Problem 42 - A Complete Resource Book in Chemistry for JEE Main

Question

Which one is a protein fibre? (a) rayon (b) cotton (c) polyester (d) silk

Step-by-Step Solution

Answer

Silk (d) is a protein fiber.

Step 1: Understanding Protein Fibers

Protein fibers are natural fibers derived from animal sources. They are composed of protein molecules, which are amino acids joined together. Common examples of protein fibers include wool and silk.

Step 2: Examine Each Option

Evaluate each option on whether it is a protein fiber or not: - (a) Rayon: A semi-synthetic, cellulose-based fiber, not a protein fiber. - (b) Cotton: A natural, plant-based fiber, also not a protein fiber. - (c) Polyester: A synthetic fiber made from petrochemicals, not a protein fiber. - (d) Silk: A natural protein fiber produced by silkworms.

Step 3: Identify the Protein Fiber

After examining the options, identify that silk is a protein fiber because it is derived from the animal source, specifically silkworms, and includes protein chains.

Key Concepts

Natural Fibers

Natural fibers are materials that are harvested from plants and animals. These fibers are highly valued for their biodegradability and renewable nature. Some common natural fibers include:

• Silk: Obtained from silkworms, known for its luxurious texture and strength.
• Wool: Sourced from sheep, it is warm and elastic.
• Cotton: Derived from the cotton plant, it is soft and breathable.

Natural fibers can be spun into yarns and used for various applications like clothing, textiles, and ropes. They are celebrated for their comfort, breathability, and environmental benefits as they decompose naturally without harming the ecosystem.

Animal Sources

Animal sources are a primary provider for certain types of natural fibers. When we mention fibers from animal sources, we typically refer to protein fibers. Animal-derived fibers have a few distinct characteristics, making them unique. Wool and silk are the two primary fibers obtained from animals:

• Wool: Comes from sheep. It acts as an excellent insulator, keeping organisms warm. It's also elastic and fire-resistant.
• Silk: Comes from silkworms. It has a natural sheen and is very strong, yet lightweight, making it highly sought after for textiles and garments.

These fibers are integral to the textile industry and are often preferable where comfort and natural textures are essential.

Amino Acids

Amino acids are the building blocks of proteins. When linked together in chains, they form the structure of protein fibers. These chains create both strength and elasticity in natural protein fibers like wool and silk. Here are some important points about amino acids:

• Amino acids have an amine group, a carboxylic acid group, and a distinctive side chain called an R group.
• There are 20 different amino acids that can combine in various sequences to create proteins.
• The sequence and nature of the amino acids influence the fiber's characteristics such as its texture and flexibility.

Understanding amino acids helps in explaining why proteins can offer such versatile fibers with varying properties.

Synthetic Fibers

Synthetic fibers are man-made materials that are created through chemical processes, often using petrochemicals as the base. Unlike natural fibers, which come from plants or animals, synthetic fibers are entirely human-engineered. Here are some insights into synthetic fibers:

• Rayon: Though derived from cellulose, it's considered semi-synthetic because it undergoes extensive processing.
• Polyester: Made from petroleum, known for its durability, resistance to shrinking, and wrinkle-proof nature.
• Nylon: Created from petrochemicals, it's valued for its strength and elasticity.

These fibers are advantageous for applications that need properties like water resistance, resilience, or easy maintainability. They tend to be less expensive to produce and are used widely in the fashion and industrial sectors.