10. What is the role of sulphur in the vulcanization of rubber?
a. It acts as a catalyst for the reaction, thereby accelerating its rate
b. It participates in di-sulphide bonds which cross-link the rubber polymers
c. It is used to increase the temperature of the process, thereby accelerating its rate
d. It preserves rubber from biodegradation

Role of Sulphur in Vulcanization of Rubber: MCQ Solved

Sulphur plays a crucial role in vulcanization by forming cross-links between rubber polymer chains. The correct answer is option b.

Option Analysis

a. It acts as a catalyst for the reaction, thereby accelerating its rate
Sulphur does not function as a catalyst; catalysts remain unchanged, but sulphur chemically reacts and incorporates into the polymer structure.​

b. It participates in di-sulphide bonds which cross-link the rubber polymers
This is correct. During vulcanization, sulphur (typically 3-5%) reacts with double bonds in polyisoprene chains, creating di-sulphide (-S-S-) bridges that form a three-dimensional network, enhancing elasticity, tensile strength, and durability.​

c. It is used to increase the temperature of the process, thereby accelerating its rate
Sulphur itself does not raise temperature; heat (around 120-140°C) activates the reaction, and accelerators like zinc oxide speed it up.​

d. It preserves rubber from biodegradation
Vulcanization improves oxidation and abrasion resistance through cross-linking, not direct biodegradation prevention, which involves other additives.​

Introduction to Vulcanization

Vulcanization transforms natural rubber from a soft, sticky material into a durable elastomer by heating it with sulphur. This process, discovered by Charles Goodyear in 1839, addresses rubber’s limitations like heat softening and low strength. The role of sulphur in the vulcanization of rubber centers on chemical modification for industrial use in tires and hoses.​

Sulphur’s Chemical Mechanism

Sulphur reacts with allylic sites on cis-1,4-polyisoprene chains, forming mono-, di-, or polysulphide bridges (-S_x-) that cross-link polymers. Typically 3-5% sulphur suffices; higher amounts yield harder rubber. Accelerators reduce activation energy from ~49 kJ/mol, enabling efficient curing.​

• Cross-links limit chain slippage, boosting elasticity and resilience.

• Process is exothermic, releasing ~18-46 kJ/mol S based on formulation.​

Benefits and Applications

Vulcanized rubber withstands temperatures from -40°C to 100°C, resists abrasion, and shows low water absorption. Key applications include automotive tires, seals, and conveyor belts. For CSIR NET aspirants, understanding this highlights polymer chemistry in materials science.​