Thermal limits in service: most common plastics are generally considered safe up to a maximum continuous-use temperature of approximately how many °C?

Introduction / Context:
Plastics soften, creep, or degrade when exposed to elevated temperatures. Designers therefore quote a maximum continuous-use temperature (CUT) or heat deflection temperature (HDT) limit for commodity thermoplastics. This question probes approximate, rule-of-thumb knowledge for general plastics—not high-performance engineering polymers.

Given Data / Assumptions:

• “Most of the plastics” refers to commodity resins such as PE, PP, PVC, PS, ABS.
• Continuous-use temperature is meant, not brief spikes.
• Unfilled, unstabilised grades are implied.

Concept / Approach:
Commodity plastics typically serve well below 100 °C for continuous applications. HDT values for PE and PP are well below 100 °C (though PP can handle hot fill briefly). Engineering polymers like nylon, PBT, PC, or PPS can exceed 100–150 °C, while high-performance plastics (PEEK, PTFE, PI) go far beyond. The safe blanket answer for “most” common plastics is therefore around 100 °C.

Step-by-Step Solution:
Identify scope → commodity plastics.Relate CUT/HDT data → typically <= 100 °C for continuous duty.Select 100 °C as the approximate maximum for “most” plastics.

Verification / Alternative check:
Datasheets show PE and PVC CUTs in the 60–80 °C range, PP somewhat higher but still often <100 °C for continuous use; hence 100 °C is a sensible upper bound.

Why Other Options Are Wrong:
150, 350, 450 °C: Typical only for engineering or high-performance polymers; not true for “most” plastics.

Common Pitfalls:
Confusing peak or short-term temperatures with continuous ratings; extrapolating from specialised materials to all plastics.

Final Answer:
100