests, etc.
Muga Silk – The natives of Assam produce this variety of fabric using semi-domesticated muga silkworms.
Sea Silk – Another name for sea silk is mussel silk since species of mussel of the Mediterranean Sea produce it.
Coan Silk – Silkworms, which feed on oak, pine, and juniper trees produce coan silk. You will find this variety in Greece, Turkey, and Italy.
Fun Facts on Silk
As much as 1.5 km of silk filament can be drawn from a single cocoon of a silkworm.
Apart from silkworms, other insects like raspy crickets and web spinners can also produce silk.
The emperors kept the production of silk as a guarded secret for more than two thousand years.
In ancient times, ordinary people were prohibited from wearing silk garments.
FAQs on Silk as a Natural Protein Polymer in Chemistry
1. What is silk in chemistry?
Silk is a natural protein polymer mainly composed of the fibrous protein fibroin produced by silkworms. In chemistry, silk is classified as a protein fibre made of long chains of amino acids linked by peptide bonds.
- The primary source is the silkworm Bombyx mori.
- Its structure contains repeating amino acids such as glycine, alanine, and serine.
- Silk is considered a natural polyamide because peptide linkages (–CONH–) connect its monomers.
2. What is the chemical composition of silk?
Silk is chemically composed of the protein fibroin, which consists of repeating amino acids like glycine (C2H5NO2), alanine (C3H7NO2), and serine (C3H7NO3).
- These amino acids are linked by peptide bonds (–CO–NH–).
- The general structure is a long-chain polypeptide.
- Strong hydrogen bonding between chains gives silk high tensile strength.
3. Is silk a polymer?
Yes, silk is a natural polymer because it is made of repeating amino acid units joined by peptide linkages.
- The monomers are amino acids.
- The polymer chain formed is called a polypeptide.
- Silk is classified as a natural polyamide due to the –CONH– linkage.
4. What type of fibre is silk in chemistry?
Silk is a natural protein fibre obtained from animal sources.
- It belongs to the category of protein-based polymers.
- Unlike synthetic fibres such as nylon, silk is biodegradable.
- Its structure is mainly β-pleated sheet arrangements that provide strength and elasticity.
5. What are the main properties of silk fibre?
Silk fibre has high tensile strength, natural luster, and good elasticity due to its protein structure.
- Strong intermolecular hydrogen bonding increases durability.
- It is lightweight and breathable.
- It is sensitive to strong acids and alkalis because peptide bonds can hydrolyse.
6. How is silk chemically different from wool?
Silk differs from wool mainly in protein structure, as silk contains fibroin while wool contains keratin.
- Silk has a smoother structure with β-sheets.
- Wool contains more sulfur due to cysteine amino acids forming disulfide bonds (–S–S–).
- Wool is more elastic, while silk is smoother and shinier.
7. Why is silk considered a polyamide?
Silk is considered a polyamide because its amino acids are linked by amide (peptide) bonds of the form –CONH–.
- Each peptide bond forms between a –COOH group and an –NH2 group.
- This linkage is chemically similar to synthetic polyamides like nylon.
- The repeated amide bonds create a long-chain macromolecule.
8. What happens when silk is treated with acids or bases?
When silk is treated with strong acids or bases, its peptide bonds hydrolyse, breaking the protein into smaller fragments.
- Acid hydrolysis converts peptide links into amino acids.
- Alkaline treatment weakens fibre strength.
- This chemical sensitivity is typical of protein fibres.
9. Is silk biodegradable?
Yes, silk is biodegradable because it is a natural protein polymer that microorganisms can break down.
- Enzymes such as proteases hydrolyse peptide bonds.
- It decomposes into amino acids in the environment.
- This makes silk more eco-friendly than many synthetic fibres.
10. What is the difference between natural silk and synthetic silk?
Natural silk is a protein-based polymer produced by silkworms, while synthetic silk (like rayon) is a regenerated cellulose fibre.
- Natural silk contains peptide bonds (–CONH–).
- Rayon is made from cellulose with repeating glucose units (C6H10O5)n.
- Silk is an animal fibre, whereas rayon is derived from plant cellulose.
