Material behavior of commodity polymers: at room temperature (≈25 °C), polystyrene typically behaves as which type of plastic?

Introduction / Context:
Polystyrene is a glassy, amorphous thermoplastic widely used in packaging, disposables, and appliance housings. Its mechanical response at room temperature is governed by the position of room temperature relative to its glass transition temperature. This question checks recognition of the brittle versus ductile nature of polystyrene in everyday conditions.

Given Data / Assumptions:

• Room temperature is around 25 °C.
• Polystyrene's glass transition temperature (Tg) is well above room temperature (approximately 95–105 °C for general-purpose grades).
• No rubber impact modifiers are assumed (i.e., not high-impact polystyrene, HIPS).

Concept / Approach:
When a polymer is tested below its Tg, the polymer chains are frozen in a glassy state. Segmental mobility is minimal, so the material exhibits high modulus and low toughness, failing with limited plastic deformation. This is the classic brittle response. In contrast, ductile behavior requires temperatures sufficiently above Tg to enable significant plastic flow before fracture.

Step-by-Step Solution:
Compare room temperature to Tg: 25 °C is far below ~100 °C.Below Tg, expect glassy, brittle fracture with low elongation at break.Select the descriptor that matches: brittle.

Verification / Alternative check:
Drop tests of general-purpose polystyrene articles show crack initiation and catastrophic failure rather than yielding. Impact-modified variants (HIPS) incorporate rubber domains to shift failure toward tougher, semi-ductile modes—but that is a different material.

Why Other Options Are Wrong:
Ductile/malleable imply significant plasticity, which polystyrene lacks at room temperature in the unmodified state.None of these is incorrect because brittle fits well-established behavior.

Common Pitfalls:
Confusing general-purpose polystyrene with HIPS; extrapolating from thin foams (EPS) whose cellular structure can cushion impacts but does not change the intrinsic brittleness of the polymer matrix.

Final Answer:
Brittle