Question

The wool fiber exhibits high elastic recovery among the natural fibers due to its \(\underline{\hspace{2cm}}\)

• A. Strong inter-molecular linkages
• B. Weak lateral forces
• C. Poor molecular arrangement
• D. High crystalline region

Hint:

Wool's secret to resilience is its structure: a coiled spring (alpha-helix) held together by strong cross-links (disulphide bonds). When you stretch it, you uncoil the spring, and the cross-links pull it back into shape.

Answer 1

The Correct Option is A

Step 1: Understand the property: "high elastic recovery." This means that when wool is stretched and then released, it has a strong tendency to return to its original length. This property is also responsible for its excellent wrinkle resistance. 
 

Step 2: Analyze the molecular structure of wool. Wool is a protein fiber (keratin). Its polymer chains have a natural coiled or helical shape (alpha-helix). These chains are held together by various types of cross-links. 
 

Step 3: Relate the structure to the property. The most important of these links are the strong, covalent disulphide bonds (cystine linkages) between adjacent polymer chains. When the fiber is stretched, the helical chains uncoil. The strong disulphide cross-links act like springs, pulling the chains back to their original coiled configuration once the force is removed. This network of strong cross-links is the primary reason for wool's high elastic recovery.

Step 4: Evaluate the options. 
- (A) Strong inter-molecular linkages: This is correct. The disulphide bonds are very strong covalent cross-links. 
- (B) Weak lateral forces: Incorrect. While wool has weaker hydrogen bonds, the disulphide bonds are strong. 
- (C) Poor molecular arrangement: Wool has a complex but highly organized structure (alpha-helix), not a poor arrangement. Its structure is what gives it its properties. 
- (D) High crystalline region: Wool has a relatively low degree of crystallinity compared to fibers like cotton or polyester. Its structure is more amorphous and spring-like. 

Conclusion: The strong inter-molecular linkages, specifically the covalent disulphide cross-links, are responsible for wool's high elastic recovery.