Vulcanisation effects: which property of rubber DECREASES when raw rubber is vulcanised?

Introduction / Context:
Vulcanisation chemically crosslinks rubber chains, typically with sulfur or other systems, transforming soft tacky gum into an elastic engineering material. Understanding which properties increase or decrease guides compounding and quality control in rubber goods.

Given Data / Assumptions:

• Raw rubber is soft, exhibits cold flow and surface tackiness.
• Crosslinking reduces chain mobility and improves elastic recovery.
• Properly compounded materials include antidegradants and fillers.

Concept / Approach:
Crosslinks limit viscous flow and interchain slippage. As a result, tensile strength, modulus, abrasion resistance, and service temperature range generally increase up to an optimum cure. Solvent and oil resistance also improve due to the network resisting swelling. The obvious property that decreases is surface tackiness: the vulcanised surface is drier, less sticky, and more dimensionally stable.

Step-by-Step Solution:
List property trends: tensile strength ↑, solvent resistance ↑, working temperature range ↑.Identify the one that goes down: tackiness ↓ after crosslinking.Select 'Tackiness (surface stickiness)' as the correct choice.

Verification / Alternative check:
Standard stress–strain and swelling tests (e.g., ASTM D412, D471) show post-cure improvements; adhesion to itself without adhesives (tack) drops markedly versus raw gum.

Why Other Options Are Wrong:
Tensile strength: typically increases with adequate cure.Resistance to organic solvents: network reduces swelling; it does not decrease.Working temperature range: the usable range broadens, not narrows.

Common Pitfalls:
Overcure can embrittle rubber, but even then, tackiness does not increase; do not confuse tack with adhesion in formulated pressure-sensitive systems.

Final Answer:
Tackiness (surface stickiness)