Effect of vulcanisation on raw rubber: which statement best describes the change after vulcanisation?

Introduction / Context:
Raw rubber is soft, tacky, and exhibits plastic flow. Vulcanisation creates crosslinks between polymer chains, converting the material into an elastic network suitable for tyres, seals, belts, and countless elastomeric products. This question focuses on the qualitative transformation produced by crosslinking.

Given Data / Assumptions:

• Sulfur or other systems provide crosslinks.
• Compounding includes fillers, accelerators, and antidegradants.
• We compare pre- and post-vulcanisation properties qualitatively.

Concept / Approach:
Crosslinks restrict chain mobility, thereby reducing viscous flow and enabling elastic recovery when stress is removed. The rubber becomes less plastic and less tacky, shows higher modulus and tensile strength (to an optimum), and withstands higher service temperatures. Therefore, the accurate qualitative description is that vulcanised rubber is more elastic and less plastic.

Step-by-Step Solution:
Recall raw rubber properties: plastic, tacky, low modulus.Apply crosslinking effect: mobility ↓, elastic recovery ↑, tackiness ↓.Choose the statement that captures this shift: more elastic and less plastic.

Verification / Alternative check:
Dynamic mechanical analysis shows increased storage modulus and lower tan delta at service temperatures after vulcanisation, consistent with improved elasticity and reduced flow.

Why Other Options Are Wrong:
Softer overall: often hardness increases; softness is not the defining change.Less elastic: opposite of actual behavior.Tackier: crosslinking reduces tack without special tackifiers.

Common Pitfalls:
Over-generalising softness; actual hardness depends on formulation and crosslink density, but the fundamental change is the transition from plasticity to elasticity.

Final Answer:
More elastic and less plastic (reduced tackiness)