Polyamides (PA, nylon) absorb moisture from the air, which makes them hygroscopic polymers. This affects both processing and the behavior of the finished part.
Why is moisture a problem?
When moist pellets reach melt temperature, steam forms and hydrolysis can shorten the polymer chains. The result:
- Silver streaks, bubbles and a dull surface
- Low impact strength and brittle parts
- Unstable flow and dimensional deviations
How should it be dried?
In common practice PA pellets are dried in a desiccant dryer at around 80 °C for several hours, aiming for a moisture content below roughly 0.2%. The exact temperature and time depend on the PA type, additives such as glass fiber and the dryer, so always follow the manufacturer's data sheet.
Moisture in service
For types such as PA 6 and PA 66, the finished part also absorbs moisture from its environment. This causes a small increase in dimensions and a decrease in stiffness, with higher impact toughness. Account for this when designing parts with tight tolerances. Types such as PA 11 and PA 12 absorb far less moisture.
In short: dried material, a sealed feed hopper and controlled storage are the foundation of good PA production.