Compare nylon-6,6 with nylon-6: which property statement correctly characterises nylon-6,6 relative to nylon-6?

Introduction / Context:
Nylon-6,6 (from hexamethylenediamine and adipic acid) and nylon-6 (from caprolactam) are closely related polyamides used in fibres and engineering plastics. Subtle chemistry differences affect melting point, hardness, and abrasion resistance, guiding material selection in high-temperature and mechanically demanding applications.

Given Data / Assumptions:

• Nylon-6,6 typically melts around 260–265°C; nylon-6 around 220–225°C.
• Abrasion resistance for nylon-6,6 is generally superior in comparable unfilled grades.
• Hardness and heat-deflection temperature are typically higher for nylon-6,6.

Concept / Approach:
The higher amide linkage density and crystallinity of nylon-6,6 raise its melting point and improve high-temperature mechanical properties. These structural features also tend to yield higher hardness and better wear resistance, though compounding can tune both families significantly.

Step-by-Step Solution:
Assess melting point: nylon-6,6 > nylon-6 → (a) true.Assess wear: nylon-6,6 commonly shows better abrasion → (b) true.Assess hardness: nylon-6,6 generally higher → (c) true.Therefore, (d) “All of the above” is correct.

Verification / Alternative check:
Datasheets and handbooks corroborate the higher Tm and improved heat resistance of nylon-6,6 compared with nylon-6 under similar conditioning.

Why Other Options Are Wrong:
Choosing any single property ignores the broader, well-documented advantages of nylon-6,6 across these metrics.

Common Pitfalls:
Over-generalising: additives, moisture content, and processing history can narrow or reverse differences for specific grades.

Final Answer:
All of the above