Nylon frente a PBT: comparación completa de termoplásticos de ingeniería

Two Engineering Plastics, Two Different Worlds

Nylon (polyamide, PA) and PBT (polybutylene terephthalate) are both semi-crystalline engineering thermoplastics widely used in automotive, electrical, and industrial applications. They often compete for the same applications—connectors, housings, structural brackets—but their performance profiles are fundamentally different. Choosing between them requires understanding not just the datasheet numbers, but how each material behaves in the real world under heat, moisture, chemicals, and mechanical load over thousands of hours and millions of cycles.

The critical distinction that drives most material selection decisions: nylon absorbs moisture and PBT doesn’t. From this single chemical difference flows a cascade of property variations that define where each material excels—and fails.

Property Head-to-Head

The Moisture Factor: Nylon’s Defining Characteristic

Nylon’s amide groups form hydrogen bonds with water molecules, absorbing 1–3% moisture at equilibrium (50% RH). This absorbed water acts as a plasticizer: strength and stiffness drop 20–40% while impact resistance increases 3–5× compared to the dry-as-molded state. This means:

• A nylon part tested right out of the mold and one that’s been in service for 6 months will have dramatically different properties
• Nylon parts get tougher over time (a rare and often pleasant surprise for design engineers)
• Dimensional changes of 0.3–0.8% are normal across humidity extremes and must be accounted for in part design

PBT’s ester linkages don’t hydrogen-bond with water. Moisture absorption is <0.1%, meaning:

• Properties are stable and predictable regardless of environmental humidity
• Dimensions remain constant—ideal for precision fits and tight-tolerance assemblies
• Electrical properties don’t degrade in humid environments

Application Selection Guide

Choose Nylon When:

• Impact toughness is critical, especially in cold environments (below -20°C)
• The operating environment is alkaline or involves exposure to bases
• Sustained load-bearing is required (nylon’s better creep resistance)
• Parts need to flex or snap-fit repeatedly (nylon’s fatigue resistance is superior)
• Cost per kilogram is the primary constraint (nylon is typically 10–20% less expensive than PBT)
• The application involves gears, bearings, or wear surfaces where nylon’s self-lubricating grades excel

Choose PBT When:

• Dimensional stability is critical—connectors, sensors, precision housings
• The part will be exposed to hot, humid environments where nylon would soften and swell
• Electrical insulation properties must be consistent across environmental conditions
• Fast cycle times are needed—PBT crystallizes much faster than nylon, enabling 20–40% shorter molding cycles
• Chemical resistance to acids, fuels, and automotive fluids is required
• The part has a Class A painted surface—PBT accepts paint far more readily than nylon

Cost Considerations Beyond Material Price

While PBT is 10–20% more expensive per kilogram, the total cost of ownership equation is more complex:

• Cycle time: PBT molds 20–40% faster, reducing machine-time cost per part
• Secado: Both materials require drying before molding, but nylon is far more sensitive to inadequate drying
• Post-molding conditioning: Nylon parts often require moisture conditioning to achieve final properties; PBT does not
• Tool design: PBT’s lower and more predictable shrinkage simplifies tool design and shortens mold development time
• Reject rate: PBT’s dimensional stability typically results in lower scrap rates for tight-tolerance parts

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