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Chapter 3

Chapter 3: Drying Process Recommendations

Drying polyamides before processing or use is a critical step to prevent material degradation due to high moisture content. Improper drying parameters can lead to structural damage of the polyamide and deteriorated mechanical and visual properties.

Key Drying Parameters:

  1. Temperature:

  2. Must be above the glass transition temperature of the polyamide and sufficiently high for rapid moisture removal, but below the melting point.

  3. For PA6 and PA66, the preferred range is 90-110°C to ensure effective drying and avoid defects such as bubbling and overheating.
  4. A temperature of 80°C is suitable only for short-term pre-drying or for materials with low initial moisture content, as prolonged exposure at this temperature may cause thermal aging of the material.

High Temperature Risks:

  • Overheating can result in bubbles, loss of transparency, and thermal oxidation. The image below shows the effects of drying PA6I/6T at 120°C.

Overheating During Drying

Figure 4. Bubbles on the polyamide surface due to overheating.

  1. Time:

  2. Prolonged drying time, especially at low temperatures (e.g., 80°C), can cause thermal aging and material degradation due to extended heat exposure.

  3. The optimal drying time is 4-8 hours at 90-120°C, effectively removing moisture without damaging the material.

  4. For materials with high initial moisture content, begin drying at a lower temperature and gradually increase it to minimize the risk of overheating.

  5. Air Circulation Speed:

  6. High air circulation speed in the dryer accelerates moisture removal, ensuring uniform heating and evaporation.

  7. A dryer equipped with a blower and the ability to remove excess moisture from the chamber significantly improves drying efficiency, maintains stable conditions, and prevents the accumulation of moist air.
  8. This system is suitable for most polyamides, helping to avoid local overheating and uneven moisture removal.

Types of Drying Equipment:

  1. Desiccant Dryers:

  2. Operate by dehumidifying air using an absorbent.

  3. Maintain stable drying conditions and minimize overheating risk.

  4. Recommended for professional use in processing polyamides and other hygroscopic materials.

  5. Vacuum Dryers:

  6. Use reduced pressure to lower the boiling point of water.

  7. Suitable for materials sensitive to high temperatures.

  8. Provide uniform moisture removal but require complex equipment.

  9. Conventional Dryers (Ovens):

  10. Accessible and easy to use, but require constant temperature monitoring.

  11. Use of a fan improves drying uniformity; however, overheating must be avoided.

  12. Plastic Dryers:

  13. Specifically designed for preparing 3D printing filaments.

  14. Equipped with temperature control and a powerful fan ensuring even airflow.
  15. Some models feature humidity control, allowing excess moisture to be vented.
  16. Recommended for drying polyamides, PLA, PETG, and other materials before printing to avoid defects in finished parts.

Requirements for Plastic Dryers:

  • Accurate temperature settings within the 90-120°C range.
  • Uniform air circulation within the chamber.
  • Ability to operate for extended periods without overheating.
  • Compact size for convenient placement in home or office environments.

Process Recommendations:

  1. Measure moisture level before drying (methods discussed in Chapter 2).
  2. Start the process at a lower temperature, gradually increasing it.
  3. Avoid prolonged drying, especially at high temperatures.
  4. Use dryers with parameter control to minimize the risk of overheating.

Practical Guide:

The graphs below show moisture removal rates at different temperatures:

Drying Rate Graph Drying Rate Graph

Figure 6. Comparison of drying rates at different temperatures.

The graph demonstrates that higher temperatures accelerate the drying process, but it is important to monitor the thermal stability limits of the material.

Conclusion:

Effective drying preserves the mechanical properties of polyamide and prevents issues during processing. By following these recommendations, you can minimize the risk of material damage. The next chapter will discuss the role of additives and fillers in enhancing the moisture resistance of polyamides.