Problem 18 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is not made of polyamides? (a) nylon (b) natural silk (c) wool (d) artificial silk

Step-by-Step Solution

Answer

Artificial silk is not made of polyamides.

Step 1: Identify Polyamides

Polyamides are a type of polymer made through the polymerization of monomers with amide linkages (-CONH-). These are often used in synthetic fibers.

Step 2: Assess Nylon

Nylon is a synthetic polymer and is a well-known example of a polyamide because it contains the characteristic amide linkages.

Step 3: Assess Natural Silk

Natural silk, produced by silkworms, is a natural protein fiber made of proteins consisting of numerous amino acids, which form polyamide linkages similar to those in synthetic fibers.

Step 4: Assess Wool

Wool is another natural protein fiber composed of keratin proteins, which similarly contain polyamide linkages due to the structure of amino acids.

Step 5: Assess Artificial Silk

Artificial silk, also known as rayon, is produced from cellulose, a plant-based material. It does not have polyamide linkages. Instead, it is considered a regenerated fiber, not a polyamide.

Step 6: Determine the Odd One Out

Given that nylon, natural silk, and wool are all made of polyamides, while artificial silk is not, the answer to the question is artificial silk.

Key Concepts

Synthetic Fibers

Synthetic fibers are man-made fibers, and they are created through chemical processes rather than harvested from natural sources. These fibers are known for their durability, strength, and resistance to various environmental factors. They are often more affordable than natural fibers due to the ease of mass production.
Examples of synthetic fibers include:

• Nylon
• Polyester
• Acrylic
• Spandex

Such fibers are typically used in applications where high resistance to wear and tear is needed, such as in clothing, upholstery, and industrial materials. The advantage of using synthetic fibers lies in their ability to be engineered with specific properties to suit a wide range of uses.
Since synthetic fibers are made from oil-based chemical compounds, they are not biodegradable. This means they can contribute to long-term environmental issues.
Nevertheless, innovations in materials science continue to improve the sustainability aspects of synthetic fibers, exploring biodegradability options and recycling methods.

Natural Fibers

Natural fibers come from plants, animals, or minerals. They have been utilized by humans for thousands of years and are often celebrated for their comfort, breathability, and environmental friendliness.
Some common natural fibers include:

• Cotton (from cotton plants)
• Wool (from sheep)
• Silk (from silkworms)
• Hemp (from the hemp plant)

Unlike synthetic fibers, natural fibers are biodegradable, which makes them more eco-friendly. They decompose naturally over time without leaving harmful residues.
Natural fibers offer inherent advantages like breathability, moisture absorption, and thermal regulation, making them ideal for many textile applications. Nonetheless, they may not always be as durable or as versatile as synthetic fibers, which sometimes limits their use in highly demanding environments.

Amide Linkages

Amide linkages are a specific type of chemical bond that is fundamental to the structure of polyamides. These linkages occur between an amino group (-NH2) of one molecule and a carboxylic acid group (-COOH) of another, forming an amide functional group (-CONH-). The formation of this bond releases a molecule of water, making it a condensation reaction.
These linkages are critical to the integrity and properties of both natural and synthetic fibers. For example, in the case of proteins like natural silk and wool, amide linkages hold the amino acids together, giving these fibers their beneficial mechanical properties.
In synthetic materials, such as nylon, amide linkages are deliberately created to mimic these properties, providing strength, elasticity, and durability, which are commonly associated with polyamides. The presence and abundance of these linkages are what define a polymer's classification as a polyamide.

Polymerization

Polymerization is the chemical process where small molecules, known as monomers, join together to form a large chain-like structure called a polymer. This process is crucial in the creation of both synthetic and natural fibers.
There are two primary types of polymerization:

• Chain-reaction (or addition) polymerization
• Step-reaction (or condensation) polymerization

Polyamides, such as nylon, are typically formed by condensation polymerization, where each bonding reaction between monomers results in the loss of a small molecule, often water. This leads to the formation of strong, resilient chains.
It's important in both synthetic polymers manufactured through industrial processes and natural polymers formed biologically. In nature, polymerization processes result in essential proteins and polysaccharides that form structural components of living organisms. Understanding polymerization helps in designing new materials with targeted properties, such as improved strength, flexibility, or biodegradability, further influencing the evolution of textile and materials science.