Conditioning (polyamide)

In plastics technology, conditioning is understood to mean storage through to weight compensation ( constant weight) through water absorption in a standard climate (23 ° C and 50% humidity). The process of conditioning is reversible.

This process is technically important , especially with polyamide plastics . The material, which is brittle when dry, only acquires its impact strength through water absorption (conditioning) of up to 3.5% . However, strength and rigidity decrease under the influence of moisture, and elongation at break increases. This must be taken into account in the design. The absorption of water results in a clear shift in the glass transition temperature towards lower values. Data sheets for polyamide must therefore always contain information on the moisture content.

A distinction is made between 3 conditioning states:

• dry - no moisture, water content <0.2%
• humid - water content 2.7% - 3%
• wet - proportion of water 7.2% - 8%

mechanism

The absorption of water occurs through diffusion processes . This is made easier by hydrogen bonds . Storage takes place predominantly in the less densely packed, amorphous areas. The moisture balance (water absorption / water release) can take several months with a wall thickness of 2 mm-3 mm. An increase in the ambient temperature accelerates the conditioning.