Question

We can remove the undesirable properties of natural rubber by heating natural rubber with

• A. Carbon
• B. Sulphur
• C. Phosphorus
• D. Silicon

Hint:

Vulcanization means heating natural rubber with sulphur to improve its strength and elasticity.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Natural rubber has several undesirable properties, such as being soft and sticky at high temperatures, brittle at low temperatures, having high water absorption, and low tensile strength. To improve these properties, a chemical process is used. This question asks to identify the substance used in this process.
Step 2: Detailed Explanation:
1. The process of improving the properties of natural rubber is called vulcanization. 2. Vulcanization was discovered by Charles Goodyear in 1839. 3. The process involves heating raw natural rubber with sulphur (or sulfur-containing compounds) to a temperature of around 140-160°C. 4. During vulcanization, the sulphur atoms form cross-links (sulphide bridges) between the long polymer chains of isoprene (the monomer of natural rubber). 5. These cross-links tie the polymer chains together, preventing them from slipping past each other. 6. This modification makes the rubber harder, more elastic, more resistant to temperature changes, and less sticky. It significantly improves its tensile strength and durability. 7. Carbon (usually as carbon black) is often added as a reinforcing filler, but sulphur is the primary vulcanizing agent that creates the cross-links. Step 3: Final Answer:
The undesirable properties of natural rubber are overcome by heating it with sulphur in a process called vulcanization. Therefore, option (B) is correct.