Identify Buna-S by material class: Buna-S (SBR) is best described as which type of material in engineering applications?

Introduction:
Buna-S is the trade name historically used for styrene–butadiene rubber (SBR), an archetypal synthetic elastomer used in tires, belts, footwear, and general-purpose molded goods. The question checks correct material classification.

Given Data / Assumptions:

• Buna-S is a copolymer of styrene and butadiene.
• Products require elasticity, resilience, and the ability to be vulcanized.

Concept / Approach:
Elastomers display large reversible deformations and require vulcanization (cross-linking) for useful strength. Buna-S fits this description. It is not a thermoplastic, thermoset resin, reinforcement fiber, or ceramic matrix.

Step-by-Step Solution:
Identify composition: styrene + butadiene → elastomeric copolymer.Relate to properties: high elasticity, good abrasion resistance after compounding and vulcanization.Select “Rubbery elastomer.”

Verification / Alternative check:
Materials databases and standards categorize SBR under synthetic rubbers; tire treads and general rubber goods commonly use SBR blends.

Why Other Options Are Wrong:

• Fibrous/ceramic options are entirely different material classes.
• Thermoplastics soften and flow on heating; elastomers like SBR require vulcanization and do not behave as typical thermoplastics.
• Thermoset resins are rigid, cross-linked networks (e.g., phenolics), unlike vulcanized elastomers in behavior and use.

Common Pitfalls:
Confusing “rubber” with “plastic”; elastomers are a separate category characterized by entropy-driven elasticity and modest modulus.

Final Answer:
Rubbery elastomer