Thermal property check: the approximate softening point of high-density polyethylene (HDPE) is closest to which temperature (°C)?

Introduction / Context:
HDPE is a semicrystalline thermoplastic used in pipes, containers, and geomembranes. A quick mental map of its softening/melting range is essential for material selection and processing limits like hot-fill, sterilisation, and service temperature envelopes.

Given Data / Assumptions:

• HDPE has higher crystallinity than LDPE, raising its melting/softening range.
• Typical DSC melting peaks for HDPE occur around 130–135 °C, formulation dependent.

Concept / Approach:
The Vicat softening temperature and melting peak of HDPE concentrate near the mid-130 °C region. While exact values vary with molecular weight and branching, 135 °C is widely accepted as a representative softening point for quick-reference MCQs.

Step-by-Step Solution:

Verification / Alternative check:
Manufacturer datasheets often quote melting temperatures near 130–135 °C and Vicat softening in a similar ballpark, confirming the selection.

Why Other Options Are Wrong:

• 85/115 °C: more typical of LDPE or soft thermoplastics.
• 165/205 °C: exceed HDPE melt; closer to PP or nylons.

Common Pitfalls:
Confusing softening (Vicat) with glass transition; HDPE has very low Tg (around -120 °C).

Final Answer:
135