Rubber Technology — Vulcanisation Step During the vulcanisation of natural rubber, the polymer is heated in the presence of which key element to improve elasticity and strength?

Introduction / Context:
Vulcanisation is a staple question in polymer science. It refers to the process of crosslinking rubber chains to enhance elasticity, tensile strength, and thermal stability. Knowing the crosslinking agent used with natural rubber (polyisoprene) is essential for exams covering materials or industrial chemistry.

Given Data / Assumptions:

• Material: natural rubber (cis-1,4-polyisoprene).
• Operation: heating with an additive to crosslink.
• Outcome: improved mechanical properties and reduced tackiness.

Concept / Approach:

In classic vulcanisation, sulphur forms crosslinks (sulphidic bridges) between polymer chains, restricting chain mobility and increasing resilience. Accelerators, activators, and fillers may be present, but sulphur is the defining agent. Alternative elements listed (carbon, silicon, phosphorous, chlorine) do not represent the standard crosslinker for natural rubber in the base process.

Step-by-Step Solution:

Recall historical origin: Goodyear’s discovery involved sulphur.Understand mechanism: sulphur bridges create network structure.Select the element directly responsible for crosslinking → sulphur.Confirm others are incorrect or used for different modifications.

Verification / Alternative check:

Compare properties before/after: vulcanised rubber shows higher modulus, less creep, and better heat resistance, consistent with sulphur crosslinking.

Why Other Options Are Wrong:

Carbon: Filler (carbon black) improves strength but is not the crosslinker.Silicon/Chlorine/Phosphorous: Not the standard vulcanising agent for natural rubber.

Common Pitfalls:

Confusing carbon black reinforcement with the chemical agent that creates crosslinks; both are important but distinct roles.

Final Answer:

Sulphur