Skip to content

Chapter 1

Chapter 1: Hygroscopicity of Polyamides and Its Impact on Properties

Polyamides such as PA6, PA66, and PA12 exhibit high hygroscopicity, meaning they readily absorb moisture from the surrounding environment. This is due to the presence of amide groups in their polymer structure, which actively bond with water molecules. This process significantly affects the mechanical properties of the materials.

Main Effects of Moisture on Polyamides:

  1. Plasticization:

  2. Water acts as an internal "plasticizer," increasing the mobility of polymer chains.

  3. This leads to reduced strength and stiffness but increases material elongation.

  4. Example: the modulus of elasticity of PA6 decreases by 40-50% upon water saturation.

  5. Hydrolysis:

  6. At high temperatures and humidity, water breaks chemical bonds in the polymer.

  7. Hydrolysis causes brittleness, which is critical for long-term use.

  8. Dimensional Changes:

  9. Moisture absorption causes swelling, which affects dimensional accuracy of parts.

Example of Polyamide Hygroscopicity:

  • The image below shows a comparison of moisture absorption levels in polyamides:

Hygroscopicity Chart

Figure 1. Comparison of moisture absorption by unreinforced PA6 under various conditions.

The chart illustrates how humidity levels and environmental conditions affect PA6's ability to absorb water. From the presented data, it is clear that:

  • PA6 absorbs moisture actively, especially under high relative humidity.
  • Polyamides with fewer amide groups, such as PA12, exhibit significantly lower water absorption, making them preferable in high-humidity conditions.
  • The comparison also highlights the importance of pre-drying for materials intended for precise and stable components.

This information underscores the necessity of selecting the appropriate polyamide based on the operating conditions.

Practical Importance:

  • For 3D printing, the material's hygroscopicity plays a critical role. Plastics like nylon (PA6, PA66) become less durable upon moisture absorption, which can lead to printing defects.
  • In high-humidity environments, pre-drying the material is crucial to ensure dimensional stability and good layer adhesion.
  • This is especially important for precise parts requiring high mechanical strength and freedom from deformation.

How to Reduce Moisture Effects:

  • The use of additives such as glass fibers reduces the degree of moisture absorption.
  • Drying before processing and applying coatings help prevent degradation.

The next chapter will examine methods for measuring moisture content to determine its level before production processes.