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Chapter 6

Chapter 6: Examples of Overheating and Drying Errors

Drying polyamides at high temperatures or for excessively long periods can cause significant material damage. These drying errors manifest as blistering, loss of transparency, reduced strength, and other defects. This chapter examines examples of such cases, their consequences, and prevention methods.

Example 1: Overheating PA6I/6T at 120°C

  • When drying PA6I/6T polyamide in an oven at 120°C for an extended period, the following changes are observed:

  • Blister Formation:

    • Blisters form due to the rapid evaporation of moisture, creating excess pressure inside the material.

    • Loss of Transparency:

    • After moisture evaporates, microvoids remain that scatter light.

Overheating Example Figure 11. Blisters on the surface of PA6I/6T after overheating.

Example 2: Drying PA6I/6T at 140°C

  • When drying conditioned PA6I/6T in an oven at 140°C, changes become even more severe:

  • After 10 minutes: large blisters appear, indicating structural integrity issues.

  • After 90 minutes: the material loses transparency, the surface becomes uneven, and significant damage is observed.

Defects at 140°C Figure 12. Changes in PA6I/6T when dried at 140°C (left - blisters, right - cloudiness).

Causes of Defects:

  1. Excessive Temperature:

  2. Leads to rapid moisture evaporation that cannot escape quickly, creating internal pressure.

  3. May cause thermal oxidation, altering the color and structure of the material.

  4. Extended Drying Time:

  5. Even at moderate temperatures, prolonged drying causes degradation of the polyamide structure.

  6. Lack of Temperature and Humidity Control:

  7. Using inappropriate equipment such as standard ovens results in uneven heating and defects.

Consequences of Overheating and Drying Errors:

  • Aesthetic Defects: blisters and loss of transparency degrade the appearance of parts.
  • Reduced Mechanical Properties: damaged material becomes weaker and more brittle.
  • Shortened Service Life: defects accelerate material degradation under operating conditions.

How to Avoid Errors:

  1. Control of Temperature and Time:

  2. For PA6 and PA66, temperatures of 80-120°C and drying times no longer than 4-8 hours are recommended.

  3. Use of Appropriate Equipment:

  4. Desiccant dryers provide uniform heating and parameter control.

  5. Moisture Check Before Drying:

  6. Measuring moisture content (e.g., using the Karl Fischer method) helps set correct process parameters.

Conclusion:

Drying errors such as overheating and prolonged exposure to high temperatures can cause severe damage to polyamides. Following the drying process recommendations from previous chapters helps avoid these issues and maintain the material's properties.