Question

During vulcanization of raw rubber, the chemical added to it is

• A. Sulphur
• B. Phosphorus
• C. Iodine
• D. Sodium

Hint:

Vulcanization of rubber is done by heating rubber with sulphur.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks to identify the chemical used in the process of vulcanization of natural rubber.
Natural rubber, in its raw state, has several disadvantages like low elasticity, high water absorption, and becoming sticky when hot or brittle when cold.
Step 2: Detailed Explanation:

The Vulcanization Process:
Vulcanization was discovered by Charles Goodyear. It involves heating raw natural rubber with a specific amount of Sulphur (usually \(3%\) to \(5%\)) at temperatures around \(100^\circ\)C to \(140^\circ\)C.
Sometimes accelerators are also added to speed up the process.

Chemical Changes:
Natural rubber is a polymer of isoprene (\(2\)-methyl-\(1,3\)-butadiene). The polymer chains have double bonds.
During heating, the sulphur atoms react at these double bond sites, forming cross-links (bridges) between the long, linear polymer chains.
These sulphur cross-links tie the chains together into a three-dimensional network.

Impact on Properties:
The cross-linking restricts the sliding of chains over one another, which significantly improves the physical properties:
1. Elasticity increases and the rubber returns to its original shape more effectively.
2. Tensile strength increases.
3. It becomes resistant to temperature changes (doesn't melt easily).
4. It becomes less permeable to gases and less soluble in organic solvents.

Other Options:
Phosphorus, Iodine, and Sodium are not used for this cross-linking purpose in the standard rubber industry.

Step 3: Final Answer:
The chemical added during the vulcanization of raw rubber is Sulphur, which creates cross-links between polymer chains.