Environmental stress cracking tendency: which polyethylene grade is most prone to stress-cracking under typical service conditions?
Chemical Engineering
Polymer Technology
Difficulty: Easy
Choose an option
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AHigh-density polyethylene (HDPE)
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BLow-density polyethylene (LDPE)
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CCross-linked polyethylene (PEX)
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DLinear low-density polyethylene (LLDPE)
Answer
Correct Answer: High-density polyethylene (HDPE)
Explanation
Introduction / Context:Environmental stress cracking (ESC) is a key failure mode in polyethylenes. Recognising which grade is more susceptible guides material selection for detergents, hydrocarbons, and long-term load exposure.
Given Data / Assumptions:
- HDPE is stiffer and more crystalline, often with lower ESCR than certain LDPE/LLDPE grades unless stabilised.
- Cross-linked PE improves crack resistance.
Concept / Approach:Higher crystallinity can raise notch sensitivity and reduce resistance to ESC in aggressive environments. LLDPE is designed for improved ESCR relative to HDPE in many packaging applications.
Step-by-Step Solution:Compare ESCR trends: HDPE tends to be more prone than LDPE/LLDPE without additives.Select HDPE as most prone among the listed choices.
Final Answer:High-density polyethylene (HDPE)