Skip to content

Chapter 5

Chapter 5: Experiments: Effect of Moisture on Mechanical Properties

The effect of moisture on the mechanical properties of polyamides is well-documented, and experiments with PA6 and PA66 show key changes in strength, elasticity, and ductility. These studies help in understanding how to control the operating and processing conditions of materials to preserve their characteristics.

Key Experimental Findings:

  1. Strength Reduction:

  2. When saturated with moisture, the tensile strength of PA6 decreases by 30-50%.

  3. Polyamides become less rigid due to plasticization.

  4. Ductility Increase:

  5. Upon water absorption, the elongation at break increases by 2-3 times.

  6. This makes the material more flexible but reduces its ability to withstand high loads.

  7. Elasticity Change:

  8. The modulus of elasticity of polyamides decreases proportionally with the humidity level.

Moisture Effect on PA6 Graph:

PA6 Stress-Strain Curves

Figure 9. PA6 stress-strain curves at different humidity levels.

  • DAM (Dry As Molded): dry material shows high strength and low elongation.
  • Conditioned (23°C, 50% humidity): intermediate behavior between dry and saturated states.
  • Saturated (100°C, full water absorption): reduced strength but increased elongation.

Example of Modulus Change:

The following graph presents data for PA66:

Modulus Graph

Figure 10. Dependence of PA66 modulus of elasticity on humidity.

  • Dry PA66: modulus of elasticity reaches 2.9 GPa.
  • When saturated with moisture: modulus drops to 1.5 GPa, demonstrating the plasticizing effect of water.

Practical Implications of the Results:

  1. Material Behavior Prediction:

  2. Experimental data allows predicting how polyamide products will behave in high humidity conditions.

  3. Drying Process Optimization:

  4. Avoiding excessive moisture before processing prevents strength degradation.

  5. Selection of Operating Conditions:

  6. For parts subject to mechanical loads, it is recommended to use stabilized or reinforced polyamides.

Conclusion:

Experiments show that humidity control is key to maintaining the mechanical properties of polyamides. In the next chapter, we will look at examples of drying errors and the consequences of material overheating.