Vulcanisation of rubber modifies several properties. Which one is NOT increased by vulcanisation?

Introduction / Context:
Vulcanisation introduces sulfur crosslinks between polyisoprene chains, transforming soft, tacky rubber into an elastic material with improved mechanical and thermal performance. Knowing which properties rise and which fall after vulcanisation is crucial for rubber compounding.

Given Data / Assumptions:

• Crosslinking reduces chain mobility.
• Elastic recovery, modulus, set resistance, and tear strength typically improve.
• Plasticity (ease of permanent flow) declines as the network constrains deformation.

Concept / Approach:
Crosslinks limit viscous flow and permanent deformation, thereby decreasing plasticity. Elasticity and resilience generally increase, while ductility (large plastic deformation) often decreases. Thus, among the listed options, “plasticity” is the property not increased.

Step-by-Step Solution:
Recall effects of crosslinking on chain mobility.Associate reduced mobility with lower plasticity.Select “Plasticity” as not increased.

Verification / Alternative check:
Standard rubber testing before and after cure shows higher modulus and lower permanent set, indicating reduced plastic flow.

Why Other Options Are Wrong:
Elasticity: increases with crosslink density (to a point).Ductility: often decreases; however the question asks which is not increased—plasticity is the clear answer.Tear strength: usually improves with appropriate crosslink density and fillers.

Common Pitfalls:
Confusing ductility with elasticity; vulcanisation boosts elastic recovery but may reduce ductility.

Final Answer:
Plasticity